Studies on cellulose derivatives. Part IV. The configuration of the polyelectrolyte sodium carboxymethyl cellulose in aqueous sodium chloride solutions

Experimental data on the molecular weight and ionic strength dependences of molecular parameters of sodium carboxymethyl cellulose (NaCMC) are discussed and interpreted using current theories. Unperturbed dimensions of NaCMC have been calculated from viscosity‐molecular weight data using the STOCKMAYER‐FIXMAN theory. The KUHN equivalent chain segment length, A m , and the ratio ( R₀² / RF² )1/2 shows that NaCMC is a typical flexible polymer in the unperturbed state. At infinite ionic strength, NaCMC is a flexible, randomly coiling chain with dimensions appreciably exceeding those in the unperturbed state; this difference is attributed to solvation of the chain. The extension is, however, smaller than that for the non‐ionic derivative hydroxyethyl cellulose. At low ionic strength, the model approximated by the molecule is that of an extended coil; there is, however, still considerable hydrodynamic interaction between segments. Possible reasons are discussed for the difference between the magnitudes of the observed virial coefficients and those calculated using recent theories. The theories of polyelectrolyte expansion are found to be unsatisfactory in predicting the extension of NaCMC in solutions of different ionic strengths. With most of the relationships used, the difference between the observed and calculated expansions was equivalent to a binding of approximately two‐thirds of the counterions.