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FLUOROSILICONE
Fluorosilicone is an elastomer compound, Polymethltrifluoropropylsiloxane (PMTFPS) being the most popular. It is commonly manufactured through the base catalyzed ring-opening polymerization of the cyclic trimer which is produced through hydrolysis of the corresponding dichlorosilane.

Fluorosilicone as an elastomer can be molded, extruded or calendered by normal methods used for Polydimethylsiloxane (PDMS) elastomers. It is widely used as fluids, surfactants, gels, coatings, adhesives and sealants and elastomers.

Structure
Polymethyltrifluoropropylsiloxane is a type of fluorosilicone with the greatest commercial application. It was commercialised under the Silastic trademark by a corporation known as Dow Corning. It has a Tg of -65°C and displaysn a medium thermal stability. Their Structure is as follows : CH3 – (Si-O)P-C2H4-CF3

Manufacture and Industrial Production
By means of a process called Hydrosilylation, monomers of Fluorosiliicone is obtained. Hydrosilylation is "the addition of a silicon hydride functional group across the unsaturated linkage". A very common way to prepare PMTFPS is though the base catalyzed ring opening polymerization of the cyclic trimer. This cyclic species is obtained by the process of hydrolysis of corresponding dichlorosilane. In recent times, a stereoregular PMTFPS has been made through the polymerisation of stereoisomers (cis- and trans-) of the cyclic trimer under conditions unfavorable for the siloxane to redistribute. This stereoregularity produces a cured PMTFPS which exhibit strain-induced crystallization that improves its mechanical properties over the ones without this property.

Physical and Chemical Properties

 * 1) Heat Resistance : a PMTFPS elastomer heat aged for 1350 hours at 200°C will show a two-point, a 40% and 15% reduction in hardness, tensile strength and elongation respectively.
 * 2) Low-Temperature Properties: PMTFPS has glass transition temperature of about -65°C which in addition to a low-temperature crystallization causes the fluorosilicone to be flexible at very low temperatures.
 * 3) Chemical Resistance: PMTFPS is 36.5% Fluorine with a Hildebrand Solubility parameter of 8.8(cal/cm3)1/2. "Cured Fluorosilicone elastomers have good resistance to jet fuels, oils and hydrocarbon solvents and fuels".
 * 4) Safety and Toxicity: Under normal conditions, PMTFPS is relatively inert.

Application and Uses

 * 1) Gels: through light cross linking of low to medium Molecular Weight PMTFPS using a platinum catalyzed hydrosilylation addition, a soft, clear and tacky gel is obtained. Gels gotten from PMTFPS provide good electrical, high and low temperature properties and an easy to apply low viscosity.
 * 2) Adhesives and Sealants: Adhesives and sealants consist of medium Molecular Weight PMTFPS vinyl or hydroxyl end-blocked, little quantity of reinforcing silica filler and either a condensation or addition cure system.
 * 3) Because of its brilliant temperature tolerance and fuel resistance, PMTFPS based fluorosilicone rubber (FSR) is largely utilized in the aircraft and astronavigation industries.

References