Investigating the photoinitiated polymerization kinetics of thioxanthone acetic acid derivatives: A computational study

In this study, we have investigated the kinetic and thermodynamic parameters of the initiation reactions of two well-known photoinitiator types; One-Component Type II and conventional Type II. Density Functional Theory (DFT) has been used in all calculations. The most suitable methodology for thioxanthone acetic acid based photoinitiators has been chosen by assessing the level of theory. Absorption spectra of thioxanthone acetic acid derivatives have been generated by Time-Dependent Density Functional Theory (TD-DFT). Dynamic and vibrational effects have been included in the calculations by including the Wigner methodology. Calculated absorption spectra have been compared with the experimental absorption spectra of thioxanthone acetic acid derivatives. In order to understand the nature of electronic transitions, Natural Transition Orbitals (NTOs) have been generated and the Phi-S index values have been calculated. Competition between the thioxanthone acetic acid based exocyclic and endocyclic radicals, which co-exist in the reaction media, have been evaluated. Furthermore, initiation efficiencies of phenyl acetic acid based radicals and thioxanthone acetic acid based radicals have been compared in terms of their kinetic and thermodynamic parameters. In order to assess the radical reactivity, spin densities and radical Fukui functions have been calculated.