Synthesis of poly(butylene terephthalate)-poly(tetramethylene glycol) copolymers using terephthalic acid as starting material: A comparation between two synthetic strategies

Poly(butylene terephthalate)-poly(tetramethylene glycol) (PBT-PTMG) copolymer is prepared with terephthalic acid (PTA) rather than its dimethyl ester (DMT) as starting material by a two-step melt polycondensation. This process includes the synthesis of PBT prepolymer from PTA with 1,4-butanediol (BDO) in the first step, followed by the synthesis of PBT-PTMG copolymer from PBT prepolymer with PTMG in the second step. The molecular weight, composition as well as thermal and mechanical properties of the products from the two-step melt polycondensation are compared with the properties of the PBT-PTMG from the traditional one-step melt polycondensation. When the PTMG content is low, there is only slight difference in molecular weight, composition, thermal and mechanical properties among PBT-PTMG copolymers obtained from these two methods. However, when the PTMG content is high, only the two-step strategy is able to give high molecular weight products, and the products have comparable thermal and mechanical properties with those from traditional one-step strategy using DMT as starting material.