Preparation of branched oligomethylsiloxanes

Low-viscosity branched oligomethylsiloxanes are prepared by the hydrolytic condensation of a mixture of methyltrichloro-, dimethyldichloro- and trimethylchlorosilanes, subsequent catalytic regrouping and the separation of the target products by rectification. 

The process of hydrolytic condensation and subsequent catalytic regrouping proceeds according to the following general scheme  

The number of silicon atoms in these oligomers ranges from 9 to 18. 

The rectification of the products of hydrolytic cocondensation and catalytic regrouping forms individual oligomethylsiloxane liquids PMS-lb, PMS-l,5b, PMS-2b, PMS-2,5b and PMS-3b, as well as higher-viscosity oligomethylsiloxanes, which differ in the number of siloxane elements in the chain. 

The process comprises the following stages (Fig. 45) the preparation of the reactive mixture hydrolytic condensation the neutralisation and drying of the cocondensation products catalytic regrouping and filtering rectification. 

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