Halogenation reactions of polystyrene

Photochlorimtion of polystyrene involves replacement of hydrogens at the a and P positions.was believed in the past that the chlorine atoms react preferentially at the a position until the chlorine content of the product reaches 20% by weight. After that, it was thought that the chlorines are introduced into the other position. Later, however, this was contradicted.In fact, when polystyrene is photochlorinated in carbon tetrachloride at low temperatures, like 13 C, it is substituted equally at both positions. At higher temperatures, like 78 C, substitutions at the p position actually predomihate.  

Chlorinations of poly(p-methyl styrene) are somewhat more selective for the pendant methyl groups and result in di- and tri-substitutions at the p-methyl position. Only small amounts of chlorine are introduced into the polymer backbones. Substitutions at the backbones, however, are possible with the use of SO2CI2 as the chlorinating agent. In this case, half of the chlorines still replace the methyl hydrogens, but the other half replace hydrogens on the backbone. 

Free-radical additions of maleic anhydride to polystyrene backbones can be carried out with the help of either peroxides or ultraviolet light.Approximately 2% of the anhydride can be introduced. If, however, the additions are carried out on a-brominated polystyrene, the anhydride content of the polymer can be raised to 15%  

Note The extra hydrogen shown above on the anhydride moiety of the product presumably comes from chain transferring. 

Bromination of polystyrene with iV-bromosuccinimide and benzoyl peroxide in CCI4 at room temperature can achieve a 61% conversion in four hours. Considerable degradation, however, accompanies this reaction. 

---