Patent ID: 8158302

Claim:
A separator seal for use in polymer electrolyte fuel cells which is formed of a sealing composition in the cured state, said sealing composition comprising (A) 100 parts by weight of a liquid organopolysiloxane containing at least two alkenyl groups each attached to a silicon atom in a molecule and having a weight average molecular weight of less than 100,000, (B) 3 to 30 parts by weight of a gum-like organopolysiloxane having a weight average molecular weight of at least 150,000, (C) 0.5 to 20 parts by weight of an organohydrogenpolysiloxane containing at least three hydrogen atoms each attached to a silicon atom in a molecule, (D) 5 to 30 parts by weight of fumed silica having a BET specific surface area of 50 to 400 m 2 /g, and (E) a catalytic amount of an addition reaction catalyst, said composition having a viscosity of 20 to 200 Pa-s at 25° C. and a shear rate of 10 s −1 .