The ozonation of N,N'-di-n-octyl-p-phenylenediamine and N,N'-di-(1,1-dimethylethyl)-p-phenylenediamine

• Published in: Rubber chemistry and technology Vol. 64; no. 5; pp. 780 - 789
• Main Authors: LATTIMER, R. P, LAYER, R. W, HOOSER, E. R, RHEE, C. K
• Format: Journal Article
• Language: English
• Published: Akron, OH American Chemical Society 01-11-1991
• Subjects: Applied sciences; Chemical reactions and properties; Degradation; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Reaction mechanism; Ozonization; Phenylenediamine; Elastomer; Antiozone
• ISSN: 0035-9475; 1943-4804
• DOI: 10.5254/1.3538590

Abstract
Ozone attack on rubber compounds causes characteristic cracking perpendicular to the direction of applied stress. This degradation is caused by reaction of ozone with the double bonds in the rubber molecules. This causes chain scission and the formation of various decomposition products. The general subject of protection of rubber against ozone attack has been reviewed by a number of authors. In order to control the effects of rubber ozonation, either paraffin waxes or chemical antiozonants are added to unsaturated rubbers. The most effective antiozonants are N,N′-disubstituted-p-phenylenediamines (PPDAs), in which at least one of the side groups is alkyl (preferably sec-alkyl). Several theories have appeared in the literature regarding the mechanism of antiozonant protection. The “scavenger” model states that the antiozonant blooms to the surface and preferentially reacts with ozone so that the rubber is not attacked until the antiozonant is exhausted. The “protective film” theory is similar, except that the ozone-antiozonant reaction products form a film on the rubber surface that prevents (physically and perhaps chemically as well) ozone attack on the rubber. A third “relinking” theory states that the antiozonant prevents scission of the ozonized rubber or else recombines severed double bonds. A final theory states that the antiozonant reacts with the ozonized rubber or Criegee zwitterion (carbonyl oxide) to give a low-molecular-weight, inert, “self-healing” film on the rubber surface. Currently, the most accepted mechanism of antiozonant action is a combination of the scavenger and protective film theories.