synopsisBis(diisopropy1)thiophosphoryl disul6de (DIPDIS) is used as a sulfur donor vulcanizing system for &-1,4polyisoprene. It is shown that the network structure consists of poly-and disulfidic crosslinks at early stages of cure, simplifying a t optimum cure to monosulfidic croaslinks. It is thought that pendent accelerator groups are bound to the rubber molecule a t early stages of cure, but are subsequently replaced by cyclic sul6dic groups. The good thermal and thermal oxidative aging behavior of the vulcanizate is due to the formation of zinc diisopropyldithiophosphate (ZDP) in situ.

SynopsisA synergistic combination of bis(diisopropy1)thiophosphoryl disulfide, dimorpholyl disulfide, and sulfur is used to produce an efficient vulcanizing system for a range of rubbers. This produces vulcanizates with the exceptional thermal and thermal-oxidative stability characteristic of sulfur donor vulcanizates and the rapid and extensive crosslinking reaction normally associated with a conventional sulfur-accelerator combination. A pronounced induction period is noted. The crosslinks initially produced in cis-1,4-polyisoprene rubbers are predominantly polysulfide but reduce to mono-and disulfides at optimum and extended cures. The crosslinks of the ethylene-propylene terpolymer and the styrene-butadiene vulcanizates are initially mainly disulfide but are rapidly reduced to monosulfides at the high curing temperatures (180°C) used. A comparison with vulcanization systems based on tetramethyltbiuram disulfide and bis(diisopropy1)thiophosphoryl triand tetrasulfides as sulfur donors and with a conventional cyclohexylbenthiazyl-2-sulfenamide-sulfur combination, respectively, shows it to have distinct advantages.