Le procédé de photopolymérisation a été optimisé en vue de l’élaboration de matériaux composites à matrice époxyde épais (> 1 mm) via un mécanisme cationique. L’étude des cinétiques de photopolymérisation de deux résines époxydes (glycidyl éther et cycloaliphatique) a montré que l’ajout d’un renfort de microsphères de silice induit un gradient de conversion dans l’épaisseur du matériau en raison d’un phénomène d’absorption et/ou de diffusion de la lumière, ce dernier étant d’autant plus important que l’écart d’indice de réfraction entre la charge et la matrice est élevé. Cependant, cette hétérogénéité de conversion a pu être compensée par une réaction de postpolymérisation à température ambiante. Une analyse des propriétés mécaniques a ensuite montré qu’il est possible d’obtenir par photopolymérisation des matériaux composites épais réticulés de façon homogène et dont la rigidité est augmentée par la présence du renfort. Enfin, la stratégie d’égalisation des indices de réfraction de la charge et de la matrice, couplée à une photopolymérisation cationique frontale induite par voie radicalaire (RICFP), ouvre des perspectives intéressantes en vue de l’élaboration de photocomposites de plusieurs centimètres d’épaisseur en appliquant uniquement un stimulus lumineux. / The photopolymerization process has been optimized for the elaboration of thick epoxy composite materials (> 1 mm) through a cationic mechanism. The study of the photopolymerization kinetics of two epoxy resins (glycidyl ether and cycloaliphatic) has shown that the addition of a silica microsphere reinforcement induced conversion gradient in the material thickness, resulting from a light absorption and/or scattering phenomenon. The light scattering is all the more important as the refractive index gap between filler and matrix is high. However, this conversion heterogeneity has been compensated by a postpolymerization reaction at room temperature. Then, the analysis of the mechanical properties has shown that it was possible to obtain thick composite materials homogeneously crosslinked and whose rigidity was increased by the presence of the filler. In addition, the strategy of equalizing the filler and matrix refractive indices, coupled with the radical induced cationic frontal polymerization (RICFP) opens interesting perspectives for the development of photocomposites several centimeters thick using only a light stimulus.

Cationic photopolymerization of multifunctional epoxides is very useful for efficient cure at room temperature and has been widely used in coatings and adhesives. Despite excellent properties of the final cured polymers, cationic photopolymerizations of epoxides have seen limited application due to slow reactions (relative to acrylates) and brittleness associated with a highly crosslinked, rigid network. To address these issues, two reaction systems were studied in this thesis: photoinitiated cationic copolymerizations of a cycloaliphatic diepoxide with epoxidized elastomers and acrylate/epoxide hybrid photopolymerizations. Oligomer/monomer structures, viscosity, compositions, and photoinitiator system were hypothesized to play important roles in controlling photopolymerizations of the epoxide-based mixtures. A fundamental understanding of the interplay between these variables for the chosen systems will provide comprehensive guidelines for the future development of photopolymerization systems comparable to the epoxide-based mixtures in this research. For diepoxide/oligomer mixtures, the observed overall enhancement in polymerization rate and ultimate conversion of the cycloaliphatic diepoxide was attributed to the activated monomer mechanism associated with hydroxyl terminal groups in the epoxidized oligomers. This enhancement increased with increasing oligomer content. The mixture viscosity influenced the initial reactivity of the diepoxide for oligomer content above 50 wt.%. Real-time consumption of internal epoxides in the oligomers was successfully determined using Raman spectroscopy. Initial reactivity and ultimate conversion of the internal epoxides decreased with increasing the diepoxide content. This trend was more pronounced for the oligomer containing low internal epoxide content. These results indicate that the reactivity of the hydroxyl groups is higher toward cationic active centers of the diepoxide than those of the internal epoxides in the oligomers. These conclusions are consistent with physical property results. The enhanced fracture toughness and impact resistance were attributed to multimodal network chain-length distribution of copolymers containing the oligomer content between 70% and 80%. For acrylate/epoxide hybrid mixtures, diacrylate oligomers significantly suppressed reactivities of cycloaliphatic mono/diepoxides, which was attributed to high mixture viscosity and highly crosslinked acrylate network. In this case, the dual photoinitiator system did not favor the epoxide reaction. Depending on the monovinyl acrylate secondary functionalities, enhanced reactivity and ultimate conversion of the diepoxide were attributed to a combined effect of a reduced viscosity and the radical-promoted cationic polymerization associated with the dual photoinitiator. The retarded and inhibited diepoxide reactivities with ether and urethane secondary groups were attributed to solvation and nucleophilicity/basicity effects, respectively. The influence of the diepoxide on the acrylate reactivity was attributed to dilution and polarity effects. In this case, high concentration of the free-radical photoinitiator is required for the dual photoinitiator system. Physical properties of hybrid polymers also varied with acrylate structures and monomer composition. Dynamic modulation methods were proposed to enhance the diepoxide reactivity and final properties in the presence of urethane acrylates.

Made available in DSpace on 2014-08-20T14:30:15Z (GMT). No. of bitstreams: 1 Dissertacao_Fernanda_Barbosa_Leal.pdf: 806160 bytes, checksum: 37717162c453100433c520a8c9d199ef (MD5) Previous issue date: 2012-12-19 / The aim of this study was synthesize, characterize and photopolymerize an alternative monomers for use in dentistry. Three siloxane-oxirane monomers were synthesized and the products conversion was followed by Fourier-transform infrared spectroscopy. The products obtained were characterized by 1H and 13C NMR and evaluated for viscosity and refractive index. The polymerization was evaluated by formulating of two experimental photoinitiation systems wich varied for the presence of 1,2 ethanediol. A ternary system with camphorquinone (CQ), ethyl 4-dimethylaminobenzoate (EDAB) and diphenyliodonium hexafluorphosphate (DPI) was used as control. The degree of conversion was accessed by FTIR and DSC-PCA. The NMR confirmed the synthesis success with 75, 87 and 55% yield for the monomers synthesized. Moreover, the presence of 1,2 ethanediol increase the degree conversion of the siloxane-oxirane monomers. This study showed simple and effective way to synthesize siloxane-oxirane monomers with a high potential for application in dental materials / O objetivo deste estudo foi sintetizar, caracterizar e fotopolimerizar monômeros alternativos para aplicação em Odontologia. Três monômeros siloxano-oxiranos foram sintetizados e a conversão de produtos foi acompanhada por espectroscopia de infravermelho por transformada de Fourier. Os produtos obtidos foram caracterizados por 1H e 13C RMN e avaliados quanto à viscosidade e índice de refração. Para investigar a polimerização, dois sistemas experimentais de fotoiniciação foram formulados, variando quanto à presença de 1,2 etanodiol. Um sistema ternário composto por canforoquinona (CQ), 4-dimetilaminobenzoato (EDAB) e difeniliodonio hexafluorfostato (DPI) foi utilizado como controle. O grau de conversão foi obtido por FTIR e DSC-PCA. As análises de RMN confirmaram a obtenção dos produtos com 75, 87 e 55% de rendimento. Além disso, a presença de 1,2 etanodiol aumentou o grau de conversão dos monômeros siloxano-oxiranos. Este estudo demonstrou um método simples e eficaz para sintetizar monômeros siloxano-oxiranos com grande potencial para aplicação em materiais dentários

Les procédés de photopolymérisation connaissent un développement important avec des applications considérables dans le milieu industriel en raison de ses avantages économiques et écologiques. Les réactions de photopolymérisation sont très représentées, elles reposent sur l’utilisation d’un composé ou d'un système photosensible sous irradiation, générant des espèces réactives capables d’amorcer la polymérisation et de réagir avec le monomère. Le principal objectif de ce travail de thèse consiste à développer des molécules efficaces comme photoamorceurs (PA) pour la photopolymérisation radicalaire (FRP) d’une part et la photopolymérisation cationique (CP) ou la photopolymérisation cationique sensibilisée par les radicaux (FRPCP) d’autre part. Nous nous sommes intéressés à des systèmes amorceurs hautes performances absorbant fortement dans le domaine du visible et permettant l’utilisation de lampes non nocives et à faible consommation d'énergie : les diodes électroluminescentes (LED). Ainsi, un procédé original portant sur la combinaison de la photopolymérisation radicalaire et la photopolymérisation cationique en une seule étape a été examiné. Cette approche a fait appel à la synthèse de réseaux interpénétrés de polymères (RIP) comportant les propriétés spécifiques de chaque polymère. Les efforts ont été consacrés au développement de nouveaux composés avec de nouvelles structures chimiques et d’excellentes propriétés d’absorption de lumière avec de coefficients d’extinctions molaires très élevés.Des systèmes construits sur l’utilisation de différentes structures comme photoamorceurs ont pu être mis au point dans le cadre de cette thèse. La possibilité d’utiliser des colorants présentant un caractère push-pull, ou des colorants étant caractérisés par une structure polyène ou une structure polyaromatique a pu être considérée. Egalement, des structures à base de xanthène sensibles dans le domaine proche visible ont pu être proposées. De plus, ce travail a permis d’étudier de nouveaux systèmes photoamorceurs à base de structures minérales telles que les polyoxométallates ou les pérovskites. Ainsi, la possibilité de proposer de nouveaux sels d’iodonium à base de coumarine a pu être démontrée. Des meilleures performances ont été atteintes en utilisant des systèmes photoamorceurs à deux composants (PA/Ph2I+) ou à trois composants (PA/Ph2I+/additif) dans des conditions d’irradiation douce. Afin d’étudier et caractériser ces photoamorceurs, la cinétique de la réaction de photopolymérisation a été suivie par spectroscopie infrarouge à transformée de Fourier (RT-FTIR). Les radicaux générés ont été détectés par résonance paramagnétique électronique (RPE). La photolyse laser éclair (LFP) a été utilisée comme technique complémentaire pour étudier l’efficacité et la réactivité de radicaux générés. / The photopolymerization reaction is used in an increasing number of industrial applications because of the remarkable performance of the process. The photopolymerization reactions require the presence of photosensitive compounds. These latter can absorb light and participate in the photoinitiation through the generation of reactive species. The main objective of this PHD was to develop efficient molecules as photoinitiators (PI) for the free radical photopolymerization (FRP), the cationic photopolymerization (CP) and the free radical promoted cationic photopolymerization (FRPCP). We were interested in new high performance photoinitiating systems (PISs) exhibiting excellent light absorption properties (especially in the visible wavelength range). The photopolymerization must be carried out under soft irradiation conditions (non harmful lamps, low energy consumption and low intensity sources: light-emitting diodes LED). Thus, a novel method involving concomitant radical/cationic photopolymerization in one step was examined. This approach involves the synthesis of interpenetrating polymer networks (IPNs) comprising the specific properties of each polymer. The efforts have been devoted to the development of new compounds with new chemical structures and excellent light absorption properties with high molar extinctions coefficients.Many PISs based on different photoinitiators structures have been developed in this work. The possibility to use dyes having a push-pull character, or dyes being characterized by a polyene or polyaromatic structures were considered. Also, originals xanthenes derivatives sensitive in the visible region have been proposed. In particular, this work has enabled the study of new PISs based on inorganic structures such as polyoxometalates and perovskites. Thus, the possibility to propose new iodonium salts based coumarin could be demonstrated. The best performance was achieved using two-components (PI/Ph2I+) or three-components (PI /Ph2I+/additive) photoinitiating systems under soft irradiation conditions. The kinetics of photopolymerization were evaluated using real time FTIR spectroscopy. The generated radicals were observed using the electron spin resonance (ESR) technique. The laser flash photolysis (LFP) was used as a complementary technique to study the efficiency and the reactivity of radicals generated.