The synthesis of polystyrene from styrene monomer typically proceeds via a free radical polymerization mechanism. The process can be divided into three main steps: initiation, propagation, and termination. Here is a stepwise description of the mechanism:1. Initiation:- A free radical initiator, such as benzoyl peroxide BPO or azobisisobutyronitrile AIBN , is added to the styrene monomer. The initiator undergoes homolytic cleavage, producing two free radicals.- The free radical generated from the initiator reacts with the styrene monomer, forming a new radical by attacking the double bond of the styrene. This results in the formation of a single covalent bond between the initiator radical and the styrene monomer, while the remaining electron from the double bond becomes a new radical on the styrene monomer.2. Propagation:- The newly formed radical on the styrene monomer reacts with another styrene monomer, attacking its double bond and forming a new covalent bond between the two monomers. This process generates another radical on the second styrene monomer.- The propagation step continues as the radical on the growing polymer chain reacts with more styrene monomers, adding them to the chain and creating new radicals. This process is repeated until the polymer chain reaches the desired length.3. Termination:- Termination occurs when two radicals react with each other, forming a covalent bond and ending the growth of the polymer chain. This can happen in several ways: a. Combination: Two growing polymer chains with radicals at their ends react with each other, forming a single, longer polymer chain. b. Disproportionation: A hydrogen atom is transferred from one radical-containing polymer chain to another, resulting in the formation of a double bond in one chain and a saturated end in the other chain. c. Radical transfer: A radical reacts with an inhibitor or another molecule, which terminates the polymer chain growth but may generate a new radical that can initiate a new polymerization.The intermediate products formed during the polymerization process are the growing polymer chains with radicals at their ends. These radicals are highly reactive and continue to react with styrene monomers or other radicals until the termination step occurs. The final product is polystyrene, a long-chain polymer made up of styrene monomers connected by single covalent bonds.