Regulating the specificity of porous polymer sorbents used as the stationary phase in gas chromatography

Summary The main features of the retention of various homologous series on polymer sorbents with different functional groups, including typical ion-exchange resins, have been studied.Dedicated to ProfessorKiselev on the occasion of his seventieth birthday.     

Complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres

A new approach to a problem of preparation, regulation of properties and formation of three-dimensional structure of complexing polymer sorbents and metal polymer complex catalysts with specially designed structure of active centres has been developed. The main principle is based on the use of “memory” of polymer composition and consists in prearrangement of macromolecules of initial complexing polymer or metal polymer complex catalyst to sorbing metal or hydrocarbon substrate followed by fixation of optimum for particular substrate conformation by intermolecular crosslinking. Using this principle a number of crosslinked complexing polymer sorbents and metal polymer complex catalysts containing phosphorylic, carboxylic, pyridine, amine and imine functional groups have been prepared. It has been shown that prearrangement leads to essential improvement of basic sorption and catalytic properties of the crosslinked complexing polymers - sorption capacity, the rate of uptake, selectivity and catalytic activity.     

Monodisperse porous polymer particles: Formation of the porous structure

Monodisperse porous styrene-divinylbenzene copolymer particles were prepared via seeded emulsion polymerization using a mixture of linear polymer (polystyrene seed) and non-solvent as inert diluent. Experimental evidence was presented to describe the mechanism of formation of porous polymer particles during the copolymerization and solvent extraction stages, in which porosity was a consequence of phase separation in the presence of diluents. Pore structure formation was investigated by changes in copolymerization kinetics, gel content, crosslinking density, particle morphology, surface area, pore volume, and pore size distribution. The process of copolymerization was presented, based on the concepts of production, agglomeration, and fixation of the interior gel microspheres of polymer particles. A portion of linear polymer used as diluent was found to participate in the network structure while the porous matrix was built-up. The influence of the removal of the linear polymer from the matrix pores during the solvent extraction process on the porous structure was also discussed.     

Plasma nanostructuring of porous polymer membranes

Several methods for membrane modification have been presented. Chemical modification of a neat polymer followed by membrane formation and modification of just formed membranes have been compared to plasma action. The following plasma modes are discussed in detail: treatment with non-polymerizable gases, treatment with vapors and plasma initiated grafting. Some examples of modified membrane properties are given. Finally, it was concluded that plasma treatment offers the fastest, environment friendly and versatile method that allows tailoring brand new membranes.     

Development of new sorbents: I. Ordered porous phase of titanium phosphate

A new phase of titanium phosphate with a highly organized porous framework has been synthesized by a non-thermal digestion method. FTIR, TGA-DTA, XRD and SEM have been employed to study the primary product, calcined and digested materials. Pore diameters in the range of 22–90 Å have been obtained for the digested material as determined by nitrogen absorption measurements. Quantitative removal of copper(II) phthalocyanine and its derivative from aqueous medium have been achieved.     

A desorption thermographic study of the nature of surface heterogeneity of catalysts and sorbents

Conclusions The type of surface heterogeneity of catalysts and sorbents may be determined by desorption thermography from the shift in position of an extreme desorption rate value relative to the extreme point on the differential thermal analysis curve.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1377–1379.     

Impact of water coadsorption for carbon dioxide capture in microporous polymer sorbents

Alcohol-containing polymer networks synthesized by Friedel-Crafts alkylation have surface areas of up to 1015 m(2)/g. Both racemic and chiral microporous binaphthol (BINOL) networks can be produced by a simple, one-step route. The BINOL networks show higher CO(2) capture capacities than their naphthol counterparts under idealized, dry conditions. In the presence of water vapor, however, these BINOL networks adsorb less CO(2) than more hydrophobic analogues, suggesting that idealized measurements may give a poor indication of performance under more realistic carbon capture conditions.     

Preparation of polymer based sorbents for solid phase extraction of polyphenolic compounds

This article discusses the preparation of different polymeric sorbents for solid phase extraction. Various monomers like acrylamide, methacrylic acid and 4-vinylpyridine (VP), cross-linkers such as divinylbenzene (DVB) and ethyleneglycoldimethacrylate (EDMA), porogens like tetrahydrofuran (THF) and dimethylsulphoxide (DMSO) / acetonitrile (ACN) with different ratios were investigated in order to optimize recoveries. Resulting polymers were characterized through scanning electron microscope (SEM) and compared with Oasis HLB (Waters, MA, USA) and Strata-X (Phenomenex, Torrance, USA) on the basis of extraction performance, recovery efficiency and loading capacity. Sample applied was a mixture of flavonoid standards (rutin, myricetin, luteolin, quercetin, apigenin and kaempferol). HPLC hyphenated with PDA was used for the analysis of samples. Results showed that among the prepared SPE materials, 4-VP-co-EDMA produced best results. Comparison of the produced polymers with of Oasis HLB and Strata-X resulted in comparable efficiencies; especially the polymer 4-VP-co-EDMA gave almost similar results for all analytes to those of commercially available SPE materials. A general trend of decrease in retention efficiency with increase in polarity has been observed in both synthesized and already available SPE materials. The newly synthesized polymeric materials can be employed as SPE sorbents for efficient extraction of polyphenolic compounds especially for flavonoid aglycons.     

Highly selective separations by capillary electrochromatography: molecular imprint polymer sorbents

Molecular imprint polymers (MIPs) are synthesized in the presence of a template, or 'imprint' molecule which results in the formation of specific recognition cavities complementary to the template in shape and chemical functionality. The resultant MIP then acts as a selective binding medium for the template molecule. The utility of MIPs lies in the selectivity of the rebinding process, which is based on molecular recognition. In many cases, the selectivity achieved with MIPs toward a particular molecule is comparable to that observed with antibodies. This has led to the application of MIPs to several areas of analytical chemistry including immunoassays, sensors and separations media. One of the most successful application areas of MIPs has been as chromatographic sorbents, where they have been utilized predominately in chiral separations. The use of MIP sorbents in CEC is attractive in that it combines the selectivity of a molecular recognition process with the enhanced flow dynamics of CEC, which can result in higher efficiency and shorter analysis times. This paper will review the use of molecular imprinted stationary phases in CEC. Following a brief introduction to molecular imprinting, various methodologies for preparation of MIP-CEC capillaries in addition to applications of the technique will be discussed.     

Sequential functionalization of porous coordination polymer crystals

Crystal extractor: Heterostructured porous coordination polymer crystals fabricated using epitaxial growth have two contradictory porous functions, namely size selectivity and high storage. The crystals not only extract linear petroleum molecules from a mixture with its branched isomer, even at very low concentrations of linear isomer (1?wt?%), but also shows improved accumulation of the molecules in its pores.     

Surface heterogeneity and contact angle hysteresis

The effect of surface heterogeneity on contact angle hysteresis is studied by using the model of Neumann and Good of a vertical plate with horizontal heterogeneous strips. The results of this study explain well known, but not understood patterns of contact angle behaviour: On the one hand, the advancing contact angle on a carefully prepared solid surface is generally reproducible; on the other hand, even a very small amount of surface heterogeneity may cause the receding contact angle to be less reproducible and to depend on several non-thermodynamic factors.     

Surface studies of polymer blends

An outlook of the literature concerning surface studies of polymer blends is given. Attention is focused on both theoretical and experimental aspects, with emphasis on the importance of sample preparation procedures.     

Surface tension of polymer solutions

Zusammenfassung Oberflächenspannung — Zeit-Kurven von Polystyrol-Cyclohexan und Polymethylmethacrylat-Heptanon-4-Lösungen in einem Temperaturbereich um die Theta-Temperatur wurden mit = exp (–Kt ⁿ) analysiert. Die GeschwindigkeitskonstantenK zeigen ein Maximum bei der Theta-Temperatur und die Exponentenn ein Minimum gleich 0.5, das zum Wert 1 beiderseits der Theta-Temperatur ansteigt. Das wird durch ein Maximum der Bindungsbeweglichkeit bei der Theta-Temperatur erklärt, welche ein kinetischer und kein thermodynamischer Punkt im Hinblick auf die Oberflächenspannung von Polymerlösungen ist.

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With 4 figures     

Surface tension of polymer solutions

Summary Heats of dilution and surface tensions of a polystyrene-cyclohexane solution have been measured in a wide temperature range covering the theta-temperature. Surface tensions as well as interaction parameters obtained from heats of dilution show no discontinuity at0. Concentration of polymer adsorbed on the surface has been calculated, it decreases with increasing temperature. Plots of interaction parameter vs.1/T give two straight lines which cut at the theta-temperature.

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Zusammenfassung Verdünnungswarmen and Oberflächenspannungen einer Polystyrol-Cyclohexan-Lösung wurden in einem großen Temperaturbereich gemessen, der die Thetatemperatur einschließt. Aus den Verdünnungswärmen wurden die Wechselwirkungsparameter berechnet. Sowohl Oberflächenspannung als such Wechselwirkung zeigen gegen die Temperatur aufgetragen keine Diskontinuität an der Thetatemperatur. Die Konzentration des an der Oberfläche adsorbierten Polymeren wurde berechnet, sic nimmt mit steigender Temperatur ab. Auftragungen des Wechselwirkungsparameters gegen die reziproke Temperatur ergeben zwei Gerade, die sich bei der Thetatemperatur schneiden.

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With 5 figures     

Molecularly imprinted CEC sorbents: investigations into polymer preparation and electrolyte composition

The influence of the sorbent preparation protocol and separation parameters on the selectivity and chromatographic efficiency of super-porous molecularly imprinted polymer (MIP) monoliths in capillary electrochromatography (CEC) was studied. Chiral templates were employed and enantiomer separation and resolution were used as measures of imprint selectivity and column efficiency, respectively; the latter was in addition studied by chromatography of non-related aromatic structures. The polymer preparation was varied with respect to monomer composition in the pre-polymerisation mixture and also the use of single versus multiple template(s). The separation parameters investigated were type and content of organic solvent and surfactant modifier in the electrolyte. It was found that acetone and acetonitrile in buffer mixtures provided enantiomer separation of enantiomers of the template and also structural analogues; however, the degree of separation was greatly influenced by the content in the electrolyte. Three surfactants, sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB) and polyoxyethylene sorbitanmonolaurate (Tween 20), were examined as electrolyte modifiers. It was found that addition of SDS decreased and CTAB and Tween 20 increased the enantiomer separation. SDS and CTAB could be used up to 1 mM concentration whereas Tween could be used up to 90 mM concentration without causing baseline disturbances. The effects found and demonstrated strongly suggest that these parameters are to be considered during optimisation of an MIP-CEC system.     

Surface oxides on porous carbon

Wet oxidation of BPL porous carbon by H₂O₂ and HNO₃ changes the pore structure and also increases the concentration of surface oxides. KOH uptake is increased by oxidation and is seen to be dependent on KOH concentration and to a lesser extent on inert electrolyte concentration. Enthalpy of immersion measurements have allowed the estimation of the enthalpy of hydration of the surface oxides and the enthalpy of neutralization of the easily accessible acid oxides.