A computational approach to the free radical polymerization kinetics of alkyl α-hydroxymethacrylate monomers: A structure–reactivity relationship

ABSTRACT

Density functional theory calculations at the B3LYP/6–31+G(d) level were carried out for 16 alkyl α-hydroxymethacrylate (RHMA) monomers, and the calculated quantum chemical descriptors were used to construct a quantitative structure–activity relationship model of the reactivity parameters of those monomers. A multiple regression analysis was adopted to predict the polymerization kinetics. The molecular descriptors used in this study are the Mulliken and APT charges of the backbone C atoms in proximity of the reactive center, the total dipole moment (µ), the energy of the highest occupied molecular orbital (E_HOMO), the energy of the lowest unoccupied molecular orbital (E_LUMO), the isotropic polarizability (α), the Mulliken atomic spin density (ρ_s), the ionization energy (IE), the electron affinity (EA), the resonance parameter (Res), the natural atomic orbital occupancies, and the bond distances of the bonds in the proximity to the reactive center of the RHMA monomers and their corresponding radicals. Among the various descriptors considered, the IE and EA of the monomers, the bond order of carbonyl double bond of monomer (BO_CO), the resonance stabilization parameter of the monomeric radical, and the Mulliken atomic spin density (ρ_s) of C5 of the radical were found to be correlated (R² = 0.9416) with the experimental rates of photopolymerization. The correlation with experiment is also satisfactory when additional monomers are included in the data set; a new correlation is thus generated (R² = 0.9186). This study is expected to shed light on predicting the reactivities of RHMA monomers prior to their synthesis and to rank their photopolymerization rates based on their quantitative structural properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2375–2384