Synthesis of New Photo-Responsive Polyesters Containing Norbornadiene Residues in the Main Chain

Several new photo-responsive polyesters containing norbornadiene (NBD) residues in the main chain were synthesized by the polyaddition of 2, 5-NBD-2, 3-dicarboxylic acid diglycidyl ester (NDGE) with diacyl chlorides. NDGE was synthesized in 75% yield by the reaction of potassium salt of 2, 5-NBD-2, 3-dicarboxylic acid with epibromohydrin using tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst at 70°C for 12h. The polyaddition of NDGE with terephthaloyl chloride in the presence of TBAB as a catalyst in NMP at 80°C for 15 h gave a new NBD polymer with a number average molecular weight of 9000. The polyadditions of NDGE with some other diacyl chlorides under the same conditions proceeded smoothly to give the corresponding NBD polyesters in good yields. The photochemical valence isomerization of various NBD moieties in the film state proceeded quantitatively to the corresponding quadricyclane (QC) groups upon irradiation with UV-light for 7h.