Reversible addition-fragmentation chain transfer polymerization of vinyl acetate and vinyl pivalate in supercritical carbon dioxide

Two highly supercritical CO2-soluble, poly(vinyl acetate) (PVAc)-based macro-reversible addition-fragmentation chain transfer (RAFT) agents were synthesized. The RAFT agents were used for the first time in RAFT/macromolecular design via the interchange of xanthates (MADIX) and polymerization of vinyl acetate (VAc) and vinyl pivalate (VPi) in supercritical carbon dioxide (scCO2). A homopolymer PVAc and a block copolymer PVAc-b-PVPi made by RAFT/MADIX polymerization were characterized, and the effects of time and RAFT agents on polymerization were examined. For the 8.4 wt% RAFT agent in VAc, the molecular mass (Mn) of homopolymer PVAc was 26,000 g mol−1 and PDI was 1.35. For the copolymerization of VPi using 9.8 wt% PVAc-RAFT agent in VPi for 24 h, the Mn and PDI of PVAc-b-PVPi reached 32,400 g mol−1 and 1.42, respectively. These results suggest that the polydispersity can be controlled during the clean production of PVAc and PVPi by RAFT/MADIX polymerization in scCO2.