The Influence of the Thiol-ene Mechanism on Polymer Network Topology

Over the past few decades, thiol-ene photopolymerization has gained popularity for synthesizing polymer networks with near-ideal architectures and predictable mechanical properties. However, growing experimental evidence of heterogeneity varying with chemical design parameters in such networks has raised questions about the chemistry’s ideality and the broader relationship between network architecture and macroscopic properties. In this work, we use a computational framework based on generalizable Kremer-Grest bead-spring representations and Monte Carlo-based reactive molecular dynamics to simulate thiol-ene-like network formation. We compare ideal step-growth thiol-ene and step-growth/chain-growth mixed-mechanism photopolymerization pathways of common thiol-based chemistries across tetra-functional cross-linker concentrations. Our results reveal the influence of synthetic variables (i.e., monomer reactivity and composition) on conversion, gelation, network architecture, and bulk mechanical properties. Additionally, we confirm these computational findings with experimental analogues, which reveal reactive accuracy through qualitative agreement between functional-group conversion and gel points. Notably, we find that network defects form more prominently at low cross-linker concentrations and with high monomer rigidity in step-growth systems, the majority of which are dangling ends. In contrast, mixed-mechanism systems produce networks less sensitive to synthetic conditions but with more heterogeneous structures, as evidenced by strand-length distributions and Voronoi volume variance. These findings underscore the role of synthetic conditions and reaction pathways in tuning network topology and provide new insights for the rational design of photopolymerization chemistries.