Effect of copolymerized butylene terephthalate chains on polymorphism and enzymatic degradation of poly(butylene adipate)

The introduction of aromatic butylene terephthalate (BT) units into the backbone chains of aliphatic poly(butylene adipate) (PBA) not only changes the mechanical performance of the resultant P(BA-co-BT) copolymers but also affects their biodegradability. Because of the polymorphism of PBA homopolymer, the copolymerized BT units may also influence the polymorphic crystal structure as well as the biodegradation behavior. In this work, three P(BA-co-BT) copolymers with BT contents as 10, 20, and 25 mol% were chosen to study their polymorphic crystal structure, thermal properties and enzymatic degradation by means of wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and gravimetric methods. The results reveal that the P(BA-co-BT) copolymers with BT contents below 25 mol% can form polymorphic crystal structures after melt-crystallization at different temperatures. However, the recrystallization and transformation of polymorphic crystals are strongly affected by the rigid BT units. The enzymatic degradation rates of P(BA-co-BT) copolymers decrease with increasing the BT contents. The influences of the BT units on the polymorphism and enzymatic degradation are discussed in terms of the motion of PBA chains that copolymerized with BT units. It has been concluded from the examination of solid-state microstructure that the influence of the aromatic BT units on the motion of biodegradable PBA chains heavily influences the biodegradability.