Block copolymer conjugates prepared by sequentially grafting from proteins via RAFT

Well-defined thermoresponsive block copolymer conjugates were prepared by two consecutive grafting-from polymerizations via reversible addition-fragmentation chain transfer (RAFT) polymerization. A RAFT agent containing an activated ester was conjugated to amines on lysozyme, and N-isopropylacrylamide was polymerized by grafting directly from the modified protein in aqueous buffer. Retention of the active thiocarbonylthio moieties on the omega end of the conjugated chains allowed chain extension via polymerization of N, N-dimethylacrylamide to yield lysozyme-poly(N-isopropylacrylamide)-b-poly(N, N-dimethylacrylamide) (LYS-PNIPAM-b-PDMA) block copolymer conjugates. Analysis of the conjugates, as well as the cleaved homopolymers and block copolymers, indicated the grafting-from polymerizations were well controlled and that chain extension during block copolymerization was efficient. The temperature-responsive aqueous solution behavior of the resulting conjugates was investigated.