However, there are now many observations that show a higher rate law order
dependence on monomer concentration (up to 2) for ethene [2, 25–27], propene
[2, 28–39], styrene [40], and diene [41] using heterogeneous ZN catalysts as well
as homogeneous and supported metallocene systems of different kinds.
This was first detected in 1962 by Firsov et al. [28, 29] and Natta at al. [30]
in studies of propene polymerization with TiCl 3 at low propene concentrations
(propene pressure <1 atm). Polymerization proceeded with an initial acceleration
to a constant rate, and the effect of propene concentration on the polymerization
rate was tested during the steady state phase of the process. It was shown that
the dependence of polymerization rate order on monomer concentration increases
from first order to some intermediate between first and second order with a
reduction in monomer concentration (Figs. 1 and 2).
Fig. 1 Dependence of
specific stationary rate of
propene polymerization on
the monomer concentration
with TiCl 3 –Be(C 2 H 5 ) 2 in
n-heptane at 70
C [29]
Fig. 2 Dependence of
stationary rate of propene
polymerization on the
monomer pressure with
TiCl 3 –Al(C 2 H 5 ) 3 in
toluene at 72
C [30]
Kinetics of Olefin Polymerization and Active Sites of Heterogeneous Ziegler. . .
103