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Influence of the polymerization temperature on the reactivity of 3-methyl- and 4-methyl-styrenes in cationic polymerization
Influence of the polymerization temperature on the reactivity of 3-methyl-and 4-methylstyrenes in cationic polymerization F. Visse and E. Marechal Institut National Sup~rieur de Chimie Industrielle de Rouen, 76130Mont-Saint-Aignan, France (Received 2 January 1974)
The variations with respect to temperature of the reactivities of 3-methyl- and 4-methylstyrenes in cationic polymerization have been studied by determination of their reactivity ratios with styrene.
Former studies on the influence of experimental conditions on the reactivity of 4-methylstyrene have been made by Tobolsky 1, 2 and Furukawa 3. It does not appear that similar studies have been done with 3-methylstyrene. In this paper the index 1 is relative to the methylated derivative and the index 2 to styrene; the reactivity ratios have been obtained by the differential method 4. Preliminary trials run at 5°C with the initiator and monomer concentrations which will be specified subsequently, have shown that the variation between r2 and the nature of solvent is very small, r l is more dependent on this parameter and its value is maximum when methylene chloride is the solvent. The solvent used here was methylene chloride previously distilled, refluxed for 48 h in the presence of H2SO4 redistilled a second time and dried on 4 A molecular sieve. The initiator was TIC14 (0.001 mol/1) and the total concentration of monomers was 0.05 mol/1. The variations of rl and r2 with respect to the polymerization temperature 0 are given in Table 1 for 3-methylstyrene and in Table 2 for 4-methylstyrene. It has been impossible to determine rl and r2 for temperatures above - 5 ° C because a preliminary copolymerization study, run with the same molar fraction of each monomer, has shown that above - 5 ° C the copolymer yield was negligible. The variation, with respect to the absolute temperature, of the rate constant k~j of the reaction between carbocation i and monomer j are given by the classical equation:
The S u - S i j and E ~ j - E , values obtained from log r2 with respect to 1/T are given in Table 3. The variations of rlr2 with respect to the polymerization temperature (0°C) for 4-methylstyrene are given in Figure 1. A decrease of rlr2 with increasing temperature is observed, which is in agreement with what is generally observed in radical copolymerization and with theory; since when 0 increases the copolymer becomes more and more statistic. However, until now, the opposite result has always been observed in all the cases studied in cationic copolymerization. The curve in Figure 1 represents the variation of rlrz with respect to 0, obtained from relations (1) and (2) and from the values shown Table 1 Variations of rz and r2 with polymerization temperature for 3-methylstyrene
8(°C)
rz
r2
1/r3
rzr2
-78 -55 -15
0.85+0.10 1 "20_+0.30 1.30_+0.10
1 "3_+0-10 1.55_+ 0.40 2,30_+0.10
0-76 0.64 0.43
1 "11 1 "86 2.99
Table 2 Variations of rz and r3 with polymerization temperature for 4-methylstyrene
8 (°C)
rl
r2
1/r2
rlr2
--75 --30 0 25
2"0_+0"3 2'5_+0.3 2.9_+0.3 3"15+0"20
0.90_+0.06 0-65_+0.10 0.48_+0.06 0"36_+0.10
1.42 1.53 2.02 2"73
1 '80 1.63 1.37 1 '14
kq = A~jexp(- E~j/RT) or, the r~ and rz definition being taken into account:
Table
Iog rl = log[ A l z/ A l2 [ - ( E 1 1 - E12)/ R T
(1)
log r2 = log IA22/A211 - (E22- E21)/RT
(2)
and with
3 Sii-Sij and Eij-Eii values obtained from log r~
S u - Sl~ 323- 331 Monomer Monomer E13-Ezz E~l-E33 (calmo1-1 (calmo1-1 1 2 (kcal/mol)(kcal/mol) °C-z) °C-1) 4-Methyl
l og[A 11/A 121 = ($11 - S19.)/R
3-Methyl-
and logl.422/A2z I = ($22- Szl)/R
styrene
-0.48
0.99
3.83
-5.15
styrene
-0.67
-1.01
3-10
5.15
styrene styrene
POLYMER, 1974, Vol 15, August
485
Reactivity of 3-methyl- and 4-methyl-styrenes : F. Visse and E. Marechal
2
~"-I
! -50
i
i
i
0
50
I00
O (oc)
Variations of rzr2 with polymerization temperature. Open circles are relative to experimental values
Figure I
in Table 3, whose equation is: rlr2=exp[-0.66+0+273J2551 As it is impossible to work above 30°C with methylene chloride as a solvent, and difficult to compare the results obtained in various solvents, we have obtained the limit temperature 01~m for which rlr2 = 1 only by extrapolation of the curve. We found Onm= 113°C and for this temperature: rz = 3.65, and r2 =0.27. The value of rlrz has been determined at 5°C in various solvents for 4-methylstyrene: CC14, 1.54; CHzC12, 1.95; CrHsNO2, 1.41. From the examination of these values it would appear that the polymer prepared in methylene chloride is the less statistic. The index 1 relative to methylstyrenes (in a general
486
POLYMER,
1974, Vol 15, A u g u s t
way) will now be changed to the index 3 for 3-methyland the index 4 for 4-methyl-styrene. As before, the index 2 is relative to styrene. The value given by Table 3 and the value E225 being taken into account, we obtain E~8- 7.50 and E24- 9.50 kcal/mol. From these values it appears that when 3-methyl- and 4-methyl-styrenes react with the same cation, the rate of the reaction depends more on the temperature for 4-methyl- than for 3-methyl-styrene. This fact is in agreement with experimental results. It is worth noting that the average value of activation enthalpy relative to a reaction of styryl cation with m- and p-methylstyrenes is exactly the one obtained for the same reaction with styrene. The relations r l = e x p ( 1 . 9 1 - 2 4 0 / T ) and r2=exp ( - 2 . 5 7 + 4 9 5 / T ) for 4-methylstyrene, and rt =exp(1.55335/T) and r z = e x p ( 2 . 5 7 - 5 0 5 / T ) for 3-methylstyrene show that, in the range of temperature used the selection between the two monomers by the same cation is highly dependent on entropy, particularly in the case of 4-methylstyrene. From this fact, it appears that the propagation reaction is probably highly dependent upon the solvation and desolvation phenomena, themselves being greatly influenced by the superdelocalizability of the active centre and the nature of the solvent. REFERENCES 1 Tobolsky, A. V., Kelley, D. J., O'Driscoll, K. F. and Rogers, C. E. J. Polym. Sci. 1958, 28, 425 20'Driscoll, K. F. and Tobolsky, A. V. J. Polym. Sci. 1959, 37, 363 3 Furukawa, J., Kobayashi, E. and Taniguchi, S. Polymer submitted (presented at Rouen Symp., 1973) 4 Ham, G. E. 'Copolymerization, High Polymers', Interscience, New York, 1964, p 18 5 Higashimura, T. 'Structure and Mechanismin VinylPolymerization', Marcel Dekker, New York, 1969, p 329
The variations with respect to temperature of the reactivities of 3-methyl- and 4-methylstyrenes in cationic polymerization have been studied by determination of their reactivity ratios with styrene.
Former studies on the influence of experimental conditions on the reactivity of 4-methylstyrene have been made by Tobolsky 1, 2 and Furukawa 3. It does not appear that similar studies have been done with 3-methylstyrene. In this paper the index 1 is relative to the methylated derivative and the index 2 to styrene; the reactivity ratios have been obtained by the differential method 4. Preliminary trials run at 5°C with the initiator and monomer concentrations which will be specified subsequently, have shown that the variation between r2 and the nature of solvent is very small, r l is more dependent on this parameter and its value is maximum when methylene chloride is the solvent. The solvent used here was methylene chloride previously distilled, refluxed for 48 h in the presence of H2SO4 redistilled a second time and dried on 4 A molecular sieve. The initiator was TIC14 (0.001 mol/1) and the total concentration of monomers was 0.05 mol/1. The variations of rl and r2 with respect to the polymerization temperature 0 are given in Table 1 for 3-methylstyrene and in Table 2 for 4-methylstyrene. It has been impossible to determine rl and r2 for temperatures above - 5 ° C because a preliminary copolymerization study, run with the same molar fraction of each monomer, has shown that above - 5 ° C the copolymer yield was negligible. The variation, with respect to the absolute temperature, of the rate constant k~j of the reaction between carbocation i and monomer j are given by the classical equation:
The S u - S i j and E ~ j - E , values obtained from log r2 with respect to 1/T are given in Table 3. The variations of rlr2 with respect to the polymerization temperature (0°C) for 4-methylstyrene are given in Figure 1. A decrease of rlr2 with increasing temperature is observed, which is in agreement with what is generally observed in radical copolymerization and with theory; since when 0 increases the copolymer becomes more and more statistic. However, until now, the opposite result has always been observed in all the cases studied in cationic copolymerization. The curve in Figure 1 represents the variation of rlrz with respect to 0, obtained from relations (1) and (2) and from the values shown Table 1 Variations of rz and r2 with polymerization temperature for 3-methylstyrene
8(°C)
rz
r2
1/r3
rzr2
-78 -55 -15
0.85+0.10 1 "20_+0.30 1.30_+0.10
1 "3_+0-10 1.55_+ 0.40 2,30_+0.10
0-76 0.64 0.43
1 "11 1 "86 2.99
Table 2 Variations of rz and r3 with polymerization temperature for 4-methylstyrene
8 (°C)
rl
r2
1/r2
rlr2
--75 --30 0 25
2"0_+0"3 2'5_+0.3 2.9_+0.3 3"15+0"20
0.90_+0.06 0-65_+0.10 0.48_+0.06 0"36_+0.10
1.42 1.53 2.02 2"73
1 '80 1.63 1.37 1 '14
kq = A~jexp(- E~j/RT) or, the r~ and rz definition being taken into account:
Table
Iog rl = log[ A l z/ A l2 [ - ( E 1 1 - E12)/ R T
(1)
log r2 = log IA22/A211 - (E22- E21)/RT
(2)
and with
3 Sii-Sij and Eij-Eii values obtained from log r~
S u - Sl~ 323- 331 Monomer Monomer E13-Ezz E~l-E33 (calmo1-1 (calmo1-1 1 2 (kcal/mol)(kcal/mol) °C-z) °C-1) 4-Methyl
l og[A 11/A 121 = ($11 - S19.)/R
3-Methyl-
and logl.422/A2z I = ($22- Szl)/R
styrene
-0.48
0.99
3.83
-5.15
styrene
-0.67
-1.01
3-10
5.15
styrene styrene
POLYMER, 1974, Vol 15, August
485
Reactivity of 3-methyl- and 4-methyl-styrenes : F. Visse and E. Marechal
2
~"-I
! -50
i
i
i
0
50
I00
O (oc)
Variations of rzr2 with polymerization temperature. Open circles are relative to experimental values
Figure I
in Table 3, whose equation is: rlr2=exp[-0.66+0+273J2551 As it is impossible to work above 30°C with methylene chloride as a solvent, and difficult to compare the results obtained in various solvents, we have obtained the limit temperature 01~m for which rlr2 = 1 only by extrapolation of the curve. We found Onm= 113°C and for this temperature: rz = 3.65, and r2 =0.27. The value of rlrz has been determined at 5°C in various solvents for 4-methylstyrene: CC14, 1.54; CHzC12, 1.95; CrHsNO2, 1.41. From the examination of these values it would appear that the polymer prepared in methylene chloride is the less statistic. The index 1 relative to methylstyrenes (in a general
486
POLYMER,
1974, Vol 15, A u g u s t
way) will now be changed to the index 3 for 3-methyland the index 4 for 4-methyl-styrene. As before, the index 2 is relative to styrene. The value given by Table 3 and the value E225 being taken into account, we obtain E~8- 7.50 and E24- 9.50 kcal/mol. From these values it appears that when 3-methyl- and 4-methyl-styrenes react with the same cation, the rate of the reaction depends more on the temperature for 4-methyl- than for 3-methyl-styrene. This fact is in agreement with experimental results. It is worth noting that the average value of activation enthalpy relative to a reaction of styryl cation with m- and p-methylstyrenes is exactly the one obtained for the same reaction with styrene. The relations r l = e x p ( 1 . 9 1 - 2 4 0 / T ) and r2=exp ( - 2 . 5 7 + 4 9 5 / T ) for 4-methylstyrene, and rt =exp(1.55335/T) and r z = e x p ( 2 . 5 7 - 5 0 5 / T ) for 3-methylstyrene show that, in the range of temperature used the selection between the two monomers by the same cation is highly dependent on entropy, particularly in the case of 4-methylstyrene. From this fact, it appears that the propagation reaction is probably highly dependent upon the solvation and desolvation phenomena, themselves being greatly influenced by the superdelocalizability of the active centre and the nature of the solvent. REFERENCES 1 Tobolsky, A. V., Kelley, D. J., O'Driscoll, K. F. and Rogers, C. E. J. Polym. Sci. 1958, 28, 425 20'Driscoll, K. F. and Tobolsky, A. V. J. Polym. Sci. 1959, 37, 363 3 Furukawa, J., Kobayashi, E. and Taniguchi, S. Polymer submitted (presented at Rouen Symp., 1973) 4 Ham, G. E. 'Copolymerization, High Polymers', Interscience, New York, 1964, p 18 5 Higashimura, T. 'Structure and Mechanismin VinylPolymerization', Marcel Dekker, New York, 1969, p 329