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Crosslinked Polysulfone Obtained by Wittig-HornerReaction in Biphase System
Adriana Popa,1 Ecaterina Avram,2 Gabriela Lisa,3 Aurelia Visa(Pascariu),1 Smaranda Iliescu,1
Viorica Parvulescu,4 Gheorghe Ilia11 Institute of Chemistry Timisoara of Romanian Academy, 24 Mihai Viteazul Blv., 300223-Timisoara, Romania
2 ‘‘Petru Poni’’ Institute of Macromolecular Chemistry Alee Gr. Ghica Voda, 41A, 700487 Iasi, Romania
3 Department of Physical Chemistry, Faculty of Industrial Chemistry, ‘‘Gh. Asachi’’ Technical University,D. Manger on Street, 71A, 700050 Easy, Romania
4 Institute of Physical Chemistry, Spl. Independence 202, 060021 Bucharest, Romania
Phase transfer catalyzed reactions are often more easilyand cheaply performed than conventional method andthey are therefore of particular interest. A polysulfonefunctionalized with phosphonate (2-PSF) was preparedunder phase transfer catalysis (PTC) conditions, and itwas evaluated by spectrometric method (Fourier trans-form infrared spectroscopy, using potassium bromide(KBr) pellet). The phosphorus content of the modified pol-ysulfone was determined, and it was used for the determi-nation the fraction of repeating units functionalized withphosphonate groups. The modified polysulfone contains1.40 mmol phosphonate/g polysulfone. Polysulfone func-tionalizedwith phosphonate groups and polysulfone func-tionalized with aldehyde groups (3-PSF) were used in Wit-tig-Horner reaction, to introduce double bonds on poly-mer and to obtain crosslinked polysulfone (4-PSF). Thereactions were performed using PTC method, solid-liquid(potassium carbonate (K2CO3), tetrahydrofuran (THF), tet-raethylammonium iodide (TEAI)) system. The structure ofpolysulfone functionalized with phosphonate groups andpolysulfone functionalizedwith aldehyde group were con-firmed by 1H-, 13C-, and 31P-nuclear magnetic resonance(NMR). The peak for phosphorus in PSF-phosphonateappears in 31P NMR spectrum as a singlet at 25.712 ppm.The thermal properties of aldehyde, phosphonate, andcrosslinked polysulfone were studied by thermogravimet-ric analysis (TG) and differential thermogravimetric analy-sis (DTG). Scanning electron microscopy images for poly-sulfone functionalized with phosphonate and crosslinkedpolysulfone are in concordance with nitrogen (N2) adsorp-tion-desorption isotherms. POLYM. ENG. SCI., 52:352–359,2012.ª 2011Society of Plastics Engineers
INTRODUCTION
Polysulfone (PSF) is an engineering thermoplastic
widely used as a membrane material in the area of liquid
and gas separations [1–3], fuel cell [4]. It is a popular
membrane material due to its thermal stability, mechani-
cal strength, and chemical inertness; it is one of the few
biomaterials that can withstand all sterilization techniques
(steam, ethylene oxide, gamma radiation). PSF micro fil-
tration membranes prepared in a similar fashion are used
increasingly for the separation of blood cells from plasma
[5, 6]. Polyarylsulfones are high performance thermoplas-
tics with such desirable characteristics, ability to form
various types of membranes, resistance to cleaning chemi-
cals as acids/bases and chlorine [7, 8].
Chemical modification of the polymers proved to be a
useful way to change their properties, such as solubility,
thermal behavior, hydrophilicity, etc. [9] also by this pro-
cess, it is possible to increase the reactivity of the main
chain by introducing new reactive functional groups that
permit further chemical reactions. The chemical modifica-
tion of polysulfones has been reported using sulfonation
[10, 11], nitration [12], lithiation [13], and by the intro-
duction of various functional groups, such as carboxylic
(COOH) [14, 15], fluorine (F) [16], amine (NH2) [17], az-
ide (N3) [18], and aliphatic unsaturated end groups [19].
Chloromethylation of polysulfone, as an example of
chemical modification, has been performed by many
research groups by different synthetic routes [20, 21]. It
was reported that the chloromethylation of the polysulfone
Udel P3500 using paraformaldehyde/chlorotrimethylsilane
mixture as a chloromethylation agent and tin(IV) chloride
as catalyst [22, 23] was performed. The main application
of such polymers resulted from the high reactivity of the
Correspondence to: Gheorghe Ilia; e-mail: ilia@acad-icht.tm.edu.ro or
gheilia@yahoo.com
DOI 10.1002/pen.22089
Published online in Wiley Online Library (wileyonlinelibrary.com).
VVC 2011 Society of Plastics Engineers
POLYMER ENGINEERING AND SCIENCE—-2012
chloromethyl functionality introduced on the polymer
backbone, with many further reactions with appropriate
partners being possible under mild conditions [24].
It is well known that phase-transfer catalysis is a very
convenient and useful method for organic synthesis. Major
advantages of PTC are: elimination of dangerous, incon-
venient, and expensive reactants (sodium hydroxide
(NaOH), potassium hydroxide (KOH), K2CO3, etc., instead
of sodium hydride (NaH), sodium amide (NaNH2), potas-
sium tert-butoxide (t-BuOK), lithium aliphatic salts of
amines (e.g., R2NLi), etc.); high reactivity and selectivity
of the active species; high yields and purity of products;
simplicity of the procedure; low investment cost; low
energy consumption; possibility to mimic counter-current
process; minimization of industrial wastes. This method
can also be used for the chemical modification of polymers
to synthesize various functional polymers [25, 26].
Preparation of benzaldehyde grafted on styrene-6.7%
divinylbenzene copolymer under PTC conditions and its
use in phase transfer catalyzed Wittig-Horner reactions in
solid-liquid-solid (s-l-s) system were presented in a previ-
ous article [27]. Also, the PTC method for the synthesis
of the polymers containing the phosphonate groups was
previously used [28, 29].
In this article, we present the synthesis of crosslinked
polysulfone with double bonds by PTC method in solid-
liquid system using polysulfone grafted with phosphonate
and polysulfone grafted with aldehyde group previously
synthesized [30]. This approach is not mentioned in the
studied literature, and it is the first time when polysulfone
chains are crosslinked by double bonds under phase trans-
fer catalysis (PTC) conditions in solid–iquid system.
EXPERIMENTAL
Materials
Diethylphosphite (P(O)(OC2H5)H, Fluka, 97%), N,N-dimethylformamide (DMF, Carlo Erba, p.a.), ethanol
(Chimopar Romania, p.a.), tetrahydrofuran (Carlo Erba,
SCHEME 1. Synthesis of polysulfone containing phosphonate groups.
FIG. 1. The numbering of the hydrogen and carbon atom in the 3-PSF and 4-PSF repetitive units.
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2012 353
p.a.), dimethylsulfoxide (Fluka, p.a.) sodium hydrogen
carbonate (NaHCO3, Chimopar, p.a.), potassium carbonate
(Chimopar, p.a.), methanol (Chimopar, p.a.), 1,2-dichloro-
methane (Chimopar, p.a.), diethyl ether (Chimopar, p.a.),
tetraethylammonium iodide (Merck) were used without
purification, and chloromethylated polysulfone (7.07% Cl,
GS¼ 0.98, 1-PSF) as mentioned in [23].
Synthesis of Polysulfone Functionalized with Phosphonate(2-PSF)
In a 100 ml round bottom flask fitted with stirrer, reflux
condenser and thermometer, 2 g sample of polysulfone
grafted with chloromethyl groups (CH2Cl) (7.07% Cl, 0.98
mmol –chloromethyl groups/g polymer, 1-PSF) and 30 ml
N,N-dimethylformamide were added. Then, diethylphos-
phite and potassium carbonate were added, to achieve a
molar ratio chloromethyl groups: diethylphosphite: potas-
sium carbonate ¼ 1:1.5:1 (1.96 mmol -CH2Cl: 2.94 mmol
phosphite: 1.96 mmol potassium carbonate) and 0.05% tet-
raethylammonium iodide catalyst, respectively. The mix-
ture was kept under stirring for 20 h at 308C, and then sol-
vent was removed using a vacuum rotary evaporator under
a vacuum of 30 mm Hg at 658C. The final viscous mixture
was precipitated in acetone-water (1:1). The precipitate
thus obtained was filtered and washed with acetone. The
solid was finally dried at 408C under vacuum for 24 h.1H nuclear magnetic resonance (NMR) (400MHz, deu-
terated chloroform (CDCl3)): d, ppm: 1.20–1.40 (m, H-
20) 1.70 (s, H-5), 3.71 (t, H-19), 4.53 (s, H-12) 6.82-7.36
(m, H-2, H-3, H-7, H-10, H-11), 6.95 (s, H-14), 7.85-8.10
(m, H-15), 10.28 (s, H-12), 31P NMR (162 MHz, CDCl3):
d, ppm: 25.71 (s).
Preparation of Polysulfone Functionalized with Aldehyde(3-PSF)
The synthesis of the aldehyde functionalized on poly-
sulfone was performed after a method previous described
[30]. Thus 2 g sample of polysulfone grafted with chloro-
methyl groups (7.07% Cl, 0.98 mmol -CH2Cl/g polymer,
FIG. 2. 1H NMR spectrum for polysulfone functionalized with alde-
hyde.
FIG. 3. 13C NMR spectrum for polysulfone functionalized with alde-
hyde. FIG. 5. 31P NMR spectrum of PSF-phosphonate.
FIG. 4. 1H NMR spectrum for polysulfone functionalized with phos-
phonate.
354 POLYMER ENGINEERING AND SCIENCE—-2012 DOI 10.1002/pen
1-PSF), sodium hydrogen carbonate (molar ratio –
CH2Cl:NaHCO3 ¼ 1:2) and 50 ml dimethylsulfoxide were
added into a 100 ml round bottom flask fitted with a
reflux condenser, mechanical stirrer, and thermometer.
The mixture was maintained under stirring for 12 h at
1308C. After cooling, the polymer was precipitated in
water and separated by filtration, washed with methanol
(3 3 20 ml) and dried at 408C for 24 h. 1H NMR (400
MHz, CDCl3): d, ppm: 1.70 (s, H-5), 6.40–7.50 (m, H-2,
H-3, H-7, H-10, H-11), 7.08 (s, H-14), 7.50–8.20 (m, H-
15), 10.28 (s, H-12), 13C NMR (100 MHz, CDCl3) :d,ppm: 30.74 (s, C-5‘), 42.41(s, C-5), 119.80 (s, C-14),
120.28 (s,C-8), 126.59 (C-11), 129.70 (s, C-15), 128.40
(s, C-10), 130.00 (s, C-7), 135.10 (s, C-16), 147.13 (s, C-
6), 152.91 (s, C-9), 161.96 (s, C-13), 188.72 (s, C-12).
General procedure for Wittig-Horner Reactions in PTCConditions
A mixture of 1 g phosphonate (1.40 mmol/g) (2-PSF),
respectively, 1 g aldehyde (1.10 mmol/g) (3-PSF) grafted
on polysulfone, tetraethylammonium iodide (0.05 g), sol-
vent (THF) (20 ml), and potassium carbonate (0.55 g) were
stirred 20 h at 458C. The final product (4-PSF) was sepa-
rated by filtration, washed with water (3 3 20 ml), ethanol
(3 3 20 ml), dichloromethane (3 3 20 ml), diethyl ether (3
3 20 ml), and then dried at 408C for 24 h.
METHODS OF INVESTIGATION
The obtained materials were characterized by Fourier
transform infrared spectroscopy with a Shimadzu spectro-
photometer, Scanning Electron Microscopy (SEM) with a
Philips XL-20 microscope. N2 adsorption–desorption iso-
therms were obtained from the volumetric adsorption ana-
lyzer (Micromeritics). Thermogravimetric analysis (TG)
and differential thermogravimetric analysis (DTG) were
performed under nitrogen flow (20 cm3/min) at heating
rate 108C/min from 25 to 7008C with a Mettler Toledo
model TGA/SDTA 851. The initial mass of the samples
was 3–5 mg. The structure of the product was confirmed
by 1H and 31P NMR. All spectra were recorded with a
Bruker DRX 400 MHz spectrometer, in CDCl3, at 298 K.
All chemical shifts were measured using the unified scale
for referencing and tetramethylsilane (TMS) as internal
standard [31].
Determination of the Chlorine Content
A sample of the product was burnt out in an oxygen
atmosphere, the gases were absorbed in an aqueous solu-
tion of hydrogen peroxide (H2O2) 0.15% (w) and the
chloride ion was quantitatively determined by potentiome-
ter titration with an aqueous solution of silver nitrate
(AgNO3) 0.05 M [27].
Determination of the Phosphorus Content
The phosphorus content of the polymer-supported
phosphonates was obtained by adsorption in water of
phosphorus pentoxide (P2O5) obtained from a sample of
the final product burnt out in an oxygen atmosphere [32,
33]. The solution obtained was titrated with an aqueous
SCHEME 2. Statistical structure of repeating unit of the functionalized polysulfone.
TABLE 1. Characteristics of polysulfone functionalized with
phosphonate.
Sample %P x-y y
gF(% mol)
Mmf
(g)
GPSFphos mmol
phosphonate/g
polysulfone
2-PSF 4.37 0.18 0.80 81.63 572.17 1.40
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2012 355
solution of cerium (III) 0.005 M in the presence of Eryo-
chrome Black T as indicator.
Determination of the Double Bond Content
To a sample of the final product (100 mg), 10 ml car-
bon tetrachloride, 10 ml distilled water, 40 ml 0.05 N po-
tassium bromate- potassium bromide (KBrO3-KBr), and
10 ml 10% sulfuric acid (H2SO4) were added [27]. The
mixture was kept under continuously stirring. After 2 h
another 4 ml 0.05 N KBrO3-KBr and 1 ml 10% H2SO4
were added, and this operation was repeated until the yel-
low-brown color persists 10 min. Then 10 ml 20% potas-
sium iodide (KI) was added. The iodide was titrated with
0.1 N sodium thiosulfate (Na2S2O3) until the color is
changed in yellow then 0.5 ml 1% starch was added, and
the titration was continued until complete discoloration.
RESULTS AND DISCUSSION
Synthesis and Characterization of Chemically ModifiedPolysulfone with Phosphonate Groups (2-PSF)
The polymer-analogous Michaelis-Becker reaction is
presented in Scheme 1.
The formation of phosphonate groups (–H2C–
P(O)(OR)2) was confirmed by IR spectroscopy. The appear-
ance of the absorption band at 1250 cm21 was associated
with the valence vibration of P¼O bond, respectively, the
apparition of the absorption band at 1010 cm21 was attrib-
uted to the valence vibration of P–O–C bond.
The numbering of the hydrogen and carbon atoms for
NMR spectra is shown in Fig. 1. The NMR data are presented
in experimental part and 1H NMR and 13C NMR spectra for
polysulfone functionalized with aldehyde and 1H NMR for
polysulfone functionalized with phosphonate in Figs. 2–4.
The peak for phosphorus in PSF-phosphonate appears
in 31P NMR spectrum as a singlet at 25.712 ppm (Fig. 5).
SCHEME 3. The reaction of polysulfone with aldehyde and phosphonate in the pendent groups, to give
olefin groups crosslinking polysulfones, under PTC conditions.
TABLE 2. Characteristics of chloromethylated polysulfone, aldehyde, and phosphonates functionalized on polysulfone and olefin groups bonded to
polysulfone.
Polysulfone Code Cl (%) P (%)
mmol
benz-aldehyde/g polysulfone
mmol phosphonates/g
polysulfone
mmol double bonds/g
polysulfone
PSF-CH2Cl 1-PSF 7.07 — — — —
PSF-CH2P(O)(OR)2 2-PSF — 4.37 — 1.40 —
PSF-CHO 3-PSF 3.57 — 1.10 — —
PSF-CH¼CH-PSF 4-PSF — — — — 0.95
THEORY
The fraction of repeating units functionalized with
phosphonate groups was determined by statistical struc-
ture of the repeat unit of final polymer (Scheme 2):
The fraction of polysulfone units bearing phosphonates
groups (Ff) was calculated from the phosphorus content
in the final products:
P% ¼ y � AP
Mmi þ yðMPSFphos �MPSFCH2ClÞ� 100 (1)
356 POLYMER ENGINEERING AND SCIENCE—-2012 DOI 10.1002/pen
The fraction of the polysulfone units bearing pendant
phosphonate groups was calculated with the Eq. 2:
y ¼ %P �Mmi
100 � AP �%P � ðMPSFphos �MPSFCH2ClÞ(2)
where:
Mmi ¼ MPSFðunitÞ þ xMCH2Cl (3)
On this basis, the functionalization degree (GPSFphos)
with phosphonate groups was calculated with Eq. 4:
GPSFphos ¼ y
Mmf
(4)
(mmol phosphonate groups/g polysulfone)where:
Mmf ¼ Mmi þ y � ðMPSF phos �MPSFCH2ClÞ (5)
The yield of the Michaelis-Becker reaction was calcu-
lated with Eq. 6:
ZF ¼ y
x� 100 ð%molÞ (6)
The characteristics of the polymer functionalized with
phosphonate groups are presented in Table 1.
Wittig–Horner Reaction on Polysulfone Supports
Introduction of double bonds on polysulfone supports
by Wittig-Horner reactions in PTC conditions is presented
in Scheme 3.
FIG. 6. SEM images of 2-PSF.
FIG. 7. SEM images of 4-PSF.
FIG. 8. N2 adsorption-desorption isotherms of the PSF samples.
FIG. 9. TG curves.
DOI 10.1002/pen POLYMER ENGINEERING AND SCIENCE—-2012 357
The main characteristics of polysulfone with
phosphonate, aldehyde [30], and olefin groups are given
in Table 2.
The morphology was investigated using SEM, and the
results are given in Figs. 6 and 7. The micrographs shown
are fully representative of the morphology of the function-
alized polysulfone samples. Polysulfone functionalized
with phosphonate sample 2-PSF (Fig. 6) shows a more
compact material, comparatively with 4-PSF samples
(Fig. 7), with spherical particles and larger pores between
them.
SEM images are in agreement with N2 adsorption-de-
sorption isotherms (Fig. 8). All the isotherms are typically
for the materials with low adsorption capacity (low poros-
ity) of micro-and mesopores and show the presence of
larger pores.
The larger pores result in the space between spherical
particles. The isotherms are type II. The functionalization
of polysulfone grafted with chloromethyl groups (7.07%
Cl, 1-PSF) with phosphonate (sample-2-PSF) decreases
significantly the porosity.
Thermogravimetric Characteristics of FunctionalizedPolysulfones
According to the thermograms in Figs. 9 and 10, thermal
degradation occurs in two, four, or five steps, with various
mass percent losses, depending on the chemical structure.
The thermogravimetric characteristics presented in Ta-
ble 3 show a significantly better thermostability for 1-PSF
and 2-PSF, respectively (the temperature at which thermal
decomposition occurs is higher than 2908C). Thermal
degradation develops throughout two stages, the most sig-
nificant mass percent loss occurring in the last stage.
Thermal degradation of the 3-PSF and 4-PSF samples
takes the form of a sequence of four or five stages, start-
ing from a temperature of about 508C. The degradation
mechanism is complex. The amount of char remaining at
temperatures higher than 7008C is much larger than that
of the first two analyzed samples and sample 2-PSF has
the highest degradation speed.
The study continued with the kinetic processing of the
thermogravimetric data, using Freeman-Caroll’s method
[34], by means of the STARe SW 9.1 soft provided by
METTLER TOLEDO. The kinetic parameters obtained
are shown in Table 4.
Samples 1-PSF and 2-PSF had higher apparent activa-
tion energy values, which accounts for their better ther-
mostability.
CONCLUSIONS
Polysulfones functionalized with phosphonate and with
aldehyde groups were used in obtaining a crosslinked
FIG. 10. DTG curves.
TABLE 3. The thermogravimetric characteristics of functionalized
polysulfones.
Sample Steps
Ti(8C)
Tmax
(8C)Tf(8C)
Mass
loss (%)
Residue
(%)
1-PSF I 315 338 362 8.58 44.72
II 446 502 608 46.70
2-PSF I 296 338 344 11.16 40.20
II 413 445 460 48.64
3-PSF I 52 66 78 2.59 51.44
II 96 100 109 3.55
III 124 138 387 15.11
IV 387 431 700 27.31
4-PSF I 49 64 102 3.35 45.68
II 102 131 371 7.70
III 371 408 460 17.38
IV 460 465 499 8.39
V 499 516 584 17.50
Abbreviations: Ti, temperature at which thermal degradation begins in
each stage; Tf, temperature at which thermal degradation finishes in each
stage, Tmax, the temperature at the maximum rate of weight loss; residue,
the amount of degraded sample remaining at temperatures higher than
7008.
TABLE 4. The kinetic characteristics of functionalized polysulfones.
Sample
Stages of
thermal
degradation ln A Ea (KJ/mol) n
1-PSF I 46.04 6 0.72 255.48 6 3.53 2.57 6 0.037
II 18.23 6 0.29 151.81 6 1.76 1.05 6 0.016
2-PSF I 19.48 6 0.47 123.56 6 2.25 0.072 6 0.001
II 37.47 6 0.37 252.27 6 2.17 0.71 6 0.001
3-PSF I — — —
II — — —
III — — —
IV 9.59 6 0.30 90.29 6 1.66 1.10 6 0.021
4-PSF I — — —
II — — —
III 17.95 6 0.20 130.90 6 1.08 0.83 6 0.001
IV 9.85 6 1.40 93.48 6 8.28 0.50 6 0.054
V 8.26 6 0.59 90.43 6 3.78 0.66 6 0.020
Abbreviations: A, pre-exponential factor; Ea, apparent activation
energy; n, reaction order.
358 POLYMER ENGINEERING AND SCIENCE—-2012 DOI 10.1002/pen
compound. The intermediates and final product were char-
acterized by IR, NMR spectroscopy; the morphology was
investigated using SEM and TG. Polysulfone functional-
ized with phosphonate shows a more compact material,
comparatively with 4-PSF sample, with spherical particles
and larger pores between them. The temperature at which
thermal decomposition occurs is higher than 2908C.Crossslinked polysulfones could be potential materials for
producing new electrolyte membranes.
The introduction of crosslinking double bonds on poly-
sulfone by Wittig-Horner reaction in PTC conditions it
was not mentioned in the studied literature.
NOMENCLATURE
x-y fraction of polysulfone units bearing pendant
–CH2Cl groups;
y fraction of polysulfone units bearing pendant
–CH2P(O)(OR)2 groups (Ff);
%P phosphorus percentage in the final polymer;
%Cl chlorine percentage in the polymer;
MPSF CH2Cl molecular weight of the repetitive unit of the
polysulfone functionalized unit CH2Cl
groups;
MPSFphos molecular weight of the repetitive unit of the
polysulfone functionalized with Ff;
Mmi average molecular weight of the repetitive
unit of the initial polymer;
Mmf average molecular weight of the repetitive
unit of the final polymer
AP atomic weight of phosphorus;
GPFS phos the functionalization degree with –P(O)(OR)2groups;
gF the yield of functionalization.
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