High strength fluorosilicone sealants

Claim 1

A method of producing a high strength, extrudable fluorosilicone sealant which cures upon exposure to moisture, said method comprising the steps of (A) mixing (i) from 30 to 50 parts by weight of hydroxyl endblocked fluorosilicone polymer of the formula HO(RR'SiO) n H, where each R is individually a monovalent saturated or aromatic hydrocarbon radical containing from 1 to 20 carbon atoms, from 50 to 100 percent of the R' radicals represent the radical RfCh 2 CH 2 -- where Rf represents a perfluoroalkyl radical containing from 1 to 10 carbon atoms, any remaining R' radicals being selected from the same group as R, and n represents an integer from 100 to 500, (ii) from 15 to 50 parts by weight of a reinforcing silica having a surface area of greater than 50 m 2 /g, (iii) from 5 to 15 parts by weight of di(trifluoropropyl)tetramethyldisilazane, and (iv) from 1.0 to 3.6 parts by weight of water, then (B) heating the mixture to a temperature of from 150° to 175° C. for from 1/2 to 3 hours while mixing, under a nitrogen purge, then (C) applying a vacuum to the heated mixture for a sufficient time to remove volatiles, then (D) admixing 100, minus the parts of fluorosilicone polymer used in step (A), parts by weight of the fluorosilicone polymer of step A, then (E) heating the devolatilized mixture to a temperature of from 150° to 175° C. for from 1/2 to 1 hour while mixing, then (F) applying a vacuum to the heated mixture for a sufficient time to remove volatiles, and then cooling to room temperature, and then (G) admixing, in the absence of moisture, a moisture activated curing system which reacts with the hydroxyl endblocked polymer, to give a fluorosilicone sealant containing an in situ treated filler, which sealant cures upon exposure to moisture to an elastomer having improved physical properties.

Claim 2

A method of producing a high strength, extrudable fluorosilicone sealant which cures upon exposure to moisture, said method comprising the steps of (A) mixing (i) from 30 to 50 parts by weight of hydroxyl endblocked fluorosilicone polymer of the formula HO(RR'SiO) n H, where each R is individually a monovalent saturated or aromatic hydrocarbon radical containing from 1 to 20 carbon atoms, from 50 to 100 percent of the R' radicals represent the radical RfCh 2 CH 2 -- where Rf represents a perfluoroalkyl radical containing from 1 to 10 carbon atoms, any remaining R' radicals being selected from the same group as R, and n represents an integer from 100 to 500, (ii) from 15 to 50 parts by weight of a reinforcing silica having a surface area of greater than 50 m 2 /g, (iii) from 5 to 15 parts by weight of di(trifluoropropyl)tetramethyldisilazane, and (iv) from 1.0 to 3.6 parts by weight of water, then (B) heating the mixture to a temperature of from 150° to 175° C. for from 1/2 to 3 hours while mixing, under a nitrogen purge, then (C) applying a vacuum to the heated mixture for a sufficient time to remove volatiles, then (D) admixing 100, minus the parts of fluorosilicone polymer used in step (A), parts by weight of the fluorosilicone polymer of step A, then (E) heating the devolatilized mixture to a temperature of from 150° to 175° C. for from 1/2 to 1 hour while mixing, then (F) applying a vacuum to the heated mixture for a sufficient time to remove volatiles, and then cooling to room temperature, and then (G) admixing, in the absence of moisture, a moisture activated curing system which reacts with the hydroxyl endblocked polymer, to give a fluorosilicone sealant containing an in situ treated filler, which sealant cures upon exposure to moisture to an elastomer having improved physical properties.