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NFDI4Chem – Minimum Standards in Polymer Chemistry

Dr. Susanne Boye

Leibniz-Institut für Polymerforschung

Session 6 –

Selected Analyses in Polymer Chemistry

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Introduction into SEC

1. What is it good for?

  • Determination of average molecular weights (molar masses) Mn, Mw, Mz and distributions, dispersity Ð = Mw/Mn, under special conditions radii can be determined

2. How it is performed?

  • Injection of a diluted sample solution into a SEC column, molecules will be transported by eluent trough the column densly packed with porous material
  • Depending on size (hydrodynamic volume) molecules will be separated

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Elution volume (ml)

Detector intensity

Separation depending on hydrodynamic volume

Porous packing material

molecules with different sizes

2. Separation Techniques and Adequate Detection

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3. What type of SEC types are applied?

  • Relative molar mass determination: elution times of narrowly distributed standards with varied molar masses will be compared with unkown sample

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  • Universal calibration intrinsic viscosities [η]xM will be plotted against elution time

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  • Absolute molar mass determination: concentration sensitive detection in combination with multi angle laser light scattering MALS, dn/dc or extinction coefficient is needed - determination of Rg is possible, too

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What is needed for ELN?

Technical equipment:

  • pump, degasser, autosampler, detectors, software data collection and processing

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Experimental conditions:

  • Eluent
  • Sample concentration, injection volume
  • Type of column, pore size, packing material, supplier
  • Type of molar mass determination: relative, universal or absolute
  • Relative or universal: Used standards (polymer type, molar masses, supplier)
  • Absolute: dn/dc, extinction coefficient, fitting model of scattering data

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Processing of data:

  • Peak ranges, baselines, despiking, units (kDa or g/mol), using MALS (fitting model of scattering data, fit order, negclection of angles)

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Outcomes:

  • Data: Mn, Mw, Mz, Ð (Mw/Mn), with LS Rg, Rh, ν; with Visco [η], α
  • Figures:

Chromatograms: (RI or UV) detector signal vs. Elution time (volume)

Molar mass distributions: log M vs. differential fraction

SEC-LS: M or R vs elution time (volume); M vs. R (scaling plot)

SEC-Visco: [η] vs. elution time, M vs. [η] (KMHS-Plot)

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Time for discussion.

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