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Transport Properties of Sulfonated Poly (Styrene-b-isobutylene-b-styrene) Triblock Copolymers at High Ion-Exchange Capacities

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Transport properties of sulfonated polystyrene-b-isobutylene-b-styrene S-SIBS triblock copolymers were examined as a function of ion-exchange capacity IEC, specifically at high IECs up to -2 mequivg. The proton conductivity of S-SIBS was -1 order of magnitude higher than sulfonated polystyrene at similar IECs and 3-fold higher than Nafion 117 at an IEC of 2 mequivg. However, all polymers in this study possessed similar selectivities i.e., proton conductivitymethanol permeability regardless of chemistry or morphology. Smallangle X-ray scattering reveals a periodic-to-nonperiodic transition in S-SIBS with an anisotropic lamellar morphology oriented in the plane of the membrane at IECs ranging from 0.5 to 1 mequivg and an isotropic cocontinuous morphology at IECs ranging from 1.1 to 2 mequivg. This morphological transition coincides with a discontinuity in the IEC-dependent transport properties. In addition, S-SIBS transport properties were measured after solution casting from 15 different solvents at a constant IEC 0.8 mequivg. Transport properties varied by almost 3 orders of magnitude when comparing S-SIBS solution cast from toluene to a tolueneethanol mixture. X-ray scattering results show morphological differences with solvent choice. This study demonstrates the significant impact of morphology on transport properties in ionic block copolymers.

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  • Nuclear Physics and Elementary Particle Physics
  • Solid State Physics
  • Polymer Chemistry

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