Polymers obtained through electronic excitation of benzophenone (BP), fluorenone (Fl), xanthone (X), thioxanthone (TX), 3,6-bis(dimethylamino)thioxanthone (BTX), acridone (Ac), or 10-methylacridone (MAc) in acetonitrile/methyl methacrylate mixtures have been isolated and analyzed with respect to their endgroups. The UV/vis-spectra combined with protonation and hydrolysis reactions served for analyzing of these polymers. With Fl the polymerization chain has proved to be initiated by a 1,4-diradical formed via addition of the ketone-triplet to the monomer. With TX, BTX, Ac, and MAc this reaction takes place only to low extent in the polymer formation process. Mainly - with BP and X exclusively - an initiation occurs through radicals built up by hydrogen abstraction of the ketone-triplet. Thus formed ketyl radicals show a very distinct behaviour. While those of Ac and MAc transfer hydrogen atoms during the termination reaction, with Fl radical combination occurs.
