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Intro
Silicones (more accurately called polymerized siloxanes or polysiloxanes) are mixed inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl, ethyl, and phenyl. These materials consist of an inorganic silicon-oxygen backbone (...-Si-O-Si-O-Si-O-...) with organic side groups attached to the silicon atoms, which are four-coordinate. In some cases organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions.
Properties
Some of the most useful properties of silicone include:
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Thermal stability (Constancy of properties over a wide operating range of –100 to 200°C) Though not lipophilic, the ability to repel water and form watertight seals Excellent resistance to oxygen, ozone, and sunlight Flexibility Good electrical insulation Anti-adhesive Low chemical reactivity Low toxicity
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High gas permeability: at room temperature (25°C) the permeability of silicone rubber for gases like oxygen is Approx.imately 400 times that of butyl rubber, making silicone useful for medical applications (though precluding it from applications where gas-tight seals are necessary).
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