Nine samples of a polymacromonomer consisting of sodium poly(styrene sulfonate) and having a side-chain polymerization degree of 15 are investigated by light scattering, small-angle X-ray scattering, and viscometry with 0.05 M aqueous NaCl at 25 degrees C as the solvent. The (total) weight-average molecular weight M-w ranges from 2.2 x 10(4) to 7.1 x 10(6). The radii of gyration, scattering functions, and intrinsic viscosities determined as functions of M-w are analyzed in terms of the cylindrical wormlike chain model. The estimated Kuhn segment length of about 120 nm is much larger than that (16 nm) for the polystyrene polymacromonomer with the equivalent side-chain length in toluene, a good solvent, while the chain thickness (5.5 nm) is comparable to or only slightly larger than that (5 nm) of the nonionic polymer. It is thus concluded that the electrostatic repulsion between side chains significantly stiffens the main chain of the polyelectrolyte brush. (C) 2008 Elsevier Ltd. All rights reserved.