A Simple New Route to Covalent Organic/Inorganic Hybrid Proton Exchange Polymeric Membranes

Abstract

The development of proton exchange membranes as electrolytes for polymer electrolyte fuel cells operating at intermediate temperatures has been achieved combining two approaches: the preparation of a cross-linked polymer and the formation of covalent organic/inorganic hybrids. A covalently cross-linked sulfonated polyetheretherketone with elevated degree of sulfonation (DS = 0.8) was prepared by reaction with HSO 3 Cl (SOPEEK). No degradation of PEEK was detected upon sulfonation, but only cross-linking via sulfonic groups with formation of SO 2 moieties was observed. The extent of ramification was calculated by analyzing the 1 H nuclear magnetic resonance (NMR) spectra of the products and resulted in 20% of the total amount of −SO 3 H groups present in the polymer. The solubility of the −SO 2 Cl precursor in organic solvents allowed easy carrying out of functionalization reactions in homogeneous conditions by lithiation and subsequent reaction with SiCl 4, thus introducing covalenly linked silicon moieties (SOSiPEEK) at the ratios 1:0.25 and 1:0.50 per monomeric unit. The products were characterized by 1 H and 13 C NMR, attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry.