Controlled synthesis of amino acid-based polymers by reversible addition fragmentation chain transfer polymerization

We here report controlled synthesis of polyacrylamides having amino acid moieties by reversible addition-fragmentation chain transfer (RAFT) polymerization. Three acrylamides, N-acryloyl-L-phenylalanine methyl ester (A-Phe-OMe), N-acryloyl-L-phenylalanine (A-Phe-OH), and N-acryloyl-L-proline methyl ester (A-Pro-OMe), were selected as amino acid-containing monomers. The RAFT polymerization of these monomers using suitable chain transfer agents allowed the synthesis of well-defined amino acid-based polymers with predetermined molecular weights, narrow molecular weight distributions, and characteristic stimuli-responsive properties. Poly(A-Phe-OH) was a weak polyelectrolyte, in which the degree of ionization of carboxylic acids can be easily controlled by the pH value. Poly(A-Pro-OMe) and the random copolymers exhibited a characteristic Lower Critical Solution Temperature (LCST = 15-45 °C) in aqueous solution.