Influence of Ester Functionalization on Crystallization and Melting of Polyethylene: Insights from Coarse-Grained Modeling

Polyethylene is one of the most widely used polymers; however, only a small fraction of it is currently recycled. Incorporating degradable ester groups into the PE backbone can offer a means to enhance recyclability while maintaining targeted properties suitable for a broad range of applications. Herein, we use coarse-grained molecular dynamics simulations to characterize the effect of ester functionalization on the crystallization and melting processes in high-density polyethylene (HDPE) and low-density polyethylene (LDPE) mimics. The model is based on the united monomer model for polyethylene, which reproduces crystallization upon cooling from the melt state. We demonstrate an increase in density and a decrease in crystallinity for both HDPE and LDPE mimics with an increase in the ester-to-methylene ratio. We track the fraction of esters contributing to the nanoscale crystalline and amorphous regions during cooling and demonstrate the uniform partitioning of ester groups between these regions in both HDPE and LDPE mimics throughout the cooling processes. This uniform partitioning of ester beads results in an approximately linear decrease in melting and crystallization temperatures with an increase in ester fraction for both HDPE and LDPE mimics. Further, we analyze the stem length distribution upon crystallization and show that the presence of ester groups reduces the frequency of longer stems and decreases the average stem length, consistent with the reduction in crystallinity characterized by the average order parameter. Our model captures the key trends observed in experiments and contributes to the understanding of the crystallization and melting processes in linear and branched polyethylenes functionalized with esters.