A new class of polymeric or polymerizable aromatic-aliphatic ketones, the preferred of which are: 2-hydroxy-2-methyl(4-vinylpropiophenone), 2-hydroxy-2-methyl-p(1-methylvinyl)propiophenone, p-vinylbenzoylcyclohexanol, p-(1-methylvinyl)benzoyl-cyclohexanol and their oligomerization and polymerization products, they being suitable for use as photoinitiators for the photopolymerization of ethylenically unsaturated monomers and prepolymers.Said ketones are produced by subjecting an aromatic substrate, preferably a monomer or oligomer of styrene type, to the following reaction cycle: polymerization - acylation - alphachlorination - nucleophilic substitution with the formation of epoxyether - hydrolysis of the epoxyether; or to other reactions as modifications or alternatives to this cycle.The ketones according to the present invention have high efficiency as photoinitiators both with regard to the useful concentration to be used and with regard to the polymerization rate.