PNNL

Abstract

The Q-e scheme was developed for interpretation of the reactivity of a monomer containing a double bond in free-radical copolymerizations. This empirical scheme has been proved to be remarkably useful and continues to be essentially the only general reactivity scheme in use today. In order to develop a reliable computational approach for theoretical prediction of the Q and e values of molecules whose experimental Q and e values have not been established, the Q-e parameters have been investigated by performing a theoretical analysis and by performing density-functional-theory calculations on molecules whose experimental Q and e values are available. It has been demonstrated that for a general choice of the Q and e values of the reference monomer, both parameters Q and e should be dependent on the energetic properties of the free-radical reaction and the polar properties of the monomer and radical. In order to correlate the Q and e parameters with these properties, the overall quality of the calibrated correlation relationships should not be affected by the choice of the reference Q and e values. Satisfactory relationships have been found for the correlations of the Q-e parameters with DFT-calculated electronegativities and reaction free energies, suggesting that the electronegativity and reaction free energy determined by the density functional theory calculations reasonably reflect the polar and energetic properties, respectively, needed for Q-e parameter development. With the particular choice of the popularly used reference values of Q = 1.0 and e = -0.8 for styrene, the parameter e is dependent only on the calculated electronegativity, and the parameter Q is dominated by the calculated reaction free energy. The satisfactory explicit relationships obtained can be used in future computational prediction of the Q and e parameters.