Conventional and living carbocationic polymerizations united .2. The conversion of conventional to living isobutylene polymerization by proton trap and a comprehensive closed-loop mechanism of proton trap mediated living polymerization

The effect of the proton trap, 2,6-di-tert-butylpyridine (DtBP), on the polymerization of isobutylene (IB) induced by the ''HX''/TiCl4, (''HX'' = protic impurity) initiating system has been studied. Significantly, in the presence of a large (similar to 40 molar) excess of DtBP relative to ''HX'', free proton-induced chain transfer-dominated conventional IB polymerization is converted to living polymerization. In the absence of the proton trap the kinetics are dominated by rapid proton-induced processes which overwhelm the relatively slower living polymerization. These investigations also led to a quantitative assessment of the concentration of initiating species: [''HX''] = 1.46 X 10(-4) mol/L. The polymerizations are first-order in monomer and the apparent rate constants of propagation drop precipituously with increasing DtBP concentration until a constant low value is reached. The rate of formation of propagating living chains has been expressed quantitatively. Chain transfer is bimolecular and first order in monomer, and kinetic investigations led to a quantitative description of the effect of proton trap concentration on the apparent first order chain transfer constant. The results have been explained in terms of a simple mechanistic scheme. (C) 1996 John Wiley & Sons, Inc.