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SynopsisDegradation of pure guayule rubber and rubber in the presence of stearic, oleic, linoleic, and linolenic acid, has been studied at high temperatures (from 150 O C to 600 O C) using thermogravimetric analysis (TGA). On-line mass spectrometric analysis of the products of decomposition has also been done to understand the mechanisn of degradation.Degradation of rubber starta around 230° C in air and 330° C in nitrogen. Presence of acids changes the onset of degradation, because of low decomposition temperature of the acids. In the derivative curve, there is one T , , for degradation in nitrogen; two for rubber; and three for rubber containing acids are observed for degradation in air. The activation energy of degradation, as observed by isothermal kinetics, in the 1-10% weight lass region, is 225 kJ/mol in nitrogen and 167 kJ/mol in air. In the 10-100% region, however, the activation energy of degradation measured by the Freeman and Carroll method using dynamic thermogravimetry, is 239 kJ/mol in both nitrogen and air atmosphere. The main products of pyrolysis in inert atmosphere are propylene, propane, isobutylene, methyl butene, isoprene, 2,3-dimethyl cyclopentene, octene, 2,4-dimethylcyclohexene, dipentene, etc. Isoprene is found to be the most abundant. Fragments having m/e values of 136,121,107,93,79, and 53 are also produced in large quantities. The ratio of concentration of dipentene to isoprene increases marginally with temperature. The concentration of other fragments however increases drastically with temperature. The additives have no effect on the nature of products obtained. The conversion to different fragments depends upon the temperature of degradation and the stability of intermediate products. All smaller molecules are obtained from either dipentene or isoprene. A mechanism of formation of these products has been suggested.

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We have evaluated the translational friction coefficient of wormlike cylinders by the Oseen-Burgers procedure. The final results may be written in terms of only the molecular dimensions. From the point of view of classical hydrodynamics, the Ullman theory is not correct; it is correct only when his parameter a (friction constant per unit length) is taken as infinity. The Hearst-Stockmayer theory is not unphysical, though its application leads to small-er estimates of the diameter of the cylinder than does the present theory in the case of typical stiff chains. An analysis of the intrinsic viscosity of wormlike cylinders will be given in the next paper.

This paper discusses the asymptotic solution of the scattering function P(θ) for large x, where x is proportional to the scattering angle, radius of gyration, and the wavenumber. The theoretical model employed for the calculation of the P(θ)-vs-x curves was presented in the preceding paper. The results are discussed with respect to the experimental data, after the results for P(θ) are corrected for various values of polydispersity. A general analysis of the theoretical P(θ)-vs-x curves is presented, and the effect of the shape of the chain-end distribution function on the asymptotic behavior of the light-scattering function is discussed.

Polystyrenes with molecular weights up to 44 x 10(6) grams per mole have been characterized by light-scattering and equilibrium ultracentrifugation methods. The Mark-Houwink equation, which relates the molecular weight and the intrinsic viscosity of flexible polymers, can be used only if the measurements are made in a theta solvent at the theta temperature.