Abstract: Novel aromatic crystalline polimides are disclosed that are synthesized from polyamide-acid and when heated to 200.degree. to 300.degree. C. become cyclized to afford an opaque polymer which by X-ray diffraction of the unoriented film exhibited 47 percent crystallinity. Differential Scanning Calorimetry (DSC) indicates a melt at 425.degree. C. with no glass transition in these crystalline polyimides.

Abstract: A method of producing poly-p-phenyleneterephthalamide or its copolymers residing in that p-phenylenediamine or p-phenylenediamine and an aromatic diamine of the diphenyl series is/are disclosed in amide-salt solvents consisting of linear or cyclic N-alkyl-substituted amides of acids and of salts of alkaline or alkaline-earth metals soluble in said amides in amounts of 1-3 moles per mole of diamines; terephthalic acid dichloride or a mixture of terephthalic acid dichloride and aromatic acid dichloride of the diphenyl series are introduced into the solutions obtained at 0.degree.-20.degree. C. in amounts equimolar to those of the diamines, a reaction mixture being thus formed; tertiary amines are introduced into said reaction mixture in amounts 2-6 moles per mole of the initial diamines; the reaction mixture is stirred for 3-70 minutes and the end product is separated from the mass obtained.