Controlled thermal depolymerization of polystyrene using metal-organic frameworks

Chemical recycling of polystyrene (PS), one of the most important and versatile plastic materials, is vital for reducing plastic waste, mitigating environmental impacts, and providing economically viable solutions that support a sustainable future. The ongoing efforts in PS depolymerization promise to enhance this process as a key technology in the transition towards a circular society. However, the highly durable nature of PS composed of only hydrocarbon backbones hampers the implementation of its chemical recycling. Multiple radical mechanisms involved in the pyrolysis of PS cause a broad product distribution, which considerably decreases the recovery yield of desired monomer. Here we show a methodology to realize the highly efficient thermal depolymerization of PS mediated by nanoporous metal−organic frameworks (MOFs). Nanoconfinement of PS into a MOF enables a consolidation of complex degradation pathways in the nanochannels, restraining the formation of styrene oligomers as unnecessary heavy oil components, but affording a styrene monomer selectively. This novel protocol by leveraging nanoconfinement effects on polymer degradations demonstrates remarkable depolymerization behaviours, just by treating MOFs and PS at elevated temperatures, representing the potential to become a game-changing technology in chemical recycling of plastic waste.