Synthesis of Sulfonated Polyphenylene Block Copolymers via In Situ Generation of Ni(0).

Proton exchange membranes (PEMs) fabricated from sulfonated polyphenylenes (sPP) exhibit superior proton conductivity and electrochemical performance. However, the Ni(0) catalyst required for Colon's cross-coupling reaction for the synthesis of sPP block copolymers is expensive. Therefore, in this study, we generated Ni(0) in situ from an inexpensive Ni(II) salt in the presence of the reducing metal Zn and NaI. The sPP block copolymers were synthesized from neopentyl-protected 3,5- and 2,5-dichlorobenzenesulfonates and oligo(arylene ether ketone) using the catalyst NiBr2(PPh3)2. The block copolymers synthesized using our strategy and the Ni(0) catalyst exhibited comparable polydispersity index values and high molecular weights. Thin, transparent, and bendable PEMs fabricated using selected high-molecular-weight sPP block copolymers synthesized via our strategy exhibited similar proton conductivities to those of the block copolymers synthesized using the Ni(0) catalyst. We believe that our strategy will promote the synthesis of similar multifunctional block copolymers.

Synthetic Approaches for Poly(Phenylene) Block Copolymers via Nickel Coupling Reaction for Fuel Cell Applications.

Several methods to synthesize poly(phenylene) block copolymers through the nickel coupling reaction were attempted to reduce the use of expensive nickel catalysts in polymerization. The model reaction for poly(phenylene) having different types of dichlorobenzene derivative monomers illustrated the potential use of cost-effective catalysts, such as NiBr2 and NiCl2, as alternatives to more expensive catalysts (e.g., bis(1,5-cyclooctadiene)nickel(0) (Ni(COD)2)). By catalyzing the polymerization of multi-block poly(phenylene) with NiBr2 and NiCl2, random copolymers with similar molecular weights could be prepared. However, these catalysts did not result in a high-molecular-weight polymer, limiting their wide scale application. Further, the amount of Ni(COD)2 could be reduced in this study by approximately 50% to synthesize poly(phenylene) multi-block copolymers, representing significant cost savings. Gel permeation chromatography and nuclear magnetic resonance results showed that the degree of polymerization and ion exchange capacity of the copolymers were almost the same as those achieved through conventional polymerization using 2.5 times as much Ni(COD)2. The flexible quaternized membrane showed higher chloride ion conductivity than commercial Fumatech membranes with comparable water uptake and promising chemical stability.

Synthetic approaches for advanced multi-block anion exchange membranes.

Despite our ability to post-functionalize poly(arylene ether sulfone) multi-block copolymers by rapid chloromethylation, bromination, or acylation, with degrees of functionalization that exceeded 70% in a few hours, materials formed during attempts to prepare fully post-functionalized multi-block copolymers are poorly soluble due to undesired side reactions, such as crosslinking or di-bromination. In particular, clustered reactive sites in multi-block copolymers increase the chance of self-reactions between polymer backbones, resulting in the formation of by-products. On the other hand, the authentic multi-block copolymer with good solubility and high molecular weight was successfully synthesized using functionalized monomers. Despite its low ion-exchange capacity, the resulting multi-block copolymer outperformed the commercial FAA-3-30 membrane in terms of anion conductivity, even under low relative humidity conditions.