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Purification

Ilona Heckler

For preparation of polymers we need pure starting materials, monomers, and these can be purified in numerous ways depending on the compound and its characteristics. If the compound is a solid it can be purified by filtration or recrystallizationhttp://en.wikipedia.org/wiki/Recrystallization_(chemistry) using various solvents like methanol, hexanes etc. If it is a liquid the most common purification techniques include flash chromatographyhttp://en.wikipedia.org/wiki/Column_chromatography, dry column vacuum chromatographyISSN 0039-7881 and distillationhttp://en.wikipedia.org/wiki/Distillation.

Soxhlet purification

Soxhlet extraction is an important way to fractionate and purify the synthesized polymer from smaller molecules like oligomers. Through this the purified polymer fraction gets a narrow molecular weight distribution. It is carried out by placing a purifying solvent in a round-bottom flask and heat it under reflux. The evaporating solvent goes through the distillation path to the condenser where it drips into a thimble, which contains the polymer. The soluble parts of the polymer material will be dissolved. When the chamber for the thimble is full, the solvent flows back into the flask through a backward drain and the purifying cycle can start again. The soluble parts will be collected in the flask, whereas the polymer which is insoluble in this solvent will stay in the thimble. Generally purification by soxhlet extraction is carried out in methanol and hexane to remove low molecular weight fractions. Afterwards, soxhlet extraction is done in chloroform to dissolve the polymer which can then be precipitated in methanol, filtrated and dried.

Figure 1: Soxhlet column.

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