- Email: [email protected]
Evaluation of relative reactivities of vinyl monomers towards t-butoxy radical by means of spin trapping technique
Le~e~
The different solvent sorption behaviour of the three polymers may be due to several factors. Some X-ray diffraction work currently in progress has shown that, as expected, the PVC/PVAC copolymer appears to be virtually amorphous while the low temperature polymerized PVC has the highest crystallinity. Crystallinity is expected to have a significant effect on solvent sorption since the polymer chains are packed more closely in crystalline regions thus restricting solvent penetration. The results obtained for the two PVC homopolymers may be explained on thisbasis. In the copolymer chain packing is also reduced by the bulky acetate groups present and the decrease in polar forces between chains caused by the replacement of chlorine atoms by these groups. Heat treatment changed the solvent sorption behaviour of the two homopolymers (Figures la and lc) but had no significant effect on the solvent sorption of the copolymer (Figure lb). For PVC 2 (Figure la), the quenched sample, in which order would be expected to be lowest, absorbs solvent most rapidly. The sample heat treated at 70°C (i.e. below the glass transition temperature of the polymer) absorbs solvent slightly more slowly, but the weight gain reaches the same equilibrium value. The sample heat treated at 110°C (i.e. above the glass transition temperature) absorbs solvent more slowly and reaches a lower equilibrium value. Also the solvent sorption curve is S-shaped in the latter case, while for the quenched sample and the sample heat treated at 70°C the initial part of the plot of weight gain versus tl/2fl appears linear before the equilibrium value is reached. The effect of heat treatment on the solvent sorption behaviour of the low temperature polymerized PVC appears 20
to be similar to that of PVC 2, but the rates of solvent sorption were much slower and none of the experiments were continued to equilibrium. The above results can be explained tentatively as follows. Heat treatment is considered to have no effect on solvent sorption behaviour of the copolymer either because the rapid uptake of solvent is governed only by the presence of acetate groups, or because the polymer structure is too irregular for crystallization to occur. For the two homopolymers results were similar to those reported by Illers 2. Quenching would be expected to remove order, and actually resulted in more rapid solvent sorption in each case. The different solvent sorption behaviour for samples heat treated above and below Tg has been attributed to changes in crystaUinity and free volume respectively2; further evidence (from density measurements, thermal analysis and X-ray diffraction) will be presented later. Figures 3 and 4 illustrate the effect of time of heat treatment at 1 IO°C on solvent sorption and provide some information about the rate of the crystallization or ordering process occurring. These results suggest that structural changes occur within quite short times. However, it is necessary to examine the effects of short term heat treatment in more detail.
Acknowledgement The authors are grateful to the Science Research Council for the award of a Research Studentship to A.G. A. Gray Present address: BP Chemicals International Ltd. Sully. Penarth. Glamorgan. UK and Marianne Gilbert Institute of Polymer Technology, Loughborough University of Technology, Loughborough, Leics LEt1 3TU, UK (Received 4 February 1975)
0 c~
References l
0
Figure 3
I
I
m
t
I
I
IO 18 26 Time (at I I O ° C ( h ) Solvent uptake for PVC 2 immersed 4 h in toluene as a
function of heat treatment time a t 1 1 0 ° C
Evaluation of relative reactivities of vinyl monomers towards t-butoxy radical by means of spin trapping technique
Szwarc I developed a concept of'methyl aft'mity', i.e. a measure of relative reactivities of various compounds, including vinyl monomers, towards the methyl radical produced by the thermal decomposition of diacetyl peroxide in iso-octane. To determine the relative reactivities, the following competitive reactions were used:
E
"g
1 Blackadder,D. A. and Vincent, P. I. Polymer 1974, 15, 2 2 lUers,K. H.Makromol. Chem. 1969, 127, 1 3 Pezzin, G. Plasticsand Polymers 1969, 37,295
2
E: C~
I
I
1
I
I
I
IO IB 26 Time a t I I O ° C ( h ) Figure 4 Solvent uptake for low temperature polvmerized PVC immersed 72 h in tolueneas a function of heat treatment time at
CH 3- + C8H18k--~ 1 CH4 + • C8H17
(1)
CH 3- + M k2> CH3-M-
(2)
2
110°C
where M represents a vinyl monomer. It has also been
P O L Y M E R , 1975, Vol 16, May
389
Letters
pointed out that the observed relative reactivities (kz/kl) of vinyl monomers towards the methyl radical correlated well with those towards a polystyryl radical 2. Subsequently Bevington and his coworkers 3'4 attempted to evaluate the reactivity (k3/k4) of the benzoyloxy radical towards vinyl monomers by using 14Cqabelled benzoyl peroxide. In this case, the reactivities were determined by the 14C-labelled end group analysis of the polymers obtained as the result of the following competitive reactions: C6H5COO" k3' C6H5" + CO2
(3)
C6HsCOO. + M k4 > C6HsCOO-M-
(4)
C6H5. + Mk-.~ 5 C6H5_ M.
(5)
They also emphasized that polar effects were more important in the reaction of the benzoyloxy radical than that of methyl radical with the monomers 4. Although order of reactivity to the methyl radical towards vinyl monomers was confirmed to be similar to that of ethyl s, n-prow1 s and phenyl radicals 6'7, no data with respect to the reactivity of the oxy radicals except benzoyloxy radical towards vinyl monomers were found. Recently, we have succeeded to trap with 2-methyl-2nitrosopropane (BNO) as a spin trapping agent, the intermediate radical species (I and II) produced from the reactions of a number of vinyl and a-methyl-vinyl monomers having X substituents with the t-butoxy radical produced by the thermal decomposition of di-t-butyl peroxalatea: t- C 4 H 9 0 - C H 2 - C - Y
I
O. (VI)
Figures 1 and 2, for example, show the e.s.r, spectra of the reaction mixtures of styrene and methyl methacrylate, respectively, with di-t-butyl !?eroxalate in the presence of BNO without p-xylene at 25vC. From the e.s.r, spectrum of Figure 1, it is seen that only a nitroxide was produced and assigned as IV(AN = 14.2 G, A#I_I= 2.3 G and A~I (2H) = 0.6 G) in which X and Y are C6H5 and H, respectively. However, Figure 2 appears to be the combined spectra of the nitroxides IV (X=COOCH3, Y=CH3; A N = 14.9 G) and V(X=COOCH3;A N = 14.8 G, Aft (2H) = 9.8 G). When reactions are carried out in p-xylene, of course, the e.s.r, spectrum due to the nitroxide VI (AN = 15.0 G, Aft (2H) = 7.5 G) is superimposed on the respective spectra of Figures I and 2. Therefore, if the relative concentrations of the nitroxides ([IV], IV] and [VII ) produced are determined from the areas of the peaks due to the respective nitroxides in the absorption spectra obtained from integration of the observed first derivative e.s.r, spectra, the relative reactivities (k6/k8 and k7/ks) of the t-butoxy radical towards the monomers can be evaluated by using the following equations [IV] _ k 6
[M]
[VII
k8 [CH3-q~-CH3]
[V]
k7
(9)
[M]
(io)
[VI] k8 [CH3-q~-CH3]
CH2=C-CH2
X (I; Y=H, CH3)
CH3-~-CH2-1~-CH4H9-t
~SG~
X (II)
When decomposition is carried out in p-xylene in the presence of a monomer, the t-butoxy radical produced participates in competitive reactions: t-C4H90"
+
M k6~ t-C4H90-M-
(6) Figure 1
t-C4HgO- + M kT, t.C4HgOH + M' (II)
(7)
E.s.r. spectrum of the reaction mixture of styrene and dit-butyl peroxalate in the presence of BNO ~10 G~
k8 t-C4H90" + CH3--~-CH3--"* t-C4H9OH + CHa-~-CH2 (III) (8) A
If this reaction is performed in the presence of BNO, the radicals (I, II and III) produced react readily with BNO to give the respective nitroxides: t- C4H90-CH2-CY-N-C4H 9- t I I X O(IV) CH2=C-CH2-1~-C4 Hg-t X
O-
(v)
390
POLYMER, 1975, Vol 16, May
Figure 2
E.s.r. spectrum of the reaction mixture of methyl methacrylate and di-tJoutyl peroxalate in the presence of BNO; the peaks A are due to t-butyl-t-butoxynitroxide which is obtained from the reaction of BNO with t-butoxy radical
Letters Table I Relative reactivities of vinyl monomers towards t-butoxy radical at 25°C: comparison with those towards benzoyloxy, methyl and phenyl radicals t-C4HgOMonomer
e
O
k6/k 8
k7 /k 8
Isobutyl vinyl ether ¢¢-Methylstyrene t-Butyl vinyl sulphide Styrene Vinyl acetate Methyl methacrylate Methyl isopropenyl ketone Methyl acrylate Methyl vinyl ketone
--1.77 --1.27 --1.1 --0.8 -0.22 0.4 0.53 0.6 0.68 0.81 1.2
0.023 0.98 0.32 1.0 0.026 0.74 1.49 0.52 0.69 1.12 0.60
9.06 6.90 7.43 29.8 0.28 1.73 2.47 1.54 2.68 0.71 0.52
. <0.05 . -1.09 0.74 --1.56 --
Methacrylonitrile
Acrylonitrile
C6H5COO -a
CH~b
C6H5 "c
k 4 (rel. value)
k2/k 1
k 5 (rel. value)
.
.
.
.
.
-
926
. 1.0 0.36 0.12 ---~0.05
792 31 1440 -1030 1900 2120 1730
1.24 1.0 ( 1.0) 0.23 (;~0.08) 1.78 ( 1.7) -0.78 --
2.46 -- (0.8)
aData of Bevington etaL3,4 at 60°C bData of Szwarc l at 65°C CData of Pryor et aL ?, who determined these values through tritium abstraction reaction of a phenyl radical, produced by phenyl azotriphenylmethane, with tritiated pentanethiol at 60°C, as the standard. The values in parentheses indicate the data of Bevington eta/. 6 who used hydrogen abstraction reaction from dimethylformamide by a phenyl radical, produced by decarboxylation of benzoyloxy radical, as the standard
methacrylonitrile. This observation seems to be related to that found for the benzoyloxy radical 4, and to provide important information on the initiation mechanism of radical polymerization of vinyl monomers with the oxy radical.
[ M ] / [ C H 3 - ¢ - C H 3] x 10 2
300
3-0
60
I
9.0
;
i
Tsuneyuki Sato and Takayuki Otsu Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Osaka 558, Japan (Received 22 January 1975; revised 11 February 1975)
2"0 >
References 1 2 3 4
I'0
I
O
I
I.O
[M]
2-0 3-0 / [ C H § ¢ - C H 3]
4.0
Figure 3 Plots of [ I V ] / [ V l ] with [ M ] / [ C H 3 - - ~ - - C H 3] : ~, Methyl acrylate, [~, styrene; O, acrylonitrile
5 6 7 8
Szwarc, M. J. Polym. ScL 1955, 16,367 e.g.,Otsu, T. Progr. Polym. ScLJapan 1971, 1, 1 Bevington, J. C. and Brooks, C. S. J. Polym. Sci. 1956, 22,257 Bevington, J. C. 'Radical Polymerization', Academic Press, London, 1961 Staid, J. and Szwarc, M. J. Am. Chem. Soc. 1956, 78, 3322 Bevington, J. C. and Ito, T. Trans. Faraday Soc. 1968, 64, 1329 Pryor, W. A. and Fiske, T. R. ibid. 1969, 65, 1865 Sato, T. and Otsu, T. Makromol. Chem. in press
Con ference A nnouncemen t
Polymer Physics where [M] and [CH3-q~-CH3] are initial concentrations of monomer and p-xylene, respectively. Figure 3 shows the plots of [IV] / [VI] with [M] / [CH3-~b-CH3] for the reactions of di-t-butyl peroxalate with styrene, methyl acrylate and acrylonitrile in p-xylene in the presence of BNO at 25°C. As can be seen from this Figure, linear relationships are obtained, and the relative reactivities of these monomers towards the t-butoxy radical are determined from their slopes. The results are summarized in Table 1, in which the relative reactivities of vinyl monomers towards methyl, phenyl and benzoyloxy radicals are also indicated. It is of interest that the relative reactivities (k6/ks) of the monomers towards addition of the t-butoxy radical are related more with their e values than their Q values, indicating that the polar effect is more important than resonance effect, similar to the case of the benzoyloxy radical 4. In connection with these results, it is also noted that the tbutoxy radical can easily abstract the allylic hydrogen ofc~methyl-vinyl monomers such as methyl methacrylate and
Shrivenham, Wilts, 2 4 - 2 6 September 1975
The Polymer Physics Group w i l l be holding its biennial meeting at the Royal Military College o f Science, Shrivenham, Wiltshire f r o m 24 to 26 September 1975. Contributed papers (20 minutes) are invited. The subject matter of this meeting is deliberately w i d e and is meant to include all aspects o f the physics of polymers and macromolecules, including the m o r p h o l o g y , mechanical, electrical and optical properties of solids, melts and solutions. Intending c o n t r i b u t o r s are asked to send a title and short abstract (250 words) to Mrs H. Higdon, Department of Physics, Brunel University, Uxbridge, Middlesex UB8 3PH, U K by 31 May 1975. Further details and application forms w i l l be available in June f r o m the Institute of Physics, 47 Belgrave Square, London SW1X 8QX, UK.
P O L Y M E R , 1975, Vol 16, May
391
The different solvent sorption behaviour of the three polymers may be due to several factors. Some X-ray diffraction work currently in progress has shown that, as expected, the PVC/PVAC copolymer appears to be virtually amorphous while the low temperature polymerized PVC has the highest crystallinity. Crystallinity is expected to have a significant effect on solvent sorption since the polymer chains are packed more closely in crystalline regions thus restricting solvent penetration. The results obtained for the two PVC homopolymers may be explained on thisbasis. In the copolymer chain packing is also reduced by the bulky acetate groups present and the decrease in polar forces between chains caused by the replacement of chlorine atoms by these groups. Heat treatment changed the solvent sorption behaviour of the two homopolymers (Figures la and lc) but had no significant effect on the solvent sorption of the copolymer (Figure lb). For PVC 2 (Figure la), the quenched sample, in which order would be expected to be lowest, absorbs solvent most rapidly. The sample heat treated at 70°C (i.e. below the glass transition temperature of the polymer) absorbs solvent slightly more slowly, but the weight gain reaches the same equilibrium value. The sample heat treated at 110°C (i.e. above the glass transition temperature) absorbs solvent more slowly and reaches a lower equilibrium value. Also the solvent sorption curve is S-shaped in the latter case, while for the quenched sample and the sample heat treated at 70°C the initial part of the plot of weight gain versus tl/2fl appears linear before the equilibrium value is reached. The effect of heat treatment on the solvent sorption behaviour of the low temperature polymerized PVC appears 20
to be similar to that of PVC 2, but the rates of solvent sorption were much slower and none of the experiments were continued to equilibrium. The above results can be explained tentatively as follows. Heat treatment is considered to have no effect on solvent sorption behaviour of the copolymer either because the rapid uptake of solvent is governed only by the presence of acetate groups, or because the polymer structure is too irregular for crystallization to occur. For the two homopolymers results were similar to those reported by Illers 2. Quenching would be expected to remove order, and actually resulted in more rapid solvent sorption in each case. The different solvent sorption behaviour for samples heat treated above and below Tg has been attributed to changes in crystaUinity and free volume respectively2; further evidence (from density measurements, thermal analysis and X-ray diffraction) will be presented later. Figures 3 and 4 illustrate the effect of time of heat treatment at 1 IO°C on solvent sorption and provide some information about the rate of the crystallization or ordering process occurring. These results suggest that structural changes occur within quite short times. However, it is necessary to examine the effects of short term heat treatment in more detail.
Acknowledgement The authors are grateful to the Science Research Council for the award of a Research Studentship to A.G. A. Gray Present address: BP Chemicals International Ltd. Sully. Penarth. Glamorgan. UK and Marianne Gilbert Institute of Polymer Technology, Loughborough University of Technology, Loughborough, Leics LEt1 3TU, UK (Received 4 February 1975)
0 c~
References l
0
Figure 3
I
I
m
t
I
I
IO 18 26 Time (at I I O ° C ( h ) Solvent uptake for PVC 2 immersed 4 h in toluene as a
function of heat treatment time a t 1 1 0 ° C
Evaluation of relative reactivities of vinyl monomers towards t-butoxy radical by means of spin trapping technique
Szwarc I developed a concept of'methyl aft'mity', i.e. a measure of relative reactivities of various compounds, including vinyl monomers, towards the methyl radical produced by the thermal decomposition of diacetyl peroxide in iso-octane. To determine the relative reactivities, the following competitive reactions were used:
E
"g
1 Blackadder,D. A. and Vincent, P. I. Polymer 1974, 15, 2 2 lUers,K. H.Makromol. Chem. 1969, 127, 1 3 Pezzin, G. Plasticsand Polymers 1969, 37,295
2
E: C~
I
I
1
I
I
I
IO IB 26 Time a t I I O ° C ( h ) Figure 4 Solvent uptake for low temperature polvmerized PVC immersed 72 h in tolueneas a function of heat treatment time at
CH 3- + C8H18k--~ 1 CH4 + • C8H17
(1)
CH 3- + M k2> CH3-M-
(2)
2
110°C
where M represents a vinyl monomer. It has also been
P O L Y M E R , 1975, Vol 16, May
389
Letters
pointed out that the observed relative reactivities (kz/kl) of vinyl monomers towards the methyl radical correlated well with those towards a polystyryl radical 2. Subsequently Bevington and his coworkers 3'4 attempted to evaluate the reactivity (k3/k4) of the benzoyloxy radical towards vinyl monomers by using 14Cqabelled benzoyl peroxide. In this case, the reactivities were determined by the 14C-labelled end group analysis of the polymers obtained as the result of the following competitive reactions: C6H5COO" k3' C6H5" + CO2
(3)
C6HsCOO. + M k4 > C6HsCOO-M-
(4)
C6H5. + Mk-.~ 5 C6H5_ M.
(5)
They also emphasized that polar effects were more important in the reaction of the benzoyloxy radical than that of methyl radical with the monomers 4. Although order of reactivity to the methyl radical towards vinyl monomers was confirmed to be similar to that of ethyl s, n-prow1 s and phenyl radicals 6'7, no data with respect to the reactivity of the oxy radicals except benzoyloxy radical towards vinyl monomers were found. Recently, we have succeeded to trap with 2-methyl-2nitrosopropane (BNO) as a spin trapping agent, the intermediate radical species (I and II) produced from the reactions of a number of vinyl and a-methyl-vinyl monomers having X substituents with the t-butoxy radical produced by the thermal decomposition of di-t-butyl peroxalatea: t- C 4 H 9 0 - C H 2 - C - Y
I
O. (VI)
Figures 1 and 2, for example, show the e.s.r, spectra of the reaction mixtures of styrene and methyl methacrylate, respectively, with di-t-butyl !?eroxalate in the presence of BNO without p-xylene at 25vC. From the e.s.r, spectrum of Figure 1, it is seen that only a nitroxide was produced and assigned as IV(AN = 14.2 G, A#I_I= 2.3 G and A~I (2H) = 0.6 G) in which X and Y are C6H5 and H, respectively. However, Figure 2 appears to be the combined spectra of the nitroxides IV (X=COOCH3, Y=CH3; A N = 14.9 G) and V(X=COOCH3;A N = 14.8 G, Aft (2H) = 9.8 G). When reactions are carried out in p-xylene, of course, the e.s.r, spectrum due to the nitroxide VI (AN = 15.0 G, Aft (2H) = 7.5 G) is superimposed on the respective spectra of Figures I and 2. Therefore, if the relative concentrations of the nitroxides ([IV], IV] and [VII ) produced are determined from the areas of the peaks due to the respective nitroxides in the absorption spectra obtained from integration of the observed first derivative e.s.r, spectra, the relative reactivities (k6/k8 and k7/ks) of the t-butoxy radical towards the monomers can be evaluated by using the following equations [IV] _ k 6
[M]
[VII
k8 [CH3-q~-CH3]
[V]
k7
(9)
[M]
(io)
[VI] k8 [CH3-q~-CH3]
CH2=C-CH2
X (I; Y=H, CH3)
CH3-~-CH2-1~-CH4H9-t
~SG~
X (II)
When decomposition is carried out in p-xylene in the presence of a monomer, the t-butoxy radical produced participates in competitive reactions: t-C4H90"
+
M k6~ t-C4H90-M-
(6) Figure 1
t-C4HgO- + M kT, t.C4HgOH + M' (II)
(7)
E.s.r. spectrum of the reaction mixture of styrene and dit-butyl peroxalate in the presence of BNO ~10 G~
k8 t-C4H90" + CH3--~-CH3--"* t-C4H9OH + CHa-~-CH2 (III) (8) A
If this reaction is performed in the presence of BNO, the radicals (I, II and III) produced react readily with BNO to give the respective nitroxides: t- C4H90-CH2-CY-N-C4H 9- t I I X O(IV) CH2=C-CH2-1~-C4 Hg-t X
O-
(v)
390
POLYMER, 1975, Vol 16, May
Figure 2
E.s.r. spectrum of the reaction mixture of methyl methacrylate and di-tJoutyl peroxalate in the presence of BNO; the peaks A are due to t-butyl-t-butoxynitroxide which is obtained from the reaction of BNO with t-butoxy radical
Letters Table I Relative reactivities of vinyl monomers towards t-butoxy radical at 25°C: comparison with those towards benzoyloxy, methyl and phenyl radicals t-C4HgOMonomer
e
O
k6/k 8
k7 /k 8
Isobutyl vinyl ether ¢¢-Methylstyrene t-Butyl vinyl sulphide Styrene Vinyl acetate Methyl methacrylate Methyl isopropenyl ketone Methyl acrylate Methyl vinyl ketone
--1.77 --1.27 --1.1 --0.8 -0.22 0.4 0.53 0.6 0.68 0.81 1.2
0.023 0.98 0.32 1.0 0.026 0.74 1.49 0.52 0.69 1.12 0.60
9.06 6.90 7.43 29.8 0.28 1.73 2.47 1.54 2.68 0.71 0.52
. <0.05 . -1.09 0.74 --1.56 --
Methacrylonitrile
Acrylonitrile
C6H5COO -a
CH~b
C6H5 "c
k 4 (rel. value)
k2/k 1
k 5 (rel. value)
.
.
.
.
.
-
926
. 1.0 0.36 0.12 ---~0.05
792 31 1440 -1030 1900 2120 1730
1.24 1.0 ( 1.0) 0.23 (;~0.08) 1.78 ( 1.7) -0.78 --
2.46 -- (0.8)
aData of Bevington etaL3,4 at 60°C bData of Szwarc l at 65°C CData of Pryor et aL ?, who determined these values through tritium abstraction reaction of a phenyl radical, produced by phenyl azotriphenylmethane, with tritiated pentanethiol at 60°C, as the standard. The values in parentheses indicate the data of Bevington eta/. 6 who used hydrogen abstraction reaction from dimethylformamide by a phenyl radical, produced by decarboxylation of benzoyloxy radical, as the standard
methacrylonitrile. This observation seems to be related to that found for the benzoyloxy radical 4, and to provide important information on the initiation mechanism of radical polymerization of vinyl monomers with the oxy radical.
[ M ] / [ C H 3 - ¢ - C H 3] x 10 2
300
3-0
60
I
9.0
;
i
Tsuneyuki Sato and Takayuki Otsu Department of Applied Chemistry, Faculty of Engineering, Osaka City University, Osaka 558, Japan (Received 22 January 1975; revised 11 February 1975)
2"0 >
References 1 2 3 4
I'0
I
O
I
I.O
[M]
2-0 3-0 / [ C H § ¢ - C H 3]
4.0
Figure 3 Plots of [ I V ] / [ V l ] with [ M ] / [ C H 3 - - ~ - - C H 3] : ~, Methyl acrylate, [~, styrene; O, acrylonitrile
5 6 7 8
Szwarc, M. J. Polym. ScL 1955, 16,367 e.g.,Otsu, T. Progr. Polym. ScLJapan 1971, 1, 1 Bevington, J. C. and Brooks, C. S. J. Polym. Sci. 1956, 22,257 Bevington, J. C. 'Radical Polymerization', Academic Press, London, 1961 Staid, J. and Szwarc, M. J. Am. Chem. Soc. 1956, 78, 3322 Bevington, J. C. and Ito, T. Trans. Faraday Soc. 1968, 64, 1329 Pryor, W. A. and Fiske, T. R. ibid. 1969, 65, 1865 Sato, T. and Otsu, T. Makromol. Chem. in press
Con ference A nnouncemen t
Polymer Physics where [M] and [CH3-q~-CH3] are initial concentrations of monomer and p-xylene, respectively. Figure 3 shows the plots of [IV] / [VI] with [M] / [CH3-~b-CH3] for the reactions of di-t-butyl peroxalate with styrene, methyl acrylate and acrylonitrile in p-xylene in the presence of BNO at 25°C. As can be seen from this Figure, linear relationships are obtained, and the relative reactivities of these monomers towards the t-butoxy radical are determined from their slopes. The results are summarized in Table 1, in which the relative reactivities of vinyl monomers towards methyl, phenyl and benzoyloxy radicals are also indicated. It is of interest that the relative reactivities (k6/ks) of the monomers towards addition of the t-butoxy radical are related more with their e values than their Q values, indicating that the polar effect is more important than resonance effect, similar to the case of the benzoyloxy radical 4. In connection with these results, it is also noted that the tbutoxy radical can easily abstract the allylic hydrogen ofc~methyl-vinyl monomers such as methyl methacrylate and
Shrivenham, Wilts, 2 4 - 2 6 September 1975
The Polymer Physics Group w i l l be holding its biennial meeting at the Royal Military College o f Science, Shrivenham, Wiltshire f r o m 24 to 26 September 1975. Contributed papers (20 minutes) are invited. The subject matter of this meeting is deliberately w i d e and is meant to include all aspects o f the physics of polymers and macromolecules, including the m o r p h o l o g y , mechanical, electrical and optical properties of solids, melts and solutions. Intending c o n t r i b u t o r s are asked to send a title and short abstract (250 words) to Mrs H. Higdon, Department of Physics, Brunel University, Uxbridge, Middlesex UB8 3PH, U K by 31 May 1975. Further details and application forms w i l l be available in June f r o m the Institute of Physics, 47 Belgrave Square, London SW1X 8QX, UK.
P O L Y M E R , 1975, Vol 16, May
391