M. P. Tsyurupa

Hypercrosslinked polymers: basic principle of preparing the new class of polymeric materials

Abstract Hypercrosslinked polystyrene networks have been recognised since the 1970s. They were prepared by extensive crosslinking of linear polystyrene chains in a strongly solvating media. Generally, the basic principle of obtaining hypercrosslinked polymers consists in the formation of a rigid highly solvated three-dimensional network. Owing to the high rigidity and reduced degree of chain entanglement, such “expanded” networks are characterized by loose chain packing, i.e., high free volume, and the unique ability to swell in both good solvents and non-solvents. In addition to the above polymer-analogues transformation of polystyrene, the article expands the synthesis techniques to polymerization and polycondensation procedures and also involves other types of polymers and monomers. Typical examples of preparing hypercrosslinked networks include the crosslinking of linear chains of polysulfone and polyarylates, copolymerization of styrene with a large amount of divinylbenzene, self-condensation of p -xylylene dichloride. All resulting materials differ substantially from classical polymers of the same chemical nature and comprise a new class of hypercrosslinked polymeric materials. Some polymers described in the literature were shown to also belong to the hypercrosslinked family.

Sorption of organic compounds from aqueous media by hypercrosslinked polystyrene sorbents ‘Styrosorbrs

Abstract Sorption experiments with a variety of organic compounds dissolved or suspended in water and a new hypercrosslinked polystyrene-type sorption material ‘Styrosorb’ (‘Macronet-Hypersol’) showed superiority of the latter to other chemically related adsorbents

Investigation of the properties of hypercrosslinked polystyrene as a stationary phase for high-performance liquid chromatography

SummaryThe mechanical rigidity, swelling properties, adsorption selectivity, and chromatographic performance of hypercrosslinked polystyrene (mainly MN-200 or Purosep-200; Purolite, UK) have been studied to evaluate the use of the material as a stationary phase for reversed-phase high-performance liquid chromatography (RPHPLC). By use of inverse size-exclusion chromatography (SEC) this adsorbent, with a high specific surface area of 1500 m2 g−1 was found to have a biporous structure with micropores of ca 1–2 nm and macropores ca 100 nm in diameter. The polymer does not change its volume significantly on changing water for organic solvents. The retention increments for methylene and phenyl groups were calculated and indicated that the mechanism of retention on the hypercrosslinked polystyrene involves π-π interactions and strong hydrophobic interactions. The column performance of the hypercrosslinked polystyrene was found to be acceptable, with reduced plate height increasing very slowly as the linear velocity of the mobile phase increased to high values (up to 20–45 cm min−1). Columns containing hypercrosslinked polystyrene were evaluated for the separation of phenols, dialkyl phthalates, and polyaromatic compounds. On-column preconcentration of trace organic compounds from aqueous media is possible. With smaller particles of hypercrosslinked polystyrene becoming available, this material can be regarded as an alternative to alkylsilica as a hydrolytically stable column-packing material for RPHPLC.

Hypercross-linked polystyrene and its potentials for liquid chromatography: a mini-review

Hypercross-linked polymeric adsorbing materials are obtained under conditions that (i) their polymeric network is formed in the presence of large amounts of a thermodynamically good solvent (porogen) and (ii) the network is rigid. Hypercross-linked polystyrene is a transparent microporous low-density material with an apparent inner surface area of over 1,000 m2/g and an unprecedented adsorption capacity. To enhance the mass transfer, the adsorbent beads may be provided with large transport pores, in addition to the inherent micropores; these beads are opaque. Hypercross-linked polystyrene sorbents are widely used for large scale adsorption of organic compounds from aqueous and gaseous media and for solid-phase extraction of trace components. Novel perspective application areas of the materials are high-performance liquid chromatography column packings and blood purification. Present mini-review summarises basic principles of obtaining hypercross-linked materials, their structural peculiarities and distinguishing properties, as well as major application areas. Important new unpublished data are also included.

Polymeric adsorbent for removing toxic proteins from blood of patients with kidney failure

A hypercrosslinked styrenic polymer with an enhanced proportion of mesopores in the range 2-20 nm has been developed. The principle of the synthesis consists of the suspension polymerization of divinylbenzene (or copolymerization of styrene with divinylbenzene) in the presence of a porogen that is a theta-solvent for polystyrene. On the scale of thermodynamic affinity, theta-solvents occupy a border position between good solvents and precipitating media for the growing polymer chains. In this case, microphase separation takes place during the final stages of the polymerization process. The polymer was shown to adsorb 93-98% of beta2-microglobulin from the blood or plasma of patients with chronic kidney failure. At the same time, large essential proteins, like albumin, are not removed to a significant extent, obviously, due to the size-exclusion effect and the difference in the hydrophobicity of the proteins. By replacing surface exposed pendant vinyl groups of the polymer with hydrophilic functional groups, the material was made hemocompatible, according to the standard battery of biocompatibility tests required by ISO 10993 guidelines. No adverse effects such as fever or hypotension were noted in dogs in direct hemoperfusion experiments with the polymer.

Use of the hyper-crosslinked polystyrene sorbents “Styrosorb” for solid phase extraction of phenols from water

The analytical HPLC procedure for the quantitation of trace amounts of phenol and chlorophenols in aqueous media has been supplemented with the on-line preconcentration of phenols in a sorption cartridge packed with microporous hyper-crosslinked polystyrene. The cartridge is coupled in succession with a reversed-phase analytical column, which is operated isocratically in an aqueous acetonitrile eluent (1:1, v/v). Phenol concentrations down to 0.5 μg/l can be detected using a simple 254 nm UV detector.Biporous hyper-crosslinked polystyrene-type sorbents were shown to effectively purify about 100 bed volumes of water from phenol under neutral or acidic conditions and linear flow rates up to 4 cm/min, which could be of great practical importance. Rapid and quantitative elution of sorbates from the hyper-crosslinked polystyrene materials is facilitated by the unique ability of the latter to additionally swell with organic or aqueous-organic eluents applied.

Hypercrosslinked polystyrene: A polymer in a non‐classical physical state

Deformation and relaxation properties of hypercrosslinked polystyrene networks have been studied by thermomechanical method at a uniaxial compression using individual spherical beads of the polymer. The networks examined were prepared by postcrosslinking of highly swollen beads of a styrene-0.3% DVB copolymer with 0.3–0.75 mole of monochlorodimethyl ether, which results in the introduction of 0.6–1.5 methylene bridges between each two polystyrene phenyl rings. The polymers obtained are shown to belong neither to typical glassy materials, nor to typical elastomers. Though no characteristic plateau of rubberlike elasticity was observed on the deformation curves of the beads, the polymers exhibit two fundamentally important features of the rubberlike state: The deformations are large (up to 30–40% of the initial diameter) and reversible. Relaxation of residual deformations, however, requires prolonged heating of the sample, or a cycle of swelling and drying. The deformation can start in the temperature range from −70 to +150°C depending on pressure applied. The crosslinking degree in the range from 40–100% and higher does not affect noticeably the behavior of the hypercrosslinked polystyrene. Nature of the high mobility of the hypercrosslinked network is discussed.

Unusual mobility of Hypercrosslinked polystyrene networks : Swelling and dilatometric studies

Hypercrosslinked polystyrene samples were prepared by an intensive post- crosslinking of highly swollen styrene- divinylbenzene copolymer beads to extremely high degrees of crosslinking that amounted to 100% or even higher. When in the dry state, the materials obtained represent transparent beads of reduced density. Despite the high degree of crosslinking, the materials manifest large increases in volume on swelling with any liquid media as well as large changes in volume on heating. The factors determining the unusual swelling ability of the hypercrosslinked polymers are briefly discussed. Thermodilatometric tests of the polymers with a moderate degree of crosslinking reveal a certain contraction of the beads at temperatures higher than 100 °C. When crosslinked far beyond 100%, the networks demonstrate unusual expansion in the 100 -220 °C range; this is followed by a sharp shrinking at higher temperatures. The former is caused by an increased intensity of the vibration movements of the network and a partial relaxation of strong inner stresses; the latter is due to partial chemical oxidation, degradation of network units, or both. This degradation, however, is not accompanied by any loss in weight of the polymer but only results in a transfor- mation into a more dense conventional nonporous material. The strained, rigid open- work structure of the homogeneous expanded hypercrosslinked polystyrene networks is responsible for their unusual mobility.

The next step from high-flux dialysis: Application of sorbent technology

The current foci of renal replacement therapy with dialysis are middle molecular weight toxins, consisting of small proteins, polypeptides and products of glycosylation and lipoxygenation. Conventional high-flux dialysis is not efficient at removing these molecules, explaining the increased interest in using sorbents to supplement dialysis techniques. Prototype biocompatible sorbents have been developed and investigated for middle molecule removal; these have been shown, in man, to remove β2-microglobulin, angiogenin, leptin, cytokines and other molecules, without reducing platelets and leukocytes. Extensive clinical studies are underway to demonstrate the clinical utility and safety of adding routinely a sorbent hemoperfusion device to hemodialysis.

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.