An investigation of the influence of R on the abilities of the polar monomers CH2CH(CH2)8OR (R = Me, PhCH 2, Ph3C, Me3Si, Ph3Si) to participate in O- rather than η2-co

Article abstract of DOI:10.1039/b908726e

Copolymerization of ethylene and propylene with polar monomers of the types CH₂CH(CH₂)_nOH (n = 1-12) in order to introduce polar functionality into the resulting polymers is possible in principle if the hydroxyl groups of

Full text of DOI:10.1039/b908726e

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www.rsc.org/dalton | Dalton Transactions
An investigation of the influence of R on the abilities of the polar monomers
=
CH2 CH(CH2)8OR (R = Me, PhCH2, Ph3C, Me3Si, Ph3Si) to participate
in O- rather than g2-coordination to metallocene alkene polymerization
catalysts; an unanticipated role for ether oxygen coordination in promoting
polymerization
Goran Stojcevic and Michael C. Baird*
Received 5th May 2009, Accepted 13th July 2009
First published as an Advance Article on the web 14th August 2009
DOI: 10.1039/b908726e
=
Copolymerization of ethylene and propylene with polar monomers of the types CH2 CH(CH2)nOH
(n = 1–12) in order to introduce polar functionality into the resulting polymers is possible in principle if
the hydroxyl groups of the polar monomers are masked such that they cannot coordinate to Lewis
2
acidic catalyst sites and prevent h -alkene coordination. Although the use of hydrolysable ethers of the
=
types CH2 CH(CH2)nOR (R = alkyl, silyl; n = 1–12) is a protecting group strategy, which has been
investigated somewhat, in fact this approach has not been investigated systematically and little is known
of the effectiveness of various R groups in hindering oxygen coordination to e.g. metallocene
polymerization catalyst systems. We report here the results (a) of an NMR study of reactions of an
archetypal metallocene polymerization catalyst, Cp2ZrMe(m-Me)B(C6F5)3, with the polar monomers
=
CH2 CH(CH2)8OR (R = Me, PhCH2, Ph3C, Me3Si, Ph3Si), all protected versions of the readily
available, long chain polar monomer 9-decen-1-ol, and (b) of an investigation of the copolymerization
reactions of these same polar monomers with ethylene and propylene catalyzed by the well known
rac-C2H4(Ind)2ZrCl2/MAO catalyst system. While increasing the steric requirements of the groups R
does decrease the apparent abilities of the ethers to displace [BMe(C6F5)3]- from the [Cp2ZrMe]+ cation,
there is no correlation of size of R with the degrees of incorporation of the polar monomers into
copolymers of ethylene and propylene. Instead, a heretofore unsuspected role for catalyst activation by
the ether linkage is suggested.
studies involving ethylene as they readily copolymerize ethylene
Introduction
with 1-alkenes to form various types of linear low density
polyethylene.3a–d By proper tailoring of the ligands, they also
offer high degrees of stereochemical control during propylene
polymerization to i-PP in addition to forming copolymers of
propylene with 1-alkenes.3e–h In principle, therefore, appropriate
masking of the polar functionality of a polar 1-alkene monomer
prior to copolymerization should provide a route to interest-
ing new materials, and this approach has been investigated
with a number of hydroxyl terminated 1-alkenes of the type
The incorporation of monomers containing polar functionality
into polyolefins is currently of great interest and importance,
both industrially and academically, since random incorporation
of polar groups such as ester, halo, cyano, hydroxyl, etc., into e.g.
polyethylene and polypropylene is expected to result in significant
enhancement of properties such as oil resistance, adhesion,
paintability and miscibility with polar polymers such as polyesters
and polyamides.1 Unfortunately the types of Ziegler catalysts,
which are most effective for the homopolymerization of ethylene
and propylene do not perform well in the presence of monomers
containing the above-mentioned polar groups because most such
catalysts are strong Lewis acids, which are extremely susceptible
to coordination of a polar functional group to a vacant site on the
metal. Thus, the “wrong” end of the polar monomer coordinates
preferentially and polymerization is prevented.1 Therefore new
methodologies for the synthesis of random copolymers containing
polar and non-polar segments are desirable.
=
CH2 CH(CH2)nCH2OH (n = 0–12). One approach to masking
has involved the use of aluminum alkyl compounds, which can
both convert the hydroxyl group to an alkoxy group (eqn (1)) and
coordinate to the oxygen as in eqn (2).4,5
(1)
Catalytic systems based on cationic metallocene complexes of
the type [Cp¢2M(Me)]+ (Cp¢ = substituted cyclopentadienyl; Me =
CH3; M = Ti, Zr, Hf)2 are obvious choices for copolymerization
(2)
A combination of these two processes results in significantly
increased steric encumbrance around the oxygen atom, thus
inhibiting its coordination to the active site of the catalyst and
Department of Chemistry, Queen’s University, Kingston, ON, Canada K7L
3N6
8864 | Dalton Trans., 2009, 8864–8877
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The Royal Society of Chemistry 2009
©

(3)
=
decreasing the extent of deactivation of the catalyst. Ultimately
the hydroxyl end groups may be restored via hydrolysis.
on the abilities of the 1-alkene monomers CH2 CH(CH2)8OMe
=
=
(A), CH2 CH(CH2)8OCH2Ph (B), CH2 CH(CH2)8OCPh3 (C)
=
=
To date, many attempts at utilizing this approach to produce
random copolymers of ethylene and propylene with monomers
containing hydroxyl end groups have been reported. For in-
stance, in a series of studies Lo¨fgren, Seppa¨la¨ et al have made
copolymers of ethylene and propylene with a number of short
and long chain hydroxyl functionalized alkenes using a vari-
ety of dichlorozirconocenes activated with methylaluminoxane
(MAO).4a–i Reported polar monomer incorporations have been,
however, invariably rather low, from 1 wt% to 3.6 mol% with
incorporation being highest for the longer chain polar monomers.
It was also found that addition of increasing amounts of polar
monomer generally resulted in catalyst deactivation, manifested
by reduction of both yields and molecular weights, and that the
ratios of MAO to both zirconium and polar monomer as well as
pretreatment of the latter with MAO had some effect on activities
while addition of triisobutylaluminum to MAO-activated systems
was in some cases found to be beneficial. Interestingly, in one
study, the surface of a material which contained a small proportion
of hydroxyl groups was shown to exhibit improved adhesive
properties.4h
Similar results have been reported by other groups using a vari-
ety of aluminum alkyls and zirconocene-based catalysts,5 although
findings vary concerning the usefulness of trimethylaluminum
(TMA) as an additive;5e–g,k whether or not the addition of TMA
is beneficial seems to depend on the metallocene used. Some very
high incorporations of longer chain protected polar monomers
have been reported in some cases (e.g. 10,5e 37,5g,5l 50,5f,k mol%),
with interesting properties attributable to comonomer incorpora-
tion. In one case, for instance, the surface of the copolymer was
found to be hydrophilic.5k
CH2 CH(CH2)8OSiPh3 (D) and CH2 CH(CH2)8OSiMe3 (E) to
coordinate via the oxygen atoms to an archetypal catalyst, the
[Cp2ZrMe]+ cation, generated in situ via Cp2ZrMe(m-Me)B(C6F5)3
(eqn (3)).2l,7a,b
We also describe a series of copolymerization experiments
of the monomers with ethylene and propylene using the rac-
8a–c
C2H4(Ind)2ZrCl2 catalyst system.
Experimental
Catalyst manipulations were carried out in an Mbraun glove
box filled with purified nitrogen, while all reactions were carried
out under purified argon using standard Schlenk line techniques.
Deoxygenated toluene, hexanes, CH2Cl2 and THF (all Aldrich)
were dried by passage through dried alumina columns, and THF
˚
and CH2Cl2 were further dried by storage over activated 4 A
molecular sieves. CDCl3, CD2Cl2 and chlorobenzene-d6 were dried
1
1
over activated 4 A molecular sieves. H and 13C{ H} NMR spectra
were run on Bruker AV300, 400 or 500 spectrometers, chemical
shifts being referenced to the residual proton signals of the
deuterated solvents. Electrospray mass spectrometry experiments
were run in positive ion modes on a Quattro VG with nitrogen as
the nebulizing gas and CH2Cl2 as the carrier solvent. Differential
scanning calorimetry (DSC) was run on a Perkin Elmer DSC 7
(TAC 7/DX), ramping at a rate of 5.00 ◦C min-1 or 10.00 ◦C min-1,
starting at a temperature range of 25 and going up to 250 ◦C.
Elemental analyses were carried out by Canadian Microanalyt-
ical Services of Delta, British Columbia. The compounds rac-
C2H4(Ind)2ZrCl2,8a–c NaH, CH3I, CHPh2Br, Ph3CCl and LiClO4
(all Aldrich) were used as received and 9-decen-1-ol (98% Alfa
Aesar), SiHPh3, NH(Me3Si)2 and benzyl chloride (all Aldrich)
˚
A complementary approach to the masking of hydroxyl end
groups involves the utilization of hydrolysable ethers, a tactic
first used many years ago with TiCl3-based catalysts6a,b and more
recently extended to metallocene-based catalytic systems.4g,5s,t,6c–g
Although significant improvements in degrees of incorporation,
conversions and molecular weights have not to this point been
observed, the approach would appear to have merit because of
decreased need for alkylaluminum protecting groups. We have
therefore embarked on an investigation into the utilization of a
˚
were degassed and dried over activated 4 A molecular sieves prior
to use, while Cp2ZrMe2 and B(C6F5)3 were prepared as in the
literature. Basic alumina (150 mesh, 58 A, Aldrich) was dried
under vacuum overnight and stored in the glove box. MAO was
obtained from Aldrich (10 wt%) and Akzo Nobel (6.9 wt%);
solutions from the two sources were used interchangeably for
ethylene polymerizations.
8d
8f
˚
=
series of alkyl and silyl ethers of the types CH2 CH(CH2)nOR
Synthesis of 10-methoxy-dec-1-ene (A)
(n = 2–10; R = alkyl, silyl), anticipating that enhanced steric
requirements of the groups bonded to the ether oxygen atoms
would result in inhibition of ether coordination and hence in
increased incorporation of the polar monomer. In addition, the
ability of silicon to efficiently delocalize the p electrons on oxygen
through p-bonding renders the oxygen atoms of the two silyl
ethers less basic than might be anticipated on the basis of simple
electronegativity considerations.6h,i
This monomer was synthesized as in the literature,9a but with
modifications. To a slurry of 3.38 g NaH (0.14 mol, 1.1 equiv.)
in 250 mL dry THF was added 20.0 g 9-decen-1-ol (0.128 mol,
1.0 equiv.) dropwise at 0 ◦C. After stirring for 2 h at room
temperature, 18.2 g methyl iodide (0.13 mol, 1.0 equiv.) was added
at 0 ◦C. The solution was stirred overnight, the volatiles were
removed under reduced pressure, and 100 mL dry hexanes were
added. The resulting mixture was filtered to remove NaI, and
the filtrate was then eluted through a 6 cm column of activated
1
We now describe a H NMR spectroscopic assessment of the
effects of varying the steric requirements of the ether substituents
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8864–8877 | 8865
©

alumina. The solvent was then removed under reduced pressure
to give colourless, liquid product (13.7 g, 63% yield). H NMR
(0.032 mol, 0.5 equiv.) was added 10.00 g 9-decen-1-ol (0.064 mol,
1 equiv.). The mixture was stirred at room temperature overnight,
followingwhich50mL CH2Cl2 was added andthe reactionmixture
was filtered. The resulting solution was eluted through a 6 cm
column of activated alumina and the solvent was then removed
under reduced pressure to yield the colourless liquid product (13 g,
89%). The purified product was tested as above for hydroxylic
impurities. 1H NMR (CDCl3) d/ppm: 5.78 (m, 1 H), 4.93 (m, 2 H),
3.55 (t, J 7 Hz, 2 H), 2.02 (m, 2 H), 1.50 (m, 2 H), 1.3–1.4 (m,
10 H), 0.9 (s, 9 H). 13C NMR (CDCl3) d/ppm: 139.3, 114.4, 62.9,
34.1, 33.0, 29.8, 29.7, 29.4, 29.2, 26.1. TOF-EI-MS (M+, calcd
228.1909, found 228.1904).
1
(CDCl3) d/ppm: 5.82 (m, 1 H), 4.95 (m, 2 H), 3.37 (m, 2 H), 3.34 (s,
3 H), 2.04 (m, 2 H), 1.56 (m, 2 H), 1.3–1.4 (m, 10 H). As a test for the
presence of residual hydroxyl-containing impurities such as water
or unreacted 9-decen-1-ol, a solution of A in C6D6 was treated
with 0.2 molar equiv. of the OH-sensitive Cp2ZrMe2. In addition
to the resonances of 9-decen-1-ol, the resulting NMR spectrum
exhibited only the resonances of Cp2ZrMe2 (d 5.73, -0.14). Not
observed was the Cp resonance of (Cp2ZrMe)2O at d 5.74 or the
resonance of methane at d 0.24, and thus no cleavage of the Zr-Me
bonds in Cp2ZrMe2 had occurred.
Synthesis of 10-benzyloxy-dec-1-ene (B)9b
Procedure for NMR monitoring of reactions of the compounds
=
CH2 CH(CH2)7CH2OR (R = Me, PhCH2, Ph3C, Me3Si, Ph3Si)
This monomer was synthesized essentially as above using 0.77 g
NaH (0.032 mol, 1.0 equiv.) in 150 mL dry THF, 5.00 g 9-decen-
1-ol (0.032 mol, 1.0 equiv.) and 4.05 g benzyl chloride (0.032 mol,
1.0 equiv.). Yield 1.5 g (20%). 1H NMR (CDCl3) d/ppm: 7.39–7.26
(m, 5 H), 5.83 (m, 1 H), 4.96 (m, 2 H), 4.52 (s, 2 H), 3.48 (t, J 7 Hz,
2 H), 2.05 (m, 2 H), 1.61 (m, 2 H), 1.34 (m, 10 H). The purified
product was tested as above for hydroxylic impurities.
with Cp2ZrMe(l-Me)B(C6F5)3
To a nitrogen filled 5 mm NMR tube was added first a solution
of 14 mg B(C6F5)3 (27.8 mmol) in 0.50 mL of C6D5Cl or CD2Cl2
and then a solution of 7 mg Cp2ZrMe2 (27.8 mmol) in 0.25 mL of
the same solvent. A 1H NMR of this solution was taken, and then
5–10 molar equiv. of a polar monomer was added. The sample was
shaken and placed quickly in the probe of an NMR spectrometer,
and the NMR spectrum of the solution was obtained.
Synthesis of 10-trityloxy-dec-1-ene (C)
General procedure for copolymerizations
This was obtained as a colourless oil as above using 5.58 g Ph3CCl.
Yield 3.19 g (40%). 1H NMR (CDCl3) d/ppm: 7.2–7.6 (m, 5 H),
5.84 (m, 1 H), 4.99 (m, 2 H), 3.08 (t, J 7 Hz, 2 H), 2.06 (m,
2 H), 1.65 (m, 2 H), 1.3–1.4 (m, 10 H). 13C NMR (CDCl3) d/ppm:
145.0, 139.6, 129.1, 128.2, 127.2, 114.5, 86.7, 64.1, 34.2, 30.4, 29.9,
29.8, 29.5, 29.3, 26.7. The purified product was tested as above for
hydroxylic impurities. Anal. calcd for C29H34O: C 87.39, H 8.60.
Found: C 87.18, 8.65.
In a typical experiment (method A), ethylene or propylene was
bubbled for 2 min into a solution containing 5 mg of rac-
8a–c
C2H4(Ind)2ZrCl2
in 15 mL of dry toluene in a flame-dried,
50 mL Schlenk tube; 1000 equiv of MAO were then added and the
solution was stirred for a further 5 min. The comonomer was then
added drop wise over one min, and the reaction mixture was stirred
for 30 min while bubbling of ethylene or propylene was continued.
The copolymerizations were quenched with 70 mL of a HCl–
ethanol (5% HCl in ethanol) mixture, the resulting mixtures were
stirred overnight, and the precipitated copolymers were filtered,
washed with ethanol, dried under vacuum at 60 ◦C for 12–15 h and
analyzed by 1H and 13C NMR spectroscopy and IR spectroscopy
and by differential scanning calorimetry. Alternatively, (method
B), an ethylene- or propylene-saturated toluene solution of rac-
C2H4(Ind)2ZrCl2 and the polar comonomer was stirred for 5 min
and then 1000 equiv. of MAO were added. The subsequent
procedure was as above.
Synthesis of 10-triphenylsiloxy-dec-1-ene (D)
This was synthesized as in the literature.9c To a mixture of 6.00 g
9-decen-1-ol (0.038 mol, 1 equiv.) and 10.00 g HSiPh3 (0.038 mol,
1 equiv.) in 150 mL of dry toluene was added drop wise a solution
of 0.786 g B(C6F5)3 (1.5 mmol, 0.04 equiv.) in 10 mL toluene.
1
Aliquots of the reaction were periodically analyzed by H NMR
spectroscopy, and it was determined that the reaction was complete
after stirring for 68 h at room temperature. The reaction mixture
was filtered, the solvent was removed under reduced pressure and
the resulting solid was dissolved in 50 mL hexanes. The solution
was eluted through a 6 cm of activated alumina and the solvent was
removed under reduced pressure to yield the product as a viscous,
colourless oil (12.6 g, 80%). The purified product was tested as
Results and discussion
In order to develop methodologies for the incorporation of
polar monomers into polyolefins, we chose to work initially with
1
above for hydroxylic impurities. H NMR (CDCl3) d/ppm: 7.4–
=
ethers of 9-decen-1-ol, CH2 CH(CH2)7CH2OR (R = Me, PhCH2,
7.8 (m, 15 H), 5.92 (m, 1 H), 5.7 (d, 2 H), 3.91 (t, J 7 Hz, 2 H), 2.14
(m, 2 H), 1.70 (m, 2 H), 1.40 (m, 10 H). 13C NMR (CDCl3) d/ppm:
139.6, 135.8, 134.9, 130.3, 128.2, 114.6, 64.4, 34.2, 32.9, 29.8, 29.7,
29.5, 29.3, 26.2. TOF-EI-MS ([M + H]+, calcd 415.2444, found
415.2457) Anal. calcd for C28H34OSi: C 81.10, H 8.27. Found: C
80.98, 7.93.
Ph3C, Me3Si, Ph3Si). Previous researchers have found that higher
incorporations of polar monomers are generally achieved with
longer chain monomers,1b,4c–e,6b possibly because of the greater
=
separation of the polar functionality from the C C bond, but
to date there has been little research into the effects of varying the
nature of the ethers as masking agents for the hydroxyl group. We
have chosen to work with the methyl, benzyl, trityl, trimethylsilyl
and triphenylsilyl ethers of 9-decen-1-ol, encompassing a range of
alkoxy and siloxy group steric requirements, as we wished to test
an hypothesis that bulkier substituents would hinder ether oxygen
Synthesis of 10-trimethylsiloxy-dec-1-ene (E)
This monomer was synthesized as in the literature.9d To a mixture
of 7.22 g (Me3Si)2NH (0.044 mol, 0.7 equiv.) and 3.4 g LiClO4
8866 | Dalton Trans., 2009, 8864–8877
This journal is
The Royal Society of Chemistry 2009
©

1
coordination and would thereby inhibit (co)polymerization the
least. Also, as noted above, the two silyl ethers are expected
to exhibit lowered basicity for purely electronic reasons hav-
the H NMR spectrum of 1-methoxy-9-decene (A), and (c) the
1H NMR spectrum of a reaction mixture containing one equiv.
of Cp2ZrMe(m-Me)B(C6F5)3 and 5 molar equiv. of A immediately
after mixing. As can be seen, the three resonances of Cp2ZrMe(m-
Me)B(C6F5)3 at d 5.91 (Cp), 0.46 (Zr–Me) and 0.32 (B–Me)
disappeared on the addition of A and were replaced by a new
Cp resonance at d 5.95, a new Zr–Me resonance at d 0.58 and
a new B–Me resonance of the free [BMe(C6F5)3]- anion at d
1.1, identified by the apparent quadrupolar broadening. Equally
important, the CH2CH2-O-CH3 triplet, the CH2-O-CH3 singlet
and the CH2CH2O multiplet of A at d 3.25, 3.16 and 1.55,
respectively, all broadened significantly, suggesting at least partial
substitution of the borate anion from the inner coordination
sphere of the zirconium by the ether oxygen of A and rapid
exchange between free and O-coordinated A as in eqn (3) (R =
Me). Thus, the observed resonances are weighted averages of the
chemical shifts of Cp2ZrMe(m-Me)B(C6F5)3, of A and of the ether
complex of A. We also note that the CH2CH2-O-CH3, CH2-O-
CH3 and CH2CH2O resonances at d 3.25, 3.16 and 1.55 all shifted
slightly upfield rather than downfield as might be expected on
coordination to a strongly Lewis acidic metal ion. This result is
presumably a result of ring current effects from the aromatic Cp
ligands,7b,c and provides further evidence for O-coordination.
Interestingly, and highly important, the olefinic multiplet res-
onances of A at d ~4.9 and ~5.8 did not shift or broaden in
the presence of Cp2ZrMe(m-Me)B(C6F5)3 (Fig. 1c), and thus
coordination of the olefinic group to the metal does not occur
significantly under these conditions. With longer reaction times
(over 24 h, not shown), these olefinic resonances did weaken and
eventually disappeared as new, broad resonances appeared in the
aliphatic region (d 1–2.2). These spectral changes are consistent
with slow reorganization of the O-bonded ether complex to the
ing to do with p-bonding between the silicon and oxygen
9a
atoms.6h,i Of the ethers utilized, CH2 CH(CH2)8OMe (A),
=
CH2 CH(CH2)8OCH2Ph (B), CH2 CH(CH2)8OSiPh3 (D)9c
and CH2 CH(CH2)8OSiMe3 (E) and are known compounds
while CH2 CH(CH2)8OCPh3 (C) has not been prepared pre-
viously. All were characterized spectroscopically, D and E by
elemental analyses also.
9b
=
=
9d
=
=
In addition, as a guarantee of the thoroughness of the purifica-
tion procedures, all of the ethers were tested to ensure that they
were free of trace hydroxylic impurities (water, unreacted alcohol)
which would coordinate preferentially to [Cp2ZrMe]+ and thus
interfere with the chemistry to be studied. To this end, a deficiency
of the OH-sensitive compound Cp2ZrMe2 was added to a benzene-
d6 solution of each and the resulting solutions were monitored
by 1H NMR spectroscopy. In no case was cleavage of the
Zr–Me bonds of the Cp2ZrMe2 indicated by the appearance of
new resonances in the Cp or methyl regions of the spectra, or by
the appearance of the resonance of methane at d 0.24.
Coordinating abilities of polar monomers A–E
In an attempt to assess the relative coordinating abilities of the
protected polar 1-alkene monomers A–E with a representative
early metal metallocene catalyst system, an NMR study was
undertaken of reactions of the monomers with the zwitteri-
onic compound Cp2ZrMe(m-Me)B(C6F5)3. The latter is formed
via methyl carbanion abstraction from Cp2ZrMe2 by B(C6F5)3,
and is a precursor of the Lewis acidic polymerization catalyst
[Cp2ZrMe]+, which is expected to coordinate to poorly protected
ether oxygen atoms (eqn (3)).2l,7a,b The NMR studies involved
addition of 5 equiv. of each of the polar monomers A–E to
solutions of the zwitterionic Cp2ZrMe(m-Me)B(C6F5)3 in C5D5Cl
or CD2Cl2 at room temperature. Similar behaviours were observed
in both solvents but precipitation of the zwitterionic intermediate
occurred in toluene-d8 and thus this solvent could not be
used.
2
h -alkene isomer and migratory insertion, as in eqn (4), followed
by oligomerization of A as in eqn (5).
A relatively strong, sharp singlet also appeared slowly at d
4.80. The chemical shift and singlet nature of this resonance are
=
characteristic of vinylidene compounds of the type H2C CRR¢ (R
and R¢ = long chain alkyl groups),10 and the presence of this type
of alkene product is consistent with formation via a b-elimination
reaction of the unsaturated oligomer shown as a product in
eqn (6).
The results of a typical experiment are shown in Fig. 1 which
shows (a) the 1H NMR spectrum of Cp2ZrMe(m-Me)B(C6F5)3, (b)
(4)
(5)
(6)
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8864–8877 | 8867
©

Fig. 1 1H NMR spectra (500 MHz, C6D5Cl) (a) of 1-methoxy-9-decene, (b) of Cp2ZrMe(m-Me)B(C6F5)3, and (c) of a solution containing one equivalent
of Cp2ZrMe(m-Me)B(C6F5)3 with 5 equiv. of 10-methoxy-1-decene immediately after mixing.
The resulting cationic zirconocene hydride is expected to exhibit
a Zr–H singlet resonance in the region d 6–8,11 but several weak
resonances are observed in this region and the hydride resonance
could not be identified. However, the cationic hydride shown would
certainly behave as an oligomerization catalyst and may have
been present in very low concentrations. Small amounts of oily
materials could be isolated from NMR reactions on removal of
the solvent, but these were not investigated because our interest
was in comparing the clearly poor protecting ability of the methyl
group to those of the bulkier groups.
Similar experiments, involving the addition of a 5-fold molar
excess of monomer B, with a somewhat larger benzyl protecting
group, to solutions of Cp2ZrMe(m-Me)B(C6F5)3 showed again
that the resonances of Cp2ZrMe(m-Me)B(C6F5)3 disappeared,
indicating at least a degree of displacement of the [BMe(C6F5)3]-
anion by the ether group. In this case the O–CH2CH2 triplet
and O-CH2Ph singlet were not broadened or shifted noticeably,
suggesting that the benzyl ether does not coordinate to the same
extent as does the methyl ether, but the olefinic resonances of B
did slowly weaken as broad resonances appeared in the aliphatic
region of the spectrum. Thus slow oligomerization did appear to
take place over 24 h although a possible vinylidene peak at d
~4.7 did not gain significant intensity. This system was not studied
further, but the results do imply that the benzyl group is also not
a very good protecting group.
Rather different results were obtained with 1-trityloxy-9-decene
(C), 10-triphenylsilyloxy-1-decene (D) and 10-trimethylsilyloxy-1-
decene (E, Fig. 2), which contain much larger ether protecting
groups and which were therefore expected to exhibit much greater
steric protection to the ether oxygen atoms than is the case for A
or B. A typical NMR spectrum, for E, is shown in Fig. 2 where
1
it is clear that the H resonances of E are not affected by the
presence of Cp2ZrMe(m-Me)B(C6F5)3. In particular the O–CH2
resonance did not broaden or shift significantly. Furthermore,
unlike the situations with A and B, there was very little or
no weakening of the olefinic resonances of C, D and E over
24 h. Thus, relatively little oligomerization occurs with these
monomers.
In summary, the above NMR experiments involving monomers
A–E suggest major differences in the abilities and the ex-
tents to which the various groups inhibit displacement of the
[BMe(C6F5)3]- anion and hence allow coordination of the ether
5
oxygen atoms to the [(h -C5H5)2ZrMe]+ cation. The differences
correlate significantly with the steric requirement of the various
groups, and, in the section below, we assess the abilities of these
same protecting groups to inhibit polar monomer incorporation
8868 | Dalton Trans., 2009, 8864–8877
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Fig. 2 1H NMR spectra (400 MHz, CD2Cl2) (a) of 1-trimethylsilyloxy-9-decene, (b) of a solution containing one equivalent of Cp2ZrMe(m-Me)B(C6F5)3
with 5 equiv. of 1-trimethylsilyloxy-9-decene immediately after mixing.
during attempted copolymerization reactions of the five polar
monomers with ethylene and propylene.
possibly desirable to induce polymerization prior to addition
of polar monomer. Although this procedure resulted in some
polyethylene or isotactic polypropylene forming in the reaction
mixtures, the new copolymers were found to be sufficiently
soluble that they could be readily separated from the relatively
insoluble polyethylene or isotactic polypropylene. An alternative
procedure (method B) involved addition of MAO to an ethylene-
or propylene-saturated solution containing rac-C2H4(Ind)2ZrCl2
and polar monomer.
In each copolymerization experiment, ethylene or propylene
was continuously fed into the reaction mixture until termination
of the reaction, which was accomplished after 30 min by quenching
with acidified ethanol to destroy the active catalyst and residual
MAO. The resulting mixture was then stirred overnight to ensure
complete MAO quenching and precipitation of the polymeric
products and, following filtration, the solid products were dried
in a vacuum oven overnight at 60 ◦C. The copolymers were
characterized by 1H and, in some cases, 13C NMR spectroscopy in
tetrachloroethane-d2 (TCE-d2) or o-dichlorobenzene–C6D6, either
at room or at high temperatures depending on solubilities. The
1H NMR spectra were used to determine the mole percent
incorporations of the polar monomers as outlined below.
Copolymerization studies of polar monomers A–E
After examining the nature and extent of the interactions of
monomers A–E with a simple early metal catalyst system, the
5
[(h -C5H5)2ZrMe]+ cation, our focus shifted to an investigation
of the abilities of the various ether functional groups to influ-
ence the incorporation of polar monomers into polyolefins, in
particular polyethylene and polypropylene. We wished to test an
hypothesis that the bulkier substituents which hinder ether oxygen
coordination the most would likewise inhibit copolymerization
the least. We chose to work initially with ethers of 9-decen-1-
ol as this monomer is less inexpensive than many shorter chain
analogues and also because previous researchers have found that
higher incorporations of polar monomers are generally better
achieved with monomers containing long chains, possibly because
=
of the greater separation of the polar functionality from the C C
bond.1b,4c–e,6b
Our initial study involved copolymerizations with ethylene and
propylene using rac-C2H4(Ind)2ZrCl2. When activated with MAO,
this is an excellent catalyst for the homopolymerization of ethylene
and the isospecific polymerization of propylene to isotactic
polypropylene (i-PP),8a–c and it also exhibits better activities for
alkene polymerization than does the Cp2ZrMe(m-Me)B(C6F5)3
system. We utilized two copolymerization procedures, method A
involving treatment of an ethylene- or propylene-saturated toluene
solution of rac-C2H4(Ind)2ZrCl2 and MAO with polar monomer
5 min after addition of MAO. Initiation of homopolymerization
processes is often slower than propagation12 and we thought it
Copolymerization studies with ethylene
Copolymerization reactions with ethylene were attempted with
all five polar comonomers, and generally proceeded rapidly to
give white materials which were purified of aluminum byproducts,
collected by filtration and dried. Fig. 3 shows a representative 1H
NMR spectrum of the materials obtained utilizing comonomer
A. As can be seen, the spectrum exhibits somewhat broadened yet
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©

Fig. 3 Representative 1H NMR spectrum (400 MHz, TCE-d2, 120 ◦C) of the isolated copolymer of experiment 1.
Table 1 Copolymerizations of ethylene with polar monomers
prominent OCH2CH2 and OCH3 resonances at d 3.43 and 3.37,
=
respectively, in accord with literature values of d 3.33 and 3.274g
and clear evidence for incorporation of A and, by integration,
making possible determination of the degree of incorporation Also
observed are the main chain polyethylene (–CH2–)n resonance at d
1.38 and the polymer methyl end group at d 0.98, which was used
for the calculation of number average molecular weight, Mn.
Fig. 4 shows a representative 1H NMR spectrum of the
copolymers obtained utilizing comonomer E; in this case the
protecting group is hydrolyzed to a hydroxyl group during the work
up procedures. In Fig. 4, the OCH2CH2 resonance is observed
at d 3.69, consistent with literature data (d 3.584g) for similar
copolymers of ethylene and 10-undecen-1-o1, but all the remaining
resonances due to the polymer main chain and polymer end
groups are similar to those in Fig. 3. Again integration of the
OCH2CH2 resonance made possible determination of the degree
of incorporation.
CH2 CH(CH2)7CH2OR, where R = Me (A), Ph3C (C), Ph3Si (D)
Me3Si (E), using the catalyst rac-C2H4(Ind)2ZrCl2/MAO
Experiment #a Comonomer Yield/g Incorp. (mol%) Tm/◦Cb
Mn
2170
4520
2870
1*
A
A
C
C
C
E
E
D
D
2.0
1.7
2.5
1.6
1.6
2.8
1.3
3.0
4.1
0.12
0.93
0.004
1.1
128
123
128
2**
3*
4**
5*
112, 126 11 500
106, 130 25 410
0.1
6*
7**
8*
0.4
1.2
0.2
0.1
129
121
127
126
51 000
8660
6820
5360
9**
a * = Method A, ** = method B. b 5.00 ◦C min-1 ramping.
◦
similar to that of high density polyethylene (120–130 C).13
The Mn values of the copolymers in Table 1 seemingly varied
from 2170 to 51 000 and were consistently high with the trityl
protecting group monomer C although the observation of two
Tm values suggests that bimodal distributions of homopolymers
were obtained. However, determination of Mn involved comparing
integrations of resonances of very different intensities and the
errors involved are unknown. In any case, since the low degrees of
incorporation of polar monomers generally rendered comparisons
of the data in Table 1 to be of little value, we continued with
propylene copolymers.
Table 1 summarizes the data obtained for the copolymerization
reactions involving ethylene. As can be seen, very low degrees
of incorporation (0.004–1.2%) of the polar comonomers were
achieved whether the catalyst was activated in the presence of
comonomer or prior to comonomer addition. Note that monomer
B is not included in Table 1 because no incorporations were
observed in several attempts. For reasons not clear, the degrees
of incorporation found here are somewhat lower than those
reported elsewhere (0.7–3.6%) for this catalyst with 10-undecen-
1-ol protected by MAO from a different source.4g However, under
the conditions utilized here, it seems that none of the polar
comonomers can compete effectively with the relatively small
ethylene molecule and, as a result, the resulting low degrees
of branching are reflected in values of Tm, which are all very
Copolymerization studies with propylene
In contrast to the above results with ethylene, it was hoped
that the use of the somewhat bulkier propylene would permit
8870 | Dalton Trans., 2009, 8864–8877
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Fig. 4 Representative 1H NMR spectrum (400 MHz, TCE-d2, 120 ◦C) of the isolated copolymer of experiment 7.
Table 2 Copolymerizations of propylene with polar monomers
greater incorporation of the polar monomers and hence better
=
CH2 CH(CH2)7CH2OR, where R = Me (A), PhCH2 (B), Ph3C (C), Ph3Si
discrimination between them. Propylene is also of interest with rac-
C2H4(Ind)2ZrCl2 as a catalyst, of course, because of the possibility
of synthesizing isotactic copolymers8a–c which would be interesting
and potentially useful materials. The copolymerization reactions
involving propylene were carried out using method B, described
above, and yielded solid white materials. All polymerization
experiments were repeated at least twice and all products were,
where possible, characterized by 1H and 13C NMR spectroscopy,
IR spectroscopy and differential scanning calorimetry (DSC). The
MAO used for these experiments was from Aldrich (10 wt% in
toluene).
(D) Me3Si (E), using the catalyst rac-C2H4(Ind)2ZrCl2/MAO
Comonomer Time/
Incorp.
Experiment #a (100 equiv.) min
Yield/g (mol% ) Tm/◦C Mn
10
11
12
13
14
15
16
17
18
19
20
21
22a
23a
24a
25a
None
None
A
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
3.9
3.7
2.6
3.0
4.6
5.2
4.2
4.1
2.7
2.8
4.9
4.9
1.9
2.0
3.0
3.0
—
—
120
118
127
126
128
124
121
123
128
128
121
118
96
900
1200
6300
4700
3100
2500
1000
950
5800
7100
1340
1600
1960
2160
1500
1460
2.0
1.7
0.5
0.2
0.4
0.5
0.9
0.7
—
A
B
B
C
C
The 1H NMR spectrum of the copolymer obtained using
comonomer A, shown in Fig. 5, exhibits the expected OCH2CH2
and OCH3 resonances at d 3.37 and 3.34, respectively, in addition
to the resonances characteristic of isotactic polypropylene at d
1.72, 1.40 and 0.87.14 The resonances of the long chain of the
polar monomer are obscured by the much stronger resonances of
E
E
D
D
—
E
0.4
0.3
—
E
102
n.t.
n.t.
D
D
—
1
the polypropylene chains. The H NMR spectra of the products
a Copolymerization performed at 60 ◦C; n.t. = no transition (i.e. amor-
obtained using copolymers B–E were very similar to that shown in
Fig. 5 but, as expected given the nature of the work up procedures,
exhibited only a triplet attributable to the OCH2CH2 group (d
3.52–3.61) in addition to the strong resonance of the polypropylene
backbone. Polymer spectra generally also exhibited two vinylidene
end group resonances at d ~4.7, barely visible in Fig. 5, which were
used for the calculation of number average molecular weights,
Mn. As with the ethylene copolymers, the integrated intensities
of the OCH2CH2 groups were used to determine the degrees of
incorporation.
phous).
are all repeats of the preceding even numbered experiments and, as
can be seen, reproducibility was generally very good. Interestingly,
addition of the comonomers to propylene polymerization reaction
mixtures did not result in either decreased polymer product yields
or decreased values of Mn, as has been reported elsewhere for
similar experiments.4 In addition, to our surprise, the greatest
degree of incorporation was observed with methoxy monomer A,
containing the smallest protecting group. Materials obtained with
comonomer B (benzyl protecting group) exhibited incorporations
Table 2 lists the results of copolymerization experiments involv-
ing propylene, including control runs in which no comonomer
was added (experiment 10, 11). The odd numbered experiments
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©

Fig. 5 1H NMR spectrum (400 MHz, ODCB–C6D6, 80 ◦C) of copolymer from experiment 12.
of polar monomer that were low (up to 0.5 mol%), and similar
product of experiment 12, containing polar monomer A (methoxy
group), resonances are observed at d 58.6 and 73.2, corresponding
to the CH2CH2O and OCH3 groups, respectively.
incorporations were obtained materials containing comonomer
C (trityl protecting group). These results suggest that bulkier
protecting groups do not promote more incorporation of polar
monomer within the polypropylene. The degrees of incorporation
for copolymers containing comonomer E (trimethylsilyl protecting
group) were slightly higher (up to 0.9 mol%), but no incorporation
was observed for comonomer D (triphenylsilyl protecting group)
as essentially homopolymer was isolated.
In an effort to determine if greater polar monomer incorpora-
tion could be achieved, experiments 22–25 were carried out at
a higher starting temperature (60 ◦C). The products obtained
in experiment 22 and 23 were copolymers (up to 0.4 mol%
incorporation), but the incorporations were actually lower than
those done at 21 ◦C and increasing the temperature for this
particular system clearly did not increase the polar monomer
content. This phenomenon was further evident in the products
of experiments 24 and 25, where only homopolymer was isolated.
In addition, increasing the amount of added polar monomer to
500 equiv. resulted in no incorporation of polar monomer; only
homopolymer was formed.
The 13C NMR spectra of the copolymers exhibit resonances
with chemical shifts consistent with their being copolymers. For
example, for the product of experiment 19, there are three major
resonances of the isotactic propylene backbone at d 47.1, 29.5
and 23.3 and for the polar monomer at d 44.5, 34.6, 31.9,
31.5, 31.2, 27.6, 27.0 and 26.0. These peak assignments are
based on literature assignments of similar copolymers4b and on
comparisons with the 13C NMR spectra of the polar monomers
and of polypropylene itself. The resonance at d 64.8 is diagnostic
of the CH2CH2OH group of the polar monomer, signifying
incorporation and effective protecting group hydrolysis. For the
Infrared spectra of the copolymers were prepared by placing
a few drops of a chloroform solution of each copolymer on a
KBr disk and allowing the solvent to evaporate to form thin
films. The IR spectra of polypropylene (Fig. 6a) and of the
copolymers obtained in experiments 12 and 13 (with methoxy
groups) exhibited the characteristic C-H stretching modes of
the polypropylene backbone at 2950–2840 cm-1, in addition to
C–H bending modes at 1457 and 1376 cm-1. In addition to these
peaks, bands at 1120–1017 cm-1 (C–O stretch) are observed in the
IR spectrum of the two copolymers. For copolymers of polar
monomers B–D, containing hydroxyl groups, a distinct broad
peak at ~3400 cm-1 is indicative of hydrogen bonding within the
copolymer (Fig. 6b).
The melting temperatures (Tm) of the various materials listed in
Table 2 were determined by DSC measurements. The isotactic
polypropylene samples synthesized in the control experiments
of this study (experiments 10, 11), as well as in two of the
copolymerization attempts which yielded only homopolymer
(experiments 20, 21), exhibited Tm values (118–121 ◦C) which
are comparable with the range of Tm values reported elsewhere
with this catalyst under varying conditions.15 Perhaps surprisingly,
many of the copolymers obtained exhibited slightly higher Tm
values although decreases would be expected in polypropylene
containing long branches because of loss of crystallinity. Materials
formed at higher temperatures (experiments 22–25) exhibited
lower values of Tm, as has been noted elsewhere,15c and that formed
in the presence of D exhibited no melting transition at all. There
is no obvious trend in the molecular weights Mn, and the values
obtained are generally comparable or slightly lower than reported
8872 | Dalton Trans., 2009, 8864–8877
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©

Fig. 6 Absorbance infrared spectra (films) of (a) pure polypropylene and (b) copolymer from experiment 18.
Table 3 Propylene copolymerizations with 1-hexene using rac-
C2H4(Ind)2ZrCl2/MAO in toluene
elsewhere from polymerizations carried out at higher pressures of
propylene.15b–15d
As noted above, the highest degrees of polar monomer incor-
poration were achieved with the methoxy comonomer A (1.7,
2.0 mol%), and the next closest was the trimethylsilyl comonomer
E (up to 0.9 mol% in experiment 18), while the trityl (experiments
16, 17) and triphenylsilyl (experiments 20, 21) comonomers,
containing much greater steric hindrance near the ether oxygen,
actually resulted in lower degrees of incorporation or none at all.
These findings are unexpected as one would anticipate, as we have
hypothesized above, that the presence of sterically more demand-
ing protecting groups would result in higher degrees of incorpora-
tion of polar comonomers. We wondered, therefore, if the presence
of ether linkages might play an unexpectedly positive role during
thepolymerizationof 1-alkenes bythe rac-C2H4(Ind)2ZrCl2/MAO
catalyst system under the conditions utilized here, and we therefore
carried out a series of similar copolymer experiments of propylene
with 1-hexene in the absence and the presence of the saturated
methoxy ether, n-decyl methyl ether.
Equiv. of
Experiment # 1-hexene added
Incorp.
Yield/g (mol.%) Tm/◦C Mn
34
—
2.53
4.38
4.03
4.00
4.67
—
2.9
1.7
9.1
13.0
120
106
127
n.t
2780
2366
1089
2184
1592
35a
36b
37a
38b
100
100
500
500
n.t
a Precatalyst and hexene combined prior to addition of MAO. b 1-Hexene
added 5 min after MAO addition. n.t–no transition.
very informative because of the overlapping of resonances, but
propylene (P) resonances at d 1.72, 1.40 and 0.87 are obvious and
some 1-hexene (H) resonances are observed at d 1.1 and 1.2. Also
apparent are two vinylidene end group resonances at d ~4.8, which
were used for the calculation of number average molecular weights,
Mn. The 13C NMR spectrum also exhibits resonances attributable
to propylene and 1-hexene units,16 and the relative intensities of
these were utilized to calculate the degrees of incorporation of
1-hexene into the polypropylene copolymers.16
Table 3 presents data for representative copolymer samples and,
as is seen, the yields, % incorporation (2.9, 1.7% in experiments
35 and 36, respectively) and Tm values are all comparable with
those in Table 2. Thus polar monomer incorporations into
polypropylene actually rival the degree of incorporation of the
Copolymerization reactions of 1-hexene with propylene, with and
without added n-decyl methyl ether
A series of copolymerization experiments was carried out as above
but utilizing 1-hexene rather than polar monomers. The products
1
were all white solids, and typical H and 13C NMR spectra are
shown in Fig. 7 and 8, respectively. The 1H NMR spectrum is not
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Dalton Trans., 2009, 8864–8877 | 8873
©

Fig. 7 High temperature 1H NMR spectrum (400 MHz, TCE-d2, 120 ◦C) of a copolymer of polypropylene with 2.9% of 1-hexene (experiment 35).
Fig. 8 High temperature 13C NMR spectrum (125 MHz, ODCB–C6D6, 80 ◦C) of a copolymer of polypropylene with 13.0% of 1-hexene (experiment
38).
non-polar 1-hexene and it would seem that ether functionalities in
the former do not hinder polar monomer incorporation, at least
not in a straightforward manner. The 1-hexene copolymerizations
did differ somewhat in that addition of 500 equiv. of 1-hexene
resulted not in catalyst degradation, as with the polar monomers,
but in higher degrees of incorporation to give non-crystalline
polymers.
Given the apparent lack of correlation of degrees of incorpo-
ration of the decenyl ethers with the steric requirements of the
series of R groups or with even the presence of an ether group, we
8874 | Dalton Trans., 2009, 8864–8877
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Fig. 9 Molecular models showing the tight ion pair formed when a MAO anion with a typical cage structure17 coordinates to [Cp2ZrMe]+: (a) ball and
stick model with green = Zr, cyan = C, small grey = H, magenta = Zr–Me, large grey = Al, red = O; and (b) space filling model. The perspective chosen
is that of a reasonable trajectory for an attacking alkene.
Table 4 Propylene copolymerizations with 1-hexene in the presence of
100 equiv. of n-decyl methyl ether
wondered if the presence of an ether group is actually as deleterious
as has long been suspected. We therefore carried out a series
of propylene-1-hexene copolymerization reactions, as above but
in the presence of n-decyl methyl ether, a saturated ether, which
would have an ether-donor property essentially identical to that
of comonomer A, which incorporates to the greatest extent.
Shown in Table 4 are the results of four such experiments. The 1H
and 13C NMR spectra of the materials obtained were assigned as
above and the percent incorporations of 1-hexene were determined
as before. As can be seen, while the yields of copolymers were
uniformly lower, the degrees of incorporation of 1-hexene and the
1-Hexene
equiv.
Incorp.
(mol%)
Experiment #
Yield/g
Tm/◦C Mn
39a
40b
41a
42b
100
100
500
500
1.11
1.29
1.03
1.32
5.1
6.5
20
118
122
n.d.
n.d.
1.4 ¥ 104
1.5 ¥ 104
6426
18
2449
a Pre-catalyst and hexene combined prior to addition of MAO. b 1-Hexene
added 5 min after MAO addition; n.t = no transition.
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©

values of Mn of the copolymers are all significantly higher. Perhaps
somewhat surprising given the greater number of branches in the
copolymers obtained, the values of Tm for experiments 39 and 40
are also somewhat higher than those observed for the products of
experiments 35 and 36, although the expected lack of crystallinity
is observed for experiments 41 and 42, with incorporations of 20
and 18%, respectively.
of ethylene and propylene. Instead, a heretofore unsuspected role
for catalyst activation by the ether linkage is suggested.
Acknowledgements
We gratefully acknowledge NSERC and Queen’s University for
funding of this research. We also thank Dr Francoise Sauriol
and Dr Emily Mitchell for assistance with the NMR experiments,
and Dr Bernd Keller for assistance with the mass spectrometry
experiments.
Thus addition of n-decyl methyl ether to the copolymerization
reactions does not result in decreases in either molecular weights or
degrees of incorporation, as conventional wisdom would presume,
but rather in the formation of copolymers of higher molecular
weights and containing greater incorporations of 1-hexene. As a
possible rationale of this behaviour, we note that while details of
the structure(s) of MAO are not known, it is generally believed to
exist in solution as an equilibrium mixture of very bulky anions.12b
Thus formation of a contact ion pair between a metallocenium
cation and a MAO anion, as in Fig. 9, will almost certainly result
in considerable steric hindrance to the approach of an alkene to the
active site on the metal. To illustrate this point, Fig. 9a shows, from
the perspective of an alkene approaching the position cis to the
Zr–Me group, the optimized (molecular mechanics) ball and stick
structure of the contact ion pair between the [Cp2ZrMe]+ cation
and the hexamethyl equivalent of the cage structure determined
experimentally for the [Al6O6(But)6Me]- anion.17 Fig. 9b shows the
analogous space filling structure with conventional van der Waals
radii for all atoms and, as is clear from the latter, even though
this particular MAO anion is one of the smaller known,12b the
metal ion is completely blocked from view and apparently not
very accessible to an alkene.
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Given that ether oxygen atoms probably have higher affinity
for hard zirconocene cations than do alkene p electron pairs,
we tentatively hypothesize that a sterically rather unencumbered
methoxy group may be able to manoeuvre itself into the space
between a bulky MAO-based counter anion and the cationic
catalytic site on zirconium, eventually displacing the MAO anion
and binding to the metal. Once anion-cation separation has been
achieved, the olefinic ether can perhaps exchange ends (as in eqn
=
(4)) such that the C C bond coordinates and migratory insertion
can ensue. Such a process would not be possible with the non-
polar 1-hexene and would probably also be more difficult with the
much bulkier phenyl-containing ethers. Once polymerization has
begun, of course, the steric requirements of the growing chain can
presumably keep the MAO anion at a distance.
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Summary
Reported here are the results (a) of an NMR study of reactions of
the archetypal metallocene polymerization catalyst, Cp2ZrMe(m-
=
Me)B(C6F5)3, with the polar monomers CH2 CH(CH2)8OR (R =
Me, PhCH2, Ph3C, Me3Si, Ph3Si), protected versions of the readily
available, long chain polar monomer 9-decen-1-ol, and (b) of
an investigation of the copolymerization reactions of these same
polar monomers with ethylene and propylene catalyzed by the
rac-C2H4(Ind)2ZrCl2/MAO catalyst system. While increasing the
steric requirements of the groups R does decrease the appar-
ent abilities of the ethers to displace [BMe(C6F5)3]- from the
[Cp2ZrMe]+ cation, there is no correlation of size of R on the
degrees of incorporation of the polar monomers into copolymers
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8864–8877 | 8877
©