Behavior of polyimides based on bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride under thermal treatment

This study investigated the preparation and thermal behavior of the polyimide based on the nonaromatic bicyclo[2.2.2]oct‑7-ene-2,3,5,6-tetracarboxylic dianhydride and aromatic 4,4´-(1,4-phenylenediisopropylidene)bisaniline. A significantly greater mass loss was detected in the nitrogen atmosphere than in the air atmosphere by using an isothermal thermogravimetric analysis of this product at 375 °C. This loss in nitrogen was reduced when approximately 1 wt% of the radical inhibitor 2,6-di‑tert-4-methylphenol was added to the polymer, whereas in the case of using an atmosphere containing oxygen, which is one from the most effective radical inhibitors, the presence of 2,6-di‑tert-4-methylphenol had practically no effect. This finding supports the application of a retro Diels–Alder reaction during the decomposition of the structure coming from bicyclo[2.2.2]oct‑7-ene-2,3,5,6-tetracarboxylic dianhydride including radical formation as intermediate products at temperatures above 350 °C, whereby the present oxygen inhibits this process very effectively. The products formed during thermal attack were analyzed via a combination of dynamic thermogravimetry with infrared spectroscopy. Some aspects of fully aromatic polyimides based on 4,4´-oxydiphthalic anhydride and 4,4´-(1,4-phenyleneisopropylidene)bisaniline were compared.