Aromatic amines are known to give very poor performance as coinitiators for camphorquinone in the photopolymerization of acidic aqueous formulations. Differential scanning photocalorimetry investigations using N-phenylglycine (NPG) as an alternative coinitiator proved the suitability of this derivative. Further-more, it was demonstrated that the generally poor photoreactivity had to be assigned to the presence of water and not to the acidity of the formulation. The poor storage stability of NPG-containing formulations was significantly improved by derivatives containing electron-withdrawing substituents in the para position of the aromatic moiety, and the photoreactivity was kept at a very high level. (c) 2005 Wiley Periodicals, Inc.