Ryozo Kitamaru

Solid-state high-resolution 13C-NMR studies of regenerated cellulose samples with different crystallinities

SummaryCP/DD/MASS 13C-NMR spectra have been obtained for regenerated cellulose samples with different crystallinities as well as for cotton, β-D-glucose, β-D-cellobiose, and cellopentaose. The spectra of the regenerated cellulose samples exhibit broad multiplicities of the C-4 and C-6 resonance lines in a similar manner as those of native cellulose samples such as cotton and ramie, and, in addition, another broad tailing of the C-1 resonance. Since these multiplicities change linearly with crystallinity, it is concluded that they are ascribed to the contributions from the crystalline and noncrystalline components. Effects of hydrogen bonds and conformations of the β-1,4-glycosidic linkage on the chemical shifts are also discussed.

Structural study of amylose polymorphs by cross-polarization-magic-angle spinning, 13C-N.M.R. spectroscopy

C.p.-m.a.s. 13C-n.m.r. spectra and 13C spin-lattice relaxation times (T1) at room temperature have been measured for recrystallized samples of different polymorphs of amylose. Although the spectra of A- and B-amyloses in the dry state are very broad and almost structureless, the respective resonance lines of the samples soaked in H2O narrow markedly, and fine splittings can be observed in the C-1 lines, namely, a triplet for the A-type crystal form and a doublet for the B-type crystal form. These multiplicities had already been reported for native A- and B-starches, but the resolution is much higher for the recrystallized samples. In contrast, all resonance lines are composed of single signals for the hydrated and anhydrous V-amyloses, without any significant effect of hydration. It is also found that 13C t1 values of the crystalline components of amyloses are much shorter than those of celluloses. This suggests that the enhanced torsional motion about the α-D-(1→ 4)-glycosyl linkages is allowable for amyloses, even in the crystalline region, because of the flexible, helical structure.

Solid-state 13C-NMR study of conformations of oligosaccharides and cellulose: Conformation of CH2OH group about the exo-cyclic C-C bond

SummaryCP/DD/MAS 13C NMR spectra have been obtained for different monosaccharides, oligosaccharides, and cellulose. It has been found that a simple linear relationship exists between the chemical shift of the CH2OH carbon and the torsion angle χ about the exo-cyclic C-C bond. The chemical shifts fall into three groups of 60–62.6 ppm, 62.5–64.5 ppm, and 65.5–66.5 ppm, which are related to gauche-gauche, gauche-trans, and trans-gauche conformations, respectively. On the basis of these results the conformation of the CH2OH carbon of cellulose is also discussed.

Cross polarization/magic angle spinning 13C n.m.r. study of solid structure and hydrogen bonding of poly(vinyl alcohol) films with different tacticities

Abstract Cross polarization/magic angle spinning (CP/MAS) 13C n.m.r. measurements have been performed at room temperature for poly(vinyl alcohol) (PVA) films with different tacticities to obtain information about the structure and hydrogen bonding in the crystalline and non-crystalline regions. 13C spin-lattice relaxation analyses have revealed that three components exist for each sample, with different spin-lattice relaxation times T1C, which are assignable to the crystalline, less disordered non-crystalline and amorphous components. Using such differences in T1C, we separately recorded the spectra of the crystalline and non-crystalline components, and then analysed the triplets of the CH resonance lines appearing in both spectra in terms of three Gaussians which should be ascribed to CH carbons associated with two, one and no intramolecular hydrogen bond(s) in the mm, mr and rr sequences. As a result, it has been found that the relative intensities of the triplets are not in accord with the contents of the triad sequences, suggesting the formation of intramolecular and intermolecular hydrogen bonds in the meso sequences at almost equal probability. The effects of water on hydrogen bonding have also been examined for the almost atactic PVA sample.

CP/MAS Carbon-13 NMR Study of Spin Relaxation Phenomena of Cellulose Containing Crystalline and Noncrystalline Components

Abstract Cross-polarization, 13C rotating frame spin-lattice relaxation and C laboratory frame spin-lattice relaxation processes have been studied for different cellulose samples by CP/MAS 13C NMR spectroscopy. It was found that the CP process can be described by a simple thermodynamic model and relative intensities of the respective resonance lines are consistent with the atomic ratios for the spectra obtained at a contact time of about 1 ms. The observed rotating frame spin-lattice relaxation times TC 10 were dominantly dependent on the time constant TD CH by which 13C nuclei were coupled to the 1H dipolar spin system. It was, therefore, impossible to obtain information about molecular

Noncrystalline contents in linear polyethylene samples, crystallized from the melt and dilute solution as revealed by proton dipole decoupled/magic angle sample spinning 13C NMR

SummaryIt is certified from identification of a chemical shift coinciding with σiso, a motionally averaged chemical shift observed for this polymer in solution that noncrystalline contents in both melt- and solution-grown crystals are in a similar chain conformation to that in the melt or solution. Furthermore, examination of magnetic relaxation times of the σiso line reveals that the local chain dynamics of the noncrystalline content are the same for both samples while a long range chain motion for the solution-crystal is somewhat restricted.

Phase structure of uniaxially oriented polyethylene films as studied by high resolution solid state 13C n.m.r. spectroscopy

Abstract High resolution solid state 13C nuclear magnetic resonance (n.m.r.) measurements have been made at room temperature for uniaxially oriented polyethylene films by setting the drawing direction parallel to the static magnetic field. Two sharp lines assignable to the crystalline and non-crystalline components appear at 11.8 and 32.6 ppm, respectively, indicating that this sample contains highly oriented crystalline regions and almost disordered non-crystalline regions. On the basis of 13C spin-spin relaxation time measurements and lineshape analyses, the non-crystalline line can be further resolved into two components, crystalline-amorphous interphase and amorphous component. The thickness of the interfacial component has been estimated to be ≈90 A † , which is extraordinarily large compared with the values for the isothermally crystallized polyethylenes and the theoretical value. On the other hand, the crystalline resonance line is found to be composed of three components with different spin-lattice relaxation times. The origin of these components is also briefly discussed.

Solid-solid phase transformation of uniaxially oriented n-alkane crystals of high purity

Abstract The 13 C solid-state NMR spectrum and the spin-lattice relaxation time, T 1C , have been measured at different temperatures for a uniaxially oriented n -C 27 H 56 crystal mat of purity 99.98%, setting the orientation axis parallel or perpendicular to the static magnetic field. On the basis of the change in the lineshape and T 1C value in the different phase A, A′, and H, the molecular motions such as rapid local fluctuation and rotation about the molecular chain axis are discussed in the respective phases.

Dipolar-decoupled carbon-13 NMR study of highly oriented polyethylene films

SummaryHigh-resolution solid-state 13C NMR spectra and 13C relaxation times T1 and T1ρ have been measured at 40–100° C for uniaxially oriented polyethylene films with the drawing direction parallel to the magnetic field; this sample has a unique morphological structure that the noncrystalline chains are nearly disordered irrespective of the high degree of drawing. A sharp resonance line(line A) appears at the position corresponding to the principal value σ33 of the chemical shift tensor for the CH2 carbons with the trans-trans conformation. Another sharp linedine B) is observed at almost the same chemical shift as for the CH2 carbons of polyethylene in solution. Although these observations are similar to those for a cold-drawn polyethylene sample reported previously, line B is much enhanced in intensity and the linewidth is narrower in the present sample, reflecting the disorientation of the noncrystalline component. It is found from T1 measurements that line A contains two components with different molecular mobility, both being assigned to the crystalline components. On the other hand, the line B is composed of a single component assignable to the noncrystalline component with liquid-like molecular mobility.

Application of High-Resolution 13C NMR To Crystalline Polymers

The basic principles of high resolution 13C NMR for solids, and some applications for studying the semicrystalline structures of polyethylene and celluloses are reviewed. Characteristic 13C spectra, determined by three principal values of the chemical shift tensor, are obtainable by applying a sufficiently large resonant oscillating magnetic field to 1H nuclei (DD). The determination of the principal axes of the chemical shift tensor of orthorhombic polyethylene is reviewed. The DD technique can be applied to oriented samples because the molecular chain axis is parallel to the tensor’s principal axis having the largest principal value. Thus 13C NMR with DD for uniaxial samples parallel to the static magnetic field shows a sharp crystalline line corresponding to the largest principal value and a non-crystalline line having the same chemical shift as observed in solution. The detailed study of the phase structure of a highly oriented sample is discussed.