The relationship between the reactivity of the monomers and the electron density of the double β-atom in the carbon-carbon double bond was determined. The density of the β-atom can be estimated from the chemical shift of the respective protons shown in ¹Н-NMR spectra. Correlation equations that allow us to determine the reactivity values of a range of vinyl monomers bearing electron-donating substituents under the influence of catalyst systems Et₂AlCl–TiCl₄ and TiCl₄ are presented. The established relationships between reaction rate constants, enthalpy, polymerization activation energy and electron density of the β-atom in the carbon-carbon double bond can be used to select the optimal duration and temperature for the synthesis of polymeric petroleum resins.