Polymer–polymer interaction parameters of polystyrene and polybutadiene from studies in solutions of toluene or tetrahydrofuran

Equations used for the determination of polymer–polymer interaction parameters for narrow molecular weight distribution polymers which have undergone phase separation in solutions are discussed. Binodals with tie lines and plait points are presented for ternary systems polystyrene-polybutadiene-toluene and polystyrene-polybutadiene-tetrahydrofuran. Typical interaction parameters determined from the experimental data for the polystyrene-polybutadiene systems are presented.     

Unrestricted Hartree-Fock spin density distributions in nitro aromatic radical anions

The spin density distributions in the radical anions of nitrobenzene and some para substituted nitrobenzenes are calculated using the unrestricted Hatree-Fock formalism of Amos and Snyder. A parameter scheme which gives satisfactory account of the electronic transitions and molecular ionisation potentials of substituted benzenes (nitrobenzene, toluene, aniline, benzaldehyde and benzonitrile) is used for spin density calculations of the nitro radical anions. The importance of spin densities on neighbouring atoms on the hyperfine splitting of nitrogen atom is discussed. It is seen that although Karplus-Fraenkel theory gives a better estimate of¹⁴N splitting constant, the simple McConnell-type of relation is approximately valid for the nitro group-nitrogen. The--parameters for use with unrestricted Hartree-Fock spin densities for the prediction of nitrogen hyperfine couplings in nitro, amino and cyano groups are summarised.

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Zusammenfassung Die Spindichteverteilungen in den Radikalanionen des Nitrobenzols und einiger parasubstituierter Nitrobenzole werden mit Hilfe des UHF-Formalismus von Amos und Snyder berechnet. Zur Ermittlung der Spindichte der nitroaromatischen Radikalanionen wird ein Parameterschema benutzt, das zufriedenstellende Darstellung der Elektronenübergänge und der molekularen Ionisationspotentiale von substituierten Benzolen (Nitrobenzol, Toluol, Anilin, Benzaldehyd, Benzonitril) gestattet. Der Einfluß der Spins von benachbarten Atomen auf die Hyperfeinaufspaltung des Stickstoffatoms wird diskutiert. Es zeigt sich, daß zur näherungsweisen Beschreibung des Stickstoffs der Nitrogruppe eine einfache Gleichung des McCornell-Typs ausreicht, wenn auch die Karplus-Fraenkel-Theorie eine bessere Abschätzung der¹⁴N-Aufspaltungskonstanten ermöglicht. Die --Parameter, die zur Voraussage der Stickstoff-Hyperfeinkopplung in Nitro-, Amino- und Cyanogruppen mit Hilfe der UHF-Spindichten erforderlich sind, werden zusammengestellt.

     

The conversion efficiency of a piezoelectric quartz crystal: Relation between input electrical power and frequency

The dependence of the conversion efficiency of a piezoelectric transducer on its frequency and the input electrical power has been examined and it is found that the efficiency is dependent not on the input power but on frequency and the nature of the liquid     

Study of the transition state in the isomerization of trans-N2F2 to cis-N2F2 by extended Hückel theory

Conclusion The quantitative agreement with experimental barrier height and the extra stabilization energy of cis-N₂F₂ over trans-N₂F₂ may not be considered to be very good, but this is only to be expected as small differences between large quantities are being calculated. It appears from our present calculations that the use of Cusachs relation for evaluating the off-diagonal matrix elements in this system is open to question since the experimentally observed planarity of N₂F₂ is not correctly predicted by the use of this relation. We therefore prefer the use of the Wolfsberg-Helmholz relation in this system. A value of K= 1.75 appears to be preferable. The results of all the E.H.T. calculations made here for difluorodiazine clearly show that a twisted transition state is more probable than a linear one (LT or LC) in the isomerization of trans-N₂F₂ to cis-N₂F₂. This conclusion also receives further support from a consideration of the high preexponential factor in the rate equation [1] and the multiplicity of the transition state.