Nature of the end groups in polystyrene prepared using benzoyl peroxide as sensitizer

Samples of polystyrene prepared using benzoyl peroxide labeled with carbon‐14 in the carboxyl group only have been used to establish the conditions necessary for complete hydrolysis of the ester end groups in the polymers. Polymers prepared using 14C‐benzoyl peroxide either uniformly labeled or labeled in the benzene rings only, contain both labeled benzoyloxy and labeled phenyl end groups. From the behavior of these polymers on hydrolysis, the proportions of the two types of end groups can be determined accurately; these proportions depend upon the conditions under which the polymers are prepared.