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Metallocene-methylaluminoxane catalysts for olefin polymerizations
Abstract
The research field of homogeneous Ziegler-Natta catalysts based on metallocene and methylaluminoxane has now attracted a tremendous attention because of their high activity, well illustrated mechanism and kinetics aspect. We focused our research on catalysts synthesis, kinetics and mechanistic study of polymerization with ethylene as the monomer. The soluble catalysts are group IV transition metallocene compounds such as CP$\sb2$ZrCl$\sb2$, CpZrCl$\sb3$, (NMCp)$\sb2$ZrCl$\sb2$, and (NMCp)$\sb2$HfCl$\sb2$ with methylaluminoxane, MAO, as cocatalyst. The catalysts showed the highest productivity for ethylene polymerization in the temperature range of 70$\sp\circ$C to 90$\sp\circ$C. Take Cp$\sb2$ZrCl$\sb2$/MAO system for example, when (Cp$\sb2$ZrCl$\sb2$) = 1.1 x 10$\sp{-6}$ M, (Al) = 1.7 x 10$\sp{-2}$ M, the productivity is 3.9 x 10$\sp7$ g $\cdot$ PE/mole Zr $\cdot$ hr $\cdot$ atm at 70$\sp\circ$C. The kinetics of ethylene polymerization was studied using different metallocene catalysts. The active sites concentrations were determined by radiotagging with tritiated methanol and $\sp{14}$CO. For Cp$\sb2$ZrCl$\sb2$, virtually all the Zr are transformed into active sites, (C$\sp*$) = (Zr), at 70$\sp\circ$C and Al/Zr = 10$\sp4$. About 80% of the Zr formed active sites at a lesser Al/Zr ratio of 10$\sp3$. Lowering the temperature of 50$\sp\circ$C and at Al/Zr = 5.5 x 10$\sp3$, only 20% of CpZrCl$\sb3$ became catalytically active center. By varing polymerization conditions such as (Cat.), (C$\sb2$H$\sb4$), temperature and Al/Zr, Al/Hf ratio, the propagation rate constants, K$\sb{\rm p}$, were determined. The average molecular weight and molecular weight distribution have been determined by GPC and viscosity. The hydrogen effect on ethylene polymerization also been studied.
Subject Area
Polymers|Chemistry
Recommended Citation
Wang, Bor-Ping Eric, "Metallocene-methylaluminoxane catalysts for olefin polymerizations" (1989). Doctoral Dissertations Available from Proquest. AAI8917418.
https://scholarworks.umass.edu/dissertations/AAI8917418