Junkichi Sohma

Basic sites and reducing sites of calcium oxide and their catalytic activities

The amounts of basic and reducing sites of calcium oxides prepared by heat-treating the hydroxide at various temperatures were measured, respectively, by titration with benzoic acid, using bromothymol blue, etc., as indicators and by observing ESR, spectra or visible reflectance spectra of adsorbed nitrobenzene or m-dinitrobenzene. The maximum amount of basic sites was found to be 0.57 mmole/g when the hydroxide was calcined at 500 ° in air, while that of reducing sites to be 5 × 1014 and 1016 sites/g, respectively, when calcined at 700 ° in air and at 500 ° in a vacuum. It has been found that the catalytic activity of various calcium oxides for the esterification of benzaldehyde correlates well with the basicities, whereas that for the polymerization of styrene does with the amounts of reducing sites. On the basis of the above results together with infrared spectra of adsorbed benzaldehyde, isopropyl alcohol, and chloroform, the nature of basic and reducing sites was discussed, the reducing sites being shown to be entirely different from the basic sites.

ESR study of V2O5 catalyst on carriers

Abstract ESR studies were carried out on V2O5 catalyst on two different carriers, Neobead and Alundum. The ESR spectrum of V2O5 catalyst on the Alundum carrier was a singlet which was similar to the spectrum of pure V2O5. A completely different spectrum having hyperfine structure was obtained from the V2O5 catalyst on the Neobead carrier. It was concluded that the ground state of V4+ in the catalyst on the Neobead was the dxy orbital. The molecular orbital interpretation of the g factors and the hf coupling constants lead to the conclusion that the unpaired electron was localized on the mother ion V4+. By computer simulation the linewidths of ESR spectra were determined. The analysis of the ESR spectrum suggests that the V4+ ion in the V2O5 catalyst on the Neobead was separately formed. The V4+ ion of V2O5 on the Alundum carrier forms a cluster.

Direct evidence of main-chain scissions induced by ultrasonic irradiation of benzene solutions of polymers

Abstract ESR studies combined with spin-trapping techniques are performed in order to obtain direct evidence of polymer chain scissions which are induced by ultrasonic irradiation in benzene solution of poly-(methyl methacrylate), poly(vinyl acetate), and polystyrene. The results show that the ESR spectra of the two spin adducts arising from pairs of radicals formed by the main-chain scission of these polymers were successfully observed.

Proton Magnetic Resonance in Chain Polymers

Proton magnetic resonance absorptions have been studied for several chain polymers. The experimental second moments of the absorption lines in the glassy state were compared with the calculated ones for the model of (– CH 2 · CHX –) n type. The temperature variations of the line widths were observed from room temperature to about 160°C. For PMMA and Polystyrene having large side chains, the line widths were found to narrow in two steps as temperature was raised. The first step of narrowing occured in neighbor of the glassy transition temperature T g and is assigned to the onset of the “hindered rotation” of the side chain. The second step of rapid narrowing started at the higher temperature than T g and is assigned to the “segmental rotation” of the main chain. In contrast with these cases, the line width transition of PVC and of PVAc occured in a single step narrowing at the higher temperature than T g which is assigned to the onset of the segmental motion. Referring to another observations information o...

ESR studies on the conversion of mechanoradicals of poly(methyl methacrylate) and its self-degradation

Abstract Mechanisms of the conversion of poly(methyl methacrylate) (PMMA) radicals produced by ball-milling have been investigated by means of ESR. The spectrum observed after a short milling time (0·1 h) at 77 K in vacuum was resolved into the three components, a triplet, a nonet and a doublet. The nonet, the triplet and the doublet are ascribed to the three kinds of radical: respectively. On the other hand, it was found that the spectrum after milling for more than 18 h at 77 K in a vacuum consisted of the nonet and the doublet, which had been converted from the triplet. The conversion of the triplet to the doublet during long milling suggests inter- and/or intra-hydrogen abstraction by the radical responsible for the triplet. The doublet observed after milling for longer than 18 h did not change its line-shape up to 263 K but on further warming to 273 K for 0·1 h the spectrum changed to give a triplet component. This reproduction of the triplet was interpretated in terms of β-bond scission to the unpaired electron of the radical (C), due to the thermal treatment. The bond scission was confirmed by the observed decrease in the molecular weight after the heat treatment. The radical (B) formed by the β-scission abstracts the hydrogen in the PMMA parent molecule to produce a radical of the species (C). This cyclic reaction leads to a self-degradation.

ESR study on molecular motion of peroxy radicals of polytetrafluoroethylene

Abstract Temperature variations of the line shapes of e.s.r. spectra from the peroxy radicals of polytetrafluoroethylene ( ptfe ) were investigated in detail and the results were quantitatively analysed based on Kneubuhls theory on the line shape. It was found that there were two kinds of rapid molecular motions, of which the correlation times were about 10 −9 s, for the peroxy radicals of ptfe ; one was the rotational motion related to the peroxy chain radical, the other was the three dimensional motion associated with the peroxy end radical. The activation energies of these molecular motions were estimated as 0·52 kcal/mol and 0·26 kcal/mol for the rotational motion and the three dimensional motion, respectively. Origins of such rapid motions were discussed in connection with the other molecular motions of polymers, which were found by other experimental methods.

Analysis of the N.M.R. spectrum of pyrrole

By the N-decoupling technique the signal of the N-H proton in pyrrole was clearly unveiled. Using the full spectrum, including the N-H band, the N.M.R. parameters for all five protons of the system were accurately determined. Assuming an AA′BB′X system, a computer simulation was performed; assignments were made for the observed lines. Based on the assignments, the N.M.R. parameters were determined with high accuracy by an iteration method. By using a partial decoupling experiment, the relative signs of the coupling constants between the N-H proton and the ring protons were determined to be the same.

Gamma-radiation induced cross-links in ethylene—propylene rubber studied by CP—MAS NMR

Abstract A new technique of 13 C-NMR, the CP-MAS method, was applied to study a chemistry of cross-links induced by ψ-irradiation of ethylene-propylene rubber. The chemical species of cross-linking points were specified with their relative concentrations by the analysis of the CP-MAS spectra obtained before and after irradiation. It was found that the short branches were also formed by the irradiation. A comparison was made between the cross-links detected by the CP-MAS method and those obtained by the Charlesby-Pinner analysis of the gelation caused by the ψ-irradiation. The conventional 13 C-NMR of the cross-linked and swollen EPR provided us an information on the sol parts of the sample but little information on the cross-links in the gel parts.

Anisotropic Hyperfine Constant in ESR Spectrum of Irradiated Solution Grown Polyethylene

ESR spectra from the alkyl type free radical, –\underset(β)CH2–\underset(α)CH–\underset(β)CH2– , produced in irradiated crystals of high density polyethylene (Sholex 6000) grown from 0.025 wt. percent solution in xylene were studied, and anisotropic hyperfine splitting due to α-proton was investigated. Hyperfine splitting due to α-proton, Dα, was obtained as |Dα|=24-5(1-3cos 2ψ) in the unit of gauss, where ψ is the angle between external magnetic field and the direction of the c-axis of the molecule. Spin density at the carbon atom bearing the unpaired electron was calculated as 0.7 from analysis of the data of the spectrum for the mat of crystals. From the observed ESR spectrum for the alkyl type free radical produced in melt grown crystals, principal values of hyperfine coupling tensor were also estimated as follows; |Az|=13.6 gauss, |Ax|=26.0 gauss, and |Ay|=40.6 gauss. These values are very close to the calculated values.

Study of carbonaceous mesophase through the e.s.r. spectra of vanadyl chelates

Abstract The behaviour of vanadyl chelate complexes in Iranian heavy oil and ethylene tar pitch during the carbonization process has been investigated by the e.s.r. technique to obtain information on the mesophase transformation. Activation energies for rotation of chelates incorporated with aromatic lamellae, and ordering parameters, are estimated from correlation times and intensities of e.s.r. spectra. The molecular plane of the chelates incorporated into the mesophase was found to be oriented parallel to the applied field. The value of activation energy is higher for a mesophase of small size than for a larger one.