Influence of operational parameters on retention of ultra-high molecular weight polystyrenes in thermal field-flow fractionation

Summary The influence of various parameters (concentration of the injected polymer solution, flow rate, temperature gradient, relaxation conditions) on the retention and shape of the fractogram of ultra-high molecular weight polystyrenes in thermal field-flow fractionation was investigated. Under the operating conditions adopted, reproducible oscillations in the peak shape are observed for molecular weights larger than a few millions, especially at relatively high polymer concentration. They are attributed to some hydrodynamic instabilities. The retention of ultra-high molecular weight polystyrenes at high flow rate is strongly dependent on the initial relaxation period. All of the investigated operational variables have a complex effect on the resulting shape of the fractogram. Consequently, the confirmation of the shear-induced focusing of macromolecules across the channel thickness requires further study. Experiments on reinjection of fractions collected after an initial high speed pass through the separation system leads to the conclusion that shear degradation of the ultra-high molecular weight polymers did not occur under the investigated experimental conditions even at the highest flow rates.     

Concerning the acidity and hydrogen bonding of hydroxyphenanthroperylene quinones like fringelite D,hypericin, and stentorin

Summary The strongly enhanced acidity of the bay hydroxyl group as compared to the respectiveperi hydroxyl groups of fringelite D, hypericin, and stentorin could be rationalized on the basis of a vinylogous carboxylic acid and was nicely corroborated by semiempirical calculations of the AM1 type. Experimental data obtained from several independent experimental methods, like polarized absorption spectroscopy, hole burning, and isotope effects, as well as from semiempirical AM1 and 6–31G levelab initio calculations conclusively pointed to dissymmetrical hydrogen bonding systems in both theperi andbay regions of the correspondingbay phenolate ions.

---

Zu Acidität und Wasserstoffbrückenbindung von Hydroxyphenanthroperylenchinonen wie Fringelit D, Hypericin und Stentorin

Zusammenfassung Die stark erhöhte Acidität der bay-Hydroxylgruppen gegenüber jener derperi-Hydroxylgruppen von Fringelit D, Hypericin und Stentorin läßt sich auf der Basis einer vinylogen Carbonsäure verstehen und wurde auch durch semiempirische Rechnungen vom AM1-Typ erhärtet. Daten aus unabhängigen Experimenten wie Polarisationsspektroskopie, Lochbrennen und Isotopeneffekte sowie semiempirische AM1- undab initio-Rechnungen auf 6–31G Niveau belegen ein unsymmetrisches Wasserstoffbrückenbindungssystem sowohl für denperi-als auch denbay-Bereich der entsprechendenbay-Phenolationen.

     

Copolymerization of ethylene and 1-butene with highly active Ticl4/THF/Mgcl2, Ticl4/THF/Mgcl2/SiO2, and TiCl3.1/3AlCl3 catalysts

Highly active catalysts for copolymerization have been prepared by the precipitation of MgCl₂/ToCl₄ complex with or without high surface area silica. Copolymerization of ethylene and 1-butene has been tested by using the prepared catalysts at various concentrations of 1-butene. The catalytic activities are 20–80 kg/g Ti h. The rate of copolymerization is strongly affected by the addition of 1-butene. The decay rate of copolymerization is first order with respect to time. Analyses of copolymers with solvent extraction, DSC, IR, XRD, and NMR were performed. Ethylene reactivity ratio (k₁₁) for TiCl₄/MgCl₂/THF catalyst is calculated to be about 26 by NMR spectrum. © 1994 John Wiley & Sons, Inc.     

Self-consistent-field – Hartree–Fock method with finite nuclear mass corrections

We have upgraded a Self-consistent-field – Hartree–Fock routine to include a finite nuclear mass correction for molecules developed in our laboratory. The new routine can handle isotopomers without calculating any nuclear kinetic energy matrix element. Tests on H₂, LiH, HF, F₂, and H₂O isotopomers indicate the equivalence of our correction to the standard diagonal adiabatic correction. A further original application to C₂H₆ illustrates the usefulness of the method for polyatomic molecules. The resulting molecular orbitals carry the nuclear mass signature, exemplified with Koopmans ionization potentials.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

On the morphology of polystyrene fractions,obtained by a multistep procedure from a radically polymerized sample

Summary A polystyrene sample obtained by free radical polymerization has been fractionated by preparative scale GPC and the structure and morphology of the fractions have been studied by¹³C-NMR spectroscopy, DSC and X-ray measurements. No changes in morphology in the course of fractionation have been obeyed. A distribution of syndiotacticity within the molecular weight distribution does not exist.

---

Zusammenfassung Eine Polystyrolprobe, die durch radikalische Polymerisation hergestellt wurde, wurde mit Hilfe der präparativen Gelpermeationschromatographie fraktioniert; die Struktur und Morphologie der Fraktionen wurde mit¹³C-NMR-Spektroskopie, DSC und Röntgenbeugung untersucht. Im Verlauf der Fraktionierung traten keine Änderungen der Morphologie der Fraktionen auf. Innerhalb der Molekulargewichtsverteilung existiert keine Verteilung der Syndiotaktizität.

---

List of abbrevations and symbols AIBN a, a-Azo-bis-(iso-butyronitrile) - D Dispersity, M _w /M _n - DSC Differential scanning calorimetry - EF Efficiency of fractionation - GPC Gel permeation chromatography - m mass of the fraction - M mass of the fractionated polymer sample - MWD Molecular weight distribution - P _r content of racemic dyads - PS Polystyrene - THF Tetrahydrofuran - U D-1 - U _ss U of the starting sample - U _f U of the fraction Auszug aus der Dissertation von U.-D. Standt: Zur Morphologie von Polystyrol, TU Braunschweig 1981.     

Molecular fractionation in isotactic polypropylene during isothermal crystallization

The nucleation frequency of isotactic polypropylene shows for certain molecular weight distributions during isothermal crystallization a “stepwise” development of the nuclei as a function of time. The resulting curve can be fitted by a superposition of exponential functions assuming a separate nucleation density for each nucleation step. The multimodal nucleation is discussed as a consequence of molecular fractionation effects during crystallization. Received: 23 October 1997 Accepted: 12 May 1998     

Isotope‐Coded Affinity Tagging Technique Using Avidin Functional Affinity Electrophoresis: An Alternative to an Avidin Affinity Column

Avidin functional affinity electrophoresis (AFAEP) is substituted for an avidin affinity column (AAC) to capture biotinylated peptides in the Isotope‐Coded Affinity Tagging (ICAT) technique which is a valuable tool in quantitative proteomics. In this new technique, the AFAEP‐captured ICAT‐labeled biotinylated peptides are extracted with the biotin tag intact from the polyacrylamide gel piece with aqueous 95% formamide (pH 8.2) at 65 °C for 20 min, and then detected by a matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometer. Bovine serum albumin (BSA) and the ¹²C‐ and ¹³C‐ICAT reagents are used to test this AFAEP‐ICAT technique. The results show that both AFAEP and AAC methods provide quantitative information of the relative amounts of ¹²C‐ and ¹³C‐ICAT‐labeled biotinylated tryptic peptides of BSA in a sample. Compared with AAC, the AFAEP is cheaper to perform, more stringent in capturing the biotinylated peptides, and capable of simultaneously processing multiple samples.     

Elution behavior of styrene oligomer fractions in supercritical fluid chromatography

Summary In supercritical fluid chromatography (SFC), the elution behavior of styrene oligomers in pentane depends greatly on the degree of oligomerization, n. The influence of capacity ratio, k, on the lower oligomers up to about n=11 resembles the behavior of other substrates of low molecular weight, like aromatic hydrocarbons. Thus, with pentane of 100 bar and below, minima are found in plots of k versus temperature. In contrast, the k of oligomers of higher molecular weight (n>11) increase monotonously with increasing temperature. The studies were performed using oligostyrene fractions obtained by semipreparative SFC fractionation.     

Concentration and characterization of dilute colloidal samples by potential-barrier field-flow fractionation

Summary Potential-barrier field-flow fractionation, which is a combination of potential-barrier chromatography and sedimentation field-flow fractionation, is shown to be a convenient and accurate method for the concentration and analysis (separation and characterization) ofdilute colloidal samples. Two sizes (0.158 and 0.271 μm) of haematite (α-Fe₂O₃) monodisperse colloidal samples diluted in volumes of up to 20 cm³ are used as model colloids. The particle diameters found by the present concentration procedure under various experimental conditions are in good agreement with those determined by conventional sedimentation field-flow fractionation, in which a small concentrated sample volume was injected directly into the column.     

Trace lead measurement and on-line removal of matrix interference in seawater by isotope dilution coupled with flow injection and ICP-MS

Isotope dilution analysis method coupled with flow injection and inductively coupled plasma mass spectrometry (ID-FI-ICP-MS), enabled trace lead concentration in seawater to be determined and the high salt concentration in the matrix, such as Na⁺, Ca²⁺ and Mg²⁺, to be removed on-line. The operational parameters of the FI system including pH for the chelating reaction, concentration of 8-hydroxyquinoline-5-sulfonic acid (8-HQS), sample loading time and injection speed, washing time and speed, eluting acid concentration and eluting speed, and instrumental parameters for ICP-MS were optimized and selected. Accurate results could be achieved because the isotope ratios required can be precisely measured in the range of the eluting peak by means of ID-FI-ICP-MS. The 3σ detection limit was 0.204 ng ml⁻¹. The trace lead concentration of seawater in south Xiamen, China was 0.988 ± 0.039 ng ml⁻¹. The recoveries of spiked Pb standard in seawater and standard reference water (GBW 08607) were 97.9 and 101.0%, respectively, with a relative standard deviation of 0.98%. This method can be used to determine trace lead concentration in high salt matrix samples, and is especially useful when the eluting peaks do not have a Gaussian-distribution.