Nonmigratory Poly(vinyl chloride)-block-polycaprolactone Plasticizers and Compatibilizers Prepared by Sequential RAFT and Ring-Opening Polymerization (RAFT-T ̵ -ROP) Zhonghe Sun, †,‡ Bonnie Choi, † Anchao Feng,* ,† Graeme Moad,* ,‡ and San H. Thang* ,†,‡,§ † Beijing Advanced Innovation Center for Soft Matter Science and Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China ‡ Commonwealth Scientific and Industrial Research Organization (CSIRO) Manufacturing, Clayton, Victoria 3168, Australia § School of Chemistry, Monash University, Clayton Campus, Victoria 3800, Australia * S Supporting Information ABSTRACT: Well-defined nonmigrating polymeric plasticizers, poly(vinyl chloride)-block-polycaprolactone (PVC-b-PCL), were synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization and ring-opening polymerization (ROP) with 2-hydroxyethyl 2-(ethoxycarbono- thioylthio)propanoate (HECP) as RAFT agent and incipient initiator for ROP of ε-caprolactone (CL, oxepan-2-one). Kinetic experiments demonstrated that HECP provided good control in RAFT polymerization of vinyl chloride (VC) with dispersity (Đ) ∼ 1.2 for 3400 < M n < 11000. Chain extension experiments with VC and vinyl acetate proved the high end-group fidelity of the macroRAFT agent formed. The hydroxy end-group of the PVC macroRAFT agent allowed its use as a ROP initiator in forming a series of PVC-b-PCL with different PCL block lengths by RAFT-T ̵ -ROP. Characterization by wide-angle X-ray diffraction (WAXD), polarized light microscopy (PLM), and differential scanning calorimetry (DSC) indicates that there is enhanced chain entanglement for PVC-b-PCL block copolymers when compared to PCL homopolymers in PVC blends, which accounts for PVC-b-PCL being able to provide permanent plasticization. The PVC-b-PCL copolymers are also effective as polymeric compatibilizers in PVC/PCL blends where they suppress the migration of PCL. PVC blends plasticized with PVC-b-PCL show similar or better ductility than PVC containing the archetypical PVC plasticizer dioctyl phthalate (DOP) for the same level of plasticizer. Most importantly, the PVC-b-PCL polymeric plasticizers are nonleaching and do not migrate under conditions where DOP is readily extractable. ■ INTRODUCTION Worldwide, poly(vinyl chloride) (PVC) is one of the most widely produced thermoplastics. 1,2 Flexible plasticized PVC (P-PVC) is extensively used in applications which range from packaging materials to biomedical materials, including disposable blood-contact devices. 3-5 Pure PVC has inherently low ductility, and plasticizers must be added in amounts of up to 50% of the total formulation weight to enhance its flexibility. Historically, these plasticizers have taken the form of phthalate esters, in particular, bis(2-ethylhexyl) phthalate (also known as dioctyl phthalate, DOP). The phthalate plasticizers are inexpensive and perform well in improving ductility. However, over time they can leach out of the PVC matrix into the surrounding medium where they present health and environ- mental issues. These concerns have caused many countries to impose strict regulations on the use of PVC containing phthalate plasticizers in direct food contact applications, medical devices, childcare equipment, toys, and so forth. 6-8 Substituting phthalates with polymeric plasticizers has proven to be a promising way of obtaining a more environmentally acceptable, plasticized PVC (P-PVC). Poly- caprolactone (PCL) has been shown to be nontoxic and biocompatible and has been proposed as an alternative to phthalate plasticizers for more than a decade. 9,10 Rusu et al. 11 investigated the total/partial replacement of DOP with PCL in P-PVC medical devices. They 11 found that PCL and PCL- DOP blends are better plasticizers than DOP alone and provide a lower leaching risk in different media. However, even with PCL there is evidence of some plasticizer loss. Kwak and co-workers 12 reported on hyperbranched PCL (HPCL) and unentangled star-PCL (UESPCL) 13 as new types of plasticizer for PVC. Their formulations showed improved plasticization, but the synthetic route to the production of HPCL is challenging. Maric’s group 14 synthesized a series of plasticizers for PVC based on PCL with terminal octanoate and benzoate functionality. However, these plasticizers showed poor migration resistance with the degree of leaching being high, even relative to DOP. Breslau and co-workers 15 reported on Received: October 6, 2018 Revised: December 23, 2018 Article pubs.acs.org/Macromolecules Cite This: Macromolecules XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acs.macromol.8b02146 Macromolecules XXXX, XXX, XXX-XXX Macromolecules Downloaded from pubs.acs.org by UNIV OF NEW ENGLAND on 02/12/19. For personal use only.