Substituent effects of tert-butyl groups on fluorenyl ligand in syndiospecific living polymerization of propylene with ansa- fluorenylamidodimethyltitanium complex

Article abstract of DOI:10.1021/ma050898i

[t-BuNSiMe₂(2,7-t-Bu₂Flu)]TiMe₂ and [t-BuNSiMe₂(3,6-t-Bu₂Flu)]TiMe₂ were synthesized and characterized by elemental analysis, ¹H NMR, and single-crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst at 0 and 25°C. The introduction of tert-butyl substituents to the fluorenyl ligand improved the activity more than 3 times regardless of the position of the substituents. The postpolymerization testified that both catalytic systems conducted the propylene polymerization in a living manner at both 0 and 25°C. The propagation rate increased linearly against the Al/Ti ratio from the range of 100-400 with keeping the number of polymer chains constant, which directly indicates that a larger amount of dMMAO enhanced the propagation rate. The introduction of tert-butyl substituents also improved the syndiospecificity: the 3,6-position was more effective than the 2,7-position, and [t-BuNSiMe ₂(3,6-t-Bu₂-Flu)]TiMe₂ gave the living polypropylene with the syndiotactic triad of 0.93 and the melting point of 142°C.

Full text of DOI:10.1021/ma050898i

Macromolecules 2005, 38, 8135-8139
8135
Articles
Substituent Effects of tert-Butyl Groups on Fluorenyl Ligand in
Syndiospecific Living Polymerization of Propylene with
ansa-Fluorenylamidodimethyltitanium Complex
†
‡
‡
,†
Zhengguo Cai, Tomiki Ikeda, Munetaka Akita, and Takeshi Shiono*
Graduate School of Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima
7
4
39-8527, Japan, and Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta-cho
259, Midori-ku, Yokohama 226-8503, Japan
Received April 27, 2005; Revised Manuscript Received August 4, 2005
ABSTRACT: [t-BuNSiMe (2,7-t-Bu Flu)]TiMe and [t-BuNSiMe (3,6-t-Bu Flu)]TiMe were synthesized
2
2
2
2
2 2
1
and characterized by elemental analysis, H NMR, and single-crystal X-ray analysis. These complexes
were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a
cocatalyst at 0 and 25 °C. The introduction of tert-butyl substituents to the fluorenyl ligand improved
the activity more than 3 times regardless of the position of the substituents. The postpolymerization
testified that both catalytic systems conducted the propylene polymerization in a living manner at both
0
and 25 °C. The propagation rate increased linearly against the Al/Ti ratio from the range of 100-400
with keeping the number of polymer chains constant, which directly indicates that a larger amount of
dMMAO enhanced the propagation rate. The introduction of tert-butyl substituents also improved the
2 2
syndiospecificity: the 3,6-position was more effective than the 2,7-position, and [t-BuNSiMe (3,6-t-Bu -
Flu)]TiMe
2
gave the living polypropylene with the syndiotactic triad of 0.93 and the melting point of 142
°
C.
Introduction
Chart 1
Since the first living polymerization of propylene was
reported with the V-based homogeneous catalyst in the
1
end of 1970s, much effort has been paid for developing
homogeneous catalysts for living polymerization of
propylene by designing the structure of complexes and
2-14
controlling the polymerization conditions.
Although
stereospecific living polymerization systems are neces-
sary to design propylene-based well-defined polymers,
there are only limited examples for the stereospecific
living polymerization of propylene.
The Mitsui group and Coates et al. reported that bis-
phenoxyimine)titanium derivatives combined with me-
(
thylalumoxane (MAO) were effective for syndiospecific
living polymerization of propylene by chain-end control
to give syndiotactic polypropylene (PP)-block-poly-
(
ethylene-co-propylene) by sequential monomer addi-
6
-10
tion.
The Mitsui group succeeded in improving the
syndiospecificity to 0.94 in syndiotactic triad (rr) by
1
0
tuning the bis(phenoxyimine) ligand. Busico et al.
reported the synthesis of isotactic PP-block-polyethylene
with the Zr complex containing phenoxyamine ligand
via “quasi-living polymerization”, and they have recently
found that the use of adamantyl-substituted phenoxy
ligands not only improved isospecificity to 0.985 in
isotactic pentad (mmmm) but also suppressed the
recently reported that the bis(phenoxyketimine)tita-
nium complex produced substantially isotactic living PP
with mmmm value of 0.61 at -20 °C and gave isotactic
PP-block-poly(ethylene-co-propylene).12 These living sys-
tems realized the block copolymers composed of stere-
oregular PP segments. The propagation rates of propy-
lene in these living systems were however much lower
than those of common nonliving systems.
1
1
monomer-induced chain transfer. Coates et al. have
†
Hiroshima University.
We have previously reported that Ti complex 1 (Chart
‡
Tokyo Institute of Technology.
1
) possessing the fluorenyldimethylsilylamido ligand
*
Corresponding author: Tel +81-82-424-7730; fax +81-82-424-
5
494; e-mail tshiono@hiroshima-u.ac.jp.
conducted syndiospecific living polymerization of pro-
1
0.1021/ma050898i CCC: $30.25 © 2005 American Chemical Society
Published on Web 08/31/2005

8136 Cai et al.
Macromolecules, Vol. 38, No. 20, 2005
Table 1. Propylene Polymerization with 2 and 3 Activated by DMMAOa
Al/Tib
time (min)
yield (g)
activityc
Mnd (×104)
Mw/Mnd
N (µmol)
e
entry
cat.
temp (°C)
1
2
3
4
5
6
7
1
2
3
2
3
2
3
0
0
400
400
400
200
200
200
200
11
3
2.42
2.28
2.32
2.36
2.14
2.44
2.20
660
2279
2318
787
16.1
20.8
19.6
20.2
16.9
19.0
16.9
1.31
1.65
1.46
1.68
1.45
1.48
1.43
15
11
12
12
13
13
12
0
3
0
0
25
25
9
7
916
6
1220
1318
5
a
Polymerization conditions: heptane ) 30 mL, Ti ) 20 µmol, propylene ) 1 atm. b Molar ratio. c Activity in kg of PP/(mol of Ti h).
d
e
Number-average molecular weight and molecular weight distribution determined by GPC using universal calibration. Calculated from
yield and Mn.
pylene at 0 °C, when activated by dried methylalumi-
noxane (dMAO) in toluene.13 We have investigated the
solvent effects on the stereospecificity of the propylene
polymerization by using 1 combined with dried modified
MAO (dMMAO), which was prepared from the toluene
solutions of MMAO by removing the solvent and free
trialkylaluminums, and found that the syndiospecificity
improved according to the decrease in the polarity of
the solvent with keeping the livingness, and the PP with
the rr value of 0.73 was obtained in heptane with high
14
activity. The Atofina group has reported that [t-BuN-
15
SiMe2(2,7-t-Bu2Flu)]TiCl2 and [t-BuNSiMe2(3,6-t-Bu2-
1
6
Flu)]TiCl2 combined with MAO produced highly sny-
diotactic PP with high activity.
In this paper, aiming at highly syndiospecific living
polymerization of propylene with high activity, we
synthesized [t-BuNSiMe2(2,7-t-Bu2Flu)]TiMe2 (2) and
Figure 1. Rate-time profiles of propylene polymerization
with 2 or 3 activated by dMMAO at 0 °C: (9) 2, ([) 3.
polystyrene standard and K ) 1.03 × 10-4, R ) 0.78 for PP
13
samples. The C NMR spectra of PPs were measured at 130
[
t-BuNSiMe2(3,6-t-Bu2Flu)]TiMe2 (3) (Chart 1) and ap-
°
C on a JEOL GX 500 spectrometer operated at 125.65 MHz
plied them for propylene polymerization in heptane
using dMMAO as a cocatalyst.
in the pulse Fourier transform mode. The pulse angle was 45°,
and about 10 000 scans were accumulated in pulse repetition
of 5.0 s. Sample solutions were prepared in 1,1,2,2-tetrachlo-
Experimental Section
2
roethane-d , and the central peak of the solvent (74.47 ppm)
was used as an internal reference. Differential scanning
calorimetry (DSC) analyses were performed on a Seiko DSC-
Materials. All operations were performed under nitrogen
gas using standard Schlenk techniques, and all solvents were
dried by usual procedures and freshly distilled before use. The
ligands of the Ti complexes and the complexes were prepared
2
20. The samples were encapsulated in aluminum pans and
annealed at 80 °C for 4 h to ensure sufficient time for
crystallization. After annealing, the DSC curves of the samples
were recorded under a nitrogen atmosphere with a heating
rate of 10 °C/min from 20 to 200 °C. Diffraction measurements
of X-ray were made on a Rigaku RAXIS IV imaging plate area
detector with Mo KR radiation (λ ) 0.710 59 Å). Indexing was
performed from two oscillation images, which were exposed
for 5 min. The crystal-to-detector distance was 110 mm.
Readout was performed with the pixel size of 100 µm × µm.
Neutral scattering factors were obtained from the standard
source.
1
6,17
according to the literature procedure.
The complexation of
the ligands and TiCl was conducted by the method reported
4
by Resconi to directly obtain the corresponding dimethyl
complexes, and the complexes were isolated as dark-red single
crystals in good yields (see Supporting Information). dMMAO
1
8
was prepared according to the method reported previously.
Reserarch grade propylene (Takachiho Chemicals Co.) was
purified by passing it through columms of NaOH, P , and
molecular sieves 3 Å, followed by bubbling it through a
NaAlH Et /1,2,3,4-tetrahydronaphthalene solution.
2 5
O
2
2
Polymerization Procedure. Polymerization was per-
formed in a 100 mL glass reactor equipped with a magnetic
stirrer and carried out as the following two methods. (i)
Semibatch method. At first, the reactor was charged with
prescribed amounts of dMMAO and solvent (heptane). After
the solution of cocatalyst was saturated with gaseous propy-
lene under atmospheric pressure, polymerization was started
by the addition of 1 mL solution of the Ti complex (20 µmol)
in heptane, and the consumption rate of propylene was
monitored by a mass flow meter. (ii) Batch-type method. After
a certain amount of gaseous propylene was dissolved in the
heptane solution of dMMAO, polymerization was started by
the addition of 1 mL solution of catalyst (20 µmol) in heptane.
Polymerization was conducted for a certain time and termi-
nated with acidic methanol. The polymers obtained were
adequately washed with methanol and dried under vacuum
at 60 °C for 6 h.
Results and Discussion
Propylene polymerizations were performed by 2 and
activated with dMMAO in heptane at 0 and 25 °C,
3
respectively. The results are summarized in Table 1.
For comparison, the result of the nonsubstituted
original complex 1 is shown in entry 1 of Table 1. 2 and
3
showed more than 3 times higher activity of 1 in the
presence of dMMAO (Al/Ti ) 400) and produced a large
amount of polymer in a few minutes to stop the stirring
(entries 2 and 3). Hence, the polymerization behaviors
could not be evaluated correctly. We therefore reduced
the Al/Ti ratio to 200 (entries 4 and 5).
The rate-time profiles of propylene polymerization
with both systems showed the constant activity after a
certain induction period until the stirring was interfered
by the polymer produced.
Both systems gave high-molecular-weight PPs (Mn >
150 000) for 7 min at 0 °C. These results indicate that
the propagation rate was improved by the introduction
Analytical Procedure. Molecular weight and molecular
weight distribution of polymer obtained were determined by
gel permeation chromatography with a Waters 150 CV at 140
°
C using o-dichlorobenzene as a solvent. The parameters for
-
5
universal calibration were K ) 7.36 × 10 , R ) 0.75 for

Macromolecules, Vol. 38, No. 20, 2005
Syndiospecific Living Polymerization 8137
Table 2. Postpolymerization of Propylene with 2 and 3a
b
4
Mw/Mnb
c
entry
cat.
propylene (g)
temp (°C)
time (min)
yield (%)
Mn (×10 )
N (µmol)
8
9
2
2
2
2
3
3
3
3
0.63
0.63 + 0.63
0.63
0.63 + 0.63
0.63
0.63 + 0.63
0.63
0.63 + 0.63
0
0
25
25
0
0
25
25
60
60 + 60
20
20 + 20
60
60 + 60
20
20 + 20
100
100
97
6.5
11.0
5.0
10.2
5.9
11.2
5.1
10.5
1.56
1.49
1.41
1.43
1.27
1.29
1.28
1.32
10
11
12
12
11
11
12
12
1
1
1
1
1
1
0
1
2
3
4
5
95
100
100
97
98
a
b
Polymerization conditions: heptane ) 30 mL, Ti ) 20 µmol, Al ) 4.0 mmol. Number-average molecular weight and molecular weight
c
distribution determined by GPC using universal calibration. Calculated from yield and Mn.
1
3
Figure 3. 125 MHz C NMR spectra of the methyl region of
polypropylenes obtained at 0 °C: (a) 1-dMMAO entry 1; (b)
2
-dMMAO, entry 4; (c) 3-dMMAO, entry 5.
of tert-butyl groups on the Flu ligand. The raise of
polymerization temperature to 25 °C improved the
activity but did not affect the number of polymer chains
(
N) and molecular weight distributions (MWDs). The N
values were about 60-65% of the Ti used, and the
MWDs were around 1.5.
To investigate the living nature of the 2-dMMAO and
-dMMAO systems, we conducted postpolymerization
3
at 0 and 25 °C: the first-step polymerization was
conducted with a certain amount of propylene for 1 h,
and the second-step polymerization was continued for
another 1 h after the addition of the same amount of
propylene with the first step. The results are sum-
marized in Table 2.
In both steps, the conversions were almost quantita-
tive regardless of the complex used and polymerization
temperature, and the Mn value became almost double
of those of the first-step polymers with keeping the N
values constant.
The GPC curves of the polymers obtained are il-
lustrated in Figure 2. The curves of second step shifted
to higher molecular weight region of that of first step
in each catalyst system, and no peak or shoulders were
observed. The results testified that propylene polymer-
Figure 2. GPC curves of polypropylenes obtained in postpo-
lymerization: (a) 2-dMMAO at 0 °C; (b) 2-dMMAO at 25 °C;
(
c) 3-dMMAO at 0 °C; (d) 3-dMMAO at 25 °C.

8138 Cai et al.
Macromolecules, Vol. 38, No. 20, 2005
Table 3. Stereosequence Distributions and Melting Temperature for Sample Entries 1, 4, and 5 in Table 1
stereosequence distributiona
b
entry
mmmm
mmmr
rmmr
mmrr
mmrm + rmrr
rmrm
rrrr
mrrr
mrrm
Tm (°C)
1
4
5
0.00
0.00
0.00
0.00
0.00
0.00
0.04
0.04
0.02
0.09
0.08
0.03
0.10
0.05
0.02
0.04
0.02
0.00
0.60
0.69
0.86
0.13
0.12
0.07
0.00
0.00
0.00
89
92
142
a
Determined by 13C NMR spectroscopy. b Melting Temperature determined by DSC.
Table 4. Effect of Al/Ti Ratio on Propylene
Polymerization with 3 Activated by dMMAO
a
time yield
Ne
Al/Tib (min)
(g)
activityc Mnd (×10 ) Mw/Mnd (µmol)
4
1
2
4
00
00
00
17
7
3
1.85
2.14
2.32
326
916
2318
15.2
16.9
19.6
1.48
1.45
1.46
12
13
12
a
Polymerization conditions: heptane ) 30 mL, Ti ) 20 µmol,
b
c
propylene ) 1 atm. Molar ratio. Activity in kg of PP/(mol of Ti
d
h). Number-average molecular weight and molecular weight
distribution determined by GPC using universal calibration.
e
Calculated from yield and Mn.
rmrr can be explained by the increase of propagation
rate by the introduction of tert-butyl groups if the chain
migration without monomer insertion is independent of
the tert-butyl groups. On the other hand, the rmmr
content was decreased only by 3: 1 (0.04) ) 2 (0.04) >
3
(0.02). These results indicate that the introduction of
tert-butyl proups at the 3,6-position is effective to
improve the enantioselectivity of the catalyst. As a
consequence, 3 gave the PP with the highest syndio-
tacticity, of which melting temperature was 142 °C.
These results are in good agreement with those reported
by Razzavi et al. in propylene polymerization with the
corresponding chloride complexes activated by MAO.1
They described the importance of 3,6-positions of the
Flu ligand for proper regulation of the coordinating
monomer and growing polymer chain compared to 2,7-
positions. The molecular structures of 2 and 3 deter-
mined by single-crystal X-ray analysis are displayed in
Figure 4.
5,16
Figure 4. ORTEP drawings of the molecular structures of 2
and 3. Hydrogen atoms are omitted for clarity. The thermal
ellipsoids are drawn at the 30% probability level.
ization proceeded in a living manner at both 0 and 25
°
C regardless of the complexes employed, although the
One of the characteristics of the living system is of
its simple kinetics: the number of active centers can
be calculated from the yield and the Mn value, and the
propagation rate can be directly evaluated from the Mn
value and polymerization time.
MWDs were slightly larger than that of an ideal living
polymerization system. Both systems show certain
induction period as shown in the rate-time profiles
(Figure 1), and the large amount of produced polymers
prohibited effective stirring to decrease the homogeneity
of the polymerization system, which should be the
reasons for the broader MWDs. The narrower MWDs
with batch system in Table 2 compared with those with
semibatch system in Table 1 support this assumption.
The C NMR spectra of methyl region of PPs obtained
with 2 and 3 at 0 °C are shown in Figure 3. The steric
pentad distributions in main chain and the melting
temperatures of the polymers obtained are summarized
in Table 3. The introduction of tert-butyl groups in-
creased the syndiotactic pentad in the following order:
Although metallocene catalysts generally need a high
Al/metallocene ratio for high activity, the reason of
which is not yet clear. The effect of Al/Ti ratio on this
living polymerization system was therefore investigated
with 3-dMMAO under an atmospheric pressure of
propylene in a semibatch system. The results are
summarized in Table 4.
The polymerization time was changed according to the
activity for keeping good stirring during the polymeri-
zation. The activity increased with increasing Al/Ti
ratios, whereas the N value was independent of the Al/
Ti. This result indicates that the high activity should
come from the high propagation rate.
13
3
(0.86) > 2 (0.69) > 1 (0.60). In the enantiomorphic-
site controlled syndiospecific polymerization with a Cs
symmetric catalyst, two types of stereodefects should
be formed: one is “rmrr” arising from the “chain
migration” without monomer insertion, and the other
is “rmmr” arising from the “monomer miss-insertion”.19
The stereosequence distributions in Table 3 indicate
that the syndiospecific propagation proceeded via enan-
tiomorphic-site controlled mechanism.
The propagation rates were calculated from the
number-average polymerization degree P (M /42) and
n
n
the polymerization time, and the values thus obtained
are plotted against the Al/Ti value in Figure 5. The
propagation rate was found to increase linearly or rather
exponentially against the Al /Ti ratio. We can therefore
conclude that the high Al/Ti ratio is necessary for high
propagation rate but not for high initiation efficiency
in the present catalyst system. The same phenomenon
The rmrr content was decreased in the following
order: 1 (0.10) > 2 (0.05) > 3 (0.02). The decrease of

Macromolecules, Vol. 38, No. 20, 2005
Syndiospecific Living Polymerization 8139
References and Notes
(
(
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(
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with 1-MMAO in toluene.20 One plausible explanation
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(
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(
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1
42 °C in high activity.
Acknowledgment. This work was supported by the
(
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thank Tosoh-Finechem Co. for donating MMAO.
Supporting Information Available: Details of catalysts
synthesis and characterization; X-ray crystallographic files in
CIF format for 2 and 3. This material is available free of charge
via the Internet at http://pubs.acs.org.
(
7432.
MA050898I