crosslinked polysulfone obtained by wittig-horner reaction in biphase system

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: [email protected] or

[email protected]

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


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)


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.


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.


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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crosslinked polysulfone obtained by wittig-horner reaction in biphase system

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