HIGH-PRESSURE SYNTHESIS AND PROPERTIES OF ALIPHATIC-AROMATIC POLYIMIDES VIA NYLON-SALT-TYPE MONOMERS DERIVED FROM ALIPHATIC DIAMINES WITH PYROMELLITIC ACID AND BIPHENYLTETRACARBOXYLIC ACID

Two aliphatic series of polyimides having well-defined structures with inherent viscosities of 0.4-2.7 dL g(-1) were readily synthesized by the solid-state thermal polycondensation under high pressure of the sa lt monomers composed of aliphatic diamines having 6-12 methylene units and both pyromellitic acid (PMA) and biphenyltetracarboxylic acid (BP A) under 220 MPa at 250 degrees C for 5 h. It is noteworthy that the p olycondensation proceeded rapidly with the elimination of water in a c losed reaction vessel under high pressure, producing high molecular we ight polyimides mostly within only 1 h. The thermal behavior (melting temperature and glass transition temperature) and crystallinity of the PMA- and BPA-based polyimides are also discussed in detail.