Cs-symmetric hafnocene complexes for synthesis of syndiotactic polypropene

Article abstract of DOI:10.1016/S0022-328X(03)00731-9

Three new C _s-symmetric ansa-hafnocene complexes such as dichloro[η¹⁰-2,4-cyclopentadienyl-1-ylidenebis (4-methyldiphenyl-methylen)[2,7-bis(1,1-di-methylethyl)-9H-fluorene-9- ylidene]]hafnium (2) were synthesized which produce partiell syndiotactic polypropylenes with very high molecular weights. The influence of the methyl and methoxy substitution in the bridge was studied on the activity, tacticity, and molar mass. The hafnocene-MAO catalysts (1-4) were active up to polymerisation temperatures of 90 °C and produces 55 000 kg polymer in 1 h by 1 mol of hafnocene. The molecular weight of the obtained elastic polypropylene reaches 2.2 million g mol^-1.

Full text of DOI:10.1016/S0022-328X(03)00731-9

Journal of Organometallic Chemistry 684 (2003) 200ꢀ205
/
www.elsevier.com/locate/jorganchem
Cs-symmetric hafnocene complexes for synthesis of syndiotactic
polypropene
Walter Kaminsky *, Andreas Hopf, Christian Piel
Institut fur Technische und Makromolekulare Chemie, Universitat Hamburg, Bundesstraße 45, D-20146 Hamburg, Germany
¨ ¨
Received 10 April 2003; accepted 17 July 2003
Dedicated to Professor Ernst Otto Fischer on the occasion of his 85th birthday
Abstract
Three new Cs-symmetric ansa-hafnocene complexes such as dichloro[h10-2,4-cyclopentadienyl-1-ylidenebis(4-methyldiphenyl-
methylen)[2,7-bis(1,1-di-methylethyl)-9H-fluorene-9-ylidene]]hafnium (2) were synthesized which produce partiell syndiotactic
polypropylenes with very high molecular weights. The influence of the methyl and methoxy substitution in the bridge was studied on
the activity, tacticity, and molar mass. The hafnoceneꢀ
and produces 55 000 kg polymer in 1 h by 1 mol of hafnocene. The molecular weight of the obtained elastic polypropylene reaches
2.2 million g molꢁ1
/
MAO catalysts (1ꢀ4) were active up to polymerisation temperatures of 90 8C
/
.
# 2003 Published by Elsevier B.V.
Keywords: Hafnocene complexes; Metallocene catalysts; Propene polymerisation; Syndiotactic polypropylene
1. Introduction
[Me2C(C5H4)(C13H8)]MCl2ꢀ/MAO and [Ph2C(C5H4)-
(C13H8)]MCl2ꢀMAO (MꢂZr, Hf). The Ph2C-bridged
catalyst showed a higher stereoselectivity, higher activ-
ities and higher molar masses than the isopropylidene
/
/
Metallocene complexes are in combination with
methylaluminoxane (MAO) highly active catalysts for
the synthesis of precisely designed polyolefins [1ꢀ4].
/
bridged catalyst [6ꢀ9]. The mechanism for the synthesis
/
They show only one active site and produce polymers
with a narrow molecular weight distribution, different
microstructures and tacticities and new physical and
mechanical properties. Depending on the ligand struc-
ture, highly isotactic or syndiotactic polypropenes can
be obtained as well as iso- and stereoblock materials.
Cs-symmetric Group-4 metallocene complexes cata-
lyse the stereospecific polymerisation to syndiotactic
polypropene [5]. The first successful synthesis of syndio-
tactic polypropene was carried out with the catalysts
of syndiotactic polypropene involves an alternating
enchainment of monomer with inverse relative config-
uration and the formation of a syndiotactic chain. This
‘enantiomorphic site control mechanism’ implies that
the chiral catalytic centres are capable of discriminating
between the two prochiral enantiofaces of a propene
molecule [10].
Theoretically studies and molecular modelling
showed that a suitable substitution of the fluorenyl
ligand of the complexes [Ph2C(C5H4)(C13H8)]MCl2
(MꢂZr, Hf) should lead to an increase in the stereo-
/
selectivity and therefore to higher racemic pentads
measured by 13C-NMR spectroscopy as rrrr-values
[11,12]. The most successful positions for a substitution
of the fluorene are the position 3/6 and 2/7. A substitu-
* Corresponding author. Tel.: ꢃ
/
49-40-42838-3162; fax ꢃ
/
49-40-
(W.
42838-6008.
E-mail
address:
kaminsky@chemie.uni-hamburg.de
Kaminsky).
0022-328X/03/$ - see front matter # 2003 Published by Elsevier B.V.
doi:10.1016/S0022-328X(03)00731-9

W. Kaminsky et al. / Journal of Organometallic Chemistry 684 (2003) 200ꢀ
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201
tion of the positions 3 and 6 with a methyl group should
result in very high tacticities as well as a substitution at
the positions 2 and 7 with bulky tert-butyl groups [12].
Substitution of the phenyl groups in the bridge with
electron drawing or pushing groups should increase this
effect. Such substituted zirconocenes and hafnocenes
were synthesized and tested in the propene polymerisa-
tion. The polypropylenes obtained by these zirconocene
complexes show highest syndiotacticities and melting
points, published [13]. Generally, the zirconocenes are
more syndiospecific than the hafnocenes but the hafno-
cenes produce polymers with higher molar masses. For a
lot of applications, high molar masses are very useful
especially if the tacticities are low and more or less
elastic polymers are formed [14]. It was goal of this
study to synthesize hafnocenes which produce polypro-
penes with high molecular masses and syndiotactic
microstructures.
equivalent amount of hafniumtetrachloride [18]. The
yield of the hafnocene complexes reaches after crystal-
lisation 40ꢀ60%.
/
2.2. Polymerisation activities
Four Cs-symmetric hafnocene complexes (Fig. 1)
were synthesized and used for the polymerisation of
propene in toluene solution.
MAO was added as cocatalyst into a 1 l Buchi glass
¨
reactor. The function of MAO is complexing of poisons
such as traces of CO2, alcohol, mercaptanes and other
compounds in the toluene and propene, methylation of
the hafnocene complexes and formation of the active
site, a hafnocene cation.
The polymerisation rate depends on the polymerisa-
tion temperature and the catalyst concentration (Fig. 2).
The activities increase with the temperature for the
hafnocene complexes 1, 2 and 4. Catalyst 3 shows only a
slight increase of activity by higher temperature. Com-
pared to the analogue zirconocene, the activities are by
the factor of 6 slower at 30 8C and of only 1.3 at 60 8C.
Most active is catalyst 4 with methyl substitutions in
para and meta positions at the phenyl groups in the
bridge. With this catalyst, 12 900 kg polypropene is
produced with 1 mol complex in 1 h and a propene
concentration of 1 mol lꢁ1 at 608C. The methyl
substitution is far away from the cationic active center
but even than electronic effects influence the formation
of the cation. The greater steric hinderence decreases the
syndiotacticity. The hafnocene complexes are more
stable by higher polymerisation temperatures than the
zirconocene complexes. At 90 8C an activity of 55 000 kg
PP/(molHf h cpropene) is obtained, while the zirconocene
complex is decomposed at this temperature.
2. Results and discussion
2.1. General synthesis
The bridged fluorenyl-cyclopentadienyl ligand is pre-
pared in three steps. The reaction of fluorene by
FriedelꢀCrafts alkylation leeds to substitution of the
/
fluorene in 2 and 7 position [15]. The synthesis of 2,7-
tert-butylfluorene is possible by electrophile substitution
of 2,6-tert-butyl cresole in the presence of AlCl3 in
nitromethane [16].
The synthesis of the substituted fulvenes goes over the
condensation of cyclopentadiene with substituted ben-
zophenons in methanolꢀTHF and sodium metal for
/
reduction analogue to literature [17] (Scheme 1). The
substituted fluorene is then deprotonised by n-butyl
lithium and reacted with the fulvene (Scheme 2). The
ligand is crystallized from diethylether solution and
received as white solids.
2.3. Melting points and tacticity
Only low melting temperatures are observed for the
synthesized polypropylene samples, corresponding to
low syndiotacticities. There is a great influence of the
After this, the ligand is treated with two equivalents of
n-butyl lithium in diethylether and reacted with the
Scheme 1. Synthesis of the substituted fulvenes.

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W. Kaminsky et al. / Journal of Organometallic Chemistry 684 (2003) 200ꢀ
/205
Scheme 2. Synthesis of the ligands.
polymerisation temperature (Table 1). For comparison,
the analogue zirconocene complex (2a) is also presented
in Table 1 [13].
Only the polymers produced at 30 8C are partial
crystalline. There are observed no melting points at
higher polymerisation temperatures (Fig. 3).
merisation temperature while the polymer of the zirco-
nocene complex 2a has a rrrr value of 93%.
At higher polymerisation temperatures, the rrrr values
decreases to 55% (60 8C) and to 30% (90 8C).
2.4. Molecular weights
These elastic polymers show only glass transition
temperatures. Polypropylene produced by the zirconium
complex 2a has a 50 8C higher melting point.
Of interest are the molecular weights obtained by the
hafnium complexes (Fig. 5).
The polymers obtained by the hafnocene complexes
are characterized by relative low syndiotacticities (Fig.
4). The meso rrrr-pentads measured by 13C-NMR
spectroscopy are between 68 and 78% at 30 8C poly-
At polymerisation temperatures up to 60 8C they
reach very high values of 1 million g/mol and more.
2.2 million g/mol can be measured by using hafnocene
complexes 2 and 4. Only polymers synthesized by
Fig. 1. New synthesized hafnocene complexes 2ꢀ4 and 1 for comparison.
/

W. Kaminsky et al. / Journal of Organometallic Chemistry 684 (2003) 200ꢀ
/205
203
Fig. 4. 13C-NMR spectroscopy measured rrrr pentads of polypropy-
lenes synthesized by hafnocene complexes 1ꢀ4 in dependence of the
polymerisation temperature.
Fig. 2. Activities of the hafnocene complexes 1ꢀ4 for the polymerisa-
tion of propene in dependence of the polymerisation temperature.
/
/
catalyst 3 show values which are between 550 000 and
650 000 g molꢁ1. The zirconocene complex 2a gives a
molecular weight of the polymer of only 210 000 g
molꢁ1 at 60 8C. The influence of the methyl substitution
in the bridge increased the molecular weight of the
polypropylene at least by 20%. Polypropylenes with a
3. Experimental
3.1. General comments
The Cs-symmetric hafnocene complexes 2ꢀ4, Fig. 1,
/
were synthesized analogue as described for 1? in the
literature [19,20]. Synthesis products were verified with
1H-NMR and 13C-NMR on a Bruker 400 MHz spectro-
meter in CDCl3 and TMS under argon atmosphere at
25 8C.
syndiotacticity of 30ꢀ70% and molecular weights of
more than one million are useful elastomers for coating
and blending.
/
3.2. Synthesis
3.2.1. Ligand synthesis
2,7-bis-tert-Buthylfluorene (5 g, 18 mmol) was dis-
solved in 80 ml diethylether and 11.25 ml of a 1.6 M
butyllithium in hexane solution was added slowly. The
solution was stirred until gas evolution was finished and
then 4.14 g of the methyl substituted 6,6-diphenyl
fulvene was added. After 10ꢀ12 h, a small amount of
/
water was added, the organic layer separated and dried
over Na2SO4. The solution was reduced and crystallized
Fig.
3. Dichloro[h10-2,4-cyclopentadien-1-ylidenbis(4-methyldiphe-
nylmethylen)[2,7-bis(1,1-di-methylethyl)-9H-fluoren-9-yliden]]zirko-
nium (2a).
at ꢁ
/
25 8C to yield colorless crystals (yield 65ꢀ70%).
/
Table 1
Melting points (Tm) and glass transition temperatures (Tg) of polypropylenes obtained by the hafnocene complexes 1, 2, 4 in dependence of the
polymerisation temperature
Polymerisation temperature (8C)
Hf compounds
1
Zr compound
2a
2
4
Tm (Tg) (8C)
99 (3)
Tm (Tg) (8C)
Tm (Tg) (8C)
Tm (8C)
30
45
60
96 (ꢁ
/
1)
96 (2,6)
141
131
122
ꢀ
/
(1)
(0.7)
ꢀ/
(ꢁ
/
01)
ꢀ
ꢀ/
/
(1.7)
(0.4)
ꢀ
/
ꢀ/
(ꢁ
/
0,5)

204
W. Kaminsky et al. / Journal of Organometallic Chemistry 684 (2003) 200ꢀ205
/
3.2.2. Hafnocene complex synthesis
The ligands 2?, 3? and 4? were dissolved in diethy-
lether, n-butyl lithium added and after gas evolution the
hafniumtetrachloride added. After filtering, the solution
was reduced and crystallized. Orangeꢀ/red crystals were
obtained, yield 40ꢀ50%.
/
3.2.2.1. Dichloro[h10-2,4-cyclopentadien-1-ylidenbis(4-
methyldiphenylmethylen)[2,7-bis(1,1-di-methylethyl)-
1
9H-fluoren-9-yliden]]hafnium (2). H-NMR d [ppm]ꢂ
1,04 (s, 18H, tert-butyl), 2.33 (s, 6H, CH3), 5.6 (m,
2HCp), 6.27 (m, 2HCp), 6.37 (m, 2H), 7.15 (dd, 2H,
/
JHH
2H, JHH
Hz), 7.78 (dd, 2H, JHH
8.84 Hz). 13C-NMR d [ppm]ꢂ
ꢂ
/
8.08 Hz, 7.84 Hz), 7.2ꢀ
8.84 Hz, 9.08 Hz), 7.74 (dd, 2H, JHH
8.08 Hz), 8.01 (d, 2H, JHH
20.8 (CH3), 30.53
/
7.4 (br, 4HAr), 7.56 (dd,
Fig. 5. Molecular masses of polypropylene samples synthesized by
ꢂ
/
ꢂ/8.08
hafnocenes 1ꢀ4 in dependence of the polymerisation temperature.
/
ꢂ
/
ꢂ
/
/
3.2.1.1. 9-[1,3-Cyclopentadien-yl-bis(4-
methylphenyl)methyl]-2,7-bis(1,1-dimethylethyl)-9H-
(C(CH3)3), 34.7 (C(CH3)3), 57.8 (PhCPh), 102.8, 110.6,
118.4, 118.8, 120.2, 120.7, 121.6, 123.9, 124.0, 126.3,
129.2, 129.4, 129.8, 136.7, 141.9, 150.2. FABMS
fluorene and isomers (2?). 1H-NMR d [ppm]ꢂ
/
1.12ꢀ
1.16 (s, 18 H, tert-butyl), 2.24 (s, 6H, CH3), 2.82ꢀ2.95
(m, 2H), 5.37ꢀ5.38 (s, 1HCp), 6.27ꢀ6.45 (m br, 3HCp),
6.93 (m br, 4HAr), 7.16ꢀ
7.37 (m, 10 HAr). 13C-NMR d
[ppm]ꢂ20.84 (CH3), 20.86 (CH3), 31.29 (C(CH3)3), 34.6
/
/
[Mꢃ+]ꢂ
784.
/
/
/
/
/
3.2.2.2. Dichloro[h10-2,4-cyclopentadien-1-ylidenbis(4-
methoxydiphenylmethylen)[2,7-bis(1,1-di-methylethyl)-
(C(CH3)3), 40.6, 43.1, 54.0, 54.5, 58.1, 59.1, 117.96,
118.08, 123.29, 123.36, 124.5, 127.8, 129.7, 129.8, 131.4,
132.2, 135.09, 135.25, 135.68, 139.4, 144.6, 144.9, 148.2,
1
9H-fluoren-9-yliden]]hafnium (3). H-NMR d [ppm]ꢂ
/
148.3. MSEI [Mꢃ+]ꢂ
536.
/
1.07 (s, 18H, tert-butyl), 3.80 (s, 6H, CH3), 5.62 (m,
2HCp), 6.3 (m, 3HCp), 6.4 (m, 2H), 6.90 (dd, 2H, 3JHH
ꢂ
/
8.84 Hz.), 6.97 (dd, 2H, JHH
7.58 (dd, 2H, 3JHH
8.84 Hz), 7.74 (dd, 2H, JHH
Hz, 8.6 Hz), 7.83 (dd, 2H, JHH 8.6 Hz), 8.01 (d, 2H,
3JHH 8.84 Hz). 13C-NMR d [ppm]ꢂ
31.4 (C(CH3)3),
ꢂ
/
8.6 Hz), 7.2ꢀ
/
7.4 (br, 4H),
3.2.1.2. 9-[1,3-Cyclopentadien-1-yl-bis(4-
methoxyphenyl)methyl]-2,7-bis(1,1-dimethyl-ethyl)-9H-
ꢂ
/
ꢂ
/
8.84
ꢂ
/
fluorene and isomers (3?). Analogous to the preparation
ꢂ
/
/
of 2?. 1H-NMR d [ppm]ꢂ
/
1.15ꢀ
3.00 (m br, 2H), 3.70 (s, 6H, OCH3),
5.34 (s, 1HCp), 6.26ꢀ6.46 (s, 3HCp), 6.62 (m br,
3HAr), 6.9ꢀ 31.4
7.5 (m br, 11HAr). 13C-NMR d [ppm]ꢂ
/
1.18 (s, 18H, tert-
34.7 (C(CH3)3), 55.2 (OCH3), 65.8 (PhCPh), 100.3,
112.3, 113.8, 114.8, 118.2, 118.4, 119.2, 119.4, 120.4,
123.8, 124.0, 124.2, 130.4, 132.0, 137.6, 139.2, 143.9,
butyl), 2.87ꢀ
/
5.31ꢀ
/
/
148.5, 150.2, 157.8, 158.0, 158.4. FABMS [Mꢃ+]ꢂ
817.
/
/
/
(C(CH3)3), 34.6 (C(CH3)3), 40.7, 42.9, 54.1, 54.6, 55.1,
57.5, 58.5, 65.8, 112.3 (br), 118.1, 118.2, 123.36, 123.43,
124.2, 124.4, 126.0, 126.8, 128.8, 130.8, 130.9, 132.3,
135.6, 139.35, 139.40, 142.0, 144.5, 144.8, 148.26,
3.2.2.3. Dichloro[h10-2,4-cyclopentadien-1-
148.35, 157.31, 157.45. MSEI [Mꢃ+]ꢂ
568.
/
ylidenbis(3,4-methyldiphenylmethylen)[2,7-bis(1,1-di-
methylethyl)-9H-fluoren-9-yliden]]hafnium and stereo
isomer (4). 1H-NMR d [ppm]ꢂ
1.05 (s, 18H, tert-
butyl), 2.25 (s, 2H, CH3), 2.34 (s, 3H, CH3), 2.41 (s, 1H),
/
3.2.1.3. 9-[1,3-Cyclopentadien-1-yl-bis(3,4-
methylphenyl)methyl)-2,7-bis(1,1-dimethyl-ethyl)-9H-
5.62 (m, 2HCp), 6.27 (m, 2HCp), 6.36 (br, 1H), 6.41 (br,
1H), 7.09 (d, 1H, JHH
ꢂ
/
732 Hz), 7.14ꢀ
/
7.35 (br, 4H),
fluorene and isomers (4?). Analogous to the preparation
3
of 2?. 1H-NMR d [ppm]ꢂ
/
1.12ꢀ
2.26 (m br, 6H, CH3), 2.86ꢀ
5.42 (s, 1HCp), 6.22ꢀ6.41 (m br, 3HCp), 6.92ꢀ
6.98 (m, 6HAr), 7.17 (m, 5HAr), 7.34 (m, 3HAr). 13C-
NMR d [ppm]ꢂ20.88 (CH3), 21.56 (CH3), 31.3
/
1.14 (s, 18H, tert-
7.56 (d, 2H, JHH
2H), 7.84 (m, 1H), 8.01 (d, 2H, JHH
NMR [ppm]ꢂ21.0 (CH3), 21.6 (CH3), 30.52
ꢂ
/
8.84 Hz), 7.67 (br, 1H), 7.76 (m,
ꢂ
8.84 Hz). 13C-
/
3
butyl), 2.15ꢀ
/
/2.98 (m br,
d
/
2H), 5.39ꢀ
/
/
/
(C(CH3)3), 31.4 (C(CH3)3), 34.7 (C(CH3)3), 35.0
(C(CH3)3), 57.6 (PhCPh), 100.3, 113.2, 113.4, 117.2,
117.3, 117.4, 119.2, 119.6, 120.5, 123.4, 123.7, 123.8,
124.1, 124.2, 126.3, 126.4, 126.5, 127.1, 127.6, 127.8,
128.7, 128.8, 129.2, 129.4, 129.5, 129.7, 129.8, 136.7,
/
(C(CH3)3), 34.6 (C(CH3)3), 40.6, 51.9, 53.8, 58.5,
117.9, 118.1, 123.3, 124.5, 126.5, 127.1, 129.7, 130.5,
135.3, 135.6, 139.4, 139.5, 144.9, 148.24, 148.26. MSEI
[Mꢃ+]ꢂ
/536.
138.4, 142.0, 144.8, 145.0, 150.1. FABMS [Mꢃ+]ꢂ
784.
/

W. Kaminsky et al. / Journal of Organometallic Chemistry 684 (2003) 200ꢀ
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205
3.3. Polymerisations
phenol) and were measured at 135 8C. All molecular
weights were calculated with the Mark-Houwink con-
stants for polypropylene which were taken from the
literature [21].
3.3.1. Polymerisation conditions
All operations were performed under a dry argon
atmosphere using standard Schlenk techniques. The
solvents used were purified passing through two col-
˚
umns with a 4-A molecular sieve and BASF copper
catalyst R3-11. MAO solution from Crompton GmbH
was filtered, the toluene was removed in vacuo and used
as a solid.
References
[1] G.W. Coates, Chem. Rev. 100 (2000) 1223.
[2] W. Kaminsky, Adv. Catal. 46 (2001) 89.
[3] R. Blom, A. Follestad, E. Rytter, M. Tilsel, M. Ystenes (Eds.),
Organometallic Catalyst and Olefin Polymerization, Springer,
Berlin, 2001.
Polymerisations were carried out in 200 ml toluene, as
a good solvent for MAO, in a 1 l Buchi glass reactor
¨
equipped with a magnetic stirrer. The concentration of
propene for every run was 1.38 mol lꢁ1 and the pressure
was kept constant during the polymerisation. The
polymerisations were started through injection of the
metallocene complex in toluene to the propene saturated
[4] J. Scheirs, W. Kaminsky (Eds.), Metallocene-Based Polyolefins,
vols. I and II, Wiley, Chichester, 2000.
[5] J.A. Ewen, R.L. Jones, A. Razavi, J.D. Ferrara, J. Am. Chem.
Soc. 110 (1988) 6255.
[6] L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 100
(2000) 1253.
tolueneꢀ
stopped by addition of 2 ml methanol. The polymer
solution was stirred over night in a methanolꢀHClꢀ
/MAO solution. After 1 h the reaction was
[7] A. Razavi, J. Ferrara, J. Organomet. Chem. 435 (1992) 299.
[8] J.A. Ewen, M.J. Elder, Makromol. Chem. Macromol. Symp. 66
(1993) 179.
/
/
water solution, filtered followed by evaporation of the
solvents and drying of the polymer under vacuo at 60 8C
over night.
[9] J.A. Ewen, M.J. Elder, R.L. Jones, L. Haspeslagh, J.L. Atwood,
S.G. Bott, K. Robinson, Makromol. Chem. Macromol. Symp. 48/
49 (1991) 253.
[10] A. Razavi, J.L. Atwood, J. Organomet. Chem. 459 (1993) 117.
[11] L. Cavallo, G. Guerra, M. Vacatello, P. Corradini, Macromole-
cules 24 (1991) 1784.
3.3.2. Polymer analysis
13C-NMR was used to verify the syndiotacticity of the
polymers. The NMR samples were prepared by the
dissolution of the polymers (10 mass%) in a mixture of
hexachloro-1,3-butadiene and 1,1,2,2-tetrachloro-1,2-di-
deuteroethane and were measured at 100 8C on a Bruker
400-MHz NMR spectrometer and referenced against
C2D2Cl4 at 100 8C, pulse angle 30 8C, delay time 5 s,
1024 scans. DSC was performed on a Mettler-Toledo
DSC 821e.
[12] W. Kaminsky, A. Hopf, M. Arndt-Rosenau, Macromol. Symp.,
(2003), in press.
[13] A. Hopf, W. Kaminsky, Catal. Commun. 3 (2002) 459.
[14] R. Mulhaupt, Macromol. Chem. Phys. 204 (2003) 289.
¨
[15] S. Kajigaeshi, T. Kadowaki, A. Nishida, S. Fujisaki, M. Noguchi,
Synthesis (1984) 535.
[16] S. Kajigaeshi, T. Kadowaki, A. Nishida, S. Fujisaki, M. Noguchi,
Bull. Chem. Jpn. 59 (1986) 97.
[17] D. Rau, U. Behrens, J. Organomet. Chem. 387 (1990) 219.
[18] H.G. Alt, R. Zenk, J. Organomet. Chem. 518 (1996) 522.
[19] H.G. Alt, R. Zenk, J. Organomet. Chem. 514 (1996) 257.
[20] T. Shiomura, M. Kohno, N. Inoue, Y. Yokote, M. Akiyama, T.
Asanuma, R. Sugimoto, S. Kimura, M. Abe, Stud. Surf. Sci. 89
(1994) 327.
The molecular weights (Mh) were determined with an
Ubbelohde viscometer (530 01/0a capillary, Kꢂ0.005
/
mm2 sꢁ2). The samples were prepared by the dissolution
of 50 mg of the polymer in 50 ml of decahydronaphtha-
line (stabilized with 1 g lꢁ1 2,6-di-tert-butyl-4-methyl-
[21] T.G. Scholte, N.L. Meijerink, H.M. Schoffelers, A.M.C. Brands,
J. Appl. Polym. Sci. 29 (1984) 3763.