Among the various types of fuel cells, polymer electrolyte membrane (PEM) fuel cells have attracted considerable attention for transportation and for portable devices for low operation temperature and fast start-up. The state-of-art- commercial PEM materials are typically based on perfluorinated sulfonic acid containing ionomers (PFSAs), represented by DuPont''s Nafion®. Despite their good chemical stability and proton conductivity at high relative humidity (RH) and low temperature, Nafion has several major drawbacks, such as high production cost, high fuel permeability, insufficient thermo-mechanical properties above 80℃, and low proton conductivity at low RH levels. In order to overcome these drawbacks, a number of alternative membranes have been studied for PEM. Many research groups are researching ways of finding applicable membranes better than Nafion. Hydrocarbon membrane is remarkable among alternative membranes because these kinds of hydrocarbon membranes have advantages of thermal stability, easy design structure and simple synthesis. therefore, we are trying to synthesis of hydrocarbon membranes.
A series of the block copolymers were successfully synthesized from post-sulfonated hydrophilic and hydrophobic polymers via three-step copolymerization. The degrees of sulfonation (DS) of the copolymers (10%, 30%, or 50%) were controlled by changing the molar ratio of the hydrophilic and hydrophobic parts. The resulting block copolymers were characterized by 1H NMR and other technologies. The membranes were successfully castusing dimethyl sulfoxide (DMSO) solution at 100℃. The copolymers were characterized to confirm chemical structure by 1H NMR and FT-IR. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated that all sulfonated block copolymers exhibited good thermal stability with an initial weight loss at temperatures above 240℃. The membranes showed acceptable ion exchange capacity (IEC) and water uptake values in accordance with DS. The maximum proton conductivity was 184 mS cm-1 in block copolymer-50 at 60℃ and 100% relative humidity, while the conductivity of Nifion-115 was 160 mS cm-1 under the same measurement conditions. AFM images of the block copolymers showed well separated the hydrophilic and hydrophobic domains. It can be seen from the observed results that the prepared block membranes can be considered as suitable polymer electrolyte membranes for the application of polymer electrolyte membrane fuel cells (PEMFC).