Block copolymer conjugates prepared by sequentially grafting from proteins via RAFT

Well-defined thermoresponsive block copolymer conjugates were prepared by two consecutive grafting-from polymerizationsvia 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 ω end of the conjugated chains allowed chain extension viapolymerization 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.