Crystallization of cross-linked polyethylene by molecular dynamics simulation

Abstract

The crystallization of polymers is not, despite its importance in science and engineering, entirely understood due to the challenge of tracking the behavior of individual polymer chains in the crystallizing melt. However, increasing computational resources have brought the crystallization process within reach of molecular simulations, and several groups have published simulations of crystal nucleation and growth in polymers. Yet, these studies have focused on linear polymer chains, and no results have been reported on cross-linked polymers, which are common in everyday applications. Here, we perform molecular dynamics simulations of the homogeneous crystallization of cross-linked polyethylene at high undercooling. Large cross-link densities cause the crystallization to slow down and reduce the final degree of crystallization. As expected, cross-links are rejected from the crystals into the amorphous phase. We observe that at all cross-link densities the intercrystalline amorphous phase is characterized by a single distribution of free segment lengths (amorphous segments with no cross-links). The findings provide a basis for detailed computational studies of semi-crystalline cross-linked polymer systems.