关键词: 聚3-羟基丁酸酯(PHB), 聚3-羟基丁酸-3-羟基戊酸酯(PHBV), 固体NMR, 结构域, 分子动力学

Abstract: Poly(3-hydroxybutyrate) is one of the most applicative biodegradable polymers. However, its industrial application remains limited, owing to several inherent deficiencies including poor mechanical properties such as brittleness due to its high crystallinity and narrow thermal processing range. To overcome these drawbacks, a number of copolymers with other similar hydroxyalkanoate monomer units have been developed such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate), [P(HB-HV)]. Compared with PHB, these copolymers exhibit outstanding improvement of physical/mechanism properties such as reduced brittleness and enhanced flexibility. Although the preparation and its physical/mechanism properties had been investigated extensively, less work has been done for answering the questions about the molecular basis of them and the relationship between the micaostructural and dynamic properties and their macroscopic properties.
Nafion is one of the most promising proton-exchange membranes used in direct methanol fuel cell (DMFC). In practice, normal Nafion materials are not applicable for DMFC due to poor mechanical stability at temperature above 100 ℃. In order to develop the higher temperature electrolyte materials, many attempts have, so far, been made by modifying the Nafion membrane with various nonconductive inorganic materials. However, little information is available on the molecular basis of such thermal stability improvement. In addition, there are few reports dealing with the molecular structure of these composite materials, the interactions between the inorganic and organic species at the molecular level and structure-property relationships which will undoubtedly be useful for future development of materials.
In this dissertation, combined with XRD various solid state NMR techniques including ¹³C CP MAS、¹³C SPE MAS NMR, proton relaxation induced spectra editing, ¹H spin-diffusion have been employed to investigate the crystallnility and domain structural character. The experimental results show that with the content of HV increasing their crystallinity decrease, domain size of amorphous region increase and domain size of rigid region decrease, which can be seen at the molecular lever that introduction of HV results in the macroscopic properties improvement of PHB. 
Furthermore, ¹H variable temperature relaxation time (T₁, T_1ρ and T₂) measurements have been employed to investigate the molecular motional parameters such as molecular rotational correlation time (τ₀) and active energy (E_a) in the PHB and its copolymers PHBV. The results imply that the higher the content of HV, the faster the molecular motion, the lower the molecular active energy, which can be correlated to their structural and molecular dynamic properties at the molecular lever.
A series of nanocomposites have been prepared from perfluorosulfonylfluoride copolymer resin (Nafion) and layered montmorillonite (MMT) modified with protonated dodecylamine by conventional sol-gel intercalation. FT-IR and ²⁹Si MAS NMR results showed no significant alteration to the lattice structure of m-MMT and addition of the organically modified MMT led to moderate improvement of the thermal stability of Nafion resin though the resin was not intercalated into the m-MMT. ¹⁹F MAS, ¹H-¹³C CP MAS and HETCOR 2D NMR experimental results, combined with XRD and element analysis, indicated strong interactions between NH⁺₃ group of surface absorption of dodecylamine and the SO^-₃ group of the resin side chain. It is concluded that interactions between the resin and the surface absorbed organic modifier probably have some contributions to the resin thermal stability enhancement resulting from addition of m-MMT.

Key words: poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-3-hydroxyvalerate), solid state NMR, domain structure, molecular dynamics