page_title: Silicone rubber
section_title: Structure
hierarchical_section_title: Silicone rubber / Properties / Structure
caption_attribution_description: Chemical structure of Polydimethylsiloxane (PDMS)
context_page_description: Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers are often one- or two-part polymers, and may contain fillers to improve properties or reduce cost.
  Silicone rubber is generally non-reactive, stable, and resistant to extreme environments and temperatures from −55 to 300 °C while still maintaining its useful properties. Due to these properties and its ease of manufacturing and shaping, silicone rubber can be found in a wide variety of products, including: voltage line insulators, automotive applications; cooking, baking, and food storage products; apparel such as undergarments, sportswear, and footwear; electronics; medical devices and implants; and in home repair and hardware with products such as silicone sealants.
context_section_description: Polysiloxanes differ from other polymers in that their backbones consist of Si–O–Si units unlike many other polymers that contain carbon backbones. Polysiloxane is very flexible due to large bond angles and bond lengths when compared to those found in more basic polymers such as polyethylene. For example, a C–C backbone unit has a bond length of 1.54 Å and a bond angle of 112°, whereas the siloxane backbone unit Si–O has a bond length of 1.63 Å and a bond angle of 130°. 
  The siloxane backbone is a more flexible polymer than the basic carbon chain backbone because the side groups are spaced farther apart. Polymer segments can move farther and change conformation easily, making for a flexible material. Polysiloxanes tend to be more stable and less chemically active because more energy is required to break the silicon-oxygen bond. Although silicon is a congener of carbon, having the same electron bonding configuration, silicon analogues of carbonaceous compounds generally exhibit different properties. The difference in total charge and mass between carbon with 6 protons and 6 neutrons, and silicon with 14 protons and 14 neutrons causes an added layer of electrons and their screening effect changes the electronegativity between the two elements. For example the silicon-oxygen bond in polysiloxanes is significantly more stable than the carbon-oxygen bond in polyoxymethylene, a structurally similar polymer. The difference is partly due to the higher bond energy, the energy required to break the Si-O bond, and also because polyoxymethylene decomposes formaldehyde, which is volatile and escapes driving decomposition forward, but Si-containing decomposition products of silicone are less volatile.
caption: Repeat unit of silicone rubber
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