Starting from 10 different 4'-substituted 4-[N,N-dihydroxyethyl]aminoazobenzenes,polymeric urethane-azo dyes (M, 42000-10200) were prepared by reacting those with hexamethylene diisocyanate. The dependence of spectral properties, redox potentials and photofading behaviour on the kind of substituents was determined and then compared with corresponding monomer and dimer model compounds. Photofading is caused by a photooxidative process. In the sequence of monomeric > dimeric > polymeric azo dyes, light stability decreases due to a diminution in thermal desactivation processes and in a possible intramolecular energy transfer. ZUSAMMENFASSUNG:Ausgehend von 10 unterschiedlich 4'-substituierten 4-[N,N-dihydroxyethyl]aminoazobenzolen wurden durch Umsetzung mit Hexamethylendiisocyanat polymere Azofarbstoffe (M,, 4200-10200) synthetisiert und die Substituentenabhangigkeit der spektralen Eigenschaften, der Redoxpotentiale und des Ausbleichverhaltens mit entsprechenden monomeren und dimeren Modellverbindungen verglichen. Die Ausbleichung erfolgt durch einen photooxidativen ProzeB. In der Reihenfolge monomerer > dimerer > polymerer Azofarbstoff sinkt die Lichtstabilitat durch die Verringerung thermischer Desaktivierungsprozesse sowie durch einen mdglichen intramolekularen Energietransfer.

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Different 4'-substituted 4-[N-ethyl-N-(2-acryloyloxy)ethyl]aminoazobenzenes were used as starting monomers for homopolymerization and copolymerization reactions with styrene and methyl methacrylate. The photofading behaviour of the obtained polymeric azo dyes (M, 4200-9000) was investigated by means of a Xenotest device and compared with that of the corresponding monomers. The decreased photostability * Correspondence author. a Part I cf.'. 0 1992 Hiithig & Wepf Verlag, Basel CCC 0003-3 146/92/$05.00

The reaction of the title compound (II) with the pyrazolone (Ia) yields the products (III), (IV) and (Va).

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