Kinetics of thiol-ene and thiol-acrylate photopolymerizations with real-time Fourier transform infrared

We used real-time Fourier transform infrared to monitor the conversion of both thiol and ene (vinyl) functional groups independently during photoinduced thio-lene photopolymerizations. From these results, the stoichiometry of various thiol-ene and thiol-acrylate polymerizations was determined. For thiol-ene polymerizations, the conversion of ene functional groups was up to 15% greater than the conversion of thiol functional groups. For stoichiometric thiol-acrylate polymerizations, the conversion of the acrylate functional groups was roughly twice that of the thiol functional groups. With kinetic expressions for thiol-acrylate polymerizations, the acrylate propagation kinetic constant was found to be 1.5 times greater than the rate constant for hydrogen abstraction from the thiol. Conversions of thiol-acrylate systems of various initial stoichiometries were successfully predicted with this ratio of propagation and chain-transfer kinetic constants. Thiol-acrylate systems with different initial stoichiometries exhibited diverse network properties. Thiol-ene systems were initiated with benzophenone and 2,2-dimethoxy-2-phenylacetophenone as initiators and were also polymerized without a photoinitiator. (C) 2001 John Wiley & Sons, Inc.