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 PBT_<i>x</i>TT_<i>y</i> copolyesters with high <i>M</i>_n up to 45.5 kDa. The insertion of HT led to excellent thermomechanical and UV shielding properties, such as the glass transition temperature (<i>T</i>_g 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 PBT_<i>x</i>TT_<i>y</i> 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.