Synthesis of polypropylene with improved MgCl₂‐supported Ziegler‐Natta catalysts, including silane compounds as external bases

Abstract

The new catalytic system comprising a diester as an internal Lewis base and a silane (triethoxyphenylsilane) as an external Lewis base presents important differences to the classical third generation catalyst with two esters in the system, i. e. a high isotacticity is obtained with a low ratio Al/Lewis base, the stereospecificity is stable with temperature and time, the sensitivity to hydrogen concerning the average molecular weight is high and the activity, which remains low without hydrogen, is greatly enhanced by the transfer agent. The selectivity of the system is controlled in a complex manner by the concentration and ratio of the cocatalytic system.

Effect of the internal/external donor pair in high‐yield catalysts for propylene polymerization, 1. Catalyst‐cocatalyst interactions

“…10) which, however, can easily be accounted for by the effect of the second stage reaction (3) on the equilibrium (4). ED The results presented here for the same system, though obtained with a differently prepared catalyst, substantially confirm the previous data.…”

Influence of Activation Conditions on the Gas Phase Polymerisation of Propylene

“…Gas phase processes offer many advantages over bulk (liquid) or slurry processes, not the least of which is much lower energy costs, which accounts for the fact that production costs per kg are generally lower in gas phase processes. On the other hand, it is well known that gas phase processes are subject to problems related to heat transfer, and that typical gas phase catalysts for PP homo‐ and copolymers are relatively sensitive to thermal degradation . In addition, Ziegler‐Natta (ZN) catalyst formulations require the use of different compounds, some of which can react together antagonistically if they are not properly treated.…”

Liquid-phase polymerization of propylene with a highly active Ziegler-Natta catalyst. Influence of hydrogen, cocatalyst, and electron donor on the reaction kinetics

“…The first type is less stereospecific and inserts propylene via the regular 1,2 insertion and irregular 2,1 insertions; the second is highly stereospecific and deactivates to a dormant center after a regioirregular 2,1 insertion; see Figure 4. Chain transfer with hydrogen may reactivate the dormant centers; see Spitz et al 9,10 and Guyot et al 6 This hypothesis is supported by the presence of n-butyl chain end groups in polymers synthesized in the presence of hydrogen; see Chadwick et al 5 Another possibil-ity is hydrogen reacts with the dormant centers to form active Ti-propyl centers. The reason for the much higher activation at lower PEEB concentrations probably is that PEEB is involved in the irreversible deactivation of the dormant sites.…”