Degradation of Polyvinyl Chloride by Sequential Dehydrochlorination and Olefin Metathesis

Abstract

Polyvinyl chloride (PVC) is a problematic waste plastic with limited options for recycling or upcycling. Herein, we demonstrate preliminary results in breaking down the long carbon chains of PVC into oligomers and small organic molecules. First, treatment with a substoichiometric amount of alkali base effects elimination of HCl to form a salt and creates regions of conjugated carbon-carbon double bonds, as determined by 1H NMR and UV-Vis spectroscopy. Olefin cross metathesis with an added partner alkene then cleaves carbon-carbon double bonds of the polymer backbone. Addition of allyl alcohol to the dehydrochlorination step introduces allyloxy groups by substitution of allylic chlorides. Subsequent metathesis of the pendant allyloxy groups provides a reactive terminal alkene to promote insertion of the metathesis catalyst onto the olefins in the all-carbon backbone. The products obtained are a mixture of PVC oligomers with greatly reduced molecular weights and a small-molecule diene corresponding to the substituents of the added alkene, as evidenced by 1H and DOSY NMR and GPC. This mild procedure provides a proof of concept towards harvesting carbon resources from PVC waste.