Double-hydrophilic poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA) self-assembled into nanostructures in basic solution upon the addition of alpha-cyclodextrin (alpha-CD) as a result of the complexation between alpha-CD and PEO. The nanostructures produced were spherical in shape as observed by transmission electron microscopy (TEM) and possessed radii that were much larger than that of a single stretched polymeric chain. The ratio of Rg/Rh (where Rg is the z-average radius of gyration and Rh is the hydrodynamic radius) obtained from laser light scattering (LLS) was approximately approximately 1.0, and the aggregation number was approximately 4100. The zeta-potential of complex particle was -45 mV, suggesting that the particle possessed a stable negatively charged surface, attributed to ionized PAA segments. The above results suggested that the nanostructures formed in the PEO-b-PAA/alpha-CD solution at high pH were likely to be spherical vesicles.

The interaction between CaCl 2 and double hydrophilic block copolymer, poly(ethylene oxide) 45- block-poly(acrylic acid) 70, PEO 45- b-PAA 70, was investigated. At a stoichiometric ratio of Ca2+:COO (-) = 0.5, Ca2+ ions were bound to COO (-) groups on PAA segments via electrostatic interaction. Small particles of 4-8 nm in diameter were observed, suggesting the formation of coil-like polymeric globule induced by charge neutralization. At Ca2+:COO (-) >or= 2.5, monodispersed aggregates of average hydrodynamic diameter of 52.0 +/- 7.4 nm were produced. The ISE, ITC, surface tension and fluorescence spectroscopic data confirmed that the formation of these aggregates is not the result of interaction between excess Ca2+ ions and the polymer, but rather it is due to changes in the water activity that triggers the structural rearrangement of Ca2+/PEO 45- b-PAA 70 complex.