Synthesis of α‐1,3‐ and β‐1,3‐glucan esters with carbon–carbon double bonds and their surface modification

Abstract α‐1,3‐glucan and β‐1,3‐glucan esters with carbon–carbon double bonds (C=C), namely, α‐1,3‐glucan butenoate (α 13 GB) and β‐1,3‐glucan butenoate (β 13 GB), were synthesized from 3‐butenoic acid and trifluoroacetic anhydride. NMR analysis of the two esters revealed that the 3‐butenoyl groups were partially transformed to 2‐butenoyl groups. The total degree of substitution (DS total ) of the esters was calculated to be 3.0. According to gel permeation chromatography analysis, α 13 GB had a molecular weight ( M w ) of 2.2 × 10 5 and β 13 GB had an M w of 11.0 × 10 5 , which was unexpectedly higher than that of the original glucan. This suggests that the β 13 GB chains were partially and intramolecularly crosslinked via the C=C bond. The α 13 GB and β 13 GB obtained had thermal degradation temperatures of 398 and 375 °C, respectively, and glass transition temperatures of 117 and 119 °C, respectively, which were higher than those of the corresponding saturated glucan butyrates. The surfaces of cast films of the esters were modified with 1 H ,1 H ,2 H ,2 H ‐perfluorodecanethiol, n ‐dodecyl mercaptan or 3‐mercapto‐1,2‐propanediol via thiol‐ene reactions. Attenuated total reflection Fourier transform infrared spectroscopy and scanning electron microscopy energy‐dispersive X‐ray spectroscopy analyses revealed that the surface of α 13 GB was more successfully modified with these thiol compounds than that of β 13 GB. The water contact angle of the surface of each cast film was measured to evaluate its hydrophobicity and hydrophilicity, and indicated the successful surface modification of the film by the thiol compounds © 2020 Society of Chemical Industry