Unraveling the Impact of Mechanism and Stoichiometry on Network Heterogeneity in Thiol-Ene Photopolymerizations

Network architecture evolution during photo-mediated gelation is critical for developing material chemistry-dependent processing guidelines in emerging fields such as photolithography and additive manufacturing. Although significant efforts have exploited gelation to control mechanical properties, molecular-level understanding of network architecture during gelation remains limited due to the challenges of characterizing network topology. To address this gap, we combine simulations and experiments of thiol-X network development to enable molecular-level insights into bulk material response. As model systems, we investigate differences between networks formed via ideal thiol-ene and mixed-mechanism melt-state polymerizations across varying crosslinker concentrations of di-ene, di-thiol, and tetra-thiol monomers. Through in-situ shear photo-rheology and in-silico molecular observations, we uncover the critical role of defect formation in defining gelation and final network architecture. Our findings reveal that ‘click’-based polymerizations can lead to strong deviations from ideal network formation. Finally, we provide insights into how this changes mechanical properties under load.