Network development in mixed step-chain growth thiol-vinyl photopolymerizations

In this study, we develop a modeling framework based on combined kinetic and statistical modeling approaches to describe pregelation and postgelation network properties of polymerization kinetics dependent mixed step-chain growth polymerizations. Specifically, we utilize this modeling framework to predict the evolution of weight-average molecular weight, gel point conversion, and cross-linking density of binary and ternary thiol-vinyl systems, with simultaneous step and chain growth polymerizations. Conversion dependent kinetics and directionality of network structures are addressed in this study. We first determine polymerization kinetics driven probability parameters that define the nearest neighbor pairs. These probability parameters are then employed in a recursive statistical modeling framework to develop relationships that describe the network structure. The modeling predictions indicate that both thiol-acrylate and thiol-ene-acrylate systems provide a facile means to control network properties such as the gel point conversion and cross-linking density, with changes in monomer functionalities and their initial stoichiometric compositions. Thus, these novel thiol-vinyl systems provide a facile route to expand upon the property ranges that are available through either pure step growth or pure chain growth polymerizations.