Grafting of N,N-dimethylacrylamide onto silk fibers via a RAFT agent controlled radical transformation process

RAFT-mediated silk graft copolymerizations with DMAAm (N,N-Dimethylacrylamide) were studied. Three types of macromolecular RAFT agents which released different R group radicals, namely, polyacrylic acid- b -polystyrene radical (PAA- b -PSt • ), polyacrylic acid- b -polybutyl acrylate radical (PAA- b -PBA • ) and polystyrene- b -polyacrylic acid radical (PSt- b -PAA • ), were chosen as the transfer agents. During the graft copolymerizations, the newly born PAA- b -PSt • in the aqueous phase enhanced the formation of silk macroradicals, consequently accelerated the copolymerization rate and improved monomer grafting efficiency ( Ge ) greatly. The Ge was less improved when the RAFT agent capable of producing PAA- b -PBA • were substituted for the one producing PAA- b -PSt • . In addition, Ge also benefited from an increase in the chain length of PSt block in PAA- b -PSt • , as well as PBA block in PAA- b -PBA • . However, the addition of RAFT agent giving rise to PSt- b -PAA • had negligible effects on Ge . The reasons were ascribed to both the radical reactivity and capacity of radical adsorption onto silk fibers.