The living carbocationic polymerization of 2.4.6-trimethylstyrene (TMeSt) was studied using the 1-chloro-1-(2,4,6-trimethylphenyl)ethane/BCl3 initiating system in CH Cl. from -70 to -20 degreesC. The equilibrium constant of ionization (K-i) was calculated from the cation concentration determined by UVvisible spectroscopy. From the apparent rate constant of propagation (hpa-) and K-i, the absolute rate constant of propagation for ion pairs kp' = 1.4 x 10(4) L mol(-1) s(-1) was calculated at -70 degreesC. The rate constant of ion collapse, k(-i) was determined from the polydispersity vs conversion plots. From K-i and k(-i) the rate constant of ionization, k(i) were also calculated. From the temperature dependence of K-i. and k(-i) the enthalpy and entropy of the ionization and deactivation were obtained. respectively. Competition experiments i.e., polymerization carried out in the presence of 2-chloropropene as a pi-nucleophile. were. also carried out at -70 degreesC to determine kp(+/-) separately. NMR spectroscopy, gel permeation chromatography. and elemental analysis suggested complete capping of the polymeric cation and the absence of -side reactions. From the limiting number-average degree of polymerization and the known rate constant of capping k(c) = 62.0 L mol(-1) s(-1), k(p)(+/-) = 8.3 x 10(4) L mol(-1) s(-1) was determined. This value is simila t r to that determined from kpapP and & thus, the utility of competition experiments is corroborated.