Olefin Polymerization and Copolymerization with Alkylaluminum-lnitiator Systems. VII. Initiation by Electrophilic Halogens

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Abstract
The discovery of initiation of cat ionic polymerization of isobutylene and styrene by electrophilic chlorine generated by the reaction of chlorine and trimethylaluminum in the temperature range -40 to -100° is reported. Bromine and trimethylaluminum is a very poor initiating system, and iodine and trimethylaluminum does not initiate the polymerization of either isobutylene or styrene. Polymerization of isobutylene initiated by chlorine and trimethylaluminum shows a linear plot of log Mv vs 1/T with an overall EDPof ∼1.9 kcal, mole. The molecular weights (Mw) of polystyrene obtained with the Cl2/Me3Al system appear to be the highest ever reported for cationic polymerization of this monomer under comparable conditions. The mechanism of initiation has been investigated by model experiments: The reaction between Cl2/ Me3Al and 2,2,4-trimethyl-l-pentene gave three chlorinated products (2-chloromechyl-4,4-dimethyl-l-pentene, 1-chloro-2,4,4-trimethyl-1-pentene, and 2-chioromethyl-2,4,4-trimethyl-pentane). The position of chlorine in these compounds indicate initiation by electrophilic chlorine, Cl. Some preliminary results obtained using diethylaluminum chloride-halogens as coinitiator-initiator systems are also described.

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