Effect of the structure of external alkoxysilane donors on the polymerization of propene with high activity Ziegler‐Natta catalysts

Abstract

AbstractPropene was polymerized in bulk in the presence of high activity heterogeneous Ziegler‐Natta catalyst with the purpose of finding correlations between the structure of an external alkoxysilane donor and the polymer. Nineteen silane compounds (1–8) of the structure RnSi(OR′)4‐n, where n = 1–4, R°C6H5, alkyl or H; R′ = C1–3‐alkyl, were used as external donors. The effect of Si/Al mole ratio was studied. The effect of the external alkoxysilane donor on the polymerization strongly depends on the number and size of alkoxy groups and the size of hydrocarbon groups attached to the silicon atom. Two major effects were observed: selective deactivation of atactic active centers and the increased production of high‐molecular‐weight isotactic polypropylene. Evidently, at least one free non‐hindered alkoxy group in the complex between alkoxysilane and AlEt3 is required for the selective deactivation. Also, the size of the hydrocarbon group of the donor strongly influences the selectivity of the deactivation.