SOLVENT EFFECTS IN ANIONICPOLYMERIZATION
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Solvent Effects in Anionic Polymerization. The Behavior of Living Polystyrene in Tetrahydrofuran-Dioxane Mixtures
by M. Van Beylen, D. N. Bhattacharyya, J. Smid, and M. Szwarc Department of Chemistry, State UnCersity College of Forestry, Syracuse University, Syracuse, New York 15810 (Received July 6, 1966)
The strikingly different behavior of living polystyrene in tetrahydrofuran (THF) and dioxane (DOX) induced us to investigate the kinetics of propagation of living polystyrene possessing the Li+ counterion (wS-,Li+) in mixtures of T H F and DOX. The viscosities, densities, and dielectric constants of various THF-DOX mixhres were determined and found to change monotonically with the mole fraction of DOX; the dependence is linear for the last two properties. The dissociation constant K d i s s of +3-,Li+ was determined for mixtures containing 0-48% DOX, and log was found to be linear with the reciprocal of the dielectric constant (E). Kinetic studies of propagation in 48% DOX led to a value for the propagation constant of the free -S- ion virtually identical with that of pure THF. Hence, the addition of dioxane (up to 47%) apparently does not affect the reactivity of -S- ion. The reactivity of the wS-,Li+ ion pair is, however, drastically reduced even by the addition of small amounts of DOX. A plot of log l i s - , ~ i +z’s. l / e or ( e - 1 ) / ( 2 ~ 1) is concave, showing a steep decrease of log ~ s - , L ; + as the mixture departs from pure THF. The significance of these facts is discussed.
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The homopropagation of living polystyrene was investigated in tetrahydrofuran‘-3 (THF) and in dioxane4-6 (DOX), different kinetic behavior being observed in each system. I n T H F the apparent rate constant of propagation, k,, increases with dilution of living ends indicating the presence of two propagating species in equilibrium with each other: the highly reactive free -S- ions and rather inert wS-,A+ ion pairs, A+ denoting an alkali ion. The dependence of the apparent k, on living ends concentration provides a method for determining the propagation rate constants of the free -S- ion and of the ion pair. A plot of k , vs. [living end^]-^'^ is linear-its slope being (kp,free ion) (K1’*dlss, ion pair) and the intercept giving /?,,ion psir. Such plots were reported by our group2 for living polystyrenes with Li+, Na+, I Nsf > K + > Rb+ > Cs+. tilled from the first flask into the second, the crystals In dioxane the observed rate constant is independent were dissolved by gentle heating, EtLi was recrystallized of the concentration of living ends14v5and the conductby chilling the solution, and the mother liquor was ance studies failed to reveal the presence of free i o n ~ . ~ again transferred into the first flask. This procedure I n vien- of the low dielectric constant of this solvent, was repeated until white crystals were obtained. l1 2.2, as compared with 7.4 for THF, this is not surAll of these operations were performed under high prising. Hence, only ion pairs propagate the polymvacuum. erization in dioxane and, contrary to the results found The benzene solution of purified EtLi was introduced in THF, their reactivities increase5 along the series into the reactor, the solvent was evaporated, and the Li+ < Ksif < I
