Copolymers of vinyl fluoride

Vinyl fluoride was polymerized by photochemical initiation in a continuous-flow cylindrical reactor at room temperature and at pressures of up to 30 atm. Copolymers with vinyl acetate were prepared in order to improve the solubility and processability of poly(vinyl fluoride) (PVF). The copolymers were hydrolyzed to the corresponding vinyl alcohol copolymers and yielded hydrophilic films that are strong and flexible only when swollen by water. It was found that on hydrolysis the T_g, T_m, and heat of fusion as well as degree of crystallinity increased. It was suggested that PVF and the copolymers with vinyl alcohol are isomorphous.     

The frattini subgroup of the absolute Galois group of a local field

LetK be a local field,T the maximal tamely ramified extension ofK, F the fixed field inK _sof the Frattini subgroup ofG(K), andJ the compositum of all minimal Galois extensions ofK containingT. The main result of the paper is thatF=J. IfK is a global field andK _solv is the maximal prosolvable extension ofK, then the Frattini group of % MathType!End!2!1!(K _solv/K) is trivial. Partially supported by a grant from the G.I.F., the German-Israeli Foundation for Scientific Research and Development.     

Effects of structure on properties of some new aromatic-aliphatic polybenzimidazoles

Polybenzimidazoles were prepared in poly(phosphoric acid) from isophthalic, m- and p-phenylene diacetic, succinic, adipic, suberic, and sebacic acids and 3,3′-diaminobenzidine, 3,3′,4,4′-tetraaminodiphenyl ether and 3,3′,4,4′-tetraaminodiphenylmethane. The thermal, mechanical, and bonding properties were studied. A 3:1 copolymer of isophthalic and m-phenylenediacetic acid with 3,3′-diaminobenzidine showed the best results as far as isothermal oxidation resistance and thermal and processing characteristics.     

Pi-stacking induced NMR spectrum splitting in enantiomerically enriched Ru(II) complexes: evaluation of enantiomeric excess

Several chiral octahedral complexes of the general formula [Ru(bpy)2 (Lig)][PF6]2 (Lig = a ligand that can participate in pi-stacking interactions such as eilatin, isoeilatin, and tpphz) were synthesized in both the racemic and enantiomerically pure/enriched forms. Nonracemic mixtures of enantiomers of all these complexes exhibit splitting of the 1H NMR spectra (NMR nonequivalence); i.e., each spectrum contains a major and a minor set of peaks. The origin of this phenomenon is attributed to a fast equilibrium between monomers and discrete dimers held together by pi-stacking interactions, and it is observed for a wide range of pi-stacking interaction strengths. The NMR spectrum splitting exhibited by these complexes can be exploited for the evaluation of their enantiomeric excess simply from the integral ratio, without addition of chiral shift reagents.     

Theory of the two step enantiomeric purification of 1,3 dimethylallene

An application of a recently proposed [P. Kral et al., Phys. Rev. Lett. 90, 033001 (2003)] two step optical control scenario to the purification of a racemic mixture of 1,3 dimethylallene is presented. Both steps combine adiabatic and diabatic passage phenomena. In the first step, three laser pulses of mutually perpendicular linear polarizations, applied in a "cyclic adiabatic passage" scheme, are shown to be able to distinguish between the L and D enantiomers due to their difference in matter-radiation phase. In the second step, which immediately follows the first, a sequence of pulses is used to convert one enantiomer to its mirror-imaged form. This scenario, which only negligibly populates the first excited electronic state, proves extremely useful for systems such as dimethylallene, which can suffer losses from dissociation and internal conversion upon electronic excitation. We computationally observe conversion of a racemic mixture of dimethylallene to a sample containing approximately 95% of the enantiomer of choice.     

An animal model of solar-aged skin: histological, physical, and visible changes in UV-irradiated hairless mouse skin

Albino hairless mice (Skh:HR-l) exposed to sub-erythemal doses of UVB or UVA radiation display physical, visible, and histological alterations. Skin surface replicas, transepidermal water loss, and skin fold thickness were found to change with irradiation. Visibly, the skin wrinkled with UVB and sagged with UVA exposure. These changes were graded on 3-point scales. Histological alterations included tissue thickening, loss of elastic fibers, elastosis, loss of collagen, and increases in muco-substances. The UVB alterations occur to a much lesser extent with an SPF-15 (7% PABA and 3% oxybenzone) sunscreen product. This sunscreen product had little effect on development of UVA-induced changes. However, an efficient UVA sunscreen (Parsol 1789) did reduce the UVA-induced changes. Many of the UVB-induced alterations regressed after UVB irradiation was stopped. No regression in UVA-induced alterations was observed when UVA irradiation was stopped. Qualitatively, the effects with UVA irradiation were like those observed in mouse chronological aging. These models and the convenient physical and visible grading methods described can be used to determine the effectiveness of topical treatments, such as sunscreens.     

Stable Subnorms II

In this paper we continue our study of stability properties of subnorms on subsets of finite-dimensional, power-associative algebras over the real or the complex numbers.