Preparation of remarkably tough polyHIPE materials via polymerization of oil-in-water HIPEs involving 1-vinyl-5-aminotetrazole

Article abstract of DOI:10.1002/pola.24075

Interconnected microcellular polymeric monoliths having unexpected high mechanical strength have been prepared using the high internal phase emulsion (HIPE) methodology. Oil-in water concentrated emulsions of aqueous 1-vinyl-5amino [1,2,3,4]tetrazole (1-VAT) mixed with a low molar ratio (7%) of N,N′-methylenebisacrylamide as crosslinking agent were prepared using dodecane as dispersed phase and a mixture of hydrophilic surfactants. "Reverse" polyHIPE materials were obtained after radical copolymerization, solvent extraction, and drying. Their morphology, chemical composition, and physicochemical behavior are discussed.

Full text of DOI:10.1002/pola.24075

Preparation of Remarkably Tough PolyHIPE Materials via Polymerization
of Oil-in-Water HIPEs Involving 1-Vinyl-5-Aminotetrazole
1
2
3
1
1
´
´
CARLOS YOUSSEF, RENAL BACKOV, MONA TREGUER, MARC BIROT, HERVE DELEUZE
1
Institut des Sciences Mol e´ culaires, Universit e´ de Bordeaux, UMR 5255-CNRS, 351 cours de la Lib e´ ration, 33405 Talence, France
Centre de Recherche Paul Pascal, Universit e´ de Bordeaux, UPR 8641-CNRS, 115 Avenue Albert Schweitzer, 33600 Pessac, France
Institut de Chimie de la Mati e` re Condens e´ e, Universit e´ de Bordeaux, UPR 9048-CNRS, 87 Avenue Albert Schweitzer, 33608
2
3
Pessac, France
Received 26 March 2010; accepted 15 April 2010
DOI: 10.1002/pola.24075
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Interconnected microcellular polymeric monoliths
having unexpected high mechanical strength have been pre-
pared using the high internal phase emulsion (HIPE) methodol-
ogy. Oil-in water concentrated emulsions of aqueous 1-vinyl-5-
were obtained after radical copolymerization, solvent extrac-
tion, and drying. Their morphology, chemical composition, and
physicochemical behavior are discussed. VC 2010 Wiley Periodi-
cals, Inc. J Polym Sci Part A: Polym Chem 48: 2942–2947, 2010
amino [1,2,3,4]tetrazole (1-VAT) mixed with a low molar ratio
0
(
7%) of N,N -methylenebisacrylamide as crosslinking agent
KEYWORDS: atom transfer radical polymerization (ATRP); block
copolymers; nitroxide radical coupling; polystyrene; single
electron transfer living radical coupling
were prepared using dodecane as dispersed phase and a mix-
ture of hydrophilic surfactants. ‘‘Reverse’’ polyHIPE materials
INTRODUCTION Vinyltetrazoles constitute a relatively novel
various environmental problems or for the isolation of pre-
cious metals. In the medical domain, tetrazole-containing
polyelectrolytes manifest pronounced, sometimes extraordi-
nary high, immunoadjuvant activity toward a vast range of
antigens. At that time, in spite of the broad spectrum of
properties of vinyltetrazole-based polymers, there is no
report on the preparation of rigid porous materials contain-
ing this kind of structure. In the course of our researches on
class of monomers. The first representatives of vinyltetra-
1
zoles were obtained 50 years ago by Finnegan and Henry
who proposed to use tetrazole-containing polymers as bind-
ing agents in the production of gunpowder and matches. A
recent comprehensive review describes the synthesis and
1
1
2
properties of vinyltetrazoles. Aminotetrazoles are nitrogen-
rich molecules, for example, 82.3 wt % for 5-aminotetrazole
(
5-AT) and 63.1 wt % for 1-VAT that possess the unique
the development of new kind of porous polymers using the
3
property to combine high positive heat of formation with
good thermal stability, because of their aromatic ring sys-
tem. Therefore, aminotetrazoles derivatives are prospective
materials for generation of gases, as blowing agents, solid
propellants and other combustibles, and thermally decom-
12–16
emulsion-template approach,
we decided to investigate
the potentialities of 1-VAT to give hydrophilic, self-standing
monoliths having potentially interesting applications in area
such as supports for heterogeneous catalysis or metal-com-
plexing devices.
4
,5
6
,7
posing systems.
Furthermore, polymeric material consti-
tuted of nitrogen-rich monomers can be seen as ‘‘green poly-
mers,’’ considering that end-of-life thermal degradation,
would generate mainly molecular nitrogen, which is an in-
Emulsion templating is a simple and versatile method for
the preparation of microcellular materials (cell size range
2–100 lm) by polymerizing the continuous phase of a high
internal phase emulsion (HIPE), the obtained materials hav-
ing been called polyHIPEs by Unilever researchers. Theo-
retically, the final solid polymer is expected to have an open-
cell morphology only for a sufficiently concentrated HIPE
8
nocuous gas. Polyvinylaminotetrazoles are carbochain poly-
1
7
mers with pendant aminotetrazole groups obtained by radi-
cal polymerization of a vinylaminotetrazole monomer. On
thermal decomposition at rather high temperature, Polyviny-
laminotetrazoles produce a relatively important solid residue
(dispersed phase volume fraction >74% of the total emul-
ꢀ
18,19
that is thermostable at 600 C and that consists of a cross-
sion).
However, this structure has been observed for
9
20
linked polymer network. Taking into consideration high
lower values. The historic polyHIPE preparation involves
the formation of a stable, water-in-oil concentrated emulsion
using hydrophobic monomers as part of the continuous
phase (mostly a mixture of styrene and divinylbenzene with,
complex-forming ability of polyvinyltetrazoles with respect
1
0
to heavy ions in aqueous media, it may be expected that
these polymers will find use as efficient sorbents to answer
Correspondence to: H. Deleuze (E-mail: h.deleuze@ism.u-bordeaux1.fr)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2942–2947 (2010) V
2010 Wiley Periodicals, Inc.
C
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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
optionally, the addition of a functionalized styrene such as 4-
vinylbenzyl chloride) and an aqueous phase as the dispersed
phase. A great deal of work coming from a continuously
increasing number of researchers has been devoted to the
vacuum to give a white paste. Recrystallization from water
followed by drying under vacuum under P O to give 1-VAT
2 5
as a white hygroscopic solid (1.2 g, yield ¼ 83%), mp 155–
ꢀ
ꢀ
ꢁ1
156 C (ref. 44 mp 156–158 C). IR (cm ): 3456, 2143,
2
1–26
1
study of this particular system.
The main topics studied
1641, 1517, 1641, 1517, 1416, and 1119. H NMR (300 MHz,
3
3
have been the good control of the porous morphology (voids
DMSO-d , ppm) 6.84 ( J ¼ 8.5 Hz, Jtrans ¼ 15.8 Hz, 1H),
6
cis
2
7–32
2
3
2
and interconnecting windows size dispersion),
and
6.0 ( J ¼ 1.6 Hz, J
¼ 15.8 Hz, 1H), and 5.76 ( J ¼ 1.6 Hz,
trans
3
13
attempts to increase the mechanical strength of the material
that is, in the native formulation, usually considered as insuf-
J
¼ 8.5 Hz, 1H), 4.45 (2H). C NMR (150 MHz, DMSO-d ,
cis
6
ppm), 154.7 (1C), 126.1 (1C), and 106.6 (1C). Anal. calcd for
C H N : C, 32.43; H, 4.43; N, 63.03. Found: C, 32.30; H, 4.44;
3
3–35
ficient for practical applications.
Efforts have been made
3
5 5
as well on the use of hydrophobic (meth)acrylate deriva-
N, 63.26.
3
6,37
tives,
whereas less work has been published on the syn-
Bulk Polymerization
A mixture of 1-VAT (600 mg, 5.3 mmol) and MBA (61 mg,
thesis of polyHIPE based on hydrophilic (i.e., water soluble)
monomers emulsified by an hydrocarbon. Krajnc et al.
reported the preparation of the so-called ‘‘reverse’’ polyHIPE
by polymerization of an oil-in-water HIPE consisting of an
0.4 mmol) was mixed with Vazo 88 (5 mg, 0.2 mmol) and
ꢀ
heated at 90 C for 48 h under a nitrogen flow. The precipi-
tate was filtered, washed with ethanol then dried under vac-
uum (624 mg, yield ¼ 94%).
0
aqueous mixture of acrylic acid and N,N -methylenebisacryla-
mide (MBA) as the continuous phase and toluene as the dis-
3
8
persed phase. Superabsorbents have been prepared using
HIPE Preparation and Polymerization
3
9
a similar approach. Concomitantly, Barbetta et al. prepared
gelatin- and dextran-methacrylate polyHIPE scaffolds using
The emulsification device is constituted of a 500-mL hemi-
spherical reactor vessel equipped with an overhead stirrer
motor connected with a stirring rod fitted with a D-shaped
paddle. Emulsifications were performed at room tempera-
ture. In a typical experiment, 1-VAT (10.0 g), Igepal CO-890
4
0,41
oil-in-water concentrated emulsions.
The use of hetero-
cyclic vinyl monomers for the preparation of polyHIPEs
materials has been scarcely studied: maleimide and bismalei-
mide monomers have been copolymerized with styrene in
concentrated water-in-oil emulsions to give polyHIPEs with
(
2.6 g), Brij 98 (2.6 g), MBA (1.0 g), Vazo 88 (0.4 g), and
double-distilled water (20 g) were placed in a test tube. The
mixture was homogenized at room temperature using ultra-
sounds then poured into the emulsification vessel. The dis-
persed phase (dodecane, 70 mL) was slowly added over a
period of 30 min using a syringe pump to the aqueous phase
and continuously stirred at 300 rpm. The thick, white opa-
que emulsion thus obtained was then placed in cylindrical
PTFE molds avoiding, as much as possible, air bubble
entrapment. The filled molds were placed in an oven and
heated at 70 C (24 h) then at 90 C (24 h) for polymeriza-
tion. After cooling at room temperature, the resulting cylin-
drical monoliths were carefully demoulded and then
extracted with refluxing ethanol (24 h) using a Soxhlet appa-
4
2
increased thermal resistance. Poly(aryl ether sulfone) poly-
HIPE materials have been synthesized by copolymerizing a
maleimide-terminated aryl ether sulfone macromonomer
4
3
with styrene and divinylbenzene in a nonaqueous HIPE.
However, to our best knowledge, no report deals with the
use of hydrophilic nitrogen-rich monomers to prepare mono-
lithic rigid polymers using the polyHIPE approach.
EXPERIMENTAL
ꢀ
ꢀ
Materials
0
N,N -MBA, tetrabutylammonium chloride and dodecane were
purchased from Acros Organics. Potassium persulfate (99%
þ, A.C.S. reagent), 5-amino-1H-tetrazole (5-AT), 1-bromo-2-
chloroethane, 1,4-diazabicyclo[2.2.2]octane (DABCO), poly-
oxy-ethylene (20) oleyl ether (Brij 98), polyoxyethylene (40)
ꢀ
ratus, then dried in a vacuum oven at 50 C until constant
weight.
Characterization of the Monoliths
Porosity Determination
0
nonylphenyl ether (Igepal CO-890), and 1,1 -azobis(cyclohex-
anecarbonitrile) (Vazo 88), were purchased from Aldrich. All
these chemicals were used as received.
The effective porosity and the connection size distribution of
each sample were determined by mercury intrusion poros-
imetry using a Micromeritics Autopore IV 9500 porosimeter.
The reported average connection size is the median pore di-
ameter by volume.
Synthesis of 1-VAT
5-AT (1 g, 12 mmol) was placed in a 50 mL, two-neck flask
under magnetic stirring. Acetonitrile (22 mL) was then
added, followed by 1-bromo-2-chloroethane (6.9 g, 48
mmol). After complete dissolution, water (1.1 mL), sodium
hydroxide (0.72 g, 18 mmol), and tetrabutylammonium chlo-
ride (33 mg, 0.12 mmol) were added to the solution. The
Specific Surface Area and Mesoporosity Determination
The specific surface area was determined by N2 adsorption
measurements performed on a Micromeritics ASAP 2010.
The collected data were subjected to the Brunauer, Emmett,
ꢀ
mixture was heated at 70 C for 18 h under stirring. After
45
and Teller treatment.
cooling at room temperature, the mixture was concentrated
under reduced pressure. The obtained residue was diluted
with dichloromethane (14 mL). DABCO (1.0 g, 8.8 mmol)
was then added, and the solution was stirred for 1 h under
strong stirring. The thick suspension was then filtered under
Electron Microscopy Investigations
The morphology of the monoliths was observed by scanning
electron microscopy (SEM) in a Hitachi TM-1000 microscope.
Photographs were taken at several different magnifications
PREPARATION OF TOUGH POLYHIPE MATERIALS, YOUSSEF ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
4
4
synthetic route was proposed later by a Russian team who
realized the direct vinylation of 5-AT with mercury vinylace-
tate in the presence of mercury acetate/boron trifluori-
de:etherate complex. In spite of the acceptable yields
reported, the toxicity of the chemicals employed conducted
us to try to improve the early alkylation-dehalogenation
route. The route followed is disclosed in Scheme 1. In a first
step, 2-chloroethanol was replaced by the more reactive 1-
bromo-2-chloroethane. The reaction, conducted under cata-
lytic phase transfer conditions, gave access to 1-(2-chlor-
oethyl)-5-amino[1,2,3,4]tetrazole exclusively (not isolated),
SCHEME 1 Synthetic route to 1-VAT.
between ꢂ1000 and ꢂ10,000. Pieces of polyHIPEs (section
2
of about 0.5 cm ) cut from the corresponding monoliths
were mounted on a carbon tab, which ensured a good con-
ductivity. A thin layer of gold was sputtered on the fragment
before analysis. An average void diameter was estimated for
some samples from SEM micrographs after image processing
with Scion Image freeware (Scion Corp., Frederick, MA). The
mean and the standard deviation were drawn by manual
measurements of diameters from a population of at least 50
cells. To get a better estimation of the real void diameter, a
statistical correction was introduced by multiplying the
4
6
without diaddition product. Dehydrohalogenation in the
4
7
second step was a modification of a published procedure
using sodium hydroxide in the presence of DABCO. The
global yield of this ‘‘one pot’’ synthesis was reproducibly 80–
4
8 1
8
5% based on 5-AT. The obtained product showed IR,
H,
1
3
49
and C NMR spectra and elemental analysis data corre-
sponding with the expected structure and previously
reported data. X-ray molecular and crystal structures have
1
/2 32
observed average value by a factor K ¼ 2/(3 ).
5
0
Mechanical Analysis
been reported recently.
Compression tests were done by the P oˆ le Europ e´ en de Plas-
turgie (Oyonnax, France) at room temperature on a Zwick
Study of the Copolymerization of 1-VAT with MBA
1
455 dynamometer with a loading cell of 200N. Cylindrical
1-VAT being much more soluble in water than in hydrocar-
bons, the emulsion to be prepared must be of the direct
type. Therefore, the crosslinking agent has to be also water
soluble. We made the choice of the commercially available
samples (diameter ¼ 8 mm and thickness ¼ 10 mm) were
ꢁ
1
compressed at constant speed rate (1 mm min ) on their
flat surfaces. The mean and the standard deviation of the
Young’s modulus E were calculated from the data obtained
with five samples of the same composition.
0
N,N -MBA (MBA). Published polymerization reports involving
1-VAT are scarce and somewhat contradictory. However, the
majority of the data seems to indicate that this compound
manifests a modest activity in the copolymerisation with
usual comonomers. For example, the Kelen-Tudos copolymer-
ization constants r for 1-VAT (1) and a second monomer (2)
Thermogravimetric Analysis
Weight loss studies of the monoliths were performed on a
Netzsch STA 409 under N56 argon atmosphere. The heating
rate was 10 C min and the temperature ranged from 25
to 1000 C.
ꢀ
ꢁ1
ꢀ
in DMF were found to be r
1
¼ 0.32, r
2
¼ 1.40 with sty-
5
1
52
rene, and, r ¼ 0.15, r ¼ 0.78 with N-vinylpyrrolidone.
1
2
Elemental Analysis
Elemental analyses were performed by the Service Central
d ’A nalyses (Vernaison, France).
In water, the reactivity is reported to be higher but without
5
3
precise data. Therefore, we decided to verify, in a first
time, the bulk radical copolymerization ability of 1-VAT with
MBA. A mixture of 1-VAT with MBA (7 mol %) was heated at
RESULTS AND DISCUSSION
ꢀ
60 C using potassium persulfate as the initiator, only a very
1
-VAT was synthesized for the first time about 50 years
low yield of polymer was obtained after 48 h. We thought
that a higher temperature was necessary to promote the po-
lymerization. For doing so, we decided to use a high-temper-
1
ago. The route used was the alkylation of 5-amino[1,2,3,4]-
tetrazole with 2-chloroethanol to obtain 1-(2-hydroxyethyl)-
0
5-amino[1,2,3,4]tetrazole, which was then treated with thi-
ature polymerization initiator: 1,1 -azobis(cyclohexanecarbo-
5
4
onyl chloride in carbon tetrachloride. The resulting 1-(2-
chloroethyl)-5-amino[1,2,3,4]tetrazole derivative was subse-
quently dehydrohalogenated by a base-catalyzed thermal
reaction. The target compound was obtained with a global
yield of about 20% in three steps from 5-AT. An alternative
nitrile), available from Dupont under the trade name Vazo
88. Vazo 88 is characterized by a half-life time (t1/2)of 10 h
ꢀ
at 88 C, whereas the same t1 value is obtained for AIBN
/2
(azobisisobutyronitrile) or potassium persulfate around
ꢀ
55
70 C. The reaction duration was set to at least 5 ꢂ t1/2 to
TABLE 1 Formulations of 1-VAT/MBA HIPEs
a
1
-VAT
MBA
(g)
Surfactant
(S ) (g)
þ S
Radical
H
2
O
Dodecane
(g)
Sample
(g)
1
2
Initiator (g)
(g)
VAT1
VAT2
VAT3
a
10.0
10.0
10.0
1.0
1.0
1.0
(2.6 þ 2.6)
(2.6 þ 2.6)
(2.6 þ 2.6)
0.4
0.4
0.4
20
20
20
70
120
160
S
1
¼ Brij 98, S ¼ Igepal CO-890.
2
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ARTICLE
FIGURE 1 SEM micrographs of PVAT1 sample (ꢂ5000 and ꢂ10,000).
ꢀ
ensure 97% decomposition of the initiator (i.e., 48 h reaction
time). An acceptable yield of 1-VAT/MBA copolymer (94%)
was obtained using Vazo 88 at 90 C for 48 h. This initiator
moval, was observed around 100 C, followed by an impor-
ꢀ
tant weight loss beginning around 250 C. The final weight
ꢀ
ꢀ
residue at 1000 C is about 10%.
was then solely used in the following of this work.
Porosity Analyses and Compressive Strength
Determination
Formulation of a Stable VAT-MBA Oil-in-Water HIPE and
PolyHIPE Preparation
Porosity characteristics and specific surface area were deter-
mined for all samples prepared. Stress-strain analyses in
compression were conducted at room temperature for all
samples prepared. The corresponding values are reported in
Table 2.
Both monomers being water soluble, the dispersed phase of
the oil-in-water concentrated emulsion should be a hydrocar-
bon such as dodecane. The choice of the surfactant is crucial
for the formation and stability of an emulsion. A (50:50 wt
%
) mixture of two nonionic surfactants, Brij 98 (hydrophilic-
lipophilic balance (HLB) ¼ 15.3) and Igepal CO-890 (HLB ¼
7.8), that we already used for similar oil-in-water emulsion
The calculated porosity of polyHIPE materials, /total, can be
estimated assuming complete removal of all the nonpolymer-
izable components of the emulsion (dispersed phase, water,
and surfactant) and in the absence of any shrinking of the
monolith during washing and drying. /disp is the calculated
porosity considering only the dispersed/continuous phase
volume ratio. /exp is the experimental porosity of the mate-
rial as estimated by mercury intrusion analysis.
1
5
6
formulation, was used in this study. 1-VAT being solid at
room temperature, the continuous phase was an aqueous so-
lution of the comonomers. The corresponding HIPE formula-
tions are reported in Table 1.
The stability of the emulsions was appreciated by visual ob-
servation. HIPEs prepared with the formulations reported in
Table 1 gave emulsions stable over more than 1-week stand-
ing at room temperature without creaming. HIPE samples
The /exp of each sample was closer to the corresponding
expected value considering only the dispersed/continuous
phase volume ratio (/disp) than to the total calculated poros-
ity value (/total), confirming the low shrinkage observed for
the monoliths, but indicating a collapse of the copolymer
network into the material walls during the water removal. In
ꢀ
ꢀ
were heated at 70 C for 24 h then at 90 C for 24 h to
achieve complete radical polymerization. The obtained 1-
VAT/MBA polyHIPE monoliths were extracted with ethanol
ꢀ
and finally dried at 50 C under vacuum until constant
weight (average yield ¼ 85%). It was observed a rather
reduced shrinking level for all samples with a slight augmen-
tation when increasing the material porosity. SEM analysis
revealed that sample PVAT1 possesses the characteristic
macroporous and open-cell structure of polyHIPE materials
(
Fig. 1).
Thermal Analysis
-VAT/MBA polyHIPE monoliths thermal degradation was
1
examined by thermogravimetric analysis. These materials
being hygroscopic, samples were dried under vacuum at 100
ꢀ
C and stored in a desiccator before analysis. Figure 2
reports the thermogram obtained for sample PVAT1 by heat-
ꢀ
ꢀ
ing under argon from 40 C to 1000 C. A mass fraction loss
of 6%, which may be attributed to the bonded water re-
FIGURE 2 Thermogravimetric analysis of PVAT1.
PREPARATION OF TOUGH POLYHIPE MATERIALS, YOUSSEF ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Porosity Characteristics and Stress-Strain Analysis of 1-VAT/MBA PolyHIPE Monoliths
Specific Surface
Area (Brunauer,
Average
Average
Void Size
(lm)
Young’s
Modulus
(MPa)
a
b
c
e
/
total
/
disp
/
exp
Emmett, and Teller)
Connection
2
ꢁ1
d
Sample
(%)
(%)
(%)
(m
g
)
Size (nm)
PVAT1
PVAT2
PVAT3
a
92
95
96
76
85
88
77.6 6 0.1
86.1 6 0.1
88.3 6 0.1
15.7 6 0.1
34.8 6 0.1
36.1 6 0.1
215.0 6 0.1
173.4 6 0.1
153.6 6 0.1
1.6 6 0.1
1.5 6 0.1
1.8 6 0.1
65.5 6 25.7
22.4 6 2.7
22.9 6 4.9
c
Total calculated porosity.
Experimental porosity estimated by mercury porosimetry.
Estimated by mercury porosimetry.
Estimated from SEM micrographs.
b
d
e
Porosity expected from the volume fraction of dispersed phase in the
emulsion.
other words, the water initially present in the continuous
phase has no porogenic behavior in that case.
REFERENCES AND NOTES
3
1,32
1
Finnegan, W. G.; Henry, R. A.
J
Org Chem 1959, 24,
The porosity morphology (average voids and connections
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1565–1567.
2
Kizhnyaev, V. N.; Vereshchagin, L. I. Russ Chem Rev 2003,
2, 143–164.
3
8
‘‘reversed’’ polyHIPEs materials. The specific surface area
7
values obtained are rather low and attest the nonporogenic
behavior of water. These results confirm that there is no (or
few) mesopores into the material walls, because of the afore
mentioned significant collapse of the polymeric network dur-
ing the removal of the water.
3
Kozyro, A. A.; Simirsky, V. V.; Krasulin, A. P.; Sevruk, V. M.;
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4 Levchik, S. V.; Ivashkevich, O. A.; Balabanovich, A. I.;
Lesnikovich, A. I.; Gaponik, P. N.; Costa, L. Thermochim Acta
The obtained compressive Young’s modulus values are very
high for nonreinforced organic polyHIPE materials, consider-
ing that the nominative molar crosslinking level was only
1
992, 207, 115–130.
5 Levchik, S. V.; Balabanovich, A. I.; Ivashkevich, O. A.;
Lesnikovich, A. I.; Gaponik, P. N.; Costa, L. Thermochim Acta
1993, 225, 53–65.
7%. As an example, a styrene/divinylbenzene (equimolar
mixture) polyHIPE with 83% porosity gave a compressive
1
3
modulus of only about 19.5 MPa. This unexpected high me-
chanical strength for the polyHIPE materials prepared in this
work with a rather low crosslinking level could be explained,
at least in part, by the specific properties of the principal
monomer used. Water solubility of polyvinylazoles is associ-
ated with the presence of basic nitrogen atoms of pyridine
type in the heterocycles that tend to form hydrogen bonds
6
Lund, G. K.; Blau, R. J. (to Thiokol Co.). U.S. Pat. 5,500,059
(
1996).
7
Ramaswamy, C. P.; Grzelczyk, C. (to Breed Automotive Tech-
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8 Stierstofer, J.; Tarantik, K. R.; Klapotke, T. M. Chem Eur J
2009, 15, 5775–5792.
5
7
with water molecules, as evidenced by NMR. These bonds
may generate strong interactions between polymeric chains,
increasing their mechanical strength. A more extensive study
of this behavior is still under development in our group to
conclude on this topic.
9
Levchik, S. V.; Balabanovich, A. I.; Ivashkevich, O. A.; Gaponik,
P. N.; Costa, L. Polym Degrad Stab 1995, 47, 333–338.
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0 Igrunova, A. V.; Sirotinkin, N. V.; Uspenskaya, M. V. Russ J
Appl Chem 2001, 74, 818–821.
1
1 Annenkov, V. V.; Kruglova, V. A.; Kazimirovskaya, V. B.;
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Pharm Chem J 1995, 29, 42–44.
CONCLUSIONS
1
2 L e´ pine, O.; Birot, M.; Deleuze, H. Macromol Mater Eng 2009,
In this work, we have prepared polyHIPE materials based on
2
94, 599–604.
0
1-vinyl-5-aminotetrazole copolymerized with N,N -MBA as
crosslinker. The obtained monoliths present the expected
open-cell morphology but behave like an unusual high me-
chanical strength to compression, particularly considering
the modest crosslinking level involved. This kind of materials
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materials, as well as reactive hyperporous polymers, as cata-
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