Highly Branched Poly(arylene ether ketone sulfone)s Bearing Flexible Sulfoalkyl Side Chains for Proton Exchange Membranes

Abstract

The crucial impact of the elevated degree of branching (DB) on improving the properties of proton exchange membranes (PEMs) has been demonstrated, yet PEMs (employing the B 3 monomer as the branching agent) with DB values exceeding 10% have not been reported. Herein, we report on the synthesis of a series of highly branched sulfonated poly(arylene ether ketone sulfone) copolymers bearing a 12.5% DB value for PEMs, namely, B-12.5-SPAEKS-x (where x represents the molar ratio of the monomer attaching the sulfoalkyl chain to the employed bisfluoride monomers). To accomplish this, a triphenol derivative was designed as the branching agent to reduce the possibility of macroscopic cross-linking during polymerization, and the flexible sulfoalkyl side chains were grafted to the polymer backbone to enhance the chain entanglement of the copolymers. Among all of the fabricated membranes, the B-12.5-SPAEKS-graft-40 membrane exhibited comparable proton conductivity (118.6 mS cm −1 ) and swelling change (20.7%) with those of Nafion 117 in a fully hydrated state at 80 °C, realizing the trade-off between the proton conductivity and dimensional stability. Furthermore, the proton conductivity of the B-12.5-SPAEKS-graft-50 membrane was evidently superior to that of Nafion 117 in both the fully hydrated state and high relative humidity conditions; therefore, a higher maximum power density of 529.5 mW cm −2 was achieved in the H 2 /air fuel cell.

Branched Poly(arylene ether ketone sulfone)s with Ultradensely Sulfonated Branched Centers for Proton Exchange Membranes: Effect of the Positions of the Sulfonic Acid Groups

“…The synthetic routes of the monomers and the related intermediates are depicted in Scheme , based on several reported studies by our group. , Branching monomer a was synthesized by a Friedel–Crafts reaction of 1,3,5-benzenetricarbonyl trichloride and fluorobenzene. An aromatic substitution between 4-methoxytriphenylmethyl chloride and phenol proceeded to yield compound 1 , and a subsequent demethoxylation mediated by boron tribromide (BBr 3 ) afforded monomer b .…”