GB792470A - Alkoxy-terminated siloxane polymers - Google Patents

Abstract

Alkoxy-terminated polysiloxanes are made by reacting, under anhydrous conditions and in the presence of an alkaline catalyst, a siloxane containing an average of from 1 to 2 hydrocarbon radicals per Si atom and free from Si-bonded alkoxy radicals, preferably a dialkyl or diaryl cyclic trimer or tetramer, with a silicon compound having at least one hydrocarbon radical and at least one alkoxy group attached to the same silicon atom. The reaction may be effected at room temperature but is preferably conducted at 50 DEG to 200 DEG C. Catalysts specified are potassium silanolate, potassium and sodium hydroxides, potassium methoxide and butoxide, tertiary amines and tetramethyl ammonium hydroxide. The molar ratio of the alkoxy compound to the siloxane may be e.g. from 1:1 to 1:100. The silicon bonded hydrocarbon radicals of the reactants may be alkyl, vinyl, aryl or aralkyl radicals, and the alkoxy silicon compounds may be alkoxy silanes, alkoxy polysiloxanes or alkoxy silcarbones in which the R1 of the OR1 groups may be the same as the Si-bonded R radicals, and may also contain nitrogen, e.g. bis(2-aminoethoxy) dimethylsilane. The molecular weight of the final polymer may be greater or less than that of the initial polymer. If desired, light fractions may be stripped from the reaction products. The products may be used as oils, dielectric agents or intermediates or be reacted with alkyd resins. In examples: (I) to (II) dialkoxy silanes are reacted with cyclic diorganopolysiloxanes, the catalyst concentration or time of reaction being varied; (12), (13) trialkoxy silanes are reacted with cyclic diorganosiloxanes; (14) trialkoxysilanes are reacted with mono-organosiloxanes; (15) to (20) specific alkoxy organosilicon polymers are prepared, the polymer of Example (16), having the general formula (O3SiRSiO) (R12SiO)n(R11)6, being made by reacting the hydrolysate of dimethyldichlorosilane with hexaethoxydisilylethane.