Kinetics of the reactions of benzhydryl cations with 2.4.6- trim ethyl styren e have been performed to determine its nucleophilicity parameters N = 0.68 and s = 1.09. which are comparable to styrene and considerably less nucleophilic than 4-methylstyrene, indicating the retarding effect of the ortho methyl groups. Kinetic investigations of the reactions of the 2.4.6-trimethylstyrl cation 6(+) and the corresponding dimer 7(+) with the reference nucleophile 2-chloropropene allow us to calculate the closely similar electrophilicity parameters E(6(+)) = 6.04 and E(7(+)) = 6.16 which are considerably lower than that of the styryl cation (E = 9.6). As a consequence, the propagation rate constant of the cafionic polymerization of 2,4,6-trimethylstyrene is considerably lower than that of styrene. Substituting these values into the correlation log k(20) (degreesC) = s(N + E) yields a propagation rate constant of 3 x 10(7) M-1 S-1. which has to be considered an upper limit because extra steric strain generated in the reaction of 7(+) with 2,4,6-trimethylstyrene is not included in this correlation.