The kinetic method for analysing consecutive reactions under isothermal conditions has been developed further. An approach to assessing the correspondence of the calculated values of the rate constants to the exact steps is suggested. As an example of application of this method, the consecutive quaternizations between N,N,N’,N’-tetramethyl-1,3-propylenediamine and bromobutane, which is a model reaction to elucidate the formation of the ionene polymers, were investigated with a conduction calorimeter in different solvents and at different temperatures. The characteristics of the described method and the influence of the solvent and temperature on the kinetic parameters of the two steps are discussed.