Development of Biobased Poly(ether ester)s from Novel Lignin-Derived Monomers Present in Lignin Oils

Lignin, a naturally abundant and renewable aromatic polymer, remains vastly underexploited, despite its immense potential for sustainable materials development. Reductive catalytic fractionation of lignocellulosic biomass results in low-molecular-weight lignin oils. A large fraction of these oils consists of 4-n-propanolguaiacol (PohG) and 4-n-propanolsyringol (PohS) and is unexplored as polyester building blocks. In this study, 4-n-propanolphenol (PohP), PohG, and PohS were modified in AB monomers by reaction with bromoalkanoates with different alkyl chain lengths. The AB monomers were subsequently polymerized into poly(ether ester)s. The resulting polymers were characterized in-depth by size exclusion chromatography, nuclear magnetic resonance, (modulated) differential scanning calorimetry, wide-angle X-ray scattering, thermogravimetric analysis, and dynamic mechanical analysis and were subsequently successfully depolymerized by base catalysis to prove the recycling potential. The produced poly(ether ester)s have high molecular weights, and clear trends in the glass transition, melting temperature, and viscoelastic properties of the resulting polymers were observed in relation to the AB monomers. The poly(ether ester)s showed comparable thermal and viscoelastic properties to poly(butylene adipate-co-terephthalate) and poly(butylene adipate-co-furanoate) and represent a novel class of semiaromatic polyesters derived from lignin.