GB835790A - Improvements in or relating to siloxane elastomers - Google Patents

Abstract

A composition cold vulcanizable to an elastomer comprises a mixture of liquid linear diorganopolysiloxanes having Si-bonded hydrocarbon or halogenated hydrocarbon radicals, a viscosity of 5000 to 500,000 c.s. at 25 DEG C. and containing at least 0.1% by weight of Si-bonded OH groups, and from 0.5 to 10% by weight of the siloxanes of methyltriacetoxysilane. The methyltriacetoxysilane, which may be made by the processes described in Specifications 622,985 and 640,834, may be diluted with octamethylcyclotetrasiloxane, dimethyl diacetoxysilane or inert powders. Fillers, e.g. natural, precipitated, combustion or surface modified silicas, alumina, or oxides of Fe, Zn or Cd, and accelerators, e.g. oxalic or p-aminobenzoic acid, morpholine, ethanolamines, diethylaminoethanol, methyl diethanolamine, o-toluene sulphonamide or urea derivatives, may also be added. Octamethylcyclotetrasiloxane (M.P. 17.5 DEG C.) was heated under nitrogen at 150 DEG C. with aqueous KOH to give an oil, to which, whilst hot, water was added in small fractions to reduce its viscosity, and when cool, the KOH content was neutralized by agitation with a precipitated silica. The resulting liquid was then heated under a current of nitrogen to remove volatiles and leave an oil having a viscosity of 21,000 c.s. at 25 DEG C. and a hydroxy content of 0.15%. In examples this oil was mixed with (1) methyltriacetoxy silane and (2) a combustion silica or a natural silica and oxalic acid; (3) various silicas, ZnO and diethylaminoethanol with or without o-toluene sulphonamide; (4, 5) natural silica and ZNO. In Example (6) the siloxane used was a methylphenyl siloxane. Uses.-For various packings, mouldings (particularly biological mouldings for use in dentistry and as prostheses), production of laminar products, sticking of silicone elastomers, insulating coating of electrical wires and treatment of fabrics.ALSO:A composition cold vulcanizable to an elastomer, for making biological mouldings for use in dentistry and as prostheses, comprises a mixture of liquid linear di-organopolysiloxanes having Si-bonded hydrocarbon or halogenated hydrocarbon radicals, a viscosity of 5000 to 500,000 cs. at 25 DEG C. and containing at least 0.1% by weight of Si-bonded OH groups, and from 0.5 to 10% by weight of the siloxanes of methyltriacetoxysilane (see Group IV (a)). Inert fillers and curing accelerators may also be added. In Example (3) diethylaminoethanol (accelerator) is added to a pasty mixture of a dimethylsiloxane oil containing 0.15% Si -OH groups, combustion silica, natural silica and zinc oxide. This mixture, which is then triturated with methyltriacetoxy silane, thickens rapidly and is moulded for 30 seconds and immediately used for taking dental impressions. Specifications 622,985 and 640,834 are referred to.