Controlled radical polymerization of an acrylamide containing L-phenylalanine moiety via RAFT

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 60 degrees C 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 degrees C and in methanol-toluene mixture at 60 degrees C were also found to afford the polymers with narrow molecular weight distributions.