Recyclable Cross-Linked Polyethylene from Self-Condensing Telechelic Polyethylene by Combining Olefin Metathesis, Hydrogenation, and Transesterification.

Abstract

Cross-linked polyethylene (PEX) is a high-performance thermoset with improved thermomechanical properties compared to its parent linear polymer, polyethylene (PE). The covalent bonds linking PEX, however, prevent efficient recycling or reprocessing, which represents a critical liability with respect to addressing the current global plastic waste crisis. Existing strategies to impart recyclability into PEX rely largely on radical chemistries, which are difficult to control and lead to side reactions. Here, leveraging the versatility of ruthenium-based catalysis, we prepare self-condensing PE with both telechelic and pendant hydroxyl and ester groups, respectively. Self-condensation of these polymers gives ester-cross-linked PEX, which can be recycled to the original linear polymer upon alcoholysis. In addition to chemical recyclability, these cross-linked materials exhibit stress relaxation at elevated temperatures, and we demonstrate their vitrimeric behavior in a simple healing experiment. Together, this study provides a design strategy for recyclable PEX and informs the design of other self-cross-linkable polymers.