GB1041081A - Improvements in or relating to organopolysiloxane elastomers - Google Patents

Abstract

A surface modified silica may be prepared by contacting a finely divided silica with a compound of the general formula X-(R2Si)-[O-(R2Si)]n-R in which each R is a monovalent hydrocarbon radical, X is H, OH, halogen, OR, or O.CO.R, and n has a value from 1 to 24. The contacting may be carried out in the presence of a catalyst capable of accelerating the reaction between the X groups and the silica surface. Catalysts are exemplified as strong acids and bases, e.g. HCl and NaOH, and also the condensation catalysts triethylamine, morpholine and pyridine, silazines, silylamines, ammonium carbonate and metal carboxylates, e.g. dibutyltin dilaurate and stannous octoate. The prepared filler may be used as an ingredient in a vulcanizable composition, the other ingredients being an organo-polysiloxane convertible to the solid state. In a preferred process, the filler is not previously treated as above, but the organo-polysiloxane, the untreated filler, and a compound of the above general formula are mixed together to give the vulcanizable composition directly. In this case, the use of strong acid and alkali catalysts for the filler treatment are avoided. A specified composition contains 100 parts by weight of the unconverted polysiloxane, from 10 to 75 parts by weight of the reinforcing silica and from two to 75 parts by weight of a compound having the above general formula. The organo-polysiloxane is preferably a di-organo-polysiloxane, in which the organic constituents comprise mainly methyl groups, any other substituents being phenyl and/or vinyl radicals. The mixture may be heated during or following the mixing operation to a temperature not exceeding 300 DEG C.ALSO:A surface modified silica may be prepared by contacting a finely divided silica with a compound of the general formula X-(R2Si)-[O-(R2Si)-]-nR in which each R is a monovalent hydrocarbon radical, X is H, OH, halogen, OR, or O.CO.R, and n has a value from 1 to 24. The contacting may be carried out in the presence of a catalyst capable of accelerating the reaction between the X groups and the silica surface. Catalysts are exemplified as strong acids and bases, e.g. HCl and NaOH, and also the condensation catalysts triethylamine, morpholine and pyridine, silazines, silylamines, ammonium carbonate and metal carboxylates, e.g. dibutyltin dilaurate and stannous octoate. The prepared filler may be used as an ingredient in a vulcanizable composition, the other ingredients being an organo-polysiloxane convertible to the solid state. In a preferred process, the filler is not previously treated as above, but the organopolysiloxane, the untreated filler, and a compound of the above general formula are mixed together to give the vulcanizable composition directly. In this case, the use of strong acid and alkali catalysts for the filler treatment are avoided. A specified composition contains 100 parts by weight of the uncoverted polysiloxane, from 10 to 75 parts by weight of the reinforcing silica and from two to 75 parts by weight of a compound having the above general formula. The organo-polysiloxane is preferably a di-organo-polysiloxane, in which the organic constituents comprise mainly methyl groups, any other substituents being phenyl and/or vinyl radicals. The mixture may be heated during or following the mixing operation to a temperature not exceeding 300 DEG C.