Concept explainers
Interpretation:
Combination and disproportionation are not feasible termination steps for the anionic
Concept introduction:
Beside the free-radical mechanism, chain-growth polymerizations can also be initiated by anions or cations, resulting in anionic polymerization or cationic polymerization respectively. Styrene can undergo anionic polymerization using butyllithium as the initiator, which forms a negative charge on the growing chain instead of an unpaired electron. In the propagation steps, the reactive intermediates are anions. Termination occurs in anionic polymerization when an acid is added to the reaction mixture. The anion is neutralized in the resulting proton transfer, which ends the propagation cycle. Combination and disproportionation are not feasible termination steps for the anionic polymerization of styrene.
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Organic Chemistry: Principles and Mechanisms (Second Edition)
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