NOVEL REGULAR NETWORK POLYIMIDE FILMS FROM MELLITIC ACID AND ALIPHATIC AND AROMATIC DIAMINES OR DIISOCYANATES

Novel regular network aliphatic-aromatic and aromatic polyimide films were prepared from mellitic acid (Y-H) and aliphatic and aromatic diamines or diisocyanates. Prepolymers prepared by solution polycondensation were cast and successively post-polymerized to form a network. The resultant films were insoluble in any organic solvents. The heat distortion temperature (T-h) and density of network polyimide films increased and then levelled off with increasing post-polymerization temperature and time. Polyimide films prepared from diisocyanates and Y-H had higher T-h values compared with those prepared from the corresponding diamines and Y-H, which is due to the enhanced degree of reaction of the former films shown by infra-red spectroscopy. On increasing the length of the methylene chain in the diamine component, the T-h values and densities decreased and the intensities of X-ray diffraction peaks increased for network aliphatic-aromatic polyimide films. The T-h values of network polyimide films were somewhat higher than those of the corresponding linear polyimide films and network polyamide films. The 6' Y-H film prepared from Y-H and hexamethylene diisocyanate (6') post-polymerized at 370 degrees C for 1 h had a T-h value of 316 degrees C; and the OYH film prepared from Y-H and 4,4-diaminodiphenyl ether (O) post-polymerized at 370 degrees C for 1 h had the highest T-h value of 449 degrees C among the polyimide films studied. Network polyimide films had much higher thermal resistance compared with the corresponding linear polyimide films at higher temperature, suggesting the preferred formation of carbonized structure.