Synthesis and enzymatic degradability of an aliphatic/aromatic block copolyester: poly(butylene succinate)-multi-poly(butylene terephthalate)

A novel multi-block copolyester, poly(butylene succinate)-multi-poly(butylene terephthalate) (m-PBST), was synthesized by the melt/solid interfacial co-polycondensation of a melt-blend of poly(butylene succinate) (PBS) and poly(butylene terephthalate) (PBT) that had been pre-formed. In this co-polycondensation, the reaction temperature was kept between the melting temperatures (T m) of PBS and PBT so as for the low-melting PBS (melt) to be effectively connected with the high-melting PBT (solid). The succinate content and persistence ratio (r) of the resulting m-PBST were affected by the time of melt-blending of PBS and PBT where their chain-scrambling reaction was induced. The average block number per polymer chain became the largest (7.3) when the blending time was properly adjusted with a PBS to PBT ratio of 2:1. Owing to the block copolymer structure, m-PBST showed thermoplastic properties that should be intermediate between those of PBT and PBS and completely different from those of the corresponding PBS/PBT random copolymer. The enzymatic degradability of m-PBST was also confirmed by the use of Lipase PS® originated from Pseudomonas cepacia. Consequently, m-PBST ought to have potential applications as a new structural material with excellent soft/hard balance and toughness.