Preparation
Silicone rubbers are prepared as follows:
Other groups may replace the methyl groups. Silicone rubbers have excellent ozone and weathering resistance, good electrical properties, and good adhesion to metal.
Industrial uses
Silicone rubber is a linear condensation polymerbased on dimethyl siloxane. In the preparation,dimethyl dichlorosilane is hydrolyzed toform dimethyl silanol, which is then condensedto dimethyl siloxane, and this, upon further condensation,yields dimethyl polysiloxane, thestandard silicone rubber.
In general, the silicone rubbers have relativelypoor physical properties and are difficultto process. However, they are the most stableof rubbers and are capable of remaining flexibleover a temperature range of –90 to 316°C. Theyare unaffected by ozone, are resistant to hotoils, and have excellent electrical properties.Their most extensive uses are for wire and cableinsulation, tubing, packings, and gaskets inaerospace and aircraft applications. In the formof dispersions and pastes, they are used for dipcoating,spraying, brushing, and spreading. Siliconerubbers are important in medical and surgicaldevices because of their property, uniqueamong elastomers, of being compatible withbody tissues. Fast, automatic, economicalinjection molding of liquid silicones has beendeveloped.
