free radical 
noun Chemistry
An uncharged molecule (typically highly reactive and short-lived) having an unpaired valency electron.It is produced through a free radical polymerization reaction of styrene monomers....
- This free radical attacks the double bonds on other monomers creating a longer chain molecule and an additional free radical.
- In the free radical polymerization of ethylene to form polyethylene, a small amount of a peroxide is added to a large volume of ethylene.