Synthesis and Characterization of Sulfonated Poly‐(styrene‐co‐acrylic acid) for Applications as Pronton Exchange Membranes

Abstract

Summary Polymeric membranes were prepared using the mass copolymerization of styrene/acrylic acid (St/AA) at 90/10, 92/8 and 94/6 ratios. Divinyl benzene (DVB) was also added at concentrations of 0.1 and 0.001% weight for each St/AA ratio. The obtained copolymers were sulfonated by treating the materials with concentrated sulfuric acid for 0, 30 and 85 minutes to enhance their ion exchange capacities. The materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), cross‐linking level by gel percentage and acidity through sodium hydroxide titration. The FTIR spectra of the membranes before sulfonation showed the existence of traditional bands that corresponded to the polymer components; some homopolymer main bands were lost, whereas two new bands appeared during the copolymerization reaction. The TGA analyses showed a higher decomposition temperature for the DVB cross‐linked membranes, while DSC did not provide much information due to the hygroscopic nature of the membranes. The gel percentage was effectively related to the DVB level. The membranes acidity increased with increasing acrylic acid content, sulfonation time and DVB percentage; however, the acidic values are highly dependent on the solubility of the materials.