PVC Modification\nthrough Sequential Dehydrochlorination–Hydrogenation\nReaction Cycles Facilitated <i>via</i> Fractionation by\nGreen Solvents

Polyvinyl chloride (PVC) is the third most produced plastic\nworldwide.\nHowever, it is also among the least recycled plastics, and research\nin PVC upcycling appears to lag behind that of other commodity plastics,\nas processing PVC waste can be more challenging. The C–Cl bond\nwhich distinguishes PVC among common polyolefins imparts unique properties\nbut also causes difficulties when PVC is heated and/or in the presence\nof chemical agents. Generally, PVC has a propensity to undergo elimination\nreactions (via dehydrochlorination) forming conjugated CC\nbond sequences (“polyenes”) in the backbone <i>via</i> the release of HCl, thus complicating efforts for the\nthermomechanical reprocessing of PVC. We have found that these polyenes\ncan be hydrogenated to aliphatic segments (<i>i.e.</i>,\n−(CH<sub>2</sub>)<sub><i>n</i></sub>−) and\nthis process can be repeated over multiple cycles. These strategies\nare enabled using “green” solvents, specifically acetone\nand ethyl acetate (EtOAc), which can leach lower molecular weight\nfractions of PVC from both virgin PVC and commercial samples containing\nplasticizers and other additive(s). The recovered PVC extracts (“PVCe”)\nwere subjected to a reaction with NaOH in THF to produce a partially\ndehydrochlorinated PVC (DHPVC) that maintains the solubility of the\nparent PVCe. The obtained DHPVC is then treated with H<sub>2</sub>/[RhCl(PPh<sub>3</sub>)<sub>3</sub>] (<i>i.e.</i>, Wilkinson’s\ncatalyst) in EtOAc at 60 °C and 60 psi. The hydrogenated\nDHPVC [H<sub>2</sub>-DHPVC] obtained exhibits the solubility of PVCe,\nwhile the polyene segments in DHPVC have been fully deconjugated,\nas evidenced by UV–vis and FTIR spectra. H<sub>2</sub>-DHPVC\nalso showed a slight reduction in the glass transition temperature\n(<i>T</i><sub>g</sub>) compared to PVC or DHPVC from which\nit was obtained. The mild conditions allow for multiple cycles of\ndehydrochlorination–hydrogenation to be performed without degradation\nthrough oxidation or cross-linking causing insolubility. Furthermore,\nthe methods presented are amenable to large-scale processing.