Phase behavior and morphology of sulfonated polystyrene systems
Abstract
Poly(styrene- ran -sulfonated styrene) (P(S-SS x )) 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-SS x ) 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-SS x ) 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, χ s/ss ≥ 25. In comparison, dPS blended with P(S-SS x ) 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-SS x ) 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-SS 0.019 ) 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, D STEM and 2R 1 show excellent agreement. Overlap in the STEM images was resolved using simulated images. STEM micrographs of solvent cast and spin cast P(S-SS 0.019 )-Ba and P(S-SS 0.019 )-Zn ionomers show the same morphology.
Subject Area
Chemical engineering
Recommended Citation
Nancy C Zhou,
"Phase behavior and morphology of sulfonated polystyrene systems"
(January 1, 2007).
Dissertations available from ProQuest.
Paper AAI3271847.
http://repository.upenn.edu/dissertations/AAI3271847
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