Synthesis of CO ₂ -Based PPCP-Si Macrodiol and Its Application as a Macromolecular Plasticizer for Polyvinyl Chloride

As a commonly used thermoplastic, PVC suffers from intrinsic stiffness and therefore requires plasticizers to facilitate processing. Conventional small-molecule plasticizers (e.g., DOP, DBP) tend to migrate out of PVC over time. Polymeric plasticizers generally exhibit reduced migration; however, when incorporated into PVC at elevated loadings, their compatibility with the polymer matrix often deteriorates. To address these issues, a carbon dioxide-based polymeric diol, PPCP-Si macrodiol, was designed and synthesized. The material was obtained via a one-pot copolymerization of CO2, propylene oxide, phthalic anhydride, and hydroxyl-terminated polydimethylsiloxane, employing a metal-free catalyst system composed of bis(triphenylphosphine)iminium chloride and triethylborane. The resulting PPCP-Si macrodiols have a tunable molecular weight from 4k to 10k (dispersity <1.25) and its soft-to-hard segment ratio could be adjusted through reaction conditions. When utilizing them as a plasticizer for PVC, PPCP-Si macrodiol demonstrates outstanding plasticization efficiency in all synthesized molecular weight range. At a loading of 10 parts per hundred resin of a 4k molecular weight PPCP-Si macrodiol, the elongation at break of PVC increased 22-fold and the glass transition temperature was halved. The plasticized PVC exhibits minimal migration, with less than 1.2% weight loss after 350 h of solvent exposure. Scanning electron microscopy confirmed the good compatibility of PPCP-Si macrodiol with the PVC matrix. These results indicate that PPCP-Si macrodiol combines the advantages of both small-molecule and macromolecular plasticizers, delivering high plasticization efficacy and stability against migration even at high molecular weights. Therefore, it represents a promising candidate for enhancing PVC flexibility in industrial applications.