Regular rigid-flexible copolymers composed of aramid segments and aliphatic chains formed of 5 to 10 CH, groups were synthesized using a two-stage procedure. A first stage consisted of synthesizing, under Yamasaki-Higashi phosphorylation conditions, poly(paraphenylene terephthalamide) blocks or macromonomers of different lengths by using an excess of phenylene diamine. These macromonomers, with functionalized amine extremities, were reacted in a second stage, using the Higashi phosphorylation conditions, with a terephthalic-acid end-capped aliphatic amine. Macromonomer molecular weights and polydispersities were estimated from viscosity and NMR measurements, whereas for block copolymers viscosity measurements and size exclusion chromatography of allylated derivatives were performed. Block polydispersity increased with increasing length of block, but remained below 1.6. Copolymers were found to have M-w values from 2500 to 8600 g mol(-1), depending on block length and aliphatic chain used. Polydispersity indices were systematically higher for block copolymers than for macromonomers, with values ranging from 1.6 to 4.7. M-v and M-w were found to be comparable for all copolyaramids, which indicates that addition of short aliphatic chains had a negligible effect on Mark-Houwink parameters. (C) 2004 Wiley Periodicals, Inc.