Abstract
AbstractThe present work is concerned with the influence of the polymerization temperature on the propagation mechanisms of polyisoprenyl‐ and polybutadienyl‐alkali metals. The thermodynamic parameters of the contact ion pairs and free ions propagations have been calculated. With Li+ in dioxane solvent, the vinyl propagation is stereospecific (for isoprene, the propagation is mainly 4–3). In comparison with benzene, the vinyl propagation of the polydienyl‐Li contact ions pairs should be due to complexation of Li+ by dioxane, an electron donor having a weak dielectric constant. In general, the stereospecificity of the propagation of contact ion pairs decreases with increasing counterion size; little difference has been observed with K+ and Cs+ ion pairs in dioxane and benzene media. For isoprene, the methyl substituant should have chiefly a steric effect in the propagation of free ions, whereas it should confer a polar character to the isoprene molecule in the presence of ions pairs.
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