Synthesis of aromatic poly(urea-imide) with heterocyclic side-chain structure

The poly(urea-imide) copolymers with inherent viscosity of 0.81–1.08 dL/g were synthesized by reacting aryl ether diamine or its polyurea prepolymer with various diisocyanate-terminated polyimide prepolymers. The aryl ether diamine was obtained by first nucleophilic substitution of phenolphthalein with p-chloronitrobenzene in the presence of anhydrous potassium carbonate to form a dinitro aryl ether, and then further hydrogenated to diamine. The polyimide prepolymers were prepared by using 4,4′-diphenylmethane diisocyanate to react with pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, or 3,3′,4,4′-sulfonyldiphthalic anhydride by using the direct one-pot method to improve their solubility, but without sacrificing thermal property. These copolymers are amorphous and readily soluble in a wide range of organic solvents such as N-methyl-2-pyrrolidone, dimethylimidazole, N,N-dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, m-cresol, and sulfolane. All the poly(urea-imides) have glass transition temperatures in the range of 205–240°C and show a 10 wt % loss at 326–352°C in nitrogen and 324–350°C in air. The tensile strength, elongation at break, and initial modulus of these copolymer films range from 42 to 79 MPa, 5 to 16%, and 1.23 to 2.02 GPa, respectively.