This article is a critical analysis of kinetic data available on carbocationic polymerizations. A survey of published propagation rate constant (k(p)) data revealed several orders of magnitude differences. In this article, an explanation of this apparent discrepancy is offered with a case study involving the carbocationic polymerization of 2,4,6-trimethylstyrene (TMS). With the polymerization mechanism originally proposed for this system, kp = 1.35 x 10(4) L mol(-1) s(-1) was extracted from experimental data with the Predici polyreaction package. The alternative mechanism yielded k(p) = 1.01 x 10(7) L mol-l S close to that predicted by Mayr's Linear Free Energy Relationship (LFER). We propose that true rate constants can only be obtained from direct competition experiments or from kinetic interpretation based on independently proven mechanisms. The second part of this review discusses critical analysis of the temperature and concentration dependence of various living IB systems. Comparison of the temperature dependence in systems initiated with 2-chloro-2,4, 4-trimethylpentane (TMPCI)/TiCl4 from various laboratories yielded of Delta H similar to -25 and -34.5 kJ/mol for high and low TMPCl/TiCl4 ratios, respectively. Aromatic (cumyl-type) initiators show Delta H similar to -40 kJ/mol, whereas H2O/TiCl4 in the presence of the strong electron-pair donor dimethylacetamide gave AH = - 12 kJ/rnol. The significant differences indicate different underlying mechanisms with complex elementary reactions. (c) 2005 Wiley Periodicals, Inc.