Application of Ab initio MO calculations to methods for predicting reactivity in free radical copolymerization

Ab initio MO calculations have been performed utilizing several different basis sets, viz. STO-3G, SV3-21G and TZV. The output from these calculations included the electronegativity of a set of vinyl monomers and their corresponding radicals formed by the addition of a hydrogen atom or a methyl radical. These electronegativities were correlated with the Patterns of Reactivity α parameters and the Ito-Matsuda II parameters. The energy of formation (E _Y ) of a radical from the monomer was also calculated and correlated with the Patterns β parameter and the Ito-Matsuda log k values. The polarity-electronegativity plots displayed a strong correlation. However, the correlation of E _Y with β was very poor and deteriorated with higher basis sets. We determined to improve matters by rescaling the Patterns scheme using styrene as the standard monomer. This attempt was unsuccessful as there were considerable problems with the Patterns scheme itself. They were attributed to the kinetic database on which it is based, both reactivity ratios and the Hammett σ _p parameters which are crucial to the successful application of the scheme. Correlations with the Ito-Matsuda parameters showed more promise but were limited by the amount of experimental data available.