Process for chain-extending unsaturated terminated polyimides and products prepared therefrom

Aromatic polyimides with reactive end groups are cured by coupling together by addition or condensation to increase molecular weight with little or no by-product formation. These polyimides can be shaped and formed prior to the coupling. The aromatic polyimides appropriate for coupling are formed by the reaction of an aromatic dianhydride and an aromatic diamine in ratios to provide the appropriate end groups, or by including in the reaction mixture a compound which will provide reactive end groups, e.g., aromatic nitrile, allyl, propargyl, styryl, etc. Depending on the reactive end groups present, coupling of the polyimide is carried out either by self-coupling or by reacting the polyimide with a complementary organic compound. Included in the latter is the reaction with an aromatic bis-dipole compound which will propagate the polymer chain.