Structure of polystyrene‐block‐poly(ethylene oxide) diblock copolymer micelles in water

Abstract

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.

Association Properties of a Diblock Copolymer of Ethylene Oxide and Styrene Oxide in Aqueous Solution Studied by Light Scattering and Rheometry

“…Unfortunately, values of the association number reported for micelles of St 10 E 68 in water at ambient range from 60 to over 400. [14,17,20] Very high values may derive from the presence of large particles, as frequently reported for samples of E/St block copolymers in dilute aqueous solution. [11,13,20] The lowest value [20] is from sedimentation velocity and so independent of a second population of particles.…”

“…The effect is disrupted by any factor which stabilises micelles at low temperature, whether thermodynamic (e. g. crystallisation of blocks in the micelle core) [51] or kinetic (glass formation in the core). [14,19,52] In the present case of E/S copolymers neither of these proven explanations obviously applies: the S block is atactic [24] so crystallisation is not a factor, while the glass transition temperature of high-molar-mass poly(styrene oxide) is only 40 8C [33] and will be lower for the short block lengths under consideration. We hope to investigate this absence of cold gelation in the E/S-water system in future work.…”

Micelle formation of poly(acrylic acid)-block-poly(methyl methacrylate) block copolymers in mixtures of water with organic solvents

“…The dissolution difficulties of many block copolymers are closely related to the observation that the exchange of single block copolymer chains between aggregates is sometimes very slow, in the range of h or days, or even beyond any detectability [8][9][10] . This observation is generally explained by the fact that the core forming block (in most of the cases polystyrene 1,[4][5][6][8][9][10][11] , but also PMMA 12,13) , poly(tert-butyl acrylate) 14) or poly(lactic acid) 15,16) ) is in the glassy state at room temperature. This means that there is not necessarily a thermodynamic but first of all a kinetic hindrance for chain exchange between these "glassy" or "frozen" micelles.…”

Supramolecular hydrogels instantaneously formed by inclusion complexation between amphiphilic oligomers and α-cyclodextrins

“…Meanwhile, for the oligomer, α-CD preferentially included CL units due to a greater inclusion affinity for more hydrophobic molecules, 35 so more EG units were remained as hydrophilic framework to form gel. The oligomers could form micelles in aqueous solution due to the amphiphilic property of diblock copolymers, 26,36,37 which can also play an important role in the instantaneous gelation of α-CD with the oligomer in aqueous solution. A cooperative effect of rapid complexation rate of α-CD with the oligomer due to the low-molecular-weight character, hydrophobic interactions between crystalline inclusion complexes, as well as the hydrophobic aggregation between the CL units can result in instantaneous gelation and formation of a stable supramolecular hydrogel.…”