Preparation of organoalkoxysiloxanes by partial acidolysis of organoalkoxysilanes

Partial polycondensation of RSi(OMe)3 (R = C6H5, CH3) by the reaction with AcOH in the presence of HCl is studied. Oligoorganomethoxysiloxanes are obtained of the average composition [RSi(OMe)O]4, [RSi (OMe)4/6O7/6]6, RSi(OMe)0.5O1.25]8, and [RSi(OMe)0.4O1.3]10. Using the method of 29Si NMR spectroscopy they were shown to contain three types of structural fragments: RSi(OMe)2O-, RSiOMe(O-)2, RSi(O-)3. Based on the kinetic data, on the composition, properties, and the 29Si NMR spectroscopy data of the products the conclusion is made that the obtained compounds have polycyclic structure with branched fragments. Using the GLC method the reaction was shown to have an induction period, whose duration can be substantially shortened by addition of HCl or methanol.