New heat‐resistant polymers derived from azomethine bismaleimides and maleimide‐terminated azomethine prepolymers

A novel class of bismaleimides containing azomethine linkages was synthesized by reacting the monomaleamic acid derived from an aromatic diamine with terephthaldehyde (TPA) in a molar ratio 2 : 1 and subsequent cyclodehydration. In addition, a series of maleimide‐terminated azomethine prepolymers (MTAPs) was synthesized. More particularly, 4,4′‐diaminodiphenylsulfone (DDS) reacted with TPA in nonstoichiometric molar quantities (2 : 1 or 5 : 4 or 8 : 7) to prepare amine‐terminated azomethine prepolymers (ATAPs). The latter reacted with maleic anhydride and then cyclodehydrated. Furthermore, a maleimide‐crosslinkable azomethine prepolymer (MCAP) was synthesized by reacting tris(3‐aminophenyl)phosphine oxide with an equimolar amount of maleic anhydride and subsequently with TPA. The polymer precursors were characterized by IR, 1H‐NMR, DTA, and inherent viscosity. The thermal stability of the cured resins was evaluated by TGA and IGA. The thermal properties of the cured resins derived from the MTAPs were compared with those of the ordinary polyazomethine prepared from the reaction of DDS with TPA. It was shown that crosslinking of these polymer precursors during their curing was attained both via the maleimide and azomethine double bonds.