Enzymatic synthesis of bio-based polyesters containing levoglucosan units

Overview & Synopsis

Levoglucosan (LGA) is an anhydrous pyrolytic sugar that has gained increasing attention in recent years. The highest focus on the conversion of LGA and other anhydro carbohydrates obtained from cellulose aims at the valorization of these molecules and their application in multiple fields such as chemical and pharmaceutical industries. LGA presents a rigid structure with three hydroxyl groups on a pyranose ring, making it a promising building block for the synthesis of bio-based thermoplastic polymers with pending OH groups as soon as a regioselective polymerization is reached. In this work, a lipase-catalyzed series of LGA-containing terpolymers were synthesized for the first time via regioselective transesterification in two-stage polymerization. LGA was reacted with diethyl adipate/sebacate and α,ω-diols to give terpolymers with up to 35% of LGA content (related to the α,ω-diol content), number-average molecular weights (Mn) of up to 7900 g·mol–1, and up to 94% yield. It was observed that the amount of LGA in the polymer structure affects the crystallinity, hydrophilicity, and melting point of the polymers. We also evaluated the effect of LGA loading and the comonomer’s size on yields, molecular weight, and the incorporation of LGA in the polymer structure. High loads of LGA lead to a decrease in the yield, but a higher molecular weight and higher extent of LGA incorporation in the polymer can be obtained.