POLYMER LETTERS VOL. 10, PP. 725-729 (1972)

STUDIES ON THE CATIONIC POLYMERIZATION OF INDENE INITIATED BY METHYL ETHYL KETONE

PEROXIDE IN LIQUID SULFUR DIOXIDE

We have recently reported that indene can be polymerized by methyl ethyl ketone peroxide in liquid sulfur dioxide (1). In this letter, we would like to report some of our experimental results on the characteristics of this polymer- ization.

Experimental

Indene (Koch-Light Ltd.) was washed first with concentrated HCl, then with a solution of 4N sodium hydroxide, and finally with water, and dried overnight in anhydrous MgS04 prior to distillation in vacuo at 92"C/30 mmHg (2). Sulfur dioxide was generated from the reaction of H z S 0 4 and NaHS03, dried by bubbling in HzS04 and through an anhydrous CaC1, col- umn. A 60% solution of methyl ethyl ketone (MEK) peroxide in methyl ethyl ketone (Resana Indlistrias Quiinicas S.A.) was used as received. The polymerizations were carried out in a 50 ml three-necked round-bottomed flask provided with a Dewar condenser, a rubber septum for addition of cata- lyst, and an adapter for the introduction of SOz from the generator. Indene (0.04 moles) was added into the flask and 30 ml of SOz was collected. The reaction was initiated by adding a few drops of MEK peroxide. The tempera- ture of the reaction was kept at -10 or -76°C. The reactions were stopped at different times by addition of 5 ml of methanol. The precipitated polymer was collected in a Buchner flask and dried in an oven at 50°C.

Gel permeation chromatograms were carried out on a Waters Associates GPC 200 (equipped with 4 ft columns of lo6, lo5, lo4, and lo3 A porosity). The polymer solutions were 0.05 wt-vol % in toluene with a flow rate of 1 ml/min at 50°C. The molecular weights were obtained from calibration curves of polystyrene and polypropyleneglycol (3). The intrinsic viscosities were de- termined at 50°C in toluene.

Results

Table I and Figure 1 show the yield versus time for indene polymerization reactions carried out at -10°C. No significant change either in the ratio xw/ An with reaction time or in the intrinsic viscosity was observed. These results seem to indicate a homogeneity of the molecular weight distribution during the reaction time, which excludes the following two possibilities:

species should show an increase in molecular weight and intrinsic viscosity ver- sus time (4) (5); or

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1) that the propagation step involves a dication species because such a

0 1972 by John Wiley & Sons, Inc.

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TABLE I

Polymerization Data of Indene at -lO°Ca

Exp. No. Tlme(m1n) Yie ld (%) CPC counts & [ ]50. ,?j

O C F - ~ ~ 15 17 30.1 1.60 0.08 60.000

OCF-18 45 47 30.0 1.82 0.10 50.000

OCF-16 75 65 30.1 1.83 0.09 55.000

OCF-17 135 80 30.2 1.81 0.091 55.000

OCF-19 175 83 30.2 1.80 0.086 58.000

An

aIndene (0.04 moles) in liquid SO2 (30 ml) and MEK peroxide ( moles/liter).

Time (hr)

Fig. 1. Plot of time vs. conversion in the polymerization of indene in SO2 at -10°C.

2) that branching of the chain during propagation can occur because in this case higher conversions would favor such reactions and the dispersion of the molecular size would increase with the conversion. A comparison of these dispersions with those obtained from cationic polymerization of indene with conventional Lewis acid catalysts (Table 11) showed larger values of Aw/ ?j;l for the latter case. This fact indicated that a more selective system for the polyindene was obtained.

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TABLE I1

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GPC Data for Polyindenes Obtained by Lewis Acid Type Cationic Catalyst (4)

- Exp. No. CPC Counts 2 [$500 M W Temp. Catalyst Solvent

~~

WDV 08 30.5 3.6 - - -76' T 1 C l 4 Dlehloromethane

3.2 0.36 - 0' A1C13 Dlchlommethane ww 10 29.5

WDV 12 29.5 4.6 - - -76' TIC14 - h e m e

WDV 14 29.5 3.5 0.40 33.000 -76' T1Cl4 2-chlorotmtane

WDV 16 29.0 3.4 0.50 71.000 -76' T1Cl4 1,l-dlohloroethane

TABLE 111

Variation of the MEK Peroxide concentration in the Polymerization of Indene in Liquid SO2 at -76"Ca

Tlme (mln.) -

Exp. No. MEK Peroxlde Conc. Yield(%) CPC Counts E f$oo wv (mol/l x lo-')

OCP-23 1 3 30.3 1.85 0.110 45.000 195

OCP-27 3.5 14 30.1 1.82 0.115 50.000 55

OCP-28 4.5 26 30.1 1.87 0.120 52.000 25

40 30.0 1.90 0 120 52.000 10 OCP-26 5 OCF-29 10 65 30.1 1.9'4 0.117 53.000 2

aIndene (0.04 moles) in liquid SOz (30 ml), time of reaction: 195 min. bTime when polymer starts to precipitate from the solution.

A decrease in the temperature of the reaction (Table 111) caused a decrease in the overall rate of polymerization using the same concentration of reagents. Dependence of conversion on concentration of initiator was also observed at -76°C (Table 111). The precipitation of polymer from the reaction medium was also dependent upon the concentration of the initiator (Table 111). These results showed that the initiation step was playing an important role in the kinetics of the reaction. It is well known that cationic polymerizations can become faster when the temperature is lowered because a higher energy of activation is generally necessary for the termination reactions (6). In our case, we observed an opposite behavior, possibly showing that the activation energy in the initiation step was higher than that for propagation.

A plot of formation of polymer versus concentration of the initiator at -76°C showed a complex curve (Fig. 2).

As previously suggested, it is believed that this polymerization involves the formation of a charge-transfer complex between SO2 and indene and that the

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Concentration (moles/l x

Fig. 2. Plot of conversion vs. concentration of MEK peroxide in the polymerization of indene (1M) in SOz at -76'C for 195 min.

cation radical generated would react with MEK peroxide to initiate the reac- tion (1). These results suggest that the initiation step involves the reaction be- tween the charge-transfer complex and MEK peroxide by a free radical type mechanism, whose reaction would be temperature controlled:

MEK In - [MEK] [SO,] [In]' - polyindene In + SOz * [In] [SOz]:

In this initiation reaction, a positive charge would be left over after the oxi- dation of the complex by the MEK peroxide.

Some characteristics of the polyindene formed in this system are shown in Table 111. No appreciable change in molecualr weight, Aw/An ratio, and in- trinsic viscosity were observed when a lower temperature for the reaction was used. It is well known that polymers obtained by cationic methods usually increase in molecular weight when the temperature is lowered (7).

These results clearly indicated that this is not a conventional cationic poly- merization.

At the moment, we are studying the structures of these polyindenes by comparing them with other structures obtained by the conventional cationic mechanism. In addition, we are investigating the use of the SO2-MEK system in other vinyl monomers.

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The authors express their appreciation for support received from Conselho Nacional de Pesquisas ( C p q ) , Banco Nacional do Desenvolvimento Econom- ico (BNDE) e CEPG da Universidade Federal do Rio de Janeiro, in the pre- paration of this work.

References

(1) 0. C. Filho and A. S. Gomes, J. Polym. Sci., B, 9, 894 (1971). (2) G. J. Schimitt and G. Schnerch, J. Polym. Sci., 49, 287 (1961). (3) W. D. Vilar, Master’s Thesis, Instituto de Quimica, Universidade

(4) S. Iwatsuki, T. Kokubo, and Y. Yamashita, J. Polym. Sci., A-1, 6,

(5) E. Tsuchida and T. Tomono, Makromol. Chem., 3, 265 (1971). (6) R. W. Lenz, “Organic Chemistry of Synthetic High Polymers,” Inter-

(7) S. Cesca, A. Roggero, N. Palladino, and A. De Chirico, Makromol.

Federal do Rio de Janeiro, Brasil, 1971.

2441 (1969).

science Publishers, New York, 1968, p. 515.

Chem., 136, 23 (1970).

Ailton de Souza Gomes* Odyr do Couto Filho

Instituto de Quiinica Universidade Federal do Rio de Janeiro Guanabara, Brasil

Received May 25, 1972 Revised June 28, 1972

*Member of the NAS/CNPq Exchange Program.