Show the intermediate that would result if the growing chain added to the other end of the styrene double bond. Explain why the final polymer has phenyl groups substituted on alternate carbon atoms rather than randomly distributed.

Chain-growth polymerisation is the formation of polymers from unsaturated monomers. There occurs no rapid loss of monomers at the beginning and an active site can be observed at the end of the polymer chain. It requires initiators to break the double bond in monomer molecule.

Orientation of addition always generates the more stable intermediate, that is, the energy difference between a primary radical and a benzylic radical is huge, the primary radical is not resonance stabilised and thus the orientation will not be observed in which chain growth occurs through primary radical. Thus, the phenyl substituents must necessarily be on alternating carbons as orientation of attack will always be the same and not random.