Morphology and temperature responsiveness-swelling relationship of poly(N-isopropylamide-chitosan) copolymers and their application to drug release

Poly [N-isopropylacrylamide (NIPAAm)-chitosan] crosslinked copolymer particles were synthesized by soapless emulsion copolymerization of NIPAAm and chitosan. An anionic initiator [ammonium persulfate (APS)l and a cationic initiator [2,2'-azobis(2-methylpropionamidine)dihydrochloride (AIBA)l were used to initiate the reaction of copolymerization. The chitosan-NIPAAm copolymer synthesized by using APS as the initiator showed a homogeneous morphology and exhibited the characteristic of a lower critical solution temperature (LCST). The copolymer synthesized by using AIBA as an initiator showed a core-shell morphology, and the characteristic of LCST was insignificant. The LCST of the chitosan-NIPAAm copolymer depended on the morphology of the copolymer particles. In addition, the chitosan-NIPAAm copolymer particles were processed to form copolymer disks. Then, the effect of various variables such as the chitosan/NIPAAm weight ratio, the concentration of crosslinking agent, and the pH values on the swelling ratio of chitosan-NIPAAm copolymer disks were investigated. Furthermore, caffeine was used as the model drug to study the characteristics of drug loading of the chitosan-NIPAAm copolymer disks. Variables such as the chitosan/NIPAAm weight ratio and the concentration of the crosslinking agent significantly influenced the behavior of caffeine loading. Two factors (pore size and swelling ratio) affected the behavior of caffeine release from the chitosan-NIPAAm copolymer disks. (C) 2004 Wiley Periodicals, Inc. 2004