Polystyrene, living polymer availability

The influence of counterions of the living polymers can be investigated for polystyrene in the solvent hexane in which macroions and counterions are available in the form of ion pairs. It is seen that the amount of polymer coverage decreases continuously with increasing ion-diameter in the sequence Li, Na, K. This means that the reactivity of the ion pairs in a graft reaction follows the same course as that for the addition of further monomer (as is well-known for anionic polymerization). 

Although synthesis will not be discussed in this chapter, this is the proper point to emphasize that the synthesis and characterization of end functionalized iiacrMolecules with narrow molecular weight distribution [MWD] are often the most difficult part of the entire probl . Several different types of polymers of the form Py-polymer-Py have been studied because of the ready availability of the corresponding polymers with -OH groups on both ends. The techniques of polymerization via living polymers is best understood for polystyrene. TT annihilation studies have been reported only for A-polystyrene-A, and exciplex measurements are known only for are known only for DMA-polystyrene-Py. 

The most straightforward method for calibrating the relationship between D and M is to measure both D and M for a set of monodisperse samples with different molecular weights. In reality, the monodisperse samples have to be replaced by narrowly distributed standards made available either by relevant living polymerization or by fractionation of a broadly distributed sample. However, only a few kinds of polymers, e.g. polystyrene and poly(methyl methylacrylate), can actually be prepared so as to have a sufficiently narrow molecular weight distribution (Mw/Mn 1.1), and the fractionation is very time consuming. Thus, the straightforward calibration of the D vs M relation is not always practical. 

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