Effective Cross-link Density: A Robust Metric for Structure-Property Relationship in Complex Polymer Networks

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 cross-link density (XLD). This study uses multi-scale molecular dynamics simulations to construct complex network structures such as acrylic-melamine systems and establish correlations between their microstructure and thermo-mechanical properties. By accounting for the elastic contribution of each cross-link point within the network, we modified the XLD and introduced effective XLD (XLDeff). Our findings reveal strong linear correlations between XLDeff and both elastic modulus and Tg, relationships that conventional XLD could not establish. This demonstrates the robustness of XLDeff as a predictive metric for thermo-mechanical properties across diverse cross-linking conversions and prepolymer systems. XLDeff thus serves as a valuable metric for the in-silico design and optimization of thermoset polymers with tailored thermo-mechanical properties.