Poly(ester urethane)-crosslinked carboxymethylchitosan as a highly water swollen hydrogel

Abstract

This work focused on the synthesis and characterization of carboxymethylchitosan (CMC)-based hydrogels modified with polyester-containing polyurethane (PU). The polyester was first synthesized from the condensation between 1,6-hexane diol and malonic acid, then reacted with an excess of 1,6-hexamethylene diisocyanate (HDI), and followed by the reaction with ethylene glycol as a chain extender to gain PU. CMC was chemically crosslinked with a water soluble crosslinker in the presence of 1-60 wt% of PU to obtain highly water swollen CMC hydrogels. Upon addition of PU, the CMC hydrogel showed excellent water swellability (up to 400 times of the dried weight), and it seemed to decrease as decreasing PU percentage but still higher than those of unmodified CMC hydrogel (95 times of the dried weight). The drop of the water swellability was attributed to hydrophobic PU presenting in hydrophilic CMC, evidenced by the formation of PU microphase both in the bulk and surface of the hydrogel with average size ranging between 32 mm and 49 mm in diameter. Addition of PU was generally enhanced tensile strength properties of the hydrogel, while an opposite trend was observed for the elongation properties.