Gel permeation chromatography of polyoxymethylene

Gel permeation chromatography of polyoxymethylene has been studied using N,N-dimethylformamide as the solvent. Polyoxymethylene samples used here are a copolymer of tetraoxane with 1,3-dioxolane and a commercial polyoxymethylene whose molecular weight distributions are moderately broad. Their intrinsic viscosities [η] range from 1.4 to 2.8 dl/g. Factors affecting chromatograms are discussed, and the operating conditions were determined by using the analytical scale GPC. On the basis of these operating conditions, the molecular weight fractionation of polyoxymethylene was carried out by using the preparative scale GPC. It was found that polyoxymethylene can be effectively fractionated to give seven to ten fractions each of them containing the fractionated polymer ranging in weight from 0.2 to 8 mg when 40 mg polymer sample was used for a run of the measurement. The fractionated polymers were also found to have a narrow molecular weight distribution within a single peak, and their M_w/M_n values decrease with increasing molecular weight.     

Gel permeation chromatography using controlled-porosity glass. I. Polyacrylamide–formamide solution

The process of characterizing polyacrylamide and its partially hydrolyzed materials by gel permeation chromatography was examined. The use of controlled-porosity glass and formamide as the stationary phase and the eluent, respectively, resulted in chromatographic behavior in accord with the hydrodynamic volume concept for polyacrylamide fractions. The addition of a salt (KCl) to the eluent was found to retard the elution of the hydrolyzed polyacrylamide.     

Gel permeation chromatography of heated fats

The high and low molecular weight components of heated fats have been separated with gel permeation chromatography. With Sephadex LH-20, as well as with Biobeads SX-1, the high molecular weight components of heated fats may be directly separated when chloroform, acetone, chloroform-methanol or tetrahydrofuran are employed as swelling agents and eluting solvents. Presented at the AOCS Meeting, Ottawa, September 1972.     

Gel permeation chromatography of poly(dimethyl siloxane). I. The universal calibration

The Benoit universal calibration method has been tested for evaluation of GPC data of polydimethylsiloxane (PDMS) in toluene at 60°C. For the conversion of the calibration curve for polystyrene to the PDMS calibration curve, the Mark–Houwink equation for PDMS in toluene at 60°C was derived: [η] = 9.77 × 10^?5 M^0.725. The applicability of this universal calibration was proved by the experimental results on five PDMS model samples. For the correct evaluation of the PDMS elution curve, the use of the true calibration is inevitable, because the hydrodynamic volume of PDMS molecular weight unit is somewhat different from the polystyrene one.     

Gel permeation chromatography on branched polymers

In gel permeation chromatography on long-chain branched polymers, calibration with linear samples leads to incorrect results. There are, however, several ways in which the data can be treated correctly. All of them call for the use of extra experimental information, such as viscosity or light scattering data of the whole polymer or the GPC eluent. The Drott—Mendelson method, using [η] of the whole polymer and GPC data, has been employed for analysing three low density polyethylene samples. The potentialities of viscometry and light-scattering measurements in the GPC effluent have also been examined. From [η], M_w and GPC data the long-chain branching index g′ can be derived in three ways, although it should be stated that the average g′-values so found for polydisperse samples are different.     

Gel permeation chromatography: Differential operation

Operation of gel permeation chromatographs in the differential mode provides a sensitive method for detecting small differences in molecular weight distribution between similar samples. The solvent used in this case is a dilute solution of the reference polymer in an organic solvent. This solution is used in both the reference and the separation column. Samples of the material to be compared are injected in the normal manner. Only differences between the samples are reflected in the resulting chromatogram. For process control, this offers a simplified data presentation and should lead to easier detection of changes in operating conditions.     

Calibration procedures in gel permeation chromatography

Procedures for the determination of the log molecular weight vs. elution volume calibration relation are reviewed for linear homopolymers. The calibration curve is readily established with narrow molecular weight distribution fractions. For broad molecular weight distribution fractions the peak molecular weight at the peak elution volume of a fraction's gel permeation chromatogram has to be calculated from average molecular weights. When well-characterised fractions of the polymer requiring analysis are unavailable, a calibration curve can be established by procedures which assume that the hydrodynamic volume of a polymer molecule in solution controls fractionation in gel permeation chromatography. These universal calibration procedures require information on Mark-Houwink viscosity constants or polymer unperturbed dimensions. The validity of hydrodynamic volume as the universal calibration parameter is discussed with special reference to the goodness of the solvent for a polymer and polymer polarity. Examples are given of the various calibration procedures which are employed in the determination of molecular weight distribution and average molecular weights for poly(methylmethacrylate), polyethylene and polyisoprene.     

Fractionation of linear polyethylene with gel permeation chromatography. IV

Reproducibility was examined on the GPC fractionation of linear polyethylenes. The experiences over the period of two and a half years were used. Calibration was done with the same batches of narrow distribution polystyrene standards. A control sample of broad-distribution polyethylene was run at each calibration. The reproducibility over ten calibrations with this control was in terms of standard deviation of ca. ±10% for the number-average and ca. ±15% for the weight-average chain length. The fractionation data of 36 commercial resins were corrected by using the control samples as an additional standard. The correction was very effective in decreasing the scattering of the data in the intrinsic viscosity–molecular weight plot, especially when the viscosity average was used for the molecular weight expression.     

Gel permeation chromatography of vegetable-oil-based printing ink vehicles

The apparent weight-average molecular weights (M_w ) of ink vehicles made from soybean, safflower, sunflower, cottonseed, and canola oils were compared by gel permeation chromatography (GPC), and the correlation between viscosity and M_w of these vehicles was established. Apparent M_w of vegetable oil gels that were used in vehicle preparation were also obtained by GPC. © 1992 John Wiley & Sons, Inc.     

Preparative gel permeation chromatography. I. Polypropylene

Preparative gel permeation chromatography was used to produce a number of polypropylene reference samples, within the molecular weight range of 10,000–600,000, from commercial materials. Some of these materials were degraded in a controlled manner to give base materials having suitable molecular weight characteristics. A procedure has been developed using a single preparative column packed with equal quantities of Styragel with nominal exclusion limits of 10², 10³, 10⁴, and 10⁵ nm. The volume of solvent for recovery was minimized by use of higher loading factors than in analytical GPC (some 2–20 times more polymer was thus fractionated in each experiment). Under these conditions the fractions first eluted were sharpest having polydispersities of about 1.5. First fractions, from different base materials, were characterized by analytical GPC, and those of similar molecular weight and polydispersity were combined to give the reference samples. Refractionation was necessary with the highest molecular weight base material because the first stage fractions were not sharp enough. Some of these fractions were recovered at elution volumes where much lower molecular weight material was expected. Comparison with results from the other base materials indicates that the primary cause of the spreading is not overloading. This spreading is explained in terms of slower partitioning of the larger molecules between the interstitial fluid and the gel particles.     

Gel permeation chromatography for characterization of graft copolymer

Summary The present paper describes the grafting of vinyl monomers onto cellulose nitrate in non-aqueous medium using benzoyl peroxide as a catalyst. The complete separation of the homopolymers and graft copolymer was carried out by selective solvent extraction. The graft copolymer was characterized by IR spectra. The GPC was used as a technique to differentiate between homopolymer, polymer mixture, polyblend, and graft copolymer.     

Studies in the molecular weight distribution of epoxide resins. I. Gel permeation chromatography of epoxide resins

The molecular weight distributions as measured by gel permeation chromatography of solid epoxide resins made by the direct addition of epichlorohydrin to bisphenol A (the “taffy” process) and by the reaction of low molecular weight liquid epoxide resins whose main constituent is the diglycidyl ether of bisphenol A with bisphenol A (the “advancement” process) have been compared with the theoretical distribution calculated by the application of Flory statistics. The model used for predicting the molecular weight distribution has been shown to be too simple to describe the real size distribution of these resins. For resins prepared by the “taffy” process, incompleteness of reaction, the presence of monofunctional epoxides, and the possibility of branching reactions through the epoxide–hydroxyl reaction lead to a distribution that more nearly resembles one calculated for a resin having a higher epoxide value than that actually measured. In the case of resins prepared by the “advancement” process, the presence of small amounts of the higher oligomeric diepoxides and monofunctional epoxides in the starting material used for the synthesis lead to complex molecular weight distributions that are not easy to deduce theoretically. The experimentally determined molecular weight distributions for the higher molecular weight epoxide resins (epoxide value <2 eq/kg) made by the “advancement” process resemble more nearly those calculated for resins having lower epoxide values than those actually measured.     

Gel permeation chromatography calibration based on fractal geometry

The previously developed model [Polym Bull 2000, 44, 525] used to characterize the porous gel inside a gel permeation chromatography (GPC) column, has been extended to also include the interstitial space between the macroscopic gel particles. The hydrodynamic dimensions for 12 polystyrene (PS) standards, measured by GPC with differential refractive index (DRI), differential viscometry (VISCO), and multiangle laser light scattering (MALLS) detectors, have been used to determine the fractal parameters of the polystyrene–divinylbenzene gel corresponding to four commercial columns. The new developed model enables to predict the calibration curve for the sets of coupled columns based on the parameters of each column. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 771–777, 2004     

Gel permeation chromatography using controlled-porosity glass. II. Polyacrylamide aqueous solutions

In a study of polyacrylamide in solutions we have required the rapid characterization on chromatographies. The application to the aqueous solution of the GPC using controlled-porosity glass has been examined from both the viewpoint of the effect of salt addition and the GPC mechanism. An adequate addition to neutral salt, 0.005M KCI to the eluent, gave rise to the elution behaviors being in accord with the hydrodynamic volume concept of the GPC separation.     

Gel permeation chromatography of high molecular weight cellulose trinitrate

Gel permeation chromatography measurements have been made upon cellulose trinitrate in ethyl acetate using samples which have already been well characterized by light scattering and osmometry. Columns were calibrated using polystyrene standards and it has been shown that the hydrodynamic volume calibration applies to cellulose trinitrate provided that all the data are extrapolated to zero concentration. It has also been shown that the resolution of the columns (as measured by the rate of change with count of logarithm of intrinsic viscosity), and the deviation from the true value of the apparent hydrodynamic volume at any given concentration depends only upon the relative viscosity of the sample. The validity of the hydrodynamic volume calibration does not necessarily mean that both polymers are fractionated solely by an exclusion process. It is possible that both react reversibly with the gel, and that there are compensatory hydrodynamic effects.     

Gel permeation chromatography of starch and other uncharged polysaccharides

Summary The experimental results given in this paper concern the gel permeation chromatography of starch and other uncharged polysaccharides (dextrans, levan, scleroglucan,...) in organic solvent. The experimental conditions (solvent, columns) are proposed to get after direct solubilization the molecular weight distribution of the polymers using a refractometric and a light scattering detectors on line.Laboratoire Propre du CNRS associé à l'Université Scientifique et Medicale de Grenoble