Fluorosilicone sealants

Condensation reactions are used for cross-linking at ambient temperatures. The acetoxy-functional condensation system is widely used in fluorosilicone sealants. The cross-linking occurs after exposure to atmospheric moisture.62 The limitation of this system is that it is effective for only relatively thin layers. Moreover, it often requires up to 14 days to cure and the acetic by-product may corrode certain substances. 

Medium-molecular-weight PMTFPS with vinyl or hydroxyl end blocks are used for adhesives and sealants. They are cured either at ambient temperature (RTV-room temperature vulcanization) or at elevated temperature. One-part moisture-activated RTV sealants have been available commercially for many years. Because of then-very high resistance to jet engine fuels, excellent flexibility at very low temperatures, and high thermal stability, they have been used in both military and civilian aerospace applications.78 Two-part, heat-cured fluorosilicone sealants have been used in military aircraft applications and for sealing automotive fuel systems.79 Special class of fluorosilicone sealants are channel sealants or groove injection sealants, sticky, puttylike compounds, which do not cure. They are used to seal fuel tanks of military aircraft and missiles.75... 

The upper temperature limit is especially critical, because it is at higher temperatures that the sealant materials soften and or break down, leading to failme of the sealant joint. Determination of thermal capability of sealants is standardized in ASTM D-573. As a rule of thumb, acrylic and polysulfide sealants are generally good to 95° C, while silicones can usually handle 200°C. A special class of fluorosilicone sealants can operate to temperatures as high as 260°C. 

Fluorosilicones, containing [(CF3CH2CH2)(Me)SiO] units, are used as specialist sealants, providing resistance to hydrocarbon fluids such as gasoline. 

Sealants - [ELASTOMERSSYNTHETIC - POLYISOPRENE] (Vol 9) - [SEALANTS] (Vol 21) -acrylics [ACRYLICESTERPOLYMERS - SURVEY] (Voll) -barium compds in [BARIUM COMPOUNDS] (Vol 3) -based on liquid polysulfides [POLYMERS CONTAINING SULFUR - POLYSULFIDES] (Vol 19) -defoamersin [DEFOAMERS] (Vol 7) -fiom fluorosilicones [FLUORINE COMPOUNDS,ORGANIC - POLY(FLUOROSILICONES)] (Volll) -hydrocarbon resins in [HYDROCARBON RESINS] (Vol 13) -lecithin in (LECITHIN] (Vol 15) -organolithiumcmpdsinprdnof [LITHIUM AND LITHIUM COMPOUNDS] (Vol 15) -polysulfide curing [PEROXIDES AND PEROXIDE COMPOUNDS - INORGANIC PEROXIDES] (Vol 18) -propylene oxide in mfg of [PROPYLENE OXIDE] (Vol 20) -PVB m [VINYL POLYMERS - VINYL ACETAL POLYMERS] (Vol 24) -rheological measurements [RHEOLOGICAL MEASUREMENTS] (Vol 21) -from styrenic block copolymers [ELASTOMERS SYNTHETIC - THERMOPLASTIC ELASTOMERS] (Vol 9) -use of dispersants [DISPERSANTS] (Vol 8)... 

There have been many investigations to determine the best chemical structures to provide for resistance to moisture and hydrolysis. Attempts have been made to synthesize epoxy adhesives with improved water resistance by replacing some hydrogen atoms by fluorine.50 However, the cost of processing of such materials has restricted commercial development. For electronic sealants, it is highly desirable to keep moisture from penetrating into critical areas. Hydrophobic polymers have been developed to accomplish this task. They are siloxyimides, fluorosilicones, fluoroacrylics, phenylated silicone, and silastyrene. 

Sealing Compound, One Part Silicone, Aircraft Firewall Adhesive/Sealant, Fluorosilicone Aromatic Fuel Resistant, One Part Room Temperature Vulcanizing... 

MAJOR APPLICATIONS Antifoam fluids, lubricants, protective gels, and elastomers and sealants in applications exposed to hydrocarbon fuels and oils and organic solvents in the automotive and aerospace industries. Longer fluorocarbon side-chain fluorosilicones are available with developing use as release coatings for silicone-based adhesives. 

Manufacturers Comments Fluorosilicone adhesive-sealant. Fuel resisteint. Chemical solvent resistance. 

Dichromate-cured polysulfides are used for applications if increased corrosion resistance is required. Epoxy-cured polythioethers are used for faster curing. Non-curing polysulfide pastes are often used as channel sealants round fuel tanks. Fluorosilicones and cyanosilicones have also been used for this application. 

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