Star polyelectrolytes represent a class of branched polymers with potential in a range of applications including biomedical engineering, energy storage and drug delivery. In this work, we used fluorescence correlation spectroscopy (FCS) to study self-diffusion of linear (LPMAA) and 4-, 6- and 8-arm star poly(methacrylic acids) (4PMAA, 6PMAA and 8PMAA or sPMAA, respectively) of matched molecular weights in solutions at different pH, salt and polymer concentrations. In dilute solutions at high pHs, hydrodynamic radius (R_h) of star PMAA polymers was smaller than that of their linear counterpart, reflecting higher compactness of star molecules. In contrast, R_h of PMAA was independent of molecular architecture at low pHs where molecular conformations were affected by intermolecular hydrogen bonding. R_h of fully ionized 8PMAA was virtually independent of the nature of counterion while R_h of LPMAA decreased in the following series: Cs⁺<K⁺<Na⁺<Li⁺. ⁷Li NMR experiments revealed a 2–fold decrease in spin–lattice relaxation time of lithium ions in solutions of 8PMAA compared to LPMAA, suggesting lower ion mobility within star polymers. Measurements of polymer self-diffusion coefficient were performed in a wide range of PMAA concentrations in the low-salt and high-salt conditions and analyzed using the scaling theory of polyelectrolyte solutions. In low-salt solutions, two polymer concentration regimes were revealed. At lower polymer concentrations, the diffusion coefficient D was independent of polymer concentration c for both linear and star polyelectrolytes, as is characteristic of the unentangled Rouse-like polyelectrolyte dynamics. At high polymer concentration, D scaled with polymer concentration as D~c^y and the negative exponent y was smaller for sPMAA (-0.48 vs -0.37 for LPMAA and 8PMAA, respectively). This work provides insight into the behavior of star polyelectrolytes in solutions in a wide range of pH, salt and polymer concentrations.

Andrey Dobrynin

Univ of Connecticut

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