Mechanistic Modeling of the Thiol-Michael Addition Polymerization Kinetics: Structural Effects of the Thiol and Vinyl Monomers

Kinetic parameters and their influence on the overall rates of base-catalyzed thiolMichael reactions proceeding via an alternating propagation and chain transfer cycle were evaluated. A kinetic model was developed that enables the determination and accurate prediction of the reaction kinetic paths for the thiolMichael addition reaction and its accompanying polymerization. Individual kinetic parameters for propagation and chain transfer steps were evaluated for three commonly used thiol and vinyl functional monomers. Chain transfer and propagation kinetic parameters were determined in binary combinations of monomers from analysis of experimental data for the reaction rates. Subsequently, eight ternary thiolMichael systems composed of thiolacrylatevinyl sulfone and thiol 1-thiol 2-vinyl were analyzed based on the binary kinetic model parameters. It was clearly demonstrated that the kinetic parameters determined from the binary reactions enabled an accurate prediction of the relative reactivity and selectivity in the multicomponent systems. Finally, the calculated kinetic parameters were utilized in network-forming polymerizations to validate the suitability of the model to predict network development, particularly in the initial stages prior to any diffusion limitations on the reaction kinetics. These results serve as a useful guide for monomer selection in designing thiolMichael-based polymers with appropriate kinetic characteristics and material properties.