Photoinitiated Graft Polymerization Research Articles

Fabrication of Hydrophobic PET Track-Etched Membranes using 2,2,3,3,4,4,4-Heptafluorobutyl Methacrylate for Water Desalination by Membrane Distillation

The world is currently facing a drinking water problem. Human activity, climate change and pollution of existing water bodies are exacerbating the problem. The scientists around the world are currently trying to purify water using effective and inexpensive methods. One such method is membrane distillation. Membrane distillation is a versatile thermally driven membrane separation process. This method of water purification has the potential to remove salts and other non-volatile components. The work is concerned with the desalination of salt solutions by membrane distillation using ion-track membranes based on polyethylene terephthalate (PET). PET ion-track membranes (PET TMs) were modified by photoinitiated graft polymerization of 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (HFBMA) to make them hydrophobic. Optimal polymerization conditions (monomer concentration, reaction time) were determined, which led to an increase of water CA from 51 to 105°. The obtained membranes were used to purify the solution from NaCl. The effect of salt concentration as well as membrane properties on performance and degree of purification was studied. The results show that large pore size PET TMs modified with HFBMA has the potential to desalinate water in an efficient manner.

Surface Modification of Polyethylene Terephthalate Track-Etched Membranes by 2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl Acrylate for Application in Water Desalination by Direct Contact Membrane Distillation.

In this work, the surfaces of poly (ethylene terephthalate) track-etched membranes (PET TeMs) with pore sizes of 670-1310 nm were hydrophobized with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA) by photoinitiated graft polymerization. Attenuated total reflection FTIR spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX), and contact angle measurements were used to identify and characterize the TeMs. The optimal parameters for graft polymerization were determined as follows: polymerization time of 60 min, monomer concentration of 30%, and distance from the UV source of 7 cm. The water contact angle of the modified membranes reached 97°, which is 51° for pristine membranes. The modified membranes were tested for water desalination using direct contact membrane distillation (DCMD) method. The effects of membrane pore size, the degree of grafting, and salt concentration on the performance of membrane distillation process were investigated. According to the results obtained, it has been concluded that large pore size hydrophobic TeMs modified by using DFHA could be used for desalinating water.

Ion-Selective Potentiometry with Plasma-Initiated Covalent Attachment of Sensing Membranes onto Inert Polymeric Substrates and Carbon Solid Contacts.

The physical delamination of the sensing membrane from underlying electrode bodies and electron conductors limits sensor lifetimes and long-term monitoring with ion-selective electrodes (ISEs). To address this problem, we developed two plasma-initiated graft polymerization methods that attach ionophore-doped polymethacrylate sensing membranes covalently to high-surface-area carbons that serve as the conducting solid contact as well as to polypropylene, poly(ethylene-co-tetrafluoroethylene), and polyurethane as the inert polymeric electrode body materials. The first strategy consists of depositing the precursor solution for the preparation of the sensing membranes onto the platform substrates with the solid contact carbon, followed by exposure to an argon plasma, which results in surface-grafting of the in situ polymerized sensing membrane. Using the second strategy, the polymeric platform substrate is pretreated with argon plasma and subsequently exposed to ambient oxygen, forming hydroperoxide groups on the surface. Those functionalities are then used for the initiation of photoinitiated graft polymerization of the sensing membrane. Attenuated total reflection-Fourier transform infrared spectroscopy, water contact angle measurements, and delamination tests confirm the covalent attachment of the in situ polymerized sensing membranes onto the polymeric substrates. Using membrane precursor solutions comprising, in addition to decyl methacrylate and a cross-linker, also 2-(diisopropylamino)ethyl methacrylate as a covalently attachable H+ ionophore and tetrakis(pentafluorophenyl)borate as ionic sites, both plasma-based fabrication methods produced electrodes that responded to pH in a Nernstian fashion, with the high selectivity expected for ionophore-based ISEs.

SENSORS BASED ON TRACK-ETCHED MEMBRANES FOR ELECTROCHEMICAL DETECTION OF CADMIUM IONS

Among electrochemical detection methods, square-wave anodic voltammetry (SW-ASV) is the most popular. However, this method has a number of limitations, for instance, mercury or bismuth electrodes are usually used as a working electrode, which are highly toxic substances. This article is devoted to the study of the use of track-etched membranes based on polyethylene terephthalate as a basis for electrochemical sensors. The modification of the surface of membranes was carried out by the method of photoinitiated graft polymerization of methacrylic acid. Magnetron sputtering with a mask was used to obtain electrodes on both sides of the membrane. The sensor has been tested for sensing toxic cadmium ions in a concentration range of 0.5 to 12.5 mg/L.

Polymer surface modification using UV treatment for attachment of natamycin and the potential applications for conventional food cling wrap (LDPE)

The purpose of this study was to develop an active non-migratory antifungal Low Density Polyethylene (LDPE) polymer for use in food packaged applications. The functional acrylic acid monomer was grafted on the LDPE film surface by photo-initiated graft polymerization using Ultra Violet light irradiation (from 0 to 5min). Natamycin, an antifungal agent, was applied to the treated film to bind with the pendent functional groups and were evaluated its performance against mold and yeast. The grafted amounts were determined by gravimetric measurement and dye absorbance. Attenuated Total Reflectance/Fourier Transfer Infrared Spectroscopy, scanning electron microscopy, mechanical strength test was used to characterize film properties. The antifungal efficacy of the film was evaluated with Saccharomyces cerevisiae and Penicillium chrysogenum on growth media and fresh cut cantaloupe. The amounts of the grafted group were increased with the longer ultraviolet exposure time. The amount of the grafted natamycin on the treated film was up to 49.87μg/cm2, and the film inhibited mycelium formation of P. chrysogenum spores by over 60%. Due to the thickness of the film (less than 12.25μm), long time UV exposure decrease the film’s mechanical strength. The application of such non-migratory active packaging film represents a promising approach to maintaining food quality with reduced additive.

Biomimetic design of chelating interfaces

ABSTRACTSiderophores are naturally occurring small molecules with metal binding constants greater than many synthetic chelators. Herein, we report a two‐step process to graft a siderophore‐mimetic metal chelating polymer from a polypropylene (PP) surface. Poly(methyl acrylate) was first grafted from the PP surface by photoinitiated graft polymerization, followed by the conversion into poly(hydroxamic acid) (PHA) to obtain PP‐g‐PHA films. ATR/FTIR, contact angle, SEM, and AFM were performed to characterize surface properties of films. Iron binding kinetics and the influence of pH (3.0–5.0) on the chelating ability of films were determined. PP‐g‐PHA exhibited significant iron chelating activity (∼80 nmol/cm2) with an equilibration time of 24 h. The materials retained 50% chelating ability at pH 3.0 compared with pH 5.0, almost double the retention of previously reported polycarboxylate chelating interfaces. By using siderophore‐mimetic surface chemistry, such effective metal chelating interfaces can extend the applications of metal chelating polymers in environmental remediation, water purification, and active packaging areas. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41231.

Metal-Chelating Active Packaging Film Enhances Lysozyme Inhibition of Listeria monocytogenes

Several studies have demonstrated that metal chelators enhance the antimicrobial activity of lysozyme. This study examined the effect of metal-chelating active packaging film on the antimicrobial activity of lysozyme against Listeria monocytogenes. Polypropylene films were surface modified by photoinitiated graft polymerization of acrylic acid (PP-g-PAA) from the food contact surface of the films to impart chelating activity based on electrostatic interactions. PP-g-PAA exhibited a carboxylic acid density of 113 ± 5.4 nmol cm−2 and an iron chelating activity of 53.7 ± 9.8 nmol cm−2. The antimicrobial interaction of lysozyme and PP-g-PAA depended on growth media composition. PP-g-PAA hindered lysozyme activity at low ionic strength (2.48-log increase at 64.4 mM total ionic strength) and enhanced lysozyme activity at moderate ionic strength (5.22-log reduction at 120 mM total ionic strength). These data support the hypothesis that at neutral pH, synergy between carboxylate metalchelating films (pKabulk 6.45) and lysozyme (pI 11.35) is optimal in solutions of moderate to high ionic strength to minimize undesirable charge interactions, such as lysozyme absorption onto film. These findings suggest that active packaging, which chelates metal ions based on ligand-specific interactions, in contrast to electrostatic interactions, may improve antimicrobial synergy. This work demonstrates the potential application of metal-chelating active packaging films to enhance the antimicrobial activity of membrane-disrupting antimicrobials, such as lysozyme.

Iron chelating polypropylene films: Manipulating photoinitiated graft polymerization to tailor chelating activity

ABSTRACTTransition metals, especially iron, enhance the oxidative degradation of lipids. Nonmigratory metal chelating active packaging can inhibit lipid oxidation and meet consumer demand for ‘cleaner' labels. Recently, the development of iron chelating films prepared by photoinitiated graft polymerization of acrylic acid on polypropylene (PP‐g‐PAA) was reported. The objective of this study was to tailor the chelating activity of PP‐g‐PAA by manipulating graft conditions. Carboxylic acids graft density and PAA graft thickness increased with graft time and acrylic acid concentration, with carboxylic acids density of up to 143 ± 32 nmol cm−2, PAA graft thickness of ∼6–18 μm, and ligand (carboxylic acid) to metal (Fe2+) binding ratio of ∼4–5. Reducing photoinitiator graft density decreased this ratio to ∼2–2.5, suggesting that graft chain density influences chelating activity. This work demonstrates the ability to tailor chelating activity of PP‐g‐PAA with potential applications in active packaging, chelation therapy, and water purification. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39948.

Modification of graphene oxide via photo-initiated grafting polymerization

In this paper, we report on an effective surface modification method for the functionalization of graphene oxide (GO) via photo-initiated radical polymerization. Two cases are investigated, i.e., photoinitiators are chemically attached on GO or are just mixed with GO. The monomer used for surface graft is water-soluble 2-(dimethylamino) ethyl methacrylate (DMAEMA). Analysis based on Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy, thermogravimetric analysis, and element analysis demonstrates that PDMAEMA chains are successfully grafted onto GO surface in both cases. In addition, we study the effects of UV irradiation energy and the concentration of initiators on the polymerization. Both UV irradiation energy and the concentration of initiators do not have significant effects on the grafting degree; however, the concentrations of the initiators have impact on the length of the polymer chains grafted onto GO in the case of mixed photoinitiators with GO. The chain length of polymer is shorter with the higher photoinitiator concentration.

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25mM detection limit and 0.25–2.5mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.

Control of Lipid Oxidation by Nonmigratory Active Packaging Films Prepared by Photoinitiated Graft Polymerization

Transition metal-promoted oxidation impacts the quality, shelf life, and nutrition of many packaged foods. Metal-chelating active packaging therefore offers a means to protect foods against oxidation. Herein, we report the development and characterization of nonmigratory metal-chelating active packaging. To prepare the films, carboxylic acids were grafted onto the surfaces of polypropylene films by photoinitiated graft polymerization of acrylic acid. Attenuated total reflectance/Fourier transform infrared spectroscopy, contact angle, scanning electron microscopy, and iron-chelating assay were used to characterize film properties. Graft polymerization yielded a carboxylic acid density of 68.67 ± 9.99 nmol per cm(2) film, with ferrous iron-chelating activity of 71.07 ± 12.95 nmol per cm(2). The functionalized films extended the lag phase of lipid oxidation in a soybean oil-in-water emulsion system from 2 to 9 days. The application of such nonmigratory active packaging films represents a promising approach to reduce additive use while maintaining food quality.

Optimization of Protein Immobilization in Microfludic Devices for Circulating Tumor Cell Capture

The isolation of metastatic circulating tumor cells (CTCs) within the blood using microfluidic devices is a promising method for the detection of cancer. In this study, protein patterning of endothelial-leukocyte adhesion molecule-1 (E-selectin) and anti-epitheal-cell-adhesion-molecule (Anti-EpCAM) within microfluidic channels is utilized to improve the capture efficiency. To create this protein patterning the protein immobilization method must first be optimized to allow for maximum capture of CTCs and minimal increase in the flow rate of cells through the device due to added coating thickness. Proteins are immobilized in alternating regions using photo-initiated graft polymerization of polyacrylic acid (PAA) and a silanization reaction. Using interferometer measurements and fluorescent tagging, PAA height was minimized and protein immobilization was optimized.

Bio-inspired CaCO3 coating for superhydrophilic hybrid membranes with high water permeability

Surface hydrophilicity is a prerequisite of polymer membranes used for clean water regeneration, although commercial membranes are generally manufactured from hydrophobic polymers. Here, we report a promising approach to hydrophilize hydrophobic membranes using a CaCO3-based mineral coating inspired by biomineralization. Poly(acrylic acid) (PAA) brushes, which are negatively charged and can induce nucleation of CaCO3, were tethered on the pore surface of microporous polypropylene membranes (MPPMs) via photoinitiated graft polymerization. The CaCO3-based coating was then fabricated on the pore surface by an alternate soaking process. The resulting mineral coating is composed of CaCO3 nanoparticles which are much smaller than the pore diameter and distributed evenly on the pore surface throughout the membrane, ensuring the separation performance of membranes. Due to the intrinsic superhydrophilicity of CaCO3, the hybrid membranes are superhydrophilic, and show excellent water permeability with high water flux and ultralow operational pressure. As such, this work provides a generally applicable and cost-effective chemical route to improve the surface hydrophilicity of membranes or other porous materials which have potential in chemical separation, microfluidics, catalysis and other applications.

Searching for novel membrane chemistries: Producing a large library from a single graft monomer at high throughput

Glycidyl methacrylate (GMA) was grafted on poly(ether sulfone) (PES) membranes via photo-initiated graft polymerization (PGP). 25 amine monomers were introduced at 90 °C for 12 h to facilitate the epoxy ring opening reaction on GMA grafts. Our high throughput platform (HTP) approach was used to test and screen for desired surface characteristics. Analysis of the fouling index ( ℜ, flux reduction upon static fouling), surface adsorption index ( q ¯ , surface adhesion of protein) and sieving coefficient ( S 0, protein permeation upon dynamic fouling) were used as criteria of success. Bovine serum albumin (BSA) and lysozyme (LYS) at 1 mg mL −1 were used as model foulants. Six of the 25 grafted species were identified as “winners” by exhibiting lower ℜ and q ¯ ( i.e. lower flux decline and protein adhesion on membrane surfaces, respectively) compared with GMA grafting alone (internal control) or with poly(ethylene glycol) (PEG) grafting. S 0 was plotted against permeability in order to analyze the flux-selectivity behavior due to grafting and fouling. Diethanolamine was resistant both to BSA with ℜ = 0.31 ± 0.12, q ¯ = 0.68 ± 0.11 , S 0 = 0.86 ± 0.03, and LYS with ℜ = −1.96 ± 0.26, q ¯ = 0.71 ± 0.03 and S 0 = 0.65 ± 0.27. The conversion of the epoxy group by the reaction with amine was confirmed with the degree of grafting analysis using FTIR/ATR.

Surface modification of poly(styrene-b-(ethylene-co-butylene)-b-styrene) elastomer via photo-initiated graft polymerization of poly(ethylene glycol)

Poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) copolymer biomedical elastomer was covalently grafted with poly(ethylene glycol) methyl ether methacrylate (PEGMA) via a photo-initiated graft polymerization technique. The surface graft polymerization of SEBS with PEGMA was verified by ATR–FTIR and XPS. Effect of graft polymerization parameters, i.e., monomer concentration, UV irradiation time and initiator concentration on the grafting density was investigated. Comparing with the virgin SEBS film, the PEGMA-modified SEBS film presented an enhanced wettability and a larger surface energy. Besides, the surface grafting of PEGMA imparted excellent anti-platelet adhesion and anti-protein adsorption to the SEBS surface.

Photoinitiated grafting polymerization of acrylic acid onto the surface of polyethylene under pulsed laser radiation

Photoinduced grafting polymerization on the surface of PE films induced by nanosecond pulsed laser radiation is studied. The grafting is performed from the liquid phase composed of acrylic acid and a photoinitiator (benzophenone) dissolved in it. Pulsed laser radiation with a wavelength of 355 nm, a pulse duration of 11 ns, and a repetition rate of 10 Hz is used. Formation of the surface-graft polymer is followed by IR-ATR spectroscopy and contact-angle measurements. It is found that the time of laser treatment sufficient for the efficient modification of the PE surface with the grafted poly(acrylic acid) is in the range from 0.5 to 1.0 s at a laser-pulse energy density of 200–500 mJ/cm2. At energy densities beyond this range, the efficiency of the reaction decreases rapidly. The results on laser grafting are compared with the results of grafting during UV irradiation with a lamp at a wavelength of 365 nm.

Multi-type carbon doping of TiO 2 photocatalyst

Carbon-doped TiO 2 nanoparticles in a pure anatase phase colored dark brown were successfully prepared using a convenient controlled nonhydrolytic sol–gel method followed by annealing at 400 °C. The UV–Vis diffuse reflectance spectra and X-ray photoelectron spectroscopy (XPS) indicate that substitutional and interstitial carbon atoms coexist in the lattice of TiO 2. The shift of photo response of TiO 2 from UV to near infrared region is responsible for the multi-type carbon doping by the formation of complex midgap states. The photo-initiated graft polymerization of methyl methacrylate (MMA) is also induced by the carbon impurities in the TiO 2 structure.

Chemically and morphologically defined ultrafiltration membrane surfaces prepared by heterogeneous photo-initiated graft polymerization

Polyacrylonitrile (PAN) ultrafiltration (UF) membranes with varied surface hydrophilicity and charge have been prepared by heterogeneous photo-initiated graft polymerization of various acrylates or methacrylates having polyethyleneglycol (PEG), carboxyl, sulfopropyl, dimethylaminoethyl or trimethylammoniumethyl side groups. A series of photo-modified membranes with about the same water permeabilities were obtained by selection of initial membrane pore size and appropriate modification conditions (monomer concentration and UV irradiation time, λ exc>300 nm). A comprehensive characterization of the new membranes was achieved using a multi-method approach. Gravimetry, FTIR-ATR spectroscopy, SEM and UF experiments provided basic information about the degree of graft polymer modification (DG, up to 1 mg cm −2) and integrity of the macroporous membrane structure after modification. No extra layer (with a thickness >1 μm) was deposited on top of the UF membranes but, depending on DG, active layer pores were more or less covered, causing reduced water permeabilities and enhanced solute selectivities. The modified membranes were monitored with scanning force microscopy (SFM), contact angle (CA) and streaming potential (ZP) measurements. The water-swollen graft polymer layers had a monomer-specific texture with larger grain size, but in the sub-micrometer range, compared with the unmodified membranes (SFM). However, interface interactions in terms of zeta potential (ZP) and hydrophilicity (CA) were unambiguously governed by the chemistry of the graft polymer side groups. Solid surface tensions (wetting/dewetting) from advancing and receding CAs, γ sv (adv.)/ γ sv (rec.), ranged from 35 mN m −1/60 mN m −1 for PAN-grafted-poly(dimethyl-aminoethyl methacrylate) to 71.5 mN m −1/71.5 mN m −1 for PAN-grafted-poly(sulfopropyl acrylate) and PAN-grafted-poly(tri-methylammoniumethyl methacrylate), whereas unmodified PAN membranes had 49 mN m −1/67 mN m −1. Concentration potential measurements revealed that ion-exchange graft-polymer-modified PAN membranes behave as barrier for co-ions via a Donnan exclusion mechanism. All analytical data enabled a classification of the photo-modified UF membranes into permanently anionic (sulfonic acid) or cationic (trimethylammonium) as well as ionizable (carboxyl, dimethylamino) or non-ionic hydrophilic, flexible (PEG) types. The results provide guide-lines for the development of new low-fouling UF and nanofiltration membranes.

Novel photochemical surface functionalization of polysulfone ultrafiltration membranes for covalent immobilization of biomolecules

The major objective of the work was to develop a heterogeneous modification method for attachment of reactive groups, suitable for covalent immobilization of active biomolecules on the surface of polysulfone ultrafilters without loss of membrane selectivity. For applying a polymer specific activation chemistry, the materials of commercial “polysulfone” UF membranes were identified using elemental analysis along with 1H NMR, FTIR-ATR and UV spectroscopy. Heterogeneous photoinitiated graft polymerization was realized using acrylic acid (AA) as model monomer and as carrier of reactive groups. Polymer structure (polysulfone, PSf, or polyethersulfone, PESf), coating with photoinitiator (benzophenone, BP, or benzoylbenzoic acid, BPC) and UV excitation energy ( λ exc220 > 300 or 350 nm) were the major parameters. Grafted polyAA (g-PAA) could be obtained under almost all conditions but with largely varying yields (DG). However, only with λ exc350 nm, polymer and pore degradation could be excluded. A new selective initiation of graft polymerization onto PSf, H-abstraction by photoexcited BP derivatives from the methyl side groups, thus avoiding polymer chain scission, was proved indirectly. Modified structures were characterized spectroscopically, including visualization with SFM of laterally patterned surfaces generated by UV irradiation through a mask. UF tests of PSf-g-PAA and PESf-g-PAA UF membranes (DG ∼ 100…150 μg/cm 2), prepared under “mildly degrading” conditions ( λ exc300 nm), indicated only slight permeability and selectivity changes compared with unmodified samples. Selective PSf functionalization (BPC coating, λ exc350 nm; DG 5 μg/cm 2) caused flux reductions and dextran selectivity increases by factors of ∼ 1.3. Covalent immobilization onto g-PAA-functionalized and carbodiimide-activated PSf or PESf membrane surfaces was studied with a protein (BSA), an enzyme (invertase, INV), an antibody-enzyme (IgG-POD) conjugate, and a peptide (“PC1”) as specific antigen of a monoclonal antibody. High binding capacities, up to 40 fold compared with a flat unmodified surface, were detected either directly (BSA) or indirectly via specific activity/binding assays (INV, IgG-POD, “PC1”). This indicated an increased outer membrane surface area due to multifunctional reactive and hydrophilic grafted polymer chains.

Surface modification of polymers by photoinitiated graft polymerization

AbstractTwo methods for modification of polymer surfaces by photoinitiated grafting have been developed and applied to films and fibers of synthetic polymers, e.g. polyethylene and polypropylene with acrylic monomers. In the batch process the substrate is enclosed in a cell containing initiator and monomer vapor. UV light through a quartz window initiates the grafting reaction by exciting the initiator (e.g. benzophenone). The grafting reaction is slow (1 to 3 min) due to the inefficient transfer of initiator and monomer through vapor phase. In the continuous process the substrate is presoaked in a solution of initiator and monomer and then drawn into a reactor “on line” where the substrate is irradiated by UV light through a quartz window. The grafting takes place in the very thin surface layer of solution on the substrate. The grafting efficiency is high (70–80% of the polymer formed is grafted) and the process is rapid (5–15 s due to the efficient transfer of initiator and monomer through the liquid phase. The continuous surface grafting process is promising for industrial applications.