Synthesis and Properties of α-1,3-Glucan with Branched and Linear Mixed Ester Side Chains

Two series of alpha-1,3-glucan with branched and linear mixed ester side chains, namely alpha-1,3-glucan pivalate hexanoate (alpha-1,3-glucan-Pi-Hex) and alpha-1,3-glucan isobutyrate hexanoate (alpha-1,3-glucan-iBu-Hex), were synthesized as biomass-based thermoplastic resins via an enzymatic polymerization and a heterogeneous chemical esterification using trifluoroacetic acid anhydride and carboxylic acids. The degree of substitution (DS) ratio of two types of ester groups was precisely controlled by adjusting the initial dosages of the two corresponding carboxylic acids. Although alpha-1,3-glucan homobranched esters, i.e., alpha-1,3-glucan pivalate and alpha-1,3-glucan isobutyrate, were crystalline and their cast films were brittle, the cast films of the mixed esters gradually lost crystallinity and finally became amorphous in proportion to increasing DS of hexanoate (DSHex), and their flexibility improved significantly. Specifically, alpha-1,3-glucan-Pi-Hex and alpha-1,3-glucan-iBu-Hex with DSHex = 1.5 had high film flexibilities and high glass-transition temperatures of 120 and 93 degrees C, respectively. These are comparable to the properties of conventional oil-based amorphous plastics such as polystyrene and poly(methyl methacrylate). The processing window widened with increasing DSHex which led to less thermal decomposition during thermal processing. The mixed ester method was effective for controlling the physical properties of alpha-1,3-glucan esters. Furthermore, alpha-1,3-glucan-Pi-Hex and alpha-1,3-glucan-iBu-Hex showed promise as transparent and flexible films with high thermal stability for electric devices of designability.

Automated summary

Two series of alpha-1,3-glucan with branched and linear mixed ester side chains were synthesized as biomass-based thermoplastic resins, showing improved flexibility with increased hexanoate substitution. The mixed ester method effectively controlled the physical properties of alpha-1,3-glucan esters, making them promising for transparent and flexible films with high thermal stability for electric devices of designability.