Characterization of geometric isomers of norbornene end‐capped imides

Three geometric isomers from the thermal isomerization of methylene‐4,4′‐bis(endo‐N‐phenylbicyclo‐[2.2.1]hept‐2‐ene‐5,6‐dicarboximide) (I) were chromatographically separated and isolated. Nmr spectroscopy was used to assign endo‐endo (I), endo‐exo (II), and exo‐exo (III) configurations to each compound. The three isomers, which serve as model compounds for norbornene end‐capped polyimides, were then characterized by several chromatographic, spectroscopic, and thermal techniques. Upon heating, each isomer was found to establish an equilibrium mixture of all three isomers. The possibility that the compounds react by different mechanisms in air and in nitrogen is proposed.