Lattice Formation of Peripherally Charged Star Polymers in Aqueous Solution

Functionalized poly(ethylene oxide) (PEO) stars (arm number f = 37−149) possessing peripheral tertiary amino groups were prepared by organized polymerization using macromonomers. Subsequently, positive charges were introduced into such peripheral tertiary amino groups by quaternization with methyl iodide. The structural ordering of these functionalized and peripherally charged stars was investigated through small-angle X-ray scattering in aqueous solution. PEO stars without charges (f > 72) formed a body-centered-cubic (bcc) structure near the overlap threshold (C*). On the other hand, peripherally charged PEO stars (f > 37) formed a lattice of bcc even below C*. The results indicate that ionization (electric double layer) of stars results in interparticle interactions giving rise to ordering. These interactions were screened by adding inorganic salt (KI).