SET-LRP of 2-hydroxyethyl acrylate in protic and dipolar aprotic solvents

Cu(0) wire-mediated single-electron transfer living radical polymerization (SET-LRP) of 2-hydroxyethyl acrylate (HEA) was performed in protic solvents, MeOH, binary mixtures of MeOH and EtOH with H2O, and H2O, and in the dipolar aprotic solvent, DMSO. The tertiary alkyl halide initiator, ethyl 2-bromoisobutyrate (EBiB), and the tris[2-(dimethylamino)ethyl]amine (Me6-TREN) ligand mediated rapid SET-LRP of HEA providing poly(HEA) (PHEA) with narrow Mw/Mn. When SET-LRP of HEA was performed at high H2O content in MeOH, and in H2O, gel formation was observed exclusively on the Cu(0) wire surface. This demonstrated the heterogeneous nature of the Cu(0)-mediated SET activation that promotes a strong adsorption of PHEA and slow diffusion of PHEA radicals generated from activation on the Cu(0) wire surface by the hydrophobic effect. High molecular weight PHEA was obtained at [M]0/[I]0 = 400 and 800 with Mw/Mn < 1.45 in MeOH + 40% H2O in 50 min. This suggests significantly less termination and a much higher rate of SET-LRP of HEA at 25 °C than in the previously reported CuX-catalyzed polymerization of HEA in bulk (90% conversion, Mn = 30 000 after 14 h at 90 °C) or solution (87% conversion, Mn = 14 700 after 12 h at 90 °C) at elevated temperatures. When targeting higher [M]0/[I]0, Mw/Mn increases with conversion but first order kinetics was observed. This was attributed to the increased hydrophobic effect of PHEA at higher Mn that is accompanied by slow desorption of the polymer from the Cu(0) wire and a reduced exchange rate between dormant and active species.