| This investigation studied the resulting nanostructure of ionic membranes composed of sulfonated copolymers with thermoplastic and elastomeric blocks. Linear poly(styrene-isoprene-styrene) (L-SIS) and branched poly(styrene-isoprene) (B-SI), were sulfonated to various levels of ion exchange capacity (IEC). Since the sulfonation occurred in both the poly(styrene) (PS) blocks and the double bonds of the poly(isoprene) (PI) segments, the resulting sulfonated polymer lost the elastomeric component of the membranes; therefore, physical blends of sulfonated and unsulfonated L-SIS and B-SI were casted and analyzed. The resulting membranes were then characterized with several techniques including: elemental analysis (EA), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR) and Small angle X-Ray scattering (SAXS). These techniques provided thermal and physical properties of the membranes, which allowed the comparison of the resulting morphologies and selectivities. Counter-ion substitution (Mg+2, Ca+2, Ba+2) was used to cross-linked the sulfonated polymers to create more selective membranes. Vapor permeabilities were measured at a temperature of 308 K using dimethyl methylphosphonate (DMMP), a chemical similar to Sarin Gas (GB), and water as permeates, in order to analyze the selectivity of the resulting membranes for chemical and biological protective clothing (CBPC). Results show a similar IEC to sulfonated poly(styrene-isobutylene-styrene) (SIBS), although the reaction kinetics was significantly faster due to the unsaturated bonds of the isoprene block. Selectivity values obtained from the permeability studies are not promising for the chemical and biological protective clothing application. However, lower sulfonation levels and blends of sulfonated/unsulfonated linear/branched resulted in unique morphologies capable of selective separations and significant differences were observed between linear and branched morphologies. |
