Organic sol-gel synthesis of microporous molecular networks containing spirobifluorene and tetraphenylmethane nodes

Article abstract of DOI:10.1002/pola.26552

The microporous molecular networks based on rigid tetrafunctional units are synthesized via organic sol-gel polymerization of 2,2′,7,7′- tetraamino-9,9′-spirobifluorene (TASBF) and/or tetrakis(4-aminophenyl) methane (TAPM) with a diisocyanate, hexamethylene diisocyanate (HDI), or p-phenylene diisocyanate. This study is performed as an extension of our previous report on the first organic sol-gel method, which enabled the synthesis of microporous molecular networks via a two-stage mechanism involving the formation of colloidal dispersions of the nanoparticulate molecular networks and their subsequent growth to monolithic networks on solvent evaporation. The sol-gel-synthesized molecular networks obtained by incorporating TASBF as a network former show improved porosity, processability, and thermal stability than the TAPM-based system. The improved porosity of TASBF-based networks is attributed to higher rigidity of the spirobifluorene compared with the tetraphenylmethane units. We also demonstrate the synthesis of mixed organic molecular networks by sol-gel copolymerization of the two network formers, TASBF and TAPM, and a diisocyanate monomer. The sol-gel transformation of TASBF/TAPM/HDI occurred at longer reaction times with increasing the amount of TASBF in the TASBF/TAPM/HDI mixture. The results indicate that the organic sol-gel method can be further optimized by adjusting various synthesis parameters to create new functional organic molecular network materials.

Full text of DOI:10.1002/pola.26552

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Organic Sol–Gel Synthesis of Microporous Molecular Networks
Containing Spirobifluorene and Tetraphenylmethane Nodes
Su-Young Moon, Hye-Rim Mo, Min-Kyoon Ahn, Jae-Sung Bae, Eunkyung Jeon,
Ji-Woong Park
Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, 261 Cheomdan-gwagiro,
Buk-gu, Gwangju 500-712, Korea
Correspondence to: J.-W. Park (E-mail: jiwoong@gist.ac.kr)
Received 1 November 2012; accepted 18 December 2012; published online 28 January 2013
DOI: 10.1002/pola.26552
ABSTRACT: The microporous molecular networks based on rigid
of the spirobifluorene compared with the tetraphenylmethane
units. We also demonstrate the synthesis of mixed organic mo-
lecular networks by sol–gel copolymerization of the two network
formers, TASBF and TAPM, and a diisocyanate monomer. The
sol–gel transformation of TASBF/TAPM/HDI occurred at longer
reaction times with increasing the amount of TASBF in the
TASBF/TAPM/HDI mixture. The results indicate that the organic
sol–gel method can be further optimized by adjusting various
synthesis parameters to create new functional organic molecular
network materials. VC 2013 Wiley Periodicals, Inc. J. Polym. Sci.,
tetrafunctional units are synthesized via organic sol–gel polymer-
0
0
0
ization of 2,2 ,7,7 -tetraamino-9,9 -spirobifluorene (TASBF) and/or
tetrakis(4-aminophenyl)methane (TAPM) with a diisocyanate,
hexamethylene diisocyanate (HDI), or p-phenylene diisocyanate.
This study is performed as an extension of our previous report
on the first organic sol–gel method, which enabled the synthesis
of microporous molecular networks via a two-stage mechanism
involving the formation of colloidal dispersions of the nanoparti-
culate molecular networks and their subsequent growth to mon-
olithic networks on solvent evaporation. The sol–gel-synthesized
molecular networks obtained by incorporating TASBF as a net-
work former show improved porosity, processability, and ther-
mal stability than the TAPM-based system. The improved
porosity of TASBF-based networks is attributed to higher rigidity
Part A: Polym. Chem. 2013, 51, 1758–1766
KEYWORDS: adsorption; copolymerization; crosslinking; kinetics
(polym.); microporous polymer network; organic molecular
networks; organic sol–gel synthesis; spirobifluorene
1
5,20,32–36
INTRODUCTION Microporous materials with high surface
units.
These materials consist of the molecular net-
2
ꢀ1
area (200–8000 m g ) and small pore size (<2 nm) have
long been regarded important for various energy- and envi-
ronment-related technology such as gas storage and separa-
works whose crosslink sizes are on the molecular length
scale. However, most of the network materials synthesized to
date, either crystalline or amorphous, are produced as intrac-
table solids, limiting their chemical functionalization or post-
processing into useful forms. Emulsion-templated synthesis
of the nanoparticles of the organic molecular network may
1
–8
tion, heterogeneous catalyst, and drug delivery.
Zeolites
and activated carbons are examples of the conventional
9
–11
microporous systems.
In recent years, crystalline micropo-
3
,12
rous materials such as metal organic frameworks,
covalent
be a potentially useful method for functionalization or
hybridization of the networks.
1
3
14
37,38
organic frameworks, and zeolitic imidazolate frameworks
have been studied intensively. In addition, various amorphous
organic or polymer networks such as polymers of intrinsic
However, if the organic
molecular networks can be made solution processable by
using a simple method without using dispersing agents or
template, there would be ample opportunity of creating new
materials via their chemical functionalization, morphological
control, and hybridization.
1
5–17
18–21
microporosity,
porous polymer networks,
conjugated
and hypercrosslinked poly-
have been studied for their microporous character-
istics. These polymer networks are attractive because of their
2
2–25
microporous polymers,
2
6–29
mers
We reported recently the first organic sol–gel method based
on the crosslinking condensation polymerization between
multifunctional amine and isocyanate monomers in polar
aprotic solvents. The resultant network consisted of TPM-
based units crosslinked via urea bonds. The growth of the
organic network proceeded via a two-stage mechanism
30,31
simple synthesis and chemical functionalization methods
and the availability of diverse monomer systems for them.
39
Many organic networks are synthesized by polymerization of
rigid multifunctional organic compounds based on tetraphe-
nylmethane (TPM), adamantane, and spirobifluorene (SBF)
Additional Supporting Information may be found in the online version of this article.
2013 Wiley Periodicals, Inc.
V
C
1
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FIGURE 1 Organic sol–gel synthesis of molecular networks.
involving the formation of colloidal dispersions in solution
and the subsequent growth to monolithic networks on evap-
oration of solvent, analogous to the sol–gel growth of inor-
their sol–gel polymerization in N,N’- dimethyl formamide
(DMF).
The gelation time (t ) of each monomer pair was determined
4
0,41
g
ganic oxide networks.
The organic molecular networks
with varying the concentration of the monomer solution. The
reaction time elapsed until the gel was visually observed at
could be produced in the form of thin films or nanoparticles
using the organic sol–gel method. Below a critical gelation
room temperature was recorded as t . Figure 2 shows the
g
concentration (c ), the polymerization solution maintained
g
gelation time (t ) plotted against their polymerization con-
g
its fluid (sol) state without gelation. Above c , the polymer
g
centration for all monomer pairs. The critical gelation con-
solution became gel after a certain elapsed time, which we
defined as the gelation time (t ). However, the molecular net-
g
works exist still in the sol state during the time before tg,
being available for further processing such as chemical func-
tionalization or blending with other materials.
centration (c ) is the monomer concentration at which the
g
gelation time is infinite; it is the maximum monomer concen-
tration in the sol state that do not transform to the gel state.
From the data in Figure 2, the c values for TASBF/PDI and
g
ꢀ1
TAPM/PDI networks were estimated to be ꢂ0.01 g mL
and those of TASBF/HDI and TAPM/HDI to be ꢂ0.03 g mL
,
,
ꢀ
1
Therefore, to exploit the organic sol–gel methods, it is desira-
ble to identify the monomer systems that polymerize at the
higher c or the longer t to ensure a sufficient time for proc-
varying with the type of isocyanate monomers. At a concen-
tration above c , the tg values increased in the order of
g
g
g
essing of the molecular networks in the sol state. In the pres-
ent work, we use the SBF-based monomers in the organic sol–
gel method in addition to the previous TPM-based systems
for the generation of microporous networks by the organic
TASBF/PDI, TAPM/PDI, TAPM/HDI, and TASBF/HDI. For
instance, the t for each of the four monomer pairs at a con-
g
ꢀ
1
centration of 0.04 g mL were 1, 8, 85, and 170 h, respec-
tively. It is shown that the monomer pairs with HDI tend to
exhibit longer t ’s and higher c ’s than those with PDI.
ꢁ
sol–gel method. The 90 -kinked structure of SBF unit pre-
g
g
vents efficient packing of segments in the matrix, yielding the
frameworks with greater morphological stability and higher
Because both TASBF and TAPM have the same aminophenyl
nucleophiles, the different t and c values should arise from
the reactivity (electrophilicity) difference of the diisocynates
g
g
3
2,42–44
surface area than the tetrahedral structure.
The results
show that the SBF-based organic networks allow longer proc-
essing time, higher thermal stability, and greater microporos-
ity than the TPM-based networks. We also demonstrate the
synthesis of mixed molecular networks via sol–gel copolymer-
ization of SBF- and TPM-based monomers. The gelation time
g
(t ) of the mixed network sols increased with the amount of
TASBF in the copolymerization mixture. The study indicates
that the potential of organic sol–gel method for creation of
new functional organic molecular network materials can be
enhanced by further optimizing various synthesis parameters.
RESULTS AND DISCUSSION
Sol–Gel Synthesis of Organic Molecular Networks Based
on SBF and TPM Monomers
We used two tetra-amines, TASBF or TAPM, as network
former (Fig. 1) in our sol–gel polymerization. The two mono-
mers were synthesized by the procedure reported previ-
4
5,46
ously.
Four combinations of monomer pairs, TASBF/HDI,
g
FIGURE 2 Gelation time t for solution with different initial
TASBF/PDI, TAPM/HDI, and TAPM/PDI were studied for
concentration for four different monomer pairs in DMF.
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The sol state of the TASBF/HDI mixture at the concentration
ꢀ
1
of 0.03 g mL was investigated by dynamic light scattering
DLS) (Fig. 5), which indicated that the polymerization pro-
(
ceeded via the formation of the sols consisting of the nano-
particle of networks and that the particle size continued to
grow even after 150 h at which the NMR-estimated conver-
sion reached over 90%.
The growth behaviors observed by the NMR and DLS study
are attributed to the two stage sol–gel polymerization mech-
39
anism as reported previously for TAPM-based networks. In
the early stage, the monomers and oligomers react rapidly,
giving a steep increase of NMR-estimated conversion. After
consumption of most of the labile reactants, the reaction rate
is slowed down because most of the remaining amino or iso-
cyanate groups are bound to the crosslinked networks. The
amine-isocyanate coupling reaction is then dominated by
slow interparticle coupling. These account for continuous
increase of the average particle size even after the reaction
rate is significantly slowed down. Broadening of particle size
distribution at longer reaction time is also an indication of
interparticle coupling reaction in the later stage.
1
ꢀ1
FIGURE 3 In situ H NMR spectra of the 0.07 g mL TASBF/
HDI crosslinking polymerization solution in DMF-d
7
.
toward aromatic amine groups. It is known that aromatic dii-
Sol–Gel Synthesis of Mixed Organic Networks by
47
socyanate is more reactive than aliphatic diisocyanate. It is
most likely that the functional groups in the growing net-
work in the sol state have the reactivity similar to the mono-
mers. Therefore, the networks from more reactive monomers
grow outward more rapidly, resulting in the formation of
macroscopically interconnected networks (gels) at lower
concentrations and shorter reaction times. The network sys-
tems with longer gelation time (t ) (TASBF/HDI or TAPM/
g
HDI) may be advantageous for blending or chemical func-
tionalization that can be performed in the sol state.
Copolymerization of TASBF and TAPM with Diisocyanate
We studied further the formation of mixed molecular net-
works via organic sol–gel copolymerization of the two net-
work formers, TASBF and TAPM. The gelation time (t ) of
g
the polymerization solution consisting of a 50/50 mixture of
TASBF/TAPM and an equimolar amount of HDI in DMF
appeared nearly the average of the t valued for TAPM/HDI
g
and TASBF/HDI [Fig. 6(a)]. For a fixed solution concentration
of the TASBF/TAPM/HDI reaction mixture, the gelation time
increased with the composition of TASBF [Fig. 6(b)].
The Structure and Properties of the
Organic Molecular Networks
The urea bonds have been known as one of the strongest
hydrogen-bond-capable organic moieties. The synthesized
organic molecular networks were characterized by FTIR
The Growth of SBF Molecular Networks
in the Organic Sols
In the previous study, we showed by monitoring in situ
NMR spectra of the polymerization solution in DMF-d7 that
the amine and isocyanate groups continued to react and gen-
1
H
(
Supporting Information Fig. S1). The network materials
1
erate new urea bonds. We obtained similar H NMR spectral
data for TASBF/HDI system at two concentrations, 0.03 and
ꢀ
1
0
.07 g mL . In the spectra, the signal of the primary amine
protons of TASBF moiety disappeared as they reacted with
isocyanate groups to form the urea bonds (Fig. 3). Amine-
to-urea conversion (a was estimated by comparing the inte-
gration of amine and urea protons, and plotted against the
reaction time (t) as shown in Figure 4.
ꢀ
1
In both concentrations of 0.03 and 0.07 g mL , the conver-
sion increased roughly in two stages; an initial rapid
increase to above 80% followed by a second stage in which
the conversion increases slowly to a plateau near 95%.
Because the cg value of the TASBF/HDI system is slightly
ꢀ
1
ꢀ1
above 0.03 g mL , the solution at 0.03 g mL maintained
the fluid (sol) state even after the conversion exceeded 90%;
ꢀ
1
whereas the solution at 0.07 g mL transformed to a gel af-
FIGURE 4 Conversion a as a function of reaction time t for
ter the t (50 h) where the conversion reached higher than
TASBF/HDI solution with different concentration; squares: 0.03,
g
ꢀ
1
90%.
circles: 0.07 g mL .
1
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ꢀ
1
FIGURE 5 Growth of the nanoparticle comprised of 0.03 g mL TASBF/HDI molecular networks in the sol state. (a) Number distri-
bution of particle diameter obtained from DLS measurements at the reaction time t ¼ 150, 350, and 500 h, respectively. (b) Aver-
age DLS particle diameter as a function of reaction time (t).
reacted up to the conversion of 95% were purified by pre-
cipitation into a nonsolvent (acetone) followed by drying
SBF-based networks than the TPM-based ones is attributed
to the additional aromatic CAC bonds of the SBF-nodes
when compared with the TPM nodes. The uniqueness of the
sol–gel-synthesized organic networks when compared with
other types of organic or polymer network materials is that
the crosslinked networks can be produced as thin coatings
or free-standing films by simple casting of the sols onto the
substrate surface. Thin films of the TASBF/HDI networks
ꢁ
under vacuum at 200 C. The resultant networks exhibited
ꢀ
1
IR absorption at 1653 cm
for carbonyl stretching and
ꢀ
1
3340 cm
for NAH stretching, both of which are lower
4
8
than those known for isolated urea bond, indicating that
the majority of the urea groups in the organic networks
were hydrogen bonded. This means that the organic net-
works produced by the sol–gel polymerization of amine and
isocyanate monomers possess crosslinking nodes consisting
both of the covalent and hydrogen bonding. The degree of
urea hydrogen bonding within the network should influence
significantly the porous properties of the molecular net-
works. Relatively small specific surface areas of the sol–gel-
produced networks may be attributed to the H-bonding of
urea networks. Currently, we are seeking methods to modify
the degree of H-bonding in the networks.
ꢀ
1
were prepared on the glass plates from 0.03 g mL
sol
showed a cross section with thickness of ꢂ20 lm and
smooth surface (Fig. 7). We controlled the thickness of films
by casting different amounts of sols in a flat substrate with
side walls (such as petri dish). In addition, when the same
volume of sols was used, higher monomer concentrations
gave thicker films. The surface roughness of the films was
below 0.6 nm as estimated by the AFM images. The smooth
surface of the resulting films indicates that sol–gel transfor-
mation occurred without formation of the precipitates during
solvent evaporation. Because the films become insoluble
monolithic networks after evaporation of the solvent, the or-
ganic sol–gel material is potentially useful as a protective
interfacial layer in the solvent-involved device fabrication
processes.
The organic networks containing SBF units showed higher
thermal stability than the TPM-based networks. On the ther-
mogravimetric analysis (Supporting Information Fig. S2), the
temperatures at 5% weight loss appeared at 290, 310, and
ꢁ
3
12 C for TAPM/HDI, TAPM/TASBF/HDI, and TASBF/HDI
networks, respectively. The greater thermal stability of the
g
FIGURE 6 (a) Comparison of gelation times (t ) for homopolymer (TAPM/HDI and TASBF/HDI) and copolymer (TAPM/TASBF/HDI,
molar ratio ¼ 1:1:2) networks. (b) Gelation time (t
g
) of the copolymers with different TAPM/TASBF compositions.
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FIGURE 7 (a) SEM image of the cross section, and (b) tapping mode AFM image of the surface of a free standing film. The films
ꢀ1
were prepared on a glass plate by solvent evaporation of 0.03 g mL TASBF/HDI solution.
4
9–51
Synthesis of Network Powders Prepared by Precipitation
of the Sols into Nonsolvent
mated by applying Dubinin-Astakhov (DA) equation,
2
ꢀ1
which appeared in the range of 200–500 m g and 0.1–0.3
3
ꢀ1
In addition to the films, the organic networks could be pro-
duced in particulate forms by precipitating the sols into non-
solvents such as acetone or water. The network nanopar-
ticles constituting the sol have different sizes and crosslink
densities, varying with the reaction time. Therefore, the mor-
phology and property of the network materials vary accord-
ing to the reaction time when the solution was poured into
nonsolvent.
cm g , respectively (Table 1).
In Figure 8(b), the specific surface area of the TASBF/HDI
network powder was plotted as a function of the conversion
at the time of precipitation of the sols. When the samples
were prepared from the sol with the concentration of 0.03 g
ꢀ1
mL , which is near the c
g
, the specific surface area and the
adsorbed amounts of gas reached the maximum for the sam-
ples prepared at the conversion of 70% [Fig. 8(b)]. In con-
trast, the samples prepared from the sols with the concen-
We used acetone as the nonsolvent for precipitating the sols.
The collected solids were washed with acetone and dried
ꢀ
1
tration of 0.07 g mL , which is higher than c , the specific
g
ꢁ
under vacuum at 200 C. The porosity of the resulting pow-
surface area values did not show much variation with the
conversion. This trend is different from that observed in the
TAPM/HDI system in which the surface area maxima were
observed for the networks prepared at the higher concentra-
tions. Currently, it is unclear how the difference between
SBF and TPM-based networks arose. We think that the
dery molecular networks was obtained by measuring carbon
dioxide adsorption isotherms at 273 K. The resulting pow-
dery materials exhibited a typical type-I adsorption isotherm
for carbon dioxide, indicative of the microporosity [Fig. 8(a)].
The specific surface area and micropore volume were esti-
39
FIGURE 8 Microporous characteristics of organic molecular networks. (a) Carbon dioxide adsorption isotherms measured for the
ꢀ1
networks precipitated at various conversions from 0.03 g mL TASBF/HDI sol states: triangles 70%, circles 50%, inverted triangles
8
0%, crosses 25%, respectively. (b) Specific surface area for the TASBF/HDI networks prepared at different solution concentrations
ꢀ1
ꢀ1
as a function of the conversion (a) at the time of deactivation: squares 0.03 g mL and circles 0.07 g mL , respectively.
1
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TABLE 1 Porosity of TAPM/HDI, TASBF/HDI, and TAPM/TASBF/
observed for the powder [Fig. 10(b)], which was prepared at
the intermediate conversions of the low concentration sols.
We postulate that the micropores within the bigger nanopar-
ticles from high concentration sols may be more difficult to
be accessed by the adsorbing gas molecules and that the net-
works formed from low conversion sols may be collapsed,
exhibiting low microporosity.
HDI Precipitated at the Conversion of 70% with the Solution of
21
the Concentration 0.03 g mL
TAPM/ TASBF/ TAPM/TASBF/
a
HDI
HDI
HDI
2
ꢀ1 b
)
Surface area (m g
229
431
205
3
ꢀ1 b
Micropore volume (cm g
)
0.11
0.21
0.10
We could not obtain nitrogen or argon adsorption isotherm
curves for most samples synthesized by the sol–gel method.
We attribute these to the difficulty of gas diffusion into the
ultra-micropores at 77 K and tightened urea H-bonded net-
a
Molar ratio of TAPM/TASBF/HDI ¼ 1:1:2.
b
47
Calculated by Dubinin-Astakhov equation.
15
works. Interestingly, however, the network samples precipi-
tated at low conversions (ꢂ25, 35, 40%), exhibited N2
adsorption behavior (Fig. 11). The samples appeared to have
mesopores of 2–3 nm and low specific surface area (20–60
different porosities of the powdery samples are related to
their different morphological structures that formed upon
precipitation of the sols into nonsolvent.
2
ꢀ1
m
g ) as calculated by the BET equation. This indicates
The pore size distribution was calculated by density func-
5
2–54
that the powdery samples prepared from low conversion
network possess both mesopores and micropores. We think
that the mesopores formed with interconnection of immature
oligomeric networks by quenching of the reaction in the
nonsolvent.
tional theory model.
The pore size of the networks was
typically in the range of 5–9 Å (Fig. 9).
The specific surface area and micropore volume of TAPM/
HDI, TASBF/HDI, and TAPM/TASBF/HDI precipitated at the
same conversion of 70% were measured (Table 1), where
TASBF/HDI networks exhibited higher specific surface area
than TAPM/HDI networks. The improved porosity may be
attributed to the structural stability of kinked and rigid SBF
crosslinks. However, the porosity of the mixed network
obtained by copolymerization of TAPM/TASBF/HDI with 1/
The Bulk Organic Networks Prepared by Solution-State
Gelation above cg
Above the critical gelation concentration of the monomer sol-
utions, the sols transform to gels on prolonged stirring. The
gelled samples were isolated and purified by precipitation
and washing with nonsolvent. We compared the porosity of
the networks prepared from different initial concentrations.
The networks gelled at higher concentrations showed
smaller microporosity (Fig. 12). In particular, the bulk net-
1
/2 ratio rather decreased and the effect of TASBF was not
revealed. This is in part consistent with the result shown in
Figure 8 in that the monomer concentrations and conver-
sions giving the best microporosity are different for each of
the two network formers. Further optimization of synthesis
parameters may be needed to obtain maximum porosity for
the mixed networks.
ꢀ
1
work synthesized at the concentration of 0.10 g mL exhib-
ited nearly no microporosity. This result may be accounted
for by the formation of the macroscopic networks with low
crosslink density as the mixture gelled rapidly at a short
reaction time. The formation of molecular scale networks are
To understand the porosity dependence on the conversion
and polymerization concentration, we compared the SEM
images of the samples precipitated at the conversion of 30
and 70% for each of the 0.03 and 0.07 g mL sols (Fig. 10).
All of the samples showed particulate morphology varying
with the sample preparation conditions. The sizes of the par-
ticles appeared much greater than those observed by DLS
ꢀ
1
(
Fig. 5), indicative of aggregation during the precipitation
ꢀ
1
process. The samples from 0.03 g mL sol consist of the
particles a few tens of nanometer for 30% conversion and
about a hundred nanometers for 70% conversion. The sam-
ples from 0.07 g mL sols showed mixture of the particles
with a wide range of diameters from several tens to several
hundred nanometers. Because we used similar amounts of
nonsolvent and stirring speed in the precipitation of each
sample, the morphological difference may be attributed to
the degree of phase segregation of the sol phase in the non-
solvent at the time pouring into the nonsolvent.
ꢀ
1
The specific surface areas of the four samples cannot be cor-
related to the SEM-observed particle sizes because the
microporosity is not related to the apparent mesoscopic size
of the particles but to the micropores inside the particles
that cannot be imaged by the SEM. Maximum porosity was
FIGURE 9 The pore size distribution (PSD) of the network pow-
ders from different monomer combinations precipitated at the
conversion of 70% from the sols with the concentration of 0.03
ꢀ1
g mL , which was calculated by density functional theory
(DFT) model.
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FIGURE 10 SEM images of the TASBF/HDI network powders prepared from different initial solution concentrations and reaction
ꢀ1
ꢀ1
ꢀ1
ꢀ1
conversion (a) 0.03 g mL , a: 30%, (b) 0.03 g mL , a: 70%, (c) 0.07 g mL , a: 30%, and (d) 0.07 g mL , a: 70%; scale bar: 200
nm.
enhanced at the concentration near to the critical gelation
concentration.
can be enhanced by adjusting detailed synthesis parameters.
Studies on various aspects of the organic sol–gel synthesized
networks such as the functionalization of particles surface and
blending of the networks with other polymers are underway.
CONCLUSIONS
The microporous molecular networks based on rigid tetrafunc-
tional units were synthesized via organic sol–gel polymeriza-
0
0
0
tion of 2,2 ,7,7 -tetraamino-9,9 -spirobifluorene (TASBF) and/or
tetrakis(4-aminophenyl)methane (TAPM) with two diisocyanate
monomers, hexamethylene diisocyanate (HDI), or p-phenylene
diisocyanate (PDI). The sol–gel-synthesized molecular networks
obtained by incorporating TASBF as a network former showed
improved porosity, processability, and thermal stability than the
TAPM-based system. The improved porosity of TASBF-based
networks was attributed to higher rigidity of the SBF compared
with the TPM units. We also demonstrated the synthesis of
mixed organic molecular networks by sol–gel copolymerization
of the two network-formers, TASBF and TAPM, and a diisocya-
nate monomer. The sol–gel transformation of TASBF/TAPM/
HDI occurred at longer reaction times with increasing the
amount of TASBF in the TASBF/TAPM/HDI mixture. The results
indicate that the potential of the organic sol–gel method for cre-
ation of new functional organic molecular network materials
ꢀ1
FIGURE 11 Nitrogen isotherms at 77 K of 0.03 g mL TASBF/
HDI networks precipitated for low conversion: diamonds 25%,
circles 35%, and triangles 40%, respectively.
1
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was added to the solution, and the mixture was stirred at
room temperature under nitrogen.
Synthesis of Polyurea Network Solution by Crosslinking
Polymerization of TASBF/PDI System
In a typical preparation of TASBF/PDI 1 w/v % solution in
DMF, TASBF (MW: 376.45, 0.118 g, 0.312 mmol) was dis-
solved in 21.8 mL of dry DMF. PDI (MW: 160.13, 0.100 g,
0.624 mmol) was added, and the mixture was stirred at
room temperature under nitrogen.
Synthesis of Polyurea Network Solution by Crosslinking
Copolymerization of TAPM/TASBF/HDI System
In a typical preparation of TAPM/TASBF/HDI, 3 w/v % solu-
tion in DMF, TAPM (MW: 380.48, 0.1056 g, 0.278 mmol), and
TASBF (MW: 376.45, 0.1044 g, 0.278 mmol) was dissolved in
FIGURE 12 Carbon dioxide adsorption isotherms of gelled
13.2 mL of dry DMF. HDI (MW: 168.19, 0.187 g, 1.11 mmol)
TASBF/HDI networks with different initial concentration after t
g
1
ꢀ
was added, and the mixture was stirred at room temperature
under nitrogen.
at 273 K: diamonds 0.05, circles 0.07, triangles 0.10 g mL
respectively.
,
Preparation of free-Standing Films from Sols
EXPERIMENTAL
In a typical preparation of thin film of TASBF/HDI, TASBF/
HDI free-standing films were prepared by casting TASBF/
HDI sol (5 mL) of 3 w/v % in DMF on the glass plate (15 ꢃ
Materials
Anhydrous N,N-dimethylformamide (DMF) and anhydrous
tetrahydrofuran (THF) were purchased from Aldrich and DC
chemical company, respectively, and used without further pu-
rification. HDI (>97%, Aldrich) was freshly distilled under
reduced pressure. PDI (Aldrich) were purified by sublima-
tion. The other materials were purchased from Aldrich and
used without further purification.
2
ꢁ
1
5 cm ) and the subsequent solvent evaporation at 80 C.
After 1 h, the film on the glass plate was separated by cut-
ting with a razor blade and then the free-standing film was
washed with water and acetone under sonication for 1 h,
respectively. The resulting free-standing film was then dried
ꢁ
ꢁ
under high vacuum at 50 C for 1 h, 100 C for 1 h, and 200
C for 48 h.
ꢁ
0
0
0
Synthesis of 2,2 ,7,7 -Tetraamino-9,9 -spirobifluorene
0
0
0
Purification
To 2,2 ,7,7 -tetranitro-9,9 -spirobifluorene (8.30 g, 16.7
mmol) in 250 mL of THF, 16.00 g (excess) of hydrazine
monohydrate and ꢂ80 g of Raney nickel were added and
refluxed for about 3 h. The mixture was hot filtered and
washed with ethanol. Solvent was evaporated and the resi-
due was washed with ethanol and dried.
The reaction mixtures remained in the fluid state (sol)
before gelation time (t ). The nanoparticle aggregates were
g
obtained by precipitation of the sol at a designated reaction
time into a copious amount of acetone. The precipitates
were stirred in pure acetone and filtered (repeated three
times). The resulting powders were then dried under high
1
ꢁ
ꢁ
ꢁ
H NMR (400 MHz, DMSO-d ): 7.38 (d, 4H, J ¼ 8.0 Hz), 6.59
6
vacuum at 50 C for 1 h, 100 C for 1 h, and 200 C for 48
h. To obtain bulk dry gel samples, the wet gel (formed after
(
dd, 4H, J ¼ 8.0 Hz, J ¼ 2.0 Hz), 5.93 (d, 4H, J ¼ 2.0 Hz),
4
5,46,55
4
.35 (bs, 8H).
g
t ) was poured into acetone followed by the same purifica-
tion procedure as the sample from the sol state.
Synthesis of Tetrakis(4-aminophenyl)methane
To the solution of tetrakis(4-nitrophenyl)methane (3 g, 5.99
mmol) in THF (200 mL), 4.00 g (excess) of hydrazine mono-
hydrate and 20 g of Raney nickel were added and refluxed
for about 3 h. The mixture was hot filtered and washed with
ethanol. The combined filtrates were evaporated, the residue
was washed with chloroform, and then the crude product
was recrystallized with ethyl alcohol to get white crystals of
TAPM.
Porosity Measurement
Gas adsorption isotherms were recorded on ASAP 2020 volu-
metric adsorption apparatus (Micromeritics) at 77 and 273
K for nitrogen and carbon dioxide within relative pressures
from 0 to 1.0 and from 0 to 0.03, respectively. Before analy-
sis, the samples were degassed in the degas port of the
adsorption analyzer at 473 K for at least 12 h. The surface
area, pore volume and pore size distribution were analyzed
using ASAP 2020 v3.00 software (Micromeritics).
1
H NMR (400 MHz, DMSO-d ): 6.65 (d, 8H, J ¼ 8.7 Hz), 6.35
6
4
5,46,55
(
d, 8H, J ¼ 8.7 Hz), 4.80 (s, 8H).
ACKNOWLEDGMENTS
Synthesis of Polyurea Network Solution by Crosslinking
Polymerization of TASBF/HDI System
In a typical preparation of TASBF/HDI solution of 3 w/v %,
TASBF (MW: 376.45, 0.112 g, 0.298 mmol) was dissolved in
This research was supported by the Basic Science Research
Program (2010-0026421) and the Korea CCS R&D Center
(KCRC) grant (2011-0031974) of the National Research Foun-
dation (NRF) funded by the Korea government (Ministry of
Education, Science, and Technology).
7.1 mL of dry DMF. HDI (MW: 168.19, 0.100 g, 0.595 mmol)
WWW.MATERIALSVIEWS.COM
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