Chemically Recyclable and Enzymatically Degradable Thermostable Polyesters with Inherent Strain from α-Pinene-Derived Chiral Diols

Abstract

Accelerated production of recyclable and biodegradable polymers is crucial in combating the socioeconomic and environmental issues connected to traditional plastics. While renewable diacids have been in the spotlight for the generation of biobased polyesters with tailored properties by varying the alkyl chain length, capitalizing on diols from biomass for this purpose is underexplored and has mainly focused on linear and branched shorter chain alcohols. Here, we explored the potential of two (−)-α-pinene-derived diols (PDOs) as building blocks to generate biobased polyesters harboring bicyclic ring structures in their backbones that can mimic aromatic fossil-based plastics’ properties. We demonstrate a concise synthesis of two novel unsymmetrical chiral PDOs on the 20–40 g scale, together with eight structurally differing heat-resistant polyesters, as reflected by high glass transition (T_g) temperatures (90 and 121 °C) for two of the polymers. The stereochemistry of PDO-derived polyesters is guided by intramolecular hydrogen bonding made possible by the protruding rings and the polyester backbone. Most of the synthesized polyesters (five) in this study showed potential as adhesives based on the analysis of tensile strength and adhesive properties on paper boards. The steric hindrance of the intact bicyclic α-pinene ring structure protruding from the backbone of the polymers can also aid in the degradation process, manifested by facile chemical recycling of these polyesters under mild conditions to recover both monomers. Finally, our results show how the generated rigid polymers are susceptible to enzymatic degradation by PETase and cutinase without any chemical pretreatment. Our results illuminate the potential of expanding the current scope of biobased monomers to bicyclic diols to generate biomaterials with tailor-made properties.