Selective chlorination of side-chains in Friedel-Crafts polymers

Aralkyl polymers with ethyl side-chains were prepared by Friedel-Crafts reactions. Ethylbenzene and bis(p-chloromethyl)benzene (BCMB) were reacted together in the presence of stannic chloride to produce polymers of various molecular weights. A study was then carried out of the chlorination of these polymers, using (a) molecular chlorine, (b) molecular chlorine with a peroxide catalyst and phosphorus pentachloride, (c) sulphuryl chloride. The objective was to determine the best conditions for chlorination to occur selectively at the α-carbon atom of the ethyl group, with minimal chlorination at either the β-position or the main-chain methylene groups. Analysis of 1H nuclear magnetic resonance spectra of the chlorinated polymers suggests that in most cases chlorination occurs extensively both in the side-chain and in the main-chain methylene groups. Conditions were found, however, which favour chlorination at the α-position. The greatest selectivity was achieved when molecular chlorine, a peroxide catalyst and phosphorus pentachloride were used in benzene solvent.