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PhenyltrimethylammoniumFunctionalized Polysulfone Anion Exchange Membranes†
Li, Nanwen,Zhang, Qiang,Wang, Chenyi,Lee, Young Moo,Guiver, Michael D. American ChemicalSociety 2012 Macromolecules Vol.45 No.5
<P>Anion exchange membrane (AEM) materials were preparedfrom commercial polysulfone (PSf) by functionalization with tertiaryamines via lithiation chemistry. By optimizing the reaction conditions,a degree of substitution (DS) of 0.81 could be achieved without evidentpolymer decomposition or cross-linking. The PSf containing pendentbis(phenyldimethylamine) substituents were then quaternized with CH<SUB>3</SUB>I and ion exchange reaction to provide bis(phenyltrimethylammonium)(PTMA) polymer with hydroxide-conductive properties. Flexible andtough membranes with various ion exchange capacities (IEC)s couldbe prepared by casting the polymers from DMAc solutions. The ionomericmembranes showed considerably lower water uptake (less than 20%),and thus dimensional swelling in water, compared with many reportedAEMs. The hydroxide conductivities of the membranes were above 10mS/cm at room temperature. The unusually low water uptake and goodhydroxide conductivity may be attributed to the “side-chain-type”structures of pendent functional groups, which facilitate ion transport.Although the PTMA substituents on the AEM were found to have insufficientlong-term stability for alkaline fuel cell application, the investigationgives some insight and directions for polymeric designs by postfunctionalization.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2012/mamobx.2012.45.issue-5/ma202681z/production/images/medium/ma-2011-02681z_0005.gif'></P>
Enhancement of Proton Transport by Nanochannels in Comb‐Shaped Copoly(arylene ether sulfone)s
Li, Nanwen,Wang, Chenyi,Lee, So Young,Park, Chi Hoon,Lee, Young Moo,Guiver, Michael D. WILEY‐VCH Verlag 2011 Angewandte Chemie Vol.123 No.39
<P><B>Frisierte Membran</B>: Kammförmige Copolymere mit Poly(arylenethersulfon)‐Rückgrat (PAES) und hoch sulfonierten Poly(phenylenoxid)‐Seitenketten (PPO) bilden Nanokanal‐Morphologien (siehe Bild) für einen effizienten Protonentransport. Ihre Protonenleitfähigkeit ist bei partieller Hydratisierung entschieden höher als bei typischen Kohlenwasserstoffpolymer‐Elektrolyten. SA: Sulfonsäuregruppe.</P>
Densely Sulfophenylated Segmented Copoly(arylene ether sulfone) Proton Exchange Membranes
Li, Nanwen,Hwang, Doo Sung,Lee, So Young,Liu, Ying-Ling,Lee, Young Moo,Guiver, Michael D. American Chemical Society 2011 Macromolecules Vol.44 No.12
<P>Segmented copoly(arylene ether sulfone) membranes having densely sulfonated pendent phenyl blocks were synthesized by the coupling reaction of phenoxide-terminated oligomers with bis(4-hydroxyphenyl) sulfone and decafluorobiphenyl (DFBP), followed by postpolymerization sulfonation of the blocks containing pendent phenyl substituents. The coupling reaction was conducted at relatively low temperature by utilizing highly reactive DFBP to prevent any possible trans-etherification that would randomize the hydrophilic–hydrophobic sequences. Segmented copolymer molecular weights were reasonably high, as determined by viscosity measurements. Postsulfonation occurred selectively on the pendent phenyl substituent to yield hydrophilic blocks that were highly sulfonated in regular sequence on the linked phenyl rings. The resulting polymers gave transparent, flexible, and tough membranes by solution casting. Morphological observation by transmission electron microscopy (TEM) and atomic force microscopy (AFM) showed that the high local concentration and regular sequence of pendent sulfonic acid groups within the hydrophilic blocks enhanced nanophase separation between the hydrophobic and hydrophilic blocks. A comparison of copolymers with similar ion exchange capacities (IECs) indicated that proton conductivity and water uptake were strongly influenced by the hydrophilic block sequence lengths. Proton conductivity and water uptake increased with increasing block length, even at low relative humidity (RH). The ionomer membrane with <I>X</I>20<I>Y</I>20 (<I>X</I> and <I>Y</I> refer to the number of hydrophilic and hydrophobic repeat units, respectively) and 1.82 mequiv/g of IEC had a proton conductivity of 3.6 × 10<SUP>–2</SUP> S/cm at 80 °C and 50% RH, which is comparable to that of perfluorinated ionomer (Nafion) membrane (4.0 × 10<SUP>–2</SUP> S/cm).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2011/mamobx.2011.44.issue-12/ma200937w/production/images/medium/ma-2011-00937w_0004.gif'></P>
A new class of highly-conducting polymer electrolyte membranes: Aromatic ABA triblock copolymers
Li, Nanwen,Lee, So Young,Liu, Ying-Ling,Lee, Young Moo,Guiver, Michael D. The Royal Society of Chemistry 2012 Energy & environmental science Vol.5 No.1
<p>Highly proton-conducting polymer electrolyte membrane (PEMs) materials are presented as alternatives to state-of-the-art perfluorinated polymers such as Nafion<SUP>®</SUP>. To achieve stable PEMs with efficient ionic nanochannels, novel fully aromatic ABA triblock copolymers (SP3O-<I>b</I>-PAES-<I>b</I>-SP3O) based on sulfonated poly(2,6-diphenyl-1,4-phenylene oxide)s (A, SP3O) and poly(arylene ether sulfone)s (B, PAES) were synthesized. This molecular design for a PEM was implemented to promote the nanophase separation between the hydrophobic polymer chain and hydrophilic ionic groups, and thus to form well-connected hydrophilic nanochannels that are responsible for the water uptake and proton conduction. Relative to other hydrocarbon-based PEMs, the triblock copolymer membranes showed a dramatic enhancement in proton conductivity under partially hydrated conditions, and superior thermal, oxidative and hydrolytic stabilities, suggesting that they have the potential to be utilized as alternative materials in applications operating under partly hydrated environments.</p> <P>Graphic Abstract</P><P>Fully aromatic ABA triblock copolymers with highly sulfonated blocks provide nanochannels leading to efficient proton transport. <img src='http://pubs.rsc.org/ej/EE/2012/c1ee02556b/c1ee02556b-ga.gif'> </P>
Lee, So Young,Kang, Na Rae,Shin, Dong Won,Lee, Chang Hyun,Lee, Kwan-Soo,Guiver, Michael D.,Li, Nanwen,Lee, Young Moo The Royal Society of Chemistry 2012 ENERGY AND ENVIRONMENTAL SCIENCE Vol.5 No.12
<P>We present a new approach of morphological transformation for effective proton transport within ionomers, even at partially hydrated states. Highly sulfonated poly(phenylene sulfide nitrile) (XESPSN) random network copolymers were synthesized as alternatives to state-of-the-art perfluorinated polymers such as Nafion<SUP>®</SUP>. A combination of thermal annealing and cross-linking, which was conducted at 250 °C by simple trimerisation of ethynyl groups at the chain termini, results in a morphological transformation. The resulting nanophase separation between the hydrophilic and hydrophobic domains forms well-connected hydrophilic nanochannels for dramatically enhanced proton conduction, even at partially hydrated conditions. For instance, the proton conductivity of XESPSN60 was 160% higher than that of Nafion<SUP>®</SUP> 212 at 80 °C and 50% relative humidity. The water uptake and dimensional swelling were also reduced and mechanical properties and oxidative stability were improved after three-dimensional network formation. The fuel cell performance of XESPSN membranes exhibited a significantly higher maximum power density than that of Nafion<SUP>®</SUP> 212 under partially hydrated environments.</P> <P>Graphic Abstract</P><P>Morphologically transformed XESPSN <I>via</I> simple thermal trimerisation of end ethynyl groups shows enhanced proton transport even at partially hydrated states. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2ee21992a'> </P>