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 -O 2 CC 6 H 4 CO 2 - and -OCH 2 CH 2 O- units through the polycondensation of succinic acid (SA) with 1,4-butanediol (BD) and bis(2-hydroxyethyl) terephthalate (BHET). Two different catalysts, H 3 PO 4 and the conventional catalyst (nBuO) 4 Ti, 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 M 2+ ions and either -CH 2 OP(O)(OH)O - or (-CH 2 O) 2 P(O)O - groups. By incorporating BHET units (i.e., -O 2 CC 6 H 4 CO 2 - and -OCH 2 CH 2 O-), the resulting copolyesters exhibited improved ductile properties with enhanced elongation at break, albeit with reduced tensile strength. The copolyesters prepared with H 3 PO 4 /M(2-ethylhexanoate) 2 displayed a less random distribution of -O 2 CC 6 H 4 CO 2 - and -OCH 2 CH 2 O- units, leading to a faster crystallization rate, higher T m value, and higher yield strength compared to those prepared with (nBuO) 4 Ti 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 (-CH 2 O) 3 P=O units. Unfortunately, the copolyesters prepared with H 3 PO 4 /M(2-ethylhexanoate) 2 , and hence containing M 2+ , -CH 2 OP(O)(OH)O - , (-CH 2 O) 2 P(O)O - groups, did not exhibit enhanced biodegradability under ambient soil conditions.