Styrene

Styrene is vinylbenzene, ${\mathrm{C}}_6{\mathrm{H}}_5\mathrm{CH}=\mathrm{C}{\mathrm{H}}_2$. The vinyl double bond is conjugated with the aromatic ring.

Addition polymerization consumes that double bond to form polystyrene while leaving phenyl groups as side substituents. This makes styrene a useful example of how a small molecular change, converting a pi bond into backbone sigma bonds, creates a macromolecular material.