Ozonolysis as a Pathway for the Depolymerization and Chemical Recycling of Polyvinyl Chloride

Depolymerization is a key pathway in the transition to polymer circularity. By breaking down polymers into their original (or new) building blocks to create new products, the polymer "cycle" can be closed. However, polyvinyl chloride (PVC), a ubiquitous thermoplastic, has been largely absent from research in depolymerization, although it has some unique advantages compared to other commodity vinyl polymers. Here, we present methods for depolymerizing PVC via ozonolysis, a well-established and practiced method for the oxidative cleavage of alkenes. By intentionally introducing sequences of conjugated C═C bonds to produce dehydrochlorinated PVC (DHPVC), the sites are introduced into the polymer backbone that are readily cleaved by ozone (O₃). Subsequently, an oxidative workup with conc. H₂O₂ results in terminal carboxylic acids. These methods resulted in molecular weight reductions on the order of 5-8 (i.e., ∼12%-20% of the initial value), depending on the source PVC used. A key achievement was the generation of a liquid/waxy "ultra-low-molecular-weight" PVC product, which has been previously unreported. Our methods successfully minimize waste while creating new and potentially valuable products. The depolymerization products formed from PVC could serve as plasticizers or feedstocks for additional chemical transformations.