Multi-acid side chain ionomers

Schaberg MS, Abulu JE, Haugen GM, Emery MA, O Conner SJ, Xiong PN, Hamrock SJ (2010) New multi acid side-chain Ionomers for proton exchange membrane fuel cells. ECS Trans 33(l) 609-627... 

Fig. 17.9 The structure of 3 multi acid side-chain ionomers. Polymer 7a, n = 4, 7b n = 2 are from reference 49, Polymers 8 and 9 are from reference [50]...

One approach is to modify the PFSA side-chains such that they cany more than one acid site since the ciystallinify and morphological properties arise essentially from the ratio of non-substituted TFE to functionalised I FE of the backbone polymer repeat unit, multi-acid side-chain ionomer membranes have the potential to demonstrate the mechanical properties of a higher EW polymer (characteristic of a single acid site per side-chain), and the proton conduction properties of a lower EW material (conferred by the presence of multi-acid sites per side-chain). This direction is being followed at 3M, where introduction of... 

Most recently, 3M has been investigating a class of membranes based on multi-acid side chain (MASC) ionomers, which also allow a lower EW with more crystallinity. A particular ionomer with MASC, a perfluoroimide acid (PFIA), with an EW of 625, has been selected for further optimization, as this new ionomer provides for lower resistance and improved performance under hot, dry conditions. A PFIA membrane, combined with nanofiber supports and chemically stabilizing additives, has been reported to meet almost all of the DOE performance requirements. The most recent status was reported at the 2011 DOE Annual Merit Review [28]. Based on the rate of progress being made with this approach, it appears that it is likely that membranes that can tolerate higher temperatures and lower hydration levels will be incorporated into future M EAs, allowing lower system costs and improved reliability. 

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