High T_g and Thermo-Oxidatively Stable Thermosetting Polyimides Derived from a Carborane-Containing Diamine

To provide high-temperature polyimide matrix resins, novel carborane-containing thermosetting polyimides are presented. First, the low-viscosity carborane-containing imide oligomers are synthesized using newly designed 1-(3-amino-4-tolyl)-2-(4-aminophenyl)-o-carborane and aromatic dianhydride as monomers, 4-phenylethynyl phthalic anhydride as the end-capping reagent. Followed by thermal curing, the resulting polyimides show high T_g (≥500 °C) and above 92.1% char yield at 800 °C both in nitrogen and air atmosphere due to the incorporation of the bulky carborane cages. Aging studies, performed at 400 and 500 °C for 5 h in air on a carborane-containing polyimide and a carborane-free polyimide, show that the polyimide with carborane groups possesses excellent thermo-oxidative stability. Moreover, the novel polyimides exhibit constant and relatively low coefficient of thermal expansion values over a wide range of temperature, indicative of a remarkable dimensional stability. Thus, this study clearly demonstrates the viability of the incorporation of carborane cages to access polyimide thermosets with ultrahigh T_g and thermo-oxidative stability.