Interaction of Cobalt bis(dicarbollide) Anion with Star-like Copolymers

The presented study is a part of project concerning the physical-chemical behavior of block copolymer complexes with sodium cobalt bis(dicarbolide) (COSAN) in aqueous solutions. COSAN gives many potential applications, mainly in medical field, as inhibitor of important enzymes. After discovering COSAN interacts with poly(ethylene oxide), poly(2-alkyl oxazoline) and poly(2-vinyl pyridine) blocks via specific interactions, many complexes of polymer-COSAN have been prepared. In this case we chose block copolymers with star-like architecture: 4-arm poly(ethylene oxide)-block-poly(2-methyl oxazoline), [PEO-PMOX]₄, in 0.154 M NaCl solution and miktoarm star-like polystyrene-block-poly(2-vinyl pyridine), PS₂₀-PVP₂₀, in 0.1 M HCl. We could observe differences between interaction of COSAN with linear and star-like polymers. It has impact on morphology of the hybrid nanoparticles. While homogeneous nanospheres were formed with linear PEO-PEOX, we detected multicompartment micelles by cryo-TEM in the case of [PEO-PMOX]₄/COSAN. As PVP block forms insoluble complex with COSAN, PS₂₀-PVP₂₀ micelles were destabilized at elevated concentration of added COSAN. Surprisingly, the micelles were stable in solution up to molar ratio of COSAN 0.1, even though linear PVP precipitated immediately with COSAN. The systems were studied by means of light scattering, NMR, AFM and cryo-TEM.