Study On The Relationship Between Microstructure And Macroproperties Of Sulfonated Poly(Arylene Ether Ketone)s

With the advantage of the low temperature fastest startup, low working temperature, high energy efficiency and long service life, polymer exchange membrane fuel cells (PEMFCs) are the rapidly developing fifth-generation fuel cell and gains wide applications . PEMFCs have received wide investigations as promising new power sources for military usages, space explorations, vehicles, area generations and portable devices. As the key component of the PEMFC, proton exchange membranes have two main functions: the first one is transferring protons from the anode to cathode. The second one is being a barrier between fuel and oxidant in electrode. The membranes which traditionally used in PEMFCs are perfluorosulfonic polymers such as Dupont Nafion?. Nafion? membranes show superior performance in fuel cells which operate at moderate temperatures (<90oC) and high relative humidity with pure hydrogen as fuel, however, the high cost, low conductivity at low relative humidity or high temperature and high methanol permeability of Nafion? have limited their usages. Hence alternative proton exchange membrane materials with low cost and high performance are being developed. Because of its thermo stability,chemical stability and superior electric properties, sulfonated poly(arylene ether ketone)s are considered to be the best substitute materials of Nafion? membranes. Our groups have explored several sulfonated poly(arylene ether ketone)s (SPAEKs) for proton exchange membranes usages and the research indicates that they all show very good potential usages in PEM.We have synthesized two kinds of sulfonated polymers: sulfonated poly(ether ether ketone)s and sulfonated poly(ether ether ketone ketone)s. As the sulfonated degree becomes higher, water uptake and proton conductivity of membranes rise higher while the mechanical properties becomes lower. When the two different polymers are at the same sulfonated degree, we find that there are quite big differences in the evaluation data above. To investigate the relationship between microstructure and macro properties, in chapter 2, we successfully synthesized a new kind sulfonated poly(arylene ether ketone)s (SPAEKs) whose microstructures are similar to polymers we synthesized before. We determined the structure through IR and NMR testing methods. This new kind polymer has good solubility and thermo stabiliy, at the same time we can obtain transparent membranes with tenacity.In chapter 3, the morphology of these three kinds of membranes was detailed investigated by various measurements, including transmission electron microscope (TEM), atom force microscope (ATM) and small angle X-ray scattering (SAXS). We found that as the sulfonated degree gets higher, the membranes form larger ion clusters and these ion clusters'diameter become bigger. At the same time, the phase separation becomes more and more obvious which leads to higher proton conductivity. However, the proton conductivity of these three different membranes is different at the same sulfonated degree. As observed from TEM, ATM, and SAXS, we found that SPEEK has the largest ionic cluster diameter, closest ionic cluster distance and the most obvious phase separation. The testing data of the new synthesized SPAEK is lower than that of SPEEK and the data of SPEEKK is the lowest. All of these are due to the microstructure of these three different polymers. In the polymer backbone matrix of SPEEK, the distance of sulfonated groups is the smallest of all. So the diameter of ionic cluster of SPEEK is the largest and the phase separation is the most obvious, both of which leads to the highest ion exchange capacity, water uptake and proton conductivity. While in SPEEKK, the distance between sulfonated groups is largest, which leads to the lowest ion exchange capacity, water uptake and proton conductivity. The sulfonated groups'distance of the new synthesized polymer SPAEK is between SPEEK and SPEEKK, so the testing data above is between the data of SPEEK and SPEEKK either. So we draw the conclusion that the distance of sulfonated groups in polymer backbone determines the macro properties of polymer membrane.