 Solution

An approximately alternating styrene–maleic anhydride copolymer is produced. Its backbone alternates a $-\mathrm{C}{\mathrm{H}}_2-\mathrm{CH}(\mathrm{Ph})-$ 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.