AbstractThe relative reactivities of the following monomers: acenaphthylene, 4‐vinyl biphenyl, and 2‐vinyl fluorene are determined both experimentally and through quantum chemistry methods. Styrene is the reference monomer. The influence of experimental conditions: solvent, temperature, nature of the initiator are studied and the activation enthalpy and entropy differences determined. The comparison of these values with the 1/r2(index 2 is relative to styrene) shows that, in a general way, the activation entropy is the determining reactivity factor. The stabilization energies are calculated both by Hückel's and Pople's methods and the values so obtained are in close agreement with experimental results. The discrepancy observed for acenaphthylene, between Hückel on the one hand, and Pople and experimental determinations on the other hand, is due to the strain of the pentagonal