Macromolecules 2004, 37, 2775-2778
2775
Mechanism for the Formation of Poly(phenylsilsesquioxane)
Sh igeyu k i Ya m a m oto,*,† Na ok i Ya su d a ,† Ak em i Ueya m a ,‡ Hir osh i Ad a ch i,† a n d
Mitsu o Ish ik a w a §
Advanced Technology R & D Center, Mitsubishi Electric Corporation, Amagasaki,
Hyogo 661-8661, J apan; Ryouden Kasei Corporation Limited, Sanda, Hyogo 669-1513, J apan; and
Department of Chemistry and Bioscience, Kurashiki University of Science and Arts, Kurashiki,
Okayama 712-8001, J apan
Received September 9, 2003; Revised Manuscript Received February 15, 2004
ABSTRACT: Poly(phenylsilsesquioxane) with molecular weight of 1400 was synthesized by hydrolysis
of phenyltrichlorosilane, followed by condensation of the resulting hydrolyzates in the presence of a
catalytic amount of hydrochloric acid in methyl isobutyl ketone. The progress of dehydration of the
hydrolyzates leading to poly(phenylsilsesquioxane) was monitored by 29Si NMR spectroscopy. Dehydration
of cis-(1,3,5,7-tetrahydroxy)-1,3,5,7-tetraphenylcyclooctasiloxane as a model compound was also investi-
gated by the 29Si NMR technique. The mechanism for the formation of poly(phenylsilsesquioxane) is
discussed.
In tr od u ction
than 10 000 by the use of this method. To our knowl-
edge, the mechanism for the hydrolysis of organotrichlo-
rosilane and condensation of its hydrolyzates has not
yet been well-defined, although mechanistic studies on
the hydrolysis of organoltrialkoxysilanes and organo-
trichlorosilanes have been reported so far.7-9
In this paper, we report the results of the 29Si NMR
spectrometric analysis for the condensation reaction of
the hydrolyzates produced by the hydrolysis of phenyl-
trichlorosilane. We also report the mechanism for the
formation of poly(phenylsilsesquioxane) on the basis of
the results obtained by the 29Si NMR spectrometric
analysis.
Recently, considerable interest has been focused on
the synthesis of polymers that can be used as micro-
electronics at the temperature above 400 °C. It is well-
known that thermal stability of polymers depends on
the bond energy of the atoms used for constraction of
the polymer backbone. Polymers composed of an Si-O
bond are very attractive for the heat-resistant sub-
stances since the bond energy of the Si-O bond is much
higher than that of the C-C and C-O bonds.
When linear organopolysiloxanes are heated at the
temperature above 300 °C, the Si-O bonds in the
polymer chain are cleaved to form cyclosiloxanes.1,2 On
the other hand, poly(organosilsesquioxane)s that have
a ladder structure are thermally stable. They do not
decompose to give the cyclic or cage products even at
above 300 °C.3
The poly(organosilsesquioxane)s are the polymers
that have a cis-syndiotactic double-chain structure and
are soluble in common organic solvents, such as tet-
rahydrofuran and methyl isobutyl ketone. When a
solution of the polymers is coated on a substrate such
as a silicone wafer by a spinner, a thin film can be
obtained.
The first synthesis of poly(organosilsesquioxane) was
reported by Brown et al. in 1960.4 They used a two-step
method, involving hydrolysis of phenyltrichlorosilane
and dehydration of the resulting hydrolyzates in the
presence of a potassium hydroxide catalyst in toluene,
for the synthesis of the polymer. Since that time, many
papers concerning the synthesis of the poly(organosil-
sesquioxane)s have been published.5,6 The polymers
have frequently been synthesized by hydrolysis of
organotrichlorosilane such as phenyltrichlorosilane, fol-
lowed by condensation of the resulting hydrolyzates. It
has been reported that the rate of hydrolysis of the
organotrichlorosilanes in these reactions is very fast and
difficult to control.4 Furthermore, it seems to be difficult
to prepare the polymers with molecular weight higher
Exp er im en ta l Section
Syn th esis of P oly(p h en ylsilsesqu ioxa n e). To a solution
of 106 g (0.50 mol) of phenyltrichlorosilane in 300 mL of methyl
isobutyl ketone was added dropwise 136 g (8.5 mol) of water
at 0 °C for 45 min. The mixture was stirred at room temper-
ature for 2 h. The organic layer was separated and washed
with water. The solvent was evaporated in vacuo to give 52 g
(80% yield) of poly(phenylsilsesquioxane) whose molecular
weight was determined to be Mw ) 1400.10,11 In this hydrolysis,
small aliquots of the solution were extracted at suitable
intervals for 29Si NMR spectrometric analysis and soaked
immediately in liquid nitrogen.12 To this was added a small
amount of Cr(acac)3 in acetone-d6 to suppress the long spin-
lattice relaxation time of 29Si. The 29Si NMR spectrum was
determined by 59.62 MHz at -57 °C, using tetramethylsilane
as an internal standard. The negative nuclear Overhauser
effect (NOE) was suppressed by gate decoupling. Data for poly-
(phenylsilsesquioxane): 1H NMR (δ in CDCl3) 6.52-8.10 (br).
13C NMR (δ in CDCl3) 128.51 (s, 2C), 131.05 (s, 1C), 134.52 (s,
2C). 29Si NMR (δ in CDCl3) -78.1 (br), -69.9 (br), -60.0 (br).
FT-IR (cm-1) 3600-3000, 3000-2800, 2000-1700, 1275, 1130-
1040, 850.10,11
Syn t h esis of cis-(1,3,5,7-Tet r a h yd r oxy)-1,3,5,7-t et r a -
p h en ylcycloocta siloxa n e. cis-(1,3,5,7-Tetrahydroxy)-1,3,5,7-
tetraphenylcyclooctasiloxane was obtained by the method
reported by Hayashi et al.13 At first, a cold mixture of 196 g
(0.93 mol) of phenyltrichlorosilane and 360 mL of acetone at
0 °C was added slowly to 7100 g (394.11 mol) of an ice-water
slurry with vigorous stirring. After stirring for 24 h, the
resulting white precipitates were filtered. The precipitates
were suspended in carbon disulfide to dissolve oily materials
and then filtered. Once again the filtrate was washed with
† Mitsubishi Electric Corporation.
‡ Ryouden Kasei Corpolation Limited.
§ Kurashiki University of Science and Arts.
10.1021/ma035337a CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/26/2004