AbstractThe aging of sulfurless tetraalkylthiuramdisulfide vulcanizates has been studied by the stress‐relaxation technique, the general behavior being independent of the nature of the alkyl group. The aging in air at 100°C. of fully cured vulcanizates is excellent before acetone extraction but rapid after it, due to removal of zine dialkyldithiocarbamates which are powerful antioxidants. In undercured vulcanizates, the network breakdown at 100°C. after extraction is much less than in fully cured samples, and there is considerable crosslinking during the aging. This behavior is attributed to the presence of a vulcanization intermediate which, at 100°C., brings about crosslinking with formation of zine dialkyldithiocarbamate and which cannot be removed by acetone extraction. The presence of such an intermediate is confirmed by the ability of extracted undercured thiuram vulcanizates to be further crosslinked in the press at 140°C. Previous theories regarding thiuram vulcanization are discussed in the light of these observations. The rapid initial relaxation of unextracted undercured vulcanizates may be due to the breakdown of this vulcanization intermediate. During the thermal aging of apparently fully cured samples, some crosslinking occurs which is considered to be due to a direct oxidative reaction of dithiocarbamates. Unextracted thiuram vulcanizates degrade very little on illumination with ultraviolet light (wavelength 365 mμ), but, after extraction, the photolytic aging becomes more rapid. There is no variation in the rate of this type of aging with degree of cure, presumably because the vulcanization intermediate is light
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