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Synthesis and Characterization of Novel Cross-linked Quaternized Poly(Vinyl Alcohol) Anion Exchange Membranes Based on Morpholine

Author: YeLi
Tutor: GuanRong
School: Hubei University
Course: Polymer Chemistry and Physics
Keywords: Anion exchange membrane poly(vinyl alcohol) Crosslinking Quaternization
CLC: TQ320.721
Type: Master's thesis
Year: 2012
Downloads: 42
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Low cost fabrication of anion exchange membranes with excellent electrical and thermal properties via relatively simple procedure in an environmental way is one of the research hotspots nowdays. With unique structural advantage, these membranes can be applied in producing of alkaline anion exchange membrane fuel cell. In this paper, firstly we prepared a mild and nontoxic quaternization agent (MGMC), which is then introduced to the backbone of poly(vinyl alcohol) with low cost and good film-forming ability by one step. Secondly the bisphenol-A epoxy resign E44(DGEBA) was innovatively choosed as a crosslinking agent which can react with QPVA generating polymer network. After alkalization, we obtained a series of novel cross-linked and quaternized anion exchange membranes. The structure of quaternization agent was tested and confirmed. The preparation and characterization of the quaternized poly(vinyl alcohol) membranes and the cross-linked and quaternized poly(vinyl alcohol) membranes were investigated, and the application of the membranes for alkaline anion exchange membrane fuel cell had been discussed.The MGMC was prepared using N-methylmorpholine (MML) and epichlorohydrin (ECH) as raw matrerials and acetonitrile as the solvent. The structure of product was confirmed by FTIR and1HNMR.With MGMC as a quaternization agent, sodium hydride as the catalyst and DMSO as the solvent, modification of PVA was carried out with varing different mole feed ratios. The quaternization reaction was confirmed by FTIR,1HNMR, CHN and XRD. which proved that aliphatic morpholine rings were grafted onto the polymer matrix. The properties of quaternized poly(vinyl alcohol) membranes, including surface morphology, solubility, DMA and TGA were investigated. The results showed that a few bulges emerged on the surface of QPVA membranes, and rugged textures and small fissures emerged on the cross-section, which all can be explained as grafted aliphatic morpholine ring units. The QPVA had good solubility in H2O and DMSO, implied its good film-forming property. The motion of polymer chain bacame harder after quaternization, leading Tg move to a higher temperature. Different from previous literatures, although the initial degration temperature was brought down to165℃, the degration mass was reduce by25.54%comparing with the unquaternized PVA, thermal stability was improved as a whole.Using DMSO as the solvent and DGEBA as a novel crosslinker, a series of different crosslinked and quaternized poly(vinyl alcohol) membranes were prepared by varing the amount of DGEBA. The crosslinking reaction was was confirmed by FTIR, solubility and XRD. The properties of crosslinked and quaternized poly(vinyl alcohol) membranes, including surface morphology, TGA, DMA, mechanical property, contact angle, wateruptake, dimensional stability, ion exchange capacity, oxidation stability and ionic conductivity were systematically investigated. The results showed that the hydrophilicity and water uptake of the QPVA membranes after crosslinking were both decreased. The dimensional stability decreased with the rasing of temperature. The membranes had good mechanical property, which could meet the requirment of AEM. Tg of QPVA raised from68℃to116℃owing to crosslinking which limitted the movement of polymer chains. The thermal and oxidation stabilities were also improved, and the thermal degration temperature could be above210℃The IEC increased with the feed mole ratio of MGMC/PVA. Ionic conductivity increased with temperature, the optimal value could reach5.21X10-2S·cm-1at60℃in water.

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