Mahdi Ali Houssein

Fatima Mariem

Julie Aurore

Alexis Valentin

Sylvie Je Remercie Spécialement : Tuba

Hedi

Wael

Je remercie tout d'abord DIEU tout puissant de m'avoir donné le courage, la force et la patience d'achever ce travail. À tous ceux qui me sont chers À mes très chers parents qui ont toujours été présents : Mouhammad et Mona. Cet effort est le fruit de vos souhaits aujourd'hui exaucés. À ma chère soeur : Fatima À mes chers frères :

Introduction générale 1. Contexte du doctorat

Les polymères sont des macromolécules composées d'enchaînements de plusieurs unités répétitives appelées monomères. Grâce à une vaste gamme de monomères polymérisables, les polymères possèdent des propriétés physiques, optiques et chimiques très variées. Ces propriétés leurs donnent la particularité d'être présents aujourd'hui dans de nombreux domaines d'application tels que le bâtiment, le transport, l'agriculture, la santé et l'informatique, etc. Ils sont très largement présents dans notre vie quotidienne.

Il est connu qu'une réaction de polymérisation consiste à ajouter à des produits de nombreuses unités monomères ''M'' créant ainsi une macromolécule. L'étape d'amorçage de cette réaction correspond à la décomposition d'une molécule (appelé un amorçeur) par un procédé (thermique ou photochimique). Cette réaction produit une espèce amorçante (radical libre) capable d'attaquer le premier motif monomère. D'autres unités s'ajoutent à cette réaction lors de l'étape de propagation permettant alors la formation des macromolécules.

(Schéma 1). [ La polymérisation redox est une technique sans consommation d'énergie, utilisée dans l'industrie pour générer donc divers types de matériaux dans des conditions douces (température ambiante, sous air). Elle a été découverte en 1937 par des chercheurs allemands [2]. Elle se produit entre deux agents redox adaptés. Par exemple, en prenant le peroxyde de dibenzoyle comme agent oxydant et l'amine aromatique comme agent réducteur pour former un système redox très efficace.

Objectif de la thèse de doctorat

Ce projet de doctorat a débuté dans le but de fournir de nouveaux systèmes ou Dans ce contexte, les objectifs de ma thèse sont :

1-) fournir de nouveaux systèmes amorceurs réactifs pour une polymérisation redox en remplaçant des systèmes peroxyde de dibenzoyle (Ph-C(O)-O-O-C(O)-Ph)/amine qui ne sont pas stables et/ou toxiques. Ces systèmes développés il y a plus de 70 ans doivent maintenant être retirés des utilisations pratiques, ce qui est un challenge très important.

2-) fournir de nouveaux systèmes amorceurs redox réactifs pour une polymérisation redox qui doivent être stables et avec une réactivité très élevée même après les tests de vieillissement.

3-) contrôler le temps de polymérisation appelé le temps de gel dans les différents systèmes pour faciliter leur utilisation dans différentes applications. Ce temps ouvert est un paramètre très délicat a contrôler, on parle même dans la littérature (d'art du temps gel).

[3]

4-) Améliorer les propriétés de polymérisation en surface sous air des polymères redox. Le mélange de deux composants assure un bon durcissement en profondeur grâce à la génération redox des espèces amorceuses ; la surface sera bien durcie grâce à la photoactivation dans le cas d'une combinaison photo/redox 5-) si possible, développer de nouveaux systèmes basés sur des produits chimiques disponibles sur le marché et en quantité raisonnable. Le choix a donc été fait ici de ne pas synthétiser de nouveaux agents redox.

Les résines polymérisables pour la polymérisation radicalaire seront composées de méthacrylates : même si les constantes de propagation sont environ 10 fois inférieures à celles des acrylates, les méthacrylates sont moins toxiques et moins sensibles à l'hydrolyse.

En parallèle, certains systèmes ont été développés en collaboration (confidentielle) avec un partenaire industriel (avec des rapports réguliers, des réunions et des essais en usine pilote). Ces derniers systèmes ne seront pas divulgués dans le présent manuscrit.

Contenu du doctorat

La thèse sera présentée en cinq parties (selon le schéma 2). Dans

Partie Bibliographique

La polymérisation fait référence à des réactions chimiques dans lesquelles de petites unités (les monomères ou oligomères) réagissent ensemble pour former des macromolécules (ou polymères) de poids moléculaires plus élevés.

De nos jours, il existe principalement deux grands types de polymérisation à l'échelle industrielle : la polymérisation cationique et la polymérisation radicalaire. Mon travail de recherche se concentre sur l'étude de nouveaux systèmes redox pour la polymérisation radicalaire même si dans la partie perspective à la fin de manuscrit un nouveau système redox pour le cationique a pu être proposé et développé.

Nous nous sommes donc concentrés sur la polymérisation radicalaire par croissance de chaîne (FRP) et la polymérisation cationique (CP), principalement utilisée dans l'industrie. D'autres exemples de techniques de polymérisation par croissance de chaîne existent comme la polymérisation anionique (récemment réalisée sous lumière visible mais avec des performances plutôt faibles en termes de vitesse de polymérisation [4], ou la polymérisation coordonnée telle que la polymérisation par métathèse par ouverture de cycles. [5]

1-La polymérisation radicalaire

La polymérisation radicalaire est le procédé industriel le plus exploité avec plus de 50% de la production totale des matériaux polymères, dont 70% de polymères vinyliques.

Parmi ceux-ci, on peut citer le polyéthylène à basse densité synthétisé sous haute pression, le poly (chlorure de vinyle), les poly (méthacrylates d'alkyle), le polystyrène et bien d'autres... Une polymérisation radicalaire est une réaction en chaîne où l'espèce réactive est un radical libre qui participe aux 3 processus élémentaires résumés ci-dessous (voire aussi Schéma 1) :  L'amorçage : La polymérisation débute avec la formation d'un radical issu de l'amorceur (A-A), susceptible de réagir avec une molécule de monomère (M) pour former le premier radical polymère (A-M•).

 La propagation : c'est l'étape principale de la polymérisation radicalaire. Le radical RM• engendré lors de l'étape d'amorçage attaque la double liaison d'un autre monomère pour former un nouveau radical. Le processus implique ainsi une croissance du radical polymère par addition successive d'un très grand nombre de molécules de monomère. Il s'agit d'une réaction en chaîne. Cette réaction est très rapide dans les premiers instants mais elle ralentit ensuite avec la diminution de la concentration en monomère et l'augmentation de la viscosité du milieu.

 La terminaison : cette réaction de terminaison des chaînes en croissance a lieu principalement par interaction biomoléculaire des macro-radicaux. Lors de la réaction de recombinaison, deux macroradicaux reforment une liaison covalente.

Quelques exemples de monomères acrylates utilisés en polymérisation radicalaire sont représentés sur le Schéma 3. Schéma 3 : Monomères de type radicalaire.

2-La polymérisation cationique

La polymérisation cationique est également très utilisée dans les domaines des revêtements, des encres ou encore des adhésifs. Les propriétés sont souvent trés différentes de celles des polymères obtenus par voie radicalaire.

La polymérisation cationique, contrairement à la polymérisation radicalaire, est insensible à l'oxygène de l'air. En effet, lors de la réaction, les espèces réactives formées qui sont des carbocations ne réagissent pas avec l'oxygène (O 2 ). Les monomères les plus utilisés sont les époxys.

La polymérisation de fonctions époxydes est obtenue par ouverture de cycles [6][7]. Un sel d'onium est généralement utilisé pour amorcer cette réaction. Celui-ci génère sous l'action de la lumière un acide fort (H + ) qui réagit ensuite avec l'époxyde pour former des ions oxoniums. Ces cations réagissent sur un nouvel époxyde provoquant une réaction en chaîne aboutissant à la formation d'un polyéther (Schéma 4).

3-Amorçage redox

L'amorçage redox (pour procédé d'oxydoréduction) est une approche à deux composants largement utilisée dans la polymérisation en émulsion, les biomatériaux, les Par exemple, dans la figure 1, le tempol a été utilisé comme stratégie d'inhibition/retardement. On peut voir que sans tempol (courbe 1), le temps de gel est rapide (environ 60 sec) tandis que (courbe 2) le temps de gel sera retardé de 120 sec en présence de tempol.

Définition de "conditions douces" pour la polymérisation redox

Ph(C=O)O

- R 3 N (r1) + (Ph(C=O)O) 2 (r3) Ph(C=O)O Ph(C=O)O Ph + CO 2 BPO amine R 3 N + + Ph(C=O)O - R 3 N + + R'C
Figure 1: l'effet du tempol sur la réaction de polymérisation (résultats obtenus au cours de cette thése).

Limites actuelles de la polymérisation redox

Dans le cas de la polymérisation redox dans les conditions douces définies ci-dessus,

Introduction:

Free radical polymerization (FRP) for the preparation of polymers under mild conditions (room temperature, under air) are of immense intrigue and industrial importance. 1- 7 Being highly relevant under these conditions, the two-component (2K) mixing of reducing and oxidizing agents in redox initiated polymerization has been broadly performed in the materials science; 8-12 However, the currently used efficient redox initiating systems (RISs) are commonly based as amine/dibenzoylperoxide (BPO) systems 13-21 which represent serious potential issues: toxicity of the amines, risk associated with peroxides handling and storage, pressing regulations on peroxides, etc… 22,23 Advancement of more secure RIS to meet the prerequisites of room temperature polymerization has in this manner been the quest for researchers. 24-31 More recently, the development of ecofriendly and safer peroxide-free and sometimes amine-free redox initiating systems was proposed for several applications. 32-35 These systems show high performances but still have some defects such as toxicity issues.

In this context, amine-free and peroxide-free organic compounds able to react in redox processes are highly researched. Particularly, our group shows the possibility to use Iodonium salts (safe/unexplosive oxidizing agents characterized by decomposition temperature >300 °C) in RFRP of methacrylates (room temperature, under air). 35 In this paper, simple, economical, and environmentally friendly DPS/metal acetylacetonate system is explored in high-efficiency and mild redox initiators; that is, it can be used both at room temperature and under air. In particular, diphenylsilane (DPS) and Manganese(III) acetylacetonate redox system has never been reported herein for free radical polymerization. In addition, an iodonium salt was also added as a third component system in order to adapt the gel time duration. Lambson Ltd) as additive.

Experimental section

Chemical Compounds.

All of the reactants were selected with high purity and used as received (Chart 1).

Diphenylsilane (DPS), dibenzoyl peroxide (BPO), manganese acetylacetonate Mn(acac) 3 and

Definition of the Two Components Used for Redox Experiments.

All redox formulations were prepared in bulk in two separate cartridges: a first cartridge (cartridge 1) with the DPS and the other one (cartridge 2) containing the Mn(III)(acac) 3 ; Figure 1B. A 1:1 Sulzer mixpac mixer was used to mix all components together at the beginning of each polymerization experiment. All polymerization experiments will be performed under mild conditions: at room temperature (RT) (21-23 °C) and under air.

Definition of the Three Components Used for Redox Experiments.

All redox formulations were prepared from the bulk resins in two separate vials: a first vial (vial 1) with the DPS and SC938, the other one (vial 2) containing the Mn(acac) 3. Then, the same volume of formulation from vials 1 and 2 was transferred to a plastic cup at the same time and was stirred about 10s quickly at the beginning of each polymerization experiment.

All polymerization experiments will be performed under mild conditions: at room temperature (RT; 21-23 °C) and under air.

Polymerization in Bulk Followed by Optical Pyrometry and Fouriertransform infrared spectroscopy (FTIR):

The use of optical pyrometry to follow polymerization reactions was used here: temperature versus time profiles were followed using an Omega OS552-V1-6 infrared thermometer (Omega Engineering, Inc., Stamford, CT) having a sensitivity of ±1 °C for 2 g (sample thickness ∼4 mm). The evolution of the methacrylate function characteristic peak for the thick samples (4 mm) was followed in the near infrared range at ~6160 cm -1 by real time FTIR spectroscopy (JASCO FTIR 4100). The procedure used to monitor is quite similar to that used in [29][30][32][33][34].

Electron Spin Resonance (ESR) Spin Trapping (ESR-ST).

Electron spin resonance-spin trapping experiments were carried out using an X-band spectrometer (Magnettech MS400). The radicals were observed under nitrogen saturated media at room temperature. N-tert-Butyl nitrone (PBN) was used as a spin trap agent in tertbutylbenzene. ESR spectra simulations were carried out using WINSIM software [29][30][32][33][34].

Cyclic voltammetry.

The oxidation or the reduction potentials (Eox or Ered vs. SCE) for the DPS and Manganese acetylacetenoate were measured in acetonitrile by cyclic voltammetry using tetrabutylammonium hexafluorophosphate (0.1 M) as the supporting electrolyte. The procedure was presented in detail in [29][30][32][33][34].

Results and discussion:

Redox Initiating Systems (RIS) based on the two-component DPS/Mn(acac) 3 Combination

The FRP of the benchmark methacrylate monomer blend (Resin 1) in the presence of the different DPS/Mn(acac) 3 couples is very efficient i.e. very high final methacrylate function conversion FC = 90% found using the two-component 2K 1wt% DPS + 1wt% Mn(acac) 3 (Figure 1). This is higher than reference amine/BPO for the same resin/setup: only 79% C=C conversion was obtained. 36 Recorded spectra before and after polymerization show a decrease of the characteristic peak at 6160 cm -1 (Figures 1C and1D). In order to investigate the polymerization ability of DPS/Mn(acac) 3 combination, different concentrations of either DPS or Mn(acac) 3 were investigated. There is a positive effect of an increase of the content of DPS and decrease of the content of Mn(acac) 3 to decrease the work time (i.e. when more DPS and less Mn(acac) 3 was added, a short time of polymerization is observed). The polymerization process is very fast if the concentration of DPS is higher than 1 wt % and of the Mn(acac) 3 is less the 1 wt% (maximum temperature reached T > 100 °C, gel time < 2 min, Figure 1A curve 2). For example, the process is quite efficient when the concentration of DPS is 2 wt % and Mn(acac) 3 0.5 wt% (maximum temperature T > 100 °C, Figure 1A, curve 3).

The selected concentrations have high potential to control the gel time; the data of polymerization based on different concentration of DPS and Mn(acac) 3 are summarized in Table 1, excellent tuning of the reaction times (up to 5 min) is made possible. In comparison (Figure 1E), it is tough to control gel time in 4-N,N TMA/BPO reference using tempol: 37 tempol lowers performance to reach acceptable gel time (> 180 sec with 0.17 % tempol, curve (ii)) and only 95°C exothermicity is reached. This is lower than the new Manganese system developed (149 °C reached in 230 seconds), confirming FTIR data. 2 wt% DPS + 0.5 wt% Mn(acac) 3 , (4) 0.8 wt% DPS +0.8 wt% Mn(acac) 3 , (5) 1.4 wt% DPS +0.4 wt% Mn(acac) 3, (6) 0.4 wt% DPS +0.4 wt% Mn(acac) 3 .E. (i) BPO = 1.0 wt% + 0.9 wt% 4,N,N-TMA; (ii) BPO = 1.0 wt% + 0.9 wt% 4,N,N-TMA + 0.17 wt% tempol (iii) BPO = 1.0 wt% + 0.9 wt% 4,N,N-TMA + 0.34 wt% tempol B. Mixing method using two cartridges corresponding to curve 2 in Figure 1A; check also the Experimental Section. C. Polymerization profiles of resin 1 (methacrylate function conversion vs. time) under air in the presence of two-component redox initiating system 1wt% DPS + 1wt% Mn(acac) 3 . D. IR spectra recorded before and after polymerization using 1wt% DPS + 1wt% Mn(acac) 3 .

Redox Initiating Systems (RISs) from Upgraded Three-Component Systems: DPS/Mn(acac) 3 /Iodonium salt

Furthermore, we investigated the initiating efficiency of DPS/Mn(acac) 3 in the presence of different concentrations of iodonium salt (SC938) salt as additive. Indeed, the DPS/Mn(acac) 3 alone was essentially efficient in resin 1 (see above Figure 1) with a short gel time. For RFRP, the control of the gel time (also called work time) is particularly important.

An iodonium salt (SC938) was tested as a third component for its capability to tune the gel time. In this context, we investigated the effect of SC938 concentration in combination with DPS in a separate cartridge and Mn(acac) 3 in another cartridge (see Figure 2B). It is well obvious that SC938 has an inhibitory effect in terms of the time to reach the maximum temperature of polymerization (e.g. for DPS/Mn(acac) 3 (2%/0.5% wt%) gel time=105s in comparison with DPS/SC938/Mn(acac) 3 (2%/2%/0.5% wt%) gel time= 180s). In fact, as concentration of SC938 increases, gel time increases (Figure 2A, curve 4 vs. curves 1, 2, 3). Therefore, the proposed upgraded DPS/ SC938/Mn(acac) 3 RIS can be considered as a good way to cure radical monomers upon mild room temperature conditions with good time gelation control.

Time (s)

Temperature (°C) Figure 2. A. Optical pyrometric measurements (sample T ( 0 C) vs. time) under air for benchmark monomers (Resin 1) in the presence of RIS, for: (1) 2 wt% DPS + 0.5 wt% Mn(III)(acac) 3 + 0.5% SC938; (2) 2 wt% DPS + 0.5 wt% Mn(III)(acac) 3 + 1% SC938; (3) 2 wt% DPS +0.5 wt% Mn(III)(acac) 3 + 2% SC938; (4) 2 wt% DPS + 0.5 wt% Mn(III)(acac) 3 . B. Mixing method using two cartridges: DPS/SC938 in Cartridge 1 and Mn(III)(acac) 3 in Cartridge 2; for the optical pyrometric measurements (check also the Experimental Section).

Application: Preparation of composites via 2K DPS/Mn(acac) 3 Combination

In order to optimize the material preparation and the reaction times, concentration of RIS has to be assessed. Indeed, gel times (corresponding to the time needed to reach the maximal temperature) of more than one minute are often required in the industry in order to have sufficient workability. For example, the 2K mixed formulation has to have sufficient time to soak the fibers or to fill the mold and then rapidly cure, avoiding premature curing during of the mix. The high-efficiency RIS developed here for room temperature meets this requirement, and the curing time can be controlled. In presence of glass fibers, the curing process is very fast when the concentration of the DPS is 2 wt % and of the Mn(III)(acac) 3 is 0.5 wt% (maximum temperature T > 100 °C, Figure 3 curves 2). When the concentration of DPS is less than 2 wt%, the RIS is also efficient in composites preparation but leads to a longer work time and reduced exothermicity. Therefore, DPS/ Mn(III)(acac) 3 is worthy to be used in composites preparation. composites in the presence of (1) 0.5 wt% DPS + 2 wt% Mn(III)(acac) 3 (2) 2 wt% DPS + 0.5 wt% Mn(III)(acac) 3 , (3) 1 wt% DPS + 1 wt% Mn(acac)3 B. Photos for impregnated glass fibers taken before and after mixing with RIS.

Chemical Mechanisms

For a better understanding of the DPS/Mn(II) interaction, ESR-spin trapping experiments were carried out (Figure 4). Using phenyl-tert-butyl nitrone (PBN) as spin trapping compound, free radical adducts are detected after mixing of DPS and Mn(III)(acac)3 in tert-butylbenzene under N 2 . Two PBN/radical adducts were detected: i) Ph 2 Si•H/PBN characterized by aN = 14.8G; aN = 5.3G and H•/PBN characterized by aN = 14.9G; aN (2) = 7.4G in agreement with literature data. 38,39 This suggests the redox reaction (r1) between DPS and Mn(III)(acac)3. Indeed, it is clear that Mn(II) is formed; the initial dark color of Mn(III)(acac)3 is reduced into the color of Mn(II) as recently observed for the redox initiating system between a phosphine and this Mn(III) specie also generating Mn(II). 40

Scheme 1. proposed chemical mechanisms.

The radicals generated in (r1) can be assumed as the initiating species for the FRP processes observed above.

Conclusion :

A new redox free radical initiating system has been discovered formethacrylate polymerization; it is based on Mn(acac)

1.Introduction

Redox initiated Free radical polymerization (FRP) is a very well-established technique for polymer production due to its applicability under mild conditions [1][2][3][4][5]. Simply put, the mixing of reducing and oxidizing agents initially separated in two cartridges leads to the formation of free radicals through a redox mechanism to initiate the polymerization process.

Such redox systems are already used in widespread research fields: adhesives, composites, biomedical materials, etc. However, the current challenge is to replace the toxic and poorly stable redox agents by safer alternatives [6][7][8][9][10][11]. More particularly, the broadly used dibenzoyl peroxide (BPO)/aromatic amine (e.g. 4-N,N-trimethylaniline (4-N,N-TMA)) initiating system is characterized by i) the toxicity issue raised by the use of an amine combined with ii) the issue resulting from peroxides handling and storage and pressing regulations on peroxides. To overcome the aforementioned risks, we propose here new redox initiating systems (RISs)

which can be more stable and eco-friendlier [12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Remarkably, these amine-free and peroxide-free systems can be efficient under mild conditions under air with controllable gel time. Precisely, diphenylsilane (DPS), selected as a potential reduction agent [26], is originally explored in combination with three oxidative metal complexes (Mn(acac) 2 or Fe(acac) 3 or Cu(AAEMA) 2 ; with acac=acetylacetonate and AAEMA=methacryloyloxyethylacetoacetate). All these redox agents have great advantages compared to peroxide (e.g., BPO) because they are stable in monomers at room temperature.

As an example of the high interest of the new proposed RISs, the polymerization of prepregs (glass or carbon fibers impregnated by organic monomers) is shown for the access to composites.

Results

Redox Initiating Systems (RISs) using DPS/Metal Complex Combination

The different chemicals used for the redox initiating systems are gathered in Scheme 1

and the chemical structure of the benchmark methacrylate monomers selected for this study are depicted in Scheme 2. We are interested in polymerization under air; indeed, redox initiating systems are used in many applications under air. Therefore, the resin 1 (scheme 2), specifically developed in previous works [24,25] (with an adapted viscosity) for polymerization under air, has been used. The Fe(acac) 3 /DPS system was not found to be very efficient at initiating the polymerization under air. For example, 1000 seconds were necessary for curing with a lower temperature (only 47 °C, Figure 2B). The results obtained here for Cu(AAEMA) 2 , Mn(acac) 2

and Fe(acac) 3 with DPS were compared with those obtained with Mn(acac) 3 that has been proposed in other redox systems [23] (Figure 2A). Interestingly, Cu(AAEMA) 2 and Mn(acac) 2 are characterized by a good efficiency (similar to that observed for Mn(acac) 3 )

(Figure 2A). The polymerization parameters for the different redox systems are gathered in Table 1. These polymerization processes were also followed by Real-Time FTIR spectroscopy.

Remarkably, very high final methacrylate function conversions (e.g., FC = 98% -Figure 3A and Table 1) were found under air using the two-component Metal complex/DPS redox systems (1/1 wt %). The recorded FTIR spectra before and after polymerization which showed a full decrease of the characteristic C=C peak at 6160 cm -1 are depicted in Figure 3B. 2) Mn(acac) 2 /DPS (1/1 %wt), ( 3) Cu(AAEMA) 2 /DPS (1/1 %wt). (B) IR spectra recorded before and after polymerization using Cu(AAEMA) 2 /DPS (1/1 wt %).

Potential Photoactivation of the new proposed RIS (DPS/Mn(acac) 2 ):

The possible photoactivation of the RIS was checked upon irradiation with an LED at 405 nm (230 mW/cm 2 ). However, it is found that this DPS/Mn(acac) 2 RIS does not show any significant photoactivation in terms of exothermicity and gel time (Figure 4). This suggests that the photo-induced redox process remains a minor pathway for the FRP compared to the dark redox process. The same behavior is also obtained for Cu(AAEMA) 2 where no effect of photoactivation is observed upon irradiation.

Stability upon Storage

Remarkably, an excellent stability of the proposed RIS was found in monomers. For example, Mn(acac) 2 , Cu(AAEMA) 2 or DPS formulations showed a stability of 7 days in accelerated aging experiments (when stored in an oven at 50 °C). Interestingly, the gel time is not significantly affected by storage compared to that obtained for fresh formulations (Figure 5). This can extend the areas of application of redox induced polymerization. Mn(acac) 3 was the best candidate in terms of reactivity (Figure 2) but is not stable in accelerated aging experiments (Figure 5C). In contrast, the other metal complexes (Cu(AAEMA) 2 and Mn(acac) 2 ) showed both excellent reactivity and stability. Therefore, the lack of stability of Mn(acac) 3 in monomers at 50 °C can limit the use of this metal complex.

Application to the Preparation of Composites

Finally, we propose to access composites as an application of the new proposed RISs which are characterized by both 1) stability in accelerated aging and 2) highly workable systems (high reactivity and adjusted gel time). Composites materials are highly recommended for different fields as they allow the combination of good mechanical properties with the high flexibility of the polymerization processes. The proposed RISs can fully meet this requirement with a curing time that can be controlled. By curing one layer of prepregs (carbon fibers; thickness ~ 0.2 mm or glass fibers; thickness ~ 0.6 mm) impregnated with organic resin, a good polymerization process is observed when using Mn(acac) 2 /DPS

(1/1 wt%). This system is efficient for the preparation of composites where only a few minutes are enough to reach tack-free surfaces (for both the surface and the bottom of the sample) (Figure 6). For composites, lower temperatures are reached as part of the heat released is absorbed by the fibers (Figure 6A). 2) Mn(acac) 2 /DPS (1/1 %wt) (carbon fibers), ( 3) Mn(acac) 2 /DPS (1/1 %wt) (glass fibers) and (B) Photos for impregnated glass fibers taken after mixing with redox initiating system for 50% glass or carbon fibers and 50% of organic resin.

Discussion

In the frame of a redox initiated polymerization, as a general rule, a higher reduction potential of the oxidizing agent (in our case of the metal complex) must lead to a better reactivity. The reduction potentials of the metal complexes follow this order: Cu(AAEMA) 2 > Mn(acac) 3 > Mn(acac) 2 (See Table 1, Figure 7). This order is not in agreement with the experimental trend in redox processes (Mn(acac) 3 > Mn(acac) 2 > Cu(AAEMA) 2 ) showing that a more complex mechanism than a pure electron transfer occurs for the formation of free radicals (see the ESR results below).

Table 1. Data of polymerization using different redox systems for the benchmark monomer blend. 7). For a better understanding of the reactivity of redox system, ESR and ESR-spin trapping experiments were carried out for DPS/metal complex systems (Figure 8). Using phenyl-tertbutyl nitrone (PBN) as the spin trap agent, free radical adducts are detected after mixing of DPS and Mn(acac) 2 (Figure 8A) or Cu(AAEMA) 2 (Figure 8B) in tert-butylbenzene and under N 2 . The radical adducts are characterized by the following hyperfine coupling constants: i) aN = 14.8G; aH = 5.3G and ii) aN = 14.9G; aH(2) = 7.4G that can be assigned to the known Ph 2 Si•H/PBN and H•/PBN adducts, respectively [27,28].

This suggests the redox reaction (r1) between DPS and metal complex.

Ph 2 SiH 2 + Metal n (acac) x →→→ Ph 2 Si•H + H• + Metal n-1 (acac) y (r1)
The radicals generated in (r1) can be assumed as the initiating species for the FRP processes observed above.

More interestingly, for Cu(AAEMA) 2 , the characteristic Cu(II) spectrum (Figure 8C)

strongly

Materials and Methods

Chemical Compounds

All chemicals were purchased with high purity and used as received (Scheme 1).

Diphenylsilane (DPS) and Mn(acac) 2 were purchased from TCI-Europe. Fe(acac)

Two Cartridges System Used for Redox Experiments

All redox formulations were prepared in bulk in two separate cartridges: a first cartridge with the DPS and the other one containing the Metal complex (Cu(AAEMA) 2 , Mn (acac) 2 or Fe (acac) 3 ). A 1:1 Sulzer mixpac mixer was used to mix the two cartridges at the beginning of each polymerization experiment. As all polymerization experiments were performed at room temperature (~20-25 °C) and under air, an oxygen inhibition can be expected, particularly for the surface in direct contact with air [20].

Redox Polymerization in Bulk Followed by Optical Pyrometry

Optical pyrometry was used to follow polymerization reactions: temperature vs. time profiles were followed using an Omega OS552-V1-6 infrared thermometer (Omega Engineering, Inc., Stamford, CT) having a sensitivity of ±1 °C for 2 g samples (thickness ∼4 mm). The redox initiator contents will be given in weight with respect to the monomer in the final blend (wt%). The optical pyrometry is used to check the gel time, i.e., the time required from a two-component mixing to go from a fluid/viscous state to a gel/solid one.

RT-FTIR spectroscopy

A JASCO 4100 Real-time Fourier Transform Infrared Spectrometer (RT-FTIR) was used to follow the evolution of the methacrylate peak functionality for the thick samples (1.4 mm) in the near-infrared range from 6130 to 6200 cm -1 .

Electron Spin Resonance (ESR) Spin Trapping (ESR-ST)

Electron spin resonance-spin trapping experiments were carried out using an X-band spectrometer (Magnettech MS400). The radicals were observed at room temperature under nitrogen saturated medium in toluene. N-tert-butyl-phenylnitrone (PBN) was used as a spin trap agent in a similar way as described in other works [21][22][23][24][25]. ESR spectra simulations were carried out using WINSIM software.

Cyclic voltammetry

The reduction potentials (E red vs. SCE) of the different metal complexes were determined by cyclic voltammetry in ACN using tetrabutylammonium hexafluorophosphate (0.1 M) as a supporting electrolyte. The procedure was reported in detail in [21][22][23][24][25].

Conclusions:

In this paper, new redox initiating systems are proposed for the free radical polymerization of methacrylate monomers. Contrary to the Mn(acac) 3 , which is not very stable in accelerated aging conditions, both Mn(acac) 2 and Cu(AAEMA) 2 showed excellent reactivity and stability. Composites materials based on glass or carbon fibers can be produced using these proposed systems. Other peroxide-free and amine-free systems that can be activated by light will be proposed in forthcoming papers to gather the advantages of photopolymerization and redox polymerization.

Introduction

Redox free radical polymerization (RFRP) is a widely used process for reaction at room temperature. The blending of two compounds (an oxidizing agent with a reducing agent)

initiates the polymerization by spontaneous formation of initiating radicals through a redox mechanism. RFRP is a very interesting method for the formation of a polymer without energy consumption (the reaction can be carried out at room temperature) and under mild conditions (under air and without monomer purification). The redox initiator system (RIS) is usually based on a mixture of peroxide (e.g. dibenzoyl peroxide -BPO) selected as oxidizing agent with a tertiary aromatic amine system used as reducing agent (e.g. 4-N,N-trimethylaniline noted 4-N,N-TMA) (1-6). The main drawbacks of these latter systems correspond to the usual lack of peroxide stability in monomers as well as the toxicity of tertiary amines. In this context, chemical compounds (organic compounds or metal complexes) that can be used in replacement of amines or peroxides are of great interest and demand.

In our previous works, sulfinates were incorporated in photoinitiating systems (PISs) in combination with camphorquinone (CQ) and CQ/sulfinate PISs were proposed to replace CQ/amine system for radical photopolymerization (7). Sulfinates were characterized by low oxidation potentials allowing the reduction of the CQ excited states through r1:

*CQ + RSO 2 -→ CQ •-+ RSO 2 • (r1)
However, photopolymerization can be associated with shadow areas and light penetration issues. Therefore, RFRP that does not require light activation can be of huge interest. Following these seminal works on sulfinates in photopolymerization, we want to use these latter structures in RIS by taking the advantage of their low oxidation potentials.

Therefore, new RISs based on the combination of metal complexes (oxidation agent) with sulfinates (reducing agent) are proposed for mild conditions and allowing a good controllability of the gel time that can be highly worthwhile for different applications (8)(9)(10)(11)(12)(13)(14)(15).

To the best of our knowledge, sulfinates were not reported before in RIS in combination with a metal salt as oxidizing agent. Finally, composite synthesis is suggested as a potential application of this new redox system.

Experimental section

Chemical Compounds

All the chemicals were purchased with high purity and used as received (Scheme 1).

Two Cartridges System (2K) for RFRP

All redox formulations were prepared in bulk in two separate cartridges: a first cartridge with the metal derivative and the other one containing the sulfinate. A 1:1 Sulzer mixpac mixer was used to mix the two cartridges at the beginning of each polymerization experiment. As all polymerization experiments were performed at room temperature (~20-25°C) and under air, an oxygen inhibition can be expected, particularly for the surface curing in direct contact with air (16-20).

RFRP in Bulk Followed by Optical Pyrometry

Optical pyrometry was used to follow the polymerization reactions: temperature vs. time profiles were followed using an Omega OS552-V1-6 infrared thermometer (Omega Engineering, Inc., Stamford, CT) having a sensitivity of ±1 °C for 2 g samples (thickness ∼4

BR:

Sulf 1

Oxidation agent: Reduction agent: mm). The redox initiator contents will be given in weight with respect to the monomer in the final blend (wt%). The optical pyrometry is used to check the gel time i.e. the time required from a two-component mixing to go from fluid/viscous state to gel/solid one. The gel time will be defined here as the time for the maximal slope in the T°C/time profile corresponding to the maximal polymerization rate.

RT-FTIR spectroscopy

A JASCO 4100 Real-time Fourier Transform Infrared Spectrometer (RT-FTIR) was used to follow after mixing of the two cartridges in real time the evolution of the methacrylate peak functionality in the near-infrared range from 6130 to 6200 cm -1 . The sample thickness was 1.4 mm.

Electron Spin Resonance (ESR) Spin Trapping (ESR-ST)

Electron spin resonance-spin trapping experiments were carried out using an X-band spectrometer (Bruker EMX-plus). The radicals were observed at room temperature under nitrogen saturated toluene solutions. N-tert-Butyl-phenylnitrone (PBN) was used as a spin trap agent in a similar way as described in other works (16)(17)(18)(19)(20). ESR spectra simulations were carried out using WINSIM software.

Cyclic voltammetry

The redox potentials (E red , E ox vs. SCE) of the different compounds were determined by cyclic voltammetry in ACN using tetrabutylammonium hexafluorophosphate (0.1 M) as a supporting electrolyte. The procedure was reported in detail in (16)(17)(18)(19)(20).

Surface Polymer Analysis (z-Profile) through Raman Confocal Microscopy

Raman spectra in depth for the cured polymers were recorded with a Labram (Horiba) spectrometer mounted on an Olympus BX40 confocal microscope, operating at 632.8 nm with a 1800 lines/mm grating. The carbonyl peak area (1690-1755 cm -1 ) was measured as an internal standard while the alkene peak area (1630-1660 cm -1 ) was used to determine the C=C conversion in depth.

Results and discussion :

Redox initiation using different metals

Effect of the oxidizing agent:

Initially, the sulfinate salts used as reducing agents were used for RFRP of a blend of multifunctional (meth)acrylate monomers (BR) with different metal oxidizing agents. The polymerization efficiencies of the various redox systems based on a combination of sulfinate/metals salt were followed by optical pyrometry (Figure 1). The Sulf 1/Mn(acetate) 3 and Sulf 1/Mn(acac) 3 showed a peak of exothermicity around 120 °C with different gel times (60 s for Sulf 1/Mn(acetate) 3 and 250 s for Sulf 1/Mn(acac) 3 ; Figure 1, curve 1 and curve 2, respectively). Sulf 1 reacts more efficiently with Mn(acetate) 3 than Mn(acac) 3 which could indicate a higher yield in initiating radicals with the acetate derivative. On the contrary, a longer gel time can be beneficial for different applications requiring longer open time.

The RISs based on copper complexes are not effective vs. the Mn ones. For example, the combination Sulf 1/Cu(hfacac) 2 is characterized by a rather low polymerization exothermicity (Figure1 curve 3, T°C ~ 45 ° C) while the Sulf 1/Cu(acac) 2 system does not lead to any polymerization process (Figure 1, curve 4).

Possible Light Activation:

Considering Sulf 1/Mn(acetate) 3 RIS having the best reactivity in the RFRP experiments, the polymerization processes were also monitored by RT-FTIR spectroscopy in

techniques can be directly linked to the difference in thickness used (1.4 mm in RT-FTIR vs.

4 mm in the pyrometry experiment) and to the associated oxygen inhibition (the polymerization is carried out in air). Polymerization kinetics were also compared with and without light activation (LED@405 nm, I = 230 mW / cm 2 ) (Figure 2A, curve 1 vs. curve 2).

Interestingly, a better polymerization profile is observed upon light activation i.e. FC increases from 53% without light to 66% upon light irradiation.

Markedly, the combination of Sulf 1/Cu(hfacac) 2 previously showing low efficiency without light (Figure 1

Redox initiation using different sulfinate salts

In this part, different sulfinate salts were studied as reducing agents in different RISs comprising metal salts as oxidation agents (e.g. Mn(acetate) 3 was chosen as efficient compoundsee results above). The three selected systems were: Sulf 1/Mn(acetate) 3 , Sulf 2/Mn(acetate) 3 and Sulf 3/Mn(acetate) 3 in BR. The polymerization efficiency of these various redox systems followed by optical pyrometry is shown in Figure 3. Redox polymerization is found very efficient using Sulf 1/Mn(acetate) 3 (gel time ~ 70 seconds). However, with Sulf 2 and Sulf 3, higher inhibition times are observed, which could be useful for delayed hardening applications. The temperatures reached ~ 120-110 ° C for Sulf 1 and Sulf 2 while ~ 80 ° C in case of Sulf 3 (Figure 3). These results show the versatility of using different reducing agents.

For sake of comparison, the reactivity trend in the sulfinate/Mn(acetate) 3 systems follows this order: Sulf 1> Sulf 2> Sulf 3 for a given concentration. This reactivity trend will be discussed in details in the proposed mechanism part.

Sulf 2/Mn(acetate) 3 (1/1 %wt), (3) Sulf 3/Mn(acetate) 3 (1/1 %wt).

Effect of the concentration in redox agents

The gel times and the temperatures reached for the different concentrations of Sulf 1/Mn(acetate) 3 redox system are gathered in Table 1. Markedly, the gel time strongly decreases from 120 s to 10 s when increasing the contents of redox agents (from 0.5 to 4 wt%). These data suggest higher yields in initiating radicals for high redox agent contents and the associated better ability to overcome the oxygen inhibition.

Control of the gel time with inhibitors

Stability study in accelerating aging @ 40°C or 50°C

The stability in accelerated aging experiments of the Sulf 1/Metal salt redox system has been investigated in Figure 5. Both cartridges were stored @40°C or 50°C for a given time and evaluated in RFRP compared to fresh cartridges. We have chosen two redox systems:

Sulf 1/Mn(acac) 3 and Sulf 1/Mn(acectate) 3 .

The less reactive Sulf 1/Mn(acac) 3 system (Figure 5A) system is not stable after 5 days of storage in the oven at 40°C or 50°C. Indeed, a decrease of reactivity for aged cartridges is found compared to fresh ones. Therefore, a small amount of inhibitor can be added to ensure better storage stability (Figure 5A, curve 1 vs. curve 2).

Markedly, the most reactive Sulf 1/Mn(acectate) 3 RIS is found rather stable for 3 days of storage at 40°C or 50°C (Figure 5B). Tack-free polymers are still obtained even with aged

Efficiency of these RISs at low temperature

Remarkably, Sulf1/Mn(acac) 3 reactivity was tested at relatively low temperatures.

Polymerization occurs at a temperature of 10 ° C within 6 min using Sulf 1/Mn(acac) 3 (3/3 %wt) (Figure 6 curve 1) and 11 min for Sulf 1/Mn(acac) 3 (2/2 % wt) (Figure 6 curve 2). This indicates that the polymerization remains effective even at low temperature demonstrating the workability of the RFRP process based on sulfinates/Mn complex combination.

Surface analysis

The efficiency of the new proposed systems related to surface curing under air has been investigated by RAMAN confocal-microscopy (Figure 7). According to Figure 7, the C=C conversion of RFRP process using the Sulf 1/Mn(acac) 3 redox couple is clearly improved (Figure 7 curve 1) compared to the benchmark redox system (BPO // 4-N,N-TMA; Figure 7 curve 2). Such a system with stable oxidizing and reducing agents has also better surface curing (in line with high exothermicity) with about 45% C = C conversion at 60 μm depth. By comparison with the BPO // 4-N,N-TMA reference, the conversion is 10% up to a 60μm depth (20). This clearly shows that the surface curing under air is better for the new proposed RIS vs. the BPO/amine reference.

Application

The composite materials are highly desired in polymer science, as they allow better mechanical properties. In this part, we propose the access to composite materials based on glass fibres and organic resin curing using Sulf 1/Mn(acac) 3 (1/1 %wt) system. The impregnation of one layer of glass fibres (thickness= 0.6 mm) with an organic resin and the proposed RIS leads to a good polymerization process (Figure 8 curve 2), where only few minutes (about 320 sec) are required to reach tack-free surfaces.

Structure/reactivity/efficiency relationship

In general, the more reactive reducing agents (in our case the sulfinates) should be characterized by low oxidation potentials. Notably, the lower oxidation potential, the more spontaneous redox process is accomplished in presence of metal salts as oxidation agents. For a better understanding of the reactivity and the efficiency of the different sulfinates and metal systems used in this work, the oxidation and reduction potentials were determined by cyclic voltammetry (Table 2). The free energy changes of the electron transfer reaction (ΔG et ) were calculated for the Sulf salts/ metals redox systems (Table 2), ΔG et = E ox (sulfinate) -E red (metal). By taking this assumption into account, the reactivity must follow this order:

Cu(hfacac) 2 ~ Mn(acetate) 3 > Mn(acac) 3 . However, polymerization data show a slightly different trend i.e. the efficiency of the redox system follows the order: Mn(acetate) 3 > ) Mn(acac) 3 > Cu(hfacac) 2 . This can be attributed to a more complex mechanism than a conventional electron transfer for the formation of initiating free radicals. Finally, this process was also investigated by ESR spectroscopy for a full characterization of the free radicals generated.

For the mixing of Sulf 1 with Mn(acac) 3 in toluene, the ESR-spin trapping experiments (Figure 9) have detected the reactive species RSO 2 • trapped by PBN. Clear correlation of experimental and simulated spectra is found using hyperfine coupling constants (HFCCs) a N = 13.4 6 G, a H = 1.7 4 G which correspond to the RSO 2 • /PBN adduct in the literature (21). These data suggest the proposed redox reaction (r2) between sulfinates as reducing agent and metals as oxidation agent:

Ox + RSO 2 -→ Ox •-+ RSO 2 • (r2)
The radicals generated in (r2) can be assumed as the initiating species for the FRP processes observed above.

Conclusions:

New sulfinate/metal complex redox initiators have been developed for the redox FRP of (meth)acrylate monomers. An excellent reactivity is observed for Sulf 1/Mn(acetate) 3 and Sulf 1/Mn(acac) 3 in mild conditions (under air, at room temperature and without purified monomers). The high efficiency is described by various key parameters: i) high exothermicity, ii) unprecedented workability and iii) good stability in accelerated aging experiments for some proposed systems. Markedly, the gel times can also be adjusted

(2)

according to the concentration of the inhibitor. As a typical application, composite materials using glass fibres are well produced. In the future, different other redox initiators systems will be proposed.

Partie II

(

)

Ox + RSO 2 -→ Ox •-+ RSO 2 •

Introduction

Radical polymerization (FRP) for polymer production is a very important method in many industrial applications. Reportedly, redox polymerization is a widespread used process for reaction at room temperature. The mixture of two compounds, one acting as an oxidizing agent and the second as a reducing agent initiates the polymerization by spontaneous in situfree radical formation. In this RFRP process, a great challenge is to produce polymer with minimal energy consumption in mild conditions i.e ideally without thermal activation, under air and without stabilizer removal. Indeed, compared to thermal polymerization, RFPR occurs under mild condition due to the low bond energy of the oxidizing agent (e.g., peroxides) which results in low activation energy when mixed with the reducing agent (e.g., amines) [1,2,3,4,5,6]. Currently, the reference of redox initiation system (RIS) is the mixture of dibenzoyl peroxide (BPO) with a tertiary amine (e.g.4-N,N trimethylaniline system noted 4-N,N-TMA), but this system poses problems related to stability (storage of peroxides: BPO is not stable in monomer) and amine toxicity [7,8,9,10,11,12,13,14]. In this context, organic compounds without amine and without peroxide capable of reacting in the redox process is in great demand. In this work, we used the combination of Thiophenium (Thio-oxidizing agent)

with sulfinate (sulf-reducing agent) that works under mild conditions and with an unprecedented control that can be worldwide for different applications.

The sulfinates were used in association with tertiary amine in order to improve dentine substrat adherence, or to obtain improved mechanical properties. In this paper, the sulfinates are originaly studied as reducing agent [15,16]. To finish, the composite synthesis is checked as a potential application for this new redox system.

Experimental section

Chemical Compounds

All the chemicals were purchased with high purity and used as received (Scheme 1).

Thiophenium salts and Sulfinates were purchased from TCI-europe and Sigma Aldrich.

Two Cartridges System Used for Redox Experiments

All redox formulations were prepared in bulk in two separate cartridges: a first cartridge with the Thiophenium derivative and the other one containing the Sulfinate. A 1:1 Sulzer mixpac mixer was used to mix the two cartridges at the beginning of each polymerization experiment. As all polymerization experiments were performed at room temperature (~20-25°C) and under air, an oxygen inhibition can be expected, particularly for the surface in direct contact with air [17].

Redox Polymerization in Bulk Followed by Optical Pyrometry

Optical pyrometry was used to follow the polymerization reactions: temperature vs.

time profiles were followed using an Omega OS552-V1-6 infrared thermometer (Omega Engineering, Inc., Stamford, CT) having a sensitivity of ±1 °C for 2 g samples (thickness ∼4 mm). The redox initiator contents will be given in weight with respect to the monomer in the final blend (wt%). The optical pyrometry is used to check the gel time i.e. the time required from a two-component mixing to go from fluid/viscous state to gel/solid one.

RT-FTIR spectroscopy

A JASCO 4100 Real-time Fourier Transform Infrared Spectrometer (RT-FTIR) was used to follow the evolution of the methacrylate peak functionality for the thick samples (1.4 mm) in the near-infrared range from 6130 to 6200 cm -1 .

Electron Spin Resonance (ESR) Spin Trapping (ESR-ST)

Electron spin resonance-spin trapping experiments were carried out using an X-band spectrometer (Bruker EMX-plus). The radicals were observed at room temperature under nitrogen saturated toluene solutions. N-tert-Butyl-phenylnitrone (PBN) was used as a spin trap agent in a similar way as described in other works [18,19,20,21]. ESR spectra simulations were carried out using WINSIM software.

Cyclic voltammetry

The reduction potentials (E red , Eox vs. SCE) of the different compounds were determined by cyclic voltammetry in ACN using tetrabutylammonium hexafluorophosphate (0.1 M) as a supporting electrolyte. The procedure was reported in detail in [18,19,20,21]

Surface Polymer Analysis (z-Profile) through Raman Confocal Microscopy

Raman spectra of cured polymer surfaces were recorded with a Labram (Horiba) spectrometer mounted on an Olympus BX40 confocal microscope, operating at 632.8 nm with a 1800 lines/mm grating. The carbonyl peak area (1690-1755 cm -1 ) was measured as an internal standard while the alkene peak area (1630-1660 cm -1 ) was used to determine the C=C conversion [19].

Results and discussion:

Redox initiation using thiopheniun salts

Effect of the reducing agent:

In the frame of redox initiated polymerization process, an oxidizing agent is mixed with reducing agent leading to the generation of free radicals to initiate FRP. In this first section, three sulfinates used as reducing agents will be investigated for FRP of multifunctional (meth) acrylate monomers for the formation of polymer networks.

The polymerization efficiencies of various redox systems based on Sulfinates/Thio A combination followed by optical pyrometry are depicted in Figure 1A. The Sulf 2/Thio A and Sulf 3/Thio A systems showed an exothermicity peak around 90°C with different gel times (⁓450 sec for Sulf 2/Thio A and ⁓570 sec for Sulf 3/Thio A, curve 1 and curve 2, respectively). Quite interestingly, a different reactivity is obtained for Sulf 1/Thio A, as illustrated in Figure 1A, curve 3, a maximum temperature of 100°C is reached 120 sec after mixing. Sulf 1 likely reacts rapidly with Thio A as it can be a consequence of a favorable reduction process. It is important to note that sometimes, a longer gel time is interesting for workable properties. The fast redox initiating ability of Sulf 1/Thio A combination makes this system highly interesting and it will be considered as the most reactive one used for the following section.

The effect of the reducing agent content is directly observed for Sulf 1/Thio A (Figure 1B). When using a low concentration of Sulf 1 (0.35%wt and 0.5%wt, curve 1 and curve 2, respectively), the Sulf 1/Thio A system leads to an exothermic peak around 95 °C after 350 seconds. On the opposite, raising the sulf 1 content to 1%wt (Curve 3, Figure 1B), a higher reactivity is observed, the gel time is reduced and the high exothermicity is reached after only 120 seconds. In this case, the optimum content of Sulf 1 is 1% wt in combination with 1% wt of Thio A for a fast polymerization. Noteworthy, different reactivity can be obtained on demand by using different contents of Sulf 1 in order to delay or accelerate the reaction.

Therefore, the excellent reactivity of Sulf 1/Thio A at low concentration points out a very efficient redox mechanism. As Sulf 1/ Thio A system shows the best reactivity in redox initiating systems, the polymerization processes were also followed by Real-Time FTIR spectroscopy (Figure 2). Interestingly, a drastic reduction of the gel time is observed due to the possible light activation upon irradiation with the LED@405nm (I=230 mW/cm 2 ): from 120 sec to 30 sec. The photoactivation of this system allows a fast control of the polymerization curing time and a higher methacrylate monomer conversion upon the first seconds of irradiation, for an "on demand" system that can be triggered by light.

Effect of monomer/resin:

The Sulf 1/Thio A system shows a good compatibility with different monomers or resins. The redox FRP is much faster using resin 1, resin 3 and resin 4 than resin 2.

Impressively, the maximum temperature is reached much faster in resin 3 (T = 200°C).

Regardless of the good solubility of PIS in resin 2 compared to other resin used, only 100°C exothermicity was observed after 900 sec, which is quite slow. The trend in efficiency by following the maximum temperature reached and the lower gel time (Figure 3A): resin 3 (T=200°C, gel time=40sec) > resin 4 (T=80°C, gel time=70sec) > resin 1 (T=100°C, gel time=120sec) > resin 2 (T=100°C, gel time=920sec). The main factor leading to a poor reactivity in resin 2, despite a good solubility, can be explained by its very low viscosity (0.006 Pa.s, Table 1). Indeed, in very low viscosity samples, the oxygen inhibition is more important and a delayed reaction can be observed. In other words, the polymerization of

Redox initiation with different thiophenium salts

Sulf 2 and Sulf 3 in combination with Thio B and Thio C did not induce any polymerization (Figure 4A), so they are discarded in this section. Therefore, the RFRP has been focused on Sulf 1/Thiophenium (Figure 4A) combination. The polymerization efficiency of various redox systems followed by optical pyrometry are depicted in Figure 4B. The redox polymerization is very efficient using Sulf 1/Thio A (gel time ~ 120 seconds). In the case of Thio B and Thio C, longer gel time are observed which is interesting when a delayed curing is required, the temperature reaches ~ 100-110°C (Figure 4B). These results explained the possibility to use different redox oxidizing agents. For comparison, the reactivity of thiophenium in Sulf 1 / Thio combination follows this order: Thio A > Thio C > Thio B. As a general rule, in the redox initiated polymerization approach, a higher reduction potential of the oxidizing agent (in our case of the thiophenium component) must lead to a better reactivity. As noteworthy point, Thio A can be described as strong electron acceptor, bearing fluorine atoms in the skeleton. The reduction and the oxidation potential will be discussed in the proposed mechanism part.

Effect of inhibitor

In order to control the reaction, a well-known radical inhibitor 4-hydroxy-2,2,6,6tetramethylpiperidin-1-oxyl (noted tempol) was added in different contents in the formulation.

Remarkably, as shown in Figure 5, the use of this inhibitor strongly affects the polymerization in terms of gel time, without important effect on the exothermicity of the reaction. Without inhibitor, the gel time is very short (~120 sec, Figure 5A, curve 1), and the workability of the system won`t be good depending on the final application of the system. Therefore, the gel time is shifted proportionally by adding different contents of inhibitor (from low content 0.02%wt in curve 2, to high content 0.15%wt, Figure 5B). The reaction is delayed; e.g. from 120 seconds without inhibitor to 600 sec in the presence of 0.04% wt of inhibitor. When very high content is added (0.15%wt, curve 6), the redox polymerization is highly inhibited (gel time = 5000 sec). The optimum content of inhibitor is an important factor for good workability. The effect of inhibitor was also demonstrated for Thio B and Thio C based redox initiating systems. The gel time for the reference without inhibitor, is roughly equal to 600 sec and 420 sec for Sulf 1/Thio B and Sulf 1/Thio C, respectively. Then, the redox reaction is easily delayed by adding the inhibitor (Table 2). The gel time can be shifted up to approximately 3400 seconds (Almost 30 min). Interestingly, a good exothermicity is still observed (110-120°C), and a desired gel time is reached depending on the content of inhibitor for a good workability.

Stability study in accelerating aging @ 50°C

As the system based on Sulf 1/Thio present excellent reactivity to initiate the redox FRP, we propose to check the stability upon storage. It has been noted that both components (Sulf 1/Thio A) is stable for 4 days of storage @ 50°C (Figure 6A). Tack-free polymers are still observed confirming the stability in accelerating aging experiments (both cartridges stored in the oven @50°C). The gel time is not significantly affected by storage comparing to a fresh formulation (Figure 6A, curve 1 vs. curve 2).

In the case of Sulf 1/Thio B (Figure 6B) and Sulf 1/Thio C (Figure 6C), a rather good stability is observed, a good exothermicity sill recorded after 7 days of storage @50°C. Even if the gel time is slightly delayed, a tack-free polymer is always obtained. The excellent stability of Sulf/Thio systems makes them highly interesting and can extend the areas of application of redox induced polymerization. days (T=50°C).

Efficiency of RIS at low temperature

More interestingly, the Sulf 1/Thio A system is also efficient at low temperatures.

When the RFRP is carried out @ 5°C, the polymerization occurs in min. This indicates that the polymerization is still efficient even at low temperatures highlighting the workability of redox FRP based on Sulf/Thio systems.

Structure/reactivity/efficiency relationship

For a better understanding of the reactivity and efficiency of different Sulfinates and thiophenium systems used in this work, the oxidation and reduction potentials were determined. by cyclic voltammetry. The free energy change of electron transfer reaction (ΔG et ) has been calculated for Sulf /Thio redox systems (Table 3), ΔG et = E ox (Sulfinate) -E red (Thiophenium). In a redox initiating system, a higher reduction potential of the oxidizing agent must lead to a better reactivity. By taking into account this hypothesis, the reactivity must follow this order: Thio B > Thio C > Thio A. In contrast, the experiments show that the efficiency of the redox system does not follow this order of reduction potential: Thio A > Thio C > Thio B. This can be ascribed to a more complex mechanism than a classical electron transfer for the formation of initiating free radicals for the RFRP.

@5 C, 12 min

Polymer RSO 2

• radicals [22]. This suggests the proposed redox reaction (r1) between Sulfinates as reducing agent and thiophenium as oxidation agent.

(r1): Ox + RSO 2 -→ Ox •-+ RSO 2

•

The radicals generated in (r1) can be assumed as the initiating species for the FRP processes observed above.

Surface analysis

To highlight the efficienty of the new proposed systems to overcome the oxygen inhibition, the surface curing has been investigated by confocal RAMAN-microscopy (Figure 8). The C = C conversion is therefore largely improved compared to the benchmark redox system (BPO // 4-N, N-TMA) (Figure 8). Such a system with stable, oxidizing and reducing agents have also better surface hardening (in line with high exothermicity) with about 40% C = C conversion at 60 μm depth. By comparison with the BPO // 4-N,N-TMA reference, the conversion is only 10% up to a 60μm depth [19].

Application

Thanks to the high reactivity of Sulf 1 / Thio A as redox initiating system with both stable and highly workable behavior, application for the curing of composites is proceeded.

The composite materials are highly desired in polymer science, as they allow better mechanical properties. In this part, we propose the access to composite materials based on

(2)

glass fibres using Sulf 1/Thio A (1/1 %wt) system. The impregnation of one layer of glass fibres (thickness= 0.6mm) with organic resin leads to a good polymerization process (Figure 9), where only few seconds (about 350 sec) is required to reach tack-free surfaces.

Figure 9.

Optical pyrometric measurements for the curing of glass fibers/Resin 1 composites in the presence of Sulf 1 / Thio A after mixing with redox initiating system for 50% glass fibres and 50% of organic resin (1/1%wt).

Conclusions :

New redox initiating systems based on Sulfinate/Thiophenium have been developed

for the redox FRP of (meth)acrylate monomers. A high efficiency is observed for Sulf 1/ Thio A under air and @ room temperature. The high efficiency is described by different key parameters: i) high exothermicity, ii) umprecedented workability and iii) excellent stability in accelerated aging. Interestingly, the gel times can also be tuned as function as the concentration of the inhibitor, which highlight the interest of these kinds of initiating systems

Cured glass fibre

for industrial applications. As a typical application, a composite material using glass fibers is well-produced. In the future, different stable redox initiating systems will be proposed for potential industrial applications.

Chapitre 2: New Pure Organic and Peroxide-free Redox Initiating Systems for Polymerization in Mild Conditions

Abstract:

Redox initiating systems are highly worthwhile for polymerization in mild conditions (at room temperature -RT) without external thermal or light activation. With high performance redox initiating systems RIS, the free radical polymerization FRP can even be carried out under air and without inhibitors/stabilizers removal from the monomers/resins.

However, efficient RIS are still based on peroxides or metal complexes. In this work, a pure organic and peroxide-free RIS is presented based on the interaction of a well-selected triarylamine derivative (T4epa) with Iodonium salt used as reducing and oxidizing agents, respectively. The redox polymerization (Redox FRP) was followed through pyometry and thermal imaging experiments. Remarkably, a full control of the work time as well as a high reactivity is observed for mild conditions.

1.Introduction

For the production of polymers, Free Radical Polymerization (FRP) is a widespread used process. [1] In this context, thermal or photochemical initiations are mostly used but twocomponent redox initiation for Redox FRP is also a highly robust technique used since the second half of the 20th century. [2][3] Compared to thermal and photo polymerization, Redox FRP can be carried out in mild conditions i.e. without energy consumption as the reaction can be performed out at room temperature without any activation (light or heat). The basic principle of Redox FRP is quite straightforward: a Redox Initiating System (RIS) is dissolved separately in two components (often called cartridges). Then, the mixing of the two components (one containing the oxidizing agent and the second one containing the reducing agent) leads to initiating free radical formation through a redox reaction.

Currently, the benchmark RIS is based on the dibenzoyl peroxide (BPO)/tertiary aromatic amine (e.g. trimethylaniline -TMA) couple. This well-established system is already used in many applications for the preparation of biomedical materials, emulsion polymerization, the curing of composites or adhesives... [4][5][6][7][8][9] Albeit, this benchmark BPO/amine system was the cornerstone of the Redox FRP, it is now necessary to replace it due to severe handling/toxicity/hazard issues. Indeed, BPO is not stable (explosive risk associated with peroxides handling, pressing regulations on peroxides…) [10][11] and classical peroxides cannot be stored in monomers leading to highly disymetrical cartridges (one with the reducing agent in the monomer and a second one for BPO alone).

However, under mild conditions (room temperature, under air, no stabilizer removal), alternative systems are not highly efficient. [12][13][14][15][16][17][18][19] This is the reason why we have proposed recently several RIS BPO-free for Redox FRP. [20][21][22][23][24][25][26] However, many of the reported systems still involved the presence of metal complexes (Mn, Cu or V) [20][21][22][23][24][25][26] due to their favorable redox potentials. Therefore, in the present paper, a pure organic and BPO-free approach preventing the use of both peroxides and metal complexes is provided. Specifically, iodonium salts were used as oxidizing agents to generate aryl radicals through their reduction by a carefully selected reducing agent (Tris [4-(diethylamino) phenyl] amine -T4epa) in r1:

ED + Ar 2 I + → ED •+ + Ar • + Ar-I r1

We have characterized the Redox FRP of a benchmark methacrylate monomer blends using different techniques (optical pyrometry and thermal imaging experiments). The workability of the resin through its gel time (GT) is also a crucial parameter: i) too short gel times don't allow the control the shape of the polymer i.e. a too fast polymerization occurs or ii) long gel time are often associated with low polymerization rates, partial curing and tacky surfaces.

Obviously, the ideal gel time depends of the final application (composites, dentistry, chemical anchors …) but an excellent polymerization must be always obtained in mild conditions (under air, in presence of stabilizers). In this work, a precise control of the gel time is provided with the new proposed RIS through the contents of redox agents or the use of an additional salts.

Materials and Methods

Chemical Compounds

All chemicals were purchased with high purity and used as received (Scheme 1).

Tris [4-(diethylamino)

Two Cartridges System Used for Redox FRP Experiments

All redox formulations were prepared in bulk in two separate cartridges: a first cartridge containing T4epa and the other one containing the iodonium salt (Iod). A 1:1 Sulzer mixpac mixer was used to mix the two cartridges at the beginning of each polymerization experiment.

As all polymerization experiments were performed at room temperature (~20-25°C) (excepted specifically indicated) and under air, an oxygen inhibition can be expected, particularly for the surface in direct contact with air [20][21][22][23][24][25][26]. For all experiments, the monomers were used without stabilizer (4-methoxyphenol) removal.

Redox FRP in Bulk Followed by Optical Pyrometry

Optical pyrometry was used to follow polymerization reactions: temperature vs. time profiles were followed using an Omega OS552-V1-6 infrared thermometer (Omega Engineering, Inc., Stamford, CT) having a sensitivity of ±1 °C for 2 g samples (thickness ∼4 mm). [20][21][22][23][24][25][26] The redox initiator contents will be given in weight with respect to the monomer in the final blend (wt%). The optical pyrometry is used to check the gel time i.e. the time required from a two-component mixing to go from fluid/viscous state to gel/solid one.

Redox Polymerization in Bulk Followed by Thermal Imaging Experiments

The temperature reached by the samples has been recorded during the reaction time thanks to an infrared thermal imaging camera (Fluke TiX500). [27] Scheme 1. T4epa and Iod used in the proposed Redox Initiating System and the salts used as additive in the RISs.

T4epa Iod

LiTFSI, NaTFSI and KTFSI:

Results

The T4epa/Iod RIS charactaerized by optical pyrometry and thermal imaging experiments

In this section, the T4epa/Iod RIS is used for the polymerization of the BM resin (Scheme 2) using the 1/1 mixing of the two cartridges i.e. one containing T4epa in BM and the other one Iod also in BM. The Redox FRP is followed by optical pyrometry that recorded the temperature vs. time after mixing. The FRP process being exothermic, an increase of temperature directly reveals the occurrence of the polymerization reaction. The Gel Time (GT) is defined here as the time where the maximal slope of the temperature is observed (corresponding to the time for the maximal polymerization rate). Remarkably, in Figure 1, T4epa/Iod RIS is found highly efficient to initiate the polymerization of BM in mild conditions (under air, at RT and without stabilizers removal) with GTs ranging from 50s to 450s depending of the concentrations of the redox active compounds i.e. it is worth noting that the GT can be finely controlled by their respective contents. Interestingly, the maximal temperature reached is similar to those obtained for dibenzoylperoxide/trimethylaniline (1%/1%) benchmack system (100°C and GT = 110s) suggesting that the new proposed RIS system is competitive in term of redox initiation ability to well-established BPO/amine references. In all case, tack-free polymers were obtained with the proposed systems vs. tacky surfaces for BPO/trimethylaniline highlighting a better ability of the T4epa/Iod RIS to overcome oxygen inhibition vs. BPO/amine reference. A multiple regression analysis was carried out to find the relationship between GT and the respective contents of T4epa and Iod (Figure 2). Interestingly, the following equation (eq.1) is found for weight contents of Iod andT4epa in the range 0.5-2% (w/w):

GT = 8,7 -2,5 [T4epa] -2 [Iod]
(r² = 0.9) eq. 1

The Eq. 1 clearly suggests that an increase of Iod or T4epa content decreases GT. Markedly, rather similar coefficients (2.5 vs. 2) suggest that the content of both compounds have a rather similar effect on GT suggesting a stoichiometric reaction. Such a relationship (eq.1) can also be highly worthwhile to control the work time in different applications. To better understand the localization of the Redox FRP process in time and in space, thermal imaging experiments in a narrow chemical pill box were realized under air (Figure 3).

Remarkably, it is found that the polymerization starts at the top air interface (t = 170s) before a frontal polymerization occurs from the top to the bottom (see for t = 180s and t = 190s).

This suggests that the oxygen positively participates to the redox initiation in agreement with the ability of the proposed T4epa/Iod RIS to overcome the oxygen inhibition vs. the classical BPO/amine systems that are usually highly inhibited. Experimental GT (min)

Calculated GT (min)

Figure 3. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using the T4epa/Iod (2%/0.6% w/w) RIS and the associated thermal imaging pictures at different times.

Salt additive effects in T4epa/Iod RISs

In this part, an iodonium salt bearing a Chloride anion (noted Iod-Cl) is used instead the idonium salt of the previous section (noted Iod) based on hexafluorophosphate anion to probe the counter anion effect on the RIS reactivity. Interestingly, for the Iod-Cl, no polymerization occurs in presence of T4epa (Figure 4, curve A) showing that the iodonium bearing PF 6 -is much more reactive. This is related to the much better solubility of Iod vs. Iod-Cl that exhibits a poor solubility in (meth)acrylates. To overcome this latter issue, an in-situ counter anion exchange is investigated by addition of different salts (with different counter anions) in the Iod-Cl cartridge. Markedly, this approach leads to excellent Redox FRP (Figure 4, curves B-G) and the GT can be controlled by the selection of the salt used i.e. GT ~ 370 s with NaBF 4 and GT ~ 70s for NaPF 6 . The GT decreases in the series: NaBF 4 > NaSbF 6 > LiTFSI > NaTFSI > NaPF 6 > KTFSI. The effect of the additional salt concentration was investigated in Figure 5. An increase of the salt concentration leads to a decrease of GT i.e. GT ~ 150s for NaPF 6 (0.5% w/w) (Figure 5, curve A) vs. GT ~ 70s for NaPF 6 (2% w/w) (Figure 5, curve B).

The same effect is observed for LiTFSI (Figure 5, curves E-H) and NaBF 4 (Figure 5, curves I-J). Therefore, the additional salt content is another elegant way to control the work time.

Inhibitor effects in T4epa/Iod RISs

Additional inhibitors are often used in practical applications to improve the stability of the cartridge and/or to control the gel time. Therefore, the effect of additional inhibitor (4-Hydroxy-TEMPO and 4-methoxyphenol) is investigated in Figure 6. In presence of 4-Hydroxy-TEMPO (0.05% w/w), GT increases (Figure 6, curve A vs. curve B) but interestingly, 4-methoxyphenol does not lead to higher GT. Therefore, we can conclude that Hydroxy-TEMPO can be recommended to adjust the GT if necessary while 4methoxyphenol can be used to improve the stability of the system upon storage without important modification of GT.

Stability in accelerated aging experiments

For a deeper characterization of the new proposed T4epa/Iod RIS, the stability of both cartridges in aging experiments has been investigated (Figure 7). A good stability is found both for aging @50°C (Figure 7, curves B and C) or at RT (Figure 7, curve D) with a low effect on the GT (change < 30s compared to the fresh cartridges -Figure 7 curve A). keeping in mind the very poor stability of peroxides (particularly BPO) that cannot be stored in monomers, the good stability of Iod and T4epa in BM is a real breakthrough for the Redox FRP field.

Reactivity at low temperatures

Finally, Redox FRP can also suffer from lower reactivity at low temperatures. To check the high reactivity of the T4epa/Iod RIS, the polymerizations @25°C and 10°C are compared in Figure 8 (curve A vs. curve B). Obviously, a higher GT is obtained @10°C

Discussion

From all the results obtained above, it clearly appears that the T4epa/Iod RIS is very efficient in mild conditions (under air, without inhibitor removal and even at low temperature). Taking into account the electron donor properties of aromatic amines and the electron acceptor properties of the iodonium salts, the expected redox reaction is depicted in Scheme 3. The reduction of iodonium salt leads to the formation of highly reactive aryl radials that correspond to highly efficient structures for the addition onto (meth)acrylates with very high addition rate constants (k ~ 10 8 M -1 s -1 ). Using Iod-Cl in presence of additional salts (e.g. NaX), an in-situ counter anion exchange is expected according to Scheme 4 leading to a more soluble and/or more electron acceptor iodonium salt than the starting Iod-Cl. This latter approach is useful to control the gel time.

Scheme 4.

Expected anion exchange to increase the reactivity of iodonium salts in the T4epa/Iod RISs.

Introduction:

Exploiting highly efficient, environmentally friendly, and economic photo/thermal dual initiators is always the pursuit of materials practitioners and innovators. 1-5 Indeed on one hand thermal manufacturing of polymers shows no spatial resolution and uses hazardous components (peroxides or aza compounds). 6 On the other hand photopolymerization is well time and spatially resolvedsee for example the photoredox work of Boydston, Hawkers and other groups 4,5,7-9but lacks of robustness in thick or filled materials (e.g. composites). 10 Recently; CTCs as a kind of efficiency, low cost in-situ formed initiator has attracted much attention due to its series priorities, such as safety, spatial control, highly efficient process at room temperature (RT) and reduced emission of volatile organic compounds (VOC). 11-17 Most importantly, high-tech composites and 3D products can be manufactured thanks to this kind of new initiators dual photo/thermal initiating ability, which cannot be obtained by single curing method. 18-23 On one hand, high-tech composites with tack free and smooth surfaces can be easily fabricated by employing these kinds of CTCs via fast photochemical curing of the surface associated with a dark thermal curing in depth. 24,25 On the other hand, large and complex structure can be manufactured by fast thermal curing of the internal volume associated with finely surface repairing or modifying by 3D photo printing. 9,26 Recently applied CTCs based on phosphine, aniline, pyrrole, and indole acceptors were exploited as photo/thermal dual initiators but without systematic study. 24-28 Some amine/Iodonium salt CTCs were also reported to initiate cationic polymerization. 13 In this paper a series of amines will be systematically investigated to find out the impacts of the amine structure on the CTCs' initiation performance (Scheme 1). The expected chemical mechanism is an electron transfer reaction between the amine (reducing agentelectron donor) and the iodonium salt (oxidizing agentelectron acceptor) that can be activated by light or by heat (possibility of dual activation). Therefore, the relationship between the amine molecular structures and the associated photo initiating ability under visible light or thermal initiating temperature will be examined.

RT-FTIR Spectroscopy for Photopolymerization

The sample was injected into a circular mold (6 mm inner diameter) that was pasted onto polypropylene film. Then it was placed on a sample holder in a horizontal accessory (transmission mode). This set-up has been used in previous works. 24-25 A Jasco 4600 Real-Time Fourier Transformed Infrared Spectrometer (RT-FTIR) was used to follow the C=C double bond conversion (for both acrylate and methacrylate functionalities) versus time for polymerizations of 1.4 mm thick samples in laminate. The decrease of the C=C double bond at 6130-6200 cm -1 was followed. A LED@405 nm (Thorlabs) having an intensity of 110 Resin 3 TMPTA mW/cm² at the sample position was used for the photopolymerization experiments. A low light intensity has been selected to better highlight the good photoinitiating ability of the CTCs. For a lower light intensity (35 mW/cm²), a photopolymerization process can also be observed, the main limitation being the oxygen inhibition for free radical polymerization processes as for classical photoinitiators.

Differential Scanning Calorimetry (DSC) for Thermal Polymerization

Different monomer formulations (10 mg) in presence of CTCs were inserted in an aluminum 100 µL crucible. Thermal polymerization was carried out from 0°C to 300°C at a heating rate of 10°C/min under nitrogen flow (100 mL/min). A Mettler-Toledo DSC differential scanning calorimeter was used.

Computational Procedure

Geometry optimizations 29 were carried out at UB3LYP/LANL2DZ level; geometries were frequency checked; the Molecular Orbitals (MOs) involved in the electronic transitions were extracted. The electronic absorption spectra for acceptor (Iod), different amine donors and [amine-Iod]CTCs were calculated from the time-dependent density functional theory at MPW1PW91/LANL2DZ level of theory on the relaxed geometries calculated at the UB3LYP/LANL2DZ level of theory (single point in DCM).

UV-visible Absorption Spectroscopy

UV-vis absorption spectra in DCM (1 cm quartz cell) were acquired using a JascoV730 spectrophotometer.

Direct Laser Write Experiments

Photopolymerizable resin (1.4 mm thick) in presence of CTC was disposed onto a microscope slide. Laser write printer using an intensity of 100 mW @405 nm (spot diameter ~50 μm). The generated patterns were analyzed by a DSX-CB numerical optical microscope.

Preparation of Composites

A Dymax UVC-5 UV light-curing conveyor was used to carry out photocuring of the composites. The prepregs were put on the conveyor belt with a speed of 2 m/min across the LED lamp irradiated area. A UV LED lamp@395 nm having an intensity of 4 W/cm² was used for the curing experiments of both glass fibers composites and carbon fibers composites (the thicknesses are: 1.5 mm/layer for glass fibers and 0.5 mm/layer for carbon fibers).

An oven was used to investigate the thermal curing behavior of the composites. The prepregs were inserted in the oven for 10 min at 150°C (curing under air).

Mechanical Performance of Composites Investigated by Dynamic Mechanical Analysis (DMA).

The storage modulus (E') and loss tangents (tan δ) of the cured samples were obtained with a Mettler DMA861 Visco analyser at 3 Hz for the temperature range from 0 to 300°C at a heating rate of 5°C/min. The 3-point bending test was carried out using bar-shaped samples, 22×10×(1-5) mm 3 , set on the dual cantilever bending fixture with 0.1% strain. The Tg value was defined as the temperature of maximum tan δ (= E''/E').

Results and discussion:

Comparison of the CTCs from Different Amine Donors

Photoinduced Polymerization Efficiency

Photoinitiating ability for the different combinations (amines/Iod) was investigated firstly. RT-FTIR curves indicated that DMA, TMA, DMAPE, PDA, PT, and TIAPPDA exhibited excellent photo initiating ability both for resin 1 and resin 2, while amines or Iod alone does not show any photoinitiating ability (see Figure 1). Three factors appear to be important for efficient amines: first triphenylamine is not very efficient as the nitrogen rich atom is very planar and does not tend to form a CTC (examples of TPATPA and CTPA, which confirms by early literature 11 ); second N-aromatic amines are efficient if aromatic cycle is electron rich and if they show a good solubility. Most of other amines because of their bad solubility in (math)acrylates only showed poor photoinitiating ability (DCDA, MG, TMPDA, CTPA, TPATPA, DMAPCHD). As comparison, four of the amines with simple structure showed better effect on the resin conversion, which can be explained by the theory that small amine molecules have better solubility and can combine with Iod easily to form CTC than that of bigger molecules (less steric hindrance). Symmetry in TMPDA does not look like a favorable structure likely due to the not enough localized electron donating character (for the CTC). All the data was summarized in Table 1.

Thermally Induced Polymerization

Then, thermal initiating ability of the combination of different amines and Iod was investigated (Figure 2). DSC curves indicated that most of the amines exhibited excellent initiating ability both for resin 1 and resin 2, which can be ascribed to the better solubility at elevated temperature. Variation of the amine structure leads to variations in either activating temperature and conversion (thermal efficiency in J/g). For activation temperature, amines with good photoinitiating ability possess lower thermal initiating temperature (<150 ℃), such as DMA, TMA, DMAPE, PDA;on the other hand, the amines with bad photo initiating ability need higher thermal initiating temperature (>150 ℃). All these data confirm that a CTC efficiently formed is both active through light and thermal stimuli. Initiating temperature range is also sometimes related to the relevant CTCs stabilization energy (higher energy barriers to be overcome, Table 1). The conversion (J/g) is higher (> 100 J/g) when N-aromatic amines have donating substituent compared to neutral (DMA not very efficient), also triphenylamine-like structure is not efficient compared to N-aromatic amines.

Molecular Modeling Investigation

To confirm the formation of CTCs, the geometry optimizations, MO calculations and simulated UV-vis spectra of the molecules were investigated through molecular modeling at the density functional theory level. The frontier MOs and calculated UV-vis spectra for Iod (acceptor) alone, amines (donors) alone and [amine-Iod]CTC are shown in Table 2. For all the CTCs with good photo initiating ability, both the LUMO (lowest unoccupied molecular orbital) and HOMO (highest occupied molecular orbital) are located on two different parts of the CTC, confirming the possibility to generate CTCs between these molecules. Interestingly, the energy gap between the LUMO and the HOMO in CTCs is lower than that of amine or Iod alone. As predicted by molecular modeling (Table 2), bathochromic light absorption further confirmed the formation of CTCs, which makes them suitable for visible light activated polymerization. The other calculated results from different amines and CTCs were listed in Table S1. Quite interestingly in the case of MG the CTC does not show a LUMO located on the iodonium salt which confirms the lack of reactivity observed. The stabilization energy calculated in Table 1 corresponds to the energetic stabilization in the CTC vs. amine and Iod alone. No clear correlation between this stabilization energy and the polymerization temperature can be found as these calculations are carried out in the gas phase and probably does not take into the solvation effects.

UV-vis Spectra Investigation

To further prove experimentally the formation of the CTCs (see the predicted bathochromic shift in Table 2), UV-vis spectral investigations were conducted. For amines alone or Iod alone, the absorption is only located in the ultraviolet region (<< 400 nm) (Figure 3 A-D, curve 1 or 2). Interestingly, upon mixing of these donors and acceptor, visible light absorption appeared as observed (Figure 3

Direct Laser Write Experiment

Laser write experiments were conducted to examine the possibility of spatial control of the CTC photoinitiation at RT for Resin 1. When the concentrations of the donor and acceptor were kept at 0.7 wt% and 0.7 wt%, respectively, well-resolved 3D written patterns (thickness ≈ 1.2 mm) from [TMA-Iod]CTC system (Figure 4) were obtained by laser induced polymerization. 3D writing results also revealed the robust towards O 2 inhibition of this CTC resin system, which makes them useful in coatings or light-induced additive manufacturing. Also, the step width between the non-polymerized and polymerized resin around 50 μm, is very close to the one of the laser beam exemplifying a good spatial resolution. Specifically, because the laser's printing speed is very fast, before the laser irradiated parts being heated, the laser has moved to the next printing point. Therefore, there is no thermal propagating effect observed during the printing process.

Conclusions :

The . aromatic amine) and an electron acceptor (e.g. thiophenium salt) at the ground state can lead to the formation of a charge transfer complex, also known as electron donor-acceptor complex (EDA). In an interesting way, the approximation of the donor-acceptor is able to provide an enhanced visible light absorption for the new formed CTC compared to the separated initial compounds which are not absorbing visble light. This change in visible light absorption also represents an easy method to identify the formed CTC. The formation of the proposed CTCs structures was examined and confirmed by UV-visible experiments and molecular modelling.

Moreover, RT-FTIR (Real-Time Fourier Transform Infrared Spectroscopy) was used to cover the photochemical study which is carried out under mild irradiation conditions (light-emitting diode (LED) @405 nm), whereas the thermal study was carried out using DSC (Differential Scanning Calorimetry) as a thermal analysis technique. Excellent Photo/Thermal initiating abilities are showed in the presence of the new proposed initiating systems for the FRP process. Finally, the structure/efficiency/reactivity relationships of the different proposed CTCs are discussed.

Introduction:

Obviously, visible light-induced polymerization reactions require the presence of a colored molecule (able to absorb light) called a "Dye" in the photoinitiating system [1,2]. It should be noted that in free radical polymerization processes, the photoinitiator (PI) can initiate the polymerization reaction either alone once it absorbs the light (e.g. Type I cleavable photoinitiator) according to a unimolecular fragmentation process [3][4][5], or combined with an additive or a co-initiator (e.g. Type II non-cleavable photoinitiator [6,7]) which do not absorb light but react with the photoinitiator through an electron and/or proton transfer mechanism, either in the presence of an appropriate photosensitizer which allows to shift the absorption spectrum of the photoinitiator towards longer wavelengths adapted with those emitted by the light irradiation source used.

Recently, the search for photoinitiators which are able to initiate the polymerization process and at the same time to be regenerated during the course of the reaction was highly desired. These photoinitiators react with an oxidizing agent or a reducing agent through an electron transfer mechanism, and they are known as "Photoredox Catalysts (PCs)". Several examples of such type of photoinitiators are reported in the literature [8][9][10][11].

Whether it is a type I photoinitiator, a type II photoinitiator, a photosensitized photoinitiator or a photoredox catalyst, all the four types lead to the formation of reactive free radicals able to initiate the polymerization process.

Apart from these types of photoinitiating systems, charge transfer complexes (CTCs) constitute a very interesting family of polymerization initiators. In such a case, a new structure called "CTC" is generated at the ground state between an electron donor and an electron acceptor [12,13]. This latter structure is characterized by an improved visible light absorption compared to the oxidizing agent alone or the reducing agent alone. Interestingly, CTCs can be used as double-acting (photochemical and thermal) initiators. Such behavior makes it possible to initiate the polymerization process either in the presence of light or in the presence of heat. Once these concerned structures (CTCs) are irradiated or heated, they are able to generate reactive initiating species (radicals or cations) responsible to initiate the polymerization process. Otherwise, this type of initiators is able to initiate the photopolymerization processes without the presence of additional dye, paving the way for dye-free photoinitiating systems. Several examples of CTCs structures are reported in the literature [13][14][15][16][17][18]. The development of new charge transfer complexes is at the center of our study due to the numerous features that accompany this type of initiators, starting from their salt also noted Thio or R 2 S (+) CF 3 ) was obtained from Tokyo Chemical Industry (TCI). N,N-Dimethyl-p-toluidine (DMT) and N-(2-Hydroxyethyl)-N-methyl-para-toluidine (MHPT) were obtained from Sigma Aldrich. 1-Phenylpyrrolidine (PP) was obtained from Alfa Aesar. A benchmark monomer blend was selected as methacrylate resin for radical polymerization.

Free Radical Polymerization (FRP) followed by Real-Time (RT)-FTIR Spectroscopy

In this research, several combinations based on Thiophenium salt/Amine (2%/2% w/w) the monomer content (w/w). The photopolymerization process was carried out under air, and the photosensitive formulation is put in a mold of ∼7 mm diameter and 1.4 mm of thickness.

Otherwise, the characteristic peak of the double bond content of methacrylate function was continuously followed by real time (RT)-FTIR spectroscopy (JASCO FTIR 4100) at about 6160 cm -1 . The procedure followed to monitor the photopolymerization profiles has been already reported in detail in [21][22][23].

Differential Scanning Calorimetry (DSC) Technique

A differential scanning calorimetry (Mettler-Toledo DSC) technique was used in order to highlight the thermal initiating abilities of the investigated charge transfer complexes (CTCs). Different combinations based on Thiophenium salt/Amine (2%/2% w/w) were tested for the thermal FRP process of methacrylates. The weight percent of the different chemicals is calculated according to the monomer content (w/w). Actually, the investigated formulations are put in 40 l aluminum crucibles. The thermal polymerization was monitored in the 0-300°C temperature range at a heating rate of 10°K/min, under a nitrogen flow of 100 ml/min.

UV-Visible Absorption Experiments

UV-Visible absorption experiments were used to unambiguously identify the formation of the charge transfer complexes (CTCs). Indeed, a bathochromic shift towards the visible region is observed once the electron donor and the electron acceptor are mixed together. A JASCO V730 UV-visible spectrometer was used in order to achieve this study.

Computational Procedure

The optimized geometries as well as the frontier molecular orbitals (HOMO and LUMO), and the predicted UV-visible absorption spectra of thiophenium salt alone, amine alone, and the formed [Amine-Thiophenium] charge transfer complexes (CTCs) were calculated at the Density Functional Theory (DFT) level (UB3LYP/6-31G*). The computational procedure was described by us in [24]. Therefore, the concerned CTCs structures should be characterized by a strong bathochromic shift compared to the primary separated reagents due to their reduced ∆E (HOMO-LUMO) . For the predicted UV-visible spectra, the results obtained also showed a bathochromic UV-visible absorption for the CTC compared to Thiophenium salt alone or amine alone for which no absorption was observed above 350 nm in agreement with the reduced ∆E (HOMO-LUMO) discussed above. The good matching between the CTC absorption spectrum and the emission spectrum of the visible light irradiation source ensures a favorable photopolymerization process activated under violet/blue light. The UV-visible absorption experiments were carried out in dichloromethane (DCM), and the results are presented in Figure 1. It should be noted that the use of a weak or non-polar solvent has a great effect when using the CTC approach. In fact, a weak or non-polar solvent promotes the formation of CTC and prevents the interaction of the primary materials with the solvent, thus providing a better detection of the CTC structure. It is fairly clear that when amine (electron donor) or thiophenium salt (electron acceptor) are severally dissolved in the solvent, no absorption was observed in the visible range for both of them and the color of the solution was transparent (Figure 1). 1A vs. Figure 1B and Figure 1C, respectively; see also Table 1 for the calculated data).

Results and discussion:

Molecular Modelling and UV-visible Absorption Experiments

This shows that MHPT exhibits perhaps a better ability to act as electron-donating compound in CTC structure, and this has also the advantage of extending the variety of wavelengths for the sources used in photopolymerization processes.

Photochemical Study of the Generated CTCs through a Free Radical Polymerization (FRP) Process

The free radical polymerization of thick (1.4 mm) methacrylate samples (using a benchmark monomer blend) was performed under air upon irradiation with the LED at 405 nm, in the presence of several Amine (DMT or MHPT or PP)/Thiophenium (2%/2% w/w) combinations (Figure 2). The generated charge transfer complexes (CTCs) resulting from these different combinations are all able to efficiently initiate the FRP process under blue light. Very high final methacrylate function conversions (FCs) and also good polymerization rates (Rp) were achieved, resulting in very active photoinitiating systems (PISs) e.g. FC = 88% for DMT/Thiophenium (curve 1 in Figure 2; Table 2). Interestingly, thiophenium salt is used for the first time in CTC formation and it can be selected as a strong electron acceptor compound. It should be noted that amines alone are not able to initiate the FRP process under the same irradiation conditions (curves 4-7 in Figure 2). Thiophenium salt alone is also characterized by a low initiation ability (curve 8 in Figure 2). The CTC behaviors are related to their inability to absorb blue light, highlighting the interest of such generated visible light absorbing CTCs structures from non-visible light absorbing compounds. Therefore, such structures (CTCs) are powerful candidates for the initiation of free radical polymerization processes under mild irradiation conditions (e.g. LED at 405 nm). In addition, such CTC approach paves the way for dye-free photoinitiating systems. It should be reported that the resin used for this study (benchmark monomer blend) is known for its difficulty to be polymerized due to its very low viscosity which increases the effect of oxygen inhibition on the polymerization processes realized under air [25].

Taking into consideration the efficiency trend for FRP, it follows the order: DMT > MHPT > PP. The purpose of this comparison is to highlight the effect of donor structures on the photoinitiating ability of the generated CTCs. The less efficiency of [PP-Thiophenium] CTC structure is due to its weakest light absorption at 405 nm (see above in Figure 1). Another parameter can also explain the lowest efficiency of such structure which is the more steric hindrance substitution of PP around the nitrogen atom compared to DMT and MHPT.

Effectively, a steric hindrance around the nitrogen atom (electron rich) of the amine could prevent its combination with the acceptor species (thiophenium salt). As shown in Figure 2,

[MHPT-Thiophenium] CTC is slightly less efficient than [DMT-Thiophenium] CTC despite that [MHPT-Thiophenium] CTC exhibits better light absorption at 405 nm (see above in Figure 1).

In addition, both MHPT and DMT have a fairly close HOMO energy (E = -4.9 eV for MHPT and -4.87 eV for DMT), showing that these compounds have probably rather similar electron donor properties. The difference in their performance can be related to the photochemical properties of the CTCs making the generation of radicals (CF 3 • ) more difficult (see below the chemical mechanisms in part 3.4). The bulkier structure around the nitrogen atom for MHPT compared to DMT could also be a parameter that should be taken into account.

Eventually, the new proposed [PP-Thiophenium] CTC is compared to the previously reported [PP-Iodonium] CTC [18]. This latter leads to a slightly better photoinitiating ability compared to the new investigated structure (curve 4 for [PP-Iodonium] CTC vs. curve 3 for [PP-Thiophenium] CTC in Figure 2). Currently, this behavior can be attributed to the better solubility of iodonium salt in the benchmark monomer blend compared to thiophenium salt.

Although, thiophenium salts can be considered as alternatives for iodonium salts in CTCs formation.

Thermal Initiator Behavior of the CTCs

The thermal initiator study of the proposed charge transfers complexes (CTCs) resulting from the combinations between the electron-donating (amines) and electron-acceptor (thiophenium salt) species (Amine/Thiophenium (2%/2% w/w) combinations) was carried out using a Differential Scanning Calorimeter (DSC) as a thermal analysis technique (Figure 3). Interestingly, the thermal polymerization experiments did not show any characteristic exothermic peak using amine or thiophenium salt alone within the whole 0-300°C temperature range, showing that no thermal polymerization can occur in the presence of such compounds (curves 4-7 in Figure 3). Therefore, they cannot be used as thermal initiators due to their high thermal stability. However, when these compounds (amine and thiophenium) are used together, the in-situ formed CTCs show excellent thermal initiating abilities and polymerization peaks appear between 75°C and 140°C, highlighting the interest of such generated structures to act as efficient in-situ thermal initiators (curves 1-3 in Figure 3). It should be noted that low thermal initiating temperatures and high thermal efficiencies (∆H (J/g)) characterize the formed CTCs. The maximum polymerization temperatures recorded for the different generated CTCs are: 95°C using [DMT-Thiophenium] CTC , 102°C using [MHPT-Thiophenium] CTC , and 116°C using [PP-Thiophenium] CTC (Table 3). These values are associated with the following enthalpy (∆H): 313 J/g, 319 J/g, and 303 J/g, respectively (Table 3). Interestingly, these in-situ formed CTCs are able to overcome the disadvantages of current thermal initiators like peroxides i.e. a risk of explosion when such compounds are stored due to the presence of thermally cleavable bonds in their structures, and also by a low stability of the concerned initiators in monomers [26][27][28]. Consequently, the ability of CTCs to overcome these disadvantages can be worthwhile for industrial applications. Finally, it should be noted that the new examined [PP-Thiophenium] CTC structure leads to a higher thermal initiating ability compared to the reported [PP-Iodonium] CTC [18], highlighting the importance of thiophenium salts for the replacement of iodonium salts in CTC approach (∆H = 303 J/g and a maximum temperature of 116°C for [PP-Thiophenium] CTC vs. 261 J/g and a maximum temperature of 148°C for [PP-Iodonium] CTC ) (Table 3). In addition, an improved solubility of the thiophenium salt could be observed under thermal conditions compared to photochemical conditions.

Chemical Mechanisms

According to recently published data [15], it is proposed that a charge transfer complex

Conclusions :

Concisely, the study of a series of charge transfer complexes (CTCs) as double-acting Photochemical/Thermal initiating systems combining a N-aromatic amine as an electron donor and a thiophenium salt as an electron acceptor in their structures was successfully done.

Both high photochemical and thermal initiating abilities are showed for the free radical polymerization of methacrylates in the presence of these new proposed CTCs, highlighting their high potential to activate the polymerization by light (under mild irradiation conditions)

or heat (under mild temperatures). Such approach is also able to generate CTCs structures characterized by reduced HOMO-LUMO energy gap (DE (HOMO-LUMO) ) compared to the electron donor alone and the electron acceptor alone. The formation of the CTCs was fully confirmed during this study. In fact, the new proposed [Amine-Thiophenium] CTCs are good alternatives for the replacement of [Amine-Iodonium] CTCs structures. The exploitation of new CTCs can be of great interest for future developments owing to their outstanding properties.

More particularly, CTCs can be used as unique dual initiators allowing fast light induced polymerization in irradiated areas associated with thermal polymerization in shadow areas.

Such properties will be used in the composites field in forthcoming works. Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air (1) 2% VITC+1% Cu(acétate) 2 / 4% eau+2% SC938 (50% ESO //50% UV1500 en poids) (2) 2% VITC+1% Cu(acétate) 2 / 4% eau+2% SC938 (50% DGEBA//50% UV1500 en poids). Tableau 1 : Réactivité de la polymérisation en fonction de la concentration de cuivre.

5-Effet de la lumière :

La photoactivation possible du système redox a été vérifiée lors de l'irradiation avec une LED à 405 nm (230 mW/cm 2 ). Cependant, on constate que ce système montre un changement très faible en termes d'exothermicité et de temps de gel (figure 6). Cela suggère que le processus redox photo-induit reste une voie mineure pour la polymérisation par rapport au processus redox simple.

Conclusion :

En conclusion, les 3 parties mises en oeuvre ne sont pour le moment que des résultats préliminaires. La première (cationique) a permis d'accéder à des produits naturels ce qui est plus écologique. Puis, la deuxième a consisté à remplacer le système peroxyde classique (instable) par un agent oxydant (stable). Concernant la dernière, la système classique toxique a été remplacé par des agents réducteurs moins toxiques. Il sera intéressant d'approfondir ces résultats afin de proposer des solutions plus durables pour l'industrie.

Conclusion générale

Les systèmes redox d'amorçage de polymérisation sont très importants dans le domaine de polymères. Ils permettent la réalisation de polymérisation en conditions douces (sans consommation d'énergie, à température ambiante).

Cependant, pour les systèmes de référence tels que peroxydes/amine ne satisfait plus aux nouvelles normes environemntales notamenet instabilités, toxicités, libération de benzène…. Il était nécessaire de trouver des alternatives, ce qui était le coeur de cette thèse.

En conclusion, nous avons développé plusieurs systèmes d'amorçage redox à deux composants pour : i) la polymérisation radicalaire, ii) la photoactivation, iii) la polymérisation cationique et iv) les complexes de transfert de charge (CTC). La recherche de nouveaux systèmes d'amorçage a été justifiée pour l'amorçage double thermique/photochimique par la nécessité de développer des systèmes plus sûrs et plus efficaces que les références actuelles.

Plus précisément, ma thèse a été divisée en trois grandes parties. La première a été basée sur l'étude de nouveaux systèmes redox en conditions douces, utilisant des métaux de nombreux systèmes ont été élaborés à l'aide de composés commerciaux ; la seconde sur des systèmes redox sans métaux. Le tableau ci-dessous résume les principaux résultats concernant les avantages et les inconvénients de chaque système avec une comparaison de leur efficacité Pendant ces trois années de thèse, j'ai eu le plaisir d'encadrer 5 stagiaires de divers niveaux.

En outre, les résultats de cette thèse ont permis une communication orale (congrès national), 7 publications dans des revues internationales à très fort impact (Chimie des Polymères). De plus, 2 publications sont en cours de rédaction.

Chapitre 1 : 2 .

 12 A New Pure Organic Redox Initiating System: Toward Sulfinate/Thiophenium combination ....................................................................................................................................................................... Abstract: ....................................................................................................................................................... 1. Introduction .......................................................................................................................................... Experimental section ................................................................................................................................. 2.1. Chemical Compounds ................................................................................................................................ 2.2. Two Cartridges System Used for Redox Experiments .............................................................................. 2.3. Redox Polymerization in Bulk Followed by Optical Pyrometry ............................................................... 2.4. RT-FTIR spectroscopy .............................................................................................................................. 2.5. Electron Spin Resonance (ESR) Spin Trapping (ESR-ST) ........................................................................ 2.6. Cyclic voltammetry ................................................................................................................................... 2.7. Surface Polymer Analysis (z-Profile) through Raman Confocal Microscopy ........................................... 3. Results and discussion: ............................................................................................................................. 3.1. Redox initiation using thiopheniun salts .................................................................................................... Effect of monomer/resin: ................................................................................................................................

3. 2 .Chapitre 2 : 2 .

 222 Redox initiation with different thiophenium salts .................................................................................... 3.3. Effect of inhibitor .................................................................................................................................... 3.4. Stability study in accelerating aging @ 50°C .......................................................................................... 3.6. Structure/reactivity/efficiency relationship .............................................................................................. 3.7. Surface analysis ....................................................................................................................................... 3.8 Application ............................................................................................................................................... 4. Conclusions : ........................................................................................................................................... References ................................................................................................................................................... New Pure Organic and Peroxide-free Redox Initiating Systems for Polymerization in Mild Conditions ................................................................................................................................................... Abstract: ..................................................................................................................................................... 1.Introduction ............................................................................................................................................. Materials and Methods ........................................................................................................................... 2.1. Chemical Compounds .............................................................................................................................. 2.2. Two Cartridges System Used for Redox FRP Experiments .................................................................... 2.3. Redox FRP in Bulk Followed by Optical Pyrometry ..............................................................................

2. 4 .

 4 Redox Polymerization in Bulk Followed by Thermal Imaging Experiments .......................................... 3. Results ..................................................................................................................................................... 3.1. The T4epa/Iod RIS charactaerized by optical pyrometry and thermal imaging experiments .................. 3.2. Salt additive effects in T4epa/Iod RISs ................................................................................................... 3.3. Inhibitor effects in T4epa/Iod RISs.......................................................................................................... 3.4. Stability in accelerated aging experiments .............................................................................................. 3.5. Reactivity at low temperatures ................................................................................................................ 4. Discussion ................................................................................................................................................ 5. Conclusions : ...........................................................................................................................................

  technologies d'amorçage (Redox et Photoredox). Ces systèmes sont capables d'étendre le durcissement aux parties les plus problématiques (les zones d'ombres) des milieux polymérisables et de briser ainsi les limites technologiques bien connues des systèmes d'amorçage photochimiques.

Schéma 2 :

 2 la partie 1, nous aborderons une introduction générale avec la recherche bibliographique associée aux systèmes redox. Dans la partie 2, des acétylacétonates métalliques stables ont été utilisés en combinaison avec de nouveaux agents réducteurs basés sur les sulfinates ou les silanes (par exemple le diphényle silane DPS). Ces nouveaux systèmes redox sont de manière originale sans peroxyde et sans amines mais utilisent cependant des complexes métalliques. Dans la 3éme partie, l'utilisation des systèmes sans métaux et sans peroxyde (tout organique) a donc été réalisée. Très peu de systèmes de ce type sont connus ce qui est une autre originalité forte de cette thèse. Dans la partie 4, nous proposons des complexes CTC amines Naromatiques/Iodonium pour avoir aussi la possibilité de photoactivation. Une partie expérimentale bien détaillée est ajoutée à chaque chapitre présenté pour regrouper les conditions pratiques de chaque étude plutôt qu'une partie expérimentale séparée. La partie 5 est composée d'une conclusion générale et de perspectives, nous avons en particulier proposé 3 nouveaux systèmes dont les résultats préliminaires ont été très encourageants pour la polymérisation de monomères époxy biosourcés en particulier. Présentation du plan de la thèse avec les 5 différentes parties du doctorat.

Schéma 4 :Schéma 5 :

 45 Polymérisation cationique d'un monomère époxyde. La vitesse de polymérisation cationique des monomères époxydes est souvent inférieure à celle des monomères acryliques. Cette différence s'explique par la faible valeur de la constante de vitesse de propagation [8-9]. Quelques exemples de monomères époxydes ou éther vinyliques très utilisés en polymérisation sont représentés sur le Schéma 5. Monomères de type cationique Ces types de monomères permettent d'obtenir des polymères présentant d'excellentes propriétés mécaniques (pouvant être flexibles ou rigides) ainsi qu'une très bonne résistance aux solvants et aux températures élevées.

3 3 . 1 Schéma 6 :

 3316 Éther vinylique Époxydesbiocapteurs, les adhésifs, les ciments dentaires et les mastics (bâtiments, automobile) ... Elle ne doit pas être confondue avec les polymères ayant des propriétés d'oxydoréduction (par exemple, la polyaniline, particulièrement utile pour les batteries). [10-17] Principes de la polymérisation par amorçage redox La polymérisation redox se produit lorsqu'un agent réducteur est mélangé à un agent oxydant, générant des espèces actives qui permettent la polymérisation du milieu environnant (Schéma 6). [10-18] En général, les agents oxydants présentent de faibles énergies de dissociation des liaisons impliquées (BDE) par exemple les peroxydes ou d'autres composés portant des liaisons O-O ou S-S faibles. Ces BDE faibles entraînent de faibles énergies d'activation lorsqu'ils sont utilisés avec des agents réducteurs (généralement de l'ordre de 40 kJ/mol), ce qui permet aux réactions de se produire dans des conditions douces par rapport à la polymérisation thermique (BDE= 125-160 kJ/mol). Polymérisation amorcée par réaction d'oxydoréduction à partir du mélange de deux composants (systèmes réducteurs et oxydants).

 7 )Schéma 7 : 3 Schéma 8 :

 7738 photopolymérisation

Schéma 10 :

 10 Réactions classiques d'amoçage/propagation/inhibition pour la polymérisation redox amorcée par un système amine/peroxyde et retardée dans le temps (temps de gel ou temps ouvert plus long). Les agents de piégeage des radicaux pour la réaction r3 (voir Schéma 10) sont généralement choisis parmi deux grandes familles : les phénols ou les nitroxydes [3]. En effet, l'utilisation de composés phénoliques en tant qu'inhibiteurs de polymérisation radicalaire est connue depuis de nombreuses années et ils sont déjà présents dans le stockage de nombreux monomères vinyliques (par exemple, de l'ordre de 100 à 1000 ppm de 4-méthoxyphénol-MEHQ). Les phénols peuvent également être utilisés afin de retarder dans le temps une polymérisation redox. Les nitroxydes sont l'autre classe de composés utilisés pour retarder la polymérisation. En particulier, il y a quelques années, il a été démontré que le 4-Hydroxy-2,2,6,6-tétraméthylpipéridine 1-oxyl (tempol) avait des propriétés très intéressantes de piégeage des radicaux -et donc de retardement -de la polymérisation redox [32-34].

de fortes limitations sont donc clairement identifiées pour les systèmes d'amorçage redox reportés dans la littérature (tableau 2 4 .

 24 Polymérisation photoactivée RedoxL'objectif de la combinaison de deux processus de durcissement est d'améliorer les propriétés du matériau qui auraient été obtenues si les deux approches de durcissement (photopolymérisation ou redox) étaient prises séparément. On appelle cette approche un mode dual-cure. Plusieurs réactions de réticulation peuvent être combinées comme par exemple thiol-acrylate, thiol-époxy, thiol-ène, Diels-Alder, réaction de Michael, polymérisation cationique et radicalaire pour la synthèse de réseaux polymères interpénètrés [1]. Il est également possible d'avoir des amorceurs photo / thermiques, à double durcissement qui produisent des échantillons épais en utilisant des résines cationiques [35]: par exemple certains sels de pyrylium peuvent subir un clivage photochimique afin de produire des protons amorçeurs; l'exothermicité de cette réaction en surface engendre une température suffisante pour décomposer les sels de pyrylium présents en profondeur. Une polymérisation thermique frontale a donc ensuite lieu. Dans notre cas, nous nous concentrerons sur les systèmes de double polymérisation Photo / redox. Une stratégie hybride entre la photopolymérisation (Schéma 11) et la polymérisation redox peut être proposée et a été appelée polymérisation photoactivée Redox. De tels systèmes sont également parfois appelés systèmes à double durcissement, mais nous avons préféré les systèmes photoactivés Redox car beaucoup plus spécifiques. Dans la polymérisation photoactivée redox, l'activation lumineuse des systèmes redox est intéressante car:  l'efficacité de la réaction photoactivée devrait fortement augmenter la conversion en surface. (Schéma 11-gauche)  une accélération du processus redox lent est possible sur demande.  la conversion globale peut être améliorée (plus d'espèces actives générées). (Schéma 11-droite) Schéma 11 : Principales caractéristiques de la photopolymérisation (à gauche), de la polymérisation redox (centre) et de la polymérisation photoactivée Redox (à droite). (Les zones polymérisées sont indiquées en bleu clair et les zones non polymérisées sont représentées en bleu foncée).[3] Un avantage de ce mode double est déjà connu dans les matériaux dentaires. Les systèmes à double polymérisation y ont déjà été largement étudiés [36]. Les propriétés de flexion du composite dentaire final étaient fortement améliorées par l'activation à la lumière.

Chart 1 .

 1 Chemical Structures of the benchmark monomer blend (Resin 1), Diphenylsilane (DPS) / Manganese acetylacetonate Mn(acac) 3 and 4-N,N trimethylaniline (4-N,N TMA)/BPO reference redox initiating system; iodonium salt (Iod -Speedcure 938 from

Figure 1 .

 1 Figure 1. Optical pyrometric measurements (sample T ( 0 C) vs. time) under air for Resin 1 in the presence of RIS, for: A. (1) 0.5 wt% DPS +2 wt% Mn(acac) 3 , (2) 1 wt% DPS +1 wt% Mn(acac) 3 , (3)

Figure 3 .

 3 Figure 3. A. Optical pyrometric measurements for the curing of glass fibers/Resin 1

Figure 4 .

 4 Figure 4. ESR spectra obtained for ESR-spin trapping experiment using [PBN] = 10 -2 M (as spin trap agent); [DPS] = 10 -1 M and [SC938] = 10 -2 M in tert-butylbenzene; under N 2 : simulated (red) and experimental (black) spectra.

Scheme 1 .Scheme 2 .

 12 Scheme 1. Chemicals used for the redox Free Radical Polymerization (FRP) initiation in this study.

Figure 1 .

 1 Figure 1. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for Redox FRP for (A): (1) Cu(AAEMA) 2 /DPS (0.5/2 %wt), (2) Cu(AAEMA) 2 /DPS (1/1 %wt), (3) Cu(AAEMA) 2 /DPS (2/0.5 %wt) and (B): (1) Mn(acac) 2 /DPS (0.5/2 %wt), (2) Mn(acac) 2 /DPS (1/1 %wt), (3) Mn(acac) 2 /DPS (2/0.5 %wt) initiating systems.

  Similar trends are observed between pyrometry and RT-FTIR data. The slight differences of gel times between both techniques can be ascribed to the different thicknesses of the samples (4 mm in pyrometry vs. 1.4 mm in RT-FTIR experiments) leading to different oxygen inhibition behaviors.

Figure 2 .Figure 3 .

 23 Figure 2. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for Redox FRP of (A): (1) Mn(acac) 2 /diphenylsilane (DPS) (1/1 %wt), (2) Cu(AAEMA) 2 /DPS (1/1 %wt), (3) Mn(acac) 3 /DPS (1/1 %wt) and (B) Fe(acac) 3 /DPS (1/1.4 wt%) initiating system.

Figure 4 .

 4 Figure 4. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air using a Redox Initiating System (RI)S Mn(acac) 2 /DPS (1/1 wt%); (1) with light (LED at 405 nm) and (2) without light.

Figure 5 .

 5 Figure 5. Optical pyrometric measurements (temperature vs. time after mixing, 4 mm thick sample) under air in resin 1 for Redox FRP of (A) (1) Mn(acac) 2 /DPS (1/1 wt%) fresh formulations and (2) Mn(acac) 2 /DPS (1/1 wt%) after 6 days of storage at 50 °C; (B) (1) Cu(AAEMA) 2 /DPS (1/1 wt%) fresh formulations and (2) Cu(AAEMA) 2 /DPS (1/1 wt%) after 6 days of storage at 50 °C; (C) Mn(acac) 3 (1 wt%) after 48h of storage in resin 1 at 50 °C.

Figure 6 .

 6 Figure 6. (A) Optical pyrometric measurements for the curing of prepregs (glass fibers or carbon fibers/Resin 1 composites) in the presence of (1) Mn(acac) 2 /DPS (1/1 %wt) (without fibers), (2) Mn(acac) 2 /DPS (1/1 %wt) (carbon fibers), (3) Mn(acac) 2 /DPS (1/1 %wt) (glass fibers) and (B) Photos for impregnated glass fibers taken after mixing with redox initiating system for 50% glass or carbon fibers and 50% of organic resin.

Figure 7 .

 7 Figure 7. Cyclic voltammetry (potential vs. saturated calomel electrode (SCE)) experiments in acetonitrile (ACN) (containing 0.2 M tetrabutylammonium hexafluorophosphate, 0.1 V/s) for the determination of (A) reduction potential of Cu(AAEMA) 2 and (B) oxidation potential of DPS.

  decreases in presence of DPS (curve 1 vs. curve 2) clearly showing the reduction of Cu(II) to Cu (I) by DPS in agreement with r1. Indeed, Cu(II) can be observed in ESR but Cu(I) is ESR silent.

Figure 8 .

 8 Figure 8. Electron Spin Resonance (ESR)-spin trapping experiment using [PBN] = 10 -2 M (as spin trap agent); for the mixing of [DPS] = 10 -1 M with (A) Mn(acac) 2 , (B) Cu(AAEMA) 2 simulated (red) and experimental (black) spectra, (C) Reduction of Cu (AAEMA) 2 ; (1) without DPS and (2) with DPS in tert-butylbenzene; under N 2 .

  Redox free radical polymerization (RFRP) is considered as a cost-effective technique for the production of polymers in a very short time scale and without any energy consumption. Its principle is based on blending two components (2K for two cartridges) composed of an oxidizing and a reducing agent, respectively. In this paper, original Redox Initiating Systems (RISs) comprising metal salts as oxidizing agents and sulfinate salts as reducing agents are developed for mild conditions (at room temperature, under air and without monomer purification or stabilizer removal). An economic, low toxicity and high stability process is attained. A good control of the gel time is also possible. Based on electron spin resonance experiments, an original chemical mechanism is also provided for these redox initiators.

Figure 1 .

 1 Figure 1. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for BR with different RISs: (1) Sulf 1/Mn(acetate) 3 (1/1 %wt), (2) Sulf 1/ Mn(acac) 3 (1/1 %wt), (3) Sulf 1/Cu(hfacac) 2 (1/1 %wt), (4) Sulf 1/Cu(acac) 2 (1/1 %wt).

Figure 2A .

 2A Figure 2A. As expected, the results obtained by the RT-FTIR experiments are well correlated

  curve 3 and Figure 2B curve 1) can be strongly activated upon LED@405 nm i.e. a peak of exothermicity around 110 ° C (Figure 2B curve 2) is observed upon irradiation vs. low reactivity (T < 40°C) without light. This shows that the light can play a huge role for the activation of RIS and more particularly the systems with low RFRP ability like copper complexes.

Figure 2 .

 2 Figure 2. (A) Redox Polymerization profiles (methacrylate C=C function conversion vs. time; mixing for t = 0 s) measured in RT-FTIR for BR with different RISs: (1) Sulf 1/Mn(acetate) 3 (1/1 %wt) without light irradiation, (2) Sulf 1/Mn(acetate) 3 (1/1 %wt) upon

Figure 3 .

 3 Figure 3. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for BR using different RISs: (1) Sulf 1/Mn(acetate) 3 (1/1 %wt), (2)

  When delayed redox reactions are required in certain applications with long open time, radical inhibitors can be added to adjust the gel time. An example is provided here with the new proposed RIS in combination with a well-known radical inhibitor (4-hydroxy-2,2,6,6tetramethylpiperidin-1-oxyl) noted TEMPOL. As shown in Figure4, the presence of TEMPOL with Sulf 1/Mn(acac) 3 (1/1 %wt) in BR strongly affects the polymerization in terms of gel time (curve 2 vs. curve 1) but without significant effect on the exothermicity of the reaction. Without inhibitor, the gel time is ~ 220 sec (Figure4, curve 1). The gel time is increased by adding a small quantity of 0.05 %wt of TEMPOL i.e. the reaction is delayed from 200 seconds without inhibitor to 1600 seconds in the presence of TEMPOL 0.05 %wt.The optimum inhibitor content can be adjusted to reach the desired open time for a given application.

Figure 4 .

 4 Figure 4. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for BR with different RISs: (1) Sulf 1/Mn(acac) 3 (1/1 %wt), (2) Sulf 1/Mn(acac) 3 (1/1 %wt) + 0.05 %wt TEMPOL.

  stored in an oven at 50°C). The gel time is also not too significantly affected by storage compared to fresh formulations (Figure5B, curve 2 vs. curve3).

Figure 5 .

 5 Figure 5. (A) Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for BR using different RISs: (1) Sulf 1/Mn(acac) 3 (1/1 %wt) fresh cartridges, (2) Sulf 1/Mn(acac) 3 (1/1 %wt) ) + 0,012 %wt TEMPOL after 5 days T=40°C,(3) Sulf 1/Mn(acac) 3 (1/1 %wt) + 0,012 %wt TEMPOL after 5 days T=50°C, (B) (1) Sulf 1/Mn(acetate) 3 (1/1 %wt) fresh cartridges, (2) Sulf 1/Mn(acetate) 3 (1/1 %wt) after 3 days (T=40°C), (3) Sulf 1/Mn(acetate) 3 (1/1 %wt) after 3 days (T=50°C).

Figure 6 .

 6 Figure 6. Optical pyrometric measurements (temperature 10°C vs. time after mixing; 4 mm thick sample) under air for BR @10°C using the different RISs: (1) Sulf 1/Mn(acac) 3 (3/3 %wt), (2) (1) Sulf 1/Mn(acac) 3 (2/2 %wt).

Figure 7 .

 7 Figure 7. Raman confocal microscopy analyses of the cured surfaces under air for with different RISs in BR: (1) Sulf 1/Mn(acac) 3 (1/1 %wt) (black points), (2) BPO//4-N,N TMA (1/1 %wt) red points.

Figure 8 .

 8 Figure 8. Optical pyrometric measurements for: (1) Sulf 1/Mn(acac) 3 (1/1 %wt) in neat BR; (2) Sulf 1/Mn(acac) 3 (1/1 %wt) in glass fibers/BR (50/50 %wt).

Figure 9 .

 9 Figure 9. ESR-spin trapping experiment using [PBN] = 10 -2 M (as spin trap agent); for the mixing of Mn(acac) 3 and Sulf 1 in toluene; under N 2 : 1) simulated (red) and 2) experimental (black) spectra.

Partie II :

  Systèmes d'amorçage redox tout organique pour la polymérisation dans des conditions douces : Cette partie sera spécifiquement consacrée au développement de systèmes d'amorçage de polymérisation radicalaire redox tout organique (RFRP). En effet, la RFRP est un procédé largement utilisé pour la réaction à température ambiante. Le mélange de deux composés (un agent oxydant avec un agent réducteur) amorce la polymérisation par formation spontanée de radicaux par un mécanisme redox. La RFRP est une méthode très intéressante pour la formation d'un polymère sans consommation d'énergie (la réaction peut être réalisée à température ambiante) et dans des conditions douces (sous air et sans purification de monomère). Les sulfinates ont été utilisés en association avec une amine tertiaire afin d'améliorer l'adhérence au substrat dentaire ou pour obtenir des propriétés mécaniques améliorées. Ces composés sont initialement étudiés comme étant des agents réducteurs. Dans nos travaux précédents nous avons pu caractériser les sulfinates par des faibles potentiels d'oxydation permettant la réduction des états excités dans des activations photochimiques. Leur utilisation dans des systèmes redox est proposée ici de manière originale. La synthèse de composites est validée comme application potentielle de ce nouveau système redox. Plus précisément, nous avons réalisé un mélange de sel de sulfinate avec le sel de thiophenium dans le chapitre 1, tout en utilisant un système dépourvu de métaux, d'amines et de peroxydes de benzoyle (BPO) pour éviter la toxicité et l'instabilité de ces composés. Puis, dans le second chapitre, une approche tout organique empêchant l'utilisation à la fois de peroxydes et de complexes métalliques est proposée. Par conséquent, les sels d'iodonium ont été utilisés comme agents oxydants pour générer des radicaux aryles par leur réduction par un agent réducteur soigneusement sélectionné (Tris [4-(diéthylamino) phényl] amine -T4epa) dans r1: ED + Ar 2 I + → ED •+ + Ar • + Ar-I ED correspond au donneur d'électron (ici le T4epa) Dans l'ensemble, nous avons caractérisé la polymérisation redox d'un mélange de monomères méthacrylates de référence en utilisant plusieurs techniques (pyrométrie optique et expériences d'imagerie thermique, RT-FTIR Spectroscopy, voltammètrie cyclique et la Résonance Paramagnétique Electronique RPE). La modification du temps de gel (GT) est également un paramètre crucial. Bien entendu, le temps de gel idéal dépend de l'application finale (composites, dentisterie, ancrages chimiques…) mais une excellente polymérisation doit toujours être obtenue dans des conditions douces (sous air, en présence de stabilisants). Dans cette étude, un contrôle précis du temps de gel est fourni avec les nouveaux systèmes d'amorçage redox proposés à travers la concentration des agents redox ou l'utilisation d'un stabilisant supplémentaire. Redox free radical polymerization (RFRP) is a handy technique in polymer production due to its applicability in mild conditions. The strategy is based on the mixing of 2 components (2K also for two cartridges) containing an oxidizing agent and a reducing agent, respectively. Here, we present a new Redox Initiating System (RIS) comprising thiophenium as new oxidation agent and sulfinate salt as reducing agent. For polymerization at room temperature and under air, the new redox system outperforms the currently used ones in terms of reactivity, stability and gel-time controllability. Remarkably, an exceptional control of the gel time or open time is observed in presence of an additional inhibitor: it can be turned from 1.5 min to 83 min without loss of reactivity. Based on electron spin resonance experiment, an

Figure 1 .

 1 Figure 1. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for Redox FRP of (A) (1) Sulf 1 /Thio A (1/1 %wt), (2) Sulf 2 /Thio A (1/1 %wt), (3) Sulf 3 /Thio A (1/1 %wt); (B) Sulf 1 /Thio A (1) (0.35/0.5 %wt), (2) (0.5/0.35 %wt), (3) (1/1 %wt).

  As expected, the results obtained by RT-FTIR experiments are correlated with pyrometry experiments. Without light at room temperature (RT), a similar trend has been observed for the two component redox system Sulf 1/Thio A: the gel time is about 120 sec by FT-FTIR vs.200 sec by pyrometry. The slight shift of gel time observed in both techniques can be directly related to the difference of thickness used (1.4 mm in RT-FTIR vs. 4 mm in pyrometry experiment) and the associated oxygen inhibition (the polymerization is carried out under air).

Figure 2 .

 2 Figure 2. Photopolymerization profiles (methacrylate C=C function conversion vs. Irradiation time) measured in RT-FTIR for the resin 1; 1.4 mm thick samples, in air. (1) Sulf 1 /Thio A (1/1 %wt) with light @405nm after 10 sec, (2) Sulf 1 /Thio A (1/1 %wt) without light irradiation.

Figure 4 .( 1 )

 41 Figure 4. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for RFRP of (A) (1) Sulf 1/Thio B (1/1 %wt); (2) Sulf 2/Thio B (1/1 %wt), (3) Sulf 3/Thio B (1/1 %wt); (B) Optical pyrometric measurements (temperature vs time after mixing; 4 mm thick sample) under air in resin 1 for Redox FRP: (1) Sulf 1/Thio C (1/1 %wt) ), (2) Sulf 1/Thio A (1/1 %wt), (3) Sulf 1/Thio B (1/1 %wt).

Figure 5 .

 5 Figure 5. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for Redox FRP of Sulf 1/ThioA (1/1 %wt) (1) + 0 % wt inhibitor, (2) + 0,02 % wt inhibitor, (3) + 0,4 % wt inhibitor, (4) + 0,07 % wt inhibitor, (5) + 0,1 % wt inhibitor, (6) + 0,15 % wt inhibitor, (B) representative the evolution of gel time in function of inhibitor content.

Figure 6 .

 6 Figure 6. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air in resin 1 for FRP of (A) Sulf 1/Thio A (1/1 %wt) (1) fresh formulations, (2) after 4 days (T=50°C), (B) Sulf 1/Thio B (1/1 %wt) (1) fresh formulation, (2) after 7 days (T=50°C), (C) Sulf 1/Thio C (1/1 %wt) (1) fresh formulations, (2) after 7

Scheme 3 .

 3 Scheme 3. Representative scheme for Sulf 1/Thio A redox initiating system in resin 1 stored @ 5°C.

Figure 7 .

 7 Figure 7. ESR-spin trapping experiment using [PBN] = 10 -2 M (as spin trap agent); for the mixing of Thio A and Sulf 1 in toluene; under N 2 : 1) simulated (red) and 2) experimental (black) spectra.

Figure 8 .

 8 Figure 8 . Raman confocal microscopy analyses of cured surface for different redox systems 1% thio A //1% Sulf 1 in Resin 1 (black points), BPO//4-N, N TMA red points.

Scheme 2 .

 2 Scheme 2. Benchmark methacrylate monomer blend (noted BM for Benchmark Monomers).

Figure 1 .

 1 Figure 1. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using different RISs: (A) T4epa/Iod (0.5%/1% w/w); (B) T4epa/Iod (1%/2% w/w); (C) T4epa/Iod (2%/0.5% w/w); (D) T4epa/Iod (0.5%/1.5% w/w); (E) T4epa/Iod (1.5%/0.5% w/w); (F) T4epa/Iod (2%/1% w/w); (G) T4epa/Iod (1%/0.5% w/w); (H) T4epa/Iod (1.5%/1% w/w); (I) T4epa/Iod (2%/1.5% w/w); (J) T4epa/Iod (1%/1% w/w); (K) T4epa/Iod (1.5%/1.5% w/w); (L) T4epa/Iod (2%/2% w/w); (M) T4epa/Iod (1%/1.5% w/w); (N) T4epa/Iod (1.5%/2% w/w).

Figure 2 .

 2 Figure 2. Correlation between the experimental gel time (GT) and the calculated GT using the equation:

Figure 4 .

 4 Figure 4. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using different RISs based on T4epa/Iod-Cl (1%/2% w/w) in presence of different salts: (A) without additional salt; (B) NaBF 4 (1% w/w); (C) NaSbF 6 (1% w/w); (D) LiTFSI (1% w/w); (E) NaTFSI (1% w/w); (F) NaPF 6 (1% w/w); (G) KTFSI (1% w/w).

  Influence de l'ajout de sel sur le système avec SP938ClSP938_Cl-SP938_Cl-+ LiTFSI SP938_Cl-+ SbF6-SP938_Cl-+ PF6-SP938_Cl-+ NaTFSI SP938_Cl-+ BF4-SP938_Cl-+ KTFSI Système de référence Temperature (°C) Time (s)

Figure 6 .

 6 Figure 6. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using a T4epa/Iod (1.5%/1% w/w) RIS in presence of different inhibitors: (A) without inhibitor; (B) 4-Hydroxy-TEMPO (0.05% w/w); (C) 4-methoxyphenol (0.05% w/w).

Figure 7 .

 7 Figure 7. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using a T4epa/Iod (1.5%/1.5% w/w) RIS for different storage time: (A) fresh cartridges; (B) aging of the two cartridges for 7 days @50°C; (C) aging of the two cartridges for 14 days @50°C; (D) aging of the two cartridges for 28 days @RT.

  . ~120s) but markedly, without decreasing the exothermicity. Therefore, this result also highlights the robustness of the proposed RIS with polymerization processes that remain possible even at 10°C.

Figure 8 .

 8 Figure 8. Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using a T4epa/Iod (1.5%/1% w/w) RIS at different temperatures: (A) @RT (23°C); (B) @10°C.

BScheme 3 .

 3 Scheme 3. Expected chemical mechanisms.

Chapitre 1 :

 1 Suite à de nombreuses études poussées et des efforts dépensés dans le domaine de la recherche sur les matériaux conducteurs et supraconducteurs, des complexes électrodonneursaccepteurs ont été découverts en 1950. Ces complexes étaient basés sur des molécules contenant des hydrocarbures aromatiques. Ensuite, en 1973, un CTC entre le tétrathiafulvalène (TTF) et le tétracyanoquinodiméthane a été découvert par Ferraris et al. Ce travail a conduit à une recherche approfondie autour du domaine du CTC visant notamment au développement de matériaux aux propriétés de supraconductivité. Dans ce domaine, peu d'exemples peuvent être cités sur le système CTC tels que : l'amine/iodure ou la morpholine/dioxyde de soufre... Dans cette partie du manuscrit, nous abordons la description des complexes de transfert de charge (CTC), ainsi que la coexistence d'une molécule donneuse et d'une autre accepteuse. En effet, les CTC reposent sur des interactions entre un accepteur (via son orbitale moléculaire inoccupée la plus basse vacante (LUMO)) et un donneur (via son orbitale moléculaire la plus haute occupée (HOMO)). Ce qui crée par approximation physique une structure où l'écart d'énergie entre LUMO et HOMO est plus petit que celle du donateur initial et de l'accepteur séparément. Dans la présente partie, nous proposons des complexes CTC amines N-aromatiques/Iodonium dans le premier chapitre. Puis, le deuxième chapitre sera consacré à la présentation d'un nouveau système amine aromatique/thiophenium. L'ensemble de ces études a été validé par la synthèse des polymères sous irradiations douces en utilisant des techniques connues telles que la RT-FTIR Spectroscopy, la Differential Scanning Calorimetry (DSC) et la spectroscopie d'absorption UV-visible. Plus précisément, les CTCs peuvent être utilisés comme amorceurs doubles uniques permettant une polymérisation induite par la lumière rapide dans les zones irradiées associée à la polymérisation thermique dans les zones d'ombre. Ces systèmes doubles sont originaux et montrent une efficacité très importante. Ils pourront être utilisés dans certaines applications comme les composites. Charge Transfer Complexes based on Various Amines as Dual Thermal and Photochemical Polymerization Initiators Abstract: Exploiting highly efficient, environmentally friendly, and economic CTCs (Charger Transfer Complexes) as photo/thermal dual initiators is a huge pursuit of materials practitioners and innovators. To investigate and find out series amines as donors in CTCs, RT-FTIR (Real-Time Fourier Transform Infrared Spectroscopy) was employed to examine the photo initiating efficiency of CTCs based on amines donors and DSC (Differential Scanning Calorimeter) was used to test their thermal initiating ability. The formation of CTCs was investigated and confirmed by molecular orbital (MO) calculations and UV-vis experimental study. Structure/reactivity/efficiency relationships will be proposed on the base of more than 10 new amine donors. At last, composites based on glass fibers and carbon fibers were fabricated by photo curing and/or photo/thermal dual curing method, which showed excellent mechanical performance in DMA (Dynamic Mechanical Analysis) characterization. This work paves the path towards flexible photo/thermal dual initiators able to react on demand thanks to orthogonal stimuli (light or heat with the same initiating

Scheme 1 .Chart 1 .Chart 2 .

 112 Scheme 1. Previous [phosphine/aniline/indole/pyrrole-iodonium/sulfonium salts]CTCs and newly proposed [amine-iodonium salts]CTC as photo, or thermal, or dual thermal and photochemical polymerization initiators (step 1); detailed investigations of the relationship between the amine structure and their initiating (photo or thermal) ability (step 2).

Figure 1 .

 1 Figure 1. Photopolymerization profiles for different CTCs (C=C function conversion vs.

  irradiation time) measured by RT-FTIR for the photoinduced polymerization: A, B in Resin 1; C, D in Resin 2; 1.4 mm thick samples in laminate, upon LED@405nm irradiation (the irradiation starts at t = 0 s, 110 mW/cm²). Initiating systems A, C:(1) 2.0 wt% TMA + 2.0 wt% Iod; (2) 2.0 wt% PDA + 2.0 wt% Iod; (3) 2.0 wt% PT + 2.0 wt% Iod; (4) 2.0 wt% TMA; (5) 2.0 wt% PDA; (6) 2.0 wt% PT; (7) 2.0 wt% Iod. B, D: (1) 2.0 wt% DMA + 2.0 wt% Iod; (2) 2.0 wt% DMAPE + 2.0 wt% Iod; (3, only for B) 2.0 wt% TIAPPDA+ 2.0 wt% Iod; (4) 2.0 wt% DMA; (5) 2.0 wt% DMAPE; (6, only for B) 2.0 wt% TIAPPDA.

Figure 2 .

 2 Figure 2. Thermal polymerization experiments using different CTCs and monomers (heat flow vs. temperature), heating rate: 10 K/min, under N 2 , A, B in Resin 1; C, D in Resin 2; Initiating systems A, C: (1) 2.0 wt% TMA + 2.0 wt% Iod; (2) 2.0 wt% PDA + 2.0 wt% Iod; (3) 2.0 wt% PT + 2.0 wt% Iod; (4) 2.0 wt% TMA; (5) 2.0 wt% PDA; (6) 2.0 wt% PT; (7) 2.0 wt% Iod. B, D: (1) 2.0

  concentration is [2 wt% amine + 2 wt% Iod]. a : all amines were purchased from TCI. b : photoinduced polymerization condition: 1.4 mm thick samples, laminated, upon LED@405nm irradiation (the irradiation starts at t=0 s, 110 mW/cm²), in Resin 1. c : Thermal induced polymerization condition: heating rate: 10 K/min, under N 2 in Resin 1 if not stated otherwise.

  alone, amine alone and the CTCs; optimized structures and their respective calculated UV-vis spectra. The UV-Vis spectra were visualized with Gabedit 30 ; F = the oscillator strength. λmax= 182 nm F= 0.533 λmax= 161 nm F= 0.431 λmax= 271 nm F= 0.044 [DMA-Iod]CTC E = -5.12 eV E = -8.49 eV λmax= 337 nm F= 0.200 λmax= 264 nm F= 0.195 λmax= 422 nm F= 0.052 TMA E = 0.33 eV E = -4.87 eV λmax= 190 nm F= 0.587 λmax= 167 nm F= 0.537 λmax= 268 nm F= 0.044 [TMA-Iod]CTC E = -5.25 eV E = -7.92 eV λmax= 543 nm F= 0.101 λmax= 379 nm F= 0.062 λmax= 295 nm F= 0.040 DMAPE E = 0.00 eV E = -5.01 eV λmax= 183 nm F= 0.578 λmax= 233 nm F= 0.428 λmax= 276 nm F= 0.042 [DMAPE-Iod]CTC E = -5.31 eV E = -7.32 eV λmax = 305 nm F= 0.032 λmax = 699 nm F= 0.005 λmax = 522 nm F= 0.002 PDA E = 0.46 eV E = -4.87 eV λmax = 192 nm F= 0.778 λmax = 159 nm F= 0.364 λmax = 261 nm F= 0.049 [PDA-Iod]CTC E = -5.09 eV E = -7.81 eV λmax = 320 nm F= 0.185 λmax = 393 nm F= 0.047 λmax = 510 nm F= 0.003 Iodonium in the cationic form; a : Isovalue=0.02

  A-D, curve 3), as a consequence of the formation of CTCs. Expectedly, photolysis of a solution of CTC for 5 min resulted in a significant change of the absorption indicating the photoreactivity of the complex (Figure 3 A-D, curve 4).

Figure 3 .

 3 Figure 3. UV-vis spectra in dichloromethane (DCM) for A: (1)20 mM DMA; (2) 20 mM Iodonium; (3) 20 mM DMA + 20 mM Iod; (4) 20 mM DMA + 20 mM Iod irradiated 5

Figure 4 .

 4 Figure 4. Numerical optical microscope observation of patterns written from the

Figure 5 .

 5 Figure 5. Macrotopography of fabric prepregs, surface cured prepregs and composites and the process of composites curing. Access to prepregs using: [2.0 wt% TMA/2.0 wt% Iod]CTC in 30/70 (w/w) Resin 1/carbon (or glass) fibers. Access to glass fiber composites and surface cured carbon fiber prepregs by photocuring using a LED@395 nm (4 W/cm²) (conveyor 2 passes). Access to carbon fiber composites: heated at 125°C for 30 min.

Scheme 1 .

 1 Scheme 1. Chemical Structures of the Acceptor (Thiophenium), Donors (N-aromatic amines), and Monomers (Benchmark Monomer Blend) used in this Study.

  have been used in order to create charge transfer complexes (CTCs) which are investigated as initiators for the FRP of methacrylates under blue light irradiation due to their improved visible light absorption. The Light-Emitting Diode (LED) at 405 nm with low intensity (I 0 = 110 mW. cm -2 ) was utilized as a light irradiation source for this photochemical study. The weight percent of the different chemicals included in the initiating systems is calculated from

Scheme 2 .

 2 Scheme 2. CTC Frontier Molecular Orbitals: Construction from the Donor-Acceptor CTC Interaction.

  /Thiophenium or Iodonium (2%/2% w/w) or in the presence of Thiophenium alone or Amines alone (2% w/w): (1) DMT/Thiophenium; (2) MHPT/Thiophenium; (3) PP/Thiophenium; (4) PP/Iodonium; (5) DMT; (6) MHPT; (7) PP; and (8) Thiophenium. The irradiation starts at t = 10 s.

Figure 3 .

 3 Figure 3. Thermal polymerization profiles (heat flow vs. temperature) of a benchmark monomer blend (heating rate = 10°K/min, under N 2 ), in the presence of different combinations based on Thiophenium alone (2% w/w), Amine alone (2% w/w), and Amine/Thiophenium (2%/2% w/w): (1) DMT/Thiophenium; (2) MHPT/Thiophenium; (3) PP/Thiophenium; (4) DMT, (5) MHPT, (6) PP, and (7) Thiophenium.

( 3 • (r3) Scheme 3 .

 33 Scheme 3. Proposed Amine/Thiophenium Interactions.

3 -Figure 2 .

 32 Figure 2.Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air dans la résine UV1500 pour différents systèmes redox (1) 2% VITC+1% Cu(acétate) 2 / 4% eau+2% SC938 fraîche, (2) 2% VITC+ 1%Cu(acétate) 2 / 4% eau+2% SC938 après 48 h de stockage a température 45°C.

4 -

 4 Mélanges de monomères dans une fraction 50/50 :Dans le but d'améliorer l'efficacité de la polymérisation en utilisant les monomères DGEBA et (ESO) (où la polymérisation n'a pas abouti), nous avons essayé de les mélanger avec l'UV1500, qui lui était réactif. D'après la figure3, les résultats de la courbe 1 ont montré que le mélange UV1500/ESO (50/50 poids) représente le système le plus réactif avec un temps de gel autour de 320 sec et un pic d'exothermicité de 115°C. Par contre, le système le moins réactif est le mélange (DGEBA/UV1500) avec un temps de gel autour de 470 sec (courbe 2). Ces résultats montrent l'intérêt d'utiliser un mélange de monomères époxy pour améliorer la réactivité de certains monomères non réactif seul.

Figure 3 .

 3 Figure3. Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air (1) 2% VITC+1% Cu(acétate) 2 / 4% eau+2% SC938 (50% ESO //50% UV1500 en poids) (2) 2% VITC+1% Cu(acétate) 2 / 4% eau+2% SC938 (50% DGEBA//50% UV1500 en poids).



  radicalaire avec de nouveaux systèmes 3 composants : Cette polymérisation radicalaire est le résultat d'un mélange de 3 composants différents avec un monomère à base de méthacrylate. De manière originale, ils utilisent un peroxyde stable comme le Cumène hydroperoxyde.  L'hydroperoxyde de Cumène (CHP) est largement utilisé dans l'industrie comme amorceur thermique. Le CHP est également utilisé dans la production de phénol et d'acétone par clivage catalytique. Ici, nous avons remplacé le dibenzoyle peroxyde par le CHP pour éviter le problème d'instabilité et de toxicité.  Les métaux acétylacétonate (Mn(III)-Cu(II)-V(II)…) représentent un modèle très largement utilisé. Ils sont largement conseillés pour leurs faibles toxicités et leur cout bas. Ces systèmes fonctionnent comme agents oxydants dans le processus de polymérisation. Le vanax est une amine aromatique tertiaire, elle est commercialisée et synthétisée spécialement pour les caoutchoucs. Dans cette étude, nous avons utilisé cette amine comme étant un donneur d'électron (agent réducteur). Toutes les formulations redox ont été préparées dans deux cartouches séparées : une première cartouche avec le vanax et l'autre contenant le mélange entre (Cumène hydroperoxide et métaux acac). Un mélangeur Sulzer mixpac (1 : 1) a été utilisé pour mélanger les deux cartouches au début de chaque expérience de polymérisation. Comme toutes les expériences de polymérisation ont été réalisées à température ambiante (~ 20-25 ° C) et sous air, on peut s'attendre à une inhibition par l'oxygène, notamment en surface là ou l'oxygène est continuellement renouvelé.

2 -

 2 Amorçage redox en utilisant différents métaux :Initialement, l'amine (vanax) est l'agent réducteur et a été utilisé pour l'amorçage redox de monomères méthacrylates avec différents agents oxydants métalliques. L'efficacité de polymérisation des divers systèmes redox basés sur une combinaison de vanax + sel métallique /Cumème hydroperoxide a été suivie par pyrométrie optique (figure4). Le système vanax + vanadium(III)/Cumème hydroperoxide a montré un pic d'exothermicité à 147°C avec un temps de gel de 10 sec. Par contre, le système vanax +manganèse(III)/Cumème hydroperoxide a montré un pic d'exothermicité autour de 130°C avec un temps de gel de 220 sec. Enfin, le vanax + Cu(acac) 2 /Cumème hydroperoxide a montré un pic d'exothermicité autour de 90°C avec un temps de gel de 900 sec (Figure4, courbe 8). Le vanax réagit plus efficacement avec le vanadium qu'avec le Mn(acac) 3 et le Cu(acac) 2 , ce qui pourrait indiquer un rendement plus élevé en radicaux amorceurs avec le vanadium. Mais, un temps de gel plus long peut être bénéfique pour différentes applications nécessitant un temps ouvert assez grand.Les systèmes redox basés sur des complexes de fer, étain, gallium et nickel n'ont pas conduit à une polymérisation. Ces résultats, bien que préliminaires, montrent que le développement de nouveaux systèmes redox utilisant des peroxydes plus sûrs (le Cumène hydropéroxyde) est possible dans de futurs travaux.

Figure 4 :

 4 Figure4: Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air dans la résine Mix-MA, (1) 1% Cu(AAEMA) 2 +1% Vanax/ 1% Cumème hydroperoxide (1% en poids), (2) 1% Fe(acac) 3 +1% Vanax/ 1% Cumène hydroperoxide, (3) 1% Mn(acac) 3 +1% Vanax/ 1% Cumène hydroperoxide, (4) 1% Ni(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (5) 1% étain(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (6)1% Gallium(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (7)1% V(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (8)1% Cu(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide.

3 -

 3 Etude de stabilité en vieillissement accéléré à 40°C ou 50°C :La stabilité dans les expériences de vieillissement accéléré du système redox vanax + sel métallique/Cumène hydroperoxide a été étudiée dans la figure5. Les deux cartouches ont été stockées à 40°C ou 50°C pendant un temps donné et évaluées au niveau de la polymérisation par rapport à des cartouches fraîches. Nous avons choisi le système redox : vanax +Cu (acac) 2 / cumène hydroperoxide.Visiblement, le vanax +Cu(acac) 2 /Cumène hydroperoxide est un système qui reste réactif même après 3 jours de stockage à 40°C ou 50°C (figure5). Des polymères non collants sont encore obtenus même avec des cartouches vieillies (formulations conservées dans une . En plus, en augmentant la concentration en métaux, le temps de gel est augmenté jusqu'à 650 sec avec 1% de concentration. Ces données suggèrent que l'effet catalytique en métaux joue un rôle important dans ce système.

Figure 6 : 8 -Schéma 4 .

 684 Figure 6 : Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air dans la résine Mix-MA (1) 1% Cu(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide sans lumiére, (2) 1% Cu(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide avec LED 405 (nm).

  Difluoro-5-(trifluoromethyl)-5Hdibenzo[b,d]thiophen-5-ium triflate

Figure 7 :Figure 8 :Tableau 2 :

 782 Figure 7 : Mesures pyrométriques optiques (température en fonction du temps après mélange, échantillon de 4 mm) sous air dans la résine Mix-MA (1) 1% DTA / 1% Thio(1), (2) 1% PDA / 1% Thio(1) (3) 1% AEAE / 1% Thio(1) (4) 1% MMCA / 1% Thio(1) (5) 1% m-XDA / 1% Thio(1) (6) 1% IPDA / 1% Thio(1).

  La troisième partie de ce travail a été basée sur des complexes de transfert de charge (CTC). Plus particulièrement, les CTC peuvent être utilisés comme amorceurs doubles thermique/photochimique uniques permettant une polymérisation rapide induite par la lumière dans les zones irradiées, associées à la polymérisation thermique dans les zones d'ombre.Deux nouveaux systèmes CTC i) amine+iodonuim ii) sels de thiophénium+amine ont été développés dans cette partie. Leurs propriétés ont été, plus particulièrement, utilisées dans le domaine des composites.Toujours dans ce travail doctoral, nous avons eu la chance, en perspectives, de développer de nouveaux systèmes peu utilisés dans l'équipe mais très avantageux. En particulier, la polymérisation cationique amorcée redox a été développée ce qui est très original par rapport à la littérature. Ce travail a ouvert de nouvelles portes pour de nouveaux projets redox et ainsi enrichir les thématiques dans notre équipe de recherche.Les protocoles les plus importants développés sont : i) l'utilisation de mélangeurs en polymérisation à 2 composants ; (ii) un contrôle strict du temps de gel dans différents systèmes ; (iii) un travail sous basse température pour ne pas avoir de consommation énergétique (procédés respectueux de l'environnement).Pendant mes trois années de doctorat j'ai eu la chance d'exercer en parallèle plusieurs fonctions. Pendant ma dernière année, j'ai également exercé le métier d'enseignant en Chimie/Biochimie pour des étudiants BTS biotechnologies et Analyses de Biologie Médicale au campus privé d'Alsace à l'école Horizon Strasbourg.Durant les deux dernières années, j'ai accompagné mon maître de thèse en tant qu'assistant enseignant pendant une durée de 128 heures pour les travaux pratiques. Les étudiants de l'ENSCMU et Master 1 physico-chimie ont été encadrés pour les travaux pratiques.

1] M RM .

  : Mécanismes d'amorçage, de propagation et de terminaison / se produisant dans les réactions de polymérisation radicalaire (FRP). En parallèle à l'amorçage thermique et photochimique qui nécessitent un apport d'énergie, l'amorçage redox est différent car il a lieu sans apport énergétique extérieur. La réaction a lieu au travers d'une réaction redox entre un agent oxydant et un agent réducteur lors de leur mélange à température ambiante. Cette réaction redox génère les radicaux amorceurs de polymérisation.

	R .	RM i .	M	RM i+1 .	P
	Amorçage	Propagation	Terminaison

Schéma 1

10, 14, 20, 27-31] 3.4 Le contrôle du temps de gel dans la polymérisation redox

	Schéma 9 : Système d'amorçage redox utilisant l'interaction amine / peroxyde de
	dibenzoyle (BPO). [3,

Les systèmes d'amorçage Mn(III)/agent réducteur (et de même, Ce(IV)/agent réducteur) ont été également mentionnés [10]. Une revue exhaustive est disponible dans la littérature par Snider pour l'utilisation du Manganèse en chimie radicalaire [3,26].En synthèse organique, les réactions sont généralement réalisées dans des conditions difficiles (atmosphère inerte ou chauffage thermique) et la vitesse de propagation des radicaux n'est généralement pas comparable à ce qui est nécessaire pour la polymérisation radicalaire. L'une des références les plus efficaces pour la polymérisation redox est basée sur la réaction des amines N-aromatiques avec le peroxyde de dibenzoyle (BPO). Elle est toujours appliquée pour de nombreuses applications et depuis de nombreuses années. Le mécanisme le plus ancien proposait que le radical cation était le principal responsable de l'amorçage mais des travaux récents confirment la génération d'espèces radicalaires Ph(C=O)O • ,Ph • et les radicaux aminoalkyles (Schéma 9). L'effet de la substitution sur la réactivité de l'amine a déjà été étudié dans les premiers travaux de Horner et Scherf [27] et la 4-N,N triméthylaniline (4-N, N TMA) s'est avérée être un excellent réactif pour cette réaction. Le système 4-N,N TMA / BPO sera donc notre système redox de référence dans le présent manuscrit car il est très réactif robuste et compatible avec de nombreuses résines organiques. Un mélange de deux composants souvent appelés deux cartouches (2K) (solides et/ou liquides) est nécessaire afin d'amorcer la production de radicaux. Immédiatement après le mélange, la formation des radicaux amorceurs se produit (voir ci-dessus les réactions r1 et r3 pour un amorçage amine/peroxyde).

Le contrôle de la réaction est donc intrinsèquement très faible et difficile, ce qui cause un problème pour de nombreuses applications : le mélange doit atteindre la partie la plus profonde (parfois en quelques minutes) de la zone de durcissement désignée. C'est pourquoi des inhibiteurs de radicaux ont rapidement été proposés afin de retarder l'amorçage de la polymérisation dans le temps (voir r3 dans le schéma 10). Le temps de gélification (Gel) est alors défini comme l'intervalle entre le mélange des deux composants et la formation du gel.

Systèmes d'amorçage Redox basés sur des sels métalliques sans amine et sans peroxyde

	La synthèse de cette partie montre l'efficacité de ces systèmes traduite par de Partie I : La polymérisation radicalaire amorcée par une réaction redox, à température ambiante nombreux avantages remarquables. En effet, nous avons atteint la stabilité attendue tout en
	(RFRP), présente de nombreux avantages dans le domaine des matériaux tels que l'économie gardant un niveau de toxicité très faible : ce qui est idéal pour les modalités de la recherche
	d'énergie, le rendement élevé, la robustesse pour la polymérisation dans les matériaux dans ce domaine. D'autre part, ces produits chimiques sont aujourd'hui commercialisés et à
	épais/composites et la facilité d'utilisation. disposition des chercheurs donc à faible coût. Ainsi, l'efficacité a été caractérisée par
	photopolymérisation	Système Redox	double durcissement
		Partie I

Cependant, les systèmes d'amorçage redox actuellement utilisés dans le commerce sont basés sur des amines aromatiques toxiques et des peroxydes dangereux (par exemple, le peroxyde de dibenzoyle). Le principe du système redox est basé sur le mélange de deux composants (2K pour deux cartouches) constitués respectivement d'un agent oxydant et d'un agent réducteur. Dans cette partie, nous proposons de nouveaux systèmes d'amorçage redox à deux composants (2K) sans amine et sans peroxyde, à base de sels métalliques comme agent oxydant en combinaison avec de nouveaux agents réducteurs. En particulier, ces nouveaux systèmes sont utilisables dans des conditions douces (à température ambiante, sous air). Les résultats de mesures de pyrométrie optique ont montré une excellente propriété d'amorçage pour les monomères de référence (méth)acrylates. Ces systèmes sont compétitifs avec une référence bien établie amine/peroxyde de dibenzoyle (BPO). Plus précisément, nous avons réalisé des combinaisons de diphényl silane avec les métaux dans les chapitres 1 et 2, tout en utilisant un système dépourvu d'amines et de BPO pour éviter la toxicité et l'instabilité de ces composés. Puis, dans le troisième chapitre, une combinaison a été réalisée entre le sulfinate (agent réducteur) avec différents métaux (agent oxydant). plusieurs techniques : pyrométrie optique, RT-FTIR, voltammètrie cyclique et la Résonance Paramagnétique Electronique (RPE). Par conséquent, pour toutes ces raisons, ces systèmes seront utilisés dans plusieurs applications, notamment les composites, la construction des bâtiments ou les procédés de collage.

Chapitre 1:

Diphenyl Silane/Manganese Acetylacetonate Redox Initiating Systems: Towards Amine-Free and Peroxide-Free Approach Abstract:

	Room temperature redox initiated free radical polymerization (RFRP) presents huge
	advantages in the field of materials such as energy saving, high efficiency, robustness in thick

materials/composites and easy operation. However, the current commercially used redox initiating systems used are based on toxic aromatic amines and hazardous peroxides (e.g., dibenzoylperoxide). In the present paper, we propose new amine-free peroxide-free redox two component (2K) initiating systems based on diphenylsilane (DPS, as reducing agent) in combination with manganese acetylacetonate (as oxidizing agent). This was studied for the first time, especially under mild conditions (RT, under air). Optical pyrometry measurement results showed that the diphenyl silane (DPS) in combination with Manganese (III) acetylacetonate exhibited an excellent initiating property for benchmark (meth)acrylate monomers, competitive with a well-established Amine/dibenzoyl peroxide (BPO) reference.

Based on electron spin resonance (ESR) experiments, the initiating chemical mechanisms of RFRP are proposed.

Table 1 .

 1 Summarized Data of Polymerization based on Different Concentrations of DPS and Mn (acac) 3 in methacrylate monomers (Resin 1).

	DPS	Mn(acac) 3	Reaction	Peak temperature (°C)
	concentration (wt	concentration (wt %)	starting time
	%)		(sec)
	0.5	2	230	149
	1	1	155	142
	2	0.5	60	152
	0.8	0.8	38	139
	1.4	0.4	45	138
	0.4	0.4	135	122
	4-N,N TMA/BPO reference a	195	95
		a: see Figure 1E, curve ii

Chapitre 2: High Performance Redox Initiating Systems Based on the Interaction of Silane with Metal Complexes: A Unique Platform for the Preparation of Composites Abstract:

	3 /DPS reaction. Three advantages have been found
	against well-known amine/benzoylperoxide system: (i) avoid pressing regulations on
	peroxides by choosing Mn oxidizing agent; (ii) avoid toxic/carcinogenic amine; (iii) easy Currently, Redox Initiating Systems (RISs) of Free Radical Polymerization (FRP) are
	tuning of gel time by selection of appropriate concentrations and/or additives. The amine-free mainly based on the interaction of aromatic amines with peroxides (e.g., dibenzoyl peroxide
	peroxide-free redox initiating system can find use to the generation of high tech carbon fibers (BPO)) that can be both toxic and unstable. In the present work, we aim to replace these
	composites as gel time is easily tuned. In the future such systems are likely easily hazardous substances in new RIS that can be peroxide-free and amine-free. Our redox two
	components (2K) initiating system is based on diphenylsilane (DPS) as reducing agent
	implemented in various areas of materials industry.
	combined with different metal complexes (Mn(acac) 2 , Cu(AAEMA) 2 or Fe(acac) 3 ) as
	oxidizing agents. For the new proposed RIS, an excellent reactivity is found for the
	polymerization of benchmark methacrylate monomers under mild conditions (redox
	polymerization done under air and at room temperature); remarkably, it is also possible to
	finely control the gel time. Different techniques (optical pyrometry, Real-Time FTIR
	spectroscopy, Cyclic Voltammetry and Electron Spin Resonance (ESR)) were used to follow
	the polymerization processes but also to shed some light on the new redox chemical
	mechanisms.

Table 1 .

 1 RFRP using Sulf 1/Mn(acetate) 3 RIS in BR for different wt%.

	entry Mn(acetate) 3 Sulf 1	Gel time (sec)	Maximum
					temperature (°C)
	1	0.5 wt%	0.5 wt%	120 sec	100°C
	2	0.8 wt%	0.8 wt%	75 sec	105°C
	3	1.2 wt%	1.2 wt%	50 sec	103°C
	4	2 wt%	2 wt%	40 sec	105°C
	5	4 wt%	4 wt%	10 sec	103°C

Table 2 .

 2 Data of polymerization using different redox systems and their redox potentials.

		Gel time	Maximum	E ox (Sulf)/E red (metal) ΔG (eV)
			temperature
	Sulf 1/ Mn(acac) 3	220 sec	123°C	0.48/-0.85	1.33
	Sulf 1/ Mn(acetate) 3	60sec	119 °C	0.48/-0.72	1.20
	Sulf 1/Cu(hfacac) 2	100sec	40 °C	0.48/-0.715	1.19
	Sulf 2/Mn(acetate) 3	100 sec	110 °C	0.475/-0.72	1.195
	Sulf 3/Mn(acetate) 3	160 sec	90 °C	0.47/-0.72	1.19

Table 2 .

 2 Viscosities of the different resins used in this study

	Viscosities (25°C)
	Resin 1 0.053 Pa.s
	Resin 2 0.006 Pa.s
	Resin 3 0.16 Pa.s
	Resin 4 0.053 Pa.s

Table 3 .

 3 Representative gel times (in seconds) obtained for Sulf1/Thio redox initiating system in resin 1; 4 mm thick sample, under air.

	Sulf 1/Thio	no inhibitor	0.01%wt inhibitor	0.06wt% inhibitor
	Thio B	600 sec	740 sec	3400 sec
	Thio C	420 sec	1420 sec	2100 sec

Figure 5 .

 5 Optical pyrometric measurements (temperature vs. time after mixing; 4 mm thick sample) under air for the BM resin for Redox FRP using different RISs based on

	T4epa/Iod-Cl (1%/2% w/w) in presence of different salts: (A) NaPF 6 (0.5% w/w); (B)
	NaPF 6 (2% w/w); (C) NaPF 6 (1% w/w); (D) NaPF 6 (1.5% w/w); (E) LiTFSI (0.63% w/w);
	(F) LiTFSI (2% w/w); (G) LiTFSI (1% w/w); (H) LiTFSI (1.5% w/w); (I) NaBF 4 (1%
	w/w); (J) NaBF 4 (3% w/w); (K) without additional salt.

Table 1 .

 1 Summarized Data for Photopolymerization and Thermal Polymerization Based on Different CTCs Based on Different Amines. a

	Abbreviation	Structure	Solubility	Photo	Thermal	Stabilization
			of amines	polymerization b	polymerization c	Energy
			in Resin 1	Start	Conversion	∆H (J	T max	(kcal·mol -1 )
				time (s)	(%) at 400 s	per g)	(℃)
	DMA		+++	10	69	216	137	8.31
	TMA		+++	0	79	262	125	8.47
	DMAPE		+++	5	77	245	124	8.50
	PDA		+++	1	82	251	65	10.77
	TIAPPDA		-	5	83	136	249	12.54
						(Resin 3)	(Resin 3)
	PT		+	5	67	212	149	23.63
	MG		++	>400	<5	283	153	47.83
	DMAPCHD		-	>400	<5	266	100	5.09
	TMPDA		+++	>400	<5	198	162	14.32
	TPPTA		-	>400	<5	53	201	5.41
	DCDA		-	10	<10	28	209
						(Resin 2)	(Resin 2)
						441.38	179.47
						(Resin 3)	(Resin 3)

Table 2 .

 2 Frontier molecular orbital properties (calculated at UB3LYP/LANL2DZ level) for Iod

  formation possibility of CTCs based on various amines as dual photo/thermal initiators were investigated. Simple N-aromatic amines (not too delocalized/low molecular weight) with electron donating substituent show good structures for combining with Iod to activate photo polymerization of (meth)acrylate monomers (both acrylate and methacrylate monomers can be photopolymerized with the proposed CTC approach). Triphenylamine types of amines are not efficient either in thermal or photopolymerization. More amines combining with Iod can activate thermal polymerization of resins, probably due to improved solubility in thermal conditions. The results from stabilization energy between amines and Iod demonstrated that amines with simple delocalized structure easily interact with Iod to form CTCs. At the same time, these kinds of new CTCs have lower stabilization energy so that they can activate photopolymerization at visible light (low energy). Other kinds of amines have poor photo initiating ability due to their poor solubility or higher stability energy in resins. The new CTCs exhibited good spatial control ability in 3D printing process and excellent initiating ability in composites fabrication. Dual photo/thermal versatile initiating systems fill technological limitations shown by single photo or thermal initiators: no storage of hazardous compounds (in situ formation of the thermal initiator), spatial resolution and robustness in thick and/or filled samples (composites). The use of these systems for the 3D printing of composites will be presented in forthcoming works.Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S.

	Replogle, J.A. Pople, Gaussian 03, Revision B-2; Gaussian Inc.: Pittsburgh, PA, 2003.
	30	A.-R. Allouche, J. Comput. Chem., 2011, 32, 174-182.

Table 1 .

 1 The molecular orbital calculations show that the frontier orbitals of the new formed [Amine-Thiophenium] CTCs structures are located on two different parts of the molecule.Actually, these structures combine the highest occupied molecular orbital (HOMO) of the electron donor (reducing agent) and the lowest unoccupied molecular orbital (LUMO) of the electron acceptor (oxidizing agent). This distribution of electrons on two different parts of the molecule confirms the formation of CTC between the involved reagents (see in

	This section is devoted to confirm the formation of the proposed CTCs structures by
	molecular modelling and UV-visible absorption experiments. The optimized geometries as
	well as the frontier molecular orbitals (Highest Occupied Molecular Orbital HOMO and
	Lowest Unoccupied Molecular Orbital LUMO), and the predicted UV-visible absorption
	spectra of the different compounds used in this study (thiophenium salt alone, amine alone,
	and [Amine-Thiophenium] CTC ) are illustrated in

Table 1 :

 1 HOMO and LUMO are mainly located on amines and thiophenium salt, respectively). It should be noted that the energy gap between HOMO and LUMO of the created CTCs structures is lower than that of the electron donor and the electron acceptor separately, resulting in a more favorable energy transitions (e.g. ∆E (HOMO-LUMO) = 1.58 eV for [MHPT-Thiophenium] CTC vs. 5.2 eV for MHPT alone and 4.35 eV for Thiophenium alone, Scheme 2).

Table 1 .

 1 Contour Plots of HOMOs and LUMOs, the Energy Gap between HOMO and LUMO, and the Predicted UV-visible Absorption Spectra of Thiophenium alone, Amine

	alone, and [MHPT-Thiophenium]CTCs; Structures Optimized at the B3LYP/6-31G* Level of
	Theory.

HOMO LUMO DE (HOMO-

LUMO) (eV) Predicted UV-visible Absorption Spectra

  visible light absorbing reagents. It should be noted that both the experimental and the predicted UV-visible absorption spectra show that [MHPT-Thiophenium] CTC structure leads to a higher and significant bathochromic shift compared to DMT and PP (curve 3 in Figure

	Their absorption bands are located in the ultraviolet
	region and do not exceed 300 nm for amines (curve 2 in Figures 1A,1B and 1C for MHPT,

DMT and PP, respectively) and 350 nm for thiophenium salt (curve 1 in Figures

1A,1B and 1C

). Once, these compounds (amine and thiophenium) are mixed together, the solution from non-

Table 2 .

 2 Final Reactive Methacrylate Function Conversion (FC%) for a Benchmark

	Monomer Blend in the Presence of Different Amine/Thiophenium or Iodonium (2%/2% w/w)
	Combinations after 400s (LED @405 nm).
	DMT/Thiophenium	MHPT/Thiophenium	PP/Thiophenium	PP/Iodonium
	88%	75%	71%	71%

Final Reactive Methacrylate Function Conversion (FC%) for a Benchmark Monomer Blend; (thickness = 1.4 mm) under air Figure 2. Photochemical polymerization profiles (methacrylate function conversion vs. irradiation time) for thick samples (1.4 mm) for a benchmark monomer blend upon irradiation with the LED @405 nm (under air), in the presence of different combinations

Table 3 .

 3 The Polymerization Enthalpy, the Maximum Polymerization Temperature for the Different Amine/Thiophenium or Iodonium Combinations in the Benchmark Monomer Blend.

evaluated from a molar heat of polymerization of 13.57 kcal/mol for the methacrylate functions from [29].

	Thiophenium/Amine		(J/g)	DH	Methacrylate Conversion (%) a Function	T max (°C)
	(1) Thiophenium 2%	DMT	+	2%	313	83	95
	(2) 2% MHPT + 2% Thiopheniumin	319	85	102
	(3) 2% PP + 2% Thiophenium	303	81	116
	(4) 2% PP + 2% Iodonium		261	70	148

a :

UV 1500) Huile de soja ESO DGEBA Acide ascorbique (VIT C) Cuivre (acétate)2 Sels d'iodonuim (SC938) Agents réducteurs Agents oxydants mélangé

  Dans ce contexte, des composés organiques sans amine et sans peroxyde capables de réagir dans les processus redox sont très recherchés. En particulier dans nos travaux, les sels d'iodonium et le cuivre acétate (II) (agents oxydants) sont mélangés avec l'acide ascorbique (vitamine C) comme agent réducteur bien soluble avec les différents monomères époxy. Puis, l'eau est ajoutée pour assurer la solubilité des produits dans la résine. Dans ce contexte, simple, économique et respectueux de l'environnement, le système Vit C+H 2 O/ sel d'iodonium + Cu (acétate) 2 est étudié comme un système amorceur redox original. Cette approche va permettre une polymérisation à température ambiante et sous air. La réaction de polymérisation a été suivie par plusieurs techniques comme la pyrométrie optique, le Raman et la spectroscopie infra rouge (FTIR). avec deux agents oxydants différents (le cuivre acétate et le SC938). Les efficacités de polymérisation des divers systèmes redox ont été suivies par pyrométrie optique (figure1).

	Parmi les Trois monomères utilisés, deux ont bien fonctionné : 1) le système VITC
	+ H 2 O/ Cu (acétate) 2 + SC938 avec le UV1500 a montré un pic exothermique autour de
	170°C avec un temps de gel de l'ordre de 3.5 minutes (figure 1, courbe 1) ; 2) le même
	système avec le (ESO) a montré un pic exothermique autour de 80°C et un temps de gel plus
	long (10 minutes) (figure 1, courbe 3). Par contre, le nouveau système redox proposé (VITC +
	H 2 O/Cu (acétate) 2 + SC938) n'a conduit à aucun processus de polymérisation (figure 1), dans
	le monomère (DGEBA). Ces résultats préliminaires sont très intéressants : le (ESO) est en
	effet un monomère époxy biosourcé.
	Tous les produits chimiques ont été obtenus avec une pureté élevée et ils ont été
	utilisés tels que présentés dans les schémas 1 et 2. Le sel d'iodonium (speedcure 938 -SC938)
	a été fourni par Lambson Ltd (Royaume-Uni), L'acétate de cuivre (II) (noté Cu (acétate) 2 ) a
	été obtenu chez TCI; l'acide ascorbique (noté VitC ) a été fourni chez alfa aesar. L'efficacité
	des différents systèmes d'amorçage redox (RIS) a été vérifiée dans 3 monomères époxy
	différents :
	1-Uvacure 1500 (UV1500).
	Figure 1. Mesures pyrométriques optiques (température en fonction du temps après le
	mélange ; échantillon de 4 mm d'épaisseur) sous air pour les différents monomères avec 2-DGEBA. différents systèmes redox : (1) 2%VITC + 4%H 2 O/ 1%Cu (acétate) 2 + 2%SC938 dans
	UV1500, (2) 2%VITC + 4%H 2 O/ 1%Cu (acétate) 2 + 2%SC938 dans DGEBA, (3)
	3-Huile de soja epoxydée (ESO). 2%VITC + 4%H 2 O/1%Cu (acétate) 2 + 2%SC938 dans (ESO). Les pourcentages sont
	donnés en poids.

1-Partie expérimentale : Schéma 1. Monomères époxy étudiés dans cette étude.

Schéma 2. Agents redox étudiés dans cette étude.

2-Résultats et discussion :

Initialement, l'acide ascorbique utilisé comme agent réducteur a été aussi utilisé pour une polymérisation cationique de monomères multifonctionnels époxy. Ce dernier a été Uvacure 1500 (

  1) 1% Cu(AAEMA) 2 +1% Vanax/ 1% Cumème hydroperoxide (1% en poids), (2) 1% Fe(acac) 3 +1% Vanax/ 1% Cumène hydroperoxide, (3) 1% Mn(acac) 3 +1% Vanax/ 1% Cumène hydroperoxide, (4) 1% Ni(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (5) 1% étain(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (6)1% Gallium(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (7)1% V(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide, (8)1% Cu(acac) 2 +1% Vanax/ 1% Cumène hydroperoxide.

Perspectives

Remerciements

initiating chemical mechanism of RFRP is proposed. Developing a new redox system viable under mild condition enables safer and cheaper access to polymer-based products in biomedical research, adhesives, composites to name but a few.

viscous resins is easier under air, i.e when the oxygen diffusion into the sample is prevented. This latter behavior is probably the case in resin 1, resin 3 and resin 4. Resin 1 is an OHcontaining monomer, while resin 4 is an OH-free system, the presence of alcohol functionality in resin 1 leads to suboptimum reactivity compared to resin 4 and a less efficient polymerization process.

As a good solubility is observed in HEMA (resin 2), and in order to ensure a good solubility of PIS in resin 1, different contents of HEMA were added. As shown in Figure 3B, the gel time can be adjusted, on demand, by adding different contents of HEMA: by increasing the content of HEMA both exothermicity and the gel time increase. These results are as expected: by adding HEMA the solubility of the redox system in resin 1 is improved and more radicals can be formed to initiate the polymerization. But the viscosity decreases and the oxygen inhibition increases the gel time. This process was also investigated by ESR spectroscopy for a full characterization of the radicals generated.

The redox reaction Sulf/ 1Thio A is leading to a radical /PBN adduct that was assigned to RSO 2 • / PBN radical adduct. The ESR-spin trapping experiments (Figure 7) show excellent correlation of experimental and simulated spectra using hyperfine coupling constants (HFCCs) of a N = 13.4 6 G, a H = 1.7 4 G which corresponds to the experimental literature of

Conclusions :

In this work, a pure organic and peroxide-free RIS is presented for polymerization n mild conditions. This latter system is characterized by a bulk polymerization efficiency comparable to the benchmarck BPO/TMA system but with the advantage of better surface curing under air. Markedly, a precise control of the gel time is possible through an appropriate content of redox agents or the use of an additional salt. The proposed RIS is highly robust and can be used for polymerization at low temperatures. Other pure organic RIS will be presented in forthcoming works.

polymerization of Resin 1 under air, photo initiator: [0.7 wt% TMA-0.7 wt% Iod]CTC; A: top surface morphology; B: 3D overall appearance. A writer using a laser diode at 405 nm (size of the spot around 50 μm) with the intensity of 100 mW was used for the spatially controlled irradiation.

Preparation of Composites by Photo or Thermal Curing Methods

The new series of CTCs as dual photo/thermal initiators were exploited to prepare glass/carbon fiber composites. A well cured thick glass fibers composite from Resin 1 was obtained by photo curing method after only two passes using a LED conveyor from [TMA-Iod]CTC system (Figure 5). It remains a challenge to prepare carbon fibers composites by photocuring method due to lower light penetration in carbon fibers vs. glass fibers: only the top surface became cured after two passes. While, thermal curing method or photo/thermal dual curing method can be exploited to prepare carbon fiber composites benefiting from the unique dual photo and thermal initiator behavior of the new amines CTCs. The carbon fiber prepreg was irradiated for the first stage for a fast surface photocuring. Then, the half cured prepregs (precomposite) was transferred into an oven for next stage of bulk thermal curing.

Excellent dual cured carbon fiber composites were manufactured by the photo/thermal dual curing method (Figure 5). Composites from Resin 2 are also fabricated as showed in Figure S1. The mechanical properties of the obtained composites were investigated by DMA (see further information in SI -Figure S2). We can see that E' of both composites is about 1.7 GPa at RT, and the Tg was observed at about 150°C. It shows that the composite materials have

Abstract :

This article is devoted to the development of new Thiophenium salt/Amine charge transfer complexes (CTCs) as double-acting (Photochemical/Thermal) initiators for the free radical polymerization (FRP) of (meth)acrylates. Interestingly, the polymerization can be activated in such a case by light or by heat leading to the possibility of a dual cure systems.

These new proposed systems are based on commercially available compounds but also stable and metal-free. It should be noted that a combination between an electron donor (e.g., N-improved visible light absorption allowing their use for 3D printing polymerization under blue light [19,20], to their dual photochemical and thermal behavior which is not observed for any type of initiators mentioned above [18], as well as their low optical density which allows an efficient light penetration in depth. This latter feature is very interesting for the production of thick and filled glass or carbon fiber composites without any inner filter effect issue [15][16][17][18], highlighting the importance of such CTC approach.

In this research, a new series of charge transfer complexes (CTCs) is developed. These

CTCs are based on several N-aromatic amines as electron donors and thiophenium salt which can be active as an electron acceptor. Such structures are examined as dual (photochemical/thermal) initiators for the free radical polymerization (FRP) of methacrylates.

Interestingly, thiophenium salts are used here for the first time as an electron-withdrawing compound for the formation of CTCs structures. It should be reported that the new suggested [Amine-Thiophenium] CTCs can be considered as efficient alternatives for [Amine-Iodonium] CTCs structures [18]. The study of both photoinitiating and thermal abilities of the new proposed donor-acceptor complexes is outlined separately. Furthermore, the proof of their formation which is confirmed by UV-visible experiments and molecular modelling is also provided. Eventually, the effect of the donor structure (N-aromatic amine) on the associated Photo/Thermal initiating abilities of the created CTC is discussed too.

EXPERIMENTAL PART

Other Chemicals Products

All commercial chemicals were selected with the highest purity available and used as

O.D

A-Polymérisation cationique redox : vers des monomères biosourcés

Les matériaux polymères à base d'époxy sont utilisés dans de nombreuses applications, tels que les revêtements, les composites, les adhésifs structuraux, etc... Ces matériaux ont des propriétés uniques, c'est-à-dire un faible retrait ainsi que des propriétés mécaniques exceptionnelles. Les résines époxy sont principalement utilisées dans les applications thermodurcissables. Dans de tels procédés, l'époxy réagit avec un agent de réticulation également appelé durcisseur.

Par conséquent, notre objectif principal dans ce système est d'obtenir une conversion élevée en un temps court dans des conditions modérées (température ambiante, sans lumière).

Le temps de gel, l'exothermicité et l'efficacité de polymérisation redox ont été suivis par différentes techniques telles que la pyrométrie optique, la FTIR, la RPE et le Raman.

1-Composants chimiques utilisés dans cette étude :

4-Effet de la concentration en agents redox :

Les temps de gel et les températures atteintes pour les différentes concentrations en système redox sont rassemblés dans le tableau 1. On remarque qu'il n'y a pas de polymérisation sans l'utilisation des métaux. Ce qui explique l'effet catalytique de métaux dans ce système avec une faible concentration (0.05% de poids) et le temps de gel est autour