Synthesis of biobased poly(ether-ester) from potentially bioproduced betulin and p-coumaric acid

For a more sustainable future, innovative polymer materials synthesized from biobased molecules are currently a key trend, in the frame of the bioeconomy. In this study, new renewable macromolecular architectures poly(ether-esters) has been synthesized from betulin and para-coumaric acid, two plant-based building blocks, poorly valorized till now, and potentially bioproduced by white biotechnologies. To date, these are the first synthesized polymers with such a reported architecture. In a first step, different chemical modifications were carried out on these biomolecules to increase their reactivities. Betulin hydroxyl groups were esterified with aliphatic acids of carbon chain lengths C6, C8 and C10 terminated by a bromine, with good yields (79–85%). P-coumaric acid was dimerized by [2 + 2] cycloaddition, and then esterified with ethanol, butanol or isobutanol with excellent yields (92–96%). These modified building blocks were finally copolymerized by Williamson polyetherification reaction, leading to various analogous materials with molar masses ranging from 9700 to 15500 g mol⁻¹. Different thermal characterizations have been then performed. TGA results show that these poly(ether-esters) displayed high thermal stabilities (up to 336 °C). Besides, DSC analyses revealed T_g ranging from 38 to 81 °C, depending on the length of the aliphatic carbon chain and the nature of the pendant ester groups for a large range of potential applications.