= Solution
\b[An approximately alternating styrene–maleic anhydride copolymer] is produced. Its backbone alternates a $\mathrm{-CH_2-CH(Ph)-}$ segment with the two former alkene carbons of a maleic anhydride unit; those latter carbons remain connected to the intact five-membered <cyclic anhydride> ring.
<Homolysis> of <benzoyl peroxide> supplies initiating <free radicals>. Cross-propagation between electron-rich <styrene> and electron-poor <maleic anhydride> is favored over successive additions of the same <monomer>. Both carbon–carbon <double bonds> become backbone <sigma bonds>, without loss of a small <molecule> from each <monomer>. Initiator-derived benzoyloxy or phenyl fragments can occur at chain ends, with carbon dioxide formed when benzoyloxy <free radicals> decarboxylate.
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