Synthesis, Characterization And Properties Of PBST Copolyester Preparated Via Direct Esterification-polycondensation

As one forerunner of world economy, the development of material is playing the pivotal role in the modern civilization, especially high-molecular compounds synthesized in the 20th century. For example, more than 50% fiber demand was the synthetic fiber over the worldwide textile industry at the beginning of the century. However, high-molecular compounds has met some question, such as energy, economy and environment. More and more people pay attention to the biodegradable high-molecular materials. Among them, aliphatic/aromatic copolyner is an important category for the balance of its biodegradability and physical properties. Poly(butylene succinate-co-terephalate) (PBST) just belongs to this kind of copolymers.At present, PBST copolymer ware prepared via transesterification route in domestic and foreign research. In our previous work, the PBST with high molecular weights were synthesized via transesterification route, and their chemical and sequential fine structures, thermal properties, crystallization behaviors and enzymatic degradation were studied intensively. However, transesterification route costs more raw materials and more energy consumption.Comparatively, the direct esterification-polycondensation route needed less investment, and the response production was the water, which was environmental-friendly. The production process was short, with less invests and higher production efficiency. And the divalent alcohol amount used in synthesis was fewer compared with the transesterification route.Based on this, a series of biodegradable aliphatic-aromatic poly(butylene succinate-co-terephthalate) (PBST) copolyesters were synthesized through the method of esterification/polycondensation from the starting materials of succinic acid, terephathalic acid and 1,4-butanediol the presence of different sets of catalysts, catalyst promoters and stabilizing agents in this paper. The influence of catalysts, catalyst promoters and stabilizing agents to synthesize would be researched, and the characterization and properties of PBST copolyester will be studied.Firstly, this paper synthesized PBST copolyesters via direct esterification-polycondensation from succinic acid, terephathalic acid and 1,4-butanediol the presence of titanium tetraisopropoxide(TTiPO), and discussed synthesis craft and phenomenon. ~1H NMR results indicated that the moral fraction of BT comonomers of the prepared products were almost 70%, which is close to feeding proportion. The GPC results showed that the weight average molecular weights(M_w) of PBST copolyeaters were in the range of 8.86×10~4～10.03×10~4. The melt index (MI) results proved that the most effective catalyst amount was l/3000mol of binary acid. Added catalyst promoters, the reactions time was reduced and the efficiency of reaction was enhanced. The most effective catalyst promoters amount was l/5000mol of binary acid. Stabilizing agents, not only enhanced reacting system's thermostability, but also made the polyester albedo to raise 4 %.Secondly, the according to DSC, TGA investigations, it was found that good themal properties were entitled to PBST copolyseters, whose melting peak temperatures at 178.37℃and decomposion temperatures at 389.1℃. And the highest crystallinity reached 25.7% calculated from thermal results. The tensile property reslults indicated that the catalyst promoters reduced the thermostability of PBST copolyesters. Stabilizing agents added with catalyst promoters may enhance the break force and the rupture elongation of the PBST copolyesters. The isothermal crystallization research indicated that the higher crystallizing temperature, the slower speed of polymer segment crystallization, and the macro-molecule chain needed longer time to arranger, which would form higher crystallinity and had higher melting point correspondingly. According to Avrami equation and POM studies, it was found that the PBST copolyesters crystallization is heterogeneous nucleation, by spherulitel form three dimensional growth. After isothermal crystallization at different temperatures, the elongation of PBST copolyesters were changed. The elongation of PBST copolyesters were elevated firstly and reduced then as the crystallizing temperatures enhanced, and when crystallizing point at 150℃, the break extends is maximum value 91 mm.