Melt-polymerizable bisimido-bisphthalonitriles containing silicon, fluoro, and ether groups: Synthesis, characterization, and NMR study

Various melt‐polymerizable bisimido‐bisphthalonitrile polymer precursors were synthesized by the reaction of 4‐aminophthalonitrile (4‐APN) with bis(3,4‐dicarboxyphenyl) dimethylsilane dianhydride (SIDA), 4,4′‐hexafluoroisopropylidene diphthalic anhydride (6FDA), bis(3,4‐dicarboxyphenyl)ether dianhydride (ODPA), and 3,3′, 4,4′‐tetracarboxylichenzophen+ne dianhydride (BTDA) in an aprotic solvent. The synthesized monomers showed crystalline melting at 269 and 271°C. Elemental analysis, differential thermal analysis (DTA), infrared (IR), nuclear magnetic resonance (1H‐NMR) and mass spectral studies were carried out to characterize the synthesized monomers. Thermogravimetric analysis (TGA) of the synthesized monomers showed their thermal stability at 410–400°C. A detailed study and NMR investigation of the first step of condensation reaction was carried out and indicated the formation of a transient charge transfer complex. Thermal cyclization of the formed intermediate, however, gave the required monomers. A preliminary study demonstrated that melt‐polymerization of the synthesized monomers gave thermallystable, tough polymers.