Method for the preparation of an organosiloxane oligomer and a novel organosiloxane oligomer thereby

A method for the preparation of an organosiloxane oligomer represented by the general formula

• YSi(R.sup.1).sub.n (--O--SiR.sub.3).sub.3-n,
• in which each of the groups denoted by R and R.sup.1 is, independently from the others, a halogen-substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, Y is a hydrogen atom or a monovalent group selected from the class consisting of methyl, phenyl, vinyl, chloromethyl, 3-methacryloxypropyl and 3-acryloxypropyl groups and n is zero, 1 or 2, which comprises reacting a cyclic or linear organopolysiloxane represented by the general formula --(--SiR.sub.2 --O--).sub.m -- with a Grignard reagent represented by the general formula RMgX, in which R has the same meaning as defined above and X is a halogen atom, to form an organosilicon halomagnesium salt of the general formula R.sub.3 Si--O--MgX and reacting the organosilicon halomagnesium salt with an organosilane compound represented by the general formula YSi(R.sub.1).sub.n (Z).sub.3-n, in which R.sub.1 and Y each have the same meaning as defined above and Z is a halogen atom or a lower alkyl group.