Visible Light-Controlled Radical Polymerization of Propargyl Methacrylate Activated by a Photoredox Catalyst fac-[Ir(ppy)3

Abstract

Despite the robustness and flexibility of thermal controlled radical polymerization (CRP), it still remains a big challenge to prepare clickable polymers bearing acetenyl groups. In this paper, visible light CRP of propargyl methacrylate (PgMA) is investigated using ethyl-α-bromophenylacetate as initiator and fac-Ir(ppy)3 as a photoredox catalyst. By controlling the polymerization time, a linear increase of Mn with monomer conversion and narrow polydispersity index is achieved. Specifically, with [PgMA]/[Initiator]/[fac-Ir(ppy)3]=210:1:0.0285, the products show Mn=8300 g/mol and Mw/Mn=1.24 at 17% monomer conversion and Mn=17100 g/mol and Mw/Mn=1.52 at 50% monomer conversion. This result is much better than that of thermally activated Cu-ATRP of PgMA. When the ratio of MMA/PgMA is 5:1, the copolymerization product shows Mn=25300 g/mol and Mw/Mn=1.75 at 66% monomer conversion. The FTIR, 1H-NMR and 13C-NMR spectra of the PPgMA show no sp2-sp2 carbon-carbon bond, indicating that acetenyl groups are intact. In conclusion, this technology offers a versatile route for the preparation of (co)polymers with pendant alkynyl groups.