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.

A triblock polymer of polystyrene-polybutadiene-polystyrene, having molecular weights 21,100, 63,400, 21,100, respectively, 38.5 wt % polystyrene, was studied by small-angle X-ray scattering to determine its three-dimensional structure. A two-phase model was assumed, one phase being a pure polystyrene phase and the other phase a pure polybutadiene phase. Spherical polystyrene domains were shown to be 356 A in diameter and assigned to an orthorhombic macrolattice of unit cell dimensions 676, 676, 566 A. The implications of this type of macrolattice are discussed. The macrolattice is itself held in a regular array by forces due to the maximization of polymer chain entropy.

A growing interest in renewable sources is developing in several countries.1*2 Among those showing the most promise, Guayule (Partheniurn argentaturn Gray) is perhaps the most important for several reasons: it grows in very poor arid lands and has a high content (10-20%) of polyisoprenic rubber.Some efforts were made i n the past to elucidate its microstructure. Staveley et a13 found by infrared spectroscopy and by the method reported by Binder and Ransaw" 97.8% cis-1,4 and 2.2% 3,4 units. The technique of Binder and Ransaw is very useful when high contents of the several structures are present; however, in small quantities the accuracy of such method is questionable, because the small changes are often within the limit of the experimental error.Golub5 used nuclear magnetic resonance spectroscopy (60 and 100 MHz) in studies of the microstructure of natural Hevea rubber, balata, and synthetic polyisoprene and found that with this high-resolution technique, the elucidation of the microstructure was more accurate than by

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SynopsisThe thermal oxidation of natural rubbers from Hevea brasiliensis (pale crepe and smoked sheet) and Partheniurn argentaturn (Guayule) were studied with differential scanning calorimetry (DSC) using the dynamic method. The atmosphere was oxygen a t 110 ml/min and the temperature range was 393"-473"K. The decomposition reactions showed a pronounced exothermic emission with shoulders on the high-temperature side. The kinetic parameters were computed by using three different mathematical approaches: the heat evolution treatment of Borchardt and Daniels, the diffusion-controlled method by Jander, and the heating rate method developed by Kissinger and Ozawa. The best agreement between these methods was achieved assuming first order in the Borchardt and Daniels method and three-dimensional diffusion with the Jander model. The mass influence was analyzed observing that good agreement is obtained working with sample weight in the order of 3-4 mg. Under such conditions the activation energies (E,) were 16-17,18-19, and 23-24 kcal/mole for the Borchardt-Daniels, Kissinger-Ozawa, and Jander models, respectively.