One- and Two-Dimensional CP/MAS 13C NMR Analyses of Dynamics in Poly(2-hydroxypropyl ether of bisphenol-A) (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Dynamic Characterisitics)

The dynamics of amorphous poly(2-hydroxypropyl ether of bisphenol-A) (PHR), quenched from the melt, has been investigated by one- and two-dimensional solid-state 13C NMR spectroscopy. CP/MAS 13C NMR spectra from .150 to 180 oC give two specific features: (1) below 23 oC, resonance lines for CH carbons of phenylene rings split into two lines; (2) linewidths of resonance lines become broad at 20 - 50 oC above the glass transition temperature. The feature (1) indicates that phenylene C-H carbons exist in chemically different two sites at low temperatures. These two sites are probably associated with OH … hydrogen bond formation. The coalescence of the resonance lines at elevated temperatures is caused by flip motion of phenylene rings, which corresponds to the relaxation for PHR. The correlation time of the flip motion is analyzed by the two-site exchange model, and is found to follow the Arrhenius equation. The apparent activation energy is 51 kJ mol-1 by assuming an inhomogeneous correlation time distribution described by a Kohlrausch-Williams-Watts (KWW) function with an exponent of 0.2. The feature (2) is caused by the so-called motional broadening, which is originated by enhanced segmental motions. This dynamics corresponds to the relaxation for PHR and can be described by William-Landel-Ferry (WLF) equation. Two-dimensional CP/MAS 13C exchange NMR experiments confirm the existence of flip angle distribution as well as the distribution of correlation times of phenylene ring flip motion with a KWW exponent of 0.2

Cellulose Assemblies Produced by Acetobacter Xylinum (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Dynamic Characteristics)

Structures of cellulose assemblies produced by Acetobacter xylinum under various conditions have been studied mainly by transmission electron microscopy. Native cellulose crystals are composites of cellulose Iα and Iβ . Twisted-ribbn cellulose assemblies produced in the HS medium at 28 °C were rich in cellulose Iα . On the contrary, splayed microfibrils produced in the presence of CMC at 28 °C were rich in Iβ . Not only the ribbon assembly but also the bundle of splayed microfibrils was determined to twist in the right-handed manner. When the bacteria were incubated at 4 °C, two kinds of band-like assemblies, “dense” and “coarse”, were extruded perpendicularly to the long axis of bacterial cells. The number of cellulose chains produced by one bacterium was different between “dense” and “coarse” assemblies. The “dense” assembly gave the electron diffraction pattern of cellulose II. In certain cases the transition region from dense to coarse portions was observed in one assembly. Initially a “dense” portion was produced and thereafter a “coarse” portion was produced. The number of cellulose synthesis sites seems to decrease, because a bacterium becomes less active after a certain period of time at 4 °C

Solid-State 29Si NMR Analyses of the Structure and Dynamics of Solid Poly(di-n-alkylsilane)s (FUNDAMENTAL MATERIAL PROPERTIES-Molecular Dynamic Characteristics)

Solid-state 29Si NMR analyses of the solid structure and dynamics have been performed for poly(di-n-butylsilane) with the order-disorder transition at 76 °C. 29Si chemical shift anisotropy (CSA) spectra are measured with an ultraslow magic angle spinning at a rate less than 100 Hz. Almost rigid CSA spectra for the 7/3 helical structure are observed below the transition temperature. In contrast, axially symmetric CSA spectra with different principal values appear above the transition temperature, suggesting the onset of the rotational motion around the molecular chain axis with trans-rich conformation. The changes of the conformation and dynamics around the transition are also discussed for other poly(di-n-alkylsilane)s such as poly(dimethylsilane) and poly(di-n-hexylsilane)

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京都大学0048新制・課程博士工学博士甲第1594号工博第406号新制||工||302(附属図書館)UT51-50-E18京都大学大学院工学研究科高分子化学専攻(主査)教授 伊勢 典夫, 教授 稲垣 博, 教授 河合 弘廸学位規則第5条第1項該当Kyoto UniversityDFA