2 research outputs found
Development of an Oxidative Photopolymerization Process of Thiol Derivates Under Air : Towards Dynamic Poly(disulfide) Coatings
Ces travaux de thĂšse portent sur le dĂ©veloppement dâun procĂ©dĂ© de photopolymĂ©risation de films poly(disulfure) en une seule Ă©tape. Pour la premiĂšre fois, un film poly(disulfure), sec aprĂšs seulement quelques minutes dâirradiation UV, a Ă©tĂ© obtenu par oxydation de dĂ©rivĂ©s thiol sous air en prĂ©sence dâun photogĂ©nĂ©rateur de base (PBG). Une investigation poussĂ©e du mĂ©canisme dâoxydation de monomĂšres thiol sous air a permis dâidentifier deux paramĂštres clefs : la prĂ©sence de la superbase dans le milieu libĂ©rĂ©e aprĂšs irradiation du PBG et une bonne permĂ©ation de lâoxygĂšne. Il a Ă©galement Ă©tĂ© dĂ©montrĂ© quâun second mĂ©canisme menant Ă la formation de ponts disulfure a lieu par arrachement dâhydrogĂšne des fonctions thiol par les rayons UV les plus Ă©nergĂ©tiques. La prĂ©dominance de ces mĂ©canismes dĂ©pend de la source dâirradiation choisie. Ce procĂ©dĂ© a Ă©tĂ© appliquĂ© avec succĂšs Ă une gamme de monomĂšres et oligomĂšres thiol, permettant une modulation des propriĂ©tĂ©s finales du film selon les composĂ©s utilisĂ©s. Une seconde partie de la thĂšse a portĂ© sur la photopolymĂ©risation de rĂ©sines commerciales poly(disulfure) liquides fonctionnalisĂ©es par des groupements thiols. Le caractĂšre dynamique des ponts disulfure prĂ©sents avant irradiation a menĂ© Ă lâobservation de deux comportements : une photopolymĂ©risation oxydative des fonctions thiol sous irradiation LED Ă 365 nm en prĂ©sence de PBG ou une photorĂ©ticulation par rĂ©arrangement des liaisons disulfure sous irradiation UV en absence de PBG. Enfin, lâeffort de valorisation des films poly(disulfure) sâest traduit par lâobtention de motifs poly(disulfure) par photolithographie UV et la dĂ©gradation de ces films en prĂ©sence dâun agent rĂ©ducteur.This thesis reports an innovative single-step photopolymerization process of poly(disulfide) films. A dry poly(disulfide) film has been obtained after only few minutes of UV irradiation via photobase-catalyzed thiol oxidative coupling under air. Two critical parameters were identified by an in-depth investigation of the thiol oxidative mechanism under air: the presence of the superbase released after irradiation of the photobase generator (PBG) and a good atmospheric oxygen permeability. It has also been demonstrated that a second mechanism leading to the formation of disulfide bridges takes place by thiol photolysis when irradiated with deep UV. The predominance of these mechanisms depends on the source of irradiation used. This process has been successfully applied to a range of thiol monomers and oligomers, making it possible to tailor final properties of the film depending on the compounds used. A second part has been focused on the photopolymerization of commercial liquid poly(disulfide) resins with terminal thiol functions. The dynamic behavior of disulfide bridges has induced two different results: an oxidative photopolymerization of thiol functions under LED irradiation with PBG and a photo cross-linking by rearrangement of disulfide bounds under UV irradiation without any PBG. Finally, in order to value the interest of these photogenerated poly(disulfide), a photopatterned film has been successfully obtained and reductive cleavage of S-S bonds has led to film degradation
Self-Photopolymerization of Poly(disulfide) Oligomers
International audienceBase catalyst and oxidant are usually necessary to promote the polymerization of poly(disulfide) oligomers through oxidative coupling of the terminal SH groups into Sâ S bonds. In this study, we prove that self-polymerization of bifunctional (disulfide) oligomer films can take place in a matter of minutes under UVC irradiation (254 nm, 10.5 mW cm â2). The resulting insoluble polymer is characterized using solid-state NMR, 1 H T 2 NMR relaxation measurements, thermal analysis, and Fourier-transform infrared spectroscopy and proves to have similar composition as a model poly(disulfide) prepared under oxidative conditions, but distinct physical properties. These differences are explained by a change in polymer architecture due to a higher ratio of cyclization relative to linear polymerization. Homolytic photocleavage of internal SâS bonds creates thiyl groups close to each other, driving an increased kinetic feasibility for the cyclization reaction by radical coupling. The subsequent formation of mechanically interlocked macrocycles (polycatenane network) is proposed to account for film properties analogous to those of a cross-linked polymer