A series of block copolymers that contain rigid liquid crystal forming blocks of poly(p-phenylene terephthalamide) (PPTA) and flexible blocks of hexamethylene adipamide (PA 6,6) have been synthesized. The polymers have been prepared in a one-pot procedure by addition of PA 6,6 monomers to an amine-terminated PPTA oligomer via a low-temperature polycondensation reaction in N-methyl-2-pyrrolidone. Via this method block copolymers are formed that were characterized by inherent viscosity measurements, size exclusion chromatography ( SEC), NMR, Soxhlet extraction, and TGA. The molecular weights of the synthesized rod-coil block copolymer materials are estimated from their intrinsic viscosities by a semiempirical model that combines both the intrinsic viscosity relations of the homopolymers and the mean-square end-to-end distance of the rod-coil copolymer.