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Fractionation: Alteration of the molecular weight distribution

Polymers are increasingly used as high-performance materials and crucial in the areas of medicine, cosmetics and technique. For sophisticated applications it is often harmful that the polymers have a broad molecular mass distribution or contain impurities. By means of fractionation we are in the position to remove unwanted material on a technical scale enabling the optimization of the polymer properties.

Modifiable Properties:

  • Viscosity

  • Refractive index

  • Density

  • Degradation

  • Crystallinity, glass temperature

  • Permeability through skin/kidney

  • Purity

  • Inflammable behaviour

  • Volatility

  • Oligomer content

  • Shelf life

  • etc.

The fractionation method is based on liquid/liquid phase separation and is therefore suitable for almost all soluble polymers. The phase separation is induced by lowering the solvent quality of an initially homogenous polymer solution. Two phases are formed: one containing the long chain material (gel-phase) and the other one contains mainly the short chain material and the low molecular mass impurities (sol-phase).
By the choice of the fractionation parameters (temperature, compositions) the “cut” through the molecular mass distribution can be varied. Narrow molecular mass distributions can be achieved by repeated fractionation.

Fractionation schema

On the next page you will find a short explanation about the separation principle.

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Polymer fractionation
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