Preparation And Properties Characterization Of Imidazolium Poly(phenylene Ether)-based High Temperature Proton Exchange Membrane

Poly?phenylene ether??PPO?has excellent thermal stability and mechanical properties as a kind of engineering plastic.Brominated PPO?BPPO?has good membrane-forming property and is less toxic than chlorinated PPO.It is an ideal material for preparing high temperature proton exchange membrane?HT-PEM?.Usually improving the conductivity can lead to the reduction of mechanical properties,so how to coordinate the conductivity and mechanical properties has become one of today's research hotspots.In this study,the preparation and properties of imidazolium salt PPO-based HT-PEM were investigated.BPPO is able to react with basic groups?such as N-methylimidazole?to graft the basic groups on the methyl of PPO structure.HT-PEMs are prepared by the adsorption of sufficient phosphoric acid around basic groups.The effect of bromination degree and Im content on the structure and performance of PEM,including chemical structure,thermal stability,phosphoric acid doping?ADL?,dimensional stability,electrical conductivity,mechanical properties and power density.Firstly,high temperature Bronsted acid-base proton exchange membrane is prepared on the base of BPPO.BPPO with different bromination degree is prepared by free radical reaction,then BPPO reacts with methylimidazole?Im?,finally prepare BPPO-Im/PA membrane by doping phosphoric acid?PA?.PEMs are characterized by¹³C NMR and FT-IR.The bromination degree is 15.33%,28.66%and 36.07%through caculation,respectively.The Im content increases with the increase of bromination degree and the PA uptake increases,but the conductivity increases firstly then decreases and the mechanical properties decrease gradually.This is because PA can supply effective protons,at the same time PA is equivalent to a plastic small molecule,which can reduce the mechanical properties of the membrane.The B12-Im/PA membrane with the bromination degree of 28.66%exhibited the best comprehensive properties.The B2-Im/PA membrane had good thermal stability below 200?detected by TG data and good tensile strength of 5.2 MPa.A high conductivity of 5.4×10^-2 S cm^-1 is achieved at 160?for the membrane.Secondly,B12-xIm/PA PEMs with different Im content are prepared on the base of B12 with bromination degree of 28.66%.The structure of PEMs was characterized by ¹³C NMR and FT-IR.The PA uptake,dimensional stability and proton conductivity of B12-xIm/PA PEMs increase firstly then decrease with the increase of Im content.M-3#/PA membrane has the best proton conductivity of 6.79×10^-2 S cm^-1 at 160?and the highest mechanical tensile strength of 4.8 MPa.Three kinds of PEMs are prepared with different membrane-forming solvents according to the BPPO and Im ratio of M-3#/PA membrane.The interaction between the membrane-forming solvent and the polymer chain affects the conductivity and mechanical properties of PEMs.The higher the thermal decomposition temperature,the lower the conductivity and mechanical properties.The M-NMP/PA membrane with moderate force exhibits the higher conductivity,and the higher than 10 times of the M-DMAc/PA membrane with strong force.The power density of M-NMP/PA PEM increases with the increase of temperature and reaches 280 mW cm^-2 at 160?.