Cationic methacrylate polymers containing chiral amino acid moieties: controlled synthesis via RAFT polymerization

Abstract

Two methacrylate containing amino acid based chiral monomers, Boc-L-alanine methacryloyloxyethyl ester (Boc-Ala-HEMA) and Boc-L-phenylalanine methacryloyloxyethyl ester (Boc-Phe-HEMA), were polymerized by the reversible addition–fragmentation chain transfer (RAFT) process to afford well-defined amino acid based polymers with controlled molecular weight, narrow molecular weight distribution, and precise chain end structure. Linear pseudo-first-order kinetics and number average molecular weight dependence on conversion were observed for the RAFT polymerizations. Di-block copolymers were prepared by RAFT polymerization of methyl methacrylate using poly(Boc-L-alanine methacryloyloxyethyl ester) or poly(Boc-L-phenylalanine methacryloyloxyethyl ester) as macro-chain transfer agents. Subsequent deprotection of the Boc group produced architectures with a primary amine moiety at the side chain, which showed pH responsiveness. The specific rotations of both the chiral monomers and corresponding homo- and block copolymers were studied and alteration of specific rotation due to transformation of monomer to polymer was noticed. In addition, the surface charge of various polymeric architectures was studied using dynamic light scattering (DLS) measurements. The self-assembly of block copolymer films was investigated by atomic force microscopy (AFM). These pH-responsive cationic polymers can potentially be extended for the delivery of small interfering RNA.