PHB/PEG Multiblock Copolymers: Preparation, Structure, Properties, And Application As Molecular Imprinting Materials

In this study, we adopted chain-extending method by the aid of coupling agents to conjugate poly(3-hydroxybutyrate) (PHB) and poly(ethylene glycol) (PEG). By varying the block composition, a series of PHB/PEG multiblock copolymers have been successfully synthesized. Molecular structures and chemical compositions of them have also been confirmed by 13C-NMR and FT-IR spectral analysis. Every copolymer molecule comprises several PHB and PEG blocks, which are extended by covalent bonds. Because of the special chemical and condensed structures, this kind of copolymers combine the optimal properties of two components, and exhibit moderate physical and chemical properties, such as mechanical properties, degradability, and amphiphilicity.Morphologies of these copolymers were observed by polar optical microscopy (POM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) from different levels. Wide angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) were utilized to characterize the structures of them. Results show that the crystalline structure of PHB phase in the copolymer is identical to that of homopolymer PHB, but the size of spherulites greatly decreases. Two different types of phase morphologies take place in copolymers with various compositions, that is, inter-lamellar and inter-fibrillar segregation.Thermal analysis by differential scanning calorimetry (DSC) reveals that both the melting point and the crystallinity of PHB phase decrease in contrast to those of homopolymer PHB. Apparent glass transition can be observed in the heating scan, and the corresponding transition temperatures are much lower than that of homopolymer PHB.We chose soil suspension system to estimate the degradability of PHB/PEG multiblock copolymers. The changes in pH values, molecular weight, weight loss, swelling ratio, mechanical properties, and surface morphology were measured to monitor the degradation behavior. The degradation behavior of PHB/PEG multiblock copolymers are different from that of homopolymer PHB, and the rate of weight loss is much lower. During the degradation process, the macromolecules were gradually...