Supercritical impregnation of polymers - ZyXEL NSA210

Current Opinion in Solid State and Materials Science 7 (2003) 399–405
Supercritical impregnation of polymers
Ireneo Kikic * , Febe Vecchione
Chemical, Environmental and Raw Materials Engineering Department (DICAMP), University of Trieste, P.le Europa, 1, Trieste 34127, Italy
Received 11 August 2003; received in revised form 4 September 2003; accepted 4 September 2003
Abstract
The interest in the supercritical fluid impregnation of polymeric materials stems from the opportunity to utilize high diffusivity,
low surface tension and the ease of solvent recovery for the preparation of new polymeric materials. This term includes a wide range
of applications of the supercritical impregnation process that will be discussed in this review: preparation of drug delivery systems
via impregnation of an active principle in a polymer matrix, dye and organic metallic complexes impregnation and polymer blends
preparation via impregnation of a monomer and an initiator in a swollen polymer matrix.
Ó 2003 Elsevier Ltd. All rights reserved.
1. Introduction
Recently, supercritical fluids have been applied for
polymerization, swelling, impregnation, fractionation,
purification and formation of powdered polymers. One
of the important effects on polymers is the plasticizing
effect of CO 2 with a decrease of the glass transition
temperature [1].
Supercritical carbon dioxide (SCCO 2 ) can reversibly
swell glassy and rubbery polymers and reduce the viscosity
of the polymer melts by up to an order of magnitude
[2].
The impregnation process is feasible when the active
substance (the solute) is soluble in the supercritical
fluid, the polymer is swollen by the supercritical solution
and the partition coefficient is favourable enough to
allow the matrix to be charged with enough solute.
The fact that a high product purity is obtained (free
of residual solvent) is important when considering the
production of foods and pharmaceuticals, where it reduces
the costs incurred in the removal of residual solvent
[3].
The interactions within the SCCO 2 -assisted impregnation
system are reported in Fig. 1.
Impregnation processes can be classified on the base
of the following criteria:
* Corresponding author. Tel.: +39-40-5583433; fax: +39-40-569823.
E-mail address: ireneok@dicamp.units.it (I. Kikic).
1. The solubility of the solute in the supercritical fluid.
2. The solute modification inside the polymer matrix.
Referring to the first one of these, it is important to
distinguish between two different mechanisms; the first
involves deposition of a substance soluble in a supercritical
fluid into the polymer matrix upon depressurisation.
In this case, even a solute that has low affinity for
the polymer matrix can be trapped within a polymer
matrix, but in this case we have the formation of recrystallized
substances within the polymer matrix without
a molecularly dispersed formulation. A different
mechanism utilizes the high partition coefficient of solute
between the polymer and fluid phases due to a high
affinity of the solute for the polymer matrices. This
mechanism has tremendous potential for the supercritical
fluid impregnation of drug molecules into polymers
[4].
Referring to the second criterion, it is possible to
distinguish between:
• Solutes which are not modified in the polymer matrix:
drugs,
dyes (both for polymer and textile).
• Solutes which undergo a modification during the impregnation
process:
organometallic complexes for the impregnation of
polymers (90% of cases),
monomers with initiator for polymer blends preparation.
1359-0286/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cossms.2003.09.001

400 I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405
dissolving
SC CO 2
1
Additive
3
swelling
4
plasticizing
Before presenting the different processes, the behaviour
of the binary system (supercritical fluid–polymer)
will be considered.
2. Supercritical fluid–polymer interaction
loading
Supercritical fluids can interact not only with polymers
at temperatures higher than the softening point but
also with polymers in the glassy state. Three concomitant
effects must be considered: the dissolution of the
SCF (polymer sorption), the swelling of the polymer
matrix and the glass transition temperature (T g ) depression,
simply called plasticization.
The plasticization effect is an important feature: the
sorbed gas acts as a kind of Ôlubricant’, making it easier
for chain molecules to slip over one another, and thus
causing polymer softening. The measured depression
reaches values as high as 60 °C for poly(methyl methacrylate)
and poly(styrene).
Measurements of glass transition temperatures at
high pressures can be only indirect; recently, a new
method has been developed for measuring the glass
transition temperature: it is based on a supercritical fluid
chromatographic technique. In this case, using the supercritical
fluid at a given pressure as mobile phase and
the polymer under investigation as stationary phase, the
retention volumes of various organic solutes are measured
at different temperatures [5,6].
Some attempts can be found in the literature to model
both the sorption of a supercritical fluid in a glassy
polymer and the glass transition temperature depression
induced by supercritical fluids.
Regarding the shift of the glass transition temperature,
the most important contribution is due to Condo
et al. [7]. In this approach the Gibbs Di Marzio criterion
(at the glass transition the entropy of the system is zero)
is used together with the Sanchez–Lacombe equation of
state. The possibility of the so-called retrograde vitrification
is suggested: when the temperature is reduced at
constant pressure, it is possible to observe a first liquid–
glass transition followed by a second transition from the
glass-back to the liquid-state.
A detailed description of the model and a discussion
on the effects of different parameters is reported in [6,8].
2
Polymer
Substrate
Fig. 1. Interactions between the SCCO 2 -assisted impregnation system.
Another approach proposed originally by Wissinger
and Paulaitis [9] introduces an additional variable (order
parameter) that describes the thermodynamic state of a
system. As the order parameter, the fraction of holes in
the lattice and the number of nearest-neighbour contacts
between polymer segments on the lattice sites are used.
The NELF model, recently proposed by Doghieri and
Sarti [10] uses as an order parameter the density of the
swollen polymeric phase and the Sanchez–Lacombe
equation of state for the evaluation of the chemical
potential of the supercritical fluid in the gas phase (pure
supercritical fluid) and in the polymeric phase. This
approach can also be modified using a different equation
of state for the gas phase, and does not require any binary
interaction parameter. In this way, the sorption
behaviour can be predicted from the swelling data alone.
Since swelling measurements are, in general, more
difficult to perform, it was recently [11] proposed to use
the model as an empirical method to correlate and
predict sorption data. Using one experimental sorption
data point, and applying the NELF model, it is possible
to predict the sorption at other pressures and temperatures.
3. Supercritical impregnation processes
3.1. Drugs impregnation
Controlled-release products have recently received
considerable attention in the pharmaceutical industry
since their use significantly reduces the problems connected
with excessive dosages.
In the preparation of controlled-release drugs, a liquid
solvent swelling the polymer matrix and serving as a
carrier for the drug component, is used. An alternative is
to substitute the liquid organic solvent by a supercritical
fluid with the advantage that the final product is completely
free of any residual solvent contamination.
Guney and Akgerman [12] investigated the impregnation
of a biodegradable polymer matrix, poly-dllactide-co-glycolide
(PLGA), with 5-fluorouracil and
b-estradiol, drugs that are used for chemotherapy and
estrogen hormone therapy, respectively.
The experimental set-up includes a saturation column
packed with the drug, and an impregnation vessel in
which the polymer is placed. Sorption experiments require
the introduction of a drug-saturated CO 2 stream
into the impregnation column. That is why the experiment
consists of two sections: solubility measurement
followed by impregnation. The apparatus is also
equipped for a qualitative determination of polymer
swelling.
For b-estradiol at 35 °C and 207 bar, the impregnated
amount (q ¼ mg drug/g PLGA) was 10.24 while at 55 °C
and 207 bar, it arrives at 26.80.

I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405 401
For 5-fluorouracil at 55 °C and 207 bar, the impregnated
amount was very low (0.49).
For these specific applications the drug loadings obtained
are even higher than necessary since the therapeutical
level for these products is much lower [12].
Kazarian and Martirosyan [4] used ATR-IR spectroscopy
to study the process of impregnation of ibuprofen
into poly(vinyl pyrrolidone) (PVP) from SCCO 2
solution.
In situ spectroscopy allows the continuous monitoring
of the amount of the impregnated drug, and the
process can be instantly stopped by depressurising the
high-pressure cell once the desired level is achieved.
It has been shown that the supercritical fluid impregnation
process results in ibuprofen being molecularly
dispersed in a polymer matrix where all drug
molecules are H-bonded to the polymer and without the
presence of ibuprofen crystals.
ATR-IR spectroscopy has also revealed specific interactions
between CO 2 molecules and carbonyl groups
of PVP and it has been shown that a competitive interaction
of impregnated ibuprofen molecules with the
carbonyl groups of PVP prevents CO 2 molecules from
interacting with the carbonyl groups of PVP. In addition,
IR spectroscopic evidence has proved that similar
interactions have an effect on water uptake into PVP.
Thus, the PVP films impregnated with ibuprofen show
much lower water uptake, presumably due to the competitive
interaction of ibuprofen with basic carbonyl
groups of PVP [4].
3.2. Dye impregnation
In the dyeing processes of the textile industry, the use
of supercritical carbon dioxide as an alternate solvent
instead of water-based processes has been gaining much
interest for environmental reasons. The conventional
dyeing process of PET fibers discharges much wastewater
that is contaminated by various kinds of dispersing
agents, surfactants and unused dye. It is very difficult
to design a conventional biological process that treats
the wastewater discharged from a conventional dyeing
PET process.
The environmentally friendly supercritical fluid dyeing
(SFD) process does not require any water, dispersing
agents or surfactants and also does not involve any
drying stage after dyeing. However, supercritical fluid
dyeing has not been adopted in any of the world dyeing
industries yet due to the high initial investment cost.
Therefore, it may be better to apply the SFD to the
hard-to-dye materials such as aramid, PE and PP fibers
and films.
Although extensive studies have been performed by
several researchers, only a limited amount of basic dyesorption
data is available. The amount of dye sorption
in polymers in the presence of supercritical carbon dioxide
is closely related to both the solubility of dye in
the fluids and the distribution of dye between the fluid
and the polymer phases. The mobility of dye molecules
between polymer chains is generally enhanced due to the
swelling of polymers in the supercritical fluids [13].
Park and Bae [14] performed the measurement of
equilibrium dye uptake in PET fiber at various temperatures
and pressures using a flow-method. The distribution
coefficient increases with the pressure increase,
because the sorption of dye in PET fiber increases more
slowly with the pressure than the dye solubility in carbon
dioxide does. This tendency is weakened with increase
of temperature [14].
Shim et al. [13] investigated sorption of some disperse
dyes (C. I. Disperse Blue 60 (B60), C.I. Disperse Red 60
(R60), C.I. Disperse Yellow 54 (Y54), and C.I. Disperse
Orange 30 (O30)) in polyethylene terephthalate (PET)
and polytrimethylene terephthalate (PTT) fibers as well
as difficult-to-dye fibers such as aramid and polypropylene
using supercritical carbon dioxide at pressures
between 10 and )33 MPa and temperatures between 35
and 150 °C. For dyeing in a co-solvent laden supercritical
fluid, ethanol, acetone, or N-methyl pyrrolidone
was also introduced in the dyeing vessel.
PET and PTT fibers were easily dyed with Y54 and
other dispersed dyes. The amount of sorption of Y54
dye in the crystalline polyester textile fibers increased
with increasing pressure up to 33 MPa at various temperatures.
The amount of sorption for PTT was (about
10%) larger than that for PET because PET has a high
degree of crystallinity of 30% which is larger than that
for PTT.
Dye molecules are generally large and their diffusion
rate is very small. They may penetrate only into the
glassy part and not in the crystalline part of a polymeric
matrix.
Dye sorption increased with pressure at the same
temperature and increased with temperature at the same
pressure, but this increasing rate was reduced with increasing
pressure [13].
Van der Kraan et al. [15] studied dyeing of synthetic
and natural textiles with a reactive dichlorotriazine dye
in the presence of supercritical carbon dioxide.
Experiments were carried out on polyester, silk, wool,
cotton and aminated cotton. Pressure and temperature
were varied from 225 to 278 bar and from 100 to 116 °C.
In these experiments a small quantity of water was added
as an enhancer of reactivity and/or accessibility of
the natural fibers. Polyester was dyed well, with fixation
percentages in the order of 95% and the color yield increased
with pressure, but not with temperature. Silk
and wool were dyed with a color yield independent of
pressure and temperature. Fixation percentages on silk
(76%) and wool (70%) were almost independent of
pressure and temperature. Comparison of the experimental
results with literature data shows that silk can

402 I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405
only be dyed in SCCO 2 when a small amount of water is
dissolved in the SCCO 2 and in the silk.
Cotton was dyed poorly under all conditions. Aminated
cotton was dyed better than cotton but not as well
as silk and wool. Fixation on aminated cotton was 87%.
It was concluded that dichlorotriazine dye can react in
moist SCCO 2 with amino groups of protein textile (e.g.
silk and wool) but not with hydroxyl groups of cellulosic
textiles (e.g. cotton) [15].
3.3. Organic metallic complexes impregnation
Synthesis of metallopolymer nanocomposites has attracted
much attention recently. Owing to their small
size, metal particles exhibit some unusual structural,
magnetic, catalytic and biological properties untypical
for large particles.
The process consists in the diffusion of an organometallic
compound from the supercritical solution into
the polymer matrix followed by its reduction/decomposition,
achieved by application of heat, chemical reagents
or radiations.
The method of impregnation from solution in SCCO 2
has several advantages:
1. The matrix tends to prevent an agglomeration of
metal particles.
2. SCCO 2 shows high penetrability into polymers.
3. It is possible to control the solvent power and the impregnation
rate and, therefore, to control the composition
and morphology of the obtained composite.
4. The final product does not require special drying.
5. Low surface tension allows impregnation even of
such barrier polymers as Teflon or obtaining of a
continuous metal layer on their surface [16].
Platinum (Pt) nanoparticles in poly(4-methyl pentene)
and poly(tetrafluoroethylene), silver (Ag) nanoparticles
on the surface of polyimide film, Ag nanoparticles in
poly(ethylether ketone) and poly(styleneme-divinyl benzene)
were investigated [17].
Preparation of noble metal (Pt, Pd) particle-dispersed
polyimide films as precursors of metal-doped carbon
molecular sieve membranes (CMS) was performed by
Yoda et al. [17] using impregnation of an acetyl-acetonate
complex dissolved in supercritical CO 2 .
Carbon molecular sieve membranes are known as
good gas separation membranes even at high temperature.
The gas separation properties of CMS membranes
can be controlled by doping metal particles having an
affinity to the relevant gas. Therefore, the hydrogen
separation performance of CMS is expected to be improved
by noble metals having an affinity to hydrogen.
Significant increase of the Pt content will depend on
the decomposition of polyimide catalyzed by Pt particles
during thermal treatment, and on the temperature. Since
the solubility of the Pt(II)(acac) 2 or Pd(II)(acac) 2 is independent
of the temperature, the increase of the metal
content should be ascribable to polyimide films, probably
to thermal relaxation of the polymer network. Both
Pt(II)(acac) 2 and Pd(II)(acac) 2 have similar solubility in
SCCO 2 . The high dispersion of Pd particles could be
related to lower decomposition temperature (>453 K in
air) than Pt(II)(acac) 2 (its melting point is 523 K) and to
chemical interactions with carboxyl structures of polyimide.
Nazem et al. [18] investigated the preparation of reflective
poly(etherether) ketone (PEEK) thin silvercoated
films via supercritical fluid impregnation with
CO 2 as the carrier and subsequent thermal reduction
of (1,5-cyclooctadiene-1,1,1,5,5,5-hexafluoroacetylacetonato)silver(I)
dimer, [Ag-(COD)HFA] 2 . No chemical
reducing agent was needed to effect silver reduction.
The resulting films were (a) reflective, (b) maintained
their flexible nature and (c) had a surface electrical resistance
higher than 10–11 X cm 1 , in spite of their
metallic appearance.
The reflectivity of the surface depends on the impregnation
and cure conditions. At constant CO 2 pressure
(15 MPa) and impregnation time (120 min) at 20%
additive, silver atomic concentration increased from
7.5% to 18.5% as the impregnation temperature increased
from 80 to 110 °C. At 10 wt.% additive and
constant temperature and pressure (110 °C and 15 MPa)
in another set of preliminary experiments, the amount of
silver increased from 9.6% to 15.5% in going from 60 to
120 min impregnation time. At constant impregnation
conditions (e.g. 110 °C, 15 MPa, 120 min) the amount of
silver on the surface decreased as the weight percent of
additive changed from 20% to 10% and 5%, as might
have been expected (e.g. 18.5%, 15.5%, 3.9%).
At constant CO 2 pressure, the reflectivity of the surface
increased increasing the impregnation temperature
and the impregnation time.
Thermal cure parameters at fixed impregnation conditions
suggested that lower cure temperatures require
longer cure times in order to obtain high reflectivity. Ten
nanometer diameter silver particles appeared in the film
bulk near the surface. Different sized silver clusters on
the surface could be grown by controlling the impregnation
and cure conditions. The silver on the surface
strongly adhered to the polymer surface [18].
New chelate complexes of copper diiminate (Cu(II)–
HFDI) and iron diiminate (Fe(III)–HFDI) were synthesized
by Said-Galiyev et al. [16]. The polymers
impregnated via supercritical CO 2 were polyarylate
(PAR) films with thicknesses of 12and 39 mm. The
equilibrium degree of polyarylate swelling in SCCO 2 at
45 °C and 8 MPa is 10%; this establishes the impregnation
operating conditions. In the case of Cu(II)–HFDI
the impregnation can be as large as 11–51% while the
content of pure copper in film is as large as 1.3–6.3 wt.%;

I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405 403
in the case of Fe(III)–HFDI it arrives at 57.6% while the
content of iron is 1.5–4.5%. It was shown that after
thermal heating the copper atom is in a nearly univalent
state. The size of metal-containing particles ranges from
15 to 60 nm (with a maximum at 34 nm), which corresponds,
for example, to the size range of catalytic particles
used in heterogeneous catalysis (2–50 nm) [16].
3.4. Monomer and initiator impregnation (polymer
blends)
One of the most interesting applications of supercritical
fluid impregnation is the modification of polymers
via the infusion of a monomer and an initiator into
aCO 2 -swollen polymer matrix with subsequent polymerization
of a monomer within the polymer matrix for
the preparation of polymer blends [19].
With SCCO 2 it is possible to obtain polymer modifications
by avoiding thermal stresses.
The impregnation of styrene and acrylic acid into a
series of polyamide products (nylon1212, nylon1010,
nylon66, nylon6) using supercritical CO 2 as additive
carrier and substrate-swelling agent was performed by
Xu and Chang [20].
The impregnation efficiency of additives into substrates
is attributed to complicated interactions within
the systems.
In the examined pressure range from 8 to 16 MPa,
acrylic acid always has a higher impregnation uptake
than styrene.
It was found that the relative solubility of the additive
in the polymer substrate and CO 2 is a major factor
governing the incorporated amount; however swelling of
the substrate and CO 2 -induced crystallization also contribute
to the value [20].
Li et al. [21] studied the preparation of nanometer
dispersed polypropylene/polystyrene (PP/PS) interpenetrating
networks (IPNs) by the radical polymerization
and crosslinking of styrene (St) within supercritical CO 2 -
swollen PP substrates. In this method, monomer styrene
(St), crosslinking agent divinyl benzene (DVB), and the
initiator benzoyl peroxide (BPO) were first impregnated
into PP matrix using SCCO 2 as a solvent and swelling
agent at 35.0 °C, and then the polymerization and
crosslinking were carried out at 120 °C.
The PP/PS IPNs mass uptake increases initially with
soaking time, and it is independent of soaking time after
about 13 h when equilibrium conditions are reached.
A maximum of PP/PS IPNs mass uptake is shown at
about 140 bar. This is due to the competition between
two opposite effects with increasing pressure: the degree
of swelling of the polymeric matrix and the solubility of
the monomers in the CO 2 -rich phase.
The composition of the IPNs can be controlled by
SCCO 2 pressure and concentrations of St and DVB in
the fluid phase.
The synthesis of conducting polymers has become an
important research area since its discovery in the past 20
years. Most conducting polymers, such as polypyrrole
(PPy), poly(3-octyl thiophene), polyaniline, were synthesized
by oxidative or electro-chemical polymerization [21].
One way to overcome the poor mechanical properties
of these conductive polymers is to blend them with another
insulating polymer.
Tang et al. [22,23] investigated the preparation of
electrically conductive polypyrrole–polystyrene composites
by supercritical carbon dioxide impregnation.
These authors studied:
1. The effect of the blending conditions;
2. The effect of doping conditions.
The host polymer was blended with pyrrole monomer
using either supercritical carbon dioxide or high-pressure
liquid carbon dioxide (HPLCO 2 ) near the supercritical
conditions as the carrying solvent. After the
blending process, the blended host polymer was soaked
in an oxidant metallic salt solution.
For blending the host polymer with pyrrole monomer,
SCCO 2 provides better conditions than HPLCO 2
at the same density. The maximum conductivity of the
polymer composites also increases with temperature and
pressure at the same SCCO 2 density and it is about one
order of magnitude higher in SCCO 2 than in HPLCO 2 .
This result can be explained by the swelling efficiency in
the blending period, which is a controlling factor for the
structure and conductivity of the resulting composites.
Referring to the doping conditions, acetonitrile and
water were used as the doping solvents and iron
perchlorate, and iron nitrate were selected as oxidants at
temperatures between 15 and 45 °C.
The maximum conductivity of the composites with
iron compounds as oxidants decreases in the following
order of anions: chloride > sulfate > perchloride > nitrate
in aqueous solutions [22,23].
The modification of the polymeric substrates bisphenol
A poly(carbonate) (PC), poly(vinyl chloride)
(PVC) and poly(tetrafluoro ethylene) (PTFE) by the
vinylic monomers styrene (S), methyl methacrylate
(MMA) and methacrylic acid (MAA) under supercritical
conditions was performed by Muth et al. [24].
The monomers solubility in SCCO 2 and their phase
behaviour have been investigated in order to achieve
impregnation in homogeneous phase and to prevent the
extraction of the impregnated monomers during the
polymerization.
At 40 °C pressure conditions must be higher than 11
MPa, while at 80 °C pressures below 11 MPa must be
chosen.
In a first step, the polymers were impregnated with
the monomers and a radical initiator (azoisobutyrodinitrile
(AIBN) for all cases), followed by a polymerization

404 I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405
inside the swollen substrates. The process parameters
were controlled by the concentration of the radical initiator
and by the solubility of the monomers in SCCO 2 .
As a result, PTFE shows the least ability to be
modified due to its limited swelling capability and high
crystallinity degree (impregnation occurs only in amorphous
domains).
In contrast the highest mass gains are obtained for
PC and PVC as substrates, and styrene and MMA as the
impregnating monomers.
PVC–PMAA was chosen as a model system for the
investigation of the limits of supercritical polymer
modification, because this system seems to be most interesting
for the possibility to generate a water-soluble
polymer PMAA inside a hydrophobic PVC matrix.
CO 2 treatment causes no changes in the chemical
structure of PVC since the thermogram of CO 2 -treated
PVC equals that of pure PVC. PMAA starts to decompose
by dehydration at 125 °C, and the decomposition
is complete by the degradation of the polymer
backbone at 400 °C, causing relatively high mass losses
in comparison to PVC and CO 2 -treated PVC [24].
One advantage of supercritical polymer modification
is the possibility to synthesize new polymer mixtures
with thermally unstable components.
With the generation of the water-soluble poly(methacrylic
acid) (PMAA) inside the hydrophobic PVC or
PMMA substrates, it was possible to obtain polymer
mixtures inaccessible by common techniques such as
melt mixing, because the PMAA would definitely decompose
during the extrusion at temperatures >175 °C.
4. Conclusions
An overview of supercritical impregnation processes
in the presence of supercritical fluids has been presented.
Supercritical carbon dioxide dissolved in glassy
polymers increases the diffusivities of additives in the
polymer matrix because of the CO 2 plasticization effect.
Supercritical fluid impregnation is a useful method
for the preparation of pharmaceutical forms. This
method presents the advantages related to the plasticizing
ability of the CO 2 that enhances drug diffusion
rates into the polymer and the ease of solvent removal.
Supercritical dye impregnation is a process based on
the affinity of the dye for the polymeric matrix. Moreover,
supercritical dye impregnation replaces water in
dyeing processes, overcoming the problem of wastewater
treatment.
SCF properties are successfully adopted for charging a
polymer matrix with metallic organic complexes in order
to prepare metal-containing nanocomposite metals.
An interesting application of supercritical impregnation
is the polymer blend preparation by the impregnation
of a polymer matrix with a monomer and an
initiator to perform the polymerization within the
polymer matrix. With this particular method it is possible
to obtain polymer blends not easy obtainable with
common techniques, i.e. melt mixing.
References
[1] Zhou H, Fang J, Yang J, Xie X. Effect of the supercritical CO 2 on
surface structure of PMMA/PS blend thin films. J Supercrit Fluids
2003;26:137–45.
[2] Wang Y, Yang C, Tomasko D. Confocal microscopy analysis of
supercritical fluid impregnation of polypropylene. Ind Eng Chem
Res 2002;41:1780–6.
[3] Diankov S, Barth D, Subra P. Supercritical impregnation
isotherm of O-HBA on PMMA in batch stirred reactor. In: 6th
International Symposium on Supercritical Fluids, 2003. p. 1599–
604.
[4] Kazarian SG, Martirosyan GG. Spectroscopy of polymer/drug
formulations processed with supercritical fluids: in situ ATR-IR
and Raman study of impregnation of ibuprofen into PVP. Int J
Pharm 2002;232:81–90.
[5] Alessi P, Cortesi A, Kikic I, Vecchione F. Plasticization of
polymers with supercritical carbon dioxide: experimental determination
of glass-transition temperatures. J Appl Polym Sci
2003;88:2189–93.
[6] Kikic I, Vecchione F, Alessi P, Cortesi A, Eva F, Elvassore N.
Polymer plasticization using supercritical carbon dioxide: experiment
and modeling. Ind Eng Chem Res 2003;42:3022–9.
[7] Condo PD, Sanchez IC, Panayiotou GC, Johnston KP. Glass
transition behaviour including retrograde vitrification of polymers
with compressed fluid diluents. Macromolecules
1992;25:6119–27.
[8] Kikic I, Vecchione F, Elvassore N. Thermodynamic analysis of
the effect of supercritical fluids on the glass transition temperature.
In: 2nd International Meeting on High-Pressure Chemical Engineering,
2001.
[9] Wissinger RG, Paulaitis ME. Molecular thermodynamic model
for sorption and swelling in glassy polymer––CO 2 systems at
elevated pressures. Ind Eng Chem Res 1991;30:842–51.
[10] Doghieri F, Sarti GC. Nonequilibrium lattice fluids: a predictive
model for the solubility in glassy polymers. Macromolecules
1996;29:7885–96.
[11] Alessi P, Cortesi A, Kikic I, Scotti F, Vecchione F. Sorption of
supercritical carbon dioxide in copolymers: use of the NELF
model. In: 5th International Symposium on Supercritical Fluids,
2000.
[12] Guney O, Akgerman A. Synthesis of controlled-release products
in supercritical medium. AIChE J 2002;48:856–66.
[13] Shim JJ, Choi JH, Ju JH, Son BK, Ahn JM, Kim BH, et al.
Dyeing of polyester, aramid and polypropylene fibers in supercritical
CO 2 . In: 6th International Symposium on Supercritical
Fluids, 2003. p. 2101–6.
[14] Park MW, Bae HK. Dye distribution in supercritical dyeing with
carbon dioxide. J Supercrit Fluids 2002;22:65–73.
[15] Van der Kraan M, Bayrak O, € Fernandez Cid MV, Woerlee GF,
VeugelersW JT, Witkamp GJ. Textile dyeing in supercritical
carbon dioxide. In: 6th International Symposium on Supercritical
Fluids, 2003. p. 2119–24.
[16] Said-Galiyev E, Nikitin L, Vinokur R, Gallyamov M, Kurykin M,
Petrova O, et al. New chelate complexes of copper and iron:
synthesis and impregnation into a polymer matrix from solution
in supercritical carbon dioxide. Ind Eng Chem Res 2000;39:
4891–6.

I. Kikic, F. Vecchione / Current Opinion in Solid State and Materials Science 7 (2003) 399–405 405
[17] Yoda S, Hasegawa A, Suda H, Uchimaru Y, Haraya K, Tsuji T, et al.
Preparation of polymer metal composite film as a precursor of metal
doped carbon membrane via supercritical impregnation. In: 6th
International Symposium on Supercritical Fluids, 2003. p. 1981–6.
[18] Nazem N, Taylor LT, Rubira AF. Metallized poly(etherether
ketone) films achieved by supercritical fluid impregnation of a
silver precursor followed by thermal curing. J Supercrit Fluids
2002;23:43–57.
[19] Kazarian SG. Polymer processing with supercritical fluids. Polym
Sci, Ser C 2000;42:78–101.
[20] Xu Q, Chang Y. Complex interactions among additive/supercritical
CO 2 /polymer ternary systems and factors governing the
impregnation efficiency. In: 6th International Symposium on
Supercritical Fluids, 2003. p. 1577–83.
[21] Li D, Liu Z, Han B, Song L, Yang G, Jiang T. Preparation of
nanometer dispersed polypropylene/polystyrene interpenetrating
network using supercritical CO 2 as a swelling agent. Polymer
2002;43:5363–7.
[22] Tang M, Wen T-Y, Du T-B, Chen Y-P. Synthesis of electrically
conductive polypyrrole–polystyrene composites using supercritical
carbon dioxide: I. Effects of the blending conditions. Eur
Polym J 2003;39:143–9.
[23] Tang M, Wen T-Y, Du T-B, Chen Y-P. Synthesis of electrically
conductive polypyrrole–polystyrene composites using supercritical
carbon dioxide: II. Effects of the doping conditions. Eur Polym
J 2003;39:151–6.
[24] Muth O, Hirth Th, Vogel H. Polymer modification by supercritical
impregnation. J Supercrit Fluids 2000;17:65–72.