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Radical reactions involving esters of fumaric acid—I. Copolymerizations
European Polymer Journal, 1971, Vol. 7, p~,. 1147-1153. Pergamon Press. Printed in England.
RADICAL REACTIONS INVOLVING ESTERS OF FUMARIC ACID--I COPOLYMERIZATIONS J. C. BEVINGTON, M. JOHNSON a n d J. P. Sm~EN* Department of Chemistry, The University, Lancaster, England
(Received 22 January 1971) Abstract--x4C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies at 60~ of their radical copolymerizations with styrene and with vinyl acetate. Changing the diluent from benzene to dimethylformamide in some of the copolymerizatious had no effect on the compositions of the copolymers. Monomer reactivity ratios have been calculated for most of the systems; comparisons have been made of the reactivities of the fumarate esters towards the polyvinyl acetate radical. THIS paper is the first of a series concerned with a general e x a m i n a t i o n of the behaviour of fumarate esters in various radical reactions. 14C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies of their radical copolymerizations with styrene a n d with vinyl acetate. Tracer techniques can give accurate m e a s u r e m e n t s of copolymer compositions even when the copolymers c o n t a i n only very small a m o u n t s of one o f the m o n o m e r s . (1) I n this work, some of the copolymers c o n t a i n e d only a few fumarate ester units so that the use of the tracer m e t h o d was particularly advantageous.
EXPERIMENTAL l"C-diethyl fumarate was prepared by refluxing fumaric acid (116 g containing 0.05 me of t4C-fumaric acid) for 14 hr with absolute ethanol (148 g), benzene (380ml)and concentrated sulphuric acid (16 g). The reaction mixture was allowed to cool and then poured with stirring into water (1 1.). The benzene layer was separated and the aqueous layer extracted once with ether. The combined benzene and ether extracts were neutralized with sodium bicarbonate solution, washed with water and dried over anhydrous magnesium sulphate. This solution was finally filtered and the labelled monomer was isolated and purified by fractional distillation under a reduced pressure of nitrogen; the ester was redistilled immediately before use. t4C-di-n-hexyl fumarate was prepared from fumaric acid (93 g containing 0.045 mc of t4C-fumadc acid) in a manner similar to that used for t4C-diethyl fumarate. 14C-ethyl n-hexyl fumarate was prepared by the esterification of fumaric acid (29 g containing 0" 1 me of t4C-fumaric acid) with a mixture containing equimolar amounts of ethanol (17 g) and n-hexanol (38 g). The resulting mixture of esters was separated by fractionation under reduced pressure of nitrogen. Gas-liquid chromatography was used to monitor the separation and an NMR spectrum of the final material showed that the fraction collected was the mixed ethyl n-hexyl ester. Styrene and vinyl acetate were commercial products which were purified in the usual manner. Polymerizations were carried out at 60° in sealed dilatometers in the complete absence of air and were allowed to proceed to about 5 per cent conversion. Benzene was used as diluent in all cases except for some styrene copolymerizations with di-n-hexyl fumarate which were carried out in dimethylformamide. Sixty per cent solutions of monomers in the diluent were used with benzoyl peroxide at 2 g/l. as initiator for the styrene/fumarate systems and at 1 g/l. for the vinyl acetate/ fumarate systems. Petroleum ether (b.p., 40-60°) was used as precipitant for polymers containing diethyl fumarate and methanol for those containing ethyl n-hexyl fumarate and di-n-hexyl fumarate. Tests showed that * Present address: Messrs. Henry Cooke & Co. (1932)Ltd., Beetham, Milnthorpe, Westmorland. 1147
Radical Reactions Involving Esters of Fumaric Acid--I
I 151
0 -0.4 -0-8 u. "7
-1-2 -I.6
-2"0
-2.4
-1
0
I
2
3
4
5
6
7
f/F 2
FtG. 5. Fineman and Ross plot for copolymerizations in benzene of vinyl acetate (monomer 1) and diethyl fumarate (monomer-2). TABLE 2. MONOMER REACTIVITY RATIOS FOR COPOLYMERIZATIONS WITH VINYL ACETATE (.MONOMER--l)
Monomer--2
Reactivity ratios
Diethyl fumarate Di-n-hexyl fumarate Ethyl n-hexyl fumarate
rl
r2
0"031 0.031 0" 034
0.32 0.27 0" 26
Errors in r~ = ± 0.005 and in r2 = ± 0"02. DISCUSSION The monomer reactivity ratios obtained in this work for styrene/diethyl fumarate (rl = 0.35, r2 -- 0.005) and vinyl acetate/diethyl fumarate (rl = 0.031, r 2 = 0-32) are somewhat different from those in the literature (5) (r~ = 0.30, r2 = 0.070 for the styrene system and rl -- 0.01 I, r2 = 0"444 for the vinyl acetate system). However, the literature values were based on the results obtained from only two monomer feeds for each system and indeed the previous workers recognized that their values might not be very reliable. It is thought that the curvature of the Fineman and Ross plots for the copolymefizations of styrene with di-n-hexyl fumarate and ethyl n-hexyl fumarate is due to a penultimate group effect,(6) but since the curvature is so small it would be very difficult to obtain a quantitative measurement of such an effect.(~) Changing the diluent from benzene to dimethylformamide in the styrene/di-n-hexyl fumarate system had very little effect on the compositions of the copolymers. This was in spite of the two non-polar n-hexyl groups in the fumarate which might be expected to protect the double bond in the monomer from attack by radicals differently in the two solvents by adopting configurations in the non-polar solvent (benzene) different from those adopted in the polar solvent (dimethylformamide). Lewis and coworkers (8) and Price and Walsh (9) have reported previously that monomer reactivity E.P,I. 718--t
1152
J.C. BEVINGTON, M. JOHNSON and J. P. SHEEN
ratios are independent of the polarity of the reaction medium and the present results are in agreement with this view. From the values of rl in Table 2 for the copolymerizations of vinyl acetate with the fumarate esters, it was possible to compare the reactivities of the fumarate esters towards the polyvinyl acetate radical. All three fumarate esters have approximately the same value of l/rl indicating that the length of the alkyl ester group has little effect upon the reactivity of the fumarates towards the polyvinyl acetate radical. Lack of marked dependency of the reactivity of such monomers on alkyl group size seems to be a general rule in free radical copolymerizations. It has, for example, been shown that the chain length of the acyl group has no effect on the reactivity of vinyl esters in copolymerizationsClO.~l~ and similar reactivities of many methacrylate esters towards polymer radicals have been reported. ~12~ The scheme due to Alfrey and Price ~13~was applied to the results of the vinyl acetate copolymerizations to obtain values of the parameters Q and e for the fumarate esters. It was calculated that all the fumarate esters had values of Q which were close to 0.5 and values of e close to 2.0. These values do not agree closely with those in the literature C~4~ for diethyl fumarate (Q = 0-61, e = 1.25). This is not altogether unexpected since Q and e values calculated for systems where the product r~r2 is very small, as is the case for all the systems investigated here, are invariably subject to large errors. In spite of this disagreement, it is apparent that fumarate esters have large positive e values indicating electron-deficient carbon-carbon double bonds in the monomers. Both mesomeric and inductive effects tend to make the fumarate double bond electron-deficient. A high positive e value has been obtained for the related compound, maleic anhydride3 t4~ The fumarate esters also have fairly high Q values due to resonance stabilization of fumarate-ended chain radicals, c5~ In all the systems studied in this work, over a fairly wide range of monomer feeds, copolymers were formed in which the two different monomer units tended to alternate along the polymer chains. This is of course a general phenomenon for systems where one monomer reactivit3.' ratio is quite small and the other is close to zero. For the copolymerizations of the fumarates with vinyl acetate, r2 is appreciably greater than rt; this result indicates that, for feeds containing comparable concentrations of vinyl acetate and fumarate ester, there is a much greater tendency for the copolymer to contain adjacent fumarate units than for it to contain adjacent vinyl acetate units. Acknowledgement--We thank the Esso Petroleum Company Limited for the award of a Re.search
Studentship to J.P.S. REFERENCES (1) (2) (3) (4) (5)
G. Ayrey, Chem. Rev. 63, 645 (1963). J. C. Bevington and M. Johnson, Makromolek. Chem. 87, 66 (1965). J. C. Bevington and T. Ito, Trans. Faraday Soc. 64, 1329 (1968). M. Fineman and S. D. Ross, J. Polym. ScL 5, 259 (1960). F. M. Lewis and F. R. Mayo, J. Am. chem. Soc. 70, 1533 (1948). (6) W. G. Barb, J. Polym. ScL 11, 117 (1953). (7) M. Berger and I. Kuntz, J. Polym. Sci. A2, 1687 (1964). (8) F. M. Lewis, C. Walling, W. Cummings, E. R.. Briggs and F. R. Mayo, J. Am. chem. Soc. 70, 1519 (1948). (9) C. C. Price and J. 13. Walsh, J. Polym. ScL 6, 239 (1951). (10) L. P. Witnauer, N. Watkins and W. S. Port, J. Polym. ScL 20, 213 (1956).
Radical Reactions Involving Esters of Fumaric Acid--I (11) (12) (13) (14)
1153
J. C. Bevington and M. Johnson, Europ. Polym. J. 4, 669 (1968). J. C. Bevington and B. W. Malpass, Europ. Polym. J. 1, 19 (1965). T. Alfrey, Jr. and C. C. Price, J. Polym. Sci. 2, 101 (1947). L. J. Young,./. Polym. Sci. 54, 411 (1961).
R6sum6---On a utilis6 des ~chantillons marquis au 1~C de fumarates de di6thyle d'6thyte-n-hexyle et de di-n-hexyle, pour 6tudier leurs copolym6risations radicalaires b. 60 ° avec le styrene et l'a~tate de vinyle. Pour quelques unes des copolym6risations 6tudi~es, on a constat6 que le far de changer de solvent du benz~ne au dim6thylformamide n'avait pas d'effet sur les compositions des copolym~res. Les rapports de r6activit6s des monom~:res ont 6t6 d6termin6s pour la plupart des syst6mes; les diff6rentes r6activit6s des fumarates vis-a-vis du radical croissant d'ac6tate de vinyle ont 6t6 compar~es entre elles. Sommario---Si sono impiegati dei campioni di dietil-, etil-n-esil-, e di-n-esil fumarati con il gruppo 1'~C, per lo studio a 60 ° deUe relative copolimerizzazioni radicaliche con stirene e acetato di vinile. Con alcune delle copolimerizzazioni, cambiando il diluente da benzene a dimetilformamide non si ha alcun effetto sulla composizione dei copolimeri. Si sono calcolati i rapporti di reattivitb, per la magg~or parte dei sistemi. Si sono fatti dei raffronti tra le reattivittt degli esteri di fumarati nei confronti del radicale di acetato di polivinile.
Zusammenfassung--Es wurden t~C-markiert¢ Proben von Di-~thyl-, .~thyl-n-hexyl- und Di-nhexylfumaraten f/.ir die bei 60 ° durchgeffihrte Untersuchung ihrer radikalischen Copolymerisation mit Styrol und mit Vinylacetat verwendet. Ein Wechsel des Verdfinnungsmittels yon Benzol zu Dimethylformamid hatte bei einigen Copolymerisationen auf die Zusammensetzung der Copolymeren keinen EinflufL Fi3r die meisten Systeme wurden die Monomerreaktivit/itsverh~.Itnisse berechnet; die ReaktivitS.ten der Fumaratester gegenfiber dem Polyvinylacetat-Radikal wurden miteinander verglichen.
RADICAL REACTIONS INVOLVING ESTERS OF FUMARIC ACID--I COPOLYMERIZATIONS J. C. BEVINGTON, M. JOHNSON a n d J. P. Sm~EN* Department of Chemistry, The University, Lancaster, England
(Received 22 January 1971) Abstract--x4C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies at 60~ of their radical copolymerizations with styrene and with vinyl acetate. Changing the diluent from benzene to dimethylformamide in some of the copolymerizatious had no effect on the compositions of the copolymers. Monomer reactivity ratios have been calculated for most of the systems; comparisons have been made of the reactivities of the fumarate esters towards the polyvinyl acetate radical. THIS paper is the first of a series concerned with a general e x a m i n a t i o n of the behaviour of fumarate esters in various radical reactions. 14C-labelled samples of diethyl-, ethyl n-hexyl- and di-n-hexyl fumarates have been used in studies of their radical copolymerizations with styrene a n d with vinyl acetate. Tracer techniques can give accurate m e a s u r e m e n t s of copolymer compositions even when the copolymers c o n t a i n only very small a m o u n t s of one o f the m o n o m e r s . (1) I n this work, some of the copolymers c o n t a i n e d only a few fumarate ester units so that the use of the tracer m e t h o d was particularly advantageous.
EXPERIMENTAL l"C-diethyl fumarate was prepared by refluxing fumaric acid (116 g containing 0.05 me of t4C-fumaric acid) for 14 hr with absolute ethanol (148 g), benzene (380ml)and concentrated sulphuric acid (16 g). The reaction mixture was allowed to cool and then poured with stirring into water (1 1.). The benzene layer was separated and the aqueous layer extracted once with ether. The combined benzene and ether extracts were neutralized with sodium bicarbonate solution, washed with water and dried over anhydrous magnesium sulphate. This solution was finally filtered and the labelled monomer was isolated and purified by fractional distillation under a reduced pressure of nitrogen; the ester was redistilled immediately before use. t4C-di-n-hexyl fumarate was prepared from fumaric acid (93 g containing 0.045 mc of t4C-fumadc acid) in a manner similar to that used for t4C-diethyl fumarate. 14C-ethyl n-hexyl fumarate was prepared by the esterification of fumaric acid (29 g containing 0" 1 me of t4C-fumaric acid) with a mixture containing equimolar amounts of ethanol (17 g) and n-hexanol (38 g). The resulting mixture of esters was separated by fractionation under reduced pressure of nitrogen. Gas-liquid chromatography was used to monitor the separation and an NMR spectrum of the final material showed that the fraction collected was the mixed ethyl n-hexyl ester. Styrene and vinyl acetate were commercial products which were purified in the usual manner. Polymerizations were carried out at 60° in sealed dilatometers in the complete absence of air and were allowed to proceed to about 5 per cent conversion. Benzene was used as diluent in all cases except for some styrene copolymerizations with di-n-hexyl fumarate which were carried out in dimethylformamide. Sixty per cent solutions of monomers in the diluent were used with benzoyl peroxide at 2 g/l. as initiator for the styrene/fumarate systems and at 1 g/l. for the vinyl acetate/ fumarate systems. Petroleum ether (b.p., 40-60°) was used as precipitant for polymers containing diethyl fumarate and methanol for those containing ethyl n-hexyl fumarate and di-n-hexyl fumarate. Tests showed that * Present address: Messrs. Henry Cooke & Co. (1932)Ltd., Beetham, Milnthorpe, Westmorland. 1147
Radical Reactions Involving Esters of Fumaric Acid--I
I 151
0 -0.4 -0-8 u. "7
-1-2 -I.6
-2"0
-2.4
-1
0
I
2
3
4
5
6
7
f/F 2
FtG. 5. Fineman and Ross plot for copolymerizations in benzene of vinyl acetate (monomer 1) and diethyl fumarate (monomer-2). TABLE 2. MONOMER REACTIVITY RATIOS FOR COPOLYMERIZATIONS WITH VINYL ACETATE (.MONOMER--l)
Monomer--2
Reactivity ratios
Diethyl fumarate Di-n-hexyl fumarate Ethyl n-hexyl fumarate
rl
r2
0"031 0.031 0" 034
0.32 0.27 0" 26
Errors in r~ = ± 0.005 and in r2 = ± 0"02. DISCUSSION The monomer reactivity ratios obtained in this work for styrene/diethyl fumarate (rl = 0.35, r2 -- 0.005) and vinyl acetate/diethyl fumarate (rl = 0.031, r 2 = 0-32) are somewhat different from those in the literature (5) (r~ = 0.30, r2 = 0.070 for the styrene system and rl -- 0.01 I, r2 = 0"444 for the vinyl acetate system). However, the literature values were based on the results obtained from only two monomer feeds for each system and indeed the previous workers recognized that their values might not be very reliable. It is thought that the curvature of the Fineman and Ross plots for the copolymefizations of styrene with di-n-hexyl fumarate and ethyl n-hexyl fumarate is due to a penultimate group effect,(6) but since the curvature is so small it would be very difficult to obtain a quantitative measurement of such an effect.(~) Changing the diluent from benzene to dimethylformamide in the styrene/di-n-hexyl fumarate system had very little effect on the compositions of the copolymers. This was in spite of the two non-polar n-hexyl groups in the fumarate which might be expected to protect the double bond in the monomer from attack by radicals differently in the two solvents by adopting configurations in the non-polar solvent (benzene) different from those adopted in the polar solvent (dimethylformamide). Lewis and coworkers (8) and Price and Walsh (9) have reported previously that monomer reactivity E.P,I. 718--t
1152
J.C. BEVINGTON, M. JOHNSON and J. P. SHEEN
ratios are independent of the polarity of the reaction medium and the present results are in agreement with this view. From the values of rl in Table 2 for the copolymerizations of vinyl acetate with the fumarate esters, it was possible to compare the reactivities of the fumarate esters towards the polyvinyl acetate radical. All three fumarate esters have approximately the same value of l/rl indicating that the length of the alkyl ester group has little effect upon the reactivity of the fumarates towards the polyvinyl acetate radical. Lack of marked dependency of the reactivity of such monomers on alkyl group size seems to be a general rule in free radical copolymerizations. It has, for example, been shown that the chain length of the acyl group has no effect on the reactivity of vinyl esters in copolymerizationsClO.~l~ and similar reactivities of many methacrylate esters towards polymer radicals have been reported. ~12~ The scheme due to Alfrey and Price ~13~was applied to the results of the vinyl acetate copolymerizations to obtain values of the parameters Q and e for the fumarate esters. It was calculated that all the fumarate esters had values of Q which were close to 0.5 and values of e close to 2.0. These values do not agree closely with those in the literature C~4~ for diethyl fumarate (Q = 0-61, e = 1.25). This is not altogether unexpected since Q and e values calculated for systems where the product r~r2 is very small, as is the case for all the systems investigated here, are invariably subject to large errors. In spite of this disagreement, it is apparent that fumarate esters have large positive e values indicating electron-deficient carbon-carbon double bonds in the monomers. Both mesomeric and inductive effects tend to make the fumarate double bond electron-deficient. A high positive e value has been obtained for the related compound, maleic anhydride3 t4~ The fumarate esters also have fairly high Q values due to resonance stabilization of fumarate-ended chain radicals, c5~ In all the systems studied in this work, over a fairly wide range of monomer feeds, copolymers were formed in which the two different monomer units tended to alternate along the polymer chains. This is of course a general phenomenon for systems where one monomer reactivit3.' ratio is quite small and the other is close to zero. For the copolymerizations of the fumarates with vinyl acetate, r2 is appreciably greater than rt; this result indicates that, for feeds containing comparable concentrations of vinyl acetate and fumarate ester, there is a much greater tendency for the copolymer to contain adjacent fumarate units than for it to contain adjacent vinyl acetate units. Acknowledgement--We thank the Esso Petroleum Company Limited for the award of a Re.search
Studentship to J.P.S. REFERENCES (1) (2) (3) (4) (5)
G. Ayrey, Chem. Rev. 63, 645 (1963). J. C. Bevington and M. Johnson, Makromolek. Chem. 87, 66 (1965). J. C. Bevington and T. Ito, Trans. Faraday Soc. 64, 1329 (1968). M. Fineman and S. D. Ross, J. Polym. ScL 5, 259 (1960). F. M. Lewis and F. R. Mayo, J. Am. chem. Soc. 70, 1533 (1948). (6) W. G. Barb, J. Polym. ScL 11, 117 (1953). (7) M. Berger and I. Kuntz, J. Polym. Sci. A2, 1687 (1964). (8) F. M. Lewis, C. Walling, W. Cummings, E. R.. Briggs and F. R. Mayo, J. Am. chem. Soc. 70, 1519 (1948). (9) C. C. Price and J. 13. Walsh, J. Polym. ScL 6, 239 (1951). (10) L. P. Witnauer, N. Watkins and W. S. Port, J. Polym. ScL 20, 213 (1956).
Radical Reactions Involving Esters of Fumaric Acid--I (11) (12) (13) (14)
1153
J. C. Bevington and M. Johnson, Europ. Polym. J. 4, 669 (1968). J. C. Bevington and B. W. Malpass, Europ. Polym. J. 1, 19 (1965). T. Alfrey, Jr. and C. C. Price, J. Polym. Sci. 2, 101 (1947). L. J. Young,./. Polym. Sci. 54, 411 (1961).
R6sum6---On a utilis6 des ~chantillons marquis au 1~C de fumarates de di6thyle d'6thyte-n-hexyle et de di-n-hexyle, pour 6tudier leurs copolym6risations radicalaires b. 60 ° avec le styrene et l'a~tate de vinyle. Pour quelques unes des copolym6risations 6tudi~es, on a constat6 que le far de changer de solvent du benz~ne au dim6thylformamide n'avait pas d'effet sur les compositions des copolym~res. Les rapports de r6activit6s des monom~:res ont 6t6 d6termin6s pour la plupart des syst6mes; les diff6rentes r6activit6s des fumarates vis-a-vis du radical croissant d'ac6tate de vinyle ont 6t6 compar~es entre elles. Sommario---Si sono impiegati dei campioni di dietil-, etil-n-esil-, e di-n-esil fumarati con il gruppo 1'~C, per lo studio a 60 ° deUe relative copolimerizzazioni radicaliche con stirene e acetato di vinile. Con alcune delle copolimerizzazioni, cambiando il diluente da benzene a dimetilformamide non si ha alcun effetto sulla composizione dei copolimeri. Si sono calcolati i rapporti di reattivitb, per la magg~or parte dei sistemi. Si sono fatti dei raffronti tra le reattivittt degli esteri di fumarati nei confronti del radicale di acetato di polivinile.
Zusammenfassung--Es wurden t~C-markiert¢ Proben von Di-~thyl-, .~thyl-n-hexyl- und Di-nhexylfumaraten f/.ir die bei 60 ° durchgeffihrte Untersuchung ihrer radikalischen Copolymerisation mit Styrol und mit Vinylacetat verwendet. Ein Wechsel des Verdfinnungsmittels yon Benzol zu Dimethylformamid hatte bei einigen Copolymerisationen auf die Zusammensetzung der Copolymeren keinen EinflufL Fi3r die meisten Systeme wurden die Monomerreaktivit/itsverh~.Itnisse berechnet; die ReaktivitS.ten der Fumaratester gegenfiber dem Polyvinylacetat-Radikal wurden miteinander verglichen.