Nylon-6-b-polyimide-b-nylon-6 copolymers were prepared by first synthesizing a series of imide oligomers end-capped with phenyl 4-aminobenzoate. The oligomers were then used to activate the anionic polymerization of molten epsilon -caprolactam. In the block copolymer syntheses, the phenyl eater groups reacted quickly with caprolactam anions at 120 degreesC to generate N-acyllactam moieties, which activated the anionic polymerization. In essence, nylon-6 chains grew from the oligomer chain ends. All of the block copolymers had higher moduli and tensile strengths than those of nylon-g. However, their elongations at break were much lower. The thermal stability, chemical resistance, moisture resistance, and impact strength were dramatically increased by the incorporation of only 5 wt % polyimide in the block copolymers.