Characterization of micelles of polyisobutylene-block-poly(methacrylic acid) in aqueous medium

Four amphiphilic block copolymers polyisobutylene-block-poly(methacrylic ac id) (IBm-MAA(n); m = 70-134, n = 52-228) were synthesized and transferred i nto aqueous medium at pH 10-12. Their structure in solution was characteriz ed by fluorescence correlation spectroscopy (FCS), static and dynamic Light scattering (SLS, DLS), analytical ultracentrifuge (AUC), and by transmissi on electron microscopy (TEM) with freeze-fracturing and staining techniques . DLS data, AUC sedimentation traces, and TEM images indicate at least two different kinds of particles. TEM shows spherical micelles; however, especi ally for polymers with larger hydrophobic blocks, additional particles are observed. FCS shows extremely low critical micelle concentrations (cmc < 0. 3 mg/L). The main part of the particles consists of micelles with diameters from 15 to 50 nm,built by 130-200 block copolymer molecules. Aggregation n umbers and diameters are consistent with a model recently proposed by Forst er et al. (J. Chem. Phys. 1996, 104, 9956-9970). The packing densities are determined from the hydrodynamic diameters and the aggregation numbers; the y vary between 6 and 32%. For large hydrophobic block lengths additional st ructures are found, in most cases with a narrow size distribution. The orig in of these structures is discussed.