A Study of the Mechanism of the Deactivation Effect

Abstract

Abstract The only method by which significant differences between the effects of antioxygenic agents and deactivating agents can be detected has been found to be a study of relaxation phenomena. An investigation by this method has also furnished further support to the theories of Tobolsky and his coworkers. The changes which take place during aging in the physical properties of vulcanized rubber are the result of two independent phenomena which occur simultaneously: (1) chain scission, and (2) formation of intermolecular bonds. As far as the aging of vulcanizates of natural rubber under normal conditions, e.g., socalled natural aging, is concerned, the chief phenomenon involved is scission of the chain molecules. In principle, therefore, there are two methods for combatting the deterioration of rubber on aging: (1) to impede chain scission by obstructing the fixation of oxygen, and (2) to promote the progressive formation of intermolecular bonds which compensate for the effects of the scission process. The first of these processes is that in which antioxygenic agents play the active part; in the second process, deactivating agents play the active part. From this viewpoint, deactivating agents play a part analogous to that of accelerators, and they may be regarded as representing a special type of acceleration. This theory makes possible a better understanding of a number of facts which, a priori, seem surprising: (1) the relationships of both chemical structure and mode of action of accelerators and deactivating agents, and (2) the protective effect of litharge, peroxides, and nitro compounds, all of which are vulcanizing agents. With respect to the intimate mechanism of the deactivating effect, one question remains unanswered, viz., how are intermolecular bonds formed under the influence of deactivating agents? This question recalls the question of the function of vulcanization accelerators, which has been the subject of many investigations, but which still remains a mystery.