Preparation of polydimethylphenylsilazane and polydimethylphenylsilazaboroxane varnishes

Polydimethylphenylsilazane varnishes (types A and B) are obtained by the coammonolysis of dimethyldichlorosilane and phenyltrichlorosilane (in the equimolar ratio) with gaseous ammonia in toluene medium  

The formed ammonia chloride is disintegrated with sodium hydroxide solution. After coammonolysis, if the required concentration of the products (87-97%) has been achieved, the toluene is distilled from the reactive mixture. This is accompanied by the polycondensation of the coammonolysis product and mostly forms a cyclolinear product. 

Polydimethylphenylsilazaboroxane varnish is obtained by the interaction of synthesised polydimethylphenylsilazane with boric acid  

In this case condensation is accompanied by secondary reactions, for example  

This reaction forms small amounts of sodium tetraborate and water, which partially hydrolyses polydimethylphenylsilazane  

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