Characterization of polyethylene terephthalate by gel permeation chromatography (GPC)

The use of the solvent mixture chloroform/hexafluoroisopropanol (98 : 2 vol %) in the GPC-analysis of polyethylene terephthalate (PET) is described. PET-samples of different molecular weight have been prepared and characterized by light scattering, viscometry, and improved techniques of osmometry and end group titration. These well characterized samples were used in calibrating the GPC. The calibration with polydisperse standards was found superior to the universal calibration procedure in the solvent system chosen.     

Polymer studies by gel permeation chromatography

Samples of polystyrene and poly(methyl methacrylate) have been prepared by bulk polymerization under conditions previously investigated in the literature. The molecular weight distributions were determined for early-conversion samples by gel permeation chromatography, and the experimental distribution curves were compared with calculated curves based on kinetic data. The agreement between the experimental and calculated curves was such as to indicate the utility of gel permeation chromatography in the investigation of polymer reaction kinetics and mechanisms.     

Characterization of the extremely high molecular mass polystyrene by gel permeation chromatography

Summary The extremely high mol. mass (EHMM) polystyrene (PS) samples prepared by emulsion polymerization with an initiator forming heterogeneous phase were characterized by gel permeation chromatography (GPC). A bicomponent eluent methyl ethyl ketone (MEK) and methanol (McOH) in a ratio slightly different from the composition of theta solvent for PS was applied in GPC measurements. The GPC apparatus was calibrated with a series of PS reference materials. The course of calibration curves in the EHMM region was mathematically or graphically simulated by the third and second degree polynomial respectively. Correction of GPC data for the broadening effect was made mathematically by solving the Tung integral equation by the iterative method ofChang andHuang. The values of the EHMM PS samples varied between 1.07 × 10⁷ and (>4 × 10⁷). The values of were higher than 1.5. Besides distribution analysis by GPC also light scattering (LS) was used for measurement of of EHMM PS samples and a sample was partially characterized also by the method of sedimentation in ultracentrifuge (UC).

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Zusammenfassung Polystyrol-Proben mit extrem hohen Molekulargewichten (EHMM-PS) wurden durch Emulsions-Polymerisation mit einem eine heterogene Phase bildenden Initiator hergestellt. Sie wurden mittels GPC charakterisiert unter Verwendung einer MEK-MeOH-Mischung, deren Zusammensetzung etwas vom -Lösungsmittel abweicht. Die Eichung erfolgte mit mehreren Referenz-Polystyrolen. Der Verlauf der Kalibrierungs-Kurven im EHMM-PS-Bereich wurde mathematisch oder graphisch unter Zugrundelegung eines Polynoms 2. und 3. Grades simuliert. Die GPC-Daten wurden unter Berücksichtigung des Verbreiterungs-Effektes unter Verwendung von in der Literatur angegebenen Gleichungen korrigiert.M _w von EHMM-PS wurde von 1,07 · 10⁷ bis > 4 · 10⁷ variiert;M _w /M _n war > 1,5. Ferner wurdeM _w mittels Lichtstreuung und für eine Probe durch Sedimentations-Messungen bestimmt.

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With 4 figures 2 tables

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Dedicated to Prof. Dr. G. Rehage on the occasion of his 60th birthday.     

Separation of dextrans by gel permeation chromatography

The role of the intrinsic viscosity [η] as separation parameter in gel permeation chromatography (GPC) was studied for dextrans (from Leuconostoc mesenteroids B512) dissolved in water with deactivated silicagel (Porasil) as the column-filling material. For that purpose specific viscosities of dextran fractions eluted by GPC were measured as a function of the elution volume v. Provided that the elution volumes are corrected for zonal spreading, they are related to the intrinsic viscosities in an unambiguous way, probably reflecting a unique relationship between degree of branching and molecular weights. This was further investigated by developing an iteration method to prepare two calibration curves γ(v) and g(v), respectively, relating ln[\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] and InM (M is the molecular weight) to v. It required that the weight-average molecular weight M _w, the number-average molecular weight M _n, and the average intrinsic viscosity [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}] for a number of dextran samples (broad distributions) be previously known. The calibration curves found lead to consistent values of the above-mentioned averages. Moreover, they allow-establishment of the [\documentclass{article}\pagestyle{empty}\begin{document}$\left[ {\bar \eta } \right]$\end {document}]-M relationship over the range 5000 < M < 500,000.     

Analysis of chitosan by gel permeation chromatography

The effect of γ-radiation on the average molecular weight and the molecular-weight distribution of chitosan has been studied. The analysis of samples by gel permeation chromatography/size exclusion chromatography (GPC/SEC) has shown that the amount of high-molecular-weight fractions decreases and the amount of fractions containing low-molecular-weight chitosans (<50 kDa) increases with an increase in the radiation dose. The radiation-chemical yield of degradation is 11.0 particle/100 eV.     

Fractionation of polyethylene by gel permeation chromatography

The performance of the gel permeation chromatography (GPC) technique was studied with several commercial samples of linear high density polyethylene. A comparison of these data was made with those obtained from the elution column technique based on fractional dissolution. GPC gave reproducible fractionation data in the molecular weight range of 10³–10⁶. These data were obtained from two columns in series with nominal capacity of 1–10⁴ and 1–10⁶A. Polyethylene fractions of known molecular weights are required as calibration standards and for many commercial polyethylenes it is necessary to increase sensitivity at molecular weight higher than 10⁶.     

Characterization of poly(D,L-lactic acid) by gel permeation chromatography

A number of samples of poly(D ,L -lactic acid) (PLA) with weight-average molecular weights M?_w in the range 15,000–350,000 were prepared by a ring-opening polymerization. The molecular weight distributions (MWDs) of these samples were determined by gel permeation chromatography (GPC). The method involves a universal calibration of the columns on the basis of polystyrene standards and a rapid iteration algorithm leading to the establishment of the Mark–Houwink relationship. In addition, osmometry and viscometry data are presented. The effect of hydrolytic degradation on the MWD of two PLA samples was studied by GPC.     

Analysis of proanthocyanidins by high-performance gel permeation chromatography

A high-performance gel permeation chromatography method was developed for the analysis of proanthocyanidins. The isocratic method consisted of two porous polystyrene-divinylbenzene columns (300 x 7.5 mm each, 5 microm, 100 and 500 A individual pore size) and a mobile phase consisting of N,N-dimethylformamide containing 1% (v/v) acetic acid, 5% (v/v) water and 0.15 M lithium chloride. The flow-rate was maintained at 1 ml/min, with a column temperature of 60 degrees C and with detection at 280 nm. The method was used to analyze proanthocyanidin fractions of increasing molecular mass and from different plant tissues. The average molecular mass of proanthocyanidin fractions as determined by acid catalysis in the presence of phloroglucinol, related well with their gel permeation chromatography column retention, yet significant differences in the retention properties between individual plant tissue isolates existed. Proanthocyanidin compositional differences between isolates may explain these differences. A second-order calibration curve was generated from fractionated grape seed proanthocyanidins and this curve was used to analyze grape seed proanthocyanidins isolated from grapes harvested at extremes of maturity.     

Flow-rate dependence of gel permeation chromatography

Analysis of polystyrene standards by gel permeation chromatography over a wide range of flow rates revealed two sources of error in volume measurement. These errors arise from solvent evaporation in the siphon chamber and from solvent continuing to flow into the siphon during discharge. Appropriate corrections are discussed, and a vapor feedback loop to eliminate the solvent evaporation error is described. The flow rate dependence of the GPC calibration curve, expressed in the corrected elution volumes, appears different from that reported in the literature. The corrected flow rate dependence of peak elution volumes is in agreement with the expectation of diffusion and exclusion theories.     

Clean-up of a pesticide-lanolin mixture by gel permeation chromatography

In this study, the efficiency of a clean-up method by gel permeation chromatography (GPC) for the separation of pesticides from lanolin is analyzed. The pesticides analyzed belong to two different families, organophosphorous and synthetic pyrethroids. Lanolin, a standard mixture of the pesticides, and a lanolin-pesticides mixture are injected in a GPC column. The recoveries and elution times from the GPC column of lanolin (by a gravimetric method) and pesticides (by gas chromatography-electron capture detector) are determined. From this column, a good separation of the lanolin-pesticides mixture is observed.     

Calibration procedure for gel permeation chromatography

A novel procedure is presented for calibrating a gel permeation chromatograph by using broad polymer fractions. The limit in accuracy is set by the accuracy of number-average and weight-average molecular weight measurements and the reproducibility of the chromatograph. In the particular calibration for linear polyethylene described here, low molecular weight fractions were prepared by nitric acid oxidation of annealed single crystals. The calibration is then of particular value in morphological studies of polyethylene. The influence in the calibration of polar endgroups on the polymer, as produced in these oxidized samples is discussed.     

Instrumental broadening in gel permeation chromatography

Summary Instrumental broadening corrections to gel permeation chromatograms have been demonstrated to be of minimal concern when using the newly available high efficiency packing materials. This was demonstrated using -Styragel as packing material on polymer standards with both narrow and broad molecular weight distributions.     

Role of diffusion in gel permeation chromatography

A theory is developed that describes the diffusion of solute into the gel particles during a gel permeation chromatographic experiment. The particles are treated as homogeneous spheres of radius a, into which diffusion takes place with diffusion coefficient D_s. The concentration in the mobile phase at any level at any time is supposed to be uniform throughout the cross-section of the column. It is shown that in the usual columns the effect of diffusion in the mobile phase is unimportant. A determinative quantity in the process is the parameter a²/D_st, where t is the time. For large values of a²/D_st an explicit expression for concentration versus time in the mobile phase at the end of the column is derived [eq. (26) and Fig. 1]. It shows a relatively long tail at large efflux volumes V, where the concentration varies at V^?3/2. For arbitrary values of a²/D_st the first three moments of the concentration versus time curve are calculated [eqs. (33)–(37)]. Pronounced skewness of the curve is found unless a²/D_st is small.     

Separation system for fractionation of polyacrylamide by gel permeation chromatography

Samples of polyacrylamide were prepared by radical polymerisation of monomer in aqueous solution. Fractions of polyacrylamide were produced by a fractional precipitation technique with methanol as non-solvent. Molecular weights of the polyacrylamides were determined by solution viscometry. Analytical gel permeation chromatography (GPC) of the polyacrylamide samples and fractions was performed with porous silicas having a chemically bonded aminopropyl phase and with an eluent consisting of formamide-water (1:5). The GPC retention results indicated the successful separation of polyacrylamides having molecular weights in the range 10⁴–10⁶. GPC of polyacrylamide with this separation system appeared to be dominated by a steric exclusion mechanism.