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Phase behavior and viscoelastic properties of entangled block copolymer gels

Authors

  • Daniel A. Vega,

    1. Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
    Current affiliation:
    1. Department of Physics, Universidad Nacional del Sur, Av. Alem 1253, 8000-Bahia Blanca, Argentina
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  • John M. Sebastian,

    1. Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
    Current affiliation:
    1. Science Research Center, 3M Corporate Research, St. Paul, Minnesota 55144-1000
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  • Yueh-Lin Loo,

    1. Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
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  • Richard A. Register

    Corresponding author
    1. Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
    2. Princeton Materials Institute, Princeton University, Princeton, New Jersey 08544
    • Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
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Abstract

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. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2183–2197, 2001

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