Synthesis, characterization, and properties of novel phenylene-silazane-acetylene polymers

Article abstract of DOI:10.1016/j.polymer.2010.09.047

New phenylene-silazane-acetylene polymers, P1 and P2, have been synthesized using Sonogashira cross-coupling reactions with a new designed ethynyl-ended silylenediamine, N,N'-bis(4-ethynylphenyl)-1,1-diphenylsilylenediamine (1), as the key monomer. This a

Full text of DOI:10.1016/j.polymer.2010.09.047

Polymer 51 (2010) 5970e5976
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Polymer
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Synthesis, characterization, and properties of novel phenylene-silazane-acetylene
polymers
,
,
,
,
Rui Wang a b, Wei Liu a b, Lei Fang a b, Caihong Xu a
*
a Beijing National Laboratory for Molecular Sciences(BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b Graduate School of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
New phenylene-silazane-acetylene polymers, P1 and P2, have been synthesized using Sonogashira cross-
coupling reactions with a new designed ethynyl-ended silylenediamine, N,N0-bis(4-ethynylphenyl)-1,1-
diphenylsilylenediamine (1), as the key monomer. This also represents the first example that
construction of polymers containing silazane unit with Sonogashira coupling reaction. The structures of
monomer and polymers were well characterized. Their thermal properties were studied by differential
scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both polymers had good thermal
stability with their temperatures at 5% weight loss (Td5) being higher than 394 ꢀC under nitrogen and
higher than 385 ꢀC in air, respectively. Their char yields at 1000 ꢀC under N2 were above 70%. The
fundamental photophysical properties in solution were also investigated. Both polymers showed fluo-
rescence in ultraviolet region with moderate quantum yields. These polymers had potential to be used as
high-temperature resistant resins and light-emitting materials with good thermal stability.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 23 June 2010
Received in revised form
4 September 2010
Accepted 16 September 2010
Available online 29 October 2010
Keywords:
Sonogashira cross-coupling
Silylenediamine monomer
Silicon-containing polymer
1. Introduction
directly connected with acetylene and/or arylene unit through SieC
bond in these polymers.
Polymers based on the arylene, acetylene, and silicon-containing
unit have been the subjects of intensive and varied interest in recent
years. These polymers show high potential application in the
microelectronic and aerospace industries, as processable light-
weight, highly heat-resistant materials [1]. Avast of research related
to such polymers has contributed to silylene-phenylene-acetylene
polymers [2] (Scheme 1, a, b) and silarylene-siloxane-acetylene
polymers (Scheme 1, c) [1a,3], which containing SieC and SieC/
SieO bonds in their main chains, respectively. Silylene-phenylene-
acetylene polymers composed of an alternating arrangement of
organosilicon, aromatic, and acetylene or diacetylene units display
high potential as functional materials for optoelectronics [4] and
high-temperature resistant thermosetting resins [5], while silar-
ylene-siloxane-acetylene polymers containing flexible siloxane
units in the main chain exhibit fascinating properties as high-
temperature elastomers or resins [6]. The silicon-containing unit is
generally monosilylene or multisilylene motif in silylene-phenyl-
ene-acetylene polymers [2,4a], and disiloxane motif in silarylene-
siloxane-acetylene polymers [3,6]. That is, silicon-containing unit is
As an important class of chemical bonds to construct silicon-
containing polymers, SieN bondhasbeenwidelystudied and various
polymers based on the bond have been synthesized [7]. However,
little attention has been paid on the polymers including SieN bond
and acetylene unit in backbone, the known examples were poly
[(silylene)acetylene silazanes] (Scheme 1, d) and poly[(silylene)
diacetylene silazanes] (Scheme 1, e) reported by Xie and co-workers
[8]. As for polymer containing SieN bond, arylene, and acetylene unit
in main chain, to the best of our knowledge, there is no report.
On the other hand, Sonogashira cross-coupling reactions [9]
have been widely used in the preparation of conjugated polymers
containing acetylene and silylene units [4], we recently have also
found the coupling reaction offer a convenient way of preparing
silarylene-siloxane-acetylene polymers under mild conditions [10].
However, there is no report on construction of polymers containing
SieN bond using the reaction. On the basis of design and synthesis
of a new ethynyl-terminated silylenediamine monomer, we have
successfully achieved the first example of polymers containing SieN
bond, phenylene, and acetylene unit in main chain, namely, phe-
nylene-silazane-acetylene polymers, by the cross-coupling reaction.
This article is concerned with the synthesis, characterization,
thermal analysis, and fundamental photophycical properties of the
new polymers. Compared with the reported partly conjugated
* Corresponding author. Tel./fax: þ86 10 62554487.
E-mail address: caihong@iccas.ac.cn (C. Xu).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.09.047

R. Wang et al. / Polymer 51 (2010) 5970e5976
5971
Scheme 1. Representative acetylene-containing organosilicon polymers.
polymers containing SieN bond, the new polymers exhibit better
environmental stability and thermal stability. They have potential to
be used as high-temperature resistant resin, precursor for SiC/Si3N4
ceramic or light-emitting materials with good thermal stability.
positive ion detection. The acceleration voltage was 19 KV and the
delayed extraction voltage was 14.5e17 KV. Average Molecular
weights were estimated by a gel permeation chromatography (GPC)
analysis with polystyrene standard calibration using a WATERS 1515
Isocratic HPLC pump and WATERS 2414 refractive index detector
equipped with HR_4 column at 35 ꢀC in THF. Differential scanning
calorimetry (DSC) measurements were performed on a SII EXTRA
6200 DSC in flowing nitrogen (50 mL/min) at a heating rate of 10 ꢀC/
min. Thermogravimetric analyses (TGA) were performed on a SII
EXTRA 6300 TG/DTA at a heating rate of 10 ꢀC/min under nitrogen or
air atmosphere. UVevis absorption and fluorescence spectra were
measured at room temperature with a Shimadzu UV-1601PC spec-
trometer and a Hitachi F4500 spectrometer, respectively.
2. Experimental
2.1. Materials
All manipulations in the experiments were performed under an
inert atmosphere of nitrogen. Dichlorodiphenylsilane (Ph2SiCl2)
was purchased from ACROS and used as received. 4-Ethynylaniline
was prepared according to literature procedure [11]. All solvents
were purchased from Beijing Chemical Co. Hexane, tetrahydrofuran
(THF) and toluene were freshly distilled from sodium/benzophe-
none ketyl before use. Triethylamine (Et3N) was distilled from
calcium hydride prior to use. All other chemicals were purchased
from Alfa Aesar and used as received.
2.3. Synthesis of N,N0-bis (4-ethynylphenyl)-1,
1-diphenylsilylenediamine (1)
A solution of 9.10 g (0.036 mol) dichlorodiphenylsilane in 50 mL
dry THF was added dropwise into a mixture of 8.42 g (0.072 mol)
4-ethynylaniline, 50 mL THF, and 100 mL Et3N at 85 ꢀC. After
completion of dropping, the reaction mixture was further stirred
for 18 h at the temperature. Then, the reaction mixture was filtered
and concentrated. The obtained yellow powder was recrystallized
from a mixed solvent of hexane and THF (v/v ¼ 60/40) to give
13.70 g (0.033 mol) of compound 1 in 92% yield as a gray white
2.2. Characterization methods
1H and 13C NMR spectra were recorded on a Bruker AVANCE 400
spectrometer at frequency of 400 MHz in CDCl3, DMSO-d6 or
acetone-d6. 29Si NMR spectra were recorded with a Bruker DMX 300
spectrometer at frequency of 300 MHz in acetone-d6. Melting point
(mp) determination was performed using a WRS-1A digital melting
point apparatus. Elemental analysis was obtained with the FLASH
EA1112 Microanalytical analyzer. Fourier transfer infrared spectra
(FT-IR) were recorded with a Bruker TENSOR-27 IR spectrometer in
the wave number range of 4000e400 cmꢁ1 using standard proce-
dures. Fourier transfer Raman spectra (FT-Raman) were recorded
with a Bruker RFS100/s Raman spectrometer in the wave number
range of3600e400 cmꢁ1. Matrix-assisted laserdesorption ionization
time-of-flight (MALDIeTOF) mass spectra were obtained using
a Bruker Biflex III MALDIeTOF mass spectrometer, equipped with
delayed extraction, a multisampling probe, a TOF reflectron analyzer,
a nitrogen laser with wave-length 337 nm and pulse width 3 ns, and
a linear flight path length of 100 cm. The flight tube was evacuated
to 10ꢁ7 Pa. All measurements were performed in linear mode and
powder. mp 168e170 ꢀC, 1H NMR (400 MHz, acetoneꢁd6):
¼ 3.37
d
(s, 2H), 5.94 (bs, 2H), 7.03 (d, J ¼ 11.4Hz, 4H), 7.15 (d, J ¼ 11.4Hz, 4H),
7.36e7.44 (m, 6H), 7.77 (m, 4H). 13C NMR (400 MHz, acetoneꢁd6):
d
¼ 147.83, 134.73, 133.86, 133.17, 130.46, 128.26, 117.54, 111.96,
84.25, 76.12. 29Si NMR (300 MHz, acetoneꢁd6):
d
¼ ꢁ32.76. Anal.
Calcd. for C28H22N2Si: C, 81.12; N, 6.76; H, 5.35. Found: C, 80.61; N,
6.84; H, 5.39.
2.4. A typical procedure for the synthesis of the polymers:
polymer P1
A mixture of 198.0 mg (0.48 mmol) 1, 157.8 mg (0.48 mmol)
1,4-diiodobenzene, 6.7 mg (9.6
(19 mol) CuI in a 3/1 toluene/Et3N mixed solvent (40 mL) was
stirred at room temperature for 24 h. Then the reaction mixture
mmol) Pd(PPh3)2Cl2, 3.6 mg
m

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R. Wang et al. / Polymer 51 (2010) 5970e5976
Scheme 2. Synthesis of new silylenediamine containing terminal ethynyl. Condition and reagents: THF, Et3N, 85 ꢀC, 18 h.
was washed with brine, extracted with chloroform. The organic
layer was dried over magnesium sulfate anhydrous, filtered, and
concentrated under reduced pressure until about 3 mL of yellow
solution was remained. Then, the concentrated solution was added
dropwise into 90 mL of vigorously stirred n-hexane to form
a yellow precipitation. After filtration, the solid was dried in
vacuum to give 180 mg of polymer P1 in 77% yield as a gray yellow
a small amount of 1 was formed after reaction of 36 h at 65 ꢀC, and
92% yield was achieved using the optimized conditions (85 ꢀC,
18 h). Compound 1 has good solubility in common organic solvents,
such as THF, acetone, chloroform, and toluene. In addition,
compound 1 has certain stability in air and no variation in its 1H
NMR spectrum was observed after storing it for 3 months under
ambient laboratory conditions.
Polymers P1 and P2 were synthesized by Sonogashira cross-
coupling reactions between monomer 1 and the requisite diiodo-
benzenes using Pd(PPh3)2Cl2 and CuI as co-catalysts (Scheme 3). The
polymerization reactions proceeded well under the common
conditions for Sonogashira cross-coupling reaction. Thus, the reac-
tion of monomer 1 with 1,4-diiodobenzene and 1,3-diiodobenzene
produced para-phenylene units containing polymer P1 and meta-
phenylene units containing polymer P2 in good yields, respectively.
Polymer P2 is easily soluble in common organic solvents, including
chloroform, toluene, DMSO, and THF. Polymer P1 shows poorer
solubility than that of P2 because of its more rigid main chain
structure, however, it still can be dissolved in THF, DMSO, hot
toluene, and hot chloroform.
powder. 1H NMR (400 MHz, CDCl3):
4H), 7.16e7.26 (m, 4H), 7.38e7.46 (m, 9H), 7.62e7.72 (m, 5H). 13C
NMR (400 MHz, DMSO-d6):
d
¼ 4.33 (bs, 2H), 6.75e6.82 (m,
d
¼ 148.06, 137.46, 134.45, 133.60,
132.78, 132.27, 131.15, 130.26, 128.13, 122.52, 117.40, 110.91, 92.44,
87.20.
2.5. Synthesis of polymer P2
Polymer P2 was synthesized essentially in the same manner as
described for P1 by the reaction of compound 1 and 1,3-diiodo-
benzene in 85% yield as an off-white solid. 1H NMR (400 MHz,
CDCl3, ppm)
7.31e7.51 (m, 9H), 7.56e7.60 (m, 1H), 7.70e7.72 (m, 4H), 13C NMR
(400 MHz, DMSO-d6, ppm) : 148.05, 138.93, 134.46, 133.60, 133.04,
d: 4.33(bs, 2H), 6.80e6.82 (m, 4H), 7.23e7.26 (m, 4H),
The structures of the monomer and polymers were character-
ized using FT-IR, FT-Raman, and NMR spectroscopies. Fig. 1 Shows
the FT-IR and FT-Raman spectra of 1, P1, and P2. Monomer 1 shows
d
132.32, 130.38, 130.25, 129.16, 128.13, 123.60, 117.40, 110.83, 91.23,
86.53.
strong characteristic bands around 2099 cmꢁ1 and 3280 cmꢁ1
,
which are attributed to the absorption of eChCe and ChCeH
groups, respectively. The absorption band of ¼NꢁH groups appears
at 3375 cmꢁ1. While, in the FT-IR spectra of polymers P1 and P2, the
characteristic band of internal ethynylene eChCe groups appears
around 2206 cmꢁ1, and both peaks are relatively weak because of
their symmetrical molecular structure [12]. The existence of
eChCe groups in the polymers is further proved by the strong
peaks at 2206 cmꢁ1 in their corresponding FT-Raman spectra. The
absorption band of ¼NeH groups in the polymers also appears at
3375 cmꢁ1. The absence of absorption around 3280 cmꢁ1 suggested
that no detectable terminal acetylene group in both polymers, and
the same result was also confirmed by their 1H NMR spectra (Fig. 2).
Figs. 2 and 3 show 1H and 13C NMR spectra of 1, P1, and P2. In the
1H NMR spectra, the characteristic peak at 2.94 ppm for monomer 1
is attributed to the terminal ChCeH groups. Broad single peak
attributed to NeH appears at 4.33 ppm for monomer and both
polymers. Peaks ranged from 6.7 to 7.8 ppm are assigned to protons
of phenyl groups. In the 13C NMR spectra, the terminal C^C carbons
in monomer 1 appear at 76 and 84 ppm, while the internal C^C
carbons in polymers appear at 87 and 92 ppm. Peaks ranged from
110 to 150 ppm are assigned to the carbons of phenyl rings. The 1H
NMR and 13C NMR spectra confirm the structure and purity of the
3. Results and discussion
3.1. Synthesis and characterizations
4-Ethynylaniline used in the present investigation was synthe-
sized according to the reported method. The new silylenediamine 1
containing terminal ethynyl groups was synthesized by aminolysis
reaction of dichlorodiphenylsilane with 4-ethynylaniline, as shown
in Scheme 2. Triethylamine was used as catalyst and acid (HCl)
scavenger in the reaction.
The aminolysis reaction was very sensitive to reaction condi-
tions. The choice of appropriate reaction temperature was very
crucial for obtaining 1 in high yield. The reaction was monitored by
1H NMR spectra, no target compound 1 was detected when the
reaction proceeded under 50 ꢀC even for 36 h. This can be attrib-
uted to lower reactivity of dichlorodiphenylsilane toward 4-ethy-
nylaniline at lower temperature, due to steric effect of bulky phenyl
groups attached to silicon atom in dichlorodiphenylsilane, and
nitrogen atom in the aniline. Besides steric effects, also the low
basicity of aniline, because of incorporation of nitrogen’s free
electron pair into
p-system, contributes strongly to the lower
reactivity. Increase of temperature was effective for the reaction,
Scheme 3. Synthesis of new phenylene-silazane-acetylene polymers. Condition and reagents: diiodobenzene, toluene, Et3N, PdCl2(PPh3)2, CuI, r.t., 24 h.

R. Wang et al. / Polymer 51 (2010) 5970e5976
5973
Fig. 3. 13C NMR spectra of monomer and polymers.
Fig. 1. FT-IR and FT-Raman spectra of monomer and polymers.
monomer and polymers. Though they contain SieN bonds, poly-
mers P1 and P2 are very stable and no variation is observed in their
1H NMR spectra (P10 and P20 in Fig. 2) after being washed many
times with water or stored in air for four months at room
temperature. This is due to the steric effects of three bulky phenyl
groups surrounding each SieN bond, which prevent the bond from
being attack by water.
The average molecular weights of the polymers were estimated
by GPC measurement using polystyrene standards. Fig. 4 shows the
GPC traces of both polymers and the detailed data obtained from
GPC analyses are listed in Table 1. The number average molecular
weights (Mn) of P1 and P2 are 2.68 ꢂ 103 and 3.06 ꢂ 103, with their
polydispersity distribution indexes (PDI) 1.28 and 1.32, respectively.
Both polymers show relatively low Mn and narrow PDI.
confirmed that only polymers with low degree of polymerization
(n ¼ 2e6) were obtained under current conditions.
3.2. Thermal properties
3.2.1. DSC analysis
The thermal properties of the monomer and polymers were
studied primarily by DSC analysis at a heating rate of 10 ꢀC/min
under nitrogen atmosphere. The DSC traces (in nitrogen) for 1 and
both polymers are shown in Figs. 6 and 7, respectively. The DSC
curve of 1 (Fig. 6) displays a sharp endothermic peak at 169 ꢀC and
a strong broad exothermic peak centered at 234 ꢀC. The endo-
thermic peak is due to melting of the compound, while the
exothermic peak is attributed to thermal cross-linking reactions of
ethynyl groups [13]. The shoulder of the exotherm begins imme-
diately after melting. The high exothermic enthalpy (739 J/g)
indicates high activity of terminal ethynyl groups in the monomer.
Fig. 7 shows the DSC traces of polymers P1 and P2. Different
from that of monomer, in the temperature range of 25e300 ꢀC,
MALDIeTOF mass spectra were utilized for further character-
izing the molecular weight of polymers. Fig. 5 shows the molecular
weight obtained from MALDIeTOF mass spectra, by which high
molecular weight polymers also was not detected. This fact further
Fig. 2. 1H NMR spectra of monomer and polymers.
Fig. 4. GPC curves of polymers.

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R. Wang et al. / Polymer 51 (2010) 5970e5976
Table 1
Average molecular weights and polydispersity index of polymers.
Yielda (%)
Mn
Mw
Mw/Mn
b
b
Polymer
P1
P2
77
85
2675
3064
3431
4041
1.28
1.32
a
After reprecipitation from n-hexane.
Estimated by GPC in THF on the basis of a polystyrene calibration.
b
melting or glass transition (Tg) points were not observed for both
polymers, and only broad exothermic peaks centered at 216 ꢀC for
P1, and 196 ꢀC for P2 were observed, respectively. In DSC traces,
there might be a small step correspond to glass transition just
before the broad exotherm for each polymer, however, it is difficult
to be distinguished from the immediate exotherm. The exothermic
transformation is related to a thermally induced cross-linking
process involving internal ethynylene, which will irreversibly
modify the backbone of the starting materials [14]. Significant
broadening of the exothermic area indicates a slow cross-linking
reaction [15].
Fig. 6. DSC traces of monomer under nitrogen.
Both polymers show lower exothermic peak temperature than
that of monomer. This may be explained by the different micro-
environment for cross-linking reactions of acetylene units between
monomer and polymers. For both polymers, there is no melting
points occurred before 160 ꢀC, from which thermal cross-linking
reaction started. Thus, the cross-linking reaction of polymers
belongs to a solid-state type polymerization of acetylenes in an
ordered crystalline-like phase [15,16]. However, the monomer 1
melts at 169 ꢀC and thus undergoes thermal polymerization of
acetylenes in a highly disordered amorphous state [15]. Consid-
ering reports that solid-state polymerization of acetylenes can
occur even at room temperature and very easily at 80 ꢀC [17], the
lower exothermic temperature of the cross-linking reactions for
both polymers than that of monomer is reasonable. The exothermic
enthalpies of polymers (68, 75J/g for P1 and P2, respectively) are
rather lower than that of monomer, indicating that the polymers
possess lower cross-linking activity. The peak temperature of P1
corresponding to exothermic maximum is higher than that of P2 by
20 ꢀC, which is probably due to its more rigid backbone endued by
para-phenylene units, meanwhile the meta-phenylene containing
main chain of P2 provides a favorable conformation for cross-
linking reactions of acetylene units [18].
3.2.2. TGA analysis
Thermal degradation behavior of the monomer and polymers
were investigated by TGA analyses under nitrogen or air atmo-
sphere at a heating rate of 10 ꢀC/min. The typical TGA thermograms
Fig. 5. MALDI-TOF mass spectra of polymers.
Fig. 7. DSC traces of polymers under nitrogen.

R. Wang et al. / Polymer 51 (2010) 5970e5976
5975
Table 2
TGA data of monomer and polymers.
Compound/polymer
TGA in nitrogen
TGA in air
Td5 (ꢀC)
Td5 (ꢀC)
weight%
at 1000 ꢀC
weight%
at 1000 ꢀC
1
P1
P2
474
394
420
30.2
72.4
75.1
e
e
386
403
13.9
9.8
and the polymers. Although in both cases there are polymerizable
acetylene groups, only in case of polymers, the polymerization of
acetylenic groups leads to such a stabilized network that efficient
carbonization is possible. This is closely related to the thermal
polymerization of acetylenic groups and the crosslinked structure
formed, which is being studied in our laboratory at present.
Compared with the reported silazane-acetylene polymers [8], the
Td5 of new phenylene-silazane-acetylene polymers are higher than
that of the dimethyl or methyl and vinyl substituted polymers, but
lower than that of the diphenyl substituted polymers. This is
probably due to their different main chain structures and different
thermal cross-linking mechanism, which significantly affects the
structure and thermal stability of the crosslinked polymers.
Under oxidative atmosphere (air), both polymers remained
stable with no weight loss until 360 ꢀC for P1 and 380 ꢀC for P2,
respectively. The decomposition temperatures at 5% weight loss of
P1 and P2 are 386 ꢀC and 403 ꢀC, respectively (Fig. 9). The abrupt
weight loss started from about 500 ꢀC and the weight had stabilized
by 680 ꢀC for P1, and 780 ꢀC for P2, with their residue weight less
than 20% at 1000 ꢀC. More than 60% weight lost in the temperature
range of 500e700 ꢀC, which was mainly caused by the oxidation of
the free carbon formed during pyrolysis of acetylene unit con-
taining organosilicon polymers [14,15].
Fig. 8. TGA traces of monomer under nitrogen.
of 1 and polymers P1eP2 are depicted in Figs. 8 and 9, respectively.
The detailed thermal data obtained from the TGA analyses are
summarized in Table 2.
The temperature of 1 at 5% weight loss (Td5) in nitrogen is 474 ꢀC
(Fig. 8), which is higher than that of both polymers by more than
50 ꢀC (Table 2). This may be attributed to higher reactivity of
terminal acetylene groups in 1, which resulted in a denser network
by thermal cross-linking reactions in the temperature range of
180e280 ꢀC, before decomposition. No weight loss was observed
below 400 ꢀC and the major weight loss occurred in the range of
450e800 ꢀC. There was still obvious weight loss above 800 ꢀC, and
a relative low char yield of 30% at 1000 ꢀC was obtained.
Under nitrogen and air atmosphere, polymers P1 and P2 exhibit
the similar thermal stability. The Td5 of P1 and P2 under nitrogen
are 394 ꢀC and 420 ꢀC, respectively (Fig. 9). Most of weight loss
occurred between 400 and 700 ꢀC was related to the extensive
thermal degradation of crosslinked structure, which was formed
during exothermic transformation of acetylene units [8b]. Both
polymers have high char yields (>70%) at 1000 ꢀC after pyrolysis in
nitrogen, suggesting their potential use as precursors for Si/C/N
based ceramics. It is interesting that the enormous difference in
char yields upon pyrolysis in nitrogen between the monomer,
which already includes all kinds of repeat units found in polymer,
3.3. Photophysical properties
Fundamental photophysical properties of the new polymers
were also investigated. UVevis absorption and fluorescence emis-
sion spectra of the polymers in toluene are shown in Fig. 10 and
their detailed photophysical data are summarized in Table 3. It is
evidently observed that the introduction of meta-phenylene units
into the polymer main chain results in significant shifts of the
absorption and emission maxima to shorter wavelengths. As shown
in Fig. 10, polymer P1 containing para-phenylene units has its
absorption maximum at 340 nm, while the absorption maximum of
Fig. 9. TGA traces of polymers.
Fig. 10. UV absorption and fluorescence emission spectra of polymers.

5976
R. Wang et al. / Polymer 51 (2010) 5970e5976
Table 3
emission maxima at 386 nm for P1 and 351 nm for P2, respectively.
Photophysical properties of polymers.
The new polymers have potential to be used as ceramic precursor
and light-emitting materials with good thermal stability. Further
studies involving the thermal cured behavior and mechanical
properties of the new polymers, as well as the use of new monomer
to synthesize other polymers containing silazane and acetylene
units by coupling reactions are underway in our group.
Polymer
UVeVisa
Fluorescencea
lmax (nm)b
386c
351
FF
d
lmax (nm)
log
3
P1
P2
340
315
4.42
4.50
0.37
0.10
a
in toluene.
b
Excited at 340 and 315 nm for P1 and P2, respectively.
P1 shown vibronic emission spectra, and only the longest emission is listed.
Determined with anthracene as a standard. The FF is the average values of
c
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p
-systems. In the case of all-para configured polymer P1, the
conjugated segments PheChCePheChCePh are efficiently
conjugated, while in polymer P2, the conjugation is interrupted on
the central meta-Ph ring, the segment then rather corresponds to
two PheChCePh units sharing a Ph without efficient conjugation.
Compared with the reported poly[(silylene)acetylene silazanes]
with phenyl substituent on Si atom [8a], the emission maximum of
P1 is red-shifed by 16 nm. This is probably due to the incorporation
of p-phenylene units into the main chains, which increased the
conjugation of polymer P1.
4. Conclusion
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On the basis of design and synthesis of new silylenediamine
monomer, two new phenylene-silazane-acetylene polymers have
been synthesized by Sonogashira cross-coupling reactions for the
first time. Their thermal properties have been studied and both
polymers showed similar thermal decomposition temperature and
high ceramic yield at 1000 ꢀC under nitrogen atmosphere. These
polymers also show good thermal stability even in air with their
temperature at 5% weight loss being higher than 386 ꢀC. The
thermal induced cross-linking polymerization of main chain acet-
ylene groups partly accounts for their high char yield at high-
temperature under nitrogen atmosphere. The photophysical
properties of the new polymers have also been investigated. Both
polymers showed fluorescence in ultraviolet region with their
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