Cross-Linked Network Polymer Electrolytes Based on a Polysiloxane Backbone with Oligo(oxyethylene) Side Chains: Synthesis and Conductivity

Article abstract of DOI:10.1021/ma0349276

A novel cross-linked siloxane-based solid polymer network has been synthesized by the hydrosilylation of polymethylhydrosiloxane (PMHS) partly substituted with oligo(ethylene glycol) methyl ether side groups and a α,ω-diallyl poly(ethylene glycol) cross-linking reagent. The ionic conductivities of the networks doped with LiTFSI are high at ambient temperature (σ = 1.33 × 10^-4 S cm^-1 at the optimum LiTFSI concentration EO/Li⁺ = 20:1). The temperature dependence of the conductivity followed the VTF form, indicating that polymer segmental motion assists the ion transport in the solid networks.

Full text of DOI:10.1021/ma0349276

9176
Macromolecules 2003, 36, 9176-9180
Cross-Linked Network Polymer Electrolytes Based on a Polysiloxane
Backbone with Oligo(oxyethylene) Side Chains: Synthesis and
Conductivity
Zh en gch en g Zh a n g, Da vid Sh er lock , Rya n West, a n d Rober t West
Organosilicon Research Center, Department of Chemistry, University of WisconsinsMadison,
1101 University Avenue, Madison, Wisconsin 53706
Kh a lil Am in e
Chemical Technology Division, Argonne National Laboratory, Argonne, Illinois 60439
Leslie J . Lyon s*
Department of Chemistry, Grinnell College, Grinnell, Iowa 50112
Received J uly 2, 2003; Revised Manuscript Received September 25, 2003
ABSTRACT: A novel cross-linked siloxane-based solid polymer network has been synthesized by the
hydrosilylation of polymethylhydrosiloxane (PMHS) partly substituted with oligo(ethylene glycol) methyl
ether side groups and a R,ω-diallyl poly(ethylene glycol) cross-linking reagent. The ionic conductivities
of the networks doped with LiTFSI are high at ambient temperature (σ ) 1.33 × 10-4 S cm-1 at the
optimum LiTFSI concentration EO/Li+ ) 20:1). The temperature dependence of the conductivity followed
the VTF form, indicating that polymer segmental motion assists the ion transport in the solid networks.
In tr od u ction
to use the complexes as separators in all solid-state
lithium polymer batteries since the glutinous materials
flow even under mild pressure at ambient temperature.
Solid polymer electrolytes (SPEs) have been widely
investigated since the discovery of ionic conductivity in
the polyether/alkali metal complex PEO/KSCN by Wright
et al. in the 1970s.1-3 Recognizing that the ionic
conductivity of polymer electrolytes is enhanced in the
elastomeric amorphous phase by the segmental motion
of the polymer chains, significant research has been
undertaken to develop a polymer structure having a
highly flexible backbone and amorphous character.
Polymer electrolytes based on poly[bis(methoxyethoxy-
ethoxy)phosphazene] (MEEP) which was studied as a
polymer electrolyte by Shriver, Allcock, and their co-
workers was a breakthrough in this area.4-8 Complexes
of MEEP doped with LiSO3CF3 exhibit room tempera-
ture ionic conductivities of up to 3 orders of magnitude
higher than those of analogous PEO complexes. The
remarkable improvement in the ionic conductivity was
ascribed to the highly flexible inorganic phosphazene
backbone which produced a totally amorphous polymer
host with a very low glass transition temperature.
The polysiloxanes, with very low glass transition
temperatures, Tg ) -123 °C for poly(dimethylsiloxane),
and extremely high free volumes, are expected to be
good hosts for Li+ transport when polar units are
introduced onto the polymer backbone. Oligo(ethylene
glycol)-substituted polysiloxanes as ionically conductive
polymer hosts have been previously investigated by
Smid,9-11 Shriver,12-14 Acosta,15 and West and co-
workers.16,17 The more recent synthesis and conductivity
studies of a bis-substituted polysiloxane with pendant
oligo(ethylene glycol) chains have been reported by
Hooper et al.18 A six-oxygen side-chain polymer host
when doped with lithium bis(trifluoromethylsulfonyl)-
imide (LiTFSI) showed the highest room temperature
conductivity (4.0 × 10-4 S cm-1) yet observed for a
polymer electrolyte. However, the dimensional stability
of these polymer electrolytes is poor. It is not possible
We now report the synthesis of a cross-linked polysi-
loxane network polymer electrolyte with pendant oligo-
(ethylene glycol) groups as internally plasticizing chains.
This free-standing polysiloxane conductive material,
when doped with LiTFSI, shows very high room tem-
perature conductivity, contributed from the vigorous
segmental motion of the pendant short PEO chains as
well as the high flexibility of the siloxane backbone.
Exp er im en ta l Section
Ma ter ia ls. Polymethylhydrosiloxane (PMHS, Mw ) 1500-
1900) was purchased from Gelest. Tri(ethylene glycol) methyl
ether (MPEO3) and poly(ethylene glycol) (Mw 600) were Aldrich
products. All were dried by using 4A molecular sieves. Allyl
bromide and platinum divinyltetramethyldisiloxane [Pt(dvs),
3% in xylene solution] were supplied by Aldrich also. Sodium
hydride (NaH, 60% dispersion in mineral oil) was purchased
from Acros Organics. THF was dried over sodium benzophe-
none ketyl and was distilled in an atmosphere of dry nitrogen
before use. NMR grade deuteriochloroform was stored over 4A
molecular sieves. Lithium bis(trifluoromethylsulfonylimide)
(LiN(SO2CF3)2) was a gift from 3M and was dried under
vacuum at 120 °C for 24 h prior to use. All other reagents were
used as received or distilled prior to use.
Preparation of Side-Chain Ethylene Oxide Monomer. Tri-
(ethylene glycol) allyl methyl ether (AMPEO3) was synthesized
by the method described by Allock et al.6 and Hooper et al.18
A solution of MPEO3 (98.4 g, 0.6 mol) in 250 mL of THF was
added dropwise to a suspension of NaH (60% dispersion in
mineral oil) (28.8 g, 0.72 mol) in THF (250 mL) chilled to 0
°C. This solution was stirred for a further 2 h followed by the
dropwise addition of allyl bromide (87.1 g, 0.72 mol). The
resulting mixture was stirred overnight and then filtered to
remove the NaBr product and excess NaH. All volatile materi-
als were removed by rotary evaporation to yield an orange oil.
This oil was dissolved in water, and unreacted MPEO3 was
extracted using 3 × 50 mL portions of toluene. The desired
10.1021/ma0349276 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/28/2003

Macromolecules, Vol. 36, No. 24, 2003
Cross-Linked Network Polymer Electrolytes 9177
Sch em e 1. Gen er a l Syn th esis of th e P olysiloxa n e
P r ecu r sor Con ta in in g a Sm a ll Nu m ber of Si-H
F u n ction a l Gr ou p s
Procedure for Preparation of Cross-Linked Polysiloxane
Network Electrolytes. In a typical preparation,20 the viscous
branched polysiloxane precursor with n/m ratio of 1/30 (0.514
g, 1.74 × 10-3 mol of Si-H) was added into dry a 10 mL flask,
and then diallyl poly(ethylene glycol) cross-linker (q ∼ 13)
(0.0465 g, 8.7 × 10-4 mol), LiN(CF3SO2)2 (2.48 × 10-4 mol, 6.75
mL of 0.0367 M THF solution), and Pt catalyst (5 µL) were
syringed into the flask. The mixture was stirred thoroughly.
The resulting solution was evacuated for 12 h and then further
evacuated on a high-vacuum line (∼10-5 Torr) for 48 h to
completely remove the THF. The flask was sealed and trans-
ferred into a glovebox, where the liquid electrolyte was loaded
into the conductivity measurement cell. After 12 h in an 80
°C oven, a transparent film resulted.
Equ ip m en t. Molecular weights and molecular weight
distributions (MWDs) (Mw/Mn) of polysiloxane precursors were
determined by a Viscotek GPC instrument equipped with a
series of three gel permeation columns (500, 104, and 105 Å)
calibrated with narrow MWD polystyrene standards, a Vis-
cotek VE3580 refractive index detector, and a Viscotek T60B
dual detector (viscometer detector and light scattering detec-
tor). The flow rate was 1 mL/min of HPLC grade toluene.
TriSEC 2000 Data Acquisition software was used for data
analysis.
product was then extracted into chloroform from the water
layer with 3 × 200 mL portions of CHCl3; this was dried with
MgSO4, and all volatile materials were removed by rotary
evaporation. 110 g (90%) of product was collected by Kugelrohr
distillation (80 °C/0.5 Torr): 1H NMR (CDCl3), δ (ppm): 5.85
(m, 1H), 5.15 (dd, 2H), 3.95 (d, 2H), 3.45-3.65 (m, 12H), 3.30
(s, 3H). 13C NMR (CDCl3), δ (ppm): 134.6, 116.8, 72.1, 71.8,
70.3-70.0, 69.2, 58.9. Mass spectroscopy: m/e 205 MH+ base
peak.
All NMR chemical shifts are reported in parts per million
(δ, ppm); downfield shifts are reported as positive values from
1
tetramethylsilane (TMS) as the standard at 0.00 ppm. The H
and 13C chemical shifts are reported relative to the NMR
solvent as an internal standard, and the 29Si chemical shifts
are reported relative to an external TMS standard. NMR
spectra were recorded using samples dissolved in CDCl3,
unless otherwise stated, on the following instrumentation: 1H
NMR Bruker AC300 (300.1 MHz) with Grant NIH 1 S10 RRO
8389-01; 13C NMR Bruker AC300 (75.5 MHz) with Grant NIH
1 S10 RRO8389-01; 29Si NMR Varian Unity 500 (99.2 MHz)
with Grants NIH 1 S10 RRO4981-01 and NIH CHE-9629688.
Carbon-13 NMR was recorded as proton-decoupled spectra,
and 29Si NMR was recorded using an inverse gate pulse
sequence with a relaxation delay of 30 s.
Preparation of Allyl-PEO-Allyl Cross-Linking Agents. The
R,ω-diallyl poly(ethylene glycol) was prepared using the same
reactions described above for compound AMPEO3. The follow-
ing reagents and quantities were used: NaH (9.6 g, 0.24 mol
of a 60 wt % solution in mineral oil), THF (100 mL), PEG (Mw
600, 60.0 g, 0.10 mol), THF (150 mL), allyl bromide (31.46 g,
0.26 mol). The crude product was purified by passing through
1
a silica gel column. Final product, 62.5 g, 92% yield. H NMR
(CDCl3), δ (ppm): 5.85 (m, 2H), 5.15 (dd, 4H), 3.95 (d, 4H),
3.45-3.65 (m, 40H), 3.30 (s, 6H). 13C NMR (CDCl3), δ (ppm):
134.6, 116.8, 72.1, 71.8, 70.3-70.0, 69.2, 58.9.
DSC measurements were recorded on a TA Instruments
model 2920 modulated DSC operated under computer control
by the TA Instruments package Thermal Advantage Version
1.0A for Windows with data analyses performed on the
software Universal Analysis for Windows Version 2.6D. Low
temperatures were achieved by using the TA Instruments
liquid nitrogen cooling accessory. Samples of preformed gels
were loaded in hermetically sealed aluminum pans. Duplicates
of all samples were measured. Glass transition temperatures
are reported as the onset of the inflection in the heating curve
from -150 to 80 °C at a heating rate of 10 °C/min. Any other
thermal transitions observed for the samples were measured
at their peaks.
Impedance measurements were performed under computer
control using a Princeton Applied Research model 273A
potentiostat/galvanostat, a Princeton Applied Research model
1025 frequency response analyzer for frequency control (75 Hz
to 100 kHz), and Princeton Applied Research PowerSine
impedance software for data acquisition. Subsequently, the
data obtained were analyzed on a PC with Microsoft Excel.
Room temperature conductivity measurements were at 23 (
1 °C while variable-temperature measurements (0-70 °C)
were made by placing the electrochemical cell in a jacketed
Preparation of Polysiloxane Precursors. The hydrosilylation
of AMPEO3 with PMHS was carried out under nitrogen at 75
°C, as described elsewhere.19 The ratio n/m (see Scheme 1) was
varied by adjusting the molar ratio of AMEPO3 and Si-H
groups. In a typical reaction to synthesize the partly substi-
tuted polysiloxane precursor, 50 µL of Pt(dvs) (100 ppm, ∼2%
in xylene) was syringed into the mixture of 30 g (0.5 mol of
Si-H) of PMHS and 102 g (0.5 mol) of AMPEO3. The
heterogeneous mixture was heated to 75 °C until no residual
AMPEO3 allyl protons were detected in the 1H NMR spectrum.
The resulting polymer was then precipitated six times in
hexane to remove side product and catalyst. Afterward, all
volatiles were removed under vacuum. One peak was observed
in the refractive index GPC measurement; Mw ) 6.9 × 103
compared to polystyrene standards (Mw/Mn ) 1.12). The n/m
ratio of 1/30 was determined by the ratio of the integration
area of Si-H at 4.6 ppm compared to Si-CH3 at 0.3 ppm from
1
the H NMR spectrum. IR shows a strong absorption band at
2161 cm-1 for ν(Si-H) and 1094 cm-1 for ν(Si-O-Si). 29Si
NMR (500 MHz, CDCl3): -23.5 ppm of CH3Si-CH2, 5.9 ppm
of (CH3)3Si-, -37.5 ppm of CH3SiH-O.
Sch em e 2. Syn th etic P r oced u r e for a Cr oss-Lin k ed P olysiloxa n e Electr olyte F ilm

9178 Zhang et al.
Macromolecules, Vol. 36, No. 24, 2003
F igu r e 1. Representative FTIR of the cross-linked SPE-2 with
EO/Li+ ) 20.
F igu r e 3. Plots of log conductivity vs EO/Li + for SPE-LiTFSI
complexes at different temperatures.
F igu r e 2. Impedance spectra of cross-linked SPEs at various
LiTFSI doping levels (EO/Li+ ) 15:1, 20:1, 24:1, 28:1, and 64:1
for SPEs 1 to 5, respectively).
holder and circulating ethylene glycol/water from a Lauda
RMT6 circulating bath. Actual temperatures were determined
via an Omega thermocouple attached directly to the cell.
FTIR spectra were recorded on a Nicolet Nexus 670 spec-
trometer as gelled films placed on the Avatar multibounce
HATR accessory.
F igu r e 4. Variable-temperature conductivities for SPEs at
various LiTFSI doping levels (symbols are experimental data;
lines are VTF fits).
Resu lts a n d Discu ssion
Ta ble 1. Con d u ctivities for SP Es a t Va r iou s LiTF SI
Dop in g Levels
P r ecu r sor Syn th esis. Cross-linkable polysiloxane
precursors were synthesized (Scheme 1) by hydrosily-
lation catalyzed by Karstedt’s catalyst and purified by
precipitation in hexane until no side products were
detected in both the NMR and IR spectrum. The extent
of hydrosilylation and purification was monitored by 1H
NMR or IR. Significant amounts (20-40% overall) of
the isomeric AMPEO3 (cis and trans) and the reduced
alkene were found at the end of the reaction.21 The
proposed mechanism for the formation of olefin isomers
can be attributed to the dissociation of the labile
divinyltetramethyldisiloxane ligand and the subsequent
generation of colloidal Pt species,22,23 leading to the
undesired side products and coloration of the product.
Con d u ctive F ilm P r ep a r a tion . For preparation of
the network electrolytes, a THF solution of precursor,
cross-linker, and LiTFSI was used to ensure better
dissolution of the salt in the precursor and cross-linker.
This necessitated the removal of the solvent which was
achieved by vacuum-drying to a pressure < 5 × 10-5
Torr. Then the viscous mixture was loaded into a two-
electrode electrochemical cell with stainless steel ion
blocking electrodes and sealed with O-rings. To prevent
any bubble defect in the resulting thin disk of electro-
lyte, the viscous polymer was poured into the polypro-
pylene containment ring instead of pipetted. After impe-
dance measurements, the resulting cross-linked film
was examined by IR and NMR spectroscopy. The film
did not dissolve in CDCl3 but was swollen by the solvent.
No Si-H absorbance at 4.7 ppm and CH2dCH- reso-
nance at 5.1 and 5.9 ppm were observed, indicating
conductivity (S cm-1
)
SPE ID n/m
p
q
[EO/Li+]
25 °C 37 °C
SPE-1
SPE-2
SPE-3
SPE-4
SPE-5
1/30
1/30
1/30
1/30
1/30
3
3
3
3
3
13
13
13
13
13
15/1
20/1
24/1
28/1
64/1
8.00 × 10-5 1.55 × 10-4
1.33 × 10-4 2.44 × 10-4
1.01 × 10-4 1.78 × 10-4
8.38 × 10-5 1.48 × 10-4
5.18 × 10-5 8.27 × 10-5
complete gelation of the reagents. The IR of the thin
film also confirmed the completion of network forma-
tion (no Si-H stretch at 2160 cm-1 was observed, see
Figure 1).
Electr och em ica l Resu lts
Ionic conductivities for the network electrolytes were
obtained as a function of temperature from the imped-
ance data. The impedance spectra, measured over the
frequency range of 75 Hz-100 kHz, were described in
an equivalent circuit of a parallel capacitance and
resistance (see Figure 2).
The magnitude of the resistance was calculated at the
points where the phase angle in the impedance data was
closest to zero using the equation R ) Z cos(θ), where
R is the resistance, Z the impedance, and θ the phase
angle. The conductivity, σ, was calculated from the
relationship σ ) 1/R × l/A, where l/A values were
typically 0.2 cm-1. Transparent thin films of cross-linked
polysiloxane SPE with lithium bis(trifluoromethane-
sulfonylimide) are ionically conductive. The LiTFSI salt-

Macromolecules, Vol. 36, No. 24, 2003
Cross-Linked Network Polymer Electrolytes 9179
Ta ble 2. VTF a n d Th er m a l P a r a m eter s for SP E-1 to SP E-5
sample
EO/Li
A (S cm-1 K1/2
)
B (K-1
)
T0 (K)
Ea (kJ mol-1
)
Tg (K)
Tm (K)
SPE-1
SPE-2
SPE-3
SPE-4
SPE-5
15:1
20:1
24:1
28:1
64:1
0.090
0.032
0.057
0.023
0.007
865.14
547.44
834.22
642.76
590.82
197.92
174.70
176.27
182.98
166.05
7.2
4.5
4.9
5.3
6.9
213.3
206.5
204.6
201.2
193.2
259.4
255.0
265.0
258.7
256.0
complexed polymers have maximum, ambient ionic
conductivities in the range from 5.18 × 10-5 to 1.33 ×
10-4 S cm-1 and 8.27 × 10-5 to 2.44 × 10-4 S cm-1 at
body temperature (∼37 °C), as shown in Table 1.
EO/Li+ indicates the total number of ether oxygens (on
side chains plus diallyl-terminated PEO cross-linker).
The effect of salt concentration on ionic conductivity
is show in Figure 3. For data collected in the temper-
ature range 25-70 °C, the conductivity increases with
increasing salt concentration from ether oxygen/lithium
ratio 64:1 to 20:1, apparently due to an increase in the
number of charge carriers. As the LiTFSI concentration
increases beyond 20:1, the conductivity decreases. The
maximum conductivity (σRT ) 1.33 × 10-4 S cm-1) was
found to occur with the electrolyte that contained a
LiTFSI concentration of EO/Li+ ) 20. Morales et al.15
recently reported slightly higher room temperature
conductivities of 2.0 × 10-4 and 5.0 × 10-4 S cm-1 for
monocomb polysiloxane-LiTFSI complexes of PMMS3M
and PMMS12M, respectively; however, these values
occurred at a higher salt concentration (O:Li ratio of
10:1) compared with that of the cross-linked polymer.
The dependence of the ionic conductivity on doping level
can be adequately interpreted by two opposing effects.
There is a buildup of charge carriers as the salt
concentration is increased, but this is eventually offset
by a decrease in the flexibility of the polymer network
which will impede the ion migration in the network
polymer electrolytes.
F igu r e 5. Thermograms for SPE-1 to SPE-3.
the highest doping level, which lowers the ionic con-
ductivity for the complexes. In the DSC thermograms,
very weak recrystallization and melt transitions (Tm)
were observed in all the cross-linked network electrolyte
samples. These features were very small and at tem-
peratures well below ambient. This confirms that the
gels are amorphous over the temperature ranges where
the ionic conductivity measurements were performed.
Interestingly, the recrystallization and melt transitions
were smaller than Morales observed in his linear
polymer samples.15 Formation of the cross-links in the
gel may decrease the organization of the pure polymer
chains and enhance the amorphous character of the
polymer electrolytes. The activation energies, Ea, range
from 4.5 to 7.2 kJ /mol, which are much lower compared
with those reported by Shriver and co-workers12 for
their cross-linked siloxane (30) (from 27.9 to 46.2
kJ /mol) at various LiSO3CF3 concentrations. This may
account for their relative lower conductivities. The
maximum conductivity for the SPE-2 with doping level
of 20:1 occurred at Ea ) 4.5 kJ /mol, the lowest activation
energy over the lithium salt doping range.
The temperature dependence of the ionic conductivity
is shown in Figure 4 for SPEs with salt concentrations
of EO/Li ) 64:1, 28:1, 24:1, 20:1, and 15:1. They show
the obvious trend, whereby conductivities increase with
increasing temperature. For the five complexes, Arrhe-
nius plots all had the curvature characteristic of ion
transport dependent on the segmental motion of the
oligoether chain as well as the polysiloxane backbone.
The Vogel-Tamman-Fulcher24 (VTF) equation
Our ongoing investigations indicate the cross-linking
density as well as chain length of the oligo(ethylene gly-
col) plays an important role in enhancing the ionic con-
ductivity of these network polymer electrolytes. Another
paper will focus on these effects in the near future.
σ ) AT-1/2e(-B/(T - T0))
has been used to fit the behavior of the temperature-
dependent conductivities of these SPE materials. Table
2 lists the values of the parameters A, reflecting the
number of charge carriers, B, the apparent activation
energy, and T0, the ideal glass transition temperature.
The T0 values are all closer to the experimental Tg than
the typical 50 K below Tg.
Thermal properties of the SPEs are characterized by
DSC measurement and are also listed in Table 2. The
major thermal feature observed was a large glass
transition (see Figure 5). As expected for a polysiloxane,
Tg was lower than poly(ethylene oxide) and similar to
other polysiloxane polymers. The glass transition tem-
perature increased with doping level, as is typical for
polymer electrolytes.
Con clu sion s
Cross-linked network polymer electrolytes based on
a polysiloxane backbone have been synthesized and
their ionic conductivities measured when doped with
LiTFSI. The solid polysiloxane network polymer elec-
trolytes display ionic conductivities comparable to those
of their liquid polysiloxane counterparts. The highest
25 °C conductivity (σRT ) 1.33 × 10-4 S cm-1) occurred
for the electrolyte with a doping level EO/Li+ of 20:1
and an activation energy of 4.5 kJ /mol, the lowest one
over the lithium salt doping range. With improved
mechanical properties, these solid electrolyte materials
may find application as both the separator and electro-
lyte in lithium electronic devices.
The VTF parameters and glass transition tempera-
tures clearly correlate well with the conductivity results;
Tg increases with the increasing salt concentration, with
the maximum Tg (213.3 K) occurring at EO/Li+ )15:1,
Ack n ow led gm en t. This work was supported by
grants from the University of Wisconsin-Industry Rela-

9180 Zhang et al.
Macromolecules, Vol. 36, No. 24, 2003
(10) Zhou, G. B.; Khan, I. M.; Smid, J . Macromolecules 1993, 26,
2202.
(11) Fish, D.; Khan, I. M.; Wu, E.; Smid, J . Br. Polym. J . 1988,
20, 281.
(12) Spindler, R.; Shriver, D. F. Macromolecules 1988, 21, 648.
(13) Spindler, R.; Shriver, D. F. J . Am. Chem. Soc. 1988, 110,
3036.
(14) Siska, D. P.; Shriver, D. F. Chem. Mater. 2002, 13, 4698.
(15) Morales, E.; Acosta, J . L. Electrochim. Acta 1999, 45, 1049.
(16) Hooper, R.; Lyons, L. J .; Moline, D. A.; West, R. Organome-
tallics 1999, 18, 3249.
tions program-Advanced Technology Program (ATP)
and NIST-ATP. We also thank 3M Co. for the gift of
LiN(CF3SO2)2. Instrumentation at Grinnell was funded
by the NSF-MRI program (Grant No. 0116159). L.J .L.
thanks Professor David J ohnson and his students, Fred
Harris and J ohn Thompson, for use of their DSC
instrument at the University of Oregon.
Refer en ces a n d Notes
(17) Hooper, R.; Lyons, L. J .; Moline, D. A.; West, R. Silicon Chem.
2002, 1, 121.
(1) Fenton, D. E.; Parker, J . M.; Wright, P. V. Polymer 1973,
14, 589.
(18) Hooper, R.; Lyons, L. J .; Mapes, M. K.; Schumacher, D.;
Moline, D. A.; West, R. Macromolecules 2001, 34, 931.
(19) Zhang, C. X.; Laine, R. M. J . Am. Chem. Soc. 2000, 122, 6979.
(20) Zhang, Z. C.; West, R. Adv. Technol. Program Q. Prog. Rep.
2002 (April 20), 9.
(21) Marko, I. E.; Sterin, S.; Buisine, O.; Mignani, G.; Branlard,
P.; Tinant, B.; Declercq, J .-P. Science 2002, 298, 204.
(22) Arduengo, A. J .; Gamper, S. F.; Calabrese, J . C.; Davidson,
F. J . Am. Chem. Soc. 1994, 116, 4391.
(2) Wright, P. V. Br. Polym. J . 1975, 7, 319.
(3) Wright, P. V. J . Polym. Sci., Polym. Phys. Ed. 1976, 14, 955.
(4) Blonsky, P. M.; Shriver, D. F.; Allcock, H. R.; Austin, P. J .
Am. Chem. Soc. 1984, 106, 6854.
(5) Allcock, H. R.; Napierala, M. E.; Cameron, C. G.; O’Connor,
S. J . M. Macromolecules 1996, 29, 1951.
(6) Allcock, H. R.; O’Connor, S. J . M.; Olmeijer, D. L.; Napierala,
M. E.; Cameron, C. G. Macromolecules 1996, 29, 7544.
(7) Allcock, H. R.; Ravikiran, R.; O’Connor, S. J . M. Macromol-
ecules 1997, 30, 3184.
(8) Allcock, H. R.; Olmeijer, D. L.; O’Connor, S. J . M. Macromol-
ecules 1998, 31, 753.
(23) Arnold, P. L.; Cloke, F. G. N.; Geldbach, T.; Hitchcock, P. B.
Organometallics 1999, 18, 3228.
(24) Fulcher, G. S. J . Am. Ceram. Soc. 1925, 8, 339.
(9) Khan, I. M.; Yuan, Y.; Fish, D.; Wu, E.; Smid, J . Macromol-
ecules 1988, 21, 2684.
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