Alkyl-aryl PPDs

DPPD is a very commonly used antioxidant of the diarylphenylene diamine class. DPPD is relatively less expensive than PPDs of the alkyl-aryl or alkyl-alkyl class. On the other hand, DPPD is also not as reactive with ozone and possesses lower solubility in rubber, which causes it to form an undesirable bloom more readily than the other antiozonants. DPPD is a widely used antioxidant however, its use as an antiozonant is much smaller. 

FIGURE 15.7 Ozonation mechanism for aryl alkyl-PPDs. (From Hong, S.W. and Lin, C.-Y., Rubber World, 36, August 2000.)... 

The principal classes of primary antioxidants for rubber remain the pheno-lics (nonblack articles) and amines (black-filled articles). Among the amine t5q>es are the substituted diphenylamines,para-phenylenediamines (PPD, (10), where R,R = alkyl or aryl), and polymeric trimethyl-dihydroquinoline (TMQ). Representative phenolic antioxidants are given in Table 14, and selected amine antidegradants are given in Table 15. The majority of tire and mechanical goods made from general-purpose rubbers are protected by the phenolic and amine antioxidants. 

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