Facile and Safe Synthesis of Novel Self-Pored Amine-Functionalized Polystyrene with Nanoscale Bicontinuous Morphology.

The chloromethyl-functionalized polystyrene is the most commonly used ammonium cation precursor for making anion exchange resins (AER) and membranes (AEM). However, the chloromethylation of polystyrene or styrene involves highly toxic and carcinogenic raw materials (e.g., chloromethyl ether) and the resultant ammonium cation structural motif is not stable enough in alkaline media. Herein, we present a novel self-pored amine-functionalized polystyrene, which may provide a safe, convenient, and green process to make polystyrene-based AER and AEM. It is realized by hydrolysis of the copolymer obtained via random copolymerization of N-vinylformamide (NVF) with styrene (St). The composition and structure of the NVF-St copolymer could be controlled by monomeric ratio, and the copolymers with high NVF content could form bicontinuous morphology at sub-100 nm levels. Such bicontinuous morphology allows the copolymers to be swollen in water and self-pored by freeze-drying, yielding a large specific surface area. Thus, the copolymer exhibits high adsorption capacity (226 mg/g for bisphenol A). Further, the amine-functionalized polystyrene has all-carbon backbone and hydrophilic/hydrophobic microphase separation morphology. It can be quaternized to produce ammonium cations and would be an excellent precursor for making AEM and AER with good alkaline stability and smooth ion transport channels. Therefore, the present strategy may open a new pathway to develop porous alkaline stable AER and AEM without using metal catalysts, organic pore-forming agents, and carcinogenic raw materials.

Preferential adsorption of nitrate with different trialkylamine modified resins and their preliminary investigation for advanced treatment of municipal wastewater.

In this paper, a series of mono-functional and bifunctional anion exchange resins with different kinds of trialkylammonium groups were synthesized and used for adsorption of nitrate from aqueous solution. The obtained resins were systematically characterized by scanning electron microscopy, Fourier transform infrared spectrometry and pore size distribution. Adsorptive behaviors and mechanisms were investigated by batch experiments. The nitrate could be preferentially adsorbed in the presence of chloride, sulfate and humic acid by longer-chain trialkylamine modified resins. Especially, the L20 resin with the triethylammonium functional group was demonstrated to possess high selectivity toward nitrate with the highest distribution coefficient among all tested resins. For both single and bi-solutes systems, the adsorption isotherm data could be well fitted with the Langmuir model, while the experimental kinetic data was well described by both pseudo first-order and second-order kinetic model. The L20 resin could be reused after many adsorption-desorption cycles with most of its virgin adsorption capacity for advanced wastewater treatment, indicating its great potential for the selective and efficient removal of nitrate from large amounts of municipal wastewater or surface water.

Preparation of quaternary ammonium-Chlorella vulgaris and its adsorption of Ag(CN)2-.

A novel anion exchange resin, quaternary ammonium-Chlorella vulgaris (QACV), was prepared by introducing quaternary ammonium groups onto dried Chlorella vulgaris as base material. Degrees of epoxy, amine and quaternary ammonium groups of QACV were measured. Water retention, optical microscopy, and Fourier transform infrared spectrometry were used to characterize QAVC. The adsorption behavior of QACV towards Ag(CN)2- in different conditions was studied carefully. The results showed that QAVC was efficient to adsorb Ag(CN)2- at pH 9-11, and adsorption equilibrium was almost reached in 30 min. Both kinetics and isotherm parameters in the adsorption process were obtained. The data indicated that the pseudo-second-order model provided a good correlation for adsorption of Ag(CN)2- on QACV and the calculated rate constant of the adsorption was 3.51 g/(mmol min). The equilibrium data fitted well in the Langmuir isotherm and the estimated maximum adsorption capacity qm was 1.96 mmol/g. The dimensionless separation factor RL was between 0 and 1, suggesting that the adsorption process of Ag(CN)2- using QACV was favorable. The QACV could be used successively three times without significantly affecting its adsorption efficiency. Chlorella vulgaris was a potential base material to be modified with quaternary ammonium groups to prepare an adsorbent for adsorption of Ag(CN)2-.

New gel-like polymers as selective weak-base anion exchangers.

A group of new anion exchangers, based on polyamine podands and of excellent ion-binding capacity, were synthesized. The materials were obtained in reactions between various poly(ethyleneamines) with glycidyl derivatives of cyclotetrasiloxane. The final polymeric, strongly cross-linked materials form gel-like solids. Their structures and interactions with anions adsorbed were studied by spectroscopic methods (CP-MAS NMR, FR-IR, UV-Vis). The sorption isotherms and kinetic parameters were determined for 29 anions. Materials studied show high ion capacity and selectivity towards some important anions, e.g., selenate(VI) or perrhenate.

Preparation of a weak anion exchange/hydrophobic interaction dual-function mixed-mode chromatography stationary phase for protein separation using click chemistry.

In this study, 3-diethylamino-1-propyne was covalently bonded to the azide-silica by a click reaction to obtain a novel dual-function mixed-mode chromatography stationary phase for protein separation with a ligand containing tertiary amine and two ethyl groups capable of electrostatic and hydrophobic interaction functionalities, which can display hydrophobic interaction chromatography character in a high-salt-concentration mobile phase and weak anion exchange character in a low-salt-concentration mobile phase employed for protein separation. As a result, it can be employed to separate proteins with weak anion exchange and hydrophobic interaction modes, respectively. The resolution and selectivity of the stationary phase were evaluated in both hydrophobic interaction and ion exchange modes with standard proteins, respectively, which can be comparable to that of conventional weak anion exchange and hydrophobic interaction chromatography columns. Therefore, the synthesized weak anion exchange/hydrophobic interaction dual-function mixed-mode chromatography column can be used to replace two corresponding conventional weak anion exchange and hydrophobic interaction chromatography columns to separate proteins. Based on this mixed-mode chromatography stationary phase, a new off-line two-dimensional liquid chromatography technology using only a single dual-function mixed-mode chromatography column was developed. Nine kinds of tested proteins can be separated completely using the developed method within 2.0 h.

Preparation and characterisation of anion exchangers with dihydroxy-containing alkyl substitutes in the quaternary ammonium functional groups.

Novel poly(styrene-divinylbenzene) (PS-DVB) based anion exchangers having one and two (2,3-dihydroxypropyl) substitutes in the quaternary ammonium functional groups are prepared and characterised by ion chromatography (IC). The introduction of bulky and hydrophilic substitutes to the anion-exchange groups allows the elimination of non-ionic interactions between the polarisable anions and the aromatic rings from the matrix and the improvement of separation selectivity as compared with the traditional trimethylammonium (TMA) functionalised ion exchangers. The synthesis of the ion exchangers includes acylation of PS-DVB particles with acetic anhydride followed by reductive amination either with methylamine hydrochloride or dimethylamine and further alkylation with oxiranes under varied conditions. The ion exchange selectivity and separation efficiency of nine adsorbents having different structure of bonded groups, ion exchange capacity (9-98µequiv.g(-1)) or particle size is studied for model mixture of inorganic anions (F(-), Cl(-), NO2(-), Br(-), NO3(-), HPO4(2-) and SO4(2-)) using carbonate and hydroxide eluents. The adsorbents with more hydrophilic substitutes provided superior columns efficiencies and better peak symmetry as compared with analogues having hydrophobic functional groups. The calculated values of column efficiencies for polarisable NO3(-) and HPO4(2-) are 18,500 and 29,000N/m, respectively, for anion-exchanger, having N-methyl-N',N″-di-(2,3-dihydroxypropyl)ammonium groups which is significantly higher than 1800 and 12,000N/m obtained for these anions with anion exchanger bearing TMA functional groups.

Effect of dissolved organic matter on nitrate-nitrogen removal by anion exchange resin and kinetics studies.

The effects of dissolved organic matter (DOM) on the removal of nitrate-nitrogen from the model contaminated water have been investigated utilizing the strong base anion exchange resins. With the increase of gallic acid concentration from 0 to 400 mg/L, the adsorption amount of nitrate-nitrogen on the commercial resins, including D201, Purolite A 300 (A300) and Purolite A 520E (A520E), would significantly decrease. However, the presence of tannin acid has little impact on nitrate-nitrogen adsorption on them.Compared to D201 and A300 resins, A520E resin exhibited more preferable adsorption ability toward nitrate-nitrogen in the presence of competing organic molecules, such as gallic acid and tannin acid at greater levels in aqueous solution. Attractively, the equilibrium data showed that the adsorption isotherm of nitrate-nitrogen on A520E resin was in good agreement with Langmuir and Freundlich equations. The rate parameters for the intra particle diffusion have been estimated for the different initial concentrations. In batch adsorption processes, nitrate-nitrogen diffuse in porous adsorbent and rate process usually depends on t1/2 rather than the contact time. The pseudo first- and the second-order kinetic models fit better for nitrate-nitrogen adsorption onto A520E resin. The observations reported herein illustrated that A520E resin will be an excellent adsorbent for enhanced removal of nitrate-nitrogen from contaminated groundwater.

Rapid capillary electrochromatographic profiling of phytohormones on a hydrophilic interaction/strong anion-exchange mixed-mode monolith.

An improved hydrophilic interaction/strong anion-exchange (HI-SAX) monolith for rapid capillary electrochromatographic profiling has been developed to detect carboxylic phytohormones with high resolution. The HI-SAX monolith was prepared by copolymerization of 2-(methacryloyloxy)ethyltrimethylammonium methyl sulfate, pentaerythritol triacrylate and porogenic solvents. Detailed polymerization compositions were investigated and improved, and the characteristics in terms of morphology, retention mechanism and column reproducibility were studied. A typical hydrophilic chromatography mechanism was observed when ACN content exceeded 30%, and the HI-SAX mixed-mode was verified with nucleic acid bases and nucleosides. Based on the improved HI-SAX monolith, capillary electrochromatographic profiling of typical phytohormones was evaluated by using indole-3-acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA(3)) as the mode analytes. Effects of the test parameters on carboxyl phytohormones were investigated, and a fast analysis with high resolution for the representative phytohormones was achieved within 4.0 min with intraday RSDs (n = 3) less than 2.6% and 6.3% for the retention time and peak area, respectively. When applied to spiked corn samples, mean recoveries between 82.3% and 95.4% were obtained.

Branched polymeric media: perchlorate-selective resins from hyperbranched polyethyleneimine.

Perchlorate (ClO(4)(-)) is a persistent contaminant found in drinking groundwater sources in the United States. Ion exchange (IX) with selective and disposable resins based on cross-linked styrene divinylbenzene (STY-DVB) beads is currently the most commonly utilized process for removing low concentrations of ClO(4)(-) (10-100 ppb) from contaminated drinking water sources. However, due to the low exchange capacity of perchlorate-selective STY-DVB resins (∼0.5-0.8 eq/L), the overall cost becomes prohibitive when treating groundwater with higher concentration of ClO(4)(-) (e.g., 100-1000 ppb). In this article, we describe a new perchlorate-selective resin with high exchange capacity. This new resin was prepared by alkylation of branched polyethyleneimine (PEI) beads obtained from an inverse suspension polymerization process. Batch and column studies show that our new PEI resin with mixed hexyl/ethyl quaternary ammonium chloride exchange sites can selectively extract trace amounts of ClO(4)(-) from a makeup groundwater (to below detection limit) in the presence of competing ions. In addition, this resin has a strong-base exchange capacity of 1.4 eq/L, which is 1.75-2.33 times larger than those of commercial perchlorate-selective STY-DVB resins. The overall results of our studies suggest that branched PEI beads provide versatile and promising building blocks for the preparation of perchlorate-selective resins with high exchange capacity.

Polyphenylene sulfide based anion exchange fiber: synthesis, characterization and adsorption of Cr(VI).

A fibrous strong base anion exchanger (QAPPS) was prepared for the first time via chloromethylation and quaternary amination reaction of polyphenylene sulfide fiber (PPS), and its physical-chemical structure and adsorption behavior for Cr(VI) were characterized by FTIR, Energy Dispersive Spectrometry, TG-DTG, elemental analysis and batch adsorptive technique, respectively. The novel fibrous adsorbent could effectively adsorb Cr(VI) over the pH range 1-12, the maximum adsorption capacity was 166.39 mg/g at pH 3.5, and the adsorption behavior could be described well by Langmuir isotherm equation model. The adsorption kinetics was studied using pseudo first-order and pseudo second-order models, and the t1/2 and equilibrium adsorption time were 5 and 20 min respectively when initial Cr(VI) concentration was 100 mg/L. The saturated fibers could be regenerated rapidly by a mixed solution of 0.5 mol/L NaOH and 0.5 mol/L NaCl, and the adsorption capacity was well maintained after six adsorption-desorption cycles.

[Development of a novel multi-functional adsorbent bearing with long-chain hydrophobic and anion exchange groups for the simple and rapid determination of residual acephate in vegetables].

A novel multi-functional adsorbent (RP-SAX adsorbent) bearing hydrophobic and anion exchange groups was synthesized for the simple and rapid determination of residual acephate (AP) in vegetables. Macroporous base resin was obtained by suspension copolymerization with glycidyl methacrylate, stearyl methacrylate and glycerin dimethacrylate, and then ethyldimethylamine was introduced at glycidyl groups on the base resin. The adsorbent was packed into a syringe-type tube and used for extraction of AP. AP in the vegetable extract was quantitatively entrapped on the adsorbent and was completely eluted with 3 mL of 30 mmol/L trisodium phosphate in 50% (v/v) methanol solution. The eluate was directly injected into an HPLC-UV detection system with a reverse-phased column. The recoveries of 5 mg/L AP spiked in vegetable extraction samples ranged from 77% to 100%.

Adsorption of chromium (VI) ion from aqueous solution by succinylated mercerized cellulose functionalized with quaternary ammonium groups.

Succinylated mercerized cellulose (cell 1) was used to synthesize an anion exchange resin. Cell 1, containing carboxylic acid groups was reacted with triethylenetetramine to introduce amine functionality to this material to obtain cell 2. Cell 2 was reacted with methyl-iodide to quaternize the amine groups from this material to obtain cell 3. Cells 2 and 3 were characterized by mass percent gain, degree of amination and quaternization, FTIR and CHN. Cells 2 and 3 showed degrees of amination and quaternization of 2.8 and 0.9 mmol/g and nitrogen content of 6.07% and 2.13%, respectively. Cell 3 was used for Cr (VI) adsorption studies. Adsorption equilibrium time and optimum pH for Cr (VI) adsorption were found to be 300 min and 3.1, respectively. The Langmuir isotherm was used to model adsorption equilibrium data. The adsorption capacity of cell 3 was found to be 0.829 mmol/g. Kinetic studies showed that the rate of adsorption of Cr (VI) on cell 3 obeyed a pseudo-second-order kinetic model.

New developments in the preparation of anion exchange media based on hyperbranched condensation polymers.

We have developed a number of new anion exchange stationary phases based on synthesis of hyperbranched condensation polymers prepared in situ on surface sulfonated wide pore, low surface area ethylvinylbenzene-divinylbenzene substrate beads. These new stationary phases are synthesized by exposing the substrate beads to a mixture containing one of several different diepoxides and methyl amine followed by exposure in an alternating fashion to diepoxide and then methyl amine in a repetitive manner. With each cycle of reaction with first diepoxide and then methyl amine, the capacity of the stationary phase doubles, allowing for the synthesis of high-capacity materials. These new phases are stable to hydrolysis in concentrated acid and base. They exhibit exceptionally low levels of hydrophobic interaction with anionic species commonly of interest in the analysis of environmental samples.

Mixed-mode ion-exchangers and their comparative chromatographic characterization in reversed-phase and hydrophilic interaction chromatography elution modes.

A set of particulate silica-supported mixed-mode RP/weak anion-exchangers (RP/WAX) (obtained by bonding of N-undecenoylated 3-aminoquinuclidine, 3-aminotropane and 2-dimethylaminoethylamine as well as of N-butenoyl-(2S,4S,5R)-2-aminomethyl-5-[(2-octylthio)ethyl]-quinuclidine to thiol-modified silica) were chromatographically characterized in comparison to selected commercially available columns using two distinct isocratic elution modes, viz. an aqueous-rich RP-type elution mode (with 40% ACN and 60% buffer) as well as an organic solvent-rich hydrophilic interaction chromatography (HILIC)-type elution mode (95 and 90% ACN). The mixed-mode RP/WAX phases showed multimodal applicability, unlike a polar embedded RP material (Synergi Fusion RP), amino phases (Luna NH(2), BioBasic AX) or typical HILIC packings (ZIC-HILIC, TSKGel Amide-80). Principal component analysis (PCA) of the RP test data confirmed that the in-house developed RP/WAX columns as well as the Acclaim Mixed-Mode WAX-1 phase resemble each other in their chromatographic characteristics having slightly lower hydrophobic selectivity (alpha(CH2) of 1.5) than the tested Synergi Fusion RP (alpha(CH2) approximately 1.8). In contrast, a decrease in mixed-mode character due to lowered ion-exchange capacity and concomitantly increased RP-like behavior could be identified for other mixed-mode phases in the order of Obelisc R > Primesep B2 > Uptisphere MM3. PCA on HILIC data revealed that the RP/WAX phases behave dissimilar to TSKGel Amide-80, ZIC-HILIC and polysulfoethyl A under the chosen elution conditions. Hence, they may be regarded as complementary to these commercial stationary phases with applicability profiles for hydrophilic but also hydrophobic solutes.

Preparation of anion exchanger by amination of acrylic acid grafted polypropylene nonwoven fiber and its ion-exchange property.

To develop the polymeric adsorbent that possess anionic exchangeable function, PP-g-AA-Am fibers were prepared by photoinduced grafting of acrylic acid (AA) onto polypropylene (PP) nonwoven fibers and subsequent conversion of carboxyl group in grafted AA to an amine (Am) group by reaction with diethylene triamine (DETA). The amination of grafted AA increased with increase in the degree of grafting, the reaction time and temperature of the chemical modification process. Catalytic effect of metal chlorides such as AlCl(3) and FeCl(3) on the amination of grafted AA was significant but not essential to lead the amination. FT-IR and solid (13)C NMR data indicate that amine group was introduced into PP-g-AA fiber through amide linkage between grafted AA and DETA. The anion exchange capacity of PP-g-AA-Am fiber increased with increase in the degree of amination, but reached maximum value at about 60% amination of 150% grafted AA. PP-g-AA-Am fiber showed much higher maximum capacity for PO(4)-P and a similar capacity for NO(3)-N compared to commercial anion resins. Furthermore, the PP-g-AA-Am fiber also has adsorption ability for cations because of unaminated residual carboxyl group.

DEUSS: a perdeuterated poly(oxyethylene)-based resin for improving HRMAS NMR studies of solid-supported molecules.

A novel resin called DEUSS (perdeuterated poly(oxyethylene)-based solid support) has been prepared by anionic polymerization of deuterated [D4]ethylene oxide, followed by cross-linking with deuterated epichlorohydrin. DEUSS can be suspended in a wide range of solvents including organic and aqueous solutions, in which it displays a high swelling capacity. As measured by proton HRMAS of the swollen polymer, the signal intensity of the oxyethylene protons is reduced by a factor of 110 relative to the corresponding nondeuterated poly(oxyethylene)poly(oxypropylene) (POEPOP) resin, thus facilitating detailed HRMAS NMR studies of covalently linked molecules. This 1H NMR invisible matrix was used for the solid-phase synthesis of peptides, oligoureas, and a series of amides as well as their characterization by HRMAS NMR spectroscopy. On-bead NMR spectra of high quality and with resolution comparable to that of liquid samples were obtained and readily interpreted. The complete absence of the parasite resin signals will be of great advantage, for example, for the optimization of multistep solid-phase stereoselective reactions, and for the conformational study of resin-bound molecules in a large variety of solvents.

Enhancing the "stickiness" of bile acids to cross-linked polymers: a bioconjugate approach to the design of bile acid sequestrants.

A series of cross-linked polymers have been synthesized by reaction of 2% cross-linked, chloromethylated polystyrene with a tertiary amine derivative (7) of cholic acid (prepared by reaction of cholic acid methyl ester with N,N-dimethyl-ethylenediamine), followed by exhaustive quaternization with trimethylamine. Increased loadings of 7 result in enhanced binding of taurocholate ion and a decrease in its rate of release upon exposure to 50 mM aqueous NaCl. Examination of particle-size effects indicates that film diffusion and particle diffusion both contribute to the observed kinetics. Interruption tests that were carried out confirmed that particle diffusion is kinetically important. The relevance of this bioconjugate approach to the design of bile acid sequestrants for the treatment of hypercholesterolemia is briefly discussed.

Synthesis and characterization of silica-based aliphatic ion exchangers.

The chemical literature describing preparation of aliphatic ion exchangers is limited, and although such phases are available commercially, the synthetic schemes are proprietary. The course of our research required the preparation of silica-based aliphatic cation and anion exchangers for which the desired base silica and/or ligand properties were not commercially available. We developed synthetic schemes to prepare silica-based aliphatic sulfonic acid, carboxylic acid and quaternary ammonium ion-exchange phases with active exchange capacities of 0.2-0.9 mumol/m2. Multiple techniques were used to characterize the intermediate and final phases produced in the syntheses, including Fourier transform diffuse reflectance infrared spectroscopy, spot tests, elemental analysis, acid-base titration and elution analysis.

High-performance anion-exchange chromatography of oligonucleotides.

Several types of high-performance silica-based supports have been found to be effective in the separation of polynucleotides. The principal difference in these materials is the type of bonded phase and the method by which it is attached to the silica support. One approach is the coupling of stationary-phase groups to the surface through siloxane bonding. This technique is simple and produces a material of high capacity and resolution, but it suffers from poor bonded-phase stability. An alternative approach is the adsorption of low-molecular-weight polyethylene imines (PEI) that are crosslinked into a surface film. The stationary phase is held in place by adsorption of the film at multiple sites. A previous report on this material showed the resolution of oligonucleotides containing up to 30 bases. This paper reports further optimization of the PEI bonding chemistry in the preparation of HP-IEC columns for oligonucleotides and tRNA species. Quaternization of the ion-exchange matrix was found to increase resolution of oligonucleotides from 30 to 50 bases. The same support was found to be capable of resolving multiple tRNA species. Separations were achieved on small (0.42 X 5 cm) columns, using a 60- to 120-min ammonium sulfate gradient. The initial solvent was 15% acetonitrile in 0.05 M potassium phosphate (pH 5.9). The addition of 1 M ammonium sulfate to the initial solvent was used to prepare the final solvent.