Ductile Copolyesters Prepared Using Succinic Acid, 1,4-Butanediol, and Bis(2-hydroxyethyl) Terephthalate with Minimizing Generation of Tetrahydrofuran

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 Tm 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.