Quantitative Determination of Polymer Formation

Stringent purity conditions are required in carrying out polymerizations. In the free radical polymerization of styrene, no more than a few ppm oxygen is needed to terminate or prevent polymerization. In polycondensation, 1 % of monofunctional impurities may limit the average degrees of polymerization to below 100 (see Section 17.2.2). 

Monomer contaminants that affect the polymerization reaction are thus removed. 

Criteria of absolute purity are difficult to define, since most methods are too insensitive for detecting traces of impurities that can interfere with polymerization even at these low concentrations. The reproducibility of kinetic measurements is a good purity criterion, particularly when the monomers have been produced and purified by different methods. 

Polymerizations can be investigated through the formation of polymer, the disappearance of the monomer, or the formation of another reaction product (e.g., elimination products in poly condensations). In ambiguous cases, all three methods can be applied. 

The formation of polymers can often be followed purely qualitatively by the increase in viscosity. The quantitative assessment of viscosity measurements is difficult, however, because the viscosity of a reactive mixture depends on the physical interactions of the ingredients in the mixture and the molecular weight of the resulting polymer, as well as on the yield. 

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