Synthesis of α-1,3-Glucan branched ester derivatives with excellent thermal stability and thermoplasticity

Abstract

α-1,3-Glucan is a linear homopolymer enzymatically polymerized from sucrose using recombinant glucosyl transferase J (GtfJ) enzyme. α-1,3-Glucan branched ester derivatives were synthesized from branched carboxylic acids and trifluoroacetic anhydride in a heterogeneous reaction. These derivatives showed unconventional thermal properties compared with other polysaccharide ester derivatives and oil-based plastics. The melting temperature (Tm) of the α-1,3-Glucan branched ester derivatives increased in proportion to the side chain length, which has not been observed for other polysaccharide ester derivatives. In addition, isobutyrate ester derivatives (iso-branched ester derivatives) and pivalate ester derivatives (tert-branched ester derivatives) showed extremely high glass transition temperatures (Tg) of 206 and 202 °C, respectively, which were much higher than those of commercial plastics, such as polyethylene terephthalate (PET: 69 °C) and polycarbonate (140 °C), and super engineering plastics, such as polyether ether ketone (PEEK: 142 °C). Furthermore, these two types of branched ester derivatives showed excellent thermoplasticity at temperatures below the thermal decomposition temperature. Therefore, α-1,3-Glucan branched ester derivatives demonstrate the possibility of realizing both high thermal stability and thermoplasticity.