Closed-loop chemically recyclable aromatic polyesters based on asymmetric dicarboxylates obtainable from lignocellulose

Abstract

The use of building blocks derived from lignocellulose is an attractive strategy towards biobased aromatic polyesters. Here, we present the straightforward synthesis of three new di-aromatic diester monomers by one-step reactions of lignin-derived hydroxybenzoates (methyl paraben, methyl vanillate and methyl syringate, respectively) with potentially sugar-based methyl 5-chloromethyl-2-furoate. The two diester monomers based on methyl paraben and methyl vanillate were polymerized with 1,6-hexanediol, 1,4-butanediol, and neopentyl glycol, respectively, to produce two series of polyesters with reasonably high molecular weights (12-37 kg mol⁻¹). The fully amorphous polyesters showed high thermal stability (Td,5 > 275 °C), tunable glass transition temperature (T_g ~ 36-75 °C) and moderately high stiffness. In addition, we have successfully demonstrated a strategy for closed-loop chemical recycling of the polyesters through depolymerization using methanolysis, which allowed for the recovery of the starting diester and diol monomers. The recovered monomers were subsequently repolymerized to produce a recycled polyester with properties comparable to the original one.