Chitin is a natural polysaccharide abundantly present in nature, and thus, very important biomass resource. However, since chitin has strong crystallinity by intermolecular hydrogen bonding between acetamido groups, it is poor in solubility and processability, leading to mostly unutilization. We have already found that an ionic liquid, 1-allyl-3-metylimidazolium bromide (AMIMBr), dissolves chitin at most in 4.8 wt %. We also found that chitin acylates (chitin esters) with high degree of substitution (DS) were obtained by acylation of chitin using acyl chlorides in AMIMBr. However, processability of the product was not largely improved, probably due to the remaining hydrogen bonds between acetamido groups. In this study, we synthesized a mixed chitin ester having adamantoyl and stearoyl groups in AMIMBr, in which the hydrogen bonds would be weaken by introducing such bulky and long alkyl groups on the chitin chain (Scheme1). The IR and 1H NMR spectra of the product indicated that chitin adamantate stearate with high DS was obtained. In the XRD profile, the diffraction peaks assignable to chitin crystalline structure greatly decreased, and a diffraction peak ascribable to end-to-end packing of stearoyl groups was shown at 2θ = 3.0°. The DSC pattern showed an endothermic peak due to enthalpy relaxation of the packing structure at 7 °C. These results have suggested that the processability of the product is potentially expressed. Indeed, as the product was dissolved in chloroform, the solution could be thinly casted to obtain a flexible film.

Synthesis of mixed chitin esters in ionic liquid

2019 Fall National Meeting

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