Dimensional properties of brush-like polymers with sodium Poly(styrene sulfonate) side chains

Abstract

Brush-like polymer samples consisting of sodium poly(styrene sulfonate) were obtained by sulfonating polymacromonomers consisting of polystyrene with 110 monomeric units on each side chain. By fractional precipitation of the sample, fractions with narrow molecular weight distributions were obtained. Light scattering measurements were made to determine the mean-square radius of gyration for each fraction in aqueous NaCl as a function of the weight-average molecular weight and the salt concentration. By analyzing the data using the theory for the wormlike chain model, the stiffness parameters λ−1 of the molecule were obtained. It was found that the dependence of λ−1 on the salt concentration was not as strong as that for linear sodium poly(styrene sulfonate). This was interpreted as the reflection of the shielded charge–charge interactions at the local ionic strength in the brush which is much higher than that of the outside solution. Salt concentration dependence of NaPSS polymacromonomer with 110 monomeric units on each side chain (unfilled circles) cannot be explained by the theory assuming the Debye–Hűckel (DH) potential under the ionic strength outside the brush (dotted line), but can be explained using the DH potential under the ionic strength inside the brush (dashed line) along with the interactions without ionic ones (dot-dashed line).