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Through the radiation-induced grafting of 2-methyl-N-vinylimidazole (MNVIm) and styrene (St) into a poly(ethylene-co-tetrafluoroethylene) film, polyvinylimidazolium hydroxide-grafted anion-conducting polymer electrolyte membranes (AEMs) (MNVIm/St-AEM (OH)) were prepared to prevent two main degradation routes of an imidazolium group (i.e., β-elimination and ring opening hydrolysis reactions). The treatment of MNVIm/St-AEM with a MNVIm/St molar ratio of 6/4 and an ion-exchange capacities (IEC) of 2.08 mmol g−1 in short time in 1 M potassium hydroxide (KOH) at 80 °C converted part of imidazolium units to ethene monomer units (En), resulting in the formation of terpolymer-grafted membranes (MNVIm/En/St-AEM) (41/26/33) with an IEC of 1.05 mmol g−1. The MNVIm/En/St-AEM (initial conductivity: 53 mS cm−1) maintained conductivity levels of higher than 10 mS cm−1 for 600 h in 1 M KOH and 1300 h with an actual fuel of 5% hydrated hydrazine in 1 M KOH at 80 °C, respectively. By using copoly(N-vinyl-2-methyl-3-hexylimidazolium hydroxide-co-St) ionomer with a polymer structure similar to that of the MNVIm/St-AEM graft copolymer, the MNVIm/St-AEM demonstrated a maximum power density of 230 mW cm−2 in a direct hydrazine hydrate fuel cell. This power density is more than three times higher than that assembled with the N-vinylimidazole containing AEM (NVIm/St-AEM).

We studied anion transport behaviors in grafted anion exchange membranes (AEMs) composed of 2-methyl-N-vinylimidazole (Im) and styrene (St) having various Im/St ratios (6/4, 4/6, and 3/7) grafted onto poly(ethylene-co-tetrafluoroethylene) films (named AEM64, AEM46, and AEM37). The transport properties were evaluated based on the transport efficiency defined as ratios of anion diffusion coefficients in AEMs to dilution solutions (D/D0) and were correlated to the morphology of AEMs analyzed by the small angle scattering method. We found a master curve of D/D0 with hydration for AEM64, regardless of the grafting degree and anion species; however, D/D0 for AEM46 and AEM37 was similar with AEM64 at low hydration conditions, but clearly deviated down from it at high hydration conditions. Such difference could be elucidated by the membrane morphology. For AEM64, the conducting phase was homogeneous comprised dispersed ions, and the conductivity correlated well with the increasing hydration. In contrast, when the styrene content increased (i.e., AEM46 and AEM37), the conducting phase changed to heterogeneous with water puddles separated from dispersed ions, and the anion transport was suppressed. Results in this work gave a mechanistic insight in the anion transport properties in proximity of the AEM morphology at various hydration conditions.

Two imidazolium based graft-type of anion-conducting electrolyte membranes (AEMs) for fuel cells with a moderate ion exchange capacity of ∼1.0 mmol/g were successfully prepared by radiation-induced grafting to introduce imidazolium and styrene units into a poly(ethylene-co-tetrafluoroethylene) (ETFE) base film. Though imidazolium groups were desired to connect with styrene groups via two different ways, i.e. parallel or perpendicular orientations to the graft-polymer chains via copolymerization (AEM1) or homo-polymerization (AEM2), both AEMs possess high ion conductivity (>100 mS/cm at 60 °C) and modest stability. The morphologies of these membranes were elucidated by small-angle neutron scattering method. Our results revealed that 1) both AEMs show clear microphase separation with a length scale of 30–40 nm, and the semi-crystalline structural feature of the hydrophobic microdomains contributes to the membrane mechanical property; 2) at the length scale

The β-hydrogen-free imidazole monomer, 2-methyl-N-methyl-4(5)-vinylimidazole (2M4VIm), is synthesized to prepare anion exchange membranes (AEMs). The radiation-induced graft polymerization of 2M4VIm and styrene is performed in poly(ethylene-co-tetrafluoroethylene), followed by N-alkylation and ion exchange reactions to prepare 4-vinylimidazolium-containing AEM (2M4VIm/St-AEM). AEMs that have a 6/4 2M4VIm/St molar ratio and 1.7 mmol g−1 ion exchange capacity (IEC) result in 75 mS cm−1 conductivity and 60% water uptake at room temperature in water, demonstrating enhanced values compared to previously reported 2-methyl-N-vinylimidazolium-containing AEMs (2MNVIm/St-AEM) that have a similar comonomer ratio and IEC. The small-angle neutron scattering measurements of dry and swollen 2M4VIm/St-AEM reveal hydrophilic/hydrophobic two-phase separation, as observed for 2MNVIm/St-AEM with a similar Im/St composition. 2M4VIm/St-AEMs exhibit higher alkaline stability in 1 m KOH at 80 °C at an early stage owing to the suppression of imidazolium β-elimination but lower long-term stability than that of 2MNVIm/St-AEM due to the ring-opening reaction of the imidazolium group due to its outward orientation from the graft main chain.

We found unprecedented reverse relationships in anion-exchange membranes (AEMs) for Pt-free alkaline fuel cell systems, i.e., the increase in hydrophobicity increased water uptake and susceptibility to hydrolysis. AEMs with graft copolymers that composed of anion-conducting 2-methyl-N-vinylimidazolium (Im) and hydrophobic styrene (St) units were employed. We characterized two new structures in these AEMs using a small-angle neutron scattering with a contrast variation method. (1) The distribution of graft polymers in conducting (ion channel) or non-conducting (hydrophobic amorphous poly(ethylene-co-tetrafluoroethylene) (ETFE)) phase was evaluated in a quantitative manner. High fraction in conducting layer for AEMs having high grafting degrees was found using the proposed structural model of "conducting/non-conducting two-phase system". (2) Assuming a hard-sphere fluid model, we found AEMs having high St contents and low alkaline durability possessed nanophase-separated water puddles with diameters of 3-4 nm. The AEM having a low St content and the best alkaline durability did not show evident nanophase separation. The above hierarchical structures elucidate the unexpected reverse relationships that the AEM having highly hydrophobic graft polymers was subjected to the morphological transition to give water puddles at nanoscale. The imidazolium groups that were located at the boundary between graft polymers and water puddles should be susceptible to hydrolysis.

The β-hydrogen-free imidazole monomer, 2-methyl-N-methyl-4(5)-vinylimidazole (2M4VIm), is synthesized to prepare anion exchange membranes (AEMs). The radiation-induced graft polymerization of 2M4VIm and styrene is performed in poly(ethylene-co-tetrafluoroethylene), followed by N-alkylation and ion exchange reactions to prepare 4-vinylimidazolium-containing AEM (2M4VIm/St-AEM). AEMs that have a 6/4 2M4VIm/St molar ratio and 1.7 mmol g−1 ion exchange capacity (IEC) result in 75 mS cm−1 conductivity and 60% water uptake at room temperature in water, demonstrating enhanced values compared to previously reported 2-methyl-N-vinylimidazolium-containing AEMs (2MNVIm/St-AEM) that have a similar comonomer ratio and IEC. The small-angle neutron scattering measurements of dry and swollen 2M4VIm/St-AEM reveal hydrophilic/hydrophobic two-phase separation, as observed for 2MNVIm/St-AEM with a similar Im/St composition. 2M4VIm/St-AEMs exhibit higher alkaline stability in 1 m KOH at 80 °C at an early stage owing to the suppression of imidazolium β-elimination but lower long-term stability than that of 2MNVIm/St-AEM due to the ring-opening reaction of the imidazolium group due to its outward orientation from the graft main chain.

We have been developing highly-conductive and alkaline-durable anion-conducting electrolyte membranes (AEMs) for a platinum-free fuel cell (FC) for liquid fuel (hydrated hydrazine) type vehicles. Even though the AEM-FC system have been significantly attractive because of non-precious metals used as active catalysts, there is no commercially available AEMs due to severe alkaline operating condition.1) We applied the radiation-induced grafting technique to introduce imidazolium-based graftpolymers into thermally and mechanically tough poly(ethylene-co-tetrafluoroethylene) (ETFE) to develop new AEMs with high conductivity and alkaline durability (Scheme 1). Our strategy to overcome the alkaline unstable character of AEMs is as follows. (1 ) Basicity control of anion-conducting groups (ACG) in AEMs. The weak base is utilized for ACG to suppress the self-degradation of the membranes and high water uptakes to be stabilized because most of the AEMs possess tetraalkylammonium hydroxides as an ACG, which is well known as one of the strongest organic bases. Furthermore, the weak base AEMs should have less water uptakes due to their own stability. From the comparison of the N-alkylated forms of 5 different diaza-compounds as an ACG, the imidazolium-based AEMs (AEM(Im)) possess the high conductivity and low water uptake compared with tetraalkylammonium-type AEMs (Scheme 2). (2) Alkaline-durability of the imidazolium-based AEMs. The N-methylated imidazolium cation in AEMs are subjected to β-elimination and hydrolytic ring opening degradation to reduce the anionic conductivity in alkaline solution (1M KOH, 80°C). Therefore, for suppressing β-elimination, we introduced the graft-copolymers of vinylimidazolium with styrene because the adjacent vinylimiazolium cations led very fast elimination due to the double β-positioned hydrogen.2) Furthermore, for suppressing hydrolysis, the protecting group is introduced at 2-posion of imidazolium ring, which are subject to hydroxide attack (Scheme 2). The AEM(MIm/St) with a MIm/St ratio of 60/40 shows gradual decreases of conductivity in the alkaline solution. The alternative copolymer grafts of 2-methylimidazolium and α-methylstyrene in AEMs (AEM(MIm/aMS)), which has no adjacent imidazolium units, totally suppressed the alkaline degradation in the alkaline solution. This durability improvement strongly indicates that the alternative structure suppressed not only β-elimination but also the ring-opening degradation. As the results, the AEM(MIm/aMS) keeps their initial conductivity (50 mS/cm) in more than 1000 hours in 1M KOH at 80 °C. The high conductivity and alkaline durability of the abovementioned methylimidazolium-based AEMs can be well elucidated from the hierarchical structures of the AEMs. By contrast variation small angle neutron scattering (SANS) technique, we revealed the detailed hierarchical structures of AEM(MIm/St); the original crystalline lamellar domains of a ETFE base film and interconnected hydrated domains, composed of the entire graft chains and water, offer good mechanical properties and the conductivity, respectively.3) Using the SAXS measurement, by which the internal structure of ion channels at a length scale < 2 nm can be observed, AEM(MIm/St) has the characteristic “ion-pair” distributed in the ion-channels at RH < 80%. Namely, the ion-channels are disconnected at 80% RH but well-connected in liquid water. Judging from this RH dependence, the disconnected ion-channels even under relatively high humidified conditions (80% RH) should be the substantial factor for lower power generation efficiency of AEM-type fuel cells than those of PEM systems. We next analyzed the AEM(MIm/St) with different monomer compositions. Contrary to the above mentioned AEM(MIm/St) (MIm/St ratio of 60/40), the AEM with higher styrene ratios (MIm/St = 40/60 and 20/80) showed less durability in the alkaline solution. By a SANS contrast variation method only the AEMs with MIm/St = 40/60 and 20/80 showed new water puddle sphere with a diameter of 3-4 nm and the volume composition of spheres increases with the increases of styrene ratios. Thus, we concluded that the imidazolium groups around the water puddle are subjected to the hydrolytic attack to lead the degradation of the AEMs. Now, we are analyzing the hierarchical structures of AEM(MIm/aMS) to reveal the structural reasons for the highest alkaline durability so far. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST). References 1) J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. Xu and L. Zhuang, Energy Environ. Sci., 7, 3135 (2014). 2) K. Yoshimura, H. Koshikawa, T. Yamaki, H. Shishitani, K. Yamamoto, S. Yamaguchi, H. Tanaka and Y. Maekawa, J. Electrochem. Soc., 161(9), F889 (2014). 3) Y. Zhao, K. Yoshimura, H. Shishitani, S. Yamaguchi, H. Tanaka, S. Koizumi, N. Szekely, A. Radulescu, D. Richter and Y. Maekawa , Soft Matter, 12, 1567 (2016). Figure 1

In our previous study (Soft Matter, 2016, 12, 1567), the relationship between the morphology and properties of graft-type imidazolium-based anion exchange membranes (AEMs) was revealed, in that the semi-crystalline features of the polymer matrix maintain its mechanical properties and the formation of interconnected hydrophilic domains promotes the membrane conductivity. Here, we report a novel ionic structure of the same graft-type AEMs with different grafting degrees, analyzed using a small-angle X-ray scattering method under different relative humidity (RH) conditions. The characteristic “ionomer peak” with a corresponding correlation distance of approximately 1.0 nm was observed at RH < 80%. This distance is much smaller than the literature-reported mean distance between two ionic clusters, but close to the Bjerrum length of water. Since the representative number of water molecules per cation, nw, was small, we proposed that dissociated ion-pairs are distributed in the hydrophilic domains (ion-channels). At RH < 80%, ion-channels are disconnected, however in liquid water, they are well-connected as evidenced by the sharp increase in nw. The disconnected ion-channels even under relatively high RH conditions should be a substantial factor for the low power generation efficiency of AEM-type fuel cells.

We investigated the morphology and swelling behavior of a new graft-type of anion exchange membrane (AEM) containing 2-methylimidazolium groups by using a contrast variation small angle neutron scattering (SANS) technique. These AEMs were prepared by radiation-induced grafting of 2-methyl-1-vinylimidazole and styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and subsequent N-alkylation with methyliodide, and possessed both high alkaline durability and high conductivity. Our results showed that the crystalline lamellar and crystallite structures originating from the pristine ETFE films were more or less conserved in these AEMs, but the lamellar d-spacing in both dry and wet membranes was enlarged, indicating an expansion of the amorphous lamellae due to the graft chains introduced in the grafting process and the water incorporated in the swelling process. For the first time, the swelling behavior of the AEMs was studied quantitatively in various water mixtures of water and deuterated water with different volume ratios (contrast variation method), and the morphology of these membranes was elucidated by three phases: phase (1) crystalline ETFE domains, which offer good mechanical properties; phase (2) hydrophobic amorphous domains, which are made up of amorphous ETFE chains and offer a matrix to create conducting regions; phase (3) interconnected hydrated domains, which are composed of the entire graft chains and water and play a key role in promoting the conductivity.

Anion-exchange membranes (AEMs) have been regarded as an alternative to proton-exchange membranes (PEMs) in energy conversion devices, due to the advantage of saving expensive platinum catalysts. However, neither the molecular design nor the property understanding is sufficient for developing AEMs capable of practical fuel cell applications. It is crucial to thoroughly study the current AEMs in terms of microphase structures and conducting properties. Recently, we developed a new graft type of AEMs by radiation-induced grafting method, where imidazolium and styrene monomers were grafted into poly(ethylene-co-tetrafluoroethylene) (ETFE) base films under a dose of 80 kGy from the 60Co γ-ray source (QST, Takasaki), followed by alkylation and ion exchange reactions. These AEMs exhibit well-balanced properties of high ion conductivity (> 100 mS/cm at 80oC) and good stability, which are believed to be controlled by the microphase structure of the membrane. In this report, we investigate the memrbane structure and reveal the relationship between structure and properties, using small-angle neutron scattering (SANS) method. Fig. 1 shows typical SANS intensity profiles, I(q), of pristine ETFE films (profile 1), grafted-ETFE membranes (profile 2), dry AEM (profile 3) and AEM equilibrated in D2O (profile 4) as a function of scattering vector q. The different morphologies which can be deduced from the SANS profiles are also shown in the figure. The experiments confirm the semi-crystalline feature of AEM conserved from the original ETFE base film, which is the key factor for the high membrane mechanical stability, and show the dependence of the structure on hydration. Contrast variation experiments performed on AEM equilibrated in water mixtures of H2O and D2O, further show that graft polymers and water consist the hydrophilic ion channels [1]. Since graft polymers distribute randomly in AEM, well-connected hydrophilic ion channels are feasibly formed, which is the key factor for the high membrane conductivity. Above all, the interplay between the morphology and properties can be characterized as follows: 1) semi-crystalline base film offers good mechanical properties; 2) graft polymers and water form ion channels to promote the conductivity. Figure 1

Anion-conducting electrolyte membrane fuel cells (AEMFCs) have attracted considerable interest due to their significant advantages over proton-conducting electrolyte membrane fuel cells (PEMFC). Because AEMFCs operate under alkaline environments, non-precious metals can be used as active catalysts (e.g. nickel, cobalt and iron) and electrochemical reactions are more facile than that in acidic medium.1) In recent years, we have developed imidazolium-type AEMs by radiation-induced grafting method and founded that copoly(N-vinylimidazolium/styrene)-grafted AEM shows moderate alkaline stability. However, the AEMs degraded via the β-elimination reaction and the ring opening reaction of C2 position.2) In this work, we synthesized p-(2-imidazoliumyl) styrene (2STZ)-grafted membrane (Pr-PrSTZ-AEM) to exclude β-hydrogen from the chemical structure and protect C2 position. The 2STZ monomer was synthesized from 4-vinylbenzyl chlorid)e via the 4-vinylbenzaldehyde. And then, the 2STZ was mono N-alkylated by sodium hydrate and propyl iodide in a standard manner to obtain propylated monomer (PrSTZ).3) Poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated with a 60Co γ-ray source (QST, Takasaki, Gunma, Japan) at room temperature in argon atmosphere with an absorption dose of 50 kGy. The pre-irradiated ETFE films were immediately immersed into the argon-purged monomer solution consisting of 50 vol% of PrSTZ in 1,4-dioxane for 1~16 h. The imidazole groups in the grafted-ETFE were N-alkylated by propyl iodide in a quantitative manner. The obtained Pr-PrSTZ-based AEMs (an iodide form) were immersed in 1M HCl and 1,4-dioxane (1 : 1 volume ratio) solution at 60 °C for 24 h to convert into a Cl- form, followed by the ion-exchange reaction in 1M KOH and 1,4-dioxane (1 : 1 volume ratio) solution at room temperature for 16 h to obtain Pr-PrSTZ-AEM (Scheme 1). The Pr-PrSTZ-based AEMs with IECexp. of 0.54~1.72 mmol/g were converted from the grafted membranes with grafting degrees of 18~98% by quantitative N-alkylation and ion-exchange reaction in more than 90% conversion. The prepared AEMs exhibited 7~78% of water uptakes and 50~181 mS/cm of ionic conductivities at 60°C (Figure 1). The alkaline stability of AEMs was evaluated by monitoring the change in conductivity of AEMs in 1M KOH at 80°C. The conductivity of AEM with a grafting degree of 47% decreased from 125 to 8 mS/cm after 600 h, whereas the conductivity of AEM with a grafting degree of 18% increased from 50 to 60 mS/cm after 600 h. This result indicates that the Pr-PrSTZ-based AEMs with the grafting degree of 18% has moderate ionic conductivity with surprised water uptake and quite high alkaline stability, comparing to copoly(N-vinylimidazolium/ styrene)-grafted AEMs. Therefore, the Pr-PrSTZ-based AEMs are expected as a promising membrane for highly alkaline durable fuel cells. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST). References: 1) J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. Xu and L. Zhuang, Energy Environ. Sci., 7, 3135-3191 (2014). 2) K. Yoshimura, H. Koshikawa, T. Yamaki, H. Shishitani, K. Yamamoto, S. Yamaguchi, H. Tanaka and Y. Maekawa, J. Electrochem. Soc., 161(9), F889- F893 (2014). 3) C. G. Overberger and Y. Kawakami, J. Polym. Sci. Polym. Chem. Ed., 16, 1237-1248 (1978). Figure 1

There has been a growing interest in noble metal-free alkaline fuel cells, in which anion conducting polymer electrolyte membranes (AEMs) required highly alkaline durability because of high temperature and highly basic fuel cell operating condition in the fuel cells. In recent years, we have developed N-vinylimidazolium-type AEMs by radiation-induced grafting for direct hydrazine hydrate fuel cells (DHFCs).1,2 The prepared poly(N-vinylimidazolium)-grafted AEMs (NVIm-AEM) showed moderate alkaline stability, however, these AEMs degraded via the initial β-elimination at the initial stage and hydrolytic ring opening reaction of the imidazolium unit at the later stage.3 In this work, we synthesized the AEM based on a homo- and co-polymer grafts of 2-methyl-N-methyl-4-vinylimidazolium with styrene (2Me-NMe-4VIm-AEM and 2Me-NMe-4VIm/St-AEM) to prevent the β-elimination and ring opening reaction (Figure 1). According to the literature, 4-vinylimidazole (4VIm) was transformed to N-methyl-4-vinilimidazole (NMe-4VIm) by the N-methylation using sodium hydrate and methyl iodide in a 64% yield.4 NMe-4VIm was then reacted with n-BuLi and methyl iodide to give a 2-methyl-N-methyl-4-vinylimidazole monomer (2Me-NMe-4VIm) in a 56% yield (Scheme 1). The poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated with a 60Co γ-ray source (QST Takasaki, Gunma, Japan) at room temperature in argon atmosphere. The pre-irradiated ETFE films were immediately immersed into the argon-purged monomer solution consisting of 5.3 mol/L 2Me-NMe-4VIm or a mixture of 2Me-NMe-4VIm and St (80 : 20 molar ratio) in 1,4-dioxane. The graft reaction proceeds smoothly and gave 2Me-NMe-4VIm and 2Me-NMe-4VIm/St graft ETFE films with the grafting degree of 33% and 54%, respectively. The grafted films were then N-alkylated and ion exchanged to obtain the hydroxide from of 2Me-NMe-4VIm-AEM and 2Me-NMe-4VIm /St-AEM with IECs of 1.38 and 1.74 mmol/g (Scheme 2). The N-alkylation reaction proceeded quantitatively while the un-methylated analogue, a 4-VIm graft ETFE film, showed less reactivity and saturated at around 66% level. 2Me-NMe-4VIm-AEM and 2Me-NMe-4VIm /St-AEM showed conductivities of 175 and 157 mS/cm with water uptakes of 53 and 86%. These AEMs show significantly higher conductivities with lower water uptakes, which are desirable properties for fuel cell applications. The alkaline stability of AEMs was evaluated by the change in conductivity of AEMs in 1M KOH at 80°C. As shown in Figure 2, the conductivity of NVIm-AEM (N-vinyl type AEM) decreased to 0 mS/cm after 100 h, while 2Me-NMe-4VIm-AEM showed higher conductivities than 20 mS/cm after 100 h. The decreasing profile of the 2Me-NMe-4VIm-AEM conductivity indicates that the initial conductivity drop resulting from β-elimination was clearly suppressed by the shift of vinyl substituent from 1- to 4-positon of the imidazolium ring. Also, the decreases of conductivity at the later period, arising from ring opening degradation become much slower for 2Me-NMe-4VIm-AEM owing to the methyl substitution effect at 2-position of the imidazolium ring. The copolymer type 2Me-NMe-4VIm /St-AEM possesses excellent initial and long term alkaline stabilities. Thus, sharp drops of conductivity at the initial stage probably caused by the graft chain detachment, and the introduction of copolymerized styrene units should suppress the detachment phenomenon by hydrophobicity.5 In conclusion, for vinylimidazolium-containing graft-type AEMs, the control of vinyl position, the methyl-protection at 2-positon, and copolymerization with styrene should be promising strategy to improve the alkaline stability, which is the essential property for alkaline fuel cells. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST). References [1] K. Asazawa, K. Yamada, H. Tanaka, A. Oka, M. Taniguchi and T. Kobayashi, Angew. Chem., Int. Ed., 46, 8024 (2007). [2] K. Yoshimura, H. Koshikawa, T. Yamaki, H. Shishitani, K. Yamamoto, S. Yamaguchi, H. Tanaka and Y. Maekawa, J. Electrochem. Soc., 161(9), F889 (2014). [3] Y. Ye and Y. A. Elabd. Macromolecules, 44, 8494 (2011). [4] C. G. Overberger and Y. Kawakami, J. Polym. Sci. Part A Polym. Chem, 16, 1237 (1978). [5] K. Enomoto, S. Takahashi, T, Iwase, T. Yamashita and Y. Maekawa, J. Mater. Chem., 21, 9343 (2011). Figure 1

Due to the growing concerns on the depletion of petroleum based energy resources and the climate change, polymer electrolyte membrane fuel cells (FCs) technologies have received much attention in recent years owing to their high efficiencies and low emissions. Among them, alkaline anion exchange membrane fuel cell (AEM-FC) is a good choice, because it avoids the consumption of acid-resistant precious metal catalysts and costs up. However, the biggest challenge in developing AEM-FCs is to fabricate AEM with high ion conductivity and mechanical stability without chemical deterioration at elevated pH and temperatures. So far, most strategies were focused on synthesizing new thermally and chemically durable fluorinated and aromatic polymers. For the first time, our group tried to develop the new type of 2Me-AEMs by radiation-induced grafting of 2-methyl-1-vinylimidazole and styrene into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and a subsequent N-alkylation with methyliodide. The resultant AEMs exhibit high ion conductivity (> 100 mS/cm) and longer alkaline durability, owing to the fact that the methyl protecting group at 2-imidazole position prevented the ring-opening degradation. 2Me-AEM with an IEC(ion exchange capacity) of 1.82 mmol/g shows the best well-balanced properties required for fuel cell applications. All these findings on one hand, are the result of sample preparation procedure of the radiation grafting method and the introduction of alkylimidazolium cations as an anion conducting group, and on the other hand, are believed to be controlled by the microphase separated structures of the membranes in the hydrated state. In this work, we aim to elucidate the morphology of these 2Me-AEMs and understand the structure related unique properties such as the mechanical property and the anion conductivity. We investigated the morphology and swelling behavior of these new graft-type AEMs by using contrast variation small angle neutron scattering (SANS) technique, performed mainly on KWS-2 SANS diffractometer operated by Juelich Centre for Neutron Science at the neutron source Heinz Maier-Leibnitz (FRM II reactor) in Garching, Germany. Our results showed that the scattering intensity and the shape of the profiles vary significantly upon grafting, but change little upon alkylation; while the incorporation of water in the hydrophilic domains upon swelling, not only increases the intensity and domain size, but also leads to the excess scattering at high-q region with q being the scattering vector. From these results, we concluded that the crystalline lamellar and crystallite structures originating from the pristine ETFE films were more or less conserved in these AEMs, but the lamellar d-spacing in both dry and wet membranes were enlarged, indicating an expansion of the amorphous lamellae due to the graft chains introduced in the grafting process and the water incorporated in the swelling process. We further quantitatively studied the swelling behavior of the AEMs in various water mixtures of water and deuterated water with different volume ratios (contrast variation method), and the morphology of these membranes was elucidated by three phases: phase 1) crystalline ETFE domains, which offer good mechanical properties; phase 2) hydrophobic amorphous domains, which are made up of amorphous ETFE chains and offer a matrix to create conducting regions; phase 3) interconnected hydrated domains, which are composed of the entire graft chains and water and play a key role to promote the conductivity.

Hematopoietic prostaglandin (PG) D synthase (H-PGDS) is responsible for the production of PGD(2) as an allergy or inflammation mediator in mast and Th2 cells. We determined the X-ray structure of human H-PGDS complexed with an inhibitor, 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at 1.9 A resolution in the presence of Mg(2+). The styryl group of the inhibitor penetrated to the bottom of the active site cleft, and the tetrazole ring was stabilized by the stacking interaction with Trp104, inducing large movement around the alpha5-helix, which caused the space group of the complex crystal to change from P2(1) to P1 upon binding of BSPT. The phthalhydrazidyl group of BSPT exhibited steric hindrance due to the cofactor, glutathione (GSH), increasing the IC(50) value of BSPT for human H-PGDS from 36.2 micro M to 98.1 micro M upon binding of Mg(2+), because the K(m) value of GSH for human H-PGDS was decreased from 0.60 micro M in the presence of EDTA to 0.14 micro M in the presence of Mg(2+). We have to avoid steric hindrance of the GSH molecule that was stabilized by intracellular Mg(2+) in the mM range in the cytosol for further development of structure-based anti-allergic drugs.

Introduction An anion exchange membrane (AEM) is one of the key materials for alkaline-type fuel cells (AEMFC), which have potential advantages against proton exchange membrane fuel cells (PEMFC). In the AEMFC, electrochemical reactions are more facile than in acidic medium, and non-precious metals such as nickel, cobalt and iron can replace platinum as the catalyst.1,2 Because of high temperature and highly basic fuel cell operating condition, it is desirable to develop alkaline durable AEMs. In recent years, we have developed imidazolium-type AEMs by radiation-induced grafting for AEMFCs, especially in direct hydrazine fuel cells and found that poly(1-vinylimidazolium (VIm))-grafted and copoly(VIm/styrene)-grafted AEMs (AEM1 and AEM2) shows moderate alkaline stability; the AEMs degraded via the initial β-elimination and following ring opening reactions of the imidazolium unit.3,4 Therefore, we synthesized the AEM based on a poly(2-methyl-1-vinylimidazolium (MVIm)) grafts by radiation-induced grafting to improve long-term stability by suppressing β-elimination and ring opening reactions. Experimental The ETFE films were irradiated with a 60Co γ-ray source (JAEA Takasaki, Gunma, Japan) at room temperature in argon atmosphere with an absorption dose of 50 kGy. The pre-irradiated ETFE films were immediately immersed into the argon-purged monomer solution consisting of 50 wt% MVIm or a mixture of MVIm/stylene (8 : 2 weight ratio) in 1,4-dioxane. The imidazole groups in the grafted-ETFE were N-alkylated using methyl iodide. The resultant AEMs (an iodide form) were immersed in 1 M NaHCO3 solution at 60°C for 24 h to convert into a HCO3 - form, followed by the ion-exchange reaction with OH- in 1 M KOH solution at room temperature for 16 h to givethe anion forms of the AEMs (AEM3 and AEM4), as shown in Scheme 1. The ionic conductivity was measured by two-point probe AC impedance spectroscopy at 100% relative humidity in N2-purged deionized water. The ion exchange capacity (IEC) was measured using standard back titration methods. Results and discussion The poly(MVIm)- and copoly(MVIm/styrene)-grafted ETFE films (precursors of AEM3 and AEM4) were prepared with grafting degrees of 36 and 55%, respectively. The copolymer-type AEM4 was synthesized for reduction of steric and electrostatic repulsions between adjacent imidazolium cations. The N-alkylation for AEM3 proceeds quantitatively. Thus, molar ratio of MVIm and stylene in AEM4 determined from the weight gain after N-alkylation given that the N-alkylation of the imidazole groups proceeded in a quantitative maner was estimated as 1.0 : 1.4. AEM3 and AEM4 with IECs of 0.99 and 0.93 mmol g-1 showed ionic conductivities of 55 and 53 mS cm-1 at 60°C, respectively. The alkaline stability of AEMs was evaluated by monitoring the change in conductivity of AEMs in 1 M KOH at 80°C. Figure 1 shows the normalized conductivities of the AEMs on the basis of the initial conductance as a function of immersion time. The homopolymer-type AEM1 and AEM3 showed similar profiles for conductivity decreases, indicating the donimant β-elimination at an initial stage for homopolymer-type imidazolium grafts in the AEMs due to the steric and electrostatic repulsions. Copolymer-type AEM3, which had no 2-methyl group on the imidazolium group, showed a slower degradation rate after the fast decrease at the initial stage. Furthermore, copolymer-type AEM4, which had 2-methyl group on the imidazolium group, showed slower decreases at the initial stage and kept excellent long-term stability with keeping maintenance factor of 22% (12 mS cm-1) after 600 h immersion. The above results strongly indicate that the introducition of methyl group at 2-position of imidazolium unit drastically enhances the long-term durability in alkaline solutions at elevated temperatures due to the resistance of nucleophilic ring opening reactions of the imidazolium cations. Accordingly, the 2-methylimidazolium units in copolymer grafts in AEMs are promising an anion exchange group for highly alkaline durable direct hydrazine fuel cells. Acknowledgement This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST). References [1] A. Serov and C. Kwak, Appl. Catal B-Environ., 98, 1 (2010). [2] K. Asazawa, K. Yamada, H. Tanaka, A. Oka, M. Taniguchi and T. Kobayashi, Angew. Chem., Int. Ed., 46, 8024 (2007). [3] K. Yoshimura, H. Koshikawa, T. Yamaki, Y. Maekawa, K. Yamamoto, H. Shishitani, K. Asazawa, S. Yamaguchi and H. Tanaka, ECS Trans., 50, 2075 (2012). [4] Y. Ye and Y. A. Elabd. Macromolecules, 44, 8494 (2011).

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Introduction A proton exchange membrane fuel cell (PEMFC) has been developed for application to a residential system, vehicles, and mobile electronic devices. However, PEMFC requires a large amount of precious metal catalysts such as platinum and ruthenium. An anion exchange membrane fuel cell (AEMFC) can potentially overcome the above mentioned problems of PEMFC because the electrode reactions are more facile than in acid, and non-precious metals such as nickel, cobalt and silver can be used as the catalyst. Since the anion conducting groups, for which quaternary ammonium hydroxides are mainly used, are subject to degradation in alkaline solutions at elevated temperatures (AEMFC operating condition), we have applied a radiation-induced grafting method to the preparation of a series of AEM having various cation groups in fluorinated polymer substrates. Previously, we prepared AEM with an imidazolium cation (AEM1) by radiation-induced grafting of vinylbenzyl chloride into poly(ethylene-co-tetrafluoroethylene) (ETFE) film followed by quaternarization of 1-methylimidazole and alkalization (Fig. 1). AEM1 showed moderate conductivity and water-uptake compared with the corresponding trimethylammonium group containing AEM. However; the conductivity of AEM1 decreased rapidly under the fuel cell operating condition (1 M KOH, 80°C). In this work, we developed alkaline durable properties of AEMs by introducing poly(Nvinylimidazolium hydroxide) by a radiation-induced grafting method for direct hydrazine fuel cells.