Ductile Copolyesters Prepared Using Succinic Acid, 1,4-Butanediol, and Bis(2-hydroxyethyl) Terephthalate with...

Poly(1,4-butylene succinate) (PBS) is a promising sustainable and biodegradable synthetic polyester. In this study, we synthesized PBS-based copolyesters by incorporating 5-20 mol% of -O₂CC₆H₄CO₂- and -OCH₂CH₂O- units through the polycondensation of succinic acid (SA) with 1,4-butanediol (BD) and bis(2-hydroxyethyl) terephthalate (BHET). Two different catalysts, H₃PO₄ and the conventional catalyst (nBuO)₄Ti, were used comparatively in the synthesis process. The copolyesters produced using the former were treated with M(2-ethylhexanoate)₂ (M = Mg, Zn, Mn) to connect the chains through ionic interactions between M²⁺ ions and either -CH₂OP(O)(OH)O^- or (-CH₂O)₂P(O)O^- groups. By incorporating BHET units (i.e., -O₂CC₆H₄CO₂- and -OCH₂CH₂O-), the resulting copolyesters exhibited improved ductile properties with enhanced elongation at break, albeit with reduced tensile strength. The copolyesters prepared with H₃PO₄/M(2-ethylhexanoate)₂ displayed a less random distribution of -O₂CC₆H₄CO₂- and -OCH₂CH₂O- units, leading to a faster crystallization rate, higher T_m value, and higher yield strength compared to those prepared with (nBuO)₄Ti using the same amount of BHET. Furthermore, they displayed substantial shear-thinning behavior in their rheological properties due to the presence of long-chain branches of (-CH₂O)₃P=O units. Unfortunately, the copolyesters prepared with H₃PO₄/M(2-ethylhexanoate)₂, and hence containing M²⁺, -CH₂OP(O)(OH)O^-, (-CH₂O)₂P(O)O^- groups, did not exhibit enhanced biodegradability under ambient soil conditions.