Photoinduced Electron Transfer-Reversible Addition- Fragmentation Chain Transfer (PET-RAFT) Polymerization of Vinyl Acetate and N?Vinylpyrrolidinone: Kinetic and Oxygen Tolerance Study

摘要

Photoinduced electron transfer-reversible addition- fragmentation chain transfer (PET-RAFT) polymerization was employed for the polymerization of unconjugated monomers, including vinyl acetate, vinyl pivalate, N-vinylpyrrolidinone, dimethyl vinylphosphonate, vinyl benzoate, and N-vinylcarbazole, in the presence of low concentration (ppm range) of photoredox catalyst, fac-[Ir(ppy)_3], under low energy visible light irradiation. Kinetic studies of vinyl acetate indicated excellent control of molecular weights and molecular weight distributions (M_w/M_n = 1.09-1.2), even with high monomer conversion (>75%), in different catalyst concentrations. High molecular weights of poly(vinyl acetate) (M_n > 100 000 g/mol) and poly(N-vinylpyrrolidinone) (M_n > 40 000 g/mol) with low dispersities (M_w/M_n < 1.25) were obtained in bulk polymerizations. Moreover, the online kinetic study using Fourier transform near-infrared (FTNIR) showed comparable kinetic rates for the polymerizations in the absence and presence of relatively large amount of air, which demonstrates that the PET-RAFT technique possesses the ability of tolerance toward oxygen. Successful chain extensions of homopolymers of poly(vinyl acetate) and poly(N-vinylpyrrolidinone) to vinyl acetate and vinyl pivalate confirmed their integrities of end-group S-(S=Z)-O.