Rapidly curable extrudable organosiloxane compositions

Claim 1

In an improved curable organosiloxane composition comprising the product obtained by mixing to homogeneity A. from 70 to 95 weight percent, based on the total weight of (A) and (B). of a first liquid diorganoalkenylsiloxy terminated polydiorganosiloxane exhibiting a viscosity of at least 12 Pa.s at 25 degrees C. and containing substantially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms. B. from 5 to 30 weight percent, based on the total weight of (A) and (B), of a second liquid diorganoalkenylsiloxy-terminated polydiorganosiloxane which is miscible with said first polydiorganosiloxane and exhibits a viscosity of at least 0.1 Pa.s at 25 degrees C., where from 1 to 5 mol percent of the non-terminal repeating units of said second polydiorganosiloxane contain an alkenyl radical, C. an amount sufficient to cure said composition of an organohydrogensiloxane that is miscible with the other liquid ingredients of said composition and contains an average of more than two silicon bonded hydrogen atoms per molecule, D. a platinum-containing hydrosilation catalyst in an amount sufficient to promote curing of said composition at a temperature of from ambient to 250 degrees C., and E. an amount of a treated reinforcing silica filler sufficient to improve the physical properties of a cured elastomer prepared from said composition, where the filler treating agent is comprised at least in part of an organosilicon compound containing an average of at least one alkenyl radical per molecule, the improvement comprising the presence, as the alkenyl radical in said second liquid diorganoalkenylsiloxy-terminated polydiorganosiloxane (B), of a radical which is terminally unsaturated and contains at least four carbon atoms.