Modification of poly(vinyl chloride). XXIX. Cross linking of poly(vinyl chloride) with 2-dibutylamino-4,6-dithiol-s-triazine and MGO

Thermal crosslinking of poly(vinyl chloride) (PVC) with 2-dibutylamino-4,6-dithiol-s-triazine (DB) and MgO has been studied to determine the kinetic parameters such as induction period (t₀), rate constant (k), and activation energy (E), and to elucidate the structure of crosslink and the crosslinking mechanism. The thermal crosslinking was treated as a pseudo-first-order reaction. In the crosslinking, k and t₀ were about 0.075 min^?1 and 6.8 min at 180°C, respectively, and E was 16.6 and 14.2 kcal/mole for k and 1/t₀, respectively. The structure of crosslink was confirmed to be indicated as the following scheme (I) from the results of model reactions and IR spectra of crosslinked products The crosslinking reaction was found to proceed through the following three processes: (1) formation of DB-Mg from DB and MgO; (2) formation of DB-Mg pendants by the reaction of PVC with DB-Mg; and (3) formation of crosslink by the reaction of PVC with DB-Mg pendants.     

ESR spectra of poly(methacrylic acid) and poly(methyl methacrylate): Reinterpretation of the 9-line spectrum

The temperature dependence of the ESR spectra of poly(methacrylic acid) and poly-(methyl methacrylate) γ-irradiated at room temperature was studied between ?196°C and +25°C. The conventional 9-line spectrum was observed throughout this range with no significant spectral change, in contrast to the propagating radical ··· CH₂? °C(CH₃)COOR found in methacrylic acid monomer or barium methacrylate dihydrate irradiated at ?196°C. In addition, the irradiation of methacrylic acid monomer with a low dose at 0°C gave the same 13-line spectrum as that of the propagating radical obtained by the irradiation at ?196°C, while prolonged irradiation at 0°C gave the same conventional 9-line spectrum as that of poly(methacrylic acid) or poly(methyl methacrylate). The conventional 9-line spectrum has a much weaker 4-line component than that of the propagating radical. The difference comes from the surrounding matrix, and the conventional 9-line spectrum is well interpreted by introducing the concept of the distribution of the conformational angle in the irregular polymer matrix. From simulation of the ESR spectrum, it was found that the intensity of the 4-line component is very sensitive to the distribution, and that the observed 9-line spectrum is well reproduced assuming a Gaussian distribution (half-height width of 5–6°) around the most probable conformation which is nearly the same as that of the propagating radical, where the conformational angles of the two C? H_β bonds to the half-filled p-orbital are 55° and 65°.     

Measurement of Timing Jitter in Wavelength Tunable Femtosecond Soliton Pulses

We investigated the root mean square (RMS) timing jitter and RMS intensity noise of the wavelength tunable femtosecond soliton pulses using the technique of radio-frequency spectrum analysis. We obtained interesting results that the generated solitons have almost constant RMS timing jitter and RMS intensity noise of approximately 410 fs and 0.03% in the wavelength region of 1600-1750 nm. It is therefore believed that the magnitudes of the jitter and noise are not greatly increased in the process of wavelength tunable soliton pulse generation. The wavelength tunable soliton pulse is confirmed to be stable and useful for practical applications.     

Furopyridines. XXIX. Reactions of furo[2,3-b:4,5-c‘]-, -[3,2-b:-4,5-c’]-, -[2,3-c:4,5-c‘]- and -[3,2-c:3,2-c’]dipyridine

Furo[2,3-b:4,5-c‘]- 1a , -[3,2-b:4,5-c’]- 1b , -[2,3-c:4,5-c‘]- 1c and -[3,2-c:4,5-c’]dipyridine 1d were derived to the N-oxides 2a-d , N‘-oxides 2′b , 2′c or N,N’-dioxide 3b-d by N-oxidation with m-chloroperbenzoic acid. Chlorination of these N-oxides, N′-oxide and N,N′-dioxides with phosphorus oxychloride afforded compounds chlorinated at the α-position(s) to the ring nitrogen 4a-d , 4′c , 14b-d and 14′b . Acetoxylation of N-oxides 2a-d and 2′c with acetic anhydride gave the corresponding pyridone compounds 6a-d and 6′c in good yields, while the acetoxylation of N,N′-dioxides gave a complex mixture from which no compound could be isolated. Cyanation of 2a-d, 2′c and 3b-d with trimethylsilyl cyanide yielded the cyano compounds 7a-d , 7′c , cyano-N-oxides 15b-d and dicyano compounds 15′c and 15′d . Monocyano compounds 7a-d and 7′c were converted to the imino esters 8a-d and 8′c by treatment with sodium ethoxide. Imino esters were derived to the carboxylic esters 9a-d and 9′c , from which the corresponding alde hydes 10a-d and 10′c were obtained by reduction with diisobutylaluminum hydride. Dicyanide 15′c was converted to dialdehyde 19 by the treatment with sodium ethoxide, and the subsequent hydrolysis of the imino ester and reduction of the carboxylic ester with diisobutylaluminum hydride.     

Rhodium-catalyzed carbonyl allylations by allylic alcohols with tin(II) chloride

Rhodium complexes such as [RhCl(cod)]₂, [Rh(cod)₂]BF₄, and [Rh(cod)(CH₃CN)₂]BF₄ function as catalysts for carbonyl allylations by allylic alcohols with 1 equimolar amount of tin(II) chloride to each allylic alcohol and aldehyde in THF at 50 °C to produce the corresponding homoallylic alcohols.     

Immobilization of cytochrome P-450 and electrochemical control of its activity

P-450_cam (camphor-induced cytochrome P-450) was immobilized on an indium tin oxide (ITO) electrode by polypyrrole and its activity was controlled electrochemically. The results showed that P-450_cam was immobilized on the ITO electrode without denaturing and the amount of P-450_cam could be easily controlled. When, the electric potential was swept repeatedly between 0.4 and 0 V, the remarkable decrease of oxygen in the reaction mixture solution was observed only in the presence of camphor. In addition, hydroxycamphor was detected only in the same system by means of gas chromatography/mass spectroscopy. These results suggested that immobilized P-450_cam catalyzed the hydroxylation of camphor by the supply of electron from the electrode. The effect of pH and ionic strength on the activity was examined, and it was found that the high activity expressed at the pH of 6.0 – 7.0 and KCl concentration of 0.1 – 0.2 M . The paper is the first report that P-450 enzyme activity could be controlled artificially. © 1998 John Wiley & Sons, Ltd.     

Isopropenyldihydrofuran derivatives. Preparation and reactions of some isopropenyldihydrofurandicarboxylates

Diethyl 5-isopropenyl-4,5-dihydrofuran-2,3-dicarboxylate 1a and methyl 5-isopropenyl-3-methoxy-carbonyl-4,5-dihydrofuran-2-acetate 2a were prepared by cylization of diethyl 2-oxosuccinate or dimethyl 3-oxoglutarate with (E)-1,4-dibromo-2-methyl-2-butene. Their chemical properties were studied.     

Double photoexcitation of helium in a strong dc electric field

We report the first experimental measurements of the effect of an applied field on the photoexcitation and autoionization of doubly excited states of helium. Ground-state photoionization spectra have been measured in the region below the He+(N=2) threshold with static electric fields of up to 84.4 kV/cm across the interaction region. The results are compared to the theoretical calculations of Chung et al. [J. Phys. B 34, 165 (2001)]], which are the only calculations available in this regime. Transitions to several states in the N=2, n=6 manifold are assigned, and a wealth of new structure is observed. Our data show that many more series are mixed in by the field than those predicted by theory.     

High-performance organic field-effect transistors based on pi-extended tetrathiafulvalene derivatives

Aromatic ring-condensed TTF derivatives exhibited excellent p-type FET performances in thin films. Introduction of fused benzene and pyrazine rings to the TTF skeleton was effective to enhance the intermolecular interactions and stability to oxygen. Ordered molecular alignment was confirmed by XRD studies. A pi-stacking structure was observed in the single crystal of diquinoxalinoTTF.