The Gel Permeation Chromatography of Asphalt and the Characterization of Its Fractions in Terms of Molecular and Unit Sheet Weights

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Asphalt obtained from a refinery in Montreal was dissolved in toluene then fractionated in a preparative gel permeation chromatograph (prep.-GPC). Twenty-three fractions differing widely in molecular weights were collected and characterized by analytical GPC, viscometry, vapor pressure osmometry (VPO), element analyses, infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR). Similar studies were also carried out, for comparison purposes, on aliphatic and aromatic hydrocarbons to elucidate structure information on the different asphalt fractions. The GPC chromatograms of the fractions generally revealed narrow distributions indicating that their separation into different component groups has been reasonably well achieved. The number-average molecular weights [mbar]n of the fractions, as computed from their GPC chromatograms making use of the calibration curve prepared with polystyrene, polyoxypropylene glycol, and polyoxyethylene glycol, did not correspond to those obtained by the VPO technique. To overcome the problem, an alternate approach was developed whereby a number of calibration curves were tested for the asphalt fractions, and the one which yielded the [mbar]n values closest to those found by VPO method was