The selective and sequential chemical recycling of commodity polymers with imino-indole zinc(ii) catalysts

Abstract

Chemical recycling of plastic waste will play a key role in both decoupling the plastics economy from fossil feedstocks and addressing growing global plastic pollution. Real-world plastic waste streams, however, are complex and heterogeneous, which presents a serious challenge to established chemical recycling methods. Here, we present a series of zinc complexes that show high activity for the chemical recycling of poly(lactic acid) (PLA), bisphenol A polycarbonate (BPA-PC), and poly(ethylene terephthalate) (PET). Crucially, the most active of these catalysts is capable of selectively deconstructing a mixed feed of these polymers in succession with selectivity governed by careful modulation of reaction temperature. This sequential approach allows for the products of each reaction to be isolated in high yields without the need for complex separations. Further, high activity is demonstrated for the direct depolymerization of PLA to lactide. This work demonstrates the feasibility of sequential chemical recycling of mixed plastic waste as a tool for a more circular plastics economy.