Dual stimuli-responsive N-phthaloylchitosan-graft-(poly(N-isopropylacrylamide)-block-poly(acrylic acid)) copolymer prepared via RAFT polymerization

In order to develop stimuli-responsive hydrogel, chitosan graft copolymer with chitosan back-bone and poly( N -isopropylacrylamide)- block -poly(acrylic acid) (PNIPAAm- b -PAA) branch chains was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization in DMF. The chain transfer agent was obtained by modification of chitosan with 3-benzylsulfanyl thiocarbonylsulfanyl propionic acid (BPATT) with 68% the degree of substitute. The graft polymerizations possessed controlled/living characteristics. The behavior of the graft copolymer in aqueous solution was investigated by dynamic light scattering, transmission electron microscopy, and UV-visible spectrophotometer. N -Phthaloylchitosan- graft -(poly( N -isopropylacrylamide)- block -poly(acrylic acid)) copolymer ( N -phthaloylchitosan- g -(PNIPAAm- b -PAA)) could assemble to micelles in aqueous solution in range of 200–300   nm with narrow size distribution, and the hydrodynamic diameter could be controlled dependent on length of branch chains and temperature. The LCST values of micelle could be modulated from 34 to 40   °C by controlling the constitution of branch chains, pH, and concentration.