Synthesis and properties of sulfur-contained poly(silylene arylacetylene)s

Article abstract of DOI:10.1002/pola.29535

Poly(silylene arylacetylene) (PSA) is a kind of poly(arylacetylene) silicon-containing resins with excellent heat resistance and good mechanical performances. In this article, the sulfur atom is introduced into the main chain of the PSA molecule to obtain

Full text of DOI:10.1002/pola.29535

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Synthesis and Properties of Sulfur-Contained Poly(silylene arylacetylene)s
Chuan Li , Jiawei Luo, Manping Ma, Junkun Tang , Qiaolong Yuan, Farong Huang
Key Laboratory for Specially Functional Materials and Related Technology, East China University of Science and Technology,
Ministry of Education, Shanghai 200237, China
Correspondence to: F. Huang (E-mail: fhuanglab@ecust.edu.cn)
Received 16 August 2019; Revised 12 October 2019; accepted 14 October 2019; published online 15 November 2019
DOI: 10.1002/pola.29535
ABSTRACT: Poly(silylene arylacetylene) (PSA) is
a
kind of
Poly(silylene ethynylene phenylene sulfoxide phenylene
ethynylene) (PSESOE) was synthesized by the oxidation of
PSESE. The structures and properties of these resins were char-
acterized and the mechanical properties of the T300 reinforced
composites were tested. The results show that the novel S-PSA
resins have excellent heat resistance and good mechanical prop-
erties, and could be used as resin matrices for high-performance
composites in high-tech fields. © 2019 Wiley Periodicals, Inc.
J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2324–2332
poly(arylacetylene) silicon-containing resins with excellent heat resis-
tance and good mechanical performances. In this article, the sulfur
atom is introduced into the main chain of the PSA molecule to obtain
a sulfur-containing poly(silylene arylacetylene), named S-PSA. By
Williamson and Sonogashira reactions, bis(4-ethynylphenyl)sulfide
and bis(4-ethynylphenyl)sulfone were synthesized. Thereafter,
through Grignard reagent way, the poly(silylene ethynylene
phenylene sulfide phenylene ethynylene) (PSESE) and
poly(silylene ethynylene phenylene sulfone phenylene ethynylene)
(PSESO2E) were synthesized from bis(4-ethynylphenyl)sulfide,
bis(4-ethynylphenyl)sulfone, and methylphenyl dichlorosilane.
KEYWORDS: poly(silylene arylacetylene); resin for advanced com-
posite; sulfur-containing polymer
aerospace and electronics.22–24 PPS is a thermoplastic resin
with high rigidity, high crystallinity, but high strength and
modulus, as well as good dimensional stability. In addition,
PPS has high fatigue resistance, good flame retardancy, high
temperature resistance, low moisture absorption, good solvent
and chemical corrosion resistance, and strong radiation resis-
tance. Poly(ether sulfone) (PES) is a typical polysulfone resins
with a structure unit composed of a sulfone group, a phenyl
group, and an ether group, which is a thermoplastic resin with
excellent comprehensive properties. The sulfone group and the
phenyl group impart excellent heat resistance and mechanical
properties to the resin, and the ether group provides flexibility
of the resin. The resin has good fluidity in molten state and is
easy to process. Below 100ꢀC, the elastic modulus of PES is the
highest among thermoplastic engineering materials, and PES
has excellent creep resistance.
INTRODUCTION Poly(silylene arylacetylene) (PSA) is a kind of
high-performance polymer materials with good processing
property, excellent heat resistance, and fantastic dielectric prop-
erty. There have been many reports on the researches of silicon-
containing arylacetylene resins. As early as 1967, Luneva et al.1 in
the previous Soviet Union reported that diacetylenyl diphenyl
silane was heated in a nitrogen atmosphere to form a heat-resistant
brittle polymer with a molecular weight of about 3500. In 1990,
Liu et al.2 carried out a dehydrogenation condensation reaction
of a phenylsilane with phenylacetylene or diacetylenylbenzene to
obtain an oligomer with a relatively low molecular weight under
the catalysis of cuprous chloride. Corriu’s research group3–8
synthesized a silicon-containing aromatic resin through Sonogashira
reaction. In 1994, Itoh’s group in Japan9–12 synthesized
poly(phenylsilylene ethynylene-1,3-phenylene ethynylene) (MSP
resin) by dehydrogenation coupling reaction of phenylsilane and
m-diacetylenylbenzene under the catalysis of magnesium oxide,
which has extremely high heat resistance with a thermal decom-
position temperature of 860ꢀC. Since 2002, our laboratory has
conducted more researches on PSA.13–21 Up to now, a series of
PSA resins have been developed. However, the brittleness of the
cured PSA resins limits their wide application.
The purpose of this article is to combine the advantages of PSA
resin and sulfur-containing resins to make a sulfur-containing
PSA resin, which is named as S-PSA. Three kinds of S-PSAs,
poly(methylphenylsilylene ethynylene phenylene sulfide phenylene
ethynylene) (PSESE), poly(methylphenylsilylene ethynylene
phenylene sulfoxide phenylene ethynylene) (PSESOE), and
poly(methylphenylsilylene ethynylene phenylene sulfone
phenylene ethynylene) (PSESO2E), were synthesized. The struc-
tures and properties of S-PSAs and their composites were
The resins containing sulfur in the main molecular chain such
as poly(phenylene sulfide) (PPS), poly(phenylsulfone), and
poly(phenylene ether sulfone) have excellent comprehensive
properties and are widely used in high-tech fields such as
© 2019 Wiley Periodicals, Inc.
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investigated, in order to explore the effect of the introduction of
sulfur on the properties of PSA resins.
1H NMR (400 MHz, CDCl3, δ, ppm): 7.06–7.08 (d, 4H, Ar-H),
7.63–7.65 (d, 4H, Ar-H). EIMS [m/z (%)]: 438 (100) [M+],
310 (15) [M+−I], 184 (12) [M+−2I].
EXPERIMENTAL
Synthesis of 4,40-(4,40-Diphenylsulfide) Bis(2-methyl-
3-butyn-2-ol)
Materials
Tetrahydrofuran (THF), glacial acetic acid, triethylamine,
toluene, dichloromethane, diphenyl sulfide, iodine, ammo-
nium persulfate, concentrated sulfuric acid, palladium
chloride, triphenylphosphine, cuprous iodide, 2-methyl-
3-butyn-2-ol, sodium hydroxide, m-chloroperoxybenzoic acid,
anhydrous potassium carbonate, magnesium powder, and
dichloromethylphenyl silane were purchased from Shanghai
Titan Scientific Co., Ltd. and used as received. All chemicals
were in AR grade. T300 carbon fiber cloth was purchased
from Toray Industries, Japan (Scheme 1).
A 1000 mL four-necked flask equipped with a constant pres-
sure funnel, a condenser, a mechanical stirrer, and a thermome-
ter was evacuated three times, and was protected with nitrogen,
and then 4,40-diiododiphenyl sulfide (I) (86.02 g, 0.250 mol),
PdCl2 (1.33 g, 7.50 mmol), PPh3 (3.94 g, 15.0 mmol), CuI
(2.38 g, 12.5 mmol), triethylamine (600 mL) were added to the
flask. Heating the reaction system slowly to 60 ꢀC and stirring
for 50 min, a mixture of 2-methyl-3-butyn-2-ol (158 mL) and
triethylamine (30 mL) was slowly added dropwise. After the
completion of the addition, the temperature was further raised
to 80 ꢀC, and the reaction was stopped after the reaction was
kept for 24 h. After the mixture was treated by hot filtration, the
filter cake was washed several times with THF (300 mL), and
the filtrate and washing liquid were combined, and the solvent
was evaporated under reduced pressure to give a crude product
of 4,40-(4,40-diphenylsulfide) bis(2-methyl-3-butyn-2-ol) (II).
The crude product (II)was recrystallized from ethyl acetate and
the obtained crystalline(II) was dried under vacuum at 60 ꢀC
for 4 h, yield 75%, mp 162 ꢀC, purity 99%. Analyses for the
intermediate (II):
Synthesis of 4,40-Diiododiphenyl Sulfide
Diphenyl sulfide (74.5 g, 0.400 mol), iodine (110.5 g, 0.436 mol),
ammonium persulfate (127.8 g, 0.560 mol), and glacial acetic
acid (600 mL) were charged in a 1000 mL three-necked flask
equipped with a condenser, mechanical stirrer, and a thermome-
ter. The reaction system was stirred at room temperature for
10 min, then slowly heated to 30 ꢀC, and then 25 mL of concen-
trated sulfuric acid was added. After being stirred for 0.5 h, the
mixture was further heated to 80 ꢀC. Then a large amount of
insoluble matter was generated. After the reaction was contin-
ued for 24 h, the reaction mixture was poured into a 1000 mL
beaker, slowly cooled to about 10 ꢀC with ice water bath, fil-
tered, and the filter cake was washed thoroughly with deionized
water until the pH value of the filtrate was near 7. Thereafter,
the cake was washed with anhydrous ethanol 3–4 times, and
then a pink powdery solid was obtained. Finally, the solid
powder was vacuum dried at 80 ꢀC for 4 h to obtain 4,40-
diiododiphenyl sulfide (I), yield 45%, mp 140 ꢀC, purity
98%. Analyses for (I):
1H-NMR (400 MHz, CDCl3, δ, ppm): 1.61 (s, 12H, CH3),7.23–7.25
(d, 4H, Ar-H),7.33–7.35 (d, 4H, Ar-H). EIMS [m/z (%)]:
350 (5) [M+], 334 (5) [M+−OH], 314 (89) [M+−2OH], 274 (100)
[M+−2OH-C(CH3)2], 234 (54) [M+−2OH-2C(CH3)2]. IR (KBr, thin
film, cm−1): 3477 (O─H, ν, s), 2979 (CH3, δ, m), 2225 (C≡C, ν, w).
Synthesis of Bis(4-ethynylphenyl)sulfide
Added 4,40-(4,40-diphenylsulfide) bis(2-methyl-3-butyn-2-ol)
(II) (35.05 g, 0.100 mol), powdered NaOH (15 g, 0.375 mol)
and toluene (350 mL) to
a 500 mL three-necked flask
equipped with a nitrogen tube, a condenser, and a magnetic
stirrer. Slowly the reaction mixture was heated to reflux with
stirring under nitrogen, and the reaction was stopped after
the reaction was conducted for 24 h. The reaction mixture
was filtered when it was hot. The filter cake was washed sev-
eral times with 100 mL of THF, and the filtrate and washed
THF solution were combined, and the solvent was evaporated
under reduced pressure to give a crude product of bis
(4-ethynylphenyl)sulfide (III). The crude product (III) was rec-
rystallized from a mixed solvent (ethyl acetate: petroleum
ether = 2:5).The obtained crystalline (III)was dried under vac-
uum at 60 ꢀC for 4 h, yield 90%, mp 115 ꢀC, purity 99%. Ana-
lyses for (III):
1H-NMR (400 MHz, CDCl3, δ, ppm): 3.12 (s, 2H, C≡C─H),
7.26–7.28 (d, 4H, Ar-H), 7.41–7.43 (d, 4H, Ar-H). EIMS [m/z
(%)]:234 (100) [M+]; 184 (6) [M+-2C≡C]; 101 (5) [C6H4─C≡CH+];
+
76 (4) [C6H4 ]. IR (KBr, thin film, cm−1): 3268 (C≡C─H, ν, s),
2108 (C≡C, ν, w).Anal. calcd. for C16H10S: C 82.05, H 4.27; found:
C 82.27, H 4.26.
SCHEME 1 Synthetic route of bis(4-ethynylphenyl)sulfide(III) and
bis(4-ethynylphenyl) sulfone(IV).
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Synthesis of Bis(4-ethynylphenyl)sulfone
the completion of the dropwise addition, the reaction was
refluxed at 70 ꢀC for 1.5 h. Then THF was distilled out, tolu-
ene (200 mL) was added to the reaction system. After the
reaction solution was cooled to below room temperature, a
mixture of glacial acetic acid (0.240 mol) and toluene 20 mL was
added dropwise to terminate the reaction, and hydrochloric acid
solution (25%, 50 mL) was added dropwise. The reaction solu-
tion was transferred to a 1000 mL separatory funnel, washed
with deionized water until the pH value of washing water was
near 7, and the upper organic phase was separated, dried over
anhydrous Na2SO4, filtered, and the solvent was evaporated
under reduced pressure, and then the product was dried in a
vacuum oven at 60 ꢀC for 4 h. PSESE was obtained with the yield
In a 500 mL four-necked flask equipped with a stirrer, thermom-
eter and condenser, bis(4-ethynylphenyl)sulfide (III) (11.72 g,
0.050 mol) and m-chloroperoxybenzoic acid (m-CPBA) (34.52 g,
0.200 mol), and dichloromethane (300 mL) were added. Reac-
tion mixture was kept at 40 ꢀC for 12 h, and then transferred to
a 500 mL separatory funnel. The mixture was washed with
deionized water until the pH value of washing water was near
7, and then washed with saturated brine 1–2 times. The upper
organic phase was separated, dried with anhydrous Na2SO4, fil-
tered, and the solvent was distilled off under reduced pressure.
Finally, the product was dried in a vacuum oven at 60 ꢀC for 4 h
to obtain bis(4-ethynylphenyl)sulfone (IV), yield 85%, mp
120 ꢀC, purity 99%. Analyses for (IV):
ꢀ
ꢀ
of 95%. GPC: Mn 1765, Mw 3286, d 1.86.
1H-NMR (400 MHz, CDCl3, δ, ppm): 3.25 (s, 2H, C≡C─H),
7.59–7.61 (d, 4H, Ar-H),7.87–7.90 (d, 4H, Ar-H). EIMS [m/z
(%)]:266 (70) [M+];149 (100) [O═S─C6H4─C≡CH+];
101 (21) [C6H4─C≡CH+]; 76 (15) [C6H4+]. IR (KBr, thin film,
cm−1): 3272 (C≡C─H, ν, s), 3087 (Ar-H, ν, w), 2113 (C≡C, ν,
w).Anal. calcd. for C16H10O2S: C 72.18, H 3.76; found: C 72.32,
H 3.78.
The synthesis procedure of PSESO2E was identical to that of PSESE
except bis(4-ethynylphenyl)sulfide instead of bis(4-ethynylphenyl)
ꢀ
ꢀ
sulfone. GPC: Mn 1983, Mw 3754, d 1.89 (Scheme 2).
Synthesis of PSESOE
Added PSESE (0.10 mol) and dichloromethane (300 mL) to a
500 mL four-necked flask equipped with a stirrer, thermome-
ter and condenser, and slowly added m-chloroperoxybenzoic
acid (m-CPBA) (0.30 mol) in an ice water bath. After the reac-
tion was carried out for 12 h at room temperature, the
obtained solution was transferred to a 500 mL separatory
funnel, washed several times with saturated potassium car-
bonate solution, then washed with deionized water until the
pH value of washing water was near 7, dried with anhydrous
Na2SO4, and filtered. The solvent was removed by distillation,
and the product was dried in a vacuum oven at 60 ꢀC for 4 h.
Synthesis of PSESE and PSESO2E
Added magnesium powder (0.300 mol) and THF (60 mL) to a
500 mL four-necked flask equipped with a stirrer, a constant
pressure funnel, a thermometer and a condenser. The mixed
solution of bromoethane (0.240 mol) and THF (20 mL) was
added dropwise in about 10 min through a constant pressure
funnel in an ice water bath. After the completion of the addi-
tion, the reaction was carried out at 40 ꢀC for 1 h to produce
a gray-black ethyl Grignard reagent. Then, the reaction solu-
tion was cooled to room temperature with an ice water bath,
and then a mixture of bis(4-ethynylphenyl)sulfide (0.120 mol)
and THF (150 mL) was added, and the ethane gas was
released, and the reaction was refluxed at 70 ꢀC for 1.5 h. The
reaction solution was cooled to below room temperature, and
a mixed solution of dichloromethylphenyl-silane (0.080 mol)
and THF (20 mL) was added through a constant pressure fun-
nel, and the dropwise addition time was about 10 min. After
ꢀ
PSESOE was obtained with the yield of 85%. GPC: Mn1864,
ꢀ
Mw 3268, d 1.75.
Preparation of Resin Castings
The mold was preheated in an oven at 160 ꢀC for 4 h, and the
release agent was evenly sprayed on the surface of the mold
to easily release the casting after curing. Weighed a certain
amount of a S-PSA in the mold and put the mold with the
resin into the vacuum oven and kept them at 140 ꢀC for about
SCHEME 2 Synthetic routes of S-PSA resins.
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0.5 h to remove the residual solvent, and then transfer to a
high temperature oven for curing. The curing procedure is:
170 ꢀC/2 h + 210/2 h + 250 ꢀC/4 h. After the curing was com-
pleted, the mold was released and the casting was obtained.
Casting sample size for bending test: 80 × 15 × 4 mm3, cast-
ing sample size for dynamic thermomechanical analysis
(DMA) test: 35 × 6 × 2 mm3.
anode X-ray powder diffractometer (Rigaku Corporation,
Tokyo, Japan).
RESULTS AND DISCUSSION
Structure Characterization of S-PSAs
The 1H-NMR spectra of S-PSAs are shown in Figure 1. As
shown in Figure 1, the peak of 3.05 ppm is attributed by the
proton of terminal ethynyl groups. The resonated peak at
0.70 ppm belongs to the proton of methyl groups on silicon
atom. The aromatic protons resonate at 7.20~8.20 ppm. The
chemical shift for the protons is affected by the sulfur groups.
With the increase of electron-withdrawing ability of the S
group, that is, from S to S═O, then to O═S═O, the chemical
shifts of the protons on the benzene ring would move toward
the lower field. For example, the protons at (c) and
(d) positions on the benzene ring resonate at 7.23, 7.41, 7.65
and 7.44, 7.58, 7.79 for PSESE, PSESOE and PSESO2E, respec-
tively. This indicates that there is no ─S─ group in PSESOE.
The ratio of the integral area of the peak of the terminal ethy-
nyl protons (a) to that of methyl protons on silicon (b) is near
1.00:3.00, which is substantially close to the ratio of designed
resin structure. In addition, the proton of deuterated chloro-
form (solvent) resonates at 7.26 ppm and the protons of
water at 1.56 ppm.
Preparation of Composite
The T300 carbon fiber cloth was cut into
a size of
15 × 10 cm2, and 12 layers of cut carbon cloth were weighed.
A certain amount of S-PSA resin was dissolved in THF to pre-
pare 38 wt% resin solution. A layer of carbon cloth was
slowly immersed in the resin solution, the solution was
completely saturated with the carbon cloth, and then the car-
bon cloth was carefully lifted for air-drying. The dried carbon
cloth prepreg was tidily stacked, placed into a vacuum oven at
80 ꢀC, and evacuated for 2 h to remove the residual solvent.
The mold was thoroughly preheated at 170 ꢀC. The carbon
prepreg is transferred to a mold, and cured in the curing pro-
cedure: 170 ꢀC/2 h + 210 ꢀC/2 h + 250 ꢀC/4 h at the pressure
of 3 MPa. After the laminate composite was naturally cooled
to room temperature, the composite was cut according to the
standard test size. The bending performance test requires the
size to be 45 × 15 × 2 mm3, and the interlaminar shear test
requires the size to be 20 × 6 × 2 mm3.
The FT-IR spectra of S-PSAs and cured-S-PSAs are shown in
Figure 2. As shown in the figure, a strong absorption at
2156 cm−1 is attributed to ─C≡C─. A strong absorption at
3284 cm−1 is for ≡C─H and a weak adsorption at 3076 cm−1
is for the aromatic C─H stretching. A strong absorption at
1050 cm−1 is due to the S═O stretching. The absorption
at 1179 cm−1 is due to the C─S─C stretching. The absorptions
at 1150 and 1300 cm−1 are due to the sulfone groups
stretching. Combined the results from 1H-NMR spectra with
those from FT-IR spectra, the structures of synthesized S-PSAs
are expected. In addition, as shown in the spectra of cured S-
PSAs, the absorption at 3284 cm−1 for ≡C─H disappears, and
the strong absorption at 2156 cm−1 for ─C≡C─ significantly
reduces, indicating that the terminal alkyne and part of inter-
nal alkyne participate in the crosslinking reactions. The
crosslinking reactions mainly include addition and coupling
reactions, such as cyclotrimerization reactions of three alkyne
groups and Diels-Alder addition reactions of alkyne, and so
on. Finally a highly crosslinked structure with a fused aro-
matic ring, a conjugated alkene, and a polyolefin is formed.25
Characterization
1H-NMR spectrum was obtained on a AVANCE500 spectrome-
ter (Bruker, Massachusetts) operating at 400 MHz with tetra-
methylsilane as the internal standard. The FT-IR spectrum
was obtained using a Nicolet iS10 infrared spectrometer
(Thermo Scientific, Madison). The melting point (mp) was
determined with a X4 melting apparatus (Shanghai Analytic
Instrument Factory, China). Mass spectrum was recorded
using a GCT Premier EI-TOF mass spectrometer (Waters, Mil-
ford). Rheological behavior was determined on a Thermo
Haake RS600 Rheometer system (Thermo Electron Corpora-
tion, Germany) in the range of rt-200 ꢀC, and the shear rate
and heating rate for the viscosity measurements were
0.01 s−1 and 2 ꢀC min−1, respectively. DSC analyses were per-
formed on a TA Instruments Q2000 analyzer (TA, New Castle)
at a heating rate of 10 ꢀC min−1 under nitrogen flow. TGA ana-
lyses were separately performed on a TGA/DSC 1LF analyzer
(METTLER TOLEDO, Greifensee, Switzerland) at a heating rate
of 10 ꢀC min−1 in nitrogen and air atmosphere. DMA was per-
formed on a DMA 1 mechanical analyzer (METTLER TOLEDO,
Greifensee, Switzerland) a heating rate of 10 ꢀC min−1. Purity
was measured on a high-performance liquid chromatography
(Ultimate 3000, DIONEX, Germany). Gel permeation chroma-
tography analysis was conducted on Waters 1515 chromatog-
raphy instrument (Waters, Milford) with polystyrene as the
standard sample and terahydrofuran as a solvent at a flow
rate of 1 mL min−1. The mechanical property was tested by
electronic universal testing machine (SANS CMT 4204, China)
according to ASTM D790-17. X-ray diffraction patterns were
recorded at room temperature by monitoring the diffraction
angle 2θ from 5ꢀ to 75ꢀ on a D/Max 2550 VB/PC rotating
Figure 3 shows the XRD diagrams of S-PSA resins. There are
strong and sharp diffraction peaks for PSESE, PSESOE, and
PSESO2E in the figure, which are ranging from 10ꢀ to 35ꢀ. This
illustrates that the resins are light crystalline oligomers.
Processing Properties of S-PSAs
Table 1 shows the solubility of S-PSAs. The three resins show
the similar solubility in the solvents used. They are insoluble
in ethanol and alkanes but completely dissolve in THF, DMF,
and so on.
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FIGURE 2 The FT-IR spectra of S-PSAs (A) and cured-S-PSAs (B).
Figure 4 shows the viscosity-temperature curves of the resins
and Table 2 shows the processing windows and viscosity of
melt resins. As shown in the figure, as the temperature rises,
the viscosity of the resin first decreases rapidly, then main-
tains at a low level within a certain temperature range, and
finally increases fast. The reason is that the solid resin is
heated to melt, the viscosity is lowered, and the low viscosity
state is maintained within a certain temperature range. When
the temperature continues to rise, some crosslinking reactions
like addition reactions occur, such as cyclotrimerization of
three alkyne groups, which causes a sharp rise on viscosity.
The temperature range in which the resin maintains a melt
state with low viscosity is named as a processing window. As
shown in Figure 4, the processing window of PSESE is the
widest, and as the oxygen atoms on sulfur atom increases, the
processing window of PSESOE and PSESO2E is narrowed in
FIGURE
PSESOE; C: PSESO2E).
1
The 1H-NMR spectra of S-PSAs (A: PSESE; B:
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FIGURE 4 The viscosity-temperature curves of PSESE, PSESOE,
and PSESO2E resins. [Color figure can be viewed at
wileyonlinelibrary.com]
FIGURE 3 X-ray diffraction diagram of PSPE resin. [Color figure
can be viewed at wileyonlinelibrary.com]
turn. The possible reason may be that with the increase in
number of oxygen atoms, the rigidity and polarity of molecu-
lar backbone correspondingly increase, hindering the move-
ment of the resin molecules, resulting in a high softening
point of the resin, and finally narrowing the processing win-
dow of the resin.
TABLE 2 The Processing Windows of PSESE, PSESOE, and
PSESO2E Resins
Resin
Processing Window (ꢀC)
PSESE
90~153
PSESOE
PSESO2E
109~158
130~162
DSC curves of the resins are shown in Figure 5 and the analy-
sis results are displayed in Table 3. As seen from the figure,
three resins exhibit similar curing exotherms with a well-
defined broad cure peak. The exotherm is attributed to the
crosslinking reactions. PSESE has a melting endotherm peak
at around 80 ꢀC. As shown in the table, the curing tempera-
ture of three resins is low (Ti < 200 ꢀC), and the exothermic
enthalpy is small, which is beneficial to the processing of the
resins.
reactions gradually shifts to a high temperature range due to
the thermal hysteresis effect.
The curing reaction kinetics of the resin can be described by
the Kissinger and the Ozawa methods.26 The corresponding
equations are shown in eqs 1 and 2, respectively.
Curing Reaction Kinetics of S-PSAs
The curing reaction kinetics of the resins were investigated by
nonisothermal DSC analyses. The resins were scanned at a
variety of heating rates. The DSC curves of PSESE are shown
in Figure 6, and the DSC curves of PSESOE and PSESO2E can
be seen in Supporting Information. It can be seen that as the
heating rate increases, the exothermal peak of the curing
TABLE 1 Solubility of S-PSA
Solvent
Solubility Solvent
Solubility
THF
+
+
+
+
−
Dichloromethane
+
+
+
−
−
DMF
Acetone
Toluene
Methylpyrrolidone
Ethanol
Dimethyl sulfoxide
n-Hexane
Petroleum ether
+ soluble; – insoluble.
FIGURE 5 The DSC curves of PSESE, PSESOE, and PSESO2E.
[Color figure can be viewed at wileyonlinelibrary.com]
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TABLE 3 The DSC Analysis Data of PSESE, PSESOE, and
PSESO2E
TABLE 4 The Calculated Ea of S-PSAs
a (kJ mol−1
E
)
Resin
Ti (ꢀC)
T
p (ꢀC)
Te (ꢀC)
4H (J g−1
)
Resin
Kissinger
Ozawa
PSESE
190
175
174
239
207
214
285
255
247
351
366
379
PSESE
86.4
63.1
81.0
88.9
68.6
85.0
PSESOE
PSESO2E
PSESOE
PSESO2E
TABLE 5 Mechanical Properties of Cured PSESE, PSESOE, and
PSESO2E
Flexural
Flexural
Cured Resin
Strength (MPa)
Modulus (GPa)
Cured-PSESE
34.8 ꢁ 4.0
36.2 ꢁ 5.3
40.5 ꢁ 5.1
2.3 ꢁ 0.1
2.7 ꢁ 0.3
2.8 ꢁ 0.3
Cured-PSESOE
Cured-PSESO2E
ꢂ
ꢃ
rate. ln β=T2p versus 1/Tp and lnβ versus 1/Tp for PSESE are
separately plotted and fitted as shown in Figure 7, and the
treatment results for PSESOE and PSESO2E can be seen in
Supporting Information. The apparent activation energy of the
resins can be obtained by the slope of the lines. The results
are listed in Table 4. As shown in the table, the apparent acti-
vation energies calculated are close, wherein the activation
energy of the PSESOE is significantly lower than that of the
other two resins, probably because the sulfoxide group con-
tained in the PSESOE is relatively easy to react.
FIGURE 6 The nonisothermal DSC curves of PSESE. [Color
figure can be viewed at wileyonlinelibrary.com]
ꢀ
ꢁ
ꢀ
ꢁ
QpAR
Ea
β
Ea
ln
= ln
−
ð1Þ
ð2Þ
2
RTp
Tp
1:052Ea
lnβ = −
+ C
Properties of Cured S-PSAs
RTp
Table 5 shows the mechanical properties of cured S-PSA
resins. It can be seen from the table that the three resin cast-
ings have high mechanical properties, and the mechanical
properties of the resin castings increase with the increase of
oxygen atoms number. The flexural strength and flexural mod-
ulus of cured PSESO2E reach 40.5 MPa and 2.8 GPa, respec-
tively, which is the highest among three cured resins. This is
probably because the introduction of oxygen atoms leads the
increase in molecular polarity and the enhancement to the
interaction between the molecular chains.27,28
where A is the prefactor, Tp is the curing peak temperature, Ea
is the apparent activation energy, R is the gas constant, C is the
constant, Qp is the exothermic enthalpy, and β is the heating
Thermal stabilities of the cured resins were determined by TGA
both in N2 and in air at the heating rate of 10 ꢀC min−1. The
TGA analysis data of the cured resins are listed in Table 6. As
TABLE 6 The TGA Analysis Data of Cured PSESE, PSESOE, and
PSESO2E
N2
Air
d5 (ꢀC)
Y
800 C (%)
T
d5(ꢀC)
Y800 C (%)
ꢀ
ꢀ
Cured Resin
T
Cured-PSESE
498
449
376
78.6
75.6
65.0
497
431
380
18.3
14.6
12.6
ꢂ
ꢃ
Cured-PSESOE
Cured-PSESO2E
FIGURE 7 ln β=T 2p versus 1/Tp and lnβ versus 1/Tp plots for
PSESE resin. [Color figure can be viewed at wileyonlinelibrary.com]
2330
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JOURNAL OF
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ORIGINAL ARTICLE
(A)
FIGURE 9 The DMA curves of PSESE, PSESOE, and PSESO2E.
[Color figure can be viewed at wileyonlinelibrary.com]
(B)
TABLE 7 Mechanical Properties of T300 Carbon Fiber Cloth
Reinforced S-PSA Compositesa
Flexural
Flexural
Composite
Strength (MPa) Modulus (GPa) ILSS (MPa)
T300/PSESE
284.6 ꢁ 5.4
48.6 ꢁ 1.2
44.6 ꢁ 0.3
48.8 ꢁ 2.3
15.6 ꢁ 0.6
20.2 ꢁ 3.5
23.2 ꢁ 2.1
T300/PSESOE
320.5 ꢁ 16.4
T300/PSESO2E 394.3 ꢁ 23.0
a Resin content 29~30 wt%.
resin to prevent resin decomposition. As shown in Figure 9, there
was no significant change of the storage modulus and loss tan-
gent tan δ of S-PSA resins in the temperature range, indicating
that the S-PSA have no glass transition in the temperature range.
FIGURE 8 The TGA curves of cured PSESE, PSESOE, and
PSESO2E (A: N2, B: Air). [Color figure can be viewed at
wileyonlinelibrary.com]
Properties of the Carbon Fiber Reinforced S-PSA
Composites
shown in Figure 8, with the increase of oxygen atoms number,
the heat resistance of the cured resin decreases to some certain
extent, and the heat resistance of cured-PSESE is the best among
Table 7 shows the mechanical properties of the T300 carbon
fiber cloth reinforced composites of the resins. It can be seen
from the table that the composites of the three resins have
good mechanical properties. As the number of oxygen atoms
in molecular chain increases, the properties of composites also
increase in turn, as the same as the variation trend of cured
resins. Among them, T300/PSESO2E composites have the
highest mechanical properties, with a flexural strength of
394.3 MPa, a flexural modulus of 48.8 GPa and a interlaminar
shear strength (ILSS) of 23.2 MPa.
the three resins with a Td5 of 498ꢀC and a Y800 C of 78.6% in
ꢀ
nitrogen. It should be noted that all cured resins show similar
thermal decomposition behaviors below 550ꢀC in nitrogen and
in air. However, when the temperature continues to rise, the
cured S-PSAs decompose rapidly in air. As shown in Table 6, the
Td5 for cured S-PSA in nitrogen is very close to the Td5 in air.
This indicates that S-PSAs have good oxidation resistance. In
addition, PSESO2E shows two distinguishable decomposed steps
in the air. The C─S bond in PSESO2E would break at high tem-
perature to release SO2 at first step. At same time, the remaining
material rearranges into a complex silicon-hydrocarbon sub-
stance. And then, when the temperature continues to rise, the
polymer further decomposes.29
CONCLUSIONS
In this article, a polar group, ─S─, ─SO─, ─SO2─, was sepa-
rately introduced into the main chain of PSA to synthesize
novel S-PSAs. S-PSAs have good solubility and processibility.
The resins display low curing temperature (<200 ꢀC). The
apparent curing reaction activation energies are located in the
range of 63~89 KJ mol−1. The mechanical properties of the
cured S-PSAs increase while the thermal stability decreases
when the number of oxygen atom in the chain unit increases.
The dynamic mechanical properties of the cured resins were
tested by DMA, and the results are shown in Figure 9. The test
temperature range was selected from 50 ꢀC to a certain high
temperature, which was 50 ꢀC lower than the Td5 of each cured
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2019, 57, 2324–2332
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ORIGINAL ARTICLE
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9 M. Itoh, M. Mitsuzuka, W. Kenji, Macromolecules 1994, 27,
7917.
The cured S-PSAs show high decomposition temperature
(>370 ꢀC) and there is not any glass transition up to the
decomposition temperature. The cured PSESE has the highest
decomposition temperature of 498ꢀC. The cured resins and
their carbon fiber composites all demonstrate high mechanical
properties. PSESO2E resin and T300/ PSESO2E composite show
high flexural strengths of 40.5 MPa and 394.3 MPa, respec-
tively. S-PSA resins are expected to be used as a resin matrix
for high performance composite materials in high-tech fields
such as aerospace.
10 M. Itoh, K. Inoue, K. Iwata, Macromolecules 1997, 30, 694.
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Acknowledgement
The authors gratefully acknowledge the support of the Funda-
mental Research Funds for the Central Universities
(No. 50321041917001).
18 X. Bu, Y. Zhou, F. Huang, Mater. Lett. 2016, 174, 21.
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