Synthesis of precision ionic polyolefins derived from ionic liquids

Article abstract of DOI:10.1021/ma9024174

The synthesis of ionic polyolefins derived from ionic liquid (IL) monomers with the use of acyclic diene metathesis polymerization was anzlyzed. The metathesis polycondensation of a fully ionic monomer was accomplished by preparing ionic monomers that are

Full text of DOI:10.1021/ma9024174

Macromolecules 2010, 43, 1699–1701 1699
DOI: 10.1021/ma9024174
Synthesis of Precision Ionic Polyolefins Derived from
Ionic Liquids
underlying theme is the exclusion of Br o€ nsted acids or
1
0
nucleophiles. Furthermore, the design of suitable ionomer
synthons requires that either of two possible polymer synthe-
sis routes be employed: postfunctionalization (ionization) of
the polymer or polymerization of an ionic monomer. The
latter path is preferred for precision polyolefin synthesis
since it does not necessitate quantitative conversion in a
postpolymerization modification.
Metathesis polycondensation of a fully ionic monomer
carries a new challenge, in that most ionic molecules are
solids with melting points well above room temperature and/
or are insoluble in organic solvents. Our approach to cir-
cumvent this problem is simply to prepare ionic monomers
that are, themselves, liquids thus allowing for bulk poly-
merization. The imidazolium hexafluorophosphate salts are
appealing as they are non-nucleophilic.
Figures 1 and 2 display the chemistry used to generate IL
dienes 3 and 12 from commercially available starting materi-
als in 88% and 16% overall isolated yields, respectively. As
catalyst poisoning can be a problem, purity was thoroughly
assessed. In both cases, no bromide ion was detected by the
Beilstein copper-flame test after anion exchange and the final
products passed elemental analysis (Anal. Calcd for 3: C,
†
‡
Brian S. Aitken, Minjae Lee, Matthew T. Hunley,
‡
‡
Harry W. Gibson, and Kenneth B. Wagener*
,†
†
The George and Josephine Butler Polymer Research Laboratory,
Department of Chemistry, University of Florida, Gainesville,
‡
Florida 32611-7200 and Department of Chemistry,
Virginia Polytechnic Institute & State University, Blacksburg,
Virginia 24061-0001
Received October 31, 2009
Revised Manuscript Received December 17, 2009
Introduction. Herein we report the use of acyclic diene
metathesis polymerization to synthesize ionic polyolefins
derived from ionic liquid (IL) monomers. New imidazolium
based ionomers and ionenes with perfectly regular repeat
units are the result. Precision placement of the ionic group
either in the polymer backbone or pendant to it generates
significant variance in physical properties.
Ionomers, ionenes, and polymer gels impregnated with
IL’s have become the focus of intense research in the field of
high performance materials and ion conductive matrices.
1
,2
57.90; H, 8.75; N, 5.40. Found: C, 57.76; H, 8.79; N, 5.39.
Calcd for 12: C, 59.98; H, 9.17; N, 5.0; Found: C, 60.02; H,
Work over several decades has shown that factors such as the
degree of ionic clustering, crystallinity, and other morpho-
logical characteristics play roles in the properties of these
9
.30; N: 4.93.)
The first attempt to polymerize 3 using standard ADMET
2
-5
conditions (melt polymerization using Grubbs’ first or sec-
ond generation catalyst under high vacuum at 45 °C) yielded
oligomers, apparently due to catalyst inhibition. While
ethylene generation was initially observed in the form of
vigorous bubbling, polymerization eventually slowed and
olefin isomerization ensued regardless of whether Grubbs I
or II was employed.
materials.
varying degrees for random ionomers and well-defined
While these features have been studied in
ionenes, fundamental studies of the former have been limited
by an inherent lack of control over the repeat unit.
2
,3,5,6
For example, consider the complexities of partially neu-
tralized poly(ethylene-co-methacrylic acid) or poly(ethylene-
co-acrylic acid) which can display up to four, often thermally
contiguous, mechanical relaxations. These relaxations likely
result from three contributing factors: multiple amorphous
phases, a distribution of crystal thicknesses due to the
statistical incorporation of comonomers, and devitrification
Ondruschka and co-workers encountered a similar situa-
tion during cross metathesis in imidazolium-based IL’s,
reporting that contamination by trace quantities of
N-alkyl-imidazole was sufficient to decrease the reaction
rate while simultaneously increasing catalyst death and ole-
3,7
of ionic domains. The situation is less complicated for
amorphous ionomers, but they too contain responses from
ion-depleted segments as well as devitrification of ion-rich
1
1
fin isomerization rates. Additionally, Schanz and P’Pool
observed that while ROMP with Grubbs I or II could be
completely inhibited with catalytic amounts of N-alkyl imi-
dazoles, full restoration of catalytic activity was achieved
after addition of phosphoric acid to protonate the inhibi-
2
,8
regions.
Devising a reliable synthetic pathway to precision iono-
mers, those containing perfectly regular repeat units, allows
us to fine-tune the interplay between dispersion forces which
govern polymer crystallization and Coulombic attraction
which regulates formation of clusters and multiplets, thus
providing us the opportunity to markedly deconvolute
experimental data. Ion conductivity is also of interest in
1
2
tor. Grubbs and co-workers also have found that, even in
the absence of inhibitors, addition of catalytic quantities of
Br o€ nsted acids can increase the rate of catalyst initiation and
turnover frequency by enhancing tricyclohexyl phosphine
1
3
dissociation.
At first we did not believe we were dealing with the
aforementioned catalyst poisoning problem. Electrospray
4
,5,6a
ionic polymers.
Prior research from our laboratory
suggests the possibility of inducing formation of channel like
ion-rich regions between lamella in highly interactive preci-
sion polymers; these materials may also be valuable as
1
13
ionization MS, as well as H and C NMR spectra for 3,
showed no evidence of N-alkyl-imidazole contamination,
and elemental analysis agreed with the theoretical values.
However, further mass spectral data collected by atmo-
spheric pressure chemical ionization, which selectively
detects semivolatile compounds, combined with HPLC
MS, qualitatively indicated the presence of trace quantities
of imidazole 1. This observation led us to investigate the use
of phosphoric acid as in Schanz and P’Pool’s work. The
concentration of acid was varied from 1 to 25 mol % with
9
unique conduction matrices.
Results and Discussion. Preparation of ADMET polymers
requires that only two criteria be met: the monomer must
contain an alpha-omega diene, and it, as well as any trace
impurities, must not poison the catalyst. Although catalysts
with varying functional group tolerances are available, the
*Corresponding author. E-mail: Wagener@chem.ufl.edu.
r 2010 American Chemical Society
Published on Web 01/20/2010
pubs.acs.org/Macromolecules

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700 Macromolecules, Vol. 43, No. 4, 2010
Aitken et al.
respect to monomer (Figure 3); olefin isomerization was
effectively halted with the addition of 10 mol % acid; higher
concentrations of H PO accelerated catalyst death, as in-
sion of terminal olefin groups to internal olefins according to
H NMR.
Analysis of polymer 4 by DSC and TGA reveals a T at
g
1
3
4
dicated by the formation of brown precipitates.
-3 °C with no melting transition up to 200 °C, near the onset
of thermal decomposition. Powerful interchain interactions
in this precision ionene 4 preclude GPC measurements;
persistent aggregation was observed in all solvents tested
(hexane, toluene, diethyl ether, chloroform, THF, methylene
chloride, 1,2-dichlorobenzene, acetone, DMF, DMSO,
methanol, water, and DMF-LiCl solutions), as indicated
by multimodality of dynamic light scattering (DLS) results.
Nonetheless, NMR measurements (end groups undetec-
table) ensure the formation of high polymer as do its
mechanical properties.
With the issues of isomerization and catalyst death ad-
dressed, driving polycondensation beyond oligomerization
became a matter of enhancing removal of ethylene from the
highly viscous polymerizing mass. Typically ADMET chem-
istry has been accomplished using magnetic agitation; how-
ever, in this case, powerful interchain interactions between
ionic moieties results in a rapid viscosity increase; magnetic
stirring becomes impossible even at low conversions.
We constructed a small scale high vacuum mechanical
stirring apparatus capable of continuously spreading the
molten polymerization matrix as a thin film, thereby max-
imizing the rate of ethylene removal under vacuum (see
Supporting Information Figure 3). Polymerization of mono-
mer 3 (Figure 3) proceeded rapidly using this device, gen-
erating polymer 4; 10 mol % phosphoric acid/Grubbs I led to
high conversion overnight as indicated by complete conver-
Polymerization of pendant IL monomer 12 (Figure 3) to
polymer 13 was achieved using similar conditions, except
that the reactor was heated to 65 °C for melt polymerization.
Conversion was completed easily, as indicated by disappear-
1
ance of the terminal olefin according to H NMR. DSC
reveals a T
at 5 °C and a T at 65 °C, quite different from
g
m
ionene 4. Polymer 4 is an amorphous elastomer, while
polymer 13 is semicrystalline. As before, a high degree of
interchain aggregation in organic solvents was observed,
again precluding GPC measurements.
Dynamic mechanical analysis (DMA) data, in tensile
geometry, was collected on melt pressed films, information
which clearly distinguishes the mechanical differences be-
tween the in-chain material and the pendant polymer. Ionene
4
displayed the onset of a glass transition at 5 °C, consistent
with the DSC result (T = -3 °C, no T ), followed by a
rubbery plateau out to 57 °C. The plateau is attributed
to ionic aggregates while the second relaxation at 57 °C
is believed to correspond to ion-hopping. The DMA of
g
m
Figure 1. Synthesis of ionic liquid monomer 3 for ionene preparation.
Figure 2. Synthesis of ionic liquid monomer 12 for ionomer preparation.
Figure 3. Modified ADMET conditions for preparation of ionenes and ionomers from imidazolium based ionic liquids.

Communication
Macromolecules, Vol. 43, No. 4, 2010 1701
ionomer 13, however, did not show a sharp glass transition
but rather a gradual relaxation with no clear onset, regard-
less of the heating rate. This broad relaxation is concomitant
with what appears to be either strain-induced or cold crys-
tallization at 50 °C, followed by liquefaction near the
DSC measured melting point. (See Supporting Information
Figures 1 and 2)
These new regioregular ionic polymers exhibit a high
degree of interchain interaction between precisely placed
ionic functionalities, an observation supported by both
persistent aggregation of the polymers in a wide variety of
organic solvents and their mechanical behaviors. Despite
nearly equivalent ion contents, the in-chain polymer 4 is an
amorphous thermoplastic elastomer, whereas the pendant
polymer 13 is semicrystalline. Detailed solid-state structural
and morphological analysis is underway to better under-
stand the behavior of this new class of ionomer/ionenes, to
include a systematic study of the relationship between pre-
cision ionomer/ionene structure and ion conduction.
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Acknowledgment. We are grateful to the Army Research
Officefor funding(W911NF-07-1-0452, Ionic Liquids InElectro-
Active Devices), Todd Prox and Joe Caruso (UF) for fabrication
of the reactor, Prof. Timothy Long (VPI & SU), Dr. Taigyoo
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assistance with DMA and DLS experiments.
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Supporting Information Available: Text giving experimental
procedures, reactor design, and thermal characterization and
figures showing DSC traces and a reactor schematic. This
material is available free of charge via the Internet at http://
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