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    Polydispersity effects in poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers

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    JChemPhys_130_234903.pdf (1.042Mb)
    Date
    2009-06-17
    Author
    Meuler, Adam J.
    Ellison, Christopher J.
    Qin, Jian
    Evans, Christopher M.
    Hillmyer, Marc A.
    Bates, Frank S.
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    Abstract
    Four hydroxyl-terminated poly (isoprene-b-styrene) diblock copolymers with comparable molecular weights and compositions (equivalent volume fractions of polyisoprene and polystyrene) but different polystyrene block polydispersity indices (Mw/Mn=1.06, 1.16, 1.31, 1.44) were synthesized by anionic polymerization using either sec-butyllithium or the functional organolithium 3-triisopropylsilyloxy-1-propyllithium. Poly (ethylene oxide) (PEO) blocks were grown from the end of each of these parent diblocks to yield four series of poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers that were used to interrogate the effects of varying the polydispersity of the middle bridged polystyrene block. In addition to the neat triblock samples, 13 multicomponent blends were prepared at four different compositions from the ISO materials containing a polystyrene segment with Mw/Mn=1.06; these blends were used to probe the effects of increasing the polydispersity of the terminal PEO block. The melt-phase behavior of all samples was characterized using small-angle X-ray scattering and dynamic mechanical spectroscopy. Numerous polydispersity-driven morphological transitions are reported, including transitions from lamellae to core-shell gyroid, from core-shell gyroid to hexagonally packed cylinders, and from network morphologies [either O70 (the orthorhombic Fddd network) or core-shell gyroid] to lamellae. Domain periodicities and order-disorder transition temperatures also vary with block polydispersities. Self-consistent field theory calculations were performed to supplement the experimental investigations and help elucidate the molecular factors underlying the polydispersity effects. The consequences of varying the polydispersity of the terminal PEO block are comparable to the polydispersity effects previously reported in AB diblock copolymers. Namely, domain periodicities increase with increasing polydispersity and domain interfaces tend to curve toward polydisperse blocks. The changes in phase behavior that are associated with variations in the polydispersity of the middle bridged polystyrene block, however, are not analogous to those reported in AB diblock copolymers, as increases in this middle block polydispersity are not always accompanied by (i) increased domain periodicities and (ii) a tendency for domain interfaces to curve toward the polydisperse domain. These results highlight the utility of polydispersity as a tool to tune the phase behavior of ABC block terpolymers.
    Department
    Chemical Engineering
    Description
    At time of publication all authors were at the University of Minnesota. Christopher Ellison is currently Asst. Professor at the University of Texas at Austin.
    Subject
    polydispersity effects
    poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers
    polymers
    anionic polymerization
    polydispersity
    poly(ethylene oxide)
    PEO block
    URI
    http://hdl.handle.net/2152/21059
    Citation
    Polydispersity Effects in Poly(isoprene-b-styrene-b-ethylene oxide) Triblock Terpolymers. A.J. Meuler, C.J. Ellison, J. Qin, C.M. Evans, M.A. Hillmyer, and F.S. Bates, Journal of Chemical Physics, 130, 234903-1 - 234903-17 (Jun. 2009).
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