Polymeric Dynamic Crosslinker for Upcycling of Fragile Low-Molecular-Weight Polypropylene

Abstract

While tremendous progress has been made in the dynamic crosslinking of polypropylene (PP) for plastic upcycling, the efficacy in addressing low-molecular-weight (MW) PP waste remains untapped. In this work, we demonstrate a simple and scalable method to convert brittle low-MW PP to vitrimer materials with enhanced thermal and mechanical properties, enabling their use in circular upcycling. Different from most previous work employing small-molecule crosslinkers, we prepare PP vitrimers (PPv) using polymeric crosslinkers, containing polyethylene glycol segments, which leads to altered crystalline structures and network formation. Importantly, by increasing the MW of crosslinkers from 200 to 1000 Da, the PPv exhibit more than 50 times increase in their fracture energy with strong ductility, which can be attributed to combined effects of strengthened amorphous regions of semi-crystalline PP domains and the phase separation between soft polyethylene glycol segments and the PP matrix. Moreover, when blending the PPv with high MW PP (PPh), the PPh/PPv blends show comparable elastic modulus, yield strength, and stretchability to that of the PPh, in sharp contrast to the widely known embrittlement of low-MW PP/PPh blends. These results demonstrate the use of polymeric dynamic crosslinkers as an important strategy for upcycling low-MW PP waste to value-added products.