Abstract: A fluorinated polydiorganosiloxane elastomer having improved physical properties can be obtained through the use of a method which first reacts a hydroxyl endblocked trifluoropropylmethylsiloxane having a Williams Plasticity Number of greater than 225 with a methylvinyldi(N-alkylacetamido)silane to give a chain extended polymer having pendant vinyl groups only at the location of the chain extension. The polymer is then reinforced with fume silica and compounded into a stock. The cured stock has improved tensile strength and tear strength when compared to similar compositions which do not contain the same type of polymer. The polymer has pendant vinyl groups located along the polymer chain, with the distance between them being relatively large. When too many vinyl pendent groups are present along the chain, the improved results are not obtained.

Abstract: A method of reducing the compression set of a silicone elastomer is accomplished by mixing an alkenyl silazane with a previously prepared, based heated, silanol-containing silicone elastomer base. Fluorosilicone elastomers prepared by these methods find use in gasketing and sealing application which are exposed to fuels and solvents.

Abstract: A silicone rubber stock, giving an elastomer upon cure by hot air-vulcanization which has a low compression set, is obtained when a silicon composition containing at least two .tbd.SiH groups is added to a silicone rubber base which contains a polydiorganosiloxane gum having at least two alkenyl groups per molecule.

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: Phosphorus-containing catalysts that are suitable for polymerizing polyorganosiloxanes are prepared from tetraorgano phosphonium halides, a basic compound, such as sodium hydroxide, and an organosilicon compound. The catalyst must be prepared at a temperature of at least 30.degree. C. The catalysts are moisture sensitive but possess improved shelf-life stability. They are used to polymerize polyorganosiloxanes and can subsequently be inactivated by heating to a temperature above approximately 130.degree. C. for a suitable length of time.