Beyond the ring flip: A molecular signature of the glass-rubber transition in tetrafunctional epoxy resins

F Vukovic and SR Swan and LQ Reyes and RJ Varley and TR Walsh, POLYMER, 206, 122893 (2020).

DOI: 10.1016/j.polymer.2020.122893

The glass-rubber structural transition of epoxy resins is a critical quantity in the design of resins for thermally demanding applications. Currently, many high T-g epoxy resins exhibit reduced mechanical performance and are not suitable for structural applications. A present lack of understanding regarding the molecular origins of the glass- rubber transition, together with the cost of resin synthesis, has limited progress in the targeted development of novel, mechanically strong, high-T-g resins. Here, molecular dynamics simulations are used to predict the molecular-level structure and thermo-mechanical properties of three tetrafunctional epoxy resins. Via introduction of a conceptual framework of monitoring local molecular motions during molecular dynamics simulations, a characteristic molecular signature of segmental dynamics, correlating with the glass transition temperature, is identified. This computational framework provides a cost-effective strategy for rapidly assessing the comparative thermal performance of novel epoxy resins. Additionally, the impact of ring substitution on the thermo-mechanical properties of the naphthalene-based resins reveals promising directions for future design to yield desirable mechanical and thermal properties.

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