Synthesis And Applications Of Ion Exchange Polymer Membranes

Ionic polymers refer to the macromolecular polymers containing ionic groups in the polymer chains.The introduction of ionic groups enables the ionic polymers with special physical and chemical properties,such as good mechanical properties,excellent thermal stability,and high electrical conductivity,which makes the ionic polymers show application prospect in smart materials,conductive materials,biomedical materials and other fields.Alkaline anion exchange membrane fuel cells?AEMFCs?are attracting growing interest due to their low fuel permeability and enhanced oxygen reduction kinetics,as well as non-precious electrocatalysts.Anion exchange membrane?AEM?is one of the key components of AEMFCs and ionic polymers exhibit excellent performance as ion-conducting supports in AEMFCs.An ideal AEM should possess high hydroxide conductivity and sufficient long-term durability at elevated temperatures in high p H solutions.However,commercial AEMFCs are with a service life of around 5,000 hours,which greatly limits the large-scale application.The most important factor which influents the service life is the low chemical stability of AEMs in high-temperature and high-alkaline environments.In view of the current severe challenges faced by AEMs,a series of novel small cationic compounds and anion exchange membranes were designed and synthesized,and the chemical stability of cations in high-temperature,high-alkali environments was systematically studied.The influence of conjugate effect,steric hindrance effect,?-? hyperconjugation effect and electron effect on the alkaline stability of cations and homologous AEMs were explored.Ionic polymers can not only be used as a polymeric electrolyte for ion conduction but also have certain advantages in suppressing the growth of cyanobacteria as an environmental friendly material.Anionic polymers were further synthesizedand stuied as anti-cyanobacterial in the control and elimination of cyanobacterial blooms in this work.The main research contents and conclusions of this work are as follows:?1?The pyridinium cations substituted with different functional groups and alkyl chains at N position were designed and synthesized.The influences of the length of alkyl chain and functional groups on the alkaline stability of pyridinium cationic compounds were studied.Side-chaintype polyvinyl and main-chain type polyether sulfone basedpyridinium cationic polymers were further synthesized and their alkaline stability were characterized.The results show that the polyether sulfone based cationic polymers with pyridinium cations embedded in the main-chainexhibited higher alkaline stability,because of the strong steric hindrance which can prevent the attack of hydroxideto the cations.?2?A series of cationic compounds based on organic cations,including quaternary ammonium,imidazolium,benzimidazolium,pyridinium,phosphonium,pyrrolidinium and their corresponding cationic polymers were designed and synthesized.The chemical stability of the synthesized compounds in various alkaline media?water,methanol,ethanol and DMSO?were systematically investigated by quantitative ¹H nuclear magnetic resonance spectroscopy?¹H NMR?and density functional theory?DFT?calculations.The results of the study suggest that both the chemical structure of the organic cations and alkaline media?fuels?applied affect the alkaline stability of AEMs.?3?Design and synthesis of anion exchange membranes?PBCE-KOH?based on crown ether coordinated metal cations.The indruction of crown-coordinated potassium ions as a carrier for hydroxide conduction solves the problem of instability of organic cations under high p H environment.The dense membrane structure,excellent tensile strength?more than 60 Mpa?and outstanding thermal decomposition temperature?exceeding 430??also make PBCE-KOH membrane be a promising material for anion exchange membranes.In addition,PBCE-K & PPO-K anion exchange membrane was further prepared by layer-by-layer self-assembly technique.The nano-ion channels formed between the polymeric layers formed in the PBCE-K & PPO-K membranes improve the conductivity of the AEMs,as well as lead the PBCE-K & PPO-K membranes maintaining high alkaline stability.?4?Polyanionic membranes?PA-M?were designed and synthesized by in situ photo-crosslinking of a sulfate-based anionic monomer,acrylonitrile and styrene followed by cation-exchange with metal cations,Fe³⁺?PA-Fe?,Cu²⁺?PA-Cu?,or Zn²⁺?PA-Zn?.The application of the polyanionic membranes in anti-cyanobacteria was studied,the results showed that the PA-M membranes exhibited excellent inhibitory effects against Microcystis aeruginosa and Aphanizomenon aquatica.In addtion,the PA-M could be recycled without obvious decline of the anti-cyanobacteria efficiency.