Direct incorporation of hydroxy groups into isotactic polypropylene via metallocene-catalyzed copolymerization of ester group containing vinyl monomer treated with dialkylaluminum hydride and propylene

Article abstract of DOI:10.1246/bcsj.20150171

Methyl 10-undecenoate treated with 2 equivalents of diisobutylaluminum hydride was quantitatively converted into a 10-undecenoxy aluminum compound, which was successfully utilized for metallocene-catalyzed copolymerization with propylene to produce functional polypropylene with hydroxy groups in its side chains.

Full text of DOI:10.1246/bcsj.20150171

Short Articles
Table 1. The reaction of UnCOOMe with alkyl aluminums
and MAO (50 °C, 1 h)
Selected Paper
[Al]/[UnCOOMe] Conversion Yield
Entry Aluminum
Direct Incorporation of Hydroxy
Groups into Isotactic Polypropylene
via Metallocene-Catalyzed
Copolymerization of Ester Group
Containing Vinyl Monomer Treated
with Dialkylaluminum Hydride
and Propylene
m.r.
/%a)
/%b)
1
2
3
4
5
DIBAL-H
DIBAL-H
TEAL
TIBAL
MAO
1.0
2.0
2.0
2.0
2.0
53
100
51
14
4.3
53
100
4.0
12
0
a) UnCOOMe conversion: determined by GC (retention time:
8.83 min). b) The yield of UnOH: determined by GC (retention
time: 8.61 min).
However, in general, hydroxy functional monomers such as 10-
undecen-1-ol (UnOH) are so expensive that it is difficult to use
them for copolymerization industrially. Therefore, we chose to
use inexpensive vinyl monomer containing ester groups, which
can be converted into alcohols by several reduction reagents.10
In this paper, we herein discuss an innovative procedure
for incorporation of hydroxy groups into polyolefin via
metallocene-catalyzed copolymerization of propylene and
vinyl monomers containing ester groups.
Ryuichi Sugimoto*1 and Tomoaki Matsugi2
1School of Environmental Science and Engineering,
Kochi University of Technology, Miyanokuchi,
Tosayamada, Kami, Kochi 782-8502
2Research Center, Mitsui Chemicals, Inc.,
580-32 Nagaura, Sodegaura, Chiba 299-0265
To evaluate reactivity and the products of the above-
mentioned reductive reaction of ester group in detail, reaction
of methyl 10-undecenoate (UnCOOMe), a relatively inex-
pensive vinyl monomer, with diisobutylaluminumhydride
(DIBAL-H) was examined in toluene solution at 50 °C.11 For
comparison, reaction of two kinds of trialkyl aluminum (tri-
ethylaluminum: TEAL and triisobutylaluminum: TIBAL) and
methyl 10-undecenoate (UnCOOMe) was also examined. Con-
version of UnCOOMe and yield of reaction products were
determined by gas chromatography (GC) of organic layers after
treating reaction mixture with 1 M HCl aq. to remove alkyl
aluminum residue. The results of the reaction for 1 h are
summarized in Table 1.
E-mail: sugimoto.ryuichi@kochi-tech.ac.jp
Received: May 12, 2015; Accepted: June 5, 2015;
Web Released: June 12, 2015
Methyl 10-undecenoate treated with 2 equivalents of
diisobutylaluminum hydride was quantitatively converted
into a 10-undecenoxy aluminum compound, which was
successfully utilized for metallocene-catalyzed copolymer-
ization with propylene to produce functional polypropylene
with hydroxy groups in its side chains.
Incorporation of polar functional groups (e.g., hydroxy,
carboxy, or amino groups) into polyolefin chains has been a
great issue to broaden applications of polyolefin. Many
attempts focusing on copolymerization of polar vinyl monomer
and olefin, using both early and late transition metal catalyst
have been done.1 Especially, by the development of the group 4
metallocene and non-metallocene single-site catalysts, whose
catalytic performance is excellent, new polyolefin has been
created (e.g., high activity, single-site active site, and good
polymerization ability for higher α-olefins, cyclic olefins and
diene compounds, etc.). However, direct copolymerization of
olefin and polar vinyl monomer has not been achieved because
of polar groups interfering with the catalyst. To avoid attacks
by the heteroatom in polar monomers on the positively charged
active center of catalyst, protected polar monomers have been
used for copolymerization. In the case of vinyl monomers
containing hydroxy groups, as protection methods to obtain
hydroxy functionalized polyolefin, use of alkyl aluminums2
and excess methylalumoxane (MAO)3-5 has been reported.
Polyolefin functionalized by hydroxy groups is expected to
improve physical properties such as wetness, adhesion and
paintability. In addition, with its high reactivity, it can also be
used as synthetic tools for novel block and graft copolymers.6-9
All of the UnCOOMe was converted into UnOH by treatment
with 2 equivalents of diisobutylaluminum hydride DIBAL-H
(Entry 2 in Table 1). No by-product was detected by GC,
suggesting all the ester groups were effectively converted into
alcohol. The time profile of yield of UnOH shows that reaction
was rapidly completed within 3 min (Figure 1).
Structures of the resulting mixture were confirmed by
1
1H NMR measurement. (Figure 2A) shows the H NMR spec-
trum of UnCOOMe. The peaks arising from an ester group
(-CH2COOCH3, ¤ = 2.27-2.33 and 3.66 ppm) of UnCOOMe
disappeared after treatment of UnCOOMe with DIBAL-H
(Figure 2B). Meanwhile the peaks attributed to aluminum oxy-
methylene (-AlOCH2-) and aluminum oxymethyl (-AlOCH3)
appeared in regions 3.65-3.73 and 3.46-3.53 ppm, respectively,
whose peak intensity ratio was 3:2. And the peaks corresponded
with isobutylaluminum groups (-AlCH2CH(CH3)2, ¤ = ¹0.04-
¹0.01, 1.76-1.89, and 0.86-0.95 ppm) observed. After hydrol-
ysis reaction and treating them with acidic H2O, only UnOH
was produced (Figure 2C). The vinyl proton peaks (CH2=CH-,
¤ = 4.91-5.02 ppm, ¤ = 5.76-5.82 ppm) in Figure 2C retained
reasonable peak areas assigned as UnOH, which showed the
vinyl group was not affected by the reduction and hydrolysis
reactions. These results reveal that one mole of diisobutylalu-
1238 | Bull. Chem. Soc. Jpn. 2015, 88, 1238–1240 | doi:10.1246/bcsj.20150171
© 2015 The Chemical Society of Japan

minum-protected UnOH (or a multi-complex based on them12)
and equimolar diisobutyl aluminum methoxide was stoichio-
metrically produced by the reaction of UnCOOMe with 2
equivalents of DIBAL-H as described in Scheme 1.
100
80
60
40
20
0
DIBAL-H 2.0 equiv
DIBAL-H 1.0 equiv
The treatment of UnCOOMe with 1 equivalent of DIBAL-H
also rapidly produced UnOH and the reaction yield was around
53% (Entry 1 in Table 1). The aldehyde species, a plausible
reaction intermediate, was not detected after the reaction,
showing that the rate of the 2nd reduction from aldehyde to
alcohol was so fast compared to that of the 1st reduction that
the resulting product was dominated by the alcohol compound.
On the other hand, the treatment of UnCOOMe with 2 equiv-
alents of TEAL and TIBAL were also converted to UnOH,
although the yields of UnOH were relatively low (TEAL; 3%,
TIBAL; 13%) with the generation of a by-product (two GC
peak at 10.1 and 12.3 min in the case of TEAL and a GC peak
at 12.4 min in case of TIBAL).
TIBAL 2.0 equiv
TEAL 2.0 equiv
0.0
0.5
1.0
1.5
2.0
㼀㼕㼙㼑㻛㼔
Figure 1. Time profile of the yield of UnOH generated by
the reaction of UnCOOMe with alkyl aluminums.
From the reaction time profile (Figure 1), the yield of UnOH
was almost saturated within 3 min in both cases. It is reason-
able to explain that the aluminum hydride species13 (dialkyl
aluminum hydride as the main one), which are known to be
generated from trialkyl aluminum as an equilibrium reaction,14
promoted the reduction to yield UnOH. From GC-MS mea-
surements, the above-mentioned by-products are thought to be
1-alkylated 10-undecenol species15 via a Grignard-type addi-
tion reaction mechanism as referred to in previously reported
literature.16 In addition, no UnOH was produced by the reaction
of UnCOOMe with methylalumoxane (MAO).
The quantitative production of the 10-undecenoxy aluminum
compound prepared from the reduction of UnCOOMe was
expected to be applicable for inexpensive copolymerization in
order to produce hydroxy-functionalized polyolefin. There-
fore, copolymerization of in-situ prepared and protected UnOH
with propylene was carried out using an ethylenebis(indenyl)-
zirconium chloride (Et(Ind)2ZrCl)/MAO catalyst system
under propylene atmospheric pressure at 50 °C in toluene.17
UnCOOMe was treated with DIBAL-H, TEAL, and TIBAL for
5 min, and then an activated catalyst solution was added to start
polymerization. After polymerization, the resulting solution
was poured into acidic methanol to remove catalyst residue and
hydrolyze alkyl aluminum species used for protection.
The polymerization results are summarized in Table 2. No
polymer was obtained when 5.0 mmol of UnCOOMe was
added without alkyl aluminum (Entry 2 in Table 2), suggesting
that the ester group of UnCOOMe coordinated to the cataly-
tic active center and prevented monomer insertion. When
UnCOOMe was treated with 2.1 equivalents of DIBAL-H
versus UnCOOMe, a white solid polymer was obtained with
high yield (Entry 4 in Table 2). In contrast, no polymer was
obtained when 1.0 equivalent of DIBAL-H, 2.1 equivalents of
TEAL and TIBAL were added. We believe that the presence of
unreacted UnCOOMe led to the catalytic deactivation.
δ/ppm
Figure 2. 1H NMR spectra of (a) UnCOOMe, (b) the
products after the reaction of a UnCOOMe with 2.0 equiv
of TIBAL-H and (c) the hydrolyzed products (250 MHz,
CDCl3, 25 °C).
(iBu)2AlH
(iBu)2AlH
H2O
O
OH
H
OAl(iBu)2
8
8
8
8
O
fast
O
(iBu)2AlOMe
Scheme 1. Reduction scheme of UnCOOMe by DIBALH.
UnOH
UnCOOMe
Bull. Chem. Soc. Jpn. 2015, 88, 1238–1240 | doi:10.1246/bcsj.20150171
© 2015 The Chemical Society of Japan | 1239

Table 2. Copolymerization results of propylene with UnCOOMe using Et(Ind)2ZrCl2/MAO catalyst systema)
d)
Functional
monomer
Yield
/g
C.C.c)
/mol %
Tm
/°C
Mn
d)
Entry
Alkyl aluminum
Activityb)
Mw/Mn
¹1
/g mol
1
2
3
4
5
6
none
none
none
37.0
0
0
29.6
0
0
7.4
0
0
5.9
0
0
0
®
122.7
9600
®
1.91
®
UnCOOMe
UnCOOMe
UnCOOMe
UnCOOMe
UnCOOMe
DIBAL-H (1.2 equiv)
DIBAL-H (2.2 equiv)
TEAL (2.2 equiv)
TIBAL (2.2 equiv)
®
®
®
0.46
®
121.5
12300
®
®
1.86
®
®
®
7
UnOH
TIBAL (1.2 equiv)
35.0
7.2
0.40
117.7
12400
1.84
a) Conditions: 50 °C, 0.1 MPa pressure, toluene; 400 mL, propylene; 100 L h¹1, UnCOOMe or UnCOH: 5.0 mmol, Et(Ind)2ZrCl =
0.005 mmol, MAO; [Al] = 3.25 mmol. b) kg/mmol-cat./h. c) Comonomer content was determined by 1H NMR measurement. d) Mw,
Mn values; GPC analysis.
Supporting Information
Detailed reaction procedure of UnCOOMe with alkylalumi-
num and general polymerization procedure. This material is
available electronically on J-STAGE.
References
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δ/ppm
Figure 3. 1H NMR spectra of hydroxylated polypro-
pylene obtained by in-situ copolymerization of pro-
pylene with UnCOOMe treated with 2 equiv of DIBAL-
H (Entry 4 in Table 2) (250 MHz, o-dichlorobenzen-d4,
120 °C).
3
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chain (Entry 1, 4, and 7 in Table 2).
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ing to the ester group were observed, and the peak assigned to
a methylene proton (-CH2-OH) was observed at 3.49 ppm
(Figure 3).
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7
8
9
The catalytic activity (5.9 kg/mmol-Ti/h) and the content
of hydroxy groups (0.46 mol %) were comparable to the case
of 10-undecen-1-ol protected with TIBAL as shown in Entry 7
(Table 2). These results indicate that the 10-undecenoxy alumi-
num compound prepared by the treatment of UnCOOMe with
2 equivalents of DIBAL-H was highly effective and acts as
comonomer for metallocene-catalyzed copolymerization.
In conclusion, we have demonstrated one-pot synthesis of
hydroxy-functionalized polypropylene using vinyl monomer
containing an ester group. Rapid 2-step reduction of the ester
group by DIBAL-H led to the quantitative production of a 10-
undecenoxy aluminum compound that successfully promoted
metallocene-catalyzed copolymerization with propylene. Thus,
a hydroxy-functionalized copolymer was produced with a
relatively inexpensive monomer, giving rise to new polyolefin
applications.
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species (as AlH3) were included in purchased TEAL and TIBAL.
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17 General polymerization procedure; see Supporting Infor-
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1240 | Bull. Chem. Soc. Jpn. 2015, 88, 1238–1240 | doi:10.1246/bcsj.20150171
© 2015 The Chemical Society of Japan