The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
Michael A Hickner - One of the best experts on this subject based on the ideXlab platform.
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functionalization of poly 2 6 dimethyl 1 4 phenylene oxide s with hindered fluorene side chains for anion exchange membranes
2016Co-Authors: Caroline M Christensen, Michael A HicknerAbstract:Functionalization of poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) was achieved by grafting hindered fluorene-based side chains to PPO via the Suzuki–Miyaura coupling Reaction using an appropriate catalyst/ligand system. Using the resulting functionalized PPO, anion-conductive copolymers, PPO with fluorene side chains with pendant alkyltrimethylammonium groups, were synthesized via the Menshutkin Reaction. The quaternized copolymers yielded ductile, transparent membranes which were soluble in dimethylformamide, dimethyl sulfoxide, and methanol at room temperature. The fluorene side chain containing membranes showed considerably higher hydroxide ion conductivities, up to 176 mS/cm at 80 °C, compared to that of typical anion exchange membranes based on the benzyltrimethylammonium motif. The results of titration and hydroxide ion conductivity measurements demonstrated excellent chemical stability of the fluorene side chain containing anion exchange membranes (AEMs), even after 1000 h immersion in 1 M NaOH at...
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Functionalization of Poly(2,6-dimethyl-1,4-phenylene oxide)s with Hindered Fluorene Side Chains for Anion Exchange Membranes
2016Co-Authors: Liang Zhu, Jing Pan, Caroline M. Christensen, Bencai Lin, Michael A HicknerAbstract:Functionalization of poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) was achieved by grafting hindered fluorene-based side chains to PPO via the Suzuki–Miyaura coupling Reaction using an appropriate catalyst/ligand system. Using the resulting functionalized PPO, anion-conductive copolymers, PPO with fluorene side chains with pendant alkyltrimethylammonium groups, were synthesized via the Menshutkin Reaction. The quaternized copolymers yielded ductile, transparent membranes which were soluble in dimethylformamide, dimethyl sulfoxide, and methanol at room temperature. The fluorene side chain containing membranes showed considerably higher hydroxide ion conductivities, up to 176 mS/cm at 80 °C, compared to that of typical anion exchange membranes based on the benzyltrimethylammonium motif. The results of titration and hydroxide ion conductivity measurements demonstrated excellent chemical stability of the fluorene side chain containing anion exchange membranes (AEMs), even after 1000 h immersion in 1 M NaOH at 80 °C. The results of this study suggest a new and scalable route for the functionalization of PPO and preparation of AEMs for practical alkaline fuel cell applications
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Highly Stable, Anion Conductive, Comb-Shaped Copolymers for Alkaline Fuel Cells
2015Co-Authors: Yongjun Leng, Michael A Hickner, Chaoyang WangAbstract:ABSTRACT: To produce an anion-conductive and durable polymer electrolyte for alkaline fuel cell applications, a series of quaternized poly(2,6-dimethyl phenylene oxide)s containing long alkyl side chains pendant to the nitrogen-centered cation were synthesized using a Menshutkin Reaction to form comb-shaped structures. The pendant alkyl chains were responsible for the development of highly conductive ionic domains, as confirmed by small-angle X-ray scattering (SAXS). The comb-shaped polymers having one alkyl side chain showed higher hydroxide conductivities than those with benzyltrimethyl ammonium moieties or structures with more than one alkyl side chain per cationic site. The highest conductivity was observed for comb-shaped polymers with benzyldimethylhexadecyl ammonium cations. The chemical stabilities of the comb-shaped membranes were evaluated under severe, accelerated-aging conditions, and degradation was observed by measuring IEC and ion conductivity changes during aging. The comb-shaped membranes retained their high ion conductivity in 1 M NaOH at 80 °C for 2000 h. These cationic polymers were employed as ionomers in catalyst layers for alkaline fuel cells. The results indicated that the C-16 alkyl side chain ionomer had a slightly better initial performance
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anion exchange fuel cell membranes prepared from c h borylation and suzuki coupling Reactions
2014Co-Authors: Angela D Mohanty, Michael A HicknerAbstract:Of the polymer materials investigated as anion exchange membranes, trimethylbenzylammonium-containing polysulfones are the most extensively studied. They are commonly prepared by chloromethylation of the aromatic backbone or radical bromination of benzylic carbons, followed by a Menshutkin Reaction between a tertiary amine and the benzyl halide. To overcome synthetic limitations involved with these two methods, we report the preparation of an anion exchange membrane by means of iridium-catalyzed C–H borylation followed by palladium-catalyzed Suzuki coupling. Owing to the use of mild Reaction conditions and high efficiency of these metal-catalyzed Reactions, we were able to minimize side Reactions and easily control the degree of functionalization for a series of trimethylbenzylammonium-containing polysulfones. The resulting membranes exhibited lower water uptake while maintaining similar hydroxide conductivity and functional group stability as compared to the corresponding chloromethylation-prepared anion...
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Anion Exchange Fuel Cell Membranes Prepared from C–H Borylation and Suzuki Coupling Reactions
2014Co-Authors: Angela D. Mohanty, Michael A Hickner, Yeong-beom Lee, Liang Zhu, Chulsung BaeAbstract:Of the polymer materials investigated as anion exchange membranes, trimethylbenzylammonium-containing polysulfones are the most extensively studied. They are commonly prepared by chloromethylation of the aromatic backbone or radical bromination of benzylic carbons, followed by a Menshutkin Reaction between a tertiary amine and the benzyl halide. To overcome synthetic limitations involved with these two methods, we report the preparation of an anion exchange membrane by means of iridium-catalyzed C–H borylation followed by palladium-catalyzed Suzuki coupling. Owing to the use of mild Reaction conditions and high efficiency of these metal-catalyzed Reactions, we were able to minimize side Reactions and easily control the degree of functionalization for a series of trimethylbenzylammonium-containing polysulfones. The resulting membranes exhibited lower water uptake while maintaining similar hydroxide conductivity and functional group stability as compared to the corresponding chloromethylation-prepared anion exchange membrane materials
Dirk Henkensmeier - One of the best experts on this subject based on the ideXlab platform.
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anion conductive membranes based on 2 mesityl benzimidazolium functionalised poly 2 6 dimethyl 1 4 phenylene oxide and their use in alkaline water electrolysis
2018Co-Authors: Angela Marinkas, Izabela Struźynskapiron, Hyun S Park, Jong Hyun Jang, Artjom Maljusch, Oliver Conradi, Dirk HenkensmeierAbstract:Abstract For development of anion exchange membrane (AEM) water electrolysis systems, a series of polymers was synthesised by reacting 2-mesityl-benzimidazole (BIM) and brominated poly-(2,6-dimethyl-1,4-phenylene oxide) (Br-PPO) in a Menshutkin Reaction, and permethylating the attached BIM groups. The degree of bromination of Br-PPO can be easily monitored by IR spectroscopy: A correlation with the shift of the band around 1190 cm−1 was found. The IEC values of the prepared materials ranged between 1.6 and 2.9 mmol OH− g−1. Only materials with an IEC value of 1.9 (PPO24-BIM) reproducibly formed self-supporting membranes. This may be related to the degree of crystallinity, which decreased from 14 to 3% when the IEC increased from 1.6 to 3 mmol OH− g−1. Materials with IEC values of 1.6 and 2.2 can form self-supporting membranes, but not reproducibly. PPO24-BIM showed a conductivity of 8 mS cm-1 at room temperature, a thermal stability well above 200 °C, and mechanical properties similar to those of commercial FAA3-30 membranes. During water electrolysis, a current density of 300 mA cm-2 at 1.8 V was obtained. At 80 °C in 1 M KOH, degradation of BIM and the PPO backbone were observed by IR spectroscopy and monitoring conductivity and weight loss.
Sason Shaik - One of the best experts on this subject based on the ideXlab platform.
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solvent organization and rate regulation of a Menshutkin Reaction by oriented external electric fields are revealed by combined md and qm mm calculations
2020Co-Authors: Kshatresh Dutta Dubey, Thijs Stuyver, Surajit Kalita, Sason ShaikAbstract:When and how do external electric fields (EEFs) lead to catalysis in the presence of a (polar or nonpolar) solvent? This is the question that is addressed here using a combination of molecular dyna...
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Catalysis of Methyl Transfer Reactions by Oriented External Electric Fields: Are Gold–Thiolate Linkers Innocent?
2018Co-Authors: Rajeev Ramanan, David Danovich, Debasish Mandal, Sason ShaikAbstract:Oriented external electric fields (OEEFs) are potent effectors of chemical change and control. We show that the Menshutkin Reaction, between substituted pyridines and methyl iodide, can be catalyzed/inhibited at will, by just flipping the orientation of the EEF (FZ) along the “Reaction axis” (Z), N---C---I. A theoretical analysis shows that catalysis/inhibition obey the Bell–Evans–Polanyi principle. Significant catalysis is predicted also for EEFs oriented off the Reaction axis. Hence, the observation of catalysis can be scaled up and may not require orienting the reactants vis-à-vis the field. It is further predicted that EEFs can also catalyze the front-side nucleophilic displacement Reaction, thus violating the Walden-inversion paradigm. Finally, we considered the impact of gold–thiolate linkers, used experimentally to deliver the EEF stimuli, on the Menshutkin Reaction. A few linkers were tested and proved not to be innocent. In the presence of FZ, the linkers participate in the electronic reorganization of the molecular system. In so doing, these linkers induce local electric fields, which map the effects of the EEF and induce catalysis/inhibition at will, as in the pristine Reaction. However, as the EEF becomes more negative than −0.1 V/Å, an excited charge transfer state (CTS), which involves one-electron transfer from the 5p lone pair of iodine to an antibonding orbital of the gold cluster, crosses below the closed-shell state of the Menshutkin Reaction and causes a mechanistic crossover. This CTS catalyzes nucleophilic displacement of iodine radical from the CH3I•+ radical cation. The above predictions and others discussed in the text are testable
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the Menshutkin Reaction in the gas phase and in aqueous solution a valence bond study
2007Co-Authors: Fuming Ying, Philippe C Hiberty, Sason ShaikAbstract:The recently developed (L. Song, W. Wu, Q. Zhang, S. Shaik, J. Phys. Chem. A 2004, 108, 6017-6024) valence bond method coupled to a polarized continuum model (VBPCM) is applied to the Menshutkin Reaction, NH 3 +CH 3 Cl→CH 3 NH 3 + +Cl - , in the gas phase and in aqueous solution. The computed barriers and Reaction energies at the level of the breathing orbital VB method (P. C. Hiberty, J. P. Flament, E. Noizet, Chem. Phys. Lett. 1992, 189, 259), BOVB and VBPCM//BOVB, are comparable to CCSD(T) and CCSD(T)//PCM results and to experimental values in solution. The gas-phase Reaction is endothermic and leads to an ion-pair complex via a late transition state. By contrast, the Reaction in the aqueous phase is exothermic and leads to separate solvated ions as Reaction products, via an early transition state. The VB calculations provide also the reactivity parameters needed to apply the valence bond state correlation diagram method, VBSCD (S. Shaik, A. Shurki, Angew. Chem. Int. Ed. 1999, 38, 586). It is shown that the reactivity parameters along with their semi-empirical derivations provide together a satisfactory qualitative and quantitative account of the barriers.
Caroline M Christensen - One of the best experts on this subject based on the ideXlab platform.
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functionalization of poly 2 6 dimethyl 1 4 phenylene oxide s with hindered fluorene side chains for anion exchange membranes
2016Co-Authors: Caroline M Christensen, Michael A HicknerAbstract:Functionalization of poly(2,6-dimethyl-1,4-phenylene oxide)s (PPO) was achieved by grafting hindered fluorene-based side chains to PPO via the Suzuki–Miyaura coupling Reaction using an appropriate catalyst/ligand system. Using the resulting functionalized PPO, anion-conductive copolymers, PPO with fluorene side chains with pendant alkyltrimethylammonium groups, were synthesized via the Menshutkin Reaction. The quaternized copolymers yielded ductile, transparent membranes which were soluble in dimethylformamide, dimethyl sulfoxide, and methanol at room temperature. The fluorene side chain containing membranes showed considerably higher hydroxide ion conductivities, up to 176 mS/cm at 80 °C, compared to that of typical anion exchange membranes based on the benzyltrimethylammonium motif. The results of titration and hydroxide ion conductivity measurements demonstrated excellent chemical stability of the fluorene side chain containing anion exchange membranes (AEMs), even after 1000 h immersion in 1 M NaOH at...
Runlian Deng - One of the best experts on this subject based on the ideXlab platform.
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poly 2 6 dimethyl 1 4 phenylene oxide containing imidazolium terminated long side chains as hydroxide exchange membranes with improved conductivity
2016Co-Authors: Gaohong He, Baolin Zhao, Xiaowei Xu, Runlian DengAbstract:Abstract Hydroxide exchange membrane fuel cells (HEMFCs) receive growing interest due to the usability of non-precious metal catalysts in the basic operating environment. The applications of HEMFCs are hindered by the trade-off between high hydroxide conductivity and good dimensional stability of the HEMs. Here, a novel poly(2,6-dimethyl-1,4-phenylene oxide) with imidazolium-terminated long side chains (PPO-COC 5 H 10 -Im) was synthesized by simple and controllable acetylation Reaction of PPO and 6-bromohexanoyl chloride in a moderate condition (at room temperature), followed by the Menshutkin Reaction with 1,2-dimethylimidazole. The introduction of long chains between imidazolium groups and polymer main chains facilitates the formation of good hydrophilic/hydrophobic micro-phase separation structure, which is illustrated by TEM. The hydroxide effective mobility in PPO-COC 5 H 10 -Im membrane is almost 2-fold that in short side chain imidazolium functionalized PPO (PPO-CH 2 -Im) membrane at a certain IEC. Given similar swelling ratios (25% vs. 27%), PPO-COC 5 H 10 -Im membrane shows much higher hydroxide conductivity than PPO-CH 2 -Im membrane (62 vs. 42 mS cm −1 ) at 60 °C. It indicates that the PPO-COC 5 H 10 -Im membranes prepared here exhibits highly enhanced conductivity without sacrificing the dimensional stability.