Fullerene as radical inhibitor in polymerization of acrylonitrile initiated by arsonium ylide

ISSN 1560�0904, Polymer Science, Ser. B, 2012, Vol. 54, Nos. 1–2, pp. 88–93. © Pleiades Publishing, Ltd., 2012.

88

1 INTRODUCTION

Fullerene chemistry is one of the emerging areas.Several polymers in which either fullerene is incorpo�rated in to the polymer [1, 2] chain are now known.Incorporation of fullerene into the polymeric materi�als modifies several properties of polymeric materials.viz. Fullerene when incorporated into the polymerbackbone, it produces greater thermal stability [3],high solubility [4], and easy process�ability [5]. Thefullerene incorporated polymers have applications invarious fields [6, 7] especially in the preparation of op�tical [8] and electro�active materials [9–11] and in or�ganic solar cells [12].

Several reports [13, 14], dealing the use of highamount of free radical initiator like AIBN or BPO andlow amount of fullerene to obtain fullerene function�alized polymers are available. In some cases fullerenehas been found to act as inhibitor/retarder [15, 16] byreacting rapidly to the free�radicals produced by initi�ator or by terminating the polymer propagatingchains.

Various ylides have been used as initiator to obtainpolymeric materials [17–19]. The fullerene contain�ing polymeric materials have also been obtained usingylides as initiators [20]. It has also been observed thatpolymerization requires less time and low amount ofinitiator, when ylide is used as initiator in presence offullerene. Use of bismuthonium ylide during the co�

1 The article is published in the original.

polymerization of fullerene with methyl methacrylateis reported in the literature [20]. However, reports arescare in the literature for the polymerization of acry�lonitrile in presence of fullerene, using arsonium ylideas initiator. Therefore, the detailed kinetics of the re�action has been studied in order to understand the na�ture of fullerene during polymerization of acrylonitrileinitiated by arsonium ylide.

EXPERIMENTAL

Materials

Acrylonitrile (Thomas Baker, India) was purifiedwith 4% NaOH followed by repeated washing withconductivity water and drying over fused CaCl2. Thenit was distilled in nitrogenous atmosphere, finally,dried over silica gel to 24 h and stored in the refrigera�tor for use. C60 (Lancaster, USA), and triphenyl arsine(Aldrich, USA) were used as such. The other reagentswere of high purity and used as such. Conductivity wa�ter was prepared by redistilling distilled water in pres�ence of alkaline KMnO4.

p�Acetyl benzylidine triphenyl arsonium ylide(p�ABTAY) was synthesized according to the proce�dure as reported by Tiwari et al [21].

Fullerene as Radical Inhibitor in Polymerization

of Acrylonitrile Initiated by Arsonium Ylide1

Ravindra Singha, Deepak Srivastavab, and Santosh K. Upadhyaya,*a Department of Chemistry

b Department of Plastic Technology Harcourt Butler Technological Institute, Kanpur 208002, India*e�mail: [email protected]

Received June 19, 2011, Revised Manuscript Received September 23, 2011

Abstract—Kinetics of polymerization of acrylonitrile (AN) in presence of fullerene (C60) has been studiedusing p�acetyl benzylidine triphenyl arsonium ylide as initiator in dioxane at 60 ± 0.1°C under the blanketof nitrogen. The rate of polymerization (Rp) at low concentration of fullerene may be represented asRp∝ [Ylide]0.5[AN]1.0 [Full]–0.6, indicating inhibition effect of fullerene on the polymerization. The energyof activation for the polymerization was found to be 71.5 ± 0.5 kJ mol–1. Fourier transform infrared spectro�scopic analysis (FTIR) confirmed the insertion of fullerene in to the final polymer. The mechanism for thepolymerization has also been proposed.

DOI: 10.1134/S1560090412020066

POLYMERIZATION

POLYMER SCIENCE Series B Vol. 54 Nos. 1–2 2012

FULLERENE AS RADICAL INHIBITOR IN POLYMERIZATION 89

Polymerization Procedure

Purified acrylonitrile (AN) was radically polymer�ized using arsonium ylide as a radical initiator, in pres�ence of fullerene, in a modified dilatometer (capillarydia. = 2 mm, lower bulb capacity = 4 ml) at 60 ± 0.1°Cfor 3 h in an inert atmosphere of nitrogen. At differenttime interval the polymer was precipitated in acidifiedmethanol and dried under vacuum in an oven to con�stant weight.

The progress of the reaction was followed by themeniscus movement with the help of a cathetometer.For calculating the rate of polymerization (Rp) a mas�ter graph was plotted between percentage conversionand volume contraction, with the help of this mastergraph, a plot was made between percentage conversionand time, the Rp was then calculated from the slope ofthe percentage conversion and time.

Kinetic Results and Discussion

The effect of ylide concentration on Rp was studiedby varying the concentration of ylide from 0.46 ×10⎯4 mol dm–3 to 7.4 × 10–4 mol dm–3 at 60°C and atconstant concentration of fullerene and AN (3.47 ×10–4 mol dm–3 and 4.71 mol dm–3, respectively). Thepercentage conversions versus time plots for differentylide concentration are given in Fig. 1. It is clear fromFig. 1, that percentage conversion and Rp increased onincreasing [Ylide]. The values of Rp at different [Ylide]are given in table. The exponent value for ylide, ob�tained from the slope of the plot of lgRp versuslg[Ylide] (Fig. 2a), was 0.5 ± 0.1.

The effect of acrylonitrile (AN) on Rp was studiedby varying AN from 0.94 mol dm–3 to 9.42 mol dm–3

at 60°C, keeping the concentration of ylide andfullerene constant (3.7 × 10–4 mol dm–3 and 3.47 ×10⎯4 mol dm–3, respectively). The Rp values were foundto be increased with an increase in the concentration

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Co

nve

rsio

n,

%

e

d

c

b

a

Fig. 1.% Conversion versus time plots at different concentration of arsonium ylide at 60°C. [Fullerene] = 3.47 × 10–4 mol dm–3,[AN] = 4.71 mol dm–3 and [Ylide] = 0.46, 0.92, 1.85, 3.70 and 7.40 × 10–4 mol dm–3 for curves a, b, c, d and e, respectively.

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RAVINDRA SINGH et al.

of AN (table). The monomer exponent value for ANobtained from the slope of the plot logRp versuslog[AN] (Fig. 2b) was 1.0 ± 0.05. The exponent valuefor ylide and AN is in accordance with the expectedvalue for ideal kinetics.

The effect of fullerene on the Rp, was studied bychanging the [Fullerene] from 0.87 × 10–4 mol dm–3

to 5.20 × 10–4 mol dm–3, keeping [Ylide] and [AN] atconstant (3.7 × 10–4 mol dm–3 and 4.71 mol dm–3, respec�tively). It was observed from the percentage conversionversus time plots (Fig. 3), that the induction period in�creased with increase in the [Fullerene] while the per�centage conversion as well as Rp, both decreased withan increase in the [Fullerene], the results indicate theinhibiting effect of fullerene on the polymerization.Inhibiting effect of fullerene was also observed by Mal�hotra [22] during the polymerization of acrylonitrileinitiated by AIBN. A plot of log Rp versus log[Fullerene] (Fig. 2c) was linear with negative slope.

The exponent value for fullerene obtained fromFig. 2c, was found to be 0.6 ± 0.1. On the basis of ki�netic results the rate of polymerization may be repre�sented as,

Rp ∝ [Ylide]0.5[AN]1.0[Full]–0.6. The effect of temperature on the rate of polymer�

ization was studied by carrying out the polymerizationat various temperatures viz. 323, 328, 333 and 338 K.The energy of activation, evaluated from Arrheniusplot, was found to be 71.5 ± 0.5 kJ mol–1.

Fourier�Transform Infrared (FTIR) Spectroscopic Analysis of Polymer

The FTIR spectrum of synthesized polymer wasobtained using Perkin–Elmer, RX�1 Infrared Spec�trophotometer, in the wavelength range of 500–4000 cm–1. Sodium chloride (NaCl) pellets were usedto get the spectrum of the polymer. For this, a drop ofviscous material was kept in between two pellets andthe pellet was placed near the window of FTIR spec�trophotometer. By using a computerized recorder,changes in the structure of the polymer at molecularlevel were studied from the recorded spectrum.

The FTIR spectrum (Fig. 4) of polymer showedpeaks at 2918 and 2849 cm–1 due to C–H stretching inmethyl and methylene group, 1759 cm–1 due tostretching, 1225–1000 cm–1 due to C–O in acetategroup, 1453–1377 cm–1 due to C–H bending, at 846and 796 cm–1 due to C–C deformation. The peak at529 cm–1 indicated that fullerene was also inserted inthe polymer [23].

Mechanism of Polymerization

On the basis of experimental results and reportedliterature, the mechanism for the polymerization of

Effect of [AN] and [Ylide] on Rp at 60°C

No. [AN], mol dm–3 [Ylide] × 104,mol dm–3

Rp × 106,

mol dm–3 s–1

1 0.94 3.70 1.7

2 1.88 3.70 3.7

3 2.82 3.70 6.5

4 4.71 3.70 13.0

5 9.42 3.70 25.1

6 4.71 0.46 5.2

7 4.71 0.92 7.7

8 4.71 1.85 10.3

9 4.71 7.40 18.7

[Fullerene] = 3.47 × 10–4 mol dm–3.

0.8

7.4

log

[Rp]

+ 6

log[AN] + 68.2 9.0

1.2

6.0

0.4

0 7.8 8.6

1.6

2.0 (a)

log[Ylide] + 66.4 6.8 7.2

log[Fullerene] + 61.6

(b) (c)

2.0 2.4 2.8

Fig. 2. (a) Plot of versus at 60°C, [Fullerene] = 3.47 × 10–4 mol dm–3 and [AN] = 4.71 mol dm–3; (b) plot of

logRp versus at 60°C, [Fullerene] = 3.47 × 10–4 mol dm–3 and [Ylide] = 3.70 × 10–4 mol dm–3; (c) plot of versus

at 60°C, [AN] = 4.71 mol dm–3 and [Ylide] = 3.70 × 10–4 mol dm–3.

Rplog Ylide[ ]log

AN[ ]log Rplog

Fullerene[ ]log



AN in presence of C60 may be proposed as in schemebelow.

Ylide R0 (Free radical) (I)Initiation

M (Monomer) + R0 MR0 (II)Inhibition

F (Fullerene) + R0 FR0 (III)Propagation

MR0 + M PAN (Polymer) (IV)Termination

(V)

MR0 + MR0 Inactive (VI)According to scheme, let f fraction of free radical

reacts with monomer (M) to initiate the polymeriza�

dk⎯⎯⎯→

ik⎯⎯→

inhk⎯⎯⎯→

pk⎯⎯⎯→

0MR F

(Fullerene terminated structure)

1

( )

tk

FTSInactive

+ ⎯⎯⎯→

→

2tk⎯⎯⎯→

tion and rest (1 – f ) fraction of free radical absorbs bythe fullerene (F), then considering that the rate of for�mation of free radical should be equal to rate of its dis�appearance, we get,

(1)

Or

(2)

Since the rate of initiation (Ri) is given as,

(3)

Substituting the value of [R0] from Eq. (1) intoEq. (3), we get,

(4)

Assuming bimolecular termination and neglectingthe rate of termination of step (V), as a small amountof fullerene terminated structure (FTS) of polymer is

Ylide R R F0 0[ ] [ ][ ] (1 )[ ][ ]d i inhk k f M k f= + −

lideYR

M F0 [ ]

{ [ ] (1 )[ ]}d

i inh

k

k f k f [ ] =

+ −

R M 0[ ][ ]i iR k=

Ylide M

M F

[ ][ ]

{ [ ] (1 )[ ]}i d

ii inh

k kR

k f k f=

+ −

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Fig. 3.% Conversion versus time plot at different [Fullerene] at 60°C. [Ylide] = 3.70 × 10–4, [AN] = 4.71 mol dm–3 and[Fullerene] = 0.87, 1.73, 2.60, 3.47 and 5.20 × 10–4 mol dm–3 for a, b, c, d and e, respectively.

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RAVINDRA SINGH et al.

formed under the experimental conditions, the rate ofinitiation may be given as,

(5)

Again the rate of polymerization (Rp) is given as,

(6)

On substituting the value of Ri from Eq. (5) to Eq. (6),the rate of polymerization is given as,

(7)

At low concentrations of fullerene, the most of thefree radical is used in the initiation of polymerizationand taking f ≈ 1, the above Eq. (7), becomes,

Rp = kp(kd/kt)1/2[Ylide]1/2[M] (8)

According to rate law (8) the rate of polymerization

is directly proportional to [M] and .Further, at high concentrations of fullerene, where

the step (III) (inhibition) becomes dominating, tak�ing, f 1 the rate law (7) reduces to

(9)

The rate law (9) indicates that at high fullereneconcentrations rate of polymerization should be pro�

portional to , which has been observed experi�mentally.

1/2Ylide M

M F

1/2 1/2

1/2

[ ] [ ]

{ [ ] (1 )[ ]}i d

it i inhk f k f

k kRk

⎛ ⎞= ⎜ ⎟

+ −⎝ ⎠

M]R [p p iR k=

Ylide M

M F

1/2 1/2 3/2

1/2

[ ] [ ]

{ [ ] (1 )[ ]}i d

p pt i inh

k kR k

k k f k f

⎛ ⎞= ⎜ ⎟

+ −⎝ ⎠

[ ]Ylide1/2

�

Ylide M

F

1/2 1/2 3/2

1/2

[ ] [ ]

[ ]i d

p pt

k kR k

k

⎛ ⎞= ⎜ ⎟

⎝ ⎠

[ ]F1/2−

CONCLUSION

On the basis of experimental results, it may be con�cluded that, fullerene (C60) acts as radical inhibitorduring the polymerization of acrylonitrile, initiated byp�acetyl benzylidine triphenyl arsonium ylide. A partof the fullerene was also incorporated into the finalpolymer.

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60

3500

Transmittance, %

Wavenumber, cm−13000 2500

100

2000

40

4000

3062

10001500 500 0

20

0

2993

2905

2251

1645

1598

1496

979

718

529

362

1468

1446

1431

1363

Fig. 4. FTIR spectrum of the polymer sample prepared with initial C60 : AN reactant molar ratio of 3.47 × 10–4 : 4.71.



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Fullerene as radical inhibitor in polymerization of acrylonitrile initiated by arsonium ylide