Synthesis And Characterization Of Temperature Sensitive Hemicellulose-based Hydrogels

Intelligent hydrogels are a kind of functional macromolecular materials that could respond to the delicate stimulus from their physiochemical environment, such as temperature, electrical field, magnetic field, light, pH, ionic intensity, pressure and etc. Since these polymers would undergo significant swelling or deswelling behaviors during stimuli-responsive processes, they are widely and potentially applicable in various areas like controlled-release drugs, drug delivery, molecular switch and tissue engineering. Moreover, as the petroleum crisis spreads and accelerates, investigation on the synthesis of biomass-based intelligent hydrogels have become a research hotspot throughout the world, which have the advantages of large raw material supplies, high recyclability and excellent biological compatibility.The hemicelluloses isolated from acetic acid pulping of eucalyptus, as well as that extracted from corncobs by traditional diluted alkali solution were employed to synthesize the temperature sensitive hemicellulose-based hydrogels via chemical modification and ultraviolet crosslinking methods in this study. The structure of hemicelluloses and its derivatives, the lower critical solution temperature (LCST) and the morphology of the hydrogels were investigated by FT-IR, IC, 1H-NMR, DSC and SEM. The swelling and de-swelling behaviors of the hydrogels under different temperatures were studied as well.Firstly, a derivative of hemicellulose (Hcel-MA) containing vinyl bonds within the side chains was prepared by grafting maleic anhydride (MA) to hemicelluloses. The Hcel-MA was then photo-crosslinked with thermo-responsive N-diethyl-Acrylamide (NIPAAm) in LiCl/DMF solvent using UV light, by which a thermo-responsive Hcel-MA-NIPAAm (*MN) hydrogel was successfully prepared. The hydrogels distinctly exhibit a feature of negative temperature sensitivity. Such property can be adjusted by changing the ratio of the maleated hemicelluloses and NIPAAm. Moreover, the *MN hydrogels exhibit a faster water uptake rate than pure PNIPAAm hydrogels.Secondly, the novel hemicelluloses derivatives containing the side chains of PNIPAAm moieties terminated with vinyl groups were prepared by introducing temperature-sensitive monomer, NIPAAm and functional monomer, Ethylene glycol dimethacrylate (EDG) via ATRP. Then, the hydrogels were obtained when the derivatives were induced by ultraviolet-triggered radical polymerization. From the results, it can be seen that the well-defined honeycomb-like hydrogels exhibit negative temperature responsive properties and their temperature sensitivity, such as LCST and the equilibrium swelling ratio, are influenced by the different ratios of temperature-sensitive and other functional moieties, the crosslinking degree of the hydrogels, suggesting their potential as smart materials for medical application.