TRANSPARENT STORAGE-STABLE POLYSILOXANES WHICH CROSSLINK UNDER ATMOSPHERIC CONDITIONS

摘要

1468467 Silicone rubber compositions BAYER AG 21 March 1975 [22 March 1974] 11923/75 Heading C3T A polysiloxane mixture which can be crosslinked under atmospheric conditions to a transparent silicone rubber comprises as essential ingredients (a) 100 p.b.w. of at least one α,#- dihydroxymethylphenylpolysiloxane containing dimethylsiloxy units with 7-15 mole per cent of diphenylsiloxy units and/or 14-28 mole per cent of methylphenylsiloxy units, and having a viscosity of from 408-500,000 cs. at 20‹ C. (b) 1-40 p.b.w. of an uncoated reinforcing filler consisting essentially of SiO 2 having a specific surface area of 40-500 m2./g. determined by the BET method, and (c) 1-10 p.b.w. of a cross-linking agent which is N,N-bis-(triethoxysilylmethyl)- allyl-amine or a compound of the formula RSiX 3 wherein R represents an alkyl, alkenyl, haloalkyl, aryl, alkaryl or aralkyl radical and X represents an alkoxy, acyloxy, oximato or alkylamino radical, or a partial hydrolysis product thereof; and optionally (d) a curing catalyst, such as an amine or a metal salt of an organic monocarboxylic acid, and optionally (e) a methyl-blocked methylphenylpolysiloxane having a viscosity of from 408 to 500,000 c.St. at 20‹ C., and optionally (f) a dialkoxydiacetoxysilane to improve the adhesion. Component (a) may be a copolymer containing dimethylsiloxy, diphenylsiloxy and methylphenylsiloxy units. In the examples siloxane mixtures are prepared from an α,#-dihydroxymethylphenylpolysiloxane (9À1-15 mole per cent diphenylsiloxy units; 27,300-180,000 c.S.), a reinforcing SiO 2 filler (surface area 130-380 m.2/g.), dibutyltin dilaurate or diacetate, and either (1) dibutoxydiacetoxysilane together with any one of vinyltriacetoxysilane, methyltriacetoxysilane, methyltris(butanonoximato)silane or N,N bis(triethoxysilylmethyl)allylamine; or (2) any one of methyltriethoxysilane, methyltrimethoxysilane, vinyltriacetoxysilane or methyltriacetoxysilane; or (3) α,#-dimethylphenylmethylpolysiloxane (14 mole per cent diphenylsiloxy units; 408 c.S.), vinyltriacetoxysilane and dibutoxydiacetoxysilane. The mixtures are cured in air to give clear silicone rubbers.