PET-RAFT copolymerization of vinyl acetate and acrylic acid

Abstract

Photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization of vinyl acetate (VAc) and acrylic acid (AA) was successfully realized in methanol at room temperature under blue LED (420 nm, 6 mW/cm2) irradiation with xanthate as RAFT agent and fac-[Ir(ppy)3] as the photocatalyst. The well-defined copolymers of poly(VAc-co-AA) with controlled molecular weights (Mn,GPC) and polydispersity index (PDI) were successfully obtained. The polymerization revealed the behaviors of controlled/living polymerization, which was verified by the observed linear relationship of ln([M]0/[M]t) with respect to irradiation time and that of the experimental molecular weights (Mn,GPC) with respect to monomer conversion. GPC curves showed a single peak and shifted to high molecular weights with increasing the irradiation time. The reactivity ratios of VAc and AA were 0.043 and 1.181, respectively in this system. The effect of the amount of fac-[Ir(ppy)3] on PET-RAFT polymerization was investigated. The monomer conversion increased with increasing the amount of fac-[Ir(ppy)3] and the PDI decreased with the increase in the amount of fac-[Ir(ppy)3]. The temporal controllable PET-RAFT polymerization of vinyl acetate (VAc) and acrylic acid (AA) was achieved. The structure of synthesized poly(VAc-co-AA) was characterized by nuclear magnetic resonance spectroscopy (1H NMR) and gel permeation chromatography (GPC), respectively. The extended experiments of poly(VAc-co-AA) with fresh AA was conducted under the irradiation of blue LED, and the results demonstrated that this extension polymerization displayed controlled polymerization behavior. The mechanism was explained in this study.