Topologically reconfigurable polypropylene composites: Boronic ester crosslinking for concurrent mechanical reinforcement and circular reprocessability

Abstract

Environmental pressures on polypropylene are intensifying, yet its current recycling rates remain alarmingly low. The primary challenges lie in the high costs of recycling and the limited value of its reuse. In this work, we present a straightforward and feasible approach to construct dynamic crosslinking structures within polypropylene, enabling its efficient recycling. The dynamic boronic ester-based crosslinked polymers (PGCs) with excellent mechanical properties and recyclability are successfully developed by thermally initiated ring-opening reaction between glycidyl methacrylate-modified polypropylene (PP-g-GMA) and 4-carboxyphenylboronic acid pinacol ester (CAPE). PGC2 exhibits the most optimal thermal and mechanical properties with the T_g, tensile strength, and elongation at break of 20.4 °C, 33.7 MPa, and 55.8 %, respectively. Subsequently, the dynamic crosslinking system is introduced into the PP matrix to evaluate the mechanical properties of the composites. The boronic ester bonds promote the topological rearrangement of the network through ester exchange reaction, endowing the PP composites with good reprocessability. It retains tensile strength and elongation at break comparable to those of the pristine sample after two reprocessing cycles. This dynamic crosslinking mechanism provides innovative ideas for the development of low-cost and high-value recycled plastics.