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To develop anion exchange membranes (AEMs) that combine high chemical stability and hydroxide conductivity, we have designed and prepared poly(arylene piperidine)s carrying tunable mono- or dicationic side chains. Poly(biphenyl piperidine) and poly(biphenyl N-methylpiperidine), respectively, were first synthesized by superacid-catalyzed polyhydroxylalkylations. Subsequently, the piperidine rings of these polymers were reacted with bromoalkylated N,N-dimethylpiperidinium (DMP) and 6-azonia spiro[5.5]undecane (ASU) cations, respectively. This gave two series of AEMs in which the polymer backbone contained tertiary and quaternary piperidine rings, respectively, resulting in mono- and dicationic side chains in series 1 and 2, respectively. In series 1, both the piperidine rings in the backbone and the pendant cations in the side chains showed excellent alkaline stability, resulting in AEMs, which retained more than 92% of the cations after storage in 2 M NaOH at 90 °C during 30 days. In addition, these AEMs reached a hydroxide conductivity up to 131 mS cm–1 at 80 °C. Benefiting from a high local ionic concentration through the dicationic configuration, the AEMs in series 2 reached a higher conductivity, almost 170 mS cm–1 at 80 °C at moderate water uptake and swelling. Still, these AEMs were more vulnerable to hydroxide attack than the ones in series 1 because of the quaternary piperidinium groups placed in the polymer backbone. In conclusion, the AEMs in series 1 can be employed in electrochemical devices that operate under harsh alkaline conditions, while those in series 2 should be preserved for less aggressive alkaline conditions. (Less)

We here present a series of thermoresponsive glycopolymers in the form of poly(N-isopropylacrylamide)-co-(2-[β-manno[oligo]syloxy] ethyl methacrylate)s. These copolymers were prepared from oligo-β-mannosyl ethyl methacrylates that were synthesized through enzymatic catalysis, and were subsequently investigated with respect to their aggregation and phase behavior in aqueous solution using a combination of 1H NMR spectroscopy, dynamic light scattering, cryogenic transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The thermoresponsive glycopolymers were prepared by conventional free radical copolymerizations of different mixtures of 2-(β-manno[oligo]syloxy)ethyl methacrylates (with either one or two saccharide units) and N-isopropyl acrylamide (NIPAm). The results showed that below the lower critical solution temperature (LCST) of poly(NIPAm), the glycopolymers readily aggregate into nanoscale structures, partly due to the presence of the saccharide moieties. Above the LCST of poly(NIPAm), the glycopolymers rearrange into a heterogeneous mixture of fractal and disc/globular aggregates. Cryo-TEM and SAXS data demonstrated that the presence of the pendant β-mannosyl moieties in the glycopolymers induces a gradual conformational change over a wide temperature range. Even though the onset of this transition is not different from the LCST of poly(NIPAm), this gradual conformational change offers a variation of the temperature-dependent properties in comparison to poly(NIPAm), which displays a sharp coil-to-globule transition. Importantly, the compacted form of the glycopolymers show a larger colloidal stability compared to the unmodified poly(NIPAm). In addition, the thermoresponsiveness can be conveniently tuned by varying the sugar unit-length and the oligo-β-mannosyl ethyl methacrylate content. (Less)

Solid single-ion conducting electrolytes based on well-defined block copolymers show great potential for use in lithium batteries. Here, we report on triblock copolymers with an ion conductive poly(ethylene oxide) (PEO) center block and two flanking blocks of poly(lithium 2,3,5,6–tetrafluorostyrene-4-trifluoromethanesulfonamide). The copolymers were prepared through atom transfer radical polymerization (ATRP) of pentafluorostyrene using a bidirectional PEO macroinitiator, followed by quantitative nucleophilic aromatic substitution of the p-fluorine atoms with sodium trifluoromethanesulfonamide. The ionic content of the copolymers was readily regulated by controlling the monomer feed ratio in the ATRP to obtain [EO]/[Li] between 4 and 88, and thermal decomposition occurred only above ~300 °C to indicate a high thermal stability. Above the melting point of the PEO center block, a copolymer containing 16 wt% of the flanking blocks ([EO]/[Li] = 40) reached a conductivity of 5.7·10-6 S cm-1 at 70 °C. The overall results indicate that well-designed polymers functionalized with lithium (N-perfluorophenyl)trifluoromethanesulfonamide groups show promise as solid single-ion conducting electrolytes. (Less)

A series of regioisomeric isosorbide mono-epoxides, as well as diastereomerically pure mono-epoxy derivatives, have been prepared and studied. Anionic ring-opening polymerization of methoxy-capped monomers produced linear polyethers tethered with isosorbide units. These reasonably high molecular weight polymers exhibited glass transition temperatures at around 10–15 °C and thermal stability up to ∼300 °C, which indicated that the mono-epoxides are promising building blocks for well-defined biobased polymers.

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. (Less)

Rigid-rod polymers tethered with delocalized anions and flexible ion conductive side chains present a synthetic pathway toward thin, single-ion conducting electrolyte membranes with low bulk resist...

Different anion-exchange membranes (AEMs) based on polystyrene (PS)-carrying benzyltrimethyl ammonium cations are currently being developed for use in alkaline fuel cells and water electrolyzers. H...

Salt-containing supramolecular assemblies of rigid-rod polymers tethered with flexible ion-solvating side chains represent a synthetic pathway towards thin ion-conducting solid electrolyte membranes with high dimensional stability. In the present work we have synthesized poly(p-phenylene)s (PpPs) carrying di-, tri- and tetra(ethylene oxide) side chains, respectively. p-Dichlorophenyl oligo(ethylene oxide) monomers were polymerized by Ni-mediated Yamamoto polymerization via in situ reduction of Ni(II). This gave PpPs with an average degree of polymerization reaching 60, where each phenylene ring carried one oligo(ethylene oxide) side chain. Results from calorimetry and X-ray scattering measurements clearly showed the formation of molecular composites, i.e., bicontinuous morphologies with mechanically reinforcing layers of the stiff PpP backbones separated by the flexible oligo(ethylene oxide) side chains. This morphology was retained after adding lithium bis(trifluoromethane)sulfonimide (LiTFSI) to form salt-in-polymer electrolytes, but with an increased distance between adjacent backbones. Furthermore, upon addition of salt the order-to-disorder transition (ODT) region increased from ∼50–170 °C to ∼75–200 °C at [EO]/[Li] = 20. Increasing salt concentrations also revealed a maximum in the ODT enthalpy at [EO]/[Li] = 40. At 80 and 160 °C, the ionic conductivity reached 1.1 × 10−4 and 1.0 × 10−3 S cm−1, respectively. Finally, we demonstrate that ionic conductivity of the polymer electrolytes can be significantly increased by additions of triglyme.

High alkaline stability is critical for polymeric anion exchange membranes (AEMs) and ionomers for use in alkaline electrochemical energy conversion and storage devices such as fuel cells, electrolyzer cells and advanced batteries. Here, we have prepared and studied ether-free polyfluorenes tethered with N,N-dimethylpiperidinium (DMP) and 6-azonia-spiro[5.5]undecane (ASU) cations, respectively, attached through heteroatom-free alkyl spacers. By employing alkyl–alkyl Suzuki cross-coupling, these alicyclic quaternary ammonium cations are attached at the 4-position to impede ionic loss. Thus, all the β-hydrogens sensitive to elimination reactions are placed in strain-free rings able to fully relax by the spacer flexibility. Consequently, the AEM carrying DMP cations shows a very high alkaline and thermal stability, retaining more than 91% of the cations after 2400 h immersion in 2 M NaOH at 90 °C. Compared with corresponding AEM functionalized with N-alkyl-N-methylpiperidinium (AMP) cations [conventionally tethered via the 1(N)-position], the ionic loss by β-elimination is successfully reduced by up to 92%. The AEM functionalized with DMP also reaches a high hydroxide conductivity of 124 mS cm−1 at 80 °C. Consequently, tethering piperidine-based cations via the 4-position instead of the 1(N)-position results in AEMs with substantially improved thermal and alkaline stability, combined with high hydroxide conductivity.

Hydroxide ion conducting poly(terphenyl alkylene)s functionalized with piperidine-based quaternary ammonium cations were synthesized via superacid-catalyzed polyhydroxyalkylations. By employing different synthetic strategies, we have systematically varied the structures of the cation and the backbone polymer to study the effects on morphology, stability and hydroxide conductivity. Two monomers were initially prepared by attaching 4-benzylpiperidine groups to trifluororacetophenone and m-terphenyl, respectively, through Suzuki coupling reactions. Polymerizations followed by quaternizations were then carried out to obtain poly(terphenyl alkylene)s with approximately the same ionic contents. These contained either m- or p-terphenyl backbone units, and were tethered with monocyclic N,N-dimethylpiperidinium (DMP) or spirocyclic 6-azonia-spiro[5,5]undecane-6-ium (ASU) cations placed on either the stiff terphenyl or the more flexible alkylene units along the backbone. Polymer chain flexibility and functionalization with DMP cations were found to promote ionic clustering and conductivity. Hence, a membrane based on a m-terphenyl backbone tethered with DMP on pendant phenyl groups achieved a hydroxide conductivity of 146 mS cm−1 at 80 °C. While the thermal stability was significantly higher for ASU-functionalized HEMs, the alkaline stability was highest for the ones carrying DMP cations, which showed less than 5% ionic loss after 720 h in 2 M NaOH at 90 °C. After 168 h at 120 °C, 1H NMR analysis suggested that the DMP cation degraded by a combination of β-Hofmann elimination and methyl substitution. Overall, the results of the study demonstrated that the structural features of the present polymers provided high alkaline stability, most probably due to aryl ether-free backbones, and that all the β-protons of the DMP and ASU cations were placed in 6-membered rings.

We report on aryl ether-free 2,7-diphenylfluorene-based copolymers tethered with quinuclidinium (Qui) cations via hexyl spacers, prepared through superacid catalyzed Friedel–Crafts polycondensation and quaternization reactions. The 2,7-diphenylfluorene monomers were synthesised by Suzuki coupling and were employed to increase polymer backbone stiffness. Corresponding copolymers and anion-exchange membranes (AEMs) tethered with piperidinium (Pip) and trimethylalkyl ammonium (TMA) cations were prepared as reference materials. At a given water content, the AEM functionalized with Qui cations was the most efficient hydroxide conductor and its OH− conductivity reached 100 mS cm−1 at 80 °C at an ion exchange capacity of 2.0 mequiv. g−1. Moreover, this membrane showed the highest thermal and alkaline stability in the series. 1H NMR analysis of AEMs stored in 2 M aq. NaOH at 90 °C over 672 h revealed the complete absence of any ring-opening β-elimination in the bicyclic cage-like Qui structure, and less than 2% β-elimination in the hexyl spacer. In contrast, the Pip cations were found to degrade via β-elimination in both the monocyclic ring structure and the hexyl spacer. Results on the Pip-modified AEM implied that a β-hydrogen in the linear alkyl spacer chain was approximately 4 times more vulnerable to elimination than a β-hydrogen in the 6-membered ring. In addition, all the cations degraded via substitution reactions to some degree, and the total loss of Qui, Pip and TMA cations over the period was estimated to be 4, 12 and 9%, respectively. The overall findings demonstrate that the combination of aryl ether-free backbone polymers and Qui cations results in durable and high-performance AEMs suitable for use in alkaline electrochemical energy conversion and storage devices.

The objective of the present work is to, in a single material, combine a number of molecular design strategies that have proven successful in the preparation of high-performance anion-exchange membranes (AEMs) for alkaline fuel cells. Hence, we here report on highly conductive and alkali-stable poly(phenylene oxide)s carrying flexible side chains attached via alkyl spacer units, where each side chain contains four quaternary piperidinium (QPip) cations interconnected with alkyl chain segments. These materials are completely soluble in, e.g., methanol and form mechanically tough transparent AEMs with efficiently segregated ions, as indicated by X-ray scattering. At 80 °C, the hydroxide ion conductivity reaches up to 170 and 221 mS cm–1 at ion-exchange capacities (IECs) of 2.1 and 2.6 mequiv g–1, respectively. Taking into account the IEC value and water uptake, the tetra-QPip side chain AEMs are found to be significantly more efficient hydroxide ion conductors than corresponding AEMs with mono-QPip side cha...

Aromatic polymers functionalised with cycloaliphatic quaternary ammonium (QA) cations are currently emerging as base-stable anion exchange membranes (AEMs) for use in alkaline fuel cells and water electrolyzers. In the present work, we first prepared poly(biphenyl piperidine)s by superacid-mediated polycondensations, and then introduced different N-spirocyclic QA cations via cyclo-quaternisation of the piperidine rings. The resulting polymers and AEMs were free of diaryl ether linkages and benzylic C–H bonds, and showed very high thermal stability and hydroxide ion conductivity. Alkaline testing up to 120 °C implied that the alkaline stability of the spirocyclic cations was limited by distortions of the ring conformations caused by the rigid polymer backbone. As a consequence, the ring directly attached to the backbone degraded significantly faster by Hofmann β-elimination than the pendant ring in the spirocyclic cations. These results provide valuable insights towards the molecular design of highly thermochemically stable AEMs functionalised with N-spirocyclic QA cations.

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 involving 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 employing bisPip side chains.

The alkaline stability of organic cations tethered to anion-exchange membranes (AEMs) is essential for the long-term performance of alkaline membrane fuel cells and electrolyzers. Here, we have prepared and studied the thermal and alkaline stability of a series of polyelectrolytes functionalized with N-spirocyclic quaternary ammonium (QA) cations. N,N-Diallylazacycloalkane quaternary salts were readily synthesized by diallylation of pyrrolidine, piperidine, azepane, and morpholine. These monomers were employed in radical-initiated cyclo-polymerizations to obtain the target poly(N,N-diallylazacycloalkane)s. 1H NMR spectroscopy revealed that the stability of the polyelectrolytes in 2 M KOD/D2O solutions critically depended on the ring size and the absence of additional heteroatoms in the ring. Thus, poly(N,N-diallylpiperidinium) showed the highest alkaline stability, with only minor signs of degradation at 120 °C after 14 days, while the polyelectrolytes based on the morpholine and azepane rings clearly deg...

Solid single-ion conducting polymers continue to attract significant interest as electrolyte materials with great potential to improve safety and performance of energy storage devices. Still, their low conductivity is a significant hurdle presently preventing their application. Here, we report on highly conductive BAB triblock copolymers with A blocks of either poly(ethylene oxide) (PEO) or poly(ethylene oxide-co-propylene oxide) (PEOPO), and B blocks of poly(lithium 2,3,5,6-tetrafluorostyrene-4-sulfonate) (PPFSLi). The copolymers were readily synthesised by atom transfer radical polymerisation (ATRP) of 2,3,4,5,6-pentafluorostyrene from polyether macroinitiators, followed by quantitative thiolation using NaSH and subsequent oxidation to form the sulfonate anions. The copolymers possessed high thermal stability and their ionic content was conveniently controlled by the block ratio during the ATRP. Above the polyether melting point, PEO-based block copolymers with [O] : [Li] = [18] : [1] showed the highest conductivity, close to 1.4 × 10−5 S cm−1 at 60 °C, while at lower temperatures, the PEOPO materials reached the highest conductivity, nearly 1.5 × 10−6 S cm−1 at 20 °C. The high conductivity of the former copolymer suggests weak interactions of the lithium ions with the pentafluorosulfonate anions in combination with a high degree of Li+ dissociation facilitated by PEO. The results of the present study demonstrate that well-designed block copolymers containing lithium pentafluorostyrene sulfonate units can approach the levels of conductivity required for high-temperature lithium battery applications.

Nanocomposites of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3,4HB)] and hydrophobically modified graphene oxide (GO) were prepared via melt blending and characterised with respect to processability, polymer degradation, as well as thermal, rheological and mechanical properties. GO prepared via the modified Hummer’s method was alkylated by reactions with butyl-, octyl- and hexadecylamine, respectively. The successful functionalisation was verified by IR spectroscopy, X-ray diffraction measurements, transmission electron microscopy and elemental analysis. The thermal decomposition temperature of the alkylated GOs increased with increasing alkyl chain length. Moreover, the alkylated GOs showed a much improved compatibility with P(3,4HB) in the melt compared to the unmodified GO, and microscopy showed an even distribution in the polymer matrix. The molecular weight of P(3,4HB) was found to decrease during the melt extrusion, and the chain degradation was found to increase after the addition of alkylated GO. However, this effect decreased with increasing alkyl chain length. Melt rheology measurements showed that percolating networks appeared at filler contents above ~2 wt%. These networks were detected as increases in shear storage modulus and decreased phase shifts towards more elastic materials over time and at low frequencies. During cooling of the melts, calorimetric measurements showed an increase in the crystallisation temperature and enthalpy with increasing filler contents up to ~2 wt%. However, at higher filler contents a decreased propensity for crystallisation was noted, which again indicated network formation. Tensile testing showed that the nanocomposites containing the GO with hexadecyl chains displayed the highest elongation at break and yield stress. However, the numbers were lower compared to the unfilled P(3,4HB), most probably because of the lower molecular weight of the P(3,4HB) in the nanocomposites. The results of the present study demonstrated that alkylation of GO greatly improves the compatibility with the polymer, and that the processability and thermo-mechanical properties of the nanocomposites are systematically influenced by the GO content and the alkyl chain length. (Less)

Poly(arylene ether sulfone)s containing randomly distributed biphenyl units tethered with precisely six imidazolium cations are designed and prepared with the aim to facilitate ionic clustering and conductivity of anion exchange membranes (AEMs). A series of statistical copolymers with different cationic contents are synthesized via K2CO3-mediated polycondensations of 2,2′,3,3′,5,5′-hexamethyl-4,4′-dihydroxybiphenyl, bisphenol-A and 4,4′-dichlorodiphenylsulfone. After near quantitative benzylic brominations, the copolymers are functionalized with N-methylimidazolium (NIM), 1,2,4,5-tetramethylimidazolium (4IM) and trimethylammonium (QA) groups, respectively. Small angle X-ray scattering of AEMs cast from solution shows that all the different hexa-functionalized moieties induce distinct phase separation. This is especially efficient in the NIM materials, which may be because the less bulky nature of this cation in comparison with 4IM. Thus, at a given water uptake the AEMs containing NIM reach a significantly higher conductivity than those with 4IM ions. In addition, AEMs containing any of the two hexa-imidazolium moieties reach higher conductivities than corresponding materials with hexa-QA moieties, which probably results from the delocalized charge of the former cations which promotes ionic dissociation despite very high local ionic concentrations. Introducing biphenyl units tethered with precisely six imidazolium cations along a copolymer backbone may be a viable synthetic strategy towards efficient AEMs for different electrochemical energy applications. (Less)

Polymeric anion-exchange membranes (AEMs) are critical components for alkaline membrane fuel cells (AMFCs) which offer several attractive advantages including the use of platinum-free catalysts and a wide choice of fuel. The development of AMFCs and other electrochemical energy systems is currently severely limited by the lack of AEMs with sufficient alkaline stability. Still, significant advances have been made in recent years and one of the most promising approaches to emerge is the design and synthesis of cationic polymers with various side chain arrangements. Especially, synthetic strategies where the cationic ion exchange groups are placed on pendant alkyl spacer chains along the backbone seem to significantly improve microphase separation, hydroxide ion conductivity, and alkaline stability in relation to standard AEMs with cations placed in benzylic positions directly on the backbone. This article reviews recent approaches to high-performance cationic membrane polymers involving different side chain designs, and discusses some possible future directions. (Less)

Anion-exchange membrane (AEM) fuel cells are promising electrochemical systems for efficient and environmentally benign energy conversion. However, the development of high-performance fuel cells requires new AEMs tailored for high conductivity and chemical stability. Herein, we present the synthesis and characterization of AEMs with polycationic side chains attached to poly(phenylene oxide) (PPO) via flexible alkyl spacer units. Three series of PPOs were functionalized with side chains to study the influence of the number (n = 2–6) of –CH2– groups in between the quaternary ammonium (QA) cations, the ion exchange capacity (IECs), and the number (q = 1–4) of QA cations per side chain. The polymers were prepared by successively reacting bromoalkylated PPO with different tertiary diaminoalkanes and 1,6-dibromohexane. Evaluation of the alkaline stability by 1H NMR spectroscopy and thermogravimetry demonstrated that solvent cast AEMs with n = 2 and 3 quickly degraded via Hofmann β-elimination in 1 M NaOH at 60 °C. In sharp contrast, no degradation was detected for AEMs with n = 4 and 6 after storage in 1 M NaOH at 90 °C over at least 8 days. At similar IECs, the OH− conductivity of the AEMs increased with n up to n = 4, whereafter a plateau was reached. This may be explained by a polyelectrolyte effect leading to counter ion condensation and incomplete ion dissociation when the QA cations were closer than the Bjerrum length (approx. 7 A). The conductivity of AEMs with n = 6 and IEC = 1.9 meq. g−1 increased only slightly with the number of QA cations per side chain up to q = 3 but then increased sharply with q = 4 to reach 160 mS cm−1 at 80 °C. The present work demonstrated that a molecular architecture with poly-QA side chains attached via flexible spacer units affords AEMs that combine efficient phase separation, high alkaline stability and OH− conductivity at moderate water uptake, provided that the side chains are properly designed to avoid Hofmann elimination and counter ion condensation.

New durable and hydroxide ion conducting anion-exchange membranes (AEMs) are currently required in order to develop alkaline fuel cells into efficient and clean energy conversion devices. In the present work we have attached quaternary piperidinium (QPi) cations to poly(2,6-dimethyl-1,4-phenylene oxide)s (PPOs) via flexible alkyl spacer chains with the aim to prepare AEMs. The bromine atoms of bromoalkylated PPOs were displaced in Menshutkin reactions to attach one or two QPi groups, respectively, via heptyl spacers. The cationic polymers have excellent solubility in, e.g., methanol, dimethylsulfoxide and N-methyl-2-pyrrolidone at room temperature, and form tough and transparent membranes. AEMs with bis-QPi side chains efficiently form ionic clusters and reach very high hydroxide ion conductivities, up to 69 and 186 mS cm−1 at 20 and 80 °C, respectively. The AEMs further have excellent alkaline stability, and 1H NMR analysis showed no degradation of the AEMs after storage in 1 M NaOH at 90 °C during 8 days. Thermogravimetry indicated decomposition only above 225 °C. The AEM properties were further tuned by controlled formation of bis-QPi crosslinks through an efficient reaction between bromoalkylated PPO and 4,4′-trimethylenebis(1-methylpiperidine) during a reactive membrane casting process. In conclusion, alkali-stable and highly conductive AEMs can be prepared by placing cycloaliphatic quaternary ammonium cations on flexible side chains and crosslinks.

The limited thermal stability of polyhydroxyalkanoates (PHAs) hinders their wide applicability, and methods to improve the processability of these biopolyesters are needed for efficient processing, e.g. by melt extrusion. In the present study we have shown by isothermal gravimetry, dynamic rheology and molecular weight analysis that the thermal stability of the PHAs at the processing temperature can be dramatically improved by simply washing the materials in a 1 mM aqueous HCl solution. Hence, the thermal decomposition temperature increased by up to 50 °C after the treatment. Subsequently, treated poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) were blended with different amounts of poly(butylene adipate-co-terephthalate) by melt extrusion in order to further enhance the processability and thermomechanical properties. Microscopy of freeze fractured samples of the biodegradable blends showed phase separated blends with poor interfacial adhesion. Melt rheology and dynamic mechanical analysis results indicated a phase inversion between 60 and 80 wt% of the respective PHA. After adding dicumyl peroxide during the extrusion, the interfacial adhesion improved significantly, and the dynamic shear and tensile storage modulii increased with increasing content of the peroxide. The results of the present study demonstrate that an acid wash may significantly improve processability of PHAs, and that combinations of blending and reactive extrusion can be employed to further enhance and tune the thermomechanical properties of the materials.

We have prepared and studied a new class of anion-conducting membrane materials functionalized with N-spirocyclic quaternary ammonium (QA) cations formed via cycloquaternization reactions involving pyrrolidine, piperidine, and azepane, respectively. These cations were introduced in pairs, adjoined through fused phenyl rings along poly(arylene ether sulfone) backbones. Despite their bulkiness, the bis-N-spirocyclic QA moieties efficiently formed ionic clusters in anion-exchange membranes (AEMs) and showed thermal stability up to 309 °C, as well as a reasonable alkaline stability. The hydroxide ion conductivity of the AEMs increased with decreasing ring size, and a fully hydrated pyrrolidine-based AEM reached a conductivity of 110 mS cm–1 at 80 °C. The results of this study indicate new synthetic pathways to high-performance AEMs based on N-spirocyclic QA groups.

Alkaline membrane fuel cells (AMFCs) have recently received increasing attention in relation to proton-exchange membrane fuel cells because the alkaline operating conditions potentially bring significant advantages, including the use of non-precious metal catalysts and improved cell efficiencies to significantly reduce cost.1 The polymeric anion-exchange membrane (AEM) is a critical component of AMFCs since its OH- conductivity and alkaline stability to a great extent determine the performance and lifetime of the system. Hence, significant research efforts are currently committed to the molecular design, synthesis and characterization of robust and highly anion-conducting polymer materials.1 Most studies of AEMs up until now have been performed on aromatic polymers functionalized with benzyltrimethylammonium groups positioned directly on the backbone.1 These materials are readily accessed via, e.g., chloromethylation of suitable aromatic polymers, followed by quaternization with trimethylamine. However, several recent results on low-molecular weight model compounds indicate that polymers containing benzylic quaternary ammonium (QA) groups possess a significantly lower stability than corresponding polymers with alkyl-substituted QA groups in the presence of aqueous OH-.2 Moreover, the location of the benzylic QA groups directly on the aromatic polymer backbones restricts their mobility and hinders the efficient phase separation necessary to reach high anion conductivity. There is thus a current need for new synthetic approaches to attach cationic groups on aromatic polymers via alkyl spacers. We have recently attached QA groups on poly(phenylene oxide) via flexible and non-hydrolysable alkyl spacers (PPO-7Q, Scheme 1) by using a straightforward synthetic route involving bromoalkylation and quaternization.3 AEMs based on these materials showed distinct small angle X-ray scattering maxima, so-called ionomer peaks, to indicate efficient phase separation (Fig. 1a). In contrast, corresponding AEMs based on polymers with QA groups placed in benzylic positions directly on the backbone (PPO-1Q, Scheme 1) showed very weak (if any) ionomer peaks. Moreover, the PPO-7Q showed a significantly enhanced OH- conductivity (Fig. 1b) and far superior alkaline stability in relation to PPO-1Q. These results clearly demonstrate the significant advantages of the alkyl spacer concept in the molecular design of AEM materials for AMFCs.3 In the present paper we will discuss further recent findings regarding molecular design principles, synthetic procedures and important structure-property relationships of these new AEM materials. 1. a) N. W. Li and M. D. Guiver, Macromolecules, 2014, 47, 2175; b) 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. W. Xu and L. Zhuang, Energy Environ. Sci., 2014, 7, 3135. 2. a) M. G. Marino, J. P. Melchior, A. Wohlfarth and K. D. Kreuer, J. Membr. Sci., 2014, 464, 61; b) A. D. Mohanty and C. Bae, J. Mater. Chem. A, 2014, 2, 17314. 3. H. S. Dang, E. A. Weiber and P. Jannasch, J. Mater. Chem. A, 2015, 3, 5280. Figure 1

In order to systematically improve the performance of anion-exchange membranes (AEMs) for alkaline fuel cells, a series of poly(phenylene oxide)s (PPOs) was tethered with cationic alkyl side chains of different lengths and configurations. PPO was first functionalized with bromomethyl and longer bromoalkyl side chains, respectively, before introducing quaternary ammonium (QA) groups via Menshutkin reactions involving trimethylamine and dimethyloctylamine, respectively. This resulted in samples with QA groups attached to PPO either directly in benzylic positions, or via flexible pentyl and heptyl spacer units, respectively. In addition, the polymers were configured with or without octyl extender chains pendant to the QA groups. All the cationic PPOs had an excellent solubility in, e.g., methanol and dimethyl sulfoxide, and flexible and mechanically robust AEMs with an ion exchange capacity of ∼1.4 mequiv g–1 were cast from solution. Analysis by small-angle X-ray scattering showed that the flexible spacer un...

In order to promote phase separation and properties of anion-exchange membranes (AEMs)we have prepared polysulfones with an exceptionally high local concentration of imidazolium groups. Statistical copolymers containing single dioxyphenylene rings directly functionalized with four cationic groups were synthesized by polycondensations of 4,4’-dichlorodiphenylsulfone, 4,4′-isopropylidenediphenol and tetramethylhydroquinone, followed by complete benzylic bromination and quaternization using N-methylimidazole, as well as trimethyl amine for reference. In contrast to the quaternary ammonium (QA) containing materials, the thermal stability of the imidazolium (Im) functionalized AEMs increased with the cationic content and only decomposed above 290 °C at high ionic contents. Small angle X-ray scattering of AEMs based on the copolysulfones showed distinct ionomer peaks indicating a characteristic separation distance of ~7 nm. At an ion exchange capacity of 2.2 meq. g-1, the Br- conductivity at 60 °°C reached 6 and 29 mS cm-1 for the QA and Im functionalized AEMs, respectively, despite a similar water content. Thus, the water in the latter membranes was utilized more efficiently for ion transport, possibly because the conjugated Im groups had a higher degree of ion dissociation than the QA groups. (Less)

The counterion condensation behavior of proton conducting sulfonated polysulfones has been investigated by combining electrophoretic NMR, pulsed magnetic field gradient NMR, and conductivity measurements on monomeric and polymeric samples with concentrations of ionic groups in the range where dissociation is not complete (IEC = 4.55–7.04 mequiv g–1). In this regime, counterion condensation is shown to critically depend on details of the molecular structure, and all atom molecular dynamics (MD) simulations reveal the formation of well-defined ionic aggregates (e.g., triple ions). The corresponding global minima of the free energy are suggested to be the result of a delicate balance of the energetics involved in conformational changes, formation of ionic aggregates, and solvation. This goes beyond Manning’s counterion condensation theory and has important implications for the development of membranes with high ionic conductivity as needed for many electrochemical applications such as fuel cells and batteries.

We have attached quaternary ammonium (QA) groups to poly(phenylene oxide) via flexible and stable heptyl side chains by using a straightforward synthetic route involving bromoalkylation and quaternization. Membranes based on these polymers showed efficient phase separation, significantly enhanced hydroxide ion conductivity and far superior alkaline stability in relation to corresponding polymers with QA groups placed in benzylic positions directly on the backbone.

Specially tailored polyelectrolytes are becoming important as energy-related materials. Here we explore a synthetic strategy to prepare fully aromatic polymers containing single phenylene rings in the backbone functionalized with four sulfonic acid groups. Thioether bridges of semifluorinated poly(arylene thioether)s were oxidized to sulfone bridges, followed by substitution of all fluorines by NaSH and quantitative oxidation of the resulting thiol groups. This gave poly(arylene sulfone)s containing octasulfonated biphenyl units, reaching ion exchange capacities up to 8 meq g−1 and unprecedented high local sulfonic acid concentrations. These polyelectrolytes are stable up to 300 °C under air and achieve proton conductivities of up to 90 mS cm−1 at 120 °C and 50% relative humidity. Despite the excellent performance of this unique new class of hypersulfonated polymers, our data suggests that incomplete proton dissociation may ultimately limit the conductivity of highly sulfonated polymers.

We have prepared poly(arylene ether sulfone) multiblock copolymers with cationic blocks containing single dioxyphenylene rings functionalized with two, three or four quaternary ammonium (QA) groups in order to investigate the influence of the ionic concentration and distribution on the anionic conductivity. Precursor blocks were prepared by polycondensation of 4,4′-difluorodiphenyl sulfone and either di-, tri- or tetramethylhydroquinone. Subsequently, these blocks were combined with precursor blocks prepared from 4,4′-dichlorodiphenyl sulfone and bisphenol A to form alternating multiblock copolymers with different block ratios. The benzylic methyl groups of the hydroquinone monomer units were then fully brominated using N-bromosuccinimide. Quaternization with trimethylamine gave multiblock copolymers with extremely high ion exchange capacities (IECs) of the hydrophilic blocks, i.e., 3.2, 4.9, and 5.8 meq. g−1, respectively, in the Br− form. X-ray scattering and atomic force microscopy of the anion exchange membranes (AEMs) showed a distinct nanophase separation of the blocks. At a given IEC, the ionic conductivity was found to decrease with increasing number of QA groups per dioxyphenylene ring, probably because of limited ionic dissociation resulting from the close proximity of the QA groups. Thus, at a similar IEC, the conductivity of a block copolymer with tetra-functionalized rings reached the same level of conductivity as a corresponding polymer with randomly distributed QA groups, whereas a block copolymer with di-functionalized rings exceeded the conductivity of the latter polymer by a factor 4.2, despite a lower water uptake. These findings strongly highlight the importance of controlling and optimizing the local ionic concentration and distribution for highly anion conductive AEMs based on block copolymers.

A series of aromatic multiblock copolymers based on alternating segments of hydrophilic sulfonated polysulfone (PSU) and hydrophobic polyfluoroether (PFE) were prepared and characterized as proton exchange membranes. PSU precursor blocks were synthesized by polycondensation of dichlorodiphenylsulfone and resorcinol, and PFE precursor blocks were prepared by combining decafluorobiphenyl and isopropylidenediphenol. After preparation of the multiblock copolymers via a mild coupling reaction of the precursor blocks, the resorcinol units of the PSU blocks were selectively and virtually completely sulfonated under mild reaction conditions using trimethylsilylchlorosulfonate. Transparent and robust membranes with different PSU-PFE copolymer compositions and ion-exchange capacities were cast from solution. Atomic force microscopy of the membranes revealed a distinct nanophase separated morphology. At 80 oC, the proton conductivity reached 10 mS cm-1 under 65% relative humidity and 100 mS cm-1 under fully hydrated conditions.

A series of copoly(arylene ether sulfone)s that have precisely two, three, or four quaternary ammonium (QA) groups clustered directly on single phenylene rings along the backbone are studied as anion-exchange membranes. The copolymers are synthesized by condensation polymerizations that involve either di-, tri-, or tetramethylhydroquinone followed by virtually complete benzylic bromination using N-bromosuccinimide and quaternization with trimethylamine. This synthetic strategy allows excellent control and systematic variation of the local density and distribution of QA groups along the backbone. Small-angle X-ray scattering of these copolymers shows extensive ionic clustering, promoted by an increasing density of QA on the single phenylene rings. At an ion-exchange capacity (IEC) of 2.1 meq g(-1), the water uptake decreases with the increasing local density of QA groups. Moreover, at moderate IECs at 20 °C, the Br(-) conductivity of the densely functionalized copolymers is higher than a corresponding randomly functionalized polymer, despite the significantly higher water uptake of the latter. Thus, the location of multiple cations on single aromatic rings in the polymers facilitates the formation of a distinct percolating hydrophilic phase domain with a high ionic concentration to promote efficient anion transport, despite probable limitations by reduced ion dissociation. These findings imply a viable strategy to improve the performance of alkaline membrane fuel cells.

Multi-step synthetic pathways to low-ion exchange capacity (IEC) polysulfone (PSU) with sulfonic acid functionalized aliphatic dendrons and sulfonated comb-type PSU structures are developed and investigated in a comparative study as non-fluorinated proton exchange membrane (PEM) candidates. In each case the side chains are synthesized and introduced in their sulfonated form onto an azide-functionalized PSU via click chemistry. Three degrees of substitution of each architecture were prepared in order to evaluate the dependence on number of sulfonated side chains. Solution cast membranes were evaluated as PEMs for use in fuel cells by proton conductivity measurements, and in the case of dendronized architectures: thermal stability. The proposed synthetic strategy facilitates exploration of a non-fluorous system with various flexible side chains where IEC is tunable by the degree of substitution.

A series of fully aromatic polymers having only sulfone bridges linking the aromatic rings have been synthesized via polycondensations and studied as proton-exchange membranes. Mixtures of tetrasulfonated 4,4′-bis[(4-chlorophenyl)sulfonyl]-1,1′-biphenyl (BCPSBP), non-sulfonated BCPSBP, and 4,4′-thiobisbenzenethiol were copolymerized by nucleophilic aromatic substitution reactions to obtain sulfonated poly(arylene thioether sulfone)s (SPATSs) with ion exchange capacities (IECs) between 2.0 and 4.0 mequiv g–1. The thioether bridges of the SPATSs were quantitatively oxidized to sulfone bridges to obtain the corresponding sulfonated poly(arylene sulfone)s (SPASs). Small-angle X-ray scattering of dry SPATS and SPAS membranes showed that the tetrasulfonated segments promoted a distinct phase separation of the ionic groups already at quite low ionic contents. The SPAS polymers degraded between 300 and 340 °C in air, which was significantly above the degradation temperature of the corresponding SPATSs polymers. M...

The morphologies and proton-transport efficiencies of segmented copoly(arylene ether sulfone) ionomers that contain tetrasulfonated sequences are compared with the corresponding copolymers with disulfonated sequences. Tetrasulfonated 4,4'-bis[(4-chlorophenyl)sulfonyl]-1,1'-biphenyl (sBCPSBP) is synthesized by metalation and sulfination. This new monomer is then used in K(2)CO(3)-mediated polycondensations of mixtures with 4,4'-dichlorodiphenyl sulfone (DCDPS) and 4,4'-dihydroxybiphenyl in dimethyl sulfoxide at 110 °C to prepare segmented copolymers with tetrasulfonated units. The corresponding disulfonated copolymers are prepared by using disulfonated DCDPS instead of sBCPSBP. Small-angle X-ray scattering measurements of the fully aromatic copolymer membranes show ionomer peaks that indicate significantly larger characteristic separation lengths of the tetrasulfonated copolymers compared to those of the corresponding disulfonated copolymers with similar ionic contents. This implies a much more efficient phase separation of the ionic groups in the segmented tetrasulfonated copolymer membranes, especially at low-to-medium ionic contents. The enhanced phase separation has a pronounced positive effect on water uptake characteristics and proton transport properties. Under a reduced relative humidity (RH), the tetrasulfonated copolymer membranes show a significantly higher conductivity than the disulfonated ones, particularly at low-to-medium ionic contents. At an ion-exchange capacity of 1 meq g(-1), the conductivity of the tetrasulfonated copolymer membrane at 30 % RH is higher than that of the disulfonated membrane at 90 % RH. Because of their relative ease of synthesis, segmented copolymers based on well-designed multisulfonated monomers may provide a viable alternative to the more complex sulfonated block and graft copolymers for use as fuel-cell membranes.

We report on multiblock copolymers consisting of highly sulfonated hydrophilic poly(arylene sulfone) (SPAS) blocks combined with hydrophobic poly(arylene ether sulfone) (PAES) blocks. Thiol-terminated precursor blocks of sulfonated poly(arylene thioether sulfone) (SPATS) were first prepared via polycondensations involving a novel tetrasulfonated dichlorotetraphenyldisulfone monomer, followed by coupling with pentafluorophenyl end-capped PAES precursor blocks under mild conditions to form SPATS–PAES block copolymers. The thioether bridges of the SPATS blocks were then selectively oxidized to obtain the SPAS–PAES copolymers with hydrophilic blocks containing exclusively sulfone bridges. Thus, the SPAS blocks were designed for high chain stiffness and stability toward desulfonation and had an ion exchange capacity (IEC) of 4.2 mequiv g–1. Membranes of the SPAS–PAES copolymers were phase separated on the nanoscale and showed an increased thermal stability and decreased water uptake in relation to the correspo...

A series of six fully aromatic ionomers with precisely sequenced sulfonated sites along the polymer chains have been designed, prepared, and characterized as proton-exchange membranes. Two straightforward and efficient synthetic strategies based on Ullmann ether reactions and a Baeyer–Villiger rearrangement were devised to obtain bisphenol monomers with four or six phenylene units linked exclusively by ether bridges to avoid transetherification reactions. Polycondensations of these bisphenol monomers with mono- or disulfonated dihalide monomers gave high molecular weight poly(arylene ether), poly(arylene ether sulfone), and poly(arylene ether ketone) homopolymers having microblock-like structures with sulfonated moieties separated by monodisperse nonsulfonated oligo(ether) spacers. The nanoscale morphology and properties of solvent cast membranes were closely related to the nature of the oligo(ether) spacers. Small angle X-ray scattering (SAXS) measurements showed intense scattering and very narrow ionome...

Multiblock copoly(arylene ether sulfone)s with different block lengths and ionic contents are tailored for highly stable and proton conducting electrolyte membranes. Two series of fully aromatic copolymers are prepared by coupling reactions between non-sulfonated hydrophobic precursor blocks and highly sulfonated hydrophilic precursor blocks containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The sulfonic acid groups are exclusively introduced in ortho positions to the sulfone bridges to impede desulfonation reactions, and give the blocks ion exchange capacities (IECs) of 4.1 and 4.6 meq./g, respectively. Solvent cast block copolymer membranes show well-connected hydrophilic nanophase domains for proton transport and high decomposition temperatures above 310 ˚C under air. Despite higher IEC values, membranes containing tetrasulfonated tetraaryldisulfone segments display a markedly lower water uptake than the corresponding ones with disulfonated diarylsulfone segments when immersed in water at 100 ˚C, presumably because of the much higher chain stiffness and glass transition temperature of the former segments. The former membranes have proton conductivities in level of a perfluorosulfonic acid membrane (NRE212) under fully humidified conditions. A membrane with an IEC of 1.83 meq./g reaches above 6 mS/cm under 30% relative humidity at 80 ˚C, to be compared with 10 mS/cm for NRE212 under the same conditions. (Less)

Graft copolymers with ionic backbones and hydrophobic fluorinated side chains have been prepared by using lithiated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a macroinitiator for anionic polymerization of 4-fluorostyrene. After grafting of the poly(4-fluorostyrene) (PFS) side chains, the PPO backbone was selectively sulfonated using trimethylsilylchlorosulfonate under mild and controlled conditions. Microscopy of solvent cast membranes revealed copolymer self-assembly into remarkably regular and well-ordered morphologies which, depending on the molecular structure, included lamellar and cylindrical arrangements of the proton conducting ionic nanophases. Thermal analysis indicated separate glass transitions of the PFS and PPO phases, and high thermal degradation temperatures of the membranes at approximately 220 and 300 °C for the H+ and the Na+ forms, respectively. The proton conductivity of fully hydrated acidic membranes was similar to that of Nafion, reaching above 0.2 S cm−1 at 120 °C. Compared ...

Poly(arylene ether sulfone) (PSU) ionomers containing disulfonated aryl-SO2-aryl and tetrasulfonated aryl-SO2-aryl-aryl-SO2-aryl segments, respectively, were synthesized and studied to establish their structure–property relationships as proton-exchange membranes. High molecular weight PSUs with different distributions of sulfone bridges in the backbone were prepared by nucleophilic aromatic substitution reactions involving 4,4′-dichlorodiphenyl sulfone (DCDPS), 4,4′-bis[(4-chlorophenyl)sulfonyl]-1,1′-biphenyl (BCPSB), 4,4′-isopropylidenediphenol (bisphenol A), and 4,4′-(1,4-phenylenediisopropylidene)bisphenol (bisphenol P). The polymers were sulfonated viametallation and reaction with sulfur dioxide, followed by oxidation of the resulting sulfinates. This procedure allowed the introduction of two sulfonic acid units on electron-deficient aryl rings in ortho positions to each sulfone bridge of the PSUs. Analysis by small angle X-ray scattering of solvent cast membranes showed that ionic clustering was promoted in ionomers containing sulfonated BCPSB residues and flexible bisphenol P residues. The fully sulfonated PSUs had ion-exchange capacities (IECs) of 3.3–4.1 meq g−1 and were water soluble. However, partly sulfonated polymers with IECs of approx. 1.7 meq g−1 showed high proton conductivity at moderate water uptake and decomposed only above 240 °C during heating 1 °C min−1 under air. This work demonstrated that BCPSB residues can be conveniently and fully tetrasulfonated, which opens possibilities to prepare various aromatic copolymers and membranes with locally very high densities of hydrolytically stable sulfonic acid groups.

Two multiblock copoly(arylene ether sulfone)s with similar block lengths and ion exchange capacities (IECs) were prepared by a coupling reaction between a non-sulfonated precursor block and a highly sulfonated precursor block containing either fully disulfonated diarylsulfone or fully tetrasulfonated tetraaryldisulfone segments. The latter two precursor blocks were sulfonated via lithiation-sulfination reactions whereby the sulfonic acid groups were exclusively placed in ortho positions to the many sulfone bridges, giving these blocks IECs of 4.1 and 4.6 meq·g−1, respectively. Copolymer membranes with IECs of 1.4 meq·g−1 displayed well-connected hydrophilic nanophase domains and had decomposition temperatures at, or above, 300 °C under air. The copolymer with the tetrasulfonated tetraaryldisulfone segments showed a proton conductivity of 0.13 S·cm−1 at 80 °C under fully humidified conditions, and surpassed that of a perfluorosulfonic acid membrane (NRE212) by a factor of 5 at –20 °C over time.

Six different ionomers having various aromatic polymer backbones with pendant 2-sulfobenzoyl side chains were prepared by nucleophilic aromatic substitution reactions of lithium 2,6-difluoro-2'-sulfobenzophenone with 4,4-biphenol, 2,7-dihydroxynaphthalene, 4,4-isopropylidenediphenol, 4,4-dihydroxydiphenyl ether, 4,4'-thiodiphenol, and 4,4'-thiobisbenzenethiol, respectively, to produce four poly(arylene ether)s, one poly(arylene ether sulfide), and one poly(arylene sulfide). Mechanically tough proton-exchange membranes with ion-exchange capacities in the narrow range from 1.9 to 2.3 mequiv/g were cast from the high-molecular-weight ionomers, and subsequently investigated with respect to their structure-property relationships. Glass transitions were only detected for ionomers in the sodium salt form, and increasing glass-transition temperatures (Tg) were found to give higher thermal decomposition temperatures. Analysis by small-angle X-ray scattering indicated that the ionic clustering was promoted for ionomers with flexible polymer backbones and low Tg values. The proton conductivity of the membranes at 80 °C under fully humidified conditions was found between 0.02 and 0.2 S/cm and appeared to depend primarily on the Tg.

Three series of fully aromatic ionomers with naphthalene moieties and pendant sulfobenzoyl side chains were prepared via K2CO3 mediated nucleophilic aromatic substitution reactions. The first series consisted of poly(arylene ether)s prepared by polycondensations of 2,6-difluoro-2'-sulfobenzophenone (DFSBP) and 2,6-dihydroxynaphthalene or 2,7-dihydroxynaphthalene (2,7-DHN). In the second series, copoly(arylene ether nitrile)s with different ion-exchange capacities (IECs) were prepared by polycondensations of DFSBP, 2,6-difluorobenzonitrile (DFBN), and 2,7-DHN. In the third series, bis(4-fluorophenyl)sulfone was used instead of DFBN to prepare copoly(arylene ether sulfone)s. Thus, all the ionomers had sulfonic acid units placed in stable positions close to the electron withdrawing ketone link of the side chains. Mechanically strong proton-exchange membranes with IECs between 1.1 and 2.3 meq g(-1) were cast from dimethylsulfoxide solutions. High thermal stability was indicted by high degradation temperatures between 266 and 287 degrees C (1 degrees C min(-1) under air) and high glass transition temperatures between 245 and 306 degrees C, depending on the IEC. The copolymer membranes reached proton conductivities of 0.3 S cm(-1) under fully humidified conditions. At IECs above similar to 1.6 meg g(-1), the copolymer membranes reached higher proton conductivities than Nafion (R) in the range between -20 and 120 degrees C. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 734-745, 2011 (Less)

The lithium salt of 2,6-difluoro-2′-sulfobenzophenone was conveniently synthesized in one-pot by reacting 2,6-difluorophenyllithium with 2-sulfobenzoic acid cyclic anhydride in THF at −70 °C whereafter the product crystallized out of solution. A poly(arylene ether) and a poly(arylene sulfide) were prepared by polycondensation reactions to demonstrate the reactivity and efficacy of this new monomer to produce sulfonated high-molecular weight aromatic polymers for fuel cell proton-exchange membranes. This work demonstrated that organolithium chemistry may offer versatile and straightforward pathways to new functional monomers with fluorine atoms activated for nucleophilic aromatic substitution reactions.

Poly(arylene ether sulfone)s carrying various aromatic mono-, di-, and trisulfonated side chains have been investigated with respect to their nanoscale structure and key membrane properties. Sulfobenzoyl, sulfonaphthoxybenzoyl, disulfonaphthoxybenzoyl, and trisulfopyrenoxybenzoyl side chains were attached to the poly(arylene ether sulfone) main chain by employing different combinations of metallation and nucleophilic aromatic substitution reactions. The nature of the sulfonated side chains was found to either promote or suppress the formation of ionic clusters, in relation to the ionic clustering occurring in corresponding polymers carrying sulfonic acid groups directly on the main chain. Analysis by small angle X-ray scattering (SAXS) of solvent cast membranes showed that the ionic clustering was promoted by placing the sulfonic acid groups on the relatively long naphthoxybenzoyl or pyrenoxybenzoyl side chains. This resulted in SAXS profiles that indicated larger characteristic separation lengths and narrower ionomer peaks, as compared with corresponding main chain sulfonated polymers. On the other hand, the ionic clustering was almost completely suppressed in membranes based on polymers functionalized with short 2-sulfobenzoyl side chains. Proton conductivity measurements at low or moderate water contents showed a trend of increasing conductivities with the length and the sulfonic acid functionality of the side chain. The structure of the side chain also influenced the thermal stability and glass transition temperature of the membranes.

A series of poly(arylene piperidinium)s (PAPipQs) devoid of any alkali-sensitive aryl ether bonds or benzylic sites are prepared and studied as anion exchange membranes (AEMs) for alkaline fuel cells. First, the excellent alkaline stability of the model compound 4,4-diarylpiperidinium is confirmed. Medium molecular weight poly(arylene piperidine)s are then synthesized in polycondensations of N-methyl-4-piperidone and either bi- or terphenyl via superelectrophilic activation in triflic acid. Film-forming PAPipQs are subsequently prepared in Menshutkin reactions with methyl, butyl, hexyl, and octyl halides, respectively. AEMs based on poly(terphenyl dimethylpiperidinium) show the best performance with no structural degradation detectable by 1H NMR spectroscopy after storage in 2 maq. NaOH at 60 °C after 15 d, and a mere 5% ionic loss at 90 °C. In the fully hydrated state these AEMs reach an OH− conductivity of 89 mS cm−1 at 80 °C. The presence of longer pendant N-alkyl chains (butyl to octyl) is found to significantly promote Hofmann ring-opening elimination reactions and the degradation rate increases with increasing alkyl chain length. The results of the present study demonstrate that PAPipQs are efficiently prepared from readily available monomers and show excellent alkaline stability and OH− conductivity when devoid of pendant N-alkyl chains. (Less)

Poly(styrene-b-vinylphosphonic acid) diblock copolymers have been prepared via sequential anionic polymerization and evaluated as nanostructured polymer electrolytes. The ionic block copolymers were synthesized by first initiating the polymerization of styrene using n-butyllithium in tetrahydrofuran at −78 °C. 1,1-Diphenylethylene was then added to the living polystyryl anions before charging diethyl vinylphosphonate to polymerize the second block. The poly(diethyl phosphonate) block was subsequently completely hydrolyzed to obtain the poly(vinylphosphonic acid) block. Analysis by calorimetry showed two distinct glass transitions of the acidic copolymers, indicating phase separation between the two blocks. The glass transition temperature of the densely phosphonated blocks was strongly influenced by the formation of anhydride links through reversible self-condensation reactions at elevated temperatures. Studies of thin copolymer films by tapping mode atomic force microscopy revealed nanophase-separated morphologies with continuous phosphonated domains. In addition, the acidic block copolymers were found to self-assemble into spherical micellar nanoparticles which, in turn, formed branched arrays of supramolecular “necklace-like” chain structures. Block copolymers equilibrated at 25 °C and 98% relative humidity reached proton conductivities in the order of 30 mS/cm at 130 °C. (Less)

Mechanically strong and flexible membranes with very high local concentrations of immobilized proton-conducting phosphonic acid have been achieved by grafting poly(vinylphosphonic acid) side chains onto polysulfones. The graft copolymers were prepared by anionic polymerization of diethyl vinylphosphonate initiated from lithiated polysulfones, followed by quantitative cleavage of the ester functions. The resulting phosphonic acid units acted like monoprotic acids to indicate a high level of intramolecular interactions, and the phase-separated nature of the copolymers was shown by dual glass transitions. Fully polymeric membranes were conveniently cast from solution and showed high proton conductivities, e.g., 5 mS/cm under nominally dry conditions at 120 °C and up to 93 mS/cm under 100% relative humidity at the same temperature. The corresponding conductivities measured for Nafion 115 under the same conditions were 0.04 and 105 mS/cm, respectively. The former membranes furthermore showed high thermal stabi...

Polysulfone main chains have been functionalized with hypersulfonated aromatic side chains where the sulfonic acid groups were highly concentrated on a local scale, with two acid groups placed on the same aromatic ring. This molecular design was implemented to promote the nanophase separation that takes place in proton-exchange membranes between the hydrophobic polymer main chain and the hydrophilic ionic groups responsible for the water uptake and conduction. Morphological investigations revealed that polysulfones functionalized with disulfonaphthoxybenzoyl or trisulfopyrenoxybenzoyl side chains contained larger and more uniform ionic clusters, as compared to conventionally sulfonated polysulfones where the acid groups are dispersed along the main chain. Membranes based on the polymers carrying hypersulfonated side chains formed efficient networks of water-filled nanopores upon hydration, which facilitated excellent levels of proton conductivity exceeding that of the commercial Nafion membrane at moderate water uptakes.

The 2000–2006 achievements in the field of synthesis, property examination, and application of proton-exchange membranes are reviewed on the basis of more than 120 papers.