Xavier Coqueret

Chapter 6 RADIATION-INDUCED POLYMERIZATION

INTRODUCTION

Polymers can be synthesized into a variety of topological structures (linear, branched and three-dimensional networks) by two types of polymerization, either of which involves a chain addition process or a step-growth mechanism. Radiation-induced polymerization, for the most part, proceeds by a chain addition mechanism [START_REF] Chapiro | Radiation effects in polymers[END_REF].

In principle, step-growth processes can be triggered by the generation of catalysts resulting from the interaction between radiation and the precursors of some acidic or basic species, or between some radiolytic products with acid or base generators. However, this step-growth process has received little attention and is currently limited to few applications of technical relevance. For example, the step-growth addition of the thiol groups on a multifunctional mercaptan derivative to diisocyanates is effectively catalyzed by photobases under ultraviolet (UV) radiation. This results in the formation of hard, fl exible materials with interesting uses in microelectronics and as binders for industrial paints and coatings [START_REF] Smith | Microlithography: science and technology[END_REF].

High energy radiation interacts with organic matter by various physical and chemical mechanisms resulting in the formation of short-lived excited species, and of chemical entities such as thermalized electrons and neutral or ionic free radicals exhibiting longer lifetimes allowing them to undergo bimolecular reactions with various molecular compounds by translational diffusion [START_REF] Ferry | Ionizing radiation effects in polymers[END_REF]. The in-situ generation of such longer-lived reactive species can be exploited to initiate chain polymerization mechanisms. The resulting process is called radiation-initiated polymerization, the propagation being, in principle, not directly affected by radiolytic events. Propagation essentially proceeds with the same mechanistic and kinetic features of conventional, thermally initiated chain polymerizations. The radiation-induced initiation process makes it possible to trigger polymerization under reaction conditions (temperature, initiation rate, type, location and spatial distribution of the initiating species) that are unusual, if not specifi c, compared to the activation with thermally cleavable initiators (such as peroxides) or with redox systems (such as a reductive metal associated with a peroxide). A number of advantages can be found from these peculiarities of radiation-initiated polymerization that benefi t processing efficiency or which produce fi nal materials with unique properties [START_REF] Matyjaszewski | Handbook of free radical polymerization[END_REF].

The basic aspects of chain polymerization are discussed in the next section. Then, the specifi c features of radiation-initiated polymerization carried out by free radical or by cationic propagation will be addressed [START_REF] Odian | Principles of polymerization[END_REF].

BASIC ASPECTS OF CHAIN POLYMERIZATION

Chain polymerization is defi ned as "a chain reaction in which the growth of a polymer chain proceeds exclusively by reaction(s) between monomer(s), (M), and reactive site(s), represented by an asterisk in Eq. ( 1), on the polymer chain with regeneration of the reactive site(s), at the end of each growth step".

~~~~ (M) n ~~~~ M* + M ~~~~ (M) n+1 ~~~~ M* (1) The chain reaction mechanism includes a sequence of steps forming a chain mechanism, that is a complex reaction path in which one or more reactive intermediates (frequently radicals) are continuously regenerated. This usually happens through a repetitive cycle of steps which propagate the reaction. When the propagation step involves a monomer that is repeatedly bound to an active center, such a process results in the formation of an oligomeric, higher molecular weight entity, which eventually grows further to form a polymeric chain that has an active end group. The most common polymerization processes involve carbon centered free radicals. However, ionic mechanisms, covalent group-transfer and organometallic complexes involved in coordination polymerization have specifi c features that may offer advantages of technical interest.

Propagation in chain polymerization usually occurs without the formation of small molecules. However, in very specifi c cases, low-molar-mass molecular by-products are formed, that are not included in the chain undergoing the propagation step. When such molecular extension process occurs, the chain process is a condensation chain polymerization. More commonly, the type of chemical reactions involved in this growth step is specifi ed by using the terms free radical chain polymerization, ring-opening chain polymerization, cationic chain polymerization, etc.

The four main steps of the chain mechanism are presented in the following sections for the free radical polymerization of unsaturated compounds such as vinyl, acrylic and styrenic monomers.

KEY STAGES OF THE CHAIN POLYMERIZATION MECHANISM

Step 1 -Chain initiation Chain initiation can take place as soon as the properly selected initiator starts to decompose into free radicals (In°). Initiation is completed when the initiator radical has added to the fi rst monomer unit, M, to produce the chain initiating species, M 1 °. From a kinetic standpoint, the rate of initiation, R i , is controlled by the initiator decomposition, which is a slower reaction than the subsequent addition of an electron-defi cient radical onto the electron rich bond of the ethylenic monomer. Though directly related to the decomposition rate of the initiator, R d , the effective initiation rate, R i , depends on an effi ciency factor that takes into account the actual fraction of generated free radicals that effectively add to the monomer for producing M 1 °, the chain initiating species. The quenching effi ciency of dioxygen for carbon-centered free radicals is extremely high, and, as a result, peroxy radicals are unable to initiate the propagation process. Consequently, free radical polymerizations are preferably conducted with the exclusion of oxygen (in vacuo or by deaeration with an inert gas). When a low residual amount of dioxygen is present in the polymerization medium, polymerization starts after an induction period corresponding to the consumption of O 2 via the quenching reaction. In some cases, particularly when a photochemical or a radiochemical activation process is used for the initiation, the rate of formation of new free radicals is high enough to overcome the quenching of O 2 that is initially present in the medium and of the amount of O 2 that constantly diffuses from the ambient atmosphere into the reaction medium. This favorable situation can be achieved under intense ultraviolet or light irradiation of properly photosensitized compositions or by processing the radically polymerizable monomers under high dose rate electron beams (EB).

Typical initiators that are activated by heat include various types of organic compounds with a scissile functional group that is decomposed at reasonable operating temperatures, such as aromatic azo derivatives (-N=N-), disulfi des (-S-S-), or peroxides (-O-O-) (Scheme 1). Inorganic and organic redox systems (such as Fenton reagent (FR), peroxide-dimethyl aniline shown Scheme 1. Examples of thermal initiators with their decomposition products: azo-bis--isobutyronitrile (AIBN) and benzoyl peroxide (BPO). in Scheme 2) offer the advantage of generating free radicals effi ciently at temperatures between 0 and 50°C, without needing to heat the reaction medium in order to induce thermal initiator decomposition.

Step 2 -Chain propagation Propagation consists of the iterative growth of the initiating radical, M 1 °, that forms, after a suffi cient number of additions, a macroradical, as shown in Eq. [START_REF] Smith | Microlithography: science and technology[END_REF].

~~~~ (M) n ~~~~ M° + M ~~~~ (M) n+1 ~~~~ M° (rate constant k p ) (2) Both for kinetic and thermodynamic reasons, the head-to-tail placement is overwhelmingly predominant for free radical addition of monosubstituted unsaturated monomers (CH 2 =CHR) that yield polymer chains where tertiary carbon atoms and methylene groups alternate. Monomers suitable for free radical chain polymerization show varying degrees of reactivity depending on the affi nity of the free radical for its monomer. The rate constants for propagation of common unsaturated monomers range between 10 2 and 10 4 L•mol -1 •s -1 (as shown in Table 1). By comparing the effects of substituents on the stability of the free radical, higher propagation rate constants are observed for less stabilized active centers. However, for achieving the formation of chains with a high degree of polymerization, the reactivity of free radicals has to be mainly directed towards propagation, limiting competing reactions of charge transfer.

Step 3 -Chain termination Active free radicals in the polymerization of unsaturated monomers are unstable and tend to undergo self-annihilation when on occasion randomly encountering another free radical. This bimolecular process results in the termination of the molecular chains propagated by two encountering macroradicals. Termination occurs either by combination or by disproportionation, which yields a single macromolecule or saturated and unsaturated polymer chains. Combination is the simplest mechanism where the two macroradicals overlap their singly occupied molecular orbital to form a stable bond, resulting in the Scheme 2. Examples of redox initiators: Fenton reagent (FR) and benzoyl peroxide-N,N--dimethylaniline system (BPO-DMA). formation of a polymer which is the sum of monomer units added by each one of the participating chains (Eq. ( 3)). Disproportionation is a redox process yielding a hydrogen saturated macromolecule together with its omega unsatu- a At T = 60°C, unless otherwise specifi ed. Data were collected from Ref. [START_REF] Odian | Principles of polymerization[END_REF].

rated counterpart (Eq. ( 4)). This takes place via the abstraction of a hydrogen atom at the saturated carbon next to the active center by the other macroradical. The activation energy required for the abstraction process is generally much higher than the straightforward combination of the two macroradicals.

Step 4 -Chain transfer Chain transfer can be considered as a competing process to propagation. Instead of adding to a monomer, the growing macroradical can react with various types of molecular compounds present in the reaction medium: the initiator, solvent, dead polymer, impurities, or any transfer agent, introduced purposely in the reaction medium to obtain a desired effect on the resulting molecular weight (MW) or on end group functionalization.

The transfer reaction can be depicted by an exchange of an atom by a free radical mechanism, the macroradical abstracting an atom, A, to form a stable polymer molecule fi tted with A as an end group, generating the free radical B° (Eq. ( 5)).

~~~ M n ~~~ CH 2 -HRC° + A-B ~~~ M n ~~~ CH 2 -HRC-A + B° (5) B° + n M

B-M n ° (6) Chain transfer can compete with propagation in a process where the active center of a growing polymer chain is transferred to various components in the polymerization medium, such as solvent, monomer, initiator, polymer or to a purposely selected additive (a transfer agent). Transfer reactions occur easily with the use of a chlorinated solvent (CHCl 3 ) or with a solvent having an easily abstractable H atom (isopropanol), a monomer, or a polymer. When the molecule subject to the transfer process is a macromolecule formed earlier in the reaction medium, the chain growing from the main polymer backbone will create a side chain. The repetition of this phenomenon leads to multi-branched polymers.

The occurrence of this event terminates the chain involved with the macroradical, but the active site is transferred to another radical, B°, which can restart a new chain polymerization (Eq. ( 6)). In such a case, the instantaneous number of growing chains is kept constant, with little or no effect on the polymerization rate. The impact of transfer on the average length of the formed polymer chain is discussed below.

KINETIC ASPECTS OF FREE RADICAL CHAIN POLYMERIZATION

Because of the fast bimolecular combination of free radicals in fl uid media, the chain reaction kinetics of free radical polymerization is governed by a steady state that results from the balance between the formation of new growing chains yielded by initiator decomposition and by the addition to the fi rst monomer unit M (Eqs. (7a) and (7b)) and the radical disappearance by termination (Eq. ( 8)).

Initiator decomposition I 2 R° (rate determining) (7a)

Formation of chain initiating radical R° + M R-M 1 ° (7b) Termination ~~ M i ° + ~~ M j ° ~~ M i+j ~~ or ~~ M i ' + ~~ M I ' (8)
The dynamic balance is expressed by equal rates for initiation and for termination yielding

2 f k d [I] = 2 k t [M°] 2 (9
) where: f -the effi ciency factor of free radicals involved in the chain initiation, k d -the rate constant for initiator decomposition, k t -the rate constant for the termination reaction, [M°] -the concentration in propagating free radicals.

Considering typical values for the rate of reaction (7b) (R i 10 -4 -10 -6 mol•L -1 •s -1 ) and for the bimolecular termination rate constant for Eq. ( 8) (k t 10 6 -10 8 L•mol -1 •s -1 ), a steady state for free radical concentration is reached within a fraction of a second. The steady-state value of a propagating free radical concentration can be introduced in the expression of the polymerization rate, R p , defi ned as the rate of monomer consumption in the propagation step,

R p = k p [M] [M°] (10) yields R p = k p (f k d /k t ) 0.5 [M] [I] 0.5 (11)
where k p is the rate constant for propagation. Rate constants k p are in the range 10 2 -10 4 L•mol -1 •s -1 , depending on the structure of the unsaturated monomer. A much higher value of k t compared to k p does not prevent propagation because the radical species are present in very low concentrations (typically 10 -8 mol•L -1 ) and because R p is inversely proportional to the square root of k t .

Besides the polymerization rate, of importance in free radical chain polymerization is the kinetic chain length,

In a chain process unaffected by transfer reactions, the kinetic chain length is defi ned as the average number of propagation steps for each initiation. This quantity corresponds to the ratio of the polymerization rate, R p , to the initiation rate, R i , or to the termination rate, R t , since the latter two quantities are equal. In chain polymerization, it is worth noting that represents the average number of monomer molecules added to a growing chain at the moment it is deactivated by termination. Depending on the relative contribution of disproportionation and combination to the overall termination process, the terminated polymer chain will exhibit a number-aver-age degree of polymerization (DP n ) between 1 (only disproportionation) and 2 (only combination) times the value.

The kinetic data derived from the chain kinetic model are instantaneous values subject to changes in the physical parameters for the reaction, such as temperature and viscosity. Autoacceleration occurs in radical chain polymerization and normally in bulk polymerization. As monomer conversion increases, the gradual formation of polymer in the reaction medium increases the viscosity, essentially reducing the effi ciency of chain termination by reducing the diffusion of the macroradicals. This change in viscosity has little effect on initiation and propagation, but it results in a strong increase of the free radical concentration. Autoacceleration, called the Trommsdorff-Norrish effect, is particularly effective when multifunctional monomers are involved in the polymerization.

Chain transfer reactions reduce the average molecular weight of the fi nal polymer while keeping constant the total number of free radicals. Therefore, transfer reactions have no direct effect on polymerization rate, but can be used to control the average degree of polymerization to form chains, acting on the kinetic chain length = R p /(R i + R tr ), where R tr = k tr [M i °] [TA] is the rate of the transfer reaction to the transfer agent TA. Thiols are particularly effi cient in this.

POLYMERIZATION THERMODYNAMICS

As polymerization reactions convert a large number of monomer molecules into a few macromolecular chains, they are generally associated with a strong decrease of entropy ( S p < 0). This situation impacts the free energy state function G p = H p -T S p that governs what happens to the chemical transformations. Polymerization can proceed if the enthalpy variation is exothermal enough ( H << 0), so that the net balance appearing in G p is negative. Monosubstituted unsaturated monomers typically exhibit polymerization enthalpies ranging from 70 to 90 kJ•mol -1 . This generally allows for an effi cient polymerization to proceed if the monomer concentration is high enough. Taking into account the reversibility of the propagation step of free radical polymerization, the growth of chains is stopped when the free energy G p = H p ° -T S p ° -RT ln [M] approaches 0. At a given monomer concentration, the temperature increases to a critical value T c = H p °/( S p ° + R ln ([M] c ), called the ceiling temperature. The polymerization of vinyl acetate, methyl acrylate and styrene is not signifi cantly affected by thermodynamic constrains under normal polymerization conditions, but for methyl methacrylate, a monomer exhibiting a lower enthalpy of polymerization due to the presence of a methyl substituent on the double bond, the ceiling temperature is 220°C for pure monomer.

MICROSTRUCTURE OF POLYMER CHAINS

Chain polymerization of vinyl monomers (CH 2 =CHR) yields polymers having stereocenters (-CH 2 -C*HR-) which can exhibit either of two different confi gurations. Free radical propagation is weakly sensitive to the infl uence of the stereocenter located at the penultimate unit on the macroradical. This results in a weak preference for the formation of a syndiotactic dyad with respect to an isotactic one at each propagation step. The fi nal polymers are therefore essentially atactic in terms of microstructure and are amorphous materials.

CONTROLLED FREE RADICAL POLYMERIZATION

The limitations due to the termination reactions taking place during conventional free radical polymerization have been overcome by using various molecules, metal complexes or stable free radicals that convert the growing Scheme 3. Principles of the three main methods for achieving controlled free radical polymerization.

free radicals into a dormant species, thus dramatically reducing the occurrence of termination [START_REF] Matyjaszewski | Handbook of free radical polymerization[END_REF]. Controlled free radical polymerization (CRP) can be achieved by using stable free radicals as nitroxides (nitroxide-mediated polymerization, NMP), by reversible addition-fragmentation chain transfer (RAFT) to various thiocarbonyl compounds, or by halogen atom transfer from a transition-metal--catalyst subject to a redox exchange (atom transfer radical polymerization, ATRP), as shown in Scheme 3. The active center is capable of reactivation, functionalization, and chain extension to form block copolymers and even more complex polymer architectures. The potential of CRP differs from ionic living polymerization processes because of the tolerance of the selected reversible chemistries to a variety of functional monomers and to unconventional polymerization media.

FREE RADICAL COPOLYMERIZATION

Chain polymerizations can be carried out with mixtures of two or more monomers to form polymeric products with an almost unlimited composition and structure, hence with new properties. The monomers enter into the copolymer in amounts determined by their relative concentrations and reactivity. Whereas alternating, statistical and random copolymers are produced by simultaneous and competing polymerization of monomer mixtures, graft and block copolymers result from a sequence of separate polymerizations. The instantaneous composition of a copolymer produced by a chain process cannot be determined simply from knowledge of the homopolymerization rates of the two monomers. The relative contribution of cross-propagation with respect to the homopolymerization is described by using the reactivity ratios of each monomer. For a mixture of two monomers, the fi rst order Markov model for copolymerization assumes that the reactivity of the propagating species is dependent only on the monomer unit at the end of the chain, with there being four possible propagation reactions (Scheme 4). The reactivity ratios of both monomers with respect to the macroradicals fi tted with A° and B° as the propagating end groups, r a = k aa /k ab and r b = k bb /k ba , respectively, are the main parameters that govern the instantaneous rate of incorporation of both monomers in the growing chains, for a given monomer composition in the reaction medium f a = [A] t /([A] t + [B] t ). The Mayo-Lewis relation (Eq. ( 10)), derived from the kinetic scheme of the terminal model, states how the instantaneous composition of the formed copolymer,

F a = d[A] t /(d[A] t + d[B] t )
, is dependent on the variable f a and on the parameters r a and r b .

F a = (r a f a 2 + f a (1 -f a ))/(r a f a 2 + 2 f a (1 -f a ) + r b (1 -f a 2 )) (12)
An important feature of free radical copolymerization is the composition drift that is expected to take place during a batch process, and the distribution of monomer units along the chain that may ideally take place at random if r a • r b = 1, or form alternating -A-B-sequences, or eventually produce isolated units of one monomer between blocks of the other.

RADIATION-INITIATED POLYMERIZATION

Compared to thermal and redox initiation processes, activation methods using radiation exhibit unique features that allow for a time and spatial control of polymerization. Several applications take advantage of these properties: the ultraviolet radiation or electron beam (UV/EB) curing of solvent-free coatings and inks in industry and in graphic arts, the synthesis of vinyl acetate or acrylate latices by emulsion polymerization initiated by using gamma rays, the out-of--autoclave curing of performance composites using EB and/or X-rays, laser or EB micropatterning and nanolithography for microfl uidic and electronic devices [START_REF] Fouassier | for polymer synthesis: scope, reactivity, and effi ciency[END_REF].

Ultraviolet radiation and high energy electron beam radiation can trigger chain polymerization either by direct interaction with monomers or through the intermediacy of some other constituents present in the reaction medium.

PHOTOINITIATED POLYMERIZATION

Unsaturated monomers can be activated by short wavelength photons, by specifi c additives called photoinitiators that generate active centers (free radical or cationic species) upon exposure to an ultraviolet source. Radical initiation mechanisms either involve the direct homolysis of a C-C of the photoexcited initiator (Type I initiation with aromatic carbonyl compounds) or a cascade of reactions (Type II initiation by electron transfer and hydrogen abstraction), as shown in Scheme 5.

Aromatic onium salts can generate cationic active centers (Brønsted acids or carbenium ions) upon absorption of ultraviolet radiation [START_REF] Crivello | of epoxy matrix composites by electron beam induced cationic polymerization[END_REF]. There are two basic classes of cationic initiators grouped by dependence on the mechanisms of photolysis. The fi rst group includes diaryliodonium and triarylsulfonium salts, which undergo fragmentation to yield aryl radicals and/or arylionium cation radicals. Dialkylphenacylsulfonium and dialkyl-4-hydroxyphenylsulfonium salts form the second group that generates yields and Brønsted acids by a reversible photolysis (Scheme 6).

Both classes of onium salts can be photosensitized in order to extend their response to long wavelength ultraviolet and to light. This can be achieved by energy transfer, electron transfer or through the intermediary of free radicals. A simplifi ed description of the direct and sensitized pathways for the generation of cationic species from a diaryliodonium salt is represented in Scheme 7. Structural variations within the cations of onium salts have a marked infl uence on the photolytic effi ciency, whereas the nature of anion mainly affects the course of the resulting cationic polymerization.

POLYMERIZATION INDUCED BY HIGH ENERGY RADIATION

Despite the high intrinsic effi ciency of commercial photoinitiators for free radical or for cationic polymerization, the effectiveness of photochemically triggered initiation is limited by the low penetration depth of ultraviolet radiation into opaque compositions. This is why accelerated electrons as well as photonic ionizing radiations (gamma and X-rays) have a signifi cant advantage over ultraviolet radiation and light. Light is the visible range of the electromagnetic spectrum. The depth of penetration is much greater with less attenuation for ionizing radiation than for ultraviolet radiation and light. Pigmented coatings, printing inks but also adhesives and sealants sandwiched between non--transparent materials as well as fi ber-reinforced composites can be cured by crosslinking polymerization of multifunctional monomer compositions.

The radiolysis of olefi nic monomers produces cations, anions, and free radicals. Such species are capable of initiating chain polymerization. The cationic polymerization of isobutylene, of vinyl ethers, of epoxies, and of styrene and the anionic polymerization of acrylonitrile have been observed in the absence of additional initiators under controlled laboratory conditions. Long-lived cationic chain reactions involving carbenium or oxonium intermediates are unlikely because of the high reactivity of active centers that make transfers and deactivation reactions very fast unless special conditions (purity of involved chemicals, low temperature) are maintained throughout the process. For that reason, onium salts are used in the monomer composition. Scheme 7. Examples of onium salts used for radiation-initiated cationic polymerization ("In" is a source of free radicals generated by any type of mechanism).

From a practical perspective, most radiation polymerizations are mediated by free radicals, since at temperatures of technical relevance ionic species are not stable and dissociate to yield radicals.

Pulse radiolysis experiments on various mono-or multiacrylate monomers monitored by time-resolved spectroscopy have permitted a better understanding of the various pathways that lead to initiation. The mechanism [START_REF] Knolle | On the mechanism of the electron-initiated curing of acrylates[END_REF] involves the attachment of a thermalized electron to an acrylate carbonyl group, and the subsequent formation of a radical anion dimer under the form of a charge transfer complex, or of a covalent adduct (Scheme 8). Protonation of the radical-anions yields the effective initiators for propagation. On the basis of experimental data, this model considers the direct formation of free radicals by homolytic dissociation of electronically excited molecular segments as a minor pathway, based on acrylates that were studied.

The subsequent steps of the free radical polymerization follow the same pathway as that of conventional crosslinking polymerization initiated by thermal or redox processes. The specifi c aspects of the cationic polymerization of epoxies are discussed below. Contrary to the mechanism of onium salt photolysis upon selective absorption of ultraviolet radiation, the dominant pathway under ionizing radiation in a medium rich in monomers is the production of free radicals which can reduce the onium salt, and generate in a second stage carbenium cations (Scheme 9). Reduction of the onium salt can also occur from its interaction with solvated electrons (reduction pathway). This mechanism was confi rmed by pulse radiolysis experiments on diglycidyl ether of bisphenol A (DGEBA) in the presence of an iodonium salt [START_REF] Fouassier | for polymer synthesis: scope, reactivity, and effi ciency[END_REF].

+ acrylate + H + O O O O - O OH O O + acrylate R R R R O O - O O R R O O - O O R R + H + O OH R
Scheme 8. Initiation mechanism for acrylate polymerization under high energy radiation [START_REF] Knolle | On the mechanism of the electron-initiated curing of acrylates[END_REF].

O O •+ + e - O •+ O O + O + + O O + Ar 2 I + + ArI + Ar R R R R R R R R (Am + ) EB • • • O O + R R O R Am (Am + ) H Scheme 9.
Initiation mechanism for epoxy polymerization under high energy radiation.

Initiation ACE propagation AM propagation

Transfer reaction Scheme 10. Propagation and transfer reactions during the cationic polymerization of epoxides.

Cationic chain propagation results from the reaction of oxonium ions with epoxy monomers by activated chain end (ACE) or activated monomer (AM) mechanisms. The ACE mechanism consists of the repeated addition of the monomer on the growing chain by the nucleophilic attack of the oxygen from the epoxy monomer on the carbon atom adjacent to the oxonium ion (Scheme 10). The AM mechanism takes place in presence of hydroxyl containing species and involves their addition to the protonated monomer followed by a charge transfer. The activated monomer is then regenerated and can react again with a hydroxylic compound. As the epoxy ring opens, hydroxyl groups are formed which favor the AM mechanism. Other transfer reactions can take place between an active chain and nucleophilic species such as water, alcohol or any other hydroxylic compounds resulting in the liberation of a proton and an inactive oligomer.

Two cationic species cannot react together. Thus, no termination reaction occurs by self-quenching of the active centers, as in the case of free radical processes. Once irradiation has ceased, cationic polymerization will continue to propagate without new initiation, by the so-called dark cure phenomenon, until the active centers are trapped in a glassy network or quenched by some inhibitor entering the material. This behavior enables further thermal activation giving rise to some benefi ts of post-curing.

GENERAL AND SPECIFIC FEATURES OF RADIATION-INDUCED POLYMERIZATION

One of the attributes of radiation as an alternative mode for activating chemical reactions is the immediacy and the control of the spatial distribution for generating active centres. The ability to trigger polymerization reactions independent of temperature is of interest for decoupling the infl uence of thermal activation on the various steps of the chain polymerization mechanism that follow initiation. This last feature can be exploited both from a fundamental perspective (mechanistic studies, determination of activation energies, pulse laser polymerization) and for technical reasons (design of low cost molding equipment, use of temperature sensitive substrates, design of thermal post--treatments).

The crosslinking polymerization of multifunctional monomers and pre--polymers is by far the largest use of this technology. Various analytic methods can be used for monitoring the kinetic behavior of polymerizable compositions exposed to ultraviolet radiation, to light and to ionizing radiation [START_REF] Fouassier | for polymer synthesis: scope, reactivity, and effi ciency[END_REF] and for studying the infl uence of the processing conditions on the properties of the materials produced. A selection of results illustrates some of the important aspects of polymerization kinetics and of network formation.

The gel effect associated with crosslinking polymerization is shown by comparing the kinetic profi les under exposure to increasing EB doses of a monoacrylate (n-butylacrylate, nBuA) with those of diacrylates (hexanediol diacrylate, HDDA and tripropyleneglycol diacrylate, TPGDA). All three monomers exhibit similar initial acrylate functionality content (7-8 mol•kg -1 ). The plots of Fig. 1 clearly show that diacrylates polymerize much faster than nBuA, as a result of the Trommsdorff effect. The extremely fast polymerization of compositions including multiacrylates is used in ink formulations for graphic arts and for coatings for optical fi bers, with curing speeds under high energy radiation as high as 1000 m•min -1 on high-performance industrial lines.

The viscosity of solvent-free radiation-curable compositions typically ranges from 0.5 to 5 Pa•s at application temperatures which facilitates the spreading of the composition onto a substrate or the impregnation of the composition as the matrix in a composite material. Since polymerization is aimed at converting the monomer and prepolymer blend into a hard material, curing proceeds with a dramatic evolution of the mobility of monomer functions in the medium, from the initially fl uid state, to a gel, and eventually to a vitreous network. The viscosity gradually increases by several orders of magnitude until solidifi cation, being infl uenced by polymerization kinetics.

An instructive result was obtained by comparing the polymerization profi le of an aliphatic polyurethane triacrylate (APU3), which has an initial acrylate content of 3.5 mol•kg -1 , with those observed for an aromatic epoxydiacrylate (bisphenol A epoxy diacrylate, EPDA) with an initial acrylate content of about 6 mol•kg -1 , being subjected to various EB dose increments (as shown in Fig. 2). The polyurethane pre-polymer possesses a fl exible backbone that forms a soft material upon curing. Its kinetic profi le shows a steep increase in acrylate fractional conversion, up to 0.75 for a dose lower than 10 kGy, regardless of the dose increment (Fig. 2A). The profi le then gently levels off to reach a conversion level higher than 0.9. The corresponding plot recorded for the aromatic epoxy diacrylate shows an initial fast polymerization to a conversion level of 0.2 for a dose of 2.5 kGy, followed by a weak reactivity with a rather small increase of conversion up to 0.4 at 60 kGy (Fig. 2B). At this point, the concen- B tration of unreacted acrylate functionality is about 3.6 mol•kg -1 , a value that is even higher than the acrylate concentration in the unreacted APU3 sample. This shows the infl uence of incipient vitrifi cation that limits the propagation step, in spite of there being a still large concentration of monomer in the partially cured EPAD samples. These experiments were conducted at room temperature with small increments of dose using thin fi lms of the curable compositions which limited any increase in temperature. Under these quasi-isothermal conditions, vitrifi cation took place in the PUA3 material at conversion levels slightly above 0.7, the critical value at which the kinetics started to level off. The vitrifi cation phenomenon took place at much lower conversion levels (typically 0.2) in the more rigid EPAD pre-polymer when cured at room temperature. These observations stress the importance of the relation between the effective curing temperature and the conversion dependence of the glass transition on the material networks.

The infl uence of dose rate on polymerization kinetics can be examined, provided that isothermal conditions are maintained within the sample. The results of a series of EB curing experiments conducted with EPAD at different dose rates ranging from 19 to 110 kGy•s -1 are plotted in Fig. 3. The rate of polymerization measured in the initial regime (steep increase) was shown to be proportional to the square root of the dose rate , as would be expected from the bimolecular termination kinetics in a fl uid medium (Eq. ( 13)).

(13) Deviations from this law were observed as soon as the initial slope weakened as a consequence of mobility being restricted. From the lines drawn in the fi nal regime, a fi rst order dependence of the polymerization rate on was observed. This situation corresponds to a chain process with monomolecular termination by occlusion of the growing free radicals in a vitrifi ed matrix. From a practical viewpoint, careful attention must be paid to the thermal effects within a sample subjected to radiation-induced polymerization. There should be a fi nely-tuned interplay between the control of the polymerization exotherm (typically 80 and 100 kJ•mol -1 , for acrylates and epoxy functionality, respectively), the energy conversion from the deposited radiation dose, the heat and radiative exchanges with the surrounding environment and the conversion dependence of vitrifi cation.

APPLICATIONS OF RADIATION-INDUCED POLYMERIZATION

High energy radiation can be used to synthetize linear polymers by emulsion free radical polymerization, but is rarely done. The process consists of irradiating an oil-in-water dispersion of one or several hydrophobic monomers in the presence of a surfactant. Hydroxyl radicals are produced by water radiolysis and are the main species responsible for the polymerization initiation after entering the monomer micelles. This process results in the formation of latex particles with the typical dimension of about 100 nm. The particles grow in size during the reaction since monomers continue to diffuse from reservoir droplets and to swell the polymer particle. Since initiation occurs at a slow rate in the aqueous phase, the kinetic chain length inside a single particle is extremely long producing polymer chains of high molecular weight. Emulsion polymerization is used to manufacture several commercially important polymers that fi nd use in adhesives, coatings, paper coatings and textile coatings. Low dose rate 60 Co gamma radiation can be used as an effi cient initiating process which can be used as alternative to thermal initiation of peroxides under modest heating conditions. The radiation process makes it possible to decouple the thermal activation of the polymerization from the initiation step and thus avoids affecting the chain length of the formed polymers. This is likely to receive increasing interest for commercial developments in the coming years.

Solvent-free formulations of adhesives, inks and coatings can be cured by radiation-induced crosslinking polymerization. This important use is expanding as a an alternative to solvent-based and/or heat-curing processes which are being restricted because of their detrimental impact on the environment. Radiation processing brings several important benefi ts in terms of ecoconception (energy saving, limitation of volatile organic compound (VOC) emission). In-situ polymerization of restorative resins infused into damaged archeological objects made of wood or into weak artistic pieces of porous structure is another illustration of the unique in-depth chemical effects that can be created using the mild ambient conditions of high energy radiation processing.

Compared to ultraviolet-initiated polymerization, a well-established technology for the curing of various coatings and inks, high energy radiation processing proves to be more effi cient than intense ultraviolet for initiating in depth the crosslinking polymerization of solvent-free compositions, including unsaturated monomers and reactive pre-polymers to yield mechanically functional and chemically resistant materials. Printed labels and materials produced by the packaging industry are fully cured using high energy EB and do not need initiators for free radical polymerization. This results in lower amounts of unreacted monomers and other extractable compounds. Adhesion to substrates can also be improved by grafting reactions that take place at the substrate-coating interface. Advances in improved formulations and in process control spur on developments in food packaging and in industrial coatings (fl ooring, building parts with long resistance to long outdoor environment).

Fiber-reinforced polymer composites can also be effi ciently cured by high energy electron beams and offer signifi cant advantages for the manufacture of a variety of aerospace, ship and ground vehicle components. The EB curing process is shorter than for conventional thermosets and yields materials with reduced residual internal stress. Innovative formulation concepts based on polymerization-induced phase separation achieve higher mechanical performance than state-of-the-art thermally cured materials. Advanced studies on network formation provide an understanding of structure-properties relationships.

Finally, the spatial control of radiation-induced polymerization is used in making photomasks. These are used in the microelectronics industry for producing opaque plates with holes or transparencies for patterning a photopolymerizable composition in the domains that are exposed to the frontal beam of ultraviolet radiation. After development in an appropriate solvent a negative

SU-8 2002 adhesion layer SU-8

A B photoresist is obtained. Micro-and nanowriting with a laser and/or an electron scanned across the radiation sensitive composition avoids using an optimask produces much fi ner patterns and lower resolutions. Figure 4A shows the scanning electron micrograph of a channel fabricated on a chip by the photomasking process using the cationic photopolymerization of aromatic epoxide. In a subsequent step, the channels were covered by a lid and a porous polymer monolith was polymerized in situ using EB radiation using an acrylate composition dissolved in a mixture of porogenic and presolvents (Fig. 4B). The interconnected polymer-sphere morphology obtained by this technique can be used for producing microreactors and separation microcolumns for lab-on-a-chip applications [START_REF] Chuda | Characteristics and fl uidic properties of porous monoliths prepared by radiation--induced polymerization Lab-on-a-Chip applications[END_REF].

CONCLUSIONS

Ultraviolet radiation and high energy electron beam radiation effi ciently initiate free radical or ionic polymerization depending on the experimental conditions, on the type monomer being used and on the presence of initiators that may be needed. Besides the specifi c features of radiation-triggered initiation, the basic mechanisms and kinetic models of conventional chain polymerization presented above can be used. However, the specifi c conditions of radiation processing, dose deposition, dose rate effects as well as thermal effects should be carefully considered. Many end uses can benefi t from the numerous advantages offered by radiation processing. Some areas of considerable technical relevance are addressed in specifi c chapters, such as the radiation synthesis of nanoparticles, radiation grafting, and composite materials.

Scheme 5 .

 5 Scheme 5. Examples of Type I and Type II photoinitiators for free radical polymerization.

Fig. 1 .

 1 Fig.1. Kinetic profi les of acrylate consumption in monomer fi lms as a function of EB radiation dose: nBuA ( ), TPGDA ( ) and HDDA ( ).

Fig. 2 .

 2 Fig.2. Kinetic profi les of acrylate consumption in pre-polymer fi lms as a function of EB radiation dose: APU3 (A) and EPDA (B).

Fig. 3 .

 3 Fig.3. Kinetic profi les of acrylate consumption in EPAD pre-polymer as a function of EB radiation dose rate.

Fig. 4 .

 4 Fig.4. Scanning electron micrographs of a microchannel made by cationic photolithography (A), and porous polymer monoliths synthetized within a closed microsystem by EB-initiated polymerization (B).

Table 1 .

 1 Propagation rate constants k p for common monomers undergoing free radical polymerization.

	Monomer	Structure	k p [L•mol -1 •s -1 )] at T = 60°C a
	Butadiene		100
	Styrene		165
	Ethylene		242
	Methyl methacrylate		515
	Acrylonitrile		1 960
	Methyl acrylate		2 090
	Vinyl acetate		2 300
	Tetrafl uorethylene		9 100 (83°C)
	Vinyl chloride		11 000 (50°C)


Xavier Coqueret
email: xavier.coqueret@univ-reims.fr

Guillaume Ranoux
email: guillaume.ranoux@univ-reims.fr

Julien Eck
email: julien.eck@airbus.com

Asensio Zapata
email: asensio.zapata@airbus.com

Denis Lavielle
email: denis.lavielle@airbus.com

Thomas Rohr
email: thomas.rohr@esa.int

Malgorzata Holynska
email: malgorzata.holynska@esa.int

METHODOLOGY FOR FINGERPRINTING OF MATERIALS AND PROCESSES

Keywords: Diglycidyl ether of bisphenol A DMA, Dynamic Mechanical Analysis DSC, Differential Scanning Calorimetry FTIR, Fourier-transform infrared spectroscopy GC, Gas chromatography HPLC, High-performance liquid chromatography NMR, Nuclear magnetic resonance SEC, Size-exclusion chromatography

This paper presents the different approaches and analytical methodologies developed in the frame of this study for gaining advanced knowledge on the composition of specific classes of materials used in aerospace industry. The results will allow the partners to anticipate potential obsolescence with rational proposals for alternative materials.

INTRODUCTION

To face the risk of obsolescence that may impact critical and strategic materials for aerospace and defense industry, there is a need for gaining a deeper knowledge and understanding on the composition-performance relationship in a variety of formulated products. These products generally include a limited number of main components together with several additives and likely high concern trace contaminants. The aim of this project is to perform detailed characterization of the physical properties and technological performances of critical products and materials as a function of their composition in key components, in order to minimize risk in program management and to reduce development and qualification costs for alternatives. The change to new materials is directly or indirectly, to environmental regulations, market disruptions or economical strategies with a dramatic industrial impact (caused reliability, planning, economic...) due to the need of re-qualifications.

The deep knowledge of materials composition and performances will allow space industries to be proactive in case of materials obsolescence, minimizing risk, cost and time to define precisely the necessary tests to be performed depending on the nature of changes made in composition. From a material perspective, the study was focused on a limited number (20) of strategic and critical materials used commonly in space industry that could be impacted (directly or indirectly) by European or country legislation and then become obsolete.

In order to anticipate the obsolescence of specific formulation compounds this study aims at:

 obtaining the spectroscopic and analytical "fingerprints" of various classes of complex compositions (paints, adhesives, varnishes, lubricants, films …),  identifying their risk with respect to obsolescence,  deformulating representative materials with different degrees of refinement,  comparing their composition and properties (old/new formulations),  suggesting orientations for new and sustainable formulations and materials.

STUDIED MATERIALS

The selection of the different materials was performed in order to cover the widest range of applications identified for space application, including structural or multi-purpose adhesives, compounds with optical or electrical properties, primers, lubricants, varnish and paint.

The proposed compositions are, for the most part, mixtures of various constituents different in nature, physical form and chemical composition (typically different polymers, pre-polymers, fillers, pigments and additives). Some materials are in the form of films or adhesive tapes.

This paper will present an extract of some results obtained in the frame of the study in order to illustrate the applied methodology.

GLOBAL APPROACH AND METHODOLOGY

The analytical approach for gaining significant information on the composition of complex blends usually consists in the isolation of each component followed by structural characterization and quantification of the ingredients. This type of approach requires time, precise fractionation methods and advanced analytical tools (spectrometers, chromatography equipment…) to reach the target resolution of 0.1 weight-% for trace components or residues of high concern. The general approach that was followed can be summarized as a sequence of steps, as follows:

Rationale of the analytical approach

1. Analysis of literature and of technical data from suppliers; 2. Fingerprinting by spectroscopic methods (IR, NMR) and relevant chromatography techniques (HPLC, SEC, GC); 3. Rough determination and quantification of the main products; 4. Procurement and analysis of model compounds likely to be present (commercially available known components of a material); 5. Refined determination of product composition (loop back to step iv and v); 6. Depending on needs, qualitative and / or quantitative analysis of minor components (detection of specific component of interest, attempt to quantity the concentration of a substance of concern).

This global strategy has been tested and evaluated by implementing the sequence of steps detailed above essentially on three families of products, namely epoxy adhesives, polyurethane varnish and silicone elastomers.

RESULTS

Chemical Analysis

We illustrate in this paper our analytic approach by showing that the selected products can be analysed with various degrees of refinement, depending on the needs for global or for specific information. Fingerprinting by spectroscopic and chromatographic methods were implemented first to get global information on bulk materials, without or with limited isolation step. A second level consists in the determination of the class and rough quantification of the main ingredients in the formulations. This will allow for comparing two grades of epoxy adhesives commercialized under the same reference, before and after a slight change in composition disclosed by the supplier. Then we demonstrate that precise analyses aiming at the determination and at the quantification of minor components of concern can be performed.

Level 1 -Spectroscopic fingerprinting of the hardener of a two-component polyurethane varnish.

FTIR analysis provides a rough fingerprint of the polyol used as the hardener of the polyurethane coating material. However, variations of the relative intensity of the main bands assigned to the functional groups or of the squeleton of the hardener can be detected by a simple control analysis. The spectrum in Fig. 3, 4 confirms the nature of the polyol, a castor-oil based triglyceride. The good sensitivity and the resolution of the 600 MHz spectrometer reveals the presence of other fatty acids as minor constituents identified as linoleyl and linolenyl esters. The hydroxyl functional ricinoleate was estimated to represent 90 mol-% of the esters linked to the glyceryl moiety.

Level 2 -Changes in composition and upgrading of formulated products

A more advanced level consists in exploiting more quantitatively the main components of a complex blend. We have applied this approach for comparing the old and updated formulation of a base component of an epoxy adhesive.

The superimposed 1 H NMR spectra in Fig. 5 do not reveal significant changes in composition in the epoxy resin. However, minor changes in very small signals corresponding to silane coupling agents were detected upon careful examination of the expanded spectra. HPLC analyses were performed on the same "old" and "new" formulations, to gain complementary information on the composition in the various oligomers of the DGEBA epoxy resin. The 2 chromatograms appear very similar, suggesting that the compositions are quite identical. This was confirmed by replicating 5 times the analyses. However, the standard deviation for the analyses conducted with the "new" grade sample was much higher than with the "old" one (Table 1). Additional experiments were also conducted to detect trace amounts of aromatic solvents in the formulations.

Level 3 -Quantification of specific components

Epoxy resins based on diglycidylether of bis-phenol A (DGEBA) are generally mixtures of various oligomers and isomers (glycidyl groups located in para, parap,p'; ortho, para -o,p'; ortho, ortho -o,o' positions).

The resins also include unreacted starting compounds and by-products. For controlling the possible presence of chemicals of concern, various epoxies and their precursors were characterized by 1 H / 13 C NMR and by HPLC as model compounds.

A calibration curve was then made to determine the bisphenol A (BPA) detection limit in solution at λ = 230 nm. Solutions including BPA at various concentrations, with or without DGEBA were analyzed by HPLC to establish a calibration curve. A representative sample of cured epoxy adhesive has been prepared and submitted to Soxhlet extraction in acetonitrile. The extracts analysed by HPLC in the same conditions as for the calibration experiments reveal the the presence of various isomers and oligomers together with a noticeable amount of BPA (Fig. 9).

Physical Analysis

The physical analysis was performed on the polymerized materials, once processed. Among the different techniques considered and depending of functional properties of interest of the materials the following ones have been implemented: -DSC, -DMA, -Shear strength test, -Thermo-optical properties. The aim of these characterizations is to identify and measure the key parameters of the material, related to their intrinsic properties (DSC, DMA) or associated to their final functional properties of interest (shear strength, adhesion, thermo-optical properties…). These reference measurements will constitute a database allowing the assessment of the potential impact of the change in formulation and to status on their acceptability with regard to the final application.

Tab. 2. Lap-shear strength for old and new formulation of two epoxy adhesives. To illustrate this approach, the results obtained during lap-shear strength test on two epoxy adhesives that have undergone a change in formulation are displayed above (Tab. 2).

Material

CONCLUSION

In the frame of this study, a panel of materials widely used in space industry has been considered and analysed. A global strategy and a specific methodology have been defined, validated and implemented in order to perform deep analysis of the materials. The results obtained in the frame of this study will allow for building of a database with reference values that will help to assess potential criticality in case of formulation change of one of these materials.

Fig. 1 .

 1 Fig. 1. Breakdown structure of the analytical approach.

Fig. 2 .

 2 Fig. 2. FTIR transmission spectrum of the hardener for a 2-component polyurethane varnish.

Fig. 3 .

 3 Fig. 3. 1 H NMR spectrum of the hardener for a 2component polyurethane varnish.

Fig. 4 .

 4 Fig. 4. 13 C NMR spectrum of the hardener for a 2component polyurethane varnish confirming the nature of the polyol, a castor-oil based triglyceride, with other fatty acids components, besides the ricinoleic ester.

Fig. 5 .

 5 Fig. 5. Superimposition of the 1 H NMR spectra of the "old" (red line) and of the "new" (blue line) grade of the epoxy-based adhesive supplied under the same reference.

Fig. 6 .

 6 Fig. 6. Simplified representation of the structure of the oligomers( n= 0, 1, 2, …) in DGEBA-based epoxy resin. Typical chromatograms obtained by HPLC analysis of both grades of the epoxy resin are reproduced in Fig. x. The oligomers with n = 1 and 2 are detected as minor constituents. The precise content can be deduced from the respective area of the different peaks after appropriate calibration.

Fig. 7 .

 7 Fig. 7. Comparison of the replicated chromatograms of the "old" and of the "new" grade of the epoxy-based adhesive supplied under the same reference.

Tab. 1 .

 1 Retention times (Rt) and fractional area (%area) of the peaks observed for the various oligomers of DGEBA in the chromatograms of Fig.7. might originate from some fluctuation of composition in the newer batch, possibly because of insufficient mixing prior to conditioning.

Fig. 8 .

 8 Fig. 8. Calibration curve based on the dependence of area of the peak assigned to BPA in HPLC chromatograms with detection at 230 nm.The detection limit for bis phenol-A (BPA) in solution was assessed at about 0.18 ppm with respect to the mass of the analyzed solution. This technique can be used to assess the amount of BPA either in the uncured resin or in the solution obtained from a cured sample submitted to Soxhlet extraction.

Fig. 9 .

 9 Fig. 9. HPLC chromatogram of the Soxhlet extracts from a cured epoxy-amine adhesive revealing the presence of various isomers and oligomers together with a noticeable amount of BPA.

Mean Failure Load (MPa)

				Failure
		Old	New	Type
	E1/2	32.7	30.8	Mixed
	E4/5	20.3	21.1	Mixed

H and 13 C NMR are much more informative, allowing for monitoring of possible evolutions in composition for a bio-based reagent, as a function of the production batch.

ACKNOWLEDGEMENTS

Airbus Defence and Space and Reims Institute of Molecular Chemistry would like to thank ESA for its support and the funding of this study.


L Barrière

O ' Shea

A "Very DIY Music" For Punk-Feminist People? Doing and listening to noise music in Ladyfest-inspired festivals

Keywords: Ladyfest, feminism, empowerment, gender roles, noise

My paper discusses the links between noise music and punk-feminist scenes, by looking at the Ladyfest network. Ladyfest festivals generally aim to challenge gender roles within the punk scene. The network draws on a punk-feminist inspiration and specifically maintains several links with the Riot Grrrl movement that developed in the 1990s 1 . Yet, their musical scope has widely expanded through the years, and Ladyfests' programs nowadays include punk as well as, for instance, electronic dance music, hip hop or, to a certain extent, noise music. Drawing on my PhD research, I have analyzed the programs of more than 100 Ladyfest and Ladyfest-inspired festivals that took place in France and Germany since 2003, and studied the place of noise music in that network. During fieldwork sessions, I have attended noise concerts, and had informal talks with artists or organizers. In the first part of my presentation, drawing on the informations I have gathered, I will therefore explain why noise music occupies a place at the margins of the Ladyfest network. Yet, I made the hypothesis that doing noise music could serve a feminist purpose. My guess was that the DIY dimension of noise music could be empowering for women and queer people who attend such festivals, because it would offer them the possibility to make music without much equipment nor musical knowledge. I thus have organized noise music workshops during various festivals over the year 2019. In the second part of my presentation, I will discuss my assumption by analyzing my experiences and multiple conversations I had with the participants.

Introduction

Last year, I did several interventions on queer and feminist punk festivals, in academic conferences. As I explain that the scene expanded to other music genres, such as hip hop or EDM, a few colleagues asked me "yes, and what about noise music?". After hearing that question quite a bit, I decided to dig a little bit further: what was the actual matter with noise music at queer_feminist punk-inspired festivals? My paper therefore discusses the links between noise music and punk-feminist scenes, by looking at the Ladyfest network. Ladyfest festivals generally aim to challenge gender roles within the punk scene. The network draws on a punk-feminist inspiration and specifically maintains several links with the Riot Grrrl movement. Drawing on my PhD research, I have analyzed the programs of more than 100 Ladyfest and Ladyfest-inspired festivals that took place in France and Germany since 2003, and studied the place of noise music in that network. During fieldwork sessions, I have attended noise concerts, and had informal talks with artists or organizers. In the first part of my presentation, drawing on the information I have gathered, I will therefore explain why noise music occupies a place at the margins of the Ladyfest network. Yet, I made the hypothesis that making noise music could serve a feminist purpose. My guess was that the DIY dimension of noise music could be empowering for women and queer people who attend such festivals, because it would offer them the possibility to make music without much equipment nor musical knowledge. I thus have started to organize noise music workshops during festivals. I will introduce this project in the second part of my presentation.

Noise and feminism: a (very short) literature review

Very short because… I haven't found a lot of academic literature on that topic, indeed.

Anyway, Marie Thompson's work specifically inspired me, especially as she qualifies "noise" as a feminine feature. Though "the participation of female artists in the noisy fields of experimental and electronic music has been sidelined", "[she outlines] various intersections of noise and femininity through which noise has been feminised and the feminine has been produced as noisy. I argue that in Eurocentric cultures, noisiness has been understood as characteristic of certain 'bad' femininities." 2 She further asks "When and how does the feminised become feminist?" and suggest that when "certain arts practices might be interpreted as 'feminist', this does not refer to the intent or political identity of the producer; rather it refers to what these practices are understood to do within a particular context. By extension, I propose that whether the feminised can be interpreted as feminist depends on what it does: What is perturbed by and through the feminised? What work does the feminised do to unsettle and transform normative gendered relations? What are the outcomes and effects of this process of feminisation?" Indeed, these questions are also underlying in my current and upcoming works on noise music and feminist festivals. She concludes "diverse historiographical and curatorial projects (...) [seem] to suggest that noise has some promise from a feminist perspective: they point to a shift from feminised noise to feminist noise."

Amongst the projects she is writing about is Tara Rodgers' book, Pink Noises 3 . In the introduction, Rodgers reflects on her own musical path and points links between noise music and the Riot Grrrl movement. This is something I found interesting as well. Rodgers writes: "My own impulses to learn electronic music production and start the website Pinknoises.com felt quite different. In addition to my established curiosity with music and computers I was inspired by the legacy of Riot Grrrl, the grassroots movement in the early 1990s that catalyzed feminist art making and political activism." That quotation shows that music movements are keen to intersect with each other. If the legacy of the Riot Grrrl movement influenced Tara Rodgers, could noise music also inspire the legacy of Riot Grrrl movement, in the form of the Ladyfest scene?

Noise & experimental music in the queer_feminist punk festival scenes: a study of German and French programs

As I mentioned in the introduction, during the process of doing research for that talk, I looked at the place occupied by noise and noise-related music in the programs of German and French punkinspired queer_feminist festivals. The creation of a database that I've been filling since my MA thesis facilitated my work curious about it.) Information I gathered include dates, locations, price, workshops and concerts programs.

Thus, I have been able to gather in a same document all the names of the bands and artists who played at least one these festivals. I have then searched for those of them who identify their own music as in some way related to "noise". Relying on the musicians' self-identification indeed helps not [imposer] the point of view of the researcher on a corpus. I also looked for artists that claimed mixing noise music with other genres (such as hardcore punk, for instance), and I aggregated other kinds of experimental music (such as ambient, dark ambient, drone, and so forth) around the "noise music" category, mostly for sonic and organological reasons.

Final results showed a very low number of artists booked by these festivals claimed performing noise or noise-related music.

Noise musicians who performed during the analysed festivals include for instance: CHRA, Cuntroaches, NADIA LENA BLUE, Lucia Lip, Pripoy, LauraL, MonsieurScary.

3. Music at the margins… I consider noise music to be at the margins of the German and French ladyfest scene. Firstly, because of statistics, of course. I have indeed showed that the festivals' organizers do not often book noise musicians. But there is also a second reason. When a noise musician happens to perform during one of these events, they often play either at the very beginning of the evening, like as an "opening act", either at the end (with the DJs). If we consider the unfolding of the concerts as a chronological line, noise therefore occupies marginal spaces in the lineup of the night. This has several implications for noise musicians' performance. Indeed, the first concert is generally not very crowded, since the evening just began and people are still arriving small groups after small groups. For the record, I observed that the peak of the evening, in terms of frequentation and occupation of the space right in front of the stage, generally happens during the last gigs, right before the "after party" with DJ sets. The introduction of DJ sets generally marks the moment at which some people start leaving, or just hang out at the bar. The room right in front of the stage becomes less crowded than during the bands' gigs. People then leave small groups by small groups until the end of the night.

Organizers explained to me that they purposely made this choice: they thought that, if they would have programed a noise act in the middle of the evening, during the peak of frequentation, it would "break the fun". And indeed, it is true that the audiences that attended the noise performances I have been able to observe didn't act the same way as the audiences that attended the following concerts. During noise music shows in punk-inspired queer feminist festivals, people would generally sit around the stage, focus on the music. The level of interaction between them is very low. Later during the night, when non-noise music bands are performing on stage, people were more likely to dance, to interact with each other, or to interact in a visible or "loud" manner with the artists (screaming, clapping hands, and so forth).

Basically, this means that, though the punk-feminist festival scene has opened up to other genres, they don't all hold the same status.

Bringing noise in punk-inspired feminist and queer festivals: an experimental approach.

Up to now, I have mostly considered the act of "listening" to noise music during ladyfest-inspired festivals, through my own ethnographic research. I will now look at the "making" of noise music. As I explained, this part of my presentation draws on workshops I have organized during festivals, named "purple noise" (not very original, but I'm bad at names). I indeed am a researcher, as a PhD student, but I'm also a musician (or at least I'm trying to). Though mostly a guitar player, I also enjoy experimenting with various mediums. This is part of what I wanted to share when I developed the concept of this workshop.

I should warn you that this is still an ongoing research. So far, I only did that workshop twice: once during Lady*fest Heidelberg (Germany) and once during Ladiyfest Strasbourg (France). When I submitted my paper proposal I hoped I could do that workshop a bit more often, but unfortunately this hasn't been possible this year. But I seek to bring it to new events next year! My idea was the following: As in several music scenes, Women and queer folks remain in the margins of the noise and experimental music worlds. This workshop aims to give people a few keys to reclaim these genres, thanks to a queer_feminist approach and low-cost music mediums such as cassette tapes.

The reasons why I developed this idea are multiple.

-First, I wanted to give something back to people I meet during fieldwork sessions. Consciously or not, they help me with my PhD research, they make my knowledge of the scene grow, and I wanted to share some of the things I know, music-wise, with them too. I also felt like it would be a way to connect with people. Like, when you come from far away and know absolutely no one in the local scene, it is sometimes hard to bond with people who hang out with each other all the time, and when I first began to do fieldwork in such festivals, I felt quite a bit lonely.

-Second, music related workshops are quite common in the scene, but they often focus on the typical rock instruments, or on practice such as DJing or MCing, since EDM and hip hop have also become common genres in the scene. A noise music workshop seemed more original, and could contribute to reclaiming the "feminine noisiness" analysed by Thompson.

-Third, if workshop attendees got attracted to noise music and the techniques they learned, it's still an easy music to perform alone and they wouldn't have to look for bandmates if they didn't feel like it or just if they didn't live in a very crowded area. Moreover, fourth reason, the material I showed people how to make music with generally remains affordable. And finally, none of this necessitate any knowledge of music theory, nor a "good ear", a "good sense of rhythm". Basically it sounded like a "very DIY music" -as one of the participants once pointed -that could find its place in both the festivals programs and the potential attendees range of interests.

The workshop consisted in three different actions. In a first part, we would generally open regular cassette tapes, in order to make loop tapes out of them. This was generally also a good time for me to explain a bit about noise music to people who didn't know a lot about it and I would generally emphasize the links between noise music and the so-called "cassette culture" (Novak). I also provided a playlist so people could discover women noise-related musicians such as Puce Mary, Pharmakon, Moor Mother, and confront themselves to the sonic characteristic of the genre, if the festival didn't book any noise musician.

In a second part, we would go to record our tape loops, thanks to a bunch of very cheap and very lofi walkman. In both workshop, people mostly recorded their own screams or noises from the environment.

In a third part, we would try making a collaborative noise music piece. Plugging the walkman in a mixing deck, and make a feedback loop with effect pedals (I mostly used cheap reverb and delay as well as distortion pedals). Everyone could play with the pedals as well as with their own walkman and the channel in which it was plugged. They could thereby make the tape run or stop, and influence its sound, while increasing/decreasing the effect levels, or playing with the bass-mediumshigh level knobs. So far, I have been able to notice the following outcomes: -So far, festivals organizers and participants enjoyed the idea of the workshop. People came to discover a new technique, a new way to make (noise) music. Some of them already had a musical practice, and even played different instruments or sung. For instance, I met a girl who told me she tried to make rap music with a friend and would like to attend the workshop so she could make her own backing tracks for her songs; at LF Strasbourg Nadia Lena Blue, who had played a guitarbased noise performance the night before, stopped by the workshop hoping she could learn a different way to make noise music. Some others didn't know much about music. But none of them had ever made cassette loops. The workshop mostly attracted people in their 20s or their early 30s (which is the main age range of the festivals' attendees). They considered the cassette tapes as a "nostalgia" thing. During one of the workshops, a participant exclaimed "I feel like I'm dissecting my childhood!". Others said they "didn't know walk-mans still existed!" These two sentences illustrate that nostalgic feeling well, and I would like to explore that sensitivity/sensibility the near future of my research.

But some limits of my research started to appear as well:

The first one considers noise music and failure. Though I consider it to be plenty part of the process, and definitely a characteristic of noise I personally enjoy, it was sometimes frustrating for the participants when their loops got scratched or just split up during the recording or music-making processes. Though the workshop doesn't require any kind of music knowledge, the (high) possibility of failure and the instability of the tape material might discourage the attendees to pursue.

I would also like to reflect on the "confrontation" of noise music with a more "typical" melodic culture of music: when I played my "women of noise" playlist at Lady*Fest Heidelberg, one of the attendees put her hands on her ears when she heard the beginning of Puce Mary's "The Spiral" and asked me if I could change the music (which I did). She said she was "okay with listening to some music, but not that" because it scared her (as like, the music of a horror film).

Both failure and the first encounter of the workshop participants with noise-related music are directions I would like to explore further in the future.

  . The database collects basic information about a total of 146 of festivals organized since 2003; 40 of them in France and 106 in Germany. (I don't really have time to explain why I chose to do fieldwork in these specific countries, but I'd happily discuss it later if you're 2 Thompson, Marie. "Feminised noise and the 'dotted line'of sonic experimentalism." Contemporary Music Review 35.1 (2016): 85-101 ; see also : Thompson, Marie. "Gossips, sirens, hi-fi wives: Feminizing the threat of noise." Resonances: Noise and Contemporary Music. Bloomsbury, (2013): 297-311 and Fitzpatrick, Susan, and Marie Thompson. "Making space: an exchange about women and the performance of free noise." Women & Performance: a journal of feminist theory 25.2 (2015): 237-248. 3 Rodgers, Tara. Pink noises: Women on electronic music and sound. Duke University Press, 2010.


come

Louise Barrière, PhD Cand. in Popular Music and Performing Arts 2L2S/Université de Lorraine Creating a German Sense of Queerness? Transatlantic reception of queer theories and queer music festivals in Post-Wende Germany For a little more than five years now, I have spent considerable time traveling across Germany to attend to various queer and feminist music festivals. At first, they were only communal spaces I visited as both a queer young woman and a strong fan of hardcore punk music. But two years ago, I also started studying them as fieldwork for my PhD dissertation. Since 2014, I have attended events such as the Lady*Fest Mannheim, Germany, the Lady*Fest Saarbrücken, Germany, the Noc Walpurgii in Berlin, Germany, the Lady*Fest Karlsruhe, Germany, or the Böse & Gemein Festival in Dresden, Germany.

Along my experiences, I have noticed that the arrangement of queer DIY music festivals in Germany always follow a similar pattern: music gigs and parties by night and workshops and debates during the day. These events are indeed inspired by American models of events, created by the punk movements of the Riot Grrrls and Queercore in the 1990s. The ways in which organizers divide the schedule ensures that their events work towards the development of interdisciplinary queer-feminism. Not only does this reflect transnational influences from the US but further highlights the intersection of pop culture and politics.

Drawing upon ethnography and the analyze of the archives of more than 100 festivals organized in Germany between 2003 and 2018, in this presentation, I will focus on the reception of "queer theories" in Germany through the lens of music and the festival scene. I will argue that queerness isn't solely the development of an American culture. Instead, its concept have circulated and evolved globally. I will therefore demonstrate how German queer music festivals shape new linguistic forms, and how this process impacts the events' vibe. Finally, I will argue that queer theories and identities also have a repercussion on songwriting, through the case-study of the song "Frauen mit Sternchen" performed by the rapper Sookee.

Queer theories and language in Post-Wende Germany

According to queer theories, gender isn't natural, rather it is performed. It is coded (and decoded) in our bodies, behaviors, clothes, etc. And, queer movements rely on a strong critique of gender and sexual binaries (that is, the opposition of masculinity and femininity). They aim to blur the line between men and women by performing untraditional, and thus non-binary, gender identities.

Yet, language is also part of what shapes gender. Queer theories, as they develop a critical approach of gender, have therefore a strong impact on the way we write and speak. Deconstructing gender norms necessarily leads to deconstruct linguistic norms.

The following example of new, queer, inclusive linguistic gender norms are taken out of academic resources, but are quite similar to what you could find in subcultural scenes. A document released by the Universität zu Köln for example states : "The well-established gender system is based on the existence of two clearly identifiable genders, namely men and women. It is thus binary. (...) Current research on intersex and transsexuality shows that this bipolar system is not sustainable: nowadays, a large number of sexual identities appeared. (...) How can the entire spectrum of genders be represented linguistically?

Possibilities include the gender gap "_" and the gender asterisk "*"."

Gender-Gap or Unterstrich and Gender-Sternchen are quite similar, yet they also have specific characteristics:

"Gender Gap The gender gap can be traced back to Steffen Herrmann, who advocated for a linguistic representation of all genders in his article "Performing the Gap -Queer

Figures and Sexual Appropriation" (2003). (…)

Gender asterisk The asterisk is another form of linguistic representation beyond the binary system. (…) Critics of the gender gap think it portrays the identities beyond the binary matrix as a "blank space" and thus denies their existence. Advocates of the gender gap see in the gap a space for the development of new identities, as in an emancipatory symbol."

We find both of these characters in the names of several queer DIY music festivals. For instance, the second edition of the Ladyfest Köln was renamed for "_fest". One of the organizers wrote, accordingly to what we have just seen: "'_fest (advancing the ideas of ladyfest: play gender 2008) … To keep up the illusion of two clearly separated genders our (German) language only knows the two articles "she" and "he", as well as the related two endings [...].

Everything that is located outside this system is constantly being denied. In contrast to this, I want to position a different space for sexuality, a space that is to be explored and that we should fight for, the space looks like this: _ This is certainly not only about opening up spaces for intersexual people, meaning people with two sexual characteristics…, because with the set mark _ a political space for resistive actions, which does not set requirements is created…' (Steffen Kitty Herrmann)" this is about. After all, you remember that, a year ago, during another festival in Berlin, one of your informants told you that no one ever asked for her pronouns outside of a queer_feminist punk event.

As you remind this anecdote, you write your chosen names and pronouns on the adhesive paper and stick it on the top of your shirt. That's at least what I did, and wrote "Louise, Sie".

During the breakfast and the following workshops, I sometimes glanced at the other attendees name and pronoun tags. Most of them display the classic feminine or masculine German pronouns, "Sie" or "Er". Sometimes, though, I can read the uncanny "Sie_Er", "Sie*Er", "Es" or even "Xie".

During the rest of the day, every single person who entered the venue was, soon or later, asked to display their names and pronouns on a similar adhesive paper.

While uncanny for any newcomer or outsider of the scene, asking the attendees to display and even invent pronouns of their choice, helps the festivals shape a queer environment and ambience.

While the festivals let the attendants introduce themselves with whatever pronouns and names they chose, the events thus authorize a distinction between physical appearance and chosen gender identity. Neutral pronouns -that is, pronouns that are neither completely feminine nor completely masculine -transcend the traditional expectations of gender binary. People presenting as feminine might as well reclaim masculine names and pronouns (and vice versa), while some people create new pronouns, drawing on the basis of masculine and feminine pronouns, plus "Sternche" or "Unterstrich". Others reclaim the traditional German neutral pronoun, and finally a last category of people create pronouns out of (almost) nothing. All these possibilities make the attendees able to shape and perform their identities outside of binary gender norms.

Yet, this is also made possible through a large range of workshops.

"Outside the box -a theoretical and practical approach to fluid gender identities

In opposition to what is usually assumed, most sciences aren't so sure anymore about the permanent and binary character of sex. More and more research results are telling us what so many people have known for years: sex, gender, desire, identity in general are fluid! This workshop is divided in two parts: the first one is about confronting common assumptions with all the arguments that are out there and that show us how sex is constructed. (...)

In the second part, we will try on new gender identities -in a literal sense! Equipped with binders, glue, bras, packers and other performance accessories, we will try to discover, rediscover or investigate other parts of our identity. This is not about wearing a costume nor is it about substituting one of the predetermined performances for the other: the aim is to enlarge our own possibilities." (Ladyfest Berlin 2013) Relying on such workshops, queer feminist DIY music festivals encourage everybody to experiment with their own gender identity; a process that is hardly possible in their daily life (at their jobs, in school, etc.). Indeed, festivals are known to provide a space that cuts their attendees from their daily lives, hence their possibility to subvert the social order as suggested by festival studies that draw on Bakhtin's "carnivalesque". The rules that regulate the social space of the queer_feminist music festival are therefore different than the rules that regulate the social space of each attendee's daily life. Practices such as name and pronoun tags and "fluid gender identities" workshops therefore provide the attendees a way to perform and embody identities hidden behind typographical signs as the "Unterstrich" (gap) and the "Sternchen" (little stars). Queer music festivals provide singular spaces where these gender identities are, for once, fluid and chosen by the festivals' attendees, and not socially determined and fixed.

Queerness in songs

Moreover, queerness and queer identities also shape songs and songwriting.

The rapper Sookee is one of the most programed artists in the German DIY queer feminist music festivals scene. In her piece "Frauen mit Sternchen", she lists a wide range of queer identities. This song is thus a typical example of what I would like to demonstrate.

First thing: the title should remind us what we saw earlier about the "Sternchen". Behind those "Sternchen" lay all the identities mentioned in the song text.

Throughout the text, we notice both English and German terms. English terms include for example Bitches, Butches, Femmes, Quings, Queers, Riot Grrrls, Tomboys.

German terms include Denker*Innen, Blaustrümpfe, König*Innen, Tribaden, Amazonen Blending two languages (English, German) is part of the construction of a queer vocabulary that is shaped by international circulation of concepts as well as by their local reception and modeling.

Plus, queer theories, as they are understood in queer DIY music festivals, aren't only dealing with the presentation of self, but also with the way artists write music. Songs experiment with gender as much as attendees of the festivals did during the workshops I analyzed earlier. The song texts help creating a sense of queerness. The rapper addresses her music to a specific public that is widely described within the lyrics. The text highlights identities that are generally marginalized within music scenes. It bespeaks of the circulation of English terms for queer identities within a German-speaking scene ("Butches", "Tomboys"), and, at the same time, underpins the history of German queer or feminist movements ("Blaustrümpfe"). The song contributes to an acknowledgement of the co-construction of the queer German movements, between American and local influences.

Conclusion

This presentation drew on queer studies as well as critical events studies and popular music studies.

I aimed to show that, the queer vibe of the festivals is shaped by language, self-presentation techniques, workshops and musical contents. Queer, non-binary identities are therefore chosen, claimed and performed by the audience but also by the artists on stage. That sense of queerness crosses language (through pronouns or names of gender identities, as listed in Sookee's lyrics), corporealities (through gender experimentation workshop), and social practices (name and pronoun labels).

Moreover, all of the characteristics of queerness I have analyzed are marked by both an appropriation of terms and behaviors inspired by the queer English-speaking world and the creation of a queer German language.

  2. A queer atmosphereNow, imagine we're Saturday morning. After a short walk in the city of Heidelberg, you finally arrive in front of the Breidenbach Studios, where the sixth edition of the local Lady*Fest festival is going to take place the whole day long. In front of the venue, people have hung a rainbow flag. Not long after you entered, someone hands you a pen and a piece of adhesive paper. The person said something like "Wir machen Namen und Pronomen Tag". Now, if you're completely new in the scene, you might not know what that is and stay stupefied by that practice. What should you write on that paper? Yet, after years of activity in the queer_feminist DIY scene, you might know what all