Polypropylene-based transesterification covalent adaptable networks with internal catalysis

Abstract

Although polypropylene (PP) has long been one of the most widely used plastics worldwide, achieving its efficient upcycling is still a critical challenge. As an emerging class of dynamic crosslinking structures that combines the advantages of thermoplastics and thermosets, covalent adaptable networks (CANs) present a viable approach towards this problem. In this work, the internal catalytic activity of anhydride side groups based on neighboring group participation (NGP) is demonstrated by small molecule model studies. Through the facile reaction of 1,6-hexanediol and maleic anhydride grafted PP, transesterification PP-CANs were successfully constructed without using external catalysts. Their crosslinking degrees were adjusted by changing the concentration of the diol crosslinker. The rheological characteristics of PP-CANs could be modulated in the domain depicted by monoesterified PP without networks and imide-crosslinked PP without dynamics. The introduction of CANs improved the mechanical performance of PP while preserving its competitive thermal and processing properties. The transesterification with NGP in this work develops a simple way to directly obtain PP-CANs from maleic anhydride grafted PP without using undesirable external catalysts, providing an attractive potential solution for PP upcycling.