Takuhei Nose

Coexistence curves of polystyrene/ poly(dimethylsiloxane) blends

The coexistence curves of blends of polystyrene (PS, Mw = 600 and 2.2 × 103 g mol−1) and poly(dimethylsiloxane) (PDMS, Mw = 460, 1400, 3700 and 2.3 × 105 g mol−1) were determined using a specially designed refractometer. The coexistence curve of the oligomer blend PS (Mw = 600)/PDMS (Mw = 460) was of the upper critical solution temperature type, and sensitively reflected molecular-weight polydispersity of the PS, although the polydispersity index Mw/Mn was less than 1.10. The coexistence curve at the critical composition could be fitted to φ± = a ±eβ + b±eβ+Δ, where φ+ and φ− are the volume fractions of PDMS of the coexisting phases (φ+ > φ−), the exponent Δ is 0.5 and e is the reduced temperature. The critical exponent β was determined to be 0.336, which was that for non-renormalized Ising behaviour, showing no polydispersity effect. The Flory—Huggins theory could reasonably describe the coexistence curves of blends with different molecular weights, although it showed a slight discrepancy for the effects of molecular-weight asymmetry on the coexistence curve. By fitting the calculated coexistence curves to the experiments, the interaction parameter % was evaluated as a function of temperature. The obtained % parameter involved a large enthalpy term, dominating the entropy term, and indicated that PS/PDMS was an extremely immiscible blend compared with other reported blends. Critical fluctuation effects on the coexistence curve were also discussed.

Interfacial tension of demixed polymer solutions near the critical temperature: polystyrene + methylcyclohexane

Abstract Interfacial tension between demixed solutions of polystyrene + methylcyclohexane has been measured near the critical temperature as a function of temperature using polystyrenes with molecular weights 9000 ∼ 1.26 × 106. The critical exponent for the interfacial tension was determined to be about 1.30 for the lower molecular weight systems. However, for higher molecular weights the exponent could not be obtained because the system departed from critical behaviour. Magnitudes of the interfacial tension were proportional to about N−0.44, where N is the polymerization index. Experimental results were compared with the recently-proposed theories and found to be in qualitative agreement. The tricritical theory of polymer solutions was also compared with the experimental results.

Aggregation behavior of poly(N, N-diethylacrylamide) in aqueous solution

Aggregation behavior of poly(N,N-diethylacrylamide) (PDEA) in dilute aqueous solution has been studied by using the static and dynamic light scattering. It has been demonstrated that PDEA is not molecularly dissolved in water but forms molecular aggregates below the cloud point in one phase region. The association number of aggregates is of the order of 100, and the aggregate is suggested to be like a swollen micro-gel. The aggregation does not come from difficulty of dissolving a frozen structure in solid state, but the aggregates are also formed in solution starting from aggregation-free state by changing the solvent quality. The detailed aggregate size and structure depend on the dissolution process of the solid sample in making the solution. Once the aggregate is formed, it is stable, and does not change its association number and dimension for a long time. But, the association number may change with temperature and depends on thermal history.

Unimolecular-micelle formation of poly(methyl methacrylate)-graft-polystyrene in iso-amyl acetate

Abstract By means of light scattering, unimolecular-micelle formation is investigated for poly(methyl methacrylate)- graft-poly(styrene)s with different graft-chain densities in a dilute solution of a selective solvent. Molecular weights of the poly(methyl methacrylate) (PMMA) backbone and the branch poly(styrene) (PS) are about 6 × 106 and 9 × 103, respectively, and the graft-chain density is relatively low, ranging from 6 to 17 of PS composition in wt%. The solvent used is iso-amyl acetate, which is a thermodynamically good solvent for PS and a poor solvent (θ-temperature: 60°C) for PMMA. Radius of gyration, hydrodynamic radius, and the second virial coefficient are measured as a function of temperature ranging from 10 to 70°C. At a branch PS composition of 6 wt%, with decreasing temperature, the copolymer chain shrinks in the same manner as the PMMA chain with no PS branches, although the θ-temperature decreases by about 25°C. This indicates that no particular order structure is formed. At higher branch densities, rod-like unimicelles are strongly suggested to be formed by intramolecular segregation between the PMMA backbone and PS branches, with the shrunken PMMA backbone forming the core rod covered with PS chains. With decreasing temperature, the dimension of the unimolecular micelle decreases probably due to decreasing contour length of the micelle core.

Association and physical gelation of ABA triblock copolymer in selective solvent

Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMA – Pt BuA – PMMA) in 1-butanol (Pt BuA selective solvent) indicated that PMMA– Pt BuA – PMMA chains are molecularly dissolved above 50 8C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and Pt BuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9– 12.0 wt%) revealed that the system was viscous sol state at 60 8C. Drastic increase of shear storage modulus ðG 0 Þ occurred with decreasing temperature, and at 25 8C, G 0 showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G 0 indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging Pt BuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time – temperature superposition along the frequency axis. Just above sol –gel transition concentration ðCgelÞ; the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging Pt BuA chain above Cgel: q 2003 Elsevier Ltd. All rights reserved.

Phase behaviour of rod with flexible side chains/coil/solvent systems: poly(α,l-glutamate) with tri(ethylene glycol) side chains, poly(ethylene glycol), and dimethylformamide

Abstract Phase behaviour is investigated for ternary solutions composed of rodlike α-helical poly(α, l -glutamate) having triethylene glycol monomethyl ether at the end of the side chains (P3EGLG), randomly-coiled poly(ethylene glycol), and N , N -dimethylformamide (DMF) as solvent. The solution containing lower molecular weight poly(ethylene glycol) (PEG10) separates into an isotropic phase, which is rich in PEG10, and an anisotropic (cholesteric) phase, which is rich in P3EGLG, when the total polymer volume fraction is higher than ca 0.13. The homogeneous anisotropic region, in which a detectable amount of PEG10 exists, is recognized along the P3EGLG-DMF axis in the triangle phase diagram. When the molecular weight of poly(ethylene glycol) is larger, additional phase-separation regions are observed: That is, isotropic-isotropic biphasic region and anisotropic-isotropic-isotropic triphasic region. Theoretical treatments based on the lattice model for nematic solutions are conducted for these rod/coil/solvent ternary systems. Calculated phase diagrams with considering flexible side chains of rodlike solute and isotropic interaction parameters are found to qualitatively reproduce the variation of the experimental phase behaviour with the change of the molecular weight of the coiled component.

Critical amplitudes and their relations in a polymer solution: Polystyrene+methylcyclohexane system

Isothermal osmotic compressibility χ and correlation length ξ near the critical temperature in a polymer solution of polystyrene–methycyclohexane for Mw=9000∼1.26×106 were measured along the critical isochore by laser light scattering. χ and ξ were proportional to M0.48±0.03 and M0.28±0.03, respectively in the region Mw≥5.0×104. The universal ratios of the critical amplitudes were investigated. One of them was almost independent of molecular weight. The scaling laws of the molecular weight dependence of the critical amplitudes proposed previously were examined and were supported by the experiments.

Comicellization of binary mixtures of block copolymers with different block lengths in a selective solvent

Abstract Comicellizations of poly(α-methylstyrene)- block -poly( p -vinylphenethyl alcohol)s (KT-326 and KT-327) with slightly different block lengths in benzyl alcohol are investigated by means of static and dynamic light scattering. The critical micellization temperature ( T 1 ) of KT-326 is lower than that ( T 2 ) of KT-327. The apparent molecular weight, radius of gyration and hydrodynamic radius have been measured for micellar solutions with different KT-326/KT-327 compositions after single-step and double-step temperature jumps ( T -jumps) from the unimer region. The following conclusions were deduced. In a single-step T -jump from unimer region I ( T > T 2 ) to region III ( T T 1 ), where both copolymers form micelles in their respective pure solutions, comicellization takes place to form micelles having a copolymer composition close to the composition of the solution. In a jump from region I to region II ( T 1 T T 2 ), where only KT-327 can form micelles in its pure solution, some fraction of KT-326 is incorporated with KT-327 to form comicelles, but the extent of the incorporation is limited even in a solution with a high KT-326 content. In a double-step T -jump from region I to region II, and subsequently to region III after the second jump, some fraction of KT-326 forms comicelles with existing micelles formed in the first jump, while another fraction of KT-326 forms micelles of pure KT-326.

Temperature-concentration diagram of polystyrene-block-polydimethylsiloxane associates formed in dilute solution of selective solvent

Abstract Association behaviour of polystyrene-block-polydimethylsiloxane (PS-block-PDMS) in dilute solution of selective solvent is investigated by static and dynamic light-scattering as a function of temperature and concentration. Number-average molecular weights of PS and PDMS blocks are 7.8 × 103 g mol−1 and 3.2 × 103 g mol−1, respectively, and the solvent is a mixture of n-octane (C8) and methylcyclohexane (MCH) with the compositions of C8/MCH = 1.23 by weight, which is selective for PDMS. On heating the solutions from 12°C to 72°C, three different micellar regions are observed over a concentration range of 10−4–10−2 g (g of solution)−1. The highest temperature region right below the unimer region is the so-called anomalous-micellization region, where large spherical particles are formed and grow, and eventually precipitate in a few days. In the second region at intermediate temperatures, hollow spherical micelles (vesicles) are formed with large association numbers of about 103. The third region is located at low temperatures and low polymer concentrations, where hollow cylindrical micelles with the estimated length/diameter ratio of less than 16 are formed. These hollow cylindrical micelles are observed on heating only, but not on cooling from the unimer region, so they are presumed not to be in equilibrium state but to be meta-stable micelles formed on micellization processes.

Micellization behavior of diblock copolymers in solution near the critical micelle temperature

Abstract Micellization behavior near the critical micelle temperature (c.m.t.) has been studied for polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) in a mixed solvent of 1,2-dichlorobenzene/benzyl alcohol, which forms micelles with PDMS as cores. Static and dynamic light scattering experiments have demonstrated the following behaviors. The dilute solution (c≅0.1–4 wt %) shows three different characteristic behaviors depending on the copolymer concentration c. In the concentrated region, the temperature dependence of scattered-light intensity exhibits a large peak just below c.m.t., which is similar to the anomalous micellization. Detailed light scattering studies have revealed the following: in this concentration region, compact micelles are formed at low temperatures and as the temperature is increased, the micelles change into expanded swollen micelles discontinuously at a certain temperature. This change occurs rather reversibly, and may be explained by a strong condensation of the core due to the decrease in solvent quality with decreasing temperature. This can be a mechanism of the anomalous micellization.