How Polymer Chains Remember Their Crystalline Past: Simulations Uncover the Molecular Origin of Melt Memory.

Melt memory in semicrystalline polymers is the remarkable ability of polymer chains to retain structural information from a prior crystalline state after being heated above the melting temperature. This phenomenon can induce extraordinary self-nucleation and strongly influence crystallization kinetics and final material properties, yet its molecular origin remains unresolved. Here, using molecular dynamics simulations of linear polymer chains in which the strength of nonbonded interchain interactions is systematically tuned, we show that enhanced interchain attractions stabilize nanoscale regions of increased density and extended trans-planar conformations that persist in the melt, as revealed by analyzing the dynamics through a density-field approach. These residual ordered regions in the melt act as self-nuclei upon cooling, providing a molecular explanation for experimental observations of persistent melt memory in polar polymers. By varying a single chemically meaningful parameter, i.e., the strength of interchain attraction, our model bridges weakly interacting polyolefins and polymers with stronger dipolar or hydrogen-bonding interactions, establishing a direct link between molecular cohesion and memory retention. The results demonstrate that melt memory originates from the interaction-mediated survival of localized structural order in the melt rather than from a completely randomized chain state. These findings provide a molecular framework connecting the chemical structure, intermolecular forces, and macroscopic crystallization behavior, offering new principles for controlling polymer solidification and designing semicrystalline materials with tailored properties.