Hydroxyalkylphenone based ynones as new α-cleavable photoinitiators in free radical polymerization

Complete text of publication follows. Most radical generating photoinitiators used in modern coating industry are based on the benzoyl chromophore, which is responsible for light absorption, cleavage process and addition rates to double bonds of the generated radical. By investigating novel types of initiators double- and triple-bonds were inserted between the aromatic ring and the carbonyl group of conventional hydroxyalkylphenone. Photo-DSC was used to measure various parameters such as the time to reach the maximum polymerization heat (tmax), double bond conversion (DBC) as well as rate of polymerization (Rp). Identification of cleavage products was carried out by irradiation with TEMPO as free radical scavenger using GC-MS analytics as well as column chromatography. By exploring new types of chromophors it has been found that enone based initiator showed only poor photoactivity, whereas cis-trans-isomers are the major photoproducts. Residues with increased electron-withdrawing effect compared to the phenyl group such as triple bonds exhibit similar photoactivity compared to the efficient hydroxyalkylphenone initiator. These new PIs still undergo Type a-cleavage