Synthesis and crosslinking kinetic study of epoxidized and acrylated/epoxidized oligoisoprenes: Comparison between cationic and radical photopolymerization
Résumé
The photoinitiated polymerization of epoxidized hydroxytelechelic cis-1,4-polyisoprene and of a dual system (epoxidized/acrylated) telechelic cis-1,4-polyisoprene in the presence of 2,2-dimethyl-1,2-hydroxyacetophenone or/and hexafluoro-phosphate triarylsulfonium salt has been studied by real-time infrared spectroscopy. The synthesis of photosensitives oligoisoprenes was achieved by chemical modifications of hydroxytelechelic cis-1,4-polyisoprene obtained by controlled degradation of high molecular weight cis-1,4-polyisoprene. Then, the effect of light intensity, photoinitiator concentration, addition of reactive diluent and concentration of functional groups on the photopolymerization process was evaluated. Concerning the cationic process, the results showed that the kinetic profile improves when photoinitiator concentration and light intensity increase. The optimum concentration of triarylsulfonium salt used as photoinitiator was determined as 5% (w/w) and the optimum light intensity was 50 mW cm−2. Reactive diluent (3-ethyl-3-hydroxymethyl oxetane) addition greatly improves the ultimate conversion and the polymerization rate. Subsequently, the photopolymerization kinetic of a dual epoxidized/acrylated system was studied. The results obtained using different photoinitiator mixtures and different intensity of irradiation showed that the crosslinking of acrylate functions at the chain-end prevents the progression of the cationic process at the oxirane groups along the chain. Thus, the mobility of the cationic reactive centers was restricted by the crosslinking at the high conversion of the acrylate double bonds.