✍ Scribed by Mikroyannidis, John A.
No coin nor oath required. For personal study only.
A novel class of fire‐ and heat‐resistant bisimide resins was prepared by thermal polymerization of maleimido or citraconimido derivatives of 1‐[(dialkoxyphosphinyl)methyl]‐2,4‐ and ‐2,6‐diaminobenzenes (1). The neat bisimide resin prepared by curing 1‐[di(2‐chloroethoxyphosphinyl)methyl]‐2,4‐ and ‐2,6‐bismaleimidobenzene exhibited a limiting oxygen index 75% higher and smoke evolution about 30 times lower compared with the parent polymer obtained by curing m‐phenylenebismaleimide. The char yield of cured bisimide resins at 700°C was 58–70% in a nitrogen atmosphere and 35–60% in air. An increase in formula weight between the imide groups slightly reduced the char yield. The polymer precursors were synthesized by reacting the phosphorus‐containing diamines (1) (1 mol) with maleic anhydride/citraconic anhydride (2 mol) or by reacting the monomaleimido derivative of (1) with benzophenone tetracarboxylic dianhydride/methylenebis(4‐phenylisocyanate) in a 2:1 mole ratio. The monomers were characterized by elemental analysis, Fourier‐transform–infrared (FT‐IR), proton nuclear magnetic resonance (^1^H‐NMR) spectroscopy, and gas chromatography–mass spectroscopy (GC‐MS). Direct cleavage of the PC bond and inversion of the synthesis reaction may occur during their pyrolysis. The thermal polymerization of the monomers was investigated by differential scanning calorimetry (DSC). Biscitraconimides are thermally polymerized at a relatively lower temperature than the corresponding bismaleimides.
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