Multiscale Simulation of the Depolymerization of Dehydrochlorinated Polyvinyl Chloride

The depolymerization of dehydrochlorinated polyvinyl chloride (DHPVC) via olefin metathesis offers a promising route for PVC recycling and upcycling. Using our MUltiscale SImulation frameworK (MUSIK), we investigate the molecular pathways governing C=C bond cleavage and key factors influencing depolymerization, including polyene content and PVC defect types. Our framework provides agreement with experimental findings without parameter fitting and explains that unproductive metathesis mechanisms can occur which ultimately slow depolymerization to negligible levels even when conjugated C=C bonds are present. Our results show that DHPVC depolymerization follows a preferential C=C bond cleavage order, beginning with terminal C=C bonds adjacent to CH₂ groups, followed by isolated C=C bonds, then terminal C=C bonds next to CHCl groups, with central C=C bonds cleaving last. Structural defects have minimal impact on reaction rates and molecular weights whereas polyene content significantly affects depolymerization. Higher polyene content (≥20%) accelerates reactions due to increased availability of C=C bonds but reduces the percentage of C=C bonds cleaved. Our results indicate that future efforts to improve depolymerization should focus on catalyst design to limit metathesis pathways that do not lead to depolymerization.