Role of alkyl chain length and mole concentration of hydrophobic moiety in association behavior of amphiphilic polyelectrolytes in aqueous media

We have studied how the hydrophobic character of amphiphilic polyelectrolytes influences their behavior in aqueous media. Specifically, we examined the association behaviors in aqueous media of poly(methacrylic acid) (PMAAc) and poly(methacrylic acid-co-n-alkyl methacrylate) with varying the alkyl chain length (12 and 18) and the mole percentage of the hydrophobic moiety (0–30 mol.%) in the polymer, and compared the microscopic and macroscopic behaviors of these polymers in deionized water and phosphate buffered saline (PBS) solutions (pH 3–7.4). Fluorescence studies showed that the amount of hydrophobic domain in the polymer aqueous solution increases as the mole concentration of the hydrophobic moiety in the polymer is increased, and that a long alkyl chain (C18) has a higher hydrophobicity than a short alkyl chain (C12). In measurements of the particle sizes in the aqueous polymer dispersions using photocorrelation spectroscopy (PCS), the results showed that the formation of nanoparticles, the size and pH-sensitivity of nanoparticles depend on the mole concentration and alkyl chain length of the alkyl methacrylate moiety.