Controlled Radical Polymerization of an Acrylamide Containing L-Phenylalanine Moiety via RAFT

摘要

Homopolymers of a monosubstituted acrylamide having an amino acid moiety in the side chain,N-acryloyl-L-phenylalanine methyl ester (A-Phe-OMe),have been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization.Two dithioesters were used as chain transfer agents:benzyl 1-pyrrolecarbodithioate (CTA 1) and benzyl dithiobenzoate (CTA 2).The controlled character of the polymerization in the presence of CTA 1 in dioxane at 60degC was confirmed by the formation of narrow polydispersity products,the molecular weight controlled by the monomer/CTA molar ratio,the linear relationship between the molecular weight and conversion,and the ability to increase the molecular weight by a second addition of monomer.Poly(A-Phe-OMe) with controlled molecular weight,low polydispersity,and enhanced isotacticity was also prepared by RAFT polymerization in the presence of catalytic amounts of Lewis acid,Y(OTf)_3.The RAFT polymerizations of A-Phe-OMe in methanol at 45 degC and in methanol-toluene mixture at 60degC were also found to afford the polymers with narrow molecular weight distributions.