Polymerization of ethylene oxide by alkali metal-naphthalene complexes in tetrahydrofuran

European Polymer Journal, 1971, Vol. 7, pp. 1421-1433. Pergamon Press. Printed in England.

POLYMERIZATION OF ETHYLENE OXIDE BY ALKALI M E T A ~ N A P H T H A L E N E COMPLEXES IN TETRAHYDROFURAN* K. S. KAZANSKXl, A. A. SOLOVYANOV a n d S. G. ENTELIS Institute of Chemical Physics, Academy of Sciences of U.S.S.R., Moscow, U.S.S.R. (Received 1 December 1970)

Abstract--The kinetics of ethylene oxide polymerization in THF, with Na, K and Cs-naphthalene complexes as initiators, have been studied in detail. Polymerization is first order with respect to monomer without chain termination or transfer. The complicated dependence of the polymerization rate on active centre concentration is due to strong association. Rate constants of the propagation and thermodynamic parameters of association have been determined from this dependence. Contact type ion pairs are shown to be the active propagating species. Their activity increases and association ability decreases from Na + to Cs+. Solvation of the active species plays the decisive part in this process. PUBLISHED d a t a c o n c e r n i n g a n i o n i c p o l y m e r i z a t i o n o f epoxides indicate t h a t the r e a c t i o n m e c h a n i s m is n o t so simple as s o m e t i m e s suggested. T h e n a t u r e o f the active centres, the m e c h a n i s m o f their i n t e r a c t i o n w i t h the m o n o m e r a n d e n v i r o n m e n t , the role o f s o l v a t i o n a n d o f dielectric c o n s t a n t a r e n o t yet clear. A l k a l i m e t a l a l k o x i d e s have been frequently used as initiators. ¢~-7) T h e low solubility o f these i n i t i a t o r s in c o m m o n solvents requires a d d i t i o n o f alcohol, so m a k i n g the investigation extremely c o m p l i c a t e d . <3-7> C o m p l e x e s such as s o d i u m n a p h t h a l e n e are m o r e c o n v e n i e n t in view o f their solubility a n d stability in s o m e ethers. T h e s e i n i t i a t o r s were used in ethylene oxide p o l y m e r i z a t i o n first b y Szwarc a n d R i c h a r d s es) a n d then b y D u d e k ¢9) in a s t u d y w h i c h is n o t widely k n o w n . T h i s p a p e r deals with the kinetics o f ethylene oxide p o l y m e r i z a t i o n in t e t r a h y d r o f u r a n ( T H F ) . S o d i u m , p o t a s s i u m a n d c a e s i u m - n a p h t h a l e n e c o m p l e x e s were used a s initiators. EXPERIMENTAL All chemicals were thoroughly purified before use. THF was treated finally with Na-naphthalene and was stored in vacuum. Ethylene oxide was treated in the same way hut partial polymerization was caused. The monomer was redistilled and the procedure was repeated. The usual high-vacuum technique was used for all manipulations. The flask wall was thoroughly heated, then treated with the initiator solution and afterwards with pure solvent. The initiator concentrations were determined either by titration or spectrophotometrically. The extinction coefficients for complexes were taken as 4750 (Na +, 364 nm), 6430 (K +, 365 nm) and 8500 M -a cm -a (Cs +, 367 nm). Cs--naphthalene was always used only freshly prepared in view of its instability. The kinetics of polymerization were studied by dilatometry. Polymerization proceeded to completion and conversion was calculated in the usual way. For bulk polymerization, thermometric and gravimetric methods were used also. * This paper was presented at the IUPAC Symposium on Macromolecniar Chemistry, Budapest, 1969; Preprint 3/27. 1421

1422

K.S. KAZANSKII, A. A. SOLOVYANOV and S. G. ENTELIS

Molecular weights were determined by viscometry in benzene* and by vapour pressure osmometry in methylethylketone. The polymers were characterized also by gel permeation chromatography (GPC). Chromatograph "Waters Ass.", Type G-200, was used, with THF as eluent (velocity 1 mL rain -~, 25°). Standard polyethyleneglycols, "'Schuchardr', Mi~nich were used for calibration. RESULTS AND DISCUSSION

Degree of polymerization. Measurements

o f the polymerization degree have shown that the initiator was quantitatively and rapidly c o n v e n e d to active centres, which were stable for a long time, i.e. a living p o l y m e r is formed. W h e n m o r e m o n o m e r was added to the completely polymerized system, the degree o f polymerization increased proportionally to the a m o u n t o f m o n o m e r added and varied linearly with conversion (Fig. 1). T h e results can be interpreted through c o m p a r i s o n of the experimental degree o f polymerization (]~cx~) with that calculated f r o m equation:

[M]o [M] [~o = -

P.x~ = vPo..o =

~,

~,

,7[M]o [p,]

(1)

,5F

2

X

o 1.0

o

"o

g o -> ID I

0.5

o" >

0

I

O. 25

I

o. 50

I

0.75

I

1.00

Conversion

Fxo. 1. Dependence of polyethylene oxide degree of polymerization on conversion; ( l ) - - K +, 1"6 x 10 -3 M; monomer 6"5 M; 50°; (2)--K +, 2-7 x 10 -3 M; 2"5 M; 60°;

(3)---Na +, 2-4 x 10 -3 M; 2"5 M; 100% * [~]=s" -- 3"97 x 10-" 1~I~°'ese [10].

Polymerization of Ethylene Oxide

1423

where [M]o and [M] are the initial and current concentration of monomer, [/]o is the concentration of initiator, equivalent to that of active centres [P*], when chain termination is excluded, ~7 is the conversion. The coefficient 7 characterizes the mechanism of initiator conversion to active centres. The results of this comparison are shown in Fig. 2.

3-

x

, /e /

"

~

i£ 2

0

I

0

I

2

3

Pth,o, X 10-4 FIG. 2. Comparison of experimental and calculated degree of polymerization at low (1) and high (2) initiator concentrations. It is seen that the system can react in two ways. At a high concentration of initiator, up to [/]o-~ 10-ZM, it can be described by Eqn. (1) with y ---- 2, but at a concentration less than 10 -4, y = 1. Such behaviour is connected with the mechanism of initiation. The GPC-curves can be used for obtaining the polydispersity ratio/~w//~,, which is close to I .08-1 • 10 in accordance with the mechanism of "living" polymerization. It will be noted that polymers obtained both at low and high concentrations (7 = 1 or y = 2) exhibit a narrow molecular weight distribution. In the transition range, the curves are clearly bimodal (Fig. 3). Mechanism of initiation. Radical-anions can react with any m o n o m e r in two ways, either by electron transfer to m o n o m e r followed by recombination o f m o n o m e r radical-anions or by direct m o n o m e r nucleophilic addition to initiating radical-anions. The subsequent fate of active centres in the second case is more complicated. The second way can be accepted for ethylene oxide. The u.v.-spectra of polymers show the existence of a dihydronaphthalene group in the chain; the extinction coefficient of this group is about 2300 M - 1 cm-1 (at 262 nm). According to published data, (t2) it means that 20 per cent of 1,2-structures are present. Reprecipitation o f polymers causes no change in their extinction. Similar results were obtained by Richards and Szwarc} 8~

1424

K. S. KAZANSKII, A. A. SOLOVYANOV and S. G. ENTELIS 4

5

Q I-.4

60

70

80 VEL~

90

1(30

I I0

cm 3

FIG. 3. Gel-permeation curves for polyethylene oxide: (1)--Cs +, 1"5 x 10 -3 M, 20°; (2)--K +, 1"9 x I0 -s M, 20°; (3)--K +, 9 x 10 -4 M, 20°; (4)----K +, 9 x 10 -4 M, 50°; polymerization at 70°; (5)---Na +, I0 -x M, 20 °, polymerization at 99"4 °.

Thus, the first step of initiation is addition of monomer to anion-radical:

~

Mete +

HzC-

CHz

,~

(2)

~.o / I Dudek's conclusion (9) that this step is rate-determining was confirmed by spectrophotometric and ESR-measurements of initiation kinetics. The process was found to be first order with respect to monomer and initiator; the bimolecular rate constant was about 1 M -1 sec -x (25°). The addition mechanism has been also accepted for interaction o f polyvinylnaphthalene radical-anions with ethylene oxide. (tl) Further conversion of intermediate radical-anions (I) occurs due to their radical reactivity. The most probable step is rapid exchange with the initial radical-anion:

Met@

+

MeP + ~

H~-. Met ~) 1T

(3)

Polymerization of Ethylene Oxide

1425

This leads to dianion formation and with further chain growth to bifunctional macromolecules with naphthalene groups in the chain. A similar mechanism was suggested earlier for some radical-anion reactions, in particular, with water, CO2, propylene sulphide (12) and ethylene oxide. Ca'9} Our molecular weight measurements confirm this mechanism only for relatively high initiator concentrations (7 = 2). It is also supported by stoichiometric relations in the initiation (Table 1). It can be seen from Table 1 that, at high concentrations, the formation of one active centre needs two initiator molecules. Proper selection of concentrations (2: I) permits detection of the intermediate product I I with characteristic absorption at 430 and 565 nm. It is relatively stable in the absence of excess monomer, but dies eventually by interaction with solvent. A different mechanism should be accepted for low concentrations. It may be conceived that the second step here is monomolecular with respect to radical-anions and involves hydrogen transfer f r o m solvent to radical-anion with subsequent growth

~

"ZC"20~Met@

~CH2 +

RH

CHzOe"Met@ ('4)

H~

"H

of monofunctional "living" macromolecules (7 = 1). The stoichiometric coefficient in the reaction of initiator with ethylene oxide decreases accordingly to 1 and no absorption due to intermediate I I is observed. TABLE 1. STOICHIOMETRYOF Na-NAVHTHAL~NEv.r~c'noN WlTH ETHYLENE OXIDeIN THF (25°) Ill. x 10s M

[M]o × l0 s M

[1] x l0 s* M

A[/]/[M]o

600 350 196 150 107 71 64 23 17 16"5 7-5 6"5

120 58 23 22 24 30 17 4"4 3"4 7"5 2"4 2"8

350 242 150 107 71 30 35 16"5 13 5"0 5"2 2-5

2"08 1-87 2"00 1-96 1"50 1-37 1"80 1"48 1"18 1"53 0-96 1"43

* The initiator concentration after completion of the reaction. A mixture of mono- and bifunctional macromolecules is formed in the transition range resulting in bimodal distribution curves (Fig. 3) and m o n o t o n o u s change of y (Fig. 4). This may be expressed as: A ~ + M-~'AMA ~- + " A M - ~ - A M " A M - --+AM-

(k,) + A (k2) (k3)

(5)

1426

K.S. KAZANSKII, A. A. SOLOVYANOV and S. G. ENTELIS

where A = is the initial radical-anion. The curve in Fig. 4 shows variations o f coefficient 7 calculated according to scheme (5) with kl = 1, k2 = 2 x 103 M - z . sec -1 and k3 = lO sec -~. 0 2.0--

0

0

0

m.>

1.0

0

I

-4

I

-5 in

-2

-I

I

C~"

F]O. 4~ R a t i o o f experimental to calculated degree o f po]ymefization (~,) as a function of

initiator concentration. Curve is calculated from scheme (5) (see text).

2

0.15 I

A ,2

0.10 o oC

~0.05

0 U

!

/

L

3

C

,5

I0

1,5

I

I r ' ~ o

I

I

I

t

I oo

20o

3,00

mln

1~o. 5. Time-~onversion curves in ethylene oxide polymerization. 1---60°, initiator--"living" polyethylene oxido---Cs, 3 x 10 -3 M ; 2 - - 7 0 °, Cs-naphthalene, 3"2 x 10 -3 M; 3--70 °, K-naphthalene, 5"5 x 10 -3 M ; A 50 °, K-naphthalene, 2-9 × 10 -3 M ; 5--99-4 °, Na-naphthalene, 3"7 x 1 0 - " M, Curves 1 t o 4 ; monomer = 2 M in THF. Curve 5, in bulk.

Polymerization of Ethylene Oxide

1427

Explanation of the detailed chemical nature of step (4) undoubtedly needs further study. Kinetics o f polymerization. The time-conversion curve for ethylene oxide polymerization (Fig. 5) shows a characteristic initial acceleration after which the process is described by a first order equation. The low solubility ofalkoxide-type living oligomers is the main reason for this behaviour. The formation of finely dispersed solid phase can be observed in some cases; when growing macromolecules attain the length of 15-20 units, they pass into solution and the process becomes stationary (Fig. 5). The observed polymerization rate constant k l = --din M/dtis a complicated function o f the active centre concentration (Fig. 6). Fractional orders are observed at high -2

:

t,

[P*]

FIG. 6, Relationship between polymerization rate constant (sec-a) and active centre concentrations, r-7--Na +, 99"4°, THF; @--K +, 30°; @--K +, 40°, in bulk; A--K +, 70*; A--K +, 80°; (3--Cs +, 60°; C)--Cs +, 70°, all in THF, [M] ~ 2 M. concentrations: 0.33 for K + and Cs ÷, about 0.25 for Na +. With decreasing concentration, the process tends to first order. For sodium, however, the fractional order is maintained over the whole range of concentration used. This behaviour can be accounted for by association o f active centres. A polymerization scheme involving association equilibrium and chain propagation via unassociated species may be represented as: ne* --~ P*n (Ka) (6) P* -4- g ~ P*

(kp)

(7)

where P* is the active centre, n is the association factor. This scheme yields equation: kl =

din[M] d-----~ ---- k'KA-1/" n-a/" [ p . ] l / . = kar n -1/" [ p . ] l / .

(8)

1428

K.S. KAZANSKII, A. A. SOLOVYANOV and S. G. ENTELIS

which agrees with experimental data. Accordingly, the association factor is 3 for K + and Cs + and close to 4 for N a +. F o r a bimolecular rate constant, Eqn. (8) takes the form: k2 = ~

kl

[P*]

= kpa

(9)

where ~ is the fraction of unassociated active centres which can be found from the following relation:

Kw = n[p,]2 ~3

(10)

With decrease of concentration [P*], this fraction tends to I, explaining the observed transition to first order. The rate constants found in this range are directly related to chain propagation. Thus the propagation rate constants and the thermodynamic constant of association can be determined f r o m polymerization rates over a wide range of concentrations of active centres. Additional information may be obtained f r o m the temperature dependences of these parameters (Table 2). Nature o f propagating species in polymerization. The true physical nature of association (6) may be various. In general it has been regarded as ionic, but the low dielectric constant of the solvent makes this doubtful.* Moreover, ionic equilibrium with such a high association factor is improbable. It would be more reasonable to assume that ion pairs can play the part of active species in chain propagation. The ion pair takes part in the association equilibrium, where autosolvation of cation is the main driving force. In the cases of K + and Cs +, the structure of the associate can be assumed to be cyclic

@Met''~''" ~ Met

d!

(ll)

.,< ..-.~

@Met

The marked tendency of alkoxy-anion to such solvation is due to high charge density on the oxygen. This view was confirmed recently by calculations. ~'~ Association is a very characteristic feature o f some metal alkoxides. ¢15~ For alkali metals, it is found f r o m spectral measurements. <1~ Association is not infrequent for anionic polymer systems. It is highly typical of carbanions in hydrocarbon solvents, but then the aggregates are readily destroyed by addition of small amounts of solvating agents, such as T H F . ~ > The increase in viscosity of "living" Li-polystyrene in its interaction with ethylene * As found recently,~13~the ionic dissociation constant of "living" polyethylene oxide at 40° in THF is 2 x 10-1° and 8 × 10-1~ mole. 1-1 for Cs + and K + as counter-ions, respectively. That finding practically excludes the participation of free ions.

THF THF THF In bulk

Na + K+ Cs + K+

4 3 3 3

n

3"7 5"3 2"6 3"2

× × x ×

kerr* 10 -5 10 -3 10 -2 l0 -2

* F r o m Eqn. (8); M -l/n. sec -1. t Ap--pre-exponential factor of the propagation.

Solvent

Counter ion . 0"94 3"5 2"0

M - I s e c -1

k~

. 18"9 11"9 20.7

.

kcal x mole -L

E~

. 8"5 × 1011 1"2 × l0 s 2"4 × 1013

A~t M-Jsec -t

5"5 × 106 3"0 × l0 s 2"4 × l0 s

KA M -2

21 '0 2"7 15"3

AHA kcal × mole -1

TABLE 2. K I N E T I C AND THERMODYNAMIC DATA ON POLYMERIZATION OF ETHYLENE OXIDE (70 °) ASA

92 38 69

C.U.

2.

¢-L O

O

g

1430

K.S. KAZANSKII, A. A. SOLOVYANOV and S. G. ENTELIS

oxide (a) or T H F "a) is due to very strong association, when oxygen appears at the growing end of the chain: e

@

e

@

,~CH2CH.Li[ + !O(CH2)n--] ~ ,~CH2 CH(CH2),O.Li[

(12)

Similar data were obtained recently by Richards. (zg) Association of alkoxide-type ionic pairs is so strong that it can be observed even in dimethylsulphoxide (2°) and hexamethylphosphoramide. (21) Association of "living" polyethylene oxide in T H F was also confirmed by viscometric measurements: for instance, at [P*] -~ 1-8 × 10 -2 M in the case of the potassium counter-ion at room temperature, the viscosity decreased about 3 times on addition of methyl iodide. The apparent molecular weight consequently decreases by a factor of about 5. It has been found also that the intrinsic viscosity of the "living" polymer* increases with its concentration, but less than would follow from the threedimensional polycondensation theory. This is accounted for by the presence o f m o n o functional macromolecules. It can be shown that ion pairs are the only form of active species in the system investigated. With two active forms present, the following equation would result:

k2 ffi k ' , a -F k"p (1 -- a) = k ' , -F (k', -- k*,) a

(13)

where k'prand k"p are rate constants. Assuming a ,-, [P*]-~ for sufficiently high concentrations, the data obtained can be expressed in terms of Eqn. 03). As can be seen from Fig. 7, all lines converge at the origin and therefore k"p = 0. The calculated 0"1!

--

.Tm

3 0 O.J(

0"05

]

I

I

o.,o

o.o

[Active

center$~-z~ 3

1

o. o

M -2/3

Fro. 7. Nature of active centres in ethylene oxide polymerization, K + as counter-ion. 1 A.O°, in bulk; 2--50 °, THF; 3--60°, THF. * Calculated by the single point method.

Polymerization of Ethylene Oxide

1431

dependence of kl on [P*] is in good agreement with experimental data (see Fig. 6, curve

4).

The stability of associates decreases with increasing cation size from Na + to Cs +. In the case of Na +, this results also in a higher value of the association factor. The complete inactivity of Li-metal in epoxide polymerization t6'2') is probably due to extremely strong association of active centres. The fact that the stability of the associates decreases with the cation ionic radius indicates the contact nature of ion pairs. The high coulomb energy prevents solvent molecules from entering between the ions. To some extent, this is confirmed by thermodynamic characteristics of association (Table 2). Heat and especially entropy changes in this process seem to be abnormal, but are characteristic of ionic association in a solvating medium. This behaviour usually is due to the difference between solvation of free ions and ion pairs. Solvation consists of two parts: specific---caused by direct solvent coordination to the ion, and non-specific. The latter contribution can be approximately estimated for ions according to Born and for ion pairs from the equations of Denison and Ramsey (2a) or Fuoss. (z4) The process of ion pair association might be represented by the following consecutive steps: extraction of ion pairs from the solvent, their association and return of these associates into solution. Assuming the cyclic structure (l l) for associates and the interaction of all ions, the enthalpy and entropy changes can be expressed as: l ' 0 3 N e 2 [1 + ~lnD~

AHA

aD

ASA .

.

1.03Ne 2 . . aD

\

(14)

a--~--TnT /

alnD ¢9T

+ ASr

(15)

where a is the equilibrium interionic distance in an ion pair, D is the dielectric constant of the solvent; ASr is the entropy loss in association of ion pair, only the translational degree of freedom being taken into account (according to Fuoss(24)). Therefore the contribution of specific interaction can be estimated from comparison of observed and calculated values of AHA and ASA, because Eqns. (14)-(15) take into account only the non-specific, electrostatic component of solvation. The results of this comparison are given in Table 3. TABLE 3. ANALYSIS OF THE THERMODYNAMIC CHARACTERISTICS OF ASSOCIATION OF LIVING POLYETHYLENE

OXIDESIN T H F (70 °) Counterion

a~

K+ Cs +

2"66 3"04

AHa,obs. AHA,calc.* AHcoord. ASA,obs. 21 "0 2"7

3"8 3"3

--17"2 + 0"6

92 38

ASr --9 --9

ASa,calc.* 81 71

AS©oord. --38 + 6

* F r o m Eqns. (14--15); enthalpy in kcal.mole - 1, entropy--in e.u. a l n D / ~ l n T = - - 1 . 1 8 ; ~31nD/aT --4.03 × 10 - s grad -1 for THF.

1432

K.S. KAZANSKII,A. A. SOLOVYANOVand S. G. ENTELIS

Ion pair association is seen to be accompanied by desolvation: n -~O.Met.x T H F ~- (~O.Met.y THF), ~ n (x-y) THF.

(16)

This is the cause of the endothermic nature and entropy increase in this process. Assuming that coordination of a solvent molecule with cation yields an energy of 3-5 kcaL mole -1 and that the entropy loss is 8-10 e.u., x - y ~ 1-2 can be obtained from these data for K ÷. This effect is not so strong in the case of Cs ÷ because of the weU-known weak solvation of this cation in THF. Undoubtedly, differences in enthalpy and entropy of free and associated ion pairs can be due not only to the number of solvent molecules in the coordination sphere of ions, but also to the different solvation energies. This is not taken into account here. Similar conclusions can be made also from thermodynamic data on the dissociation of ion pairs of "living" polyethylene oxide in THF. (la) The chain propagation parameters. The rate constants for the anionic polymerization of ethylene oxide are much lower than those for styrene, for instance, mainly due to energy reasons. The high electrostatic stability of the ion pair is probably the main hindrance to the entry of a monomer molecule. Indeed, a higher rate constant and lower activation energy are observed for Cs +. The high activation energy for epoxide polymerization is in part compensated for by the abnormally high pre-exponential factor of 1011-10la M - L sec-L More usual values of these factors are 10s-109. High values can be explained in terms of desolvation in the transition state. This would explain the normal value of the pre-exponential factor for Cs + as solvation of this cation in T H F is weak. More information on the propagation mechanism could be obtained from the dependence of polymerization rate on dielectric constant but, in view of the strong specific solvation effects, selection of an appropriate solvent would be difficult. High values of rate constants in bulk polymerization (D = 14 for monomer) confirm the effect of dielectric constant on propagation kinetics. These questions are under investigation. REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (I0) (11) (12) (13) (14) (15) (16)

G. Gee et al.,J, chem. Soc. 1338, 1345 (1959). G. J. Stockburger and J. D. Brandner, J. Am. Oil chem. Soc. 40, 590 (1963). I. Ishii et al., J. chem. Soc., Japan, Industr. chem. Sect. 62, 105, 413 (1959); ibid. 65, 360 (1962). N. N. Lebedev and Yu. L Baranov, Vysokomolek. Soed. 8, 198. (1966); ibid. Kinetika i Kataliz 7, 619 (1966). N. N. Lebedev and V. F. Shvets, Kinetika i Kataliz 6, 782 (1965). M. F. Sorokin et al., Lakokrasochn. Mater. No. 3--4 (1962). M. F. Sorokin et al., Kinetika i Kataliz 9, 548, 666 (1968). D. H. Richards and M. Szwarc, Trans. Faraday Soe. 55, 1644 (1959). T. L. Dudek, Diss. Abstr. 22, 1407 (1961). G. Allen, C. Booth, S. J. Hurst, N. M. Jones and C. Price, Europ. Polym. J. 8, 391 (1967). A. Rembaum, J. Moacanin and E. Cuddihy, J. Polym. Sci. CA, 529 (1963). S. Boileau, G. Champetier and P. Sigwalt, J. Polym. Sci. C16, 3021 (1967). A. A. Solovyanov and K. S. Kazanskii, Vysokomolek. Soed. In press. N. S. Baird, Can. J. Chem. 47, 2306 (1969). I). C. Bradley, Progress in Inorganic Chemistry, Vol. II, p. 303. A. P. Simonov, D. N. Shigorin, T. V. Talalaeva and K. A. Kocheshkov, Izv. Akad. Nauk SSSR, Khim. Ser. 1126 (1962).

Polymerization of Ethylene Oxide (17) (18) (19) (20) (21) (22) (23) (24)

1433

M. Szwarc, Carbanion, Living Polymers and Electron-Transfer Processes, New York (1969). L. J. Fetters, J. Polym. Sci. B2, 425 (1964). D. H. RJehards, J. Polym. Sci. B6, 417 (1968). V. A. Bessonov et al., Zh. obshch. Khim. 37, 109 (1967). J. E. Figueruelo and D. J. Worsfoeld, Europ. Polym. J. 4, 439 (1968). E. C. Steiner, R. R. Pelletier and R. O. Trucks, J. Am. chem. Soc. 86, 4678 (1964). J. T. Denison and J. B. Ramsey, J. Am. chem. Soc. 77, 2615 (1955). R. M. Fuoss and F. Accascina, Electrolytic Conductance, New York (1959).

Rq~mm~--On a ~tudi6 en d~tail les cin~tiques de polym~risations d a m le T H F de l'oxyde d'~thyl~ne, amo~ par les complexes naphtal~ne-Na, K et Cs. La polym~risation est du premier ordre par rapport au monora~re sans terminaison ni transfert de chaines. La relation compliqu6~ existant entre la vitesse de polym~risation et la concentration des centres actifs est due aux fortes associations. A partir de cette relation on a d~termin6 les constantes de vitesse de propagation et les param~tres thermodynamiques de l'association. On a montr6 que les esp/~ces actives de la propagation ~taient du type palres d'ions en contact. Lorsque l'on passe du N a + au Cs + leur activit~ croit et leur tendance ~t l'association d/x~roit. La solvatation des esp/~:es actives joue un rule primordial dans ce processus. Sonunario--Si ~: studiata dettagliatamente la cinetica della polimerizzazione di ossido ci etilene in T H F con complessi naftalenici Na, K e Cs come iniziatori. La polimeri~azione ~ di primo ordine rispetto al monomero, senza trasferimento o terminazione di catena. La complicata dipendenza della velocita di polimeri~Ta~ione dalla concentrazione attiva di centro/~ dovuta a forte associazione. Da tale dipendenza sono state determinate le constanti di velocit~ di propagazione e i parametri termodinamici d'associazone. Si mostra che le coppie di ioni di tipo a contatto sono di attiva propagazione. Dal Na + al Cs + aumenta la loru attivita e diminuisce il loro potere di associazione. In tale processo gioca la parte decisiva la solvatazione delle coppie attire. Z a ~ m m e n f a u u n g - - D i e K.inetik der Polymerisation des .~thylenoxids in T H F mit Na, K und CsNaphthalin Komplexen als Initiatoren wurde eingehend untersucht. Die Polymerisation ist erster Ordnung in Bezug auf das Monomere, ohne Kettenabbruch oder 0bertragung. Die komplizierte Abhangigkeit der Polymerisationsgeschwindigkeit v o n d e r Konzentration der aktiven Zentren beruht auf starker Assoziation. Aus dieser Abhangigkeit wurden die Wachstumskonstanten und thermodynamische Parameter der Assoziation bestimmt. Es wird nachgewiesen, dab Ionenpaare vom Kontakttyp die aktive, alas Wachstum ausl6sende Spezies sind. Von N a + zum Cs + nimmt ihre Aktivitat zu und ihre Assoziationsneigung ab. Die Solvatation der aktiven Spezies spielt bei diesem Prozess die entscheidende Rolle.