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 -OCCHCO- and -OCHCHO- units through the polycondensation of succinic acid (SA) with 1,4-butanediol (BD) and bis(2-hydroxyethyl) terephthalate (BHET). Two different catalysts, HPO and the conventional catalyst (nBuO)Ti, were used comparatively in the synthesis process. The copolyesters produced using the former were treated with M(2-ethylhexanoate) (M = Mg, Zn, Mn) to connect the chains through ionic interactions between M ions and either -CHOP(O)(OH)O or (-CHO)P(O)O groups. By incorporating BHET units (i.e., -OCCHCO- and -OCHCHO-), the resulting copolyesters exhibited improved ductile properties with enhanced elongation at break, albeit with reduced tensile strength. The copolyesters prepared with HPO/M(2-ethylhexanoate) displayed a less random distribution of -OCCHCO- and -OCHCHO- units, leading to a faster crystallization rate, higher value, and higher yield strength compared to those prepared with (nBuO)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 (-CHO)P=O units. Unfortunately, the copolyesters prepared with HPO/M(2-ethylhexanoate), and hence containing M, -CHOP(O)(OH)O, (-CHO)P(O)O groups, did not exhibit enhanced biodegradability under ambient soil conditions.