Rigid and little moldable curdlan, a linear β‐1,3‐glucan having intra‐ and interchain hydrogen bonds, was reacted with several alkyl isocyanates, which gave thermoplastic curdlan alkyl carbamates (CrdC) with degree of substitution about 2. The alkyl carbamation at hydroxy groups in the glucan skeleton effectively broke the interchain hydrogen bonds of curdlan and increased flexibility of CrdC, while the newly formed carbamate moieties could moderately keep the hydrogen bonding ability in CrdC. Elongating the alkyl groups in the carbamate side chains increased solubility in organic solvents and thermoplasticity of CrdC, which enabled to make homogeneous and free‐standing films by both methods of solution‐casting and hot‐pressing.
Curdlan alkylcarbamate (CrdC) with a degree of substitution (DS) of ~2 was chemically modified via postesterification using carboxylic anhydride at a residual OH. Fully substituted mixed esters of curdlan carbamate/carboxylate (CrdCE) (DS = 3) with carbamate hydrogen bonding ability were obtained in high yields (>80%). Owing to replacing the residual OH with alkanoates, the glass transition temperature of CrdCE was lower than that of the corresponding CrdC. All the CrdCE displayed a greater deformability evaluated by elongation at break, being more remarkable when introducing longer esters (almost two times higher than the unmodified CrdC) than shorter esters (1.4 times higher). On the other hand, the effect on both Young's modulus and tensile strength depended on the length of the esters, observing an increase on both parameters when using shorter esters (19% and 17% higher, respectively), and a decrease for longer esters (33% and 6% lower, respectively). Thus, it was established that the physical properties of the thermoplastic CrdC could be controlled by modifying the residual OH with an appropriate ester group.
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