Preparation of spherical poly(methylsilsesquioxanes) beads and their properties

Article abstract of DOI:10.1080/15421400802333303

The spherical poly(methylsilsesquioxane) (PMSQ) beads with the diameter of 2, 5 and 10 micron, respectively were prepared from methyltrimethoxysilane (MTMS) by two steps, acid hydrolysis and base condensation process in aqueous solution. Acetic acid and a

Full text of DOI:10.1080/15421400802333303

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Preparation of Spherical
Poly(methylsilsesquioxanes)
Beads and Their Properties
Heon Seung Chae a , Seog Jeong Song b & Yun Heum
Park a c
a Department of Chemical Engineering ,
Sungkyunkwan University , Suwon , South Korea
b Kolon Central Research Park , Yongin , Gyeonggi-
Do , South Korea
c Hyperstructured Organic Materials Research
Center , Seoul , South Korea
Published online: 31 Aug 2012.
To cite this article: Heon Seung Chae , Seog Jeong Song & Yun Heum Park
(2008) Preparation of Spherical Poly(methylsilsesquioxanes) Beads and Their
Properties, Molecular Crystals and Liquid Crystals, 492:1, 28/[392]-38/[402], DOI:
10.1080/15421400802333303
To link to this article: http://dx.doi.org/10.1080/15421400802333303
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Mol. Cryst. Liq. Cryst., Vol. 492, pp. 28=[392]–38=[402], 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802333303
Preparation of Spherical Poly(methylsilsesquioxanes)
Beads and Their Properties
Heon Seung Chae1, Seog Jeong Song2,
and Yun Heum Park1,3
1Department of Chemical Engineering, Sungkyunkwan University,
Suwon, South Korea
2Kolon Central Research Park, Yongin, Gyeonggi-Do, South Korea
3Hyperstructured Organic Materials Research Center, Seoul,
South Korea
The spherical poly(methylsilsesquioxane) (PMSQ) beads with the diameter of 2, 5
and 10 micron, respectively were prepared from methyltrimethoxysilane (MTMS)
by two steps, acid hydrolysis and base condensation process in aqueous solution.
Acetic acid and ammonium hydroxide were used to initiate the acid hydrolysis
and base condensation, respectively. The bead size was affected and controlled
by the reaction variables, such as the agitation speed, reaction temperature, sol-
vent and concentration of monomer and catalyst. The prepared PMSQ beads were
characterized by 29Si CP=MAS NMR and FT-IR. Especially in preparing the
spherical PMSQ bead with the diameter of 10 micron, it was found that organic
solvent was necessary to obtain the desired size compared with the preparation
condition of 2 and 5 micron beads. The prepared PMSQ beads showed good ther-
mal stability and compression recovery ratio. The haze value of PMSQ beads was
remarkably higher than that of acrylic beads due to the relatively low refractive
index of PMSQ.
Keywords: compression recovery; condensation; haze value; hydrolysis; poly(methylsil-
sesquioxane)
The Korea Science and Engineering Foundation through the Hyperstructured
Organic Materials Research Center supported this work. Also KOLON Central Research
Park assisted to make progress this study. We wish to acknowledge the support with
thanks.
Address correspondence to Yun Heum Park, School of Applied and Chemical
Engineering, Sungkyunkwan University, Suwon 440-746, South Korea. E-mail:
yhpark@skku.edu
28=[392]

The Preparation and Properties of Poly(methylsilsesquioxanes)
29=[393]
1. INTRODUCTION
Polyorganosilsesquioxane (POSQ) is a ladder or cage type siloxane
polymer [1] used widely in paint, cosmetics and coating applications by
its thermal stability and mechanical strength. Since Brown et al. [2]
¨
first introduced the structure of POSQ and Stober et al. [3] developed
the preparation system of POSQ, many scientists have studied syn-
thetic methods including size control [4–9] and applications of POSQ
[10–11]. But almost all studies were related to the preparation of POSQ
beads with the diameter of around 2 mm and it was difficult to prepare
larger spherical beads with the diameter of over 2 mm. Recently, poly
(methylsilsesquioxane) (PMSQ) beads with the diameter of over 2 mm
become increasingly needed for the applications to light diffuser film
and plate in liquid crystal display because optical properties are
strongly related to the size and refractive index of PMSQ beads.
In this paper, the optimum preparation condition for preparing
spherical PMSQ beads with the diameters of over 2 mm and with the
narrow diameter distribution was intensively studied by controlling
the experimental variables such as the agitation speed, concentration
of monomer and catalyst, reaction temperature and solvent. The thermal
stability, elastic property and optical properties of prepared PMSQ beads
were investigated for the applications of light diffuser film and plate.
2. EXPERIMENTAL
Chemicals
The chemicals used for the preparation of PMSQ beads were ACS
grade (Aldrich). Methyltrimethoxysilane (MTMS) as starting mono-
mer, acetic acid (AA) as hydrolysis catalyst, ammonia water (NH4OH)
as condensation catalyst and methoxytrimethylsilane (MOTMS) as
end-capping monomer were purchased from Aldrich. Deionized water
(DIW) was used as main solvent and additional organic solvent, isopro-
pyl alcohol (IPA) and 1-hexanol were used without further purification.
Preparation of Poly(methylsilsesquioxane) (PMSQ) Beads
For the preparation of PMSQ beads, hydrolysis and condensation reac-
tions shown in Scheme 1 were carried out under dry inert nitrogen gas.
Step 1. Acid hydrolysis of MTMS
DIW and AA were mixed and stirred for 10 min under nitrogen atmos-
phere in 1L double jacket glass reactor and followed by addition of
MTMS.

30=[394]
H. S. Chae et al.
SCHEME 1 The preparation route of PMSQ beads.
Step 2. Base condensation of methoxysilanol
DIW was added and mixed into the solution of step 1 for 10 min, fol-
lowed by addition of 28% ammonia water. When turbidity formed,
stopped stirring and stayed for 3 hours at room temperature. Methoxy-
trimethylsilane (MOTMS) was added and stirred for 10 min, then kept
overnight. The precipitate was filtered and washed with DIW and
dried in vacuum oven for 3 hours at 150ꢀC.
Characterization and Analysis of PMSQ Beads
The structure of prepared PMSQ beads was characterized by 29Si cross
polarization-magnetic angle spinning (CP=MAS) NMR (Bruker) and
FT-IR (Perkin Elmer, Spectrum 2000) spectroscopy. The size and mor-
phology of resulting beads were determined with a field emission scan-
ning electron microscope (FE-SEM, HITACHI S-4300). The bead size
distribution was measured with a particle size analyzer (Beckmann
Coulter, LS 13 320).
Thermal Stability and Compression Property of PMSQ Beads
The thermal stability of prepared PMSQ beads was investigated with
a TGA (TA Instrument Q50). The compression and elastic property of
prepared PMSQ and commercial poly(methyl methacrylate) (PMMA)
beads (KOLON, Diasphere1 PU-510) were determined by nano
indenter (Shimadzu Co., MCT-W500). The recovery ratio was calcu-
lated using the following equation [12]
ðD1 ꢁ D2Þ
Recovery ratio ð%Þ ¼
ꢂ 100;
D1
where D1 is the indented depth at the force of 1 gf, D2 is the depth
indentation after removing force.

The Preparation and Properties of Poly(methylsilsesquioxanes)
31=[395]
Application and Optical Properties of PMSQ Beads
Light diffuser films were prepared by coating the formulation solution
with PMSQ beads and PMMA beads, respectively. Acrylic resin
(Aekyoung Co.), methyl ethyl ketone, toluene and PMSQ or PMMA
beads were well mixed and dispersed by mill. Prepared composition
mixture was coated on 188 mm PET film, the final coating thickness
of 25 mm was obtained after drying. The light diffuser plate was pre-
pared by melt-extruding polystyrene mixed with prepared PMSQ
and PMMA beads, respectively. The light transmittance (TT) and haze
value (Hz) of diffuser film and plate were calculated in the backlight
unit (BLU) system composed of lamp, reflection sheet, light diffuser
plate and film.
3. RESULTS AND DISCUSSION
The prepared PMSQ was reacted additionally with end capping
monomer, MOTMS because the existing free hydroxyl group in PMSQ
as shown in Figure 1 diminishes the water resistance. The prepared
PMSQ was characterized by 29Si CP=MAS NMR and FT-IR spectra
as shown in Figures 2 and 3, respectively. In 29Si CP=MAS NMR
spectrum, only two characteristic methyl modified peaks at ꢁ57.6
and ꢁ66.5 ppm were appeared, which indicated that silanol group
originally at ꢁ100.3 ppm was completely converted to the networked
SiꢁOꢁSi bond. FT-IR spectrum shows the peaks at 2890–2950, 1260
and 1000–1100 cmꢁ1 corresponding to CꢁH stretch, SiꢁCH3 symme-
tric deformation and SiꢁOꢁSi asymmetric stretch, respectively.
Especially no peak at 3440 cmꢁ1 from SiꢁOH was observed, which
means that complete condensation reaction has occurred.
In order to find the optimum condition for preparing the spherical
PMSQ beads with larger diameter and narrower diameter distri-
bution, the agitation speed, reaction temperature and concentration
FIGURE 1 Chemical structure of PMSQ.

32=[396]
H. S. Chae et al.
FIGURE 2 29Si CP=MAS NMR spectrum of PMSQ.
FIGURE 3 FT-IR spectrum of PMSQ.

The Preparation and Properties of Poly(methylsilsesquioxanes)
33=[397]
TABLE 1 Effect of Agitation Speed and Temperature on the Final PMSQ
Bead Diameter at the Condition of [AA] ¼ 0.01 mol%, [NH4OH] ¼ 0.1 mol%,
[MTMS] ¼ 1.39 mol%, [MOTMS] ¼ 0.04 mol% and [DIW] ¼ 98.47 mol%
Process Parameter
Results
Experiment
No.
Agitation
speed (rpm)
Temperature
(ꢀC)
Average
diameter (mm)
C.V.
(%)
A-1
A-2
A-3
B-1
B-2
B-3
C-1
C-2
C-3
100
100
100
50
50
50
20
20
20
10
20
40
10
20
40
10
20
40
3.4
2.9
1.5
2.8
2.6
1.7
2.5
2.4
1.8
48.1
49.5
50.2
14.2
20.7
35.2
8.1
8.5
20.1
of monomer and catalyst were varied systematically. As shown in
Table 1, high agitation speed at step 2 led to obtain the spherical
PMSQ bead with larger diameter but broad diameter distribution with
coefficient value (C.V.) of over 40%. This might be due to the following
argue, high speed agitation makes more frequent collision between
small aggregates and consequently gives larger coagulations. The
result of this preparation technique is contrary to that of the seed-
growth preparation technique such as the emulsion polymerization.
However, the desired beads with narrow diameter distribution were
obtained at the temperature below 20ꢀC. The minimum amount of
AA as a hydrolysis catalyst was needed only to decrease the reaction
time because the PMSQ beads were not formed in this step 1 and
AA did not affect critically on the final bead size. When introduced
the alkali (NH4OH) catalyst in hydrolyzed solution, the turbidity
was formed and the final bead diameter decreased gradually with
the increase of alkali concentration. From the several repeated experi-
ments it was found that the optimum AA and NH4OH concentration
for preparing PMSQ beads were 0.01 mol% and 0.1 mol%, at the pH
range of 3.5–3.6 and 9.4–10.5, respectively. The effect of monomer
(MTMS) concentration on the diameter of PMSQ beads is shown in
Figure 4. The final bead diameter increased drastically with the
increase of the monomer concentration in the range of below 2.19%
but the bead size gradually decreased in the range of above 2.19%.
From the result of Figure 4 it was concluded that the beads with
the diameter of below 8 mm can be prepared by varying monomer

34=[398]
H. S. Chae et al.
FIGURE 4 Effect of MTMS concentration on the final PMSQ bead diameter
and diameter distribution at the condition of [AA] ¼ 0.01 mol%, [NH4OH] ¼
0.1 mol%, [MOTMS] ¼ 0.04 mol%, T ¼ 20ꢀC and agitation speed ¼ 20 rpm.
concentration, whereas the beads with the diameter of above 8 mm
cannot be obtained easily by controlling the monomer concentration
under the condition of agitation speed (20 rpm), temperature (20ꢀC)
and concentration of AA (0.01 mol%) and NH4OH (0.1 mol%) at
20ꢀC. Recently, S.M. Koo et al. [13] reported that the spherical beads
with the diameter of 1–2 mm could be prepared from the seed-growth
technique through hydrolysis and condensation process with the intro-
duction of additional solvent such as alcohol.
In order to obtain the spherical PMSQ beads with the diameter of
10 mm in this preparation technique, 1-propanol and 1-hexanol in
addition to DIW were used, respectively. 0.33 mol% of 1-hexanol was
useful for preparing 10 mm beads with relatively narrow diameter dis-
tribution (C.V. of 35%) under the MTMS concentration of 4.07 mol%.
FIGURE 5 SEM images of spherical PMSQ beads with the diameter of (a)
2 mm, (b) 5 mm, and (c) 10 mm.

The Preparation and Properties of Poly(methylsilsesquioxanes)
35=[399]
FIGURE 6 TGA curve of PMSQ bead.
When introduced the shorter chain alcohol, 1-propanol, the bead diam-
eter was increased to 10 mm but the diameter distribution was broad
(C.V. of over 56%). It was explained that long chain alcohol lowered
repulsive polarity and made the colloidal particles more stable. The
SEM images of prepared PMSQ beads with the diameter of 2, 5 and
10 mm, respectively are shown in Figure 5.
Thermal stability of PMSQ beads was investigated by thermogravi-
metric analysis (TGA) in N2 flow at 20–800ꢀC. As shown in Figure 6,
the initial decomposition occurred at about 250–300ꢀC originated from
the thermal decomposition of methyl group of PMSQ and total weight
loss in the range of 200–600ꢀC was under 4%, which was in accordance
with the decomposition of typical polysilsesquioxane. Hardness
and elasticity of polymeric beads are important for the evaluation of
resistance to external compression and scratch. To evaluate the
compression and recovery property, prepared PMSQ and commercial
TABLE 2 Compression and Recovery Ratios of PMSQ and PMMA Beads
Compression and recovery ratio
Bead type
Bead size (mm)
D1 (mm)
D2 (mm)
Recovery ratio (%)
PMSQ
PMMA
5.745
5.215
2.704
2.454
2.252
2.246
16.7
8.5

36=[400]

The Preparation and Properties of Poly(methylsilsesquioxanes)
37=[401]
poly(methyl methacrylate) (PMMA) beads with the diameters of 5 mm
were adopted and compared. It can be known from the value of D1 and
recovery ratio in Table 2 that the prepared PMSQ bead is less hard
and more elastic than the PMMA bead. It is assumed that these
results are due to the ladder or cage type molecular structure of pre-
pared PMSQ beads. In order to evaluate the potential application to
light diffusion film and plate, the optical properties of prepared PMSQ
and commercial PMMA bead with the diameter of 5 mm, respectively
were investigated. The comparative results were shown in Table 3.
In general, the haze value could be described by the equation shown
as below.
ðDFÞ
Haze value ¼
ꢂ 100ð%Þ
ðTTÞ
where (DF: Diffuse Luminous Transmittance, TT: Total Luminous
Transmittance)
According to the equation, haze value correlates with DF value
which is directly influenced by different refractive indices of two media
as the light passes through. Therefore, the higher haze value of the
diffusion film and plate with PMSQ was obtained, which is due to
greater difference of refractive indices between PMSQ bead and PET
film or polystyrene plate than that of refractive indices between
PMMA bead and PET film or polystyrene plate.
4. CONCLUSION
The spherical PMSQ beads with the diameter of 2, 5 and 10 mm were
successfully prepared by two steps, acid-catalyzed hydrolysis and
alkali-catalyzed condensation of MTMS monomer under the appropri-
ate preparation condition. In preparing PMSQ beads with the diam-
eter of 2 and 5 mm, MTMS concentration had an important effect on
the desired bead size under the condition of agitation speed (20 rpm),
temperature (20ꢀC) and concentration of AA (0.01 mol%) and NH4OH
(0.1 mol%). Organic solvent, 1-hexanol was needed to prepare the
10 mm PMSQ bead with the narrow diameter distribution under the
MTMS concentration of 4.07 mol%. The prepared PMSQ beads showed
good thermal stability, elasticity and high haze value.
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