Synthesis and aggregation behavior of chitooligosaccharide-based biodegradable graft copolymers

A series of novel "jellyfish-like" graft copolymers with chitooligosaccharide (COS) as shorter backbone and poly(epsilon-caprolactone) as longer branches were synthesized using ring-opening polymerization of epsilon-caprolactone via a protection-polymerization-deprotection procedure with trimethylsilylchitooligosaccharide as intermediate and triethylaluminum as catalyst precursor. The obtained chitooligosaccharide-graft-poly(epsilon-caprolactone) polymers possess amphiphilic structure with hydrophilic COS backbone and hydrophobic palycaprolactone branches. Because of this unique "jellyfish-like" structure, these graft copolymers could self-assemble to form various morphologies of aggregates in a mixture solution of water and tetrahydrofuran. The transmission electron microscopy studies revealed that the formed aggregates exhibited necklace-like, flower-like onion vesicle, and tubular morphologies. It is found that the hydrogen-bonding formed by the hydroxyl and amino groups remained on the COS backbone played an important role during the aggregation of these graft copolymers, and their morphologies were changed with the varying length of poly (epsilon-caprolactone) branches, the concentration of the graft copolymer, and the self-assembly process. (C) 2008 Wiley Periodicals, Inc.