Living cationic polymerization of vinyl ethers with a urethane group

To study the possibility of living cationic polymerization of vinyl ethers with a urethane group, 4-vinyloxybutyl n-butylearbamate (1) and 4-vinyloxybutyl phenylearbamate (2) were polymerized with the hydrogen chloride/zinc chloride initiating system in methylene chloride solvent at -30 degreesC ([monomer](0) = 0.30 M, [HCl](0)/[ZnCl(2)](0) = 5.0/2.0 mM). The polymerization of 1 was very slow and gave only low-molecular-weight polymers with a number-average molecular weight (M.) of about 2000 even at 100% monomer conversion. The structural analysis of the products showed occurrence of chain-transfer reactions because of the urethane group of monomer 1. In contrast, the polymerization of vinyl ether 2 proceeded much faster than I and led to high-molecular-weight polymers with narrow molecular weight distributions (MWDs less than or equal to similar to1.2) in quantitative yield. The M(n)'s of the product polymers increased in direct proportion to monomer conversion and continued to increase linearly after sequential addition of a fresh monomer feed to the almost completely polymerized reaction mixture, whereas the MWDs of the polymers remained narrow. These results indicated the formation of living polymer from vinyl ether 2. The difference of living nature between monomers 1 and 2 was attributable to the difference of the electron-withdrawing power of the carbamate substituents, namely, n-butyl for 1 versus phenyl for 2, of the monomers. (C) 2004 Wiley Periodicals, Inc.