Characterization of Macromolecules

Regarding industrial methods for isolation of polymers, the reader is referred to the relevant literature. 

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)) can be accomplished by dialysis or electrodialysis. However, the most widely used method of purification is by reprecipitation in which the solution of polymer (concentration less than 5-10 wt.%) is dropped into a 4- to 10-fold excess of precipitant, with stirring. If necessary, this operation is repeated with other solvent/precipitant pairs until the impurities are no longer detectable. 

There is no general mle 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). 

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P. Wyatt, Light scattering and the absolute characterization of macromolecules, Anal. Chim. Acta, 272, 1 (1993). 

The change in authors has not altered the basic concept of this 4th edition again we were not aimed at compiling a comprehensive collection of recipes. Instead, we attempted to reach a broader description of the general methods and techniques for the synthesis, modification, and characterization of macromolecules, supplemented by 105 selected and detailed experiments and by sufficient theoretical treatment so that no additional textbook be needed in order to understand the experiments. In addition to the preparative aspects we have also tried to give the reader an impression of the relation of chemical structure and morphology of polymers to their properties, as well as of areas of their appUcation. 

In this context numerous changes were made. The chapter Properties of Polymers was revised and a new section Correlations of Structure and Morphology with the Properties of Polymers was added. The chapter Characterization of Macromolecules was revised and enlarged. 15 examples have been deleted as they did no longer represent the state of the art and/or were of minor educational value. Several new experiments (plus background text) were added, as, for example controlled radical polymerization - enzymatic polymerization - microemulsions - polyelectrolytes as superabsorbants - hyperbranched polymers - new blockcopolymers - high impact polystyrene - electrical conducting polymers. 

Interpretation of the hydrodynamic data of a macromolecule requires that the shape of the molecule in a given solvent be known in advance from other sources and that there exist adequate expressions to relate the hydrodynamic quantities under consideration to a few parameters characterizing the dimensions of the molecule. Thus, in general, hydrodynamic measurements are informative as a supplementary means for the characterization of macromolecules. 

Characterization of Macromolecule-Ligand Interactions by Difference Spectroscopy... 

Pollet, R.J. (1985) Characterization of macromolecules by sedimentation equilibrium in the air-turbine ultracentrifuge, Methods Enzymol. 117, 3-27... 

Jl ield-flow fractionation (FFF) is a separation method convenient for the analysis and characterization of macromolecules and particles of synthetic or natural origin. Under the appropriate experimental conditions, it also can be applied for the preparative fractionation. The separation is due to a simultaneous action of the effective field forces and of the carrier liquid flow inside an open channel on the dissolved or suspended macromolecules or particles. The carrier liquid flows in the direction of the channel longitudinal axis and the field forces act in the perpendicular direction across the channel thickness. Each component of the fractionated sample interacting with the field forces is selectively transported across the channel. This concentrating process... 

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