Terpolymerization of Cyclopentene, Sulfur Dioxide, and Acrylonitrile

13 Terpolymerization of Cyclopentene,

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Sulfur Dioxide, and Acrylonitrile YUYA Y A M A S H I T A , SHOUJI IWATSUKI, and ΚΟΖΟ SAKAI Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Nagoya, Japan Spontaneous copolymerization of cyclopentene (CPT) with sulfur dioxide (SO ) suggests the participation of a charge transfer complex in the initiation and propagation step of the copolymerization. The ESR spectrum together with chain transfer and kinetic studies showed the presence of long lived SO radical. Terpolymerization with acrylonitrile (AN) was analyzed as a binary copolymerization between C P T - S O complex and free AN, and the dilution effect proved this mechanism. Moderately high polymers showed enhanced thermal stability, corresponding to the increase of AN content in the terpolymer. 2

2

2

Tfxtensive studies have been reported on the copolymerization of various olefins and sulfur dioxide to yield polysulfones (3, 7). Attention was paid to the significant alternating tendency irrespective of monomer feed ratios and to the presence of ceiling temperature. The mechanism of such peculiar alternating copolymerization has been a matter of considerable discussion, although polymerization through a charge transfer complex suggested by Barb ( J ) was favored by Furukawa (6) and by us (15). Recently Zutty (16) discovered spontaneous copolymerization of norbornene and sulfur dioxide, suggesting propagation through biradical coupling, and Frazer (4) reported on the unusual initiation of 1,5-cyclooctadiene and sulfur dioxide by bubbling oxygen. As a development of our studies on charge transfer complexes and polymerization, we reported on the spontaneous copolymerization of cyclopentene and sulfur dioxide (11), and kinetic evidence for the partici pation of the charge transfer complex i n the copolymerization was pre sented. This paper discusses the terpolymerization of cyclopentene, sulfur dioxide, and acrylonitrile to give further evidence for the charge transfer 211 Platzer; Multicomponent Polymer Systems Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

212

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complex mechanism. discussed.

The thermal stability of

P O L Y M E R SYSTEMS

polysulfones

is also


Experimental Materials. Cyclopentene ( C P T ) was prepared by dehydration of Commercial acrylonitrile ( A N ) was washed with dilute sulfuric acid and fractionally distilled after adding lithium aluminum hydride to re move traces of hydroperoxide, which is an active initiator for the present system. Commercial sulfur dioxide ( S 0 ) was used without purification. Commercial acrylonitrile ( A N ) was washed with dilute sulfuric acid and water, dried over calcium hydride, and fractionally distilled. Toluene was washed repeatedly with concentrated sulfuric acid until the acid was colorless, and after washing with water it was dried over calcium hydride and fractionally distilled. N,2V-Dimethylformamide ( D M F ) was dried over phosphorus pentoxide and distilled carefully. Polymerization. A weighed mixture of monomer and solvent in a 30-ml ampoule was cooled in a dry ice bath and flushed with nitrogen, sealed and set without stirring in a bath. After polymerization, excess petroleum ether was added to precipitate the copolymer, which was dried under reduced pressure. Characterization of the Copolymer. The S0 content in the copoly mer was calculated from the sulfur content determined by the Schoniger method. The reduced viscosity of the copolymer was determined at 30 °C with an Ostwald viscometer. D M F containing 0.1% L i C l was used as solvent at 0.2 gram/100 ml. The melting point of the terpolymer was measured by a hot-stage microscope. 2

2

Results and Discussion CPT-SO » System. Bulk copolymerization of C P T and SO > takes takes place spontaneously at a remarkable rate even at —15 °C. In com parison with the thermal initiation of p-dioxene and maleic anhydride which proceeds through a similar charge transfer complex at room tem perature (13), the interaction between C P T and S 0 seems more pro nounced, giving the propagating species at a lower temperature. Dilution with toluene slowed the copolymerization rate, and kinetic measurements were carried out in toluene at 0°-30°C. As reported pre viously ( I I ) , the over-all activation energy of the spontaneous copoly merization of C P T and S 0 was calculated to be 16.5 kcal/mole from the Arrhenius plot of the initial rate vs. polymerization temperature. D e pendence of the intial rate of copolymerization upon monomer concen tration was checked at various monomer concentrations and found to be quite high ( I I ) ; this could not be explained without participation of the monomer in the initiation step. L

L

2

2

R

P

= k [ C P T ] [S0 ] p

3

2

2

Platzer; Multicomponent Polymer Systems Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

YAMASHiTA


13.

ET AL.

213

Terpolymerization

Figure 1. Rehtionship between conversion and reduced viscosity. CPT, 0.68 gram; SO , 0.64 gram; toluene, 1.25 ml at 30°C. Reduced viscosity, 0.2 gram/100 ml at 30°C in DMF + 0.1% LiCl g

Figure 2.

ESR spectrum of CPT-SO system measured at the temperature of the polymerization system in toluene 2


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A yellow color developed when C P T and S 0 were mixed, and the equihbrium constant of the molecular complex formation was measured as Κ = 0.0353 ( 40°C, in hexane) (2). This complex might be the inter mediate in this alternating copolymerization, and it might participate both i n the initiation and propagation steps of this spontaneous copolymerization.


2

The following scheme is proposed to explain the high dependence of the polymerization rate on monomer concentration, assuming initiation from the complex and C P T and propagation through the complex. Κ

CPT + S0

2

«=>

complex

ki

complex + C P T

R · Κ R · + complex —> R · Assuming a non-steady state polymerization involving a long lived radical, the following equation is derived ( 9 ) : -Λ

Ri = ki [CPT] [complex], [complex] = Κ [CPT] [SO,] R = Κ [R · ] [complex] = k> k K* [ C P T ] [SO,]* P

p

3

The validity of the non-steady state assumption is shown i n Figure 1, where the molecular weight of the copolymerization mixture increases with conversion at the beginning of copolymerization. The long lived radical is observed from the E S R spectrum i n Figure 2, measured at room temperature for polymerization i n toluene; this agrees with the S 0 radi cal similar to the norbornene-S0 system (16). 2

2

The nature of the propagating radical was examined from chain transfer studies. The effect of some chain transfer agents on the reduced viscosity of the copolymer is shown i n Table I. The fact that carbon tetrabromide is more effective than n-butylmercaptan as a chain transfer agent and that 1,4-dioxane decreases the reduced viscosity of the co polymer shows the presence of an acceptor radical (10) i n agreement with the E S R study. Thus, copolymerization between cyclopentene and SO2 is explained by regarding the charge transfer complex as a new monomer, and propagation proceeds only through the S 0 radical. 2

The copolymer produced during the polymerization precipitated as a white powder, soluble i n D M F , chloroform, and liquid S 0 . Elemen tary analysis proved the exact alternating composition irrespective of monomer feed ratio. O n heating, they decomposed at 220°-230°C with out melting. 2


13.

YAMASHiTA

Table I.

Effect of Chain Transfer Agent on the Reduced Viscosity of the Copolymer" Conversion, %

Chain Transfer A gent

6

—

C B r , 0.005 0.048 0.16 4


215

Terpolymerization

ET AL.

n - B u S H 0.03 0.06

3.20 2.18 1.20 6.17

1.25 0.335 0.191 0.143

5.49 6.46

0.420 0.346 1.56 1.03

50.9 52.0

Dioxane 1.7 4.0

Solvent = toluene (2.5 ml) for all but the last two runs. Molar ratio of chain transfer agent to monomer; C P T , 0.68 gram; S 0 , 0.04 gram; temp., 30°C. α

6

2

C P T - S O — A N System. Terpolymerizations were carried out to clar ify the nature of the intermediate complex and the propagating radical in the C P T - S 0 copolymerization system (21). V i n y l monomers are grouped by the electron density of their double bonds into three classes; donor, acceptor, and indifferent. Strong donors such as isobutyl vinyl ether polymerizes cationically by adding C P T - S 0 at 30 °C. Moderate donors such as styrene, which can give polysulfone with S 0 , can copolymerize with C P T - S 0 to give a random copolymer of ( C P T - S 0 ) and ( 2 - S t - S 0 ) . Acceptors such as maleic anhydride are expected to yield a random copolymer from our previous experiment on the terpoly merization of butadiene-S0 -maIeic anhydride system (8). Indifferent monomers such as acrylonitrile, methyl acrylate, methyl methacrylate, and vinylidene chloride are expected to form a random copolymer with the C P T - S 0 system because their double bonds have intermediate electron density and they copolymerize randomly with another charge transfer complex between p-dioxene and maleic anhydride. However, vinylidene chloride showed very low reactivity and methyl methacrylate, which was reported to polymerize by S 0 (5), d i d give a block copolymer consisting of C P T - S C ^ and M M A blocks (probably because of steric hindrance). L

2

2

2

2

2

2

2

2

2

The terpolymerization of C P T - S 0 and acrylonitrile is shown in Table II. It was necessary to accelerate the polymerization by adding azobisisobutyronitrile ( A I B N ) as initiator. The nature of the propagating species may not be different with a different initiator. Polymerization ceased at a low conversion at 40 °C in toluene. The terpolymer composi tion calculated from elemental analysis of C , Η, N , and S showed an equimolar ratio of C P T and S 0 . The terpolymers are white powders, soluble i n D M F , can be cast into transparent film different from the CPT—SO2 copolymer, and showed melting temperature without decompo2

2


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Table II.

Terpolymerization of CPT-SO »-AN at 40°C in Toluene" L


CPT, AN, Toluene, Time, so2, grams hrs ml grams grams 2.04 0.68 1.36 1.36 1.36 1.36 0.68 β 6 c


1.94 0.64 1.28 1.28 1.28 1.28 0.64

1.06 0.60 1.08 2.13 3.20 4.24 3.18

3.8 2.2 6 2.5 1.5 2 2.5

4.5 2.0 4.0 3.5 2.9 2.9 2.0

Con version,

%

12.8 0.64 —

2.5 2.5 2.0 1.0

Terpolymer Composi tion, AN/ CPT-S0

b

2

Mp% °C 139 ~ 153

0.385 0.535 0.574 1.07 1.65 2.91 4.81

—

193 ~ 200 138 ~ 145 188 ~ 199 — —

A I B N (5 mg) added as initiator for all runs except the second. Molar ratio of A N to C P T - S 0 . Microscopic melting temperature. 2

0

50 monomer feed (cPiféOt) [CPTfeo,)+(AN]

CO x

jqo

Figure 3. Copolymer composition diagram of CPTS0 -AN expressed as a binary copolymer 2

Ο AIBN initiated φ Thermally initiated

sition. The terpolymers richer i n A N were insoluble i n chloroform, and those poorer i n A N were soluble i n chloroform. Fractional extraction by chloroform proved the homogeneity of the terpolymer composition, showing the randomness of the terpolymerization.



13.

YAMASHiTA

0

217

Terpolymerization

ET AL.

β

2.S

I

solvent vol/vol monomer Figure 4. Effect of dilution on terpolymer composition of CPT-S0 -AN system at 40°C. AIBN, 5 mg; CPT, 1.0 X 10' mole; SO , 1.0 X 10~ mole; AN, 1.6 X 10~ mole. 2

2

Φ Θ Ο 3 © C

2

g

2

Bulk Toluene Benzene Chloroform Carbon tetrachloride Acetone

Considering the terpolymerization of C P T - S O 2 - A N system as a binary copolymerization of C P T - S O 2 complex and free acrylonitrile, the copolymerization equation can be derived as follows, assuming a fast equilibrium. Κ C P T + SO,

Terpolymerization of Cyclopentene, Sulfur Dioxide, and Acrylonitrile

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