High strength fluorosilicone rubber

Claim 1

A method of making a fluorinated polydiorganosiloxane base which when cured gives an elastomer having improved tensile strength and tear strength, the method consisting essentially of (A) shearing in a mixer which is heated to a temperature of from 23° to 100° C. which is being swept by a stream of dry nitrogen (1) 100 parts by weight of hydroxyl endblocked trifluoropropylmethylsiloxane having a Williams Plasticity Number of greater than 225, for a period of time sufficient to remove any free water from the siloxane, then (B) mixing with (2) from 0.1 to 1.5 parts by weight of methylvinyldi(N-alkylacetamido)silane, while continuing the dry nitrogen sweep, at a temperature below 80° C., for a period of time sufficient to increase the Williams Plasticity Number of the polymer, then (C) admixing from 5 to 20 parts by weight of hydroxyl endblocked methyl(trifluoropropyl)polysiloxane having a viscosity of about 0.1 Pa.s at 25° C. and about 6 weight percent hydroxyl radicals, until a uniform mixture is obtained, (D) admixing from 0 to 4 parts by weight of a polydiorganosiloxane fluid having about 5 to 15 weight percent vinyl radicals with the remainder methyl radicals, then (E) admixing from 25 to 50 parts by weight of fume silica having a surface area of at least 200 m 2 /g at a rate such that the silica is uniformly dispersed into the polymer mixture to give a uniform, high viscosity mixture, then (F) heating while mixing under a vacuum of at least 150 mm Hg, to a temperature of at least 130° C. for a period of at least 1 hour, to give a base.

Claim 2

A method of making a fluorinated polydiorganosiloxane base which when cured gives an elastomer having improved tensile strength and tear strength, the method consisting essentially of (A) shearing in a mixer which is heated to a temperature of from 23° to 100° C. which is being swept by a stream of dry nitrogen (1) 100 parts by weight of hydroxyl endblocked trifluoropropylmethylsiloxane having a Williams Plasticity Number of greater than 225, for a period of time sufficient to remove any free water from the siloxane, then (B) mixing with (2) from 0.1 to 1.5 parts by weight of methylvinyldi(N-alkylacetamido)silane, while continuing the dry nitrogen sweep, at a temperature below 80° C., for a period of time sufficient to increase the Williams Plasticity Number of the polymer, then (C) admixing from 5 to 20 parts by weight of hydroxyl endblocked methyl(trifluoropropyl)polysiloxane having a viscosity of about 0.1 Pa.s at 25° C. and about 6 weight percent hydroxyl radicals, until a uniform mixture is obtained, (D) admixing from 0 to 4 parts by weight of a polydiorganosiloxane fluid having about 5 to 15 weight percent vinyl radicals with the remainder methyl radicals, then (E) admixing from 25 to 50 parts by weight of fume silica having a surface area of at least 200 m 2 /g at a rate such that the silica is uniformly dispersed into the polymer mixture to give a uniform, high viscosity mixture, then (F) heating while mixing under a vacuum of at least 150 mm Hg, to a temperature of at least 130° C. for a period of at least 1 hour, to give a base.