Regulation of alkoxysilane on stereoregular polymerization of Butene-1 catalyzed by TiCl4/MgCl2 Ziegler-Natta catalysts

Abstract

External electron donors (ED) as one of the components in traditional Ziegler-Natta (Z-N) catalysts play important roles in determining the activity, stereoregularity of the active species for ɑ-olefin polymerization. Alkoxysilanes with different size and different electron-donating alkyl substituents were investigated to study the stereoregular polymerization of butene-1 catalyzed by TiCl4/MgCl2 Z-N catalysts. The obtained polybutene-1 (PB) was fractionated into three components including high isotactic PB (HiPB), medium isotactic PB (MiPB) and atactic PB (aPB) and the number of active centers ([C*]/[Ti]) of each component were measured accordingly. The mmmm sequence concentration, weight-average molecular weight (Mw), molecular weight distribution (MWD), and crystallizability of PB were studied by carbon-13 nuclear magnetic resonance spectrometry (13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The addition of dimethyldimethoxysilane (D1) with 120.1 Å3 volume and 0.6802 a.u. electron density had little influence on the stereoregular polymerization of butene-1. The incorporation of diphenyldimethoxysilane (D3) with higher steric hindrance (231.2 Å3 volume), stronger electro-donating ability (0.6969 a.u. electron density) produced PB with higher HiPB component, higher mmmm sequence concentration, accompanying by the reduced catalytic activity and [C*]/[Ti]. The probably active center models absorbing different ED were proposed to explain the catalytic behaviors for butene-1 polymerization and formation of PB with different components.