An important use of radical-chain reactions is in the polymerization of ethylene and substituted ethylene monomers such as propene, vinyl chloride (the synthesis of which was discussed in Section \(7.6\) along with its use in the synthesis of poly(vinyl chloride), \((\mathrm{PVC}))\), and styrene. The reaction for the formation of PVC, where \(n\) is the number of repeating units and is very large, follows. (a) Give a mechanism for this reaction (see Chapter 29). (b) Give a similar mechanism for the formation of poly(styrene) from styrene. Which end of the styrene double bond would you expect R- to attack? Why?

Question: Explain the mechanisms for the formation of PVC and poly(styrene) through radical-chain reactions, and point out which carbon atom of the styrene double bond is attacked by the initiator radical. Answer: The mechanisms for the formation of PVC and poly(styrene) involve radical-chain reactions, consisting of initiation, propagation, and termination steps. For both PVC and poly(styrene), the initiation step involves the reaction between an initiator radical (R.) and the respective monomer to form a new radical intermediate. The propagation step involves the reaction of the growing radical intermediate with another monomer, leading to the extension of the polymer chain. Termination occurs when two radical intermediates react, forming the final polymer. In the case of poly(styrene), the initiator radical attacks the carbon atom of the styrene double bond that is bonded to the phenyl group. This is due to the stabilizing effect of the phenyl group's resonance on the generated radical, making that site more susceptible to attack by radicals.