Synthesis And Characterization Of PBS And Its Copolymers

The application of polymer materials made our daily life more comfortable and convenient. However, it also causes serious environmental problems because they are hard to degrade in nature. Therefore, it is important to develop biodegradable polymers. Aliphatic polyesters, with outstanding biodegradability, bioabsorbability and biocompatibility, have attracted great interest of researchers in recent few decades. Comparing with other aliphatic polyesters, Poly (butanediol succinates)(PBS) has its own special characters, such as higher melting point and extensive application fields. However, PBS cannot satisfy different requirements as materials, therefore, in this paper, the modification of PBS was successfully fulfilled by copolymerization and blending to further enlarge its application fields.In detail, the various homopolymers of PBS with different end groups and molecular weights have been synthesized by polycondensation of 1,4-butanediol and succinate. Moreover, the effects of the molecular weight on thermal and biodegradability properties of PBS have been discussed. The results showed that the degree of crystallinity and the melting enthalpy of PBS decreased with the increase of the molecular weight. It also found that the biodegradation speed gradually increased with degradation time. Besides, the biodegradation speed was higher for PBS with lower molecular weight. In order to improve the thermal and mechanical properties of PBS, the new copolyester, poly (butylene succinate -co-ethylene succinate-co- ethylene terephalate)(PBEST) was synthesized through the polycondensation of three prepolymers of polybutylenes succinate, polyethylene succinate and polyethylene terephthalate. Furthermore, the structures and properties of PBS were characterized using 1H-NMR, DSC, WAXD, TGA, and compost test. The results showed that esterification occured during polycondensation and a kind of random copolyester formed. In addition, the degree of crystallinity would vary with the composition of the copolyesters. Moreover, The melting point of the copolyesters PBEST is much higher than that of the poly (butylene succinate –co-ethylene succinate) (PBES). From the biodegradability test in compost condition, it was concluded that the biodegradability of copolyeters was greatly affected by the content of ET.PBS, as a fully biodegradable polymer with relatively low cost and higher melting point, can also be used to modify other polyesters. In order to overcome the low melting point and high cost of PCL, a new block copolymer PBS-b-PCL was synthesized using SnOct2 as catalyst. Moreover, the structures and properties of PBS-b-PCL (65%mol) were characterized. The results showed that the melting point of PBS-b-PCL is higher than that of PCL, expecting a wider application field. Besides, it was proved that the catalytic efficiency of SnOct2 was much higher than that of AlEt3 for synthesis of PBS-b-PCL. The modification of PBS was also made by blending PBS with PCL. The thermal properties of PBS/PCL blends were investigated using DSC. The results showed that the degree of crystallinity and melting point of PCL decreased with the increase of PBS, while PCL almost had no influence on the thermal properties of PBS. After adding compatibilizer, the degree of crystallinity and melting point of PCL decreased further, and PCL also decreased the crystalline temperature of PBS in certain PCL content.The rheology properties of the PBS/PCL blends were investigated using a Capillary Rheometer. The results showed that PBS/PCL blends exhibited a shear-thinning phenomenon, which were the characteristics of the pseudoplastic flow. Besides, the apparent viscosity is more sensitive to the change of the shear rate for PBS/PCL blends with higher content of PCL. Furthermore, when compatibilizer was added, the pseudoplastic flow behaviors of the blends were not changed. However, the apparent viscosities of the blends decreased after adding compatibilizer especially for low shear rate.