Molecular geometry and electronic structure of molecules in free-radical copolymerization of styrene and methyl methacrylate derived from density functional calculations

The molecular geometry and electronic structure of styrene and methyl metha crylate as well as corresponding radicals formed by the addition of a methy l radical to the beta -carbon of the monomer were determined using the dens ity functional theory at the B3LYP/6-311+G** level. Results were in good ag reement with the theoretical and experimental data available in the literat ure. Full optimized molecular geometry of methyl methacrylate showed the tr ans form of the molecule. Monomers transformed into corresponding radicals preserved the main structural parameters of substituents whereas bonds betw een substituents and adjacent radical carbon atoms shortened. It was found that the correlation of the theoretically calculated electronic parameters for monomers and the corresponding radicals with the Q and e parameters fro m the Alfrey-Price scheme strongly depends on the level of calculations. Ap plication of the higher level of theory including the correlation effect ch anges the relationship discussed in the literature between energy (E-y) of formation of a radical from the monomer, the experimental e parameter, and the Q parameter and monomer/average electronegativity, respectively. The to tal atomic spin density at the radical carbon atom correlated with the radi cal parameter P in the Alfrey-Price scheme was computed to be higher for th e methoxycarbonyl-l-methyl-ethyl radical when compared with the I-phenyl-pr opyl radical. These values are in good agreement with the localization ener gies and the P values determined from the kinetic measurements for macrorad icals ending with styrene and methyl methacrylate monomer units. (C) 2001 J ohn Wiley & Sons, Inc.