Participation of lewis base on vinyl chloride polymerization with Al(C2H5)3CCl4 catalyst system

Participation of Lewis base on vinyl chloride polymerization with AI(C2Hs)3/CCI4 catalyst system Akira Akimoto Central Research Laboratory, Toyo Soda Manufacturing Co. Ltd, Yamaguchi-ken, Japan (Received 26 September 1973) The polymerization of vinyl chloride has been investigated using an AI(CsHs)8/CCI4 catalyst system in the presence of various Lewis bases. Effective Lewis bases are y-butyrolactone, diglyme and diethylenetriamine which are multidentate. The rate of polymerization is dependent not only on the basicity of the Lewis base used but also on a coordination number of one. The latter is the predominant factor. For the effect of polymeric amines, a tentative hypothesis is discussed.

INTRODUCTION Polymerization of vinyl chloride initiated by organoaluminium compounds, which, unlike the known Ziegler-Natta processes, proceeds via a free-radical mechanism, is of great interest. The AI(C2Hs)3/CCI41, 2, Al(C2Hs)a/Lewis base/CCl4 a and AI(C2H5)3/CuCI/CC14 catalyst systems 4 are known to initiate the free-radical polymerization of vinyl chloride. These systems are significant especially in respect of the polymerization catalyst behaviour of the organometallic compound. In recent years systems based on aluminium alkyls and acyl peroxides have been used to initiate the polymerization of vinyl chloride 5. The effective polymerization of vinyl chloride with this catalyst system could be carried out in the presence of the complexing agent-ester, ether and nitrile6. The role of complexing agent is characteristic. This was also found for the vinyl chloride polymerization with Al(C2Hs)s/Lewis base/CCl4 catalyst system3. In this paper the participation of the Lewis base is dealt with in the vinyl chloride polymerization with AI(C2Hs)a/CC14 catalyst system in greater detail. Some features of this catalyst system are discussed. EXPERIMENTAL

Reagents Vinyl chloride monomer (Toyo Soda Manufacturing Co. Ltd) was dried and purified by passing it through a column containing calcium chloride and then one containing phosphorus pentoxide. Benzene was purified by the usual methods and distilled over calcium hydride. The middle fraction was then stored with sodium wire in a dry box. Lewis bases were refined according to the conventional methods7. Triethylaluminium (Texas Alkyls Inc.) was redistilled under reduced pressure and nitrogen atmosphere. 1 mol/1 stock solution of AI(C2Hs)a in anhydrous benzene was prepared prior to use.

216 POLYMER, 1974, Vol 15, April

Carbon tetrachloride was washed with concentrated sulphuric acid, then with water, and distilled before the polymerization.

Polymerization procedure The polymerization was carried out in a sealed glass tube, which was shaken in a water bath maintained at a given temperature. After the glass tube had been evacuated, vinyl chloride was distilled into a glass tube, kept below -78°C, in which was the required amount of the catalyst AI(C2Hs)a, Lewis base, carbon tetrachloride and solvent. After a definite time, the polymerization mixture was poured into a large amount of methanol containing hydrochloric acid.

I.r. spectra of AI(C~Hs)3 complex Infra-red spectra were taken using a sealed cell of potassium bromide to protect the organoaluminium compound from moisture and air. RESULTS A N D DISCUSSION Vinyl chloride was polymerized with the AI(CzHs)a/CCI4 catalyst system in the presence of various Lewis bases at 40°C. Figure 1 presents the relation between the yield of poly(vinyl chloride) (PVC) and the electron donating power (AvD) of the Lewis base s. The results in Figure 1 indicate that the yield of PVC first rose, then passed through a maximum with an increase in the AVD values. The rate of polymerization of vinyl chloride was increased by using Lewis bases which had AVD values from about 60 to about 110. y-Butyrolactone was the most effective complexing agent of all those studied, and /3-propiolactone was more effective than methyl acetate regardless of their A VDvalue. It is interesting to note that cyclic esters such as ~,-butyrolactone and fl-propiolactone are more effective Lewis bases than linear aliphatic esters which have

Lewis base in vinyl chloride polymerization with AI(C~H~)s/CCl4: A. Akimoto 12

itttG

IO

-o

I

K ~

E >-

•

i

- - .%..

C /

o~' ,D

O

50 IOO 150 200 Electron donating power, AVD(Cm-I )

behave as multidentate ligands. In the presence of multidentate Lewis bases the yield of PVC is always higher than in the presence of the corresponding monodentate Lewis base. In particular, when diethylenetriamine is used as a multidentate Lewis base, the increase in the yield of PVC is significant. For the effect of polymeric amines some reasons are considered. It has been reported that an amine-alkyl halide combination is a very active catalyst system for free radical polymerization of vinyl monomers z~-z4. Then, the effect of order of mixing was studied to Table 1 Effect of various esters on polymerization of vinyl chloride with AI(C~H~)s/CCI4 systema

Figure 1 Polymer yield vs. electron-donating power, Vinyl chloride, 5ml; Cell6, 5ml; AI(C~HB)~, lmo1% on monomer; catalyst ratio AI(C~H~)~/CCI4/Lewis base=1:1:1 ; polymerization at 40°C for 20h. A, Vinyl acetate; B, methyl acetate; C, ethyl acetate; D, acetonitrile; E, fl-propiolactone; F, cyclohexanone; G, 7-butyrolactone; H, THF; J, DMF; K, ethyl ether; L, pyridine; M, ethylamine

the same number of carbon atoms, such as ethyl acetate and methyl acetate. Infra-red spectra of the mixture of AI(C2Hs)s and Lewis base were studied to clarify the effect of y-butyrolactone, and also to check which oxygen atom of the ester group takes part in the complexing interaction. Comparing the spectra of Al(C2Hs)s/~,-butyrolactone and Al(C2Hs)s/ethyl acetate complexes with those of the corresponding free 9,-butyrolactone and ethyl acetate, it follows that in the presence of AI(C2Hs)3 the carbonyl oxygen absorption band of y-butyrolactone is shifted towards low frequencies (1721cm -1) from the single band of the corresponding free y-butyrolactone (1795 c m - 1).

The carbonyl oxygen absorption band of ~,-butyrolactone is shifted towards lower frequencies (1665cm -1) in the SnCl4/y-butyrolactone complex9. The carbonyl oxygen absorption band in the infra-red spectra of Al(C~Hs)s/ethyl acetate complex is split into two bands, one of which corresponds to the carbonyl oxygen of the free ethyl acetate (1752cm-1), the other corresponding to the carbonyl oxygen of the ethyl acetate in the complex of Al(CgHs)3 (1678cm-Z). The results obtained lead to the conclusion that the complexing between AI(CzHs)s and 7-butyrolactone occurs both with the carbonyl oxygen and with the ether oxygen, and the one between Al(CzHs)s and ethyl acetate occurs only with the carbonyl oxygen. It seems likely that these structural differences of complexes reflect the activity of the polymerization catalysts. In Table 1 are shown the results of polymerizing vinyl chloride with AI(CzH~)z/CC14 catalyst in the presence of various esters. The effect of esters on catalytic activity permits some assessment to be given of the electronic nature of esters. Table 2 shows the Taft polar constants of substituents present in the ester. A correlation was found to exist between the Taft induction constants (a*) 10 and the catalytic activity shown by the relative rate (Figure 2). As shown in Figure 2, the relative rate became smaller, as ~r* became larger. However, the influence of substituent in the ester is small. 7-Butyrolactone is the most effective Lewis base and the different complexing seems to cause the high catalytic activity. Table 3 presents the results of polymerizing vinyl chloride with AI(CzH~)s/CC14 catalyst in the presence of Lewis bases that are able to

Ester

Yield (%)

Relative

No. 4 2 3 1 8 6 5 7

Methyl acetate Ethyl acetate Butyl acetate Ethyl propionate Methyl cyanoacetate Methyl benzoate Ethyl benzoate Methyl chloroacetate

4.60 5.70 5.66 5.90 0.37 3.68 4.20 1.84

1-00 1-24 1.23 1.28 0.08 0.67 0.91 0.40

rate

aVinyl chloride, 5ml; C6H8, 5ml; AI(CsHs)s, 1 mol% on monomer; catalyst ratio Al(C2Hs)~/CCI4/ester= 1:1:1 ; polymerization at 40°C for 40h Table 2 Taft polar constants of substituents present in RCOOR'

R

R'

erR

erR'

o*= crR.l,aR'

CHs CH3 CHs n-CsHz7 CH~(CN) Cell5 Cell5 CH~CI

CH8 C~H5 n-C4H9 C~H5 CH8 CHs C2H5 CHs

0'00 0.00 0"00 -0"12 +1-30 + 0- 60 +0"60 ÷ 1" 05

0'00 -0.10 -0"13 -0-10 0-00 0.00 -0"10 0"00

0'00 -0"10 -0"13 -0"22 +1 "30 + 0" 60 +0"50 -I- 1" 05

2"0

"

>~ I-0

o''

-0"2

,

,

0

,

,

'

. . . . . .

0.5

' " '

I'0

'

Figure 2 Relative rate as function of the Taft polar constants o* of substituents present in RCOOR' compounds Table3 Effect of multidentate ligand Lewis bases on polymerization of vinyl chloride with AI(C2Hs)s/CCI4 systema

No.

Lewis base

Yield (%)

Pn b

9 10 11 12

H~NCHsCH2NHCH~CH~NH~ CHsCH2NH2 CHsOCHsCH2OCH~CH~OCHs CHsCH~OCH~CHs

38"0 4'1 9'6 5" 1

450 420 490 450

a Vinyl chloride, 5ml; C6He, 5ml; AI(C2Hs)s, 1 mol% on monomer; catalyst ratio AI(C~Hs)3/CCI4/Lewis base=l :t :1 ; polymerization at 40°C for 40h b By measurement on dilute nitrobenzene solution at 30°C. Pn was calculated using the following equation: Pn=500(antilog It/I/0.168-1)zz

POLYMER, 1974, Vol 15, April

21"/

Lewis base in vinyl chloride polymerization with AI(C=Hs)3/CCl4: A. Akimoto Table 4 Order of mixing and catalyst activity on vinyl chloride polymerizationa Yield No.

Order of mixing

(%)

9 13

Amine*-CCI4*--AI(C3Hs)3 CCI4/amine*- AI(CzHs)3 b

38.0 37.4

14

Amine/Al(CzH~)3*- CCI4c Amine*-CCI4

37-6 0.0

23

aVinyl chloride, 5ml; CsHe, 5ml; AI(C~Hs)3, 1 mol% on monomer; catalyst ratio AI(C~Hs)s/CCI4/ diethylenetriamine=l "1:1 ; polymerization at 4O°C for 40h b CCI4 and amine were premixed at room temperature and then AI(C2Hs)8 was added cAmine and AI(CsH5)3 were premixed at room temperature and then CCI4 was added

Table 5 Effect of various amines on polymerization chloride with AI(C2Hs)s/CCI4 systema

of vinyl

No.

Amine

Yield (%)

Pn b

9 15 16 10 17 18 19 20 22

Diethylenetriamine Triethylenetetramine Tetraethylenepentamine Ethylamine 2-Ethylhexylamine Stearylamine Ethylenediamine N,N,N',N'-tetramethylethylenediamine --

38.0 31.2 33.2 4.1 2.0 2.1 0.6 trace 1-6

450 470 460 420 ------

a Vinyl chloride, 5ml; CsHe, 5ml; AI(C2Hs)3, 1 mol% on monomer; catalyst ratio Al(C2Hs)8/CCI4/amine=l:l:l; polymerization at 40°C for 40h b By measurement on dilute nitrobenzene solution at 30°C. Pn was calculated by using the following equation: ,~n=500(antilog [r/]/O"168-1) zl

elucidate the high catalytic activity in the presence of diethylenetriamine (Table 4). In Table 4, amine, CC14, and Al(C2Hs)3 were added in this order in a glass tube for No. 9. For No. 13, CC14 and amine were premixed at room temperature and then Al(C2Hs)3 was added. For No. 14, amine and Al(C2H5)3 were premixed at room temperature and then CC14 was added. The yield of PVC was constant in spite of any order of mixing. Therefore, charge transfer interaction etc. between amine and CC14 does not contribute to the initiation reaction of polymerization. Furthermore this is well supported by the fact that amine-CCl4 cannot initiate the polymerization of vinyl chloride in the absence of AI(C2H5)3. The effect of diethylenetriamine seems to be due to complexing between amine and AI(C2Hs)s. It has been found that complexing the Cr z+ ion with ligands such as ethylenediamine greatly enhances its ability to reduce even primary alkyl halides to alkaneslL On polymerization of vinyl chloride catalysed by ethanolamine and CC14, any trace metal can play a significant part in the initiation of the polymerization ~6. Ultimately in this case the formation of a complex with multidentate ligands is assumed to be responsible for the changes in the catalytic activity.

218

POLYMER, 1974, Vol 15, A p r i l

Table 5 presents the results of vinyl chloride polymerization with AI(C2Hs)3/CCI4 in the presence of various amines. Diethylenetriamine, triethylenetetramine and tetraethylenepentamine are effective Lewis bases, and monodentate amines (such as ethylamine, 2-ethylhexylamine and stearylamine) are not effective ones. Among these polymeric amines, ethylenediamine and N , N , N ' , N ' - t e t r a m e t h y l e t h y l e n e d i a m i n e do not initiate the polymerization of vinyl chloride at all. In alkylaluminium chemistry, alkylaluminium forms only a tetradentate 1:1 complex with excess amine having a monodentate figand. However, it is evident that alkylaluminium forms a pentadentate complex with a rigid bidentate amine such as dipyridyl z7-19. A pentadentate aluminium complex with amine is known to be the most effective catalyst in the anionic polymerization of methyl methacrylate. Therefore it is likely that the catalytic activity is dependent on the type of aluminium-amine complex. Polymeric amines seem to form pentadentate complexes according to their structural characteristic. This complex is the most effective. However, ethylenediamine and N , N , N ' , N ' - t e t r a m e t h y l e t h y l e n e d i a m i n e , although bidentate bases, form tetradentate complexes by their flexible main chain. Tetradentate complexes seem to have lower activity.

ACKNOWLEDGEMENTS The author is grateful to Dr Y. Kosaka and Mr S. Imura for valuable discussions. REFERENCES 1 Minsker, K. S., Sangalov, Yu. A. and Razuwayev, G. A. J. Polym. Sci. (C) 1967, 16, 1489 2 Razuwayev, G. A., Sangalov, Yu. A., Minsker, K. S. and Kovaleva, N. V. Polym. Sci. USSR 1965, 7, 597 3 Breslow, D. S., Christman, D. L., Espy, H. N. and Lukach, C. A. J. Appl. Polym. Sci. 1967, 11, 73 4 Kawai, W., Ogawa, M. and Ichihashi, T. J. Polym. Sci. (A-l) 1970, 8, 3033 5 Milovskaya, E. B., Zhuravleva, T. G. and Zamoiskaya, L. W. J. Polym. Sci. (C) 1967, 16, 899 6 Milovskaya, E. B., Kopp, E. L., Mikhailicheva, O. S., Denisov, V. M. and Koltsov, A. I. Polymer 1972, 13, 288 7 Weisberger, A. 'Organic Solvents', Interscience, New York, 1955, Vol VII 8 Kagiya, T., Sumida, Y. and Inoue, T. Bull. Chem. Soc. Japan 1968, 41, 767 9 Ito, K., Inoue, T. and Yamashita, Y. Makromol. Chem. 1970, 139, 153 10 Taft, R. W. J. Am. Chem. Soc. 1953, 75, 4231 11 Sakurada, I., Matuda, J., Shiotani, S. and Kawasaki, A. Kogyo Kagaku Zasshi 1958, 61, 1362 12 Furukawa, J., Tsuruta, T. and Fueno, T. J. Polym. Sci. 1955, 15, 594 13 Chapiro, A. and Hardy, G. J. Chem. Phys. 1962, 59, 993 14 Imoto, M., Takemoto, K. and Azuma, K. Makromol. Chem. 1968, 114, 210 15 Kochi, J. and Mocadlo, P. J. Am. Chem. Soc. 1966, 88, 4094 16 Imoto, M. and Takemoto, K. Makromol. Chem. 1969, 125, 294 17 Thiele, K. H., Miiller, H. K. and Briiser, W. Z. Anorg. Allgem. Chem. 1966, 345, 194 18 Thiele, K. H. and Briiser, W. ibid. 1966, 348, 179 19 Thiele, K. H. and Briiser, W. ibid. 1967, 349, 33