Initiator

Another meaning of initiator is SCSI initiator.

In polymer chemistry, an initiator is a chemical compound that initiates a chain reaction. Typically these compounds decompose to form either radical, anionic, or cationic species, which in turn serve as a reactive center for the propagation of chain polymerization. An example of a commonly used radical initiator would be tertiary-butyl hydroperoxide. This is a water soluble compound that, upon mild heating, breaks into two radical species.