The problem of describing quantitatively the selectivity of cationic copolymerizations leads to a new method of calculating kinetic parameters of the copolymerization. The “individual rate constants” for the binary first-order copolymerization calculated this way are well suited to describe the “dynamics of the copolymerization” and to predict copolymer characteristics, e. g., composition and microstructural parameters. By means of cationic copolymerizations of vinyl monomers, theoretical calculated copolymer characteristics and experimentally independently determined ones are compared.