Poly(styrene- b-isobutylene- b-styrene) block copolymer ionomers (BCPI) and BCPI/silicate nanocomposites. 2. Na +BCPI sol–gel polymerization templates

Abstract

Polystyrene (PS) blocks in poly(styrene- b-isobutylene- b-styrene) (PS–PIB–PS) block copolymers were partially sulfonated and the acid groups converted to Na +SO 3 − groups to create ionomers. Then, dimethylacetamide was used to selectively swell the ionic PS domains and the swollen films were exposed to sol–gel reactive tetraethylorthosilicate solutions. (EtO) 4− x Si(OH) x monomers then permeated films so that sol–gel reactions occurred within/around the ionic PS domains. Environmental scanning electron microscopy/energy dispersive X-ray spectroscopy investigations showed that silicate structures can be incorporated within the interior of the ionomer films. Differential scanning calorimetry studies indicated that there is no variance in the PIB block T g with respect to ionomer formation, or with respect to silicate loading of the ionomer at low levels, which suggests that the silicate component does not reside in the PIB phase. 23Na solid state NMR spectroscopy detected isolated Na +SO 3 − groups as well as aggregated SO 3 −Na + ion pairs for ‘as cast’ and ‘dry’ non-silicate containing ionomer samples. In a hydrated sample, almost all Na + ions were solvent-separated. AFM analysis showed that phase separation exists, but that the degree of order is significantly less than that for hybrids based on the corresponding benzyltrimethylammonium ionomer. This frustrated morphology was also seen in the results of small angle X-ray scattering experiments. Given the scale of organic/inorganic heterogeneity, these hybrids are properly classified as nanocomposites.