The silicon-oxygen bond at the heart of every silicone is unusually strong and stable, even at high temperatures. This is why silicones resist breaking down under heat and sunlight. They also outlast most carbon-based plastics when exposed to harsh chemicals.
The most widely used silicone is polydimethylsiloxane, often abbreviated PDMS, in which every silicon atom carries two methyl groups. Chemists control a silicone’s physical form by adjusting its chain length. They also adjust crosslinking, meaning how much bridging occurs between chains during manufacturing.
Short, loosely linked chains produce runny liquids, longer chains produce thick gels, and heavily crosslinked chains produce solid rubbery materials. This tunability lets manufacturers design silicones for very different jobs from a single chemical family. The organic groups on the outside of the siloxane backbone make silicones water-repellent.
These groups do not attract water molecules. Combined with their chemical stability, this makes silicones useful in many products. Sealants made from silicone keep water out of buildings and cars.
Lubricants resist breaking down under heat, and medical implants can sit safely inside the body for years. A common misconception is that silicones are the same as silicon, the element used in computer chips. Silicon is a single element. Silicone is a polymer built from repeating units that include silicon, oxygen, and carbon-based groups.