The dielectric loss factor and dielectric permittivity of 8–16 mol% solutions of chlorobenzene, o‐dichlorobenzene, and 1‐chloronaphthalene in cis‐decalin; 50–60 mol% mixtures of pyridine with chlorobenzene, bromobenzene, 1‐chloronaphthalene, and toluene; 50–60 mol% mixtures of tetrahydrofuran with bromobenzene and 1‐chloronaphthalene; the pure liquids cis‐decalin, o‐terphenyl, iso‐propylbenzene, propylene carbonate; and two fused salt systems, 45 mol% Ca(NO3)2–KNO3 mixture and Ca(NO3)2·4H2O have been measured from 50 Hz to 1 × 105 Hz from − 196° in the vitreous state to about 30° above their respective glass transition temperatures. The Tg's of the organic glasses have been measured by DTA. With the exception of propylene carbonate, all glasses show the presence of one secondary relaxation between − 196° and their respective Tg's either as a peak or shoulder in a tanδ–temperature plot at a single frequency, or in the dielectric loss spectrum. Arrhenius plots of the frequency of maximum loss against temper...

Viscous Liquids and the Glass Transition. II. Secondary Relaxations in Glasses of Rigid Molecules

A review of heat treatment on polyacrylonitrile fiber

Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by an in situ free-radical polymerization process with 38 and 17 nm diameter γ-alumina nanoparticles. At extremely low filler weight fractions (<1.0 wt % of 38 nm fillers or < 0.5 wt % of 17 nm fillers) the glass-transition temperature (Tg) of the nanocomposites drops by 25 °C when compared to the neat polymer. Further additions of filler (up to 10 wt %) do not lead to additional Tg reductions. The thermal behavior is shown to vary with particle size, but this dependence can be normalized with respect to a specific surface area. The nanocomposite Tg phenomenon is hypothesized to be because of nonadhering nanoparticles that serve as templates for a porous system with many internal interfaces that break up the percolating structure of dynamically heterogeneous domains recently suggested by Long, D.; and Lequeux, F. Eur Phys J E 2001, 4, 371 to be responsible for the Tg reductions in polymer ultrathin films. The results also point to a far field effect of the nanoparticle surface on the bulk matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4371–4383, 2004

Glass-transition temperature behavior of alumina/PMMA nanocomposites

The influence of oxygen on the chemical reactions during stabilization of pan as carbon fiber precursor

The compression yield behaviour of PMMA has been investigated, here, over a wide range of experimental conditions which cannot be reached in tensile tests owing to the brittle nature of the material. The plot of the ratio of the compression yield stress to absolute temperature, as a function of the logarithm of the strain-rate, gives a set of parallel curves which can be accurately superimposed by shifting along a slanting straight line. A master curve is built from which the yield behaviour may be predicted for any state of stress, or value of temperature and strain-rate in the glassy range, using Bauwens' yield criterion.

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The compression yield behaviour of polymethyl methacrylate over a wide range of temperatures and strain-rates

The preparation of five samples of poly(methyl methacrylate) covering a wide range of tacticity and their electron irradiation to produce series of varying molecular weight are described. The glass transition temperature Tg of each polymer was determined by DTA techniques. Plots of Tg and the reciprocal of the molecular weight are well fitted in every case by a straight line. The data are also fitted to the Gibbs-DiMarzio theory and the values of the energy and free-volume parameters obtained are discussed. A method of estimating Tg of pure syndiotactic poly(methyl methacrylate) by extrapolation is presented, the value obtained being 160°C.

Edward V. Thompson

Papers

Dependence of the glass transition temperature of poly(methyl methacrylate) on tacticity and molecular weight

The thermal behavior of acrylonitrile polymers. I. On the decomposition of polyacrylonitrile between 250 and 325°C.

Electron irradiation and racemization of isotactic poly(methyl methacrylate)

Secondary processes of poly(methyl methacrylate) and their activation energies as determined by shear and tensile creep compliance measurements