Ozone rubber

This mechanism is based on the fact that the ozone uptake of elongated rubber containing a substituted p-phenylene diamine type of antiozonant is very fast initially and then decreases rather rapidly with time and eventually stops almost completely. The film has been studied spectroscopically and shown to consist of unreacted antiozonant and its ozonized products, but no ozonized rubber is involved [64], Since these ozonized products are polar, they have poor solubility in the rubber and accumulate on the surface. 

Ozone Rubber and elastomers of lead sulphide Cracking, weakening... 

Bradley, C. E., and A. J. Haagen-Smit. The application of rubber in the quantitative determination of ozone. Rubber Chem. Technol. 24 750-755, 1951. 

Newton, R. G. Mechanism of exposure-cracking of rubbers, with a review of the influence of ozone. Rubber Chem. Tech. 18 504-556. 1945. 

Involvement of the Ozonized Rubber Moieties in Antiozonant Mechanism. The rubber chain relinking theory (30) is consistent in part with the self-healing film formation theory (37) a reaction between an antiozonant or some of its transformation products and ozonized elastomer is considered. Either scission of ozonized rubber is prevented in this way or severed parts of the rubber chain are recombined (i.e., relinked). A "self-healing" film resistant to ozonation is formed on the rubber surface. Such a film formed by the contribution of nonvolatile and flexible fragments of the rubber matrix should be more persistent than any film suggested in the protective film theory. 

Formation of the protective film from ozonized rubber and AOZ creates a barrier against penetration of 03 into rubber [3,4]. Reactions of AOZ with ozonides 3, zwitterions 4 and aldehydic fragments 8 are envisaged. The respective reactivities are lower than the direct ozonation and the relevant contribution to the antiozonant mechanism is therefore inferior to the ozone scavenging. The reactivity of the ozonized rubber with AOZ accounts for rubber chain repairing, classified also as chain relinking or selfhealing mechanisms [4,21,247-249]. This contributes to formation of relaxed surface films. 

Aldehydic fragments 8 formed in ozonized rubbers or by PD/acid assisted ringopening of ozonides react with 11 under formation of bound-in species 161 or various relinked systems, e.g. 162 able to form crosslinks [3,4] (Scheme 30). 

The decomposition of ozonides up to acids and aldehydes goes in main on the ionic mechanism and is accompanied by destraction. However in parallel, the small amounts of free radicals are formed and it can initiate polymerization processes. Due to this before and ozonized rubbers it is easy modify by an grafting [65,66],... 

The relinking and self-healing film theories require chemical interaction between the antiozonant, or ozonized antiozonant, and the rubber or ozonized rubber. The evidence for these interactions is sparse in the literature. The products of the ozone-antiozonant reaction are soluble in acetone. Thus if only the scavenger and protective film mechanisms are operative, no nitrogen from the antiozonant should be left in the rubber after ozonation and subsequent acetone extraction. Nitrogen analyses of extracted rubber showed, however, that some of the nitrogen was unextractable this nitrogen was presumably attached chemically to the rubber network. 

Subsequent recombination produces a secondary ozonide (or just ozonide). In small olefins, ozonide formation is generally a facile process. In stretched rubber, however, ozonide formation is more difficult, since the cleaved intermediates may be forcefully separated to relieve the stress. Interestingly, both crosslinking and chain scission products may form during rubber ozonation. Rubbers containing trisubstituted double bonds (e.g., polyisoprene, IR, and butyl rubber, IIR) are more prone to yield chain scission products. Several pathways can lead to chain scission. 

Differences between Polymers. The degree of required ozone protection varies with the type of rubber. Saturated elastomers need no antiozonant protection, because they have no sites for reaction with ozone. Rubbers such as EPDM, which have a low olefin concentration, need essentially no protection against the effects of ozone. St5rene-butadiene rubber (SBR) requires antiozonant, while NR and synthetic pol5dsoprene (IR) may require somewhat increased dosages of antiozonant. Nitrile rubber (NBR) is very difficult to protect against ozone attack. 

A review is presented of the literature on the protection of rubber against ozone. Particular attention is paid to the historical background, ozone formation, chemistry of the ozone-rubber reaction, physical requirements for ozone cracking, physical methods of ozone protection, chemical antiozonants, chemical antioxonants for polychloroprene, mechanism of action of chemical antiozonants, chemistry of the reaction of ozone and p-phenylenediamine, free-radical mechanism, and critical stress and antiozonants. 88 refs. USA... 

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