Polymerization of isobutylene catalyzed by aluminum tribromide

Abstract Solution polymerization of isobutylene in heptane, catalyzed by aluminum tribromide, takes place at high rate even at low catalyst and monomer concentrations, without addition of water as cocatalyst. The overall rate of polymerization is of first order with respect to the monomer and of second order to the catalyst. The activation energy of the polymerization is practically zero within the temperature range investigated (‐60 to +20°C.). A value of −3.9 kcal. has been found for the “activation energy of degree of polymerization”; the extrapolated ceiling temperature is +131°C. Additions of water substantially decrease the rate of polymerization. The concentration of residual moisture in the polymerization apparatus was so low that no detectable isobutylene polymerization catalyzed by boron trifluoride or titanium tetrachloride was observed. Additions of water were necessary for polymerization in the presence of these two catalysts.