Concentration Dependence of Loop Fraction in Styrene−Isoprene−Styrene Triblock Copolymer Solutions and Corresponding Changes in Equilibrium Elasticity

Watanabe, Hiroshi; Sato, Toru; Osaki, Kunihiro

doi:10.1021/ma991979f

Cited by 75 publications

(140 citation statements)

References 17 publications

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“…A challenge to this loop/bridge problem was made with the aid of the dielectric data measured for the copolymers having barely entangled PI blocks with onceinverted type-A dipoles. 96,97 Those data, detecting the fluctuation of the midpoint of the PI blocks, were found to be similar to the data of PS-PI diblock copolymers detecting the free end fluctuation of the tail-type PI blocks therein. A thermodynamic consideration for this similarity gave an estimate, b ¼ $ 0:4 in bulk 97 and concentrated solutions in a PI-selective solvent (copolymer concentration c ¼ 50 wt %), 96 which agrees well with the self-consistent field calculation.…”

Section: Discussionsupporting

confidence: 71%

“…96,97 Those data, detecting the fluctuation of the midpoint of the PI blocks, were found to be similar to the data of PS-PI diblock copolymers detecting the free end fluctuation of the tail-type PI blocks therein. A thermodynamic consideration for this similarity gave an estimate, b ¼ $ 0:4 in bulk 97 and concentrated solutions in a PI-selective solvent (copolymer concentration c ¼ 50 wt %), 96 which agrees well with the self-consistent field calculation. 105 On dilution of the copolymer to c ¼ 20 wt % (a little above the syneresis point), b decreased to ¼ $ 0:2 because of the stretching/destabilization of the bridge conformation.…”

Section: Discussionsupporting

confidence: 71%

“…The usefulness of this combination has been noted also for a variety of multicomponent systems containing PI. 68,[96][97][98][99][100][101][102][103][104] For example, for miscible blends of PI with poly(p-tert-butyl styrene) having no type-A dipole, the PI dynamics was observed dielectrically thereby enabling us to examine the effect of dynamic heterogeneity on the global chain dynamics. [100][101][102] Another example is found for microphase-separated PS-PI-PS triblock copolymers composed of PI and polystyrene (PS) blocks.…”

Section: Discussionmentioning

confidence: 99%

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Slow Dynamics in Homopolymer Liquids

Watanabe

2009

Polym. J.

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139

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Dynamic physical properties of homopolymer liquids relax through global motion of the polymer chains over their dimension. This motion is affected by a variety of factors. For high molecular weight (M) chains, the entanglement retards the global motion to affect the properties. This entanglement effect changes with the chain architecture as well as the molecular weight distribution. The effect of the chain architecture on the global chain dynamics is found also for non-entangled low-M chains as well. This article gives a very brief summary of the experimental facts and molecular interpretations for these effects.KEY WORDS: Homopolymer Liquid / Relaxation / Slow Dynamics / Entanglement / Viscoelastic Property / Dielectric Property / Type-A Dipole / Needless to say, flexible polymer chains are composed of monomeric units covalently connected in a thread-like structure. In a local length scale, they have their own chemical functionalities such as the polorizability and electron susceptibility to exhibit intrinsic spectroscopic properties, for example, optical and electronic properties. In this sense, chemically different polymers cannot be regarded as the same class of materials. At the same time, however, the threadlike structure of polymer chains allows such chemically different chains to exhibit some universal properties. For example, flexible linear polymer melts exhibit the universal power law dependence of the zero-shear viscosity 0 on the molecular weight M, 0 / M with ¼ $ 1 and ¼ $ 3:5 in low-and high-M regimes, respectively.1 This dependence and related slow viscoelastic relaxation of polymer melts are believed to result from the fundamental thread-like structure of polymer chains irrespective of their chemical details. Scientifically, it is very interesting to explore a relationship(s) between such universal behavior of flexible polymer chains and their slow dynamics and further examine the factors that affect the slow dynamics and properties.This article follows the above viewpoint to give a very brief review of slow viscoelastic and dielectric relaxation behavior of homopolymer liquids. We place our main focus on homopolymer systems where the entanglement resulting from mutual uncrossability of real polymer chains plays the essential role. The entanglement, often modeled as mutual winding/hooking of threads, is equivalent to a topological constraint for thermal motion of the polymer chains that changes its magnitude according to the time and length scales. The linear and nonlinear viscoelastic behavior and related dielectric behavior of homopolymer melts/solutions are summarized on the basis of this molecular understanding. BASICS Molecular Expression of Viscoelastic Relaxation FunctionFor a series of chemically identical linear polymer melts having different molecular weights M, Figure 1 schematically shows the relaxation behavior of shear stress ðtÞ under a small step shear strain :1 The relaxation modulus, GðtÞ ðtÞ=, is double-logarithmically plotted against the time t after imposition of strain. The...

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Section: Discussionsupporting

confidence: 71%

Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

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Slow Dynamics in Homopolymer Liquids

Watanabe

2009

Polym. J.

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139

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“…1(b)], the bridging chains produce an association, which can lead to phase-separated solutions at low polymer contents 2,4 and physical networks at high polymer contents. [5][6][7][8][9][10][11][12][13][14] Watanabe and coworkers 9,10 conducted extensive investigations of styrene-isoprene-styrene (SIS) triblocks in the midblock-selective solvent tetradecane at various polymer concentrations. The fraction of bridges was directly determined by an elegant dielectric technique and was shown to decrease as the triblock was diluted.…”

Section: Introductionmentioning

confidence: 99%

Phase behavior and viscoelastic properties of entangled block copolymer gels

Vega

Sebastian

Loo

et al. 2001

J Polym Sci B Polym Phys

131

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Triblock copolymers in midblock-selective solvents can form physical gels. However, at low triblock contents (near the percolation threshold), the bridging of chains between micelles can lead to macrophase separation. Adding a styrene-isoprene diblock to a styrene-isoprene-styrene triblock copolymer in squalane can eliminate macrophase separation, yielding a wide range of stable, single-phase gels with a disordered arrangement of micelles. The plateau modulus of these triblock gels scales with the 2.2 power of polymer content, indicating the importance of entanglements in dictating the modulus. Comparing gels made from the midblock-saturated derivative of the same polymer [styrene-(ethylene-alt-propylene)-styrene] in squalane reveals that the modulus differences in the gels are a direct consequence of the difference in the entanglement molecular weight of the midblock homopolymer in bulk. Finally, the broad relaxation spectrum of these triblocks is well-described by a recent theory for the dynamics of entangled star polymers, with the breadth of the relaxation spectrum dictated by the number of entanglements per midblock in the gel.

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“…This scatter suggests that the bcc lattice cell is not the independent entropic unit sustaining the lattice elasticity. This point can be most clearly noted for the two pip-circles indicating the G e data for the 16 ). If the bcc lattice cell is the independent entropic unit, each cell should sustain the modulus of the order of k B T and thus G e =k B T should be close to the number density of the cell, D À3 .…”

Section: Structural Factors Determining Equilibrium Modulusmentioning

confidence: 67%

Further Investigation of Equilibrium Modulus of Diblock Copolymer Micellar Lattice

Tan

Watanabe

2004

Polym J

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ABSTRACT:Polystyrene-polybutadiene (PS-SB) and polystyrene-polyisoprene (PS-PI) diblock copolymers form spherical micelles with PS cores and PB/PI corona in a PB/PI-selective solvent, n-tetradecae (C14). At high concentrations, the micelles are further arranged on bcc lattices. Structural factors governing the equilibrium modulus G e of these PS-PB and PS-PI micellar lattices are discussed in this study. It turned out that G e is primarily determined by the number density of the corona blocks corona and proportional to corona while the number density of the bcc lattice cell, D À3 with D being the lattice spacing (determined from SAXS), has only secondary effects on G e . The proportionality between G e and corona reflects the thermodynamic origin of the lattice elasticity, the entropic elasticity of the corona PB/PI blocks having osmotically correlated conformations. These results suggest a necessity of re-examination of a previous hypothesis that the cell number density primarily determines G e of bulk copolymer systems forming cubic phases [Kossuth et al., J. Rheol., 43, 167 (1999)]. Furthermore, the G e = corona ratio was found to be moderately different for the PS-PB/C14 and PS-PI/C14 micellar lattices. This difference can be related to a difference in the magnitude of the osmotic correlation for the PB and PI corona blocks due to a slight difference of their solubilities in C14. [DOI 10.1295/polymj.36.430] KEY WORDS Diblock Copolymer Micellar Lattice / Equilibrium Modulus / Osmotic Requirement / Lattice Stability / Diblock copolymers form micelles with precipitated cores and solvated corona in selective solvents. These micelles form cubic lattices at high concentrations where the corona blocks of neighboring micelles are overlapping each other. [1][2][3][4][5][6] This lattice formation results from a compromise of contradicting thermodynamic requirements, an elastic requirement of randomizing corona conformation and an osmotic requirement of reducing the spatial gradient of the corona concentration.1,4-6 Under these requirements, the corona blocks of neighboring micelles are forced to have mutually correlated conformations. The micelles are arranged on cubic lattices so as to satisfy the thermodynamic requirements and minimize this correlation.The micellar lattice is the thermodynamically stable structure and exhibits equilibrium elasticity.1-6 For polystyrene-polybutadiene (PS-PB) copolymers in a PB-selective solvent, n-tetradecane (C14), the equilibrium modulus G e was found to be proportional to the number density corona of the corona PB blocks and the proportionality constant (G e = corona ratio) was smaller than the constant k B T expected for the simplest case of the entropic elasticity of independent corona blocks (k B = Boltzmann constant and T = absolute temperature). [4][5][6] This proportionality reflects the thermodynamic origin of the lattice. Namely, the osmotically correlated corona blocks sustain the lattice and thus their number density is the primary factor determining G e . At the same ...

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Concentration Dependence of Loop Fraction in Styrene−Isoprene−Styrene Triblock Copolymer Solutions and Corresponding Changes in Equilibrium Elasticity

Cited by 75 publications

References 17 publications

Slow Dynamics in Homopolymer Liquids

Slow Dynamics in Homopolymer Liquids

Phase behavior and viscoelastic properties of entangled block copolymer gels

Further Investigation of Equilibrium Modulus of Diblock Copolymer Micellar Lattice

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