Graft copolymerization kinetics of silk and its grafting structure

Two kinds of RAFT( Reversible addition-fragmentation chain transfer) agents were introduced to mediate graft copolymerizations of silk fibers with DMAAm( N,N'-dimethyl acrylamide). New oligomer radicals generated from the chain transfer reactions between RAFT agents and propagation radicals. The RAFT-ST3 released an oligomer radical of PAA-PST*( polyacrylic acid-b-polystyrene),which accelerated graft copolymerization and increased silk grafting yield and monomer grafting efficiency. However,the kinetics was little influenced by the oligomer radical originated from RAFTAA30 agent that had a chain structure of PST-PAA*. FT-IR( Fourier transform infrared spectroscopy)spectra showed that,RAFT agents and their derivatives did not covalently bond with silk fibers. The grafting yield was still contributed by the grafted PDMAAm chains. SEM( Scanning electron microscopy)analysis showed that,compared with conventional silk graft copolymerization( without RAFT agent),RAFT agents mediated reaction produced silk fibers with grafted PDMAAm chains distributing much more evenly on the outer surface.