Optically clear reinforced organosiloxane compositions

Claim 1

In a curable composition comprising 1) a diorganovinylsiloxy-terminated polydiorganosiloxane, 2) an amount of a resinous organosiloxane copolymer sufficient to improve the physical properties of the elastomer obtained by curing said composition, 3) an amount of an organohydrogensiloxane sufficient to cure said composition, and 4) an amount of a platinum-containing hydrosilation catalyst sufficient to promote curing of said composition, the improvement comprising (a) selecting said polydiorganosiloxane from those exhibiting a viscosity of at least 12 Pa·s at 25°C. and wherein at least 95% of the repeating units are dimethylsiloxane units and any remainder are diorganosiloxane units wherein the organic groups bonded to silicon are monovalent hydrocarbon radicals or monovalent halogenated hydrocarbon radicals (b) selecting said organo­siloxane copolymer from those consisting essentially of SiO₂, trimethylsiloxy and dimethylvinylsiloxy units, where the molar ratio of the combination of trimethylsiloxy and dimethylvinylsiloxy units to SiO₂ units is from 0.6 to 1.1, inclusive and said copolymer contains from 1.5 to 3.5 weight percent of vinyl radicals, and (c) maintaining the concentration of said organosiloxane copolymer within the range of from 1 to about 45 weight percent, based on the weight of said polydiorganosiloxane to achieve a reduction in the viscosity of said composition relative to the viscosity of the composition in the absence of said copolymer.