Micellization SEBS (original) (raw)
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Polymer, 1998
The micellization thermodynamics and micelle structural parameters for polystyrene-b-poly(ethylene/butylene)b-polystyrene copolymers (SEBS) in n-octane were studied. This solvent is selective for the middle poly(ethylene/butylene) block of the copolymer. The copolymer samples have similar chemical composition and different molar mass. Standard thermodynamic functions of micellization (ΔG°, ΔH° and ΔS°) were determined by light scattering. All the functions showed more negative values for the SEBS copolymer with a larger molar mass. The structural parameters of micelles formed by different triblock copolymers were determined from static light scattering and viscosity measurements. Micelle molar mass, association number and viscometric hydrodynamic radius increase with the length of the copolymer chain for a constant copolymer composition; however, the radius of gyration decreases. Finally, the results found for SEBS micelles in n-octane are compared to those found for SEBS micelles in 4-methyl-2-pentanone. The different behaviour found supports the idea that the micelles of a triblock copolymer in a selective so vent of the middle block will show a shell formed by loops of the middle block in order that the two outer blocks go into the micelle core and even some poorly solvated outer blocks could be extended out of the micelle.
Formation of block copolymer micelles in solutions of a linear homopolymer in a good solvent
Macromolecular Rapid Communications, 1995
The existence of micelles of polystyrene-block-poly(ethylene/propene) in solutions of polystyrene in toluene was investigated. Toluene is a good solvent of both copolymer blocks whereas polystyrene and poly(ethylene/propene) are immiscible polymers. The presence of homopolystyrene at high enough concentration can induce the micellization of polystyreneblock-poly(ethylene/propene) in solution of a good solvent such as toluene. The thermodynamics of this new micelle system at a given polystyrene concentration was studied. Light scattering measurements were carried out in order to determine the critical micelle temperature (CMT) of different micellar solutions. Standard Gibbs energy, enthalpy and entropy of micellization were estimated from CMT and concentration data. The numerical values found were less negative than those found for micelle systems consisting in a block copolymer dissolved in a single selective solvent.
Langmuir, 2006
A triblock copolymer of ethylene oxide and 1,2-butylene oxide, denoted B 10 E 410 B 10 , was prepared by sequential oxyanionic polymerization and characterized by 13 C NMR spectroscopy and gel permeation chromatography. Micellization and the formation of micelle clusters in dilute aqueous solution, the latter a consequence of micelle bridging, was confirmed by dynamic light scattering, and average association numbers of the micelles were determined by static light scattering for T) 20-40°C. The frequency dependence of the dynamic storage and loss moduli was investigated for solutions in the range of 5-20 wt %. Comparison with results for poly(oxyethylene) dialkyl ethers (10 wt %, T) 25°C) indicated that the viscoelasticity of a copolymer with terminal B 10 hydrophobic blocks was roughly equivalent to one with terminal C 14 alkyl chains. The temperature dependence of the modulus was investigated for 15 wt % solutions at T) 5-40°C. Superposition of the data led, via an Arrhenius plot, to an activation energy for the relaxation process of-40 kJ mol-1. The negative value contrasts with the positive values found for poly-(oxyethylene) dialkyl ethers and related HEUR copolymers with urethane-linked terminal alkyl chains. This difference is attributed to the block-length distribution in copolymer B 10 E 410 B 10 , whereby the activation energy of the relaxation process has a positive contribution from the disengagement of B blocks from micelles but a negative contribution from micellization. The negative value of the activation energy for solutions of B 10 E 410 B 10 was confirmed by determining the temperature dependence of the zero-shear viscosity of its 15 wt % solution.
Polymer, 1996
Solutions of polystyrene-b-poly(ethylene/propylene) block copolymer and homopolystyrene in toluene (a good solvent of both copolymer blocks) were studied by dynamic light scattering and viscometry. The presence of homopolystyrene in the solution induces the formation of micelles with a core which consists of poly(ethylene/propylene) blocks. The dynamic light scattering measurements showed that these micelles have a narrow size distribution. The influence of the polystyrene concentration on the structural parameters of the micelles was analysed. The hydrodynamic radius and molar mass remained constant in the polystyrene concentration range studied. However, the diffusion of the micelles was very influenced by the increment of the solution viscosity caused by the polystyrene chains.
Journal of Applied Polymer Science, 2010
The recent studies deal with a diblock copolymer, polystyrene-poly(ethylene oxide). Infrared spectroscopy, proton resonance spectroscopy (1 H-NMR), and laser light scattering techniques have been used to characterize the polymer. It has been concluded that the sample investigated is diblock copolymer polystyrene-poly(ethylene oxide) having molecular mass 1.656 Â 10 4 g/mol and blocks ratio 1 : 2. The micellization behavior is explored through 1 H-NMR, laser light scattering, light absorption, surface tension, and conductance and viscosity measurements. The results conclude that the critical micelles concentration of copolymer is 0.0951 g/dL at 25 C. It has been observed that the surface tension of solution decreases with the temperature and its impact is maxima in dilute concentration region. In addition, new methodologies have been introduced to get accurate critical micelles concentration and critical micelles temperature. V
Die Makromolekulare …, 1993
Solubilization of poly(isobutene) a) by micelles of polystyrene-block-poly(ethylene/propene) block copolymer with a copoly(ethylene/propene) core was investigated. The weight of poly(isobutene) solubilized was found to be proportional to the concentration of block copolymer in the solution. No influence of the presence of poly(isobutene) on the critical micelle temperatures has been found. However, the addition of poly(isobutene) to the micellar solution seems to favour the anomalous behaviour found in micellar solutions of the block copolymers used in this study.
Macromolecules, 1997
Introduction. The association behaviors of block copolymers in selective solvents have been extensively reported during the last few years. 1,2 It has been noted that the core-shell micellar structure is fairly common for closed association mechanisms. In an open association mechanism, more open and extended structures are sometimes formed at low polymer concentrations and the polymer solution becomes a gel-like network at high concentrations. The bridging function is achieved from an extended soluble middle block between the small clusters formed by the poorly solvated end blocks. Although the characterization of the micellar systems has become routine, the results from different research groups and through different physical techniques can sometimes be amazingly different. 1 This problem, combined with the limit in the number of available samples and the uncertainties among the samples (e.g., different polydispersities), makes it difficult for the readers to draw conclusive results, e.g., quantitative relations between micellization parameters and the block lengths of block copolymers. The most noticeable study in this area is on alkylpoly(oxyethylene) glycol ethers (C n E m ) in aqueous solution where the quantitative effects of chain lengths on cmc and thermodynamic parameters were systematically reported. 5,6 However, even for the polymers C n E m , which show very good chemical homogeneity and can be used as a standard model, there is no report on the relations between chain length and association number or micellar size. Yang et al. 7, made some valuable attempts on studying block poly(oxyalkylene)s (B n E m , B n E m B n , and E n B m E n , where B and E were oxybutylene and oxyethylene, respectively) in aqueous solution. However, due to the limited numbers (three B n E m B n samples with one being in the unimer state) of samples studied, they were not able to make quantitative conclusions. In spite of the shortage of experimental data, theoretical approaches on the relation between the block length and the micellar properties for diblock copolymer micelles have been developed and reviewed. 2 Here we present the linear relations between the micellar lengths and two important micellar parameters: the association number (n w ) and the hydrodynamic radius (R h ) in B n E m B n /water systems. (The data of B 7 E 22 B 7 and B 10 E
Diblock Copolymer Micelles in Solvent Binary Mixtures. 2. Selective Solvent/Good Solvent
Macromolecules
Solutions of polystyrene-b-poly(ethylene/propylene) block copolymer in mixtures of 4-methyl-2-pentanone (a selective solvent of the polystyrene block) and 2-chlorobutane (a good solvent of both copolymer blocks) were studied by static and dynamic light scattering and viscometry, Micelle structural parameters and micellization thermodynamics have been analyzed as a function of the solvent composition. The micelle molar mass decreased as the 2-chlorobutane percentage in the binary mixture increased. However the apparent radius of gyration, the second virial coefficient, and the hydrodynamic radius hardly showed variations. Static light scattering was used to establish the dependencies of the critical micelle temperature on concentration. The standard Gibbs energies, enthalpies, and entropies of micellization have been calculated for the different solvent mixtures from these relationships, The three thermodynamic magnitudes became less negative as the good solvent percentage increased.
Block Copolymer Micelles in Aqueous Media
Collection of Czechoslovak Chemical Communications, 1993
Micellization of di- and triblock copolymers, poly(methacrylic acid)-block-polystyrene and poly(methacrylic acid)-block-polystyrene-block-poly(methacrylic acid), varying in molecular weight and composition, has been studied by static and dynamic light scattering, and sedimentation velocity. Micelles with polystyrene cores were prepared in water-dioxane mixtures, rich in dioxane, and transferred into water-rich mixtures, water, and aqueous buffers via stepwise dialysis. It has been shown that, in dioxane-rich mixtures, the micellar system was in dynamic equilibrium, while in water-rich solvents, water, and aqueous buffers the micellization equilibrium was frozen and micelles behaved like autonomus particles. Under certain conditions, micelles were accompanied by independent large particles. This phenomenon, known from other micellar systems as an "anomalous micellization", is discussed.