| 1. |
- Yang, Yi, et al.
(author)
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Using an ionomer as a size regulator in γ-radiation induced synthesis of Ag nanocatalysts for oxygen reduction reaction in alkaline solution
- 2023
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 646, s. 381-390
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Journal article (peer-reviewed)abstract
- Ag nanoparticles (Ag NPs) are among the most promising candidates to replace Pt as the catalyst for the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs). However, synthesizing size-controlled Ag NPs with efficient catalytic performance is still challenging. Herein, uniform Ag NPs are produced through a γ-radiation induced synthesis route in aqueous solutions, using the ionomer PTPipQ100 as both an efficient size regulator in the synthesis and a conductor of hydroxide ions during the ORR process. The origin of the size control is mainly attributed to the affinity of the ionomer to metallic silver. The resulting Ag NPs covered with ionomer layers can be applied as model catalysts for ORR. The nanoparticles that were prepared using 320 ppm ionomer in the reaction solution turned out to be coated with a ∼1 nm thick ionomer layer and exhibited superior ORR activity as compared to other Ag NPs of similar size studied here. The improved electrocatalytic performance can be attributed to the optimal ionomer coverage that enables fast oxygen diffusion, as well as interactions at the Ag-ionomer interface which promote the desorption of OH intermediates from the Ag surface. This work demonstrates the advantage of using an ionomer as the capping agent to produce efficient ORR catalysts.
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| 2. |
- Allushi, Andrit, et al.
(author)
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Highly conductive hydroxide exchange membranes containing fluorene-units tethered with dual pairs of quaternary piperidinium cations
- 2021
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In: Journal of Membrane Science. - : Elsevier BV. - 0376-7388. ; 632
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Journal article (peer-reviewed)abstract
- In the pursuit of anion exchange membranes (AEMs) with high alkaline stability and hydroxide conductivity, we have prepared and characterized a series of poly(fluorene alkylene)s in which each fluorene unit was functionalized with dual pairs of quaternary piperidinium cations on flexible alkyl spacer chains. First, ether-free precursor polymers were synthesized in superacid mediated polyhydroxyalkylations of 2,2,2-trifluoroacetophenone, 9,9-dimethyl-2,7-diphenyl-9H-fluorene, and different amounts of 2,7-dibromo-9,9-bis(6-bromohexyl)-fluorene to regulate the degree of bromoalkylation. Subsequently, the bromoalkyl side chains were utilized to introduce bis-piperidinium (bisPip) cations via Menshutkin reactions. These materials formed transparent and mechanically strong AEMs upon casting. At 80 °C, the hydroxide conductivity of bisPip AEMs reached 85 and 150 mS cm–1 at ion-exchange capacities (IECs) of 2.0 and 2.8 mequiv g–1, respectively. Moreover, the bisPip AEMs showed high alkaline stability with an ionic loss of merely 6% following immersion in 5 M aq. NaOH solution for a period of 168 h at IEC = 2.8 mequiv g–1. Under these conditions, 1H NMR data indicated that a β-hydrogen in an alkyl spacer chain was about 8 times more susceptible to attacks by hydroxide ions than a β-hydrogen in a piperidinium ring. In comparison, corresponding AEMs with fluorene units functionalized with monoPip cations (i.e., a single pair of piperidinium cations per fluorine unit) showed lower conductivity and alkaline stability under the same conditions, demonstrating the advantage of locally concentrating the cations in the polymer structure by employingbisPip side chains.
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| 3. |
- Allushi, Andrit, et al.
(author)
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Polyfluorenes Bearing N,N-Dimethylpiperidinium Cations on Short Spacers for Durable Anion Exchange Membranes
- 2023
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:3, s. 1165-1176
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Journal article (peer-reviewed)abstract
- Alicyclic quaternary ammonium cations having all the β-protons in a strain-free ring structure are in general highly base resistant, and are thus very attractive to employ for anion exchange membrane (AEM) applications. However, tethering cations such as N,N-dimethylpiperidinium (DMP) to polymer backbones without introducing any weak links is quite challenging. In the present study, we have attached pairs of piperidine rings in their 4-position to fluorene and 2,7-diphenylfluorene via methylene bridges using straightforward SN2 reactions. These fluorenes were subsequently utilized as monomers in polyhydroxyalkylations to prepare poly(fluorene alkylene)s with different contents of the piperidine groups. AEMs were cast after quaternizing the piperidine groups to introduce DMP and spirocyclic 6-azonia-spiro-[5,5]undecane-6-ium (ASU) cations, respectively. The AEMs reached very high hydroxide ion conductivities, 100-156 mS cm-1 at 80 ºC, in the ion exchange capacity (IEC) range 1.8-2.4 mequiv. g-1. X-ray scattering showed ionomer peaks indicating ionic clustering with a characteristic distance d = 2.0-2.9 nm depending on IEC. The AEMs displayed high thermal stability, up to ~250 ºC, and 1H NMR data indicated no degradation after storage in 5 M aq. NaOH during 168 h at 90 ºC. However, degradation started under very severe conditions (10 M, 90 °C) with ~75% of the total ionic loss in all the AEMs assigned to Hofmann β-elimination. The overall results show that fluorene-based AEMs carrying DMP and ASU cations via methylene bridges display an attractive combination of ionic phase separation, thermal and chemical stability, and hydroxide conductivity.
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| 4. |
- Jannasch, Patric, et al.
(author)
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Charge transport in nonstoichiometric 2-fluoropyridinium triflate protic ionic liquids
- 2019
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:38, s. 23427-23432
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Journal article (peer-reviewed)abstract
- Pyridinium triflate protic ionic liquids have been demonstrated to be highly dissociated, and nonstoichiometric compositions have been used in protic energy devices such as the all-organic proton battery. Herein, we use a combination of pulsed field gradient NMR spectroscopy and electrochemical impedance spectroscopy to investigate the charge transport properties of the nonstoichiometric protic ionic liquid 2-fluoropyridinium triflate and the variation with acid doping level. While all diffusion coefficients decreased with the amount of acid doping, the room temperature conductivity increased due to the concurrent increase in charge carrier concentration. The maximum room temperature conductivity was 7.33 mS/cm, obtained when 14% of the pyridine was protonated with triflic acid, while higher acid doping levels lead to liquid/solid mixtures with low conductivity. PEDOT supercapacitor cells with this electrolyte demonstrated very high capacitance (83.9 F/g) and charge storage capacity (23.3 mAh/g). In addition we predict that using a lower acid doping level than previously will result in superior electrolyte performance in proton batteries due to improvements in conductivity, processability and electrochemical stability.
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| 5. |
- Kang, Na Rae, et al.
(author)
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Durable and highly proton conducting poly(arylene perfluorophenylphosphonic acid) membranes
- 2021
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In: Journal of Membrane Science. - 0376-7388. ; 623
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Journal article (peer-reviewed)abstract
- Phosphonated aromatic polymers show several important advantages as proton exchange membranes (PEMs), including high thermal and chemical stability. However, the conductivity needs to be significantly enhanced for most electrochemical applications. Here, we have prepared a series poly(p-terphenyl perfluoroalkylene)s functionalized with highly acidic perfluorophenylphosphonic acid by first carrying out triflic acid mediated polyhydroxylations of p-terphenyl, 2,2,2-trifluoroacetophenone and perfluoroacetophenone. Subsequently, the resulting polymers were quantitatively and selectively phosphonated in the para positions of the pendant perfluorophenyl units by employing an efficient Michaelis-Arbuzov reaction. X-ray scattering of proton exchange membranes (PEMs) based on the phosphonated polymers showed efficient ionic clustering with the interdomain distance depending on the acid content of the polymer. Although the water uptake and swelling was moderate (even at high temperature) the PEMs showed high proton conductivity, up to 111 mS cm-1 at 80 °C fully hydrated, and reaching 4 mS cm-1 at 50% RH at the same temperature. This may be ascribed to the distinct phase separation and high acidity of the polymers. The stability of the PEMs was excellent with thermal decomposition only above ~400 °C. Moreover, no change in weight, appearance or molecular structure was detected after 5 h immersion in Fenton’s reagent at 80 °C, demonstrating an excellent chemical resistance of the PEMs towards free-radical attack. The radical resistance of the present phosphonated PEMs was found to increase with the acid content, which is contrast to corresponding sulfonated PEMs. The combination of high thermochemical stability and high conductivity implies that the present materials are attractive for use as ionomers in catalyst layers and as PEMs in fuel cells and water electrolyzer applications.
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| 6. |
- Khataee, Amirreza, et al.
(author)
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Poly(arylene alkylene)s functionalized with perfluorosulfonic acid groups as proton exchange membranes for vanadium redox flow batteries
- 2023
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In: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 671
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Journal article (peer-reviewed)abstract
- With the aim to develop vanadium redox flow battery (VRFB) membranes beyond state of the art, we have in the present work functionalized poly(p-terphenylene)s with highly acidic perfluorosulfonic groups and investigated their performance as proton exchange membranes (PEMs). Consequently, two poly(p-terphenylene alkylene)s tethered with perfluoroalkylsulfonic acid and perfluorophenylsulfonic acid, respectively, were synthesized through superacid-mediated polyhydroxyalkylations and cast into PEMs. Compared with Nafion 212, the PEM carrying perfluorophenylsulfonic acid groups (PTPF-Phenyl-SA) was found to exhibit higher ionic conductivity and eight times lower vanadium (IV) permeation rate. The latter explains the longer self-discharge duration of the VRFB based on the PTPF-Phenyl-SA. In addition, the VRFB assembled with the PTPF-Phenyl-SA PEM exhibited a high average coulombic efficiency of 99.6% for over 100 cycles with a capacity fade of 0.24% per cycle, which was 50% lower than when Nafion 212 was used. More importantly, excellent capacity retention was achieved through electrochemical rate performance experiments at different current densities.
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| 7. |
- Laanesoo, Siim, et al.
(author)
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Combining isosorbide and lignin-related benzoic acids for high-Tg polymethacrylates
- 2024
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In: European Polymer Journal. - 0014-3057. ; 202
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Journal article (peer-reviewed)abstract
- The insertion of rigid aliphatic or aromatic building blocks in polymer structures is an efficient synthetic strategy towards high-Tg polymer materials. In the present work, we have functionalized isosorbide 5-methacrylate with various aromatic lignin-inspired esters to yield a series of isosorbide-2-aryl carboxylate-5-methacrylate monomers (ArIMAs) as single regioisomers. The selection of phenyl carboxylate side groups included benzoate, p-cyanobenzoate, meta/para-methoxybenzoates, and different vanillic acid esters. This afforded a range of seven bio-based monomers with different size, polarity, and substitutions. Polymerizations were carried out by conventional free radical initiation to obtain the corresponding high molecular-weight poly(aryl carboxylate isosorbide methacrylate)s (PArIMAs). The polymerizations were evaluated in different solvents, including toluene, EtOAc, γ-valerolactone, 2-MeTHF, and DMSO to identify the most suitable conditions. The polymers exhibited high glass transition temperatures (Tgs) in a broad range, from 80 to 168 °C, and were thermally stable up to 268 °C. Furthermore, dynamic rheology experiments indicated that the polymers were sufficiently stable for melt processing. The availability of the building blocks combined with the high stability of the polymers make these materials attractive for use as high-performance plastics and coatings.
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| 8. |
- Laanesoo, Siim, et al.
(author)
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Poly(alkanoyl isosorbide methacrylate)s: from amorphous to semi-crystalline and liquid crystalline biobased materials
- 2021
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 22:2, s. 640-648
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Journal article (peer-reviewed)abstract
- We have prepared a series of twelve D-isosorbide-2-alkanoate-5-methacrylate monomers as single regioisomers with different pendant linear C2 to C20 alkanoyl chains by using biocatalytic and chemical acylations. By conventional radical polymerization, these monomers afforded high-molecular weight biobased poly(alkanoyl isosorbide methacrylate)s (PAIMAs). Samples with C2-C12 alkanoyl chains were amorphous with glass transition temperatures from 107 to 54 °C, while C14-C20 chains gave semi-crystalline materials with melting points up to 59 °C. Moreover, PAIMAs with C13-C20 chains formed liquid crystalline mesophases with transition temperatures up to 93 °C. The mesophases were studied by polarized optical microscopy, and rheology showed stepwise changes of the viscosity at the transition temperature. Unexpectedly, a PAIMA prepared from a regioisomeric monomer (C18) showed semi-crystallinity but no liquid crystallinity. Consequently, the properties of the PAIMAs were readily tunable by controlling the phase structure and transitions through the alkanoyl chain length and the regiochemistry to form fully amorphous, semi-crystalline or semi-/liquid crystalline materials.
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| 9. |
- Mankar, Smita V., et al.
(author)
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Short-Loop Chemical Recycling via Telechelic Polymers for Biobased Polyesters with Spiroacetal Units
- 2023
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In: ACS Sustainable Chemistry & Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:13, s. 5135-5146
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Journal article (peer-reviewed)abstract
- Spirocyclic acetal structures have recently received growing attention in polymer science due to their dual potential to raise the glass transition temperature (Tg) and enable chemical recycling of biobased polymers. In the present work, a vanillin-based diol with a spirocyclic acetal structure was incorporated in a series of rigid amorphous polyesters based on neopentyl glycol and dimethyl terephthalate (DMT). Up to 50 mol % of spirocyclic diol (with respect to DMT) could be incorporated in the copolyesters, but a reasonably high molecular weight was only achieved when ≤30 mol % of the spirocyclic diol was used. The presence of the spiroacetal units in the polyesters not only enhanced the Tg (up to 103 °C) and thermal stability (T5 ≥ 300 °C) but also the oxygen barrier of solution-cast films. We found that the acetal units in the copolyesters could be selectively hydrolyzed under acidic conditions while virtually retaining all of the ester bonds in the polymer backbone. After acidic hydrolysis, telechelic polymers exclusively terminated by two aldehyde end groups were obtained. In this work, we have demonstrated that these telechelic polyesters can be conveniently converted back into poly(acetal-ester)s via cycloacetalization reactions with pentaerythritol.
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| 10. |
- Matt, Livia, et al.
(author)
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Covalent Adaptable Polymethacrylate Networks by Hydrazide Crosslinking Via Isosorbide Levulinate Side Groups
- 2023
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In: ACS Sustainable Chemistry & Engineering. - 2168-0485. ; 11:22, s. 8294-8307
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Journal article (peer-reviewed)abstract
- Reversible crosslinking offers an attractive strategy to modify and improve the properties of polymer materials while concurrently enabling a pathway for chemical recycling. This can, for example, be achieved by incorporating a ketone functionality into the polymer structure to enable post-polymerization crosslinking with dihydrazides. The resulting covalent adaptable network contains acylhydrazone bonds cleavable under acidic conditions, thereby providing reversibility. In the present work, we regioselectively prepare a novel isosorbide monomethacrylate with a pendant levulinoyl group via a two-step biocatalytic synthesis. Subsequently, a series of copolymers with different contents of the levulinic isosorbide monomer and methyl methacrylate are prepared by radical polymerization. Using dihydrazides, these linear copolymers are then crosslinked via reaction with the ketone groups in the levulinic side chains. Compared to the linear prepolymers, the crosslinked networks exhibit enhanced glass transition temperatures and thermal stability, up to 170 and 286 °C, respectively. Moreover, the dynamic covalent acylhydrazone bonds are efficiently and selectively cleaved under acidic conditions to retrieve the linear polymethacrylates. We next show that recovered polymers can again be crosslinked with adipic dihydrazide, thus demonstrating the circularity of the materials. Consequently, we envision that these novel levulinic isosorbide-based dynamic polymethacrylate networks have great potential in the field of recyclable and reusable biobased thermoset polymers.
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