STABLE CROSS-LINKS BY DITHIOALKANE VULCANIZATION - A ROUTE TO HEAT-RESISTANT DIENE ELASTOMERS

The development of aging resistant curing systems started with a study of 1.2-dithiacyclooctane. This substance, even though yielding revers ion resistant vulcanizates, proved to be no alternative to sulfur vulc anization due to its difficult synthesis. When an open chain derivativ e with dithiocarbamate endgroups is employed instead, such as 1.6-bis( diethylthiocarbamoyl-disulfido) hexane, natural rubber vulcanizates of good aging stability are obtained in a vulcanization proceeding witho ut reversion. In an optimized curing system, 1,6-bis(dibenzylthiocarba moyl-disulfido) hexane, prepared from a ''safe amine'', was used, toge ther with small amounts of sulfur and additional accelerator yielding polyisoprene vulcanizates of exceptional aging resistance at acceptabl e reaction rates. Even after considerable overvulcanization, no deteri oration of physical properties was observed. Oven aging of the elastom ers up to 28 days at 100-degrees-C shows advantages even against EV an d thiuram systems. 1,6-Bis(thiobenzoyl-disulfido) hexane, with small a mounts of sulfur and additional accelerator, gave aging resistant poly isoprene vulcanizates in a rapid reaction without reversion.