Polyethylene building blocks by catalyzed chain growth and efficient end functionalization strategies, including click chemistry

Article abstract of DOI:10.1002/anie.200804445

(Chemical Equation Presented) A means to an end: Polyethylene chains obtained by catalyzed chain growth on magnesium and exhibiting molar masses up to 5000 g mol^-1 have been end-functionalized in high yield with iodide, azide, and amine reactiv

Full text of DOI:10.1002/anie.200804445

Angewandte
Chemie
DOI: 10.1002/anie.200804445
Reactive Polyolefins
Polyethylene Building Blocks by Catalyzed Chain Growth and Efficient
End Functionalization Strategies, Including Click Chemistry
Rꢀmi Briquel, Jꢀrꢁme Mazzolini, Tristana Le Bris, Olivier Boyron, Fernande Boisson,
Frꢀdꢀric Delolme, Franck DꢂAgosto,* Christophe Boisson, and Roger Spitz
Polyethylene and polypropylene are the largest volume
thermoplastics manufactured in the world, and new polymer
materials based on these polymers could have a strong impact
on our everyday life. The combination of the excellent
chemical and physical properties of polyolefins along with
their low cost of manufacture makes this class of polymer very
attractive for commercial purposes. The modification of
polyolefins has always been both an academic and an
industrial challenge.[1a] The scientific difficulty is due to the
fact that functional or polar groups can hardly be incorpo-
rated into these materials when produced industrially by
catalytic olefin polymerization.[1b] The development of new
strategies to incorporate polar segments into polyolefins in a
controlled fashion is one of the long-term goals in polymer
chemistry, since the materials would exhibit new architectures
with many desirable properties.[1a] Some of the existing
methods to produce polyolefins bearing polar groups or
segments are based on the use of reactive polyolefins.[1c] The
functional polyolefins can serve as building blocks for
constructing multisegmented polymers or more complex
architectures based on polyolefins. The difficulty lies in
finding an efficient and simple way of introducing appropriate
functional groups, such as reactive or polymerizable groups,
and initiators or control agents for other polymerization
techniques.
Mg-PE) were prepared by the polymerization of ethylene
using the [(C5Me5)2NdCl2Li(OEt2)2] complex in combination
with n-butyloctylmagnesium (BOMg).
Although not originally exploited,[3] the nucleophilicity of
the carbon moiety in PE-Mg-PE has been reported to favor
the introduction of various functional groups at the end of the
PE chain.[4] Narrowly distributed (PDI < 1.2) short alkyl
chains to crystalline polyethylene (up to 5000 gmolꢀ1) can be
synthesized with this catalytic system, and we report here the
implementation of very simple strategies for the end-func-
tionalization of these chains (Scheme 1), which will enable
their further modification or incorporation into more com-
plex architectures. Examples of 1) functionalized polyethy-
lene, 2) polymerizable polyethylene, and 3) control agents for
free-radical polymerization based on polyethylene are given
below.
We discovered that the addition of iodine after polyeth-
ylene catalyzed chain growth on magnesium led to highly
functionalized end-halogenated polyethylene (PE-I). This
successful introduction of an iodide atom was confirmed by
1
the H NMR spectrum (Figure 1), which showed a triplet at
d = 3.00 ppm corresponding to the methylene group adjacent
to the iodine atom. Degrees of functionalization ranging from
73.0% up to 96.8%, as determined by 1H NMR spectroscopic
analysis, demonstrated the efficiency of the end-functionali-
zation. The decrease in the degree of functionalizationwith an
increasing molar mass of the polyethylene correlates with the
use of lower Mg/Nd ratios. The control of the polymerization
being less efficient, an increase in the proportion of product
with a vinyl group at the chain end as a result of b-H
elimination during the catalytic process is observed. The
obtained PE-I chains, in which the chain end is now electro-
philic, open the way to a much broader range of possible
reactions, including those involving nucleophilic attack.
These reactions include the simple introduction of an
azide end group by reaction with NaN3. As shown by 1H NMR
analysis (Figure 1), an almost quantitative substitution of the
iodine atom by an azide group (Table 1) resulted from heating
a mixture of PE-I and NaN3 in DMF at reflux for two hours.
This successful substitution was also confirmed by FTIR
analysis of PE-N3 (see the Supporting Information), which
showed, along with the expected PE absorption bands, an
additional band corresponding to -N3 at 2095 cmꢀ1.
The possibility of taking advantage of the reactivity of
carbon–metal bonds in catalytic olefin polymerization pro-
cesses has been enhanced by the discovery of specific features,
such as chain-shuttling events in the forming chains between
the active metal and a second metal center, in certain catalytic
systems.[2] To make the most of this particular concept of
chain shuttling, dipolyethylenylmagnesium compounds (PE-
[*] R. Briquel, J. Mazzolini, T. Le Bris, O. Boyron, Dr. F. D’Agosto,
Dr. C. Boisson, Dr. R. Spitz
Universitꢀ de Lyon, Univ. Lyon 1, CPE Lyon, CNRS UMR
5265 Laboratoire de Chimie Catalyse Polymꢁres et Procꢀdꢀs (C2P2),
LCPP team
Bat 308F, 43 Bd du 11 novembre 1918, 69616 Villeurbanne (France)
Fax : (+33)4-72-43-17-70
E-mail: dagosto@lcpp.cpe.fr
Homepage: http://www.lcpp-cpe.com
Dr. F. Boisson
Service de RMN du Rꢀseau des Polymꢀristes Lyonnais
CNRS UMR5223 (France)
These newly synthesized PE-N3 compounds can very
easily and quantitatively be reduced with LiAlH4 to give
functional chains with an amine end group (PE-NH2). The
disappearance of the azide band in the FTIR spectra was
evident. Furthermore, in the 1H NMR spectra, the resonance
corresponding to the methylene group adjacent to the azide
F. Delolme
CNRS USR 59 SCA, Echangeur de Solaize, Chemin du canal
69360 Solaize (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200804445.
Angew. Chem. Int. Ed. 2008, 47, 9311 –9313
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9311

Communications
Supporting
Information),
and is thus consistent with
the structure proposed on the
basis of the NMR data, and
illustrates the success of the
reaction. The tolerance, ver-
satility, and cleanliness of the
reaction together with it
being quantitative fulfil the
requirements
for
click
chemistry.[5] In addition, the
extraordinary short reaction
times required (less than
15 min) to perform the Huis-
gen
[1,3] cycloaddition
makes this polyethylene
functionalization pathway a
very attractive one. This is
the first report on polyethy-
Scheme 1. General strategy.
lene functionalization using
click chemistry. The proof of
end group disappeared while a resonance appeared at d =
concept that such compounds can genuinely be used as
building blocks was provided by showing that these macro-
monomers can be readily (co)polymerized, for example, by
free-radical polymerization. Thus, PE-M was copolymerized
with methyl methacrylate (MMA) in toluene by using
azobis(isobutyronitrile) (AIBN) as an initiator (see the
Supporting Information). After three hours of reaction at
858C, the MMA was completely consumed. Analysis of the
polymerization medium by size-exclusion chromatography
(SEC) revealed the presence of two populations: PE-M
starting material (Mn = 1040, PDI = 1.19, PE calibration) and
an additional population with Mn = 20000 gmolꢀ1 (PDI = 2.0,
universal calibration). To determine if PE-M is effectively
inserted into the newly formed polymer, the conversion of
PE-M was determined by analyzing the residue of the
polymerization medium by 1H NMR spectroscopy after
drying. According to the obtained spectrum, a copolymer
was formed effectively and 76% of the starting PE-M was
inserted into the PMMA backbone; this value corresponds to
2.4% PE units.
2.78 ppm corresponding to the methylene group adjacent to
the introduced amine end group. These observations thus
demonstrate the successful formation of PE-NH2 (see Table 1
and the corresponding analyses in the Supporting Informa-
tion).
The resulting functionalized polyethylenes (PE-I, PE-N3,
PE-NH2) are interesting starting points to expand the range of
reactive polyolefins. As an example, PE-N3 has been eval-
uated in highly efficient click reactions[5] involving a Huisgen
[1,3] cycloaddition with alkyne-containing reagents. Thus,
commercially available propargyl acrylate and propargyl
methacrylate were treated with PE-N3 in the presence of
CuSO4 and sodium ascorbate in DMF at 1308C. The resulting
products (PE-A and PE-M) were all characterized by FTIR
1
and H NMR spectroscopy as well as by MALDI-TOF mass
spectrometry (see the Supporting Information).
Acrylate functionalization at the chain end was supported
by the disappearance of the azide band at 2095 cmꢀ1 and the
presence of a carbonyl band at 1732 cmꢀ1 and of a CH2 CH
=
band at 1634 cmꢀ1 in the IR spectrum of the resulting
polyethylene. A comparison of the 1H NMR spectra of
starting PE-N3 and the obtained product shows the complete
disappearance of the signal corresponding to the methylene
group (at d = 3.05 ppm) adjacent to the azide group. The
observation in the 1H NMR spectrum of a signal at d =
7.22 ppm for the triazole proton and two signals at d =
4.00 ppm and 5.22 ppm that could be assigned to methylene
groups adjacent to the triazole ring, together with the
corresponding integrals, support the complete assignments
proposed in Figure 1 and the Supporting Information, and
show that the acrylate moiety had successfully been intro-
duced in a yield of 95.3%. MALDI-TOF mass spectrometry
analysis was successfully performed on PE-A and PE-M; this
technique is seldom used for this kind of polymer, which lacks
functional groups that can complex cations. Very clean
spectra were obtained and the main, and almost exclusive,
population observed corresponds to the expected one (see the
A dithioester end group, which can control the free-
radical polymerization of a broad range of monomers in the
reversible addition-fragmentation chain transfer (RAFT)
process, was introduced by reaction of PE-NH2 with an
activated ester containing a RAFT agent (Scheme 1) through
a mechanism reported previously by our research group.[6]
The success of the reaction, as confirmed by 1H NMR
analyses of the resulting product (see the Supporting Infor-
mation), makes the elaboration of a broad range of block
copolymers possible, which we are currently studying. As an
example, n-butyl acrylate was polymerized using PE substi-
tuted with a RAFT group (PE-NH-RAFT) to mediate a
RAFT process. This experiment was compared to a blank
experiment performed under the same conditions with
unfunctionalized polyethylene instead of PE-NH-RAFT.
While the medium rapidly turned into a gel in the control
experiment (uncontrolled polymerization), the PE-NH-
RAFT-mediated polymerization medium remained slightly
9312
www.angewandte.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2008, 47, 9311 –9313

Angewandte
Chemie
Table 1: Molar mass characteristics and yields of end-functionalized
polyethylene and end-functionalization for PE-I, PE-N3, and PE-NH2
% PE-I[c] % PE-N3
% PE-NH2
[a]
[b]
[c]
[c]
Entry Mn
Mn
[gmolꢀ1
(Xn)[a]
]
[gmolꢀ1
(PDI)[b]
]
(yield%)[d] (yield%)[d]
1
2
3
1148 (41)
2296 (82)
4536 (162) 4980 (1.37) 73.0
1020 (1.23) 96.8
2230 (1.26) 86.7
94.1 (97.2) 94.1 (100)
86.0 (99.2) 85.8 (99.8)
68.4 (93.6) n.d.
[a] Mn values of the alkyl chain of functionalized PE determined by
1H NMR spectroscopy and the corresponding degree of polymerization
(Xn). [b] Mn value of PE-I determined by high-temperature SEC analyses
and the corresponding polydispersity index (PDI). [c] Functional group.
[d] Reaction yields. n.d.: not determined.
obtained low PDI (see the Supporting Information), the
growth of the chains is controlled by the PE-NH-RAFT
moiety.
In conclusion, the use of a polyethylene catalyzed chain
growth on magnesium in combination with simple and
efficient functionalization strategies enables the synthesis in
high yield of polyethylenes highly end-functionalized with
iodine, azide, or amine groups. The functional groups can then
be reacted further by using modular chemistry approaches to
generate new functional polyolefins that can be used as
building blocks for the design of macromolecular architec-
tures.
Received: September 9, 2008
Published online: October 29, 2008
Keywords: catalysis · click chemistry · macromonomers ·
.
polymers · RAFT polymerization
[1] a) T. C. Chung, Prog. Polym. Sci. 2002, 27, 39 – 85; b) A.
Berkefeld, S. Mecking, Angew. Chem. 2008, 120, 2572 – 2576;
Angew. Chem. Int. Ed. 2008, 47, 2538 – 2542; c) R. Godoy Lopez,
F. DꢀAgosto, C. Boisson, Prog. Polym. Sci. 2007, 32, 419 – 454.
[2] a) G. J. P. Britovsek, S. A. Cohen, V. C. Gibson, P. J. Maddox, M.
Van Meurs, Angew. Chem. 2002, 114, 507 – 509; Angew. Chem. Int.
Ed. 2002, 41, 489 – 491; b) V. C. Gibson, Science 2006, 312, 703 –
704; c) D. J. Arriola, E. M. Carnahan, P. D. Hustad, R. L. Kuhl-
man, T. T. Wenzel, Science 2006, 312, 714 – 719.
[3] J. F. Pelletier, A. Mortreux, X. Olonde, K. Bujadoux, Angew.
Chem. 1996, 108, 1980 – 1982; Angew. Chem. Int. Ed. Engl. 1996,
35, 1854 – 1856.
[4] a) R. Godoy Lopez, C. Boisson, F. DꢀAgosto, R. Spitz, F. Boisson,
D. Gigmes, D. Bertin, J. Polym. Sci. Part A 2007, 45, 2705 – 2718;
b) R. Godoy Lopez, C. Boisson, F. DꢀAgosto, R. Spitz, F. Boisson,
D. Gigmes, D. Bertin, Macromol. Rapid. Commun. 2006, 27, 173 –
181.
[5] a) H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001,
113, 2056 – 2075; Angew. Chem. Int. Ed. 2001, 40, 2004 – 2021;
b) M. Meldal, Macromol. Rapid Commun. 2008, 29, 1016 – 1061;
c) W. H. Binder, R. Sachsenhofer, Macromol. Rapid Commun.
2008, 29, 952 – 981.
Figure 1. 1H NMR (C6D6/TCE 1:2 v/v, 400 MHz, number of scans =
1024, 363 K) spectra of a) PE-I, b) PE-N3, and c) PE-acrylate. Starting
PE-I = sample 1 in Table 1. Signals marked by an asterisk are solvent
impurities.
[6] M. Bathfield, F. DꢀAgosto, R. Spitz, M. T. Charreyre, T. Delair, J.
Am. Chem. Soc. 2006, 128, 2546 – 2547.
viscous up to the end of the polymerization (see the
Supporting Information). As shown by the observed increase
in the molar masses versus conversion together with the
Angew. Chem. Int. Ed. 2008, 47, 9311 –9313
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
9313