GB862576A - Improvements in or relating to siloxanes - Google Patents

Abstract

A siloxane, vulcanizable at room temperature and having the general formula <FORM:0862576/IV (a)/1> in which Ac is a saturated or unsaturated acyl radical, each R and R1 is a monovalent hydrocarbon, halohydrocarbon or other organic radical unreactive to the acyloxy radicals or an organosiloxane side chain, an n is an integer of at least 5, is made by reacting a hydroxylated siloxane of the formula <FORM:0862576/IV (a)/2> with an excess of a silane of the formula R1Si(OAc)3, in the substantial absence of moisture. The reaction can be effected, e.g. at 20 DEG to 100 DEG C. and, if desired, in the presence of an inert solvent. Ac can be propionyl, butyryl, hexoyl, 2-ethylhexoyl, octanoyl, isovaleryl, stearyl, crotonyl, acrylyl or propiolyl, and R and R1 can be alkyl, alkenyl, cycloalkyl or -alkenyl, alkaryl, aryl, halo-alkyl, -alkenyl or -aryl, or organo-nitrile or -nitro radicals. The acyloxysiloxanes, with or without fillers, e.g. silica (fume, aerogels and precipitated, with or without organosilyl surface modification), diatomaceous earth, crushed quartz, TiO2, Fe2O3, ZnO and asbestos and glass fibres, plasticizers, e.g. trimethylsilyl endblocked dimethylsiloxanes, pigments, sun-screen agents, oxidation inhibitors, dielectric materials, e.g. graphite and C black, and siloxane resins, are cured merely by exposure to moisture. The fillers &c. may be added to the acyloxysiloxane or to the hydroxysiloxane. In a typical example, (1) a liquid hydroxylated dimethylpolysiloxane was mixed with a solution of methyltriacetoxy silane in a low viscosity trimethylsilyl end-blocked dimethylpolysiloxane and heated at 100 DEG C. under reduced pressure, with subsequent stripping of acetic acid, excess silane and solvent, to yield a liquid of the formula <FORM:0862576/IV (a)/3> (Me=methyl) Uses.-For caulking applications on buildings, airplanes and automotive equipment; for protective coatings on wood and other heatsensitive materials.