Organic-inorganic polymer hybrids using polyoxazoline initiated by functionalized silsesquioxane

Article abstract of DOI:10.1021/ma021303b

New hybrid polyoxazolines (CubePOZO) were synthesized by ring-opening polymerization of 2-methyl-2-oxazoline initiated by functionalized polyhedral oligomeric silsesquioxane (POSS) with various feed ratios. The hybrid micelles derived from CubePOZO with both seven hydrophobic cyclopentyl groups of POSS and polyoxazoline (POZO) as a hydrophilic segment were prepared in an aqueous phase. Compared to POZO initiated by cyclohexyl iodide or methyl p-toluenesulfonate, increased hydrophobicity caused by the structure of POSS in CubePOZO played a major role in the micelle formation. This depended on the amount of POSS incorporated into the POZO. The CubePOZO100 and CubePOZO200 formed micelles in an aqueous phase with critical micelle concentrations (cmc) of 55 and 100 mg/L, respectively. Transparent polymer hybrids, homogeneous dispersion of hydrophobic POSS bonded covalently to POZO in the silica gel matrix at the molecular level, were obtained through hydrogen-bonding interaction between CubePOZO and silica gel. The obtained polymer hybrids from CubePOZO showed excellent solvent resistance, similar to that of polymer hybrids having an interpenetrating polymer network structure. It was concluded that the solvent-resistant property came from the size of POSS and the hydrophobic interaction between the POSS in the silica gel matrix. In addition, thermal stability of the polymer hybrids from CubePOZO was much increased compared to that of the polymer hybrids from homoPOZO and POSS.

Full text of DOI:10.1021/ma021303b

Macromolecules 2003, 36, 867-875
867
Organic-Inorganic Polymer Hybrids Using Polyoxazoline Initiated by
Functionalized Silsesquioxane
Kyu n g-Min Kim , Don g-Ki Keu m , a n d Yosh ik i Ch u jo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Yoshida,
Sakyo-ku, Kyoto 606-8501, J apan
Received August 12, 2002; Revised Manuscript Received November 12, 2002
ABSTRACT: New hybrid polyoxazolines (CubePOZO) were synthesized by ring-opening polymerization
of 2-methyl-2-oxazoline initiated by functionalized polyhedral oligomeric silsesquioxane (POSS) with
various feed ratios. The hybrid micelles derived from CubePOZO with both seven hydrophobic cyclopentyl
groups of POSS and polyoxazoline (POZO) as a hydrophilic segment were prepared in an aqueous phase.
Compared to POZO initiated by cyclohexyl iodide or methyl p-toluenesulfonate, increased hydrophobicity
caused by the structure of POSS in CubePOZO played a major role in the micelle formation. This depended
on the amount of POSS incorporated into the POZO. The CubePOZO100 and CubePOZO200 formed
micelles in an aqueous phase with critical micelle concentrations (cmc) of 55 and 100 mg/L, respectively.
Transparent polymer hybrids, homogeneous dispersion of hydrophobic POSS bonded covalently to POZO
in the silica gel matrix at the molecular level, were obtained through hydrogen-bonding interaction between
CubePOZO and silica gel. The obtained polymer hybrids from CubePOZO showed excellent solvent
resistance, similar to that of polymer hybrids having an interpenetrating polymer network structure. It
was concluded that the solvent-resistant property came from the size of POSS and the hydrophobic
interaction between the POSS in the silica gel matrix. In addition, thermal stability of the polymer hybrids
from CubePOZO was much increased compared to that of the polymer hybrids from homoPOZO and
POSS.
In tr od u ction
cage structures and property enhancements via POSS
to polymers.10-12 POSS is easily incorporated into
common plastics by means of copolymerization or blend-
ing, requiring little or no alteration to existing synthetic
processes because POSS have an inorganic SiO2 core
surrounded by eight organic groups, which make it
soluble in various organic solvents. POSS containing
copolymers or blends have increased oxygen perme-
ability, are thermoplastic or curable, have oxidation
resistance, and higher thermal properties than those
without the POSS moiety. We have recently explored
various organic-inorganic hybrid nanocomposites based
on POSS as an inorganic precursor. Such examples are
hybrid gels,13 hybrid LC polymers,14,15 self-assembly of
metal nanoparticles,16 hydrophobic CaCO3 composite
particles,17 and homogeneously transparent polymer
hybrid materials combined at the molecular level.18-20
Considerable efforts have recently been directed
toward the exploitation of new nanostructured hybrid
organic-inorganic composites for their scientific interest
and their industrial applications.1-3 That is because of
their utility and potential as catalysts,4 sensors,5 optical
and electronic applications,6 gas selective membranes,7
etc. In general, composite materials are formed when
at least two different types of materials (organic,
inorganic, and metallic) are mixed. The combination of
organic and inorganic materials is expected to provide
remarkable and complementary properties, which can-
not be obtained with a single material. Organic-
inorganic nanocomposites, in which two components
were mixed at the nanometer level, usually exhibit
improved performance properties compared to conven-
tional composites, in which two components were mixed
on a macroscopic scale (> micrometers), owing to their
unique phase morphology and improved interfacial
properties.8
The most extensively explored synthetic approach is
via the sol-gel technique for preparing inorganic oxides
at ambient temperature by polymerization and coagula-
tion of tri- or tetramethoxysilanes and other metal
alkoxides. Organic phases (polymers or gels) could be
incorporated without any separation into the silica
matrix by using covalent bond or physical interactions
between two phases or by controlling gelation of poly-
mers and formation of silica gel through various mo-
lecular designs.9 Organic-inorganic nanocomposites
show highly optical transparency, excellent thermal,
mechanical, and solvent-resistant properties.
Here we describe the preparation of hybrid polyox-
azolines initiated by new POSS having only one io-
dopropyl group as an initiator (CubePOZO) and also of
polymer hybrids from CubePOZO utilizing the sol-gel
reaction of tetramethoxysilane (TMOS). It is expected
that the introduction of the hydrophobic POSS having
seven cyclopentyl groups to hydrophilic POZO can
induce self-association of CubePOZO, leading to the
formation of hybrid micelles in an aqueous phase. This
is an interesting method for preparing micelles using
enhanced hydrophobicity caused by the structure of
POSS even though little of POSS is incorporated into
the hydrophilic polymer chain as an initiator. It is really
difficult to obtain homogeneous polymer hybrids using
hydrophilic POZO and hydrophobic POSS in the silica
gel matrix. On the other hand, hydrophobic POSS
having seven cyclopentyl groups bonded covalently to
POZO could be homogeneously dispersed in the silica
gel matrix at the nanometer level. We describe the
properties of CubePOZO and micelle characteristics of
CubePOZO in an aqueous phase. In addition, the
Polyhedral oligomeric silsesquioxanes (POSS), inter-
mediate (RSiO1.5)n between silica (SiO2) and silicone (R2-
SiO), are interesting inorganic particles which can
replace sol-gel-derived materials. They currently have
a great impact on the field of material science because
of their hybrid chemical compositions with nanosized
10.1021/ma021303b CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/08/2003

868 Kim et al.
Macromolecules, Vol. 36, No. 3, 2003
Sch em e 1
preparation of polymer hybrids from CubePOZO and
TMOS utilizing the sol-gel reaction and the effect of
the hydrophobic POSS on the pore size and solvent-
resistant property of the polymer hybrids are described.
Exp er im en ta l Section
Mea su r em en ts. 1H NMR spectra were recorded using a 270
MHz J EOL-J NM-GX270 NMR spectrometer. UV absorption
spectra were obtained with a J ASCO V-530 spectrophotometer.
Fourier transform infrared (FT-IR) spectra were recorded on
a Perkin-Elmer 1600 infrared spectrometer. The thermal
behavior was examined with differential scanning calorimetry
(DSC) and thermogravimetric analysis (TGA) (TG/DTA6200,
Seiko Instruments) under nitrogen and air atmospheres,
respectively. Gel permeation chromatography (GPC) analysis
was carried out on TSK gel R-3000 by using DMF as an eluent
at 40 °C after calibration with the standard polystyrene
samples. The morphologies of polymer hybrids were observed
by scanning electron microscopy (SEM) (J EOL J SM-5310/LV).
The crystallinities of CubePOZO and polymer hybrids were
determined by X-ray diffraction (XRD) (Perkin-Elmer system
2000). Fluorescence excitation spectra were recorded on a
Perkin-Elmer LS50B luminescence spectrometer. Nitrogen
absorption porosimetry was conducted with a BEL J apan Inc.
Ma ter ia ls. 2-Methyl-2-oxazoline (Aldrich) was distilled over
potassium hydroxide and stored under nitrogen. Cyclopentyl-
trichlorosilane (Gelest), pyrene (Aldrich), cyclohexyl iodide
(Aldrich), and 3-chloropropyltrichlorosilane (TCI) were used
as received. Chloroform and acetone were dried and distilled
from calcium carbonate and potassium carbonate, respectively.
Tetrahydrofuran (THF) and triethylamine (TEA) were distilled
over sodium and calcium hydride, respectively. The other
reagents were used as supplied without further purification.
Syn th esis of Cu be-1Cl. Incompletely condensed trisilanol
(c-C5H9)7Si7O9(OH)3 was prepared in 29% yield by the hydro-
lytic condensation reaction of cyclopentyltrichlorosilane in
reflux aqueous acetone, according to the procedure reported
before.21 The obtained trisilanol (3.05 g, 3 mmol) and triethyl-
amine (1.23 g, 12 mmol) were dissolved in THF. The solution
was cooled in an ice bath, and 3-chloropropyltrichlorosilane
(0.74 g, 3 mmol) in THF was added slowly to the mixture. The
resulting solution was stirred overnight at room temperature.
After removal of insoluble salts by filtration, the filtrate was
concentrated to 5 mL and poured into acetonitrile. The white
precipitate was collected by filtration and dried in vacuo to
F igu r e 1. (a) DSC and (b) TGA thermograms of CubePOZO
with a heating rate of 10 °C min-1 under nitrogen and air
atmospheres, respectively. (a) DSC: (a) homoPOZO, (b) Cube-
POZO50, (c) CubePOZO100, and (d) CubePOZO200. (b) TGA:
(a) homoPOZO, (b) CubePOZO20, (c) CubePOZO50, (d) Cube-
POZO100, (e) CubePOZO200.
1
produce a white solid (2.50 g, 64%). H NMR (CDCl3): δ 3.54
(t, 2H), 1.87 (m, 2H), 1.48-1.80 (m, 56H), 0.97 (m, 7H), 0.74
(m, 2H). 29Si NMR (CDCl3): -66.52, -67.11.

Macromolecules, Vol. 36, No. 3, 2003
Organic-Inorganic Polymer Hybrids 869
Sch em e 2
Sch em e 3
Syn th esis of Cu be In itia tor (Cu be-1I). A mixture of
Cube-1Cl (2.20 g, 2 mmol) and sodium iodide (11.7 g, 78 mmol)
was added in THF (120 mL) and acetone (40 mL) cosolvent
under a nitrogen atmosphere. The mixture was refluxed for
24 h, cooled to room temperature, and evaporated. A fine solid
of sodium chloride formed during the mixture was refluxed.
The white mixture was extracted with methylene chloride, and
the insoluble parts were removed by filtration. After evapora-
tion of methylene chloride and drying in a vacuum, the raw
product was again reacted with sodium iodide in THF and
acetone cosolvent. The workup procedure was repeated three
times, and then the product was obtained as a yellow solid
Syn th esis of P olyoxazolin e In itiated by Cu be-1I (Cu be-
P OZO). The polymerization of 2-methyl-2-oxazoline using
POSS as an initiator ([monomer]/[initiator] ) 1/20, 1/50, 1/100,
1/200) was carried out in dry chloroform at 70 °C for 7 days
under nitrogen. As a representative example, the hybrid
polymer, CubePOZO100, which has 100 molar ratio of 2-meth-
yl-2-oxazoline to Cube-1I, was synthesized by the following
procedure: To a solution of 2-methyl-2-oxazoline (0.80 g, 9
mmol) in chloroform (6 mL) was added Cube-1I (0.1 g, 0.09
mmol) at room temperature under nitrogen. The reaction
mixture was heated at 70 °C for 7 days. The resulting yellow
solution was diluted with 15 mL of chloroform. This polymer
solution was poured into ca. 200 mL of diethyl ether to
precipitate the polymeric product. The white precipitate was
collected by filtration and dried in a vacuum (0.73 g, 81%).
1
(1.20 g, 58%). H NMR (CDCl3): δ 3.22 (t, 2H), 1.89 (m, 2H),
1.40-1.80 (m, 56H), 0.97 (m, 7H), 0.72 (m, 2H). 29Si NMR
(CDCl3): -66.52, -67.93.

870 Kim et al.
Macromolecules, Vol. 36, No. 3, 2003
F igu r e 2. 1H NMR spectra of CubePOZO100 in CDCl3 (a) and CD3OD (b).
P r ep a r a tion of Hybr id Micelles fr om Cu beP OZO. For
the measurement of fluorescence spectra, pyrene solution was
prepared following a literature procedure.22 The pyrene solu-
tion was mixed with CubePOZO in a distilled water to obtain
CubePOZO concentration from 2 × 10-4 to 2.5 g/L. The pyrene
concentration of the samples was 6 × 10-7 M. All the samples
were sonicated for 1 h and were allowed to stand for 1 day in
a dark place before fluorescence measurements.
Soxh let Extr a ction of P olym er Hybr id s. The powders
of polymer hybrids were put in a cellulose timber and extracted
with methanol or chloroform using a Soxhlet apparatus for
14 days. The powders in a timber were dried in a vacuum for
the TGA measurement and nitrogen absorption porosimetry.
X-r a y Diffr a ction Mea su r em en t of Cu beP OZO a n d
P olym er Hybr id s. All the measurements were made in θ/2θ
mode at room temperature. The 2θ scan data were collected
at 0.02° interval, and the scan speed was 2° (2θ)/min.
P r ep a r a tion of P olym er Hybr id s fr om Cu beP OZO. The
obtained polymer having POSS moiety (CubePOZO20, 50, 100,
200) was dissolved in methanol, and the resulting mixture was
stirred for 1 h. To the solution was added TMOS and 0.1 M
aqueous HCl as a catalyst for sol-gel reaction. The weight of
CubePOZO was fixed to 0.05 g. The weight of TMOS was
varied to that of CubePOZO (4/1, 10/1, 20/1). Four equivalents
of aqueous HCl to TMOS was added. The resulting mixture
was stirred at room temperature for 1 h in a sealed bottle.
Then, the mixture was placed in a container covered with a
paper towel and left in air to evaporate the solvent. After the
complete removal of the solvent, the polymer hybrids were
obtained as a glassy material.
Nitr ogen Absor p tion P or osim etr y. The preparation of
samples for nitrogen absorption porosimetry was made by
two methods to remove the organic parts in the silica matrix.
One is that the powders of polymer hybrids are heated at
600 °C under an ambient atmosphere. The other is solvent
extraction of the powders of polymer hybrids with methanol
using a Soxhlet apparatus for 14 days. The samples were then
heated to 150 °C for 2 h and dried at 150 °C for 2 h at reduced
pressure under a nitrogen atmosphere. Surface areas were
calculated with the BET equation23 in the range of 0.05-0.30
(p/p0), and the pore size distribution was calculated by the BJ H
method.24

Macromolecules, Vol. 36, No. 3, 2003
Organic-Inorganic Polymer Hybrids 871
Ta ble 1. P r ep a r a tion of Cu beP OZO In itia ted by
Silsesqu ioxa n es
time temp
yield
c
run [1]/[2]a (days) (°C)
Mn
Mw
PDb (%) Td
1
2
3
4
20
50
100
200
7
7
7
7
70
70
70
70
3 000 10 000 3.45
5 200 12 000 2.30
10 000 21 000 2.13
20 000 42 000 2.03
62
64
81
83
367
342
335
a
b
Feed ratio of 1 to 2. Polydispersity. c Temperature at which
a 10% weight loss was observed under air.
Resu lts a n d Discu ssion
Syn th esis of Hybr id Cu beP OZO In itia ted by
P OSS. POSS as an initiator (Cube-1I) were prepared
by corner-capping reaction of incompletely condensed
trisilanol with a coupling reagent followed by nucleo-
philic substitution with sodium iodide, as shown in
Scheme 1. In the 29Si NMR, two resonances were shown
at -67.93 and -66.52 ppm with a ratio of 1 to 7. The
1H NMR spectra of Cube-1I showed the chloromethylene
group (δ ) 3.54 ppm) derived from Cube-1Cl completely
shifted to the iodomethylene group (δ ) 3.22 ppm). The
structure of Cube-1I, in which POSS has seven cyclo-
pentyl groups and only one iodopropyl group for polym-
erization, was thus characterized by 1H NMR, 29Si
NMR, and FT-IR.
The new hybrid polyoxazolines using POSS as an
initiator were synthesized by varying the feed ratio of
2-methyl-2-oxazoline to Cube-1I (Scheme 2). The hybrid
polymers were denoted as CubePOZO20, CubePOZO50,
CubePOZO100, and CubePOZO200, which have 20, 50,
100, and 200 molar ratios of 2-methyl-2-oxazoline to
Cube-1I, respectively. The results of the preparation of
hybrid polymers are summarized in Table 1. Long
reaction times around 7 days were necessary for 60-
80% conversion in this polymerization, unlike the
system using methyl p-toluenesulfonate as an initiator.
This result is due to the steric hindrance, that is, the
decreased initiation activity of the iodopropyl group
surrounded by bulky cyclopentyl groups of POSS. Figure
1 represents DSC and TGA thermograms for Cube-
POZO. The hybrid CubePOZO show an increase in glass
transition temperature (Tg) except CubePOZO50, com-
pared to that of homoPOZO initiated by methyl p-
toluenesulfonate. This can be attributed to the reduction
of segmental mobility of POZO in CubePOZO, which
was caused by the incorporation of the hard, compact
POSS moiety (Figure 1a). In the case of CubePOZO50,
no increase in Tg was observed because the real molec-
ular weight of CubePOZO50 was too small to reveal the
effect of POSS on the mobility of POZO. The thermal
stabilities of CubePOZO increased as the weight percent
of POSS was increased (Figure 1b). This is a measure
of the effect of the inorganic POSS unit on polymer
thermal properties. CubePOZO show the strong reflec-
tions (2θ ) 17°-19°) indicative of crystallinity of Cube-
1I, which confirm the formation of CubePOZO consisting
of POSS and POZO moieties.
F igu r e 3. Excitation spectra of pyrene as a function of (a)
CubePOZO and (b) cyclohexylPOZO concentration in aqueous
solution.
POSS (0.7, 0.9, and 1.3-1.8 ppm) and POZO (2.1 and
3.5 ppm) moieties were clearly observed in CDCl3, the
peaks of POSS disappeared in CD3OD, which indicated
the limited molecular motion of hydrophobic POSS
surrounded by the hydrophilic POZO. The critical
micelle concentration (cmc) of CubePOZO micelles was
determined by using pyrene as a fluorescence probe,
which partitioned into the hydorphobic POSS core of
micelles above the cmc value.
Excitation spectra of pyrene are shown at varying
concentrations of CubePOZO100 and POZO initiated by
cyclohexyl iodide (cyclohexylPOZO100) (Figure 3). Above
the critical concentration region, the remarkable shift
of pyrene spectra from 334 to 339 nm was observed,
reflecting the change in vibrational structure of pyrene
emission (Figure 3a). On the other hand, with increasing
concentration of cyclohexylPOZO100, the distinct red
shift from 334 to 339 nm was not observed in cyclo-
hexylPOZO100 (Figure 3b). This means that enhanced
hydrophobicity of cyclopentyl groups derived from the
structure of POSS leads to form the POSS core of hybrid
micelles. The fluorescence intensity ratio at the two
excitation wavelengths (I339/I334) was used to determine
the cmc value of CubePOZO.
P r ep a r a tion of Hybr id Micelles of Cu beP OZO.
CubePOZO self-assembled in an aqueous solution to
form a novel hybrid micelle structure by serving POSS
segments as a hydrophobic core and POZO segments
as a surrounding hydrophilic outer shell. The micelle
formation of CubePOZO was confirmed by NMR spec-
troscopy, a fluorescence technique, and SEM.25,26 Figure
2 shows the 1H NMR spectra of CubePOZO100 in CDCl3
(a) and CD3OD (b). While the whole peaks from both
Figure 4 shows the intensity ratio (I339/I334) of pyrene
excitation spectra depending on the concentration of
CubePOZO100 and cyclohexylPOZO100. The cmc value
was determined from the threshold concentration, where
the intensity ratio I339/I334 begins to increase markedly
(Figure 4a), whereas there was no distinctly increased

872 Kim et al.
Macromolecules, Vol. 36, No. 3, 2003
F igu r e 4. Intensity ratio (I339/I334) of pyrene in the excitation
spectra as a function of logarithm of (a) CubePOZO100 and
(b) cyclohexylPOZO concentration.
F igu r e 5. Scanning electron micrographs of hybrid Cube-
POZO100 micelles.
intensity ratio I339/I334 despite the increase of cyclohexyl-
POZO100 concentration (Figure 4b). No cmc value in
methylPOZO initiated by methyl p-toluenesulfonate was
observed alike. The cmc values of CubePOZO200 and
CubePOZO100 were 55 and 100 mg/L, respectively.
CubePOZO having a higher POSS moiety, CubePOZO20
and CubePOZO50, could not form the micelle formation
in an aqueous phase, which might be ascribed to their
rather poor dispersion caused by the increased POSS
moiety in aqueous media. The micelles of CubePOZO
were visualized as the spherical shape by SEM as shown
in Figure 5. The cmc and the micelle size of CubePOZO
were higher and larger than those of other amphiphilic
block copolymers.27,28 This phenomenon indicated that
high concentration of CubePOZO was necessary to make
micelle formation because of weaker hydrophobicity of
CubePOZO than that of normal amphiphilic block
copolymer. Any precipitation or aggregation was not
observed even after the micelle solution of CubePOZO
was left in air for 1 month, indicating the high stability
of hybrid micelles from CubePOZO in an aqueous phase.
P olym er Hybr id s fr om Cu beP OZO a n d TMOS
Utilizin g th e Sol-Gel Rea ction . Transparent and
homogeneous polymer hybrids were prepared in a wide
range of compositions utilizing hydrogen-bonding in-
teraction between CubePOZO and silica gel (Scheme 3).
In other words, hydrophobic POSS was homogeneously
dispersed with POZO in the silica gel matrix. Initial
contents of CubePOZO and TMOS were varied as shown
in Table 2. The mixing of homoPOZO, Cube-1I, and
TMOS resulted in the phase separation between hydro-
philic POZO and hydrophobic POSS in the silica gel
Ta ble 2. P r ep a r a tion of P olym er Hybr id s fr om
Cu beP OZO
polymer
content
HCl
TMOS (0.1 M)
materialsb
(g)
runa
1
(g)
(mL) appearancec calcd obsdd
homoPOZO
0.24
0.12 turbid
Cube-1I (0.01)
CubePOZO20
CubePOZO50
CubePOZO100
CubePOZO200
CubePOZO20
CubePOZO50
CubePOZO100
CubePOZO200
2
3
4
5
6
7
8
9
0.2
0.2
0.2
0.2
0.5
0.5
0.5
0.5
1.0
1.0
1.0
1.0
0.1
0.1
0.1
0.1
transparent
transparent 38.7 38.5
transparent 38.7 37.4
transparent
0.24 transparent
0.24 transparent
0.24 transparent 20.2 23.2
0.24 transparent
0.47 transparent
0.47 transparent
0.47 transparent 11.2 17.4
0.47 transparent
10 CubePOZO20
11 CubePOZO50
12 CubePOZO100
13 CubePOZO200
a
b
Methanol was used as a solvent. CubePOZO and homoPOZO
were fixed at 0.05 g. c Homogeneity was observed optically. Mea-
d
sured by TGA.
matrix (run 1). The optically transparent polymer
hybrids were obtained in most cases except run 1. This
methodology can be effectively used to prepare polymer
hybrids from hydrophilic and hydrophobic materials
with TMOS, whose polymer hybrids have been thought
to be prepared with difficulty.
FT-IR measurement of polymer hybrids confirms the
shift of amide carbonyl peaks caused by hydrogen-

Macromolecules, Vol. 36, No. 3, 2003
Organic-Inorganic Polymer Hybrids 873
F igu r e 6. FT-IR spectra of polymer hybrids from CubePOZO.
F igu r e 7. DSC thermograms of polymer hybrids from Cube-
POZO.
bonding interaction between CubePOZO and silica gel.
Figure 6 is representative IR spectra of CubePOZO and
CubePOZO and TMOS hybrid. The amide carbonyl
peaks of CubePOZO were downshifted from 1644 to
1630 cm-1 with the formation of hydrogen-bonding
interaction. The disappearance of Tg of the polymer
hybrids using CubePOZO was determined by DSC
(Figure 7). These results indicate the complete and
homogeneous mixing of CubePOZO and inorganic phase.
The homogeneity of polymer hybrids was confirmed
by SEM. As shown in Figure 8, the polymer hybrids
from CubePOZO and TMOS with various ratios showed
a homogeneous dispersion of CubePOZO in the silica
gel matrix at the molecular level (Figure 8b-d). On the
other hand, an aggregation of homoPOZO and Cube-1I
in the silica gel matrix brought about the phase separa-
tion (Figure 8a).
The solvent-resistant property by the effect of POSS
in the hybrid system was estimated by means of solvent
extraction experiments. The results are shown in Table
3. Surprisingly, very little CubePOZO component was
extracted with CH3OH and CHCl3, while 70-80% of
homoPOZO initiated by methyl p-toluenesulfonate was
extracted with CH3OH. This excellent solvent resistance
is similar to that of polymer hybrids having an inter-
penetrating polymer network structure. It is likely that
the hydrophobic interaction between two or three Cube-
POZO with hydrophobic POSS moiety, which is poorly
soluble in methanol itself, results in the strong resis-
tance against solvent extraction.
F igu r e 8. SEM images of polymer hybrids from CubePOZO:
(a) homoPOZO/Cube-1I/TMOS ) 0.05 g/0.01 g/0.24 g; (b)
CubePOZO20/TMOS ) 0.05 g/0.5 g; (c) CubePOZO100/TMOS
) 0.05 g/0.2 g; (d) CubePOZO200/TMOS ) 0.05 g/1.0 g.
The quantity and the size of organic domain were
evaluated by nitrogen absorption porosimetry as com-
pared with calcined hybrids (Figure 9a) and Soxhlet
extraction hybrids (Figure 9b). The pore size distribution
of calcined hybrids had a maximum at 1.7 nm, while
Soxhlet extraction hybrids had very few quantity of pore
and more larger pore size of 2.9 nm, compared to those
of calcined hybrids. This result of nitrogen absorption
porosimetry is consistent with that of solvent extraction
experiments. It was considered that calcined hybrids
had a smaller pore size by the transformation from

874 Kim et al.
Macromolecules, Vol. 36, No. 3, 2003
Ta ble 3. Solven t-Resista n t P r op er ty of P olym er Hybr id s
fr om Cu beP OZOa
polymer content
solvent
(wt %)c
extraction
run
solvent
efficiency (%)
Pa
Pb
1
methanol
chloroform
methanol
3.5
5.7
70.7
33.
32.5
17.4
33.8
33.8
41.8
2
3b
(homoPOZO)
a
The polymer content in polymer hybrids before (Pb) and after
(Pa); solvent extraction efficiency E was calculated according to
the equation E ) 100(Pb -Pa)/Pb(100 - Pa). b Polymer hybrids from
homoPOZO and TMOS. c Measured by TGA.
F igu r e 10. Schematic illustration for hydrophobic interaction
between CubePOZO having hydrophobic POSS moiety them-
selves in the silica gel matrix.
Con clu sion
A new class of hybrid POZO initiated by POSS
(CubePOZO) with various feed ratios was synthesized.
CubePOZO composed of POSS as a hydrophobic portion
and POZO as a hydrophilic portion formed the hybrid
micelles in an aqueous phase, indicating that enhanced
hydrophobicity caused by the structure of POSS par-
ticipated in the formation of the micelle structure. No
aggregation of hybrid CubePOZO micelles in an aqueous
solution for long period indicated that their self-as-
sembling tendency was stable enough. Transparent
polymer hybrids from CubePOZO and TMOS utilizing
sol-gel reaction were prepared and characterized by
DSC, TGA, FT-IR, SEM, and nitrogen absorption po-
rosimetry. Hydrophobic POSS bonded covalently to
POZO were homogeneously dispersed in the silica gel
matrix at the nanometer level. The obtained polymer
hybrids from CubePOZO showed the high solvent
resistance, similar to that of polymer hybrids having an
interpenetrating polymer network structure. This novel
method for preparing hybrid micelles and polymer
hybrids from hydrophobic and hydrophilic materials
with TMOS can be potentially used to enlarge the
pathways for new organic-inorganic polymer hybrids.
F igu r e 9. Pore size distribution of (a) calcined and (b) Soxhlet
extraction CubePOZO/silica polymer hybrids.
Refer en ces a n d Notes
POSS to Si8O16 than Soxhlet extraction hybrids by no
change of CubePOZO (even little CubePOZO was ex-
tracted), as demonstrated in Figure 10.
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