Effects of Reactivity Ratios on Network Topology and Thermomechanical Properties in Vinyl Ester/Styrene Thermosets: Molecular Dynamics Simulations

Styrene-based thermoset polymers using vinyl ester crosslinkers offer the potential ability to tune material properties via control of network topology, measured primarily by the distribution of poly(styrene) molecular weight between vinyl esters. Clearly, demonstrating a relationship between topology and properties in the glassy state has so far proven difficult using experimental approaches. Here, an approach to control network topology in molecular simulations of randomly crosslinking systems via relative reactivity is presented. Several models of nearly fully cured (vinyl ester)/styrene (VE/ST) thermosets at fixed monomer composition but with a large range of distributions of molecular weight between crosslinks, M-c, are generated. It is found that fully cured VE/ST thermosets have glass transition temperatures and glassy Young's moduli that are insensitive to M-c distributions at fixed monomer composition. Using extreme cases of relative reactivity, it is also established that glassy-state thermomechanical properties are sensitive to the overall density of crosslinks.