Preparation of chitosan‐g‐polycaprolactone copolymers through ring‐opening polymerization of ϵ‐caprolactone onto phthaloyl‐protected chitosan

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Abstract
The new biodegradable chitosan graft copolymer, chitosan‐g‐polycaprolactone, was synthesized by the ring‐opening graft copolymerization of ϵ‐caprolactone onto phthaloyl‐protected chitosan (PHCS) at the hydroxyl group in the presence of tin(II) 2‐ethylhexanoate catalyst via a protection–graft–deprotection procedure. Toluene acted as a swelling agent in this heterogeneous system. The grafting reactions were conducted with various PHCS/monomer/toluene feed ratios to obtain chitosan‐g‐polycaprolactone copolymers with various polycaprolactone contents. The chemical structure of the chitosan‐g‐polycaprolactone was characterized by Fourier transform infrared and one‐ and two‐dimensional NMR spectroscopy. After deprotection, the phthaloyl group was removed and the amino group was regenerated. Thus the obtained chitosan‐g‐polycaprolactone was an amphoteric hybrid with a large amount of free amino groups and hydrophobic polycaprolactone side chains. Some properties of the final product were also investigated, such as crystallinity, thermal property, and solubility. © 2005 Wiley Periodicals, Inc. Biopolymers, 2005