Marie Martin
email: marie.martin@aphp.fr

Jean-Claude Claude Alvarez

Positive blood ethanol concentration without alcohol consumption in the living subject: The auto-brewery syndrome. Clinical and forensic consequences

Keywords: yeast, auto-brewery syndrome, gut fermentation syndrome, alcohol intoxication, endogenous ethanol Résumé Syndrome d'auto-fermentation, syndrome d'auto-brasserie, intoxication à l'éthanol, éthanol endogène, levures

scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Le syndrome d'auto-fermentation ou syndrome d'auto-brasserie, parfois appelé syndrome de fermentation intestinale ou alcoolique, ou « auto-brewery syndrome » en anglais, est un phénomène rare, peu documenté et soumis à controverse [START_REF] Painter | Auto-brewery Syndrome (Gut Fermentation)[END_REF][START_REF] Eaton | Gut fermentation: a reappraisal of an old clinical condition with diagnostic tests and management: discussion paper[END_REF]. Il correspond à une production endogène d'éthanol après ingestion d'aliments riches en glucides, associée à une prolifération anormale de levures dans le tractus gastro-intestinal, particulièrement des genres Candida ou Saccharomyces [START_REF] Kaji | The autobrewery syndrome-the repeated attacks of alcoholic intoxication due to the overgrowth of Candida (albicans) in the gastrointestinal tract[END_REF]. Ce syndrome apparaît préférentiellement chez des sujets ayant des comorbidités intestinales. Les patients présentent très souvent un état d'ébriété et doivent faire face aux conséquences médicales et sociales de l'alcoolisme dont la conduite en état d'ivresse et l'hospitalisation en cure de désintoxication, ce qui peut poser un réel problème médical et judiciaire [START_REF] Malik | Case report and literature review of auto-brewery syndrome: probably an underdiagnosed medical condition[END_REF]. L'objectif de cette revue est de recenser les cas rapportés à ce jour dans la littérature afin d'améliorer les connaissances sur ce syndrome. Les aspects physiopathologiques, cliniques et diagnostiques seront abordés avant de s'intéresser aux aspects médico-légaux.

Méthode

La recherche bibliographique a été effectuée sur les bases de données PubMed et Google Scholar, jusqu'à la période de février 2020. Les termes recherchés étaient « auto-brewery syndrome », « gut fermentation », « endogenous ethanol production ». La majorité des articles correspondaient à des études de cas. Les résumés et articles disponibles ou accessibles sur la base de données Inserm ont été également étudiés. La glycolyse permet la transformation du glucose en pyruvate. En condition d'anaérobiose, la fermentation alcoolique par les levures aboutit à la conversion du pyruvate en éthanol, parallèlement à l'oxydation du NADH [START_REF] Kang | Converting Sugars to Biofuels: Ethanol and Beyond[END_REF][START_REF] Henningsen | Increasing Anaerobic Acetate Consumption and Ethanol Yields in Saccharomyces cerevisiae with NADPH-Specific Alcohol Dehydrogenase[END_REF]. La majorité des cas d'auto-fermentation rapportés dans la littérature mettent en évidence des levures de la famille Candida dans le contenu gastrique et/ou intestinal des patients. D'autres germes peuvent également être mis en cause tels que la famille

Physiopathologie et clinique

Le

Saccharomyces.

Le syndrome d'auto-fermentation intestinale est à distinguer du syndrome de fermentation vésicale pour lequel deux cas ont été décrits à ce jour, chez des patientes diabétiques avec une glycosurie et une éthanolurie élevées sans éthanolémie positive, présentant des germes de type Candida glabrata dans les urines (voir plus loin). Saccharomyces cerevisae comme agent causal, associé à la bactérie Helicobacter pylori [START_REF] Cordell | A Case Study of Gut Fermentation Syndrome (Auto-Brewery) with Saccharomyces cerevisiae as the Causative Organism[END_REF].

Facteurs favorisants ou associés

Certains

Saccharomyces cerevisae a été retrouvée en association avec Candida albicans chez un homme atteint d'une pseudo-obstruction intestinale chronique avec prolifération bactérienne de l'intestin grêle, traitée par amoxicilline-acide clavulanique [START_REF] Spinucci | Endogenous ethanol production in a patient with chronic intestinal pseudo-obstruction and small intestinal bacterial overgrowth[END_REF]. L'arrêt du traitement et un régime pauvre en glucides a permis le retour à une éthanolémie négative, qui s'est de nouveau positivée lors de la reprise de l'antibiothérapie et de l'ingestion de glucides. qui soutiennent que la production éthanolique maximale de Candida albicans in vivo (1 mg d'alcool par gramme de contenu gastrique et par heure) ne dépasse pas la capacité normale du foie à métaboliser l'alcool [START_REF] Geertinger | Endogenous alcohol production by intestinal fermentation in sudden infant death[END_REF].

Complications cliniques

Les patients peuvent présenter un état d'ébriété, avec vomissements, éructations, étourdissements, perte de coordination, trouble de l'élocution, désorientation, perte de mémoire, chutes et donc des blessures, symptômes du côlon irritable, syndrome de fatigue chronique engendrant des problèmes d'anxiété, de dépression, de tensions sociales et une faible productivité [START_REF] Painter | Auto-brewery Syndrome (Gut Fermentation)[END_REF], jusqu'à une désocialisation. Un syndrome de sevrage (tremblements, anxiété, agitation, dépression, nausées, malaises voire convulsions) [START_REF]Syndrome de sevrage[END_REF] peut apparaître chez des patients diagnostiqués tardivement, présentant une éthanolémie positive chronique sans consommation d'alcool. La confusion avec l'alcoolisme chronique est fréquente, à l'origine d'une orientation des patients vers un suivi psychiatrique ou une cure de désintoxication.

Enfin, il semblerait que la production endogène d'éthanol semble jouer un rôle dans le développement de la maladie du foie gras non alcoolique (ou NAFLD pour Non Alcoholic Fatty Liver Disease) [START_REF] Baker | Role of alcohol metabolism in non-alcoholic steatohepatitis[END_REF][START_REF] Zhu | Gut microbiota produce alcohol and contribute to NAFLD[END_REF][START_REF] Aragonès | Gut Microbiota-Derived Mediators as Potential Markers in Nonalcoholic Fatty Liver Disease[END_REF].

Diagnostic

Hunnisett et Howard ont mis en place un test de dépistage chez des patients suspectés de syndrome d'auto-fermentation en mesurant l'éthanolémie 1 heure après ingestion de 5 g de glucose [START_REF] Hunnisett | Gut Fermentation (or the 'Auto-brewery') Syndrome: A New Clinical Test with Initial Observations and Discussion of Clinical and Biochemical Implications[END_REF]. 61% des 510 sujets ont présenté une éthanolémie augmentée, entre 0,01 et 0,07 g/L. Ces éthanolémies restaient toutefois peu élevées. -des analyses de laboratoire (bilan métabolique, dosage de l'éthanol, dépistage de drogues, coproculture).

-l'élimination d'autres causes telles que l'alcoolisme, des problèmes psychiatriques, un traumatisme crânien.

-un test de provocation aux glucides via l'absorption de 200 g de glucose par voie orale, la mesure de l'éthanolémie et de l'alcool expiré par éthylotest à 0, ½, 1, 2, 4, 8, 16 et 24 heures.

-une endoscopie supérieure et inférieure avec échantillons des sécrétions gastro-intestinales pour cultures bactérienne et fongique, et réalisation de test de sensibilité aux antifongiques.

La recherche d'autres perturbations biologiques ou marqueurs biologiques induits par la fermentation alcoolique devrait être envisagée, afin de de faciliter le diagnostic du syndrome d'autofermentation.

Prise en charge médicale

Les antibiotiques ont un impact significatif sur le microbiote intestinal [START_REF] Iizumi | Gut Microbiome and Antibiotics[END_REF][START_REF] Maier | Extensive impact of nonantibiotic drugs on human gut bacteria[END_REF]. Plusieurs cas [START_REF] Spinucci | Endogenous ethanol production in a patient with chronic intestinal pseudo-obstruction and small intestinal bacterial overgrowth[END_REF][START_REF] Welch | Auto-brewery Syndrome in the Setting of Long-standing Crohn's Disease: A Case Report and Review of the Literature[END_REF] démontrent le lien entre la prise d'antibiotiques et le syndrome d'auto-fermentation. Ainsi, une antibiothérapie contrôlée pourrait préserver l'équilibre de la flore intestinale et diminuer la production endogène d'éthanol. L'utilisation de probiotiques est aussi à évaluer pour maintenir l'équilibre du microbiote [START_REF] Cordell | A Case Study of Gut Fermentation Syndrome (Auto-Brewery) with Saccharomyces cerevisiae as the Causative Organism[END_REF].

De plus, une diminution des apports en glucides via un régime alimentaire strict riche en protéines a été mise en place pour tous les cas présentés ici. Le suivi par un nutritionniste est à envisager dans la prise en charge de la maladie pour maintenir un régime pauvre en glucides sur le long terme et s'abstenir de boire de l'alcool. L'administration d'antifongiques a été rapporté dans de nombreux cas [START_REF] Cordell | Auto-Brewery as an Emerging Syndrome: Three Representative Case Studies[END_REF]. Certains germes peuvent être résistants au fluconazole habituellement prescrit [START_REF] Dahshan | Auto-Brewery Syndrome in a Child With Short Gut Syndrome: Case report and review of the Literature[END_REF]. De la micafungine et/ou de la nystatine peuvent alors être administrées, notamment chez les patients présentant des germes Saccharomyces [START_REF] Malik | Case report and literature review of auto-brewery syndrome: probably an underdiagnosed medical condition[END_REF][START_REF] Saverimuttu | A Case of Auto-brewery Syndrome Treated with Micafungin[END_REF].

Une dépendance à l'alcool et un syndrome de manque peuvent apparaître chez les patients. Un suivi psychiatrique pour alcoolisme ou troubles du comportement ainsi qu'une cure de désintoxication peuvent alors être instaurés, faisant souvent suite à l'incompréhension et au scepticisme des professionnels de santé.

Aspects médico-légaux

D'un point de vue médico-judiciaire, les patients peuvent être dépistés positifs à l'éthanol, lors d'un contrôle routier de routine [START_REF] Akhavan | Drunk Without Drinking: A Case of Auto-Brewery Syndrome[END_REF] et confirmés par la méthode de référence qui est la chromatographie en phase gazeuse. Ils peuvent dépasser la limite légale de conduite (0,5 g/L dans le sang total en France) sans avoir consommé d'alcool, posant un réel problème judiciaire. Ce sujet est soumis à controverse. Simic et al. [START_REF] Simic | Endogenous ethanol production in patients with diabetes mellitus as a medicolegal problem[END_REF] soutiennent par exemple que l'augmentation de l'éthanolémie chez des patients diabétiques n'atteint pas la limite légale (moyenne de 2,65 mg/L vs 0,4 mg/L chez les témoins, soit des valeurs inférieures à 0,1 g/L) et n'impacte donc pas les poursuites judiciaires. De même, Logan et Jones [START_REF] Logan | Endogenous ethanol "auto-brewery syndrome" as a drunk-driving defence challenge[END_REF]

  syndrome d'auto-fermentation peut être diagnostiqué chez des patients ayant une concentration d'éthanol sanguine ou sérique élevée, jusqu'à plus de 4 g/L [5], sans aucune consommation d'alcool ni antécédents d'alcoolisme, souvent après un repas riche en glucides et présentant une pathologie intestinale chronique.

  facteurs semblent influencer le développement d'un syndrome d'auto-fermentation alcoolique. Kaji et al. ont recensé 39 cas au Japon depuis 1952, âgés entre 1 et 75 ans [8]. Des germes de la famille Candida ont été retrouvés chez tous les patients. Le mode de vie, une chirurgie abdominale, une perturbation du tractus intestinal ou une antibiothérapie répétée semblent favoriser la stagnation du bol alimentaire et la prolifération d'agents responsables de la fermentation alcoolique. Ce syndrome est appelé « Metei-sho » en japonais, traduction d'autofermentation alcoolique intragastro-intestinale. a-Le mode de vie L'étude publiée en avril 2019 par Cordell et al. [9] a comparé le mode de vie, l'alimentation et les antécédents médicaux de 28 patients ayant un syndrome d'auto-fermentation à 18 témoins. Les résultats ont montré que les patients consomment plus d'eau et moins de thé et de café, mangent moins de produits laitiers, moins de bonbons et dinent moins souvent à l'extérieur de chez eux. Tout ceci dans le but de limiter les symptômes. Les patients souffrant de ce syndrome présentent par ailleurs des épisodes de diarrhées et des cas d'haleine malodorante en plus grand nombre. Leurs analyses de selles montrent une présence plus importante de levures. Ils se déclarent par ailleurs en moins bonne santé. Enfin, les patients ont une utilisation de médicaments antibactériens contre l'acné plus longue que le groupe témoin. Un déficit en oligoéléments avait également été mis en évidence par Eaton et al. en 2004 [10]. b-Antibiothérapie L'administration d'antibiotiques perturbe le microbiote intestinal, pouvant favoriser la production endogène d'éthanol. Cordell et McCarthy ont reporté le cas d'un homme de 61 ans avec la levure

  c-Comorbidités digestives et hépatiquesDiverses co-morbidités sont souvent associées (maladie de Crohn, syndrome du grêle court, pseudoobstruction, troubles hépatiques…) au syndrome d'auto-fermentation.Le cas d'un homme de 71 ans atteint de la maladie de Crohn depuis 50 ans et présentant des symptômes d'ébriété (confusion, troubles de l'élocution, démarche ébrieuse, chute…) a été rapporté par Welch et al. en 2016[START_REF] Welch | Auto-brewery Syndrome in the Setting of Long-standing Crohn's Disease: A Case Report and Review of the Literature[END_REF]. Le patient a subi plusieurs cures d'amoxicilline-acide clavulanique dans les mois précédant son hospitalisation. A son arrivée à l'hôpital, son éthanolémie s'élevait à 2,34 g/L.Une grande quantité de Candida glabrata a été retrouvée dans les fluides recueillis à proximité d'une sténose de l'intestin grêle. Les traitements antibactériens sont en effet connus pour entrainer un déséquilibre de la flore digestive et une prolifération des germes fongiques, notamment des levures[START_REF] Young | Disruption of the Gut Ecosystem by Antibiotics[END_REF].Hafez et al.[START_REF] Hafez | Auto-brewery syndrome: Ethanol pseudotoxicity in diabetic and hepatic patients[END_REF] ont étudié la production endogène chez des patients atteints de diabète (n= 14), d'une cirrhose hépatique (n= 14) et des deux pathologies associées (n= 14), en comparaison avec un groupe témoin. Ils ont mesuré l'éthanolémie après ingestion d'aliments riches en glucides. Dans chaque groupe, l'éthanolémie était significativement augmentée par rapport aux sujets sains : une moyenne de 0,003 g/L chez les sujets témoins, 0,05 g/L chez les sujets diabétiques, 0,03 g/L chez les sujets atteints de cirrhose et 0,11 g/L chez les sujets ayant les deux pathologies. Ces concentrations restaient toutefois peu élevées. d-Le diabète Deux cas de syndrome d'auto-brasserie urinaire (et non intestinale), appelé aussi fermentation vésicale ont été décrits chez deux femmes diabétiques, non compliantes dans le traitement de leur diabète. Gruszecki et al. ont rapporté en 2005 le cas d'une jeune femme de 19 ans décédée d'un arrêt cardiaque à la suite d'une acidocétose diabétique, qui présentait des concentrations de glucose sanguin et urinaire à respectivement 5,5 et >10 g/L [16]. Un test de dépistage aux drogues s'est révélé positif pour l'éthanol. Il n'a néanmoins pas été retrouvé d'alcool dans le sang, mais l'éthanolurie s'élevait à 3,2 g/L lors de l'autopsie réalisée moins de 24 heures post-mortem. Des levures de type Candida glabrata ont été retrouvées dans ses urines. Le second cas a été publié en février 2020 [17]. Il s'agit une femme de 61 ans atteinte d'un diabète mal contrôlé et d'une cirrhose, qui s'est vu refuser l'accès à une greffe hépatique et orienter vers un traitement de l'alcoolisme, à cause de son éthanolurie à 1,8 g/L. Elle niait toute consommation d'alcool et aucun prélèvement sanguin n'a révélé la présence d'éthanol. L'éthylglucuronide urinaire, métabolite de l'éthanol et marqueur de la consommation d'alcool, était aussi négatif. Sa glycosurie s'élevait à plus de 10 g/L et des levures de type Candida glabrata ont été également retrouvées dans ses urines. Ses deux cas illustrent la possibilité d'une fermentation des sucres par Candida glabrata dans la vessie, à l'origine d'une production endogène d'éthanol urinaire. e-Chirurgie abdominale2. Cas chez l'enfantLe premier cas de production alcoolique endogène a été décrit en 1948 par Ladkin et Davies chez un enfant africain de 5 ans, hospitalisé pour une tumeur de l'hypogastre[START_REF] Ladkin | Rupture of Stomach in African Child[END_REF]. Il présentait une distension abdominale avec altération de la conscience. Le patient est décédé d'une rupture de la paroi gastrique et une forte odeur d'alcool se dégageait du contenu gastrique à l'autopsie, sans aucune administration d'alcool connue. La cause du décès a été attribuée à la fermentation du dîner copieux de patates douces pris la veille, ayant produit du gaz à une pression suffisante pour rompre l'estomac. D'autres cas chez l'enfant ont été rapportés[START_REF] Jansson-Nettelbladt | Endogenous ethanol fermentation in a child with short bowel syndrome[END_REF][START_REF] Logan | Endogenous ethanol production in a child with short gut syndrome[END_REF][START_REF] Dahshan | Auto-Brewery Syndrome in a Child With Short Gut Syndrome: Case report and review of the Literature[END_REF][START_REF] Green | Twelve-year-old female with short bowel syndrome presents with dizziness and confusion[END_REF]. En 2001, Dahshan a rapporté le cas d'une jeune fille de 13 ans ayant un syndrome du grêle court qui présentait des symptômes d'ébriété (désorientation, somnolence, haleine alcoolique) et une éthanolémie jusqu'à 3,5 g/L, en niant toute consommation d'alcool [27]. Son père, médecin, a mis en évidence une forte corrélation entre ses concentrations d'éthanol sérique et son ingestion d'aliments riches en glucides ou de boissons contenant du fructose. Candida glabrata et Saccharomyces cerevisae ont été mis en évidence dans les selles et un traitement par antifongique, à savoir le fluconazole, a été entrepris, rendant négative l'éthanolémie de la jeune fille et faisant disparaître les symptômes. Le cas d'une petite fille de 3 ans avec un syndrome du grêle court et des épisodes récurrents d'ébriété lors de la consommation de jus de fruits sucrés a été publié par Jansson-Nettelbladt en 2006 [25]. Une concentration sanguine d'éthanol à 0,7 g/L et la présence de Candida kefyr dans le contenu gastrique et les fèces ont été mis en évidence. Dès 1985, Bivin et Heinen [29] ont soupçonné que la production d'éthanol induite par la fermentation des préparations pour nourrissons par les levures pourrait jouer un rôle dans le syndrome de mort subite du nourrisson. Cette hypothèse a été controversée par Geertinger et al.

D

  'autres critères doivent être évalués lors du diagnostic. Malik et al. ont proposé un protocole de détection du syndrome d'auto-fermentation comprenant [4] : -la recherche des antécédents complets concernant l'alimentation, la consommation d'alcool et les épisodes d'intoxication inexpliquée, y compris ceux des membres de la famille, ainsi qu'un examen physique.

  ont remis en cause ce problème juridique, en mettant en évidence des concentrations d'éthanol endogène dans le sang veineux périphérique d'individus sains et de personnes souffrant de divers troubles métaboliques (diabète, hépatite, cirrhose) inférieures à 0,8 mg/L. Néanmoins, des cas d'éthanolémie sans consommation d'alcool déclarée et dépassant les 2 g/L ont été rapportés [5,27,39]. Malik et al. ont publié le cas d'un homme de 46 ans, en bonne santé, présentant des troubles dépressifs, des pertes de mémoire, une semaine après la fin d'une antibiothérapie [4]. Il a été arrêté pour conduite en état d'ivresse avec une alcoolémie à 2 g/L et a nié toute absorption d'alcool. Un suivi psychiatrique et des procédures judiciaires ont été mises en place. Après de multiples investigations, Saccharomyces cerevisae et Saccharomyces boulardii ont été retrouvés dans ses selles. Le diagnostic de syndrome d'auto-fermentation a pu être posé a postériori par quantification de l'augmentation de l'éthanolémie (à 0,57 g/L) suite à un repas riche en glucides. Un traitement par fluconazole a été instauré pendant 14 jours, sans effet, puis par nystatine pendant 10 jours, améliorant ces symptômes. Quelques mois plus tard, le patient a été hospitalisé en centre neurologique après un traumatisme crânien lors d'un épisode d'ébriété et présentait une éthanolémie variant de 0,5 à 4 g/L au cours de son hospitalisation. Un traitement par micafungine a permis de négativer son éthanolémie. La mise en place d'un régime strict pauvre en glucides et la prise au long cours de probiotiques ont permis de maintenir une éthanolémie négative. Il est à noter qu'aucun cas reporté dans la littérature ne présente d'antécédents d'alcoolisme et qu'aucun cas de syndrome d'auto-fermentation n'a été décrit en France à ce jour. Ce syndrome reste un phénomène très rare et apparait chez des patients présentant une pathologie sous-jacente avec perturbation du microbiote intestinal. En cas de contestation d'une décision médico-judiciaire, l'accusé devra démontrer à posteriori son atteinte via un diagnostic complet, notamment par un test de provocation aux glucides lors d'une hospitalisation. Conclusion Le syndrome d'auto-fermentation est un syndrome rare. Quelques cas sont néanmoins décrits dans la littérature, mettant en évidence un état d'ébriété à l'origine de grandes difficultés pour les patients. L'alcool, qu'il soit exogène ou produit de façon endogène, a les mêmes manifestations toxiques. Le syndrome d'auto-fermentation devrait être reconnu en raison de ses implications sociales possibles telles que la perte d'emploi, les difficultés relationnelles, la stigmatisation et même l'arrestation ou l'incarcération. L'information médicale doit être poursuivie afin d'envisager ce diagnostic chez un patient présentant une concentration d'éthanol élevée alors qu'il nie et qu'il apporte la preuve de ne pas avoir ingéré de l'alcool. Mais la difficulté repose sur le fait que de très nombreux contrevenants clament ne pas avoir consommé d'alcool dès lors que des sanctions judiciaires peuvent survenir. C'est pourquoi un diagnostic standardisé semble être nécessaire en cas de contestation.


Pierre Boisaubert

Nasreddine Kébir
email: nasreddine.kebir@insa-rouen.fr

Anne-Sophie Schuller

Fabrice Burel

Photo-crosslinked Non-Isocyanate Polyurethane Acrylate (NIPUA) coatings through a transurethane polycondensation approach

Keywords: Polyurethane, non-isocyanate, NIPU, transurethanization, coating, acrylates, UV-Curing

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Polyurethanes (PUs) are a very important family of polymer materials displaying versatile properties and chemical structures, which afford them a large spectrum of application fields such as shipbuilding, biomaterials, automotive, paints, coatings, adhesives, clothes and footwears.

Polyurethane acrylate systems (PUAs) are formulations containing acrylateterminated resins that are widely used to produce protective coatings. These coatings generally have very good abrasion resistance, high chemical resistance and very flexible mechanical properties. [START_REF] Fu | Research progress of UVcurable polyurethane acrylate-based hardening coatings[END_REF][START_REF] Oprea | Poly(urethane-methacrylate)s. Synthesis and characterization[END_REF] PUAs are conventionally obtained by functionalizing hydroxylterminated oligomers, synthesized by the conventional reaction between polyols and toxic diisocyanates, which are synthesized from amines and toxic phosgene. [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF] Since the early 2000s, some groups have begun to adapt the synthesis of PUA materials by non-isocyanate routes (NIPUAs). [START_REF] Assumption | Photopolymerization of urethane dimethacrylates synthesized via a non-isocyanate route[END_REF][START_REF] Figovsky | Foamable photopolymerized composition[END_REF][START_REF] Huang | Synthesis and properties of UVcurable tung oil based resins via modification of Diels-Alder reaction, nonisocyanate polyurethane and acrylates[END_REF][START_REF] Hwang | Functional polyurethane prepolymer, method of preparing polyurethane by using the same, and application method thereof[END_REF][START_REF] Monnier | Oligomères uréthane acrylates mono ou multifonctionnels sans isocyanate[END_REF][START_REF] Monnier | Oligomère uréthane acrylé ou méthacrylé sans isocyanate[END_REF][START_REF] Hwang | A new UV-curable PU resin obtained through a nonisocyanate process and used as a hydrophilic textile treatment[END_REF][START_REF] Wang | Investigation of non-isocyanate urethane dimethacrylate reactive diluents for UV-curable polyurethane coatings[END_REF] Some works have described the photochemical crosslinking of poly(hydroxyurethane) acrylate (PHUA) oligomers, obtained by polyaddition of cyclic dicarbonate and diamine monomers followed by various functionalization techniques. [START_REF] Monnier | Oligomères uréthane acrylates mono ou multifonctionnels sans isocyanate[END_REF][START_REF] Monnier | Oligomère uréthane acrylé ou méthacrylé sans isocyanate[END_REF][START_REF] Soucek | Preparation of non-isocyanate urethane (meth)acrylates for urethane functional latex[END_REF][START_REF] Figovsky | Foamable photo-polymerized composition[END_REF][START_REF] Zareanshahraki | Synthesis of non-isocyanate polyurethanes and their application in radiation-curable aerospace coatings[END_REF] However, as far as we know, no studies have been carried out on the photo-crosslinking of NIPUA systems obtained by the transurethane polycondensation reaction, which is one of the most promising free isocyanate routes to polyurethanes. [START_REF] Unverferth | Renewable non-isocyanate based thermoplastic polyurethanes via polycondensation of dimethyl carbamate monomers with diols[END_REF][START_REF] Duval | Synthesis and properties of renewable nonisocyanate polyurethanes (NIPUs) from dimethylcarbonate[END_REF][START_REF] Martin | Synthesis and properties of allyl terminated renewable non-isocyanate polyurethanes (NIPUs) and polyureas (NIPUreas) and study of their photo-crosslinking[END_REF][START_REF] Kébir | Nonisocyanate thermoplastic polyurethane elastomers based on poly(ethylene glycol) prepared through the transurethanization approach[END_REF][START_REF] Li | Synthesis and properties of nonisocyanate aliphatic crystallizable thermoplastic poly(ether urethane) elastomers[END_REF][START_REF] Shen | A comparison of nonisocyanate and HDI-based poly(ether urethane): Structure and properties[END_REF][START_REF] Li | Synthesis and characterization of aliphatic thermoplastic poly(ether urethane) elastomers through a non-isocyanate route[END_REF] This technique involves the reaction of dialkyl dicarbamates [START_REF] Unverferth | Renewable non-isocyanate based thermoplastic polyurethanes via polycondensation of dimethyl carbamate monomers with diols[END_REF][START_REF] Duval | Synthesis and properties of renewable nonisocyanate polyurethanes (NIPUs) from dimethylcarbonate[END_REF][START_REF] Martin | Synthesis and properties of allyl terminated renewable non-isocyanate polyurethanes (NIPUs) and polyureas (NIPUreas) and study of their photo-crosslinking[END_REF][START_REF] Kébir | Nonisocyanate thermoplastic polyurethane elastomers based on poly(ethylene glycol) prepared through the transurethanization approach[END_REF] or dihydroxyethyl dicarbamates [START_REF] Li | Synthesis and properties of nonisocyanate aliphatic crystallizable thermoplastic poly(ether urethane) elastomers[END_REF][START_REF] Shen | A comparison of nonisocyanate and HDI-based poly(ether urethane): Structure and properties[END_REF][START_REF] Li | Synthesis and characterization of aliphatic thermoplastic poly(ether urethane) elastomers through a non-isocyanate route[END_REF] with diols, in presence of organic or organo-metallic catalysts. However, with dihydroxyethyl dicarbamates, a back-biting side reaction may occur at certain conditions leading to formation of urea moieties. [START_REF] Li | Synthesis and properties of nonisocyanate aliphatic crystallizable thermoplastic poly(ether urethane) elastomers[END_REF][START_REF] Shen | A comparison of nonisocyanate and HDI-based poly(ether urethane): Structure and properties[END_REF][START_REF] Li | Synthesis and characterization of aliphatic thermoplastic poly(ether urethane) elastomers through a non-isocyanate route[END_REF] On the other hand, unlike the aminolysis of cyclic carbonate route leading to poly(hydroxyurethane) structures (PHUs), [START_REF] Cornille | A perspective approach to sustainable routes for non-isocyanate polyurethanes[END_REF][START_REF] Lambeth | Organocatalytic synthesis of (poly)hydroxyurethanes from cyclic carbonates and amines[END_REF][START_REF] Duval | Organocatalytic synthesis of novel renewable non-isocyanate polyhydroxyurethanes[END_REF] this technique has the advantage of yielding conventional PU structures. Another advantage of this approach, is the wide choice of BMC monomers comparing to diisocyanate monomers, which offers a higher potential for variations in structure and properties of the final polyurethane materials.

In this work, we describe the synthesis of new NIPUA oligomers through the use of the transurethane polycondensation reaction between dialkyl dicarbamates and diols, followed by an acrylation step. The preparation of coatings by photo-crosslinking of the prepared NIPUAs as well as the assessment of their thermal and mechanical properties are reported.

EXPERIMENTAL

Materials

Poly(tetramethylene oxide) (PTMO) of = 650 and 2000 g/mol, 1,6-diaminohexane (98%), 1,5,7-triazabicyclo [4.4.0]dec-5-ene (TBD, 98%), dimethyl carbonate (DMC, 99%, anhydrous), 1,4butanediol (99%), and 4,4'-methylenebis(cyclohexylamine) (H12MDA, >98%) were obtained from Sigma Aldrich. Acryloyl chloride (96%), trimethylolpropane (TMP, 99%), 4-methoxyphenol (MeHQ, 99%) and triethylamine (99%) were supplied by Fisher Scientific. Diphenyl (2,4,6trimethylbenzoyl)phosphine oxide (Irgacure 819 or BAPO) and Ethyl phenyl (2,4,6-trimethylbenzoyl) phosphinate (TPO-L or LucirinL) were supplied by BASF. All the other reagents and solvents were used without further purification.

Synthesis

Preparation of dimethyl dicarbamate monomers

In a round-bottomed flask equipped with a magnetic stirrer, diamine (1 eq.), TBD (0.1 eq.) and DMC (10 eq.) were added and stirred for 5 h at 80°C (24 h for BMC-H12). The reaction medium was then cooled to room temperature. Crystallized products (BMC-C6 and BMC-H12) were recovered by filtration (yield > 85 %) and washed by distilled water to remove TBD. In the case of BMC-Pr, the liquid product was washed with distilled water in diethyl ether medium. Then, the organic phase was dried over MgSO4 , filtrated and the solvent was evaporated. Dimethylhexane-1,6-dicarbamate (BMC-C6)

Preparation of hydroxy-terminated NIPU oligomers (H-Ol)

In a three-necked round-bottom flask equipped with a mechanical stirrer, a Dean Stark condenser and connected to a vacuum pump (or a 5 L-four-necked-jacketed glass reactor equipped with a mechanical stirrer and thermometer for 1kg scale), bismethylcarbamate (BMC), poly(tetramethylene oxide) (PTMO) and chain extender were added at an appropriate molar ratio previously calculated by Carothers theory to reach the desired Mn. The temperature was progressively risen to 160 °C under nitrogen flow and stirring. Then, 10 mol% KOMe catalyst relative to BMC monomer was added. After 1 h of reaction at 160 °C, Dean Stark condenser was removed and the reaction mixture was placed under vacuum (400 mbar, 1 h). Finally, the pressure was carefully reduced to 0.5 mbar for 4 h. After cooling to room temperature under nitrogen flow, the obtained oligomers were recovered without any purification. In the case of using BD as chain extender, evaporation was quantified by NMR calculations. In order to obtain the oligomer with the right molecular weight, the experiment was performed a second time, adjusting BD equivalents.

Preparation of Acrylate-terminated NIPU Oligomers (A-Ol)

In a round bottom flask equipped with a magnetic stirrer (or a 5 L-four-necked-jacketed glass reactor equipped with a mechanical stirrer and thermometer for 1kg scale), a hydroxy-terminated NIPU oligomer was introduced, under a nitrogen stream. The oligomer was solubilized in anhydrous DCM. Triethylamine (3.5 eq.), previously distilled over KOH pellets, was added to the reaction mixture. After cooling the mixture to 0 °C with an ice bath, acryloyl chloride (3 eq.) was added dropwise to the reaction mixture. Then, the mixture was allowed to react for 6 h at room temperature. Filtration of triethylammonium salts was carried out. The mixture was then washed three times by HCl (1M), NaOH (1M) and brine. First organic phase was recovered and the oligomer parts remaining in the aqueous phase were extracted by DCM. The organic phases were combined, dried over MgSO4, and filtrated. 4-methoxyphenol stabilizer was added (from 100 to 500 ppm depending of the oligomer molecular weight) and solvent was evaporated. Finally, the resulting yellow product was dried using high vacuum at 25°C.

Preparation of photo-crosslinked NIPU coatings (NIPUAs)

The formulations were prepared by dissolving A-Ol in an appropriate amount of butyl acetate to reach a convenient viscosity. Subsequently, 3.3 wt% of BAPO-TPOL photoinitiator mixture (1:1) was added to the medium. Formulations were stirred (heated to 70 °C if necessary) for 2 hours to obtain homogeneous medium. Then, the formulations obtained were cast on rigid mat steel "Q-panel" plates supplied by Labomat. After degreasing the plates with a cloth soaked in ethanol (EtOH), two types of coatings were obtained for each type of formulation, i.e "thin" and "thick" films. In order to obtain thin films, the desired formulation was applied on top of the plate and the wet thickness was controlled by a roll coater. To obtain thick films, blades of adhesive tape were used on the edges to calibrate the thickness. The plates were then placed in a UV conveyor (UV Fusion Light Hammer 6) to perform the photo-crosslinking.

Measurements and Instrumentation

1 H and [START_REF] Figovsky | Foamable photo-polymerized composition[END_REF] C NMR analysis were performed on a Bruker 300 Fourier Transform spectrometer at 300 MHz and 75 MHz, respectively, in CDCl3 solutions containing tetramethylsilane (TMS) as internal standard. FTIR spectra were acquired with Perkin-Elmer Spectrum 2000 FTIR, provided with a diamond ATR device (Attenuated Total Reflection). Spectra were recorded from 10 scans in the 650 to 4000 cm -1 range.

Average molecular weights of polymers (Mn and Mw) and dispersity (Ð = Mw/Mn) were assessed by Size Exclusion Chromatography (SEC). Polymers were dissolved in dichloromethane, filtered (0.45 µm) and analyzed at 25°C by a Varian PL-GPC50 system provided with two mixed packed columns (PL gel mixed type C). Dichloromethane was used as the mobile phase and PMMA standards (from 875 to 62000 g mol -1 ) were used for calibration.

Thermo-Gravimetric Analysis (TGA) was achieved with a TGA Q500 device (TA Instruments), using a heating rate of 10°C/min under a nitrogen flow. The temperature at 5% of weight loss (T5%) was used as reference to estimate the degradation of polymers.

Differential Scanning Calorimetry (DSC) analysis was performed with a DSC Q2000 device (TA Instruments), using a heating rate of 10°C/min under a nitrogen flow. The midpoint method was used to evaluate the glass transition temperature (Tg). Melting temperature (Tm) was measured at the maximum of the endothermic signal. DSC curves were recorded in a temperature range of -70 to 250°C.

The thickness of crosslinked thin films was measured in accordance with ISO 2808: 2007 by magnetic determination using the PosiTector 6000. Films characterized by this device had thicknesses of less than 50 µm with an accuracy of ± 1.0 micron. The device consists of a probe to be applied against the coating, previously deposited on a flat surface. The thickness of the thick crosslinked films (between 100 µm and 1 mm) was measured with the Digimatic micrometer, with an accuracy of ± 1.0 micron. The coating was clamped by a micrometer screw between the two circular measuring surfaces of the device.

The tensile analyses were performed on a Zwick/Roell device equipped with a 500 N force sensor, two jaws (pneumatic or manual clamping, depending on the type of sample characterized) and a movable crosshead. The tests were carried out in accordance with ISO 527_3 "Test conditions for films and foils". For each coating, between 5 and 15 rectangular specimens were cut out with a scalpel. Specimens with unevenness or notches were systematically removed. The manually clamped jaws limit the width of the specimens to 6 mm, the specimens had the following dimensions: a total length l3 of 50 mm; a width b of exactly 4 mm; a thickness h always less than 1 mm. The values of b and h were measured precisely at three points and the average of the three measurements were used for the calculations. The distance between jaws L0 is fixed at 35 millimetres. The test speed υ was fixed at 20 mm/min, and the preload value was maintained at 0.05 MPa. After each sample has been broken, the following values shall be determined as a function of the cross-section A (A = b × h, expressed in mm 2 ) of the sample: The breaking strength of the material σr (MPa) which corresponds to the stress experienced when the specimen breaks, equal to the maximum stress; the elongation at break εr (%) which corresponds to the elongation of the material before it breaks; Young's modulus or Elasticity E (MPa) which corresponds to the slope of the stress/strain curve in the range between ε1 = 0.05% and ε2 = 0.25% of the elongation of the material considered reversible.

For swelling tests, mass (mi) samples of approximately 15 mg (thin films) and 50 mg (thick films) are placed in 4 mL pill dispensers containing 3.5 mL volume of THF and then placed under magnetic agitation at room temperature for 24 hrs. The samples were removed from the solvent, dried on the surface with absorbent paper and weighed (mh). These samples were then dried in a vacuum oven at 40°C for 24 h and weighed (mf). Then, we have calculated: -The extractables rate (τEX) of the samples, expressed in %: = mi -mf mi × 100 Eq.1

-The swelling (Q) of the samples, expressed in %:

Q = mh mf mf × 100
Eq.2

RESULTS AND DISCUSSION

Synthesis and characterizations of acrylated NIPUs oligomers

Bis(methyl carbamate) monomers (BMC, Scheme 1) were prepared by reacting a large excess of dimethylcarbonate (DMC) (to avoid cyclization and chain extension) with several diamines, using TBD as catalyst, as previously described. [START_REF] Duval | Synthesis and properties of renewable nonisocyanate polyurethanes (NIPUs) from dimethylcarbonate[END_REF][START_REF] Martin | Synthesis and properties of allyl terminated renewable non-isocyanate polyurethanes (NIPUs) and polyureas (NIPUreas) and study of their photo-crosslinking[END_REF][START_REF] Kébir | Nonisocyanate thermoplastic polyurethane elastomers based on poly(ethylene glycol) prepared through the transurethanization approach[END_REF] The monomers mixture was allowed to react during 6 h at 80 °C. Three diamines were used, i.e. hexamethylene diamine (C6) which can be considered as potentially biobased; [25][26] 4,4'-methylenebis(cyclohexylamine) (H12) which is a petroleum-based monomer ; and Priamine (Pr) from Croda which is fully biosourced (from vegetable oils). Furthermore, DMC [START_REF] Choi | Selective and high yield synthesis of dimethyl carbonate directly from carbon dioxide and methanol[END_REF][START_REF] Ballini | TBD-catalysed solventless synthesis of symmetrically N,N'-substituted ureas from primary amines and diethyl carbonate[END_REF] can also be obtained from renewable feedstock. Solid BMCs (C6 and H12) were recovered by crystallization, whereas liquid BMC-Pr was recovered by extraction in diethyl ether after washing with water.

Hydroxyl terminated oligomers (H-Ol)

Polyol or chain extender In order to obtain NIPU oligomers with hydroxyl chain-ends (H-Ol), the synthesized BMCs were engaged in a transurethane polycondensation reaction with an excess of poly(tetramethylene oxide) (PTMO), a di-hydroxylated polyether with different molecular weights ( = 650 or 2000 g/mol) (Scheme 1). PTMO affords interesting properties by giving the final material good resistance to hydrolysis and good mechanical characteristics. [START_REF] Suryawanshi | Advances in the synthesis of non-isocyanate polyurethanes[END_REF] The obtained oligomers were denoted "H-BMC-PTMO". As an example, the H-Ol oligomer synthesized from BMC-Pr and PTMO of = 2000 g/mol was denoted "H-Pr-2000". Two NIPU materials bearing butane diol (BD) or trimethylolpropane (TMP) as chain extenders were also prepared (A-C6-2000/BD-1/2 and A-C6-650/TMP-1/0.5, respectively).

HO O N H O R N H O O O H n O O N H O R N H O O O n O O

Acrylate terminated oligomers (A-Ol)

The targeted values for NIPU series based on PTMO650 and PTMO2000, were of 2000 and 5500 g/mol, respectively. Thus, the targeted Xn was deduced from the following equation: Using Carothers' theory, 30 the degree of polymerization " " as well as the number of repeating units "n", can be expressed as follows: 31

= 1 + 1 + -2 = 2 + 1
Eq.4

With: -= stoichiometric ratio of reagents, with r < 1 -= conversion of the limiting reagent monomer.

Assuming that p → 1, the stoichiometric excess of diols to be used « 1/ » can be deducted as follows:

1 = + 1 - 1
Eq.5

The hydroxy-terminated (H-Ol) NIPU oligomers were functionalized by the use of acryloyl chloride to obtain oligomers with acrylate chain-ends designated as A-Ol. After reaction at room temperature in DCM, the medium was washed several times with acidic and basic aqueous solutions to remove reaction by-products, and then the A-Ol was obtained after drying over MgSO4 and evaporation of DCM. The double bonds were stabilized before the evaporation step by adding around 300 ppm of methoxyphenol (MeHQ) to prevent crosslinking of the products. The A-Ol obtained were named "A-BMC-MnPTMO".

The FTIR spectra (Figure 1) showed the disappearance of the stretching band of the terminal hydroxyl functions (H-O) at around 3500 cm -1 , as well as the appearance of the bending bands of the C-H bond of the acrylate group at around 1410 cm -1 (in-plane) and at around 810 cm -1 (out-of-plane). The C=O stretching vibration band of the ester-acrylate groups appeared at around 1725 cm -1 , and was overlapped with the C=O stretching vibration band of the free urethane groups (1720 cm -1 ). Other urethane bands were also observed at 1686 cm -1 (H-bonded C=O, stretching) and 1526 cm -1 (N-H bending). The band at around 3300 cm -1 arose from stretching vibration of N-H bonds of urethane groups.

1H NMR analysis (Figure 2) showed that the signal "6" of the terminal methylene groups was strongly shifted by the electron-withdrawal inductive effect of the introduced acrylate groups. (t, from δ = 3.61 ppm (CH2-OH) to approximately δ = 4.17 ppm (CH2-OCOCH=CH2)). The new acrylate proton signals appeared at around δ = 6.39 ppm (signal "10", dd, R-OCOCHCHtransH, [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF] Jtrans = 17 Hz, 2J ≈ 1 Hz), δ = 6.11 ppm (signal "9", dd, R-OCOCHCH2, [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF] Jtrans = 17 Hz, [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF] The physico-chemical characteristics of A-Ol are listed in Table 1. They have a yellowish appearance and were obtained in good yields. The lowest yields (59 -65 %) were obtained with A-C6-A B 650/TMP-1/0.5 and A-C6-2000/BD-1/2 because of their lower solubility in DCM, which was the reaction and extraction solvent. This low solubility is ascribed to higher percentages of urethane functions and hard segments (%UA-ol, %HS) within these materials.

Table 1: Physico-chemical characteristics of some prepared A-Ol oligomers.

A-Ol [START_REF] Fu | Research progress of UVcurable polyurethane acrylate-based hardening coatings[END_REF] Step η 2 (%) Global η 2 (%)

Mn 3 (g/mol) Mn 4 (g/mol)

Ð [START_REF] Assumption | Photopolymerization of urethane dimethacrylates synthesized via a non-isocyanate route[END_REF] %UA-Ol (%HS) 1 Kg means kilogram scale; the ratio PTMO650/TPM was 1/0.5; the ration PTMO/BD was 1/2) [START_REF] Oprea | Poly(urethane-methacrylate)s. Synthesis and characterization[END_REF] Step η: Mass yield of Acrylation step; Global η: overall mass yield of the 3 synthesis steps (Scheme 1). [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF] Calculated by 1 H NMR. [START_REF] Assumption | Photopolymerization of urethane dimethacrylates synthesized via a non-isocyanate route[END_REF] Calculated by GPC. [START_REF] Figovsky | Foamable photopolymerized composition[END_REF] In summary, we have obtained more than ten oligomers with exclusively acrylate (A-Ol) chain-ends, using a simple process. The synthesis of some A-Ol was developed on a kilogram scale in a 5-litre reactor, with good mass yields (see Table 1, orange lines). At both laboratory and kilogram scale, the yields obtained throughout the synthesis process were highly dependent on the yields of the acrylation stage (ηglobal = 59 -92 %).

Preparation and characterizations of photo-crosslinked coatings

The acrylate oligomers A-Ol were formulated with a combination of two type I free-radical photoinitiators (TPO-L and BAPO (1:1), Scheme 2) at 3.3 wt.%, in butyl acetate (AcOBu). The formulations were photo-crosslinked under a UV conveyor equipped with a parabolic mercury vapor lamp. For reproducibility, the light dose received by the sample after one pass was adjusted to about 1.2 J/cm 2 at a total intensity of about 10 W/cm 2 in the UVA + UVB + UVC ranges, the conveyor speed was kept constant at 5 m/min. The coatings were prepared in two sets of thicknesses, i.e. around 50 µm (thin films) and around 200 µm (thick films). The photochemical process was chosen because of its multiple advantages comparing to a conventional thermal process (time and energy savings, etc.). The obtained coatings were yellowish, transparent, smooth and have regular surfaces. Photographs of some obtained coatings are available in the supporting data. However, A-C6-2000/BD-1/2 was rough and opaque, due to the partial solubilization of the segregated hard segments of this oligomer in AcOBu.

Crosslinked NIPUA coatings

The conversions were calculated by FTIR by monitoring the evolution of the absorbance ascribed to the C-H bond deformation band in the plane of the C=C acrylate group at σ = 1410 cm -1 . The conversion χ was calculated as follows: For the NIPUA-C6-650 film, FTIR spectra were recorded for each side of the thin and thick coatings. The overlay of the bands at 1410 cm -1 is shown in Figure 3. No significant differences in conversion were noted at any interface or coating thickness. The study of other films confirmed these claims. Thus, we chose to calculate FTIR conversion only at the film/air interface of thin coatings.

The conversion values (χ) of the acrilic functions are depicted in Table 2. Overall, one can observe that χ values are dependent on the molecular weight of A-Ol. Indeed, A-Ol with molecular weight around 2000 g/mol (Cc=c > 2.0 meq/g) exhibited high conversion (χ > 90 %), whereas A-Ol with molecular weight around 5000 g/mol (Cc=c > 0.7 meq/g) exhibited lower conversion (χ ≈ 75 %). These conversions are in good agreement with the values in the literature for conventional PUAs systems. [START_REF] Fu | Research progress of UVcurable polyurethane acrylate-based hardening coatings[END_REF][START_REF] Oprea | Poly(urethane-methacrylate)s. Synthesis and characterization[END_REF][START_REF] Llorente | Study of the crosslinking process of waterborne UV curable polyurethane acrylates[END_REF] In order to discuss the crosslinking properties of the prepared films, we have defined 9(" ") as the average molecular weight between acrylate functions, i.e. knots of the crosslinked network. With the use of polyfunctional trimethylolpropane (: = 3), 9(" ") was estimated with respect to the theoretical functionality of the precursor A-C6-650/TMP-1/0.5 (: = 2,33), according to the following equation:

9(" ") = 2 × (" )
: (" ) Eq.7 with

("

) and : (" ) : the molecular weight and functionality of the A-C6-650/TMP-1/0.5 oligomer, respectively.

The swelling tests were conducted in THF, the percentages of extractables ( / ) and swelling (Q) are listed in Table 3. One can observe that the / values of the NIPUA coatings are below 13 %, and most of them are below 6 %, which is a characteristic of good crosslinked networks. Furthermore, these coatings did not undergo any significant degradation in THF. As expected, crosslinking density, which increases with decreasing Mc(A-A), had a clear impact on the swelling properties. Indeed, the swelling percentages of coatings with Mc(A-A) values around 2000 g/mol were lower than those of coatings with Mc(A-A) values around 5000 g/mol. Nevertheless, thick films, except NIPUA-C6-2000/BD-1/2 film, swell more in THF than their thin analogues with more and less the same amount of extractables. This complex phenomenon could be ascribed to samples geometric reasons. For Mc(A-A) values around 2000 g/mol, swelling percentages ranged from 24 to 45 % for thin films, and from 61 to 121% for thick films. For Mc(A-A) values around 5000 g/mol, swelling percentages varied from 127 to 232 % for thin films, and from 287 to 557 % for thick films. Thick NIPUA-C6-2000/BD-1/2 film, which has Mc(A-A) = 2800 g/mol, exhibited and intermediate swelling percentage (266%). However, its thin analogue was out of the trend (Q=f( Mc(A-A)) curves in the supporting data) and displayed a relatively high swelling percentage (281%). Table 3: Extractables and swelling percentages of NIPUA coatings.

Coating code

Mc(A-A)

(g/mol) 1 Thin films τEx (%) Q (%) Thick films τEx (%) Q (%) NIPUA-C6-

Thermal properties

The thermal stability of the synthesized NIPUA coatings was evaluated by TGA under nitrogen atmosphere. The temperatures at 5% of weight loss (T5%) are displayed in Table 4. Typical TGA curves are shown in Figures 4 and5. As with conventional polyurethane, [START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF][START_REF] Hwang | Enhanced thermal and surface properties of waterborne UVcurable polycarbonate-based polyurethane (meth)acrylate dispersion by incorporation of polydimethylsiloxane[END_REF] thermal degradation of NIPUA-Ol coatings is a two-step process, with degradation of the hard segment parts (HS, Tmax ≈ 320 °C) followed by the PTMO soft segment parts (SS, Tmax ≈ 410 °C). T5% ranged from 255 to 338 °C showing very good thermal stabilities. The A-Ol oligomers showed similar two-step degradation profiles, suggesting that crosslinking reaction has no significant influence on thermal stability. TGA curves showed also that NIPUA-650 series are less thermally stable in terms of weight loss than their NIPUA-2000 analogues, which is consistent with a higher concentration of urethane functions within the NIPUA-650 series. Table 4: Thermal properties of NIPUA coatings.

Coating code T5%

T# 3 (°C) The thermal properties of the NIPUA coatings were assessed by DSC. The thermal parameters are presented in Table 4. Typical DSC curves are displayed in Figure 6 and supporting data. The glass transition temperature of the soft segments (Tg (SS)) was observed for only three coatings in the scanned temperature range (T > -60°C). These are NIPUA-H12-650-kg and NIPUA-Pr-650-kg, made with asymmetrical BMC-H12 and BMC-Pr respectively, and NIPUA-C6-650/TMP-1/0.5 containing trimethylolpropane (TMP) as branching agent. These non-regular structures, bearing low molecular weight PTMO650, would promote SS and HS phase interactions and miscibility, which would increase values of Tg (SS). [START_REF] Das | Effect of symmetry and H-bond strength of hard segments on the structure-property relationships of segmented, nonchain extended polyurethanes and polyureas[END_REF] Tg (SS) of the other coatings were not observed in the same scanning conditions, likely due to the higher molecular weight of PTMO2000, their lower urethane content, and the use of symmetrical BMC-C6 promoting HS -HS interactions. [START_REF] Koshiba | Properties of ultra-violet curable polyurethane acrylates[END_REF] Thus, the Tg values of these materials were probably lower than -70°C, which is the limit of detection of the DSC system used.

ΔH# 3 (J/g) Tg 2 (°C) NIPUA-C6-650 282 - - - - 139 69 - NIPUA-C6-650-kg 304 - - - - 164 7
It can also be noted that NIPUA coatings with Mc(A-A) higher than 2000 g/mol exhibited semicrystalline behavior. The melting (Tm) and crystallization temperatures (Tc) ranging from 9 to 34°C and from -37 to 3°C, with associated enthalpy values of 21 to 47 J.g -1 , and of 17 to 46 J.g -1 , respectively, correspond to the organized parts of the PTMO soft segments. The melting temperature of the hard segments (Tm= 186°C) was observed only in the case of NIPUA-C6-2000/BD-1/2, i.e. where a chain extender (BD) is used, but with a low melting enthalpy (5 J.g -1 ) and without any recrystallization during the cooling cycle. This result is often observed in the case of conventional polyurethanes and is due to the low content of hard segments in these materials. Furthermore, an exothermic phenomenon was observed during the first heating cycle of the DSC analysis, which can be explained by the thermal conversion of the residual acrylate groups and/or the degradation of the photoinitiators.

Mechanical properties

The mechanical properties of the prepared thick NIPUAs films have been studied by the uniaxial tensile test. The results are depicted in Table 5. Typical stress/strain curves are presented in Figures 7 to 10.

For PTMO650-based coatings, the stress/strain curves are shown in Figure 7. The Young's modulus values of these NIPUA series show no significant dependence on the type of BMC used (E between 4.94 and 6.63 MPa, Table 5). These coatings exhibited a low elasticity, with εr ranging from 20 to 47%, as well as a low mechanical stress at break (σr between 1 and 2 MPa, Table 5).

The stress/strain curves of PTMO2000-based coatings are shown in Figure 8. Comparing to NIPUA-650 series, NIPUA-2000 coatings exhibited lower Young's modulus (E = 2 -4 MPa) and higher elongations at break (εr from 170 to 470 %, Table 5). The breaking stress σr ranged from 1.66 to 11.8 MPa. NIPUA based on BMC-C6 was the most elastic and the most resistant material, which can be explained by its symmetric structure leading to more HS-HS interactions. Furthermore, the shape of its tensile curve implies strain-induced crystallization and self-strengthen. For the same molecular weight, the incorporation of trimethylolpropane (TMP) into the NIPUA structures improves all the mechanical parameters of the photo-crosslinked films (Figure 9 and Table 5). Indeed, its use has a double effect: -the percentage of urethane (%HS) is doubled, resulting in an increase in -H bonds; -the crosslinking density increases due to its trifunctional nature.

The impact of the increase in %HS can also be seen by comparing the properties between NIPUA-C6-2000-kg (%HS = 4.4%, Mc= 5650 g/mol) and NIPUA-C6-650-5030 (%HS = 17%, Mc=5030 g/mol) coatings (Table 5, Figure 10). Stiffness properties are increased fourfold, i.e. E increased from 2.69 MPa to 9.22 MPa. However, strength properties (σr around 10.5 MPa) and elasticity (εr around 500 %) were quite similar.

NIPUA based on BD as the chain extender, exhibited Young's modulus E around 7 MPa, elongations at break εr around 300% and σr around 9 MPa (Figure 10, Table 5). Compared to NIPUA-C6-2000-kg, NIPUA-C6-2000/BD-1/2 exhibited higher percentage of hard segments (%HS), which

Strain (%)

NIPUA-C6-650/TMP-1/0,5 NIPUA-C6-650 explain its higher rigidity, and exhibited lower molecular weight between knots (Mc(A-A)), which explain its lower elasticity. Nevertheless, these two parameters do not appear to have any influence on the ultimate stress at break. In summary, the incorporation of urethane functions effectively improves the mechanical properties of NIPUAs coatings, whether through the incorporation of a chain extender (BD) or a crosslinking agent (TMP), or by increasing the amount of urethane groups within the polymer backbone. However, the average molecular weight between knots must be sufficient to afford the elasticity properties.

CONCLUSIONS

NIPUs oligomers with exclusively acrylate chain-ends (A-Ol) and controlled molecular weights were synthesized by transurethane polycondensation followed by reaction with acryloyl chloride. Ten NIPUs-acrylate coatings (NIPUAs) were prepared by photo-crosslinking of A-Ol formulations under a high-intensity UV system. Analysis of the thermal and mechanical properties of NIPUAs coatings highlighted the importance of the urethane function, especially for increasing strength and rigidity of the materials, without excessive loss of elasticity. Thus, we have successfully synthesized a range of coatings with thermal and mechanical properties in line with those of the flexible PUs currently developed on the market, which can be amorphous or semi-crystalline (T5% > 255°C, E = 2.6 -9.2 MPa, σr up to 11.8 MPa, εr = 20 -520 %) by a route that totally eliminates the use of isocyanates. Finally, some of the NIPUAs developed, in particular those based on the monomer BMC-C6, have biosourced carbon levels very close to 100%, where only the acrylate functions at the chain-ends derive from petroleum resources.

1 H 1 H 1 H

 111 NMR (300 MHz, CDCl3, δ): 4.67 (s, broad, 2H; NH), 3.65 (s, 6H; NH(CO)OCH3), 3.15 (m, 4H; NHCH2); 1.48 (m, 4H; NHCH2CH2), 1.32 (m, 4H; NHCH2CH2CH2). 13 C NMR (75 MHz, CDCl3, δ): 26.2, 29.9, 40.7, 52.0, 157.1 ; IR (ATR): ν∼3300 cm -1 (m; νNH), ∼1700 (s, νCO H-bonded) cm -1 , ∼1530 cm -1 (s, νNH bending). DSC: Tm=115°C. 4,4'-methylenebis(cyclohexylamine) (BMC-H12) -NMR (300 MHz, CDCl3, δ): 3.77 and 3.40 (m, 2H; NHCH); 3.66 (s, 6H; NH(CO)OCH3), 2.1 to 0.75 (20H; methylene and cycle CH and CH2). 13 C-NMR (75 MHz, CDCl3, δ): 156.4 (C=O), 51.9 (OCH3), 50.5 (NHCH), 47.1 (NHCH), 44.1 (NHCHCH2), 42.9 (NHCHCH2), 33.7 and 33.6 (CH), 33.4 (bridge CH2), 32.6 (CH), 32.0 (bridge CH2), 29.7 (CH2), 28.0 (CH2). DSC: Tm= 189 °C. Dimethyl Dicarbamate of Priamine 1074 (BMC-Pr) -NMR (300 MHz, CDCl3, δ): 4.68 (s, broad, 2H; NH), 3.65 (s, 6H; NH(CO)OCH3), 3.15 (m, 4H; NHCH), 2 to 1 (54H; CH and CH2), 0.87 (m, 6H, CH3). 13 C-NMR (75 MHz, CDCl3, δ): 157.2 (C=O), 52.0 (OCH3), 41.2 (NHCH2), 37.2 (CH2), 33.7 (CH2), 32.0 (CH2), 30.1 (CH2), 29.8 (CH2), 29.6 (CH2), 29.4 (CH2), 26.8 (CH2), 22.8 (CH2), 19.8 (cycle CH), 14.2 (CH3). DSC: Tm<-70 °C.

Scheme 1 .

 1 Scheme 1. Synthesis approach of acrylated NIPU oligomers.

  molecular weight of "PTMO + chain extender" mixture, with respect to their equivalent ratio. -= Molecular weight of BMC. -= Molecular weight of methanol.

  Jcis = 10 Hz) and δ = 5.81 ppm (signal "11", dd, R-OCOCHCHcisH, 3 Jcis = 10 Hz, 2J ≈ 1 Hz). 13C NMR analysis (supporting data) revealed the signals of the two acrylate carbons (δ = 130.5 and 128.6 ppm), as well as the quaternary carbon of the acrylate ester group (δ = 166.3 ppm).

Figure 1 :

 1 Figure 1: FTIR spectra of the oligomers H-C6-650 and A-C6-650.

Figure 2 : 1 H

 21 Figure 2: 1 H NMR spectra of H-C6-650 (A) and A-C6-650 oligomers (B).

  molar fraction; . = chain extender molar fraction, with " a + b = 1". * Partially soluble in DCM.

Scheme 2 .

 2 Photoinitiator s( 3,3 w%)

With 6 7 and 6 8 7

 8 the absorbance values of the δ(=C-H) band at 1410 cm -1 , of the starting A-Ol and the NIPUAs films formed after crosslinking, respectively. 6 % 8 and 6 8 % 8 are the absorbance values of the stretching band of the C-H sp3 bonds of these compounds.

Figure 3 .

 3 Figure 3. FTIR spectra of several interfaces of thin and thick films NIPUA-C6-650 before and after crosslinking.

  [START_REF] Assumption | Photopolymerization of urethane dimethacrylates synthesized via a non-isocyanate route[END_REF] Y = Yellow, S = Soft, SR = Semi-rigid, F = Fragile, T = Transparent, O = Opaque. * Estimated in relation to the theoretical functionality of the A-C6-650/TMP-1/0.5 oligomer (f = 2.33).

Figure 4 :

 4 Figure 4: TGA curves (solid) and their first derivative curves (dashed) of NIPUA coatings based on BMC-C6.

Figure 5 :

 5 Figure 5: TGA curves (solid) and their first derivative curves (dashed) of NIPUA-Ol coatings using different BMC and PTMO types.

Figure 6 :

 6 Figure 6: DSC thermograms of NIPUA-2000 film series. 1 st heating (solid curves) et 2 nd heating (dashed curves).

2 E

 2 = Young modulus; σr = breaking stress; εr = elongation at break. 3 %HS = Hard segment percentage. 4 Double bond concentration of the A-Ol oligomer. * Very fragile material. Value of the best test. ** Estimated through the theoretical functionality of the A-C6-650/TMP-1/0.5 precursor (f = 2,33 and Mn= 1750 g/mol).

Figure 7 :Figure 8 :

 78 Figure 7: Typical stress/strain curves of the NIPUA-BMC-650 series.

Figure 9 :

 9 Figure 9: Typical stress/strain curves of NIPUA with and without TMP.

Figure 10 :

 10 Figure 10: Typical stress/strain curves of NIPUA coatings with different urethane contents.

  Photo-curingCoatings NIPU

Table 2 :

 2 Conversion and appearance of NIPUA coatings.

	Coating code	CC=C 1 (meq/g)	DE 2 (%)	χ 3 (%)	Aspect 4	Thickness (µm)
	NIPUA-C6-650	2.4	45	> 95	Y, S, T	24 ± 8 194 ± 4
	NIPUA-C6-650-kg	2.6	53	> 95	Y, S, T	23 ± 4 153 ± 13
	NIPUA-H12-650-kg	2.1	68	90	Y, S, T	28 ± 4 219 ± 1
	NIPUA-Pr-650-kg	2.4	83	> 95	Y, S, T	40 ± 3 132 ± 24
	NIPUA-C6-650/TMP-1/0.5	3.0*	40	> 95	Y, SR, T	10 ± 3 131 ± 4
	NIPUA-C6-650-5030	0.9	26	84	Y, SR, T	24 ± 4 153 ± 6
	NIPUA-C6-2000-kg	0.8	52	75	Y, S, T	28 ± 4 160 ± 11
	NIPUA-H12-2000	0.8	62	73	Y, S, F, T	23 ± 3 165 ± 6
	NIPUA-Pr-2000	0.8	61	76	Y, S, F, T	27 ± 5 205 ± 5
	NIPUA-C6-2000/BD-1/2	1.6	40	84	Y, SR, O	23 ± 4 153 ± 9

1 Double bond concentration of A-Ol oligomers.

[START_REF] Oprea | Poly(urethane-methacrylate)s. Synthesis and characterization[END_REF]

Dry extract from A-Ol AcOBu formulations.

[START_REF] Maurya | A Review on Acrylate-Terminated Urethane Oligomers and Polymers: Synthesis and Applications[END_REF]

Conversion of acrylate double bonds estimated by FTIR.

Table 5 :

 5 Mechanical properties of NIPUA coatings.

	Coating	Mc(A-A) 1 (g/mol)	E 2 (MPa)	σr 2 (MPa)	εr 2 (%)	%HS 3 (%)	CC=C 4 (meq/g)
	NIPUA-C6-650-kg	1750	6.63 ± 0.90 1.15 ± 0.24	20 ± 5	12	2.6
	NIPUA-C6-650	1900	4,94 ± 0,39 0,96 ± 0,09	26 ± 5	8,7	2,37
	NIPUA-H12-650-kg	2100	6.34 ± 0.51 2.03 ± 0.05	47 ± 2	18	2.1
	NIPUA-Pr-650-kg	1850	6.32*	1.32*	29*	28	2.4
	NIPUA-C6-2000-kg	5650	2.69 ± 0.32 11.8 ± 3.5	470 ± 37	4.9	0.8
	NIPUA-H12-2000	5600	2.62 ± 0.39 1.66 ± 0.70	210 ± 99	7.3	0.8
	NIPUA-Pr-2000	5800	2.60 ± 0.91 1.78 ± 1.28 170 ± 110	14.4	0.8
	NIPUA-C6-650/TMP-1/0,5	1500	7,38 ± 0,77 2,39 ± 0,38	41 ± 8	22	3,00**
	NIPUA-C6-650-5030	5030	9.22 ± 2.46 10.2 ± 1.82	520 ± 51	17	0.89
	NIPUA-C6-2000/BD-1/2	2800	6.80 ± 0.58 9.17 ± 1.81	300 ± 37	18	1.61

[START_REF] Fu | Research progress of UVcurable polyurethane acrylate-based hardening coatings[END_REF]

Average molecular weight between two acrylate functions.

Average molecular weight between two acrylate functions.

Data availability

The processed data required to reproduce these findings are available to download from http://dx.doi.org/10.17632/7dnbdptv46.3.

Authors thank Mäder research company for the financial support. This manuscript is a tribute to the 50 year anniversary of the French Polymer Group (Groupe Français des Polymères -GFP).