Thermoresponsive block copolymer-protein conjugates prepared by grafting-from via RAFT polymerization

Well-defined "smart" block copolymer-protein conjugates were prepared by two consecutive "grafting-from" reactions via reversible addition-fragmentation chain transfer (RAFT) polymerization. The initiating portion (R-group) of the RAFT agent was anchored to a model protein such that the thiocarbonylthio moiety was readily accessible for chain transfer with propagating chains in solution. Well-defined polymer-protein conjugates of poly(N-isopropylacrylamide) (PNIPAM) and bovine serum albumin (BSA) were prepared at room temperature in aqueous media. The retained trithiocarbonate moiety on the free end group of the immobilized polymer allowed the homopolymer conjugate to be extended by polymerization of N,N-dimethylacrylamide. Polyacrylamide gel electrophoresis, size exclusion chromatography, and NMR spectroscopy confirmed the synthesis of the various conjugates and revealed that the polymerizations were well controlled. As expected, the resulting block copolymer-protein conjugates demonstrated thermoresponsive behavior due to the temperature-sensitivity of the PNIPAM block, as evidenced by turbidity measurements and dynamic light scattering analysis.