Synthesis of well-defined ω-oxanorbornenyl poly(ethylene oxide) macromonomers via click chemistry and their ring-opening metathesis polymerization

Article abstract of DOI:10.1021/ma100779q

ω-Oxanorbornenyl poly(ethylene oxide) monomethyl ether macromonomers were synthesized with molecular weights ranging from 500 g/mol to 5000 g/mol through the Huisgen 1,3-dipolar cycloaddition between acetylene-functionalized oxanorbornene and ω-azido poly(ethylene oxide) monomethyl ether. Thermal analysis showed that the ω-exo-norbornenyl end-group of the macromonomers is converted into a maleimide group through a retro-Diels-Alder process at 130° C. Ring-opening metathesis polymerization (ROMP) of these macromonomers was investigated using Grubbs' catalyst in dichloromethane at room temperature. Poly(oxanorbornene)-g-poly(ethylene oxide)s were obtained with polydispersities between 1.04 and 1.17 and molecular weights between 9900 and 57 800 g/mol leading to comb or brush copolymers according to the lengths of backbone and graft chains.

Full text of DOI:10.1021/ma100779q

Macromolecules 2010, 43, 5611–5617 5611
DOI: 10.1021/ma100779q
Synthesis of Well-Defined ω-Oxanorbornenyl Poly(ethylene oxide)
Macromonomers via Click Chemistry and Their Ring-Opening Metathesis
Polymerization
D. Le,† V. Montembault,† J.-C. Soutif,† M. Rutnakornpituk,‡ and Laurent Fontaine*,†
†LCOM-Chimie des Polymeꢀres, UCO2M, UMR CNRS 6011, Universiteꢁ du Maine, Avenue O. Messiaen,
72085 Le Mans Cedex 09, France, and ‡Department of Chemistry, Faculty of Science, Naresuan University,
Muang, Phitsanuloke, 65 000, Thailand
Received April 9, 2010; Revised Manuscript Received June 3, 2010
ABSTRACT: ω-Oxanorbornenyl poly(ethylene oxide) monomethyl ether macromonomers were synthe-
sized with molecular weights ranging from 500 g/mol to 5000 g/mol through the Huisgen 1,3-dipolar
cycloaddition between acetylene-functionalized oxanorbornene and ω-azido poly(ethylene oxide) mono-
methyl ether. Thermal analysis showed that the ω-exo-norbornenyl end-group of the macromonomers is
converted into a maleimide group through a retro-Diels-Alder process at 130 °C. Ring-opening metathesis
polymerization (ROMP) of these macromonomers was investigated using Grubbs’ catalyst in dichloro-
methane at room temperature. Poly(oxanorbornene)-g-poly(ethylene oxide)s were obtained with polydis-
persities between 1.04 and 1.17 and molecular weights between 9900 and 57 800 g/mol leading to comb or
brush copolymers according to the lengths of backbone and graft chains.
Introduction
dichloro(phenylmethylene)bis(3-bromopyridine) ruthenium).51
The oxanorbornene-based group was chosen as the “ROMP-able”
Macromonomers are unique precursors for the preparation of
well-defined graft copolymers using the so-called “grafting through”
strategy which allows the control of grafts, backbone length, and
grafting density.1-3 The combination of ring-opening metathesis
polymerization (ROMP) and various ionic and radical processes
has been used for the preparation of graft copolymers starting
from inimers (initiator-monomers) bearing “ROMP-able” entities
such as norbornene,4-26 oxanorbornene,27-29 cyclobutene,30-34
and cyclooctadiene moieties.35
Poly(ethylene oxide) (PEO), also referred as poly(ethylene
glycol) for structures bearing hydroxyl end-groups, is one of
the most important and most widely used polymer in pharma-
ceutical and biomedical applications. Despite considerable work
devoted to PEO in the literature, very little has been reported
on PEO macromonomers which undergo ROMP.20-24,35-37 The
synthesis of such “ROMP-able” PEO macromonomers was pio-
entity for two reasons. First, pure exo-oxanorbornene diastereo-
isomers are easily prepared starting from exo-7-oxabicyclo-
[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, available in high yield
through Diels-Alder cycloaddition.52 Indeed, it is well-known that
exo-diastereoisomers are much more reactive in ROMP than their
endo- counterparts.53-59 Second, as pointed out by Czelusniak
et al.,28 it is expected that the oxygen in the oxanorbornene group
makes the backbone more hydrophilic60 and hence increases the
probability of biocompatibility of the resulting graft copolymers.
The simple and flexible method reported in this work, precluding
the need for anionic polymerization of ethylene oxide, yields
polymers of unique structures, which are potential candidates for
biomedical applications.
Experimental Section
Materials. Dichloromethane (DCM, 99%þ) and triethyl-
amine (99%) were distilled over CaH2 and were stored at -4 °C
after purification. Prior to use, PEO monomethyl ether (PEO-
OH) 500 (Mn,NMR=530 g/mol), 2000 (Mn,NMR=2010 g/mol)
and 5000 (Mn,NMR=4590 g/mol) were heated at 120 °C for 3 h
under nitrogen atmosphere to remove excess water. Grubbs’
catalyst [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidene]
dichloro(phenylmethylene)bis(3-bromopyridine) ruthenium(II)
ꢁ
neered by Heroguez et al., who polymerized ethylene oxide
anionically from a norbornene functionalized initiator.36,37
Huisgen 1,3-dipolar cycloaddition reaction between azides and
terminal alkynes, one of the different “click” reactions described
by Sharpless and co-workers,38 has attracted widespread atten-
tion in polymer science.25,26,39-50 “Click” chemistry provides an
ideal platform for the synthesis of various well-defined macro-
monomers starting from commercially available polymers such
as PEO. However, while 1,3-dipolar “click” reactions have been
widely used for the functionalization of ROMP polymers, only a
few examples of such a combination have been reported so far in
the literature for the preparation of graft copolymers.25,26
Herein, wereport the synthesis ofnew ω-oxanorbornenyl-PEO
macromonomers using Huisgen 1,3-dipolar cycloaddition (click
chemistry) and their ROMP using third generation Grubbs’
catalyst ([1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidene]
C
38H40Br2Cl2N4Ru (G3)51 and exo-7-oxabicyclo[2.2.1]hept-
5-ene-2,3-dicarboxylic anhydride22,52 (1) were prepared accord-
ing to literature procedures. All other chemicals were purchased
from commercial sources and used without further purification.
Azido-terminated PEO monomethyl ethers (PEO-N3) were
synthesized according to literature procedures.61,62
General Characterization. NMR spectra were recorded on a
Bruker Avance 400 spectrometer for 1H NMR (200 MHz) and
13C NMR (50 MHz). Chemical shifts are reported in ppm
relative to the deuterated solvent resonances. Molecular weights
and molecular weight distributions were measured using size
exclusion chromatography (SEC) on a system equipped with a
*Corresponding author. Telephone: þ33 (0)2 43 83 33 30. Fax: þ33
(0)2 43 83 37 54. E-mail: laurent.fontaine@univ-lemans.fr..
r 2010 American Chemical Society
Published on Web 06/15/2010
pubs.acs.org/Macromolecules

5612 Macromolecules, Vol. 43, No. 13, 2010
Le et al.
SpectraSYSTEM AS 1000 autosampler, with a Guard column
(Polymer Laboratories, PL gel 5 μm Guard column, 50 ꢀ 7.5 mm)
followed by two columns (Polymer Laboratories, 2 PL gel 5 μm
MIXED-D columns, 2 ꢀ 300 ꢀ 7.5) and with a SpectraSYSTEM
RI-150 detector. The eluent used was tetrahydrofuran (THF) at a
136.59 (dCH), 123.69 (CdC-Ntriazole), 80.98 (CH-O), 71.91
(CH2-O-CH3), 70.55 (-CH2-O), 69.37 (Ntriazole-CH2-CH2-
O), 59.04 (CH3-O), 50.26 (Ntriazole-CH2-CH2-O), 47.55 (CH-
CO), 34.15 (N-CH2).
ω-exo-Oxanorbornenyl PEO Monomethyl Ether M 5000. White
powder. Yield: 78%. 1H NMR (200 MHz, CDCl3), δ=7.68(s, 1H,
triazole), 6.52 (s, 2H, dCH), 5.29 (s, 2H, CH-O), 4.79 (s, 2H,
N-CH2), 4.50(t,J= 5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 4.00 (t,
J = 5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 3.50-3.90 (m, 412H,
flow rate of 1 mL min-1 at 35 °C. Polystyrene standards (580 to
3
4.83 ꢀ 105 gmol-1) were used to calibrate the SEC. High resolution
mass spectra were recorded on Waters-Micromass GCT Premier
spectrometers. MALDI-TOF MS analyses were realized on a
Bruker Biflex III using 2-[(2E)-3-(4-tert-butylphenyl)-2-methyl-
prop-2-enylidene]malononitrile (DCTB) as the matrix. Thermo-
gravimetric analyses (TGA) were performed on a TA Instruments
Q500 apparatus measuring the total mass loss on approximately
10 mg samples from 30 °C up to 600 °C at a heating rate of 10 °C.
CH2-CH2-O), 3.38 (s, 3H, O-CH3), 2.90 (s, 2H, CH-CO). 13
C
NMR (50 MHz, CDCl3): δ=175.47 (CO), 141.93 (CdC-Ntriazole),
136.52 (dCH), 123.48 (CdC-Ntriazole), 80.93 (CH-O), 71.97
(CH2-O-CH3), 70.48 (-CH2-O), 69.38 (Ntriazole-CH2-CH2-
O), 59.08 (CH3-O), 50.28 (Ntriazole-CH2-CH>2-O), 47.4 (CH-
CO), 34.09 (N-CH2).
min-1 in a nitrogen flow of 90 mL min-1
.
3
General Procedure for ROMP of Macromonomers. In a typical
experiment, a dry Schlenk tube was charged with the macromono-
mer (100 mg) and a stir bar. The Schlenk tube was capped with a
rubber septum, and cycled three times between vacuum and nitro-
gen to remove oxygen. The desired amount of degassed, anhydrous
DCM ([M]0 = 0.05-0.10 mol/L) was added via syringe under a
nitrogen atmosphere to dissolve the macromonomer. A stock solu-
tion of catalyst G3 in degassed anhydrous DCM ([G3] = 24 μmol/
L for M 500 and M 2000 in [M 2000]0/[G3]0 ratio =10, [G3] =
7 μmol/L for the other experiments) was prepared in a separate vial.
The desired amount of catalyst was injected into the macromono-
mer solution to initiate the polymerization. The Schlenk tube was
stirred at room temperature under nitrogen. The polymerization
was terminated by the addition of two drops of ethyl vinyl ether.
The solvent was removed under reduced pressure for NMR and
SEC measurements. The reaction mixture was then diluted in DCM
and precipitated into 10 mL of stirring cold diethyl ether.
Polyoxanorbornene-g-PEO monomethyl ether 500 PONB-g-
PEO 500. Brown plastic. 1H NMR (200 MHz, CDCl3): δ=7.72
(bs, 1H, triazole), 6.05 (bs, 2H, CHdCH, trans), 5.75 (bs, 2H,
CHdCH, cis), 5.00 (bs, 2H, CH-O-CH, cis), 4.75 (bs, 4H,
CH-O-CH, trans; N-CH2), 4.49 (bs, 2H, Ntriazole-CH2-
CH2-O), 3.84 (bs, 2H, Ntriazole-CH2-CH2-O), 3.80-3.50
(m, 40H, CH2-CH2-O), 3.38 (s, 3H, CH-CdO, O-CH3).
13C NMR (50 MHz, CDCl3): δ = 175.17 (CO), 141.43 (CdC-
exo-N-Prop-2-ynyl-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarbo-
ximide (2). Anhydride 1 (2.00 g, 12.0 mmol) was suspended in
MeOH (50 mL) and the mixture cooled to 0 °C. A solution of N-
propargylamine (1.07 g; 18.0 mmol) in 20 mL of MeOH was added
dropwise (10 min), and the resulting solution was stirred for 5 min at
0 °C and then 30 min at ambient temperature and finally refluxed for
72 h. After cooling the mixture to ambient temperature, the solvent
was removed under reduced pressure, and the yellow residue was
dissolved in 150 mL of DCM and washed with 3 ꢀ 100 mL of water.
The organic layer was dried over MgSO4 and filtered. Removal of the
solvent under reduced pressure furnished 2 as a yellow solid. Yield:
1.97 g (9.72 mmol, 81%). 1H NMR (200 MHz, CDCl3): δ = 6.54 (s,
2H, =CH), 5.30 (s, 2H,-CH-O), 4.24 (d, 2H, CH2-N), 2.90 (s,
2H, CH-CO), 2.20 (t, 1H, tCH). 13C NMR (50 MHz, CDCl3):
δ=172.81 (CdO), 134.58 (dCH), 78.92 (CH-O), 74.48 (CtCH),
69.52 (tCH), 45.58 (CH-CO), 25.84 (N-CH2). HRMS(CI-Hþ):
calcd for C11H9NO3 þ Hþ, 204.2060; found, 204.0661.
General Procedure for Synthesis of Macromonomers via
“Click” Coupling Reactions between Azido-Terminated PEO
Monomethyl Ethers and 2. In a typical experiment, the azido-
terminated PEO monomethyl ether (0.4 mmol) and N,N,N0,N0,
N00-pentamethyldiethylenetriamine (PMDETA; 0.1 g, 0.6 mmol)
were charged to a dry Schlenk tube along with degassed
DMF (5 mL). The tube was sealed with a rubber septum and
subjected to six freeze-pump-thaw cycles. This solution was
then cannulated under nitrogen into another Schlenk tube,
previously evacuated and filled with nitrogen, containing CuIBr
(0.023 g, 0.16 mmol), 2 (0.1 g, 0.4 mmol), and a stir bar. The
resulting solution was subsequently stirred at room temperature
for 4 h. The reaction mixture was diluted with DCM and then
washed with 3 ꢀ 100 mL of an aqueous ethylenediaminetetra-
acetate solution (0.03 mol/L) to remove the catalyst. The organic
layer was dried over MgSO4 and filtered. The resulting macro-
monomers were isolated by precipitation into diethyl ether for
the ω-exo-oxanorbornenyl PEO monomethyl ethers M 2000
and M 5000 or by removal of the solvent under high vacuum for
the ω-exo-oxanorbornenyl PEO monomethyl ether M 500.
ω-exo-Oxanorbornenyl PEO Monomethyl Ether M 500. Yellow-
brown oil. Yield: 80%. 1H NMR (200 MHz, CDCl3): δ=7.68 (s,
1H, triazole), 6.50 (s, 2H, dCH), 5.29 (s, 2H, CH-O), 4.78 (s, 2H,
N-CH2), 4.49 (t, J=5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 3.85 (t,
J = 5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 3.60-3.70 (m, 40H,
N
triazole), 130.92 (dCH), 123.86 (CdC-Ntriazole), 80.73 (CH-
O), 71.89 (CH2-O-CH3), 70.54 (-CH2-O), 69.35 (Ntriazole
-
CH2-CH2-O), 59.00 (CH3-O), 53.36 (Ntriazole-CH2-CH2-O),
50.51 (CH-CO), 34.07 (N-CH2).
Polyoxanorbornene-g-PEO monomethyl ether 2000 PONB-g-
PEO 2000. Brown powder. 1H NMR (200 MHz, CDCl3): δ =
7.76 (bs, 1H, triazole), 6.02 (bs, 2H, CHdCH, trans), 5.70 (bs,
2H, CHdCH, cis), 5.02 (bs, 2H, CH-O-CH, cis), 4.76 (bs, 4H,
CH-O-CH, trans; N-CH2), 4.50 (bs, 2H, Ntriazole-CH2-
CH2-O), 3.82 (bs, 2H, Ntriazole-CH2-CH2-O), 3.80-3.60
(m, 172H, CH2-CH2-O), 3.40 (s, 3H, CH-CdO, O-CH3).
13C NMR (50 MHz, CDCl3): δ = 174.99 (CO), 141.41 (CdC-
Ntriazole), 131.72 (=CH), 123.70 (C = C-Ntriazole), 80.71 (CH-O),
71.89 (CH2-O-CH3), 70.52 (-CH2-O), 69.31 (Ntriazole-CH2-
CH2-O), 58.99 (CH3-O), 53.35 (Ntriazole-CH2-CH2-O), 50.22
(CH-CO), 34.12 (N-CH2).
Polyoxanorbornene-g-PEO monomethyl ether 5000 PONB-g-
PEO 5000. Brown powder. 1H NMR (200 MHz, CDCl3): δ =
7.73 (bs, 1H, triazole), 6.05 (bs, 2H, CHdCH, trans), 5.78 (bs,
2H, CHdCH, cis), 5.04 (bs, 2H, CH-O-CH, cis), 4.78 (bs, 4H,
CH-O-CH, trans; N-CH2), 4.51 (bs, 2H, Ntriazole-CH2-
CH2-O), 3.80 (bs, 2H, Ntriazole-CH2-CH2-O), 3.80-3.60
(m, 412H, CH2-CH2-O), 3.38 (s, 3H, CH-CdO, O-CH3).
CH2-CH2-O), 3.38 (s, 3H, O-CH3), 2.96 (s, 2H, CH-CO). 13
C
NMR (50 MHz, CDCl3): δ=175.53 (CO), 141.93 (CdC-Ntriazole),
136.57 (=CH), 123.73 (CdC-Ntriazole), 80.97 (CH-O), 71.91
(CH2-O-CH3), 70.48 (-CH2-O), 69.38 (Ntriazole-CH2-CH2-
O), 59.02 (CH3-O), 50.28 (Ntriazole-CH2-CH2-O), 47.54 (CH-
CO), 34.14 (N-CH2).
ω-exo-Oxanorbornenyl PEO Monomethyl Ether M 2000. White
powder. Yield: 85%. 1H NMR (200 MHz, CDCl3): δ=7.67 (s, 1H,
triazole), 6.50 (s, 2H, dCH), 5.29 (s, 2H, CH-O), 4.78 (s, 2H, N-
CH2), 4.49 (t, J=5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 3.85 (t, J=
5.1 Hz, 2H, Ntriazole-CH2-CH2-O), 3.60-3.70 (m, 172H, CH2-
CH2-O), 3.38 (s, 3H, O-CH3), 2.89 (s, 2H, CH-CO). 13C NMR
(50 MHz, CDCl3): δ = 175.44 (CO), 141.98 (CdC-Ntriazole),
Results and Discussion
Synthesis of Oxanorbornenyl PEO Macromonomers. The
oxanorbornene-based monomer with an alkyne functionality
was designed and prepared from exo-7-oxabicyclo[2.2.1]hept-
5-ene-2,3-dicarboxylic anhydride (1) and N-propargylamine,

Article
Macromolecules, Vol. 43, No. 13, 2010 5613
Figure 1. 1H NMR spectra of (A) 2, (B) ω-exo-oxanorbornenyl PEO monomethyl ether M 500, and (C) polyoxanorbornene-g-PEO 500 (Table 2,
run 2); solvent: CDCl3.
Scheme 1. Synthesis of Compound 2
and the synthetic route is illustrated in Scheme 1. An excess
of N-propargylamine is necessary to increase the yield, and the
suitable ratio of N-propargylamine to 1 was 1.5:1. Under these
conditions, exo-N-prop-2-ynyl-7-oxabicyclo[2.2.1]hept-5-ene-
2,3-dicarboximide (2) was obtained with a 81% yield. The 1H
NMR spectrum (Figure 1A) shows the resonance signal of
N-CH2-CtCH at 4.24 ppm, while the signal of CHdCH
protons at 6.54 ppm are still observed, and importantly the
integration area ratios of the characteristic resonances of 2:2 are
in agreement with the ratios of corresponding protons, which
demonstrates that full condensation occurred. Furthermore,
the molecular weight (MþHþ=204.0661) of 2 from HRMS
analysis was in good accordance with the calculated value
(M þ Hþ=204.2060).
mesylate chain-end groups into azido groups via reaction
with NaN3 in DCM for PEO-N3 50061 or in THF for
PEO-N3 2000 and PEO-N3 5000.62 The presence of an
azido group at the chain-end was checked by 13C NMR
spectroscopy. The carbon bearing the azido group appears at
50.66 ppm, whereas the one carrying the terminal hydroxyl is
located at 61.66 ppm. Moreover, the chain-end functionality
was proved to be quantitative, as evidenced by the dis-
appearance of the CH2OH peak in the PEO-O-SO2CH3
spectra and the disappearance of the -O-SO2CH3 peak in
the PEO-N3 spectra (Figure S2 in the Supporting In-
formation).
Next, macromonomers were synthesized by coupling
azido-terminated PEO-N3 and alkyne-containing 2. The
“click” reactions were carried out in DMF at room tempera-
ture using a stoichiometric molar ratio between PEO-N3
and alkynyl groups in the presence of a catalytic amount of
Cu(I)Br with PMDETA as the ligand (Scheme 2). After 4 h of
reaction, click chemistry afforded the targeted ω-exo-oxa-
norbornenyl PEO monomethyl ether macromonomers with
different molecular weights M 500, M 2000 and M 5000,
obtained from PEO-N3 500, 2000, and 5000, respectively.
Azido-terminated linear PEO monomethyl ether chains
(PEO-N3; Mn,NMR = 530, 2010, and 4590 g/mol, see Table
S1 in the Supporting Information) have been synthesized
from hydroxyl-terminated PEO monomethyl ether chains
(PEO-OH) with different molecular weights. PEO-OH
were first converted to mesylate-terminated PEO mono-
methyl ether chains (PEO-OSO2CH3) by reaction with
methanesulfonyl chloride, followed by transformation of

5614 Macromolecules, Vol. 43, No. 13, 2010
Le et al.
Figure 2. MALDI-TOF spectrum of ω-exo-oxanorbornenyl PEO monomethyl ether macromonomer M 2000 (matrix: DCTB þ sodium
trifluoroacetate).
Scheme 2. Synthesis of Macromonomers
Table 1. Characteristics of ω-exo-Oxanorbornenyl Poly(ethylene
The MALDI-TOF spectrum of M 2000 is shown in Figure
2. It is interesting to note that besides the expected product, i.e.,
oxide) Monomethyl Ether Macromonomers
c
d
the macromonomer plus one sodium ion, an additional series
was observed which differs by 68 mass units from the main
series. The difference in mass of each signal of both series was
roughly estimated as 44, indicating the signals were assignable
to the PEO homologues. Since no side reactions were detect-
able by NMR (see Figure S4 in the Supporting Information),
the fragment signals can be ascribed to the retro-Diels-Alder
reaction63 (Scheme 3) caused by ionization.
sample
name
convna
(%)
Yieldb
(%)
Mn,NMR
(g/mol)
Mn,SEC
(g/mol)
PDId
M 500
M 2000
M 5000
100
100
100
80
85
78
757
2240
4817
890
3400
7800
1.05
1.06
1.05
a Determined by 1H NMR from the reaction mixture, CDCl3 as
solvent. b After purification. c Number-average molecular weight deter-
mined by 1H NMR, CDCl3 as solvent. d Number-average molecular
weight and polydispersity measured by THF SEC with RI detector;
calibration with linear polystyrene standards.
The conversion of the ω-exo-norbornenyl end-group of
the macromonomer to a maleimide group could also be
monitored by thermogravimetric analysis (TGA) (Figure
S6 in the Supporting Information). M 2000 TGA thermo-
gram clearly exhibits a first loss of 3.07 wt % between 134
and 150 °C, which is attributed to the release of furan64
(calculated % weight loss =3.04 for M 2000, Mn,NMR= 2
240 g/mol). Additionally, the macromonomers exhibited a
major thermal degradation at 405 °C (50% weight loss). The
presence of the maleimide functionality was checked after a
The results of the coupling reactions are reported in Table 1.
The 1H NMR spectrum of M 500 (Figure 1B) clearly indicates
the shift of the alkyne proton at 2.20 ppm (e, Figure 1A) to 7.68
ppm (e0, Figure 1B) as well as the shift of the methylene group
next to the alkyne group at 4.24 ppm (d, Figure 1A) to 4.78 ppm
(d0, Figure 1B), which corresponds to the proton linked to the
formed triazole ring. The “click” reaction occurred in a quan-
titative way since integrations of norbornenyl olefin peak (a0,
Figure 1B at 6.50 ppm) and the proton on the triazole ring (e0,
Figure 1B at 7.68 ppm) gave a 2:1 ratio. The same conclusions
could be drawn from the reactions between 2 and PEO-N3
2000 or 5000 (Figure S4 in the Supporting Information). The
SEC traces (Figure S5 in the Supporting Information) show
that the coupling product M 500 has a slightly higher apparent
molecular weight than the PEO-N3 500 precursor, determined
by SEC in THF with linear PS standards, indicating the
formation of the macromonomer.
1
thermal treatment of M 2000 at 250 °C. The resulting H
NMR spectrum (Figure S7 in the Supporting Information)
clearly shows the disappearance of the oxatricyclo vinyl
signals (CHdCH and CH-O protons at 6.50 and 5.29
ppm, respectively) and the appearance of the maleimide peak
at 6.74 ppm. It should be noted that such maleimide end-
functionalized poly(ethylene oxide) can undergo further
Diels-Alder cycloaddition or thiol-ene reaction, giving
access to modular block copolymers, stars, bioconjugates,
and other functional telechelics.50

Article
Macromolecules, Vol. 43, No. 13, 2010 5615
Scheme 3. Retro-Diels-Alder Reaction of Macromonomers
Scheme 4. Ring-Opening Metathesis Polymerization of Macromonomers
Table 2. ROMP of Macromonomers Using Catalyst G3a
Mn,theo
(g/mol)
convnd 1
NMR (%)
H
convne
SEC (%)
Mn,SEC
(g/mol)
yield
(%)
trans/
cisg
c
f
b
run
macromonomer
[M]0/[G3]0
t (h)
PDI f
1
2
3
4
5
6
7
8
M 500
M 500
M 500
M 500
M 2000
M 2000
M 2000
M 2000
M 2000
M 5000
M 5000
M 5000
M 5000
10
50
100
100
10
50
50
50
100
10
10
50
7661
37 941
75 791
75 791
22 491
112 091
112 091
112 091
224 091
48 261
48 261
240 941
481 791
1
1
1
4
1
100
100
90
100
100
25
99
99
90
100
98
9900
22 800
20 000
23 500
29 300
97
97
95
100
100
1.06
1.17
1.09
1.15
1.07
50/50
50/50
50/50
50/50
57/43
1
4
61
60
58
60
5
90
90
61
1
37 700
46 300
1.10
1.04
57/43
57/43
24
24
4
24
24
24
9
10
11
12
13
90
57 800
57 800
67 500
98
93
1.06
1.06
1.08
75/25
100
a Results are representative of at least duplicated experiments. b Macromonomer to Grubbs’ catalyst G3 ratio. Mn,theo = Mn,NMR[M]0/[G3]0 þ
c
Mextr..
d Determined by comparing the peak areas of grafted copolymer and residual macromonomer from SEC measurement of the crude product.
e Determined by comparing the peak areas of oxanorbornenyl ring of the grafted copolymer and residual macromonomer from 1H NMR of the crude
product. f Number-average molecular weight and polydispersity measured by THF SEC with RI detector, calibration with linear polystyrene standards.
g Determined by comparing the peak areas of Hcis and Htrans of the CHd groups of the backbone from 1H NMR of the grafted copolymer.
The MALDI-TOF spectrum of M 500 also exhibits the
second minority series. For M 5000, only the series resulting
from the retro-Diels-Alder reaction was detected (Figure S8
in the Supporting Information).
ROMP of Macromonomers. Third generation Grubbs’
catalyst (G3) was used to polymerize the macromonomers
(Scheme 4). Reactions were carried out in DCM with various
macromonomer-to-catalyst ratios at room temperature with
a macromonomer concentration of 0.05 M (Table 2). DCM
was preferred to THF since M 2000 and M 5000 show a poor
solubility in THF at the used concentrations. M 500 was
easily polymerized to near quantitative yield in 1-4 h
depending on the desired molecular weight (Table 2, runs
1-4). 1H NMR spectroscopy indicated the disappearance of
the vinyl proton signal at 6.50 ppm (Ha’) as shown in
Figure 1C and the emergence of the trans and cis vinyl
proton resonances at 6.05 and 5.75 ppm, respectively
Figure 3. SEC traces of (A) ω-exo-oxanorbornenyl PEO monomethyl
ether M 500, (B) polyoxanorbornene-g-PEO 500 (Table 2, run 1) and
(C) polyoxanorbornene-g-PEO 500 (Table 2, run 2).
(Figure 1C, Table 2, run 2). NMR spectroscopy also evi-
denced that the triazole moieties are preserved throughout
the ROMP process (resonances in 1H NMR: 7.72 ppm;
triazole-H). GPC traces of the polymers are shown in Figure
3. As can be seen (Figure 3, parts B and C), the line profile is
perfectly symmetrical with no observable high or low mo-
lecular weight shoulders, which occur frequently when
macromonomers are polymerized. All polymers issued from
M 500 were obtained with low polydispersities (Table 2, runs
1, 2 and 4) ranging from 1.06 to 1.17. These results are in
contrast to those already reported in literature,21,22,65 where
broad polydispersities were observed, typically around 1.6,
when (co)polymerizing PEO functionalized imide monomer
(however using other Ru-based catalysts), suggesting to be
caused by the combination of PEO with the imide func-
tionality.22 The number-average molecular weights obtained
from SEC in THF (calibrated with polystyrene) were as

5616 Macromolecules, Vol. 43, No. 13, 2010
Le et al.
much more lower than the targeted ones as the macromo-
nomer-to-catalyst ratio is high (Table 2, runs 1-4). This dis-
parity can be attributed to different hydrodynamic volumes
of these polymers compared to linear polystyrene standards.66
It is also well-known in the literature that the measured
values for the molecular weights underestimate the true
molecular weights of comb polymers by up to a factor of
10.20 Additionally, THF is a poor solvent for PEO in which
the copolymer contracts substantially, leading to a dramatic
decrease in hydrodynamic volume.35
the efficiency of the ROMP process was affected by the molecular
weight of the macromonomers. A series of poly(oxanorbornene)-
g-PEO 500 with various lengths of the overall backbone was
prepared by controlling the macromonomer-to-catalyst ratio,
giving access to narrowly dispersed brush copolymers. This syn-
thetic approach is very general and is applicable to a widerange of
macromonomers, derived from various azido end-functionalized
polymers and bearing other “ROMP-able” entities such as
norbornene or cyclobutene.
However, M 2000 and M 5000 were only able to form
polyoxanorbornene-g-PEO with relatively short backbone
length (Table 2, runs 5 and 10). The resulting grafted copoly-
mers have been characterized using both SEC and NMR
techniques. The grafted copolymers had higher apparent
molecular weights than the macromonomers precursors,
and the molecular weight distribution of the grafted copo-
lymers remained as narrow as PDI=1.06-1.07 (Table 2,
runs 5 and 10, Figures S10 and S11 in the Supporting
Information). The 1H NMR results (see Figure S12 in the
Supporting Information) were similar to the one shown
in Figure 1C. Increase of the reaction time for macromo-
nomer to catalyst ratios of 50 and 100 did not allow
reaching the complete conversion of the macromonomers
(Table 2, runs 6-9 and 12). The macromonomer chain
length seems to be a critical factor toward the conver-
sion, probably due to the limiting effect of the macromo-
nomer steric hindrance during the propagation step.
Furthermore, the rich-oxygen macromonomers could give
competitive coordination with the ruthenium with the
result of lowering the rate of polymerization. Indeed, the
trapping of catalyst has already been described for PEO
macromonomers.36
Acknowledgment. M.R. thanks Naresuan University for
support. Part of this work was supported by the Agence Natio-
nale de la Recherche (ANR) under Contract ANR-08-BLAN-
0104 (“Cyclo-ROMP”).
Supporting Information Available: Figures showing addi-
tional 1H and 13C NMR spectra, SEC traces and MALDI-TOF
spectra of PEO precursors, macromonomers, and copolymers,
and TGA thermograms and a table of characteristics of azido-
terminated poly(ethylene oxide) monomethyl ether chains. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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