Photodegradation behavior of tert-butyl vinyl ketone polymers and copolymers with styrene and α-methylstyrene

Photodegradation behavior of atactic and isotactic polymers of tert-butyl vinyl ketone (t-BVK) and its copolymers with styrene and α-methylstyrene was studied in dioxane as a solvent at room temperature. The quantum yield of main-chain scission of atactic poly(t-BVK) was found to be larger than that of isotactic poly(t-BVK) and atactic poly(methyl vinyl ketone). From the Stern-Volmer plots on the quenching study of atactic poly(t-BVK) with naphthalene and 2,5-dimethyl-2,4-hexadiene, it was found that 60–70% of its photochemical reaction underwent main-chain scission from the triplet state. It was also found that the increase in t-BVK contents of both copolymers accelerated the photodegradation, and the copolymer with styrene was more photodegradable than that with α-methylstyrene. These results seemed to suggest that the main-chain scission of these vinyl ketone polymers and copolymers proceeded through a Norrish type II photoelimination mechanism.     

Synthesis of substituted polymethylenes by radical polymerization of N,N,N′,N′-tetraalkylfumaramides and their characterization

Radical polymerization of N,N,N′,N′-tetraalkylfumaramides (TRFAm) bearing methyl, ethyl, n-propyl, isopropyl, and isobutyl groups as N-substituents (TMFAm, TEFAm, TnPFAm, TIPFAm, and TIBFAm, respectively) was investigated. In the polymerization of TEFAm initiated with 1,1′-azobiscyclohexane-1-carbonitrile (ACN) in benzene, the polymerization rate (R_p) was expressed as follows: R_p = k [ACN]^0.28 [TEFAm]^1.26, and the overall activation energy was 102.1 kJ/mol. The introduction of a bulky alkyl group into N-substituent of TRFAm decreased the R_p in the following order: TMFAm > TEFAm > TnPFAm > TIBFAm > TIPFAm ～ 0. The relative reactivities of these monomers were also investigated in radical copolymerization with styrene (St) and methyl methacrylate (MMA). In copolymerization of TRFAm (M₂) with St (M₁), monomer reactivity ratios were determined to be r₁ = 1.07 and r₂ = 0.20 for St–TMFAm, and r₁ = 1.88 and r₂ = 0.11 for St–TEFAm, from which Q₂ and e₂ values were estimated to be 0.35 and 0.44 for TMFAm, and 0.19 and 0.47 for TEFAm, respectively. The other TRFAm were also copolymerized with St, but copolymerization with MMA gave polymers containing a small amount of TRFAm units. The polymer from TRFAm consists of a less-flexible poly(N,N-dialkylaminocarbonylmethylene) structure. The solubility and thermal property of the polymers were also investigated.     

Molecular metamagnet [Ni(4ImNNH)(2)(NO(3))(2)] (4ImNNH = 4-imidazolyl nitronyl nitroxide) and the related compounds showing supramolecular H-bonding interactions

A new chelating radical ligand 4ImNNH (2-(4-imidazolyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide) was prepared, and complexation with divalent transition metal salts gave complexes, [M(4ImNNH)(2)X(2)], which showed intermolecular ferromagnetic interaction in high probability (7 out of 10 paramagnetic compounds investigated here). The nitrate complexes (X = NO(3); M = Mn (1), Co (2), Ni (3), Cu (4)) crystallize isomorphously in monoclinic space group P2(1)/a. The equatorial positions are occupied with two 4ImNNH chelates and the nitrate oxygen atoms are located at the axial positions. Magnetic measurements revealed that the intramolecular exchange couplings in 1, 2, and 4 were antiferromagnetic, while that in 3 was ferromagnetic with 2J/k(B) = +85 K, where the spin Hamiltonian is defined as H = -2J(S(1).S(2) + S(2).S(3)) based on the molecular structures determined as the linear radical-metal-radical triads. The intramolecular ferromagnetic interaction in 3 is interpreted in terms of orthogonality between the radical pi and metal dsigma orbitals. Compounds 1-3 exhibited intermolecular ferromagnetic interaction ascribable to a two-dimensional hydrogen bond network parallel to the crystallographic ab plane. Complex 3 became an antiferromagnet below 3.4 K and exhibited a metamagnetic transition on applying a magnetic field of 5.5 kOe at 1.8 K. The complexes prepared from metal halides, [M(4ImNNH)(2)X(2)] (X = Cl, Br; M = Mn, Co, Ni, Cu), showed intramolecular antiferromagnetic interactions, which are successfully analyzed based on the radical-metal-radical system. The crystal structures determined here on 1-4, [Mn(4ImNNH)(2)Cl(2)], and [Cu(4ImNNH)(2)Br(2)] always have intermolecular hydrogen bonds of H(imidazole).X(axial ligand)-M, where X = NO(3), Cl, Br. This interaction seems to play an important role in molecular packing and presumably also in magnetic coupling.     

Classification of Simple Oxides: A Polarizability Approach

A simple oxide classification has been proposed on the basis of correlation between electronic polarizabilities of the ions and their binding energies determined by XPS. Three groups of oxides have been considered taking into account the values obtained on refractive-index- or energy-gap-based oxide ion polarizability, cation polarizability, optical basicity, O 1s binding energy, metal (or nonmetal) binding energy, and Yamashita-Kurosawa's interaction parameter of the oxides. The group of semicovalent predominantly acidic oxides includes BeO, B₂O₃, P₂O₅, SiO₂, Al₂O₃, GeO₂, and Ga₂O₃ with low oxide ion polarizability, high O 1s binding energy, low cation polarizability, high metal (or nonmetal) outermost binding energy, comparatively low optical basicity, and strong interionic interaction, leading to the formation of strong covalent bonds. Some main group oxides so-called ionic or basic such as CaO, In₂O₃, SnO₂, and TeO₂ and most transition metal oxides show relatively high oxide ion polarizability, O 1s binding energy in a very narrow medium range, high cation polarizability, and low metal (or nonmetal) binding energy. Their optical basicity varies in a narrow range and it is close to that of CaO. The group of very ionic or very basic oxides includes CdO, SrO, and BaO as well as PbO, Sb₂O₃, and Bi₂O₃, which possess very high oxide ion polarizability, low O 1s binding energy, very high cation polarizability, and very low metal (or nonmetal) binding energy. Their optical basicity is higher than that of CaO and the interionic interaction is very weak, giving rise to the formation of very ionic chemical bonds.     

X-ray scattering by water molecules studied by using synchrotron radiation

The energy spectra of free water molecules were measured at scattering angles 2θ ranging from 10.5° to 75.7°, using an angle-dispersive-type diffractometer and synchrotron radiation as an X-ray source. A silicon (111) monochrometer was used to obtain incident X-rays with the wavelengths of (1.543/n) Å (n = 1,3,4,5). Observed inelastic scattering peaks are clearly separated from eleastic ones at s values [s = (4π/λ) sin Å] larger than 8 Å^?1. The increase of the separation with an increasing s value was consistent with the classical theory of the Compton shift. The total (elastic plus inelastic) intensities were obtained over a range of s = 0.74–5.0 Å^?1. Experimental difference intensities Δσ_ee and Δσ_ne were obtained separately by combining the X-ray and high-energy electron scattering data. The experimental results are in reasonable agreement with the theoretical intensities calculated from SCF and CI molecular wave functions with a basis set of double-zeta plus polarization functions. © 1994 John Wiley & Sons, Inc.     

Mechanism of antioxidant action of pueraria glycoside (PG)-1 (an isoflavonoid) and mangiferin (a xanthonoid).

The antioxidant activities of pueraria glycoside (PG)-1 (isoflavonoid) and mangiferin (xanthonoid) were studied and compared with PG-3 and daidzein (isoflavonoids) and with wogonin (flavonoid). PG-1 and mangiferin rapidly scavenged 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, and inhibited lipid peroxidation which was initiated enzymatically by reduced nicotinamide adenine dinucleotide phosphate (NADPH) or non-enzymatically by ascorbic acid or Fenton's reagent (H2O2 + Fe2+) in rat liver microsomes. Wogonin inhibited the enzymatically induced lipid peroxidation but had no scavenging effect on DPPH radical or on the non-enzymatic peroxidation. PG-3 and daidzein did not show any of these effects. Formation of Fe2+ by NADPH-dependent cytochrome P-450 reductase was inhibited by wogonin, but not by PG-1 or mangiferin. PG-1 and mangiferin had no effect on terminating radical chain reaction during the lipid peroxidation in the enzymatic system of microsomes or in the linoleic acid hydroperoxide-induced peroxidation system. These results suggest that PG-1 and mangiferin have an antioxidant activity, probably due to their ability to scavenge free radicals involved in initiation of lipid peroxidation. In contrast, wogonin may affect NADPH-dependent cytochrome P-450 reductase action, since it inhibited only the enzymatically induced lipid peroxidation.     

Efficient synthesis of a 4,5-epoxy-2-cyclohexen-1-one derivative bearing a spirolactone via a Diels-Alder reaction with high pi-facial selectivity: a synthetic study towards scyphostatin

The Diels-Alder reaction of spirolactones with cyclopentadiene afforded the adduct with high pi-facial selectivity; a hydrophilic analogue of scyphostatin was synthesized from the Diels-Alder adduct.     

1,3-Dipolar cycloaddition reaction of phenanthridinium N-imines and N-benzoylimine with acetylenic compounds

N-Aminophenanthridinium salt reacted with dimethyl acetylenedicarboxylate in the presence of potassium carbonate to give a 3,3a-dihydropyrazolo[1,5-f]phenanthridine but with mono-substituted acetylenes (ethyl propiolate and benzoylacetylene) it produced aromatized pyrazolo-[1,5-f]phenanthridines (XII and XIII). The reaction of the N-benzoylimine with di-substituted acetylenes (dimethyl acetylenedicarboxylate and methyl phenylpropiolate) and mono-substituted acetylenes (ethyl propiolate and benzoylacetylene) yielded 1,3a-dihydropyrazolo[1,5-f]phenanthridines and the aromatized products (XII and XIII), respectively.     

Effects of ortho-substituents on reactivities,tacticities, and ceiling temperatures of radical polymerizations of phenyl methacrylates

Radical polymerization and copolymerization of some o-alkylphenyl methacrylates were carried out and the effect of the ortho-substituents on the ability to homopolymerize, on the monomer reactivities, and on the ceiling temperatures of the monomers was studied. The effect of the substituent on tacticities and thermal stabilities of the polymers formed was also discussed. The ability to honiopolymerize and the monomer reactivity were considerably decreased by the introduction of the o-substituent. 2,6-Di-tert-butylphenyl methacrylate formed no methanol-insoluble polymer at 60°C. On the basis of the tacticity determined it was noted that the o-substituted phenyl methacrylates preferred syndiotactic addition in the propagation reaction less than did phenyl methacrylate or methyl methacrylate. The polymers formed from the o-substituted monomers were thermally less stable than poly(phenyl methacrylate), and, consistent with this finding, ceiling temperatures of the o-substituted phenyl methacrylates seemed to be lower than that of phenyl methacrylate. The effects observed were characteristic of the o-substituents conformationally close to the carbon-carbon double bond of the monomer or the carbon carrying the unpaired electron of the polymer radical.     

Aqueous Titanate Sols from Ti Alkoxide-α-Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols

Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with -hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO₂) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH₃ (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH₃ (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions.