Gel Permeation Chromatography: Problems Caused by Polydispersity in the Application of the Benoit's Universal Parameter

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Abstract
The application of the Benoit's universal calibration Ln(η). M = f (Ve) in GPC is examined through the general problem of polydispersity, when an attempt is made to represent a mixture of different macromolecules by a single parameter (η).M. The recently proposed (η). Mn parameter leads to an ambiguous interpretation of universal calibration; we try to classify the problems into three families. For the comparison of linear homopolymers of different polydispersities only by their peak apex, there is no general form of universal parameter. In the characterization of heterogeneous polymers, such as branched polymers or copolymers, (η)i. Mni is the form to be used in the GPC calculations. It leads to (η) and Mn when using the GPC-viscometer coupling but Mw can only be strictly obtained by the light scattering coupling. Finally, the apparent polydispersity caused by instrumental spreading cannot generally be represented by the (η)i.Mni parameter.