A Biobased Bicyclic Monomer toward Poly(butylene terephthalate) Copolyesters with Dual Closed-Loop Recyclability and Improved Performance

The integration of excellent performance and facile closed-loop recycling of poly(butylene terephthalate) (PBT) copolyesters remains a significant challenge. Herein, a biobased rigid diol (denoted as HT) was prepared by an acid-catalyzed acetalization reaction from 5-hydroxymethylfurfural (HMF) and trimethylolpropane (TMP). HT was copolymerized with PBT to prepare a series of PBTxTTy copolyesters with high Mn up to 45.5 kDa. The insertion of HT led to excellent thermomechanical and UV shielding properties, such as the glass transition temperature (Tg of 47.3 °C) and strength (43 MPa) of PBT80TT20 outdistancing those of PBT. More importantly, the acetal-based HT enabled dual closed-loop recycling pathways for PBTxTTy copolyesters via selective cleavage of acetal or ester bonds, allowing the recovery of structures terminated with aldehyde/hydroxyl end groups or PBT. Both recycled products could be repolymerized. Overall, HT is an effective biobased precursor that can prepare PBT-based copolyesters with excellent physical properties and dual closed-loop recyclability.