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Radical polymerizations involving esters of vinyl alcohol—I Reactivities of monomers towards the benzoyloxy radical
European Polymer Journal, 1968. Vol. 4, pp. 373-375.
Pergamon Press.
Printed in England.
RADICAL POLYMERIZATIONS INVOLVING ESTERS OF VINYL ALCOHOL--I. REACTIVITIES OF M O N O M E R S TOWARDS THE BENZOYLOXY RADICAL J. C. BEVINGTON and M. JOHNSON Department of Chemistry, The University, Lancaster (Received 3 January 1968)
Abstract--l*C-benzoyl peroxide has been used at 60° to initiate polymerizations of vinyl formate, propionate, butyrate, benzoate and phenyl acetate at various concentrations in benzene. The relative numbers of benzoyloxy and phenyl end-groups in the various polymers have been determined; these numbers have been used to deduce the relative reactivities of the monomers towards the benzoyloxy radical. COMPARISONS have been made of the reactivities of many monomers towards the benzoyloxy radical, a) One such study m involved esters of methacrylic acid; it showed that there may be significant differences between the reactivities of monomers which are closely related structurally. A similar study is now reported for esters of vinyl alcohol; it forms part of a more general examination of the behaviour of these monomers during radical polymerizations. The experimental procedures have been described already, m In the present work, two sets of polymers were prepared using x4C-benzoyl peroxide as initiator at 60°; in the one case, the labelling was confined to the benzene rings and, in the other, to the carboxyl carbon atoms. Comparisons of the results for the two sets leads to determination of the ratios of benzoyloxy and phenyl end-groups in the polymers. This information is used to examine the competition between the reactions C, Hs" CO. O- -->Cell5 • + CO2 velocity constant = kt Cells" CO. O" + CH, : CHX--> C6H5" CO. O- CH,. CHX. velocity constant = k.. A fraction x is defined as no. of benzoyloxy end-groups (no. of benzoyloxy] (no. of phenyl] end-groups ] + k end-groups ] The values of x are determined by the end-group analysis for polymers prepared with various values of [M]. On certain justifiable assumptions m 1/x ----- 1 q- k,/k, [M]
where [M] is the concentration of monomer prevailing during polymerization. The ratio k~/k2 can therefore be determined and the relative values of k2 for various 373
374
J.C. BEVINGTON and M. JOHNSON
m o n o m e r s can therefore be found. Extension o f the w o r k to cover a range of temperatures leads to values o f (E1--E,z) so that differences in E2 for various m o n o m e r s can be recognized.
EXPERIMENTAL Preparation of the labelled samples of benzoyl peroxide has been described ~3~. The monomers (Eastman Kodak) were purified by fractionation at reduced pressure in nitrogen, pre-polymerization and distillation in vacuum. Polymerizations were performed in vacuum dilatometers at 60°. Benzene was used as diluent to vary monomer concentration. Rates of polymerization were reproducible so that experiments with the two types of labelled peroxide were strictly comparable. Polymers were recovered by precipitation in n-bexane and purified by reprecipitation from benzene solutions. Tests showed that the procedure was satisfactory for removal from the polymers of unreacted labelled initiator. Materials were assayed by gas counting. RESULTS AND DISCUSSION Plots of 1/x against 1/[M] are s h o w n in Fig. 1. T h e values o f kl/k., a n d the relative values o f k2 are given in T a b l e 1. It is a p p a r e n t that the reactivities of the esters o f vinyl alcohol differ significantly a l t h o u g h the structural differences between the m o n o m e r s are at sites not close to the olefinic b o n d . The difference between vinyl p r o p i o n a t e a n d vinyl b u t y r a t e is quite pronounced. It has been shown ~2' that there is for m a n y m o n o m e r s a general correlation between the relative reactivity t o w a r d s the b e n z o y l o x y radical a n d the value o f e in the Q a n d e scheme.C"~ It will be shown in a later p a p e r t h a t the present results m a y be a guide when assigning, f r o m c o p o l y m e r i z a t i o n data, values o f e for m o n o m e r s .
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~
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1.25 I'o00
0-2
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'
(Monomer conch.,
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I
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,
mole/t ) -t
FIo. 1. Plot of l/x against I/[M] for polymerizations at 60 °. x = (no. of benzoyloxy end-groups)/(sum of numbers of benzoyloxy and phenyl end-groups) O and line A - - vinyl formate • and line B m vinyl benzoate and line C - - vinyl propionate ® and line D ~ vinyl phenylacetate and line E m vinyl butyrate
Radical Polymerizations Involving Esters of Vinyl Alcohol--I
375
TABLE i. REACTIVITLES OF MONOMERS TOWARDS THE BENZOYLOX'Y
RADICALA T 60 ° Monomer Vinyl formate Vinyl acetate( *' Vinyl propionate Vinyl butyrate Vinyl phenylacetate Vinyl benzoate Styrene m
kt/k~, in mole/l
Relative value of k,
1- 33 i" 10 1" 00 0" 46 0.61 1.16 0- 4
0" 30 0" 36 0" 40 0" 87 0.65 0.34 i" 00 (standard)
Acknowledgement--The work described in this paper was performed with the aid of a research grant from the Science Research Council.
REFERENCES (I) See, for example, J. C. Bevington, Radical Polymerization, p. 41, Academic Press, London (1961). (2) J. C. Bevington, D. O. Harris and M. Johnson, Europ. Polym. J. 1, 235 (1965). (3) C. A. Barson and J. C. Bevington, Tetrahedron 4, 147 (1958). (4) C. A. Barson, J. C. Bevington and D. E. Eaves, Trans. Faraday Soc. 54, 1678 (1958). (5) J. C. Bevington, Proc. R. Soc. A239, 420 (1957). (6) T. Alfrey, Jr. and C. C. Price, J. Polym. Sci. 2, I01 (1947). R4sum&-Du peroxyde de benzoyle marqu% au uC a ~t~ utilis6 ~t 60" pour amorcer la polymdrisation des monom&es suivants darts des solutions benz~niques de concentrations vari~es: formiate, propionate butyrate, benzoate et ph~nylac~tate de vinyle. On a d&ermin~ les nombres relatifs des groupes benzoyloxy et ph~nyle en bout de chaine des diff~rents polyrn6res obtenus. On en a d6duit les r~activiti,% relatives des monom~res vis4t-vis du radical benzoyloxy. Sommario--II perossido di t( C-benzoile % stato impiegato a 60 ° per avviare la polimeri~TaTione del formiato, propionato, butirrato, benzoato vinilici e dell'acetato fenilico a varie concentrazioni in benzene. E' stato determinato il numero relativo dei radicali benzoilossidici le fenilici; tali humeri sono stati impiegati per dedurre la reattivit/i relativa dei monomeri verso il radicale benzoilossidico. Zusammeafassung--uC-Benzoylperoxid wurde als Initiator for Polymerisationen von Vinylformat, -propionat, -butyrat, -benzoat und -phenylacetat bei 60 ° und verschiedenen Konzentrationen in Benzol verwendet. Die relative Zahl yon Benzoyloxy- und Phenyl-Endgruppen wurde in den verschiedenen Polymeren bestimmt. Mit Hilfe dieser Zahlen wurden die relativen Reaktivit~iten der Monomeren gegenLiber dem Benzoyloxy-Radikal abgeleitet.
e o W,,'MeR
4/3.--n
Pergamon Press.
Printed in England.
RADICAL POLYMERIZATIONS INVOLVING ESTERS OF VINYL ALCOHOL--I. REACTIVITIES OF M O N O M E R S TOWARDS THE BENZOYLOXY RADICAL J. C. BEVINGTON and M. JOHNSON Department of Chemistry, The University, Lancaster (Received 3 January 1968)
Abstract--l*C-benzoyl peroxide has been used at 60° to initiate polymerizations of vinyl formate, propionate, butyrate, benzoate and phenyl acetate at various concentrations in benzene. The relative numbers of benzoyloxy and phenyl end-groups in the various polymers have been determined; these numbers have been used to deduce the relative reactivities of the monomers towards the benzoyloxy radical. COMPARISONS have been made of the reactivities of many monomers towards the benzoyloxy radical, a) One such study m involved esters of methacrylic acid; it showed that there may be significant differences between the reactivities of monomers which are closely related structurally. A similar study is now reported for esters of vinyl alcohol; it forms part of a more general examination of the behaviour of these monomers during radical polymerizations. The experimental procedures have been described already, m In the present work, two sets of polymers were prepared using x4C-benzoyl peroxide as initiator at 60°; in the one case, the labelling was confined to the benzene rings and, in the other, to the carboxyl carbon atoms. Comparisons of the results for the two sets leads to determination of the ratios of benzoyloxy and phenyl end-groups in the polymers. This information is used to examine the competition between the reactions C, Hs" CO. O- -->Cell5 • + CO2 velocity constant = kt Cells" CO. O" + CH, : CHX--> C6H5" CO. O- CH,. CHX. velocity constant = k.. A fraction x is defined as no. of benzoyloxy end-groups (no. of benzoyloxy] (no. of phenyl] end-groups ] + k end-groups ] The values of x are determined by the end-group analysis for polymers prepared with various values of [M]. On certain justifiable assumptions m 1/x ----- 1 q- k,/k, [M]
where [M] is the concentration of monomer prevailing during polymerization. The ratio k~/k2 can therefore be determined and the relative values of k2 for various 373
374
J.C. BEVINGTON and M. JOHNSON
m o n o m e r s can therefore be found. Extension o f the w o r k to cover a range of temperatures leads to values o f (E1--E,z) so that differences in E2 for various m o n o m e r s can be recognized.
EXPERIMENTAL Preparation of the labelled samples of benzoyl peroxide has been described ~3~. The monomers (Eastman Kodak) were purified by fractionation at reduced pressure in nitrogen, pre-polymerization and distillation in vacuum. Polymerizations were performed in vacuum dilatometers at 60°. Benzene was used as diluent to vary monomer concentration. Rates of polymerization were reproducible so that experiments with the two types of labelled peroxide were strictly comparable. Polymers were recovered by precipitation in n-bexane and purified by reprecipitation from benzene solutions. Tests showed that the procedure was satisfactory for removal from the polymers of unreacted labelled initiator. Materials were assayed by gas counting. RESULTS AND DISCUSSION Plots of 1/x against 1/[M] are s h o w n in Fig. 1. T h e values o f kl/k., a n d the relative values o f k2 are given in T a b l e 1. It is a p p a r e n t that the reactivities of the esters o f vinyl alcohol differ significantly a l t h o u g h the structural differences between the m o n o m e r s are at sites not close to the olefinic b o n d . The difference between vinyl p r o p i o n a t e a n d vinyl b u t y r a t e is quite pronounced. It has been shown ~2' that there is for m a n y m o n o m e r s a general correlation between the relative reactivity t o w a r d s the b e n z o y l o x y radical a n d the value o f e in the Q a n d e scheme.C"~ It will be shown in a later p a p e r t h a t the present results m a y be a guide when assigning, f r o m c o p o l y m e r i z a t i o n data, values o f e for m o n o m e r s .
225t ,oo
1.75
~
C
7<
1.25 I'o00
0-2
o.4
'
(Monomer conch.,
o.6
I
o! 8
,
mole/t ) -t
FIo. 1. Plot of l/x against I/[M] for polymerizations at 60 °. x = (no. of benzoyloxy end-groups)/(sum of numbers of benzoyloxy and phenyl end-groups) O and line A - - vinyl formate • and line B m vinyl benzoate and line C - - vinyl propionate ® and line D ~ vinyl phenylacetate and line E m vinyl butyrate
Radical Polymerizations Involving Esters of Vinyl Alcohol--I
375
TABLE i. REACTIVITLES OF MONOMERS TOWARDS THE BENZOYLOX'Y
RADICALA T 60 ° Monomer Vinyl formate Vinyl acetate( *' Vinyl propionate Vinyl butyrate Vinyl phenylacetate Vinyl benzoate Styrene m
kt/k~, in mole/l
Relative value of k,
1- 33 i" 10 1" 00 0" 46 0.61 1.16 0- 4
0" 30 0" 36 0" 40 0" 87 0.65 0.34 i" 00 (standard)
Acknowledgement--The work described in this paper was performed with the aid of a research grant from the Science Research Council.
REFERENCES (I) See, for example, J. C. Bevington, Radical Polymerization, p. 41, Academic Press, London (1961). (2) J. C. Bevington, D. O. Harris and M. Johnson, Europ. Polym. J. 1, 235 (1965). (3) C. A. Barson and J. C. Bevington, Tetrahedron 4, 147 (1958). (4) C. A. Barson, J. C. Bevington and D. E. Eaves, Trans. Faraday Soc. 54, 1678 (1958). (5) J. C. Bevington, Proc. R. Soc. A239, 420 (1957). (6) T. Alfrey, Jr. and C. C. Price, J. Polym. Sci. 2, I01 (1947). R4sum&-Du peroxyde de benzoyle marqu% au uC a ~t~ utilis6 ~t 60" pour amorcer la polymdrisation des monom&es suivants darts des solutions benz~niques de concentrations vari~es: formiate, propionate butyrate, benzoate et ph~nylac~tate de vinyle. On a d&ermin~ les nombres relatifs des groupes benzoyloxy et ph~nyle en bout de chaine des diff~rents polyrn6res obtenus. On en a d6duit les r~activiti,% relatives des monom~res vis4t-vis du radical benzoyloxy. Sommario--II perossido di t( C-benzoile % stato impiegato a 60 ° per avviare la polimeri~TaTione del formiato, propionato, butirrato, benzoato vinilici e dell'acetato fenilico a varie concentrazioni in benzene. E' stato determinato il numero relativo dei radicali benzoilossidici le fenilici; tali humeri sono stati impiegati per dedurre la reattivit/i relativa dei monomeri verso il radicale benzoilossidico. Zusammeafassung--uC-Benzoylperoxid wurde als Initiator for Polymerisationen von Vinylformat, -propionat, -butyrat, -benzoat und -phenylacetat bei 60 ° und verschiedenen Konzentrationen in Benzol verwendet. Die relative Zahl yon Benzoyloxy- und Phenyl-Endgruppen wurde in den verschiedenen Polymeren bestimmt. Mit Hilfe dieser Zahlen wurden die relativen Reaktivit~iten der Monomeren gegenLiber dem Benzoyloxy-Radikal abgeleitet.
e o W,,'MeR
4/3.--n