Influence of crosslinkable site position on the topological structure and mechanical properties of polymer networks:...

This study employs molecular dynamics simulations to investigate, from a microscopic perspective, the effects of crosslinkable site position, site distance, and crosslink density on the topological structure and mechanical properties of polymer networks. The central site system forms a compact and homogeneous network, characterized by a short average strand length 〈L_st〉, a low defect fraction (P_dl < 0.5), and a high network constraint (κ = 10.58). This distinct topology endows the system with a superior tensile stress response, pronounced nonlinear elasticity, and enhanced bond energy accumulation compared to the random site system. The structural relaxation behavior is further analyzed using the incoherent intermediate dynamic structure factor. The tensile stress-strain curves fitted using the semi-empirical Mooney-Rivlin equation show high C₁ and low C₂ parameters, indicating a strong network effect and reduced interchain entanglement. The prediction of the affine model and the phantom model implies network uniformity and consistency in regional and overall motion capabilities. Additionally, short crosslinkable site distances enhance chain confinement, tensile strength, and energy dissipation, while a monotonic enhancement in mechanical properties is observed with increasing crosslink density. These molecular-level insights link the nanoscale crosslink network topological structure to macroscopic functionality, providing valuable guidance for the rational design of high-performance crosslinked polymers.