Purification and Drying of Polymers

Careful purification and drying of polymers is important not only for analytical characterization, but also because the mechanical, electrical, and optical properties are strongly influenced by impurities. Not the least important aspect of purification is the fact that even traces of impurities may cause or accelerate degradation or crosslinking reactions. 

The conventional techniques for the purification of low-molecular-weight compounds, such as distillation, sublimation, and crystallization, are not applicable to polymers. In some cases, it is possible to remove the impurities by cold or hot extraction of the finely powdered polymer with suitable solvents or by steam distillation. Separation of low-molecular-weight components from water-soluble polymers [e.g., poly(acrylic acid),poly(vinyl alcohol), poly(acryl amide)] 

There is no general rule for the prevention or avoidance of occlusion. In some cases, a change of solvent/precipitant system may help to achieve this goal. Raising the drying temperature is also beneficial. 

An important prerequisite for successful drying is to subdivide the polymer as finely as possible (see Sect. 2.5.1). 

For the unequivocal characterization of a low-molecular-weight compound, it is sufficient to specify a few physical or chemical properties, for example, boiling point, melting point, angle of optical rotation, refractive index, elemental analysis, IR and NMR spectra. If two low-molecular-weight samples have the same characteristic properties, they may be considered as identical. 

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