Ernest W. Anderson

Diffusion in Liquids

Self‐diffusion coefficients have been measured for water, nitromethane, acetone, benzene, cyclohexane, isopentane, and neopentane. Temperature and pressure dependences have been determined for nitromethane, acetone, cyclohexane, and isopentane. The temperature dependence has been determined for neopentane and the pressure dependence has been determined for water and benzene. The results are discussed in terms of a semiempirical theory for transport in liquids and it is shown that semiquantitative predictions of self‐diffusion, viscosity, and thermal conductivity coefficients can be made.

NMR Study of Rotational Barriers and Conformational Preferences. I. Cyclohexyl Fluoride

The equatorial:axial ratio and rate of conformational isomerization of cyclohexyl fluoride has been measured by observation of the 19F resonance as a function of temperature (—87.6° to +29.5°) for a 25 vol.% solution in CCl3F. Rate information is readily obtained over a wide temperature range, since the equatorial and axial fluorines differ in chemical shift by 20.5 ppm; the equatorial and axial α protons differ in chemical shift by only 0.46 ppm.Interpretation of the spectra in terms of isomerization rates is complicated by the following: (a) the equatorial and axial conformers are present in unequal proportions; (b) their ratio changes with temperature; and (c) 19F–H coupling produces fine structure and/or peak broadening. The general expression for spectral line shape resulting from exchange between two unequal, chemically shifted spin populations is plotted (using the IBM 7090 computer), chemical shift and conformer ratio data being obtained from the low temperature 19F spectra. The observed spectra f...

Dielectric Properties of Linear Polyamides

The dielectric constant and loss have been measured for several linear polyamides over a range of frequency and temperature. At low frequencies and elevated temperatures, proton conduction through the amorphous regions gives rise to a Maxwell‐Wagner loss, while at high frequencies and high temperatures dipole relaxation of the amide groups contained in the amorphous regions gives rise to a typical loss peak. Nylons 6, 6–6, 6–10, 7–9, 6–9, and 10–10 yield very similar results. The N‐methylated derivative of nylon 10–10 exhibits a much smaller direct current conductivity than nylon 10–10 (when compared at temperatures of equivalent chain activity) owing to the absence of amide protons.

Diffusion in Ethylene Polymers. IV

Self‐diffusion coefficients have been measured for two low molecular weight fractions (M = 4100 and 5800) of a linear polyethylene. The activation energy for the M = 4100 fraction is 5.3 kcal/mole which is near the value 5.6 kcal/mole found for n — C32H66. At 150°C, for this fraction, D = 1.6×10—7 cm2/sec and as 10—7 is near the lower limit of detectability the activation energy is probably not accurately determined. The diffusion coefficient for the M = 5800 fraction is 1.1×10—7 cm2/sec at 150°C. These results, combined with previous results, show that D = κn—5/3, where D is the coefficient of self‐diffuison for the normal paraffin CnH2n+2. κ is a constant at a given temperature, 4.5×10—3 cm2/sec at 200°C and 2.5×10—3 cm2/sec at 150°C.

Self‐Diffusion in Liquids: Paraffin Hydrocarbons

The pressure dependence of the self‐diffusion coefficients of several normal paraffin hydrocarbons and the isomers of hexane have been determined. In addition, the temperature dependence of self‐diffusion coefficients has been measured for the isomers of hexane. Energies and volumes of activation have been calculated. With the exception of 2, 2‐dimethyl butane, these parameters do not change significantly with branching in the isomers of hexane. The volumes of activation are about 10–20% of the molar volumes in all cases. Diffusion coefficients computed from a semiempirical modification of an equation derived by Longuet‐Higgins and Pople are compared with the experimental results.

NMR Study of Rotational Barriers and Conformational Preferences. II. d11‐Cyclohexane

The rate of conformational isomerization of cyclohexane has been measured over the temperature range —75.0 to —47.0° by observation of the NMR spectrum of C6HD11, which is much simpler than that of cyclohexane itself and is amenable to exact kinetic treatment. The line broadening arising from D—H coupling was eliminated by double resonance. It is found that ΔF‡ is equal to ΔH‡ within experimental error for the chair‐to‐chair reaction and is 10.5 kcal (206.0°K) (10.2 kcal for the chair‐to‐boat process); ΔS‡ for the chair‐to‐chair process is thus about zero and for the chair‐to‐boat process is about +1.4 eu.

Polymer NMR Spectroscopy. X. The Use of H1–H1 Spin Decoupling in the Elucidation of Polymer Structure

High‐resolution NMR spectroscopy of vinyl polymers in solution is an effective means of determination of the stereochemical configuration of their chains. In polymers having only a single α substituent, however, spin coupling of α and β protons complicates the interpretation of the spectrum considerably and also makes it difficult to observe those stereoisomeric sequences which are present as minor components. Decoupling of the α‐ and β‐proton spins has been found to be helpful in the interpretation of the spectra of polyvinyl chloride, polyvinyl fluoride, and polyvinyl methyl ether. It is not helpful for polyvinyl acetate in carbon tetrachloride, since here the chemical shift of the α and β protons is not sensitive to stereochemical configuration.

Self‐Diffusion of Nearly Spherical Molecules. Neopentane and Tetramethyl Silane

Self‐diffusion coefficients have been measured for neopentane and tetramethyl silane by means of the nuclear magnetic resonance spin‐echo technique. Both pressure and temperature dependences have been determined, thus allowing evaluation of energies and volumes of activation; neopentane, ED=3.5 kcal/mole and ΔVΔ=31 cm3/mole tetramethyl silane, ED=1.16 kcal/mole and ΔVΔ=22 cm3/mole. The numbers given for neopentane are average values as the lnD vs 1/T and lnD vs p plots were not straight lines. Kirkwoods theoretical relation for the self‐diffusion coefficient of spherical molecules has been tested for the quasi‐spherical neopentane. At 0°C the theoretical value is 6×10—5 cm2/sec while the experimental value is 2.6×10—5 cm2/sec. The Kirkwood equation for the self‐diffusion coefficient is discussed in detail.

Self‐Diffusion in Linear Dimethylsiloxanes

The pressure and temperature dependences of the self‐diffusion coefficients of the linear dimethylsiloxanes, containing from two to nine silicon atoms have been determined by the NMR spin‐echo technique. Activation energies and volumes are presented as derived quantities; the constant‐volume activation energy is estimated from these data. Extensive comparisons between the diffusion properties of the dimethylsiloxanes and equivalent hydrocarbons are made. From these comparisons, it is concluded that diffusion in siloxanes is controlled to a much larger extent by chain configurational effects. This concept is formalized by expressing the chain‐size effects in an entropy of activation model.

Fourier transform dielectric spectrometer

Examples of the utilization of this spectrometer will be given. In the high frequency region the spectrometer was utilized in interpreting the compatibility of polymer blends. The effect of composition on polymer transitions was noted. In the low frequency regime the isothermal time dependent volume contraction of polymers near their glass transition was studied and correlated with other techniques.