Photochromic cooligomers from pyridazinespirodihydroindolizine and styrene

New cooligomers 5 of styrene and 4-vinylpyridazine have been prepared by th e controlled free radical polymerization technique. The addition of spirocy clopropene has led to cooligomers 6 in which the pendant pyridazine subunit s are transformed into photochromic spirodihydroindolizines. Characterisati on by NMR and SEC was carried out with 5 and 6. Molecular masses (M) of 5 a nd 6 have been found to be in the range of oligomers. Studies by UV-VIS-spe ctroscopy have shown the photochemical properties of 6 and of the reference compound 3. The absorbance of 6 is similar to that of 3. The fatigue resis tance (Z(80)=4-10) of the cooligomers 6 shows 6 to be more stable than 3. T he half life of the cooligomers 6 was found to be (100 +/- 20 s).