Influence of Crosslinking and Deformation on Polymer Crystallization and Melting: A Molecular Dynamics Study

We investigate the crystallization of crosslinked and entangled polymers under external deformation using a coarse-grained poly(vinyl alcohol) (CG-PVA) model and molecular dynamics simulations. Following uniaxial deformation, the systems are cooled at a constant rate to form semicrystalline states and subsequently heated at a constant rate to induce melting. For unstretched systems, network junctions do not significantly affect the nucleation temperature but increase the amorphous fraction and reduce the melting temperature. Uniaxial deformation accelerates nucleation and markedly increases the crystallization temperature, with more strongly crosslinked polymers exhibiting larger shifts that correlate with an enhanced orientation order parameter. We further compare cooling and heating cycles under constant strain and constant stress conditions. Under constant stress, crystallization induces additional elongation beyond the initial pre-stretch and leads to pronounced mechanical hysteresis upon heating, a behavior characteristic of reversible shape-memory materials.