The diffusion of polyelectrolytes in low-salt or salt-free aqueous solutions is a controversial question. It has been intensively discussed since it was discovered in 1978. Most previous experimental data were obtained from dynamic light scattering (DLS), whose precision, however, was reduced by stringent sample preparation and weak scattering of polyelectrolyte in low-salt solution. For the most commonly studied polyelectrolyte, poly(styrenesulfonate sodium salt) (NaPSS), the harsh polymerization condition and the manufacturing procedure lead to hydrophobic defects and aggregations, which also block a correct insight about the diffusion of polyelectrolyte. In contrast to DLS, fluorescence photobleaching recovery (FPR) directly looks on the optical trace of the self-diffusion of labeled molecule and is relatively insensitive to the thermodynamic interactions among the polymer. In this work, an efficient synthesis of fluorescein isothiocyanate (FITC) labeled poly(styrenesulfonate sodium salt) (NaPSS) under mild conditions is presented. This fluorescent polyelectrolyte, with 100% degree of sulfonation and no hydrophobic defects, was directly synthesized from monomer. The product was characterized by mass spectrometry, GPC/MALLS, 1H NMR, and fluorimetry. Twelve fractions with various molecular weights were obtained by injecting the sample solution into an analytical-scale GPC. The self-diffusion of some fractions was measured with FPR. The dependence of the diffusion coefficient on molecular weight is in agreement with the power-law. The partial specific volume of NaPSS in aqueous solution and salt solution were also determined by examining the densities of these solutions
