Synthesis of well‐defined responsive membranes with fixable solvent responsiveness

A versatile method is described to synthesize a new family of solvent‐responsive membranes whose response states can be not only tunable but also fixable via ultraviolet (UV) irradiation induced crosslinking. The atom transfer radical polymerization (ATRP) initiator 2‐bromoisobutyryl bromide was first immobilized on the poly(ethylene terephthalate) (PET) track‐etched membrane followed by room‐temperature ATRP grafting of poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(2‐hydroxyethyl methacrylate‐co‐2‐(dimethylamino)ethyl methacrylate) (P(HEMA‐co‐DMAEMA)) respectively. The hydroxyl groups of PHEMA were further reacted with cinnamoyl chloride (a photosensitive monomer) to obtain photo‐crosslinkable PET‐g‐PHEMA/CA membrane and PET‐g‐P(HEMA/CA‐co‐DMAEMA) membrane. The length of grafted polymer chains was controllable by varying the polymerization time. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in attenuated total reflection and thermogravimetric analysis were employed to characterize the resulting membranes. The various membrane surface morphologies resulting from different states of the grafted chains in water and dimethylformamide were characterized by scanning electron microscopy. It was demonstrated that the grafted P(HEMA/CA‐co‐DMAEMA) chains had more pronounced solvent responsivity than the grafted PHEMA/CA chains. The surface morphologies of the grafted membranes could be adjusted using different solvents and fixed by UV irradiation crosslinking. © 2014 Society of Chemical Industry     

Study on the influence of reaction time on the structure and properties of the PVDF membrane modified through the method of atom transfer radical polymerization

A thermo‐responsive membrane, poly(vinylidene fluoride) (PVDF‐g‐PNIPAAm), was successfully prepared from PVDF membrane through surface‐initiated atom transfer radical polymerization (ATRP) of a thermo‐responsive monomer, N‐isopropyl acrylamide (NIPAAm). The influence of the reaction time on ATRP was studied in detail. The grafting membrane was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS). The results showed that NIPAAm was successfully grafted on the PVDF membrane, the membrane pores became smaller and the reaction time of 36 h was in favor of surface‐initiated ATRP. The thermal stability of PVDF membrane and PVDF‐g‐PNIPAAm membranes was characterized by differential scanning calorimetry (DSC). Contact angles of membrane surface, water penetration and protein solution permeation were tested. Water contact angles of PVDF membrane reduced after the surface grafting of NIPAAm, which illuminated that the hydrophilicity of the grafted membrane was improved. The PVDF‐g‐PNIPAAm membranes exhibited good thermo‐responsive permeability and antifouling property. POLYM. ENG. SCI., 54:1013–1018, 2014. © 2013 Society of Plastics Engineers     

Fabrication of a poly(N‐vinyl‐2‐pyrrolidone) modified macroporous polypropylene membrane via one‐pot reversible‐addition fragmentation chain‐transfer polymerization and click chemistry

In this study, a macroporous polypropylene membrane (MPPM) was grafted with hydrophilic poly(N‐vinyl‐2‐pyrrolidone) (PNVP) based on a one‐pot reversible‐addition fragmentation chain transfer (RAFT) polymerization and click chemistry. First, we prepared the clickable membrane by bromination and following S_N2 nucleophilic substitution reaction; then, click chemistry and RAFT polymerization were performed in one‐pot to graft PNVP to the MPPM surface. The surface characterizations, including attenuated total reflectance/Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and field‐emission scanning electron microscopy, illustrated that PNVP was really grafted onto the MPPM surface. The permeation and antifouling characteristics of the MPPMs were measured by the filtration of a bovine serum albumin dispersion; this showed that in contrast to the nascent membrane, the grafted membrane efficiently obstructed protein molecules because of the compactly grafted polymer chains. The hydrophilicity and antifouling properties of MPPM were greatly ameliorated after modification. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42649.     

Surface initiated ATRP of acrylic acid on dopamine‐functionalized AAO membranes

A facile method for surface‐initiated atom transfer radical polymerization (ATRP) on the anodic aluminum oxide (AAO) membranes has been developed. The AAO membrane was firstly functionalized by poly(dopamine), the bromoalkyl initiator was then immobilized on the poly(dopamine) functionalized AAO membrane surface in a two‐step solid‐phase reaction, followed by ATRP of acrylic acid in a aqueous solution. The poly(acrylic acid) (PAAc)‐grafted AAO membranes were characterized by X‐ray photoelectron spectroscopy, fourier transform infrared spectroscopy and scanning electron microscopy. The XPS and FTIR results indicated that PAAc was successfully grafted on the AAO membrane surface. The degree of grafting increases linearly with the increase of monomer concentration, and it reaches a plateau when the reaction time up to 4 h. The results indicate that the thickness of the grafted polymer inside the isocylindrical pores of AAO membranes could be well controlled by changing the reaction time and monomer concentration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Initiation of surface graft polymerization by ceric ions on polymer microspheres

The surface graft polymerization of acrylamide on poly(styrene‐co‐acrylonitrile) copolymer microspheres by the initiation of ceric ions was studied. The grafting was verified by IR spectra and X‐ray photoelectron spectroscopy measurements. The resultant microspheres with surface‐grafted polymer chains were employed in the preparation of polymer‐microsphere‐supported palladium composite particles. The composite particles were then studied by transmission electron microscopy and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 936–940, 2003     

Temperature‐sensitive membranes prepared by the plasma‐induced graft polymerization of N‐Isopropylacrylamide into porous polyethylene membranes

A temperature‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAAm), was grafted onto porous polyethylene membranes by a plasma‐induced graft polymerization technique. A wide range of grafting was achieved through variations in the grafting conditions, including the postpolymerization temperature, time, monomer concentration, and graft‐reaction medium. The active species induced by plasma treatment was proven to be long‐living via a postpolymerization time of 95 h. Different solvent compositions, that is, water, methanol, benzene, and water/methanol, were used as reaction media, and water showed a much higher polymerization rate than the organic solvents. Based on the hydrophilicity of the active species, a mechanism explaining the solvent effect in plasma‐induced graft polymerization was examined. Characterizations by scanning electron microscopy, X‐ray photoelectron spectroscopy (XPS), and micro Fourier transform infrared showed that the grafted polymers were located on both the outer surface and inside pores of the membranes. The XPS analysis also confirmed that the polar amide groups tended to distribute more outward when grafted PNIPAAm was in its expanding state than when it was in its shrinking state. Water permeation experiments showed that the permeability of the grafted membranes varied dramatically with a slight temperature change in the vicinity of the lower critical solution temperature (LCST) of PNIPAAm. The effective pore radii of the grafted membranes above and below the LCST could be depicted by Hagen‐Poiseuille's law. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3180–3187, 2003     

Functionalization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) films via surface‐initiated atom transfer radical polymerization: Comparison with the conventional free‐radical grafting procedure

We modified hydrophobic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV) films with hydrophilic chains to control their surface properties. We designed and investigated surface‐initiated atom transfer radical polymerization (SI‐ATRP) to modify the PHBHV films by grafting poly(2‐hydroxyethyl methacrylate) (PHEMA) from the surface. This method consisted of two steps. In the first step, amino functions were formed on the surface by aminolysis; this was followed by the immobilization of an atom transfer radical polymerization initiator, 2‐bromoisobutyryl bromide. In the second step, the PHEMA chains were grafted to the substrate by a polymerization process initiated by the surface‐bound initiator. The SI‐ATRP technique was expected to favor a polymerization process with a controlled manner. The experimental results demonstrate that the grafting density was controlled by the reaction conditions in the first step. The grafted films were analyzed by Fourier transform infrared spectroscopy, contact angle testing, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. The results show that grafted chains under the SI‐ATRP method were preferentially located on the surface for surface grafting and in the bulk for conventional free‐radical polymerization initiated by benzoyl peroxide. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Gating Characteristics of Thermo‐Responsive Membranes with Grafted Linear and Crosslinked Poly(N‐isopropylacrylamide) Gates

Thermo‐responsive porous membranes with grafted linear and crosslinked poly(N‐isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma‐induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo‐responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40 °C or 25 °C. Under high operation pressure (e.g., higher than 0.14 MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25 °C (below the LCST of PNIPAM) show larger thermo‐responsive gating coefficients than those prepared at 40 °C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25 °C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNIPAM gates are grafted at 40 °C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo‐responsive “open‐close” switch performances under the operation pressure of 0.26 MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo‐responsive gating membranes with desirable performances.     

Thermo‐Responsive Gating Characteristics of Poly(N‐isopropylacrylamide)‐Grafted Membranes

Both hydrophilic Nylon‐6 membranes and hydrophobic poly(vinylidene fluoride) (PVDF) membranes, with a wide range of grafting yields of poly(N‐isopropylacrylamide) (PNIPAM), were prepared using the plasma‐graft pore‐filling polymerization method. The effect of the physical and chemical properties of the substrates on the thermo‐responsive gating characteristics of the PNIPAM‐grafted membranes was investigated experimentally. For both the PVDF and Nylon‐6 membranes, the grafted PNIPAM polymers were found not only on the membranes outer surface, but also on the inner surfaces of the pores throughout the entire thickness of the membrane. The thermo‐responsive gating characteristics of the PNIPAM‐grafted membranes were heavily affected by the physical and chemical properties of the porous membrane substrates. The PNIPAM‐g‐Nylon‐6 membranes exhibited a much larger thermo‐responsive gating coefficient than the PNIPAM‐g‐PVDF membranes. Furthermore, to achieve the largest thermo‐responsive gating coefficient, the corresponding optimum grafting yield of PNIPAM for the PNIPAM‐g‐Nylon‐6 membranes was also larger than that for the PNIPAM‐g‐PVDF membranes.     

Preirradiation‐induced emulsion graft polymerization of glycidyl methacrylate onto poly(vinylidene fluoride) powder

An epoxy‐group‐containing monomer, glycidyl methacrylate (GMA), was grafted onto poly(vinylidene fluoride) powder via preirradiation‐induced emulsion graft polymerization. The existence of graft chains was proven by chemical structure characterization with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy analysis. The degree of grafting was calculated by means of fluorine content analysis. A kinetic study indicated that, with the emulsion graft polymerization system, the GMA conversion rate was high, exceeding 80%. The variation in the molecular weight of the grafted polymer was measured by gel permeation chromatography, and its crystallinity was investigated with differential scanning calorimetry. The epoxy groups in graft chains were found to be suitable for further chemical modification. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Similarly sized protein separation of charge‐selective ethylene‐vinyl alcohol copolymer membrane by grafting dimethylaminoethyl methacrylate

Similarly sized protein separation was investigated using a charge‐selective membrane, which prepared by grafting dimethylaminoethyl methacrylate (DMAEMA) onto ethylene vinyl alcohol copolymer (EVAL) membrane. Bovine serum albumin (BSA) and bovine hemoglobin (BHb) was used as model proteins. P(DMAEMA), the weak cationic polyelectrolyte with ionizable tertiary amine groups, contributed to the charge‐selective separation for BSA and BHb. At pH 6.0, the grafted EVAL membrane surface was positively charged and BSA was negatively charged, while BHb was positively charged. The BSA was adsorbed onto the membrane surface due to electrostatic interaction and the BHb passed through the membrane into the permeate. The charge‐selective behavior resulted in the separation of the similarly sized protein. The maximum separation factors of static adsorption separation for model protein and binary mixture were 32.4 and 37.2, respectively. In the dynamic separation process, the maximum separation factor value was 6.2. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46374.     

Low protein fouling polypropylene membrane prepared by photoinduced reversible addition‐fragmentation chain transfer polymerization

In this study, 2‐hydroxyethyl methacrylate and N‐isopropyl acrylamide was block grafted onto the polypropylene macroporous membrane surface by photo‐induced reversible addition‐fragmentation chain transfer (RAFT) radical polymerization with benzyl dithiobenzoate as the RAFT agent. The degree of grafting of poly(2‐hydroxyethyl methacrylate) on the membrane surface increased with UV irradiation time and decreased with the chain transfer agent concentration increasing. The poly(2‐hydroxyethyl methacrylate)‐ grafted membranes were used as macro chain transfer agent for the further block graft copolymerization of N‐isopropyl acrylamide in the presence of free radical initiator. The degree of grafting of poly(N‐isopropyl acrylamide) increased with reaction time. Furthermore, the poly(2‐hydroxyethyl methacrylate)‐ grafted membrane with a degree of grafting of 0.48% (wt) showed the highest relative pure water flux and the best antifouling characteristics of protein dispersion. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication of pH‐ or temperature‐responsive single wall carbon nanotubes via a graft from photopolymerization

An ultraviolet light initiated “graft from” polymerization method to fabricate polymer‐functionalized single wall carbon nanotubes (SWNTs) with pendant pH‐ and temperature‐responsive polymer chains is utilized. The attached polymer chains, formed from methacrylic acid and poly(ethylene glycol) methyl ether methacrylate monomers, are well established for its pH‐responsive swelling/deswelling behavior. This special property was utilized here to control the aqueous dispersibility of the carbon nanotubes. Furthermore, poly(N‐isopropylacrylamide), a temperature‐responsive polymer, was utilized in the fabrication of SWNTs whose dispersibility was dependent on solution temperature. The morphology of the polymer‐functionalized carbon nanotubes was characterized by scanning electron microscopy (SEM) before and after functionalization. Environmental SEM was used to further characterize the morphology of the functionalized SWNTs. In addition, covalent bonding of the polymer to the carbon nanotube surface was established using Raman and Fourier transform infrared spectroscopic techniques. The physical and chemical properties of the functionalized nanotubes were further characterized by energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2980–2986, 2012     

Synthesis of an amphiphilic glucose‐carrying graft copolymer and its use for membrane surface modification

A graft copolymer of poly(vinylidene fluoride) (PVDF) with a glucose‐carrying methacrylate, 3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐D ‐glucofuranose, was synthesized via the atom transfer radical polymerization technique with commercial PVDF as the macroinitiator. After a treatment with 88% formic acid, the isopropylidenyl groups of the precursor graft copolymer [poly(vinylidene fluoride)‐g‐poly(3‐O‐methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐ D ‐glucofuranose)] were converted into hydroxyl groups, and this produced an amphiphilic graft copolymer (PVDF‐g‐PMAG) [poly(vinylidene fluoride)‐g‐poly(3‐O‐methacryloyl‐α,β‐D‐glucopyranose)] with glycopolymer side chains and a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight < 1.29). This glucose‐carrying graft copolymer was characterized with Fourier transform infrared, proton nuclear magnetic resonance, gel permeation chromatography, and thermogravimetric analysis. A novel porous membrane prepared from blends of PVDF with PVDF‐g‐PMAG via an immersion–precipitation technique exhibited significantly enhanced hydrophilicity and an anti‐protein‐adsorption property. The surface chemical composition and morphology of the membrane were studied with X‐ray photoelectron spectroscopy and scanning electron microscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Antifouling poly(vinylidene fluoride) hollow fiber membrane with hydrophilic surfaces by ultrasonic wave‐assisted graft polymerization

Acrylic acid (AA)‐grafted poly(vinylidene fluoride) (PVDF) hollow fiber membrane was obtained by ultrasonic wave‐assisted graft polymerization. The grafting density (GD) of AA on the PVDF membrane surface could be controlled by altering the reaction conditions, such as ultrasonic time, ultrasonic power, monomer concentration and initiator concentration. The attenuated total reflectant Fourier transform infrared spectra (FITR‐ATR) and X‐ray photoelectron spectroscopy were used to investigate the chemical composition of modified membranes. The changes of surface morphology and roughness were characterized by field emission scanning electron microscope and atomic force microscopy. Results show that AA was successfully grafted on the membrane surface. With increasing GD, the static water contact angle was decreased from 95.7 to 41.4°, indicating that hydrophilicity of modified membrane was significantly enhanced. Pure water flux before and after bovine serum albumin (BSA) contamination was measured. The modified membrane with the GD of 0.76 mg/cm² has the highest water flux as high as 350 L/m²·h. When compared with the pristine membrane(M0), the flux recovered ratio was improved from 52.75 to 96.29% at the GD 2.76 mg/cm² (M3), which suggested the protein fouling could be effectively prevented for the modified membrane. POLYM. ENG. SCI., 2018. © 2018 Society of Plastics Engineers POLYM. ENG. SCI., 59:E446–E454, 2019. © 2018 Society of Plastics Engineers     

A facile preparation of pH‐temperature dual stimuli‐responsive supramolecular hydrogel and its controllable drug release

A series of pH‐temperature dual stimuli‐responsive random copolymers poly[N,N‐dimethylaminoethyl methacrylate‐co‐poly(poly(ethylene glycol) methyl ether methacrylate][poly(DMAEMA‐co‐MPEGMA)] were synthesized by free radical polymerization. The supramolecular hydrogel was formed by pseudopolyrotaxane, which was prepared with the host‐guest interactions between α‐cyclodextrin (α‐CD) and poly(ethylene glycol) (PEG) side chains. Fourier transform infrared (FT‐IR), nuclear magnetic resonance (¹H NMR), and X‐ray diffraction (XRD) confirmed the structures of the hydrogels. The pH‐temperature dual stimuli responsive properties of the hydrogels were characterized by rheometer. Finally, the controllable drug release behavior of the hydrogel, which was used 5‐fluorouracil (5‐Fu) as the model drug, was investigated at different temperatures and different pH values. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43279.     

Surface‐initiated atom transfer radical polymerization of regenerated cellulose membranes with thermo‐responsive properties

Using atom transfer radical polymerization (ATRP), thermo‐responsive regenerated cellulose membranes were synthesized. Regenerated cellulose membranes were firstly modified by reacting the hydroxyl groups on the surface with 2‐bromoisobutyryl bromide, followed by grafting with poly(N‐isopropylacrylamide). The membranes had obvious thermally modulated permeability properties. Analysis was carried out by means of X‐ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The results showed that N‐isopropylacrylamide had been grafted successfully on the surface of the regenerated cellulose membranes. The thermally modulated permeability properties of the grafted membranes were studied using water flux measurements. It was found that the thermally modulated permeability properties of a cellulose surface can be tailored by the use of the ATRP method. Copyright © 2010 Society of Chemical Industry     

Surface modification on nanoscale titanium dioxide by radiation: Preparation and characterization

Electron beam mutual radiation to induce graft polymerization has been carried out respectively, between nanoscale anatase‐ or rutile‐titanium dioxide particles surface and methyl methacrylate (MMA). The composition and properties of surface modified titanium dioxide were investigated by a number of surface sensitive techniques: X‐ray photoelectron spectrum (XPS), FTIR, X‐ray diffraction (XRD), and NMR. Results of the technological measurements show how surface chemistry is affected throughout the surface modification process, finally leading to a complete and homogeneous vinyl compound overlayer on top of the titanium dioxide samples. In comparison with stereochemical structures of the graft molecular chains and the PMMA induced by radiation polymerization, the surfaces of the oxides are considered to provide a template for the graft polymerization. The grafted titanium dioxide is found to produce a stable colloidal dispersion, in good solvents for the grafted polymer, and the dispersibility of grafted dioxides is influenced by temperature. In addition, the wettability of the surface of titanium dioxide to water is readily controlled by grafting of hydrophilic or hydrophobic polymers. Based on the above results, it is concluded that MMA is covalently linked to the surface of titanium dioxide by a surface modification process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 100: 3510–3518, 2006     

Surface modification of polyethylene by plasma pretreatment and UV‐induced graft polymerization for improvement of antithrombogenicity

The purpose of this study was to enhance blood compatibility of polyethylene (PE) films. Glycidyl methacrylate (GMA) was grafted onto the surface of PE by Ar plasma pretreatment and UV‐induced graft polymerization without photo‐initiator, then heparin was immobilized onto the poly (glycidyl methacrylate) segments. The surface compositions and microstructure of GMA graft polymerized PE films were studied by X‐ray photoelectron spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transfer Infrared (ATR‐FTIR) spectroscopy. It was confirmed that heparin was successfully immobilized onto the surface of PE films by XPS analysis. The antithrombogenicity of the samples was determined by the activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), and plasma recalcification time (PRT) tests and platelet adhesion experiment. Results indicated that the antithrombogenicity of modified PE was improved remarkably. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2014–2018, 2004     

Biocompatible polypropylene prepared by a combination of melt grafting and surface restructuring

To construct biocompatible surfaces of polypropylene (PP), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) was melt‐grafted onto PP backbones; this was followed by the restructuring of the surface mircostructure of the grafted PP by water treatment. The grafted products were analyzed by Fourier transform infrared spectroscopy and ¹H‐NMR; the surface microstructure of the graft copolymer was characterized by X‐ray photoelectron spectroscopy and atomic force microscopy, and the biocompatibility was evaluated by water contact angle, protein adsorption, and platelet adhesion measurements. This study showed that highly biocompatible surfaces of PP could be obtained by a combination of melt grafting and surface restructuring techniques, and the formation of hole‐with‐rim patterns and the enrichment of the PEGMEMA chains on the topmost surface were the key factors for the improved biocompatibility. This work advances functionalized PP generated by melt grafting as a promising candidate for applications in blood‐contact devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012