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D.V. Stukalov et al. / Journal of Catalysis 266 (2009) 39–49
species, creates the so-called bulkiness for monomer molecule to
be oriented at the active center in a certain way [5–7]. Considering
the entire catalytic surface, it is clear that the ID covering, being a
matrix for TiCl4, regulates the TiCl4 location on the MgCl2 surface.
Since the ID covering is a matrix for TiCl4 on the MgCl2 surface,
the ID nature should be expected to affect the TiCl4 adsorption.
Coadsorption with VP, EB, BB, DIBP, and DOP decreased the TiCl4
content in the sample to a different degree, indicating that IDs dif-
fer in their ability to block the MgCl2 surface for TiCl4. Diesters
(DIBP and DOP) block the MgCl2 surface more efficiently than
monoesters (EB and BB). In addition, a common regularity was ob-
served in each of these groups: the larger is the ID hydrocarbon
radical, the lower is the amount of TiCl4 adsorbed on the MgCl2
surface (Table 6, samples 3 and 5, 6 and 7, respectively). It is evi-
dent that hydrocarbon radical of the adsorbed ID takes part in
blocking of the MgCl2 surface for TiCl4. To understand the nature
of this effect, we tested the influence of the adsorption order.
To this end, adsorption of the ID (EB and DOP) and TiCl4 was
carried out in the reverse order: first TiCl4, and then the ID (Table
6, samples 4 and 8). In the case of EB, only a minor influence of
adsorption order was observed: the contents of EB and TiCl4 in
samples 3 and 4 were close to each other. In the case of DOP,
adsorption of TiCl4 before DOP provided a 1.6-fold increase in the
TiCl4 content in comparison with the reverse adsorption order
(Table 6, samples 7 and 8). This indicates that a part of low-coordi-
nated Mg cations in sample 7 is not accessible to TiCl4 because of
kinetic difficulties produced by hydrocarbon radicals of the ad-
sorbed DOP. In this connection, a part of Ti species in the catalyst
containing the ID with a large hydrocarbon radical is expected to
be inactive in polymerization due to kinetic screening of the MgCl2
surface.
The activated MgCl2 surface contains ca. 90% of five-coordinated
Mg cations residing on the (104) surface and ca. 10% of four-coor-
dinated Mg cations residing on the (110) surface.
The study of adsorption of the ID with different chemical struc-
tures on activated MgCl2 revealed that:
(i) the monoesters are coordinated by both oxygen atoms with
the MgCl2 surface;
(ii) the role of steric factor is more significant on the (104)
MgCl2 surface than on the (110) MgCl2 surface: the larger
is the ID hydrocarbon radical, the smaller is the number of
complexes formed by ID on the (104) MgCl2 surface;
(iii) the IDs with methyl as a hydrocarbon radical are more active
than other IDs: the formation of both the surface complexes
and the molecular compounds takes place;
(iv) adsorption of DAP (the ID with several types of nucleophilic
centers) obviously confirms that there are only two types of
adsorption sites on the activated MgCl2 surface.
The study of TiCl4 and ID coadsorption on the activated MgCl2
sample and comparison of these data with adsorption of individual
compounds allow us to formulate the following coadsorption
principles:
(i) coadsorption of the ID and TiCl4 is noncompetitive: TiCl4
forms much weaker complexes than the ID on the MgCl2
surface;
(ii) the ID forms a special matrix for TiCl4 on the MgCl2 surface:
TiCl4 occupies the adsorption sites that are inaccessible to
the ID for steric reasons;
(iii) the TiCl4 surface species are located in the tight environment
of the ID surface species;
(iv) the ID blocks the MgCl2 surface for TiCl4 due to coordination
with the surface Mg cations and screening of the nearest
adsorption sites by hydrocarbon radicals of the adsorbed ID.
Special situations were observed in experiments 9 and 10 (Table
6) in which the ID interacted with activated MgCl2 entirely. In
these samples, the content of TiCl4 was significantly higher than
that in sample 1 (Table 6). As shown above, the interaction of AA
and DMP with activated MgCl2 (Table 4, samples 7 and 8) results
in the formation of molecular complexes MgCl2ÁnID; so, we sup-
pose that the additional amount of TiCl4 in samples 9 and 10 (Table
6) can be associated with the formation of TiCl4ÁnID complexes,
which form as a result of interaction between molecular complexes
MgCl2ÁnID and TiCl4.
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4. Conclusions
The study of the influence of reaction conditions on the interac-
tion of EB and DIBP with activated MgCl2 showed that the type of
solvent strongly affects the selectivity of the interaction. Only the
chemisorption of the ID occurs in CB (polar solvent), whereas a less
selective interaction – formation of both the surface complexes
and molecular complexes MgCl2ÁnID – takes place in n-heptane
(nonpolar solvent). A pronounced effect of temperature on adsorp-
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coordinated Mg cations and a less compact packing of the ID on
the MgCl2 surface.
The samples in which EB and DIBP were only in chemisorbed
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