Internal molecular disorder in the nematic and smectic phases of thermotropic liquid crystals studied by NMR SPDE experiments

The recently developed NMR SPDE experiment is shown to provide a new and particularly convenient technique for probing the conformational dynamics of mesogens in thermotropic liquid crystals. Measurements have been made in the nematic and smectic phases of the 4,4′-di-n-alkoxyazoxybenzenes. It is shown for the first time that the internal disorder of the alkyl end chains is intimately related to the molecular organization of these mesophases.     

Molecular weight distribution studies. I. Radiation-induced polymerization of liquid α-methylstyrene

The concentration of water in purified and BaO-dried α-methylstyrene was found to be 1.1 × 10^?4M. The radiation-induced bulk polymerization of the α-methylstyrene thus prepared was studied in the temperature range of ?20°C to 35°C. The polymerization rate varied as the 0.55 power of the dose rate. The theoretical molecular weights and molecular weight distribution were calculated from a proposed kinetic scheme and these values were then compared with those found experimentally. The agreement between these two was reasonably close, and therefore it was concluded that, from the molecular weight distribution point of view, the proposed kinetic scheme for the cationic polymerization of α-methylstyrene is an acceptable one. The rate constant for chain transfer to monomer k_f changed with temperature and was found to be responsible for the decrease in the molecular weight of the polymer with increase in temperature. k_f and k_p at 20°C were found to be 0.95 × 10⁴ l./mole-sec and 0.99 × 10⁶ l./mole-sec, respectively.     

Graft polymerization of vinyl monomers onto cellulose in presence of soda lime glass. I

Sodium bisulfite–soda lime glass has proved to be a good initiator for polymerization and graft polymerization onto cellulose of some vinyl monomers. A scheme dealing with the mechanism of initiation has been proposed assuming trapping of the bisulfite radical inside the glass frame-work to form a so-called sulfur-impregnated solid. Such a solid has paramagnetic properties and acts on the vinyl monomers and cellulose as any free-radical-producing source thus leading to polymerization and graft polymerization onto cellulose. Other radicals containing sulfur, such as sulfite, sulfate, and persulfate failed to give such property with soda lime glass. With the sodium bisulfite–soda lime glass system the reactivity decreases in the order methyl methacrylate > ethyl acrylate > acrylonitrile which is inconsistent with the arrangement of acceptor monomers with decreasing electron-donating ability. This may reflect interference of the addition reaction which may take place between the monomer and bisulfite and the rate of which may depend on the activation energy of the monomer.     

Spectrometrie de Masse D'ozonides Aliphatiques

A primary cleavage of aliphatic ozonides by electron-impact, implying O? O and C? C bond breaking, is described. This mode of degradation, which is not observed for aromatic ozonides, is fav oured by electron releasing substituents. For the cis and trans 4-methyl-2pentene ozonides, the ionization potentials are 8.81 and 8.86 (±0.5) eV, respectively. Two formation thresholds are observed for the [RCHO₂]⁺ion which are interpreted in terms of different modes of ozonide cleavage.     

Effects of anharmonicities on radiationless transitions in large molecules

A new computational method to account for the effect of anharmonicities on non-radiative decay rates of large molecules in the statistical limit is given by using expansions of the generating functions which have been used successfully in multiphonon processes. This method is free from the ambiguity which, as in previous conventional methods, arises from the factorization which separates the decay rate into a product of an electronic term, a Franck-Condon factor and a density of final states. The rate expression is asymmetric with respect to the sign of the displacement of the accepting modes. Actual calculations are performed for a model molecule which closely resembles benzene. The numerical data for the decay rate exceed the results of the harmonic approximation by about two orders of magnitude.     

g tensor of transition ions in a crystalline matrix: Interstitial V(IV) and Ti(III) in rutile TiO2

In order to check if the parametrized crystal field approach is efficient in the analysis of an EPR powder spectrum we study defects of known geometry as if we did not know it. The g tensor of an interstitial V⁴⁺ ion in a single crystal of rutile TiO₂ can be interpreted without ambiguity, and the optimized parameters compare well with their theoretical values. For an interstitial Ti³⁺ ion, two solutions are found: both of them correspond to interstitial positions, but they differ in the principal axis orientation.     

Kinetische Uttersuchungen zur strahleninduzierten Lösungspolymerisation von Tetrafluoräthylen

Ohne Zusammenfassung     

Dual-basis orthonormality-constrained variation method

The method of orthonormality-constrained variation is extended using a dual-basis set instead of a single orthonormal basis. The complete and the partial variation methods are discussed and applied to electronic systems. It is found that the present formulation leads to the most general equation in the coupling operator method.