High-Pressure Synthesis and Properties of Aliphatic−Aromatic Polyimides via Nylon-Salt-Type Monomers Derived from Aliphatic Diamines with Pyromellitic Acid and Biphenyltetracarboxylic Acid

Abstract

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 salt monomers composed of aliphatic diamines having 6−12 methylene units and both pyromellitic acid (PMA) and biphenyltetracarboxylic acid (BPA) under 220 MPa at 250 °C for 5 h. It is noteworthy that the polycondensation proceeded rapidly with the elimination of water in a closed reaction vessel under high pressure, producing high molecular weight 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.