Synthesis and Morphology Study of SEBS Triblock Copolymers Functionalized with Sulfonate and Phosphonate Groups for Proton Exchange Membrane Fuel Cells

Abstract

Aromatic rings of poly(styrene-b-(ethylene-r-butylene)-b-styrene) triblock copolymer (SEBS) were functionalized with various acid functional groups for proton exchange membrane (PEM) applications. Three different acid functional groups (fluoroalkylsulfonic acid, arylsulfonic acid, and arylphosphonic acid) were introduced into SEBS via borylation of aromatic C−H bonds and Suzuki coupling reactions. The incorporation of acid side groups selectively into the polystyrene block of SEBS created nanometerscale phase separated morphology composed of hydrophilic and hydrophobic domains in which the morphology structures and interdomanin distances are dependent on the chemical structure of acid side chains. Despite high ion exchange capacity value, the aryl phosphonated polymer (SEBS-P) showed the lowest water uptake and significantly lower proton conductivity compared to sulfonated SEBS PEMs because of the low acidity of phosphonic acid. Compared to aryl sulfonated SEBS-S 2 , fluoroalkyl sulfonated SEBS-S 1 showed better proton conductivity at low relative humidity condition (<50%), which is ascribed to the stronger acidity and more compact ionic domains. Morphology study of SEBS-S 1 indicates that due to both hydrophobic and oleophilic nature of fluoroalkyl chains, fluoroalkyl sulfonate chains of SEBS-S 1 induced more dense ionic self-aggregation.

A mild and quantitative route towards well-defined strong anionic/hydrophobic diblock copolymers: synthesis and aqueous self-assembly

“…Amphiphilic block copolymers that contain both hydrophobic and ionic features are promising materials for various applications, such as surfactants for emulsion polymerizations, 1,2 thickening agents for enhanced oil recovery, 3 lubricants in aqueous media, 4 the preparation of photonic fluids, 5 fabrication of proton-exchange membrane fuel cells, 6 and the preparation of adhesives for use in wet environments. 7,8 The ionic block is frequently based on a weak polyelectrolyte, i.e., the charge density is dependent on the pH, making the hydrophobic/ionic block copolymer soluble in polar organic solvents.…”

Synthesis of Sulfonated Poly(arylene ether)s in a One‐Pot Polymerization Process and Their Nafion‐Blend Membranes for Proton Exchange Membrane Fuel Cell Applications

“…For the blend membranes, this step mass loss was decomposition of sulfonic acid group in both SPAE and Nafion . At last, distinct step of thermal degradation, starting at about 450 °C, was assigned to the thermal degradation of polymer backbone …”

Triblock SEBS/DVB crosslinked and sulfonated membranes: Fuel cell performance and conductivity

“…Thereby, the development of more affordable PEMs based on hydrocarbon structures of sulfonated aromatic polymers may involve incentive and cost‐effective opportunities in this field. Numerous examples of potential membrane materials functionalized with sulfonic groups have been proposed and can be found in the recent related bibliography such as poly(ether‐ether ketones), 4–7 poly(vinyl alcohol), 8–12 polyimides, 13–16 poly(benzimidazoles), 17–20 poly(phosphazenes) 21–23 or polystyrene‐block copolymers 24–27 …”