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

Abstract

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-methoxy-1-(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.