Low Water Uptake Research Articles

Heat-Treated Wood as a Substrate for Coatings, Weathering of Heat-Treated Wood, and Coating Performance on Heat-Treated Wood

Heat treatment is a method of wood modification with increasing market acceptance in Europe. The major patented European commercial heat treatment processes have trade names ThermoWood, Platowood, Retiwood, Le Bois Perdure, and Oil-Heat-Treated Wood (OHT). To what extent modification of wood affects the resistance of wood to weathering is also an important aspect for wood applications, especially where appearance is important. Unfortunately, heat-treated wood has poor resistance to weathering, and surface treatment with coatings is required for both protection and aesthetic reasons. As a substrate for coating, heat-treated wood has altered characteristics such as lower hygroscopicity and liquid water uptake and changed acidity, wettability, surface free energy, and anatomical microstructure. Various wood species, heat treatment method, treatment intensity, and treatment conditions exhibited a different extent of changes in wood properties. These altered properties could affect coating performance on heat-treated wood. The reported changes in acidity and in surface energy due to heat treatments are inconsistent with one another depending on wood species and temperature of the treatments. This paper gives an overview of the research results with regards to properties of heat-treated wood that can affect coating performance and weathering of uncoated and coated heat-treated wood.

Synthesis and curing of amino‐containing benzoxazine as a novel hardener for diglycidyl ether of bisphenol‐A

Benzoxazines containing various additional functional groups have been extensively reported to improve the properties of polybenzoxazines. In this work, a novel amino‐containing benzoxazine (PDETDA‐NH2) was conveniently synthesized from diethyltoluenediamine (DETDA), 2‐hydroxybenzaldehyde, and paraformaldehyde and was used as a hardener for diglycidyl ether of bisphenol‐A (DGEBA). The curing behaviors of PDETDA‐NH2 and PDETDA‐NH2/DGEBA systems were studied by DSC, FT‐IR, and 1H NMR. When curing, PDETDA‐NH2 was firstly polymerized to N,O‐acetal‐type polymer and then rearranged to Mannich‐type polymer at elevated temperature, while the addition reaction between amino and benzoxazine was discouraged because of the steric hindrance of alkyl substituents. During PDETDA‐NH2/DGEBA curing, it was found that the reactions happened in the order of addition polymerization of amino and epoxide, ring‐opening polymerization of benzoxazine, etherification between phenolic hydroxyl of the polymerized benzoxazine, and epoxide. Compared with DETDA cured DGEBA, PDETDA‐NH2 cured DGEBA showed higher modulus, higher char yield, and much lower water uptake.

Decreasing the dielectric constant and water uptake by introducing hydrophobic cross-linked networks into co-polyimide films

The high durability of low-k value is the key parameter for the low dielectric materials especially used under humid conditions, because the k value is very sensitive to moisture. Here, to decrease the dielectric constant and improve the water resistance, a series of novel co-polyimides are successfully prepared based on cross-linkable diamine monomer by a two-step pathway combining polymerization and crosslinking reaction. It is intriguingly found that with the gradual increase content of cross-linkable group, the dielectric properties, water resistance as well as thermal and mechanical properties of those co-polyimides can be finely tuned. After cross-linking, the dielectric properties are significantly enhanced and the film surface changed from hydrophilic (78.7–89.2°) to hydrophobic (93.0–104.2°), which endow the cross-linked films with superior water resistance and high durability of low-k value. The best performance is obtained for cross-linked co-polyimide (CL-Co-PI-4) containing 30% cross-linkable group. The CL-Co-PI-4 exhibits low dielectric constant of 2.32 and dielectric loss of 0.016 at 1 MHz. Excitingly, the CL-Co-PI-4 demonstrates an extremely low water uptake of 0.051 ± 0.010%, which represents the best water resistance for the reported polyimides. After exposing to different humidity conditions for 12 h, the increasing percentage of k value is very low and below 0.84%. The CL-Co-PI-4 still keep its k value below 2.35 after equilibrating at 75% R.H. for 14 days. The excellent moisture resistance and overall performance make the CL-Co-PI-4 a good candidate for dielectric material under both dry and humid conditions.

Investigation of Biological Activity, Open Porosity and Water Absorption of Ternary Polymeric Blend (Polymethylmethacrylate / Starch) used for Bone Scaffold

In this study a fabrication of three groups of biological system for bone scaffold, which consist of first group samples (Acrylic bone cement: % X poly methyl meth acrylate ), second group samples (poly methyl meth acrylate: % X Acrylic bone cement), with selected weight percentages of second material are (5, 10,15 and 20 % wt.) and third group, (Acrylic bone cement: 15 % poly methyl meth acrylate : % X starch) with selected weight percentage ratios of starch are (2, 4 and 6 %wt.). In vitro biological activity and water absorption have been studied. The results clarified that the in vitro biological activity test showed that all fabricated samples have no biological influence on the gram positive bacteria Bacillus subtilis and gram negative bacteria Escherichia coli . The results show that the first group of polymer blend have low open porosity and water uptake capacity than a second group. The increasing in starch weight fraction for the third group led to increasing in open porosity and water absorption..

Recent development of membrane for vanadium redox flow battery applications: A review

Abstract Responding to rapid growth of the renewable energy applications, it is crucial to develop low cost and high efficient large-scale energy storage systems in order to smooth out the intermittency of the renewable energy resources. As one of the most promising large-scale energy storage systems, vanadium redox flow battery (VRFB) has attracted great attention in recent times. Membrane is one of the key components of VRFB which not only affects the whole cyclability performance but also determines the economic viability of the system. The membrane separates the positive and negative half-cells and prevents the cross-mixing of vanadium ions while providing required ionic conductivity. The ideal membrane should have good ionic exchange capacity; high ionic conductivity, low water uptake, swelling ratio, area electrical resistance and vanadium and other poly-halide ions permeability; and good chemical stability, as well as low cost. Numerous efforts have been spent on the development of different types of membranes, including different functional groups ion exchange membrane and non-ionic porous membrane. This paper reviews the research on membranes in VRFB system, including the properties, development of traditional commercial membranes as well as recently developed membranes. It explores various methods of fabrication of the membrane products which have received relatively little attention. A detailed summary table of the new membranes with their properties, fabrication and costs is provided to serve as a reference guide for researchers and industrialists interested in VRFB system building and dynamic modelling set. Subsequently, the challenges and future directions of membrane research are examined.

Synthesis and properties of pyrazine-based oligomeric phthalonitrile resins

The pyrazine-based oligomeric phthalonitrile (PN) monomer, 2,6-bis[3-(3,4-dicyanophenoxy)phenoxy]pyrazine (BCPP), was synthesized from the reaction of an excess amount of resorcinol with 2,6-dichloropyrazine in the presence of potassium carbonate, followed by end-capping with 4-nitrophthalonitrile in a two-step, one-pot reaction. 4-(Aminophenoxy)phthalonitrile was applied to promote the curing reaction. The curing behavior was investigated by differential scanning calorimetry and rheological behavior, showing a wide processing window of 94°C, a complex viscosity of less than 1.5 Pa·s and a lower reaction activation energy of 32.57 kJ mol−1. The structure of the BCPP monomer was confirmed by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The unit cell was determined to be tetragonal system by wide-angle X-ray diffraction. The monomer was cured to yield cross-linked polymers, which exhibited a high initial storage modulus, excellent glass transition temperature, outstanding thermal stability, and low water uptake.

Molecularly designed, solvent processable tetraalkylammonium-functionalized fluoropolyolefin for durable anion exchange membrane fuel cells

A new generation of solvent processable fluoropolyolefin was prepared and explored for durable anion exchange membrane fuel cells. By one-pot Ziegler-Natta copolymerization of a fluorinated monomer (1-(but-3-en-1-yl)-4-fluorobenzene) with 11-bromo-1-undecene and subsequent quaternization with trimethylamine, a series of tetraalkylammonium-functionalized fluoropolyolefin was synthesized by varying the molar ratio between monomers. The excellent solubility of the quaternized fluoropolyolefins provided by fluorinated moieties enabled the solvent processability to afford transparent and robust AEMs (PBFB-QA). Compared to heterogeneous quaternized membranes (H-PBFB-QA) and the corresponding non-fluorinated AEMs counterparts, the homogeneous quaternized PBFB-QA membrane showed lower water uptake due to the high hydrophobicity of fluorine atoms and more compact entanglement of polymer chains during solvent casting process. It was found that PBFB-QA membrane with an IEC of 1.47 meq/g showed the highest hydroxide conductivity of 29.2 mS/cm at 20 °C in spite of its low water uptake (11.9 wt%) and hydrated number (λ = 4.4). Thus, fluoropolyolefin AEMs standed out from the other reported polyolefin-based AEMs with the highest λ-normalized hydroxide conductivity, indicating the efficient ion transport in AEMs with the aid of less water. In addition to high ionic conductivity, fluoropolyolefin AEMs also exhibited excellent alkaline stability, and the retention of the conductivity of PBFB-QA-18 membrane was 89.5% after 700 h of aging in 1 M NaOH at 80 °C. More importantly, in contrast to the non-fluorinated polyolefin-based AEMs, fluoropolyolefin AEM showed better initial fuel cell device performance with a maximum power density of 133 mW/cm2 at 60 °C, and impressive device durability of alkaline fuel cell using the fluoropolyolefin AEM was observed with no loss of performance over 80 h of operation at 60 °C at a constant cell voltage of 0.3 V.

Long-side-chain type imidazolium-functionalized fluoro-methyl poly(arylene ether ketone) anion exchange membranes with superior electrodialysis performance

Developing highly ion conductive and desirable electrodialysis (ED) performance anion exchange membranes (AEMs) is of great significance. In this work, we report a strategy for fabricating novel AEMs based on a series of fluoro-methyl poly(arylene ether ketone)s having long-side-chain imidazolium groups for ED. Having hydrophilic conductive flexible side-chain imidazolium groups and rigid hydrophobic backbone within AEM matrix, the optimized AEM (PAEK-60-im) shows low water uptake of 24.9% at 80 °C and desirable ion conductivity of 22.01 mS cm–1 at 30 °C. In NaCl removal application of ED, PAEK-60-im shows the NaCl removal ratio of 69.66% within 120 min, outperforming commercial AEM-Type II (68.98%). Accordingly, it has a higher current efficiency of 83.7% but lower energy consumption of 5.9 kWh kg–1, compared with the commercial one (82.0%; 6.6 kWh kg–1). In particular, in selectrodialysis application, possibly owing to the synergistic effect of pore-size sieving effect resulting from macro-separation morphology and hydration energy difference of SO42– ions (–1000 kJ mol–1) and Cl– ions (–317 kJ mol–1) in feeding solution, PAEK-60-im shows significantly superior monovalent anion perm-selectivity (Cl−/SO42−) of 7.70 at 30 min, relative to commercial anion-selective Neosepta ACS (5.27) and many other reported mono-valent anion selective AEMs having elegant surface modified layers. The superior ED performance of the homogeneous PAEK-60-im is suggestive of its potential separation application.

Sustainable polycondensation of multifunctional fatty acids from tomato pomace agro-waste catalyzed by tin (II) 2-ethylhexanoate

Bioplastics were prepared from the fatty fraction (i.e., unsaturated and polyhydroxylated fatty acids) of tomato pomace agro-wastes. Aliphatic polyesters were synthesized at different temperatures (125, 150, and 175 °C), reaction times (0.25, 0.5, 0.75, 1, 3, 5, and 7 h), and amounts of tin (II) 2-ethylhexanoate (0, 0.02, 0.05, and 0.10 mmol) used as a catalyst. The rate constants and activation energies were calculated from infrared spectra. The right combination of reaction temperature and amount of catalyst improved the reaction kinetics (apparent k from ∼1 to ∼8.5 h−1), whereas the activation energy was reduced from ∼39 without catalyst to ∼28 kJ/mol when tin (II) 2-ethylhexanoate was present. Glass transitions between ca. −25 and ∼0 °C were measured by differential scanning calorimetry, strictly depending on the degree of polymerization. The amorphous character of the samples was confirmed by X-ray diffraction. Young's modulus and hardness were calculated from indentation tests and were typical of soft materials, although increased as the polycondensation reaction progressed. High water-contact angles (maximum value ∼109°) and low water uptakes (minimum value ∼2.1%) were determined. Physical properties were compared with those of common man-made plastics and polymers, finding that these tomato pomace bioplastics could be their realistic alternatives.

Anion-conductive poly(2,6-dimethyl-1,4-phenylene oxide) grafted with tailored polystyrene chains for alkaline fuel cells

A series of polystyrene (PS)-grafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) having pendent quaternary ammonium groups were synthesized as anion exchange membranes (AEMs) by the “grafting onto” method via a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed click chemistry. The length of PS grafting chains was controlled readily during ATRP. As expected, the polystyrene grafting chains showed excellent miscibility with PPO backbone. Therefore, transparent, flexible and tough membranes were obtained by solution casting. The miscible PS grafting chains induced well-defined hydrophobic-hydrophilic separation of the as-obtained PPO AEMs as confirmed by small-angle X-ray scattering (SAXS) technology. Moreover, the hydrophobic grafting chains can effectively control the water absorption, and thus improve the dimensional stability of AEMs in water. The PS-grafted AEMs showed higher IEC-normalized hydroxide conductivity but lower water uptake than the typical AEM without PS side chains, which may be attributed to the well-defined micro-phase separation in AEMs. The highest hydroxide conductivity of 15.9 mS/cm was achieved at 20 °C in spite of its low IEC value of 1.21 meq./g. Alkaline stability testing in 1 M NaOH at 80 °C demonstrated that PS-grafted PPO AEMs with side-chain-type QA cations showed excellent alkaline stability as evidenced by the change of hydroxide conductivity and the 1H NMR analysis after 500 h testing. Further H2/O2 alkaline fuel cell using PS-grafted PPO AEMs showed the maximum power density of 64.4 mW/cm2 at a current density of 140 mA/cm2, which is much higher than that of typical AEMs with C-16 alkyl grafting chains.

Organosoluble and transparent cardo polyimides with high Tg derived from 9,9-bis(4-aminophenyl)xanthene

9,9-Bis(4-aminophenyl)xanthene (BAPX) was prepared simply and effectively via one-pot, two-step procedure using xanthenone and aniline as main substrates. The monomer BAPX was reacted with six aromatic dianhydrides in N, N-dimethylacetamide (DMAc) to yield the corresponding polyimides (PIs) via the poly(amic acid) precursors and subsequent thermal or chemical imidization. The resulting PIs exhibited good thermal stability with glass transition temperatures of 308–348°C, initial decomposition temperatures of 470–510°C, 10% weight loss temperatures of 540–565°C, and char yields of 55–59% at 800°C in nitrogen, respectively. All polymers were amorphous and readily soluble in organic solvents such as N-methyl-2-pyrrolidone and DMAc. The PI films had tensile strengths of 71–92 MPa, tensile moduli of 1.91–2.35 GPa, and elongations at break of 5–13%. Meanwhile, these polymer films also had high optical transparency with a cutoff wavelength in the range of 367–415 nm, lower dielectric constants (3.02–3.34 at 10 MHz), and low water uptake of 0.30–0.52%.

Repeated summer drought delays sugar export from the leaf and impairs phloem transport in mature beech.

Phloem sustains maintenance and growth processes through transport of sugars from source to sink organs. Under low water availability, tree functioning is impaired, i.e., growth/photosynthesis decline and phloem transport may be hindered. In a 3-year throughfall exclusion (TE) experiment on mature European beech (Fagus sylvatica L.) we conducted 13CO2 branch labeling to investigate translocation of recently fixed photoassimilates under experimental drought over 2 years (2015 and 2016). We hypothesized (H1) that mean residence time of photoassimilates in leaves (MRT) increases, whereas (H2) phloem transport velocity (Vphloem) decreases under drought. Transport of carbohydrates in the phloem was assessed via δ13C of CO2 efflux measured at two branch positions following 13CO2 labeling. Pre-dawn water potential (ΨPD) and time-integrated soil water deficit (iSWD) were used to quantify drought stress. The MRT increased by 46% from 32.1 ± 5.4 h in control (CO) to 46.9 ± 12.3 h in TE trees, supporting H1, and positively correlated (P < 0.001) with iSWD. Confirming H2, Vphloem in 2016 decreased by 47% from 20.7 ± 5.8 cm h-1 in CO to 11.0 ± 2.9 cm h-1 in TE trees and positively correlated with ΨPD (P = 0.001). We suggest that the positive correlation between MRT and iSWD is a result of the accumulation of osmolytes maintaining cell turgor in the leaves under longer drought periods. Furthermore, we propose that the positive correlation between Vphloem and ΨPD is due to a lower water uptake of phloem conduits from surrounding tissues under increasing drought leading to a higher phloem sap viscosity and lower Vphloem. The two mechanisms increasing MRT and reducing Vphloem respond differently to low water availability and impair trees' carbon translocation under drought.

Transport Properties of Perfluorosulfonate Membranes Ion Exchanged with Cations.

In this work, the properties of univalent, that is, Li+, Na+, NH4+, and TEA+ form perfluorosulfonate (PFSA) membranes are studied and compared to the properties of H+ form materials. Properties of these polymer membranes including water uptake, density and conductivity, were investigated for membranes exposed to various water activity levels. The water uptake by the membranes decreased in the order H+ > Li+ > Na+ > NH4+ > TEA+, the same order as the hydration enthalpy (absolute values) of cations. Conductivity values did not strictly follow this order, indicating the importance of different factors besides the hydration level. The partial molar volume of water is derived from the density data as a function of water content for the various membrane forms. This provides further insight into the water, cation, and polymer interactions. Factors that contribute to the conductivity of these membranes include the size of cations, the electrostatic attraction between cations and sulfonate group, and the ion-dipole and hydrogen bonding interactions between cations and water. NH4+ transport is surprisingly high given the low water uptake in NH4+ form membranes. We attribute this to the ability of this ion to develop hydrogen bonded structures that helps to overcome electrostatic interactions with sulfonates. Pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) was used to measure the diffusion coefficient of water in the membranes. FT-IR spectroscopy is employed to probe cation interactions with water and sulfonate sites in the polymer. Overall, the results reflect a competition between the strong electrostatic interaction between cation and sulfonate versus hydration and hydrogen bonding which vary with cation type.

Improvement of dimensional stability of wood by silica nanoparticles

ABSTRACTThe improving effect of nanoparticles on wood dimensional stability is barely known nowadays. The expected result of the research was the improvement of the dimensional stability through bulk hydrophobization, as a result of impregnation with hydrophobic SiO2 nanoparticles. Two different wood species, beech (Fagus sylvatica) and scots pine (Pinus sylvestris) were investigated. Two different treatments with silica nanoparticles were used. One treatment was a pure emulsion of modified (hydrophobized) silica nanoparticles (carrier material: ethanol), and another one was modified (hydrophobized) silica nanoparticles in tetrahydrofuran carrier material in combination with polydimethylsiloxane (PDMS) as a bonding agent. PDMS was used to improve the bonding of the silica nanoparticles to the wood structure. The impregnation with nanoparticles was successful. Shrinking and swelling properties decreased by 17–33%, depending on wood species and treatment. Water uptake and equilibrium moisture content decreased significantly as a result of the treatments (40–58%). Application of PDMS did not provide better dimensional stability compared to the treatment without it, however, it resulted in lower equilibrium moisture content and water uptake compared to the basic nano-SiO2 treatment.

Synthesis and properties of a novel high-temperature vinylpyridine-based phthalonitrile polymer

A novel vinylpyridine-based phthalonitrile monomer, 2,6-bis[3-(3,4-dicyanophenoxy)styryl]pyridine (BDSP), was resoundingly produced by a nucleophilic substitution reaction of 2,6-bis(3-hydroxystyryl)pyridine with 4-nitrophthalonitrile in the presence of potassium carbonate. The chemical structure of the synthesized BDSP was confirmed by proton (1H) and carbon (12C) nuclear magnetic resonance (NMR) as well as Fourier transform infrared (FTIR) analysis. The curing behavior of BDSP was investigated by FTIR and differential scanning calorimetry (DSC) analyses. The resin showed a low complex viscosity in the wide processing window between the monomer melting temperature and the curing temperature of the polymer, as discovered by rheological analysis. In addition, the properties of the polymer were studied by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Based on the test results, the BDSP polymer demonstrated superior processing performance, excellent thermal stability, outstanding mechanical properties, and low water uptake, and these advanced performance characteristics are critical to many fields.

A Bio‐Based Allylphenol (Eugenol)‐Functionalized Fluorinated Maleimide with Low Dielectric Constant and Low Water Uptake

AbstractA bio‐based allylphenol (eugenol)‐functionalized fluoro‐containing maleimide derived from easily available cyanuric chloride is synthesized, and it is thermally transformed to a cross‐linked polymer. It is found that the polymer displays a 5% weight loss temperature of up to 413 °C, a glass transition temperature (T g) of up to 274 °C, and a thermal expansion coefficient (CTE) of 66.21 ppm °C−1 varying from 50 to 300 °C. The polymer is also found to exhibit lower water uptake (1.06%) than commercial 4,4′‐bismaleimidodiphenylmethane (BMI) resins (3%) and allyl‐modified bismaleimides (4.5%). This polymer is also found to indicate good dielectric properties with a dielectric constant (D k) of below 2.9 and a dissipation factor (D f) of less than 7 × 10−3 for frequencies varying from 40 Hz to 25 MHz. It is reported that, compared to the commercial BMI with CTE of 77.85 ppm °C−1 and D k of 3.50, this eugenol‐functionalized fluoro‐containing maleimide possesses good properties, suggesting that this new maleimide has potential application in the microelectronic industry.

Highly conductive anion exchange membranes with low water uptake and performance evaluation in electrodialysis

The present work reports the preparation of a series of novel highly durable imidazolium-decorated anion exchange membranes (AEMs), with 3D network structure, via ultraviolet crosslinking reaction between 1-vinylimidazole and 1,6-hexanedithiol. AEM modified with trimethylamine (TMA) groups (no crosslinking, 45.7%) showed a significantly reduced water uptake within a range of 14.4–23.6% at 80 °C. Due to relatively good alkali-resistant of imidazolium groups and the compact structure stemmed from crosslinking network, the optimum cross-linked AEM (BPPO-Im 0.3) can retard the degradation and exhibits superior alkaline stability in 1.0 M NaOH at 60 °C for over 15 days, compared with TMA modified AEM. In ED application, BPPO-Im 0.3 AEM has a higher NaCl removal ratio of 77.82% than that of commercial AEM-Type II (74.13%) within 3 h experimental time. Accordingly, it shows higher current efficiency (67.43%) and lower energy consumption (1.94 kWh kg−1 NaCl), compared to commercial one (62.83%; 2.05 kWh kg−1). The facile fabrication process and the better-performance are suggestive of that BPPO-Im 0.3 is potentially applicable in ED.

Anion-exchange membrane for membrane capacitive deionization prepared via pore-filling polymerization in a porous polyethylene supporting membrane

Most polymer membranes with a high ion-exchange capacity (IEC) are not dimensionally stable in water because of their excess water uptake. In this study, an anion-exchange membrane was synthesized by performing a pore-filling polymerization in a porous polyethylene membrane used as the supporting substrate. The membrane was found to exhibit a high IEC (3.0 meq/g) but a very low water uptake (8%) and low electrical resistance (0.30 Ω·cm2). The membrane capacitive deionization (MCDI) cell assembled from components including the fabricated anion-exchange membrane and a commercial cation-exchange membrane (CMX) was found to exhibit a higher salt adsorption capacity and a higher current efficiency than that using a commercial anion-exchange membrane (AMX, IEC = 1.5 meq/g, electrical resistance = 4.8 Ω·cm2) and CMX. This improved performance compared to that of the AMX cell is ascribed to the higher IEC of the new membrane and its lower electrical resistance.

Performance mapping of cation exchange membranes for hydrogen-bromine flow batteries for energy storage

Electricity storage is essential for the transition to sustainable energy sources. Hydrogen-bromine flow batteries (HBFBs) are promising cost-effective energy storage systems. In HBFBs, proton exchange membranes are required to separate the two reactive materials, enabling proton transport for charge balancing. In this paper, we present a comprehensive overview of the key properties and an experimental performance map of cation exchange membranes for HBFBs. Our study shows that membrane water uptake is an important property due to its strong correlation with membrane resistance and bromide species crossover. Long chain perfluorosulfonic acid (LC PFSA) membranes are shown to have a better power density–crossover tradeoff and a higher stability than other types of functionalized membranes. The good power density-crossover tradeoff of LC PFSA membranes is the result of the high level of separation of hydrophobic and hydrophilic domains in the membrane, leading to well-connected ionic pathways for proton transport. Reinforcement of long chain LC PFSA membranes further improves their tradeoff because it mechanically constrains the swelling (lower water uptake), resulting in a lower crossover but a similar peak power density. Consequently, reinforced LC PFSA membranes are the most promising option for HBFBs.

A Low-Dielectric Polymer Derived from a Biorenewable Phenol (Eugenol)

A novel dielectric polysiloxane with low dielectric constants (<2.77) at frequencies ranging from 0.1 to 30.0 MHz was synthesized. The monomer was prepared from renewable eugenol using an extremely low amount of B(C6F5)3 catalyst. After thermal curing, the polysiloxane displayed high thermostability with degradation onset and glass transition temperatures of 400 and 201 °C, respectively. The coefficient of thermal expansion was 64 ppm/°C, and it displayed a low water uptake (<0.15%) when immersed in deionized water at room temperature for 144 h. These properties are comparable to those of other high-performance synthetic polymers, and thus, eugenol could be considered as a sustainable feedstock to prepare high-performance polymers.