Addition reaction-curable liquid silicone rubber compositions and process of preparing same

Abstract

An addition reaction-curable liquid silicone rubber composition includes an organopolysiloxane containing at least one Si-bonded vinyl group only at each end of its backbone and having a viscosity of from 1 to 1,000 Pa·s at 25° C., an organopolysiloxane containing at least two Si-bonded vinyl groups only in side chains on its backbone and having a viscosity of from 0.1 to 100 Pa·s at 25° C., the amount of siloxane units bonded to the vinyl groups being from 2 to 20 mole % of its total siloxane units, finely divided silica having a specific surface area of at least 50 m/g, hexamethyldisilazane, water, an organohydrogenpolysiloxane containing at least two Si-bonded hydrogen atoms per molecule, and a hydrosilation catalyst. Another addition reaction-curable liquid silicone rubber composition additionally includes a specific non-functional dimethylpolysiloxane. The silicone rubber compositions are cured into products having a hardness of at least 75 as measured by a type-A durometer and an elongation at break of at least 200%.