High energy radiation grafting of fluoropolymers

Designing Advanced Cross-Linked Proton Exchange Membranes with Enhanced Structural Homogeneity and Proton Conductivity via Radiation-Induced RAFT Polymerization

This study introduces an innovative approach to fabricate well-defined cross-linked proton exchange membranes (PEMs) using radiation-induced reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization on cost-effective ethylene tetrafluoroethylene (ETFE) films. The incorporation of the RAFT mechanism into the cross-linking process significantly enhanced structural homogeneity, providing uninterrupted proton conductivity. Thorough characterizations confirmed the successful grafting of polystyrene (PS) chains onto ETFE films and subsequent sulfonation. Despite a reduction in proton conductivity attributed to restricted chain movements, a notable improvement in chemical stability was observed after cross-linking reactions. Chemical stability of the cross-linked membranes increased approximately 4-fold compared to those synthesized without a cross-linker. The synthesized PEMs with degrees of grafting at 45% and 67% demonstrated superior proton conductivity, outperforming various alternatives, including commercial Nafion samples. Specifically, these cross-linked membranes exhibited promising proton conductivity values of 93.7 and 139.1 mS cm-1, respectively. This work highlights the potential of radiation-induced RAFT-mediated polymerization in carrying out cross-linking reactions as an efficient pathway for designing well-defined high-performance PEMs, offering enhanced homogeneity and conductivity compared to existing literature counterparts.

A PEGylated PVDF Antifouling Membrane Prepared by Grafting of Methoxypolyethylene Glycol Acrylate in Gama-Irradiated Homogeneous Solution

In this study, methoxypolyethylene glycol acrylate (mPEGA) served as a PEGylated monomer and was grafted onto polyvinylidene fluoride (PVDF) through homogeneous solution gamma irradiation. The grafting process was confirmed using several techniques, including infrared spectroscopy (FTIR), thermodynamic stability assessments, and rotational viscosity measurements. The degree of grafting (DG) was determined via the gravimetric method. By varying the monomer concentration, a range of DGs was achieved in the PVDF-g-mPEGA copolymers. Investigations into water contact angles and scanning electron microscopy (SEM) images indicated a direct correlation between increased hydrophilicity, membrane porosity, and higher DG levels in the PVDF-g-mPEGA membrane. Filtration tests demonstrated that enhanced DGs resulted in more permeable PVDF-g-mPEGA membranes, eliminating the need for pore-forming agents. Antifouling tests revealed that membranes with a lower DG maintained a high flux recovery rate, indicating that the innate properties of PVDF could be largely preserved.

Connective tissue inspired elastomer-based hydrogel for artificial skin via radiation-indued penetrating polymerization

Robust hydrogels offer a candidate for artificial skin of bionic robots, yet few hydrogels have a comprehensive performance comparable to real human skin. Here, we present a general method to convert traditional elastomers into tough hydrogels via a unique radiation-induced penetrating polymerization method. The hydrogel is composed of the original hydrophobic crosslinking network from elastomers and grafted hydrophilic chains, which act as elastic collagen fibers and water-rich substances. Therefore, it successfully combines the advantages of both elastomers and hydrogels and provides similar Young's modulus and friction coefficients to human skin, as well as better compression and puncture load capacities than double network and polyampholyte hydrogels. Additionally, responsive abilities can be introduced during the preparation process, granting the hybrid hydrogels shape adaptability. With these unique properties, the hybrid hydrogel can be a candidate for artificial skin, fluid flow controller, wound dressing layer and many other bionic application scenarios.

Radiation-Grafting on Polypropylene Copolymer Membranes for Using in Cadmium Adsorption

Graft copolymerization has been a popular technique in recent years for adding different functional groups to polymers. In our research, polypropylene (PP) films are grafted with acrylonitrile (An) and acrylic acid (AAc) monomers to make them hydrophilic while retaining their mechanical qualities. Gamma radiation is used in this approach to establish active spots on an inert polymer that are appropriate for adding monomers radicals to form grafts, a procedure that is extremely difficult to perform using normal chemical processes. The graft parameters are investigated in order to acquire the highest percentage of graft. FTIR (Fourier transform infrared spectroscopy) spectra are used to analyze the grafting of AAc and An. SEM (scanning electron microscopy) and XRD (X-ray diffraction) micrographs are used to validate them. The specimens' tensile strength and hardness are measured and contrasted with blank PP films. Measurements are made of the effects of grafting on the tensile strength and elongation of the films, and a crucial grafting degree is established in order to preserve these properties. Water uptake is measured to adapt the copolymer to water treatment, and thermal behavior TGA (thermal gravimetric analysis) and DSC (diffraction scanning calorimeter) of the produced copolymer were performed. The elimination of cadmium was verified by an atomic absorption spectrophotometer (AAS) under different conditions of pH, time, and degree of grafting.

Highly Efficient One-Step Protein Immobilization on Polymer Membranes Supported by Response Surface Methodology

Immobilization of proteins by covalent coupling to polymeric materials offers numerous excellent advantages for various applications, however, it is usually limited by coupling strategies, which are often too expensive or complex. In this study, an electron-beam-based process for covalent coupling of the model protein bovine serum albumin (BSA) onto polyvinylidene fluoride (PVDF) flat sheet membranes was investigated. Immobilization can be performed in a clean, fast, and continuous mode of operation without any additional chemicals involved. Using the Design of Experiments (DoE) approach, nine process factors were investigated for their influence on graft yield and homogeneity. The parameters could be reduced to only four highly significant factors: BSA concentration, impregnation method, impregnation time, and electron beam irradiation dose. Subsequently, optimization of the process was performed using the Response Surface Methodology (RSM). A one-step method was developed, resulting in a high BSA grafting yield of 955 mg m−2 and a relative standard deviation of 3.6%. High efficiency was demonstrated by reusing the impregnation solution five times consecutively without reducing the final BSA grafting yield. Comprehensive characterization was conducted by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and measurements of zeta potential, contact angle and surface free energy, as well as filtration performance. In addition, mechanical properties and morphology were examined using mercury porosimetry, tensile testing, and scanning electron microscopy (SEM).

Crosslinked Fluorinated Poly(arylene ether)s with POSS: Synthesis and Conversion to High-Performance Polymers

This study reports on a series of crosslinked poly(arylene ether)s with POSS in the main chain. The fluorinated and terminated poly(arylene ether)s were first synthesized by the nucleophilic reaction of diphenol POSS and decafluorodiphenyl monomers, including decafluorobiphenyl, decaflurobenzophenone, and decafluorodiphenyl sulfone. They were then reacted with 3-hydroxyphenyl acetylene to produce phenylacetylene-terminated poly(arylene ether)s. The polymers were of excellent processability. When heated to a high temperature, the polymers converted into a crosslinked network, exhibiting a low range of dielectric constant from 2.17 to 2.58 at 1 HMz, strong resistance against chemical solutions, low dielectric losses, and good thermal and hydrophobic properties.

Radiation-Induced Graft Immobilization (RIGI): Covalent Binding of Non-Vinyl Compounds on Polymer Membranes

Radiation-induced graft immobilization (RIGI) is a novel method for the covalent binding of substances on polymeric materials without the use of additional chemicals. In contrast to the well-known radiation-induced graft polymerization (RIGP), RIGI can use non-vinyl compounds such as small and large functional molecules, hydrophilic polymers, or even enzymes. In a one-step electron-beam-based process, immobilization can be performed in a clean, fast, and continuous operation mode, as required for industrial applications. This study proposes a reaction mechanism using polyvinylidene fluoride (PVDF) and two small model molecules, glycine and taurine, in aqueous solution. Covalent coupling of single molecules is achieved by radical recombination and alkene addition reactions, with water radiolysis playing a crucial role in the formation of reactive solute species. Hydroxyl radicals contribute mainly to the immobilization, while solvated electrons and hydrogen radicals play a minor role. Release of fluoride is mainly induced by direct ionization of the polymer and supported by water. Hydrophobic chains attached to cations appear to enhance the covalent attachment of solutes to the polymer surface. Computational work is complemented by experimental studies, including X-ray photoelectron spectroscopy (XPS) and fluoride high-performance ion chromatography (HPIC).

Mixed Matrix Membranes Based on Fluoropolymers with m- and p-Terphenyl Fragments for Gas Separation Applications

Novel mixed matrix membranes (MMMs) based on fluoropolymers with m- and p-terphenyl fragments and NaX zeolites were prepared. The fluoropolymers were synthesized by a one-pot, room-temperature, metal-free superacid-catalyzed stoichiometric and nonstoichiometric step polymerization of 2,2,2-trifluoroacetophenone with two multiring aromatic nonactivated hydrocarbons (p-terphenyl and m-terphenyl). MMMs were characterized by scanning electron microscopy (SEM) and infrared (Fourier transform infrared (FTIR)) spectroscopy and used in gas permeability tests. SEM analysis showed interfacial voids in MMMs prepared in N-methyl-2-pyrrolidone (NMP), The interfacial adhesion in the polymer-zeolite system was considerably improved when chloroform was used as a solvent. Permeability coefficients for pristine polymer membranes were 1.3-fold higher in CHCl3 than in NMP for p-terphenyl fragment and 2.0 times higher in NMP than in CHCl3 for the polymer with m-terphenyl fragment. The incorporation of NaX zeolites in the polymeric matrices improved the gas permeability coefficients compared to the pristine membranes. The effects of polymer architecture, casting solvent, and interaction between the organic matrix and the inorganic particles on the gas separation performance of the developed MMMs were investigated.

Gamma Radiation-Induced Unsaturated P(VDF-CTFE) Membranes with Improved Mechanical Properties

Poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) membranes were prepared by drop-casting with tetrahydrofuran (THF), and were then radiated by a low dose of gamma radiation without any other reagents. The apparent colour of the freshly prepared film was a semi-transparent white, which gradually darkened and finally turned black after 10.2kGy gamma radiation. Meanwhile, the yield and breaking strength of the membrane both improved. X-Ray diffraction (XRD) spectra showed that the structure of the microcrystal of the irradiated P(VDF-CTFE)-THF membrane was not changed. FT-IR analysis showed that the structure of the newly formed double bonds was dominated by –CF2–CF=CH–CF2–, which was formed by both dehydrofluorination and dehydrochlorination. This structure was further confirmed by 1H NMR spectra. The intermediates, such a radical-containing double bonds (–(CF=CH)n–C•F–) formed in this process were traced by electron paramagnetic resonance (EPR) spectroscopy. The thermal and mechanical properties were studied by gel permeation chromatography (GPC), thermogravimetric analysis (TGA), stress–strain and dynamic mechanical analysis (DMA), and all the changes of microstructure and optimization of apparent properties were not found in the corresponding membrane prepared by a solution-cast method with ethyl acetate (EtOAc). Therefore, this paper briefly analyses the probable mechanism of using low dose of gamma radiation to improve the mechanical properties of the P(VDF-CTFE) film prepared with THF.

Polymerization Reactions and Modifications of Polymers by Ionizing Radiation

Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in "nanocompartments", i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.

Radiation Induced Surface Modification of Nanoparticles and their Dispersion in the Polymer Matrix

Polymer grafted inorganic nanoparticles attract significant attention, but pose challenges because of the complexity. In this work, a facile strategy to the graft polymer onto the surface of nanoparticles have been introduced. The vinyl functionalized SiO2 nanoparticles (NPs) were first prepared by the surface modification of the unmodified SiO2 using γ-methacryloxy propyl-trimethoxylsilane. The NPs were then mixed with polyvinylidene fluoride (PVDF), which was followed by the Co-60 Gamma radiation at room temperature. PVDF molecular chains were chemically grafted onto the surface of SiO2 nanoparticles by the linking of the double bond on the NPs. The graft ratio of PVDF on SiO2 NPs surface can be precisely controlled by adjusting the absorbed dose and reactant feed ratio (maximum graft ratio was 31.3 wt%). The strategy is simple and it should be applied to the surface modification of many other nanoparticles. The prepared PVDF-grafted SiO2 NPs were then dispersed in the PVDF matrix to make the nanocomposites. It was found that the modified NPs can be precisely dispersed into the PVDF matrix, as compared with pristine silica. The filling content of modifications SiO2 NPs on the PVDF nanocomposites is almost doubled than the pristine SiO2 counterpart. Accordingly, the mechanical property of the nanocomposites is significantly improved.

Cleavage of the Graft Bonds in PVDF-g-St Films by Boiling Xylene Extraction and the Determination of the Molecular Weight of the Graft Chains

To determine the molecular weight of graft chains in grafted films, the polystyrene graft chains of PVDF-g-St films synthesized by a pre-irradiation graft method are cleaved and separated by boiling xylene extraction. The analysis of the extracted material and the residual films by FTIR, nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) analyses indicates that most graft chains are removed from the PVDF-g-St films within 72 h of extraction time. Furthermore, the molecular weight of the residual films decreases quickly within 8 h of extraction and then remains virtually unchanged up to 72 h after extraction time. The degradation is due to the cleavage of graft bonds, which is mainly driven by the thermal degradation and the swelling of graft chains in solution. This allows determination of the molecular weight of graft chains by GPC analysis of the extracted material. The results indicate that the PVDF-g-St prepared in this study has the structure where one or two graft chains hang from each PVDF backbone.

Reactive Radicals on Reactive Surfaces: Heterogeneous Processes in Catalysis and Environmental Pollution Control

Many reactions that occur on solid surfaces are mediated by free radicals. A review is presented of both mechanistic and practical investigations in relation to catalysis and environmental applications. The review begins with actual imaging of surface adsorbed reactive radicals using scanning tunnelling microscopy (STM), and then discusses a range of examples, mainly as underpinned by electron spin resonance (ESR) measurements. Included are surface defects and their reactions, studies of the redox behaviour of zeolites, and the use of radicals adsorbed in zeolites as molecular surface probes of diffusion and reactivity within these important materials. Photocatalysis, mainly using TiO2-based materials, is reviewed both from the fundamental perspective and in terms of some practical examples relating to pollution control. Other reactive oxide surfaces are considered, including silica, and the nature of paramagnetic centres that may be induced thereon by a variety of activation procedures. Evidence is presented for the formation of radical species during heterogeneous reactions on metal surfaces. Finally, the role of free radical generation in creating and modifying polymer and nanomolecular systems is discussed, and the health implications of the ability of some solids such as quartz to generate reactive oxygen radicals in contact with biological media.

Hydrophilic modification and anti-fouling properties of PVDF membrane via in situ nano-particle blending

Two hydrophilic poly-vinylidene fluoride (PVDF) ultrafiltration membranes were prepared via in situ embedment of nanoparticles (NP), i.e., TiO₂ and Al₂O₃, respectively, and their anti-organic-fouling and anti-biofouling were comprehensively investigated. Characterization of modified PVDF-NP membranes by XRD and FTIR exhibited that nanoparticles were embedded successfully. Series of fast filtration tests demonstrated that in contrary to virgin PVDF membrane, PVDF-NP membranes have high permeability and anti-organic-fouling ability by decreasing the possibility of organic matters deposition and accumulation. Co-existed Ca²⁺ in feed solution deteriorated the organic fouling in virgin PVDF and PVDF-NP membranes, which was mainly caused by gelation of macromolecular foulants. PVDF-NP membranes were used to form MBR modules for domestic wastewater treatment, and the long-term monitoring evidenced that hydrophilic modified membranes achieved stably high COD and [Formula: see text] rejection efficiencies, and better organic rejection capability than mAO process. PVDF-NP membranes possessed consistently high anti-biofouling ability to maintain stable membrane permeability.

pH-sensitive microfiltration membrane prepared from polyethersulfone grafted with poly(itaconic acid) synthesized by simultaneous irradiation in homogeneous phase

Poly(itaconic acid) (PIA) was grafted onto polyethersulfone (PES) by homogeneously phased γ-ray irradiation. Kinetic polymerization observed was studied by analyzing the effect of irradiation dosages and monomer concentrations. Then, a pH-sensitive microfiltration (MF) membrane was prepared from these PES-g-PIA polymers with different degrees of grafting under phase inversion method. Finally, the contact angles, morphologies, pore sizes, deionized water permeability and filtration performance for aqueous polyethylene glycols solution of the MF membranes were studied. The results show that grafting PIA groups onto PES molecular chains endowed the MF membranes with effective pH-sensitive properties.

Nitrogen-Containing Fabric Adsorbents Prepared by Radiation Grafting for Removal of Chromium from Wastewater

To remove chromium from wastewater effectively, two types of nitrogen-containing fabric adsorbents, having amidoxime ligand groups and quaternary ammonium anion exchange groups, respectively, were prepared by radiation grafting. In brief, the amidoxime adsorbent is obtained by grafting of acrylonitrile (AN)/methacrylic acid (MAA) onto a nonwoven fabric and subsequent amidoximation with hydroxylamine, while the ammonium adsorbent is obtained by grafting of chloromethylstyrene (CMS) followed by quaternization with trimethylamine. The AN/MAA-grafting reaches a high degree of grafting more than 100%, and the resulting amidoxime adsorbent reaches a high amidoxime density of 4.53 mmol/g. On the other hand, the CMS-grafting reaches a much higher degree of grafting above 200%, and the resulting ammonium adsorbent reaches a high ammonium density of 3.51 mmol/g. FTIR/ATR and TGA/DTA are used for the characterization of the grafted fabrics as well as the relevant fabric adsorbents. Furthermore, the chromium removal of the prepared fabric adsorbent is tested in both batch and column modes. It has been confirmed that the chromium removal was largely dependent on the pH of the solution. At pH 5.0, the amidoxime adsorbent shows a high Cr(III) adsorption capacity of 31.68 mg/g, while the ammonium adsorbent shows a much higher Cr(VI) adsorption capacity of 130.65 mg/g.

Grafting Polytetrafluoroethylene Micropowder via in Situ Electron Beam Irradiation-Induced Polymerization

Decreasing the surface energy of polyacrylate-based materials is important especially in embossed holography, but current solutions typically involve high-cost synthesis or encounter compatibility problems. Herein, we utilize the grafting of polytetrafluoroethylene (PTFE) micropowder with poly (methyl methacrylate) (PMMA). The grafting reaction is implemented via in situ electron beam irradiation-induced polymerization in the presence of fluorinated surfactants, generating PMMA grafted PTFE micropowder (PMMA–g–PTFE). The optimal degree of grafting (DG) is 17.8%. With the incorporation of PMMA–g–PTFE, the interfacial interaction between polyacrylate and PTFE is greatly improved, giving rise to uniform polyacrylate/PMMA–g–PTFE composites with a low surface energy. For instance, the loading content of PMMA–g–PTFE in polyacrylate is up to 16 wt %, leading to an increase of more than 20 degrees in the water contact angle compared to the pristine sample. This research paves a way to generate new polyacrylate-based films for embossed holography.

Facile synthesis and properties of a cation exchange membrane with bifunctional groups prepared by pre-irradiation graft copolymerization

A new type of a cation exchange membrane named ETFE-g-poly(AA-co-SSS) with bifunctional groups was synthesized by a one-step method. Its preparation by an electron beam-induced pre-irradiation grafting method and the effects of reaction temperature, monomer concentration, pH value of the grafting solution, storage time and temperature of the irradiated poly(ethylene-alt-tetrafluoroethylene) (ETFE) films on the grafting yield were studied. A total concentration of 2 mol L⁻¹ of monomers was found to be beneficial for acrylic acid (AA) and sodium styrene sulfonate (SSS) co-grafting onto the ETFE films. Infrared spectroscopic analysis of the grafted membrane confirmed the existence of sulfonate and carboxylic acid groups. The contact angle of the grafted membrane decreased from 94.3 to 46.7° with the increase in grafting yield. The higher the grafting yield, the faster the response and recovery rate with respect to humidity. AFM images showed that the diameter of the grafted chains on the surface of ETFE membranes was about 30 nm. The voltage of the grafted membrane was stable after 100 cycles of charge–discharge; thus, the prepared membranes have great potentials to be used as separators in secondary batteries.

Low-cost and anti-degradation ion-exchange membrane named ETFE-g-poly(AA-co-SSS) with bifunctional groups prepared by the pre-irradiation grafting method.

Sulfonic Membrane Sorption and Permeation Properties: Complementary Approaches to Select a Membrane for Pervaporation

In this contribution, the physical and chemical properties of the dense sulfonic membrane IonClad R4010 in the lithium form were studied to evaluate its potential application in pervaporation. To develop new membrane materials, it is necessary to know the influence of the membrane structure on the membrane equilibrium and transport properties. For this purpose, the sorption and permeation measurements of water and methanol in the liquid and vapor states were performed and correlated to the ion pairs/solvent interactions analyzed by the infrared spectroscopy. The IonClad R4010 equilibrium and transport properties were found to be quite different depending on the permeant nature. The sorption and diffusion behavior of water and methanol was well described by means of the type II sorption model (BET theory). The swelling capacity of the IonClad R4010 membrane in methanol was found to be much lower than that in liquid water. In contrast to methanol, the total dissociation of the ion pairs in the IonClad R4010 membrane was obtained in the presence of water but only at high activity (∼0.8). Besides, the dispersion of the water molecules in the membrane was found to be homogeneous. The infrared spectroscopy results revealed that the methanol molecules had weaker interactions with the sulfonic groups of IonClad R4010 in agreement with the sorption data. The permeation properties were investigated by means of the sweeping gas and gravimetric methods in order to evaluate the membrane performance for pervaporation. The permeation results are in accordance with those obtained by sorption, thus confirming the complementariness of the two approaches.

Effects of RAFT Agent on the Chloromethylstyrene Polymerizations in a Simultaneous Radiation Grafting System

Reversible addition-fragmentation chain transfer (RAFT) agent was added into a simultaneous radiation grafting system and its effects on graft polymerization and homopolymerization were investigated. Chloromethylstyrene (CMS) was graft polymerized onto ethylene-tetrafluoroethylene copolymer (ETFE) films under γ-ray sources via simultaneous irradiation. The non-grafted poly(CMS) in the grafted films were extracted by xylene at 120 °C. The poly(CMS) was characterized by NMR and GPC instruments. Addition of the RAFT agent suppressed both graft polymerization and homopolymerization. However, under a high concentration of RAFT agent, the homopolymerization in the monomer solution could occur through a typical RAFT polymerization while polymerization in the ETFE films proceeded via RAFT and conventional radical polymerization, resulting in poly(CMS) in the ETFE films with molecular weight dispersity higher than 1.0 but lower than that without RAFT agent. Furthermore, it was found that the molecular weight of the poly(CMS) in the ETFE films was several times higher than that of the poly(CMS) in the monomer solution.

Surface modification of polyvinylidene fluoride (PVDF) membrane via radiation grafting: novel mechanisms underlying the interesting enhanced membrane performance

This study provided the first attempt of grafting hydrophobic polyvinylidene fluoride (PVDF) membrane with hydrophilic hydroxyethyl acrylate (HEA) monomer via a radiation grafting method. This grafted membrane showed an enhanced hydrophilicity (10° decrease of water contact angle), water content ratio, settling ability and wettability compared to the control membrane. Interestingly, filtration tests showed an improved dependence of water flux of the grafted membrane on the solution pH in the acidic stage. Atomic force microscopy (AFM) analysis provided in-situ evidence that the reduced surface pore size of the grafted membrane with the solution pH governed such a dependence. It was proposed that, the reduced surface pore size was caused by the swelling of the grafted chain matrix, with the pH increase due to the chemical potential change. It was found that the grafted membrane showed a lower relative flux decreasing rate than the control membrane. Moreover, flux of the bovine serum albumin (BSA) solution was noticeably larger than that of pure water for the grafted membrane. Higher BSA flux than water flux can be explained by the effects of electric double layer compression on the polymeric swelling. This study not only provided a pH-sensitive PVDF membrane potentially useful for various applications, but also proposed novel mechanisms underlying the enhanced performance of the grafted membrane.

In vitro mineralization of dual grafted polytetrafluoroethylene membranes

The modification of biomaterials by radiation induced grafting is a promising method to improve their bioactivity. Successful introduction of carboxyl and amine functional groups on the surface of a polytetrafluoroethylene membrane was achieved by grafting of acrylic acid (AA) and 2-aminoethyl methacrylate hydrochloride (AEMA) using simultaneous gamma irradiation grafting. Chemical characterization by attenuated total reflectance Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy confirmed the presence of amine and carboxylate functionalities and indicated that all protonated amines formed ion pairs with carboxyl groups, but not all carboxyl are involved in ion pairing. It was found that the irradiation doses (2, 5, or 10 kGy) affected the grafting outcome only when sulfuric acid (0.5 or 0.9 M) was added as a polymerization enhancer. The use of the inorganic acid successfully enhanced the total graft yield (GY), but the changes in the graft extent (GE) were not conclusive. Dual functional films were produced by either a one- or a two-step process. Generally, higher GY and GE values were observed for the samples produced by the two-step grafting of AA and AEMA. The in vitro mineralization in 1.5× simulated body fluid (SBF) induced the formation of carbonated hydroxyapatite as verified by FITR. All samples showed an increase in weight after mineralization with significantly larger increases observed for the samples which had the 1.5× SBF changed every third day compared to every seventh. For the dual functional samples, it was found that the sample grafted by the one-step method shows a significantly higher increase in weight despite a much lower GY compared to the sample prepared by the two-step method and this was attributed to the different architecture of grafted chains.

Polymerization of polyhedral oligomeric silsequioxane (POSS) with perfluoro-monomers and a kinetic study

The polymerization of diphenol polyhedral oligomeric silsequioxane (2OH-DDSQ) with a series of perfluoro-monomers was studied to obtain the optimized reaction for the preparation of POSS-containing fluorinated poly(arylene ether)s.

A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

Raman spectro-microscopy on a radiation-grafted anion-exchange membrane detected alkali degradation throughout its cross-section that quantitatively matched loss of ion-exchange capacity.

Electron-Beam Lithographic Grafting of Functional Polymer Structures from Fluoropolymer Substrates

Well-defined submicrometer structures of poly(dimethylaminoethyl methacrylate) (PDMAEMA) were grafted from 100 μm thick films of poly(ethene-alt-tetrafluoroethene) after electron-beam lithographic exposure. To explore the possibilities and limits of the method under different exposure conditions, two different acceleration voltages (2.5 and 100 keV) were employed. First, the influence of electron energy and dose on the extent of grafting and on the structure's morphology was determined via atomic force microscopy. The surface grafting with PDMAEMA was confirmed by advanced surface analytical techniques such as time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. Additionally, the possibility of effective postpolymerization modification of grafted structures was demonstrated by quaternization of the grafted PDMAEMA to the polycationic QPDMAEMA form and by exploiting electrostatic interactions to bind charged organic dyes and functional proteins.