Patent ID: 7674857

Claim:
A curable sealant composition comprising: (a) diorganopolysiloxane exhibiting permeability to gas, wherein the diorganopolysiloxane ranges in amount of from about 50 weight percent to about 99 weight percent of the total composition; (b) at least one polymer having a permeability to gas that is less than the permeability of diorganopolysiloxane polymer (a); (c) cross-linker; and, (d) catalyst for the cross-linker reaction wherein the cross-linkers (c) is an alkylsilicate having the formula: (R 14 O))(R 15 O)(R 16 O)(R 17 O)Si where R 14 , R 15 , R 16 and R 17 are chosen independently from monovalent C 1 to C 60 hydrocarbon radicals, wherein said curable sealant composition, once cured has a permeability to argon of no more than about 800 barrer units at 25 degrees C. and under 100 psi pressure, said composition containing at least one adhesion promoter in an amount of from about 0.5 weight percent to about 20 weight percent of the total composition and further comprising a clay filler, wherein the clay is selected from the group consisting of montmorillonite, sodium montmorilloriite, calcium montmorillonite, magnesium montmorillonite, nontronite, beidellite, volkonskoite, laponite, hectorite, saponite, sauconite, magadite, kenyaite, sobockite, svindordite, stevensite, vermiculite, halloysite, aluminate oxides, hydrotalcite, illite, rectorite, tarosovite, ledikite, and kaolinite, and mixtures thereof.