K. W. Rollmann

Effects of domain and molecular orientations on the mechanical properties of a styrene-butadiene block polymer

Abstract A 70 : 30 styrene-butadiene block polymer with lamellar morphology was formed into sheets with either lamellar orientation only or with both lamellar and molecular orientation. Lamellar orientation led to the expected anisotropy in modulus and strength properties. Molecular alignment within the polystyrene lamellae greatly enhanced tensile strength in the direction of orientation and resulted in significant increases in puncture impact strength.

Behavior ofcis-Polybutadiene during Mastication

Abstract Cold mastication of natural rubber in presence of oxygen leads to scission by a shear mechanism with subsequent stabilization of the free radicals by oxygen, while at high temperatures oxidative scission becomes the dominant mechanism. Studies of the behavior of cis-polybutadiene reveal that similar reactions are effective, but occur at much reduced rates. Shear degradation is particularly difficult to achieve in typical cis-polybutadienes. This is related to the molecular weight distribution of these polymers which usually lack the very high molecular species most subject to shear-induced degradation, in agreement with the theory of F. Bueche. It is shown that when such a high molecular weight fraction is supplied, shear breakdown may be realized. All cis-polybutadienes undergo oxidative breakdown at high temperatures, the scission rate becoming appreciable above 140° C. A number of oxidation catalysts have been found which markedly increase the scission rate without leading to a correspondingly...

THE EFFECT OF CARBON BLACKS ON THE FREE RADICAL THERMAL POLYMERIZATION OF STYRENE

Carbon blacks inhibit the free radical thermal polymerization of styrene. On completion of an induction period the same carbons accelerate the polymerization. There is strong evidence that the inhibition reaction is due to surface quinone groups. No entirely satisfactory mechanism has been found for the accelerating action. Calcination or graphitization destroy both initiator and inhibitor activity, but catalytic reduction at room temperature only eliminates the inhibiting effect, presumably by reducing the quinones to hydroquinones which are not inhibitors per se.