C O M M U N I C A T I O N S
Figure 3. Activity and 1-octene incorporation with 1/MAO are proportional
to comonomer concentration in ethylene/1-octene copolymerizations (Tp )
75 °C; 80 psi ethylene in toluene). The activity response of Me2Si(η5-2-
Me-benz[e]Ind)(η1-N-tBu)TiCl2/MAO is shown for comparison.8
Figure 2. Activity and 4-methyl-1-pentene incorporation with 1/MAO are
proportional to comonomer concentration in ethylene/4-methyl-1-pentene
copolymerizations (Tp ) 75 °C; 80 psi ethylene in toluene). The activity
response of Me2Si(η5-2,3-Me2-benz[e]Ind)(η1-N-tBu)TiCl2/MAO is shown
for comparison.6
Advanced Technology Program (No. 010366-0196-2003). We thank
Dr. Jerzy Klosin and The Dow Chemical Company for providing
Ti-CGC 2. This paper is dedicated to Professor John E. Bercaw on
the occasion of his 60th birthday.
Astoundingly, the activity for ethylene homopolymerization is one-
sixth that of 1-octene homopolymerization. Indeed, 1/MAO can
exhibit an inVerted preference for R-olefin homopolymerization oVer
ethylene homopolymerization. We know of no precedent for this
tendency.
Table 1 also highlights the copolymerization ability of 1/MAO.
As long as ethylene is present, the copolymerization activity of
2/MAO is comparable to that of 1/MAO. However, when 4-methyl-
1-pentene and 1-octene are copolymerized by 1/MAO, the activity
is less than when ethylene is present but, nonetheless, is 52 times
more active than with 2/MAO and easily excels that of any known
CGC for the copolymerization of two bulky R-olefins. These
findings further emphasize the unusually high reactivity of 1/MAO
toward R-olefins.
Although some ethylene polymerizations initially exhibit a
measurable increase in activity upon introduction of an R-olefin
(the comonomer effect),14 the oVerall trend for homogeneous
Ziegler-Natta olefin copolymerization systems invariably reveals
a diminished activity as R-olefin concentration further increases.
1/MAO operates contrary to this trend. In ethylene/4-methyl-1-
pentene copolymerizations with 1/MAO, the actiVity follows an
approximate linear relationship with 4-methyl-1-pentene concentra-
tion at all concentrations, including neat comonomer. Figure 2
illustrates this relationship and also indicates the mol % of 4-methyl-
1-pentene incorporated into the polymers. In neat comonomer,
4-methyl-1-pentene incorporation (>95%) is comparable to or
greater than its feed fraction (ca. 94%). Figure 3 illustrates a similar
unyielding comonomer effect for ethylene/1-octene copolymeriza-
tions with 1/MAO, for which activities are even greater.
In summary, the sterically expanded catalyst system of 1/MAO
produces homopolymers and copolymers of R-olefins with unprec-
edented activities and incorporation rates. A tentative explanation
to be investigated is that the spatial accessibility of 1 renders a
sterically indiscriminate catalyst and selectivity then defaults to
electronic considerations, which favor coordination and insertion
of the more electron-rich R-olefins over ethylene.
Supporting Information Available: Synthesis and characterization
data for 1 as well as polymerization details and polymer characterization
data. This material is available free of charge via the Internet at http://
pubs.acs.org.
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)
2
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Acknowledgment. This research is supported by grants from
The Robert A. Welch Foundation (No. A-1537) and the Texas
JA044678G
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