Chemical Recycling of Poly(butylene terephthalate) into Poly(ethylene brassylate-co-butylene terephthalate) with Tunable Thermal, Mechanical and Biodegradable Properties

We report here a high-value-added strategy for the chemical recycling of poly(butylene terephthalate) (PBT) into poly(ethylene brassylate-co-butylene terephthalate) (PEBBT) copolyesters. By cyclodepolymerization, postconsumer PBT can be first depolymerized to attain cyclic oligo(butylene terephthalate)s (COBTs), which are further copolymerized with ethylene brassylate (EB) and 1,10-decanediol for the preparation of PEBBT copolyesters using a cascade polycondensation coupling ring-opening polymerization (PROP) method. The chemical structures of PEBBT copolyesters are carefully characterized through quantitative ¹H and 2D ¹H–¹H gCOSY NMR spectroscopies. By changing the initial feeding ratio of COBTs and EB, the contents of aromatic and aliphatic polyester segments in PEBBT can be flexibly tuned, which can be further used to modulate the crystallinity, mechanical and biodegradable properties. These PEBBT copolyesters exhibited remarkable mechanical performance with high strength, elongation at break and toughness. Moreover, in the presence of lipase, complete biodegradation can be achieved for copolyesters with high aliphatic polyester segment contents.