Chemical conversions of halogenated polyolefines caused by organo-lithium compounds

Organo-lithium compounds

1721

REFERENCES 1. K. J. IVIN, H. A. ENDE and G. MEYERHOFF, Polymer 3: 129, 1962 2. C. Ya. FRENKEL' and S. I. KLENIN, Vysokomol. soyed. 6: 1420, 1964 (Translated in Polymer Science U.S.S.R. 6: 8, 1511, 1965) 3. A. V. POD_ALINSKII, Zh. fiz. khim. 37: 1189, 1963 4. I. Ya. PODDUBNYI, V. A. GRECHANOVSKII, M. I. MOSEVITSKII and A. V. POD/LLINSKII, Vysokomol. soyed. 5: 1042, 1963 (Translated in Polymer Science U.S.S.R. 5: 1, 97, 1965) 5. U. BIANCHI, V. MAGNASCO and C. ROSSI, Chimieale Industria 40: 263, 1958 6. H. G. ELIAS, Makromol. Chem. 54. 78, 1962 7. I. Ya. PODDUBNYI and V. A. GRECHANOVSKII, Dokl. AN SSSR, 153: 1122, 1963 8. F. W. IBRAHIM, J. Polymer Sci. A3: 469, 1965 9. L. MANDELKERN, W. R. KRIGBAUM, H. A. SCHERADA and P. J. FLORY, J. Chem. Phys. 20: 1392, 1952 10. I. Ya. PODDIYBNYI and V. A. GRECHANOVSKII, Vysokomol. soyed. 6: 64, 1964 (Translated in Polymer Science U.S.S.R. 6: 1, 74, 1965)

CHEMICAL CONVERSIONS OF HALOGENATED POLYOLEFINES CAUSED BY 0RGANO-LITHIUM COMPOUNDS* N. A. PLATE, S. L. DAVYDOVA, M. A. YAMPOL'SKAYA, B. A. I~UKI~ITDIIVOVA and V. A. KA~Gn~ Institute of Petroleum Synthesis, U.S.S.R. Academy of Sciences

(Received 17 July 1965) POLYOLEFINES are c h e m i c a l l y i n e r t a n d t h e i r chemical modification is difficult to o b t a i n [1]. I t is t h e r e f o r e u n d e r s t a n d a b l e t h a t t h e presence of an alkali m e t a l in t h e chain of s p a r i n g l y r e a c t i v e polyolefines w o u l d m a k e possible t h e s u b s e q u e n t i n t r o d u c t i o n o f a l m o s t a n y f u n c t i o n a l groups. F u r t h e r m o r e t h e g r a f t i n g o f o t h e r m o n o m e r s o n t o p o l y o l e f m e s w o u l d t h u s be facilitated, which w o u l d itself be a n e x a m p l e of t h e possibility of ionic g r a f t c o p o l y m e r i z a t i o n r e a c t i o n s on polyolefines, since all t h e m a n y g r a f t i n g r e a c t i o n s on polyolefmes so f a r k n o w n are b a s e d on radical processes. A n u m b e r of r e p o r t s h a v e b e e n p u b l i s h e d on t h e m e t a l l a t i o n o f h a l o g e n a t e d p o l y s t y r e n e [2, 3], b u t t h e r e are no d a t a on t h e i n t r o d u c t i o n of l i t h i u m into polyolefine chains. * Vysokomol. soyed. 8: No. 9, 1562-1567, 1966.

N . A . PLATE et al.

1722

This paper presents a study of the introduction of metallic lithium into the polymer chain of polyolefines; the possibility of using this modified polyolefine as a basis for further reactions is examined. The substances investigate d were polyethylene and polypropylene containing a certain amount of halide, and the lithium was introduced through "indirect metallation" by lithium-organic compounds. EXPERIMENTAL Chlorinated polyethylene was obtained b y passing gaseous chlorine through a suspension of low-density polyethylene in chlorobenzene, as previously described in [4]. The phenyllithium and butyllithium were produced b y the methods described in [5, 6]. Interaction of chlorinated polyethylene with B L i and ~ubs~quent conversions. To a fuor-fold excess of RLi at --20 °, while stirring in a stream of argon, was added a solution of 2 g of chlorinated polyethylene in 100 ml of absolute tetrahydrofuran during 2-3 hr. The mixture was then heated for 30 m i n at 50 °, then cooled to room temperature, after which a 20-fold excess of an organic reagent was added (Table 1), stirred for 1 hr, and decanted into methanol acidified with hydrochloric acid. The precipitated polymer was filtered off, after removal of the organic reagent b y extraction with methanol and ether the polymer was dried to a constant weight at 35 °. Anionic grafting on metallated polyethylene. To a suspension of metallated polyethylene produced at room temperature from butyllithium and a solution of chlorinated polyethylene i n benzene, as described in the former experiment, 20 ml of the appropriate monomer was added at 0 ° (Table 2). The reaction mixture was stirred for 17 hr at 0 ° a n d poured into methanol acidified with hydrochloric acid. The homopolymer was extracted from the graft copolymer in a Soxlet apparatus for 50 hr, using the following solvents: polymethylmethacrylate-acetone, polyacrylonitrile-dimethylformamide, polyisoprene-benzene. To verify T A B L E ] . I N T E R A C T I O N OF C H L O R I ' N A T E D P O L Y E T H Y L E N E S

Test, No.

Metallizing agent

Reagent with which the metallated polyethylene was treated

Solvent

•

WITH ORGANO-LITHIUM COMPOUNDS

Chlorine, ~o Analysis,

%

I

initial

residual

87

C6H~Li

C~HsCHO

THF

34"5

18"1

87'

CeHsLi

CO2

THF

29"4

14"1

128

n-C4HgLi

CBHsCHO

THF

29"4

12"9

129

n-C4HgLi

COs

THF

29"4

9-3

131 132 138

n-C4H~Li n-C4HgLi n-C4HgLi

(C6H~)BSnC1 (CH3)3SiC1 (C,H~)2PC1

THF THF Benzene

29"4 29'4 29"4

11"5 12.4 24.2

C H (O) C tI (O) C H (O) C H (O) Sn Si

69.84; 9.11 2.95 66.7; 8"70 10.5 65.70; 9.64 11-76 70-24 10.07 10.39 2.2 0"82

1)

1"99

Organo-lithium compounds

1723

that the extraction was complete, control tests were made in which a mechanical mixture of chlorinated polyethylene and homopolymer was extracted for 50 hr with the appropriate solvents. TABLE 2. A_~uo~rm GRATING O~¢MET~T~LATEDPOLYETHYLE~rE (Solvent--benzene; metallizing agent--n-CtHpLi) Chlorine, Test No.

%

Monomer being grafted

Analysis,

% initial

residual

134

Methylmethacrylate

29"4

22"1

137 144

Acrylonitrile Isoprene

29"4 29"4

9"8 27"4

166

Styrene

29"4

19"7

C H (O) N C H C H

Number of units grafted,

%

57"28 33 8"32 12"3 1"65 6"25 58"03 Not calculated 8"30 Ditto 68"89 8"37

Infrared spectra of the washed polymers showed a complete absence of the characteristic bands of homopolymers, which had been removed by washing. The infrared spectra of the polymers were recorded on a UR-10 infrared-speetrophotometer. The samples for spectral investigation were prepared in the form of films produced in a compression mould with heating up to 120-150 ° under a pressure of 50-70 arm. DISCUSSION OF RESULTS

O f all t h e possible m e t h o d s of p r o d u c i n g organo-lithium derivatives o f polyolefines t h e m o s t fruitful was t h e so called " i n d i r e c t m e t a l l a t i o n " m e t h o d [7] consisting o f a n exchange r e a c t i o n b e t w e e n a low-molecular weight organolithium c o m p o u n d a n d a halogen d e r i v a t i v e o f a polyolefine CH2--CHR X

i

~

A-R'Li ~t ~w CH2--CHR+R'X

f

Li

T h e initial h a l o g e n a t e d olefines were b r o m i n a t e d p o l y e t h y l e n e w i t h a 12% b r o m i n e content, chlorinated p o l y e t h y l e n e s w i t h chlorine contents o f 29.4 a n d 34.5~/o a n d chlorinated p o l y p r o p y l e n e with 2 9 . 9 % chlorine. Owing to the e x t r e m e instability of lithium-containing polyolefines a n d t h e impossibility o f separating t h e m in a free state, p r o o f o f their f o r m a t i o n was o b t a i n e d b y reacting the m e t a l l a t e d p o l y m e r with different organic r e a g e n t s - b e n z a l d e h y d e , d r y ice, trimethylchlorosilane, diphenylchlorophosphine, trip h e n y l c h l o r o s t a n n a n e , a n d also b y ionic grafting reactions. I n the reaction o f chlorinated p o l y e t h y l e n e w i t h b u t y l l i t h i u m in t e t r a h y d r o f u r a n with s u b s e q u e n t processing with a n u m b e r o f reagents (Table 1) a modified p o l y e t h y l e n e was obtained, microanalytical tests show (tests 128, 129 a n d 138)

1724

N.A. PLATE et aL

that approximately half of the reacted chlorine atoms in the polymer molecule are replaced by the metal. When the polyethylene metallated in this way is processed with benzaldehyde or dry ice the infrared spectra reveal bands characteristic for the absorption of functional groups formed when the lithium-containing polymer interacts with the appropriate reagent (3450 and 3610 cm -1 for OH; 1720 cm -1 for C----O). Elementary analysis shows t h a t oxygen appears in the composition of both polymers (Table 1, tests 128, 129). After the polyethylene metallated with butyllithium had been treated with derivatives of tin, silicon or phosphorus by the general reaction: CH,--CH ~

~-RMX

-> ~

CII~--CH ~

~-LiX

MR n (where M--Si, P, Sn, n----2.3) infrared spectra of the products revealed no bands characteristic for the absorption of derivatives of these elements. Apparently this can only be explained by a low degree of conversion in the interaction of metallated polyethylene with element-organic derivatives, and consequently with a small amount of the absorbing groups. However, elementary analysis shows that the corresponding elements are present in the composition of the polymers (Table I). The replacement of a halogen by lithium RXWR'Li ~ RLi-PR'X is reversible, and the equilibrium position is determined by the relative electronegativity of the R and R' radicals. I t is therefore understandable that in the case described in the literature where halogenated polystyrene is treated with butyllithium the metallation proceeds quantitatively [8], while in the case of halogenated polyolefines no high yield of the metallated product is to be expected as aliphatic radicals do not differ greatly in regard to their electronegativity. Certainly, as was indicated above, in the case under consideration only half of all the chlorine that reacted is replaced by the metal. Besides, for aliphatie compounds under "indirect metallation" conditions Wurtz' reaction occurs readily, so that crosslinked products are formed CH2--CHR

~

÷ R ~ L i -->~

CH,--CHRR'

~

+LiX

i

x

(where R----H, CHs) , as well as a dehydrohalogenation reaction caused by a nucleophilic organometallic. CH,--CR-- CHI--CHR ~ I x

~R'Li -> ~ CH~CR--CH,--CHR ~ ,

where R----H, CH3. In fact in the infrared spectra of the chlorinated polyethylenes treated with

Organo-lithium compounds

1725

butyllithium (tests 128, 129, 131, 132, 138) the intensity of the 1378 cm -1 band is increased; this band characterizes the degree of branching of the polyethylene, while the band appearing at 977 cm -1 indicates the formation of a symmetricallysubstituted double bond due to the dehydrochlorination. Tests where phenyllithium was used as the metallizing agent (Table 1, tests 87 and 87') also provided convincing evidence t h a t in the process under investigation three competing reactions occur: metallation, a Wurtz-Fittich reaction (condensation) and the splitting off of hydrogen chloride. However, the total degree of conversion through chlorine is slightly lower than in the case of butyl-. lithium. Thus on treating chlorinated polyethylene with phenyllithium in tetrahydrofuran and subsequently with benzaldehyde (test 87) a polymer is obtained the infrared spectrum of which reveals bands characteristic for the absorption of a monosubstituted aromatic nucleus (a series of bands from 1600 to 1800 cm -~, 3035 and 3070 cm-1), the bands characteristic for absorption of a hydroxyl group (3450 and 3612 cm -1) and the 977 cm -1 band characteristic for a symmetrically-substituted double bond. In the treatment of chlorinated polyethylene with phenyllithium and then with dry ice (test 87') a polymer was obtained with characteristic absorption at 1603 cm -1 (monosubstituted benzene nucleus), 1720 cm -1 (carbonyl group), 3450 and 3612 cm -1 (hydroxyl group). The 978 cm -1 band characterizes the absorption of the symmetrically-substituted double bond. In contrast with chlorinated polyethylene, in the treatment of chlorinated polypropylene with phenyl- and butyllithium it is apparently only condensation and dehydrochlorination reactions that occur. This suggests t h a t the chlorine atom attached to the tertiary carbon atom is less reactive in replacement by a metal in "indirect metallation". I t was found on investigating the reaction of brominated polyethylene with butyllithium that in this case the metallation is extremely slight, the predominating reaction being dehydrobromination, as is shown by the infrared spectra and by elementary analysis. In the interaction of chlorinated polyethylene with butyl- or phenyllithium it is advisable to use a large excess of the metallizing agent as this enables the yield of metallated polyethylene to be considerably increased in the reverse reaction where a chlorine atom is replaced by lithium. I t should be noted t h a t an equilibrium displacement in the reaction RX--kR'Li~RLi--kR'X in the direction desired is facilitated in the presence of strongly solvating solvents, although the latter too are split to some extent by organo-lithium compounds [5]. The exceptional reactivity of metallated polyethylene also enabled the latter to be used as a polymer catalyst in the anionic polymerization of several monomers such as methylmethacrylate, acrylonitrfle, styrene and isoprene. As a' result of this reaction one would expect the formation of graft eopolymers with main chains from the polyethylene and side chains from the corresponding units of the monomers t h a t are introduced:

1726

N . A . P~A~S ~

~.

CH,--CH-- CH,--CHC1 l

CHR.J,~ CH, eC~ HLi @ The initial polymer catalyst was obtained by diluting a chlorinated polyethylene solution in benzene and using an excess of butyllithium in heptane.

Thus in the reaction medium there was in addition to polylithiumpolyethylene excess butyllithium which initiated the anionic homopolymerization of the monomers that were added. Examination of the infrared spectra after homopolymers of the reaction products had been carefully washed out of them revealed bands at 1730 cm -1 characteristic for the absorption of an ether group (in the grafting of methylmethacrylate) as well as bands at 2253 cm -1 for the absorption of a nitrile group (in the grafting of acrylonitrile). When isoprene is grafted the infrared spectrum of the product shows bands at 898 and 1645 cm -~ and a shoulder at 3030 cm -~ on the broad band of valence vibrations of the CHs-group, and the intensity of the 1380 em -1 band is increased, characterizing the higher degree of branching of the polyethylene. The infrared spectrum of the polyethylene/styrene graft copolymer has bands at 1495, 1603, 3037, 3070 and 3090 cm -1 characteristic for aromatic absorption. Moreover in the spectra of the graft copolymers all the main absorption bands peculiar to polyethylene are retained. It is noteworthy that one would also expect a graft copolymer to be formed as a result of termination of the growing homopolymer chain by the chlorinated polyethylene: (CH,-- CH).-- CH s- CH-Li + + ~ CH~-- CH ~ -* ~ CHs -- CH ~ + LiHg R

Hal

HR

LCH, J,, This reaction was in fact observed by the authors in the homopolymerization of styrene by butyllithium with subsequent addition of chlorinated polyethylene. However under conditions of the metallation and grafting reaction it was impossible to detect any significant part played by the reaction as there is practically no polyethylene in grafting products soluble in benzene. The results of elementary analysis (Table 2) together with the infrared spectra suggest that it is possible to graft other monomers onto metallated polyethylene by anionic grafting. It has thus been shown by this investigation of the changes in halogenated polyolefines due to the action of organo-lithium compounds that in fact the replacement of a halogen atom by lithium in a polyolefine chain is completely possible. These results also show that the reaction R X + R ' L i ~-RLI-t-R'X, being reversible, is made very complex by rival processes resulting in dehydrohalo-

Organo-lithium compounds

1727

genation of the polymer, and also in nucleophilic replacement of a halogen by the radical of an organo-lithium compound. However in a number of cases the yield in the metallation reaction was fully adequate to make practicable the realization of several chemical changes on this metallated polyolefine with compounds containing functional groups, and also to realize the ionic grafting of monomers capable of anionic polymerization CONCLUSIONS

(1) Using the example of chlorinated polyethylene it is demonstrated t h a t in the reaction of halogenated polyolefines with low-molecular weight organolithium compounds "indirect metallation" of the polymer chain occurs resulting in the formation of polymetallolefines. (2) The formation of polymetallolefines is proved b y several chemical changes including ionic grafting of methylmethacrylate, acrylonitrile, isoprene and styrene on metallated polyethylene. TranslaZed by R. J. A. H~DnY REFERENCES

1. M. A. SMOOK, W. J. REMINGTON and D. E. STRAIN, Polythene, ed. by A. Renfrew and Morgan, p. 389, London, 1960 2. D. BRAUN, Kunststoffe 50: 1375, 1960 3. W. KERN and D. BRAUN, Angew. Chem. 73: 197, 1961 4. S.L. DAVYDOVA, N. A. PLATE, M. A. YAMPOL'SKAYAand V. A. KARGIN, Vysokomol. soyed. 7: 1946, 1965 (Translated in Polymer Science U.S.S.R. 7: 11, 2136, 1966) 5. H. G. GILMAN aad B. J. GAJ, J. Organ. Chem. 22: 1165, 1957 6. K. A. KOCHESHKOVand T. V. TALALAYEVA,Synthetic methods in the field of organometallic compounds, publ. by AN SSSR, vol. 1, p. 24, 1947 7. H. GILMAN and R. G. JONES, Organic Reactions 6: 339, 1951 8. D. BRAUN, Makromolek. Chem. 30: 85, 1959