Exploring Cross-Link Density and Additive Effects on Mechanical and Morphological Behaviors of Cross-Linked Polymers

Abstract

Cross-linked thermoset polymeric materials are widely used in various engineering applications due to their excellent mechanical properties, thermal stability, and chemical resistance. Recent research highlights the role of cross-link density and additives in influencing segmental dynamics and thermomechanical behavior of polymers. This study employs coarse-grained molecular dynamics (CG-MD) simulations to explore the thermomechanical and morphologic behaviors of cross-linked polymers with molecular additives. Specifically, it is systematically investigated how cross-link density (c) and different additive concentrations (m) affect key glass-forming characteristics, along with the resulting changes in mechanical and morphologic properties of network materials as they approach their glass transition temperatures (T_g). Relatively weaker interaction between the polymer network and additives can lead to additive aggregation, significantly affecting the morphology and T_g as the m increases. Increasing c leads to an increase in both T_g and fragility while increasing m decreases them. The simulation reveals that both c and m moderately influence the mechanical properties (i.e., shear and tensile modulus) of cross-linked polymers with additives. This study provides valuable insights into how cross-link density and additive concentrations influence glass-forming and morphological behaviors, offering a molecular design strategy for developing advanced cross-linked thermosets.