Synthesis and physical properties of Curdlan branched Ester derivatives

Curdlan is a high-molecular-weight linear β-1,3-glucan synthesized by microorganisms. A series of curdlan branched esters with a degree of substitution of three were synthesized and their physical properties and structures were compared with those of curdlan linear esters. Thermal degradation temperatures of all the curdlan branched esters were ca. 360 °C; almost the same as those of curdlan linear esters. The curdlan branched esters had melting temperatures (T _m ) higher than those of the corresponding curdlan linear ester with the same side-chain carbon number. In particular, comparing T _m of curdlan propionate, curdlan isobutyrate, and curdlan pivalate, the latter two had high T _m of over 335 °C, suggesting that the degree of branching of the side chain affects the stability of molecular chains with helix structure in their crystals. Highly transparent films were prepared from the curdlan branched esters. These films exhibited higher Young’s modulus and tensile strength compared with those of films composed of the linear equivalents with the same side-chain carbon numbers. These results indicate that curdlan branched esters are promising thermoplastics with favorable thermal and mechanical properties because of the closer packing structure of their molecular chains than that of the corresponding curdlan linear esters.