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Solution polymerization of acrylamide using potassium persulfate as an initiator: kinetic studies, temperature and pH dependence
European Polymer Journal 37 (2001) 1507±1510
Short communication
www.elsevier.nl/locate/europolj
Solution polymerization of acrylamide using potassium persulfate as an initiator: kinetic studies, temperature and pH dependence Hong-Ru Lin * Department of Applied Chemistry, Chia Nan University of Pharmacy and Science, Tainan 71710, Taiwan, ROC Received 17 December 1999; received in revised form 5 October 2000; accepted 6 December 2000
Abstract The kinetics of the radical polymerization of acrylamide in aqueous solution using potassium persulfate as initiator has been investigated by the gravimetric technique. Up to 94% conversion was obtained. The rate of polymerization was governed by the expression at 55°C Rpo k K2 S2 O8 0:5 M1:26 0 The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to monomer was greater than unity. The eects of temperature and pH on the polymerization rate were also investigated. An overall activation energy of 45:1 0:1 kJ/mol was obtained over the temperature range 35±55°C. It was found that the rate of conversion increased with increasing polymerization temperature, while the polymerization rate was insensitive to the change of pH value when monomer and initiator concentrations, and temperature were all kept constant. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Polymer kinetics; Solution polymerization; Acrylamide; Potassium persulfate
1. Introduction In recent years, scientists and engineers working on environmental and industrial problems have renewed their interest in water-soluble polymers. The most important of these synthetic water-soluble polymers is polyacrylamide [1]. These polymers have many applications in the ®elds of paper chemicals, mineral processing, water treatment, oil-well stimulation and friction reduction [2].
*
Fax: +886-6-2666411. E-mail address: [email protected] (H.-R. Lin).
The previous workers [3±8] made a series of comprehensive studies to elucidate the reaction mechanism for the solution polymerization of acrylamide in water. However, kinetic studies reported in the literature are limited to the low conversion range, generally less than 10% conversion. There is apparently not much published work on the polymerization of acrylamide initiated by the conventional peroxidic initiator. Riggs [9,10] was the ®rst one to use potassium persulfate as an initiator to initiate the polymerization of acrylamide by the dilatometer technique. In this study, however, a dierent technique, gravimetry, was used to determine the dependence of polymerization rate on initiator and monomer concentrations for the solution polymerization of acrylamide using potassium persulfate as an initiator. The eects of pH and reaction temperature on the polymerization rate were also investigated.
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 0 ) 0 0 2 6 1 - 5
1508
H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
2. Experimental 2.1. Reagent purity Acrylamide was supplied by Aldrich Chemical Company, Inc., Milwaukee, Wisconsin. This technical grade monomer contains an appreciable amount of impurities and needs to be puri®ed by method as reported elsewhere [5]. The initiator, potassium persulfate, used was of analytical grade and was not puri®ed further. Since the polymerization reaction was air sensitive, a three-neck round bottom ¯ask and a condenser was built, to eliminate the oxygen from water, monomer and initiator. Water used as solvent was distilled, deionized and deaerated by bubbling argon gas through it for at least an hour. 2.2. Procedure For this study, a series of steps were carried out as follows: (1) The desired amount of puri®ed acrylamide (monomer) was weighed out and transferred to a test tube which was then ¯ushed with argon for one minute at a moderate gas ¯ow rate. The tube was immediately capped with a septum and secured with a thin wire. (2) Water was deaerated by deaeration unit. A syringe was used to transfer the desired amount of water into the sealed tube containing the monomer. A second syringe needle was also inserted into the septum to release some pressure built up by positive volume replacement of the transferred water. (3) The tubes containing the dissolved monomer were then put in the constant temperature water bath at the desired reaction temperature for at least 10 min. (4) Steps (1) and (2) were repeated for the initiator. (5) The desired amount of initiator solution was then transferred to the monomer solution tube described in step (3). Polymerization was assumed to start at this time and could be stopped at any desired time as described below. (6) After the polymerization reaction was carried out for a certain amount of time, the reaction tube was opened and the polymer solution was poured out into a beaker containing cold methanol (twice the volume of the polymer solution) then the mixture was stirred immediately. (7) The methanol/water/polymer mixture was then ®ltered and dried in an oven for at least 12 h at 160°C. (8) The dry polymer was weighed and the conversion was obtained. The dependence of polymerization rate on initiator and monomer concentrations was determined by varying concentration of one species while keeping the other constant and vice versa. The eects of pH and temperature on the conversion were investigated by varying one
condition at constant monomer and initiator concentrations, respectively.
3. Results and discussion The in¯uence of acrylamide on the polymerization rate was studied over a concentration range, 0:35±1:76 mol/l, the initiator concentration was kept at a constant value, 2:25 10 3 mol/l, the temperature was 55°C, and the pH was 5:2 0:1. Fig. 1 shows the conversion versus polymerization time with variation of monomer concentration. All the curves in this ®gure showed the same trend with increase in conversion as the polymerization proceeded. The monomer conversion rate was very fast at early stage of polymerization. The conversion increased with increasing monomer concentrations. When the monomer concentration increased up to 1.76 mol/l, the conversion reached about 94% after polymerization proceeded 60 min. In this study, the technique, gravimetry, was employed to study the polymerization kinetics and the overall conversion was greater than other studies [3,5±7,9]. Most of the previous workers used the dilatometer technique to study the radical chain polymerization. Dilatometry utilizes the principle that the volume will change when the polymerization occurs. Because of the large dierence in density [11] between monomer and polymer, it is often the most accurate method for radical chain polymerizations. Gravimetry, however, is probably the most direct method of determining the conversion of monomer to polymer by stopping the polymerization, isolating and weighing the
Fig. 1. Eect of monomer concentration on the conversion rate. M0 0:35±1:76 mol/l, I 2:25 10 3 mol/l, T 55°C, and pH 5:2 0:1.
H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
resulting polymer. There are some disadvantages, however, such as the extra handling of the polymer in the steps of precipitation, ®ltration, and drying, may well lead to unavoidable losses reducing the precision attainable. The initial polymerization rate, Rpo , was obtained from the slope of the conversion versus time curve. The relationship of polymerization rate with monomer concentration was obtained by plotting the log Rpo versus log [M]0 and the form Rpo / M1:26 was obtained from 0 the line of the slope (not shown). The reaction rate was greater than ®rst order in monomer concentration as also indicated by other studies [6,9,12], and in good agreement with studies by Riggs and Rodiguez [9] and Ishige and Hamielec [6]. The abnormality of order with respect to monomer concentration can be explained by the solvent-transfer [13,14], complex [15], and cage-eect [16] theories as indicated elsewhere. Fig. 2 shows conversion versus polymerization time with variation of initiator concentration from 0:45 10 3 to 2:25 10 3 mol/l, under constant monomer concentration of 0.70 mol/l, at 55°C, and pH 5:2 0:1. The conversion increased as polymerization proceeded and it also increased with increasing initiator concentration, which may be due to the increase in concentration of active species S2 O28 [17]. The dependence of initiator concentration on polymerization rate was found to be Rpo / I0:5 , which clearly indicates that termination occurs through bimolecular interaction of growing polymer chain radicals [18±22]. The polymerization rate with respect to initiator concentration in this study was consistent with the classical kinetic theory,
Fig. 2. Eect of initiator concentration on the conversion rate. M0 0:70 mol/l, I 0:45 10 3 ±2:25 10 3 mol/l, T 55°C, and pH 5:2 0:1.
1509
Fig. 3. Eect of pH value on the conversion rate at dierent temperatures. M0 0:7042 mol/l, I 2:25 10 3 mol/l, T 35±55°C, and pH 3:2±11:2 0:1.
which predicts the polymerization rate depends on the square root of the initiator concentration, as also indicated by most of the previous workers [3,5±7,9,12]. The eect of pH on polymerization rate at various temperatures was shown in Fig. 3. The pH varied from 3.2 to 11:2 0:1. From Fig. 3, it is found that there was no monomer converted to polymer at low polymerization temperature (35°C) if pH value was greater than 5.2. At this low temperature, it was also found that there was no monomer being converted to polymer at early stage of polymerization until reaction time reached 90 min, and at this low temperature, there was only about 30% monomer conversion after polymerization proceeded 150 min. As the temperature increased (45°C and 55°C), the rate of production of primary free radicals increased, thus increasing the polymerization rate [22]. The overall activation energy of the present polymerization system (M0 0:70 mol/l, I 2:25 10 3 mol/ l, T 35±55°C, and pH 5:2 0:1) is 45:1 0:1 kJ/ mol determined by plotting ln Rpo versus 1=T (K) (not shown). This value corresponds well with the typical activation energies of propagation in free radical polymerization [22,23]. When the pH was decreased, the hydrogen ion would catalyze the reaction of thermal decomposition of potassium persulfate, which was dierent from the uncatalyzed reaction as indicated elsewhere [24±26]. The hydrogen ion catalyzed reaction involves the unsymmetrical rupture of the O±O bond of the HS2 O8 ion to form sulfur tetroxide and bisulfate [24]. The mechanism of hydrogen ion catalyzed reaction was established by the following equations:
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H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
S2 O28 H ! HS2 O8
1
HS2 O8 ! SO4 HSO4
2
1 SO4 ! SO3 O2 2
3
In strong acid, Eq. (3) will be replaced by the following equation: SO4 H2 O ! H2 SO5
4
The oxygen liberated by the uncatalyzed reaction comes from the water while the oxygen liberated by the acid-catalyzed reaction comes from the persulfate ion [19]. From Fig. 3, it is also shown that, in general, polymerization rate was not very sensitive to the change of pH at constant temperature. The initial polymerization rates were determined by measuring the slope of the tangent to the conversion curves for zero polymerization time. The range of deviations for these slopes were within 5% at constant temperature. Although it may cause the growing polymer radical to acquire increasing amounts of negative charge as the pH was increased, the development of this charge may increase electrostatic repulsion between growing radicals or change the mobility, ¯exibility, and con®guration in the polymer solvents. Currie et al. [27] studied the eect of pH on the polymerization of acrylamide in water and found the same result. They claimed that rate constant of propagation, kp , and rate constant of termination, kt , both diminish by about on order of magnitude as the pH was changed from 1 to 13 but kp =kt1=2 was almost constant. Although the rate of persulfate decomposition does depend on pH, the overall rate of polymerization was insensitive to pH changes when monomer and initiator concentrations, and temperature were all kept constant. 4. Conclusions An experimental investigation was made on polymerization of acrylamide in water with potassium persulfate as an initiator. Conversion of monomer to polymer was measured gravimetrically. Up to 94% conversion was obtained. The rate of polymerization is expressed by Rpo / K2 S2 O8 0:5 M1:26 0 . The dependence of initiator concentration on polymerization rate followed the classical kinetic theory. The dependence of monomer agreed well with polymerization initiated by other initiators where the order was always greater than unity. The overall energy of activation was found to be 45:1 0:1 kJ/mol for the present polymerization system.
The monomer conversion increased as polymerization temperature increased, while the change of pH value did not have any signi®cant eect on the monomer conversion at constant temperature.
Acknowledgements The author is grateful to the Chia Nan University of Pharmacy and Science for the ®nancial support. The author also thanks Mr. Shyr-Jou Liou for his assistance in the experimental work.
References [1] George MH, Ghosh A. J Polym Sci Polym Chem 1978;16:981. [2] Kurenkov VF, Mysgchenkov VA. Eur Polym J 1980; 16:1229. [3] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:476. [4] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:499. [5] Dainton FS, Tordo M. Trans Faraday Soc 1958;53:666. [6] Ishige T, Hamielec AE. J Appl Polym Sci 1973;17:1479. [7] Cavell EAS. Makromol Chem 1962;54:70. [8] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:357. [9] Riggs JP, Rodiguez F. J Polym Sci Part A-1 1967;5:3151. [10] Riggs JP, Rodiguez F. J Polym Sci Part A-1 1967;5:3167. [11] Collins EA, Bares J, Billmeyer Jr FW. Experiments in polymer science. New York: Wiley-Interscience; 1973. p. 8 (Chapter 5). [12] Venkatarao K, Santappa M. J Polym Sci Part A-1 1967;5:637. [13] Allen PW, Merrett FM, Scanlan J. Trans Faraday Soc 1955;51:95. [14] Burnett GM, Loan LD. Trans Faraday Soc 1955;51:214. [15] Husemann E, Schultz GV, Staudinger H. Z Physik Chem 1938;B39:246. [16] Matheson MS. J Chem Phys 1945;13:584. [17] Behari K, Bahadur L, Das R, Agarwal U. Polym Prepr 1994;35:117. [18] Bamford CH, Scho®eld E. Polymer 1983;24:433. [19] Konar RS, Palit SR. J Polym Sci A 1964;2:1731. [20] Mishra GS, Rebellow J. J Macromol Chem 1974;175:3117. [21] Mishra GS, Bajpai UDN. J Macromol Sci Chem A 1977;13:1135. [22] Behari K, Taunk K, Das R. Polym Int 1998;46:126. [23] Cowie JMG. In: Allen G, Bevington JC, editors. Comprehensive polymer science, part 1, vol. 3. Oxford: Pergamon; 1989. p. 1. [24] Koltho IM, Miller IK. J Am Chem Soc 1951;73:3055. [25] Bartlett PD, Cotman Jr JD J Am Chem Soc 1949;71:1419. [26] Green L, Masson O. J Chem Soc 1910;97:2083. [27] Currie DJ, Dainton FS, Watt WS. Polymer 1965;6:451.
Short communication
www.elsevier.nl/locate/europolj
Solution polymerization of acrylamide using potassium persulfate as an initiator: kinetic studies, temperature and pH dependence Hong-Ru Lin * Department of Applied Chemistry, Chia Nan University of Pharmacy and Science, Tainan 71710, Taiwan, ROC Received 17 December 1999; received in revised form 5 October 2000; accepted 6 December 2000
Abstract The kinetics of the radical polymerization of acrylamide in aqueous solution using potassium persulfate as initiator has been investigated by the gravimetric technique. Up to 94% conversion was obtained. The rate of polymerization was governed by the expression at 55°C Rpo k K2 S2 O8 0:5 M1:26 0 The order with respect to initiator was consistent with the classical kinetic rate equation, while the order with respect to monomer was greater than unity. The eects of temperature and pH on the polymerization rate were also investigated. An overall activation energy of 45:1 0:1 kJ/mol was obtained over the temperature range 35±55°C. It was found that the rate of conversion increased with increasing polymerization temperature, while the polymerization rate was insensitive to the change of pH value when monomer and initiator concentrations, and temperature were all kept constant. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Polymer kinetics; Solution polymerization; Acrylamide; Potassium persulfate
1. Introduction In recent years, scientists and engineers working on environmental and industrial problems have renewed their interest in water-soluble polymers. The most important of these synthetic water-soluble polymers is polyacrylamide [1]. These polymers have many applications in the ®elds of paper chemicals, mineral processing, water treatment, oil-well stimulation and friction reduction [2].
*
Fax: +886-6-2666411. E-mail address: [email protected] (H.-R. Lin).
The previous workers [3±8] made a series of comprehensive studies to elucidate the reaction mechanism for the solution polymerization of acrylamide in water. However, kinetic studies reported in the literature are limited to the low conversion range, generally less than 10% conversion. There is apparently not much published work on the polymerization of acrylamide initiated by the conventional peroxidic initiator. Riggs [9,10] was the ®rst one to use potassium persulfate as an initiator to initiate the polymerization of acrylamide by the dilatometer technique. In this study, however, a dierent technique, gravimetry, was used to determine the dependence of polymerization rate on initiator and monomer concentrations for the solution polymerization of acrylamide using potassium persulfate as an initiator. The eects of pH and reaction temperature on the polymerization rate were also investigated.
0014-3057/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 1 4 - 3 0 5 7 ( 0 0 ) 0 0 2 6 1 - 5
1508
H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
2. Experimental 2.1. Reagent purity Acrylamide was supplied by Aldrich Chemical Company, Inc., Milwaukee, Wisconsin. This technical grade monomer contains an appreciable amount of impurities and needs to be puri®ed by method as reported elsewhere [5]. The initiator, potassium persulfate, used was of analytical grade and was not puri®ed further. Since the polymerization reaction was air sensitive, a three-neck round bottom ¯ask and a condenser was built, to eliminate the oxygen from water, monomer and initiator. Water used as solvent was distilled, deionized and deaerated by bubbling argon gas through it for at least an hour. 2.2. Procedure For this study, a series of steps were carried out as follows: (1) The desired amount of puri®ed acrylamide (monomer) was weighed out and transferred to a test tube which was then ¯ushed with argon for one minute at a moderate gas ¯ow rate. The tube was immediately capped with a septum and secured with a thin wire. (2) Water was deaerated by deaeration unit. A syringe was used to transfer the desired amount of water into the sealed tube containing the monomer. A second syringe needle was also inserted into the septum to release some pressure built up by positive volume replacement of the transferred water. (3) The tubes containing the dissolved monomer were then put in the constant temperature water bath at the desired reaction temperature for at least 10 min. (4) Steps (1) and (2) were repeated for the initiator. (5) The desired amount of initiator solution was then transferred to the monomer solution tube described in step (3). Polymerization was assumed to start at this time and could be stopped at any desired time as described below. (6) After the polymerization reaction was carried out for a certain amount of time, the reaction tube was opened and the polymer solution was poured out into a beaker containing cold methanol (twice the volume of the polymer solution) then the mixture was stirred immediately. (7) The methanol/water/polymer mixture was then ®ltered and dried in an oven for at least 12 h at 160°C. (8) The dry polymer was weighed and the conversion was obtained. The dependence of polymerization rate on initiator and monomer concentrations was determined by varying concentration of one species while keeping the other constant and vice versa. The eects of pH and temperature on the conversion were investigated by varying one
condition at constant monomer and initiator concentrations, respectively.
3. Results and discussion The in¯uence of acrylamide on the polymerization rate was studied over a concentration range, 0:35±1:76 mol/l, the initiator concentration was kept at a constant value, 2:25 10 3 mol/l, the temperature was 55°C, and the pH was 5:2 0:1. Fig. 1 shows the conversion versus polymerization time with variation of monomer concentration. All the curves in this ®gure showed the same trend with increase in conversion as the polymerization proceeded. The monomer conversion rate was very fast at early stage of polymerization. The conversion increased with increasing monomer concentrations. When the monomer concentration increased up to 1.76 mol/l, the conversion reached about 94% after polymerization proceeded 60 min. In this study, the technique, gravimetry, was employed to study the polymerization kinetics and the overall conversion was greater than other studies [3,5±7,9]. Most of the previous workers used the dilatometer technique to study the radical chain polymerization. Dilatometry utilizes the principle that the volume will change when the polymerization occurs. Because of the large dierence in density [11] between monomer and polymer, it is often the most accurate method for radical chain polymerizations. Gravimetry, however, is probably the most direct method of determining the conversion of monomer to polymer by stopping the polymerization, isolating and weighing the
Fig. 1. Eect of monomer concentration on the conversion rate. M0 0:35±1:76 mol/l, I 2:25 10 3 mol/l, T 55°C, and pH 5:2 0:1.
H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
resulting polymer. There are some disadvantages, however, such as the extra handling of the polymer in the steps of precipitation, ®ltration, and drying, may well lead to unavoidable losses reducing the precision attainable. The initial polymerization rate, Rpo , was obtained from the slope of the conversion versus time curve. The relationship of polymerization rate with monomer concentration was obtained by plotting the log Rpo versus log [M]0 and the form Rpo / M1:26 was obtained from 0 the line of the slope (not shown). The reaction rate was greater than ®rst order in monomer concentration as also indicated by other studies [6,9,12], and in good agreement with studies by Riggs and Rodiguez [9] and Ishige and Hamielec [6]. The abnormality of order with respect to monomer concentration can be explained by the solvent-transfer [13,14], complex [15], and cage-eect [16] theories as indicated elsewhere. Fig. 2 shows conversion versus polymerization time with variation of initiator concentration from 0:45 10 3 to 2:25 10 3 mol/l, under constant monomer concentration of 0.70 mol/l, at 55°C, and pH 5:2 0:1. The conversion increased as polymerization proceeded and it also increased with increasing initiator concentration, which may be due to the increase in concentration of active species S2 O28 [17]. The dependence of initiator concentration on polymerization rate was found to be Rpo / I0:5 , which clearly indicates that termination occurs through bimolecular interaction of growing polymer chain radicals [18±22]. The polymerization rate with respect to initiator concentration in this study was consistent with the classical kinetic theory,
Fig. 2. Eect of initiator concentration on the conversion rate. M0 0:70 mol/l, I 0:45 10 3 ±2:25 10 3 mol/l, T 55°C, and pH 5:2 0:1.
1509
Fig. 3. Eect of pH value on the conversion rate at dierent temperatures. M0 0:7042 mol/l, I 2:25 10 3 mol/l, T 35±55°C, and pH 3:2±11:2 0:1.
which predicts the polymerization rate depends on the square root of the initiator concentration, as also indicated by most of the previous workers [3,5±7,9,12]. The eect of pH on polymerization rate at various temperatures was shown in Fig. 3. The pH varied from 3.2 to 11:2 0:1. From Fig. 3, it is found that there was no monomer converted to polymer at low polymerization temperature (35°C) if pH value was greater than 5.2. At this low temperature, it was also found that there was no monomer being converted to polymer at early stage of polymerization until reaction time reached 90 min, and at this low temperature, there was only about 30% monomer conversion after polymerization proceeded 150 min. As the temperature increased (45°C and 55°C), the rate of production of primary free radicals increased, thus increasing the polymerization rate [22]. The overall activation energy of the present polymerization system (M0 0:70 mol/l, I 2:25 10 3 mol/ l, T 35±55°C, and pH 5:2 0:1) is 45:1 0:1 kJ/ mol determined by plotting ln Rpo versus 1=T (K) (not shown). This value corresponds well with the typical activation energies of propagation in free radical polymerization [22,23]. When the pH was decreased, the hydrogen ion would catalyze the reaction of thermal decomposition of potassium persulfate, which was dierent from the uncatalyzed reaction as indicated elsewhere [24±26]. The hydrogen ion catalyzed reaction involves the unsymmetrical rupture of the O±O bond of the HS2 O8 ion to form sulfur tetroxide and bisulfate [24]. The mechanism of hydrogen ion catalyzed reaction was established by the following equations:
1510
H.-R. Lin / European Polymer Journal 37 (2001) 1507±1510
S2 O28 H ! HS2 O8
1
HS2 O8 ! SO4 HSO4
2
1 SO4 ! SO3 O2 2
3
In strong acid, Eq. (3) will be replaced by the following equation: SO4 H2 O ! H2 SO5
4
The oxygen liberated by the uncatalyzed reaction comes from the water while the oxygen liberated by the acid-catalyzed reaction comes from the persulfate ion [19]. From Fig. 3, it is also shown that, in general, polymerization rate was not very sensitive to the change of pH at constant temperature. The initial polymerization rates were determined by measuring the slope of the tangent to the conversion curves for zero polymerization time. The range of deviations for these slopes were within 5% at constant temperature. Although it may cause the growing polymer radical to acquire increasing amounts of negative charge as the pH was increased, the development of this charge may increase electrostatic repulsion between growing radicals or change the mobility, ¯exibility, and con®guration in the polymer solvents. Currie et al. [27] studied the eect of pH on the polymerization of acrylamide in water and found the same result. They claimed that rate constant of propagation, kp , and rate constant of termination, kt , both diminish by about on order of magnitude as the pH was changed from 1 to 13 but kp =kt1=2 was almost constant. Although the rate of persulfate decomposition does depend on pH, the overall rate of polymerization was insensitive to pH changes when monomer and initiator concentrations, and temperature were all kept constant. 4. Conclusions An experimental investigation was made on polymerization of acrylamide in water with potassium persulfate as an initiator. Conversion of monomer to polymer was measured gravimetrically. Up to 94% conversion was obtained. The rate of polymerization is expressed by Rpo / K2 S2 O8 0:5 M1:26 0 . The dependence of initiator concentration on polymerization rate followed the classical kinetic theory. The dependence of monomer agreed well with polymerization initiated by other initiators where the order was always greater than unity. The overall energy of activation was found to be 45:1 0:1 kJ/mol for the present polymerization system.
The monomer conversion increased as polymerization temperature increased, while the change of pH value did not have any signi®cant eect on the monomer conversion at constant temperature.
Acknowledgements The author is grateful to the Chia Nan University of Pharmacy and Science for the ®nancial support. The author also thanks Mr. Shyr-Jou Liou for his assistance in the experimental work.
References [1] George MH, Ghosh A. J Polym Sci Polym Chem 1978;16:981. [2] Kurenkov VF, Mysgchenkov VA. Eur Polym J 1980; 16:1229. [3] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:476. [4] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:499. [5] Dainton FS, Tordo M. Trans Faraday Soc 1958;53:666. [6] Ishige T, Hamielec AE. J Appl Polym Sci 1973;17:1479. [7] Cavell EAS. Makromol Chem 1962;54:70. [8] Collinson E, Dainton FS, McNaughton GS. Trans Faraday Soc 1957;53:357. [9] Riggs JP, Rodiguez F. J Polym Sci Part A-1 1967;5:3151. [10] Riggs JP, Rodiguez F. J Polym Sci Part A-1 1967;5:3167. [11] Collins EA, Bares J, Billmeyer Jr FW. Experiments in polymer science. New York: Wiley-Interscience; 1973. p. 8 (Chapter 5). [12] Venkatarao K, Santappa M. J Polym Sci Part A-1 1967;5:637. [13] Allen PW, Merrett FM, Scanlan J. Trans Faraday Soc 1955;51:95. [14] Burnett GM, Loan LD. Trans Faraday Soc 1955;51:214. [15] Husemann E, Schultz GV, Staudinger H. Z Physik Chem 1938;B39:246. [16] Matheson MS. J Chem Phys 1945;13:584. [17] Behari K, Bahadur L, Das R, Agarwal U. Polym Prepr 1994;35:117. [18] Bamford CH, Scho®eld E. Polymer 1983;24:433. [19] Konar RS, Palit SR. J Polym Sci A 1964;2:1731. [20] Mishra GS, Rebellow J. J Macromol Chem 1974;175:3117. [21] Mishra GS, Bajpai UDN. J Macromol Sci Chem A 1977;13:1135. [22] Behari K, Taunk K, Das R. Polym Int 1998;46:126. [23] Cowie JMG. In: Allen G, Bevington JC, editors. Comprehensive polymer science, part 1, vol. 3. Oxford: Pergamon; 1989. p. 1. [24] Koltho IM, Miller IK. J Am Chem Soc 1951;73:3055. [25] Bartlett PD, Cotman Jr JD J Am Chem Soc 1949;71:1419. [26] Green L, Masson O. J Chem Soc 1910;97:2083. [27] Currie DJ, Dainton FS, Watt WS. Polymer 1965;6:451.