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 23 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 ([?]) of PBST than the other two factors. The number-average molecular weight (Mn) of the PBST was determined from the intrinsic viscosity by using the Berkowitz model of Mn?=?1.521?X?105[?]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 [?] reaching 0.49 dL/g when the temperature was held at 250?degrees 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?degrees 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%. (c) 2011 Curtin University of Technology and John Wiley & Sons, Ltd.