Title

Investigations of Crystallization and Ionic Interactions of Sulfonated Syndiotactic Polystyrene Ionomers

Date of Award

2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Robert B. Moore

Advisor Department

Polymers and High Performance Materials

Abstract

Syndiotactic polystyrene (sPS) is a semicrystalline polymer that crystallizes rapidly and exhibits several polymorphic crystal structures. Crystallization of sPS from the melt results in an all-trans chain conformation comprised of α (hexagonal unit cell) and β (orthorhombic unit cell) crystal forms. Crystallization of sPS from solution produces helical crystal structures. To ascertain the link between ionic aggregation and crystallization in semicrystalline ionomers, sulfonated syndiotactic polystyrene (SsPS) has been selected as a model system. 23 Na SSNMR (Solid-state NMR) spectra have also been utilized to analyze the influence of a surfactant (i.e., dodecyl benzene sodium sulfonate (DBSNa)) on the state of ionic aggregation. Increasing the surfactant content within SsPS ionomers caused a downfield shift coupled with a decrease in width, for the peak corresponding to the ionic aggregates. Added DBSNa molecules can disrupt interactions within the ionic aggregates and consequently weaken the electrostatic network in SsPS. The influence of nonpolar/polar additives on syndiotactic polystyrene was also evaluated utilizing isothermal crystallization, 23 Na SSNMR, 13 C CPMAS (Cross-polarization Magic-angle spinning) NMR and WAXD (Wide-angle X-ray Diffraction) investigations. To evaluate the influence of crystallization on ionic aggregation in SsPS ionomers, 23 Na and 13 C SSNMR techniques have been utilized. Polymorphic nature was not significantly affected by the incorporation of ionic groups, as indicated by the identical 13 C spectra for sPS and SsPS polymers. A densification of the crystalline domains is likely to affect the conformations of amorphous chains attached to the crystallite surfaces. This perturbation in chain conformation may then result in a disruption of the state of ionic aggregation. The retention of the state of ionic aggregation within SaPS upon annealing clearly indicates that the disruption in the ionic domains of the SsPS ionomer originates from the polymorphic transition. (Abstract shortened by UMI.)