Studies On The Molecular Design And Modifications Of Biodegradable PBS-based Polyesters

The polyesters have been used widely in various fields of human life because of their excellent performances. Though the application of polyesters made our daily life convenient and comfortable, the wastes also caused serious environmental problems. Therefore, the development of novel biodegradable polymer materials and the modification of traditional plastics with biodegradability has become a necessity. As a research hotspot in the world, aliphatic polyesters, with special ester bonds which was easier to be hydrolyzed, are susceptible to break the bond in natural environment and in biosomes. Poly(butylenes succinates)(PBS) is one classic aliphatic polyester. PBS has attracted great interests of researchers during recent few decades because of its high performance, but the degree of crystallinity of PBS is up to 40%～60%, so PBS has low degradation rate, on the other hand, PBS also has low melting point compared to conventional plastics, the processing performance and thermal stability of PBS is difficult to meet various requirements. On these accounts, we should improve the properties of polyesters by copolymerization and chain extension to meet the further requirements of polyester materials. Main contents and results are as follows:1. The present status of research as well as the development tendency of polyesters was summarized.2. A series of poly(butylene succinate-co-butylene sebacate)(PBSu-co-PBSe) random copolyesters were synthesized by polycondensation reaction. The structure and physical properties of the resulting aliphatic polyesters were characterized by hydrogen nuclear magnetic resonance spectrum(1H-NMR), X-ray diffraction(XRD), differential scanning calorimetry(DSC), thermogravimetry analysis(TGA) and lipase enzymatic degradation test. XRD showed that the crystal structure of copolyesters changed with the increasing of PBSe component and the cocrystallization behavior had appeared; DSC test showed that the melting point of the product first reduced and then elevated, the glass transition temperature decreased monotonously; TGA analysis indicated that copolymers had better thermal stability with the increasing content of sebacic acid; The lipase enzymatic degradation test indicated that the copolyester had better degradability, when the content of PBSe reached 40mol%, the copolyester had the fastest degradative rate.3. A series of biodegradable Poly(1,3-butylene terephthalate-co-1,4-butylene terephthalate)-b-poly(ethylene glycol) block copolymers were synthesized and characterized by means of Fourier transform infrared spectroscopic(FT-IR), hydrogen nuclear magnetic resonance spectrum 1H-NMR), differential scanning calorimetry(DSC), thermogravimetry analysis(TGA) and hydrolytic degradation. FT-IR and 1NMR analysis showed that the synthetic copolymers were the expected products; DSC test showed that with the increasing of 1,3-BDO component, the melting point(Tm) gradually decreased from 158.24℃to 104.19℃and the glass transition temperature(Tg) gradually increased from 4.86℃to 24.56℃, the synthetic copolyesters tended to be amorphous; TGA analysis indicated that the copolyester had lower thermal stability with the increasing content of 1,3-BDO, but all the copolyesters still had good thermal stability, the initial decomposition temperature was higher than 310℃, so there was no need to use any heat stabilizer during the synthesis. The result of hydrolytic degradation test indicated that the rate of degradation of copolyesters had significantly increased with the higher ratio of 1,3-BDO component.4. Biodegradable poly(ester urethane)s(PPCLBSTs) were obtained through chain-extension reaction of prepolymers, poly(s-caprolactone)(PCL-OH) and poly(butylenes succinate-co-butylenes terephthalate)(PBST-OH) using H12MDI as chain extender. PCL-OH was synthesized by ring-opening polymerization while PBST-OH was synthesized by melting polycondensation reaction. The structure and composition of PPCLBST was characterized by 1H-NMR and FT-IR, the molecular weight of prepolymers of PCL-OH and PBST-OH were 2598 and 5883 calculated by the results of 1H-NMR. The thermal and crystallization properties of PPCLBSTs were investigated by DSC. The crystallization of PPCLBSTs was mainly caused by PBST-OH segments, and it was difficult for PCL-OH segments to crystallize which was sterically hindered by hexatomic rings of H12MDI, poly(ester urethane)s had a decrease in glass transition point and were trend to be amorphous with the increasing content of PCL-OH segments. The thermal stability of polymers were measured by TGA, it showed that the decomposition of PPCLBSTs under went a two-stage process. PCL-OH segments degraded in the first and the PBST-OH segments degraded in the second, PPCLBST had good thermal stability because of aromatic structure in polymer chain. The test of water absorption showed that the novel poly(ester urethane) PPCLBST had better hydrophilic ability than that of PBS.