Living polymerization of acrylic monomers with aluminum alkyls

Abstract

Polymerization of acrylic monomers was attempted by various aluminum alkyls. Polymerization N,N-diphenyl acrylamide (DPAA) with aluminum alkyls including trimethyl aluminum (TMA), triethyl aluminum (TEA), tripropyl aluminum (TPA), triisobutyl aluminum (TIBAL), trioctyl aluminum (TOA) and methyl alumoxane (MAO) resulted in quantitative yield of polymer with high molecular weight and relatively low molecular weight distribution. In the case of using triisobutyl aluminum as an initiator in THF solution, polymerization of N,N-diphenyl acrylamide showed living character even at relatively high temperature, 0℃. Polymerization with TEA or TIBAL exhibit quantitative yield of high molecular weight polymers with relative low molecular weight distribution regardless of reaction temperature even at 60℃, indicating the polymerization proceeded by different way from anionic polymerization. The poly(DPAA) showed lack of stereoselectivity compared to general radical polymerization that resulted in relatively high syndiotactic poly (DPAA). By controlling the condtion of the polymerization, monomeric and dimeric intermediates initiated by TEA or TIBAL were obtained. The structural analysis of the intermediates revealed that the polymerization with TIBAL involved an initiation step by both hydride and isobutyl anion transfer from TIBAL to the vinyl group of monomer to form aluminum enolates that carried out propagation by aluminum-oxygen bond exchange analogous to group transfer polymerization. The polymerization with TEA initiated by ethyl anion transfer from TEA. However, the polymerization with TIBAL under the living condition was initiated only by hydride transfer. Polymerization of various acrylic monomers including N-acryloylpiperidine (NAPP), N-phenyl acrylamide (NPA), N-methyl-N-phenyl acrylamide (MPAA), dimethyl acrylamide (DMAA), phenyl acrylate (PA) and methyl acrylate (MA) and methacrylic monomer such as N,N-diphenyl methacrylamide (DPMA), methyl methacrylate (MMA) wa...