Thermo-responsive behavior and gelation of curdlan alkyl-ethers prepared by homogeneous reaction

To resolve the major obstacles of poor water solubility and few functional derivatives in the practical utilization of curdlan, we prepared highly soluble and thermal-responsively alkylated curdlan with different degrees of substitution (DS) via homogeneous reaction. The properties of these derivatives were investigated by rheology, inline attenuated total reflective-Fourier transform infrared spectroscopy, Raman and fluorescence spectroscopy, micro-differential scanning calorimetry, dynamic light scattering, and in vitro cytotoxicity assay. The newly developed methylated and ethylated curdlan can form thermal reversible heat-set hydrogels accompanied by volume shrinkage due to syneresis. Their gelation temperatures depend strongly on the DS, size of hydrophobic groups, and the order of the Hofmeister series salts added. Experimental results indicated that the gel network was induced by the enhanced hydrophobic interaction among macromolecular chains and weakened hydrogen bonding between the polymer and water on heating, leading to phase separation and gelation.