Poly(arylene ether sulfone) containing thioether units: Synthesis, oxidation and properties

Article abstract of DOI:10.1039/c4ra02829e

Two kinds of high glass temperature poly(arylene ether sulfone)s containing thioether and biphenyl units (PASSs) have been developed. The polymers were prepared by a polycondensation reaction of 4,4′-bis(4-chlorophenylsulfone) biphenyl (BCPSB) and 4,4′-di

Full text of DOI:10.1039/c4ra02829e

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PAPER
Poly(arylene ether sulfone) containing thioether
units: synthesis, oxidation and properties
Cite this: RSC Adv., 2014, 4, 23191
a
b
b
a
ac
*
*
Gang Zhang, Shu-shan Yuan, Zhi-min Li, Sheng-ru Long and Jie Yang
Two kinds of high glass temperature poly(arylene ether sulfone)s containing thioether and biphenyl units
(PASSs) have been developed. The polymers were prepared by a polycondensation reaction of 4,40-
bis(4-chlorophenylsulfone)biphenyl (BCPSB) and 4,40-dimercaptodiphenyl sulfone (DMDPS) (or 4,40-
bis(4-mercaptophenylsulfone)biphenyl (BMPSB)). They showed good thermal properties such as a
relatively high glass transition temperature of 263–282 ꢀC and a 5% weight-loss temperature (T5%) of
441–445 ꢀC. The water flux and retention rate of the resultant membranes were 0.61–2.48 L mꢁ2 hꢁ1
and 89.47–94.91%, respectively. Interestingly, we found that the corrosion resistance of the membranes
had been largely improved with the oxidization treatment. They were even insoluble in NMP, DMSO,
concentrated H2SO4, aqua regia and so on, while the polymers without oxidation were soluble or
destroyed in above solvents. In addition, we found the water flux of the oxidized membrane was also
improved but the retention rate only decreased a little.
Received 31st March 2014
Accepted 15th May 2014
DOI: 10.1039/c4ra02829e
www.rsc.org/advances
resistance and thermal properties of PAES. In recent decades,
these approaches had been reported, Jian developed a kind of
membrane materials containing aromatic heterocycle,23–25 Shin
Introduction
Membrane separation processes have become gradually
important in the last three decades for their applications in
high technology areas such as biotechnology and membrane-
based energy devices. As a class of high performance engi-
neering thermoplastic materials, poly(arylene ether sulfone)s
(PAES) are found to have high glass transition temperature,
thermal stability, good mechanical properties, solubility and
excellent resistance to hydrolysis.1–11 So they have been widely
used in industrial, especially in membrane separation such as
microltration and ultraltration process in the elds of
biomedicine, food, hemodialysis, water purication12,13 and so
on. However, the performance of traditional PAES is not good
enough for some special applications. With respect to improve
or endow the polymer novel properties, the chemical structure
modication or molecular design is frequently required. Zhao
et al. modied polyether sulfone (PES) with poly(acrylic acid),14
carboxyl15 and aniline16 endow PES to be pH-sensitive or pho-
toresponsive, respectively. M. D. Guiver and B. D. Freeman
developed a series of high performance separation membranes
of poly(arylene ether sulfone).17–22 In order to make the
membrane can be used in much more rigorous environments.
Our interest is focused on the improvement of corrosion
and Bottino synthesized a new kind of materials with poly-
cyclic,26,27 Park etc. developed a kind of poly(arylene ether
sulfone) containing amide group.28–30 They are all high glass
transition temperature membrane materials and have good
corrosion resistance. Poly(aryl thioether)s, such as poly-
(phenylene sulde) and poly(phenylene sulde sulfone)31–34 are
of well-known high performance engineering thermoplastics.
They all have excellent thermal and corrosion resistance prop-
erties. On the basis of these considerations, we designed a kind
of polymer that containing thioether, sulfonyl and diphenyl
units to achieve high glass transition temperature, good corro-
sion resistance and lm-forming properties. This article reports
the synthesis and properties of PASSs containing thioether and
biphenyl ring, which prepared from 4,40-bis(4-chlorophenyl-
sulfone)biphenyl (BCPSB) and 4,40-dimercaptodiphenyl sulfone
(DMDPS)
(or
4,40-bis(4-mercaptophenylsulfone)biphenyl
(BMPSB)). The resultant PASSs exhibited high glass transition
temperature in the range of 263–282 ꢀC. They were 40–60 ꢀC
ꢀ
higher than that of polyether sulfone (Tg: ꢂ230 C) and PVDF
ꢀ
(Tg: ꢂ40 C). They can be used in higher temperature environ-
ment. Interestingly, we found that the corrosion resistance of
the membranes had been largely improved with moderate
oxidation treatment. They were even insoluble in NMP, DMSO,
concentrated H2SO4, aqua regia and so on, while the polymers
without oxidation were soluble or destroyed in above solvents.
We studied the water ux and retention rates of the
membranes. And the mechanism of the oxidization reaction
was also studied in detail.
aInstitute of Materials Science & Technology, Analytical & Testing Center, Sichuan
University, Chengdu 610064, P. R. China. E-mail: gangzhang@scu.edu.cn; ppsf@
scu.edu.cn; Fax: +86-28-8541-2866
bCollege of Polymer Science and Engineering of Sichuan University, Chengdu, 610065,
P. R. China
cState Key Laboratory of Polymer Materials Engineering (Sichuan University),
Chengdu, 610065, P. R. China
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Yield: 65.5 g, 65.8%. Elemental analysis (%): found: C, 57.46
(57.81); H, 3.49 (3.64); S, 25.83 (25.72) (data in brackets are
calculated); FT-IR (KBr, cmꢁ1): 3081 (C–H aromatic ring), 2562
(–SH), 1578, 1477 (C]C aromatic ring), 1315, 1156 (–SO2–),
Experimental
Materials
Commercially available 4,40-bis(4-chlorophenylsulfone)biphenyl
(BCPSB) (99%, ShenZhen, Advanced Technology & Industrial
Company Limited), 4,40-dichlorodiphenylsulfone (DCDPS) (AR,
Suzhou Yinsheng Chemical Industry Company), sodium
hydroxide (NaOH) (AR, SiChuan ChengDu ChangLian Chemical
Reagent Company), sodium hydrosulde (NaHS$xH2O, NaHS%
z 70%) (Nane Chemical Industry Group Co., Ltd.), N-methyl-2-
pyrrolidone (NMP) (JiangSu NanJing JinLong Chemical Industry
Company), sodium benzoate, sodium 4-methylbenzenesulfo-
nate (AR, Aladdin Reagent Company) and other reagents and
solvents were commercially obtained.
1
1072 (C–S–C), 821 (para-substituent of aromatic ring); H-NMR
(600 MHz, DMSO-d6/TMS, ppm): 3.391 (s, 2H, H1), 7.500–7.514
(d, 4H, H2), 7.797–7.810 (d, 4H, H3), 7.910–7.924 (d, 4H, H4),
8.005–8.019 (d, 4H, H5).
4,40-Dimercaptodiphenyl sulfone (DMDPS) was synthesized
with a similar method as our earlier reports.11
Polymer synthesis (PASS-1) (shown in Scheme 1). A typical
polymerization was performed as shown in Scheme 1. In a
250 mL three-necked ask tted with a mechanical stirrer and
thermometer, DMDPS (14.1 g, 0.05 mol), BCPSB (25.2 g, 0.05
mol), potassium carbonate (10.4 g, 0.075 mol), toluene (30 mL)
and NMP (120 mL) were added. The mixture was stirred at 130–
180 ꢀC for 1 h to remove water; then stirred at 190–200 ꢀC for 6 h
to yield a viscous pale-yellow solution. Next, the reaction solu-
tion was poured into water to obtain a white brous precipitate.
Then the precipitate was washed with water and ethanol, and
dried under vacuum. At last the brous precipitate was
pulverized to powder, and washed with water and ethanol
again. Aer drying under vacuum at 100 ꢀC for 12 h, 33.4 g
(93.7%) of PASS-1 was obtained.
PASS-1: elemental analysis (%), found: C: 60.23 (60.57); H:
3.50 (3.53); S: 22.74 (22.46) (data in brackets are calculated). FT-
IR (casting lm, cmꢁ1): 3087 (C–H aromatic ring), 1590, 1572,
1473 (C]C aromatic ring), 1315, 1153 (–SO2–), 1071 (C–S–C),
817 (para-substituent of aromatic ring). 1H-NMR (600 MHz,
DMSO-d6/TMS, ppm): 7.407–7.586 (m, 8H, H1–2), 7.801–7.885
(m, 8H, H3–4), 7.931–7.983 (d, 4H, H5), 8.016–8.086 (d, 4H, H6).
13C-NMR (Ca–Cl): 116.12, 121.93, 126.11, 128.15, 128.65, 130.34,
131.30, 131.41, 132.02, 139.73, 139.86, 140.57.
Monomer synthesis
4,40-Bis(4-mercaptophenylsulfone)biphenyl (BMPSB) (shown
in Scheme 1). DMF (600 mL), sodium hydrosulde (48 g, 0.6
mol), BCPSB (100.6 g, 0.2 mol), sodium benzoate (2.8 g, 0.02
mol) and sodium 4-methylbenzenesulfonate (3.8 g, 0.02 mol)
were added into a 1000 mL three-necked ask tted with a water
segregator, reux condenser, mechanical stirrer and ther-
mometer. The mixture was stirred at 140 ꢀC for 1 h; during this
time, 33.6 mL of liquid was removed. The reaction ask was
stirred at 150 ꢀC for another 6 h (the little amount H2S produced
during the reaction must be trapped and oxidized by passing
through a solution of NaOH and NaOCl.). The reaction solution
was then poured into the mixture of ice and water. Then the
solution was ltered, the lter liquor was acidied with 1 mol
Lꢁ1 HCl to precipitate a cottony crude product under stirring.
The crude product was washed several times with deionized
water to remove possible residual salts. Next, the puried
product was ltered, dissolved in a solution of NaOH, ltered
and precipitated in hydrochloric acid. Aer ltration and
washing twice by the precipitant, the product was vacuum-dried
PASS-2 was prepared following a similar procedure as that of
PASS-1.
PASS-2: 16.3 g, yield: 91%, elemental analysis (%), found: C:
61.78 (61.91); H: 3.55 (3.68); S: 21.02 (20.66) (data in brackets are
ꢀ
at 30 C for 36 h to yield a pale-yellow powder.
Scheme 1 Synthesis routes of monomers and PASSs.
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calculated). FT-IR (casting lm, cmꢁ1): 3063 (C–H aromatic measurements was 10 ꢀC minꢁ1. Thermogravimetric analysis
ring), 1591, 1573, 1475 (C]C aromatic ring), 1317, 1156 (–SO2–), (TGA) measurements were performed on a TGA Q500 V6.4 Build
1
1076 (C–S–C), 820 (para-substituent of aromatic ring). H-NMR 193 thermal analysis instrument with a heating rate of 10 ꢀC
(600 MHz, DMSO-d6/TMS, ppm): 7.539–7.561 (d, 4H, H1), 7.841– min under nitrogen atmosphere. Mechanical testing: an Instron
7.861 (d, 4H, H2), 7.940–7.960 (d, 4H, H3), 8.045–8.066 (d, 4H, Corporation 4302 was used to study the stress–strain behavior
H4). 13C-NMR (Ca–Ck): 116.67, 126.23, 128.16, 128.69, 130.94, of the lms (according to GB 13022-91). Membrane cross-
131.35, 139.89, 140.59.
sections were prepared by mechanically fractured in liquid
We also synthesized comparative samples poly(phenylene nitrogen and sputtering-coated with a thin layer of gold, and
sulde sulfone) (PPSS) to compare their thermal properties with then examined under a JSM 6701 eld emission scanning
PASS-1 and PASS-2.
electron microscope (SEM) operated at 10 keV. The samples
were also characterized by atomic force microscopy (AFM-SPA-
400 SPM UNIT). XPS analysis was used to evaluate the element
valence and quantity changes on the membrane surfaces. It was
carried out on a Krais ULFRADLD spectrometer employing a
MgKa (1253.6 eV) achro-matic X-ray source operated at 14 keV
with a total power of 300 W. The retention rates of the
membranes were evaluated by deionized water and 100 mg Lꢁ1
bovine serum albumin solutions in a dead-end ultraltration
(UF) cell with an effective membrane. The pure water ux (J)
through the membrane could be calculated by the following
equation:
Preparation of membranes
The PASSs solution (16–22 wt%) were cast onto glass plates aer
degassing. The membranes were immediately immersed into
the deionized water at room temperature for phase separation.
Then the resultant membranes were stored in deionized water
bath to remove the residual solvent NMP. The thickness of the
membranes was in the range of 110–126 mm.
Oxidation of membranes
These PASSs membranes were oxidized in a solution of glacial
acetic acid with 30% hydrogen peroxide and about 1–5%
content of concentrated sulfuric acid for about 24–36 h at room
temperature. Aer that the membranes were immersed into the
deionized water.
V
J ¼
ADtDp
where V is the volume of permeate, A is the membrane area, Dt
is the permeation time and Dp is trans-membrane pressure.
The solutes (bovine serum albumin) retention rate (R) was
dened as the following equation:
Characterization
ꢀ
ꢁ
Cp
Cf
Limiting viscosity and molecular weights analysis: the limiting
Rð%Þ ¼ 1 ꢁ
ꢅ 100
ꢀ
ꢁ
hsp
viscosities ½hꢃ ¼ lim
of PASSs were obtained by one-point
where Cp and Cf (mg mLꢁ1) were the concentration of permeate
and feed solutions, respectively. The concentrations of the feed
and permeate solutions were examined by UV-Vis spectroscopy.
Experiment of solubility: the solubility of polymers in various
solvents was tested at room temperature and the boiling point
of the solvent.
c/0
C
method at 30 ꢄ 0.1 ꢀC with 0.500 g of polymer dissolved in 100
mL of NMP, using a Cannon-Ubbelhode viscometer:
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
À
Á
2 hsp ꢁ ln hr
½hꢃ ¼
C
where hr ¼ h/h0, hsp ¼ h/h0 ꢁ 1.
The number average molecular weights (Mn) and weight
average molecular weight (Mw) were obtained via GPC per-
formed with a Waters 1515 performance liquid chromatography
Results and discussion
Synthesis of monomers
pump, a Waters 2414 differential refractometer (Waters Co., In this study, the monomer (BMPSB) containing sulfone and
Milford, MA) and a combination of Styragel HT-3 and HT-4 thiol groups was prepared with the nucleophilic substitution
columns (Waters Co., Milford, MA), the effective molecular reaction in the presence of sodium benzoate and sodium 4-
weight ranges of which were 500–30 000 and 5000–800 000, methylbenzenesulfonate. This reaction generated little amount
respectively. N,N-Dimethyl formamide (DMF) was used as an byproduct such as hydrogen sulde, so the exhaust must be
eluent at a ow rate of 1.0 mL minꢁ1 at 35 ꢀC. Polystyrene absorbed by the solution of NaOH and NaOCl. It is better to
standards were used for calibration. Elemental analysis: the control the temperature of vacuum-drying below 35 ꢀC, or
samples of monomer and polymers were measured with an BMPSB may be oxidized to disulde compounds. The structure
elemental analyzer (EURO EA-3000). Chemical structure anal- of BMPSB was characterized by elemental analysis, FT-IR and
ysis: FT-IR spectroscopic measurements were performed on a 1H-NMR spectrum. The FT-IR spectra of BMPSB showed char-
NEXUS670 FT-IR instrument. Nuclear magnetic resonance (1H- acteristic absorptions near 2560, 1320, 1150 and 1075 cmꢁ1
NMR and 13C-NMR) spectra were determined on a BRUKER-600 attributed to the thiol, sulfone and thio–ether groups, respec-
NMR spectrometer in deuterated chloroform or deuterated tively. Fig. 1 shows the 1H-NMR spectrum of BMPSB consisting
dimethyl sulfoxide. Thermal analysis: differential scanning of one single peak at 3.391 ppm and four double signals at
calorimetry (DSC) was performed on a NETZSCH DSC 200 PC 7.500–8.019 ppm which due to the thiol and benzene protons,
thermal analysis instrument. The heating rate for the DSC respectively. The ratio of the corresponding integral curves was
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Fig. 1 1H-NMR spectrum of BMPSB.
1
also about 1 : 2 : 2 : 2 : 2. That is consistent with the calculated 2560 cmꢁ1 (–SH) disappeared. Fig. 3 shows the H-NMR spec-
results.
trum of PASS-1. The signals of protons on benzene ring were in
the range of 7.407–8.086 ppm. Four groups of peaks appeared in
the 1H-NMR spectra. The calculated result should have six
group peaks and the ratio of corresponding integral curves was
1 : 1 : 1 : 1 : 1 : 1, but the chemical shi of H1 and H2, H3 and
H4 was so approximate that it could not be separated. The
Synthesis and characterization of polymers
The polycondensation reaction was carried out by nucleophilic
substitution polymerization using potassium carbonate as the
catalyst. The reaction temperature was about 180–200 C. The
ꢀ
ratio of corresponding integral curves was (H1 + H2) : (H3
+
molecular weights of the polymers were measured by limiting
viscosity and GPC. As shown in Table 1, the [h] values of PASS-1
and PASS-2 were 0.56 and 0.49 dL gꢁ1, the Mn values were 5.2 ꢅ
104 and 4.3 ꢅ 104, Mw values were 9.7 ꢅ 104 and 8.9 ꢅ 104,
respectively. The polydispersity indices (PDIs) of polymers PASS-
1 and PASS-2 were 1.86 and 2.07, respectively.
The structures of the resultant polymer were characterized
by elemental analysis, FT-IR and NMR spectrum. The FT-IR
spectra (Fig. 2) of polymers exhibited the characteristic
stretching absorption of sulfone and thioether near 1315, 1150
and 1070 cmꢁ1, respectively. Comparing with the spectrum
of monomer (BMPSB), the characteristic absorption around
Table 1 Limiting viscosity ([h]), molecular weights and thermal prop-
erties of PASSs
Polymers [h] (dL gꢁ1
)
Mn (g molꢁ1
)
Mw (g molꢁ1
)
PDI (Mw/Mn)
PASS-1
PASS-2
0.56
0.49
5.2 ꢅ 104
4.3 ꢅ 104
9.7 ꢅ 104
8.9 ꢅ 104
1.86
2.07
Fig. 2 FT-IR spectra of PASS-1, PASS-1O (oxidation sample), PASS-2
and PASS-2O (oxidation sample).
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Fig. 3 NMR spectrum of PASS-1.
H4) : H5 : H6 ¼ 2 : 2 : 1 : 1. The 13C-NMR spectrum of PASS-1
showed twelve groups of peaks Ca–Cl ranged from 116.12 to
140.57 ppm. Combined with the FT-IR and elemental analysis
results suggest that the polymerization proceeds as descript in
Scheme 1. The structures of PASS-2 were also characterized by
NMR (Fig. 4), FT-IR spectra and elemental analysis.
Thermal properties of polymers
The thermal properties of polymers were evaluated by TGA and
DSC measurements. The results of weight loss temperatures
(T5%) and glass transition temperatures are summarized in
Table 2. The glass transition temperature (Tgs) of the polymers
was estimated by DSC. As shown in Fig. 5, the Tg of the resultant
Fig. 4 NMR spectrum of PASS-2.
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Table 2 Thermal and tensile properties of PASSs
had not nd the endothermic melting peak of polymers. That
suggests the amorphous nature of the polymers. As shown in
Fig. 6, the initial degradation temperatures of PPSS, PASS-1 and
PASS-2 in nitrogen (T5%) were 431, 441 and 445 ꢀC, respectively.
Char
yield
(%)
Tensile
strength
(MPa)
Young's
modulus
(GPa)
Elongation
at break
(%)
Tg
T5%
Polymers
(ꢀC)
(ꢀC)
ꢀ
They provided about 40.8%, 42.6%, 43.9% char yield at 800 C
PPSS
PASS-1
PASS-2
223
263
282
431
441
445
40.8
42.6
43.9
72
94
78
0.8
1.1
1.4
18
16
12
in nitrogen (Table 2). The TGA data indicated that these poly-
mers had good thermo-stability. From Table 2 we found that
PASS-2 had the highest thermal stability among these three
kinds of polymers. The main reason was that PASS-2 had much
higher content of sulfone and biphenyl units in the polymer
main chain than that of PPSS and PASS-1. The thermal
decomposition curves also revealed the degradation process of
PPSS, PASS-1 and PASS-2 was one step.
Tensile properties
The average tensile strengths of the casting lms of polymers
(treated at 130 ꢀC for 10 h, then at 180 ꢀC for 12 h) are given in
Table 2. As shown in Table 2, the average tensile strengths and
Young's modulus values of the lms were 72–94 MPa and 0.8–
1.4 GPa, respectively. It suggests the resultant polymers have
good mechanical properties. While the elongation at break was
more than 10%, suggesting the lms have better toughness
than that of earlier reported by our group.11
Oxidation of PASSs membranes
Fig. 5 DSC curves of PPSS and PASSs at a heating rate of 10 ꢀC per min
in N2.
FT-IR analysis of oxidized PASSs. FT-IR analysis was used to
study the chemical group changes of the oxidation reaction. As
shown in Fig. 2, Comparing with the spectra of untreated PASS-
1 membrane, the spectra of oxidized PASS-1 and PASS-2
polymers were 263 and 282 ꢀC, respectively. They were 40–60 ꢀC
higher than that of poly(phenylene sulde sulfone) (Tg: 207–ꢀ222
ꢀC),32 polyether sulfone (Tg: ꢂ230 ꢀC) and PVDF (Tg: ꢂ40 C).
Compared with PES and PVDF, they can be used in higher
temperature environment. In particular, PASS-2 has about 19 ꢀC
higher Tg than that of PASS-1 because of the much more content
rigid structure of biphenyl unit. Also from the DSC curves we
Fig. 7 X-ray photoelectron spectroscopy (XPS) of sulfur in PASSs
(unoxidized and oxidized).
Table 3 XPS surface elements contents (C, O, S) for the PASSs before
(PASS-U) and after oxidation (PASS-O)
Element (%)
C
O
S
PASS-1U
PASS-1O
PASS-2U
PASS-2O
75.13
67.72
77.59
73.51
18.81
22.82
16.16
18.20
6.05
9.47
6.26
8.29
Fig. 6 TGA curves of PPSS and PASSs at a heating rate of 10 ꢀC per min
in N2.
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Table 4 Corrosion resistance behavior of PASSs
while the thioether content has decreased with the oxidation
reaction. It indicates that the thioether group on the membrane
surface of PASS-1 has been converted to sulfone (–SO2–) units
with the oxidation treatment.
Polymers
Solvents
PASS-1U PASS-1O PASS-2U PASS-2O
XPS analysis of oxidized PASSs membrane surface. X-ray
photoelectron spectroscopy (XPS) was used to characterize the
valence and content changes of the chemical elements with the
oxidation treatment. As shown in Fig. 7, un-oxidized PASSs
exhibited two sulfur peaks, which suggested that the S atom in
the polymer main chain had two kinds of valence states (–SO2–:
ꢂ167.5 eV and –S–: 163.5 eV).32 We found that the sulfur peak
near 163.5 eV attributed to thioether moiety almost disappeared
aer oxidation treatment, while the peak near 167.5 eV got more
large than that of un-oxidized sample. We also fond a new peak
near 165–166 eV with the oxidation reaction. It may be attrib-
uted to the little amount of sulfoxide (–SO–) group. It revealed
the thioether was converted into sulfoxide and sulfone group
with the oxidation process. As shown in Table 3, with the
treatment of oxidation, the content of oxygen was raised from
18.81–16.16% to 22.82–18.20%. It also indicated the thioether
was converted to sulfone unit with the treatment. That was
agreed with the results of FT-IR analysis.
concentrated sulfuric acid
Formic acid
NMP
DMF
DMAC
Pyridine
Acetone
Chloroform
DMSO
1,4-Dioxane
Toluene
++a
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
++
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
++
++
++
+ꢁ
ꢁ
++
++
++
ꢁ
ꢁ
+ꢁ
++
ꢁ
+ꢁ
+
ꢁ
ꢁ
ꢁ
Cyclohexanone
Phenol + tetrachloroethane ++
ꢁ
ꢁ
++
a
++: soluble at room temperature; +: soluble at solvents boiling point;
+ꢁ: swelling with heating; ꢁ: insoluble with heating.
membranes (PASS-1O and PASS-2O) showed signicantly
absorption increasement near 1320 cmꢁ1 and 1150 cmꢁl
(attributed to the vibration of sulfone group: –SO2–), at the same
time we found the absorption decreasement near 1073 cmꢁl
(attributed to the vibration of thioether unit: –S–). The FT-IR
result suggests that the content of sulfone group has increased,
Properties of oxidized PASSs membranes
Corrosion resistance properties of oxidized PASSs
membranes. The corrosion resistance of PASS-1U (untreated),
Fig. 8 The images of PASS-1 membrane (unoxidized-the left sample, oxidized-the right sample) kept for different time (a. 5 min, b. 24 h, c.
15 days, d. 180 days) in solvents (NMP, concentrated sulfuric acid, aqua regia, NaOH).
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Fig. 9 The oxidation reaction mechanism and three-dimensional diagrammatic sketch.
PASS-1O (oxidized) PASS-2U (untreated) and PASS-2O (oxidized)
are summarized in Table 4. Comparing with PASS-1U and
PASS-2U, PASS-1O and PASS-2O showed a relatively excellent
corrosion resistance. PASS-1U and PASS-2U dissolved in some
strong polar solvents such as DMF, DMAC, NMP, concentrated
sulfuric acid and so on. While PASS-1O and PASS-2O absolutely
had no changes aer keeping for about 6 months in NaOH
(2 M), NMP, concentrated sulfuric acid and even aqua regia
(as shown in Fig. 8). The main reason was that the thioether
bonds in the polymer backbone were almost oxidized to
sulfone groups35,36 (as described in Fig. 9) with the mixture of
H2O2–CH3COOH–H2SO4 (small amount) under moderate
condition. The aromatic ring planes lie essentially orthogonal
to
a
plane dened by the bridging C–S–C groups in
, and the diaryl sulfone
Fig. 10 Flux of PASSs membrane before and after oxidation.
Fig. 11 Retention rate (bovine serum albumin) of PASSs membrane Fig. 12 SEM images of cross-section of PASSs membrane (18 wt%)
before and after oxidation.
before and after oxidation.
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Fig. 13 AFM images of surface of PASSs membrane before and after oxidation.
units adopt near-perfect open-book conformations and the ultraltration (UF) cell under 0.1 MPa. Each membrane was
molecules crystallize with the aromatic rings of laterally adja- initially pre-pressurized with deionized water for 2 h at 0.2 MPa.
cent chains essentially parallel as shown in Fig. 9. This results As shown in Fig. 10, The ux of PASS-1 and PASS-2 were 0.61–
was similar with the earlier reports about that the poly(1,4- 2.02 and 0.74–2.48 L mꢁ2, respectively. We found that the ux
phenylenesulfone) is highly crystalline and insoluble.37
value decreased with the resin concentration increased. It was
Flux and permeation of oxidized PASSs membranes. The ux consistent with the regularity of the water ux of separation
of PASSs was tested with deionized water in a dead-end membrane. Also we found the pure PASSs had minor ux than
Fig. 14 Contact angle of PASSs membrane (18 wt%) before and after oxidation.
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commercial products such as PVDF, PES and so on, we will
improve its water ux property next. Interestingly, we found that
the ux of PASS-1 and PASS-2 became more large than that of
untreated samples (PASS-1O: 1.06–2.52 L mꢁ2, PASS-2O: 1.25–
3.56 L mꢁ2) aer oxidation treatment. Whereas the retention
rate (bovine serum albumin) decreased a little in a reasonable
range as shown in Fig. 11. In order to investigate this
phenomenon, the SEM and AFM was carried to observe the
section and surface of the membranes. As shown in Fig. 12, the
oxidized and un-oxidized membranes exhibited similar asym-
metric structure: a dense top layer, a porous nger-like and
sponge-like sub layer. From the AFM images (Fig. 13), we found
that the microporous on the oxidized membranes surface
became much more obvious than that of un-oxidized samples.
The main reason is that the polymer chain is tend to appear
local order structure with the oxidation treatment as demon-
strated in Fig. 9. The surface of the membrane begun to shrink,
then the microporous structure got more and more clear. We
also further studied the changes of ux and retention rate
before and aer oxidization with the contact angle experiment.
As shown in Fig. 14, the contact angle became smaller with the
oxidation treatment. It suggested the hydrophilicity of the
membrane got better aer oxidation treatment. And that was
benecial for the contamination resistance of the membranes.
It could be concluded that both the surface structure and
hydrophilicity of the membrane before and aer oxidation
affected the ux and retention rate results.
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