Thermally polymerizable bisaryloxy-bisimido-bisphthalonitriles containing dimethylsilane, hexafluoroisopropylidene, ether, and keto groups: Synthesis, characterization, and NMR study

A proton‐NMR study of the condensation reaction (step 1) of 4‐(3′‐aminophenoxy)phthalonitrile (4‐3′APPN) (I) in an aprotic solvent with various aromatic dianhydrides demonstrated the formation of the corresponding bisamic acid within 5–10 min. There was no effect of the electron affinity of the used aromatic dianhydrides on the time of the condensation reaction and also no charge‐transfer complex formation was indicated. Proton‐NMR study of the synthesized bisaryloxy‐bisimido‐bisphthalonitriles at 250.1 MHz has revealed general findings for their NMR characterization. The coupling constant (J) value for the ortho‐coupled protons of the phthalonitrile ring of the 4–3′‐APPN portion is 8.8 ± 0.05 Hz and that for the ortho‐coupled protons of the aminophenoxy ring of 4–3′‐APPN is 8.1 ± 0.05 Hz. The coupling constant (J) values for ortho‐coupled protons of the dianhydride portion range from 8.1 to 7.5 Hz. Various thermally polymerizable bisaryloxybisimido‐bisphthalonitriles (BBBP) (X, XI, XII, and XIII) containing dimethylsilane, hexafluoroisopropylidene, ether, and keto groups, suitable for the development of thermooxidative stable, void‐free composites, were synthesized by two methods. In method 1,4–3′‐APPN (I) in N,N‐dimethylacetamide (DMAC) was condensed (step 1) with bis(3,4‐dicarboxyphenyl)dimethylsilane dianhydride (SIDA) (II), 4, 4′‐hexafluoroisopropylidenediphthalic anhydride (6FDA) (III), bis(3,4‐dicarboxyphenyl)ether dianhydride (ODPA) (IV), and 3,4,3′,4′‐benzophenonetetracarboxylic dianhydride (BTDA) (V), respectively, to give the corresponding bisamic acids. Thermal cyclodehydration of the intermediate bisamic acid at 160°C gave the bisphthalonitriles. In method 2, the second step of thermal cyclodehydration was performed in situ in refluxing toluene. The characterization of the synthesized bisaryloxy‐bisimido‐bisphthalonitriles (BBBP) was performed using FT‐IR, 1H‐NMR, 13C‐NMR, mass spectroscopy, and elemental analysis. A preliminary study indicated that thermal‐polymerization of these bisphthalonitriles (BBBP) gave tough, thermosetting polymers, useful for high‐temperature applications. © 1993 John Wiley & Sons, Inc.