Molecular dynamics predictions of thermal and mechanical properties of thermoset polymer EPON862/DETDA

We use molecular dynamics (MD) to perform an extensive characterization of the thermo-mechanical response of a thermoset polymer composed of epoxy EPON862 and curing agent DETDA. Our simulations, with no adjustable parameters, show that atomistic simulation can capture non-trivial behavior of amorphous thermosets including the role of polymerization degree, thermal history, strain rate and temperature on the glass transition temperature (Tg) and mechanical response (including ultimate properties) and lead to predictions in quantitative agreement with experiments. We find a significant increase in Tg, Young’s modulus and yield stress with degree of polymerization while yield strain is significantly less sensitive to it. For structures cured beyond the gel point (percolation of a 3D network) conversion degree and temperature affect yield stress in a similar way with yield stress linearly dependent on T−Tg; however, we find non-linear and non-universal relationship below the gel point. Our results show that a relative small variation in polymerization degree (∼5%) can explain the spread in experimental measurements of Tg and elastic constants available in the literature.