Diene rubbers ozone degradation

This discussion of the structures of diene polymers would be incomplete without reference to the important contributions which have accrued from applications of the ozone degradation method. An important feature of the structure which lies beyond the province of spectral measurements, namely, the orientation of successive units in the chain, is amenable to elucidation by identification of the products of ozone cleavage. The early experiments of Harries on the determination of the structures of natural rubber, gutta-percha, and synthetic diene polymers through the use of this method are classics in polymer structure determination. On hydrolysis of the ozonide of natural rubber, perferably in the presence of hydrogen peroxide, carbon atoms which were doubly bonded prior to formation of the ozonide... 

Formation of a strong interfacial layer is the key factor of the mechanism describing retardation of ozone degradation of a diene rubber by elastomer additives with a low degree of unsaturation [1-4]. The effect of comonomer ratio in ethylene-propylene-diene terpolymers (EPDMs) and stereoregularity of propylene units on the interfacial interaction and the amount of crosslinks in ihe interfacial layer was considered for heterophase crosslinked blends with butadiene-acrylonitrile mbbers (BNRs) of different polarities. 

Approaches to the prediction of the long-term ageing behaviour of vulcanised diene rubbers are discussed, and studies of the photooxidative and ozone degradation of polybutadiene, polyisoprene, SBR and nitrile rubber under accelerated artificial ageing conditions are reported. 12 refs. 

The unsaturated structure of the diene hydrocarbon rubbers makes them susceptible to attack by both oxygen and ozone. Oxidative degradation of all rubbers, irrespective of their structures, is inevitable as the energy associated with incident natural light is approximately three times that of a typical carbon-carbon or carbon-hydrogen bond. 

The role of ozone is also very important in the degradation of rubber. It was found that on exposing a stressed rubber sample to ozone, small cracks formed on the surface. These cracks are perpendicular to the direction of applied stress [450]. The velocity of cracking depends on the chemical structure of the polymer, time of exposure, magnitude of applied stress, content of plasticizers, and so on [13, 14, 111, 186, 239, 360, 361, 553, 554]. Several workers [13, 184] have indicated that the ozonization of diene elastomers is accompanied by an autocatalytic... 

In the spectra of the ozonized polybutadienes the appearance of bands at 1,111 and 1,735 cm, which are characteristic for ozonide and aldehyde groups, respectively, is observed [22, 31], It was found that the integral intensity of ozonide peak in the l,4-cz5-polybutadiene Emulsion Butadiene Rubber (E-BR) spectrum is greater and that of the aldehyde is considerably smaller in comparison with the respective peaks in the Diene 35 NFA (BR) spectrum at one and the same ozone conversion degree of the double bonds. The differences in the aldehyde yields indicate that, according to IR-analysis, the degradation efficiency of the BR solutions is greater. 

The rubber-modified aromatic polymeric materials, for example, high-impact polystyrene (HIPS) and acrylonitrile-butadiene-styrene (ABS) are the least stable because of the rapid photooxidation of the rubber component, which sensitizes the polymer to further oxidation. Diene-based rubbers are also susceptible to degradation by ozone, which causes chain scission of the main-chain... 

Since the double bonds of conventional butyl rubber are integral with the chain backbone such a rubber will slowly degrade under ozone attack. If a diene is incorporated into the chain in the form of a ring the effect of ozone is much less catastrophic. For this reason isobu-tene-cyclopentadiene copolymers are virtually ozone resistant. They are believed to be of the following structure the cyclopentadiene entering in a 1,4- manner ... 

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