Studies on the optimal conditions for synthesizing poly(butylene succinate‐co‐terephthalate) copolyesters with targeted properties

The aliphatic‐aromatic copolyesters are becoming more important due to their desirable mechanical properties and biodegradability. In this study, a series of Poly(butylene succinate‐co‐terephthalate) (PBST) of various monomer compositions were synthesized from succinic acid (SA), dimethyl terephthalate (DMT), and 1,4‐butanediol (BDO) in the presence of tetrabutyl titanate (Ti(Obu) 4 ). The experiment was divided into three parts. The first part is a 2 3 factorial design with permutations of three factors, namely, temperature, molar ratio of BDO/DMT, and molar ratio of SA/DMT in polycondensation. Our statistical analysis showed that the temperature has a more significant effect on the intrinsic viscosity ([η]) of PBST than the other two factors. The number‐average molecular weight (M n ) of the PBST was determined from the intrinsic viscosity by using the Berkowitz model of M n  = 1.521 × 10 5 [η] 1.5 . The second part of the experiment is a time course investigation of polycondensation under various temperatures, molar ratios of BDO/(DMT + SA), and concentrations of Ti(Obu) 4 . Our results showed the best polycondensation occurred at 1.5 hr with [η] reaching 0.49 dL/g when the temperature was held at 250 °C, BDO/(SA + DMT) = 1.2 mol/mol with SA/(SA + DMT) = 50 mol%, and 0.97 mmol of Ti(Obu) 4 per mol of SA + DMT. The third part of the experiment involves searching for the best molar ratio of SA/(SA + DMT) in obtaining desirable polymer properties and biodegradability. The results showed that the highest melting point of PBST can be as high as 177 °C at SA/(SA + DMT) = 30 mol%. The maximum tensile strength of 25.6 MPa is obtained at SA/(SA + DMT) = 30 mol%. The maximum elongation at break of 269.3% and the maximum Young's modulus of 754.8 MPa are reached at SA/(SA + DMT) = 60 mol% and at SA/(SA + DMT) = 30 mol%, respectively. The fastest lipase‐decomposition rate of PBST reached 100 % at day six for samples with molar ratio SA/(SA + DMT) = 80 mol%. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.