Process for preparation of organosilicon compositions

A process for the preparation of organosilicon compositions consisting of prepolymer A or a mixture of prepolymers A+B, the content of B being between 0 and 30% by weight of the mixtures, in which said prepolymers have the following structural formula:

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• wherein:
• R is methyl or ethyl;
• R1 is absent or is an organic hydrocarbon, aliphatic, cycloaliphatic, aromatic or ether radical containing 1 to 18 carbon atoms;
• R2 is a divalent organic radical with a molecular weight of between 2,000 and 20,000 Daltons deriving from a polyether glycol, preferably constituted by a polypropylene oxide or a propylene oxide and ethylene oxide copolymer of the statistical and/or block type, in which the polyethylene oxide fraction does not exceed 20% by weight;
• R3 is a divalent hydrocarbon, aliphatic, cycloaliphatic or aromatic radical containing 4 to 36 carbon atoms;
• n=0, 1 and 2;
• said process comprising the following steps, which are carried out in a single reactor:
• a) synthesis of unsaturated prepolymer A1, or of the mixture of unsaturated prepolymers A1+B1, where the content of B1 is between 0 and 30% by weight of the mixture
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• where R, R1, R2 and R3 are as defined above, and
• b) conversion of A1 or A1+B1 to A and A+B respectively by silylation catalysed with alkoxysilanes generated in situ by reaction between chlorosilanes with structure C
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• and orthoformates with structure D
• HC(OR)3 (D)
• where n and R are as defined above.