The work described consists of explorative studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the

The work described consists of explorative studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variation in physical characteristics. Infrared spectrographic techniques were found to be admirably suited for the reflection of accumulation or depletion of specific structural linkages in polymer molecules undergoing ozonization. Purified gum specimens of Hevea, GR-S, nitrile rubber, Neoprene, and GR-I were dissolved in chlorinated hydrocarbon solvents such as ethylene dichloride or o-dichlorobenzene, and subjected to a stream of ozonized oxygen containing approximately 50 p.p.m. of ozone. Infrared spectrograms of films cast from the treated solutions show progressive intensification of clearly defined absorption bands at 2.9 and 5.8 mµ, reflecting the functional groups hydroxyl and carbonyl, respectively. Methods for quantitating these changes by calibration against reference compounds are described. A means is available for following ozone degradation of polymers in terms of specific variations in molecular structure. Basic information of this nature is potentially useful in the development of an accelerated ozone aging test correctable with aging under conditions of actual service.

Studies were made to provide information for use in the development of SBR elastomers with improved resistance to attack by high energy radiation. Changes of molecular structure were investigated by viscometric techniques and by measuring gel content. Chemical changes were followed by use of infrared spectrophotometry. Results indicate that the polymer in toluene, when subjected to radiation doses in the range 0–100 Mrep, is randomly scissioned. When similarly treated in chloroform, the polymer is initially randomly crosslinked and then the newly formed elastomer network undergoes random scission. The nature of the end chemical changes is shown to depend on environmental factors. In the presence of a limited supply of oxygen, the polymer is partially oxidized. The oxidation reaction appears to have no influence, however, on the random nature of the degradation process. The external butadiene structures are shown to be attacked more rapidly than the internal groups. The phenyl rings of the styrene groups in the polymer molecules, on the other hand, are only moderately affected in this respect. The results obtained in these solution studies are used to predict the effects of radiation damage to SBR vulcanizates.