Diblock copolymers consisting of poly(hexano-6-lactam) hard blocks and highly N-methylated (or N-ethylated) softer blocks of poly(dodecano-12-lactam) or poly(octano-8-lactam) were prepared by anionic polymerization of hexano-6-lactam initiated with diacylamine branching sites of multifunctional precursors of polymeric initiators (PPI). The PPI were prepared by the acidolytic copolymerization of the respective N-alkylactams (greater than or equal to 90 mol %), N-benzoyllactams (less than or equal to 5 mol %) and lactams (less than or equal to 5 mol %). The method provides diblocks accompanied by small amounts of the homopolymers. The PPI and block copolymers were characterized by H-1 NMR, imide and carboxyl group analysis, viscosity, SEC, DSC, mechanical properties and water sorption. (C) 2000 Elsevier Science Ltd. All rights reserved.