The Influence of Thiol-Ene Mechanism on Polymer Network Topology

In recent years, thiol-ene photopolymerization has gained popularity as a synthesis method for networks with near-ideal architectures and predictable mechanical properties. However, there has been growing experimental evidence of heterogeneity varying with chemical design parameters in such networks, posing questions regarding the chemistry's ideality and the broader relationship between network architecture and macroscopic properties. In this work, we employ a computational framework to simulate the photopolymerization of thiol-ene-like networks to investigate the differences between networks formed via ideal step-growth (TE) and mixed mechanism (MM) polymerizations with thiol-ene based chemistry as a representative case. The step-growth and mixed mechanism polymerization pathways of thiol-ene chemistries are modeled using Kremer-Grest bead-springs and simulated using Monte Carlo-based reactive Molecular Dynamics. We reveal the influence of synthetic conditions on conversion, gelation, defectivity, network strand lengths, and spatial heterogeneity. Notably, we find that network defects are formed more prominently at low crosslinker concentrations and with high monomer rigidity in step-growth systems, the majority of which are dangling ends. In contrast, mixed mechanism networks are less sensitive to synthetic conditions but are more topologically and spatially heterogeneous. Our findings provide new insights for the rational design of photopolymerization chemistries.