Preparation And Blending Modification Of N-Heterocyclic Quaternary Ammonium Polymers With Good Alkali Stability

The performance of anion exchange membranes?AEMs?is the main factor affecting the performance of anion exchange membrane fuel cell?AEMFC?,and the durability of AEMs under operating conditions has become one of the current research topics.How to design polymer structures with excellent durability,overcome the"trade-off"effect between conductivity and water uptake or mechanical properties of AEMs and meet their application requirements is still a great challenge in current research.Polystyrene AEMs with high electron cloud density and N-heterocyclic quaternary ammonium?QA?have excellent alkali stability.However,how to effectively introduce functional cations into the main chain of polymers is a difficult point.In this paper,side-chain and main-chain N-heterocyclic QA polymers were prepared,and the properties of their blend membranes were studied.The main contents and conclusions are as follows:?1?Firstly,alkyne-functionalized piperidine and spirocyclic quaternary ammonium were prepared,then side chain piperidine and spirocyclic quaternary ammonium polystyrene polymers?PS-DMP-X and PS-ASU-X?were prepared by mild and efficient"click chemistry"reaction.¹H-NMR study showed that PS-ASU-30 had no obvious new peaks?except H-D exchange?after soaking in1M NaOH CD₃OD/D₂O solution at 80?for 3000 h,and displayed excellent alkali resistance.PS-DMP-X and PS-ASU-X were blended with 10 wt%Polystyrene-b-Poly?ethylene-co-butylene?-b-polystyrene?SEBS?to form films,and their water swelling,conductivity,alkali resistance,thermal stability and mechanical properties were studied.Although the IEC_w?1.5 meq./g?of SEBS/PS-ASU-30 was lower than that of SEBS/PS-DMP-30?1.62 meq./g?,the OH^-conductivity of SEBS/PS-ASU-30?23.5 mS/cm?at room temperature was slightly higher than that of SEBS/PS-DMP-30?18.6 mS/cm?.When the blend membrane SEBS/PS-ASU-30 was immersed in 1 M NaOH solution at 80?for900 h,its OH^-conductivity decreased only about 10%of the initial value,while the conductivity of SEBS/PS-DMP-30 OH^-decreased about 16%,indicating that the spiral structure polymer was more stable than piperidine.Compared with the main chain of polyphenyl ether?PPO?with the same side chain structure,the alkali stability of polystyrene?PS?main chain is much better.Although the IEC_w value of PS-ASU-30 is low,the peak power density of AEMFC is 130 mW cm^-2,which is obviously higher than that of PS-DMP-30 under the same conditions(6.5 mW cm^-2).This may be related to the solubility of polymers.?2?A variety of small N-spirocyclic molecules were prepared,and their alkali stability was tested and calculated by ¹H-NMR and density functional theory?DFT?.The results show that QA1 can exist stably for 2000 h in 80?1M NaOD/D₂O.Two kinds of stable main chain N-spiro-functional group polymers were synthesized by cyclic polycondensation,and new anion exchange membranes were prepared by blending with novel polybenzimidazole?N-PBI?.The results show that the OH^-conductivity of the blend film S₁80N20 is as high as 36 mS/cm at room temperature.The maximum power density of the membrane is 135 mW cm^-22 at 250 mA cm^-22 current density,and the battery life is as high as 100 h.Compared with the battery performance in literature,the performance of the blend film S₁80N20 is better.