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 cs at the studied polymer concentration.
Highlights
Intermolecular association and aggregate formation are important in nature and technology
Very stable inter-polymer complexes are formed when a cationic and an anionic polyelectrolyte are mixed in solution; this is a result of strong electrostatic attraction between the oppositely charged polyions and of the concomitant entropy increase due to the release of their counterions into the solution
We focus on intermolecular association between the isotactic poly(methacrylic acid), iPMA, chains in aqueous solutions. iPMA is a highly regu
Summary
Intermolecular association and aggregate formation are important in nature and technology. Hydrogen bonding is a major driving force for complexation of poly(carboxylic acids).[2,3,4,5] a single H-bond can be rather weak (with an energy 2–167 kJ/mol),[6] simultaneous formation of a large number of such bonds between two macromolecules (a cooperative phenomenon) may lead to very strong association In this contribution, we focus on intermolecular association between the isotactic poly(methacrylic acid), iPMA, chains in aqueous solutions. It was shown that Li+ and Na+ ions better support interchain aggregation than do Cs+ ones.[16] That study[16] was performed at a single salt concentration, i.e. in 0.1 M CsCl, NaCl, and LiCl. In the present investigation we want to further explore the effect of decreasing/increasing the concentration of CsCl, cS, on intermolecular association and slow mode phenomenon in iPMA solutions
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