Potassium peroxodiphosphate-cysteine hydrochloride redox-couple-initiated polymerization of methacrylamide in an aqueous medium

P~/ww Vol. 37 No. 6, pp. 1013-1017. 1996 Copyright cr 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0032-3861/96/$15.00+0.00

Potassium peroxodiphosphate-cysteine hydrochloride redox-couple-initiated polymerization of methacrylamide in an aqueous medium Kunj Behari”,

Lal Bahadur,

Uma Agrawal

and Rima Das

Polymer Science Research Laboratory, Department of Chemistry, Allahabad 2 11002, India (Received 30 April 1994; revised 2 February 1995)

University

of Allahabad,

The kinetics of the aqueous polymerization of methacrylamide has been studied under an inert atmosphere employing the potassium peroxodiphosphate-cysteine hydrochloride redox pair. The order with respect to monomer and activator has been found to be unity and initiator showed half order. The polymethacrylamide samples collected under different kinetic conditions have been used for the determination of intrinsic viscosity [n], viscometric average molecular weight tiv and degree of polymerization P,. (Keywords: PDP-Cys.HCI

redox couple; methacrylamide;

kinetics)

Prirnar)) radical,forrnation

INTRODUCTION Potassium peroxodiphosphate has been used along with various activators’-” but a literature survey shows that no attempt has been made to study the kinetics of aqueous polymerization of methacrylamide initiated by the potassium peroxodiphosphate-cysteine hydrochloride (PDP-CysHCl) redox system.

PIO;tp + 2HSCH,-CH&H3.Cll I

COCH (RSH) :2C1KH3N+-CHCH2-S

+2HPO;-

I COOH

EXPERIMENTAL Methacrylamide (Fluka A-G) was purified as reported elsewhere4. PDP was received as a gift sample from FMC, New York, and was used as supplied. All other chemicals used were of AnalaR (BDH) grade. The kinetics of polymerization was followed bromometrically5. The Mv was determined by dissolving the polymethacrylamide sample in magnesium perchlorate solution and by using the equation given by Chatterjee

(1)

(RS’)

Initiation CHI I Cl-H3N+-CH-CH,-S’

et al.‘.

+ CH2=C

COOH

I CONH?

(RS)

(M) CH3

RESULTS AND DISCUSSION On the basis of experimental results the following steps have been proposed in order to ascertain the kinetic behaviour of methacrylamide polymerization initiated by the PDP-Cys.HCl redox pair and to elucidate possible anomalies, if any.

(2)

5 ClH$CH-CH2-S-CH2-C’ I CONH?

COOH (Mr) Propagatiorl

,

Cl-H3NCH-CH?-S-CH2-C’ COOH (M;) * To whom correspondence

should

+ CH2 = C 2 Cl-H?N+CH-CH?-S-CH,-C-CH2-C’ CONHz

CONH? (M)

COOH (Mi )

CONH2

(3) CONH?

be addressed

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1013

initiated

PDP-Cys.HCI

polymerization

of methacrylamide:

Table 1

5

M;+M-+M;

(4)

fi, M ,z I+M+M,;

(5)

Termination

The following above scheme:

K. Behari

M,, + M,,, 3 M,W! rate expression can be derived

(6) from the

R, = kp(k/2k,)“‘[M][PDP]‘i’[RSH] The kinetic chain length can be written

et al.

Effect of PDP concentration

on ‘1. M, and P,

[PDP] x IO’ (moldm I)

‘1 x 10: (dig ‘)

,&I\,

P”

4.0 2.0 1.5 I .o

13.2 14.3 IS.? 16.3

54 450 62950 70310 79 800

640.58 740.58 X17. I7 93X.82

Temp. = 45 C: [methacrylamidc] I .O x IO-’ mol dmm3

= 2.0 x IO-’ moldmm3:

[Cys.HCI]

=

(7) as:

v = k,[M]/(?kk,)(PDP]“‘[RSH]

(8)

All the observed experimental results are satisfactorily explained by the above rate expression (7). Rate rlependeme

on initiator c’oncentration

The order of reaction with respect to PDP is found to be 0.68 and 0.65 for conditions A and B respectively, which deviate from the ideal value of 0.50 (Figure 1). This indicates that termination of the growing chain radical is predominantly due to mutual combination of polymer chain radicals7.8 along with little primary radical termination’. On the other hand, [rl], &iv and P, decrease with the increase of PDP concentration (Table 1). which can be explained by the fact that propagating chain radicals undergo termination rather than propagation’O. Rate ~epencieme

OHactivator

m

0.1

The order of reaction with respect to Cys.HCl has been found to be unity for both conditions A and B (Figure 2). which can be explained by the fact that the polymerization is initiated only by the cysteine radical produced by the interaction between Cys.HCl and PDP. The sharp i.r. absorption spectral band at 704cm-’ (for --CH2-SCH?- group) in the resulting polymer clearly indicates the presence of -CH_2+WXgroup. On the other hand [q], Mv and P, increase with the decrease of

Effect of Cys.HCI

concentration

on ‘1, II?, and P,

[Cys.HCl\ x lo” (moldm~-)

‘, x 10: (dig ‘)

M”

P”

‘0.0 12.5 10.0 5.0 2.5

9.17 10.0 IO.3 Il.36 12.04

28 050 32810 34 990 -II030 45710

330.00 3X6.00 411.64 482.58 537.76

Temp. = 45 C; [methacrylamide] 1.0 x IO ’ moldm~-’

Cys.HCl concentration with equation (8).

1.5

mol dmS3

Figure 2 Plot of R, vs. Cys.HCl concentration. at temp. = 45 C: [methacrylamide] = 2.0 x IO- ’mol dm-’ I .5 x IO-’ moldm-’ (A). (B); [PDP] = I .O y IO-’ mold rn~j (A). X.0 K lO~‘moldm ’(B) Table 2

uwcentration

1.7

3 + log (Cysteinehydrochloride]

= 7.0 x IO-’ moldm

‘:

[PDP] =

(Table 2). which is in accordance

r

The order of reaction with respect to methacrylamide has been found to be unity for both conditions A and B (Figure 3). The values of [q], A?v and P, also increase with the increase of methacrylamide concentration (Tab/e 3 ) as required by equation (8). Slope A = 0.68 B = 0.65

4 + log [PDP] mol dme3 Figure I Plot of R, vs. PDP concentration, at temp. = 45 ‘r; [methacrylamide] = 2.0 x 10-‘moldm-3 (A), 1.51 x IO- moldm (B); [cys.HCl] = 1.0 x IO-’ moldm-’ (A). 1.50 x IO-’ mol drn-” (B)

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Rate depentierzce OHtemperature The overall energy of activation has been found to be 41.54 i I and 43.39 * 1 kJ mol-’ for conditions A and B respectively from the plot of log R, versus T -’ (Figure 4). On the other hand, [v], tiv and P, decrease gradually with the increase of temperature (Table 4). This can be attributed to the increase of termination rate as compared to propagation, which may be due to bimolecular termination. At higher temperatures, the viscosity decreases, thus increasing the mobility of growing chain radicals, and hence there may be enhancement of bimolecular termination.

POP-Cys.HCI

initiated

polymerization

Table 4

of methacrylamide:

K. Behari et al.

Effect of temperature on 7, I& and P,

Temperature (“C)

gx IO’ (dig-‘)

NJ

Pn

35 40 45 50 55

12.1 11.2 10.3 9.3 8.25

46 450 40 360 34 990 28 770 23 120

546.4 474.8 411.4 338.4 272.0

[Methacrylamide] = 2.0 x 10-l moldm-‘; dmm3: [Cys.HCl] = 1.0 x IO-‘moldm-’

[PDP] = 1.0 x 10m2mol

25 I 0.11 0.4

I

I

I

I

0.8

1.2

1.6

2.0

I

2.4

2 + log [Methacrylamide] mol dmm3 Figure 3 Plot of R vs. methacrylamide concentration, at temp. = 45°C: [Cys.HClr = 1.0 x IO-’ moldmm3 (A) 1.5 x lo-’ mol dme3 (B); [PDP] = 1.0 x 10~2moldm~3 (A), 8.0 x 101’moldm-’ (B)

z g ‘Z 5 2

15

IO

8

Table 3

5

Effect of monomer concentration on 17,I!& and p,

[Methacrylamide] x lo2 (mol dme3)

rjx 10: (dlg-‘)

MV

P”

4.0 2.0 1.0 0.5

12.8 10.3 9.1 8.4

51400 34 990 21670 24 150

604.00 411.00 325.00 282.00

Temp. = 45°C: lo-’ mol dm-’

[PDP] = 1.0 x IO-’ moldm-3;

[Cys.HCl] = 1.O x

2.1-

7 .E

E

? “3 7) s E PC”0.9

-

$ + *

0.5 -

0.11 0.4

I

I

I

0.8

1.2

1.6

I 2.0

I 2.4

T-‘/K-’ x 10’ Figure 4 Temperature effect on R,: [methacrylamide] = 2.0 x 10-l mol dmm3 (A), 1.51 x 10-‘moldm~3 (B); [Cys.HCl] = 1.0x lo-” moldm-’ (A). 1.50 x IO-’ moldm~m3(B); [PDP] = 1.0 x 10m2mol dmm3 (A), 8.0 x 10e3 moldm-3 (B)

E#ect of additives

The retarding effect on the rate of polymerization on addition of water-miscible organic solvents is due to the fact that these solvents decrease the area of shielding” of the strong hydration layer in the aqueous medium and also decrease interchain hydrogen bonding between polymethacrylamide chains, resulting in an increase in

0

20

40

60

80

100

120

Time (min) Figure 5 Percentage conversion as a function of time, at temp. = 45°C: [methacrylamide] = 2.0 x 10-l moldm-‘. [Cys.HCl] = 1.0 x 10~‘moldm~3, [PDP] = 1.0 x lo-’ moldm-3. [solvent] = 1 M. Solvents used: 1. controlled experiment; 2, methanol: 3. ethanol; 4, propanol; 5, dimethylformamide; 6. butanol

mutual termination of the polymer chain. The retarding effect increases from methanol to butanol (Figure 5), which are in order of decreasing dielectric constant. Similar results have also been observed by other workers”. Both anionic and cationic detergents reduce the rate of polymerization (Figure 6). The value of R, decreases, due to the positively charged micelles produced by cationic detergent (cetyltrimethylammonium bromide, CTAB), which favours the orientation of growing polymer for termination. The retarding effect of cations may also be due to specific ion-pair bonding of P20;fanion with cation, which lowers the rate of primary radical generation. On the other hand, the dissociation of anionic detergents (sodium lauryl sulfate, SLS) provides negatively charged micelles, which probably exert a repelling force between P20i- anion and negatively charged ionic micelles, thus lowering the rate of primary radical generation. Hence a retarding effect is observed. The retarding effect (Figure 7) due to addition of inorganic salts can be explained as follows: (A) In the case of alkali-metal chloride the basic character of alkali-metal ion increases, i.e. ionic radius increases from Li to K. (B) In the case of neutral salts (NH4Cl and Na2S04) the decrease in the rate may be due to thickening of the medium, or the process of salting out causes interference with the usual reaction, resulting in premature termination of the growing chain. Similar results have also been reported by others13.

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PDP-CyxHCI

initiated polymerization

of methacrylamide:

K. Behari et al.

25

25

20

20

15

10

5

0

40

20

60

80

120

100

Time (min) 0

40

80

120

180

200

240

Time (mitt) Figure 6 Effect of detergent concentration on R,. at temp. = 45 ‘C: [methacrylamide] = 2.0 x IO-’ moldm-s, [CysHCI] = I .O x IO-‘mol drn-‘, [PDP] = 1.0 x IO-’ moldm-‘. Detergents used: 1. controlled 3, sodium experiment; 2. sodium lam I sulfate (1 x IO-‘moldm~‘): ?’ bromide oleate (1 .O x IO-’ mol drn-- ); 4. cetyltrimethylammonium t 1.O x I 0d3 mol dm-‘)

Effect of concentrations of complexing agent and transitionmetal ion on R,. at temp. = 45 C: (methacrylamide] = 2.0 x 1OY’moldm-“. = 1.0 x 10-‘moldm~3. = 1.0 x 2, [PDP] = 0.5 x lO~‘moldm ‘. Curves: [CysHCl]1, controlled experiment; moldmm3; 4. [NaF] = 1.0 x 10ml 1O~‘moldm~’ moldm-‘; 3, [CuSO,] = 1.0 x 10ml

25 -

20

I5

g u

IO

5

I

I

I

I

I

I

40

80

120

160

200

240

I

280

Time (min) 0

20

40

60

80

loo

120

140

Time (min) Figure 7 Effect of inorganic salts on R,. at temp. = 45 C: [methacrylamide] = 2.0 x 10-l moldm-‘. [CysHCI] = I.0 x lo-’ mol [salt] = 2.0 x lO~‘moldm-‘. drn-‘, [PDP] = I.0 x lo-‘moldm-‘, Salts used: I, controlled experiment; 2, MnS04: 3. NH4Cl; 4, KCI; 5. LiCI; 6, NaCI; 7. Na2S04

The rate of polymerization increases with the addition of MnS04 (Figure 7) where Mn’+ is easily oxidized to Mn’+ by the interaction of PDP, which in turn produces free radicals’4m’6 by the interaction of Cys.HCl as: P20im + Mn’+ * Mn3+ + P.Oi- + PO:P’Oi- + Mn*+ d Mn3+ + PO:Mn3’ + RSH 4 Mn-‘+ + RS’ where RSH = Cys.HCl and RS’ = cysteine free radical. On the other hand, the addition of CuS04 decreases the R, (Figure S), which is due to formation of Cu2+ radical pair”. The retarding effect is also observed by the addition of NaF, which can be explained by the fact that

1016

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Figure 9 Effect of pH on R,. at temp. = 45’C: [methacrylamide] = 2.0 ,x 10-l moldm~‘. [CysHCl] = I.0 x IO~‘moldm~‘, [PDP] = 1.0 x 1O-- mol dm ‘. Curves: I, no addition of H$O,; 2. pH 2.69; 3. pH 3.0: 4, pH 3.30

NaF, being a complexing agent (Figure U), lowers the effective concentration of PDP’s. As the concentration of hydrogen ion increases (pH decreases) the formation of HP.04 and P’Oi- radical ion increases, which enhances the R,: PZO;f--+ H+ 4 HP’04 + P.0;

CONCLUSION R, increases with the increase of [PDP], [CysHCI] and

[methacrylamide] respectively, as expected by the following equation: R, = kp(k/2kt)“‘[M][PDP]t”[RSH]

The energy of activation being 41.54 31 1 kJ mol-’ is indicative of free-radical polymerization of methacrylamide by PDP-Cys.HCl system. The addition of organic

POP-Cys.HCI

solvent, detergent and inorganic salts shows decreasing effect on R, while the MnS04 and H2S04 (H+) addition shows increasing effect on R,.

initiated polymerization

6 7 8

ACKNOWLEDGEMENTS The authors are grateful to FMC, New York, for a gift sample of PDP, and the State-CSIR, UP, Lucknow, is gratefully acknowledged for financial support to U. Agrawal.

9 10 11 12

13

REFERENCES 14

1 2 3 4 5

Baral. N., Pati. N. C., Nayak. P. L. and Desh. S. B. J. Murromol. Sci.. Chem. (A) 1983, 18, 1123 Gopalan, A., Paulrajan. S., Venkatarao. K. and Subharathan. N. R. Eur. Poitw~ J. 1983, 19, 817 Sarasvathi, S. and Venkatarao. K. Makromol. Chem. Rapid Commun. 1981, 2, 219 Behari, K., Agrawal, U. and Das, R. Polymer 1993.344557 Wallace. R. A. and Young, D. G. J. Polym. Sri. (Al) 1966,4. 1179

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K. Behari et al.

Chatterjee, S. K.. Prokopova, E. and Bohdanecky. M. Eur. Polym. J. 1978, 14, 665 Mishra, G. S. and Bajpai, U. D. N. J. Mucromol. Sci., Chem. (Al 1979, 13 (8), 1135 Flory, P. J. ‘Principles of Polmer Chemistry’, Cornell University Press, Ithaca, NY, 1967, p. 309 Deb, P. C. and Meyerhoff, G. Eur. Polym. J. 1974, 10, 709 Behari, K., Gupta, K. C. and Verma. M. Angrw. Makromol. Chem. 1985.67. 130 Lange, N. A. ‘Handbook of Chemistry’. McGraw-Hill, New York. 1967, p. 1234 Palit, S. R. and Konar, R. S. J. Polym. Sci. 1962, 58, 85; Thomas. W. H., Gleason, E. A. and Mino. G. J. Polwn. Sci. 1957.24.43 Mishra. G. S.. Shukla, J. S. and Narain, H. Makromol. Chew. 1968, 119. 74 Okomoto, T., Takahashi. M. and Inaki. Y. .4rzgen,. Mukromol. Chem. 1974. 38. 8 I Waters, W. A. and Littler, J. A. ‘Oxidation in Organic Chemistry’ (Ed. K. B. Wiberg), Academic Press, London. 1965, p. 3 Pradhan, A. K., Pati, N. C. and Nayak, P. L. J. Mucromol. Sci.. Chem. (A/ 1982, 18 (3). 395 Manickahra, S. P.. Subhrathan, N. R. and Venkatarao, K. J. Polym. Sri.. Polym. Chem. Edn. 1980, 18, 1679 Rebellow. J. J. Mukromol. Chem. 1975, 176, 2203

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