Formulation and characterization of poly(styrene- co-isobutylene-co-styrene) block copolymer - silicon oxide nanocomposites

David A. Reuschle


Poly(styrene-co -isobutylene-co -styrene) block copolymers possess phase separated morphologies. The particular morphology depends upon the volume fraction of the two block components. The triblock copolymer will typically exhibit polystyrene (PS) spheres, cylinders, or lamellae when PS is the minor component. Equilibrium morphologies are such that spheres occur between 0-20% volume, cylinders occur between 20 and 40% volume, and lamellae are observed at over 40% volume. This natural phase separated morphology serves as a template for in situ sol-gel reactions of tetraethyl orthosilicate (TEOS), such that a silicate (silicon oxide) network is inserted into the minor PS domains. In an effort to modify the water permeability properties of these materials, PS-PIB-PS BCPs were sulfonated, and subsequently neutralized to either the Na+ or benzyltrimethylammonium (BTMA) form ionomer. These block copolymer ionomer (BCPI) materials were then solvent cast to form films. Solvent cast films of Na+ form and BTMA form BCPI were modified by in situ sol-gel reactions. Thermal analysis of the PS-PIB-PS BCPs was conducted. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were utilized to monitor the PIB glass transition (Tg ) and onset of BCP degradation (T d ), respectively. Tapping mode(TM) atomic force microscopy (AFM) was used to investigate the phase separated morphology of poly(styrene-co-isobutylene-co-styrene) BCP, BCPI and BCPI - silicon oxide nanocomposite materials. The phase separated morphology of the BCP was revealed by TM AFM phase imaging of freshly microtomed surfaces. A close correspondence between a Bragg spacing obtained by SAXS, and the domain spacing determined by a section analysis of TM AFM phase images, was demonstrated. In the case of the Na+ form BCPI - silicon oxide nanocomposite, SAXS analysis indicates a spherical morphology, however not well-ordered. A water swelling study showed an increase in water solubility in the following order: BCP [arrow right] Na+ form BCPI [arrow right] Na + form BCPI - silicon oxide nanocomposite, which is reasonable in terms of the internal polarity progression. 23 Na NMR spectroscopy revealed complete hydration of Na+ ions present in a BCPI sample. Water contact angle measurements showed that surface wetting was best for the suffonated BCPI. Surface wetting for homopolymer PIB was the same as that for the parent BCP. (Abstract shortened by UMI.)