Kinetics of anionic polymerizations of styrene and its m- and p-derivatives: Hammett's relations

Abstract

The kinetics of anionic polymerizations of styrene, m-methylstyrene, p-isopropylstyrene, and pmethylstyrene were investigated in tetrahydrofuran (THF) at 25°C with Cs+ as gegenion in the presence and absence of an electric field. Anionic polymerizations of m-and p-methylstyrenes in 2-methyltetrahydrofuran (MTHF) with Na+ as gegenion were also studied. The ion-pair rate constants kk, the free ion rate constants k; and the dissociation constants K of the styrene derivatives were generally smaller in both solvents than those of styrene. Conductance studies showed that the K values of the caesium salts are practically the same in THF. It was found that the free anions of these living polymers in MTHF are half as reactive as in THF. The field acceleration effect was hardly perceptible in THF. Following earlier studies of the field effect, the solvation ability of ethereal solvents to free carbanions was concluded to decrease along the series dimethoxyethane @ME) >THPe MTHF > THF. A value of (12&2)x lo4 M-l s-1 was attributed to the '' desolvated " free ion rate constant for living polystyrene. Hammett's relations of the two systems Cs+/THF and Na+/ MTHF were examined for k,, k;, k;, and K, independently. The reactivity constants p for k, and K were dependent on systems whereas those for k," were not.* This article is part 20 of Ionic Polymerization under an Electric Field.

"Living" Coordination Polymerization of Propene Initiated by the Soluble V(acac)3-Al(C2H5)2Cl System

“…The effect of different alkylaluminum halides on the polymerization was complex. The rate of chain propagation decreased in the following series of aluminum components: A12(C2H5)3C13 > A1(C2H5)2C1 > A1(C2H5)C12 > Al(C2H5)2Br (5) In contrast, the rate of chain transfer decreased in the following way: A12(C2H5)3C13 > A1(C2H5)C12 > A1(C2H5)2C1 * Al(C2H5)2Br « 0 (6) Both the chain propagation and the chain transfer were highest with A12(C2H5)3C13. Several binuclear complexes composed of transition metal alkyl and aluminum components have been proposed as models of the active centers in the Ziegler-type catalysts.16,25 If these binuclear models are valid, the aluminum components must influence the electronic structure of the active carbon-vanadium bond by inductive effects.…”

“…These limiting conditions have been achieved in the anionic polymerization of most vinyl monomers initiated by the organic derivatives of alkali metals. [3][4][5][6][7] The living anionic polymerization is of great utility in the preparation of monodisperse polymers and block and graft copolymers, since the chain ends remain active for long periods of time. Ziegler-type catalysts have been used to make block copolymers of -olefins8,9 even though there is no known example of such a catalyst meeting all the requirements for a true living polymerization.…”