The Vulcanisation of Elastomers with Bis (Dialkyl) Thiophosphoryl Disulphides

Abstract

Bis(diisopropyl)thiophosphoryl disulphide is used as a sulphur donor vulcanising system for cis-1,4-polyisoprene. It is shown that the network structure consists of polyand disulphidic crosslinks at early stages of cure, simplifying at optimum cure to monosulphidic crosslinks. Pendent accelerator groups bound to the rubber molecule form at early stages of cure, but are subsequently replaced by cyclic sulphidic groups. The good thermal and thermal oxidative ageing behaviour of the vulcanisate is due to the formation of zinc diisopropyldithiophosphate during vulcanisation. The level of technologically useful properties is low, but when used as a codonor with dimorpholyl disulphide a reasonable level of properties results. The codonor system vulcanises synthetic rubbers, notably styrene butadiene, ethylene propylene termonomer and nitrile elastomers, to give good scorch times, fast rates of cure and thermally stable modulus levels. Bis(diisopropyl)thiophosphoryl tri- and tetrasulphides are evaluated eas sulphur donors for cis-1,4-polyisoprene. These give higher levels of physical properties, whilst maintaining the simple network structure and good thermal and thermal oxidative ageing properties shown by the disulphide. As a result of the work, new accelerators are suggested for the vulcancanisation of cis-1,4-polyisoprene and general purpose synthetic elastomers.