P-xylylene Dichloride Research Articles

Construction of bifunctional triazine-based imidazolium porous ionomer polymers by a post-crosslinking tactic for efficient CO2 capture and conversion

Porous ionomer polymers (PIPs), as a class of materials with special functions, have been extensively studied due to their easy preparation and designability. In this work, a series of novel triazine imidazolium functionalized PIPs are successfully constructed by a post-crosslinking tactics for CO2 capture and conversion. Both structure and properties of PIPs are adjusted neatly by changing ionic salt monomers (ISM-n) and external cross-linkers p-xylylene dichloride (DCX), α,α'-dibromo-p-xylene (DBX), and 4,4′-bis(chloromethyl)-1,1′-biphenyl (BP), as well as the cross-linked ratios. It is found that the CO2 adsorption capacity of as-prepared PIPs constructed by post-crosslinking strategy is significantly increased from 9.3 to 103.2 mg·g−1 at 273 K and 1.0 bar than corresponding ionic salt monomer (an improvement of about 10 times). Kinetic and thermodynamic studies for CO2 adsorption processes indicate that the adsorption of CO2 by PIPs is a spontaneous physical adsorption process. Particularly, these triazine-based imidazolium PIPs can also be used as recyclable catalysts for CO2 conversion into cyclic carbonates with up to 99 % yields and the unprecedented turnover number (TON) of 4025, it is much higher than those ionic polymer catalysts reported in previous literature. Combined CO2 reaction kinetics, reaction activation energies catalyzed by different catalysts, and in situ FTIR experimental results of CO2 adsorption and conversion, a synergistic catalytic mechanism based on triazine group and imidazolium is proposed. Our study provides new insights into the design of functionalized PIPs materials with great potential for applications in CO2 separation and conversion.

The stabilization of ultrafiltration membrane blended with randomly structured amphiphilic copolymer: Micropollutants adsorption properties in filtration processes

In this study, a blend membrane consisting of polyvinylidene fluoride (PVDF) and tertiary amine containing random copolymer poly(methyl methacrylate-r-dimethylamino-2-ethyl methacrylate) (P(MMA-r-DMAEMA)) was fabricated and utilized as an adsorptive membrane for micropollutants (anionic dye and heavy metal ions) removal from aqueous solutions. Cross-linking the random copolymer by p-xylylene dichloride (XDC) produced the membrane with improved copolymer retention ratio and stability, while slightly variated physicochemical properties. Besides, the fluxes of crosslinked blend membranes dramatically increased from 0.7 ± 0.1 L/(m2h) to 118.6 ± 5.9 L/(m2h). Then the present blend membrane was carried out adsorption and filtration experiments to investigate the influence of various of operation parameters including initial solution pH value, contacting time, initial solution concentration, and recycling efficiency on micropollutants removal. The experimental results showed that the removal of the anionic dyes and heavy metal ions on this tertiary amine containing blend membrane was a pH-dependent process with the maximum adsorption capacity at the initial solution pH of 3.5 for anionic dyes and 6.0 for metal ions, respectively. The membrane showed highly efficient capture of sunset yellow (above 99%). Meanwhile, the captured sunset yellow was recovered and concentrated with a small volume of alkaline solutions at pH 10.0, which simultaneously regenerated the membrane for its reuse. In a 3-cycle capture-recovery test, the membrane demonstrated a high sunset yellow recovery ratio and a volumetric concentration ratio as high as 400%. Our study provides an alternative strategy for functionalized membrane fabrication, micropollutants removal and recovery.

Preparation of anti-fouling zwitterionic nanofiltration membrane with tunable surface charge

Anti-fouling property is of vital significance and remains a challenge in the membrane separation field. In this work, N-diethylethylenediamine (DEEDA) was incorporated into the polyamide matrix first. Then, an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge was fabricated by the grafting of p-xylylene dichloride (XDC) on the membrane surface. The resulting nanofiltration membrane possessed zwitterionic groups of positively charged N+ and negatively charged COO-. Meanwhile, the surface charge could be tuned precisely by the concentration of XDC. A neutrally charged nanofiltration membrane was obtained when the concentration of XDC was 1.0 ​wt% and the preparing membrane showed permeance of 9.1 ​L·m-2·h-1·bar-1 with high rejection of CaCl2 (90.8%) and Na2SO4 (91.3%) at pH ​= ​6.5. This membrane exhibited excellent anti-fouling properties towards not only negatively charged bovine serum albumin but also positively charged lysozyme. The optimum membrane, PA-XDC-1.0, had flux recovery rates of 95.0% and 94.0% for bovine serum albumin and lysozyme, respectively, which was higher than those of PA-DEEDA-0 (86.1% and 80.7%). This work offered a facile way to fabricate an anti-fouling zwitterionic nanofiltration membrane with tunable surface charge, which had wide applications in water purification.

Adsorptive removal of nitrogen compounds from fuel oil by a poly ionic liquid PVIm-PXDC

ABSTRACTA poly ionic liquid, poly(1-vinyl imidazole)-p-xylylene dichloride (PVIm-PXDC), was synthesized and used for fuel oil denitrogenation. The structure of PVIm-PXDC was characterized and the denitrogenation performance was investigated. Results indicate that the pseudo-second-order kinetic model and Langmuir model are appropriate to describe the adsorption kinetics and thermodynamics, respectively. The adsorption ability of PVIm-PXDC for different nitrogen compounds follows the order of indole > pyrrole > quinoline > pyridine. The equilibrium adsorption amount decreased about 10% for all the nitrogen compounds after six regeneration cycles and the denitrogenation and regeneration processes have no influence on the structure of PVIm-PXDC.

From ultrafiltration to nanofiltration: Nanofiltration membrane fabricated by a combined process of chemical crosslinking and thermal annealing

An integrally skinned dense ultrafiltration (UF) membrane was prepared using partially di-quaternized poly(sulfone-co-ethernitrile) random copolymer (PSF-co-DQAPEN) via classical nonsolvent induced phase inversion process (NIPS). Then the original UF membrane was molecularly restructured through a combined process of chemical quaternization-crosslinking reaction and thermal annealing for the preparation of a crosslinked nanofiltration (NF) membrane, in which p-xylylene dichloride (PXDC) and isopropanol were employed as crosslinking agent and nonsolvent treating medium, respectively. The influence of reaction time and crosslinker concentration on membrane performance were investigated. X-ray photoelectron spectroscopy (XPS) of membrane surface and solubility test of membrane were employed to study the chemical composition and crosslinking properties of membranes, and those results revealed that the original membrane had been successfully crosslinked after this post treatment process. The separation performance of membrane was ultimately changed from UF-level to NF-level after the quaternization-crosslinking reaction and thermal annealing treatment process. The optimum crosslinked NF membrane possessed MgCl2 rejection of 98.2% and water permeate flux of 4.12 L m−2 h−1 bar−1. Moreover, owning to the excellent chemical stability of membrane material, the crosslinked membrane had outstanding resistance to chlorine, acid and base, thus it can be used for water softening and removing of positive dyes. Given the convenience and feasibility of this modification method, integrally skinned NF membrane could be easily fabricated via the post chemical crosslinking and thermal annealing process of UF membrane using proper treating approaches.

A novel positively charged nanofiltration membrane formed via simultaneous cross-linking/quaternization of poly(m-phenylene isophthalamide)/polyethyleneimine blend membrane

A novel positively charged nanofiltration membrane was designed and prepared by a simultaneous cross-linking/quaternization of poly(m-phenylene isophthalamide)/polyethyleneimine (PMIA/PEI) blend precursor membrane. To improve the PEI retention ratio during precursor membrane fabrication, propanetriol glycidyl ether (PTGE) was used as a cross-linker. For nanofiltration preparation, the cross-linking time and p-xylylene dichloride (XDC) concentration were optimized. A comprehensive characterization of the nanofiltration membrane was conducted in terms of chemical composition, surface morphology, surface charge, pore structures and separation properties. Results indicated that the density of the positive charge increased after the simultaneous cross-linking/quaternization. The nanofiltration membrane with pore size in the range of 0.5–2 nm exhibited high MgCl2 rejection of 94.4% and water permeability of 37.3 L m−2 h−1 at 0.4 MPa. Furthermore, to make a comparison between the PMIA/PEI nanofiltration membrane and the other PEI based nanofiltration membranes in the previous studies, an empirical upper bound correlation between water permeability and water/salt selectivity was established. Due to the high density of positive charge on the membrane, the mono-/divalent ion (Na+/Mg2+) selectivity of this novel nanofiltration membrane was at a high level compared with recent reports and much higher than commercial nanofiltration membranes. This work provides an effective method for fabricating the highly positively charged nanofiltration membrane which has great potential for multivalent cations separation.

Poly (N-vinyl imidazole) gel-filled membrane adsorbers for highly efficient removal of dyes from water

Energy-efficient and time-saving process for recovery of hazardous dyes from wastewater is highly desired in dyeing industry. In this work, poly(N-vinyl imidazole) (PVI) gel-filled membrane adsorbers were developed for highly efficient recovery of dyes through adsorption filtration. The membrane adsorbers were fabricated via dip-coating of Nylon macroporous membranes in PVI solutions followed by quaternization crosslinking with p-xylylene dichloride (XDC). Physicochemical characterizations indicated that PVI gel was successfully filled and fixed inside the Nylon matrix. In optimized conditions. The treating capacity of membrane adsorbers to typical dye sunset yellow (25 ppm of the feed concentration) reached up to 197 mg/g with the removal ratio >99%. Both the treating capacity and the removal ratio were kept steady even when the permeation flux was as high as 1000 L/m2 h. The membrane adsorbers developed in this work were able to not only remove anionic dyes from water, but also separate anionic dyes from cationic ones. The zeta potential and adsorption tests showed that the electrostatic interaction between PVI gel and dye molecules was responsible for the high removal efficiencies to anionic dyes. The membrane adsorbers can be regenerated effectively with NaOH solution and demonstrated good stability in both acidic and alkaline conditions.

Heterogeneous anion-exchange membrane: Influences of charged binders with crosslinking structure on electrodialytic performance

It has practical significance to improve the electrodialytic performance of heterogeneous ion-exchange membrane. In this work, appropriate amount of N,N-dimethylaminoethyl methacrylate (DMAEMA) was added into conventional casting solution composed of poly(vinylchloride), anion-exchange resin particles and N,N-dimethylformamide. After the polymerization of DMAEMA and solvent evaporation, the membrane precursor was formed and then treated by p-xylylene dichloride for the simultaneous quaternization and crosslinking of PDMAEMA. Subsequently, the effects of charged binders with a semi-interpenetrating crosslinking structure on the electrochemical properties of anion-exchange membranes (AEMs) were investigated. Above all, the evolution of chemical composition and morphology changes were recorded by FTIR and SEM, respectively. Moreover, the novel membranes were evaluated from different perspectives, such as Water uptake, Fixed ion concentration, Area electrical resistance, Transport number of counter-ion, Salt permeability coefficient, Limiting current and compared with those of the conventional heterogeneous AEMs with a similar ion-exchange capacity. At last, as-prepared AEMs were applied in simulated electrodialysis experiments. Results showed that the novel membrane-preparing technology made the heterogeneous AEM look and behave more like homogeneous one. Of course, the scheme is also suitable to the hot-pressing technology for the preparation of heterogeneous AEM.

Hypercrosslinked Polycondensation Networks: Copolymers of p-Xylylene Dichloride

It was shown that self-condensation of p-xylylene dichloride (p-XDC) and its co-polycondensation with naphthalene, anthracene, benzyl alcohol, and benzhydrol in presence of the Lewis acids in solution leads to the formation of hypercrosslinked polymers characterized by developed porosity and ability to swell in nonpolar and polar media. Swelling and porosity of the polycondensed network do not depend on dilution of the initial monomer mixture or catalyst amount involved in the reaction as opposed to the properties of hypercrosslinked polymer. The similarities and differences of the regularities of formation of structures obtained at intense crosslinking of linear polymers (polystyrene) and polycondensed networks were examined. It was also estimated that copolymers with naphthalene and anthracene demonstrate perfect ability to extract furfural (which is able to participate in strong π–π interactions) even from methanol solution.

Synthesis and catalytic activity of porous polymer containing ionic liquid structures

A novel porous polymer containing ionic liquid (IL) structures was synthesized via quternization and condensation of 4-vinylpyridine and p-xylylene dichloride. The ionic liquid structures were incorporated in the polymeric framework and for this reason bulky IL molecules can hardly block pores and neutralize active sites. The polymer shows a high BET surface area and easily accessible active sites. Catalytically the polymer is very active in Michael additions with averaged yields over 96.0% achieved after short reaction times. The high BET surface, remarkable activity, operational simplicity, wide applicability and improved stability are the key properties of the polymer.

Effects of quaternization on the morphological stability and antibacterial activity of electrospun poly(DMAEMA-co-AMA) nanofibers

Electrospun nanofibers with antibacterial activity are greatly promising for medical treatment and water purification. Herein we report antibacterial nanofibers electrospun from a series of poly(dimethylamino ethyl methacrylate-co-alkyl methacrylates) (poly(DMAEMA-co-AMA)) and to distinguish the effects of free and cross-linked cations derived from quanternization on the antibacterial activity. Poly(DMAEMA-co-AMA)s are simply synthesized by free radical polymerization from commercial monomers. DSC analysis indicates that they have Tg lower than room temperature and thus the electrospun nanofibers adhere to each other and evenly tend to form films, instead of keeping cylinderic shape. Benzyl chloride (BC) and p-xylylene dichloride (XDC) can quaternize DMAEMA units and to generate cations on the nanofiber surface. XPS analysis and colorimetric assay determine the quaternization degree and the surface accessible quaternary amines (N+), respectively. It is very promising that this quaternization endows the electrospun nanofibers with both stable morphology and antibacterial activity. The BC-quaternized fibers show better antibacterial behavior against Escherichia coli and Staphylococcus aureus than those of the XDC-quaternized/cross-linked ones, because cross-linking suppresses the chain mobility of cations. Our results confirm that antibacterial nanofibers can be facilely prepared and chain mobility of the formed cations is the necessary prerequisite for their antibacterial activity.

Preparation of novel NF membrane via interfacial cross-linking polymerization

The goal of present work is the preparation of a novel positively charged nanofiltration (NF) membrane and its development for the cation removal of aqueous solutions. This NF membrane was fabricated by the surface modification of polysulfone (PSf) ultrafiltration support. The active top-layer was formed by interfacial cross-linking polymerization of poly(ethyleneimine) (PEI) with p-xylylene dichloride (XDC) and then quaternized with methyl iodide to form a perpetually positively charged layer. In order to improve the efficiency of nanofiltration membrane, the concentration of PEI, XDC and methyl iodide solutions, PEI coating and cross-linking time have been optimized. As a result, a high water flux and high CaCl2 rejection (1,000 ppm) was obtained for the composite membrane with values of 18.29 L/m2.h and 93.62% at 4 bar and 25°C, respectively. The rejections of NF membrane for different salt solutions followed the order of Na2SO4 < MgSO4 < NaCl < CaCl2. Molecular weight of cut off (MWCO) was calculated via retaining of PEG solutions with different molecular weights that finally, it revealed the Stokes and hydrodynamic radius of 1.457 and 2.507 nm on the membrane selective layer, respectively. The most efficient positively charged nanofiltration membrane exhibited a Ni2+ rejection of 96.26% for industrial wastewater from Shamse Hadaf Co. (Kashan, Iran).

Positively-charged nanofiltration membrane formed by quaternization and cross-linking of blend PVC/P(DMA-co-MMA) precursors

To explore low-pressure-driven nanofiltration (LPDNF) membranes with high permeate flux, a novel preparation route was proposed and investigated. First, an amphiphilic copolymer of poly (methyl methacrylate-co-dimethylaminoethyl methacrylate) (P(MMA-co-DMA)) was synthesized via free-radical copolymerization, and then blended with polyvinyl chloride (PVC) to fabricate precursor membranes via non-solvent induced phase separation (NIPS) process. Utilizing the quaternization and cross-linking reaction between p-xylylene dichloride (XDC) and tertiary amine units in PVC/PMMA-co-DMA precursor membranes, positively charged PVC/PMMA-co-DMA LPDNF membranes were obtained. Element alanalysis, X-ray photoelectron spectroscopy and scanning electron microscopy were employed to characterize the composition and morphology of the membranes. Effects of PMMA-co-DMA content and XDC concentration on the LPDNF membranes’ performance were studied and discussed. With the optimized condition, the NF membrane showed the highest salt rejection (R) and water flux (J), e.g., RMgCl2=89.1%, JMgCl2=22.1L/(m2h) and RNaCl=45.1%, JNaCl=27.6L/(m2h) at a pressure of 0.3MPa. Besides, the rejections of the LPDNF membranes for inorganic salts increased in an order of Na2SO4<MgSO4<NaCl<CaCl2<MgCl2. Together with the good stability, PVC/PMMA-co-DMA blend membrane was approved as a promising positively charged LPDNF membranes.

Synthesis of a crosslinked polymer with a benzyl(triphenyl)phosphonium ionic liquid moiety and its catalytic activity

A novel crosslinked polymer with a benzyl(triphenyl)phosphonium ionic liquid moiety was synthesized from triphenylphosphine and p-xylylene dichloride.

Synthesis of a Thermostable Polymer-supported Strongly Basic Catalyst and its Catalytic Activity

A novel strongly basic polymer-supported catalyst with guanidine groups has been synthesized and its thermal stability has been investigated. To obtain a thermally stable, cross-linked structure, guanidine groups bound to a polystyrene matrix were allowed to react in a nucleophilic manner with p-xylylene dichloride. Compared with the conventional strongly basic anion-exchange resin 201, it possesses higher thermal stability when placed in deionized water at 95°C for 60 h. This was confirmed by thermogravimetric analysis. The excellent thermal stability can be attributed to the unique structure of guanidine and the cross-linking connection mode between this base and the polymeric matrix. The obtained resin was found to efficiently catalyze Knoevenagel condensation reactions with remarkably high yields. Furthermore, the catalytic efficiency of the resin was found to remain unaffected for seven cycles, whereas that of 201 resin was reduced by 25 % owing to degradation of the strongly basic groups.

Synthesis and characterization of cross-linked poly(arylene ether ketone) containing pendant quaternary ammonium groups for anion-exchange membranes

We report an effective and simplified procedure for the synthesis of cross-linked alkaline anion-exchange membranes (AEMs). A new monomer containing two tertiary amine groups on 4,4'-dihydroxydiphenyl ether (DABPE) is used in nucleophilic aromatic substitution step-growth copolymerization with 4,4'-difluorobenzophenone, 2,2',6,6'-tetramethyl-4,4'-biphenol to obtain the corresponding poly(arylene ether ketone) copolymers containing tertiary amine groups. After partial quaternization, the residual tertiary amine groups of the polymer react with p-xylylene dichloride to produce a cross-linked membrane, which is followed by anion exchange with hydroxide ions. The resulting cross-linked membranes exhibit high hydroxide ion conductivity (above 10(-2) S cm(-1) at room temperature), good mechanical properties, and reduced water uptake relative to the linear uncross-linked membrane. This facile synthetic approach enables the preparation of cross-linked materials with the potential to meet the demands of hydrogen-powered fuel cells as well as direct methanol fuel cells. (c) 2012 Elsevier B.V. All rights reserved.

A novel positively charged nanofiltration membrane prepared from N, N-dimethylaminoethyl methacrylate by quaternization cross-linking

A novel method for the preparation of hydrophilic and positively charged nanofiltration (NF) membranes was developed. An active top-layer with NF characteristic was composited onto polysulfone (PSf) ultrafiltration substrate by UV-induced graft polymerization of N, N-dimethylaminoethyl methacrylate (DMAEMA) followed by quaternization cross-linking with p-xylylene dichloride (XDC). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy were employed to monitor membrane surface chemical and morphological changes after poly(DMAEMA) grafting and quaternization cross-linking. The influences of UV irradiation time, monomer DMAEMA concentration, the cross-linker XDC concentration on the separation and permeation properties of membrane were investigated. The surface hydrophilicity of the composite membranes was evaluated by contact angle measurement. It was found that membrane hydrophilicity was obviously enhanced after UV-induced grafting and quaternization cross-linking. As the UV irradiation time and DMAEMA monomer concentration were increased, salts rejection of the composite membranes increased while water permeability decreased. Under the optimized preparing conditions, water flux and MgCl 2 rejection (1.0 g/L) of the composite membranes reached 60.3 L/(m 2 h MPa) and 93.2%, respectively. The membrane surface charge property was measured via a streaming potential method. It was found that, at pH from 4.5 to 9, the composite membranes showed positive zeta potentials. The rejections of the composite membranes to different salts followed the order Na 2SO 4 < NaCl < MgSO 4 < MgCl 2 < CaCl 2. Moreover, the composite NF membranes showed a good stability in water-phase filtration process.

Phosphoric acid-doped cross-linked porous polybenzimidazole membranes for proton exchange membrane fuel cells

Cross-linked porous polybenzimidazole (PBI) membranes were prepared by mixing a low-molecular-weight compound (porogen) and a cross-linker with the polymer to form cross-linked polymer membranes in order to increase the mechanical strength and proton conductivity. SEM images of the cross-section of the porous polymer membranes show the pore size and morphology. The cross-linking by p-xylylene dichloride can effectively improve the mechanical properties of the porous PBI membranes after phosphoric acid doping. The CpPBI-60 membrane, which is doped with 9 moles of phosphoric acid, has a tensile modulus of 0.45 GPa. The good mechanical strength of the cross-linked porous PBI membranes makes them able to hold more phosphoric acid and, consequently, have higher proton conductivity. Fenton's test indicated that the covalently cross-linked structure played an important role in the radical oxidative stability of the porous membranes. The doping level of phosphoric acid in the cross-linked porous PBI membranes showed that the enhanced conductivity was due to the increase of porosity, which results in the increase of acid uptake. Impedance analysis showed that the conductivity of the cross-linked porous PBI membranes could reach 2.1 × 10−2 S cm−1 at 160 °C under anhydrous conditions.

Preparation and characterization of a novel nanofiltration membrane

In this study, poly[2-(N, N-dimethyl amino)ethyl methacrylate] (PDMAEMA) was prepared by bulk polymerization using AIBN as an initiator. Aqueous PDMAEMA solution was then purified by hollow fiber ultrafiltration membrane technology to remove oligomers. PDMAEMA/polysulfone (PSF) positively charged nanofiltration (NF) membrane was developed by interfacial polymerization by using PSF ultrafiltration membrane as the substrate, PDMAEMA aqueous solution as the coating solution and p-xylylene dichloride dissolved in n-heptane as the organic crosslinker. Effects of substrate material, concentration of monomer, pH value of PDMAEMA, coating time and crosslinking time were then carefully examined on the separation properties of the prepared NF membrane. Data suggested that the rejection rate of the composite NF membrane to 1 g/l of MgSO4 was around 86.7 %, and the water flux was about 18.4 L·m−2·h−1. Therefore, the developed NF membrane is suitable for rejection and desalination of alkaline dyes.

A New Method To Generate Polystyrene Gels

Gels made of cross-linked polystyrene have been prepared and investigated since the dawn of polymer science. Besides network formation by cross-linking copolymerization of the monomer with a suitable multifunctional cross-linker, random or directed successive cross-linking of preformed linear polymers has been used widely to generate networks in a more controlled manner. It is expected that networks made by successive crosslinkingof preformedpolymers aremorehomogeneous than those synthesized via cross-linking copolymerization. Unfunctionalized PS has been cross-linked making use of the electrophilic aromatic substitution reaction with p-xylylene dichloride or chlorodimethyl ether in the presence of Lewis acids. Randomly functionalized PS like poly(styrene-coaminomethylstyrene), P(S-co-AMS), could be cross-linked by reaction with terephthaldialdehyde. So-called model networks have been made by end-linking of telechelic precursors. Contrary to purely chemical reactions, photochemical crosslinking provides the opportunity of controlling the rate and the extent of the reaction atwill, simultaneously offeringpotential for spatial differentiation. Photochemical cross-linking has been applied to a number of polymers where the linear precursors carried anthracene, cinnamate, indene, dimethylmaleimide, or coumarin moieties. Most of these groups are bulky, and it is unclear howmuch they influence the properties of the polymer. In this paper, we will show that PS carrying a small number of mere aminomethyl groups can be photo-cross-linked in an easy and straightforward way. The aminomethyl moieties in p-position dimerize upon irradiation in the presence of thioxanthone (TX), thus forming benzylidenebenzylamine linkages. Starting from functionalized PSs of different molecular weights, the gelation process was followed by oscillatory shear measurements. Static light scatteringwas applied toobtain some structural information on the networks in addition to the macroscopic properties obtained by rheology.