Combined Molecular Dynamics and Synchrotron X-ray Analysis of Structure–Property Relationships in Nonaromatic Triazine-Based Epoxy Resins

This study investigated the effects of side-chain length on the thermomechanical and structural properties of a nonaromatic triazine-based epoxy resin, tris(2,3-epoxypropyl)isocyanurate (TEPIC). Three types of TEPIC with different side-chain lengths were cured with phthalic anhydride and characterized by mechanical testing, synchrotron wide-angle X-ray scattering (WAXS), and molecular dynamics (MD) simulations. Mechanical tests revealed that longer side chains reduced stiffness but improved ductility. MD simulations using the cured resin model showed that flexible long-chain systems suppressed void coalescence, supporting the observed mechanical behavior. Synchrotron WAXS measurements captured a clear structural evolution: short-chain systems exhibited ordered domains at low scattering angles, whereas long-chain systems formed relaxed, isotropic three-dimensional networks. The scattering spectra calculated from MD reproduced the experimental WAXS profiles with high fidelity, validating the cured resin MD models. Furthermore, MD analysis enabled direct assignment of the WAXS peaks to specific atomic-scale correlations, providing a molecular interpretation of the experimental diffraction features. This integrated MD–synchrotron approach bridges atomic structure and macroscopic mechanics, offering a predictive framework for designing advanced epoxy resins with tailored mechanical and optical performance.