MODERN METHODS FOR DETERMINING THE MOLAR MASS-DISTRIBUTION OF POLYMERS - GENERAL-CONSIDERATIONS AND APPLICATION TO SEDIMENTATION EQUILIBRIUM

Autor(en): LECHNER, MD
MACHTLE, W
Stichwörter: ANALYTICAL ULTRACENTRIFUGE; OPTICS; Polymer Science
Erscheinungsdatum: 1992
Herausgeber: HUTHIG & WEPF VERLAG
Journal: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR SYMPOSIA
Volumen: 61
Startseite: 165
Seitenende: 175
Zusammenfassung: 
A new procedure for the determination of the molar mass means M(n), M(w) and M(z) and of the molar mass distribution W(M) = f(M) of polymers is proposed and applied on measurements of the sedimentation equilibrium. The procedure includes the extrapolation of the experimentally determined polydisperse measurable quantity at different concentrations to zero concentration. From the values the molar mass distribution is calculated by nonlinear least squares routines of the integral equation. This method of calculation is, contrary to the inverse transformation of the integral equation, which has been used up to now, well conditioned and stable. The proposed method has been applied to sedimentation equilibrium. In this case the reduced concentration profiles (interference optic, absorption optic) or reduced concentration gradient profiles (schlieren optic) measured at different concentrations must be extrapolated to zero concentration and followed by nonlinear regression of the integral equation U(W)(X) = integral W(M) U(X,M) dM. Measurements on polystyrenes with different polydispersities and modalities (e.g. bimodal molar mass distributions), and on the polyelectrolytes sodium polystyrene sulfonate and polyethylene imine exhibit resonable results. The result of the investigation is, that the proposed procedure is a suitable and reasonable possibility for the determination of molar mass distribution of polymers by sedimentation equilibrium. For polyelectrolytes in particular this method is better than gel permeation or size exclusion chromatography.
Beschreibung: 
HAMBURG MACROMOLECULAR SYMP ON ANALYSIS OF POLYMERS : MOLAR MASS AND MOLAR MASS DISTRIBUTION OF POLYMERS, POLYELECTROLYTES AND LATTICES, UNIV HAMBURG, HAMBURG, GERMANY, SEP, 1991
ISSN: 02580322

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