Abstract: A method for preparing organopolysiloxane bases with high levels of fillers. The present inventors have found that by mixing the components of the base at a temperature below about 60.degree. C. for a period of time sufficient to effect essentially a homogeneous blend, a base composition is formed which can be further blended with a platinum group metal-containing catalyst, an organohydrogensiloxane, and optionally an inhibitor to form a curable liquid silicone rubber (LSR) composition. The curable LSR composition has improved flow characteristics and improved shelf life when compared to similar materials where the base is prepared at temperatures above about 60.degree. C. The improved flow characteristics allows larger quantities of fillers to be incorporated into the curable LSR composition while still maintaining acceptable flow characteristics.

Abstract: A platinum curing organosiloxane composition having improved hysteresis characteristics when cured. The composition requires the presence of a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 20 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms and a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 0.1 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C., where from 1 to 5 percent of the non-terminal repeating units of the siloxane comprise a vinyl radical. In addition, the present composition comprises 10 to 30 weight percent of a reinforcing silica filler that has been treated with hexamethyldisilazane and 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and an organohydrogen siloxane crosslinker comprising at least ten silicon-bonded hydrogen atoms per molecule.