Friedel‐Crafts crosslinking of polystyrene

Polystyrene may be crosslinked by p‐dichloromethylbenzene (DCMB) in 1,2‐dichloroethane solution with SnCl4 as catalyst. Combined intra‐ and intermolecular crosslinking can be measured by evolution of hydrogen chloride and by an ultraviolet spectral method, and the results for the two methods are in excellent agreement. Intermolecular crosslinking may be calculated separately from number‐average molecular weight measurements, so that the extent of intramolecular crosslinking may be deduced by difference. Rate equations for the overall, intermolecular, and intramolecular reactions have been obtained as follows: The anomalous behavior with respect to polystyrene concentration may be due to inhibition of the intramolecular reaction because of increasing interpenetration of polystyrene molecules as the concentration of polystyrene is increased. The rate constant for the intermolecular reaction, which shows “normal” kinetic behavior has been compared with values for the reaction of DCMB with the model compounds benzene, toluene, diphenylmethane, and benzyl chloride. The very much smaller value for polystyrene compared with the models has been accounted for in terms of adverse steric effects when the reaction is occurring in the polymer chain environment.