Method for the preparation of organopolysiloxane by polymerization and rearrangement of cyclic siloxanes

A process for the preparation of polyorganosiloxanes by ring-opening polymerization and/or redistribution polymerization of cyclic polyorganosiloxanes and of linear and/or nonlinear polyorganosiloxanes, said process comprising the following steps:

• a) polymerizing the cyclic polyorganosiloxanes and the linear and/or nonlinear polyorganosiloxanes, by the steps of:
• a-1) preparing a reaction composition at ambient temperature, where the reaction composition comprises:
• (i) at least 20% by weight with respect to the total weight of the composition of at least one cyclic siloxane of following formula (I):
• in which:
• n=3, 4, 5, 6, 7 or 8;
• R1 is a hydrogen atom, an optionally substituted, linear or branched, C1-C12 alkyl radical, an alkenyl radical, an optionally substituted C5-C10 cycloalkyl radical, an optionally substituted C6-C18 aryl radical or an optionally substituted aralkyl radical, and
• R2 is a radical such as R1 or an —OR3 radical, with R3 being a hydrogen atom or an optionally substituted, linear or branched, C1-C12 alkyl radical;
• and
• (ii) optionally up to 80% by weight with respect to the total weight of the composition of at least one polyorganosiloxane comprising siloxyl units, which are identical to or different from one another, of general formula (II):
• (R3)x(R4)zSiO(4-x-z)/2
• in which:
• x and z=0, 1, 2 or 3 and x+z≦3;
• R3 is a hydrogen atom, a linear or branched C1-C12 alkyl radical which is optionally substituted by one or more atoms, such as chlorine and/or fluorine, an optionally substituted C1-C12 alkenyl radical, an optionally substituted C1-C12 haloalkyl radical, an optionally substituted C1-C12 haloalkenyl radical, an optionally substituted C3-C8 cycloalkyl radical, an optionally substituted C3-C8 cycloalkenyl radical, an optionally substituted C3-C4 cyanoalkyl radical or an optionally substituted C6-C12 phenyl, alkylphenyl or phenylalkyl radical;
• and
• R4 is a radical such as R3 or an —OR5 radical with R5 having the same definition as R3;
• a-2) adding a catalytic system to the reaction composition, wherein the catalytic system is composed of x mmol of at least one alkaline catalyst (III) and y mmol of at least one cryptand (IV) which is a macroheterobicyclic diamine, and
• a-3) adjusting the temperature of the reaction mixture to a temperature of between 100° C. to 190° C.;
• b) neutralizing the reaction mixture;
• and
• c) optionally devolatilizing the reaction mixture;
• wherein for the alkaline catalyst (III), the number of mmol x used meets the following criterion:
• 0.005≦x≦5 mmol per 500 g of cyclic siloxane (I), and for the cryptand (IV), the number of mmol y used meets the criterion defined by the molar ratio y/x<0.040.