Abstract
The ultra-violet/visible absorption spectrum of poly(butadienyl-lithium) anions in living anionic polymerization reactions changes significantly in the presence of the complexing agent 1,2-dipiperidinoethane (DIPIP). In the absence of complexing agent the poly(butadienyl-lithium) anion has an absorption maximum at 275 nm in cyclohexane, but on adding DIPIP two broad unresolved absorption maxima are observed in the range 250 to 400 nm, and the extinction coefficients for these peaks vary with the molar ratio of DIPIP to the living chain ends. A method has been developed for the determination of the concentration of the complexed living polyanions in cyclohexane by monitoring the absorbances at two different wavelengths (275 and 325 nm), which provides a useful means of obtaining a quantitative understanding of the living polymerization process in the presence of the complexing agent that was not possible before. The living-end concentrations obtained using the method proposed here have been found to be in good agreement with values obtained by measurement of the number-average molecular weights of the final products. Using this method, it has also been demonstrated that, in addition to forming a complex, DIPIP reacts slowly with the poly(butadienyl-lithium) anions.
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