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 th e polymerization of isobutylene (IB) induced by the ''HX''/TiCl4, (''H X'' = protic impurity) initiating system has been studied. Significant ly, in the presence of a large (similar to 40 molar) excess of DtBP re lative to ''HX'', free proton-induced chain transfer-dominated convent ional 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 polymer ization. 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 ra te constants of propagation drop precipituously with increasing DtBP c oncentration until a constant low value is reached. The rate of format ion of propagating living chains has been expressed quantitatively. Ch ain transfer is bimolecular and first order in monomer, and kinetic in vestigations led to a quantitative description of the effect of proton trap concentration on the apparent first order chain transfer constan t. The results have been explained in terms of a simple mechanistic sc heme. (C) 1996 John Wiley & Sons, Inc.