Thin-film calorimetry and the kinetics of photoinitiated thiol-ene polymerizations

Todd Michael Roper


The field of photoinitiated thiol-ene polymerizations has experienced significant growth in the past decade due to numerous advantages of the polymers thus produced over traditional solvent based polymeric materials. Although current utilization of thiol-ene technology is multi-faceted, numerous opportunities exist for the exploration of structure-kinetic relationships and new material applications. The research in this dissertation includes a fundamental study of the effect that alkene structure has on thiol-ene polymerization kinetics and mechanisms, the development of a novel instrument for photopolymerization kinetics measurements, and the application of thiol-ene chemistry to pigmented systems. The first fundamental study probes structure-reactivity relationships in photoinitiated thiol-ene polymerizations. More specifically, the influence of alkene structure on the reactivity and mechanism of thiol-ene photopolymerizations is described. Structure-reactivity relationships between monofunctional hydrocarbon alkenes and monofunctional thiol are identified and used to explain the photopolymerization mechanism and kinetics of a series of multifunctional thiol-ene systems. Results demonstrate the significant effect that ene accessibility, location, substitution, and conformation all have on the on the reactions kinetics, extent of conversion and polymer network structure for thiol-alkene systems. The impact of cis/trans isomerization reactions on the thiol-ene polymerization mechanism is illustrated with various multifunctional alkenes. As an extension of the model thiol-ene structure-reactivity work, the polymerization kinetics for photoinitiated reactions between thiol and terminal n-dienes is described. The reactivity of these thiol-ene systems depend on the thiol structure, ene substituents, and thiol functionality. Results from this work are used to analyze the development of thermal and mechanical properties with respect to the crosslinking kinetics of thiol-ene polymer networks. In addition to understanding the structure-reactivity relationships in thiol-ene polymerizations, new applications of this technology which emphasize the susceptibility of acrylate systems to oxygen inhibition are developed. (Abstract shortened by UMI.)