Synthesis, photoinitiation, and photopolymerization of novel multifunctional monomers

Tai Yeon Lee


In spite of the short history of UV curing technology, UV curing has become an established technology due to an extensive list of advantages over traditional solvent based systems. However, problems in UV curing still remain. The research in this dissertation includes topics which advance the basic scientific and technical aspects of radiation curing and overcome several existing problems. Particular attention is given to development of self-initiating systems and other new monomers. Their polymerization kinetics and oxygen inhibition are reported. The self-initiating monomers evaluated contained more than two different double bonds in the same molecule connected by a carbonyl group, and were synthesized by a transesterification reaction between vinyl acetate and acid compounds. The photochemical properties such as UV absorption behavior and photoinitiation efficiency were investigated and explained on the basis of their chemical structures. A self-initiation mechanism for polymerization was suggested based on the analysis of the photolyzed product of the self-initiating monomers in the presence of TEMPO. In addition, the homopolymerization and copolymerization of thiols and vinyl ethers were investigated in great detail. It was found that the presence of two carbon-carbon double bonds on the same molecules dramatically enhances the absorption of low energy UV light in these monomer initiators. The absorptivity and red-shift in the UV spectrum are strongly dependent on the structures of the monomers. The two different types of double bonds present in the self-initiating monomer exhibited enhanced copolymerization rate with various comonomers. It is proposed that self-initiating monomers produce radical species by α-photocleavage upon irradiation. Multifunctional vinyl ester monomers and dendrimers were synthesized by an amine catalyzed Michael addition reaction between multifunctional thiols and vinyl acrylate. The homopolymerization both in air and nitrogen was studied and the effect of the thioether group present in the monomer on oxygen inhibition was investigated. The influence of multifunctional vinyl ester monomers on multifunctional acrylate polymerization both in air and nitrogen was discussed and the effect of dendritic structure on polymerization kinetics and thermal properties was also explained. (Abstract shortened by UMI.)