Synthesis of regioselective chitosan copolymers with beta-cyclodextrin and poly(N-isopropyl acrylamide)

摘要

This work aimed to design a synthetic route under mild conditions allowing the main chitosan chain to be grafted with beta-cyclodextrin (beta-CD) and poly(N-isopropyl acrylamide) (PNIPAm), at C2 and C6 positions, respectively. For this reason, the regioselectivity of proposed reactions is an important factor to be considered. beta-CD is an oligosaccharide with a cyclic structure capable of forming inclusion complexes with hydrophobic molecules. Grafting beta-CD onto the chitosan backbone by reductive N-alkylation at C2 position was carried out. With this purpose, the previous preparation of beta-CD monoaldehyde was required. PNIPAm is a thermosensitive polymer with a transition temperature near 33 degrees C. To regioselectively anchor poly(N-isopropyl acrylamide) chains onto chitosan at C6 position, it was required to attach at the C6 position of chitosan an alkyl group for the subsequent grafting of PNIPAm-N-3 by means of copper-catalyzed azide-alkyne cycloaddition click reaction. To guarantee the regioselectivity of the functionalization of chitosan with a C6 terminal alkyne, its oxyalkylation with glycidyl propargyl ether in a solvent composed of LiOH/KOH/urea was used. The structure of all derivatives was confirmed by FT-IR and H-1-NMR spectroscopy.