Abstract: The organopolysiloxane compositions are prepared by mixing(1) organopolysiloxanes which contain on average at least 2 aliphatic carbon-carbon multiple bonds per molecule,(2) prehydrophobized oxidic reinforcing fillers having a carbon content, obtained by the hydrophobizing, of at least 0.5% by weight and(3) compounds which are chosen from(3a) silanol compounds of the formulaR--[SiR.sub.2 --O--].sub.a H (I)in whichR is identical or different monovalent, C.sub.1 - to C.sub.10 -hydrocarbon radicals which are free from aliphatic carbon-carbon multiple bonds anda has values from 1 to 10, and(3b) saturated C.sub.1 - to C.sub.18 -alkanols.

Abstract: The organopolysiloxane compositions are prepared by(1) organopolysiloxanes, and(2) prehydrophobicized oxidic stiffening fillers being blended and kneaded in a kneading machine 1 having at least two kneading chambers 2 which are arranged in series next to one another, each contain two axially parallel kneading tools 3 drivable so as to corotate or counterrotate, and communicate with one another via openings 5 through which passage is possible transversely to the axes 4 of the kneading tools 3, the first kneading chamber 2 having a charging port 6 and the final kneading chamber 2 having a discharge port 7.