Synthesis And Properties Of Poly (Arylene Ether Ketone)s Based On Multiple-quaternized Carbazole Derivative Side Chains

With the current global environmental and energy problems becoming more and more serious,people have made great efforts in searching for the new energy sources.Fuel cell,as a new energy technology,because of its high efficiency,stability,low or even zero emissions,shows the huge potential to replace traditional fuels.Among them,the proton exchange membrane fuel cell(PEMFC)has a high energy conversion efficiency,low temperature start,etc.,these advantages have made it plenty of research and development.But meantime PEMFC must use expensive platinum electrode catalyst,which greatly affects its commercialization.Anion exchange membrane fuel cell(AEMFC)possesses the conductive polymer film as an electrolyte which is similar to proton exchange membrane fuel cell.Meanwhile AEMFC can use non-precious metal catalyst,which is more affordable than PEMFC who must use platinum and other precious metal catalyst.Based on the above advantages,AEMFC has received increasing attention in the past few years.Anion exchange membranes(AEM),as the core component of AEMFC,have not met the commercialized films that satisfy the requirements.This is mainly due to the fact that most of the commercial AEMs currently have a low conductivity,poor dimensional stability and chemical stability,etc.In order to solve these problems,the current research workers generally stand in two angles for AEM research,respectively,the synthesis of new anionic conductive groups and specific polymer structure design.The purpose of this former is to focus on the anion conductivity and chemical stability of many different anionic conductive groups.The study of polymer structure design focuses more on obtain an AEM withexcellent performance through designing the molecular structure of polymer.Many researchers have attempted to quaternizate the corresponding AEM directly in the backbone of PPO or poly(arylene ether).But when the degree of quaternization is too high,AEM exhibits uncontrollable swelling,and more water absorption also increases the risk of hydroxide nucleophilic attack.Therefore researchers attempted to introduce quaternary amine groups in the polymer side chain to separate the hydrophobic phase,while concentrating the quaternary amine groups to form a more aggregate hydrophilic phase.This will achieve the purpose of ensuring the ionic conductivity while reducing the swelling of AEM.Therefore,we introduce this kind of idea in this paper,design and synthesize polymer containing high concentration quaternary ammonium groups on pendant,hoping to get the AEM material with relatively excellent ion conductivity,dimensional stability and chemical stability.First,we selected PAEK as hydrophobic chain skeleton.The iodine-containing hydroquinone was obtained and reacted with 4,4'-difluorobenzophenone and 4,4'-(hexafluoroisopropylidene)diphenol.A series of side chain iodinated poly(arylene ether ketone)s(I-PAEK-x)were prepared.The carbazole-containing grafting monomer was obtained by Suzuki coupling reaction and grafted to I-PAEK-x by Urmann coupling to obtain MeCz-PAEK-x.Hereafter MeCz-PAEK-x was brominated with NBS and BPO to obtain BrCz-PAEK-x.Due to the bromination reaction that occurs on the benzene ring on the carbazole consuming part of the NBS,we had conducted a number of tests to explore the conditions to meet the requirements of bromination.Followed by filming and quaternization,we obtained QACz-PAEK-x AEMs.The 1H NMR results showed that the grafting rate of I-PAEK-x and the bromination rate of MeCz-PAEK-x were all above 80%,which was basically satisfied with our requirements.In addition,QACz-PAEK-x has good thermal properties,mechanical properties,dimensional stability,ion conductivity and chemical stability.In particular,comparing with other main chain-type quaternized AEMs with similar main chain structures,QACz-PAEK-x have higher conductivity and lower swelling under the same IEC conditions.These excellent properties are attributed to the apparent hydrophobic microphase separation resulting from their side chain dense quaternized structure,which is more conducive to the formation of ion transport channels.At the same time,QACz-PAEK-x showed good alkali stability in 4 mol/L NaOH solution,which was mainly due to the inhibition of hydroxide attack by continuous conjugated carbazole groups.Of course,the continuous rigid side chain structure makes the polymer with high IEC more brittle,which decreased the mechanical properties of the material.In the subsequent second part of the experiment,we continued to maintain the side chain dense quaternized structure of the polymer to increase the more effective phase separation.In the meanwhile we establish alkyl space between the hydrophobic backbone and the hydrophilic side chain to avoid the disadvantages of rigid molecular structure.In the specific experimental procedure,we obtained the grafting monomer by reacting 1,6-dibromohexane with the carbazole monomer synthesized in the first part.The grafting monomer was attached to the PAEK-OH-x to obtain side chain poly(alkyl ether ketone)containing long alkyl quaternized carbazole(PAEK-HMeCz-x).Through the free radical bromination,filming and quaternization of PAEK-HMeCz-x,we can obtain poly(arkyl ether ketone)anion exchange membrane(PAEK-HQACz-x)containing long alkyl quaternary carbazole side chains.The performance of PAEK-HQACz-x anion exchange membrane was tested,and we found that PAEK-HQACz-0.7 with the highest IEC have pretty high hydroxide conductivity(98.1 mS/cm at 80 oC).The PAEK-HQACz-x has a significant increase in tensile elongation compared to QACz-PAEK-x.Correspondingly,the alkali stability of PAEK-HQACz-x has been greatly improved.It is mainly due to that the electron donation of the alkyl chain can inhibit the hydroxide ion nucleophilic attack on quaternary amine groups.In summary,we chose poly(arylene ether ketone)as a hydrophobic backbone,and introduced large free volume and rigid tetrabenzyl quaternized carbazole and long alkyl space tetrabenzyl quaternized carbazole in the side chain respectively to get two different kind of AEM.Then the characterization and performance tests of the two groups were also investigated,and further discussions will be carried out.The results confirm that side chain densely quaternized AEMs have excellent performance and potential prospects.