Masatomo Minagawa

Assignment of finely resolved 13C NMR spectra of polyacrylonitrile

Abstract Finely resolved 13C NMR spectra of atactic and isotactic-rich polyacrylonitriles were determined. Assignments of nitrile carbon spectra with pentads were quantitatively confirmed. Methylene carbon spectra were assigned with hexads. Radically obtained polymer obeyed Bernoullian statistics. The polymerization mechanism of isotactic-rich polymer obtained from urea–canal complex is complicated and both the first and the second-order Markov statistics do not hold. The chemical shifts of nitrile carbon signals moved considerably toward up-field as the temperature is raised, due to change of solvation.

The steric effect of solvent molecules in the dissolution of polyacrylonitrile from five different N,N-dimethylformamide derivatives as studied using Raman spectroscopy

Abstract The steric effect of solvent molecules in the dissolution of polyacrylonitrile (PAN) from five different kinds of N,N-dimethylformamide (DMF) derivatives was studied using Raman spectroscopy and a laboratory constructed laser optical instrument. The dissolution behavior of PAN from solvents such as DMF, N,N-dimethylacetamide N,N-diethylformamide, N,N-dimethylcarbamylchloride, and N,N-dimethyltrichloro-acetamide was studied with the laser optical method. Raman spectra of the solvents and solutions provided significant information on the intermolecular interaction between nitrile and the solvents (i.e., dipole—dipole interaction). The carbonyl band in each solvent shifted from a lower to a higher frequency when nitriles were added, and the extent of the shift was directly related to the structure and geometry of a subtituent in each solvent molecule. An inverse linear relationship between the value of the dissolution temperature (Tsol) and the extent of the Raman carbonyl shift is demonstrated. It seems reasonable to explain this in terms of the steric effect of solvent molecules in the dissolution of PAN.

Dynamic nuclear magnetic resonance and Raman spectroscopic measurements of five kinds of N,N-dimethylformamide derivatives in relation to the dissolution mechanism of polyacrylonitrile

Abstract The internal rotation of five kinds of N,N -dimethylformamide (DMF) derivatives was studied by dynamic nuclear magnetic resonance (n.m.r.) and Raman spectroscopic measurements in relation to the dissolution mechanism of polyacrylonitrile (PAN). The dissolution temperature ( T sol ) of PAN was determined by the steric effect of the solvent molecules, i.e. the higher the bulkiness of a substituent, then the higher was the T sol of PAN. The intermolecular interaction between the nitrile group and the solvents was evaluated by Raman spectra in terms of the large carbonyl shift ( ν co ). Dynamic 1 H n.m.r. spectroscopy measurements revealed that the value of the coalescence temperature ( T c ) was not proportional to the steric factor, suggesting that the solvent properties are not determined solely by the latter and that internal rotation of the solvent molecules is defined by the extent of looseness in the packing of the solvent molecules in the liquid state. The significance of both intra- and intermolecular factors of the solvent molecules in the dissolution of PAN was also discussed.

13C n.m.r. and g.p.c.—low-angle laser light scattering measurements on polyacrylonitrile prepared by urea clathrate polymerization in the solid state for the optimization of tacticity

The molecular weight and molecular weight distribution of isotactic polyacrylonitrile (PAN) prepared by urea clathrate polymerization in the solid state were studied by the g.p.c.—low-angle laser light scattering (l.a.l.l.s.) method. The experimental details of this method for PAN are described. Measurements were carried out on three different kinds of urea clathrate PAN, and the results were compared with those of free-radical PAN (i.e. prepared using the aqueous redox slurry system). The characteristics of the urea clathrate PAN were (1) an asymmetrical shape in the g.p.c.—L.a.l.l.s. curve and (2) a remarkable contribution of the lower-molecular-weight component to the high stereoregularity (>80%) of the sample. An experimental prediction for the solid-state synthesis of a perfectly stereoregular PAN sample (isotacticity of 100%) has been derived from a combination of the g.p.c.—l.a.l.l.s, and 13 C n.m.r. results.

Surface modification processing of synthetic rubbers by ultraviolet irradiation and sputter ion etching treatment

The mechanism by which surface modification of two kinds of synthetic rubbers (ethylene-propylene and chloroprene) was brought about by ultraviolet (UV) irradiation and sputter ion etching treatments was studied from a physicochemical point of view. The most remarkable effect of this irradiation treatment was the rapid increase in adhesion properties and the simultaneous decrease in self-stickiness. This nonsticking effect was particularly important for the rapid production of articles from thin rubber sheets. The surface modification mechanism was studied by use of SEM, ESCA, FTIR, and related interfacial analytical procedures. It was shown that surface roughening with a quite thin layer of surface oxidation (∼0.5 μm in depth) is a key factor for the development of nonsticking properties.

Solid-state characterization and the thermal properties of stereoregular poly(vinyl chloride) prepared by urea clathrate polymerization

The solid-state characterization of highly stereoregular poly(vinyl chloride) (PVC) prepared by urea clathrate polymerization was carried out by using various instrumental analyses. The structural differences of PVC appeared most remarkably in solubility to organic solvents, IR, WAXD, and solid-state 13 C-NMR spectra. The value of the glass transition temperature (T g ) was about 90°C, not as high as expected, although its detection was quite difficult. The thermal stability was poor, as evidenced by the easy discoloration of this polymer by heat treatment, which was related to the absence of a termination reaction. Dynamic ESR spectra in the solid state clearly indicate that the radical formation occurs at such a low temperature as 160°C in the initial degradation stage. The degradation characteristics of urea clathrate PVC were critically discussed.