Preparation of polyorganosilazanes and polyorganosilazane varnishes

Nowadays polyorganosilazanes are used more and more often. Until recently, due to the small hydrolytic stability (in acid and neutral media) of compounds with a Si—N bond, the possibility of their practical application seemed doubtful. However, the increased ability to hydrolyse and the chemical activity of the Si—N bond in polyorganosilazanes predetermined their industrial applications. It was found that polyorganosilazanes are hydrolysed when kept in air even at room temperature, with 80-85% of si-lazane bonds replaced by siloxane bonds. Probably, due to the high gas permeability of siloxane film the ammonia released during the hydrolysis is withdrawn out of the system without disrupting the film, even in case of considerable thickness (1-2 mm). 

The hydrolysis forms polyorganosilazoxanes, i.e. polymers which contain both Si—N and Si—O bonds, are stable ahd have good physicome-chanical characteristics and adhesion to various materials. 

Polyorganosilazanes are obtained by the ammonolysis or coammonoly-sis of various organochlorosilanes and subsequent polycondensation of the products of ammonolysis. 

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