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

Abstract

Dynamic behavior of isotactic polymethacrylic acid, iPMA, chains was studied by static, SLS, and dynamic light scattering, DLS, at 25°C in aqueous solutions with added CsCl at various concentrations, cs (= 0.05-0.20 M), and in dependence on degree of neutralization of the polyion’s carboxyl groups, αN. DLS data were analyzed together with those obtained from SLS. It was demonstrated that iPMA chains with αN = 0.27 (somewhat above the solubility limit of iPMA in aqueous solutions) are strongly aggregated. The size of the aggregates increases with increasing cs, whereas the shape parameter, r, is approximately constant (r » 0.64), irrespective of cs. The low r value together with the measured scattering functions suggests that aggregates have characteristics of microgel particles with a dense core surrounded by a less dense corona. The diffusion of iPMA was investigated also at higher αN, up to αN = 1. The polyion slow mode arising from electrostatic interactions between charged chains was observed for all αN > 0.27 even at the highest cs (= 0.20 M). The diffusion coefficients for the show mode were nearly independent of αN and cs at the studied polymer concentration.

Keywords

• isotactic poly(methacrylic acid)
• light scattering
• hydrodynamic radius
• shape parameter
• aggregation
• polyelectrolyte slow mode