Kinetic study of RuIII-catalyzed polymerization of methylmethacrylate initiated with n-butylamine in the presence of carbon tetrachloride by a charge-transfer mechanism

Kinetic Study ofRuIII-CatalyzedPolymerization ofMethylmethacrylateInitiated with n-Butylaminein the Presence of CarbonTetrachloride by a Charge-Transfer MechanismRAJESH TIWARI, GERARD T. CANEBA

Department of Chemical Engineering, Michigan Technological University, Houghton, MI 49931

Received 8 February 2010; revised 7 July 2010, 5 August 2010; accepted 5 August 2010

DOI 10.1002/kin.20534Published online 12 November 2010 in Wiley Online Library (wileyonlinelibrary.com).

ABSTRACT: Ruthenium trichloride (RuCl3 or RuIII) catalyzed polymerization of methylmethacry-late (MMA) initiated with n-butylamine (BA) in the presence of carbon tetrachloride (CCl4) by acharge-transfer mechanism has been investigated in a dimethylsulfoxide (DMSO) medium byemploying a dilatometric technique at 60◦C. The rate of polymerization (Rp) has been obtainedunder the conditions [CCl4]/[BA]≤1 and [CCl4]/[BA]≥1. The kinetic data indicate the possibleparticipation of the charge-transfer complex formed between the amine–RuIII complex andCCl4 in the polymerization of MMA. In the absence of either CCl4 or BA, no polymerizationof MMA is observed under the present experimental conditions. The rate of polymerization isinhibited by hydroquinone, suggesting a free-radical initiation. C© 2010 Wiley Periodicals, Inc.Int J Chem Kinet 43: 70–77, 2011

Correspondence to: Rajesh Tiwari; e-mail: [email protected] orrajeshtiwari [email protected]© 2010 Wiley Periodicals, Inc.

INTRODUCTION

The role of platinum group metals as homogeneouscatalysts has been investigated widely in several redox

KINETIC STUDY OF RuIII-CATALYZED POLYMERIZATION OF METHYLMETHACRYLATE 71

reactions [1–10]. In some cases, the inhibition effectof RuIII on the rate of reaction has also been observed[11]. However, not much attention has been paid to theuse of these metal ions in polymerization reactions.The acceleration of the rate of polymerization of somemonomers by PdII has been observed [12,13]. Poly-merization of methylmethacrylate (MMA) initiated byamines in the presence of CCl4 by a charge-transfermechanism [14–25], amines, and RuIII complexes isalso a very effective system in atom transfer radicalpolymerization mechanism [26,27], and a free-radicalretrograde-precipitation polymer mechanism has beenstudied widely by many investigators [28–35]. It hasbeen observed that two different mechanisms [36,37]for the initiation of polymerization of MMA, involv-ing the charge-transfer complex formed by the in-teraction of amine and CCl4—under the conditions[CCl4/amine]≤1—and by the interaction of amine andMMA—under the conditions [CCl4/amine]≥1 havebeen proposed.

Preliminary studies made by us on the polymer-izations of MA by amino alcohols in the presence ofCCl4 and RuIII have shown that RuIII catalyzed therate of polymerization of MA. Therefore, the kineticsof RuCl3-catalyzed polymerization of MMA initiatedwith n-butylamine (BA) in the presence of CCl4 bya charge–transfer mechanism has been investigated indetail and results are reported in this paper.

EXPERIMENTAL

Materials

All chemicals are purchased from Sigma-Aldrich Corp.(St. Louis, MO). MMA (>99%), dimethylsulfoxide(DMSO) (>99.9%), and CCl4 (>99.9%) are purifiedbefore use. BA (>99.5%) is distilled under reducedpressure prior to use. The stock solution of RuCl3 isprepared by dissolving 1.0-gm sample of rutheniumtrichloride in 25 mL 0.01 N hydrochloric acid (HCl)then diluting it to 250 mL (H2O). The RuCl3 contentof the stock solution is checked spectrophotometricallyfrom time to time.

Polymerization Procedure

The polymerization of MMA is carried out in adilatometer [38] (bulb capacity of 5.0 mL, with an11-cm-long capillary of a 3-mm diameter) under ni-trogen atmosphere at 60◦C using DMSO as a solvent.The required amounts of BA, MMA, CCl4, RuCl3, andDMSO are taken in the dilatometer, which is imme-diately sealed and placed in a thermostatic water bath

maintained at 60 ± 0.1◦C. Progress of the reaction ismonitored with the help of a cathetometer. The poly-merization is not allowed to proceed beyond 25% toavoid the formation of side products and the effectsdue to an increase in the viscosity [39]. The polymeris precipitated with acidified methanol and is dried toa constant weight.

Evaluation of the Rate of Polymerization

The rate of polymerization (Rp) of MMA is given as

Rp(mol dm−3 s−1) = w × 103

t × 60 × 100.12(i)

where w is the weight of polymer obtained from1 mL of MMA (molecular weight of 100.12 g mol−1

and density of 0.94 g cm−3), t is the time in minutesof polymerization of MMA. The percentage of conver-sion (C) can be defined as

C = w × 100

1 × 0.94(ii)

From Eqs. (i) and (ii), Rp may be given as

Rp = 0.94 × C × 103

100 × t × 60 × 100.12

or, on simplification

Rp = 1.564 × C × 10−3

t(iii)

Thus, according to Eq. (iii), Rp may be evaluated fromthe slope of the plot of C vs. t . In actual experiments,C is obtained from a master graph plotted betweenthe percentage of conversion and volume contraction(Fig. 1). Then the obtained percentage of conversion(C) is plotted against time (t) (Fig. 2) to calculate therate of polymerization (Rp).

RESULTS AND DISCUSSION

The rates of polymerization (Rp) of MMA, BA, CCl4,and RuCl3 are measured at various concentrationskeeping the concentrations of other reactants constant.The results are given in Table I. The rate of polymeriza-tion (Rp) of MMA is measured at various concentra-tions of MMA keeping the concentrations of BA, CCl4,and RuCl3 constant. The monomer exponent value cal-culated from the slope of the linear plot between log Rp

International Journal of Chemical Kinetics DOI 10.1002/kin

72 TIWARI AND CANEBA

Figure 1 Master graph plotted between percentage conver-sion and volume contraction for RuIII-catalyzed polymeriza-tion of MMA at 60◦C in DMSO medium.

Figure 2 Percentage of conversion vs. time plots at 60◦Cfor polymerization of MMA in DMSO medium. [BA] =0.94 mol dm−3, [CCl4] = 0.77 mol dm−3, [RuCl3] = 5.70× 10−6 mol dm−3 and [MMA] = 0.81, 1.32, 1.77, 2.64,3.11, 3.54, and 4.42 mol dm−3 for series 1, 2, 3, 4, 5, 6, and7, respectively.

Table I Effect of [Reactants] on Rate of RuIII−Catalyzed Polymerization of MMA at 60◦C in DMSO Medium

[MMA] [BA] [CCI4] [RuCI3]×10−6 Rp× 104

(mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3s−1)

0.81 0.94 0.77 5.70 0.371.32 1.94 0.77 5.70 0.651.77 0.94 0.77 5.70 0.952.64 0.94 0.77 5.70 1.563.11 0.94 0.77 5.70 1.903.54 0.94 0.77 5.70 2.244.42 0.94 0.77 5.70 2.903.54 0.18 0.77 5.70 0.993.54 0.37 0.77 5.70 1.403.54 0.56 0.77 5.70 1.703.54 0.75 0.77 5.70 1.983.54 0.94 0.77 5.70 2.243.54 1.13 0.77 5.70 2.403.54 1.32 0.77 5.70 2.613.54 0.94 0.19 5.70 0.373.54 0.94 0.29 5.70 0.623.54 0.94 0.38 5.70 0.993.54 0.94 0.48 5.70 1.373.54 0.94 0.58 5.70 1.683.54 0.94 0.68 5.70 2.003.54 0.94 0.77 5.70 2.243.54 0.94 0.77 Nil 0.303.54 0.94 0.77 1.14 1.053.54 0.94 0.77 2.28 1.453.54 0.94 0.77 3.42 1.753.54 0.94 0.77 4.56 2.053.54 0.94 0.77 5.70 2.243.54 0.94 0.77 6.84 2.45



Figure 3 Plot of log Rp vs. log [MMA] at 60◦C for poly-merization of MMA in DMSO medium. Other conditions arethe same as in Fig. 2.

and log [MMA] (Fig. 3) is found to be ∼1.05, indicat-ing a first-order variation of the rate of polymerizationof MMA under the experimental conditions, that is,when [CCl4]/[amine] ≤ 1.

Rp is measured at fixed concentrations of MMA,CCl4, and RuCl3 and at varying concentrations of BA.Rp is found to be proportional to [BA]1/2 as the slope oflog Rp vs. log [BA] (Fig. 4) is obtained approximately0.6.

Rp increased with an increase in CCl4 or RuCl3 atfixed concentrations of other reactants. The relation-

Figure 4 Plot of log Rp vs. log [BA] at 60◦C for polymer-ization of MMA in DMSO medium. Other conditions are thesame as in Fig. 2.

Figure 5 Plot of log Rp vs. log [RuCl3] at 60◦C for poly-merization of MMA in DMSO medium. Other conditions arethe same as in Fig. 2.

ship between the rate of polymerization and RuCl3or CCl4 is determined from the slopes of the plots oflog Rp vs. log [RuCl3] (Fig. 5) and log Rp vs. log[CCl4] (Fig. 6). The slope in each case is found tobe approximately 0.5, indicating the normal half-orderdependence of the rate of polymerization on [RuIII] or[CCl4].

The mechanism for the initiation of polymerizationof MMA by amine in the presence of CCl4 under ex-perimental conditions, that is, when [CCl4]/[amine]≤1,has been explained [36] on the basis of formation of

Figure 6 Plot of log Rp vs. log [CCl4] at 60◦C for poly-merization of MMA in DMSO medium. Other conditions arethe same as in Fig. 2.



the charge-transfer complex by the interaction of theamine with CCl4 and its subsequent decomposition toproduce

•CCI3. There are also reports [40] that poly-

merization of amine with CCl4 systems is vastly accel-erated by transition metal ions such as Fe3+, Cu2+ andso on. In some cases, formation of the {Fe3+-amine}complex [41] and its reaction with CCl4 to give

•CCI3

is also reported. The RuIII complexes of amines andamino alcohols have also been confirmed during otherkinetic investigations [11]. No polymerization is ob-served in the absence of either BA or CCl4 under thepresent experimental conditions.

The charge-transfer complex (I ) could not be de-tected in the polymerization system, because this istoo reactive. Therefore, we have explored the possibil-ity of formation of the charge-transfer complex, i.e.,between {RuIII-BA} complex and CCl4. In light of thepreceding facts and on the basis of experimental resultsand discussion, the following mechanism may be pro-posed for the RuIII-catalyzed polymerization of MMAinitiated with BA in the presence of CCl4by charge-transfer:

BA(RNH2)

+ RuIII K1⇔ (CComplex) (1)

(CComplex) + CCI4k2⇔k2

I (charge-transfer complex)

(2)

Ik3−→ RuIII +

·RN+ H2CI−+

·CCI3

(·R )

(3)

·R + M

k4−→ ·MI

(initiation) (4)

According to the preceding scheme

[CComplex] = K1[BA][RuIII] (5)

From Eq. (1), by applying the steady-state conditionwith respect to I , [I] may be given as

[I] = k2[C][CCI4]

{k2 + k3}or

[I] = k2K1[BA][RuIII][CCI4]

{k2 + k3} (6)

Again by applying the steady-state condition with re-spect to [R] we get

k3[I] = k4[M][·R ]

and therefore

[·R] = k3k2K1[BA][RuIII][CCl4]

k4[M]{k2 + k3} (7)

The rate of initiation is given by

Ri = d[·

M1]

dt= k4[

·R ][M]

On substituting the value of [·R] from Eq. (7), the rate

of initiation may be obtained as

Ri = K1k2k3[BA][RuIII][CCI4]

{k2 + k3} (8)

The overall rate of polymerization Rp can be given as

Rp = kp[M]

(Ri

kt

)1/2(9)

On substituting the value of Ri from Eq. (8), the Rp

may be obtained as

Rp = kp

k1/2t

[M]

[K1k2k3[BA][RuIII][CCI4]

(k2 + k3)

]1/2

(10)

and therefore

Rp = kp

k1/2t

[K1k2k3

k2 + k3

]1/2

[M][BA]1/2[RuIII]1/2[CCl4]1/2

(11)

CONCLUSION

To confirm the validity of rate law (11), the plots ofRp vs. [MMA], [BA]1/2, [RuIII]1/2, and [CCl4]1/2 havealso been obtained. The plot of Rp vs. [BA]1/2 (Fig. 7)is found to be linear passing through the origin. Theplot of Rp vs. [RuIII]1/2 (Fig. 8) is linear with an inter-cept. The Rp value for polymerization of MMA in theabsence of RuIII under the present experimental condi-tions is also obtained and is found to be the same as thatobtained from the intercept of plot of Rp vs. [RuIII]1/2.Thus, it is clear that polymerization of MMA initiatedwith BA in the presence of CCl4 also occurs in the ab-sence of catalyst as reported earlier [14,15]. Rate law(11) does not reflect the intercept of the plot of Rp vs.[RuIII]1/2 (see Fig. 8), because steps responsible for un-catalyzed polymerization of MMA under the present



Figure 7 Plot of Rp vs. [BA]1/2 at 60◦C of polymerizationfor MMA in DMSO medium. Other conditions are the sameas in Fig. 2.

experimental conditions have not been included in theproposed mechanism for the RuIII-catalyzed polymer-ization of MMA.

However, the plot of Rpvs. [MMA] (Fig. 9) or theplot of Rp vs. [CCl4]1/2 (figure not given) intercept onthe [MMA] or [CCl4]1/2 axis. The mechanism of un-catalyzed polymerization of MMA has been explainedon the basis of forming a charge-transfer complex be-

Figure 8 Plot of log Rp vs. [RuCl3]1/2 at 60◦C for poly-merization of MMA in DMSO medium. Other conditions arethe same as in Fig. 2.

Figure 9 Plot of Rp vs. [MMA] at 60◦C for polymerizationof MMA in DMSO medium. Other conditions are the sameas in Fig. 2.

tween amine and MMA that initiates polymerization inthe presence of CCl4. Thus, it is possible that MMA andCCl4 up to these limiting concentrations are not freeto initiate polymerization of MMA under the presentexperimental conditions.

The intrinsic viscosity [η]int of the polymer is de-termined in a chloroform solution with an Ubbelohdeviscometer at 25◦C. The average degree of polymer-ization (Pn) is calculated by using Eq. (12) as follows:

[η]int = 1.91 × 10−3P.0.80n (12)

The molecular weight of the polymer (Mn) is cal-culated [34] from the viscometric data by using thefollowing equation:

[η]int = 4.8 × 10−5M0.80n (13)

Table II [η]int, Pn , and Mn Data for RuIII-CatalyzedPolymerization of MMA by BA in the Presence of CCl4 at25◦C

[MMA] [BA] [η]int

(mol dm−3) (mol dm−3) (dL g−1) Pn Mn× 105

0.81 0.94 0.48 886 1.411.32 0.94 0.60 1,698 1.951.77 0.94 0.68 2,400 2.372.64 0.94 0.77 3,296 2.913.11 0.94 0.83 4,060 3.523.54 0.94 0.91 4,890 3.914.42 0.94 0.98 5,651 4.59

[CCI4] = 0.77 mol dm−3 and [RuCI3] = 5.70 × 10−6 mol dm−3.



Table III Effect of [Hydroquinone] on the Rate of RuIII-Catalyzed Polymerization of MMA at 60◦C in DMSO Medium

[MMA] [BA] [CCI4] [RuCI3] × 10−6 [Hydroquinone] Rp× 104

(mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3s−1)

3.54 0.94 0.77 5.70 Nil 2.243.54 0.94 0.77 5.70 0.018 1.653.54 0.94 0.77 5.70 0.036 1.10

Table IV Effect of Temperature on the Rate of RuIII-Catalyzed Polymerization of MMA in DMSO Medium

[MMA] [BA] [CCI4] [RuCI3] × 10−6 Temperature Rp× 104

(mol dm−3) (mol dm−3) (mol dm−3) (mol dm−3) (◦C) (mol dm−3s−1)

3.54 0.94 0.77 5.70 50 1.453.54 0.94 0.77 5.70 55 1.853.54 0.94 0.77 5.70 60 2.243.54 0.94 0.77 5.70 65 2.603.54 0.94 0.77 5.70 70 3.01

Table V Activation Parameters for RuIII-Catalyzed Polymerization of MMA with BA in the Presence of CCI4

[MMA] [BA] Eact �H # −�S# �G#

(mol dm−3) (mol dm−3) (kJ mol−1) log A (kJ mol−1) (J K−1mol−1) (kJ mol−1)

3.54 0.94 48.0 + 1.0 10.± 05 60.0 + 1.0 27.0 + 1.0 71.0 + 1.0

[CCI4] = 0.77 mol dm−3 and [RuCI3] = 5.70 × 10−6 mol dm−3.

The [η]int,Pn, and Mn are obtained and given inTable II. The experiments are also carried out at dif-ferent concentrations of hydroquinone, as presented inTable III, a well–known retarder, and it is observed thatan increase in the concentration of hydroquinone de-creases the Rp in the presence of BA (Fig. 10), which

Figure 10 Plot of Rp vs. [hydroquinone] at 60◦C for poly-merization of MMA in DMSO medium. Other conditions arethe same as in Fig. 2.

confirms that the free-radical polymerization is opera-tive in the system.

The overall activation energy for the polymerizationreaction is computed from the Rp and is determined at50, 55, 60, 65, and 70◦C, as presented in Table IV. Theactivation parameters are given in Table V. The over-all activation energy (Eact) evaluated from the slope ofthe Arrhenius plot of log Rp vs. (1/T ) is found to be∼ 48.0 ± 1.0 kJ mol−1, and the enthalpy change (�H #)is evaluated from energy of activation and is found tobe ∼60.0 ± 1.0 kJ mol−1. The negative entropy of acti-vation (�S#) indicates the compactness of the preparedpolymers in comparison with their monomer. Free en-ergy change (�G#) indicates that the polymerizationof monomer in the presence of BA follows the similarmechanism.

Thanks are due to Prof. Gerard T. Caneba, Director of theCenter for Environmentally Benign Functional Materials(CEBFM), Michigan Technological University, Houghton,Michigan, for his keen interest in the work.

BIBLIOGRAPHY

1. Gupta, S.; Upadhyay, S. K. Int J Chem Kinet 1989, 21,315.



2. Puttaswamy, S. A.; Shubha, J. P. J Mol Catal A: Chem2009, 310, 24.

3. Shukla, A.; Gupta, S.; Upadhyay, S. K. Int J Chem Kinet1991, 23, 279.

4. Silva, Fabiano de A.; Ruiz, J. A.; Desouza, Katia R.Appl Catal A: Gen 2009, 364, 122.

5. Del, A. P.; Dominguez, J. M.; Montoya, J. A. J. Langmuir2000, 16, 7210.

6. Bett, J. S.; Kunz, H. R.; Aldykiewicz, A. J., Jr. Elec-trochim Acta 1998, 43, 3645.

7. Gonzalez-Velasco, J. R.; Botas, J. A.; Ferret, R. CatalToday 2000, 59, 395.

8. Balcells, D.; Nova, A.; Clot, E.; Gnanamgari, D. Organ-metallics 2008, 27(11), 2529.

9. Dahlenburg, L.; Gotz, R. Inorg Chem Commun 2003,6(5), 443.

10. Yatsimirskii, K. B. J Ind Chem Soc 1974, 51(1), 32.11. Kambo, N.; Upadhyay, S. K. Trans Met Chem 2000,

25(4), 461.12. Srivastava, P. K.; Upadhyay, S. K. Int J Chem Kinet

2000, 3, 171.13. Pachauri, M.; Srivastava, P.; Upadhyay, S. K. Asian J

Chem 2001, 13, 612.14. Dwivedi, P. C.; Pandey, S. D.; Tandon, A.; Singh, S.

Colloid Polym Sci 1995, 273, 822.15. Dass, N. N.; Gogoi, A. K. J Macromol Sci, Chem 1983,

20(8), 807.16. Sen, S. R.; Dass, N. N. Eur Polym J 1982, 18(6),

477.17. Hussain, S.; Baruah, S. D.; Dass, N. N. J Polym Sci,

Polym Lett 1978, 16(4), 167.18. Pachauri, M.; Upadhyay, S. K. Ind J Chem Technol 2003,

10(4), 402.19. Dass, N. N.; Gogoi, A. K. J Polym Mater 1984, 1,

183.20. Goswami, A.; Baruah, S. D.; Dass, N. N. J Appl Polym

Sci 1996, 60(7), 991.21. Pachauri, M.; Upadhyay, S. K. Ind J Chem A 2000,

39(7), 747.

22. Dass, N. N.; Sen, S. R. 28th IUPAC—InternationalUnion of Pure and Applied Chemistry, Macromolecu-lar Symposium, University of Massachusetts, Amherst,MA, 1982, p. 133.

23. Shirota, Y.; Fujioka, H.; Mikawa, H. J Polym Sci, PolymLett 1978, 16, 425.

24. Oshiro, Y.; Mikawa, H. J Polym Sci 1974, 12, 2099.25. Yoshimura, M.; Shirota, Y.; Mikawa, H. J Polym Sci

1973, 11, 457.26. Hamasaki, S.; Sawauchi, C.; Kamigaito, M. J Polym Sci,

Polym Chem 2002, 40, 617.27. Grishin, D. F.; Grishin, I. D. Am Chem Soc Symp Sr

2009, 8, 115.28. Caneba, G. T.; Xu, Z.; Dar, Y. L. J Appl Polym Sci 2009,

113, 3872.29. Zao, Yi.; Dar, Y. L.; Caneba, G.T. Ind Eng Chem Res

2008, 47, 3568.30. Caneba, G. T.; Zao, Y.; Dar, Y. L. J Appl Polym Sci

2003, 89, 426.31. Dar, Y.; Caneba, G. T. Chem Eng Commun 2002, 189,

571.32. Aggarwal, A.; Saxena, R.; Wang, B.; Caneba, G. T. J

Appl Polym Sci 1996, 62, 2039.33. Caneba, G. T. Adv Polym Technol 1992, 11, 277.34. Rao, P. G.; Vijayaraghavan, R.; Raghavan, K. V. Asia

Pacific J Chem Eng 2009, 4, 495.35. Vijayaraghavan, R.; MacFarlane, D. R. Aust J Chem

2004, 57, 129.36. Dwivedi, P. C.; Srivastava, A.; Rathi, R. S. J Polym Sci

A: Polym Chem 1990, 28, 3279.37. Tiwari, R.; Upadhyay, S. K.; Rai, J. S. P. Int J Chem

Kinet 2006, 38, 585.38. Srivastava, A. K.; Mathur, G. N. Ind J Chem 1980, 19,

1118.39. Billmeyer, F. W. Textbook of Polymer Science; Inter-

science: New York, 1965, p. 227.40. Hussain, S.; Dass, N. N. Eur Polym J 1982, 18, 795.41. Saha, S. K.; Chaudhari, A. D. J Polym Sci A 1987, 25,

519; 1988; 26, 901.


Documents

Kinetic study of RuIII-catalyzed polymerization of methylmethacrylate initiated with n-butylamine in the presence of carbon tetrachloride by a charge-transfer mechanism