Abstract: The present invention relates to solutions of polyamide-imides which can be spun and shaped, and to a process for their preparation.They contain 5 to 30% of a polyamide-imide in a solvent mixture comprising 40-80% by weight of butyrolactone and 20-60% of an aprotic amide solvent. They are obtained by the reaction, in butyrolactone as polycondensation solvent, of a diisocyanate, an aromatic acid anhydride, optionally an alkali or alkaline-earth metal dicarboxybenzenesulfonate, and optionally another aromatic diacid, the concentration of polyamide-imide being from 15 to 36%, followed by dilution in an amide solvent, at a temperature between 120.degree. and 165.degree. C.The solutions obtained are clear at room temperature, are storable, and possess improved color.

Abstract: The present invention relates to a novel chain extender for use in making moldings. The chain extender broadly comprises the reaction product of an aromatic diamine and a cyclic carboxylic acid anhydride.