Effective Cross-Link Density as a Metric for Structure–Property Relationships in Complex Polymer Networks: Insights from Acrylic Melamine Systems

The structural complexities of polymer networks, i.e., multiple functional groups, diverse connection sites, and various defects, make it difficult to accurately describe their microstructure using theoretical models and traditional metrics such as the cross-link density (XLD). This study uses multiscale molecular dynamics simulations to construct complex network structures such as acrylic-melamine systems and establish correlations between their microstructure and thermomechanical properties. By accounting for the elastic contribution of each cross-link point within the network, we modified the XLD and introduced effective XLD (XLD^eff). Our findings reveal strong linear correlations between XLD^eff and both elastic modulus and T_g, relationships that conventional XLD could not establish. This demonstrates the robustness of XLD^eff as a predictive metric for thermomechanical properties across diverse cross-linking conversions and prepolymer systems. XLD^eff thus serves as a valuable metric for the in silico design and optimization of thermoset polymers with tailored thermomechanical properties.