Abstract: During the polymerization of diorganocyclosiloxane, to produce a polymer for use in manufacturing silicone rubber, a small amount of --SiOH is formed. The amount of --SiOH present in the polymer can be controlled by controlling the water vapor pressure present in the reaction container during polymerization.

Abstract: A high molecular weight polydiorganosiloxane, produced by the alkaline catalysis of dialkylcyclotetrasiloxane, has a lower --SiOH content when the catalyst is neutralized with a composition of the formula R'.sub.3 SiOC(O)R" where R' is a hydrocarbon radical of from 1 to 6 carbon atoms inclusive and R" is a hydrocarbon radical of from 1 to 8 carbon atoms inclusive.

Abstract: An improved silicone elastomeric sealant composition is produced by mixing alkoxy functional polydiorganosiloxane having alkoxysilethylene ends with a combination of trifunctional or tetrafunctional silane crosslinker and defunctional silane chain extender. The sealant composition is stable upon storage in the absence of moisture, but cures to an elastomer upon exposure to moisture. The cured composition can be adjusted for the desired elongation by varying the ratio of crosslinker to chain extender, but there must be at least 50 mol percent of crosslinker in the composition to ensure that the composition cures to a non-tacky surface.

Abstract: A composition curable to a silicone elastomer is prepared by mixing a triorganosiloxy endblocked polydimethylsiloxane fluid where the triorganosiloxy is dimethylvinylsiloxy or methylphenylvinylsiloxy, a reinforcing silica having a surface treated organosiloxane groups which contain 0.05 to 0.32 percent by weight vinyl, a fluid organohydrogensiloxane, a platinum catalyst and optionally a platinum catalyst inhibitor. The polydimethylsiloxane fluid has a major peak molecular weight of 68,000 to 135,000, a dispersity index greater than 3.8, the lowest molecular weight species between 854 and 3146 and the highest molecular weight species between 174,000 and 370,000. These compositions are readily extrudable under low pressure and cure to high strength elastomers with a high durometer.