Syntheses Of Aliphatic-aromatic Copolyesters By A Melting Bulk Reactive Blending And Its Biodegradability

A serie of new biodegradable Aromatic-Aliphatic copolyesters materials with satisfactory thermal properties were synthesized by Melting Bulk Reactive Blending between/among Aromatic and Aliphatic polyesters. High molecular mass poly(1,4-butylene terephthalate-co-DL-lactide) (BLA) copolymers was synthesized by the Poly(1,4-butylene terephthalate) (PBT) tranesterificated with D,L-Oligo(lactic acid) (OLA) in the melt leading. The analysis from ~1H NMR reveals that transesterification is unavoidable between butylene terephthalate (BT) and lactide (LA) segments during synthesis. The BLA copolymers were confirmed to be segmented copolyesters with certain random properites as show by the sequence structure of BLA copolyester chains and by their thermal behavior. The BLA copolyesters show only one melting temperature (T_m), crystallization temperature (T_c), and thermal decomposition temperature (T_d) when the reaction between PBT and OLA takes place at 280℃for more than 0.5 h. With OLA composition increase, the T_m, T_c and T_d decrease due to fewer aromatic sequences. The copolyester with a PBT/OLA feeding molar ratio of 5.9/94.1 is soluble in chloroform, while pristine PBT is only soluble in mixed chloroform/phenol solvent. The weight-average molecular weight of the copolyester (5.9/94.1 mol/mol PBT/OLA), determined by the Gel permeation chromatography, was to be 11200 g/mol.Because of the poor mechanical property of BLA, a reactive blend of poly(ethylene glycol) (PEG) and D,L-oligo(lactic acid) (OLA) is obtained at high temperature to produce partial PEG/OLA multiblock copolymer without purification prior to preparation of copolyesters. The reactive blend of PEG/OLA multiblock copolymer easily further reacts with poly(l,4-butylene terephthalate) (PBT) in the melt leading to the formation of high molar mass poly(l,4-butylene terephthalate-co-ethylene oxide-co-D,L-lactide) (PBTEOLA) copolymers. The analysis of ~1H NMR combined with solubility test reveal that the transesterification between butylene terephthalate (BT), ethyleneoxide (EO) and lactide (LA) segments is unavoidable during synthesis. The copolyesters are segmented copolyesters with certain random properties, as confirmed by their thermal behavior. The copolyesters show only one melting temperature (T_m) on the second heating run and one crystallization temperature (T_c) on the cooling cycle from differential scanning calorimetry (DSC) measurement, and one thermal decomposition temperature (T_d) from thermogravimetry (TG) measurement when the reaction between PBT and PEG/OLA takes place at 260℃for 1.5 h. With increase of OLA feeding composition in PEG/OLA blend or increase of content of PEG/OLA blend, the T_m and T_c of copolyesters decrease, and solubility increases. The obtained copolyesters are soluble in chloroform. And the weight-averaged molecular weight of the copolyester was estimated to be as high as 66600 g/mol by the Gel permeation chromatography. Mechanical tests indicate that the copolyesters exhibit high Young's modulus of 50-100 MPa and good elongation at break of 32-137%. A bracket of tissue engineer with poly(1,4-butylene terephthalate-co-ethylene oxide-co-DL-lactide) (PBTEOLA) copolymers was produced by using NaCl hole forming technique. Encouraging results on biocompatibility were received by initial studies of cell growth on the bracket.