Effect of crosslinkers on the preparation and properties of ETFE‐based radiation‐grafted polymer electrolyte membranes

This study concerns a comparative study of three crosslinkers, divinylbenzene (DVB), 1,2‐bis(p,p‐vinylphenyl)ethane (BVPE), and triallyl cyanurate (TAC) crosslinked poly(ethylene‐co‐tetrafluoroethylene) (ETFE)‐based radiation‐grafted membranes, which were prepared by radiation grafting of p‐methylstyrene onto ETFE films and subsequent sulfonation. The effect of the different types and contents of the crosslinkers on the grafting and sulfonation, and the properties such as water uptake, proton conductivity, and thermal/chemical stability of the resulting polymer electrolyte membranes were investigated in detail. Introducing crosslink structure into the radiation‐grafted membranes leads to a decrease in proton conductivity due to the decrease in water uptake. The thermal stability of the crosslinked radiation‐grafted membranes is also somewhat lower than that of the noncrosslinked one. However, the crosslinked radiation‐grafted membranes show significantly higher chemical stability characterized in the 3% H₂O₂ at 50°C. Among the three crosslinkers, the DVB shows a most pronounced efficiency on the crosslinking of the radiation‐grafted membranes, while the TAC has no significant influence; the BVPE is a mild and effective crosslinker, showing the moderate influence between the DVB and TAC crosslinkers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4565–4574, 2006     

Synthesis and characteristics of radiation‐grafted membranes for fuel cell electrolytes

Proton exchange membranes were prepared by simultaneous radiation grafting of styrene onto polytetrafluoroethylene (PTFE) films at room temperature and subsequent sulfonation by chlorosulfonic acid. A series of grafted films with degree of grafting ranging from 0.947% to 35.4% were obtained. The effect of styrene concentration on the grafting yield was investigated and the maximum value was obtained at a monomer concentration of 70‐vol%. The structure of PTFE‐graft‐polystyrene sulfonic acid membranes was studied by infrared spectroscopy. The membrane properties, such as water uptake, ion exchange capacity, swelling performance and ionic resistance, were studied as functions of the degree of grafting. The thermal and chemical stability of the sulfonic acid membranes was also investigated. The membrane properties were found to depend on the degree of grafting and the amorphous character of the membrane structure, and the better membrane properties were obtained at a degree of grafting in the range 12–21%. Copyright © 2003 Society of Chemical Industry     

Proton conducting crosslinked polymer electrolyte membranes based on SBS block copolymer

A series of crosslinked polymer electrolyte membranes with controlled structures were prepared based on poly(styrene‐b‐butadiene‐b‐styrene) (SBS) triblock copolymer and a sulfonated monomer, 2‐sulfoethyl methacrylate (SEMA). SBS membranes were thermally crosslinked with SEMA in the presence of a thermal‐initiator, 4,4′‐azobis(4‐cyanovaleric acid) (ACVA), as confirmed by FT‐IR spectroscopy. The water uptake and ion exchange capacity (IEC) of membranes increased almost linearly with SEMA concentrations due to the increase of SO groups. However, the proton conductivity of membranes increased linearly up to 33 wt % of SEMA, above which it abruptly jumped to 0.04 S/cm presumably due to the formation of well‐developed proton channels. Microphase‐separated morphology and amorphous structures of crosslinked SBS/SEMA membranes were observed using wide angle X‐ray scattering (WAXS), small angle X‐ray scattering (SAXS), and transmission electron microscopy (TEM). The membranes exhibited good mechanical properties and high thermal stability up to 250°C, as determined by a universal testing machine (UTM) and thermal gravimetric analysis (TGA), respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymer electrolyte membranes having sulfoalkyl grafts into ETFE film prepared by radiation‐induced copolymerization of methyl acrylate and methyl methacrylate

Polymer electrolyte membranes (PEMs) containing alkylsulfonic acid grafts can be prepared by radiation‐induced graft copolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) into a poly(ethylene‐co‐tetrafluoroethylene) film followed by sulfonation of the MA units in the copolymer grafts using an equimolar complex of chlorosulfonic acid and 1,4‐dioxane (ClSO₃H‐Complex). PEMs with MA/MMA copolymer grafts that are 33%–79% MA units were prepared by preirradiation with a dose of 20 kGy and grafting in bulk comonomers at 60°C. The grafted films are treated with ClSO3H‐Complex to obtain PEMs with ion exchange capacity of 0.36‐0.81 mmol/g (sulfonation degrees of 20%–40%) and proton conductivity of 0.04‐0.065 S/cm. These values can be controlled by changing the MA content the sulfonation occurring at an α‐carbonyl carbon. The PEMs with higher MMA content showed higher durability in water (80°C) and under oxidative conditions (3% H₂O₂) at 60°C. This is because the PMMA grafts in the PEMs have no proton at an α‐carbonyl carbon, which is considered to be a trigger of the degradation of grafting polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of ion‐exchange membranes by hydrolysis of radiation‐grafted polyethylene‐g‐polyacrylamide membranes

Polyethylene‐g‐polyacrylamide membranes were prepared by graft polymerization of acrylamide onto polyethylene films using a preirradiation method. The ion‐exchange membranes were obtained by the hydrolysis of grafted films so as to transform amide groups into carboxyl groups. The fraction of amide groups transformed into carboxyl groups was limited to ～0.5. The characterization and thermal behavior of membranes with different degrees of grafting were evaluated by FTIR, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) measurements. The heat of fusion and the crystallinity of polyethylene decreased considerably in the hydrolyzed membranes depending on the degree of grafting. It was found that the grafting of acrylamide led to the reduction in crystallinity due to disruption of the crystallites (crystal defects) and dilution of the inherent crystallinity (dilution effect). The contribution of the hydrolysis step to the crystallinity decrease was negligible. The thermal stability of the membranes as obtained from TGA showed considerable enhancement after hydrolysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 149–154, 2003     

Synthesis of fluorinated polymer electrolyte membranes by radiation grafting and atom transfer radical polymerization techniques

A novel polymer electrolyte membrane was synthesized by radiation-induced grafting and consequent atom transfer radical polymerization (ATRP). First, bromine-containing perfluorinated grafts were prepared by radiation grafting of 2-bromotetrafluoroethyl trifluorovinyl ether (BrTFF) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film. Then, the bromine atoms in the ETFE-g-PBrTFF grafted films were acted as initiators, and the films were treated with Cu(I)-based catalytic system of a CuBr and 2,2′-bipyridyl (bpy) for the ATRP. By adjusting the molar ratio of initiator/CuBr/bpy and the reaction temperature, branched poly(styrene) with a grafting yield of above 100% on the poly(BrTFF) main chains was constructed in ETFE-g-PBrTFF films. Thermal analysis revealed that the perfluorinated poly(BrTFF) main chains were miscible to ETFE, whereas the hydrocarbon poly(styrene) branches were phase-separated from the ETFE-g-PBrTFF film. Sulfonic groups could be further introduced into the poly(styrene) grafts of ETFE-g-PBrTFF-g-PS films with homogeneous distribution in a perpendicular direction to the membrane surface. The resulting membrane with a styrene grafting yield of 15% exhibited higher proton conductivity than commercial Nafion 117 membrane. Likewise, it had better chemical stability than ETFE-g-PSSA membrane prepared by conventional radiation-induced grafting.     

Comparative investigations of radiation‐grafted proton‐exchange membranes prepared using single‐step and conventional two‐step radiation‐induced grafting methods

Proton‐exchange membranes containing poly(styrene sulfonic acid) grafts hosted in poly(vinylidene fluoride) (PVDF) films were prepared using two radiation‐induced grafting methods: a single‐step grafting method (SSGM) involving grafting of sodium styrene sulfonate onto electron beam (EB)‐irradiated PVDF films and a conventional two‐step grafting method (CTSGM) in which styrene monomer is grafted onto EB‐irradiated PVDF films and subsequently sulfonated. Differential scanning calorimetry, universal mechanical testing and scanning transmission electron microscopy were used to evaluate the thermal, mechanical and structural changes developed in the membranes during the preparation procedures. Physicochemical properties such as water uptake, hydration number and ionic conductivity were studied as functions of ion‐exchange capacity and the results obtained were correlated with the structural changes accompanying each preparation method. Membranes obtained using the SSGM were found to have superior properties compared to their counterparts prepared using the CTSGM suggesting the former method is more effective than the latter for imparting desired functionality and stability properties to the membranes. Copyright © 2010 Society of Chemical Industry     

Polymer electrolyte membranes for high‐temperature fuel cells based on aromatic polyethers bearing pyridine units

This review is focused on the design and synthesis of new high‐temperature polymer electrolytes based on aromatic polyethers bearing polar pyridine moieties in the main chain. Such materials are designed to be used in polymer electrolyte fuel cells operating at temperatures higher than 100 °C. New monomers and polymers have been synthesized and characterized within this field in respect of their suitability for this specific application. Copolymers with optimized structures in order to combine excellent film‐forming properties with high mechanical, thermal and oxidative stability and controlled acid uptake have been synthesized which, after doping with phosphoric acid, result in ionically conducting membranes. Such materials have been studied in respect of their conductivity under various conditions and used for the construction of membrane‐electrode assemblies (MEAs) which are used for fuel cells operating at temperatures up to 180 °C. New and improved, in terms of oxidative stability and mechanical properties in the doped state, polymeric membranes have been synthesized and used effectively for MEA construction and single‐cell testing. Copyright © 2009 Society of Chemical Industry     

Effect of solvents on radiation‐induced grafting of styrene onto fluorinated polymer films

The effect of solvents on radiation‐induced grafting of styrene onto commercial fluorinated polymer films such as poly(tetrafluoroethylene) (PTFE), poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) and poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) was investigated by a simultaneous irradiation technique. Three solvents, ie methanol, benzene and dichloromethane, were used to dilute styrene under various irradiation doses, dose rates and monomer concentrations. The effect of addition of mineral and organic acids on the degree of grafting in the presence of the three solvents was also studied. The degree of grafting was found to be strongly dependent upon the type of solvent and composition of the monomer/solvent mixture. Dilution of styrene with dichloromethane in various grafting conditions was found to enhance dramatically the degree of grafting compared with other solvents, and the maximum degree of grafting was achieved at a monomer/solvent mixture having a composition of 60:40 (v/v). The formation of polystyrene grafts in the three fluorinated films was verified using FTIR spectrometry. © 2001 Society of Chemical Industry     

Carrier‐free dyeing of radiation‐grafted polyester fabrics with disperse dyes

Carrier‐free dyeing of radiation‐grafted polyester fabrics with disperse red dye was studied in the temperature range 283–363 K. 1‐vinyl 2‐pyrrolidone (NVP), acrylic acid (AA) or their mixture was used to graft poly(ethylene terephthalate) (PET) fabric. The effects of pH of the dye solution, graft yield (GY), dyeing time (t), dye concentration (C), and dyeing temperature (T) on the colour difference (CD) of PET fabric were studied. The best dyeing condition was achieved at pH 5.5. CD increases linearly with the increase in GY, with slopes depending on the type of grafted copolymer. CD increased rapidly as the dyeing time increased; this was followed by a relatively slow dyeing rate within a few minutes. The initial dyeing rate (R) was found to increase with an increase in C and T. The dyeing rates for all grafted samples followed 0.35‐order kinetics and are temperature‐independent. Average activation energy 9.26 kJ mol^?1 is calculated for the dyeing process and is independent of the fabric treatment. Pre‐exponential rate constants 1976, 1839, and 1579 (CD/GY) s^?1 were calculated for dyeing PET samples grafted with AA/NVP mixture, NVP and AA, respectively, while 1074 CD s^?1 was evaluated for carrier dyeing of ungrafted fabric. Analysis of the kinetic parameters and the dyeing mechanism revealed that dyeing PET fabric was diffusion‐controlled. Grafting PET fabric improved significantly the dyeing affinity of the DR dye over ungrafted samples dyed in solutions containing a carrier. Copyright © 2005 Society of Chemical Industry     

Grafting design: a strategy to increase the performance of radiation‐grafted membranes

The polymer design concept of short versus long side chains was successfully adapted to radiation‐grafted membranes, the fabrication of which is an easy and up‐scalable process. This concept was investigated by the generation of two model membranes based on polystyrene sulfonic acid‐grafted ethylene‐alt‐tetrafluoroethylene, prepared using a low versus high irradiation dose. It was shown to be essential to adjust the grafting parameters of both systems to obtain two membranes with similar composition in through‐plane direction. In particular, the high‐dose system showed pronounced grafting fronts. A structure–property correlation was found regarding the influence of the graft lengths on the performance characteristics of electron beam‐grafted ethylene‐alt‐tetrafluoroethylene‐based proton exchange membranes, e.g. the membrane type associated with a higher number density of short grafted chains showed higher water sorption behaviour as well as increased proton conductivity, especially in the lower relative humidity range. © 2015 Society of Chemical Industry     

Novel polymer electrolyte membranes based on semi‐interpenetrating blends of poly(vinyl alcohol) and sulfonated poly(ether ether ketone)

In this work, the properties of novel ionic polymer blends of crosslinked and sulfonated poly(vinyl alcohol) (PVA) and sulfonated poly(ether ether ketone) (SPEEK) are investigated. Crosslinking and sulfonation of PVA were carried out using sulfosuccinic acid (SSA) in the presence of dispersed SPEEK to obtain semi‐interpenetrating network blends. PVA–SSA/SPEEK blend membranes of different compositions were studied for their ion‐exchange capacity, proton conductivity, water uptake, and thermal and mechanical properties. The hydrated blend membranes show good proton conductivities in the range of 10^?3 to 10^?2 S/cm. When compared with pure component membranes, the PVA–SSA/SPEEK blend membranes also exhibit improvement in tensile strength, tensile modulus, and delay in the onset of thermal and chemical degradation. Semi‐interpenetrating nature of the blends is established from morphology and dynamic mechanical analysis. Morphology of the membranes was studied using scanning electron microscopy after selective chemical treatment. The dynamic mechanical properties of the membranes are examined to understand the miscibility characteristics of the blends. The relative proportions of PVA and SPEEK and the degree of crosslinking of PVA–SSA are important factors in determining the optimum properties for the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of novel grafted cellophane‐phosphoric acid‐doped membranes for proton exchange membrane fuel‐cell applications

This work concerns preparation of acid‐base polyelectrolyte membranes for fuel‐cell applications from cellulosic backbones for the first time. Grafted cellophane‐phosphoric acid‐doped membranes for direct oxidation methanol fuel cells (DMFC) were prepared following three steps. The first two steps were conducted to have the basic polymers. The first step was introducing of epoxy groups to its chemical structure through grafting process with poly(glycidylmethacrylate) (PGMA). The second step was converting the introduced epoxy groups to imides groups followed by phosphoric acid (? PO₃H) doping as the last step. This step significantly contributes to induce ion exchange capacity (IEC) and ionic conductivity (IC). Chemical changes of the cellophane composition and morphology characters were followed using FTIR, TGA, and SEM analysis. Different factors affecting the membranes characters especially IEC, methanol permeability, and thermal stability were investigated and optimized to have the best preparation conditions. Compared to Nafion 117 membrane, cellophane‐modified membranes show a better IEC, less methanol permeability, and better mechanical and thermal stability. IEC in the range of 1–2.3 meq/g compared to 0.9 meq/g per Nafion was obtained, and methanol permeability has been reduced by one‐order magnitude. However, the maximum obtained IC for cellophane‐PGMA‐grafted membrane doped with phosphoric acid was found 2.33 × 10^?3 (S cm^?1) compared to 3.88 × 10^?2 (S cm^?1) for Nafion 117. The obtained results are very promising for conducting further investigations taking into consideration the very low price of cellophane compared to Nafion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Physicochemical investigation of radiation‐grafted poly(acrylic acid)‐graft‐poly(tetrafluoroethylene–ethylene) copolymer membranes and their use in metal recovery from aqueous solution

ET‐g‐PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene–ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K⁺, Ag⁺, Hg²⁺, Co²⁺, and Cu²⁺ in a mixed aqueous solution. The ion‐exchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg²⁺ ion content of the membrane was more than that of either the K⁺ or Ag⁺ ions. The presence of metal ions in the membranes was studied by infrared and energy‐dispersive spectroscopy measurements. Scanning electron microscopy of the grafted and metal‐treated grafted membranes showed modification of the morphology of the surface due to the adsorption of K⁺ and Ag⁺ ions. No change was observed for the surface of the membrane that was treated with Hg²⁺ ions. The thermal stability of different membranes was improved more with Ag⁺ and Hg²⁺ ions than with K⁺ ions. It was found that the modified grafted membranes possessed good hydrophilicity, which may make them promising candidates for practical applications, such as for cation‐exchange membranes in the recovery of metals from an aqueous solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2692–2698, 2002     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. III. Thermal stability of the membranes

Thermal stability of cation exchange, PFA‐g‐polystyrene sulfonic acid membranes prepared by radiation‐induced graft copolymerization of styrene onto PFA films followed by sulfonation was studied by thermal gravimetric analysis (TGA) and oven heat treatment. The tested samples included original and grafted PFA films as reference materials. All the membranes showed multistep decomposition patterns due to dehydration, desulfonation, dearomatization, and decomposition of the PFA matrix. Investigations of the individual decomposition behaviors showed that the weight loss strongly depends upon the degree of grafting. However, the decomposition temperatures were found to be independent of the degree of grafting. The loss in some selected membrane properties such as ion exchange capacity and water uptake was found to be function of the degree of grafting, temperature, and the time of heat treatment. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1877–1885, 2000     

Immobilization of imidazole in polymer electrolyte membranes for elevated temperature anhydrous applications

A novel functional absorbent, polyvinyltetrazole fiber (PVT), was made from polyacrylonitrile fiber through [3+2] azide-nitrile cycloaddition reaction of cross-linked polyacrylonitrile with sodium azide. The obtained PVT showed strong adsorption ability to the investigated heavy-metal ions, Cu(II), Cd(II), Ni(II), and Zn(II), with the maximum adsorption capacities of 323, 278, 200, and 175 mg g⁻¹, respectively. The adsorption process was described as an ion exchange mechanism. The adsorption isotherms were better fitted for Langmuir model, while adsorption kinetics was better described by the pseudo-second order equation. In addition, the tested heavy-metal ions could be desorbed efficiently from PVT at pH below 2.0, and the adsorption capacity of the regenerated PVT had no loss until seven cycles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Semi-interpenetrating gel polymer electrolyte based on PVDF-HFP for lithium ion batteries

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based gel polymer electrolyte (GPE) is considered one of the promising candidate electrolytes in the polymer lithium ion battery (LIB) because of its free standing, shape versatility, security, flexibility, lightweight, reliability, and so on. However, the pristine PVDF-HFP GPE cannot still meet the requirement of large-scale LIBs and other electrochemical devices due to its relatively low ionic conductivity and deterioration of mechanical strength caused by the incorporation of organic liquid electrolyte into the polymer matrix as well as high cost. In order to overcome above deficiencies of PVDF-HFP based GPE, ultraviolet (UV)-curable semi-interpenetrating polymer network is designed and synthesized through UV-irradiation technique, and the as-prepared semi-interpenetrating matrix is constituted by pentaerythritol tetracrylate polymer network and PVDF-HFP. The ionic conductivity of the optimized GPE is as high as 5 × 10⁻⁴ S/cm and electrochemical window is up to 4.8 V at room temperature. Especially, the LIB prepared by GPE shows the high initial discharge specific capacity of 151 mAh/g at 0.5 C and good rate capability. Therefore, the semi-interpenetrating GPE based on PVDF-HFP exhibits a promising prospect for the application of rechargeable LIBs.     

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films. II. Properties of sulfonated membranes

Proton exchange membranes were prepared by radiation‐induced grafting of styrene onto commercial poly(tetrafluoroethylene‐co‐hexafluoropropylene) films using a simultaneous irradiation technique followed by a sulfonation reaction. The resulting membranes were characterized by measuring their physicochemical properties such as water uptake, ion exchange capacity, hydration number, and proton conductivity as a function of the degree of grafting. The thermal properties (melting and glass transition temperatures) and thermal stability of the membrane were also investigated using differential scanning calorimetry and thermal gravimetric analysis, respectively. Membranes having degrees of grafting of 16% and above showed proton conductivity of the magnitude of 10⁻² Ω⁻¹ cm⁻¹ at room temperature, as well as thermal stability at up to 290°C under an oxygen atmosphere. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2443–2453, 2000     

Immobilization of some biomolecules onto radiation‐grafted polyethylene beads for possible use in immunoassay applications

Functionalization of polyethylene (PE) beads was accomplished via radiation induced graft copolymerization of acrylic acid/acrylamide (AAc/AAm) binary comonomer of different compositions onto such beads. Factors affecting the grafting yield were optimized and the occurrence of the grafted chains was confirmed by following the FTIR spectra of the grafted beads. SEM analyses were used to follow the variation of the morphology of the grafting and immobilization onto PE beads. Some bio‐active molecules such as Follicle‐stimulating hormone (FSH), Luteinizing hormone (LH), Thyroid‐stimulating hormone (TSH), and Prolactin were immobilized to the radiation functionalized PE beads. The parameters may affect the immobilization process such as degree of grafting, temperature, and pH of the coupling buffer and the coupling period were investigated. The obtained results show that the grafting of AAc offers a better immobilization environment than those of AAm and their copolymer. It is found that the highest immobilization degree would be achieved at pH 7 and 37°C for 24 h. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012