Calibration of size exclusion chromatography columns for molecular weight determination of polyacrylonitrile and poly(vinylpyrrolidone) in N,N-dimethylformamide

Abstract

Calibration curves for poly( acrylonitrile) (PAN) and poly(v1-nyipyrroiidone) (PVP) were constructed by using polyethylene oxide (PEO) as primary standards. Molecular weight of PEO at retentlon volume I , (MA),, was converted to molecular weight of PAN or PVP, (M&, by the equation M, = 8(MA);.Constants 8 and f were calculated by using two polymer samples of PAN or PVP of known molecular weights and the PEO Calibration curve. Constants 8 and t for PAN were 12.76 and 0.866, and those for PVP were 3.15 and 0.959. The Mark-Houwink parameters for PAN and PVP were estimated by the SEC method Independently of those for PEO. The relationships between [VIM and retention volume for those polymers suggest that PVP elutes under the mechanism of size excluslon, while PAN suffers the secondary effects even if LlBr Is added to dhnethylformamlde (DMF). Elution behavior of PAN and PVP In DMF and the effect of adding LlBr to DMF are discussed.Poly(acrylonitri1e) (PAN) and poly(vinylpyrro1idone) (PVP) are important polymers as synthetic fibers and as capsular material for medical use, respectively, and accurate determination of molecular weight for these polymers is of primary importance for process and quality controls. Size exclusion chromatography (SEC) is a widely used analytical technique for the characterization of synthetic polymers. Most commonly employed solvents for SEC are tetrahydrofuran (THF) and chloroform, both of which, however, do not dissolve these two polymers. N,N-Dimethylformamide (DMF) has found widespread application in SEC analysis, but it has also been noted that peculiarities of elution behavior for such polar polymers are directly related to the use of DMF. The addition of lithium bromide (LiBr) to DMF has been attempted to eliminate these peculiarities (1-3).In SEC, the construction of a calibration curve for the column system is required at first and a series of polystyrenes (PS) of relatively monodisperse character are mostly employed for this purpose. Because of the poor solubility of PS in DMF, the retardation of retention volume (V,) for PS was observed (3), and as the result of the retardation, the divergence between the universal calibration curves for PS and PAN obtained by plotting [VIM and V , (4) is a matter of course. The abnormality of elution of PS in DMF may be explained by partitioning or adsorption of PS on the gel. Polar polymers such as poly(ethy1ene oxide) (PEO) must be employed as standards. Comparison of the PEO calibration curve in DMF with one obtained on the same column set in THF revealed no difference between them (5).To calculate the molecular weight averages for any polymers other than PEO by a PEO calibration curve, it is necessary to transform molecular weight units of PEO in the curve to those for the polymer specified. One of the techniques used to transform the molecular weight units is so-called "universal calibration" (6), and this method has been shown to have wide applicability. In order to aply the universal calibration method, however, it must be clear that the elu...

Size-exclusion chromatography of perfluorosulfonated ionomers

“…Aggregate structures create early eluting shoulders and prepeaks in SEC chromatograms [17] that are suppressed by the addition of low concentrations, e.g. 0.01 M, of LiBr or LiNO 3 .…”

Well-Defined High-Molecular-Weight Polyacrylonitrile via Activators Regenerated by Electron Transfer ATRP

“…Gel permeation chromatography (GPC) of PAN in N,N-dimethylformamide (DMF) as the eluent significantly overestimates the molecular weight of the PAN in comparison with linear polystyrene standards. 41 Because of this, GPC with a multiangle laser light scattering detector (MALLS-GPC) was used to determine the absolute molecular weights of the PAN. After comparing the results from the two procedures, it was concluded that the measured absolute molecular weights by MALLS were 2.5-2.7 times smaller than those estimated from linear polystyrene standards GPC (M w GPC) (as shown in Table S1 of the Supporting Information).…”

Large Molecular Mass Materials in Coal-Derived Liquids by 252Cf-Plasma and Matrix-Assisted Laser Desorption Mass Spectrometry

“…[32][33][34][35] We have shown in recent SEC work using a naphthalene mesophase pitch and a mixture of fullerenes that signal at/near the exclusion limit of the column may be clearly observed in chromatograms of entirely nonpolar samples. 36 Figure 4, c and d, presents SEC chromatograms of the Point of Ayr coal extract and its hydrocracking product 22 with the detector set at 350 and 450 nm, respectively.…”