Living radical polymerization by polyhedral oligomeric silsesquioxane- holding initiators: Precision synthesis of tadpole-shaped organic/inorganic hybrid polymers

Article abstract of DOI:10.1021/ma048877w

Incompletely condensed polyhedral oligomeric silsesquioxane (POSS) with the highly reactive group of trisodium silanolate was used for the synthesis of two initiators for atom transfer radical polymerization, one with a 2-bromoisobutyl group and the other

Full text of DOI:10.1021/ma048877w

Macromolecules 2004, 37, 8517-8522
8517
Living Radical Polymerization by Polyhedral Oligomeric
Silsesquioxane-Holding Initiators: Precision Synthesis of
Tadpole-Shaped Organic/Inorganic Hybrid Polymers
Kohji Ohno,† Satoshi Sugiyama,† Kyoungmoo Koh,† Yoshinobu Tsujii,†
Takeshi Fukuda,*,† Mikio Yamahiro,‡ Hisao Oikawa,‡ Yasuhiro Yamamoto,‡
Nobumasa Ootake,‡ and Kenichi Watanabe‡
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan, and Goi Research
Center, Chisso Petrochemical Corporation, 5-1 Goi-Kaigan, Ichihara, Chiba 290-8551, Japan
Received June 8, 2004; Revised Manuscript Received September 8, 2004
ABSTRACT: Incompletely condensed polyhedral oligomeric silsesquioxane (POSS) with the highly reactive
group of trisodium silanolate was used for the synthesis of two initiators for atom transfer radical
polymerization, one with a 2-bromoisobutyl group and the other with a chlorosulfonyl group. These
initiators were applied to solution polymerizations of styrene and methyl methacrylate in the presence
of a copper complex. In both systems, polymerization proceeded in a living fashion, as indicated by the
first-order kinetics of monomer consumption, the evolution of molecular weight in direct proportion to
monomer conversion, the good agreement of molecular weight with the theoretical one, and the low
polydispersity, thus providing tadpole-shaped polymers with an “inorganic head” of POSS and an “organic
tail” of well-defined polymer. Thermogravimetric and differential scanning calorimetric studies showed
that both thermal degradation and glass transition temperatures of the organic/inorganic hybrid polymers
with molecular weights up to about 20 000 were enhanced as compared to those of model polymers without
the POSS moiety.
Introduction
fascinating compound because it undergoes corner-
capping reaction with chlorosilanes, transition metal
complexes, and metal alkyl complexes so as to produce
a wide variety of functional POSSs.14,15 Very recently,
we developed an efficient method for the synthesis of
incompletely condensed POSS with the highly reactive
group of trisodium silanolate, heptaphenyltricyclohep-
tasiloxane trisodium silanolate (7Ph-T7-(ONa)3, Scheme
1). The reaction of 7Ph-T7-(ONa)3 with varied types of
trichlorosilanes proceeded much faster and more selec-
tively than the conventional one using the trisilanol
group, thus giving the desired products in a high yield.16
The goal of this study is to demonstrate that 7Ph-
T7-(ONa)3 can be used to produce a more efficient and
versatile initiator for copper-mediated ATRP for the
synthesis of well-defined, tadpole-shaped polymeric
hybrids with a POSS at the end of polymer chain. This
will be illustrated by the synthesis of two types of
initiators that will eventually yield POSS-carrying low-
polydispersity polymers with a wide range of molecular
weights. The thermal properties of the resultant hybrids
will also be demonstrated in terms of glass transition
and thermal degradation temperatures.
Polyhedral oligomeric silsesquioxanes (POSSs), cube-
octameric molecules with Si-O-Si framework, have
attracted much interest as a nanoscale building block
for the construction of organic/inorganic hybrid materi-
als.1 Strategies have been made for the synthesis of
hybrid materials by incorporating POSSs into polymers
to improve their thermal and mechanical properties as
a result of homogeneously dispersing inorganic sub-
stances into polymers at the nanometer level.2,3 Vinyl
monomers with a pendant group of POSSs were copo-
lymerized with a variety of monomers.4 POSSs func-
tionalized with reactive groups such as epoxy, amine,
isocyanate, and vinyl ones were used as a cross-linker
to produce cross-linked hybrid polymers.5,6 Poly(ethyl-
ene oxide) (PEG)-functionalized POSS was synthesized
by the reaction of octahydrido-POSS with allyl-PEG in
the presence of a Pt catalyst.7 Hybrid polyoxazolines
were synthesized by ring-opening polymerization of
2-methyl-2-oxazoline with an initiator-functionalized
POSS.8 Atom transfer radical polymerization (ATRP)9,10
was also applied to the synthesis of POSS-based hybrid
polymers.11,12 Matyjaszewski et al. showed that a com-
mercially available benzyl chloride-holding POSS served
as an initiator for ATRP of styrene (S), yielding poly-
styrenes (PSs) having a POSS moiety at the end of
polymer chain.12 Laine et al. reported that a star
polymer having a POSS core was synthesized by ATRP
of methyl methacrylate (MMA) initiated by an octafunc-
tional POSS initiator.13
Experimental Section
Materials. Ethyl 2-bromoisobutylate (98%, 2-(EiB)Br) was
used as received from Nacalai Tesque Inc., Osaka, Japan.
L-Sparteine (99%, Sp) was purchased from Aldrich and used
without further purification. Methyl methacrylate (99%, MMA)
and styrene (99%, S) were obtained from Nacalai Tesque Inc.
and purified by distillation under reduced pressure over
calcium hydride. 2-(4-Chlorosulfonylphenyl)ethyltrichlorosilane
(50% in dichloromethane, CTS) was obtained from Gelest Inc.
7Ph-T7-(ONa)3 was prepared as described in the patent.16 All
other reagents were purchased from commercial sources and
used as received.
Incompletely condensed POSS, which has a trisilanol
moiety at one corner of the cubelike framework, is a
† Institute for Chemical Research, Kyoto University.
‡ Goi Research Center, Chisso Petrochemical Corp.
* To whom correspondence should be addressed. E-mail:
fukuda@scl.kyoto-u.ac.jp.
Measurements. Gel permeation chromatographic (GPC)
analysis was carried out at 40 °C on a high-speed liquid
10.1021/ma048877w CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/21/2004

8518 Ohno et al.
Macromolecules, Vol. 37, No. 23, 2004
Scheme 1. Synthesis of (a) 7Ph-T8-CSPE and (b) 7Ph-T8-BIE
1
chromatography system (Shodex GPC-101) equipped with a
guard column (Shodex GPC KF-G), two 30 cm mixed columns
(Shodex GPC KF-804L, exclusion limit ) 400 000), and a
differential refractometer (Shodex RI-101). Tetrahydrofuran
(THF) was used as an eluent at a flow rate of 0.8 mL/min.
Poly(methyl methacrylate) (PMMA) and polystyrene (PS)
standards were used to calibrate the GPC system. Nuclear
magnetic resonance (1H, 13C, and 29Si NMR) spectra were
obtained on a JEOL/AL400 400 MHz spectrometer. Thermo-
gravimetric analysis (TGA) was performed on a Perkin-Elmer
TGA 7 thermogravimetric analyzer. Measurements were car-
ried out under a continuous flow of He gas from 50 to 800 °C
at the heating rate 20 °C/min. The degradation temperature
Tdeg was defined as the point of the maximum mass decrement
rate. Differential scanning calorimetry (DSC) was performed
on a Perkin-Elmer DSC 7 under a N2 atmosphere. The
instrument was calibrated with known standards: indium (Tm
) 156.6 °C) and zinc (Tm ) 419.5 °C). The sample was heated
from 50 to 180 °C at the rate 200 °C/min and kept at 180 °C
for 5 min and then cooled to 10 °C at the rate -200 °C/min.
After the sample was kept at 10 °C for 3 min, measurement
was carried out with the scan rate of 10 °C/min within the
temperature range 10-150 °C. The glass transition temper-
ature Tg was obtained at the midpoint of the specific heat
increment.
Synthesis of 2-(4-Chlorosulfonylphenyl)ethylhepta-
phenyl-T8-silsesquioxane (7Ph-T8-CSPE, Scheme 1). 50
wt % of CTS in dichloromethane (10.17 g, 15 mmol of CTS)
was quickly added to a cold solution of 7Ph-T7-(ONa)3 (10 g,
10 mmol) in dry THF (200 mL) at 0 °C. The mixture was
magnetically stirred for 1 h at 0 °C. The resultant precipitate
was removed by filtration, and the filtrate was concentrated
by a rotary evaporator to obtain a slightly yellow oil. The
residue was diluted with ethyl acetate (100 mL), and the
mixture was again concentrated by a rotary evaporator until
a slightly cloudy solution was obtained. The system was cooled
in a refrigerator to obtain a white solid, which was recrystal-
lized from ethyl acetate (4.88 g, 42%). IR (KBr, cm-1): 1430
and 1135-1090 (Si-Ph), 1380 and 1190 (-SO2Cl), and 1090-
1020 (Si-O-Si). H NMR (CDCl3, 400 MHz): δ 1.23 (t, 2H,
Si-CH2-), 2.91 (t, 2H, -CH2-C6H4), 7.30-7.79 (m, 39 H, Si-
C6H5 and -C6H4-SO2Cl). 13C NMR (CDCl3, 100 MHz): δ 13.0
(Si-CH2-), 29.0 (-CH2-C6H4), 128.1, 130.2, 131.1, and 134.3
(Si-C6H5), 127.2, 129.3, 142.0, 152.3 (-C6H4-SO2Cl). 29Si
NMR (CDCl3, 79 MHz): δ -66.69 (-CH2-SiO1.5), -78.35,
-78.41, and -78.67 (C6H5-SiO1.5). Anal. Calcd for C50H43O14-
SClSi8: C, 51.77; H, 3.74. Found: C, 52.08; H, 3.74.
Synthesis of 2-Bromoisobutyryloxyethylheptaphenyl-
T8-silsesquioxane (7Ph-T8-BIE, Scheme 1). 7Ph-T8-BIE
was synthesized via the three step reactions described below.
First, 7Ph-T7-(ONa)3 (10 g, 10 mmol), triethylamine (1.5 g, 14.8
mmol), and dry THF (200 mL) were charged into a round-
bottom flask, to which acetoxyethyltrichlorosilane (3.3 g, 14.8
mmol) was quickly added at room temperature. The mixture
was magnetically stirred for 2 h at room temperature and then
poured into n-hexane (1 L) to obtain a crude product. The
resultant solid was redissolved in toluene (100 mL) and
washed three times with water (3 × 330 mL). The organic layer
was collected and dried over anhydrous MgSO4. After filtra-
tion, ethanol (100 mL) was added into the filtrate to yield
acetoxyethylheptaphenyl-T8-silsesquioxane (7Ph-T8-AE) as a
white solid (6.88 g, 66%). IR (KBr, cm-1): 1740 (CdO), 1430
and 1135-1090 (Si-Ph), 1240 (C-O), 1090-1000 (Si-O-Si).
1H NMR (CDCl3, 400 MHz): δ 1.33-1.37 (t, 2H, Si-CH2-),
1.84 (s, 3H, CH3-CdO), 4.28-4.32 (t, 2H, -O-CH2-), 7.31-
7.46 and 7.72-7.82 (m, 35 H, Si-C6H5). 13C NMR (CDCl3, 100
MHz): δ 13.2 (Si-CH2-), 20.8 (CH3-CdO), 60.6 (-O-CH2-
), 128.1, 130.2, 131.0-130.1, and 134.3-130.4 (Si-C6H5), 171.2
(CdO). 29Si NMR (CDCl3, 79 MHz): δ -67.97 (-CH2-SiO1.5),
-78.36 and -78.67 (C6H5-SiO1.5).
Second step: 7Ph-T8-AE (2.58 g, 2.47 mmol), methanol (175
mL), and chloroform (175 mL) were charged in a round-
bottomed flask, to which concentrated H2SO4 (0.7 mL) was
added at room temperature. The mixture was magnetically
stirred for 72 h at room temperature and concentrated by a
rotary evaporator. The oily residue was redissolved in ethyl
acetate (500 mL) and washed twice with water (2 × 500 mL).
Drying over anhydrous MgSO4, filtration, and evaporation of

Macromolecules, Vol. 37, No. 23, 2004
Polyhedral Oligomeric Silsesquioxane 8519
the solvent produced a white solid, which was recrystallized
from toluene to obtain hydroxyethylheptaphenyl-T8-silsesqui-
oxane (7Ph-T8-HE) (2.3 g, 91%). IR (KBr, cm-1): 3600-3200
(OH), 1420 and 1135-1090 (Si-Ph), 1090-1000 (Si-O-Si).
1H NMR (CDCl3, 400 MHz): δ 1.26-1.31 (t, 2H, Si-CH2-),
1.42-1.62 (br, 1H, -OH), 3.85-3.87 (t, 2H, -O-CH2-), 7.31-
7.46 and 7.72-7.82 (m, 35 H, Si-C6H5). 13C NMR (CDCl3, 100
MHz): δ 17.5 (Si-CH2-), 58.6 (-O-CH2-), 127.9-128.1,
130.3, 131.0-130.1, and 134.1-134.5 (Si-C6H5). 29Si NMR
(CDCl3, 79 MHz): δ -67.31 (-CH2-SiO1.5), -78.42 and -78.79
(C6H5-SiO1.5).
1.74 mmol), and diphenyl ether (4.37 g) carried out at 110 °C
for 9 h gave a monomer conversion of 46% and a POSS-PS
product with Mn ) 25 600 and Mw/Mn ) 1.28.
Results and Discussion
Synthesis of POSS-Holding Initiators. Matyjas-
zewski et al. showed that a commercially available
benzyl chloride (BzCl)-functionalized POSS, which con-
tains seven cyclopentyl groups for providing increased
solubility in organic solvents and one BzCl moiety for
initiation site for ATRP, was useful for the synthesis of
well-defined PS with one bulky POSS moiety at the end
of polymer chain.12 BzCl, however, is not a particularly
good ATRP initiator, for the dissociation rate constant
of the C-Cl bond of benzyl chloride is smaller than those
of the carbon-halogen bonds of most other common
Third step: 2-Bromoisobutyryl bromide (0.3 g, 1.3 mmol)
was added to a cold solution of 7Ph-T8-HE (1.21 g, 1.2 mmol)
in dry dichloromethane (5 mL) with triethylamine (0.12 g, 1.19
mmol) at -78 °C. The mixture was magnetically stirred for 1
h at -78 °C and then another 2 h at room temperature. After
filtration, the filtrate was diluted with dichloromethane (100
mL) and washed with water (300 mL), twice with 1 wt % of
aqueous NaHCO3 solution (2 × 300 mL), and again twice with
water (2 × 300 mL). After drying over MgSO4 and filtration,
the filtrate was concentrated by a rotary evaporator. Methanol
(400 mL) was added into the resultant residue, and the
mixture was kept in a freezer to yield the final product 7Ph-
T8-BIE as a white solid (1.13 g, 81.4%). IR (KBr, cm-1): 1740
(CdO), 1430 and 1135-1090 (Si-Ph), 1270 (C-O), 1090-1000
initiators when compared in the same conditions.17
A
fast initiation is an important requisite for obtaining
low-polydispersity polymers. To introduce a better
initiation site into one corner of POSS, we exploited the
chemistry that involves the corner-capping reaction of
7Ph-T7-(ONa)3 by trichlorosilanes.
1
We first tried to introduce a chlorosulfonylphenyl
moiety, a precursor of which 2-(4-chlorosulfonylphenyl)-
ethyltrichlorosilane (CTS) is easily available from a
commercial source. The chlorosulfonylphenyl moiety
provides a good initiation site for ATRP, in particular,
of methacrylates.18 The corner-capping reaction of 7Ph-
T7-(ONa)3 with CTS was carried out in THF at 0 °C.
The crude product before purification was analyzed by
liquid chromatography and thin-layer chromatography,
which apparently showed the presence of byproducts,
presumably tosylates arising from the reaction of sul-
fonyl chloride group of CTS with sodium silanolates. The
byproducts and unreacted starting materials were easily
removed by repeated recrystallization to give 7Ph-T8-
CSPE in about 40% yield. Its high purity was confirmed
(Si-O-Si). H NMR (CDCl3, 400 MHz): δ 1.39-1.43 (t, 2H,
Si-CH2-), 1.79 (s, 6H, -BrC(CH3)2), 4.37-4.41 (t, 2H, -O-
CH2-), 7.31-7.46 and 7.72-7.82 (m, 35 H, Si-C6H5). 13C NMR
(CDCl3, 100 MHz): δ 12.9 (Si-CH2-), 30.6 (-BrC(CH3)2), 55.8
(-BrC(CH3)2), 62.5 (-O-CH2-), 128.0-128.1, 130.1-130.2,
131.1, and 134.3 (Si-C6H5), 171.7 (CdO). 29Si NMR (CDCl3,
79 MHz): δ -68.27 (-CH2-SiO1.5), -78.4 and -78.7 (C6H5-
SiO1.5). Anal. Calcd for C48H45O14BrSi8: C, 50.11; H, 3.94.
Found: C, 50.11; H, 4.01.
ATRP of MMA by 7Ph-T8-CSPE. A Y-shaped glass tube
with two compartments was charged in one side with a
predetermined amount of Cu(I)Br, Sp, and anisole and in the
other side with a mixture of MMA, the rest of anisole, and
7Ph-T8-CSPE. The glass tube was attached to a vacuum line
and subjected to three freeze-pump-thaw cycles. The reac-
tants were mixed by pouring the solutions into each compart-
ment and then collected in one side. The mixture was degassed
again by one freeze-pump-thaw cycle and subsequently
sealed off under vacuum. The polymerization was carried out
in a shaking oil bath (TAITEC Corp., Saitama, Japan, Personal
H-10) thermostated at 70 °C and, after a prescribed time t,
quenched to room temperature. An aliquot of the solution was
taken out for NMR measurement to estimate monomer
conversion and for GPC measurement to determine molar
mass and molecular weight distribution. The rest of the
reaction mixture was diluted by THF and precipitated in an
excess of n-hexane to obtain a polymer POSS-PMMA as a
white powder.
In a typical run, the solution polymerization of MMA with
the starting materials of MMA (2.88 g, 28.7 mmol), 7Ph-T8-
CSPE (67 mg, 0.057 mmol), Cu(I)Br (16 mg, 0.115 mmol), Sp
(54 mg, 0.23 mmol), and anisole (2.74 g) carried out at 70 °C
for 18 h gave a monomer conversion of 46% and a POSS-
PMMA product with Mn ) 27 800 and Mw/Mn ) 1.17.
ATRP of S by 7Ph-T8-BIE. A Pyrex glass tube was charged
with a predetermined amount of Cu(I)Br, to which was quickly
added a mixture of S and diphenyl ether containing a
prescribed concentration of 7Ph-T8-BIE and Sp. The system
was immediately degassed by three freeze-pump-thaw cycles
and subsequently sealed off under vacuum. The polymerization
was carried out in a shaking oil bath thermostated at 110 °C
and, after a prescribed time t, quenched to room tempera-
ture. The characterization of the resultant polymer was car-
ried out in a similar way as the ATRP of MMA. Methanol
was used as a nonsolvent for the purification of the polymer
POSS-PS.
1
by H, 13C, and 29Si NMR and elemental analysis.
The 2-bromoisobutyryl group is among the most
common initiation sites for ATRP. It has wide ap-
plicability to ATRP of various monomers including
styrenes and (meth)acrylates and is easily introduced
to many types of materials with a hydroxyl group by
reaction with commercially available 2-bromoisobutyryl
bromide.10 Therefore, we next tried to introduce the
2-bromoisobutyryl group into one corner of POSS. First,
we synthesized acetoxyethyl group-carrying POSS, 7Ph-
T8-AE, by the corner-capping reaction of 7Ph-T7(ONa)3
with acetoxyethyltrichlorosilane. 7Ph-T8-AE was then
treated with acid to deprotect the acetoxy group to
obtain hydroxyl group-carrying POSS (7Ph-T8-HE). A
dilute acidic condition must be used for the deprotection
to prevent the decomposition of the Si-O-Si framework
of POSS. Finally, the acylation of 7Ph-T8-HE with
2-bromoisobutyryl bromide and the subsequent purifi-
cation by repeated recrystallization gave the desired
product 7Ph-T8-BIE in a moderate overall yield of 50%.
ATRP by POSS-Holding Initiators. 7Ph-T8-CSPE
was employed for polymerization of MMA mediated by
a copper complex in anisole at 70 °C. Figure 1a shows
the first-order plot of monomer concentration for the
polymerization. The plot can be approximated by a
straight line passing through the origin, thus giving
first-order kinetics with respect to monomer conversion.
This means that the concentration of propagating spe-
cies is constant throughout the course of polymerization.
Figure 1b shows the number-average molecular weight
In a typical run, the solution polymerization of S with the
starting materials of S (4.53 g, 43.5 mmol), 7Ph-T8-BIE (100
mg, 0.869 mmol), Cu(I)Br (12 mg, 0.869 mmol), Sp (41 mg,

8520 Ohno et al.
Macromolecules, Vol. 37, No. 23, 2004
7Ph-T8-BIE was used for solution polymerization of
styrene with a copper complex in diphenyl ether at 110
°C. As Figure 2a,b shows, the polymerization proceeded
in a living manner, as indicated by the first-order
kinetics of monomer consumption, the evolution of Mn
in direct proportion to monomer conversion, the good
consistency of Mn with the theoretical value, and the
low polydispersity. Thus, no influence of the bulky POSS
on the initiation efficiency of 7Ph-T8-BIE was observed,
as in the case of 7Ph-T8-CSPE. The versatility of 7Ph-
T8-BIE was also confirmed by the successful control of
ATRP of MMA. For instance, the solution polymeriza-
tion of MMA (50 wt %) with the initial molar ratio of
[MMA]0/[7Ph-T8-BIE]0/[CuBr/2Sp]0 ) 500/1/1 carried
out in anisole at 70 °C for 3 h gave a monomer
conversion of 44% and a POSS-PMMA product with
Mn ) 27 700 and Mw/Mn ) 1.16.
Thermal Analysis of POSS-Carrying Polymers.
Interesting thermal properties, such as improved ther-
mal oxidative stability and increased glass transition
temperature, have been reported for a variety of POSS-
carrying polymers prepared by different techniques.3,6,19
In the following we will describe some of our preliminary
results for the thermal properties of POSS-PMMAs
prepared in this work.
DSC analysis was carried out to estimate the glass
transition temperature, Tg, of POSS-PMMAs with
different molecular weights and a series of PMMA
control samples synthesized by ATRP with p-toluene-
sulfonyl chloride as an initiator (Ts-PMMA). Figure 3
shows the Tgs of POSS-PMMA and Ts-PMMA as a
function of Mn. For both samples, Tg increases with
increasing Mn, leveling off at around 125 °C. This is a
well-known behavior of PMMA.20 Importantly, the Tg
value of POSS-PMMA is higher than that of the
corresponding Ts-PMMA, in particular, in the lower
molar mass region. Assuming that Tg of the POSS
segment is very large, the increased Tg of POSS-PMMA
is reasonably explainable by the Gordon-Taylor theory21
of the composition dependence of the Tg of random
copolymers. This theory simply states that the Tg of a
copolymer or a mixture forming one phase is given by a
composition average of those of the components. Namely,
the observed Tg enhancement may be attributed to the
high Tg or the low mobility of the POSS segment.
Thermogravimetric analysis was carried out to esti-
mate the thermal degradation temperature, Tdeg, of
POSS-PMMA and Ts-PMMA. Chen et al. previously
showed that the vinylidene-terminated PMMAs pro-
duced by the conventional free radical polymerization
with disproportionation termination thermally degrade
at lower temperature than the saturated PMMAs
prepared by the technique using the combination of
lactams and thiols.22 They explained this result in terms
of the difference in initiation mechanism of degrada-
tion: namely, the degradation of the vinylidene-
terminated PMMA is initiated by scissions at the weak
bond of the unsaturated end of the polymer chain, while
the degradation of the saturated PMMA is initiated
mainly by the random scission on the polymer main
chain.22,23 PMMA prepared here by ATRP is expected
to have a very small fraction of such an unsaturated
chain end due to the living character of the polymeri-
zation process. In fact, the Tdegs of Ts-PMMAs are
higher than that of the vinylidene-terminated PMMA
and are as high as that of the saturated PMMA
prepared by Chen et al. Figure 4 compares the Tdegs of
Figure 1. (a) Plot of ln([M]0/[M]) vs t for the polymerization
of methyl methacrylate (MMA) and (b) evolution of number-
average molecular weight (Mn) and polydispersity index (Mw/
Mn) of POSS-PMMAs as a function of monomer conversion.
Solution polymerization of MMA (50 wt %) in anisole at 70 °C
with 7Ph-T8-CSPE: [MMA]0/[7Ph-T8-CSPE]0/[Cu(I)Br]0/[Sp]0
) 500/1/2/4. The full line in (b) represents the theoretical
prediction.
Mn and the polydispersity index Mw/Mn of the produced
polymer, both estimated by PMMA-calibrated GPC, as
a function of monomer conversion. The Mn increases
linearly with conversion, remaining close to the theo-
retical value Mn,theo calculated as the molar ratio of
polymerized monomer to the initiator. To check the
validity of the GPC analysis, 1H NMR measurement of
one sample with Mn (GPC) ) 3500 was carried out. The
estimated Mn value was 3450, in good agreement with
the GPC value. These results indicate that the initiation
efficiency of 7Ph-T8-CSPE is approximately 100%. The
Mw/Mn ratio gradually decreases with increasing mono-
mer conversion, approaching less than 1.1 at about 50%
of monomer conversion, and after this conversion, it
gradually increases with monomer conversions but still
stays lower than 1.3. This system could be successfully
applied to the synthesis of PMMA with a higher mo-
lecular weight by simply changing the molar ratio of
starting materials. For instance, the bulk polymeriza-
tion of MMA with the initial molar ratio of [MMA]0/
[7Ph-T8-CSPE]0/[CuBr/2Sp]0 ) 1000/1/4 carried out at
70 °C for 12 h gave a POSS-PMMA product of Mn )
108 000 and Mw/Mn ) 1.2. These results show that the
chlorosulfonylphenyl moiety attached to the bulky POSS
works as an efficient initiation site for ATRP like the
low molar mass initiator, p-toluenesulfonyl chloride, for
example.

Macromolecules, Vol. 37, No. 23, 2004
Polyhedral Oligomeric Silsesquioxane 8521
Figure 4. Thermal degradation temperatures Tdegs of POSS-
PMMA (b) and Ts-PMMA (O) as a function of number-
average molecular weight (Mn). The data are the mean of the
two individual experiments.
ability of bond scission should be independent of chain
length.24
More interestingly, in the studied range of Mn, the
Tdeg value of POSS-PMMA is higher than that of the
corresponding Ts-PMMA by a maximum of 30 °C.
Clearly, the POSS moiety has a marked effect on the
thermal stability of PMMA. Even though we cannot
provide a definite explanation for this phenomenon at
present, we would consider that it has something to do
with the low mobility of the POSS segment. If the
polymer radical mediating degradation should chain
transfer to other polymer to produce a new degradation
point there, this process would be correlated with the
mobility of the chains or the system as a whole. In this
regard, POSS-PMMA and Ts-PMMA can be different,
as suggested by the above-noted Tg experiments.
Although we do not present the data, the POSS-PS
hybrids showed qualitatively similar thermal behavior
to POSS-PMMA.
Figure 2. (a) Plot of ln([M]0/[M]) vs t for the polymerization
of styrene (S) and (b) evolution of number-average molecular
weight (Mn) and polydispersity index (Mw/Mn) of POSS-PSs
as a function of monomer conversion. Solution polymerization
of S (50 wt %) in diphenyl ether at 110 °C with 7Ph-T8-BIE:
[S]0/[7Ph-T8-BIE]0/[Cu(I)Br]0/[Sp]0 ) 500/1/1/2. The full line in
(b) represents the theoretical prediction.
Conclusions
Two types of ATRP initiators, one with a 2-bro-
moisobutyl group and the other with a chlorosulfonyl
group, were synthesized by the reaction of incompletely
condensed POSS and trichlorosilanes. The solution
polymerization of S or MMA using these initiators
mediated by a copper complex proceeded in a living
fashion, thus providing tadpole-shaped polymers with
an “inorganic head” of POSS and an “organic tail” of
well-defined polymer. TGA and DSC studies showed
that both Tdeg and Tg of the organic/inorganic hybrid
polymers were more and more enhanced compared to
those of the model polymers without a POSS moiety,
as the polymer tail became shorter or the weight
fraction of the POSS moiety became larger.
Figure 3. Glass transition temperatures Tgs of POSS-PMMA
(b) and Ts-PMMA (O) as a function of number-average
molecular weight (Mn). The data are the mean of the three
individual experiments.
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