Kinetic studies of radical reactions using time-resolved EPR

The presented work has demonstrated, that TR-EPR is a powerful tool for
the determination of the decisive structural and kinetic parameters for the
evaluation of photoinitiator efficiency. Additional insights are provided by
the application of theoretical calculations. This combination of experimental
and theoretical methodology provides a basis for the design and development
of innovative phototriggers.
On the bases of the results presented in this thesis we can make the fol-
lowing conclusions:
- TR-EPR allows the determination of addition rate constants in the
cases where optical spectroscopy doesn't have sufficient resolution as
well as provides structural information of the reactive species.
- Phosphinoyl radicals generated by photolysis of acyl and bis(acyl)phosphine
oxides, possess high rate constants of addition to n-butyl acrylate,
HDDA, styrene and 1-vynil-2-pyrrolidon. Analysis of the spin popu-
lation at the phosphorus atom supports the experimental observations
of TR-EPR spectra that greater localization of the spin population at
the phosphorus atom results in faster rates of addition.
- A series of substituted benzoyl radicals have been generated by laser
flash photolysis of -amino ketones and bis(acyl)phosphine oxides. The
benzoyl radicals were characterized by time-resolved EPR in toluene so-
lution and their absolute rate constants for addition to n-butyl acrylate
were determined. The experiments demonstrate two concentration do-
mains of reactivity. The reactivity of benzoyl radicals decreases at high
viscosity.
- Benzoyl radicals react faster with oxygen than phosphinoyl radicals,
therefore, they can be used as oxygen scavenges.
- The fluorescence properties of the photoinitiators can be used to in-
crease the in depth cure of the formulation.
- DFT and ab initio calculations have shown to be in a good agreement
with the experimental data.