AbstractCold 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 ofcis‐polybutadiene reveal that similar reactions are effective, but occur at much reduced rates. Shear degradation is particularly difficult to achieve in typicalcis‐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. Allcis‐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 large increase in crosslinking. Significant improvements in processing may be realized in thi
展开▼
