Synthesis And Characterization Of Biodegradable Poly(3-hydroxybutyrate)/Poly(Ethylene Glycol) Multiblock Copolymers

Poly(3-hydroxybutyrate) (PHB) is a aliphatic polyester produced by a number of bacteria. It has many special properties such as biocompatibility, biodegradability, piezoelectric property and so on. Meanwhile, PHB is fragile, hydrophobic and its degradation time is too long. In this thesis, the basic properties of PHB, the synthesis and purification of PHB, and its modification as well as the applications of it were expatiated. At the same time, the resorbable polymeric materials used to prevent postsurgical adhesions were also reviewed in detail. We introduce poly(ethylene glycol)(PEG) as a second component to modify PHB. The incorporation of PEG into a PHB matrix can improve the hydrophilicity, flexibility and degradation rate. In order to improve the properties of PHB in essence, especially to improve the mechanical properties, hydrophilicity and degradability, the approach taken in the effort described here is based on multiblock copolymers. The detailed synthesis process is as follows. First, natural-origin PHB of high molecular weight was degraded by alcohololysis to provide low molecular weight and dihydroxy-terminated prepolymers. Then PHB-diol and PEG were multiblock copolymerized with hexamethylene diisocyanate (HDI) as coupling agent. Characterization by means of NMR, IR, DSC, POM, GPC and so on was carried out. The results showed that the prepolymers with special end-groups and destined molecular weight could be prepared by the alcohololysis in the presence of acid as the catalyst. No clear spherulitic morphology was observed in polarizing optical micrograph of PHB-diol. In the process of reaction, the degradation of the polymer follows a random chain scission mechanism. Every part of the molecular chain has an equal reactive probability. Under certain conditions, PHB/PEG multiblock copolymers can be synthesized in the presence of HDI. The chemical structures of multiblock copolymers were confirmed by IR, 13C NMR. The GPC chromatographs of copolymers showed, in all cases, peaks which were unimodal. During the heating scan of copolymer, obvious glass transition was detected. In addition, the Tg value is much higher than that of pure PHB. The copolymers were of high toughness and its elongation rate at break can reach to 150%. The tensile strength, Yong's modulus and elongation at break decreased with increasing the content of PHB-diol. The introduction of PEG dramatically improved the hydrophilicity (Swelling Ratio). And as the PEG content was increased, SW increased. By contrast to pure PHB, the degradation rates of copolymers were also raised by increasing the availability of water within the matrix.