Abstract: Proposal is given of a method for the preparation of an organopolysiloxane highly freed from any trace amount of the residue of sulfuric acid or fuming sulfuric acid by the siloxane rearrangement reaction of organosiloxane oligomers into equilibirium by using the acid catalyst. The inventive method comprises subjecting the reaction mixture, after completion of the reaction but before the conventional step of washing with a large volume of water to remove the acid residue, to a hydrolysis reaction of the acid residue bonded to the organopolysiloxane molecules with admixture of a limited amount of water and separating the mixture into aqueous and organopolysiloxane phases to discard the acid-containing aqueous phase.

Abstract: An organopolysiloxane composed of tetrafuctional siloxane units SiO.sub.2 and monofunctional siloxane units R.sub.3 SiO.sub.0.5 can be prepared by reacting an alkyl orthosilicate, e.g., ethyl silicate, or a partial hydrolysis product thereof and an oligomeric organopolysiloxane containing the monofunctional siloxane units in the presence of a catalytic compound which is, different from conventional hydrogen chloride, selected from the group consisting of sulfonic acid group-containing compounds, e.g., sulfuric acid and p-toluene sulfonic acid, and phosphonitrile chloride. In particular, cation exchange resins of sulfonic acid type and fluorinated polysulfonic acid resins can be used as the catalyst in a continuous process in which the reaction mixture is passed through a bed of the catalyst continuously. The inventive method is advantageous over conventional methods because of the absence of the problems of heavy corrosion of the apparatuses and waste disposal due to the hydrogen chloride.