Progress in Polymer Science 34 (2009) 1333–1347
Contents lists available at
Progress in Polymer Science
j o u r n a l h o m e p a g e :
w w w . e l s e v i e r . c o m / l o c a t e / p p o l y s c i
Ionic liquids as solvents for polymerization processes—Progress and
challenges
Przemysław Kubisa
Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łód´z, Poland
a r t i c l e i n f o
Article history:
Received 6 July 2009
Received in revised form 27 August 2009
Accepted 4 September 2009
Available online 15 September 2009
Keywords:
Ionic liquids
Polycondensation
Radical polymerization
Ionic polymerization
Solvent properties
a b s t r a c t
Ionic liquids (ILs) are organic salts that are liquid at ambient temperatures. Ionic liquids have
emerged as a new class of solvents for practical applications due to their unique combina-
tion of low volatility, chemical stability, high conductivity, wide electrochemical window,
ability to dissolve organic and inorganic solutes and gases, and tunable solvent properties.
In polymer science ionic liquids are used as solvents for polymerization processes and as
components of polymeric materials. In this review the advantages and limitations of appli-
cation of ionic liquids as solvents for polymerization processes are critically discussed, with
special emphasis on results published within last 5 years.
© 2009 Elsevier Ltd. All rights reserved.
Contents
1.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1334
1.1.
Ionic liquids and their properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1334
1.2.
Application of ionic liquids as solvents for chemical reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1335
2.
Polycondensation processes in ionic liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1335
2.1.
Enzymatic polycondensations in ionic liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1336
2.2.
Polycondensation processes in ionic liquid under microwave irradiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1337
3.
Radical polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1337
4.
Ionic polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1339
4.1.
Cationic polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1339
4.2.
Anionic polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1340
5.
From ionic liquids to supramolecular polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1340
6.
Ionic liquids as solvents for cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1341
7.
Miscellaneous application of ionic liquids in polymer chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1342
8.
Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1342
9.
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1343
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1343
∗ Tel.: +48 42 681 96 08; fax: +48 42 684 71 26.
E-mail address:
.
0079-6700/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:
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P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1. Introduction
1.1. Ionic liquids and their properties
Ionic liquids (ILs) are organic salts that are liquid at
ambient temperatures, preferably at room temperature
(RTIL – room temperature ionic liquids). Ionic liquids are
composed of large organic cations and small inorganic or
organic anions. Examples of typical cationic and anionic
components of ILs are shown in
It is estimated that the number of possible combinations
resulting in properties that are characteristic for ILs exceeds
10
6
. Thus ILs are very versatile class of solvents and their
properties can be easily tuned for specific application (so-
called task-specific ionic liquids) but at the same time it
is difficult to discuss their properties in general because
some properties may differ considerably depending on the
structure of cation and anion. The most common group of
ILs are imidazolium ILs and further discussion will mainly
be related to this class of ILs.
Although different authors use different abbrevia-
tions for ILs, most commonly abbreviations for cation
and anion structure are given in square brackets
(without charges) thus [bmim][PF
6
] denotes 1-butyl-
3-methylimidazolium hexafluorophosphate, [emim][Cl]
denotes 1-ethyl-3-methylimidazolium chloride, etc.
Room temperature ionic liquids (sometimes abbrevi-
ated as RTILs) have emerged as a new class of solvents for
practical applications due to their unique combination of
low volatility, chemical stability, high conductivity, wide
electrochemical window, ability to dissolve organic and
inorganic solutes and gases, and tunable solvent proper-
ties. Those properties of ILs are frequently taken as granted
without proper understanding of possible limitations.
Ionic liquids are indeed non-volatile in that sense that at
near ambient temperatures their vapor pressure is negligi-
ble. It has been shown recently, however, that at least some
ionic liquids can be distilled
. Several ionic liquids can
be vaporized under high vacuum at 200–300
◦
C and then
recondensed. Convincing proofs that volatilization involves
ionic species (without dissociative proton or alkyl transfer)
have been presented
. Vapor pressure of ILs remains,
however, negligible at near ambient conditions thus for all
practical purposes they may be considered as non-volatile
solvents.
Also the earlier opinion that ILs are highly polar solvents
has more recently been questioned. The concept of polarity
is not easily defined. In IUPAC document polarity is defi-
Fig. 1. Typical cationic and anionic components of ionic liquids.
ned as “the sum of all possible, non-specific interactions
between the solute ions and molecules and solvent mole-
cules, excluding such interactions leading to definite chem-
ical alterations of the ions or molecules of the solute”
Intuitively it can be expected that because ILs are
composed of positively and negatively charged ions, they
should be highly polar. In order to qualify solvents as polar
or non-polar the commonly used parameter is a dielectric
constant. ILs are electrolytes therefore direct measurement
of dielectric constant is not possible. Measurements of
polarity of ILs using solvatochromic and fluorescent probes
indicated that their polarity was close to polarity of lower
alcohols
. Application of dielectric spectroscopy in
megahertz/gigahertz regime with extrapolation to zero fre-
quency led, however, to static dielectric constant values
markedly lower (
ε in the range of 10–15) than values found
by spectroscopy with polarity-sensitive solvatochromic
dyes
. Those results indicate that ILs are solvents of only
moderate polarity
. Dielectric relaxation spectroscopy
(DRS) studies over the range of temperatures and concen-
trations confirmed the modest polarity of ionic liquids and
provided insight into mechanism of dielectric relaxation
In a recent mini-review entitled “Ionic Liquids: fact and
fiction” there is the following statement: “all that can be
unequivocally stated is that ionic liquids are not as polar as
often assumed and many more studies are required to gain
a better understanding of their microscopic properties”
Another factor that is seldom considered by synthetic
chemists using ILs as solvents is a competition between
two kinds of interactions that are possible in bulk ILs, i.e.
electrostatic interactions of fragments where charges are
localized and collective short-range interactions involv-
ing non-polar parts of the side chains (e.g. alkyl groups
in alkylimidazolium cations)
. Therefore, ILs do not
behave like simple molecular solvents and form spatially
heterogeneous domains. Due to electrostatic interactions
and extended hydrogen-bond systems in liquid state ILs are
highly structured
thus, as recently was pointed out,
there is some analogy between structure of ILs and three-
dimensional hydrogen-bonded network of water
behavior of ILs as a pre-organized medium can modify the
molecular reactivity by formation of inclusion complexes
between reactive species and ILs
ILs are generally considered as chemically stable sol-
vents. This is essentially true but again chemical stability
cannot be taken as granted. Proton in C(2)-position of imi-
dazolium cation is acidic and deprotonation leading to
carbene is possible under basic conditions
. This phe-
nomenon was exploited in polymer chemistry by applying
imidazolium ILs as precatalysts for carbene initiated poly-
merizations
Acidity of C(2)-protons may also lead to unex-
pected side-reactions of imidazolium ILs. Thus, when
paraformaldehyde was dissolved in imidazolium IL slow
insertion of formaldehyde occurred leading to imida-
zolium cation containing –CH
2
OH group as substituent
at 2-position
. In attempted anionic polymerization
of methyl methacrylate (MMA) in imidazolium IL, chain
transfer to ionic liquid involving substitution of N-alkyl
group by growing poly-MMA chain was observed
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1335
These examples show that although in most cases when
ILs were used as solvents for polymerization processes they
acted as chemically inert reaction media, the possibility of
side-reactions cannot be a priori excluded because ILs are
not entirely chemically stable under any condition.
In many papers dealing with application of ionic liquids
as solvents authors stress the “green chemistry” aspect.
This is sometimes overemphasized in reports when ILs are
used as solvents for polymerization but volatile organic
solvents have to be used for polymer isolation and purifi-
cation. What is more important, one cannot claim that ILs
as a class conform to 12 Principles of Green Chemistry
as defined by US Environmental Protection Agency
that require among other such properties as biodegrad-
ability and low toxicity. These points were addressed in
a paper under somewhat provocative title: “Are ionic liq-
uids green solvents?” presented at 2002 ACS Symposium
on Ionic Liquids
. Unquestionable advantage of ILs is,
however, their recyclability thus ILs (frequently containing
dissolved catalyst) can be repeatedly used in subsequent
reaction cycles
1.2. Application of ionic liquids as solvents for chemical
reactions
Ionic liquids are intriguing solvents and their potential
to replace organic solvents in different areas of chemistry
has been firmly established
. The growth of number of
publications and patents devoted to ionic liquids in recent
10 years is steeper than simply exponential. Although
application of ILs in polymer chemistry not always elim-
inates the need for volatile organic solvents (quite often
resulting polymers have to be separated from ILs using
organic solvents) the set of properties displayed by ILs
may be advantageous for certain specific applications
In order to take benefit of rather unusual properties of
those liquids it is, however, necessary to really understand
advantages and limitations of using ILs as solvents for poly-
merization processes.
The use of ionic liquids in polymer science is not lim-
ited to their application as solvents. Ionic liquids are used as
additives to polymers (plasticizers, components of polymer
electrolytes, porogenic agents). More recently properties
of polymers containing chemically bound ionic liquid moi-
ety (polymeric ionic liquids) are studied and possibilities
of their applications are being explored. These subjects
have been discussed in recently published reviews entitled:
“Macromolecules in ionic liquids: Progress, challenges, and
opportunities”
and “Advanced applications of ionic liq-
uids in polymer science”
. In these reviews application
of ionic liquids as solvents for polymerization processes is
only briefly discussed. Review papers dealing specifically
with the application of ionic liquids as polymerization sol-
vents were published before year 2005
. Since then
not only several papers appeared concerning this subject
but also our understanding of properties of ionic liquids
has advanced considerably. The aim of the present review
is therefore to critically review the progress in the field
of application of ionic liquids as solvents for polymeriza-
tion processes on the basis of recent literature, with main
emphasis on possible advantages and limitations.
There is a growing number of papers published every
year describing application of ionic liquids as solvents for
polymerization processes. It is, however, not always clear
what authors expect to achieve by replacing typical organic
solvents with ionic liquids. In spite of improved meth-
ods of synthesis and commercial availability of various
ionic liquids
they are still more expensive than typical
organic solvents. Therefore, application of ILs as solvents
for polymerization processes were justified only if due to
their specific properties some special effects, difficult to
achieve in more conventional solvents, could be expected.
The “green aspect” of ILs is often overestimated because
at present it is difficult to imagine application of ILs as
solvents in large scale industrial processes.
What are the properties of ILs that may be of interest for
synthetic polymer chemists?
Good thermal stability and non-volatility may offer
some advantage for the processes which require removal
of by-products at relatively high temperatures such as
polycondensation processes. Another property of ILs is
their ability to dissolve several inorganic or organometal-
lic compounds that are used as catalysts in polymerization
processes. This offers at least two advantages. Polymer-
izations in ILs may be conducted under homogeneous
conditions otherwise difficult to achieve (an example is a
solubility of ATRP catalysts in ILs). Other advantage is a pos-
sibility of recycling and reusing solutions of catalyst in ILs,
especially when expensive catalysts (e.g. those based on
noble metals) are used.
Polarity of ionic liquids is often cited as a property that
justify application of ILs, especially as solvents for ionic
polymerization. On the basis of recent reports, as discussed
later in the text, it seems, however, that in spite of their
ionic nature ILs are only moderately polar solvents and
their estimated dielectric constant values are lower than
these of e.g. nitromethane or dimethylformamide. On the
other hand the high charge density in ILs, existence of
hydrophobic (longer alkyl chains) and hydrophilic (ionic
groups) domains in bulk ILs, ability of certain ILs (e.g. 1-
alkyl-3-methylimidazolium chloride) to break hydrogen
bonds and possibility of specific interactions of cationic or
anionic components with growing species or monomers
may lead to effects that do not appear in solution in
typical organic solvents. Investigations of polymerization
processes in ILs may therefore provide useful information
concerning polymerization mechanism.
In the subsequent sections the possible advantages and
limitations of application of ionic liquids as solvents for
polycondensation, radical polymerization and ionic poly-
merization will be discussed. Resent results concerning
enzymatic polymerization, and microwave-assisted poly-
merization will be presented separately. Electrochemical
polymerization leading to conducting polymers in ILs will
not be discussed because it has been covered in recent
reviews
2. Polycondensation processes in ionic liquids
Polycondensation is typically conducted at relatively
high temperature thus non-volatile and thermally stable
ILs seem to be suitable solvents for polycondensa-
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P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
Fig. 2. Polycondensation of aromatic dianhydrides with aromatic diamines.
Fig. 3. Polycondensation of glycolic acid.
tion processes. Research in this area has mainly been
directed towards synthesis of polyamides, polyimides and
polyesters.
In the early studies on polycondensation of di- or tetra-
carboxylic acid chlorides or anhydrides with diamines,
limitations due to the limited solubility of some aromatic
substrates in ILs were indicated
. On the other hand
in some studies of polycondesation catalytic effect of ILs
was observed. Thus when dicarboxylic acids (less toxic
although less reactive than corresponding chlorides or
anhydrides) were used in direct polycondensation with
diamines, relatively high molecular weight polyimides
were obtained in the absence of any added catalysts and
it was concluded that ILs act not only as solvents but also
as catalysts
. In polycondensation of aromatic dian-
hydrides with aromatic diamines, shown schematically in
, solubility of starting materials could be improved
by addition of imidazolium type zwitterion which led to
higher molecular weights of resulting polyimides
Ionic liquids were also used as solvents for the synthesis
of various optically active polyamides
. Polyimide
networks have been obtained by polycondensation of
pyromellitic anhydride with aromatic di- and tri-amines.
Due to the compatibility between branched polyimide
network and ionic liquids, products that formed self-
supporting gels even at low content of polyimide (6 wt%)
were formed. Gels showed good thermal stability and sta-
ble ion conduction in a wide temperature range
liquids were also employed for interfacial polymerization
(at hexane/IL interface) leading to polyureas with macrop-
orous structure. It was concluded that surface interactions
between IL and polyurea were responsible for observed
porous structure
Other group of processes that has been studied in IL
solutions involves synthesis of polyesters by polyconden-
sation (cf.
). Direct polycondensation of glycolic acid
in ILs gave only oligomeric products. Postpolycondensa-
tion of a preformed oligomer in IL led to polyesters with
moderate molecular weights (DP
n
up to 45). Higher molec-
ular weights could not be achieved due to precipitation of
polymers
Poly(glycolic acid) oligomers (PGA) were further used
for the synthesis of PGA/CL copolymers. Polymerization
of
-caprolactone (CL) in ILs with PGA in the presence of
Ti(OBu)
4
catalyst with subsequent transesterification led
to random copolymers
More recently two step procedure (involving post-
polycondensation in IL) was applied for polycondensation
of sebacic, adipic and succinic acid with aliphatic diols.
Aliphatic polyesters with M
w
up to 6
× 10
4
were obtained
and again it was noted that solubility of polyesters in
IL was a limiting factor. Solubility depends on structure
of IL (nature of cation and anion) and correlation was
found between the miscibility of aliphatic polyester/ionic
liquid system and the extent to which their solubility
parameters matched
. Thus, in reports dealing with
synthesis of polyesters by polycondesation in ILs, difficul-
ties in obtaining high molecular weight polymers due to
limited solubility of monomers and/or polymers are clearly
indicated.
Catalytic effect of ionic liquids was observed in other
type of polycondensation process namely in polycondensa-
tion of phenol and formaldehyde
. This approach may
lead to preparation of transparent ion conductive phenol
resin-ionic liquids hybrid films in which ionic liquids are
dispersed in phenol resin matrix at the nanometer level.
Enzyme catalyzed polycondensation processes in ILs
have also been studied as discussed in separate section.
Presented results show that application of ILs as sol-
vents for polycondensation processes offers only limited
advantage. In some systems additional catalysts can be
avoided because ILs catalyze polycondensation reaction.
More interesting seems to be an application of ILs as sol-
vents for polycondensations leading to networks that form
hybrid gels with ILs embedded and finely dispersed in poly-
mer matrix, which may lead to interesting ion-conducting
materials.
2.1. Enzymatic polycondensations in ionic liquids
Ionic liquids (ILs) have been investigated as an inter-
esting alternative to organic solvents for enzymatic
conversion of small molecules
. An enzyme deacti-
vation, frequently observed in many polar organic solvents
like methanol or DMF, is typically diminished in common
ILs.
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1337
Introduction of enzymes for polymer synthesis in
organic solvents has led to increased research efforts in this
field
and ionic liquids have been tested as possi-
ble replacement of organic solvents in polymer synthesis.
In several reports synthesis of polyesters by polyconden-
sation of hydroxyacids or ring-opening polymerization
of lactones was described
and in some cases
enhanced enzyme activities (with additional microwave
irradiation) was observed. Activity of enzyme (lipase) in IL
solution was analyzed in terms of anion’s H-bond basicity,
enzyme dissolution, anion ionic association ability, cation
hydrophobicity, and substrate ground-state stabilization or
hydrophobic interactions
2.2. Polycondensation processes in ionic liquid under
microwave irradiation
Application of ILs as media for microwave-assisted
reactions offers several advantages
. Typical organic
solvents are frequently flammable and volatile, which is
a safety hazard for high-temperature and closed-vessel
applications using microwaves. In contrast, ILs have high
boiling-points, low vapor pressures and high thermal
stabilities. In addition, typical ILs have moderately high
dielectric constants (in the range of 10–15), and relatively
low heat capacities (in the range of 1–2 J/g K)
. This
combination allows ILs to absorb microwaves efficiently.
Owing to these advantages, ILs have been investigated
as solvents in a number of microwave-mediated reac-
tions. Accelerating effect of ILs (as compared to common
organic solvents) was observed for microwave-assisted
polymerization of oxazoline
-caprolactone
. Microwave heating in ionic liquids was used also
for polycondensation reactions leading to polyamides
and poly(urea–urethanes)
. Although indeed ILs, due
to their properties, are suitable solvents for microwave-
assisted chemical processes, application of this approach
for polymer synthesis is still limited. Certain advantages
have been indicated, but until now only slight improve-
ment of reactions conditions (more efficient heating, higher
rates) has been achieved.
3. Radical polymerization
In 2002 the first report appeared indicating that rate
constants of propagation and termination in radical poly-
merization may be significantly affected by ILs. Kinetics
of radical polymerization of methyl methacrylate (MMA)
in [bmim][PF
6
] was studied by Pulse Laser Polymeriza-
tion (PLP) technique. The k
p
of MMA increased steadily
as the concentration of IL increased. At 50 vol.% of IL k
p
was approximately twice that of bulk MMA
. It was
argued that increase of k
p
value was due to lowering of
activation energy for propagation. Further investigation of
this system revealed that also the rate of termination was
affected by IL
. The rate of termination decreased by
an order of magnitude as IL concentration was increased
to 60 vol.%. The enhancement of propagation rate was
attributed to increasing polarity of the medium allow-
ing greater contribution from charge-transfer structures
and lowering thus the energy of transition state while the
Fig. 4. Schematic representation of PSt-b-MMA block copolymer forma-
tion.
decrease in termination rate was related to increasing vis-
cosity of the medium. Taken together these effects explain
higher overall rates and higher molecular weights observed
for polymerization of MMA in ionic liquids
. Those
conclusions were confirmed later by results of the investi-
gation by the same method of propagation rate coefficients
(k
p
) of methyl methacrylate (MMA) and glycidyl methacry-
late (GMA) radical polymerizations in four different ionic
liquids
Extending of the range of investigated ILs is important
because it has been pointed out that the course of radi-
cal polymerization depends on the structure of IL, i.e. the
length of the alkyl substituent in cation and the nature of
anion
An interesting observation related to application of
ILs as solvents for radical polymerization was that block
copolymer of styrene and methyl methacrylate could be
formed efficiently in conventional radical polymerization
. This was explained by poor solubility of polystyrene
in IL used ([bmim][PF
6
]) and precipitation of polymer
hindering diffusion and increasing life-time of propagat-
ing radicals. Upon addition of second monomer, which
was miscible with the polymer dispersion, polymeriza-
tion continued and block copolymer was formed, as shown
schematically in
Indeed it should be remembered that only some poly-
mers are soluble in typical ILs thus solubility factors may
play important role. The role of polymer solubility in ILs
has been discussed in a recent review
. Alternative
explanation was forwarded recently, involving assumption
that a “protected” radical mechanism was in operation.
The observed effect was explained by radical “protection”
in IL as a part of the process of monomer separating into
extremely small domains in the IL leading to significant
partitioning of radicals into IL domain. The existence of
“protected” radicals leads to formation of block copolymer
when other monomer (MMA) is added to a system after
polymerization of the first monomer (St)
. No indica-
tion of “trapped radical” effect was observed, however, in
RAFT polymerization of styrene in pyridynium ionic liquids
in which polystyrene was soluble
Effect of enhancement of polymerization rate was
also observed for photoinitiated polymerization of poly
(ethylene glycol) mono- and di-methacrylates
. Mea-
surements of viscosity revealed an interesting pheno-
menon—viscosity of monomer/IL mixture for some ILs was
higher than simple additive combination of components.
It has been postulated that this viscosity synergism is
important for observed kinetic effects
. Influence of the
viscosity on the propagation and the termination reaction
as well as the molecular weight distribution in MMA poly-
merization was also observed by other researchers
1338
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
Fig. 5. Schematic representation of activation–deactivation processes in
ATRP.
Fig. 6. Disproportionation of Cu(0) species.
In the last few years several papers appeared confirm-
ing that when conventional radical polymerizations are
conducted in ionic liquid media the rates and molecu-
lar weights are higher than for polymerization in bulk or
organic solvents
. Observation, that in radical
polymerization in ILs rate constants of propagation are
higher and rate constants of termination are lower than
in polymerization in bulk or typical organic solvents, has
a special significance for processes of controlled radical
polymerization, especially atom transfer radical polymer-
ization (ATRP) shown schematically in
Controlled radical polymerization is not living because
termination is not eliminated. Any factor leading to the
increase of k
p
/k
t
ratio would therefore widen the window
of polymerization conditions within which polymeriza-
tion can be controlled. This is one of the advantages
of conducting controlled radical polymerization in ILs.
Another advantage is solubility of several transition metal
complexes that are used as ATRP catalysts (e.g. Cu salts
in conjunction with amine ligands) in ILs
. Thus in
many systems polymerization proceeds under homoge-
neous conditions and catalyst can be easily separated from
polymer
. In several cases solution of catalyst in IL was
recovered and reused
Ionic liquids, among other polar solvents, have been
found to favor disproportionation of Cu(I)X species
(X = halogen) into Cu(0) and Cu(II)X2 species (as shown in
) in the presence of different N-containing ligands
(catalytic systems frequently used in ATRP).
Cu(II) species provide the reversible deactivation of rad-
icals into alkyl halide species while Cu(0) promotes the
activation of active species. It has been postulated that
this process proceeds by the outer-sphere single electron
transfer process with low activation energy. Therefore,
activation and deactivation steps are very fast and
bimolecular termination is negligible. Very fast controlled
polymerization leading to very high molecular weight
polymers (M
n
up to 1.5
× 10
6
) was achieved for a range of
monomers containing electron-withdrawing groups such
as acrylates, methacrylates, and vinyl chloride, initiated
with alkyl halides, sulfonyl halides, and N-halides
For polymerization of MMA initiated with arenesulfonyl
chlorides in [bmim][PF
6
] catalyzed by Cu
2
O/2,2
-bipyridine
system a strong accelerating effect of IL was observed
. Nearly complete conversion of MMA to polymer with
DP
n
= [monomer]
0
/[initiator]
0
and M
w
/M
n
∼ 1.1 could be
obtained at room temperature within a few hours. These
results indicate that although polymerization is fast, the
good control is still maintained. No mechanistic interpre-
tation of the accelerating effect of IL in the studied system
was presented until now.
Fig. 7. Schematic representation of reactions involved in RAFT polymer-
ization.
An interesting feature of ILs as solvents for ATRP is that
in some systems organic ligand (typically amine) may be
avoided. This was shown for polymerization of MMA with
iron-based catalysts in phosphonium type ILs
or poly-
merization of acrylonitrile in imidazolium ILs
effects as for ATRP in ILs have been observed also for reverse
ATRP
An interesting application of ILs for growing polymer
brushes was reported recently
. Thus, small droplets
of IL containing ATRP catalyst were placed on a surface
of silicon wafer and methyl methacrylate was introduced
into the droplet. Polymer brushes were formed only at the
area covered by IL droplets. Thus, IL droplets were used as
microreactors in which polymerization proceeded in con-
fined geometry.
Lower
(meth)acrylates
are
frequently
used
as
monomers for polymerizations in ILs because both
monomers and polymers are readily soluble in most ILs.
The limitations due to the polymer solubility were clearly
pointed out in the first report on reversible addition-
fragmentation chain transfer (RAFT) polymerization
(shown schematically in
) in imidazolium ionic
liquids.
While homogeneous RAFT polymerizations of methyl
methacrylate (MMA) and methyl acrylate (MA) were fully
controlled leading to polymers with M
n
close to calcu-
lated values and low dispersity, polymerization of styrene
stopped at limited conversion due to polymer precipitation
. Recently, however, successful RAFT polymer-
ization of styrene in pyridinium ILs under homogeneous
conditions was reported
. Analysis of the course of RAFT
polymerization in different ILs led to conclusion that it
depends on both nature of RAFT agent employed and type
of IL
. The effect of IL structure was related to solubility
of monomer and polymer in IL and it was shown that many
of those phase partitioning effects may be overcome by
using IL-tethered RAFT agent (IL functionalized with RAFT
agent by click chemistry, as shown in
Nitroxide mediated radical polymerization of methyl
acrylate (MA) in imidazolium ILs was successfully con-
ducted although relatively high temperature (140
◦
C) was
required. At these conditions significant contribution of
spontaneous initiation was noted
ILs have been used also as solvents for radical copoly-
merization processes. It has been shown that in IL solution,
statistical copolymers from methacrylates of strongly dif-
ferent polarities and solubilities are formed. The relative
reactivity of monomers and thus the composition of
copolymers depended on the structure of imidazolium ILs
Reactivity ratios in copolymerization in ILs may also be
modified by changing the mechanism of copolymerization
from radical to charge-transfer (CT) mechanism. Thus for
styrene–methyl methacrylate pair reactivity of styrene in
CT copolymerization was enhanced as compared to radical
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1339
Fig. 8. Synthesis of IL-tethered RAFT agent.
Fig. 9. Cationic polymerization of styrene initiated by organoborate acids (HBOB).
polymerization
. The effect of ILs on CT homopolymer-
ization of methyl methacrylate and styrene have also been
studied
4. Ionic polymerization
4.1. Cationic polymerization
Ability of ionic liquids to dissolve wide range of
inorganic compounds was exploited in the study in
which organoborate acids (HBOB) (bisoxalatoboric acid,
bissuccinatoboric acid and bisglutaratoboric acid) were
used as initiators of the cationic polymerization of
styrene in pyrollidonium, imidazolium and phospho-
nium bis(trifluromethanesulfonyl)amide ILs as shown in
. At relatively high initiator concentration
([Styrene]
0
/[HBOB]
0
in the range of 10–30) at 60
◦
C poly-
merization proceeded to practically complete conversion
giving polymers with dispersity
∼1.3. M
n
values were close
to calculated up to DP
n
about 20. Above this value observed
M
n
s were considerably lower than calculated indicating
chain transfer. Authors described studied system as con-
trolled polymerization.
Earlier belief that ILs are highly polar solvents stim-
ulated another study of polymerization of styrene in the
system in which equilibrium between dormant and active
species governs the concentration of growing ionic species
. It has been expected that polarity of ionic liquids
would favor ionization of C Cl bond (cf.
Indeed it has been shown that 1-phenylethyl chlo-
ride even in the absence of coinitiators (Lewis acids such
as TiCl
4
or BCl
3
are typically used) initiates polymeriza-
tion of styrene
. Analysis of MALDI TOF spectra of
polymers revealed, however, that some macromolecules
contain head-groups resulting from initiation by proton
(most probably formed by transfer). Observed molecular
weights differed from calculated values and dispersity was
rather broad. These observations indicated that although
ionization of C Cl bond indeed proceeded in IL solution
even in the absence of coinitiators, full control of polymer-
ization could not be achieved. Ionization of C Cl bond in
IL solution was confirmed by measurements of the rate
of racemization of optically active 1-phenylethyl chloride
(model of dormant species)
. Although racemization
(proceeding by reversible ionization of C Cl bond) was
observed, its rate was relatively low as compared with the
rate of polymerization therefore the requirement of fast
interconversion of active and dormant species was appar-
ently not fulfilled in the studied system. More recently it
has been shown that ionization of C Cl bond may proceed
more efficiently in IL/SO
2
mixtures (several ILs may dis-
solve up to 2 moles of SO
2
per 1 mole of IL
the rate of ionization was still not sufficient to achieve con-
trolled cationic polymerization of styrene
In another study cationic polymerization of styrene ini-
tiated with AlCl
3
in IL ([bmim][PF
6
]), supercritical CO
2
and
organic solvent (CH
2
Cl
2
) was investigated. The only conclu-
sion was that in ILs rates and molecular weights are higher
than in organic solvent
There were also some attempts to apply ILs for cationic-
ring-opening polymerization (ROP). Imidazolium IL with
PF
6
−
anion was used as solvent for ROP of lactones with
Fig. 10. Schematic representation of activation–deactivation processes in controlled cationic polymerization of styrene.
1340
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
rare-earth metal triflates as catalysts and it was shown
that catalyst may be recycled (at least three times) with-
out losing activity
. Considering cost of catalyst this
approach may offer some advantage. It was also observed
that ILs have accelerating effect on polymerization of
caprolactone initiated with polymer supported scan-
dium triflate
. In other attempt imidazolium IL was
used as solvent for cationic polymerization of 3-ethyl-3-
hydroxymethyloxetane (EOX). In cationic polymerization
of EOX, leading to branched multihydroxyl polyethers in
organic media intramolecular hydrogen bonding leads to
intramolecular chain transfer to polymer. It was expected
that hydrogen bonding could be minimized in IL solution
allowing preparation of higher molecular weight poly-
mers. Only a limited effect was, however, observed
Cationic polymerization of 3,3-bis(chloromethyl)oxetane
in ILs has been also reported but molecular weights were
limited
4.2. Anionic polymerization
As mentioned in Section
, under basic conditions ILs
are not entirely stable therefore they do not seem to
be suitable solvents for anionic polymerization. In spite
of that there are a few reports on anionic polymeriza-
tion in IL. Group transfer polymerization (GTP) of methyl
methacrylate (MMA) in IL was studied
. GTP is not a
typical anionic polymerization but at present it is believed
that propagation proceeds on anionic species that are
reversibly deactivated
. Although reported yields
were not always high (between 20 and 99%) and dis-
persities were rather high (1.7–2.4) authors claimed that
polymerization proceeded as living process
. More
recently anionic polymerization of MMA initiated with
alkyl lithium initiators was reported
. Observed lim-
ited yields (
∼10%) and high dispersities (PDI ∼2) were
attributed to deactivation of initiator by acidic proton in
2-position of imidazolium ring. Another side-reaction in
anionic MMA polymerization initiated by alkyl lithium
initiators was observed in our laboratory
the end-group structure by MALDI TOF we have found
that chain transfer to ionic liquid occurs at the early
stages of polymerization according to a scheme shown in
Although this reaction puts a limit on molecular weights
(M
n
< 2000) yields are high (up to 98%) and practically all
the macromolecules contain ionic end-groups derived from
IL, which may be of synthetic interest.
Fig. 11. Chain transfer to ionic liquid in anionic polymerization of methyl
methacrylate.
Anionic polymerization of styrene initiated by butyl
lithium (BuLi) or sodium acetate (NaAc) in phosphonium
type IL was also reported
. At relatively high initia-
tor concentration (
∼2 mol% with respect to styrene) BuLi
initiated polymerization gave 20% yield after 70 h at 60
◦
C,
with NaAc yield was still lower (10%). Yields were improved
upon addition of butyl imidazolium butane sulfonate zwit-
terion (cf. the structure shown in
) up to 75% in
70 h and 94% in 140 h. Molecular weights were high (up
to 400,000) with dispersity in the range of 1.4–2.1. This
indicates that transfer reactions are not important in this
system thus perhaps phosphonium ionic liquids are more
suitable as solvents for anionic polymerization than imi-
dazolium ionic liquids (although imidazolium cation was
present in zwitterionic additive).
Complications arising from the presence of acidic pro-
ton at 2-position of imidazolium ring may be eliminated
if proton is replaced by other group. We have found
that when paraformaldehyde is dissolved in 1-alkyl-3-
methylimidazolium chloride slow reaction proceeds by
which C(2) H group is quantitatively converted into
C(2) CH
2
OH group
. By this reaction not only acidic
proton is removed but additionally functional group is
introduced into imidazolium ring of IL. By reaction with
NaH alkoxide ions were formed which were used to ini-
tiate anionic polymerization of ethylene oxide (EO)
Up to DP
n
∼30 polymerization proceeded without any side-
reactions giving with quantitative yields imidazolium ionic
liquids containing short polyoxyethylene chains attached
at 2-position, as shown in
Blending of those materials with high molecular weight
polyoxyethylene (POE) resulted in the reduction of crys-
tallinity of POE. Because addition of ILs to polymer
electrolytes leads to enhanced ionic conductivity, ILs with
chemically bound POE chains may find application in the
field of solid polymer electrolytes
An accelerating effect of ILs on polymerization of
propylene oxide in the presence of double metal cyanide
catalysts has been observed. Addition of IL led not
only to about 10-fold increase of reaction rate but
also to significant reduction of the content of terminal
unsaturation
. ILs were used also as solvents for poly-
merization of N-carboxyanhydrides (NCA) initiated with
amines. Poly(amino acid)s having low dispersity, molec-
ular weights close to the theoretical values, and helical
secondary structures were obtained
5. From ionic liquids to supramolecular polymers
In very recently published Highlight article an inter-
esting possibility of formation of supramolecular ionic
networks in ILs composed of multivalent cations and anions
is discussed
. By combining dication (two covalently
linked tetraalkylphosphonium cations) and tetraanion
(ethylenediaminetetraacetate anion) ionic liquids show-
ing high dynamic viscosity—more than order of magnitude
higher than simple phosphonium type ILs were formed.
Replacement of ethylenediaminetetraacetate anion with
a porphyrin tetracarboxylate gave materials that could be
pulled into fibers or molded into shape-persistent objects
in which porphyrine moiety retained its fluorescent prop-
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1341
Fig. 12. Synthesis of imidazolium ionic liquid containing –CH
2
OH substituent and its application as initiator of anionic polymerization of ethylene oxide.
erties which is important for possible applications as e.g.
sensors
. This observation may pave a way for manu-
facturing of a new type of materials combining mechanical
properties of ionomers with the homogeneity and high
charge density typical for ionic liquids.
Recently dendritic ionic liquids that self-assemble into
supramolecular columns and spheres undergoing self-
organization into liquid crystalline and crystalline lattices
has been reported.
These supramolecular structures contain the ionic liq-
uid part segregated as a core forming thus nanoreactors
that may be used to perform reactions in confined ionic
liquids geometries
6. Ionic liquids as solvents for cellulose
The application of ILs as solvents in carbohydrate chem-
istry has recently been reviewed
. Some ionic
liquids, especially those containing Cl
−
anion, are dissolv-
ing cellulose including lignocellulosic biomass
Cellulose with a degree of polymerization in the range
from 290 to 1200 could be dissolved in [bmim][Cl] to
relatively high concentration (up to
∼20%) without degra-
dation although solubility decreased with increasing DP
n
.
Without using any catalyst, cellulose derivatives with high
degree of substitution could thus be prepared in IL solutions
.Graft copolymers of cellulose were obtained by
ATRP of methacrylates or styrene after functionalization of
HO- groups in cellulose with 2-bromopropionyl bromide
, as shown in
Graft copolymers were also prepared by ring-opening
polymerization of cyclic esters initiated by HO- groups of
cellulose in IL solution
Taking advantage of cellulose solubility in IL cellu-
lose functionalized with acrylate group was polymerized
in solution in IL. The isolated product was a composite
consisting of cellulose and the polymerized ionic liquid
. Dissolution of cellulose in imidazolium IL containing
polymerizable group (
∼10 wt% solution) and subsequent
polymerization led to IL/cellulose composite in which both
components were efficiently compatibilized
. Solu-
tion of cellulose (microcrystalline cellulose or even wood)
in IL in the presence of solid acid catalysts could be selec-
tively depolymerized first to oligocellulose and than to
simple sugars
Ability of ILs to dissolve materials that are strongly
hydrogen bonded and thus hardly soluble has been
employed also in other systems. Nylon 6 was depolymer-
Fig. 13. Functionalization of cellulose in ionic liquid and synthesis of graft copolymer.
1342
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
Fig. 14. Formation of carbene from imidazolium ionic liquid.
ized in IL in high yield (>85%) to caprolactam and recycled
IL could be used in subsequent reaction cycles
7. Miscellaneous application of ionic liquids in
polymer chemistry
Owing to their specific physical and chemical properties
ILs may find specific applications in polymer chemistry. ILs
have been found to be effective in reducing the exothermic
self-heating in thermal polymerization of styrene and acry-
lonitrile and reducing the thermal product decomposition
Chemical instability of ILs under specific conditions was
employed in the system in which imidazolium IL was used
as a precatalyst reservoir in a phase-transfer polymeriza-
tion with an immiscible THF solution of monomer (lactide)
and initiator (BuOK). In situ activation of the ionic liquid
produced carbene (cf.
) that migrated to the organic
phase initiating polymerization of lactide
ILs are suitable solvents for preparing polymer stere-
ocomplexes and studying their properties. Isotactic and
syndiotactic poly(methyl methacrylate) (PMMA) formed a
stereocomplex in ionic liquids ([bmim][PF
6
]). The stereo-
complex formation brought about the gelation of IL and was
fully thermoreversible. Due to non-volatility and thermal
stability of IL rapid stereocomplex formation and its disso-
ciation could be achieved. The possibility of preparing two-
and three-dimensional arrangements of C
60
molecules by
stereocomplexation of fullerene end-capped poly-MMA
has been indicated
Aqueous solutions of ionic liquids have been used as
novel and environmentally friendly reaction media to syn-
thesize and “control” the size of different cross-linked
polymer beads by suspension polymerization reactions.
The average size of polymer beads can be varied from the
macro- to the nanoscale
8. Outlook
Ionic liquids are no longer laboratory curiosity, finding
already industrial applications
. The first indus-
trial process using ionic liquid is so-called BASIL
TM
process
(Biphasic Acid Scavenging using Ionic Liquids) developed
by BASF, other processes are also in operation or in the
development stage
Still it is rather difficult today to imagine wider appli-
cation of ionic liquids as solvents for mass production of
commodity polymers. In polymer science ionic liquids may
rather find application as components of polymeric system
(plasticizers, ion-conducting components).
Is it therefore purposeful to study and develop typical
polymerization processes in ionic liquids?
There are certain applications in which ionic liquids may
offer significant advantage. Wide electrochemical window
(5–6 V) may justify their application as solvents for electro-
chemical polymerization leading to specialty conducting
polymers
Less obvious is an answer to the question whether it
is justified to study conventional polycondensation (syn-
thesis of polyesters or polyamides) or polymerization
processes (leading e.g. to polystyrene, polymethacrylates
or polyacrylates). Certainly the mass production of e.g.
polystyrene or poly(meth)acrylates involving application
of ionic liquids as solvents (even considering environmen-
tal issues) is difficult to imagine.
Ionic liquids, however, may offer significant advantage
as model solvents for elucidating the details of polymer-
ization mechanism in general and this aspect may be
important for the further progress of polymer chemistry.
Radical polymerization (conventional as well as controlled)
is a good example of possibilities offered by application of
ionic liquids as solvents. Rate constants of elementary reac-
tions in radical polymerization depend on viscosity. This is
especially pronounced for the rate constant of termination
which requires the encounter of two growing
radicals but there is also evidence that rate constants of
other elementary reactions may depend on viscosity
ILs have a very broad range of viscosities. Depending
on the structure of cation and anion viscosity may vary
between 20 and 40,000 cP as compared with viscosities of
typical organic solvents which are in the range between
0.2 and 100 cP
. Viscosity of particular ionic liquid
may be tuned additionally by even minute amounts of
water or organic solvents
. In the course of polymer-
ization viscosity of reaction medium (especially for bulk
polymerization) may increase significantly and the depen-
dence of rate constants of elementary reactions on viscosity
is studied by analyzing the kinetics at different stages of
polymerization. Viscosity, however, is not the only param-
eter that changes with conversion thus other factors may
possibly contribute to observed effects. Ionic liquids, in
which only minor change of structure may result in sig-
nificant change of viscosity, offer thus a unique possibility
of studying the effect of viscosity alone, under otherwise
identical conditions. As described earlier in this review,
Haddleton et al. studying the polymerization of methyl
methacrylate in imidazolium ionic liquid at different pro-
portion of monomer to IL found that termination rate
constant decrease significantly with increasing fraction of
IL in the mixture and related this effect to increasing viscos-
ity
. Studies of systems at constant ratio of monomer
to structurally similar ionic liquids of different viscosity
could provide more straightforward information of the
dependence of termination rate constant on viscosity.
The enhancement of rate constant of propagation in ILs
has also been observed. The origin of this phenomenon is
still a matter of dispute. In the first paper in which this
observation was reported
, possible causes have been
discussed and it was concluded that the observed accel-
eration is due to the increased polarity of the medium,
which allows a greater contribution from charge-transfer
structures, lowering the energy of the transition state.
The alternative hypothesis was recently formulated
assuming the presence of protected radical (through for-
mation of radical–IL adduct) and the presence of monomer
domains within IL. In the report on RAFT polymerization in
P. Kubisa / Progress in Polymer Science 34 (2009) 1333–1347
1343
Fig. 15. Schematic representation of counterion exchange in ionic polymerization in ionic liquids.
pyridinium ILs, however, it was concluded that either pro-
tected radicals are not present or they have very little or no
influence on the kinetics
. It has been pointed out that
interaction between cations and anions in ILs may signifi-
cantly affect the course of reaction involving radicals with
dipole moment. Radical reactivity may depend on minor
changes in the media and until now these phenomena for
radicals in ILs have not been described and compared with
organic solvent
. Thus it seems that more kinetic stud-
ies of radical polymerization in ILs are needed to explain the
effect of IL on reactivity of radicals in propagation, which
may shed some light on the problem of radical reactivity in
general.
There is much less interest in ionic polymerization in
ILs. ILs cannot be treated as neutral solvents for ionic poly-
merization because they are composed of ions. Cations or
anions are counterions for growing species in anionic or
cationic polymerisation, respectively. If ionic polymeriza-
tion is conducted in IL solution, there is a large excess of ions
that constitute ionic liquid. It is therefore not obvious which
ion is really the counterion for growing species. This may
be especially important if ion-pairs are involved in propa-
gation. Polarity of ILs is not as high as previously suggested
therefore propagating species may exist predominantly in
form of ion-pairs. To what extent an exchange of coun-
terions between ion-pairs (according to scheme shown in
) could occur cannot be easily predicted. Such possi-
bility should certainly be considered.
Exchange of anions was observed recently in systems
in which two different ILs (each liquid at room tempera-
ture) were mixed together. After mixing, gelation occurred
which was attributed to exchange of ions and formation of
ion-pairs of IL that was solid at room temperature
It has to be remembered also that interactions between
cationic and anionic components in ILs are quite complex
and the nature of those interactions may depend on the
fraction of IL in monomer/IL solution, i.e. on concentration
of monomer in polymerizing mixture
An interesting albeit still unexplored area in which
application of ILs may be fruitful is stereospecific poly-
merization in chiral ILs. Chiral solvents have been used
by organic chemists as inducers of chirality in asymmetric
synthesis but limited enantioselectivity coupled with high
cost of chiral solvents hampered the progress in this area.
With developing of relatively simple methods of synthesis
of chiral ionic liquids it has been recognized that chiral ILs
could overcome some of these obstacles. Examples of chiral
ILs are shown in
The possibility of recycling and reusing chiral ILs elimi-
nates the main obstacle, i.e. high cost of chiral solvent
Interest of polymer chemists in application of chiral ILs has
been limited until now
. Small but clearly detectable
effect on polymer tacticity was observed for ATRP of acry-
lates in chiral imidazolium IL
. Chiral ILs were also
used as solvents for reverse ATRP of methyl methacrylate
Fig. 16. Examples of chiral ionic liquids.
. Thus only very preliminary information concerning
the effect of chiral ILs on the stereochemistry of polymer-
ization is available until now.
There is much more activity in this area among organic
chemists and it is believed that although the use of chiral
ILs is still in its infancy, it is an area with great potential that
will expand in coming years
. It remains to bee seen
whether this optimistic view can be shared by polymer
chemists.
ILs may be useful solvents for the synthesis of inorganic
coordination polymers and stabilization of their nano-sized
objects such as cyano-bridged metallic nanoparticles of dif-
ferent size. ILs act in such systems both as the stabilizing
agent and solvent, so that no additional ligand is required
to obtain stable colloidal solutions
9. Conclusion
Ionic liquids are intriguing solvents and their unique
properties, although still not fully understood, will
undoubtedly stimulate curiosity driven research in the area
of polymer chemistry. We have already reached a stage
when some basic features of polymerization processes in
ILs have been established. It seems that further progress
in this field can be achieved by careful selection of studied
systems in which application of ILs may either offer real
synthetic advantage or provide new insight into polymer-
ization mechanisms rather than by showing just another
examples of processes that may be conducted in ILs.
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Document Outline
- Ionic liquids as solvents for polymerization processes-Progress and challenges
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