Preparation and characterization of phosphoric acid composite membrane by radiation induced grafting of 4‐vinylpyridine onto poly(ethylene‐co‐tetrafluoroethylene) followed by phosphoric acid doping

Preparation of phosphoric acid composite membranes by radiation induced grafting of 4‐vinylpyridine (4‐VP) onto electron beam irradiated poly(ethylene‐co‐tetrafluoroethylene) film followed by phosphoric acid doping was investigated. The effect of grafting parameters (monomer concentration, absorbed dose, reaction time, and temperature) on the degree of grafting (G%) in the membrane precursor and its relation with the amount of acid doped was studied. The proton conductivity of the obtained membranes was evaluated in correlation with G% and temperature using ac impedance. Fourier transform infrared, thermal gravimetric analysis, X‐ray diffraction, and universal mechanical tester were used to investigate chemical composition, thermal resistance, structure, and mechanical properties of the membranes, respectively. The membranes of 34 and 49% recorded high proton conductivity in the magnitude of 10^‐2 S cm^‐1 without humidification. The membranes were also found to have reasonable mechanical integrity together with thermal stability up to 160°C. The obtained membranes are suggested to be less‐water dependent and have potential for testing in high temperature polymer electrolyte membrane fuel cell. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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     

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     

Functionalization of crosslinked polyacrylamide through γ‐radiation‐induced grafting of 4‐vinylpyridine

Crosslinked polyacrylamide beads were irradiated in air with a Co⁶⁰ γ‐radiation source. The preirradiated beads were graft‐copolymerized through heating with 4‐vinylpyridine in the presence of benzoyl peroxide. Grafting was studied as a function of various reaction parameters and was determined from the increase in the weight of the original polymer and the estimation of pyridine pendants in the homopolymer‐free graft copolymer. Although making the polymer basic in character, this modification retained the hydrophilic nature of polyacrylamide. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2613–2620, 2002     

Homogeneous and heterogeneous grafting of 4‐vinylpyridine onto chitosan

Modification of chitosan by grafting with 4‐vinylpyridine (VP) was carried out both in homogeneous and heterogeneous phases, using potassium persulfate (K₂S₂O₈) and sodium bisulfite (NaHSO₃) as redox initiators. The effect of monomer concentration, initiator concentration and redox ratio, time and temperature on the extent of grafting (G%), homopolymer formation, and the efficiency of grafting were studied. Values of grafting percentages up to 96% were reached in heterogeneous conditions and up to 130% in homogeneous conditions (in 5% acetic acid). The grafting was confirmed by FTIR and ¹H NMR spectroscopy. The grafted samples were characterized by scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis. The crystallinity of the used chitosan was not affected by grafting, it even increased slightly. Dye uptake of the grafted samples towards the different types of dyes (acidic and basic) was investigated and was found to improve profoundly over the native chitosan with a higher uptake for the acidic dye. The grafted samples showed an increased swelling in water, which increased further upon quaternization of the graft copolymers. The extent of swelling is higher in acidic and basic media more than in neutral pH. The grafted copolymers are soluble with difficulty in warm acetic acid solution. The quaternized graft copolymer was found to be soluble in water. The biological activity of the quaternized graft copolymers (G = 130 and 80%) was investigated and was found to have an inhibition effect on both the Azotobacter fungus and the bacterium Fusarium oxysporium. The effect on the micro organisms is proportional to the amount of VP in the graft copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3308–3317, 2006     

Irradiation‐induced grafting of poly(vinylidene fluoride)‐graft‐poly(styrene sulfonic acid) for the preparation of planar and tube‐shaped air‐drying membranes

A novel air‐drying membrane was developed and investigated as an alternative for planar and tube‐shaped drying membranes composed of Nafion^®. The new membrane is based on poly(vinylidene fluoride) (PVDF) polymer types grafted with polystyrene sulfonic acid. Modification of the PVDF membrane by chemical grafting was initiated via γ‐irradiation of pre‐made film and tube‐shaped samples. The grafting was conducted while the pre‐irradiated PVDF samples were immersed in styrene monomer solution. Three unique characterization methods were introduced to evaluate the ion exchange and barrier functions of the membrane. This investigation focuses on optimizing the degree of grafting yield, and subsequently the control of the membrane's overall functional performances, through (1) monitoring the PVDF's degree of crystallinity and (2) monitoring the styrene monomer solution temperature, respectively. Different levels of crystallinity were achieved by melt blending the PVDF‐copolymer with PVDF‐homopolymer, in various mixing ratios. Another variable examined in this investigation was the introduction of an ionic complex on the sulfonic acid end groups, and its effect on the membrane functional performance was studied. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Polymer electrolyte membranes composed of an electrospun poly(vinylidene fluoride) fibrous mat in a poly(4‐vinylpyridine) matrix

Newly proposed polymer electrolyte membranes (PEMs) composed of an electrospun poly(vinylidene fluoride) (PVDF) fibrous mat embedded in a poly(4‐vinylpyridine) (P4VP) matrix were successfully fabricated in order to improve the mechanical and dimensional stabilities and ionic conductivity of membranes in lithium rechargeable batteries. Fourier transform infrared spectroscopic analysis showed that as a result of the use of a high voltage during electrospinning the crystalline structure of PVDF changed partially from α‐phase to β‐phase. Energy‐dispersive X‐ray spectroscopy confirmed the existence of crosslinked P4VP in the PVDF fibrous mat. The electrolyte uptakes of PVDF and PVDF/P4VP composite mats were higher than that of PVDF cast film. The tensile properties of PVDF/P4VP composite mat were considerably improved compared to those of the pristine PVDF fibrous mat under both dry and wet (soaked with electrolyte) conditions. In addition, the mechanical and dimensional stabilities of the PVDF/P4VP composite PEM were further enhanced due to crosslinking between the P4VP chains. Furthermore, the PVDF/P4VP composite PEM exhibited an ionic conductivity that was an order of magnitude higher than that of traditional PVDF film. © 2012 Society of Chemical Industry     

Antifouling microfiltration membranes prepared from poly(vinylidene fluoride)‐graft‐Poly(N‐ vinyl pyrrolidone) powders synthesized via pre‐irradiation induced graft polymerization

Poly(vinylidene fluoride) (PVDF) powders were grafted with N‐vinyl pyrrolidone using the pre‐irradiation induced graft polymerization technique. The effects of reaction time, absorbed dose, and monomer concentration on the degree of grafting were investigated, and the grafted PVDF powders were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The grafted PVDF powders were also cast into microfiltration (MF) membranes via the phase‐inversion method. The contact angle and water uptake were measured. The membrane morphology was studied by scanning electron microscopy, and the water filtration properties of the membranes were tested. The antifouling properties were determined through measurements of the recovery percentage of pure water flux after the MF membranes were fouled with bovine serum albumin solution. The results confirmed that the existence of poly(N‐vinyl pyrrolidone) (PVP) graft chains improved the hydrophilicity and antifouling properties of the MF membranes cast from PVDF‐g‐PVP powders. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Surface characterization and study of Langmuir films of poly(4‐vinylpyridine) quaternized with n‐alkylbromide

The surface behaviour of poly(4‐vinylpyridine)s (P4VP) quaternized with four different alkyl chains (pentyl, hexyl, octyl and decy bromide) were studied. Surface pressure–area isotherms (π–A) at the air–water interface were determined. Depending on the length of the side‐chains, the π–A isotherms show a plateau region. An extensive plateau is observed for n > 6. The plateau pressures are similar for n = 8 and n = 10. The monolayers are stable and exhibit hysteresis phenomena. Brewster angle microscopy (BAM) is used to monitor the monolayer topography of the polymer on water subphase. To obtain information about the surface energy (SE) and the degree of hydrophobicity of these systems, we have estimated the critical surface tension, γ_c, and the dispersion force and polar contributions to SE, γ_D and γ_P, respectively, by measurements of the contact angle (CA) of water and bromobenzene on the polymer surface. The results obtained are depend on the length of the alkyl lateral chain of the functionalized polymers. © 2001 Society of Chemical Industry     

Synthesis and swelling characteristics of poly(4‐vinylpyridine) gels crosslinked by irradiation

The effect of irradiation under vacuum on thermal properties and swelling behavior on poly(4‐vinylpyridine) (P4VP) was investigated. The gel percentage in the irradiated P4VP films was determined by Soxhlet extraction. UV spectroscopy was also used to determine sol percentage, which decreased as the radiation dose increased. The changes in thermal properties, such as glass‐transition temperature (T_g), were followed by differential scanning calorimetry before and after Soxhlet extraction. The gels prepared after irradiation were characterized with respect to their swelling properties and network structures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2609–2614, 2001     

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     

Properties and thermal degradation study of blend films with poly(4‐vinylpyridine) and lignin

A series of blend films with different ratio of poly(4‐vinylpyridine) (PVP) to lignin were subjected to dynamic DSC and TGA measurement under nitrogen atmosphere at various heating rates. DSC curves showed that the glass transition temperatures of these blends decreased with the increase of lignin content. TGA studies indicated that the lignin content produced obvious effect on the thermal stability of these blends. The kinetic model function of the thermal decomposition of these blends obeyed the Avrami‐Erofeev model equation, g(α) = [‐ln(1‐α)]^1/m. The degradation kinetic parameters were also obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1875–1879, 2005     

Preparation of pH‐responsive crosslinked materials from natural rubber and poly(4‐vinylpyridine)

Stimuli‐responsive elastomers are smart materials for sensing applications. Natural rubber (NR) is a renewable elastomer with excellent elasticity and fatigue resistance. In this work, a straightforward method for the preparation of pH‐responsive crosslinked materials from NR and poly(4‐vinylpyridine) (P4VP) via free radical crosslinking reaction using benzoyl peroxide (BPO) as an initiator is described. The effects of P4VP and BPO concentrations, reaction time and reaction temperature on immobilization percentage were investigated. It was found that the immobilization percentage reached 90% when using a P4VP concentration of 150 phr and a BPO concentration of 10 phr for 24 h at 90 °C. The pH responsiveness of the crosslinked materials was studied via water swelling, water contact angle and dye release measurements. Unlike unmodified rubber, the P4VP‐crosslinked NR was found to be pH‐responsive in acidic solution. Indigo carmine adsorption studies showed the Langmuir isotherm suggesting monolayer coverage of dye on the rubber surface. The dye could also be released upon increasing the pH of solution above 4. Based on these results, the introduction of pH responsiveness to NR will lead to novel responsive rubber‐based materials that can be used in biomedical and sensing applications. © 2016 Society of Chemical Industry     

Preparation and catalytic application of poly 4‐vinylpyridine microspheres

Poly 4‐vinylpyridine (P4VP) microspheres between 170 and 728 nm were synthesized by Emulsifier‐Free Emulsion Polymerization. The monomer concentration, ionic strength, and initiator concentration affected the microsphere size and size distribution. The increasing monomer concentration led to the increase of microsphere size, whereas the size distribution of the resultant P4VP microspheres increased with the increasing ionic strength of the reaction systems. Mo(O₂)₂O·2DMF was successfully anchored onto the P4VP microspheres by ligand exchange, and the heterogeneous catalyst showed high‐catalytic activity for epoxidation of cis‐cyclooctene with environmentally friendly hydrogen peroxide. The size and morphology of the supported microspheres has important influence on the catalytic activity. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Highly efficient interpenetrating polymerization of styrene and 4‐vinylpyridine with poly(ethylene terephthalate) using benzoyl peroxide

A polymerization method for the preparation of an interpenetrating network polymer with poly(ethylene terephthalate) is reported. Two types of monomer, styrene and 4‐vinylpyridine, were chosen as hydrophobic and hydrophilic representatives, respectively, in order to show the versatility of this polymerization method. The polymer‐immobilized poly(ethylene terephthalate) samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy and X‐ray photoelectron spectroscopy. The immobilization efficiency of styrene as a function of reaction temperature, monomer‐to‐initiator molar ratio, reaction time, addition of solvent, surface hydrophilicity and immersion in initiator was studied. The maximum immobilization percentage of styrene reaches 111%. The immobilization efficiency is proportional to polymer molecular weight and sample thickness. Based on these results, this strategy is shown to be an efficient, versatile method for preparing interpenetrating network polymers and can be used as a means to modify the structures and properties of polymeric substrates. © 2013 Society of Chemical Industry     

Sulfonation of styrene‐grafted poly(vinylidene fluoride) films

Electron‐beam irradiated and styrene‐grafted poly(vinylidene fluoride) films are sulfonated with chlorosulfonic acid in dichloroethane under various conditions. The impact of the reaction time, the concentration of the sulfonating agent, and the reaction temperature on the properties of the sulfonated film is examined. Sulfonation proceeds via a reaction front mechanism. Sulfonation of surface‐grafted films is incomplete at room temperature. The number of side reactions taking place appears to be linearly dependent on the concentration of the sulfonation solution. Dimensional changes suggest that sulfone crosslinking is significant at higher concentrations. This reduces the ion‐exchange capacity and proton conductivity of the films but increases the resistance to oxidation in a H₂O₂ solution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1572–1580, 2001     

A study on compatibility of polymer blends of polystyrene/poly(4‐vinylpyridine)

Blends of polystyrene/poly (4‐vinylpyridine) have been prepared by casting from a common solvent. The compatibility of the blends was studied by using dilute solution viscometry (DSV), differential scanning calorimetery (DSC), Fourier transformation‐infrared spectroscopy (FT‐IR), and scanning electron microscopy (SEM). The relative viscosity versus composition plots for the blends are not perfect linear. The corresponding intrinsic viscosity values show negative deviation from ideal behavior when plotted against composition. Also, the modified Krigbaum and Wall interaction parameter, Δb, shows small and negative values for all compositions except for the blend PS/P4VP (25 : 75). The results indicate that the polymers are incompatible but small interaction values predict physically miscible blends which eventually show phase separation, as is observed in the present studies. However, the blends as obtained show a single, composition‐dependent, glass transition temperature that fits the Fox equation well, indicating the presence of homogeneous phase. The constant, k obtained from Gordon‐Taylor equation suggests intermolecular attraction between these polymers. FT‐IR and SEM support the results of DSV and DSC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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