The phase behavior of a low molecular weight (M W = 4000) diblock copolymer of polystyrene and poly(ethylene oxide), PS−PEO, in the bulk as well in aqueous, D2O, solutions has been studied using small-angle neutron-scattering, dynamic and static light-scattering, and rheological methods. At low temperature the pure block copolymer forms a lamellar mesophase driven by the crystallization of PEO. The melting point of PEO, T ≈ 64 °C, is correspondingly accompanied by an order-to-disorder transition. The melt is typified by single-exponential depolarized correlation functions in the dynamic light-scattering spectra, observed in the temperature range 60 to 100 °C. Neutron scattering fails to show concentration fluctuations in the amorphous, disordered phase due to lack of contrast. In aqueous solutions up to roughly 20% polymer concentration, PS−PEO self-associates into spherical micelles with a core size of R c ≈ 56 Å and an interaction radius R hs ≈ 115 Å, corresponding to an aggregation number of 470. The hydrodynamic radius R h = 140 Å obtained from dynamic light scattering is close to but somewhat larger than the interaction radius, as expected. Extended clusters, displaying a small but significant anisotropy, form at above C = 10% and coexist with the single spherical micelles. These clusters may be due to association of spherical micelles or micelles of different form attributed to residual aggregates of PS moities.

Micellization in water of two homologous series of AB-type diblock copolymers, composed of polystyrene (PS) as the A block and poly(ethy1ene oxide) (PEO) as the B block, were investigated by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). The copolymers have molecular weights &, in the range 2000-34800, and have in a given series, the same number of repeating units of the PS block, (Nps = 10 and 38), and a variable number of repeating units of the PEO block (NpEo values in the range 23-704).In order to avoid secondary association of micelles, a dialysis technique was used to prepare the micellar systems, in the case of copolymers having high I @ , , values of the PS block. The experimental micelle properties such as the core radius R, and the aggregation number N of non-equilibrium structures, so called "frozen micelles", obtained by dialysis, were found to be independent of the copolymer characteristics. However, for equilibrium structures, obtained by direct solubilization of the copolymers (Nps = 10) in water, R, and N were found to decrease with increasing NpEo for the homologous series.

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