A Multifunctional Tetracyclic Monomer toward Bio-Based Polyesters with Excellent Performance and Facile Chemical Closed-Loop Recycling

The development of multifunctional biobased polyesters with facile chemical closed-loop recyclability remains challenging. Herein, (((oxybis(methylene))bis(5-ethyl-1,3-dioxane-5,2-diyl))bis(furan-5,2-diyl))dimethanol (HD), a tetracyclic biobased diol compounded by acetal and furan rings, was synthesized via an acid-catalyzed acetalization reaction from 5-hydroxymethylfurfural (HMF) and ditrimethylolpropane (di-TMP). HD exhibited high reactivity to be polymerized with various diols to prepare biobased polyesters PDX with high Mn over 30 kDa. The resulting polyesters exhibited a high glass transition temperature (Tg of 67 °C) and tough mechanical properties (tensile strength up to 53 MPa), which had great potential to compete with commercial poly(ethylene terephthalate) (PET) and poly(lactic acid) (PLA). In addition, the furan rings in HD endowed PDX polyesters with excellent UV shielding properties, with a maximum shielding cutoff of 420 nm, effectively blocking the entire spectrum of UV radiation. More significantly, HD-based polyesters achieved closed-loop recycling through methanolysis at 80 °C for 4 h. The repolymerized polyester still maintained its material structure and performance. Density functional theory (DFT) calculations revealed that hydrogen bonding between HD and methanol played a key role in facilitating the cleavage of polyester ester bonds and accelerating PDX depolymerization. Overall, this work transitions from degradable furan-polyesters toward chemically recyclable materials, positioning HD as a promising multifunctional precursor for the development of biobased polyesters with excellent performance and easy chemical closed-loop recycling.