Linear wholly aromatic polyimide highest thermal stability. When the polyimide is heated to above 300 ℃, TG will be gradually increased, soluble into insoluble, indicating the formation of a cross-linked product. The temperature will rise further decomposition. When the pyrolysis gas main products are CO2, CO and water. Below 350 ℃ CO2 as the major product, CO began to appear above 350 ℃. And a major product at 400 ℃. Description In this case due to the presence of moisture occurred imide ring ring-opening polymerization and decarboxylation, (Moisture may be present in the sample or sample adsorption bring a small amount of amide acid units generated by thermal cyclization may also be due to thermal decomposition.) so polyimide imide ring is the weakest element. CO2 is formed in addition to the decarboxylation also may be due to the heat generated imide ring isocyanate solution, and then dimerization of carbodiimide and CO2. Some people think that because the imide ring at high temperatures for the rearrangement of iso-imide and release CO2, but this assumption is usually not recognized. Because different when heated imide is readily converted to an imide, the inverse process never have been discovered. As appears under infrared spectrum of 1660 cm-1 absorption is not really different from the imide. But because of the acid with an excess of sodium amide obtained by reacting ortho diamide, or produced imide linkages between molecules. These reactions are also a way of cross-linked polyimide, but this response is still difficult to obtain universal recognition. Because ortho diamide off at high temperatures the formation of amine imide.