  We report chain self-diffusion and viscosity data for sodium polystyrene
sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed
field gradient NMR and rotational rheometry respectively. The observed
concentration dependence of $\eta$ and $D$ are consistent with the Rouse-Zimm
scaling model with a concentration dependent monomeric friction coefficient.
The concentration dependence of the monomeric friction coefficient exceeds that
expected from free-volume models of diffusion, and its origin remains unclear.
Correlation blobs and dilute chains with equivalent end-to-end distances
exhibit nearly equal friction coefficients, in agreement with scaling. The
viscosity and diffusion data are combined using the Rouse model to calculate
the chain dimensions of NaPSS in salt-free solution, these agree quantitatively
with SANS measurements.
