Kinetics of propylene polymerization in the initial acceleration stage

The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)₂/benzoyl chloride/TiCl₄ co-activated with AlEt₃ in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dR_p/dt)₀ extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt₃ could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt₃] increased. © 1994 John Wiley & Sons, Inc.