Synthesis and characterization of temperature responsive graft copolymers of dextran with poly (N-isopropylacrylamide)

Poly (N-isopropylacrylamide) (PNIPAAm) was grafted to dextran using ceric ion as redox initiator. The graft copolymers formed temperature responsive materials and can be used to construct polymeric micelles as drug carriers for colon-site specifically delivery. The chemical structure of the graft copolymers was characterized by FTIR, H-1- and C-13-NMR spectroscopy. The influence of reaction conditions on the grafting parameters was investigated. It was found that the percentage of homopolymer formation (H%), the grafting efficiency (GE%) and the grafting (G%) of the copolymers increased with increasing the amount of the ceric catalyst used. Extension of the duration of graft reaction increased GE% and G% of the copolymers, suggesting that G% of the copolymers could be readily manipulated by changing copolymerization duration. Higher grafting temperature was in favor of increasing GE% and G%, however, when the reaction temperature was above the LCST of the copolymers, GE% and G% decreased. The optical transmittance of the copolymers in the aqueous solution was examined by UV-Vis instrument. The result showed that the phase transition of the graft copolymer in aqueous solution moved slightly to higher temperature when G% of the graft copolymers decreased. The results of atomic force microscopy and dynamic light scattering measurement indicated that the graft copolymers form micelles in a spherical morphology, and for the copolymer with the G% of 33.8% formed micelles in the mean diameter of less than 30 nm in aqueous solution. (C) 2002 Elsevier Science B.V. All rights reserved.