Description:
<jats:title>Abstract</jats:title><jats:p>The determination of single‐chain properties for heterogeneous molecules such as a rigid‐flexible block copolymer requires the use of solvents capable of reducing selective interactions involving the blocks and the diluent. Molecular dispersion is displayed by a two‐block copolymer of benzoyl‐terminated poly(<jats:italic>p</jats:italic>‐benzamide) (poly(imino‐1,4‐phenyl‐enecarbonyl) and anilino‐terminated poly(<jats:italic>m</jats:italic>‐phenyleneisophthalamide) in 96 wt.‐% sulfuric acid. For a series of such copolymers, intrinsic viscosities were measured avoiding degradation effects due to H<jats:sub>2</jats:sub>SO<jats:sub>4</jats:sub>. The intrinsic viscosity ([η]) of the copolymers was found to decrease with increasing length of the flexible block, but [η] remained larger than the value corresponding to an equimolar blend of rigid and flexible homopolymers. These results are explained by theoretical considerations within the framework of the hydrodynamic behavior of single rodlike and single coiled macromolecules.</jats:p>