Synthesis Of Aromatic-Aliphatic Copolyester By Rare Earth Catalysts

To obtain a polymer material with satisfactory mechanical properties and biodegradability, aliphatic-aromatic copolyester P(BA-co-BT) was synthesized via direct polycondensation from 1,4-butanediol with dimethylterephthalate and adipic acid in the presence of rare earth catalysts. The polymerization characteristics of various rare earth catalysts are examined and the resulting copolyesters were characterized by GPC, XRD, ¹H NMR and TGA.Among various rare earth catalysts tested, NdCl₃, Nd(O₃SC₁8H₂9)₃ and Nd[OOC (CH₂)₁6CH₃]₃ have better catalytic activity. The catalytic activity of heavy rare earth catalyst Dy[OOC (CH₂)₁6CH₃]₃ is better than light rare earth catalyst Nd[OOC (CH₂)₁6CH₃]₃. For the polymerization, it can proceed with Dy[OOC (CH₂)₁6CH₃]₃ at 0.0625mol%o of the total amount of diacid material but with Nd[OOC (CH₂)₁6CH₃]₃ at 0.125mol%o. The [η] of the copolyester decreased with the decreasing catalyst amount.The chain structure of the aromatic-aliphatic copolyestr have been characterized by ¹H NMR and all the resonance line are clearly distinguished. Respectively, we get the molar ratio of butylene adipate unit (FR-BA) and butylene terephthalate unit (FR-BT) both about 50mol%. The number-average sequence lengths of butylene adipate unit (SL-BA) and butylene terephthalate unit (SL-BT) both about 1.92, when the degree of randomness is near 1.0. It suggest that the sequence structure of copolyester can be described as AATTAATTAATTAATTAATT.The X-ray diffraction of the copolyesters with 40mol%, 50mol% and 60mol% BT are similar to the PBT homopolymer, which suggested that those copolyesters contain PBT crystals. According to DSC observation, the glass transition temperature is -28.35℃ and melting temperature is 134.96℃. TGA shows high stability of the copolyester having high decompose temperature around 400℃.The contact angle of water on the surface of several copolyesters had been measured. The measurement shows that DP40/AA60 and DP60/AA40 have a contact angle less than 90° which indicating they may have better biodegradability.