Aggregates of isotactic poly(methacrylic acid) chains in aqueous CsCl solutions: A static and dynamic light scattering study

Abstract

Properties of isotactic polymethacrylic acid, iPMA, chains were studied at 25°C in aqueous solutions at various CsCl concentrations, c s (= 0.05-0.20 M), in dependence on degree of neutralization of the polyion's carboxyl groups, α N, using static, SLS, and dynamic light scattering, DLS, measurements. It was demonstrated that iPMA chains with α N somewhat above the solubility limit of iPMA in aqueous solutions (in the present case at α N ≈0.27) are strongly aggregated. The size of the aggregates increases with increasing c s, whereas the shape parameter, ρ, is approximately constant (ρ ≈0.6), irrespective of c s. The low ρ value suggests that the aggregates have characteristics of microgel particles with a dense core surrounded by a less dense corona. The diffusion of iPMA chains was investigated also at higher α N, up to α N = 1. The polyion slow mode arising from electrostatic interactions between charged chains was observed for α N exceeding the value 0.27 even at the highest c s (= 0.20 M). The diffusion coefficients for the show mode were nearly independent of α N and c s at the studied polymer concentration.