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 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.     

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 chromatographic analyses of resole phenolic resins

Tetrahydrofuran 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.     

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.     

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 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     

Studies in the molecular weight distribution of epoxide resins. III. Gel permeation chromatography of epoxide resins subject to postglycidylation

Unambiguous evidence has been provided for the existence of a branched structure in liquid epoxide resins which have been subjected to postepoxidation with excess epichlorohydrin in the presence of a powerful nucleophilic catalyst, tetramethylammonium chloride. Gel chromatography of the resin on Sephadex LH-20 followed by isolation and identification of the relevant fraction by spectroscopic techniques revealed the presence of a novel trifunctional epoxide having a molecular weight of 680.     

Gel permeation chromatography: Dispersion effects on molecular weight monitor-installed gel permeation chromatograph

Computer simulation was carried out to examine the performance of a molecular weight (MW) monitor-installed gel permeation chromatograph (GPC), by taking account of the effects of limited column resolution according to Tung's phenomenological scheme. Efficiency of GPC fractionation was discussed also in the same light. For simulated GPC fractionation results of model polymers having log-normal distribution, various average MW's and MWD functions were calculated from the data obtained by the MW monitor method as well as the conventional MW calibration methods, and compared with the given true values. The MW monitor method generally tends to predict narrower distributions than the true ones, as opposed to the conventional calibration methods which usually predict broader distributions. For certain simple cases, semiquantitative relation between the extent of column resolution and these deduced average MW's was derived. The efficiency of GPC fractionation (as judged, for example, by the polydispersity of recovered fractions) is limited by such factors as fraction size, column resolution, and polydispersity of the original sample itself.     

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     

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.     

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.     

A study of urea-formaldehyde resins using gel permeation chromatography

Gel permeation chromatography is a powerful technique for the investigation of molecular weight distributions of UF resins. Combinations of aqueous solvents with hydrophilic gels, or of organic solvents with organophilic gels, can be used to follow urea-formaldehyde reactions and also to analyse the condensates obtained. Useful additional information is obtainable by analysing a given material on several different gels of the same type but having different exclusion limits. Recent work has indicated that g.p.c. gels based on vinyl acetate can give excellent resolution of low molecular weight species in UF resins.     

An investigation of novolac resins by gel permeation chromatography

In the preparation of novolac resins, three possible dimers with slightly different molecular dimensions may be produced in the polymerisation reaction. Gel permeation studies were carried out on four novolac resins prepared using different acid catalysts, and the results indicated that the nature of the catalyst influences the type and quantity of dimer produced. The weight and number average molecular weights were also calculated from the chromatograms obtained.     

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.