Because of the poor photoreactivity of camphorquinone-amine-based photoinitiator systems in dental acidic aqueous primer formulations, we were interested to evaluate a commercially available bisacylphosphine oxide as photoinitiator. Because of the promising results on photoreactivity and storage stability, new oligo(ethylene glycol)-substituted bisacylphosphine oxides were synthesized and investigated. Beside good solubility and significantly increased reactivity in aqueous acidic formulations, sufficient storage stability was found. Additionally, the influence of the type of substitution on the photopolymerization behavior in aqueous, hydrophilic, and hydrophobic resins is discussed. (c) 2006 Wiley Periodicals, Inc.