Various epoxy monomers containing norbornadiene (NBD) moieties were prepared by reactions of potassium salts of NBD derivatives with excess epichlorohydrin using tetrabutylammonium bromide (TBAB) as a phase transfer catalyst; The copolymerization of glycidyl 13-phenyl-2,5-norbornadien-2-yl)carboxylate (GPNC) with phthalic anhydride (PAn) proceeded smoothly using TBAB as a catalyst in sulfolane at 100 degrees C for 24 h to give polyester P-1 containing pendant NBD moieties. Copolymerizations of various epoxy monomers containing certain NBD moieties with carboxylic anhydrides gave the corresponding NBD polyesters in good yields. The photochemical valence isomerizations of the NBD moieties in the polymers were carried out in the film state or in the solution. Rates of the isomerizations of some NBD moieties in the polymers were strongly enhanced by the addition of photosensitizers such as 4-(N,N-dimethylamino)benzophenone (DABP). The T(g)s of the polyesters having NBD residues and stored thermal energy in the corresponding quadricyclane (QC) groups in the polymers were measured by DSC analysis. The T(g)s of the NBD polymers were 45-93 degrees C. Polyesters having QC groups after photoirradiation released their stored thermal energies (about 90 kJ/mol) at temperatures above the T(g)s of the corresponding NBD polymers.