Transformation from xanthate-type cationogen mediated metal-free RAFT cationic polymerization with “HCl·Et2O” into RAFT radical polymerization to form poly(alkyl vinyl ether)-b-polyvinyl alcohol amphiphiles

Abstract

To elucidate the applicable range of metal-free RAFT cationic polymerization (MRCP) with “HCl·Et2O”, the effects of the monomer structure on the transformation from MRCP to RAFT radical polymerization were investigated. The MRCP with HCl·Et2O was conducted using the xanthate-type cationogen, O-ethyl S-(1-ethoxyethyl) carbonodithioate (EVEX) at 0 °C for alkyl vinyl ethers (ALVE) such as n-butyl (NBVE), isobutyl (IBVE), isopropyl (IPVE), and tert-butyl vinyl ethers (TBVE). It was demonstrated that EVEX acted efficiently as a RAFT cationogen for the cationic polymerization initiated by HCl·Et2O with good control over the molecular weight, polydispersity, and chain ends of the resulting poly(ALVE), regardless of the monomer structure of ALVE. The resulting chain-transfer constants indicate that EVEX is a substantially effective RAFT cationogen for MRCP of ALVE with HCl·Et2O. The resulting poly(ALVE) was utilized as a macromolecular chain transfer agent (macro-CTA) for RAFT radical polymerization since it had 0.72–0.76 of ω-end functionality for the xanthate group [–S–C(=S)OC2H5], as determined from 1H NMR and MALDI-TOF-MS spectra under the optimal conditions. However, when the resulting poly(TBVE) was employed for subsequent RAFT radical polymerization, no block copolymerization proceeded due to the poor stability of the vinyl ether radical. Thus, poly(ALVE) but not poly(TBVE) obtained by MRCP was available as a macro-CTA for RAFT radical polymerization to synthesize novel block copolymers such as poly(IPVE)-b-poly(vinyl acetate). In addition, the selectively saponified block copolymer, poly(IPVE)-b-polyvinyl alcohol, formed spherical micelles in water, demonstrating the successful results of the one-pot transformation from MRCP to RAFT radical polymerization.