Correlating Chlorinated Polyethylene Molecular Structure to Compatibilization Efficiency for Mixed Polymer Waste

Abstract

There is growing interest in the management of end-of-life plastic waste due to the lack of recycling of these materials into valuable products. This is due, in part, to the challenge of waste plastics collection, sorting, and limitations arising from the immiscibility of reprocessed plastic blends. Mixtures of these immiscible polymer components have poor properties due to weak interfaces, driven by phase separation. To address this, compatibilizers are often used to strengthen the interface between phases and stabilize the blend morphology. Previous research by our group has examined the ability of chlorinated polyethylene (c-PE) to compatibilize polyvinyl chloride (PVC) and polyolefin elastomers (POE). However, the specific molecular level processes that improve the interface of these amorphous-semicrystalline materials are not fully understood. To address this knowledge gap, a series of gradient c-PE copolymers were synthesized via ring-opening metathesis polymerization (ROMP) with varying ratios of dichlorinated cyclooctene and cyclooctene monomers. The ability of these polymers, with molar masses ranging from ~25-150 kg/mol, to strengthen the PVC/POE interface were compared to that of commercial blocky c-PEs. The results of this study elucidate the role of crystallinity and molecular sequence distribution of the compatibilizer on its efficacy as a compatibilizer. Herein, we show that the blockiest and most crystalline commercial samples exhibit the greatest improvement in interfacial adhesion whereas the synthesized gradient copolymer compatibilizers increase interfacial adhesion as a function of increasing PE-like segment block length. This indicates that while co-crystallization between semicrystalline components is important in compatibilization, entanglement between polymer phases is also necessary and may be notably impacted by the comonomer sequence distribution along the compatibilizer backbone. These studies provide insight into the molecular design and crucial molecular-level processes that drive the development of morphology and properties of compatibilized phase-separated amorphous-semicrystalline polymer blends, including those that are most relevant for mixed waste streams in polymer recycling.