Hisashi Odani

Determination of degree of deacetylation of chitosan by 1H NMR spectroscopy

SummaryThis paper describes a novel method to determine the degree of deacetylation of chitosan by 1H NMR spectroscopy. Measurements were carried out at 70°C by using 2 wt% CD3COOD/D2O and 2 wt% DC1/D2O as solvents for chitosan. In the case of DC1/D2O system, effect on hydrolysis of chitosan should be taken into consideration, and the pulse repetition delay required for 45° pulse is 40s. Whereas, in regard to CD3COOD/D2O system, 6s pulse repetition delay is enough for 45° pulse, and moreover, high magnetic field NMR apparatus is necessary, because signal of CD2H residue in CD3COOD overlaps with that of CH3 residue in N-acetyl residue and determination of the difference of two spectra is required. The proposed method is more effective, precise and simple, comparing with the conventional colloid titration and elemental analysis methods. Assignments of 1H and 13C NMR spectra of chitosan are also reported.

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.

High-resolution solid-state 13C nuclear magnetic resonance study of the combined process of 1H spin diffusion and 1H spin-lattice relaxation in semicrystalline polymers

Abstract The combined process of spin diffusion and 1 H spin-lattice relaxation is measured for uniaxially oriented polyethylene films by high-resolution solid-state 13 C nuclear magnetic resonance spectroscopy with the 1 H- 13 C cross-polarization method. The experimental data are compared with a numerical simulation of the diffusion equation containing the relaxation term in order to estimate 1 H spin-diffusion coefficients and 1 H spin-lattice relaxation times for crystalline, interfacial and amorphous regions. For these regions, the 1 H diffusion coefficients and the relaxation times are estimated as 6 × 10 −12 , 6 × 10 −12 and 2.5 × 10 −12 cm 2 s −1 and 4.0, 0.4 and 0.13 s, respectively.

Diffusion and solution of methanol vapor in poly(2-vinylpyridine)- block- polyisoprene and poly(2-vinylpyridine)-block-polystyrene☆

Abstract Diffusion and solution behavior of methanol vapor in two diblock copolymers, poly(2-vinylpyridine)—block—polyisoprene [P(2VPbI)] and poly(2-vinylpyridine)—block—polystyrene [P(2VPbS)], was studied by the weighing method at 25°C. The domain structure of films of both copolymers showed an alternating lamellar arrangement. Methanol is a good solvent for P2VP, but a nonsolvent for PI and PS. Methanol dissolved exclusively in the P2VP phase of the copolymers. For both copolymer systems, absorption and desorption processes of non-Fickian type were observed as characterized by a thickness anomaly. However, the magnitude of the deviations from purely Fickian behavior was small, and the integral diffusion coefficient, D, was obtainable with reasonable accuracy. At low and medium concentrations, D for P(2VPbI) was greater, by about one order of magnitude, than that for P2VP, while D for P(2VPbS) was lower than that for P2VP. A similar trend was observed in plots of the permeability coefficient against the vapor pressure of methanol. The results indicate that the rubbery PI phase may facilitate the transport of penetrant molecules in the P(2VPbI) film. On the other hand, the glassy PS phase in the P(2VPbS) film merely interferes with the transport of methanol molecules.

Structure characterization of alginate and conformational behaviors of various alkali-metal alginates in solution

SummaryThe M/G ratio, i. e., number-ratio of D-mannuronate (M) to L-gluronate (G), and diad (MM, GG, MG, etc.) and triad (MMM, MMG, MGM, etc.) frequencies were determined with 100 MHz 13C-NMR spectra for two alginate samples, M-rich and G-rich samples. The M/G ratios obtained were in accord with those determined from chemical analysis on hydrolyzed products fairly well. Molecular chain dimensions in solution were investigated by viscosity method for five alkali-metal alginates carrying Li, Na, K, Rb and Cs, and the results were discussed based on ion radius and electronegativity of alkali-metals. Finally, ion-exchange characteristics of these alginates by Ca++ ion were interpreted with M/G ratio and electronegativity.

Transport and solution of gases and vapors in styrene-butadiene block copolymers: Absorption and desorption of n-hexane vapor

Abstract The integral absorption and desorption of n-hexane vapor by styrene-butadiene block copolymers were studied as a function of film thickness and vapor pressure at 25°C by use of a weighing method. The morphologies of the samples were (1) polystyrene rods dispersed in a polybutadiene matrix and (2) a series of alternating lamellae of styrene and butadiene components. For both copolymer samples (1) and (2), reduced solvent weight uptake plots for films of differing thicknesses did not give a single curve ½ when plotted against the Fickian variable, t½/X, where t is time and × is film thickness, though the individual absorption and desorption curves appeared to have a Fickian shape. In certain concentration regions, the two-stage type of non-Fickian behavior was observed with copolymer film having a type (2) morphology. As expected, absorption and desorption processes in homopolybutadiene films were purely Fickian. From these results it was concluded that the segmental motions in the polybutadiene ph...

Features and Interpretation of Sorption Processes in Polymer-Vapor Systems

The process in which gases or vapors of low molecular weight are absorbed into or desorbed out of polymeric solids is of great technical interest. The loss of solvents from paint films during drying and that from textile fibers in the course of spinning are primarily diffusioncontrolled. Numerous studies have been made to describe such absorption and desorption processes phenomenologically. However, it has not been until recently that efforts have been made to interpret observed data in terms of fundamental concepts such as structural features of high polymeric materials. In the present review we shall summarize some basic information so far obtained in this field and attempt to clarify molecular mechanisms which are likely to correlate closely with observed phenomena.