Fluorinated bis(phenoxyketimine)titanium complexes for the living, isoselective polymerization of propylene: Multiblock isotactic polypropylene copolymers via sequential monomer addition

Article abstract of DOI:10.1021/ja077772g

A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex 12/MAO promoted the living, isoselective polymerization of propylene ([m⁴] = 0.73, α = 0.94). This catalyst system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing has revealed that each is elastomeric with elongations at break between ～790-1000%.

Full text of DOI:10.1021/ja077772g

Published on Web 03/18/2008
Fluorinated Bis(phenoxyketimine)titanium Complexes for the
Living, Isoselective Polymerization of Propylene: Multiblock
Isotactic Polypropylene Copolymers via Sequential Monomer
Addition
Joseph B. Edson,† Zhigang Wang,‡ Edward J. Kramer,‡ and Geoffrey W. Coates*,†
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell UniVersity,
Ithaca, New York 14853, and Mitsubishi Chemical Center for AdVanced Materials and the
Departments of Materials and Chemical Engineering, UniVersity of California,
Santa Barbara, California 93106
Received October 9, 2007; E-mail: gc39@cornell.edu
Abstract: A series of bis(phenoxyketimine)titanium dichloride complexes were synthesized and evaluated
as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO).
Catalysts bearing phenoxyketimine ligands with different substituents at the ortho and para positions of
the phenolate ring and substituents at the ketimine carbon were investigated. The identity of the ketimine
substituent had the largest effect on the activity and isoselectivity of propylene polymerization. Complex
12/MAO promoted the living, isoselective polymerization of propylene ([m4] ) 0.73, R ) 0.94). This catalyst
system was used for the synthesis of a number of block copolymers featuring isotactic polypropylene
semicrystalline blocks and poly(ethylene-co-propylene) amorphous blocks. Several triblock samples with
varying block lengths, a pentablock, and a heptablock copolymer were synthesized. Mechanical testing
has revealed that each is elastomeric with elongations at break between ∼790-1000%.
Introduction
which are most typically prepared via sequential monomer
addition. Block copolymers incorporating isotactic polypropy-
One of the ultimate challenges in polymer chemistry is the
ability to synthesize polymers and copolymers with well-defined
stereochemistry while controlling molecular weight, molecular
weight distribution, and sequence. The development of non-
metallocene olefin polymerization catalysts has become a rapidly
expanding area as new catalyst systems are discovered and
improvements upon existing ones are made.1,2 Homogeneous
catalyst systems now exist that enable precise control over
polymer stereochemistry through the design of sterically and
electronically tunable ancillary ligand frameworks that exert a
defined geometry around an active metal center.3 Until recently,
olefin polymerization catalysts have been inferior to other chain-
growth polymerization methods (e.g., cationic, anionic, radical)
in their ability to promote consecutive enchainment of monomer
units without chain transfer or termination, i.e., living polym-
erization. However, a number of olefin polymerization catalysts
that suppress chain termination or transfer events have been
developed; these catalysts display living olefin polymerization
behavior.4,5 Living polymerization allows for the synthesis of a
wide variety of polymer architectures such as block copolymers,
lene (iPP) segments are envisioned to provide materials with
many potential applications such as compatibilizers and ther-
moplastic elastomers.6-8 Therefore, the synthesis of block
copolymers containing iPP domains is one of the most highly
sought after goals in the field of olefin polymerization.
The living and highly isoselective polymerization of higher
R-olefins has been reported. Sita,9 Kol,10 Mashima,11 Sundarara-
jan,12 and Coates13 have developed catalyst systems capable of
polymerizing 1-hexene in a living manner with moderate to
extremely high levels of isoselectivity. However, despite the
exquisite stereochemical control manifested in these systems,
(6) Hotta, A.; Cochran, E.; Ruokolainen, J.; Khanna, V.; Fredrickson, G. H.;
Kramer, E. J.; Shin, Y. W.; Shimizu, F.; Cherian, A. E.; Hustad, P. D.;
Rose, J. M.; Coates, G. W. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 15327-
15332.
(7) Harney, M. B.; Zhang, Y. H.; Sita, L. R. Angew. Chem., Int. Ed. 2006, 45,
2400-2404.
(8) Coates, G. W.; Waymouth, R. M. Science 1995, 267, 217-219.
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(b) Zhang, Y. H.; Keaton, R. J.; Sita, L. R. J. Am. Chem. Soc. 2003, 125,
9062-9069. (c) Zhang, Y. H.; Sita, L. R. Chem. Commun. 2003, 2358-
2359. (d) Zhang, Y. H.; Sita, L. R. J. Am. Chem. Soc. 2004, 126, 7776-
7777. (e) Kissounko, D. A.; Zhang, Y. H.; Harney, M. B.; Sita, L. R. AdV.
Synth. Catal. 2005, 347, 426-432.
† Cornell University.
‡ University of California.
(10) (a) Tshuva, E. Y.; Goldberg, I.; Kol, M. J. Am. Chem. Soc. 2000, 122,
10706-10707. (b) Segal, S.; Goldberg, I.; Kol, M. Organometallics 2005,
24, 200-202.
(1) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed.
1999, 38, 428-447.
(2) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283-315.
(3) Coates, G. W. Chem. ReV. 2000, 100, 1223-1252.
(4) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002,
41, 2236-2257.
(11) Yasumoto, T.; Yamagata, T.; Mashima, K. Organometallics 2005, 24,
3375-3377.
(12) Sudhakar, P.; Sundararajan, G. Macromol. Rapid Commun. 2005, 26, 1854-
1859.
(5) Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. S.
Prog. Polym. Sci. 2007, 32, 30-92.
(13) Domski, G. J.; Lobkovsky, E. B.; Coates, G. W. Macromolecules 2007,
40, 3510-3513.
9
4968
J. AM. CHEM. SOC. 2008, 130, 4968-4977
10.1021/ja077772g CCC: $40.75 © 2008 American Chemical Society

Multiblock Isotactic Polypropylene Copolymers
A R T I C L E S
Figure 1. Catalysts used for the synthesis of block copolymers incorporating isotactic polypropylene segments.
poly(1-hexene), regardless of its tacticity, is amorphous and thus
not suitable for applications requiring the strength, durability
and/or crystallinity of a material such as iPP. While there are
numerous catalysts capable of highly isoselective propylene
polymerization3,14 and a growing number of catalysts capable
of living olefin polymerization,4,5 highly active catalysts for both
the living and highly isoselective polymerization of propylene
remain elusive.15 This is despite significant research efforts since
Natta’s first synthesis of iPP more than half a century ago.16
For example, in 2003 Busico and co-workers reported that
various diamine bisphenolate zirconium catalysts exhibit “quasi-
living” propylene polymerization behavior producing highly
isotactic polypropylene. However, chain lifetimes are relatively
short.17 In 2004, Coates and co-workers reported that fluorinated
bis(phenoxyketimine)titanium catalysts are living but only
moderately isoselective for propylene polymerization producing
polypropylene with 53% of five consecutive monomer sequences
possessing the same stereoconfiguration ([m4] ) 0.53).18 The
following year, Coates and co-workers reported a C2-symmetric
R-diimine Ni(II) catalyst that is living and highly isoselective
for propylene polymerization at low temperatures, however,
catalyst activities were extremely low and molecular weight
distributions broaden under these conditions.19 Sita reported in
2006 that monocyclopentadienylzirconium acetamidinate cata-
lysts polymerize propylene in a living manner, albeit with
moderate isoselectivity ([m4] ) 0.71).7 While each of these
systems can be considered deficient in some regard (e.g., living
behavior, isoselectivity, or activity), each has been utilized to
synthesize block copolymers incorporating iPP segments. These
catalysts and the block copolymers produced are depicted in
Figure 1.
For example, Busico and co-workers were able to prepare
iPP-block-PE (PE ) polyethylene) copolymers using the
aforementioned diamine bisphenolate zirconium catalysts.17
Coates and co-workers reported the synthesis of an iPP-block-
PEP (PEP ) poly(ethylene-co-propylene)) diblock copolymer
employing 1/methylaluminoxane (MAO).18 With their C2-
symmetric R-diimine Ni(II) catalyst, Coates and co-workers
were able to prepare an iPP-block-rirPP-block-iPP (rirPP )
regioirregular polypropylene) triblock copolymer and an iPP-
block-rirPP-block-iPP-block-rirPP-block-iPP pentablock copoly-
mer by adjusting the temperature throughout the course of the
polymerization to effect changes in the microstructure of each
block.6 Sita and co-workers utilized a degenerative-transfer
living polymerization process with a monocyclopentadienylzir-
conium acetamidinate catalyst system to generate a number of
isotactic-atactic stereoblock polypropylene copolymers.7 Despite
these efforts, the synthesis of block copolymers containing two
or more iPP segments via sequential monomer addition has yet
been achieved. While the ability to use a single monomer to
make block copolymers, as shown by Coates,6 Sita,7 and
Waymouth,8 is advantageous from both a synthetic and an
industrial standpoint, a larger variety of architectures are
accessible if more than one monomer is used. For example,
thermoplastic elastomers employing PEP for amorphous blocks
should exhibit utility over a broader temperature range than those
employing atactic polypropylene (aPP) amorphous blocks. This
is due to the fact that PEP exhibits a much lower glass transitions
temperature (Tg) than aPP (-50 °C vs 0 °C).
Our group20 and researchers at Mitsui Chemicals21-23 have
independently explored the use of bis(phenoxyimine)titanium
dichloride olefin polymerization catalysts for propylene polym-
erization. Complexes in which the phenoxyimine ligands (PHI,
see Figure 2) contain an ortho-fluorinated N-aryl group and a
bulky ortho substituent on the phenolate ring, produce highly
(14) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. ReV. 2000, 100,
1253-1345.
(15) We define highly isoselective polymerization of propylene as one with >
95% selectivity at the pentad level of analysis.
(16) Natta, G.; Pino, P.; Corradini, P.; Danusso, F.; Mantica, E.; Mazzanti, G.;
Moraglio, G. J. Am. Chem. Soc. 1955, 77, 1708-1710.
(20) Tian, J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39, 3626-3629.
(21) Saito, J.; Mitani, M.; Mohri, J.; Ishii, S.; Yoshida, Y.; Matsugi, T.; Kojoh,
S.; Kashiwa, N.; Fujita, T. Chem. Lett. 2001, 576-577.
(17) (a) Busico, V.; Cipullo, R.; Friederichs, N.; Ronca, S.; Togrou, M.
Macromolecules 2003, 36, 3806-3808. (b) Busico, V.; Cipullo, R.;
Friederichs, N.; Ronca, S.; Talarico, G.; Togrou, M.; Wang, B. Macro-
molecules 2004, 37, 8201-8203.
(22) Makio, H.; Kashiwa, N.; Fujita, T. AdV. Synth. Catal. 2002, 344, 477-
493.
(18) Mason, A. F.; Coates, G. W. J. Am. Chem. Soc. 2004, 126, 16326-16327.
(19) Cherian, A. E.; Rose, J. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem.
Soc. 2005, 127, 13770-13771.
(23) Mitani, M.; Fujita, T. In Beyond Metallocenes: Next-Generation Polym-
erization Catalysts; Patil, H. O., Hlatky, G. G., Eds.; American Chemical
Society: Washington, D. C., 2003; Vol. 857, pp 26-45.
9
J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008 4969

A R T I C L E S
Edson et al.
Results and Discussion
Phenoxyimine Polymerization Catalysts. Because of their
close structural relationship to PKI catalysts, a brief discussion
of the polymerization behavior of PHI catalysts would be
beneficial. Bis(phenoxyimine)titanium dichloride complexes
were originally explored for the polymerization of ethylene.30
When activated with MAO, these catalysts displayed high
ethylene polymerization activities which prompted a more
detailed investigation of this class of catalyst. In our laboratory,
a pooled, combinatorial approach was used to develop a library
of related complexes and from this was identified a catalyst
capable of syndioselective propylene polymerization.20 Further
elaboration of the ligand framework showed that incorporation
of ortho-fluorine substituents on the N-aryl moiety resulted in
living and highly syndioselective propylene polymerization.21,24
Catalysts bearing meta- and para-fluorine substituents on the
N-aryl moiety exhibited high activity, but were not living for
propylene31 or ethylene polymerization.22 Although isoselective
polymerization of propylene would be expected from a C2-
symmetric catalyst precursor,3 the polypropylene produced
by the PHI catalysts is actually syndiotactic. The highly
syndioselective polymerization of propylene via chain-end
control proceeds with prevailing secondary (2,1) monomer
insertion.20,32-35 It is this highly unusual secondary insertion
mode that causes fluxional isomerization of the octahedral sites
between successive monomer insertions.20,25,26 Quantum me-
chanical/molecular mechanical calculations performed on these
catalysts predict high isoselectivity for propylene polymerization
if the insertion rate is much faster than catalyst isomerization.25
Complexes with ligand structures that could possibly prevent
catalyst isomerization have been developed. For example,
zirconium dichloride complexes bearing binaphthyl-bridged
Schiff-base PHI ligands were prepared by Pellecchia and co-
workers.36 When activated with Bu3Al/MAO or with Bu3Al//
[Ph3C][B(C6F5)4], these catalysts yielded high molecular weight,
atactic polypropylene. In the absence of triisobutylaluminum,
low olefin polymerization activity was observed. Interestingly,
isotactic polymers were obtained under similar conditions from
the polymerization of 1-butene, 1-pentene, and 1-hexene.
Analogous titanium catalysts yielded mostly aPP with small
fractions (ca. 10 wt %) of iPP ([mm] ) 95%), while complexes
bearing a methyl group adjacent to the imine functionality on
the phenolate ring resulted in the formation of moderately
isotactic PP ([mm] ) 75%).37 In all cases, it appears that reaction
between the ligand and the alkylaluminum present in the
activation cocktail results in the in situ reduction of the
imine functionality, leading to multiple active species
Figure 2. Phenoxyimine polymerization catalysts.
syndiotactic polypropylene (sPP) in a living manner when
activated with MAO.21,24 The syndioselectivity is a result of
chain-end control. These catalysts are C2-symmetric in the solid
state and in solution, and are therefore expected to provide
isotactic polymer via a site-control mechanism. However, a
proposed catalyst isomerization event that occurs between each
successive monomer insertion overrides the expected site control
and leads to the unexpected syndioselectivity that is ob-
served.20,25,26 As the ortho substituent on the phenolate moiety
decreases in size, the syndioselectivity of propylene polymer-
ization decreases.27 Using zirconium or hafnium PHI complexes,
Fujita and co-workers were able to generate iPP when iBu3Al/
[Ph3C][B(C6F5)4] was employed as the activator.28 Under these
conditions, the PHI ligands react with the aluminum cocatalyst
in situ to generate a new phenoxyamido complex. Activation
with MAO22 results in the formation of regioirregular, atactic
polypropylene. Our group has reported a series of phenox-
yketimine (PKI) titanium complexes bearing bulky tBu groups
at the ortho position of the phenolate ring, which are living for
ethylene polymerization when activated with MAO.29 These
catalysts were sparingly active for propylene polymerization.
However, decreasing the steric demand at the ortho position of
the phenolate ring and employing the N-pentafluorophenyl
moiety leads to living and moderately isoselective propylene
polymerization.18
i
i
We have extensively explored the PKI ligand design space
in search of a catalyst capable of polymerizing propylene in a
living and highly isoselective manner. In the course of our
exploration, we found that 12/MAO (Scheme 1) was the most
isoselective PKI catalyst reported to date. Employing this
catalyst, we prepared a number of unique block copolymers
including an iPP-block-PEP-block-iPP triblock copolymer, iPP-
block-PEP-block-iPP-block-PEP-block-iPP pentablock copoly-
mer, and iPP-block-PEP-block-iPP-block-PEP-block-iPP-block-
PEP-block-iPP heptablock copolymer. Mechanical testing revealed
that each of these polymers displayed good elastomeric proper-
ties.
and
broad
molecular
weight
distributions.
This
(30) Matsui, S.; Tohi, Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.; Nitabaru,
M.; Nakano, T.; Fujita, T. Chem. Lett. 1999, 1065-1066.
(31) Mason, A. F.; Tian, J.; Hustad, P. D.; Lobkovsky, E. B.; Coates, G. W.
Isr. J. Chem. 2002, 42, 301-306.
(24) Tian, J.; Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 5134-
5135.
(32) Saito, J.; Mitani, M.; Onda, M.; Mohri, J. I.; Ishi, J. I.; Yoshida, Y.; Nakano,
T.; Tanaka, H.; Matsugi, T.; Kojoh, S. I.; Kashiwa, N.; Fujita, T. Macromol.
Rapid Commun. 2001, 22, 1072-1075.
(25) Milano, G.; Cavallo, L.; Guerra, G. J. Am. Chem. Soc. 2002, 124, 13368-
13369.
(26) Corradini, P.; Guerra, G.; Cavallo, L. Acc. Chem. Res. 2004, 37, 231-
241.
(33) Hustad, P. D.; Tian, J.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 3614-
3621.
(27) Mitani, M.; Furuyama, R.; Mohri, J.; Saito, J.; Ishii, S.; Terao, H.; Nakano,
T.; Tanaka, H.; Fujita, T. J. Am. Chem. Soc. 2003, 125, 4293-4305.
(28) (a) Saito, J.; Onda, M.; Matsui, S.; Mitani, M.; Furuyama, R.; Tanaka, H.;
Fujita, T. Macromol. Rapid Commun. 2002, 23, 1118-1123. (b) Prasad,
A. V.; Makio, H.; Saito, J.; Onda, M.; Fujita, T. Chem. Lett. 2004, 33,
250-251.
(34) Lamberti, M.; Pappalardo, D.; Zambelli, A.; Pellecchia, C. Macromolecules
2002, 35, 658-663.
(35) Talarico, G.; Busico, V.; Cavallo, L. J. Am. Chem. Soc. 2003, 125, 7172-
7173.
(36) Lamberti, M.; Consolmagno, M.; Mazzeo, M.; Pellecchia, C. Macromol.
Rapid Commun. 2005, 26, 1866-1871.
(37) Strianese, M.; Lamberti, M.; Mazzeo, M.; Tedesco, C.; Pellecchia, C. J.
Mol. Catal. A: Chem. 2006, 258, 284-291.
(29) Reinartz, S.; Mason, A. F.; Lobkovsky, E. B.; Coates, G. W. Organome-
tallics 2003, 22, 2542-2544.
9
4970 J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008

Multiblock Isotactic Polypropylene Copolymers
A R T I C L E S
Scheme 1. Titanium Phenoxyketimine Compounds
in situ ligand modification may also be the source of the
observed isoselectivity.
R3 ) Br, R4 ) Ph) produced aPP. This lies in stark contrast to
the observed isoselectivity of PKI titanium complexes bearing
alkyl substituents.18 In all cases, molecular weight distributions
were broad (Mw/Mn g 1.6) indicative of a non-living polym-
erization system.
We reasoned that placing substituents on the carbon atom of
the imine moiety would inhibit the fluxional behavior for this
class of catalysts, thereby enforcing the C2-symmetry of the
active species. Titanium complexes bearing these PKI ligands
with N-pentafluorophenyl groups resulted in the living and
moderately isoselective polymerization of propylene.18 The
microstructure of the iPP was consistent with an enantiomorphic
site-control mechanism. Zirconium dichloride complexes bearing
PKI ligands have been prepared by Hu and co-workers.38 When
activated with MAO, these catalysts yielded high molecular
weight polyethylenes with broadened molecular weight distribu-
tions (Mw/Mn g 1.7).
Synthesis of Phenoxyketimine Complexes. The PKI cata-
lysts were synthesized as previously described.29 Reaction of
the appropriately substituted phenol with the desired imidoyl
chloride and AlCl3 in 1,2-dichloroethane gave the corresponding
PKI ligands in 4-77% yield, with the major impurity being
the O-imidoylated product. Deprotonation of the PKI ligand was
effected with n-BuLi, and the resulting ligand salt was trans-
ferred to a tetrahydrofuran (THF) solution of TiCl4 to give the
bis-ligated complex. Recrystallization of the compounds from
CH2Cl2/pentane or toluene/pentane provided the complexes as
dark brown to red crystals in 27-61% yield. For all complexes,
1H, 13C, and 19F NMR spectra showed the presence of a single
C2-symmetric isomer in both benzene-d6 and chloroform-d at
room temperature.
We have previously investigated titanium complexes sup-
ported by PKI ligands bearing different alkyl substituents at
the ortho position of the phenolate moiety (R1).18 As this
substituent decreases in size, polymerization activity and the
isotacticity of the resultant polypropylene increases. The highest
isotacticity was observed with complexes bearing ortho-methyl
substituents on the phenolate rings of the ligand. Due to the
interesting behavior reported by Pellecchia for halogenated PHI
catalysts,39 we reasoned that complexes bearing halogens at the
ortho position of the phenolate ring could be worth investigating.
A series of PKI complexes with pentafluorophenyl N-aryl
groups, a phenyl ketimine (R4) substituent and various ortho
substituents on the phenolate ring (R1) were investigated to
optimize facial selectivity (Scheme 1, complexes 1-6). In this
series, the ortho substituents on the phenolate moiety were
chosen on the basis of having pronounced steric and electronic
differences. We expected that the propylene polymerization
catalyzed by 1-6/MAO would follow the trends observed for
previously reported PKI catalysts, where decreasing the size of
the R substituent leads to higher activities and stereoselectiv-
ites.18 From this initial report, it was shown that a methyl group
at the ortho position of the phenolate ring was optimally sized
to provide good facial selectivity for propylene polymerization.
Effect of the Ortho Substituent on the Phenolate Ring.
Recently, Pellecchia and co-workers have shown that titanium
complexes bearing PHI ligands with halide substituents at the
ortho position of the phenolate ring and N-pentafluorophenyl
groups quite unexpectedly promoted moderately isoselective
polymerization of propylene (R1 ) R3 ) I, R4 ) H; [mm] )
0.73, R ) 0.90; see Scheme 1).39 A related PKI complex (R1 )
Table 1 provides the propylene polymerization data for
complexes 1-6. When activated with MAO, all complexes were
active with the exception of 4, and produced isoenriched
polypropylene with [m4]-values ranging from 0.30 to 0.57. All
active catalysts formed polymers with very narrow molecu-
lar weight distributions (Mw/Mn e 1.12), which suggests
living behavior. Compared to 1, the halogenated complexes (2
and 3) showed much higher activity. This could be
attributed to both the increase in electronegativity of
(38) Chen, S. T.; Zhang, X. F.; Ma, H. W.; Lu, Y. Y.; Zhang, Z. C.; Li, H. Y.;
Lu, Z. X.; Cui, N. N.; Hu, Y. L. J. Organomet. Chem. 2005, 690, 4184-
4191.
(39) Mazzeo, M.; Strianese, M.; Lamberti, M.; Santoriello, I.; Pellecchia, C.
Macromolecules 2006, 39, 7812-7820.
9
J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008 4971

A R T I C L E S
Edson et al.
Table 1. Propylene Polymerization Data for Catalysts 1-6/MAOa
1
b
c
cplx
T (h)
yield (g)
TOF (h-
)
Mntheo (g/mol)
Mn (g/mol)c
Mw/Mn
[mmmm]d
Re
Tg
(
°
C)f
Tm (°
C)f
1
2
3
4
5
6
6.0
6.0
6.0
6.0
6.0
6.0
0.55
2.24
1.34
traceh
0.04
0.15
230
890
530
55 000
224 000
134 000
43 000
148 000
93 300
1.10
1.09
1.08
0.52
0.31
0.57
0.88
0.79
0.89
-12.4
-9.4
n.d.g
n.d.g
73.4
-14.3
20
58
4000
15 000
3000
15 000
1.10
1.12
0.43
0.54
0.84
0.89
-23.2
-13.3
n.d.g
85.1
a General conditions: 10 µmol of the complex in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti]
) 150) at 0 °C. b Average turnover frequency (TOF): mol propylene/(mol Ti‚h). c Determined using gel permeation chromatography in 1,2,4-C6H3Cl3 at
140 °C versus polyethylene standards. d Determined by integration of the methyl region of the 13C NMR spectrum. e Enantiofacial selectivity parameter,
calculated from the 13C NMR spectrum using the equation [m4] ) R5 + (1-R)5. f Determined using differential scanning calorimetry (second heating).
g None detected. h Polymer yield was insufficient for characterization.
Table 2. Propylene Polymerization Data for Catalysts 7-9/MAOa
1
b
c
cplx
T (h)
yield (g)
TOF (h-
)
Mntheo (g/mol)
Mn (g/mol)c
Mw/Mn
[mmmm]d
Re
Tg
(
°
C)f
Tm (°
C)f
7
8
9
6.0
6.0
3.0
0.32
1.05
1.45
130
420
1170
32 000
105 000
146 000
70 000
77 500
78 200
1.13
1.07
1.98
0.53
0.51
0.51
0.88
0.87
0.87
-14.2
-12.8
-8.5
n.d.g
n.d.g
145.8
a General conditions: 10 µmol of the complex in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti]
) 150) at 0 °C. b Average turnover frequency (TOF): mol propylene/(mol Ti‚h). c Determined using gel permeation chromatography in 1,2,4-C6H3Cl3 at
140 °C versus polyethylene standards. d Determined by integration of the methyl region of the 13C NMR spectrum. e Enantiofacial selectivity parameter,
calculated from the 13C NMR spectrum using the equation [m4] ) R5 + (1-R)5. f Determined using differential scanning calorimetry (second heating).
g None detected.
the halogen substituent as well as a decrease in steric congestion
near the active site. Interestingly, 3 (R1 ) Br) was approximately
two times more active than 1 for propylene polymerization, and
the resultant polymer had an [m4]-value of 0.57 and a melting
temperature (Tm) of 73.4 °C. However, 2 (R1 ) Cl) provided
polypropylene with an [m4]-value of 0.31 and no melting
transition, thus illustrating the extreme sensitivity of the
relationship between the facial selectivity and the size of the
ortho substituent of the phenolate ring. Complex 4 (R1 ) Ph)
only produced trace amounts of polymer, while complex 5,
bearing a bulkier benzyl substituent, showed a marginally higher
activity. Complex 6, derived from tetrahydronaphthol, was
sparingly active and produced a polymer with an [m4]-value of
0.54 and Tm of 85.1 °C. The polypropylene produced by
6/MAO, despite having a similar [m4]-value, showed a higher
Tm than the polypropylene produced by 3/MAO. This could be
attributed to a decrease in the number of regioinversions of the
polypropylene produced by 6/MAO versus 3/MAO (see Sup-
porting Information).
Effect of the Para Substituent on the Phenolate Ring. Once
the role of the ortho substituent on the phenolate ring (R1) was
established, the effect of the para substituent (R3) was investi-
gated. Scheme 1 (entries 7-9) summarizes the series of
complexes that were synthesized and screened for propylene
polymerization behavior. We anticipated that electron-withdraw-
ing R3 groups with greater electronegativities would increase
catalyst activity by increasing the electrophilicity of the metal
center. We did not expect these changes to effect the facial
selectivity of the catalyst due to the remote location of the para
substituent relative to the active site.
pylene with very narrow molecular weight distributions (Mw/
Mn e 1.13). Surprisingly, 9 (R3 ) OMe) had an activity five
times higher than that of 1. The GPC trace for the polypropylene
produced by 9 was broad and multimodal, indicative of multiple
active species. The resultant polypropylene showed a Tm of
145.8 °C and could be separated into ether-soluble (ca. 24 wt
%) and ether-insoluble (ca. 76 wt %) fractions, both giving GPC
traces that were again broad and multimodal. One possible
explanation for this observation is that the methoxy group on
the ancillary ligand reacts with the cocatalyst in situ to generate
one or more new active species. We are currently investigating
the source of this unusual polymerization behavior.
Effect of Alkyl Substituents on the Ketimine Carbon. PKI
catalysts previously studied for propylene polymerization
contained a phenyl ketimine substituent (R4). Although remote
from the active center, we reasoned that by investigating other
substituents off of the ketimine carbon that improved isoselec-
tivity for propylene polymerization could be achieved. To probe
the difference between a phenyl and alkyl groups at this position,
complexes bearing various alkyl ketimine substituents (R4)
incorporating the 2,4-dimethylphenol moiety were synthesized
and screened for propylene polymerization behavior (Scheme
1, entries 10-14).
Table 3 provides the propylene polymerization data for
complexes 10-14. When activated with MAO, all catalysts were
active and produced polypropylene with [m4]-values ranging
from 0.61 to 0.73. In all cases, catalysts bearing alkyl substit-
uents on the ketimine carbon were more isoselective for
propylene polymerization than 1 (R4 ) Ph). Catalyst 10 (R4 )
Me) furnished a polymer with [m4] ) 0.61 and Tm ) 90.3 °C,
but the activity was approximately an order of magnitude lower
than 1. Increasing the steric demand of the R4 substituent led
Table 2 provides the propylene polymerization data for
complexes 7-9. When activated with MAO, all catalysts were
active and produced polypropylene with [m4]-values ranging
from 0.51 to 0.53. Catalyst activities did not follow the expected
trend where more electron-withdrawing substituents give higher
activities. For example, 7 (R3 ) Cl) had an activity ap-
proximately half that of 1, whereas 8 (R3 ) F) had an activity
approximately twice that of 1. Both 7 and 8 formed polypro-
i
to improved tacticity. For example, catalyst 11 (R4 ) Pr)
polymerized propylene with an activity comparable to 10 and
furnished a polymer with [m4] ) 0.67 and Tm ) 114.5 °C. A
i
further gain in tacticity was achieved upon replacing the Pr
ketimine substituent with cyclohexyl as catalyst 12 exhibited
similar activity to 10 and 11 but provided polymer with [m4] )
9
4972 J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008

Multiblock Isotactic Polypropylene Copolymers
A R T I C L E S
Table 3. Propylene Polymerization Data for Catalysts 10-14/MAOa
1
b
c
cplx
T (h)
yield (g)
TOF (h-
)
Mntheo (g/mol)
Mn (g/mol)c
Mw/Mn
[mmmm]d
Re
Tg
(°
C)f
Tm (°
C)f
10
11
12
13
14
14g
6.0
6.0
6.0
6.0
6.0
4.0
0.08
0.10
0.07
0.09
1.53
0.29
30
41
30
30
604
340
8000
10 000
7000
9000
153 000
58 000
8000
8500
8000
8000
364 000
76 000
1.14
1.25
1.22
1.23
1.33
1.09
0.61
0.67
0.73
0.69
0.68
0.67
0.91
0.92
0.94
0.93
0.93
0.92
-14.4
-11.4
-12.9
-11.5
-11.3
-13.0
90.3
114.5
116.8
111.9
93.8
93.3
a General conditions: 10 µmol of the complex in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti]
) 150) at 0 °C. b Average turnover frequency (TOF): mol propylene/(mol Ti‚h). c Determined using gel permeation chromatography in 1,2,4-C6H3Cl3 at
140 °C versus polyethylene standards. d Determined by integration of the methyl region of the 13C NMR spectrum. e Enantiofacial selectivity parameter,
calculated from the 13C NMR spectrum using the equation [m4] ) R5 + (1-R)5. f Determined using differential scanning calorimetry (second heating).g A
5-µmol portion of the complex in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti] ) 150) at -40 °C.
Table 4. Propylene Polymerization Data for Catalysts 15-19/MAOa
1
b
c
cplx
T (h)
yield (g)
TOF (h-
)
Mntheo (g/mol)
Mn (g/mol)c
Mw/Mn
[mmmm]d
Re
Tg
(
°
C)f
Tm (°
C)f
15
16
17
18
19
6.0
6.0
2.0
6.0
6.0
0.65
0.12
0.41
0.76
1.33
250
49
490
310
538
65 000
12 000
41 000
76 000
133 000
45 000
12 000
87 000
83 000
170 000
1.08
1.19
3.19
1.28
1.11
0.52
0.66
0.53
0.32
0.58
0.88
0.92
0.88
0.80
0.89
-12.0
-12.4
-7.1
n.d.g
105.2
144.1
n.d.g
68.8
-6.5
-15.1
a General conditions: 10 µmol of the complex in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti]
) 150) at 0 °C. b Average turnover frequency (TOF): mol propylene/(mol Ti‚h). c Determined using gel permeation chromatography in 1,2,4-C6H3Cl3 at
140 °C versus polyethylene standards. d Determined by integration of the methyl region of the 13C NMR spectrum. e Enantiofacial selectivity parameter,
calculated from the 13C NMR spectrum using the equation [m4] ) R5 + (1-R)5. f Determined using differential scanning calorimetry (second heating).
g None detected.
0.73 and Tm ) 116.8 °C. Despite incorporating the bulkier
cycloheptyl ketimine substituent, catalyst 13 resulted in a
polymer with [m4] ) 0.69 and Tm ) 111.9 °C, although the
activity was comparable to that observed with 12. Catalysts 10-
13 formed polypropylene with narrow molecular weight dis-
tributions (Mw/Mn e 1.25) and with good agreement between
the number average molecular weight (Mn) and that expected
based on the assumption of one chain per metal center (Mntheo).
To investigate the difference between alkyl and fluorinated alkyl
substituents, catalyst 14, which bears a trifluoromethyl ketimine
substituent (R4 ) CF3), was synthesized. Polymerization of
propylene with 14/MAO proceeded with an activity ap-
proximately 20 times that of 10 and provided a polymer with
[m4] ) 0.68 and Tm ) 93.8 °C. The resultant molecular weight
distribution (Mw/Mn ) 1.33) was slightly broadened upon
replacing the methyl ketimine substitution for CF3, and there
was a discrepancy between Mn and Mntheo. Cooling the reaction
to -40 °C led to a more controlled polymerization where the
giving approximately the same molecular weight, activity, and
level of isoselectivity. Upon changing the connectivity (16, R4
) 1-naphthyl), the activity decreases 5-fold from 15 and
furnishes PP with an [m4] ) 0.66 and Tm ) 105.2 °C. Catalyst
17 (R4 ) 4-methoxyphenyl) provided polypropylene with a high
Tm (144.1 °C) but behaved similarly to 9 in that a multimodal
GPC trace was obtained. Because this behavior is only observed
with ligands featuring methoxy groups, we believe an interaction
between the aluminum cocatalyst and the methoxy group could
be causing this unusual behavior. Catalyst 18, which contains
a mesityl ketimine (R4) substituent, exhibits an activity that is
slightly higher than 1 and produces PP with [m4] ) 0.32.
Employing a perfluorophenyl ketimine substituent, 19/MAO
exhibited an activity twice that of 1 and produced PP with [m4]
) 0.58 and Tm ) 68.8 °C. In all cases, the PP produced from
15-19/MAO displayed narrow molecular weight distributions
(Mw/Mn e 1.28).
Microstructural Analysis of Polypropylenes by 13C NMR
Spectroscopy. Figure 3 provides the 13C NMR spectrum of iPP
obtained from 12/MAO at 0 °C. The major stereoerrors present
correspond to mmmr, mmrr, and mrrm pentads. These three
pentads are present in a 2:2:1 ratio, which is indicative of an
enantiomorphic site-control enchainment mechanism. The 13C
NMR spectra of iPPs obtained from 1-11 and 13-19/MAO
were similar in appearance to that obtained from 12/MAO (see
Supporting Information) and show varying degrees of stereo-
control with the major stereoerrors present corresponding to
mmmr, mmrr, and mrrm pentads in a 2:2:1 ratio. This is
consistent with previously reported PKI catalysts,18 but is quite
different from the previously reported syndioselective PHI
catalysts which have stereoerrors resulting from a chain-end
control mechanism.20
theo
disparity between Mn and Mn was smaller and the resultant
polypropylene showed a much narrower molecular weight
distribution (Mw/Mn ) 1.09). However, lower reaction temper-
ature did not have a pronounced effect on the activity of the
polymerization and furnished polypropylene with similar tac-
ticity; [m4] ) 0.67 and Tm ) 93.3 °C.
Effect of Aryl Substituents on the Ketimine Carbon. To
investigate the effect of the aryl ketimine substituents (R4),
catalysts incorporating the 2,4-dimethylphenol moiety were
synthesized and screened for propylene polymerization (Scheme
1, entries 15-19). In light of the trends observed with PKI
catalysts bearing different alkyl substituents, we reasoned that
bulkier aryl substituents would give increased isoselectivity for
propylene polymerization.
Table 4 provides the propylene polymerization data for
complexes 15-19. When activated with MAO, all catalysts were
active and produced polypropylene with [m4]-values ranging
from 0.32 to 0.66. Catalyst 15/MAO bearing a 2-naphthyl
ketimine substituent behaved almost identically to catalyst 1,
While the polymer obtained from 12/MAO is very regio-
regular, resonances corresponding to head-to-head and tail-to-
tail misinsertions can be detected in the δ 14-16 and δ 31-46
ppm regions of the 13C NMR spectrum.14 The occurrence of
regioerrors varied in polypropylenes produced using 1-19/
9
J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008 4973

A R T I C L E S
Edson et al.
Figure 3. 13C NMR spectrum (1,1,2,2-C2D2Cl4, 125 MHz, 135 °C) of isotactic polypropylene formed by 12/MAO at 0 °C. The presence of the unmarked
peak in the methyl region is due to regioinversions.
MAO. The PP produced by 18/MAO displayed the lowest
occurrence of regioerrors (see Supporting Information). Despite
being more isoselective than 1, the PP produced by 19/MAO
displayed the highest occurrence of regioerrors of the catalysts
studied (see Supporting Information).
Living Behavior of Bis(phenoxyketimine)titanium Com-
plexes. The narrow molecular weight distribution of the iPP
produced by 12/MAO, coupled with the observed good agree-
ment between Mn and Mntheo, indicate that propylene polymer-
ization catalyzed by 12/MAO is living. The living behavior of
12/MAO is further exemplified by the observation that Mn
increases linearly with polypropylene yield (Figure 4). The
molecular weight distribution for shorter reaction times is
somewhat broadened (t ) 6 h; Mw/Mn ) 1.30), but narrows for
longer reaction times (t ) 48 h; Mw/Mn ) 1.15). This is
presumably due to slow initiation.
Block Copolymers from Propylene and Ethylene. While
one drawback of a living polymerization system is that only
one polymer chain per metal center is produced, the real utility
of these systems lies in the ability to synthesize well-defined
block copolymers and identify new polymer architectures with
promising physical, mechanical, and chemical properties. There
are few examples of block copolymers incorporating iPP
segments in the literature,5-8,17,18 which is due in large part to
the fact that few catalyst systems have been reported that are
capable of polymerizing propylene in a living manner with high
isoselectivity and activity. Block copolymers incorporating sPP,
however, have been synthesized with much greater ease.
In 1988, Doi and co-workers synthesized an sPP-block-PEP-
block-sPP triblock copolymer with a narrow molecular weight
distribution (Mw/Mn ) 1.24) and a high molecular weight (Mn
) 94 kg/mol) utilizing a catalyst system composed of V(acac)3/
Et2AlCl/anisole.40 Bis(phenoxyimine)titanium complexes em-
ploying the N-pentafluoroaniline moiety and bulky tert-butyl
ortho phenolate groups have been used to synthesize an sPP-
block-PEP diblock24,41 and an sPP-block-PEP-block-sPP triblock
copolymer.6 This class of catalysts has also been used to produce
a PE-block-sPP diblock copolymer and a PE-block-PEP-block-
sPP triblock copolymer.42 A sPP-block-poly(propylene-co-MCP-
co-3-VTM) (MCP ) methylene-1,3-cyclopentane; 3-VTM )
3-vinyl tetramethylene) diblock copolymer has also been
produced via sequential monomer addition using propylene and
1,5-hexadiene with this class of catalysts.43
Owing to the living behavior and the relatively high isos-
electivity of 12/MAO for propylene polymerization, we reasoned
that it would make an ideal catalyst for the synthesis of block
copolymers incorporating iPP segments (Scheme 2). Living
polymerization of propylene at 0 °C resulted in the formation
of iPP ([m4] ) 0.73). Once a block of the desired length was
formed (typically after 15 h), a slight overpressure of ethylene
was added and copolymerized with the unreacted propylene to
produce a PEP block. The molecular weight of the PEP block
was adjusted by varying the duration of polymerization (Table
5, entries 1-3). Triblock iPP-block-PEP-block-iPP copolymers
were synthesized by the removal of ethylene and by reestablish-
ing the propylene feed for the specified time. To our knowledge,
this is the first synthesis of an iPP-block-PEP-block-iPP triblock
copolymer via sequential monomer addition. A pentablock
(40) Doi, Y.; Ueki, S.; Keii, T. Makromol. Chem. Rapid Commun. 1982, 3,
225-229.
(41) Kojoh, S.; Matsugi, T.; Saito, J.; Mitani, M.; Fujita, T.; Kashiwa, N. Chem.
Lett. 2001, 822-823.
(42) Mitani, M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui,
S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.; Matsugi, T.; Kashiwa,
N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327-3336.
(43) Hustad, P. D.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 11578-11579.
9
4974 J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008

Multiblock Isotactic Polypropylene Copolymers
A R T I C L E S
Figure 4. Plot of polypropylene Mn (O) and Mw/Mn (9) vs polypropylene yield using 12/MAO at 0 °C.
Scheme 2. Synthesis of Block Copolymers from Ethylene and Propylene
Table 5. Block Copolymer Characterizationa
b
sample
Mn,tot (kg/ mol)b Mw/Mn
block lengths (kg/ mol)c
wt. % of hard blocksd Fe total (mol %)e Tg C)f Tm C)f
(° (°
iPP-b-PEP-b-iPP (isoTB-1)
iPP-b-PEP-b-iPP (isoTB-2)
iPP-b-PEP-b-iPP (isoTB-3)
iPP-b-PEP-b-iPP-b-PEP-b-iPP (isoPB)
iPP-b-PEP-b-iPP-b-PEP-b-iPP-b-PEP-b-iPP (isoHB)
102
144
235
195
227
1.13 12-75-15
26
17
12
22
26
16
17
15
20
18
-35
-33
-39
-40
-33
115
107
95
94
88
1.18 14-117-13
1.30 14-206-15
1.15 14-74-15-78-14
1.13 13-74-7-51-32-44 -6
a General conditions: 10 µmol of 12 in toluene (5 mL) was added to a propylene-saturated PMAO-IP solution (100 mL of toluene; [Al]/[Ti] ) 150)
at 0 °C. After the desired time, a C2H4 feed was established. The C2H4 feed was discontinued and the reactor was vented to 0 psig, 30 psig of
propylene reconnected and polymerization allowed to proceed for the desired time. b Determined using gel permeation chromatography in 1,2,4-C6H3Cl3
at 140 °C versus polyethylene standards. c Determined by the difference in Mn of aliquots pulled after the formation of each block. d Wt. % of hard blocks
) (Σ Mn,hard)/(Mn,tot). e Mole fraction of ethylene (Fe) determined by integration of the 13C NMR spectrum. f Determined using differential scanning calorimetry
(second heating).
copolymer (isoPB) and heptablock copolymer (isoHB) were
made in an analogous manner (Table 5, entries 4 and 5). Due
presumably to decreased diffusion efficiency resulting from the
high viscosity of the polymerization mixture, a higher overpres-
sure of ethylene was required to install the second and third
PEP block of the pentablock and heptablock copolymer,
respectively.
The iPP segments had a melting temperature between 99 and
115 °C, decreasing with increasing overall molecular weight
for the triblock copolymer samples (Table 5, entries 1-3).
Ethylene fractions (Fe) in the triblock copolymers ranged from
15 to 17 mol %. The melting temperature of the pentablock
copolymer was 94 °C and had an Fe of 20 mol %, while the
heptablock copolymer had a Tm of 88 °C and an Fe of 18 mol
9
J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008 4975

A R T I C L E S
Edson et al.
Figure 5. GPC profiles after the formation of each block of the isoPB synthesized using complex 12/MAO at 0 °C.
Table 6. Block Copolymer Mechanical Testing Data
%. All block copolymers showed a Tg between -40 and
-33 °C. The high melting temperatures and low glass transition
temperatures are indicative of block copolymers incorporating
iPP and PEP segments. A representative GPC profile of the
pentablock copolymer is shown in Figure 5, where aliquots were
removed from the polymerization mixture after the formation
of each block, and the resultant polymers were analyzed via
gel permeation chromatography.
Young’s
Modulus
(MPa)a
strain at
true stress
melting
elastic
recovery (%)b
sample
break (%)
at break (MPa)
enthalpy (J/g)
isoTB-1
isoTB-2
isoTB-3
isoPB
10.9
6.9
12.0
11.7
9.0
∼1000
∼800
∼950
∼790
∼830
120
64
112
84
14.3
11.8
16.1
16.8
13.1
80
81
68
79
85
isoHB
100
Mechanical Properties of Block Copolymers. The initial
Young’s modulus is partly determined by the connectivity
between crystalline lamellae, which is why it correlates roughly
with the melting enthalpy and thus crystallinity. After about a
500% prestrain, the Young’s modulus after unloading decreases
dramatically to values between 1.2 and 2.5 MPa that are more
typical of an elastomer. The prestrain presumably breaks up
the network of crystalline lamellae into individual iPP fibrils
separated by the rubbery PEP blocks.
a Measured in tension at strain of 15%. b After 750% prestrain.
MPa and a 79% recovery up to elongation of 750%, while the
heptablock copolymer showed an elongation at break of ∼830%
with a tensile true stress of 100 MPa and an 85% recovery up
to elongation of 750%. While the mechanical properties of the
block copolymers are similar, it is apparent that incorporation
of large PEP segments leads to a decrease in the percent
recovery of the materials.
The block copolymers all displayed surprisingly similar
elastomeric behavior. The triblock copolymer (isoTB-1) dis-
played an elongation at break of ∼1000% with a tensile true
stress of 120 MPa and an 80% recovery up to elongation of
750%. Increasing the midblock PEP segment length of the
triblock copolymers led to diminished values for elongation at
break and tensile true stress. For example, isoTB-2, exhibited
an elongation at break of ∼800% and a tensile true stress of 64
MPa with an 81% recovery up to elongation of 750% while
isoTB-3 exhibited an elongation at break of ∼950% and a tensile
true stress of 112 MPa with a 68% recovery up to elongation
of 750%. The pentablock copolymer (isoPB) displayed an
elongation at break of ∼790% with a tensile true stress of 84
The triblock copolymer (isoTB-1) displayed the highest
ultimate elongation at break (∼1000%) relative to the other
copolymers studied herein. This value is lower than the triblock
copolymer comprised of iPP-b-rirPP-b-iPP (∼1700%)6 and
tetrablock copolymer comprised of iPP-b-aPP-b-iPP-b-aPP
(∼1200%).7 The lower elongation at break displayed for
isoTB-1 could be due to a number of factors such as overall
crystallinity, molecular weight, or amorphous segment identity.
Conclusions
Bis(phenoxyketimine)titanium catalyst systems bearing dif-
ferent substituents at the ortho and para positions of the
phenolate rings, and ketimine carbon susbstituents featuring an
9
4976 J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008

Multiblock Isotactic Polypropylene Copolymers
A R T I C L E S
N-pentafluorophenyl moiety all displayed activity for propylene
polymerization. All catalysts were isoselective with [m4]-values
between 0.31 and 0.73 for the resultant polypropylenes. The
prevailing mode of stereocontrol was an enatiomorphic site-
control mechanism as evidenced by the 2:2:1 ratio of the
resonances corresponding to the mmmr:mmrr:mrrm pentads in
the 13C NMR spectra of the polypropylenes formed. Complexes
bearing ortho-halide substituents on the phenolate ring displayed
much higher activity than those bearing alkyl substituents with
the size of the substituent determining the level of facial
selectivity. The identity of the para substituent had a dramatic
influence on the activity of the polymerization but had no effect
on the selectivity. Varying the substituents at the ketimine carbon
of the ancillary ligand had the most pronounced effect on both
the activity and the isoselectivity of propylene polymerization.
All of the catalyst systems screened showed living behavior
except those with methoxy groups on the ancillary ligand. Using
12/MAO, a number of new block copolymers from propylene
and ethylene were synthesized via sequential monomer addition.
Specifically an iPP-b-PEP-b-iPP triblock copolymer, iPP-b-PEP-
b-iPP-b-PEP-b-iPP pentablock copolymer, and iPP-b-PEP-b-
iPP-b-PEP-b-iPP-b-PEP-b-iPP heptablock copolymer were pre-
pared. The block copolymers displayed elastomeric behavior
and exhibited excellent mechanical properties.
Acknowledgment. We thank Dr. A. F. Mason for preliminary
work and helpful discussions and acknowledge support from
Mitsubishi Chemical Corporation. This research made use of
the Cornell Center for Materials Research Shared Experimental
Facilities and the UCSB Materials Research Laboratory Central
Facilities supported through the NSF MRSEC program (DMR-
0520404 and DMR-0520415 respectively).
Supporting Information Available: Ligand, complex, poly-
mer syntheses, and 13C{1H} NMR spectra of polypropylenes
produced from complexes 1-19/MAO. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
JA077772G
9
J. AM. CHEM. SOC. VOL. 130, NO. 14, 2008 4977