Effect of the composition of the initiating complex acyl halides/aluminium bromide on the cationic polymerization of isobutylene

On the basis of H-1 and C-13 spectra obtained for solutions of complexes of acyl halides with aluminium bromide RCOX . nAlBr(3) (X = Cl, Br; n =1, 2), it is shown that these adducts can exist in solution as donor-acceptor complexes, acyl salts, or combinations of both forms. The nature of the cationic initiating species for each case is predicted. The predictions coincide well with experimental results obtained by analysis of the isobutylene polymers prepared with these initiating complexes. Initiation by the 1:2 complexes allows polymeric molecules to be synthesized with an acyl group at one end. These polymerization processes have some of the characteristics of living polymerizations. The possibility for quantitative estimation of such systems using the criteria of 'approach to livingness' is demonstrated. (C) 2000 Society of Chemical Industry.