FWF - PTC - Photoinitiators with ß-phenylogous cleavage

Photoinitiated radical polymerization is an efficient and environmentally friendly tool to convert monomers such as acrylates within the fraction of a second into solid polymers. The photoinitiator (PI) is the core part of the formulation; light is converted to chemically reactive intermediates. Recently, we have found that photoinitiators based on benzophenone covalently linked with aromatic glycines by a methylene spacer give a significant impulse for new concepts in radical photoinitiators. The new photoinitiator provides several advantages compared to the state of the art. - The benzophenone-based PI can be easily prepared in a two step synthesis. - This PI combines the advantages of high reactivity usually found in - -cleavage PIs with the good surface cure of amine based Type II PIs. - Preliminary investigations indicate a new mode of initiation (-phenylogous cleavage) - Glycine derivatives give improved reactivity due to spontaneous decarboxylation mechanism (avoids back electron transfer). The formed CO2 replaces O2, thus reducing oxygen inhibition. - No amine based coinitiator is necessary. - Good migration stability because benzophenone residue is also covalently bonded in the polymer matrix and low volatility To extend this new and promising field of photoinitiation, fundamental research is necessary to understand the mode of initiation. From resent results, different and unusual types of initiation can be expected. By exploring the photochemistry and photophysics (laser flash photolysis) of this compound, especially by identification of the initiating species (Photo-CIDNP) and photoproducts, optimization of the benzophenone based photoinitiator and expansion of this promising concept to other photoinitiating systems should be possible.