Sulfonated Block Copolymers: Synthesis, Chemical Modification, Self-Assembly Morphologies, and Recent Applications

Scientific research based on the self-assembly behavior of block copolymers (BCs) comprising charged-neutral segments has emerged as a novel strategy mainly looking for the optimization of efficiency in the generation and storage of electrical energy. The sulfonation reaction re- presents one of the most commonly employed methodologies by scientific investigations to reach the desired amphiphilic character, leading to enough ion concentration to modify and control the entire self-assembly behavior of the BCs. Recently, several works have studied and exploited these changes, inducing improvement on the mechanical properties, ionic conduction capabilities, colloidal solubility, interface activity, and stabilization of dispersed particles, among others. This review aims to present a description of recent works focused on obtaining amphiphilic block copolymers, specifically those that were synthesized by a living/controlled polymerization method and that have introduced the amphiphilic character by the sulfonation of one of the segments. Additionally, relevant works that have evidenced morphological and/or structural changes regarding the pristine BC as a result of the chemical modification are discussed. Finally, several emerging practical applications are analyzed to highlight the main drawbacks and challenges that should be addressed to overcome the development and understanding of these complex systems.

Chemically stable thioether cross-linked membranes derived from sulfonated poly(arylene ether ketone)s for direct methanol fuel cells

A series of thioether cross-linked membranes based on sulfonated poly(arylene ether ketone)s containing propenyl groups were prepared to solve the problem of high methanol permeability for proton electrolyte membrane in direct methanol fuel cells (DMFCs). For this purpose, 4,4′-thiobisbenzenethiol was selected as cross-linker, and the cross-linked structure was formed via thiol-ene click chemical reaction between propenyl and thiol groups. Compared with pristine membrane, the thioether cross-linked membranes exhibited improved mechanical properties and dimensional stabilities. As the cross-linker increased, the swelling ratio decreased from 11.01% to 8.64% at 20°C and from 15.18% to 10.69% at 80°C. Furthermore, the modified membranes exhibited reduced methanol permeability coefficients (down to 4.03 × 10−7 cm2 s−1), which was nearly half of the pristine membrane (7.66 × 10−7 cm2 s−1). Due to the thioether units, the cross-linked membranes showed enhanced oxidative stabilities, and the longest elapsed time in Fenton’s reagent was 225 min, which was 2.5 times longer than that of pristine polymeric membrane. Although the proton conductivity decreased upon the addition of cross-linker agent, the selectivity value increased due to the lower methanol permeability. Thus, all the results implied that the thioether cross-linked membranes were promising alternative materials for DMFCs application.