SYNTHESIS AND SOLAR-ENERGY STORAGE PROPERTY OF POLYMERS CONTAINING NORBORNADIENE MOIETIES

Polymers having a pendant 3-[(p-substituted phenyl)carbamoyl]-2,5-norbornadiene-2-carboxylate moiety and their model compounds were prepared from the reaction of poly[4-(chloromethyl)-styrene] and benzyl chloride with corresponding potassium salts using phase-transfer catalyst in dimethylformamide, respectively. The photochemical valence isomerization of pendant norbornadiene (NBD) to the quadricyclane (QC) moiety proceeded smoothly in the film state or polymer solution upon irradiation by sunlight or high-pressure mercury lamp. The rate of isomerization was strongly affected by the substituent of [(p-substituted phenyl)carbamoyl]-2,5-norbornadiene-2-carboxylate moiety in the polymers. Especially, the polymer containing a pendant 3-[(p-acetylphenyl)carbamoyl]-2,5-norbornadiene-2-carboxylate moiety showed higher photochemical reactivity than the other NBD polymers. Furthermore, it was found that the rate of photochemical reaction in the polymer solution was much higher than that of the corresponding model compounds. On the other hand, the resulting QC groups in the polymer film scarcely reverted to the original NBD without any catalyst if it were kept in dark at room temperature for a long time and showed excellent storage stability. However, the reversion proceeded smoothly when (5,10,15,20-tetraphenyl-21H,23H-porphine)cobalt(II) (Co-TPP) was added to the polymer solution as a catalyst. The reaction was proportional to the product of both concentrations of QC group and Co-TPP, and did not appreciably depended on the para substituent of 3-[(p-substituted phenyl)carbamoyl]-2,5-norbornadiene-2-carboxylate moiety in the polymers. Furthermore, it was found that the storage energy for the QC moiety derived from the para substituent of 3-(phenylcarbamoyl)-2,5-norbornadiene-2-carboxylate moiety was about 60 kJ/mol by DSC measurement of the irradiated polymers.