Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films. I. Effect of grafting conditions

The simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films was studied at room temperature. The effects of grafting conditions (type of solvent, irradiation dose, dose rate, and monomer concentration) were investigated. The degree of grafting was found to be dependent on the investigated grafting conditions. The dependence of the initial rate of grafting on the dose rate and the monomer concentration was found to be of 0.5 and 1.3 orders, respectively. The results suggest that grafting proceeds by the so‐called front mechanism in which the grafting front starts at the surface of the film and moves internally toward the middle of the film by successive diffusion of styrene through the grafted layers. Some selected properties of the grafted films were evaluated in correlation with the degree of grafting. We found that the grafted FEP films possess good mechanical stability, which encourages their use for the preparation of proton exchange membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 220–227, 2000     

Simultaneous radiation grafting of vinylbenzyl chloride onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films

In this study, we demonstrated that vinylbenzyl chloride (VBC), a versatile monomer with reactive a chloromethyl group could be grafted onto a poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) film without a degradation of the chloromethyl group during a simultaneous irradiation process. The effects of various irradiation conditions such as the total dose, dose rate, solvent, and VBC concentration on the degree of grafting of VBC onto a FEP film were also investigated. The prepared PVBC‐grafted films were characterized using FTIR, TGA, and SEM EDX. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of sulfonated poly(arylene‐co‐naphthalimide)s for use as proton exchange membranes

In this study, conductive porous composites were fabricated using the host substrate with an interconnected porous network, followed by the penetration and deposition of polypyrrole (PPy) to create a continuous conductive network. The open‐porous host substrate was processed using polylactide (PLA) with compression molding and salt leaching techniques. Three different salt contents were varied from 75 wt %, 85 wt %, and 90 wt %, which were referred to by their salt‐to‐polymer mass ratios of 3, 6, and 9, respectively. The porous network was made conductive by coating its interior surfaces through in situ polymerization of PPy using iron (III) chloride as the oxidant species. These porous composites were then characterized to analyze the relationships between their morphology and their physical, conductive, and mechanical properties. The mechanical properties were then fitted with numerically simulated results from finite element modeling (FEM). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cation exchange membranes by radiation‐induced graft copolymerization of styrene onto PFA copolymer films. II. Characterization of sulfonated graft copolymer membranes

PFA‐g‐polystyrene sulfonic acid membranes were prepared by simultaneous radiation‐induced graft copolymerization of styrene onto poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA) film followed by sulfonation. The membrane physico‐chemical properties such as swelling behavior, ion exchange capacity, hydration number, and ionic conductivity were studied as a function of the degree of grafting. Thermal as well as chemical stability of the membranes was also investigated. The membrane properties were found to be mainly dependent upon the degree of grafting. The water uptake, ion exchange capacity, hydration number, and ionic conductivity of the membranes were increased, whereas the chemical stability decreased as the degree of grafting increased. The membranes showed reasonable physico‐chemical properties compared to Nafion 117 membranes. However, their chemical stability has to be further improved to make them acceptable for practical use in electrochemical applications. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1–11, 2000     

Part II. Properties of the grafted and sulfonated membranes

The physical and chemical properties of polystyrene grafted and sulfonated polytetrafluoroethylene (PTFE‐graft‐PSSA) membranes prepared by radiation‐induced grafting of styrene onto commercial PTFE films using simultaneous irradiation technique followed by a sulfonation reaction are evaluated. The investigated properties include water uptake, ion exchange capacity, hydration number and ionic conductivity. All properties are correlated with the amount of grafted polystyrene (degree of grafting). The thermal stability of the membrane evaluated by thermal gravimetric analysis (TGA) is compared with that of original and grafted PTFE films. The membrane surface structural properties are analysed by electron spectroscopy for chemical analysis (ESCA). Membranes having degrees of grafting of 18 % and above show a good combination of physical and chemical properties that allow them to be proposed for use as proton conducting membranes, provided that they have sufficient chemical and mechanical stability. © 2000 Society of Chemical Industry     

Radiation-induced graft polymerization of acrylonitrile onto isotactic polypropylene and poly(tetrafluoroethylene–ethylene) copolymer films

Direct radiation-induced grafting of acrylonitrile (AN) onto both isotactic polypropylene (IPP) and (tetrafluoroethylene–ethylene) copolymer (ET) films has been studied. The effect of grafting conditions such as inhibitor and monomer concentrations and irradiation dose on the grafting yield was investigated. Homopolymerization of acrylonitrile was reduced to a minimum using ferric chloride (FeCl₃), and the suitable optimum concentration of the inhibitor was found to be 0.1 wt%. The higher the monomer concentration, the higher the degree of grafting obtained. It was observed that the degree of grafting onto IPP was higher than onto ET, at given grafting conditions. The effect of aging on IPP was also examined. IR spectroscopy showed that IPP was susceptible to photooxidation by aging. The swelling behaviour and electrical conductivity of the graft and hydrolysed graft films were investigated. The electrical conductivity was improved by hydrolysis of polyacrylonitrile in the graft chains.     

Preparation and properties of poly(ether‐ester‐amide)/poly(acrylonitrile‐co‐butadiene‐co‐styrene) antistatic blends

A novel antistatic agent poly(ether‐ester‐amide) (PEEA) based on caprolactam, polyethylene glycol, and 6‐aminocaproic acid was successfully synthesized by melting polycondensation. The structure, thermal properties, and antistatic ability of the copolymer were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, and ZC36 megohmmeter. Test results show that PEEA is a block copolymer with a melting point of 217°C and a thermal decomposition temperature of 409°C, together with a surface resistivity of 10⁸ Ω/sq. Antistatic poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) materials were prepared by blending different content of PEEA to ABS resin. The antistatic performances, morphology, and mechanical properties were investigated. It is indicated that the surface resistivity of PEEA/ABS blends decrease with the increasing PEEA content, and the excellent antistatic performance is obtained when the antistatic agent is up to 10–15%. The antistatic performance is hardly influenced by water‐washing and relative humidity, and a permanent antistatic performance is available. The antistatic mechanism is investigated. The compatibility of the blends was studied by scanning electron microscopy images. The ladder distribution of antistatic agent is formed, and a rich phase of antistatic agent can be found in the surface layer. The elongations at break of the blend are improved with the increasing antistatic agent; the tensile strength and the notched impact strength kept almost the same. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Acid‐synergized grafting of sodium styrene sulfonate onto electron beam irradiated‐poly(vinylidene fluoride) films for preparation of fuel cell membrane

The role of acid addition in synergizing radiation induced grafting of sodium styrene sulfonate (SSS) onto electron beam‐irradiated poly(vinylidene fluoride) (PVDF) films as a single‐step route for preparation of proton exchange membranes containing sulfonic acid groups was systematically investigated. The grafting reaction, known for its poor kinetics, was studied using SSS diluted in various solvents and solvent/acid solutions of different concentrations and volumes. The addition of acid solution was found to marvelously synergize the grafting reaction from very low values (e.g., 0.5%) to achieve high degrees (e.g., 65%) of grafting and such synergetic effect depends on the type, concentration and volume of the added acid. The degree of grafting was also found to be function of the monomer concentration and the irradiation dose at constant acid concentration and volume. The obtained membranes were investigated with Fourier transform infrared spectroscopy (FTIR), scanning transmission electron microscopy (STEM), and X‐ray diffractometry (XRD). The results of present study reveal that grafting of SSS to levels suitable for fuel cell application onto PVDF film is only possible by adding aqueous acids solution. Moreover, the addition of acid makes this shorter single‐step method more economical route for preparation of proton exchange membranes for fuel cells. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films. I. Effect of grafting conditions and properties of the grafted films

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films was studied by a simultaneous irradiation technique. Grafting was carried out using γ‐radiation from a ⁶⁰Co source at dose rates of 1.32–15.0 kGy h⁻¹ at room temperature. The effects of type of diluent, dose rate, irradiation dose, and the initial monomer concentration in the grafting solution on the degree of grafting were investigated. The degree of grafting was found to be strongly dependent upon the grafting conditions. The dependence of the initial rate of grafting on the dose rate and the initial monomer concentration in the grafting solution was found to be in the order of 0.6 and 1.7, respectively. The chemical structure and the crystallinity of the grafted PTFE films were studied by means of Fourier‐transform infrared, (FTIR), electron spectroscopy for chemical analysis (ESCA) and X‐ray diffractometry (XRD). © 2000 Society of Chemical Industry     

Thermal properties of blends of poly(hydroxybutyrate‐co‐hydroxyvalerate) and poly(styrene‐co‐acrylonitrile)

Thermal properties of blends of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) and poly(styrene‐co‐acrylonitrile) (SAN) prepared by solution casting were investigated by differential scanning calorimetry. In the study of PHBV‐SAN blends by differential scanning calorimetry, glass transition temperature and melting point of PHBV in the PHBV‐SAN blends were almost unchanged compared with those of the pure PHBV. This result indicates that the blends of PHBV and SAN are immiscible. However, crystallization temperature of the PHBV in the blends decreased approximately 9–15°. From the results of the Avrami analysis of PHBV in the PHBV‐SAN blends, crystallization rate constant of PHBV in the PHBV‐SAN blends decreased compared with that of the pure PHBV. From the above results, it is suggested that the nucleation of PHBV in the blends is suppressed by the addition of SAN. From the measured crystallization half time and degree of supercooling, interfacial free energy for the formation of heterogeneous nuclei of PHBV in the PHBV‐SAN blends was calculated and found to be 2360 (mN/m)³ for the pure PHBV and 2920–3120 (mN/m)³ for the blends. The values of interfacial free energy indicate that heterogeneity of PHBV in the PHBV‐SAN blends is deactivated by the SAN. This result is consistent with the results of crystallization temperature and crystallization rate constant of PHBV in the PHBV‐SAN blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 673–679, 2000     

Solvothermal process for grafting dibutylmaleate onto poly(ethylene‐co‐1‐octene)

Solvothermal process was successfully developed to graft dibutylmaleate (DBM) onto poly(ethylene‐co‐1‐octene) (POE) with dicumyl peroxide (DCP) as free radical‐initiator. FTIR spectra demonstrate that DBM is successfully grafted onto the backbone of POE by this novel method. The influences of DBM content, DCP concentration, POE concentration, reaction temperature and reaction time on the grafting copolymerization have been investigated in detail through grafting degree (GD). It is worthy to indicate that high grafting degree (above 15%) can be achieved through the one‐pot way when the graft reaction is carried out in 40 mL toluene at 150°C for 5 h with 1.6 g DBM, 6–8 g POE and 0.35 g DCP. This developed solvothermal process is becoming an effective way to prepare POE‐g‐DBM graft copolymers, and can be extended to other systems. In addition, TGA results show that the thermal properties of POE are enhanced after the grafting reaction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Selective separation of water from aqueous alcohol mixtures through functionalized syndiotactic poly(styrene‐co‐4‐methylstyrene) membranes by pervaporation

The pervaporation performances of a series of functionalized syndiotactic poly(styrene‐co‐4‐methylstyrene) (SPSM) membranes for various alcohol mixtures were investigated. The syndiotactic polystyrene copolymers, poly(styrene‐co‐4‐methylstyrene) (SPSM), were prepared by styrene with 4‐methylstyrene using a Cp*Ti(OCH₃)₃/methyl aluminoxane (metallocene/MAO) catalyst. The effect of functionalization on the thermal properties and polymer structure of the SPSM membranes were also investigated. The crystallinity of the functionalized SPSM membrane is lower than that of the unfunctionalized SPSM membranes. The water molecules preferentially permeate through the SPSM membranes. Compared with unfunctionalized SPSM membranes, the functionalized SPSM membrane effectively increases the membrane formation performances and the pervaporation performances. The optimun pervaporation performance (a separation factor of 510 and permeation rate of 220 g/m²h) was obtained by the bromination of SPSM (SPSMBr) membrane with a 90 wt % aqueous ethanol solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2247–2254, 2002     

Proton exchange membranes based on poly(vinylidene fluoride) and sulfonated poly(ether ether ketone)

Blend membranes were obtained by solution casting from poly(vinylidene fluoride) (PVDF) and sulfonated poly(ether ether ketone) (SPEEK) in N,N-dimethylacetamide (DMAc). DSC and XRD were used to characterize the structure of the blend membranes. The effect of PVDF content on the membrane properties was investigated. The methanol permeability, water uptake and the swelling ratio of blend membranes decreased with the increase of PVDF content. Though the proton conductivity decreased upon the addition of PVDF, they were still comparable to that of Nafion^® 117 membrane. Higher selectivities were also found for most blend membranes in comparison with Nafion^® 117 membrane. The effect of methanol concentration on solution uptake, swelling ratio and methanol permeability of the blend membranes was also studied.     

Influence of the radiation grafting conditions on the cross‐sectional distribution of poly(vinylbenzyl chloride) grafted polymer onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films

Poly(vinylbenzyl chloride) (PVBC)‐grafted poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films were prepared as precursors for ion‐exchange membranes with a radiation grafting technique. A scanning electron microscopy–energy dispersive X‐ray spectroscopy (SEM‐EDX) instrument was used to investigate the effects of the radiation grafting conditions on the distribution profiles of the grafts in the FEP‐g‐PVBC films because the properties of the ion‐exchange membranes were largely affected not only by the degree of grafting (DOG) but also by the distribution of the graft chain. These results indicate that the distribution profile of the grafts largely depended on the grafting parameters, such as the solvent, monomer concentration, film thickness, and irradiation dose. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of crystallinity on surface morphology and light transmittance of poly(vinylidene fluoride‐co‐hexafluoropropylene) thin film

Homopolymer of vinylidene fluoride and its copolymers containing hexafluoropropylene (HFP) were prepared from free radical solution polymerizations and spin‐coated on the glass slides to fabricate thin film with a thickness of ～ 1 μm. It was found that the surface morphology of fluorinated thin films was strongly dependent on the crystallinity of polymers. In addition, the surface morphology was the most important factor to determine the optical transmittance of glass coated with the fluoropolymer thin film. As decreasing the crystallinity of the polymer by introducing HFP with a bulky CF₃ moiety, the surface of thin film became flattened and the transmittance of visible light was increased by reducing scattering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of tacticity of poly(methyl methacrylate) on the miscibility with poly(styrene‐co‐acrylonitrile)

Isotactic, atactic, and syndiotactic poly(methyl methacrylates) (PMMAs) (designated as iPMMA, aPMMA, and sPMMA) with approximately the same molecular weight were mixed separately with poly(styrene‐co‐acrylonitrile) (abbreviated as PSAN) containing 25 wt % of acrylonitrile in tetrahydrofuran to make three polymer blend systems. Differential scanning calorimetry (DSC) was used to study the miscibility of these blends. The results showed that the tacticity of PMMA has a definite impact on its miscibility with PSAN. The aPMMA/PSAN and sPMMA/PSAN blends were found to be miscible because all the prepared films were transparent and showed composition dependent glass transition temperatures (T_gs). The glass transition temperatures of the two miscible blends were fitted well by the Fox equation, and no broadening of the glass transition regions was observed. The iPMMA/PSAN blends were found to be immiscible, because most of the cast films were translucent and had two glass transition temperatures. Through the use of a simple binary interaction model, the following comments can be drawn. The isotactic MMA segments seemed to interact differently with styrene and with acrylonitrile segments from atactic or syndiotactic MMA segments. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2894–2899, 1999     

Mechanical properties and ionic conductivity of gel polymer electrolyte based on poly(vinylidene‐fluoride‐co‐hexafluoropropylene)

The main thermodynamic parameters were evaluated for the dextran/methoxy ethylene glycol (MEG) system by viscosity measurements at 25, 30, 35, 40, and 45°C. The long-range and short-range interaction parameters were determined by extrapolation methods, i.e, Kurata-Stockmayer-Fixman, Berry, and Inagaki-Suzuki-Kurata equations. Calculated values, as well as the unperturbed root-mean-square end-to-end distance and hydrodynamic expansion factor, were interpreted mainly on the basis of hydrogen-bond formation between polymer segments and dextran/MEG molecules in solution. The thermodynamic interaction parameter was also evaluated for the same system. The theta temperatures were obtained from the temperature dependence of the interaction parameter, dependence of (1/2-χ) and the second virial coefficient in the temperature interval of 25 and 45°C for the system and quite a good accordance was indicated with the calculated values evaluated via extrapolation and interpolation methods. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 948–953, 2001     

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     

Influence of hydrogen donors on peroxide‐initiated melt grafting of vinylsilane to poly(ethylene‐co‐vinyl acetate)

A technique has been examined for reducing the extent of crosslinking resulting from 1,1‐di(t‐butylperoxy)‐3,3,5‐trimethylcyclohexane (L‐231) initiating melt grafting of vinyltriethoxysilane (VTEOS) onto poly(ethylene‐co‐vinyl acetate) (EVA). Using measurements of crosslink density and VTEOS conversion, a standard of selectivity for the EVA/VTEOS/L‐231 system at 145 °C was defined and used to assess the influence of a range of additives (0.25 mol per mole VTEOS). The data indicated that compounds such as 4‐nonene, N,N‐dimethylaniline, and cumene improve reaction selectivity, whereas dodecane and cyclohexyl acetate have no effect. A strong correlation between the minimum C? H bond dissociation energy and the influence of a given compound is evident, suggesting that a labile C? H bond is the key element of an effective additive. A mechanism of additive function on the basis of hydrogen atom donation is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2397–2402, 2002     

Proton exchange membranes by grafting of styrene–acrylic acid onto FEP by preirradiation technique. II. Physicochemical properties of the membrane and its sulfonated derivatives

Poly(tetrafluoroethylene‐co‐haxafluoropropylene) (FEP)‐g‐styrene–acrylic acid and its sulfonated derivative membranes were prepared by graft copolymerization of styrene–acrylic acid onto FEP by using preirradiation of γ‐ray technique followed by sulfonation. The physiochemical properties such as ion exchange capacity, water uptake, ionic resistance of the grafted membranes, and their sulfonated derivatives were studied as a function of degree of grafting. These membranes on sulfonation gave acid base, indicating property. The membranes gave yellow color in acidic medium and purple color in alkali medium. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2318–2325, 2004