Preparation And Properties Of Vinyl Benzyl Chloride/Acrylonitrile Copolymer Alkaline Anion Exchange Membrane

Anion exchange membrane fuel cell（AEMFC）has the advantages of high energy conversion efficiency,high efficiency,cleanness and low noise.Anion exchange membrane（AEM）,as the key material of AEMFC,will always be in a high temperature and strong alkaline environment.Therefore,the actual commercial application at this stage puts forward higher requirements for the conductivity and stability of anion exchange membrane in high temperature and strong alkaline environment.In this paper,4-vinylbenzyl chloride and acrylonitrile were used as raw materials to synthesize polyolefin-type full-carbon main chain polymers through copolymerization.Trimethylamine was used for quaternization through homogeneous and heterogeneous methods.The effects of different content and distribution of quaternary ammonium groups in the membrane on various performance indexes were compared.In addition,three piperidine groups with better alkali resistance were selected for quaternization of the main chain to explore the effects of steric and electronic effects on the alkali resistance of the polymer.The specific research conclusions are as follows:（1）P（VBC-co-AN）-X（X=3,4.5,6,7.5,9）was prepared by copolymerization of 4-vinylbenzyl chloride（VBC）and acrylonitrile（AN）with styrene and acrylonitrile.Trimethylamine was selected for quaternization to prepare heterogeneous benzyl trimethyl ammonium anion exchange membrane（Heter-X）and homogeneous benzyl trimethyl ammonium anion exchange membrane（Homo-X）.¹H NMR,FT-IR,EA and GPC proved that VBC and AN successfully synthesized P（VBC-co-AN）-X with high molecular weight,and trimethylamine successfully quaternized the copolymer.AFM results show that Homo-X has higher quaternization degree than Heter-X,forming a more obvious microphase separation structure.Homo-X also has good thermal stability,mechanical properties and dimensional stability.Among them,the comprehensive performance of Homo-6 is the best.Under the condition that the water absorption（25°C is 30.1%,80°C is 65.3%）and swelling degree（25°C is 13.3%,80°C is 24.9%）do not affect the normal operation of the sample membrane,the conductivity of Homo-6 membrane reaches 17.3 m S cm^-1 and 41.6 m S cm^-1 at 25°C and 80°C,respectively.After soaking in 1 M KOH solution for 480 h,the ionic conductivity of Homo-6 and Heter-6 remained 91.4%and 89.5%,respectively,and the IEC loss rates were 17.21%and 17.75%,respectively.（2）In the above copolymerization system P（VBC-co-AN）-6,three piperidine groups with better alkali stability were selected to quaternize the side chains,and the effects of steric hindrance and electronic effect on the alkali stability of piperidine groups were compared.It was proved by ¹H NMR and FT-IR that the three piperidine groups were successfully attached to the P（VBC-co-AN）-6 side chain.AEM series films also have good thermal stability,tensile properties（13.65 MPa～23.21 MPa）and elongation at break（18.58%～31.32%）.AFM test results showed that AEM-Pip-CO had a more obvious hydrophilic and hydrophobic microphase separation structure than AEM-Pip-OH,which was also the reason why AEM-Pip-CO showed higher ionic conductivity,which was 25.6 m S cm^-1 and 53.5 m S cm^-1 at25°C and 80°C,respectively.After soaking in 1 M KOH solution for 480 h,the ionic conductivity of AEM-Pip-CO and AEM-Pip remained 91.8%and 96.5%,respectively,and the IEC loss rates were 15.17%and 10.56%,respectively.