Synthesis And Properties Of Quaternized Poly(Arylene Ether Ketone)s With Quaternary Ammonium Groups On Pendant

In the21stcentury, power sources and environment are attracting the attention of the wholeworld. A fuel cell is a device that converts the chemical energy from fuel into electricity through achemical reaction with oxygen or another oxidizing agent. The reason for higher efficiency of fuelcells is that they are electrochemical engines, not heat engines, and as such they are not subject toCarnot cycle limitations. Hence fuel cells and their applications with rapid development havebecome a hot area of research for decades. Compared to the well-developed proton exchangemembrane fuel cells (PEMFCs), the electrolyte of alkaline fuel cell is in alkali environment. Thenon-noble metal catalyst can be employed in AFCs and oxygen reduction reaction will be moreefficient. This type of fuel cell will never suffer from the high cost of platinum catalyst. The onlydisadvantage of AFCs is the carbonation of electrolyte which will degrade the performance. Anionexchange membrane fuel cells (AEMFCs) are similar with PEMFCs in the polymer membraneelectrolyte. AEMFCs combine the advantage of AFCs and PEMFCs. The unexpected carbonationcan be avoided by use of polymer membrane electrolyte. So AEMFCs may be an ideal replacementof PEMFCs and AFCs.For now, most of the commercialized AEMs possess the high thickness which lead to a highresistance and low ion conductivity. They still have a curve to climb to meet the requirements ofAEMFCs. Heterogeneous AEMs, AEMs based on interpenetrating polymer network (IPN) andhomogeneous AEMs were developed. The definition of the heterogeneous AEMs is an anionexchange materials embedded in an inert compound. Limited by the nature of polymers, excessaddition of inert compound will inevitably break the stability of polymers. The life duration ofAEMs will be shorten as a result of backbone degradation. IPN is a combination of at least twopolymer in network form, of which at least one is synthesized and/or cross-linked. The dimensionalstability of AEMs based on IPN are well controlled because of the high degree of crosslinking.But the strong phase-separation breaks the connection of hydrophilic domains and a highconductivity cannot be obtained. With the biggest concern, Homogeneous AEMs with covalentlyconnected conductive groups form a one-phase system. According to the synthetic route, homogeneous AEMs can be obtained from three strategies: polymerization of an ionized monomer,introduction of cationic character on a preformed film, introduction of cationic moieties bychemical modification in to a polymer. The most common method is post-modification on apolymer. To disentangle the conductivity-dimensional stability dilemma, the aggregation ofsulfuric groups is proved to be effective in the study of PEMs. In the thesis, the same idea is appliedto prepare high performance AEMs materials.This thesis includes four parts. First,3,5-dimethylphenyl hydroquinone was synthesized andconfirmed by1H NMR spectroscopy. Along with4,4’-difluobenzophenone and4,4’-(hexafluoroisopropylidene) diphenol, DMPAEK-x were obtained from nucleophilicpolycondensation. Using NBS as the bromination agent and BPO to initiate the free radicalreaction, DMPAEK-x were brominated to BrPAEK-x. The BrPAEK-x membranes were immersedinto trimethylamine aqueous solution to convert to QMPAEK-x via quaternization. The degree ofbromination is about70%. Good thermal stability, dimensional stability, chemical stability andmethanol resistance were observed in QMPAEK-x. Compared to some reported main chain typeAEMs, high conductivity was observed in QMPAEK-x. Higher elongation was observed inQMPAEK-x than poly(arylene ether) with one-trimethylbenzylammonium groups on pendant.This shows that the performance of AEMs are enhanced because conductive groups were graftedon pendant.Secondly, a difluoride monomer with tetra-phenyl moieties were designed and synthesized.Comb-shaped PAEK-TPM-x were copolymerized from the difluoride monomer,4,4’-difluobenzophenone and4,4’-(hexafluoroisopropylidene) diphenol. The electron-rich phenyls onthe terminal of side chain can be chloromethylated and the phenyls on backbone were deactivatedby the electron-withdrawing groups. After optimizing the condition of chloromethylation onPAEK-TPM-x, the degree of chloromethylation is about90%. The deactivation of main chain wasconfirmed by blank test on PAEK-TPM-0. The quaternized PAEK-QTPM-x were prepared fromPAEK-CTPM-x membranes. The highest chloride conductivity at80oC of PAEK-QTPM-30was0.047S cm-1. The conductivity of PAEK-QTPM-x membranes have advantages over AEMs withsimilar structures, especially at low level of IEC. The nano-phase separation was observed inPAEK-QTPM-30by SAXS. It means that the ionic cluster was concentrated in membrane and webelieve this is the reason for the enhancement in PAEK-QTPM-x. In the third part, homogeneous and heterogeneous quaternization on PAEK-CTPM-x werecompared and1,2-dimethylimidazole was employed for homogeneous quaternization. The effectof different quaternization methods and conductive groups was investigated. By analyzing theresults, different quaternization methods have no effect on IEC which means that PAEK-hoQTPM-x and PAEK-heQTPM-x are same in chemical structure. Lower water uptake contents and swellingratio were observed in PAEK-hoQTPM-x membranes, but conductivity and methanol permeabilitywere a bit higher than PAEK-heQTPM-x membranes. Mechanical properties, chemical stabilityand thermal stability make no difference. It means that cations on the ionized PAEK-hoQTPM-xwere aggregated in the film casting solution. The aggregation benefits the conductivity anddimensional stability. It is worth mentioning, PAEK-ImTPM-x exhibited better thermal stabilityand chemical stability due to the very stable pentacyclic imidazole.In the last part, a tertiary amine carrying quaternary ammonium chloride was synthesized toprepare high densely di-quaternized PAEK-DQTPM-x via homogeneous quaternization.Compared with mono-quaternized PAEK-QTPM-x, higher chloride conductivity was observed inPAEK-DQTPM-x. At the same level of IEC, improvements of water uptake contents, swellingratio and mechanical properties were found in PAEK-DQTPM-x. The degree of ionic clusteraggregation is higher than mono-quaternized PAEK-QTPM-x. The PAEK-DQTPM-x membranesshowed a stronger aggregation than PAEK-QTPM-x. The space between hydrophilic domains isinversely proportional to IEC and much smaller than PAEK-QTPM-x. It is proved that PAEK-DQTPM-x with higher ionic cluster aggregation possess better performance.In summary, several series of poly(arylene ether ketone)s with quaternized pendant weresynthesized. The relationship between structure and properties was studied. The thesis proved thataggregated conductive groups located on side chain will enhance the integrated performance.