Triphenylmethyl hexafluoroarsinate-initiated polymerization of 1,2-butylene oxide

The polymerization of 1,2-butylene oxide initiated with triphenylmethyl hexafluoroarsinate in the ?20 to +25°C temperature range with 1,2-dichloroethane as solvent is characterized by a rapid nonstationary initial stage. This is followed by a second slower stage, during which the disappearance of monomer is first-order with respect to its concentration. The conversion of monomer at the end of the first stage is related to the initial catalyst concentration but not to the initial monomer concentration. Invoking the hypothesis of an instantaneous initiation reaction, the experimental results lead to the conclusion of the existence of a unimolecular termination step. Propagation-to-termination rate constant ratios yield a propagation–termination activation energy difference of 5.9 kcal/mole. The termination step proposed is thought to involve the formation of stable macrocyclic oxonium ions. These, in turn, can reactivate the polymerization by an intramolecular reaction leading to the formation of new active centers. An energy of activation of 8.7 kcal/mole was calculated for this reactivation. GPC analyses of the reaction products recovered at the end of the first stage revealed the presence of large proportions of oligomers. Based on kinetic data, the formation of oligomers is explained by a backbiting process similar to the reactivation reaction suggested for the initiation of the second stage.