Ruthenium(III) Catalysisin Polymerization of VinylMonomers by Charge-Transfer Mechanismwith Aminoalcoholsand Carbontetrachloride:A Kinetic StudyRAJESH TIWARI, S. K. UPADHYAY, J. S. P. RAI

H. B. Technological Institute, Kanpur 208 002, India

Received 18 June 2005; revised 27 January 2006; accepted 26 February 2006

DOI 10.1002/kin.20190Published online in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The kinetics of ruthenium(III) catalyzed polymerization of vinyl monomers (M)(methyl-, ethyl-, and butylacrylates) by charge-transfer mechanism with aminoalcohols (AA)(namely, ethanol-, diethanol-, and triethanol amines) and carbontetrachloride in dimethylsul-foxide medium have been studied. The rate of polymerization depends on the [CCl4]/[AA] ratioand may be represented as

Rp ∝ [M][CCl4]1/2[Ru3+]1/2[AA]1/2, when [CCl4]/[AA] ≤ 1

and

Rp ∝ [M]3/2[Ru3+]1/2[AA]1/2, when [CCl4]/[AA] > 1

The rate of polymerization of monomers with each aminoalcohol was found to be in theorder Rp (methyl-) > Rp (ethyl-) > Rp (butylacrylate) while that of each monomer with differ-ent aminoalcohols was found to be in the order of Rp tertiary > Rp secondary > Rp primaryaminoalcohol. The suitable mechanism for the polymerization process consistent with kineticdata has been proposed. C© 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 585–592, 2006

Correspondence to: S. K. Upadhyay.Present address: Department of Chemistry, H. B. Technologi-

cal Institute, Kanpur 208002, India; e-mail: upadhyay s k@rediffmail.com.

Present address of J. S. P. Rai: Department of Plastic Technology,H. B. Technological Institute, Kanpur 208002, India.c© 2006 Wiley Periodicals, Inc.

586 TIWARI, UPADHYAY, AND RAI

INTRODUCTION

Platinum group metals have ability to form coordina-tion and chelate complexes [1–3] due to their stereo-chemistry and stabilities of different oxidation states.These complexes have widely been used as hetero-geneous as well as homogeneous catalysts in vari-ous reactions including polymerization of olefins andacetylenes [4,5].

The kinetics of polymerization of vinyl monomersinitiated by the charge-transfer mechanism in the pres-ence of CCl4 have been studied by many investiga-tors [6–11] and different mechanisms for the reactionshave been proposed. RhIII and RuII complexes have alsobeen reported to accelerate the rate of polymerization ofvinyl monomers initiated by the charge-transfer mecha-nism [12]. Recently, PdII and RuIII ions catalyzed poly-merization of methylmethacrylate [13,14] by aminesand aminoalcohols in the presence of CCl4 indicatedthe participation of charge-transfer complex between{Catalyst–Amine} adduct and CCl4 or monomer de-pending upon the [CCl4]/[Amine] ratio during initia-tion of polymerization. In order to throw more light onthe nature of the catalyst in the mechanism of polymer-ization, the detailed kinetics of RuIII ion catalyzed poly-merization of some more vinyl monomers (M), namely,methyl-, ethyl-, and butylacrylates with aminoalcohols,namely, ethanolamine (EA, primary), diethanolamine(DEA, secondary), and triethanolamine (TEA, tertiaryaminoalcohol) in the presence of CCl4 in dimethylsul-foxide (DMSO) medium have been studied and resultsare reported in the present communication.

EXPERIMENTAL

Materials

Purification of monomers, namely, methylacrylateand ethylacrylate (Thomas Baker), n-butylacrylate(s.d.fine), and CCl4 (E-Merck), was done by a standardmethod. DMSO, EA, DEA, and TEA (all E-Merck,AR grade) were used as such. Stock solution of RuCl3(LOBA) was prepared by dissolving the sample in dil.HCl (0.01 mol dm−3) and was stored in a black bottleto avoid photochemical effect.

Method

The polymerization was carried out in a dilatome-ter (bulb capacity 5 mL, with a 11-cm-long capillaryof 3-mm diameter) under nitrogen atmosphere usingDMSO as solvent. The required amounts of M, AA,RuCl3, CCl4, and DMSO were taken in the dilatometer

and placed in thermostatic water bath maintained at de-sired temperature (±0.5◦C). The progress of reactionwas monitored with the help of a cathetometer by therecording meniscus movement (i.e., volume per unittime). The polymerization was not allowed to proceedbeyond 30% to avoid formation of side products and toobtain reliable kinetic data.

Determination of Rate of Polymerization

The rate of polymerization (Rp) of monomer is givenby

Rp (mol dm−3 s−1) = w × 103

t × 60 × Mw

(i)

where w is the weight of the polymer obtained from1 mL of monomer (molecular weight, Mw and density,d). If C is the percentage conversion and t is time inminutes of polymerization, then

C = w × 100

1 × d(ii)

and, therefore, with the help of Eqs. (i) and (ii) Rp maybe obtained:

Rp = C × d × 103

100 × t × 60 × Mw

(iii)

Figure 1 Master graphs showing the relationship between

% conversion and volume contraction for polymerization of

monomers: (◦) methylacrylate; (•) ethylacrylate; (�) buty-

lacrylate; [CCl4] = 0.90 mol dm−3 and [RuCl3] = 2.86 ×10−6 mol dm−3.

RUTHENIUM(III) CATALYSIS IN POLYMERIZATION OF VINYL MONOMERS 587

M = 86.09, 100.12, and 128.7 and d = 0.953, 0.912,and 0.898 in the case of methyl-, ethyl-, and butylacry-late, respectively.

In actual experiments, C was obtained from a mas-ter graph plotted between volume contraction andpercentage conversion (Fig. 1). The percentage con-version thus obtained was plotted against time t tocalculate Rp.

Determination of Viscosity Data andMolecular Weight of Polymer

The intrinsic viscosity [η]int of polymer was determinedin benzene (acetone in the case of ethylacrylate) solu-tion using a Ubbelohde viscometer. The viscosity av-erage molecular weight (Mv) was calculated by usingthe Mark–Houwink equation:

[η]int = KM�

where K = 3.56, 20.0, and 4.0 (×10−5) and α= 0.798,0.66, and 0.73 [15] were taken in the case ofmethyl-, ethyl-, and butylacrylate, respectively. Fur-thermore, the average degree of polymerization (Pn)was calculated from Mv.

RESULTS AND DISCUSSION

The kinetics of polymerization were studied at variousinitial concentrations of reactants. The polymerizationof monomers was carried out in the absence of ei-ther AA or CCl4 at 50–65◦C and no polymer wasformed, which clearly indicates that the polymeriza-tion definitely requires the presence of both, i.e., AAand CCl4.

Figure 2 represents the typical plots of % conver-sion versus time for the polymerization of variousmonomers with all the three aminoalcohols at 60◦C.It is apparent from Fig. 2 that the percentage conver-sion increases linearly with time. Therefore, the rateof polymerization of monomers (Rp) at various initialconcentrations of the reactants was evaluated from theslopes of these plots. It is also observed from Fig. 2that the rate of polymerization (Rp) is in the order ofmethyl-, ethyl-, and butylacrylate in the case of eachaminoalcohol while the rate of polymerization of eachmonomer is in the order of TEA > DEA > EA.

The values of Rp at various initial concentrationsof monomers at 60◦C under the experimental condi-tions [CCl4]/[AA] ≤ 1 and [CCl4]/[AA] > 1 are givenin Table I. It is apparent from Table I that an increasein [Monomer] increases the Rp under both the ex-perimental conditions and at constant [RuCl3]. The

Figure 2 Plots of % conversion versus time for polymer-

ization of monomers at 60◦C: (a) [EA] = 1.57 mol dm−3; (b)

[DEA] = 0.98 mol dm−3; and (c) [TEA] = 0.95 mol dm−3,

[CCl4] = 0.90 mol dm−3, and [RuCl3] = 2.86 × 10−6 mol

dm−3. (◦) [Methylacrylate] = 2.08 mol dm−3; (•) [Ethy-

lacrylate] = 1.73 mol dm−3; (�) [Butylacrylate] = 1.32 mol

dm−3.

monomer exponent value calculated from the slope ofthe linear plots between log(Rp) and log[Monomer](figures are not given) was found to be 0.95 ± 0.05and 1.40 ± 0.05 under the experimental conditions of[CCl4]/[AA] ≤ 1 and [CCl4]/[AA] > 1, respectively.The varied monomer exponent value indicates the dif-ferent type of mechanism of the reaction under theabove-mentioned conditions.

The effect of [CCl4] on Rp at 60◦C was also stud-ied under both the experimental conditions and the re-sults are represented graphically in Figs. 3a and 3b.Under the conditions [CCl4]/[AA] ≤ 1, the plot of Rp

versus [CCl4]1/2 (Fig. 3a) was found to be linear pass-ing through the origin, suggesting that Rp ∝ [CCl4]1/2.However, under the conditions [CCl4]/[AA] > 1, theplot of Rp versus [CCl4] (Fig. 3b) deviated from lin-earity and Rp became nearly independent of [CCl4] athigher CCl4 concentrations. The effect of [CCl4] on Rp

again indicates that two different mechanisms are op-erating in both the experimental conditions. The plot oflog(Rp) versus log[AA] (Fig. 4) was linear with slope∼0.5 ± 0.05 under both the conditions, suggesting thatRp ∝ [AA]1/2.

The effect of [RuCl3] on Rp was studied at con-stant [AA], [CCl4], and [Monomer] and the results arepresented in Fig. 5. The experiments were also carriedout in the absence of RuCl3 and Rp was determined.From Fig. 5, it is apparent that Rp ∝ [RuCl3]1/2 with

588 TIWARI, UPADHYAY, AND RAI

Table I Effect of [Monomer] on Rp at 60◦C

Rp × 103 (mol dm−3 s−1)

[CCl4]/[AA] ≤ 1a [CCl4]/[AA] > 1b

[Monomer] (mol dm−3) EA DEA TEA EA DEA TEA

Methylacrylate

0.52 0.27 0.35 0.39 0.30 0.40 0.49

1.04 0.61 0.92 1.20 0.80 1.00 1.30

1.56 1.30 1.50 1.80 1.25 1.60 2.05

2.08 1.80 2.00 2.30 1.90 2.39 2.97

2.61 2.20 2.60 2.80 2.63 3.30 4.00

3.12 2.60 3.00 3.40 3.49 4.30 5.06

Ethylacrylate

0.86 0.42 0.95 1.05 0.51 0.58 0.71

1.30 0.99 1.08 1.14 0.84 1.02 1.21

1.73 1.30 1.40 1.53 1.33 1.47 1.75

2.16 1.63 1.75 1.88 1.72 1.78 2.04

2.63 1.84 2.06 2.60 2.04 2.14 2.29

Butylacrylate

0.66 0.06 0.08 0.15 0.11 0.14 0.17

0.99 0.15 0.20 0.25 0.22 0.24 0.28

1.32 0.21 0.29 0.37 0.32 0.36 0.40

1.65 0.33 0.40 0.49 0.42 0.47 0.54

1.98 0.43 0.55 0.62 0.57 0.63 0.73

[CCl4] = 0.90 mol dm−3, [RuCl3] = 2.85 × 10−6 mol dm−3.a [EA], [DEA], and [TEA] = 1.57, 0.98, and 0.95 mol dm−3, respectively.b [EA], [DEA], and [TEA] = 0.78, 0.48, and 0.35 mol dm−3, respectively.

an intercept, which indicates that the polymerization ispossible even in the absence of RuCl3. The values ofRp calculated from the intercepts were matching withthe observed value of Rp at [RuCl3] = 0.

The experiments were also carried out at differentconcentrations of hydroquinone, a well-known retarderof free-radical polymerization reactions and it was ob-served that an increase in the concentration of hydro-quinone decreased the Rp in the presence of EA, DEA,and TEA, which confirms that the free-radical poly-merization is operative in the system.

Table II Activation Parameters for RuIII Catalyzed Polymerization of Monomers with Aminoalcohols in the Presenceof CCl4

Monomer Aminoalcohol Eact (kJ mol−1) Log A �H# (kJ mol−1) −�S# (J K−1 mol−1) �G# (kJ mol−1)

Methylacrylate EA 68.0 ± 1.0 11.08 66.0 ± 0.0 33.0 ± 1.0 72.0 ± 2.5

DBA 61.0 ± 1.0 9.96 58.0 ± 1.0 55.0 ± 1.0 70.0 ± 2.5

TEA 49.0 ± 1.0 8.20 47.0 ± 1.0 88.0 ± 1.0 71.0 ± 2.5

Ethylacrylate EA 80.0 ± 1.0 12.65 77.0 ± 1.0 34.0 ± 1.0 75.0 ± 2.5

DEA 65.0 ± 1.0 10.32 62.0 ± 1.0 47.0 ± 1.0 75.0 ± 2.5

TEA 53.0 ± 1.0 8.62 50.0 ± 1.0 80.0 ± 1.0 75.5 ± 2.5

Butylacrylate EA 82.0 ± 1.0 12.62 78.O ± 1.0 39.0 ± 1.0 72.0 ± 2.5

DEA 68.0 ± 1.0 11.45 66.0 ± 1.0 46.0 ± 1.0 74.0 ± 2.5

TEA 53.0 ± 1.0 9.16 55.0 ± 1.0 70.0 ± 1.0 73.0 ± 2.5

To obtain the activation parameters for the polymer-ization, the Rp were determined at 50, 55, 60, and 65◦C.The activation parameters in each case are given inTable II. The value of energy of activation (Eact) and en-thalpy change (�H #) in the case of each monomer werein the order of EA > DEA > TEA. This is in agreementwith the rate of polymerization of monomer with TEA,DEA, and EA. The negative entropy of activation (�S#)indicates the compactness of the prepared polymers incomparison to their monomer and it increases by re-placing EA by DEA and TEA. However, the value of

RUTHENIUM(III) CATALYSIS IN POLYMERIZATION OF VINYL MONOMERS 589

(A)

(B)

Figure 3 (A) Plots of Rp versus [CCl4]1/2 for poly-

merization of monomers at 60◦C under the condi-

tion [CCl4]/[AA] ≤ 1: (a) [EA] = 0.35 mol dm−3; (b)

[DEA] = 0.49 mol dm−3; and (c) [TEA] = 0.88 mol dm−3.

Other conditions are same as in Fig. 2. (B) Plots of Rp versus

[CCl4] for polymerization of monomers at 60◦C under the

condition [CCl4]/[AA] > 1: (a) [EA] = 0.78 mol dm−3; (b)

[DEA] = 0.49 mol dm−3; and (c) [TEA] = 0.35 mol dm−3.

Other conditions are same as in Fig. 2.

free energy change (�G#) indicates that the polymer-ization of monomers in the presence of AA follows thesimilar mechanism.

[η]int, Pn, and Mv of the polymers were obtainedat different [Monomer] at 60◦C using EA, DEA, andTEA (Table III). It was observed that Pn increases al-most linearly with increase in [Monomer] (Fig. 6) inthe presence of each aminoalcohol.

Figure 4 Plots of log(Rp) versus log[AA] for polymeriza-

tion of monomers at 60◦C. Other conditions are same as in

Fig. 2.

Figure 5 Plots of Rp versus [RuCl3]1/2 for polymerization

of monomers at 60◦C. Other conditions are same as in Fig. 2.

Figure 6 Plots of Pn versus [Monomers] for polymer-

ization of monomers. [CCl4] = 0.90 mol dm−3; [RuCl3] =2.86 × 10−6 mol dm−3. (a) [EA] = 1.57 mol dm−3; (b)

[DEA] = 0.98 mol dm−3; and (c) [TEA] = 0.95 mol dm−3.

Other conditions are same as in Fig. 2.

590 TIWARI, UPADHYAY, AND RAI

MECHANISM OF POLYMERIZATION

There are reports [16] that the polymerization of vinylmonomers by amine and CCl4 is vastly acceleratedby transition metal-ions like Fe3+, Cu2+, Ru2+, Rh3+,etc. In some cases the formation of the {Fe3+–Amine}complex and its reaction with CCl4 to give CCl3 isalso reported [17]. Ruthenium(III) complexes withamines/aminoalcohols have also been confirmed dur-ing the other kinetic investigations [18].

The charge-transfer complex could not be detectedin the polymerization systems, because they are tooreactive, and therefore we have explored the possi-bility of formation of both charge-transfer complexes,namely, between {Ru3+–AA} complex and CCl4 andbetween {Ru3+–AA} complex and monomer. Basedon the experimental results and above discussion,the mechanism for the initiation of Ru3+ catalyzedpolymerization of monomer by AA in the presence ofCCl4 is proposed as given in Scheme 1.

Scheme 1

where M+x represents metal complex with oxidationstate x . R1, R2 or R3 represent H or CH2CH2OHdepending upon primary, secondary or tertiaryaminoalcohol. R1R2R3N+Cl− formed in steps (iii) and(v) may undergo dissociation in the polar solvent likeDMSO to give R1R2R3N+, which reacts with CCl4to produce CCl3 as suggested by Takemoto and co-workers [19].

According to Scheme 1

[Ccomplex] = K1[Ru3+][AA], from step (i) (1)

On applying steady-state condition with respect to [I1],the (I1) is obtained:

[I1] = k2 K1[Ru3+][AA][CCl4]

{k2 + k3[M]} (2)

Similarly, on applying steady-state condition withrespect to [I2], we get

RUTHENIUM(III) CATALYSIS IN POLYMERIZATION OF VINYL MONOMERS 591

Table III [η]int, Mv for the RuIII Catalyzed Polymerization of Monomers with Aminoalcohols in the Presence of CCl4

EAa DEAb TEAc[Monomer]

(mol dm−3) [η]int Mv × 105 [η]int Mv × 105 [η]int Mv × 105

Methylacrylate

0.52 0.48 1.49 0.50 1.72 0.52 1.81

1.04 0.60 1.97 0.62 2.25 0.66 2.44

1.56 0.68 2.31 0.72 2.72 0.77 2.96

2.08 0.77 2.96 0.80 3.10 0.83 3.25

2.81 0.83 3.25 0.84 3.30 0.86 3.40

Ethylacrylate

0.43 0.73 8.64 0.80 2.78 0.82 2.88

0.86 1.02 4.01 1.09 4.44 1.13 4.60

1.73 1.45 6.84 1.50 7.20 1.60 7.94

2.16 1.63 8.17 1.68 8.56 1.75 9.10

2.63 1.78 9.33 1.85 9.90 1.90 10.30

Butylacrylate

0.33 0.47 1.88 0.52 2.15 0.56 2.36

0.66 0.68 3.04 0.73 3.34 0.78 3.64

0.99 0.84 4.00 0.91 4.44 0.97 4.85

1.65 1.05 5.35 1.14 5.95 1.20 6.36

1.98 1.17 6.16 1.26 6.33 1.34 7.35

[CCl4] = 0.90 mol dm−3, [RuCl3] = 2.86 × 10−6 mol dm−3.a [EA] = 1.57 mol dm−3.b [DEA] = 0.98 mol dm−3.c [TEA] = 0.95 mol dm−3.

[I2] = k4 K1[Ru3+][AA][M]

{k4 + k5[CCl4]} (3)

If ‘α’ is the fraction of the (Ccomplex) used for the for-mation of (I1), (1 −α) becomes the fraction used forthe formation of (I2), then rate of formation of (R) maybe given as

d[R]

dt= �k3[I1][M] + (1 − �)k5[I2][CCl4] (4)

On substituting the value of [I1] and [I2] from Eqs. (2)and (3), respectively in Eq. (4), we get

d[R]

dt= �k2k3 K1[Ru3+][AA][CCl4][M]

{k2 + k3[M]}

+ (1 − �)k4k5 K1[Ru3+][AA][CCl4][M]

{k4 + k5[CCl4]} (5)

Assuming bimolecular termination, the rate ofinitiation (Ri) may be given as

Ri = 1

k1/2t

[�k2k3 K1[Ru3+][AA][CCl4][M]

{k2 + k3[M]}

+ (1 − �)k4k5 K1[Ru3+][AA][CCl4][M]

{k4 + k5[CCl4]}]1/2

(6)

where k t is rate constant for termination step.

The overall rate of polymerization (Rp) can beexpressed as

Rp = kp[M]Ri (7)

where kp is the rate constant for propagation step. Onsubstituting the values of Ri, we get

Rp = kp

k1/2t

[M]

[�k2k3 K1[Ru3+][AA][CCl4][M]

{k2 + k3[M]}

+ (1 − �)k4k5 K1[Ru3+][AA][CCl4][M]

{k4 + k5[CCl4]}]1/2

(8)

When charge-transfer complex (I1) predominates,αmay be taken as unity and Eq. (8) reduces to

Rp = kp

k1/2t

(k2k3 K1)1/2[Ru3+]1/2[AA]1/2[CCl4]1/2[M]3/2

{k2 + k3[M]}1/2

(9)

Since step (iii) is fast and, therefore, taking k3[M] � k2,Rp may be given as

Rp = kp

k1/2t

(k2 K1)1/2[Ru3+]1/2[AA]1/2[CCl4]1/2[M]

(10)

The experimental results are in agreement with Eq. (10)under the conditions when [CCl4]/[AA] ≤ 1.

592 TIWARI, UPADHYAY, AND RAI

When the charge-transfer complex (I2) predomi-nates, α may be taken as zero and Eq. (8) reduces to

Rp = kp

k1/2t

(k4k5 K1)1/2[Ru3+]1/2[AA]1/2[CCl4]

1/2[M]3/2

{k4 + k5[CCl4]}1/2

(11)

Again, since step (v) is fast and, therefore, takingk5[CCl4] � k4, Rp may be obtained as

Rp = kp

k1/2t

(k4 K1)1/2[Ru3+]1/2[AA]1/2[M]3/2 (12)

The above rate law (12) explains the experimental re-sults under the conditions [CCl4]/[AA] > 1.

The observed order of rate of polymerization, i.e.,Rp(methylacrylate) > Rp(ethylacrylate)> Rp(butylacrylate), is prob-ably due to an increase in bulky group in acrylate, whichreduces the rate of polymerization. An increase in num-ber of OH groups (electron-repelling group) in EA toTEA increases the tendency of formation of complexwith Ru3+ and, therefore, the rate of polymerizationof a monomer increases from EA to TEA (primary totertiary aminoalcohol).

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