(ТМC-2 and ТМC-3), and catalyst containing an internal and external donor
(ТМC-4). Polymers obtained with these catalysts have been fractionated into
three fractions: PP5, atactic fraction soluble in boiling pentane; PP7, stereoblock
fraction soluble in boiling heptane; and IPP, isotactic fraction insoluble in boiling
heptane. C p and k p values have been calculated for separate fractions to account
for the content of every fraction in the total polymer.
Following conclusions can be made from results presented in Table 11:
1. For all catalysts, k p values increase considerably at transition from aspecific
active centers (РР5 and PP7 fractions) to isospecific centers (IPP fraction) and
reach values of (2.5–2.8)Â10
3 L/mol s.
2. k p values for isospecific centers (IPP fraction) are close for ТМC of various
compositions.
Conclusions (1) and (2) agree with results obtained by the SF method in
works [190–192].
3. The proportion of aspecific and low specificity centers (PP5 and PP7 fractions)
in the catalysts that do not contain internal or external donors (TiCl 3 , ТМC-1)
is great enough (70–84%).
4. Addition of the external donor to ТМC, containing the internal donor, has little
effect on the total number of active centers (catalysts TMC-2 and ТМC-4).
However, the proportion of isospecific active centers increases considerably
from 34% to 63%. This is possibly because aspecific centers in ТМC-2 (РР5
fraction) transform into isospecific centers (IPP fraction).
The results presented show that data on the number of active centers and the
propagation rate constants allow us to explain many questions connected with
the role of the separate components of catalysts in the formation of active centers
and their transformations during polymerization, revealing the factors that define
the activity and stereospecificity of catalysts.
The information about the number of active centers and the propagation
rate constants is also important for analysis of some kinetic features of olefin
polymerization:
– The causes of heterogeneity of the catalyst active centers
– Exact estimation of activation energy of reactions of propagation and transfer
of polymer chain is impossible without data on the effect of temperature on
the number of active centers
– The reasons for the widespread comonomer effect in ZN catalysis
– Data on the dependence of active site number on monomer concentration might
help in understanding the deviation from the low linear rate of polymerization
with changing monomer concentration
Kinetics of Olefin Polymerization and Active Sites of Heterogeneous Ziegler. . .
129
(ТМC-4). Polymers obtained with these catalysts have been fractionated into
three fractions: PP5, atactic fraction soluble in boiling pentane; PP7, stereoblock
fraction soluble in boiling heptane; and IPP, isotactic fraction insoluble in boiling
heptane. C p and k p values have been calculated for separate fractions to account
for the content of every fraction in the total polymer.
Following conclusions can be made from results presented in Table 11:
1. For all catalysts, k p values increase considerably at transition from aspecific
active centers (РР5 and PP7 fractions) to isospecific centers (IPP fraction) and
reach values of (2.5–2.8)Â10
3 L/mol s.
2. k p values for isospecific centers (IPP fraction) are close for ТМC of various
compositions.
Conclusions (1) and (2) agree with results obtained by the SF method in
works [190–192].
3. The proportion of aspecific and low specificity centers (PP5 and PP7 fractions)
in the catalysts that do not contain internal or external donors (TiCl 3 , ТМC-1)
is great enough (70–84%).
4. Addition of the external donor to ТМC, containing the internal donor, has little
effect on the total number of active centers (catalysts TMC-2 and ТМC-4).
However, the proportion of isospecific active centers increases considerably
from 34% to 63%. This is possibly because aspecific centers in ТМC-2 (РР5
fraction) transform into isospecific centers (IPP fraction).
The results presented show that data on the number of active centers and the
propagation rate constants allow us to explain many questions connected with
the role of the separate components of catalysts in the formation of active centers
and their transformations during polymerization, revealing the factors that define
the activity and stereospecificity of catalysts.
The information about the number of active centers and the propagation
rate constants is also important for analysis of some kinetic features of olefin
polymerization:
– The causes of heterogeneity of the catalyst active centers
– Exact estimation of activation energy of reactions of propagation and transfer
of polymer chain is impossible without data on the effect of temperature on
the number of active centers
– The reasons for the widespread comonomer effect in ZN catalysis
– Data on the dependence of active site number on monomer concentration might
help in understanding the deviation from the low linear rate of polymerization
with changing monomer concentration
Kinetics of Olefin Polymerization and Active Sites of Heterogeneous Ziegler. . .
129