http://www.engr.uconn.edu/~jmfent/membrane%20review%201.pdf

Proton-conducting polymer electrolyte membranes based on hydrocarbon polymers

Synthesis and characterization of sulfonated poly(ether ether ketone) for proton exchange membranes

The sodium salts of sulphonated poly(aryl-ether-ether-ketone) (PEEK): Preparation and characterization

The nanostructure and morphology of proton conducting polymers is of considerable interest in the search for next generation materials and optimization of existing ones. Synthetic methodologies for tailoring molecular structures that promote nanoscopic phase separation of ionic and non-ionic domains, and the effect of phase separation on parameters such as proton conductivity, are considered. Rather than distinguish proton conducting polymers according to chemical class, they are categorized under sub-headings of random, block, and graft copolymers. The synthetic methodology available to access archetypal polymer structures is dependent on the nature of the monomers and restrictive compared to conventional non-ionic polymer systems. Irrespective of the methodology, ionic aggregation and phase separation are consistently found to play an important role in the proton conductivity of low ion exchange capacity (IEC) membranes, but less of a role in high IEC membranes. Significant research is required to further develop relationships between polymer architecture, morphology, and electrolytic properties.

Synthetic Strategies for Controlling the Morphology of Proton Conducting Polymer Membranes

Aromatic and heteroaromatic polymers are well known for their often excellent thermal and chemical stability as well as their good mechanical properties and high continuous service temperatures. Therefore, they have long been considered promising candidates for the development of proton-conducting membranes for fuel cells, especially for applications above 80 °C. Typically, sulfonic or phosphonic acid groups are introduced to provide acidic sites. While it is possible to introduce these groups by post-modification of the preformed polymers, the preferred method in many cases is modification of the monomers and subsequent polymer synthesis, because this allows better control of the number, distribution, and position of the acidic sites. Compared to perfluorosulfonic acid polymers, such as Nafion, proton-conducting membranes based on aromatic hydrocarbon polymers tend to exhibit excellent conductivities in the fully hydrated state and significantly reduced crossover, especially of methanol in DMFC applications. However, this often comes at the expense of a higher degree of swelling and a greater loss of conductivity with decreasing water content, which is considered a severe drawback e.g., for automotive applications. Recent approaches to improving the property profile of hydrocarbon membranes include block copolymers, rigid rod polymers, and the attachment of acidic groups via side chains.

Sulfonated Aromatic Polymers for Fuel Cell Membranes

: Polyaromatic ether-ketones and polyaromatic ether-keo-sulfones were sulfonated by suspending the polymer powders in dichloroethane containing liquid sulfur trioxide and trialkyl phosphate at room temperature. It was found that more than one sulfonic group can be introduced per each repeating unit of the polymers without degradation. The sulfonated polymers were soluable in various organic solvents, and solubility and mechanical properties depended on the initial molecular weight of polymers as well as the degrees of sulfonation. Strong films can be cast from their dimethylformamide solutions.

Polyaromatic Ether-Ketones and Ether-Keto-Sulfones Having Various Hydrophilic Groups,

Polyaromatic ether-ketones prepared from isophthaloyl dichloride, diphenyl ether, and various amounts of biphenylene and its derivative, were compressed to films under various conditions, and their crosslinking behaviors were studied. Although strong and flexible films could be obtained from low melting crosslinkable polymers, the low molecular weight polymers, which melt below 300°C, decompose at the biphenylene ring opening temperature of over 290°C, giving films full of gas bubbles. The addition of metal complexes to decrease the biphenylene ring opening temperature did not improve the film quality, although gas bubbles could be avoided. The strong and flexible films were amorphous, and the brittle films were mixtures of crystalline and amorphous polymers.

Takeshi Ogawa

Papers

Polyaromatic Ether-Ketones and Ether-Keto-Sulfones Having Various Hydrophilic Groups,

Crosslinking of polyaromatic ether‐ketones with biphenylene derivatives