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How do silicone rubber molecules differ from carbon-chain elastomers?

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Silicone rubber molecules differ fundamentally from carbon-chain elastomers in their molecular backbone composition. While most industrial elastomers are built upon a backbone of carbon atoms, silicone rubbers (polysiloxanes) consist of alternating silicon and oxygen atoms.12

This structural difference leads to several distinct properties:

Flexibility: Siloxane molecules rotate freely around the Si–O bond, granting silicone rubber high molecular flexibility.12
Thermal Stability: The Si–O bond is highly heat-resistant and resistant to oxidation and ozone, making silicones remarkably stable across a wide temperature range.12
Glass Transition: Silicone rubber possesses the lowest glass transition temperature of any elastomer, allowing it to remain resilient at temperatures where other materials might become rigid.13
Permeability: Silicones exhibit the highest permeability to gases among elastomers.12
Chemical Vulnerability: Unlike many carbon-chain polymers, the Si–O bond is susceptible to hydrolysis and attack by acids and bases. Additionally, silicone rubbers are relatively weak and prone to swelling when exposed to hydrocarbon oils.12