Structural Optimization And Performance Study Of Heterocyclic Location And Sulfonation Site Of Poly(aryl Ether Ketone) Proton Exchange Membranes

Proton exchange membranes（PEMs）,as the core components of proton exchange membrane fuel cells,function to conduct protons and block fuels,while also requiring excellent thermal properties,oxidative stability and mechanical properties.At present,the most well-known commercial proton exchange membrane is the Nafion series perfluorosulfonic acid membrane produced by DuPont.These membranes have high proton conductivity under high humidity,but there are also limitations in the loss of conductivity at low humidity and poor barrier properties to alcohol fuels.Sulfonated polyaryletherketone（SPAEK）is considered by many scientific research teams to be a possible replacement for Nafion.because of its excellent thermal,chemical,mechanical stability,easy modification of functional groups,and low production cost.Over the years,researchers at home and abroad have conducted a lot of research on sulfonated poly（aryl ether ketone）polymers,and introduced many new functional groups.However,the effects of these new groups on polymers are often multifaceted.It also increases the difficulty of synthesis.In this paper,we hope that by designing the molecules,we will not rely on the introduction of new groups,and by modulating the position of the nitrogen heterocycles in the polymer and the sulfonation sites to make them better interact to make our membranes have better performances.The tail end of the SPAEK membrane side chain of this paper combines a nitrogen-containing heterocyclic ring and a sulfonic acid group containing a secondary amine.First,the 5-carboxybenzotriazole is sulfonated and purified to obtain a sulfonated carboxybenzotriazole（SCBTA）.Preparation of side chain amino group-containing PAEK terpolymer by nucleophilic polycondensation,coupling SCBTA to PAEK side chain by amidation reaction,adjusting the ratio of amino group-containing monomer 4-aminophenyl hydroquinone in PAEK matrix,preparation a series of side chain bifunctional groups of SPAEK membranes（NmAn-SCBTA）.The experimental results show that this method of controlling the position of different groups has a great influence on the performance of the membrane.Taking N7A3-SCBTA as an example,it not only maintains excellent thermal,oxidation,and mechanical properties compared with conventional side chain sulfonated PAEK,but also exhibits a better micro-phase separation structure,and has a high selectivity(91.9×10⁴ S·s·cm^-3)based on higher proton conductivity.The proton exchange membrane synthesized by this scheme has great potential for application to direct methanol fuel cells.Next,the synthesis route and the structure of the polymer are further optimized,and the monomer 4-aminophenyl hydroquinone used for the synthesis of PAEK is changed to4,4-bis（4-hydroxyphenyl）pentanoic acid to prepare an alkyl group side chain terpolymer,sulfonation purification of 2-aminobenzimidazole to sulfonated aminobenzimidazole（SNBI）,regulation of 4,4-bis（4-hydroxyphenyl）pentanoic acid content ratio,synthesis of a series of new Side chain bifunctional group SPAEK membranes（CmAn-SNBI）.The experimental results also show that the membrane conductivity of CmAn-SNBI is significantly improved compared with the previous scheme,and the conductivity of C8A2-SNBI reaches 0.137 S cm^-1 at 90°C.Even though the more easily migrated side chains and polysulfonation reduce mechanical properties and selectivity,the CmAn-SNBI membranes still exhibits a good ability to be applied to proton exchange membranes.