The kinetics of anionic polymerization of o-methylstyrene were investigated in 2-methyltetrahydrofuran (MTHF) at 25°C with Li+, Na+, K+ and Cs+ as gegenions in the presence and absence of an electric field. Conductance studies showed that the dissociation constants K vary remarkably with the gegenion and that the lithium and sodium salts are dissociated to larger extents than the respective polystyryl salts. The free ion rate constant k$ was -2 X lo4 M-' s-which was smaller than that of polystyrene. From the conductivity data, the field effect was concluded to be due to an increase in k i with increase of the field strength as in other systems. The k i reached a limiting value of w3 x lo4 M-l s-' above 3 kVlcm. The ion pair rate constants kb were 2, 1, 16 and 30 M-' s-l for Li+, Na+, K+ and CS+, respectively. Comparison with polystyrene systems led to the conclusion that the behaviour of poly(o-methylstyryl) salts are due to steric hindrance effects of the methyl group in the ortho position. The field-accelerating effects reflected in the k i term as in other systems are smaller than that of poIystyrene systems. This is discussed in terms of the ortho effect. The kinetics of the caesium salt of poly(o-methylstyrene) were also studied in tetrahydrofuran (THF) at 25°C. The results are compared with those in MTHF.* This article is part 19 of Ionic Polymerization under an Electric Field.
The kinetics of anionic polymerizations of styrene, m-methylstyrene, p-isopropylstyrene, and pmethylstyrene were investigated in tetrahydrofuran (THF) at 25°C with Cs+ as gegenion in the presence and absence of an electric field. Anionic polymerizations of m-and p-methylstyrenes in 2-methyltetrahydrofuran (MTHF) with Na+ as gegenion were also studied. The ion-pair rate constants kk, the free ion rate constants k; and the dissociation constants K of the styrene derivatives were generally smaller in both solvents than those of styrene. Conductance studies showed that the K values of the caesium salts are practically the same in THF. It was found that the free anions of these living polymers in MTHF are half as reactive as in THF. The field acceleration effect was hardly perceptible in THF. Following earlier studies of the field effect, the solvation ability of ethereal solvents to free carbanions was concluded to decrease along the series dimethoxyethane @ME) >THPe MTHF > THF. A value of (12&2)x lo4 M-l s-1 was attributed to the '' desolvated " free ion rate constant for living polystyrene. Hammett's relations of the two systems Cs+/THF and Na+/ MTHF were examined for k,, k;, k;, and K, independently. The reactivity constants p for k, and K were dependent on systems whereas those for k," were not.* This article is part 20 of Ionic Polymerization under an Electric Field.
Kinetics of homopropagation of living poly-p-methoxystyrene has been investigated in tetrahydrofuran at 25°C in the presence and absence of an electric field. The rate constants of ion pairs were evaluated to be 40, 40 and 15 M-l s-l for sodium, potassium and caesium salts, respectively, being smaller than those for the corresponding salts of living polystryene. The rate constant of free anion was 4 . 0 ~ * This is part 17 of Ionic Polymerization under an Electric Field, and was presented at the Annual Meeting of the Chemical Society of Japan, Tokyo, April, 1970.
It is well known that, in living anionic polymerizations of styrene in ethereal solvents, the active ends can be ion pairs, free ions,1*2 and triple ions.*+ When only the two types of the active ends, ion pairs and free ions, are responsible for the propagation and when the concentration of the free ions is much less than that of the ion pairs, the apparent propagation rate constant k , is given1** by k , = k , ' + ~C~* K~/~/ [ L E ] ' /~(1 1 where k, ' and k," are the rate constahts of ion pairs and free ions, respectively, K is the dissociation constant of ion pairs, and [LEI is the concentration of living ends. It has been found that k,' and K for the anionic polymerizations of styrene are highly dependent on gegenions as well as on solvents.a-12 Furthermore, a comparison of anionic polymerizations in tetrahydrofuran of p-methoxystyrene with that of styrene has revealed that the k,' and K values of living poly-p-methoxystyrene are much smaller than those of living polystyrene when N a + ion is used as a gegenion.13 On the other hand, the values for Cs salts of these two living polymers are about the same.13 Most recently, we have studied systematically the effects of the alkali metal cations on the propagation kinetics of styrene in 2-methyltetrahydrofuran (MTHF) and found that the k , ' and K in this solvent are not sensitive toward the gegenions.14 Therefore, this solvent seemed suib able for comparative study of anionic reactivities of various monomers. Thus, in the present paper, we report anionic polymerizations of sodium salts of poly-o-methylstyrene and poly-p-methylstyrene in MTHF and describe the influence of methyl group on the kinetic and dissociation behavior in comparison with the results of styrene. Though living polymers in MTHF were not so stable as in THF, kinetic and conductivity studies are possible if MTHF is most elaborately purified. Equation (I) also applies to the polymerizations of 0-and p-methylstyrenes in MTHF, as is shown in Figure 1. Apparently, the slope k,"K'/' of o-methylstyrene is larger than that of p-methylstyrene. The propagation rate constant was determined spectrophotometrically. 3654 NO'I'ESThe intercepts and slopes obtained from Figure 1, together with those of styrene, are given in Table I. The k,' can also be determined in the presence of NaBPh. Recently, the validity of this method was questioned by Schula et al.16 They found that in the presence of the added salt, the ultraviolet absorption measurement gives higher values of the living end concentration and lower values of the k,' than in the absence of the salt. Thus, we determined the k,' by the extrapolation procedure. Since the slope is not so steep in the present case, the k,' values we obtained seem reliable. The dissociation constant K obtained from conductivity values is listed in the fourth column of Table I. Furthermore, from the K value and the slope of k , versus [LEI -'12 plot, the free-ion rate constant kp" was obtained and is given in the last column of Table I. We note that o-methylstyrene has the s...
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