Z. K. Blinnikova

Hypercrosslinked Polystyrene: The First Nanoporous Polymeric Material

The principles of synthesis—the structural and distinctive features of hypercrosslinked polystyrene—are described. The material is obtained by intensely crosslinking the solvated polystyrene chains with rigid bridging spacers. The resulting single-phase open-worked elastic network can be considerably deformed upon swelling or the application of an external force. The huge free volume in the rigid hypercrosslinked network, which is essentially a porosity of a new type, is formed by interchain nanosized cavities (1.5–3 nm). The complete availability of the interior structure of hypercrosslinked polystyrene for low-molecular-weight compounds and the considerable uncompensated force field of polymer chains separated by spacers determines the excellent adsorption properties of the material. Several processes that are possible only due to the use of nanoporous hypercrosslinked polystyrene as a sorbent for chromatography or a matrix for preparing nanocomposites are briefly described in the paper.

Hypercrosslinked polystyrene networks with ultimate degrees of crosslinking and their sorption activity

Hypercrosslinked networks with 43, 100, 200, 300, 400, and 500% nominal crosslinking, respectively, were prepared by crosslinking the dichloroethane-swollen styrene copolymer with 0.5% divinylbenzene by Friedel-Crafts reaction using 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 mol of a bifunctional reagent (monochlorodimethyl ether), respectively. The dependences of the free (pore) volume of networks and their equilibrium swelling in water on the degree of crosslinking are extrema with the maximum parameters 0.63 cm3/g and 1.31 ml/g corresponding to the polymer with 300% crosslinking. The apparent specific surfaces of samples with 43–400% bridges are comparable, 1300–1500 m2/g. The ability of water-swollen hypercrosslinked polymers to extract synthetic organic dyes from aqueous solutions is independent of their specific surface measured for dry samples, but depends on the volume of absorbed water.

Thermodynamics of liquid-phase adsorption on hypercrosslinked polystyrene networks with ultimate degrees of crosslinking

ISSN 00125016, Doklady Physical Chemis try, 2015, Vol. 462, Part 2, pp. 135–139.

Physicochemical and adsorption properties of hypercross-linked polystyrene with ultimate cross-linking density

The paper describes unexpected properties of hypercross-linked polystyrenes with ultimate cross-linking degrees of 300, 400, and 500%, where three, four, or five methylene links, respectively, could bind each polystyrene phenyl ring to its spacious neighbors. The polymers exhibit a strong electron spin resonance signal, unusual spectra in IR, UV, and visible ranges, and they are not typical dielectrics. The nonfunctionalized hypercross-linked polymers absorb significant amounts of inorganic acids, salts, and bases due to interactions of protons or other cations with electron-donating fragments of the aromatic network with the high extent of mutual connectivity and also due to dispersion interactions of anions with the polymer matrix.

On the origin of absorbance band around 1700 cm−1 in FTIR spectra of hypercrosslinked polystyrene

This paper deals with some new arguments corroborating the absence of carbonyl moieties [1] in the chemical structure of hypercrosslinked polystyrenes in spite of the high intensity of the absorption band around 1700 cm−1 in their FTIR spectra. Three additional facts testify to the benefit of this conclusion. First is the appearance of the absorbance band at 1700 cm−1 in a computer-simulated IR spectrum of a rigid highly crosslinked model network that contains no C=O groups. Second, thermal degradation of the hypercrosslinked network with a formal 500% crosslinking density results in emergence in its mass-spectrum of benzene, alkylbenzenes and hydrogen chloride, only. Third, testing the above hypercrosslinked polystyrene as a stationary phase in a GC column shows the polymer to retain aliphatic hydrocarbons, alcohols and ketones largely by dispersion interactions, thus revealing no polar oxygen-containing groups on its surface.

Ion Size Exclusion Chromatohtaphy on Hypercrosslinked Polystyrene Sorbents as a Green Technology of Separating Mineral Elecyrolites

The review considers a new preparative method of separating concentrated solutions of mineral electrolytes into individual components by size exclusion chromatography on neutral nanoporous hypercrosslinked polystyrene sorbents NanoNets (Purolite International Ltd., UK and USA). Basic principles of the method as well as factors determining the selectivity of separations are discussed. Unprecedented effect of a spontaneous increase in the concentration of separated components is explained on the basis of the concept of ideal separation process. The unprompted partial resolution of inorganic salts into parent acids and bases is a logical consequence of the size exclusion mechanism of ion separation; at the same time, this resolution proves the correctness of our understanding of the separation mechanism. The review discusses briefly previous works in this field and true reasons for well-known “acid retardation” process, the process of separating mineral acids from their salts on anion exchange resins under conditions excluding ion exchange.

Selective adsorption of organic compounds from solutions on hyper-cross-linked polystyrenes with ultimate degrees of cross linking

The adsorption selectivities of a series of organic compounds from solutions on hyper-cross-linked polystyrene networks (HPNs) with ultimate degrees of cross linking were studied by high performance liquid chromatography (HPLC). The thermodynamic characteristics of adsorption (TCA) of substances under study from water–organic solutions on such HPNs in the Henry region were determined. The TCAs of organic compounds on the HPNs under study as a function of their molecular structures are discussed. It was established that the magnitude of the Gibbs energy change upon adsorption increases with increasing the number of π-electrons in the adsorbed molecules in a series of both aromatic hydrocarbons and their sulfurcontaining heterocyclic analogs. As an example, a model mixture of organic compounds was separated on HPNs by HPLC. It was shown that middle and heavy oil fractions can be fractionated on HPNs into the groups of mono-, di-, and tricyclic aromatic compounds.

NMR investigation of the porosity of hypercrosslinked polystyrene and the properties of water confined in its nanopores

The melting of water frozen preliminarily at 180 K in a free internal volume of water-swollen hypercrosslinked polystyrene networks with degrees of crosslinking ranging from 43 to 500% is studied by NMR. It is found that ice melts within a narrow range of low temperatures, 195–225 K, demonstrating that the pores in the networks are small and uniform in size. It is, however, impossible to calculate the pore size via the Gibbs-Thomson equation, since the structure of water (and hence its properties) depend on a sample’s rate of freezing. We conclude that the activation of the orientational motions of water molecules starts to manifest itself already at 200 K; upon reaching 220–230 K, the total mobility of water molecules is due largely to translational motions with an activation energy of 27–28 kJ/mol.

1H NMR cryoporosimetry of swollen hypercrosslinked polymers

The porous structure of two laboratory samples of hypercrosslinked polystyrene networks with a crosslinking degree of 200%, the commercial hypercrosslinked sorbent MN-270 (Purolite Int.), and macroporous polystyrene sorbents Amberlite XAD-4 and Amberlite XAD-1600 were investigated by means of 1H NMR cryoporosimetry. It was determined that the signal intensity of benzol, dioxane, dichloroethane and water protons previously frozen in polymer pores increases during solvent melt. Dependencies of the integral proton signal intensities on the sample temperature obtained in various solvents are discussed in terms of sample micropore accessibility and solvent—polystyrene interaction energy. Pore dimensions are estimated using the melting temperature value of ice according to the Gibbs—Thomson equation. We conclude that the obtained distribution curves reveal all hypercrosslinked polymers to be mainly microporous with diameter distribution maxima around 10 Å. It is shown that along with pores 120 Å in diameter, XAD-4 has a considerable amount of micropores. In contrast, XAD-1600 is ranged as a mesoporous sorbent.

A Selective Sorbent for Removing Bacterial Endotoxins from Blood

Synthetic ligands carrying a positive charge and capable of selective binding of bacterial endotoxins are covalently immobilized on surfaces of domestic hemosorbent Styrosorb-514 based on hypercrosslinked polystyrene. It is shown that the resulting sorbent aimed at treating sepsis exceeds imported specific hemosorbent in Toraymyxin™ columns in removing lipopolysaccharides, and can be used in domestically-produced Desepta columns.