Organic acids as efficient catalysts for group transfer polymerization of N,N-disubstituted acrylamide with silyl ketene acetal: polymerization mechanism and synthesis of diblock copolymers

The group transfer polymerization (GTP) of N,N-diethylacrylamide (DEAA) was studied using various combinations of an organic acid of N-(trimethylsilyl) bis-(trifluoromethanesulfonyl) imide (Me3SiNTf2), 1-(2,3,4,5,6-pentafluorophenyl)-1,1-bis(trifluoromethanesulfonyl) methane (C6F5CHTf2), and tris(pentafluorophenyl) borane (B(C6F5)(3)) and a silyl ketene acetal (SKA) of 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene (MeSKA), 1-methoxy-1-(triethylsiloxy)-2-methyl-1-propene (EtSKA), 1-methoxy1-(triisopropylsiloxy)-2-methyl-1-propene (iPrSKA), and 1-methoxy-1-(triphenylsiloxy)-2-methyl-1-propene (PhSKA), among which the combination of B(C6F5)(3) and EtSKA afforded a relatively better control over the molecular weight distribution. The polymerization behavior of DEAA using B(C6F5)(3) and EtSKA was then intensively investigated in terms of the polymerization kinetics, chain extension experiments, and MALDI-TOF MS analyses, by which the polymerization was proven to proceed in a living fashion though an induction period of tens of minutes occurred. The B(C6F5)(3)-catalyzed GTP was further extended to various N, N-disubstituted acrylamides (DAAs), such as N, N-dimethylacrylamide (DMAA), N, N-di-n-propylacrylamide (DnPAA), N-acryloylpiperidine (API), N-acryloylmorpholine (NAM), N-(2-methoxyethyl)-N-methylacrylamide (MMEAA), N, N-bis(2-methoxyethyl) acrylamide (BMEAA), N, N-diallylacrylamide (DAlAA), and N-methyl-N-propargylacrylamide (MPAA). Finally, the livingness of the polymerization was used to synthesize acrylamide-acrylamide block copolymers and methacrylate-acrylamide hetero-block copolymers.