Highly Branched Polycaprolactone/Glycidol Copolymeric Green Plasticizer by One-Pot Solvent-Free Polymerization

This study aims to develop a simple, low-cost method for synthesis of highly branched polycaprolactone (hbPCL) for use as effective "green" plasticizers for poly(vinyl chloride) (PVC). We demonstrate the facile synthesis of hbPCL with tunable molecular architecture using glycidol as a branching monomer. A series of hbPCLs is prepared via one-pot, solvent-free copolymerization of ε-caprolactone and glycidol, wherein the molecular architecture is readily controlled by varying the molar ratio of glycidol to ε-caprolactone. Further, studying the kinetics of copolymerization reveals the preferential reaction of glycidol over ε-caprolactone, resulting in a multiarm star-like copolymer after the ring-opening of the two monomers. The crystallization ability of hbPCL is found to gradually weaken with the introduction of the branching structure, and its molecular mobility is improved substantially by esterification with butyric anhydride, following which a maximum mobility is realized at an intermediate level of branching. The butyl-esterified hbPCL (hbPCL-C4) is miscible with PVC, and their mixtures have excellent flexibility comparable to that of PVC/bis(2-ethylhexyl) phthalate (DEHP). In particular, the stretchability of PVC/hbPCL-C4 is superior to that of PVC/DEHP, owing to its better structural homogeneity. Furthermore, PVC/hbPCL-C4 shows outstanding migration stability with the weight loss after extraction being >85% lower than that of PVC/DEHP.