Phase behavior and morphology of sulfonated polystyrene systems

Nancy C Zhou, University of Pennsylvania

Abstract

Poly(styrene-ran-sulfonated styrene) (P(S-SSx)) random copolymers and its neutralized ionomers have many unique properties that result in a wide variety of applications. In this dissertation, the phase behavior and morphology of sulfonated polystyrene systems have been examined. Our goal is to obtain a comprehensive knowledge on the nanoscale morphology of P(S-SSx) ionomers, and establish relationships to their phase behavior and physical properties. The homopolymer:acid copolymer phase behavior of deuterated polystyrene with sulfonated polystyrene P(S-SSx) was explored using the depth profile technique of elastic recoil detection (ERD). ERD profiles reveal full miscibility for x ≤ 0.002 and complete immiscibility for x ≥ 0.026. Using the Flory-Huggins theory in combination with the copolymer mixing theory, we estimate a styrene - styrene sulfonate segmental interaction parameter to be extraordinarily large, χs/ss ≥ 25. In comparison, dPS blended with P(S-SSx) ionomers have a higher upper critical solution temperature (UCST), and the UCST is higher when P(S-SS 0.007) is neutralized with divalent cations rather than with monovalent cations. Complementary linear viscoelastic measurements show that the rubbery plateau of P(S-SS) ionomer extends to lower frequencies indicating slower polymer chain relaxations. The specific interactions that produce these physical crosslinks also impede blend miscibility. Phase separation within P(S-SSx) random copolymer due to inhomogenous sulfonation levels was examined. Miscibility results from blending acid copolymer:acid copolymer resulted in a small window of miscibility. When two different ionomers at the same acid content (x = 0.026, 125% neutralization) were blended, only the monovalent ionomer blend pairs were miscible. We also examine the nanoscale morphology of P(S-SS0.019) ionomers using model dependent X-ray scattering and direct imaging technique of scanning transmission electron microscopy. Using the Kinning-Thomas SAXS model, the ionic aggregate size has been reconciled by STEM and SAXS where the ionic aggregate diameters, DSTEM and 2R1 show excellent agreement. Overlap in the STEM images was resolved using simulated images. STEM micrographs of solvent cast and spin cast P(S-SS0.019)-Ba and P(S-SS0.019 )-Zn ionomers show the same morphology.

Subject Area

Chemical engineering

Recommended Citation

Zhou, Nancy C, "Phase behavior and morphology of sulfonated polystyrene systems" (2007). Dissertations available from ProQuest. AAI3271847.
https://repository.upenn.edu/dissertations/AAI3271847

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