Metal-catalyzed radical polyaddition as a novel polymer synthetic route

Article abstract of DOI:10.1039/b616598b

A new class of polymerizations was developed via metal-catalyzed C-C bond forming radical polyaddition; the monomers were designed to have a reactive C-Cl bond, which can be activated by the metal catalysts to generate a carbon radical species, along with a C=C double bond, to which the carbon radical generated from another molecule adds to form a C-C backbone polymer with an inactive C-Cl pendant. The Royal Society of Chemistry.

Full text of DOI:10.1039/b616598b

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COMMUNICATION
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Metal-catalyzed radical polyaddition as a novel polymer synthetic
route{
Kotaro Satoh, Masato Mizutani and Masami Kamigaito*
Received (in Cambridge, UK) 14th November 2006, Accepted 11th December 2006
First published as an Advance Article on the web 11th January 2007
DOI: 10.1039/b616598b
polymers via the activation of both the original and the resulting
C–X bonds.8
A new class of polymerizations was developed via metal-
catalyzed C–C bond forming radical polyaddition; the mono-
mers were designed to have a reactive C–Cl bond, which can be
activated by the metal catalysts to generate a carbon radical
species, along with a CLC double bond, to which the carbon
radical generated from another molecule adds to form a C–C
backbone polymer with an inactive C–Cl pendant.
Herein, we designed ester-linked monomers (1 and 2), which
would afford aliphatic polyesters, and another monomer (3),
which could apparently produce the equivalent structure of the
alternating copolymer of vinyl chloride (VC) and methyl
methacrylate (MMA). All these monomers were designed to have
unconjugated double bonds, and the activated C–Cl bond adjacent
to the carbonyl group.
The metal-catalyzed atom transfer radical addition (ATRA) is one
of the highly efficient carbon–carbon bond forming radical
reactions, in which the radical species is generated through the
metal-catalyzed cleavage of a carbon–halogen (C–X) bond and
adds to an olefin to form the 1 : 1 adduct of the halide and olefin.1
This chemistry has been effectively and widely applied to radical
addition polymerizations of vinyl monomers that developed into
the metal-catalyzed living radical polymerization or atom transfer
radical polymerization (ATRP) and to open a new era of precision
polymer synthesis.2–6 The radical addition polymerization proceeds
via the metal-catalyzed reversible formation of the growing radical
species from the dormant polymer terminal with a C–X bond,
which originates from the halide initiator, and the addition of the
growing radical species to the vinyl monomers.
For the first attempts to show the new radical polyaddition
reactions, 1, which can be easily obtained from allyl alcohol and
2-chloropropionyl chloride, was examined in conjunction with
various transition metal complexes, such as RuII, FeII, and CuI, in
toluene at 100 uC (Fig. 1). The reactions were carried out by the
appropriate combinations of the metals and the ligands, all of
which are effective for the metal-catalyzed living radical
polymerizations; i.e., the RuCl2(PPh3)3 complex with an amine
additive, FeCl2 with 4 equiv. of Pn-Bu3 or N,N,N9,N0,N0-
pentamethyldiethylenetriamine (PMDETA), and CuCl with
4 equiv. of PMDETA were used.2,3,9–11 The monomer was
smoothly consumed and the conversion reached over 90% to
afford polymers in high yield with the RuCl2(PPh3)3, FeCl2–
Pn-Bu3, and CuCl–PMDETA systems.
In this communication, novel radical polyaddition reactions are
developed for a designed monomer that possesses an active C–X
bond and an unconjugated carbon–carbon double bond via metal-
catalyzed carbon–carbon bond forming radical reactions
(Scheme 1). Namely, the active or dormant C–X bond in the
monomer is activated by the metal catalysts to form a radical
species, which adds to the CLC double bond of another monomer
molecule to generate a C–C bond as the main chain, along with an
inactive C–X bond as the pendant. The original C–X bond in the
monomer or the resulting oligomer or polymer is active in
the catalysis due to the adjacent carbonyl group while the resulting
C–X bond is inactive due to the absence of the adjacent carbonyl
moiety.7 These conceptually new polyaddition reactions can
provide new types of linear polymers, such as the equivalents for
the sequence-regulated vinyl polymers, as shown below. While
monomers with a C–X bond and a conjugated CLC double bond
were used in the metal-catalyzed radical addition polymerizations,
the monomers served as an ‘‘ini-mer’’ to produce highly branched
Fig. 2 shows the size-exclusion chromatography (SEC) curves of
the polymers obtained using FeCl2–Pn-Bu3 and CuCl–PMDETA.
The peaks of the SEC curves shifted to a higher molecular weight
and the peak areas of the lower molecular weight regions
decreased as the polymerization proceeded. Similar to the
conventional step polymerizations, the molecular weight of the
Department of Applied Chemistry, Graduate School of Engineering,
Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
E-mail: kamigait@apchem.nagoya-u.ac.jp; Fax: +81-52-789-5112;
Tel: +81-52-789-5400
{ Electronic supplementary information (ESI) available: Synthetic proce-
dures, spectroscopic data, and additional experiments. See DOI: 10.1039/
b616598b
Scheme 1 Transition
metal
catalyzed
intermolecular
radical
polyaddition.
1260 | Chem. Commun., 2007, 1260–1262
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polymers increased exponentially at the later stage of the
polymerizations. These results indicated that the step-growth
polyaddition reactions effectively took place without unwanted
ring-closing processes.12
Table 1 summarizes the polymerizations of 1–3 with a series of
the catalysts under various conditions. The reactions proceeded in
all cases to produce the polymers, although the molecular weights
of some polymers were relatively low. For 1 and 2, the reaction
rates and the molecular weights of the polymers were dramatically
changed by a combination of the central metals and the ligands.
Among them, higher molecular weights were attained with the
FeCl2–Pn-Bu3 and CuCl–PMDETA systems that reached Mw
y 5 6 103. Furthermore, upon the addition of tin 2-ethylhex-
anoate [Sn(EH)2], which recently proved effective as a reducing
agent for the oxidized catalyst in the Cu-mediated ATRP,13 the
reactions of 2 with the Cu and Fe systems were accelerated and the
molecular weights of the polymers became the highest (ESI{).
These indicate that the polyaddition proceeded via a one-electron
redox reaction of the metal center and that this polyaddition
reaction also suffered from the formation of small amounts of
inactive catalysts during the metal-catalyzed radical reactions. For
3, which possesses a C–Cl bond similar to that derived from
methacrylate, the RuCl2(PPh3)3 system was more effective, giving
a higher monomer conversion than the others. These results are
consistent with the fact that the RuII-based systems are more
suitable for methacrylates in terms of the control of the polymeri-
zations.2,9 The addition of Sn(EH)2 also accelerated the polyaddi-
tion of 3 with FeCl2–Pn-Bu3, though the effects on the polymer
molecular weight increase were smaller than those for 2.
Fig. 1 Time–conversion curves for the polyaddition of allyl 2-chlor-
opropanoate (1) with various metal complexes: [1]0 = 4.0 M; [Mt]0
=
100 mM; [ligand]0 = 400 mM in toluene at 100 uC. [n-Bu3N]0 = 400 mM
(for RuII).
The structures of the obtained polymers were then analyzed by
1H NMR and matrix-assisted laser-desorption-ionization time-of-
flight mass (MALDI-TOF-MS) spectroscopy. Fig. 3 shows the 1H
NMR spectra of monomer 2 and typical samples of poly(2), which
were obtained using FeCl2–Pn-Bu3 and CuCl–PMDETA and
purified by preparative SEC to remove the residual monomer and
the catalysts. In both spectra of the polymers, a series of
sharp peaks (19–69) were observed, similar to those in the
monomer (1–6), which indicates the presence of the double bond
Fig. 2 Size-exclusion chromatograms of poly(1) obtained with the
FeCl2–Pn-Bu3 (left) and CuCl–PMDETA (right) systems: [1]0 = 4.0 M;
[Mt]0 = 100 mM; [Pn-Bu3]0 = 200 mM (for Fe); [PMDETA]0 = 400 mM
(for Cu) in toluene at 100 uC.
Table 1 Transition metal catalyzed radical polyaddition of 1–3a
Temperature/uC Time/h Conversion (%)e Mn
Mw
Mw/Mn
f
f
f
Monomer Metal
Ligand
[Ligand]0 Additive
b
1
1
1
1
1
1
2
2
2
2
2
2
2
3
3
3
3
a
RuCl2(PPh3)3
—
—
n-Bu3Nc
None
None
Sn(EH)2
None
None
None
None
Sn(EH)2
None
None
100
100
100
100
100
100
100
100
100
100
80
60
60
100
100
100
100
330
1180
750
750
310
240
250
300
480
460
240
1350
500
700
1500
480
540
90
94
91
87
60
99
91
47
.99
97
97
99
.99
92
75
79
410
460
710
630
1100
1300
620
820 2.01
1000 2.28
1800 2.51
1500 2.35
4000 3.70
5600 4.21
1200 1.95
610 1.52
3500 2.32
3000 2.74
5500 3.30
FeCl2
FeCl2
FeCl2
FeCl2
CuCl
FeCl2
FeCl2
FeCl2
CuCl
CuCl
CuCl
CuCl
RuCl2(PPh3)3
FeCl2
FeCl2
CuCl
Pn-Bu3
Pn-Bu3
Pn-Bu3
PMDETA 400 mM
PMDETA 400 mM
Pn-Bu3
PPh3
Pn-Bu3
PMDETA 400 mM
PMDETA 400 mM
PMDETA 400 mM
PMDETA 400 mM
400 mM
200 mM
200 mM
d
d
200 mM
400 mM
200 mM
400
1500
1100
1700
None
2600 11 000 4.12
4600 21 000 4.60
540
470
490
570
c
d
d
Sn(EH)2
n-Bu3Nc
None
Sn(EH)2
None
b
—
—
910 1.68
660 1.42
770 1.57
980 1.73
Pn-Bu3 200 mM
Pn-Bu3 400 mM
PMDETA 400 mM
62
b
Polymerization conditions: [M]0 = 4.0 M; [Metal]0 = 100 mM in toluene. RuCl2(PPh3)3 was used as purchased. [n-Bu3N]0 = 400 mM.
d
e
[Sn(EH)2]0 = 45 mM; EH: 2-ethylhexanoate. Determined by gas chromatography. The number-average and weight-average molecular
f
weight (Mn and Mw, respectively) and polydispersity index (Mw/Mn) were determined by size-exclusion chromatography.
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Fig. 4 MALDI-TOF-MS spectra of poly(1) (Mn = 1600, Mw/Mn = 2.51)
and poly(2) (Mn = 1300, Mw/Mn = 3.07) obtained with CuCl–PMDETA:
[M]0 = 4.0 M; [CuCl]0 = 100 mM; [PMDETA]0 = 400 mM in toluene at
100 uC.
Fig. 3 1H NMR spectra of (A) 3-butenyl 2-chloropropionate (2) and
poly(2) obtained in toluene with (B) FeCl2–Pn-Bu3 at 100 uC or (C) CuCl–
PMDETA at 80 uC.
in progress to explore the systems for designing the equivalents to
the sequence-regulated vinyl polymers.
and the active C–Cl bonds at the chain ends of the polymers. In
addition to these signals, broad and relatively large peaks (a–f)
appeared, assignable to the main chain protons of the repeating
units of the aliphatic polyester that should be generated via the
expected polyaddition reactions. No unsaturated protons, possibly
caused by chlorine elimination, were detected other than those of
the original terminal CLC bond, further indicating that the
effective polyaddition reactions proceeded without any significant
side reactions under the appropriate conditions. The molecular
weights determined from the relative peak areas of the main-chain
repeat units (e) to the end-group moiety (19 and 29) were close to
those determined by SEC. These results show that the polymers
were produced via the expected intermolecular polyaddition.
Fig. 4 shows the MALDI-TOF-MS spectra of poly(1) and
poly(2) obtained using the CuCl–PMDETA system. The spectra
consist of a series of peaks each separated by 148.3 and 161.8 Da
intervals, which correspond to the formula weight of monomers 1
and 2, respectively. The molecular weights of each individual peak
were very close to the calculated values; i.e., multiples of the
formula weight of 1 or 2 plus the sodium ion from the salt for the
MS analysis. This again indicates that the polymerizations proceed
via intermolecular polyaddition. Both spectra exhibited a minor
series of peaks, shifted by ca. 35 Da from the major series, which
most probably suggests some loss of the reactive Cl atom at the
chain end during the laser-induced ionization. Similar Cl-capped
polymers synthesized via the living radical polymerization also lose
the halogen at the v-end during the MS analysis.14 In contrast, the
resulting C–Cl bonds in the main chain are more stable even
toward the laser ionization.
This work was supported in part by a Grant-in-Aid for
Scientific Research (B) No. 18350061 by the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
Notes and references
1 (a) M. S. Kharasch, E. V. Jensen and W. H. Urry, Science, 1945, 102,
128; (b) F. Minisci, Acc. Chem. Res., 1975, 8, 165; (c) J. P. Iqbal,
B. Bhatia and N. K. Nayyar, Chem. Rev., 1994, 94, 519; (d)
R. A. Gossage, L. A. van de Kuil and G. van Koten, Acc. Chem.
Res., 1998, 31, 423.
2 (a) M. Kato, M. Kamigaito, M. Sawamoto and T. Higashimura,
Macromolecules, 1995, 28, 1721; (b) M. Kamigaito, T. Ando and
M. Sawamoto, Chem. Rev., 2001, 101, 3689; (c) M. Kamigaito, T. Ando
and M. Sawamoto, Chem. Rec., 2004, 4, 159.
3 (a) J.-S. Wang and K. Matyjaszewski, J. Am. Chem. Soc., 1995, 117,
5614; (b) K. Matyjaszewski and J. Xia, Chem. Rev., 2001, 101, 2921.
4 V. Percec and B. Barboiu, Macromolecules, 1995, 28, 7970.
5 C. Granel, Ph. Dubois, R. Je´roˆme and Ph. Teyssie´, Macromolecules,
1996, 29, 8576.
6 D. M. Haddleton, C. B. Jasieczek, M. J. Hannon and A. J. Shooter,
Macromolecules, 1997, 30, 2190.
7 V. Coessens, J. Pyun, P. J. Miller, S. G. Gaynor and K. Matyjaszewski,
Macromol. Rapid Commun., 2000, 21, 103.
8 (a) J. M. J. Fre´chet, M. Henmi, I. Gitsov, S. Aoshima, M. Leduc and
R. B. Grubbs, Science, 1995, 269, 1080; (b) K. Matyjaszewski,
S. G. Gaynor and A. H. E. Mu¨ller, Macromolecules, 1997, 30, 7034.
9 S. Hamasaki, M. Kamigaito and M. Sawamoto, Macromolecules, 2002,
35, 2934.
10 (a) T. Ando, M. Kamigaito and M. Sawamoto, Macromolecules, 1997,
30, 4507; (b) K. Matyjaszewski, M. Wei, J. Xia and N. E. McDermott,
Macromolecules, 1997, 30, 8161.
11 J. Xia and K. Matyjaszewski, Macromolecules, 1997, 30, 7697.
12 F. De Campo, D. Laste´coue`res and J.-B. Verlhac, J. Chem. Soc., Perkin
Trans. 1, 2000, 575.
13 (a) W. Jakubowski and K. Matyjaszewski, Macromolecules, 2005, 38,
4139; (b) W. Jakubowski, K. Min and K. Matyjaszewski,
Macromolecules, 2006, 39, 39.
In conclusion, metal-catalyzed intermolecular radical polyaddi-
tions successfully proceeded for the designed monomers and
proved a novel polymer synthetic method. Further studies are now
14 H. Nonaka, M. Ouchi, M. Kamigaito and M. Sawamoto,
Macromolecules, 2001, 34, 2083.
1262 | Chem. Commun., 2007, 1260–1262
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