Silicones are polymers of silicon that also include carbon, hydrogen and sometimes other elements. Room-temperature vulcanization (RTV) sealants are made of silicon polymers that become cross-linked in a reaction that takes place at room temperature.
Natural rubbers are sticky and deform easily in warm conditions. Vulcanization makes rubbers more stable, or "cures" them, by introducing sulfur cross-links between adjacent polymer chains. Vulcanization ordinarily takes place at high pressures and temperatures.
Unlike the vulcanization of rubber, the vulcanization process in an RTV sealant takes place at room temperature. The presence of water triggers a condensation reaction that forms cross-links between adjacent polydimethylsiloxane chains; these chains formed of silicon and oxygen atoms with two methyl groups attached to each silicon.
RTV sealant is stored in airtight squeeze tubes. When the RTV sealant is squeezed out of the tube onto a surface, the material comes in contact with moisture in the air, triggering the reaction that will cause it to cure and harden. RTV sealant is useful for a variety of applications, including sealing gaskets in cars and boats, and engine repair.