The Effect of Impurities on the Molecular Weight Distributions of Anionic Polymers

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Abstract
The deactivating influence of impurities in anionic polymerizations is considered from the point of view of the ultimate molecular weight distributions obtained with various systems. With the assumption that initiation is much faster than propagation, theoretical expressions for the weight distribution functions and the weight‐to‐number average chain length ratios are derived for the cases in which mono‐ and bifunctional growing chains are subjected throughout the course of polymerization to given, fixed ratios of monomer to impurity concentrations. The relationships obtained are shown to be applicable to systems of practical interest. The molecular weight distributions of both mono‐ and bifunctional anionic polymers derived from the foregoing model are found to broaden with increasing impurity content in the monomer supply. The molecular weight distributions for the latter are narrower than those for the former at corresponding levels of impurity content. For moderate degrees of deactivation, the weight distribution function for bifunctional polymers exhibits the characteristic maximum as well as the rudiments of a second relative maximum at lower molecular weight.