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Fascinating Silicone™ Chemistry Corner – Silicones vs. Organics

Silicone vs. organic polymers

Compared to carbon-based polymers, polydimethylsiloxane (PDMS) polymers:

  • Have more open, more flexible molecular chains – are less rigid.
  • Have the ability to form much longer chains without solidifying.
  • Have stronger, more stable bonds and are more resistant to harsh environmental, processing, and operating conditions.
  • Are more flexible and flowable at low temperatures, and do not break down under high temperatures.
  • Are able to align their organic substituents more effectively at interfaces; can more easily “connect” with other materials and formulation ingredients.
  • Flow more easily and are capable of forming thinner films.

Carbon and silicon – so close ... and yet, so different

CarbonCarbon is a plant-based materialSiliconSilicon is a mineral-based material
C is organic (plant-based)Si is inorganic (mineral-based)
C forms covalent bondsSi forms hybrid ionic/covalent bonds
CO2 is a simple gasSiO2 is a complex solid polymer
CCl4 is a reasonably stable fluidSiCl4 is highly reactive to water and some organic substances

Did you know ... A 100 cs polydimethylsiloxane fluid will flow more quickly and easily and create a thinner, more complete film than a hydrocarbon fluid with the same viscosity!


Some important differences between silicon and carbon

  • The silicon atom is larger than the carbon atom. Its bonds are longer and more flexible with wider bond angles.
  • Silicon is less electronegative than carbon (1.8 for silicon vs. 2.5 for carbon); it is able to give up more of its electrons to form strong, energetic bonds with other elements.
  • Silicon only forms single bonds, not multiple bonds (single bonds are more stable and harder to break than double or triple bonds).

The Si-O bond – the key to silicone’s unique properties

  • The Si-O bond has higher bond energy than the C-O bond.
  • The Si-O bond is longer and flatter than the C-O bond.
  • The Si-O bond has a lower barrier to rotation than the C-O bond and higher free volume.

All of these factors contribute to silicone’s open, flexible structure and low glass transition temperature.

Compare the numbers.

Learn more about the physical and chemical properties of silicones.


Did you know ... hydrocarbon angles are considered “fixed,” but siloxane bond angles have been reported between 105 and 180 degrees!

Did you know ... a high-molecular-weight silicone remains fluid while an organic polymer with the same molecular weight forms a solid!

Expand your understanding

Learn about:
Silicon vs. carbon bond characteristics
Typical performance properties
Commercial benefits
Surface & interface applications
Silicone rheology

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