Crosslinked Polystyrene Gels Research Articles

An unexpected reaction pathway in the synthesis of the ABCE framework of strychnine-type alkaloids – A multidisciplinary study

Acid-catalyzed cyclization of spirocyclic 1′-benzyl-2′-(prop-2-en-1-yl)spiro[indole-3,3′-pyrrolidine]-5′-one (1) was performed. The pentacyclic product of Povarov-like imino-Diels-Alder reaction was isolated in high yield instead of expected tetracyclic aza-Prins intermediate. The unusual exotic alkaloid-type structure of the resulting molecule 2 was unambiguously confirmed by a detailed NMR analysis using a set of 2D NMR spectra including an INADEQUATE experiment. The relative configuration of 2 was predicted from the synthesis mechanism and DFT geometry calculations and independently confirmed using NOESY and residual dipolar coupling (RDC) assisted NMR analysis in stretched crosslinked polystyrene gels. The reversibility of the cycloaddition in aprotic solvents was observed. A new reaction pathway yielding a rare 6-5-5-5 tetracyclic spiroindoline 3 was suggested. The relative configuration within the tetracyclic framework was ultimately proved using Single-crystal X-ray diffraction analysis of compound 4.

Adsorption Property and Chromatographic Affinity of Dye-Like Poly (Styrene Sodium Sulfonate) Sorbent toward Human Serum Albumin

Adsorption of proteins on various polymer surfaces plays an important role in different fields particularly in immobilization of enzymes and chromatographic processes for purification of biologically active compounds. On the basis of interactions of albumin with a multitude of endogenous and exogenous substances such as dyes, insoluble cross-linked polystyrene gel beads functionalized by sulfonate groups, the major chemical group of dyes was synthesized and its adsorption property and chromatographic affinity toward human serum albumin (HSA) was investigated in batch and by column respectively. The adsorption rate at interface was significantly high and the affinity constant evaluated by Langmuir model was in the order of 7.78 × 105 M−1. The affinity of HSA onto this adsorbent achieved in two pH ranges demonstrates that almost full albumin was adsorbed. The elution accomplished by using a continuous pH gradient allows substantially recovery in the range of 70–80% of the initial content.

Affinity adsorption of human vitamin K-dependent coagulation factor IX onto heparin-like poly (styrene sodium sulfonate) adsorbent

Adsorption of proteins on polymer material plays an important role in a number of fields, particularly in separation of biomolecules by chromatographic methods. The work reports here the synthesis of modified cross-linked polystyrene gel beads as a stationary phase in liquid chromatography for the purification of factor IX. Suitable chemical groups, such as sulfonate which confer this polymer heparin-like adsorbing property, were grafted on the aromatic ring of the hydrophobic matrix. This functional group was chosen on the basis of the biospecific molecular interactions between factor IX and its ligand particularly heparin in such manner to enhance its binding ability and efficacy. Adsorption of factor IX on to this functional polymer was performed under physiological conditions according two modes: non-competitive adsorption (adsorption of factor IX alone) and competitive adsorption (adsorption of factor IX in the presence of another vitamin-K dependent coagulation factors). The adsorbed factor IX content at the interface allows to establish the chemisorption isotherm curves. The adsorption rate in both cases was found to be significantly high and the affinity constants, estimated by the Langmuir model, were: 4.7 × 10 8 and 4.1 × 10 8 l/M respectively. Affinity chromatography on column using this functional polymer as a stationary phase confirms its high ability to adsorb factor IX at low ionic strength. Thus, the synthesized packing material gel functionalised by sulfonate group can be used advantageously as a heparin-like adsorbent in purification of factor IX.

Diffusional behavior of amino acids in solid-phase reaction field as studied by 1H pulsed-field-gradient spin-echo NMR method

The diffusion coefficients ( D) of tert-butyloxycarbonyl- l-phenylalanine (Boc-Phe) in Merrifield network polystyrene gels, used as a solid-phase reaction field have been determined as a function of the amino acid concentration over the temperature range from 30 to 50 °C by means of the 1H pulsed-field-gradient spin-echo NMR method. From these experimental results, it was found that the D value of Boc-Phe in DMF-d 7 solution, in DVB 1 and 2% cross-linked network polystyrene gels depends on the amino acid concentration. The D value of Boc-Phe·Cs( tert-butyloxycarbonyl- l-phenylalanine cesium) salt in the solid-phase reaction field under chemical reaction was determined at 50 °C. Further, it was found that the D value depends on the NMR observation time, that is the applied two field-gradient pulse interval. Details of its analysis were discussed.

Separation of Styrene - Methyl Methacrylate - Acrylonitrile Terpolymers by Composition Using High-Performance Liquid Chromatography

Separation of styrene - methyl methacrylate - acrylonitrile terpolymers by chemical composition was studied using high-performance liquid chromatography (HPLC). Cross-linked polyacrylamide (PAA) gel or polyacrylonitrile (PAN) gel was used as a stationary phase for normal-phase HPLC and cross-linked polystyrene (PS) gel for reversed-phase HPLC. Each system was based on a solvent gradient, and the separation was governed by an adsorption mechanism. Terpolymers were successfully separated by the cross-fractionation, i.e., the combination of two types of HPLC systems with PAN and PAA columns or PAN and PS columns. The chemical composition distribution (CCD) of a high-conversion terpolymer was analyzed by this cross-fractionation technique with the combination of PAA and PAN columns. The CCD obtained experimentally was reasonably consistent with that of theoretical calculation.

A Qualitative Analysis of Secondary Mechanisms in SEC of Polymers Through the Mean Value of the Viscosimetric Exponent

Size exclusion chromatography (SEC) universal calibration curves for poly(dimethylsiloxane), polybutadiene and poly(2-vinylpyridine) samples have been obtained in columns packed with cross-linked polystyrene gel using cyclohexane, toluene, benzene, dioxane and tetrahydrofuran as eluents at 25°C. The eluents exhibit different thermodynamic quality for the polymeric solutes and for the gel matrix which is reflected in the values of their Mark-Houwink-Sakurada exponents a. The plots of log(hydrodynamic volume) versus retention volume for the polymeric solutes in different eluents are displaced to higher retention volumes than that of THF-polybutadiene (ideal SEC), evidencing the existence of secondary mechanisms. This elution behavior could be qualitatively explained through the mean average value ā, but a quantitative analysis requires the knowledge of solute—solvent, solvent—gel, solute—gel and ternary interaction parameters.

Degradation of High Molecular Weight Polystyrenes During the SEC Separation Process, as Demonstrated by SEC Coupled with Lalls and by Static Light Scattering

In order to investigate the phenomenon of polymer degradation during the SEC separation process, we compared the weight-average molecular weights of a series of polystyrene (PS) samples with Mw going from 2.3×103 to 1.84×107, which were determined by static light scattering (LS) and by SEC-LALLS using various crosslinked PS gels. For all the gels considered, there was a good agreement between LS and SEC-LALLS values for Mw up to 2×106. For higher Mw, the values given by SEC-LALLS were lower than those given by LS; the decrease in Mw was different in various SEC columns. Since the same chromatographic equipment was used for all the SEC-LALLS measurements, we presumed that the decrease in Mw reflected the degree of shear degradation of PS molecules during their elution through the SEC columns. It depended on the origins of gels, the size of gel particles, the porosity of frits at column ends, the eluent flow rate, the usage of a pre-column filter, and of the third detector, a capillary viscometer.

Application of high-performance gel-permeation chromatography clean-up in the determination of hexaflumuron residues in soil

A high-performance gel-permeation chromatography (HPGPC) column (7.5 mm I.D.), packed with a divinylbenzene cross-linked polystyrene gel (10 μm particles and 5 nm pore size) was used to produce a simple, one-stage clean-up procedure for determination of the insecticide hexaflumuron in three typical agricultural soils. Conventionally, hexaflumuron extracts are purified by a series of time-consuming liquid-liquid partitions and solid-phase purification prior to high-performance liquid chromatography. HPGPC allows isolation of hexaflumuron from soil matrices with improved sensitivity in a shorter analysis time. The use of HPGPC methodology has been validated over the range 0.01–1.0 mg/kg with recoveries in the range 73–119% (mean 98%). HPGPC gave excellent separation of hexaflumuron from other extracted materials with significant reduction in clean-up time and solvent consumption. This methodology has been successfully applied to samples derived from field trials.

Molecular-weight estimation for native proteins using size-exclusion high-performance liquid chromatography.

AbstractThe chromatographic separation of proteins from small molecules on the basis of size was first described by Porath and Flodin, who called the process “gel filtration” (1). Moore applied a similar principle to the separation of polymers on crosslinked polystyrene gels in organic solvents, but named this “gel permeation chromatography” (2). Both terms came to be used by manufacturers of such supports for the separation of proteins, leading to some confusion. The name size-exclusion chromatography is more descriptive of the principle on which separation is based and has largely replaced the older names (3).KeywordsSolute MoleculeElution VolumeBlue DextranDihydrogen OrthophosphateHydrogen OrthophosphateThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

NMR characterization of crosslinked polystyrene gels

Application de la RMN MAS avec polarisation directe a l'etude de la structure de gels copolymeres du styrene avec le divinylbenzene ou le bis(vinylbenzyl) dimethylsilane, notamment pour l'observation directe des liaisons transversales. L'application possible a l'etude de la cinetique de copolymerisation-reticulation au voisinage du point de gel est discutee

Separation of Stereoisomers of Poly(methyl methacrylate) by High Performance Liquid Chromatography

Poly(methyl methacrylate) (PMMA) was separated by stereoisomerism using high performance liquid chromatography (HPLC). Using a cross-linked polyacrylonitrile gel as the stationary phase and a mixture of dichloromethane and n-hexane, ethyl ether, or benzene as the eluent, isotactic PMMA eluted faster than syndiotactic PMMA. With a cross-linked polystyrene gel and a mixture of dichloromethane and nitromethane, syndiotactic PMMA eluted earlier. With some eluent forming stereocomplex of PMMA after injecting a mixture of isotactic and syndiotactic polymers, the sample did not elute or eluted at a different elution time from that expected from an experiment of a separate injection. From the cloud point it was found that the separation was done by an adsorption mechanism rather than phase separation.

Coupled column chromatography for copolymer characterisation

AbstractCoupled column chromatography has been performed with two chromatographic systems in which fractions from a size exclusion column are injected into a second column where retention is determined by non‐exclusion mechanisms. This has been accomplished by directing the eluent from the first column system through the injection valve of the second column system. The first column system contained crosslinked polystyrene gel with the eluent tetrahydrofuran as good solvent. The second column system contained crosslinked polystyrene gel (or crosslinked polyacrylamide gel) with a mobile phase consisting of a solvent/non‐solvent mixture which is a poor solvent promoting non‐exclusion mechanisms for statistical copolymers of styrene and n‐butyl methacrylate. Separations dependent on copolymer composition as a function of the non‐solvent component in the mobile phase and the polarity of the stationary phase in the second column system have been accomplished by isocratic elutions.

Polymer-supported aminopyridinium salts as versatile catalysts for the synthesis of aryl fluorides

Immobilized N-alkylaminopyridinium salts on divinylbenzene cross-linked polystyrene gel was reusable at least 8 times on the reaction of 4-chloronitrobenzene with anhydrous potassium fluoride in tetrahydrothiophene 1,1-dioxide to give 4-fluoronitrobenzene in high yield. The immobilized catalyst was also successfully used for a synthesis of several aryl fluorides in good yields.

Size Exclusion Chromatography of Polyamides

Abstract We report here a new chromatographic method for characterization of polyamides and polyether-block-amide copolymers by Size Exclusion Chromatography. First, it concerns absolute characterization of polyamide probes by classical light scattering and Ubbelohde viscometry measurements and the choice of narrow distribution standards to calibrate the GPC system. The GPC analysis of polyamides 6, 11, 12 and copolymers is based upon the dual detection refractometer/on-line continuous viscometer at 130°C using columns packed with cross-linked polystyrene gels, benzyl alcohol as mobile phase and polytetrahydrofuran standards for calibration. The main results are absolute average molecular weights and distribution curve, intrinsic viscosity and viscosity law. In addition, viscometric data produced evidence of long-chain branching occuring beyond a limiting molecular weight in some polyamide 12 samples.

Asymmetric reduction of acetophenone O-methyloxime with the reagent prepared from borane and polymer-supported ( S)-(−)-2-amino-3-(4-hydroxyphenyl)-1,1-diphenylpropan-1-ol

Copolymerization of a new optically active amino alcohol monomer, ( S)-(−)-2-amino-1,1-diphenyl-3-[4-(4-vinylphenylmethoxy)phenyl]propan-1-ol ( 2), with styrene provided a linear copolymer (LC) containing 33 mol% of 2. The suspension copolymerization of 2 with styrene and divinylbenzene (DVB) provided crosslinked insoluble polymers (gel 2) containing 10 mol% of 2 which swelled in THF. Another polystyrene-supported chiral amino alcohol (gel 1) was also prepared from chloromethylated 2% crosslinked polystyrene gel and ( S)-(−)-2-amino-3-(4-hydroxy)-1,1-diphenylpropan-1-ol ( 1). Addition of borane to the polymer-supported optically active amino alcohols gave the polymeric chiral reducing agents. Acetophenone O-methyloxime was reduced asymmetrically with the polymer reagent prepared from well swollen gel 2 at room temperature to yield the optically active 1-phenylethylamine in very high enantioselectivity (∼99% ee).

Dynamic processes in polymeric networks as studied by NMR relaxation methods

By means of NMR pulse methods molecular motions of polymer subchains in crosslinked polystyrene gels are studied. The temperature dependence of the effective transverse relaxation timeT2 eff is explained by a local reorientation process. The local configuration of the elastic chains of the network is shown to be mainly determined by polymer-solvent interaction. The results are compared with those of concentrated solutions. The influence of static-like contributions to the 2nd moments is discussed.

Scaling analysis of mechanical and swelling properties of random polystyrene networks

The equilibrium swelling and shear moduli at swelling equilibrium of randomly cross-linked polystyrene gels have been determined in the excluded-volume limit (good solvent conditions), at the e temperature, and in intermediate regimes (below and above the 8 temperature). The results have been compared with data obtained by small-angle neutron scattering and quasi-elastic light-scattering measurements on the same gels and discussed by using current analogies between gels and semidilute solutions. An attempt has been made to correlate both macroscopic and molecular behavior in terms of a fundamental thermodynamic correlation length t,, the range of the monomer-monomer pair correlation function. Power law behavior for moduli and diffusion coefficients similar to that which has been reported for semidilute solutions was found in some cases, but departures from simple scaling behavior were also evident. Some of these discrepancies have tentatively been attributed to an increasingly loose structure in the gels as the cross-linking density decreases.

Determination of correlation lengths in swollen polymer networks by small-angle neutron scattering

The analogy between semidilute polymer solutions and swollen polymer networks is reviewed and some implications of current theories are considered. Small-angle neutron scattering has been used to measure a characteristic correlation length in randomly cross-linked polystyrene gels at swelling equilibrium in cyclohexane over the range 308-333 K and in toluene at ambient temperature. The equilibrium polymer volume fraction ranged from ca. 0.01 to 0.3, depending on the cross-link density and the solvent used. These results, together with those from earlier quasi-elastic light scattering measurements, were compared with reported scaling laws for polymer solutions. Although similar behavior was noted, the presence of permanent cross-links restricts the region wherein strong excluded volume effects are evident.

Motional restrictions and chain conformation in various swollen crosslinked polystyrene gels from 1H n.m.r. line-shape analysis

1H high resolution (HR), broad-line (BL) and magic-angle rotation n.m.r. spectra of polystyrene crosslinked with 2–10 mol% divinylbenzene or ethylene dimethacrylate, swollen to equilibrium in CCI 4, CDCI 3 and benzene, were measured. The spectra were analysed as a folding of a narrow line-shape function approximated by the MAR n.m.r. spectrum, and an orientation-dependent dipolar broadening function. A molecular interpretation of the parameters obtained is presented. From MAR n.m.r. spectra, the rate of conformational transition depends on solvent, temperature and degree of crosslinking, but it remains very rapid even at 10% crosslinking. The second moment of the dipolar broadening function depends on the degree of crosslinking and is almost independent of temperature and solvent. The linear dependence of the dipolar broadening parameter on degree of crosslinking indicates that, in gels swollen to equilibrium, the statistical-average conformation of inter-crosslink chains is independent of their length, and is equal to that of linear polystyrene chains in dilute solution.

Gel permeation chromatographic analyses of resole phenolic resins

AbstractTetrahydrofuran solutions of resole polymers were analyzed by gel permeation chromatography (GPC) on crosslinked polystyrene gel packings. The best separation was obtained with low solvent flow rates in low porosity columns. Irregular elution volumes were observed, but the effects of this erratic behavior can be eliminated by referencing retention times to that of a marker compound such as benzene or phenol. A calibration and data analysis method are presented which utilizes hydrodynamic volumes. Phenolic polymers vary in shape and ability to form hydrogen bonds with solvent; hence their molecular weights cannot be estimated from GPC data. Separation of the constituent species of resole samples is shown to be incomplete, because of aggregation between the various phenol derivatives. Particular peaks in the GPC chromatogram could generally not be assigned to individual species. Despite these limitations, GPC is a useful tool for charcterizing phenolics, and several applications are reviewed here.