Synthesis of new photocurable oligoisoprenes and kinetic studies of their radical photopolymerization

New photosensitive oligoisoprenes were synthesized by controlled degradation of high molecular weight cis-1,4-polyisoprene and successive chemical modification of the chain-ends. Oligomers with diacrylate extremities were synthesized, characterized, and used in photocrosslinking reactions in different conditions. The photoinitiated polymerization of the diacrylate oligoisoprenes was carried out using 2,2-dimethyl-2-hydroxyacetophenone (Darocur 1173) as initiator and the reaction was monitored by photocalorimetry-DSC and real time FTIR spectroscopy. The influence of oxygen, photoinitiator concentration, light intensity, diluting agent, and oligomers molecular weight on the reaction rate was investigated. It was found that the presence of oxygen does not influence the photopolymerization kinetics of the diacrylate oligoisoprenes. Maximum conversion was obtained for a photoinitiator concentration of 5% (w/w) and for a light intensity of 13.5 mW/cm2. Decreasing the formulation viscosity by addition of a diluent (1,6-hexanediol diacrylate) raised the photopolymerization rate, by increasing the reactive species mobility. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013