Nonclassical dependence of polymerization rate on initiation rate observed in thiol-ene photopolymerizations

A study was conducted to find the nonclassical polymerization rate on initiation rate observed in radical-mediated and step-growth thiol-ene photopolymerizations. The thiol-ene photopolymerization is found to proceed through sequential propagation and chain transfer steps while termination is assumed to occur by bimolecular recombination of radical species. The studies also found that in the event of an inadequate photoinitiator, the initiation rate would drop below its initial value and would limit the validity of any scaling based on initiation rates. The chemistry of both the thiol and vinyl functionalities is found to affect the scaling exponents. The deviation from classical bimolecular termination for a step-growth, such as thiol-ene photopolymerization, is unexpected as the molecular weight increases geometrically before gelation.