Initiators Based on Benzaldoximes: Bimolecular and Covalently Bound Systems
Markus Griesser1, Arnulf Rosspeintner, Claudia Dworak
1Institute of Physical and Theoretical Chemistry, Graz University of Technology , Stremayrgasse 9, 8010 Graz, Austria.
Abstract:
Typical bimolecular photoinitiators (PIs) for radical polymerization of acrylates show only poor photoreactivity because of the undesired effect of back electron transfer. To overcome this limitation, PIs consisting of a benzaldoxime ester and various sensitizers based on aromatic ketones were introduced. The core of the photoinduced reactivity was established by laser flash photolysis, photo-CIDNP, and EPR experiments at short time scales. According to these results, the primarily formed iminyl radicals are not particularly active. The polymerization is predominantly initiated by C-centered radicals. Photo-DSC experiments show reactivities comparable to that of classical monomolecular type I PIs like Darocur 1173.
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