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Ion triplets in the cationic polymerization of β-propiolactone over (C2H5)2HOSbF6 as initiator
Polymer Science U.8.B.R. Vol, 20, pp. 6S9--646. Pergamon Presto Ltd. 1979. Printed in Poland
0052-$950/78/0801-0~9507.50/0
ION TRIPLETS IN THE CATIONIC POLYMERIZATION OF fl-PROPIOLACTONE OVER (C2H5)2HOSbFs AS INITIATOR* B. G. BELEI~'KAYA and Y~.. B. LYUDVIG L. Ya. Karpov Physical Chemistry Research I n s t i t u t e
(Received 4 M a y 1977) The rate of fl-propiolactone (PL) polymerization over (C~Hs)~HOSbF6 as initiator in CH~Cl~ or CHsNO2 is described b y the equation: V=kpKc ~"[M]/[M]$ (½ < x < 2 ) t y p ical for the cationic polymerization of lactones on triplet ions. The process mechanism differs slightly at low and larger initial concentrations of the monomer; this is linked with the form in which the majority of the growing chain ends is present and results in differences of the order of the reaction with respect to the monomer (x=½ for low a n d x = 2 for larger monomer concentrations), of the K dependence on the dielectric constant of the medium, and of the activation energy of these two processes.
THE previous study [1] had shown the cationic polymerization of 8-caprolactone (CL) at 50 ° and of fl-propiolactone (PL) at 20°C, when initiated by the oxonium salts forming the SbCI~ cation, or the SbF~ cation in the case of the CL polymerization at ti0°C, to proceed on free ions with a complete dissociation of the growing chain ends. The reaction rate is described in the case of PL by the equation [2]: d[M] kvc[M] or~" [M]0 k,c . -- d---~=KI[M]---~ m ~-~ K-~]o t , (1) in which [Mo] and [M] are the original and current monomer concentration; c, initiator concentration; k p / K , constant of the "lactone" chain propagation. The slope of the kinetic response line is a function of the initiator and the original monomer concentrations. Experiments [2] showed it to be independent of the dielectric constant of the medium. We are describing in this report the study of the PL polymerization over the dialkyloxonium salt (C2Hs)2HO+SbF~ and compare the effects of the SbCl~ and SbF~ counter ions on the PL and CL polymerizations. EXPERIMENTAL
The (C,H6)~HOSbF6 initiator was synthesized b y reacting the a n t i m o n y pentafluorido etherate with a n ether solution of dry, gaseous hydrogen fluoride according to +
SbFd(C~Hs)sO+HF/(C2Hs~20 -> (C2Hs)2OHSbF; * Vysokomol. soyed. A20: No. 3, 565-571, 1978. 639
640"
:
:.
.
. . . .
B. G. BELEN'KAYA et al.
.'
The SbFs etherate was produced b y slowly adding drops of SbF5 to a supercooled (--78°C) dry ether while mixing; this yielded a hard, white suspension which changed at 0°C to a n achromatic solution. The combination of this etherate solution with the,,dry I-IF solution
n," tl''-'o r ~1
'
lu~ -~-~r rsV 5
17
I]
l
,.. 171i 0.8
ia
'~
3
g
O'#
1000
2000
3000
"I°g ~M]~/ 1.8~
L#0@O
log ~-Q ".,4
"VJ 1_51
s
.A "
T,'me,min
,0.~
#
_
o,.//, 4
0.8
a
o.~
O'Z~
O. l I
I
I
i
I
l
I
I
Z
I
log
e, mi/~
O'q I
2000
l
I
#000
I
l
GOO0
i
I
8000 Time, m/n
FIG. 1. The kinetic curves of the P L polymerization over (C2Hs)=HOSbF6 in: a, b--CH3Cla; c, d--CHaNO 3 at various concentrations of: a, d - - t h e initiator; b, v - - t h e monomer, at 20°C: a--monomer----3.5 mole/1, c×10a; 1--1.395; 2--2.00; 3--3.45; 4--5.80; 5--9-31; 6--17-1 mole/1, 2.7x 10 -3 mole/1, initiator; b - - c = 8 . 7 3 x 10 -a mol0/1., monomer, mole/1.: •--6-2; 2--4.92; 3--3.76; d--1.66; 5--1.03; c--v----3"72X10-3 mole/1, monomer, mole/L: 1--6.05; 2--3.84; 3--2.96; 4--1.176; 5--1.01; d - - 5 mole/1, monomer, v × 103, mole/1.: 1--1.45; 2--2.61; 3--4.65; 4--8.55.
Cationic polymerization of fl-propiolactone
641
in dry ether at 0°C gave a mixture of two liquid phases of which the lower was separated, washed repeatedly with ether, and then subjected to a vacuum while mixing. The above product was analysed in a "Brfiker ttX-90" PMR instrument. The chemical shifts were determined against tetramethylsilane as reference. The PMR spectrum of the product was identical with that of the dialkyloxonium salt [3]. RESULTS
T h e kinetic curves o f t h e P L p o l y m e r i z a t i o n over the (C~Hs)2HOSbF ~ i n i t i a t o r in m e t h y l e n e chloride as solvent axe shown in Fig. 1 at various i n i t i a t o r a n d m o n o m e r concentrations. F i g u r e l a contains for comparison also those in w h i c h t h e process was carried out over (C~Hs)2HOSbC1 e as initiator. T y p i c a l for t h e presence of the S b F ~ cation is t h e following: 1) a slower process rate; 2) t h e existence o f a n initial " j u m p " due to the process being v e r y rapid in t h e initial stage; 3) a change o f the slope of the kinetic c u r v e during t h e r e a c t i o n . T h e u p w a r d c u r v a t u r e of t h e response lines m u s t be associated w i t h t h e effect o f t h e dielectric c o n s t a n t of the m e d i u m on t h e process. T h e T a b l e compares its value on the 3 c o m p o n e n t s o f t h e s y s t e m a t 20°C. Component pL PPL solution CHIC12 in CH2CI~ (~ 6 mole/1.) 44*
8.9
9.2
Special e x p e r i m e n t a l d e t e r m i n a t i o n s showed t h e dielectric c o n s t a n t o f t h e PL-CH2C12 m i x t u r e to be calculable b y a d d i t i v i t y f r o m the dielectric c o n s t a n t s o f its components. T h e large e-differences b e t w e e n P L a n d P P L result in a substantial change o f t h e dielectric properties of t h e m e d i u m during polymerizat i o n a n d this could affect ket in the equation: In ([M~0/[M])----]ceft. T h e f a c t t h a t e for the m e d i u m affects ket was confirmed b y the decrease o f the process r a t e on changing f r o m CH2C12 t o CH2N03 as solvent (Fig. 1). Vital to the discovery of the process m e c h a n i s m was the order of the reaction w i t h respect to the initial c o m p o n e n t s concentration, i.e. to find kef =f(c, [M]o ). Iso-dielectric conditions were o b v i o u s l y essential to the d e t e r m i n a tion of this function of ]Cef and e. T h e order w i t h respect to the initiator was f o u n d as follows. A series of tests was m a d e a t identical m o n o m e r c o n c e n t r a t i o n (3.5 mole/1.) b y v a r y i n g the initiator c o n c e n t r a t i o n (Fig. la), to get the same °/o conversion; in these the ]cef was f o u n d as the angle of the t a n g e n t d r a w n to the kinetic curves (kef-----tan a). T h e logarithmic dependences o f these values on the initial initiator c o n t e n t at v a r i o u s conversions is a bundle o f parallel lines (Fig. 2). The order of the reaction f o u n d f r o m the slope of these lines was 3/2. T h e same value was got for lower (1 mole/1.) a n d higher (6.2 mole/1.) m o n o m e r concentrations. A test series a t identical initiator a n d differir~g m o n o m e r concentrations~ was set up to d e t e r m i n e the order o f the reaction w i t h respect t o the initial m o n o m e r c o n c e n t r a t i o n (Fig. lb). P o i n t s for differing conversions, b u t s y s t e m , * This value is more precise than that published earlier [2].
B. G. BELEN'KAYA et al.
642
h a v i n g t h e s a m e dielectric c o n s t a n t , w e r e selected in this case for t h e isodielectrie plots. T h e dielectric c o n s t a n t of t h e s y s t e m w a s e v a l u a t e d for v a r i o u s c o n v e r s i o n s b y t h e a d d i t i v i t y s c h e m e in w h i c h t h e 8 o f its c o m p o n e n t s w h i c h h a d b e e n g i v e n -lot ;÷an o~ i
•
-Iogfan~ 5.0
2
-logc
3 o.2 o., ~Slo9tM1o
Y'zo. 2
l~a. 3
Fie. 2. Determination of the order of the reaction with respect to the initiator for 3.5 mole/1. monomer in CHIC12; log [M]0/[M] ratios: 1--0.2; 2--0.4; 3--0.6; 4--0-8. l~ko. 8. The determination of the order of reaction in CHIClj with respect to the monomer; c--18-37X 10 -s mole/l. Dielectric constant: 1--10.6; 2--11.4; 3--12-2; 4--13.6. a b o v e w e r e considered. T h e l o g a r i t h m i c d e p e n d e n c e o f t h e isodielectric c o n s t a n t s ket on t h e initial m o n o m e r c o n c e n t r a t i o n is i l l u s t r a t e d in l~ig. 3. One c a n see i t t o b e a b u n d l e o f c u r v e s for v a r i o u s ~ v a l u e s w h i c h indicates a change o f -lo9 ~an ct -lo
a
9 ~an ( r
6.4(
¢8-
6'0
5.~
5"6
5"Z
2
5.0
5"2
2"0
b
"i
1
I
i
2.z/-
I
I
2.8 -1o9 c
I
o.!
r
T
I
I,
I
O.Z+os[M.To-
FIe. 4. Determination of the order of reaction: a--with respect to the initiator; b--with respect to the monomer; CHsNOI as solvent. Dielectric constant: 1--38.65; 2--38.75.
Cationic polymerization of fl-proplolactone
643
the reaction order with respect to the monomer when its concentration increases. One gathers from these results t h a t the order (evaluated from the tan ~ of the curves in Fig. 3) changes from --~ to --2 as [M]o increases from 1 to 6.2 molefl. [2Vl]o kc+ log [M] -- 2.3[M]~ t
(2)
Equation (2) was verified in a series of experiments in which nitromethane was used as the solvent. The latter has a larger dielectric constant (ea¢=38), so t h a t one can approximate the conditions in the initial process stages to isodielectric ones. Figure lc and d show the kinetic curves of a process in which the component concentrations were varied, while Fig. 4 shows the logarithanio dependence of ket on the initial components concentrations. The order of the reaction with respect to the initiator, like in methylene chloride, equalled 3]2, and with respect to the monomer ranged from --½ to --2, depending on its concentration (Fig. 4). Equation (2) thus described the P L polymerization in solvents differing in polarity. The process rate differences are due in the examined systems to the effect of e on kef. In our earlier work [1] we had examined the cationic polymerization kinetics of lactones over ionic associates in the shape of triplet ions: (q+) 0
(X) 0
'0
(P+)
0
0
0
~C---O=C ~ C =O+,~C+ + O=C
0
-~- ~ ;== O=C (CH2)n
~ o (a-) 0 0 I1÷ I K~' I
(Y)
0 II
~ C---O=C~ ~-~ CC=+0A+- ~~ I (Q)
0 II
0 I[
A-
0
0 0 I1. /I ~---~ (~---O=C\
/I --i-O=C\II
K T X , I ~ - ~ - - ~ KTA
(CH*)n
(CHz)n
(P)
(CH,z)n
0 II
C+A-+C ~
A- ~ C+A -
(Tx)
(TA)
Where the triplet ions Tx were the reactive centres, the process will be described b y the equation: T X~ A log [M]° kpKTc ( I + K T c ) t [M] =
+
+
+.,
KxK1 [M]o
(3)
in Iwhich k~ is the chain propagation constant on ion triplets under the condi-
644
B.G.
BELEN'KAYA e$
al.
tion t h a t the main portion of the growing chains exists as paired ions Y, and b y equation T
X
[~]- kpKTKxc
log [M]°
-]-
A
(KaKI[M]i-KTKxC)* , ~ ~ t KaK1 [M]0
(4)
where the main proportion of the growing chains exists as paired ions P. I n the ease of K~c<
7.T ~ r X .
~ p ~ x T t~
log ~
K~K~M~t
log [M]0
kpKTKxC
[M]--
x ~L jo T X ~ *
,t
K~ K 1[M]o
(5)
(6)
These equations describe the reaction kinetics for two different states of the main proportion of growing chain ends. These states, which are extremes, can change from one into the other and form an intermediate series of systems in which the extreme states are presented as different specific weights. The portion of states P will obviously increase as the initial monomer concentration increases. The order of the reaction with respect to [M]0 will change in this case from --½ to ~2.
The comparison of equations (5) and (6) with the experimentally found eqn. (2) showed them to be identical. For low monomer concentrations will apply: T X kpKT K~K'-~ - - , ~ KxK1
(7)
and for large ones, T
X
K =-K"-- kpKTKx ~ k~K1
(8)
Our analysis of the process kinetics in the range of low and higher monomer concentrations shows the polymerization in these two systems to have slightly differing mechanisms which are characterized by having a different reaction order with respect to the monomer, but also different constants K. The comparison of eqn. (7) and (8) naturally leads to the assumption t h a t firstly constants K' and K " must have differing dependences on e, and secondly t h a t the activation energies of the two examined processes must differ. The K' and K " dependences on the dielectric constant of the medium, D, are reproduced in l~ig. 5, which also contains the dependence of an averaged constant which was calculated for a medium concentration of the monomer. The points belonging to the largest D values belong to system PL-CHaNO 2. The fact that the points are easily connected by straight lines confirms the above.. conclusion about the identity of the mechanisms of the PL polymerization i~
Cationic polymerization of fl-propiolactone
645
these two solvents. The results also show that the extent to which K depends on e increases on changing from K " to K'. The analytical shape of the K' and K " dependences on e according to Fig. 5 is: 26 log K ' = - - 1 . 6 8 ~ - - - for [M]0=l mole/1. 55 log K"----3.53-~- - - for [M]o=6.2 mole/1. The activation energies of the two systems are 91.5 a n d 103.5 kJ/mole f o r [lY[]0= 1.0 and 6.2 mole/1, respectively.
,~,cm2/ohrn.equig I'0
30
0'5
25 ....
I
6
.=
lg
I
8
20
m//D
FIG. 5
30 l/0 OxlO~, rnole/l.
FIG. 6
:FIG. 5. T h e d e p e n d e n c e o n t h e dielectric c o n s t a n t o f t h e m e d i u m of c o n s t a n t s : 1--K'; 2--K"; 3 - - a v e r a g e c o n s t a n t K . Fzc. 6. T h e
electroconductance
of
polymerization a t 20°C.
system
PL-(C2Hs)=OHSbF~-CHzCI=
The examined mechanism of the P L polymerization over SbF~ shows the ion triplets to be chiefly responsible for the process kinetics. This idea is supported b y the anomalous dependence of the equivalent eleetroconductance on dilution (Fig. 6). The comparison of the results reported here with those of earlier work [1, 2] shows the SbCl~ and SbF~ counter ions differently affect the P L polymerization at 20°C; their behaviour is practically identical in the CL polymerization at 50°C. Although the latter process is more alkaline, the transition to the triplet range takes place approximately in the same concentration range as with P L and the reason appears to be the concentration difference of the initiator as well as that of the process temperature in these two processes. Translated by K . A. ALLEN
~}46
S . P . RUDOBASHTAet a~. REFERENCES
1. B. G. BELEN'KAYA, Ye. B. LYUDVIG and A. I. LEVENKO, Vysokomol. soyed. A20: 559, 1978 (Translated in Polymer Sei. U.S.S.R. 20: 3, 1978) 2. Ye. B. LYDAVIG and A. K. KHOMYAKOV, Dokl. Akad. Nauk SSSR 201: 877, 1971 3. B. G. BELEN'KAYA and Ye. B. LYUDVIG, Dokl. Akad. Nauk SSSR 224: 583, 1975
PolymerScienceU.S.S.R. Vol. 20, pp. 646-653. ~ ) PergamonPress Ltd. 1979.Printed in Poland
POLYMER
MEMBRANES
0032-$950178/0301-0646507.50/0
AND
TO WATER
THEIR
PERMEABILITY
VAPOUR*
S. P. RUDOBASHTA, V. ~[. DMITRIEV a n d A. N. PLANOVSgn Chemical Engineering Institutes, Tambov and Moscow
(Received 17 May 1977) The diffusion equilibria and the mass transport of water vapour through poly~mide 6, 12 and through PVC films have been studied and the results analysed. The isothermal concentration dependences of the mass transport coefficients were obtained by stationary and non-stationary methods; these agreed well. Equations have been formulated for the gas phase permeability and mass transport coefficients using the partial kinetic parameters for stationary conditions. A zonal method of calculating the moisture sorption kinetics by a hygroscopic material tightly packed in a polymer film are explained by using mass transport data. T H E h e r m e t i c p a c k i n g o f chemicals, foods, p h a r m a c e u t i c a l s a n d o t h e r p r o d u c t s , a s well as o f i n s t r u m e n t s a n d m a c h i n e r y , t o p r e s e r v e t h e i r quality, is t o d a y o f g r e a t i m p o r t a n c e . N o n - p o r o u s p o l y m e r films are u s e d all o v e r t h e world for t h i s p u r p o s e . T h i s m a k e s it v i t a l to k n o w t h e m e c h a n i s m o f t h e w a t e r v a p o u r p e r m e a t i o n o f t h e s e m a t e r i a l s as well a s t h e kinetics o f this process. T h e r e are v a r i o u s w a y s in w h i c h a g a s o f v a p o u r can p e r m e a t e a m e m b r a n e ; t h e s e d e p e n d on t h e s t r u c t u r e of t h e l a t t e r . A m a t e r i a l w i t h a c a p i l l a r y p o r o u s z t r u c t u r e will p r o d u c e t h e t r a n s p o r t o f t h e gas or v a p o u r b y t h e p h e n o m e n a w h i c h t ~ k e place in t h e pores [1], while a n o n - p o r o u s m a t e r i a l will give rise to a migration by molecular,diffusion. T h e m a s s t r a n s f e r t h r o u g h a n o n - p o r o u s m e m b r a n e is t h e result o f a sequence o f t h e following e l e m e n t a r y acts: a diffusion (molecular or t u r b u l e n t ) o f t h e d i s t r i b u t e d c o m p o u n d f r o m t h e b u l k o f t h e m e d i u m to t h e surface o f t h e m e r e * Vysokomol. soyed. A20: No. 3, 572-578, 1978.
0052-$950/78/0801-0~9507.50/0
ION TRIPLETS IN THE CATIONIC POLYMERIZATION OF fl-PROPIOLACTONE OVER (C2H5)2HOSbFs AS INITIATOR* B. G. BELEI~'KAYA and Y~.. B. LYUDVIG L. Ya. Karpov Physical Chemistry Research I n s t i t u t e
(Received 4 M a y 1977) The rate of fl-propiolactone (PL) polymerization over (C~Hs)~HOSbF6 as initiator in CH~Cl~ or CHsNO2 is described b y the equation: V=kpKc ~"[M]/[M]$ (½ < x < 2 ) t y p ical for the cationic polymerization of lactones on triplet ions. The process mechanism differs slightly at low and larger initial concentrations of the monomer; this is linked with the form in which the majority of the growing chain ends is present and results in differences of the order of the reaction with respect to the monomer (x=½ for low a n d x = 2 for larger monomer concentrations), of the K dependence on the dielectric constant of the medium, and of the activation energy of these two processes.
THE previous study [1] had shown the cationic polymerization of 8-caprolactone (CL) at 50 ° and of fl-propiolactone (PL) at 20°C, when initiated by the oxonium salts forming the SbCI~ cation, or the SbF~ cation in the case of the CL polymerization at ti0°C, to proceed on free ions with a complete dissociation of the growing chain ends. The reaction rate is described in the case of PL by the equation [2]: d[M] kvc[M] or~" [M]0 k,c . -- d---~=KI[M]---~ m ~-~ K-~]o t , (1) in which [Mo] and [M] are the original and current monomer concentration; c, initiator concentration; k p / K , constant of the "lactone" chain propagation. The slope of the kinetic response line is a function of the initiator and the original monomer concentrations. Experiments [2] showed it to be independent of the dielectric constant of the medium. We are describing in this report the study of the PL polymerization over the dialkyloxonium salt (C2Hs)2HO+SbF~ and compare the effects of the SbCl~ and SbF~ counter ions on the PL and CL polymerizations. EXPERIMENTAL
The (C,H6)~HOSbF6 initiator was synthesized b y reacting the a n t i m o n y pentafluorido etherate with a n ether solution of dry, gaseous hydrogen fluoride according to +
SbFd(C~Hs)sO+HF/(C2Hs~20 -> (C2Hs)2OHSbF; * Vysokomol. soyed. A20: No. 3, 565-571, 1978. 639
640"
:
:.
.
. . . .
B. G. BELEN'KAYA et al.
.'
The SbFs etherate was produced b y slowly adding drops of SbF5 to a supercooled (--78°C) dry ether while mixing; this yielded a hard, white suspension which changed at 0°C to a n achromatic solution. The combination of this etherate solution with the,,dry I-IF solution
n," tl''-'o r ~1
'
lu~ -~-~r rsV 5
17
I]
l
,.. 171i 0.8
ia
'~
3
g
O'#
1000
2000
3000
"I°g ~M]~/ 1.8~
L#0@O
log ~-Q ".,4
"VJ 1_51
s
.A "
T,'me,min
,0.~
#
_
o,.//, 4
0.8
a
o.~
O'Z~
O. l I
I
I
i
I
l
I
I
Z
I
log
e, mi/~
O'q I
2000
l
I
#000
I
l
GOO0
i
I
8000 Time, m/n
FIG. 1. The kinetic curves of the P L polymerization over (C2Hs)=HOSbF6 in: a, b--CH3Cla; c, d--CHaNO 3 at various concentrations of: a, d - - t h e initiator; b, v - - t h e monomer, at 20°C: a--monomer----3.5 mole/1, c×10a; 1--1.395; 2--2.00; 3--3.45; 4--5.80; 5--9-31; 6--17-1 mole/1, 2.7x 10 -3 mole/1, initiator; b - - c = 8 . 7 3 x 10 -a mol0/1., monomer, mole/1.: •--6-2; 2--4.92; 3--3.76; d--1.66; 5--1.03; c--v----3"72X10-3 mole/1, monomer, mole/L: 1--6.05; 2--3.84; 3--2.96; 4--1.176; 5--1.01; d - - 5 mole/1, monomer, v × 103, mole/1.: 1--1.45; 2--2.61; 3--4.65; 4--8.55.
Cationic polymerization of fl-propiolactone
641
in dry ether at 0°C gave a mixture of two liquid phases of which the lower was separated, washed repeatedly with ether, and then subjected to a vacuum while mixing. The above product was analysed in a "Brfiker ttX-90" PMR instrument. The chemical shifts were determined against tetramethylsilane as reference. The PMR spectrum of the product was identical with that of the dialkyloxonium salt [3]. RESULTS
T h e kinetic curves o f t h e P L p o l y m e r i z a t i o n over the (C~Hs)2HOSbF ~ i n i t i a t o r in m e t h y l e n e chloride as solvent axe shown in Fig. 1 at various i n i t i a t o r a n d m o n o m e r concentrations. F i g u r e l a contains for comparison also those in w h i c h t h e process was carried out over (C~Hs)2HOSbC1 e as initiator. T y p i c a l for t h e presence of the S b F ~ cation is t h e following: 1) a slower process rate; 2) t h e existence o f a n initial " j u m p " due to the process being v e r y rapid in t h e initial stage; 3) a change o f the slope of the kinetic c u r v e during t h e r e a c t i o n . T h e u p w a r d c u r v a t u r e of t h e response lines m u s t be associated w i t h t h e effect o f t h e dielectric c o n s t a n t of the m e d i u m on t h e process. T h e T a b l e compares its value on the 3 c o m p o n e n t s o f t h e s y s t e m a t 20°C. Component pL PPL solution CHIC12 in CH2CI~ (~ 6 mole/1.) 44*
8.9
9.2
Special e x p e r i m e n t a l d e t e r m i n a t i o n s showed t h e dielectric c o n s t a n t o f t h e PL-CH2C12 m i x t u r e to be calculable b y a d d i t i v i t y f r o m the dielectric c o n s t a n t s o f its components. T h e large e-differences b e t w e e n P L a n d P P L result in a substantial change o f t h e dielectric properties of t h e m e d i u m during polymerizat i o n a n d this could affect ket in the equation: In ([M~0/[M])----]ceft. T h e f a c t t h a t e for the m e d i u m affects ket was confirmed b y the decrease o f the process r a t e on changing f r o m CH2C12 t o CH2N03 as solvent (Fig. 1). Vital to the discovery of the process m e c h a n i s m was the order of the reaction w i t h respect to the initial c o m p o n e n t s concentration, i.e. to find kef =f(c, [M]o ). Iso-dielectric conditions were o b v i o u s l y essential to the d e t e r m i n a tion of this function of ]Cef and e. T h e order w i t h respect to the initiator was f o u n d as follows. A series of tests was m a d e a t identical m o n o m e r c o n c e n t r a t i o n (3.5 mole/1.) b y v a r y i n g the initiator c o n c e n t r a t i o n (Fig. la), to get the same °/o conversion; in these the ]cef was f o u n d as the angle of the t a n g e n t d r a w n to the kinetic curves (kef-----tan a). T h e logarithmic dependences o f these values on the initial initiator c o n t e n t at v a r i o u s conversions is a bundle o f parallel lines (Fig. 2). The order of the reaction f o u n d f r o m the slope of these lines was 3/2. T h e same value was got for lower (1 mole/1.) a n d higher (6.2 mole/1.) m o n o m e r concentrations. A test series a t identical initiator a n d differir~g m o n o m e r concentrations~ was set up to d e t e r m i n e the order o f the reaction w i t h respect t o the initial m o n o m e r c o n c e n t r a t i o n (Fig. lb). P o i n t s for differing conversions, b u t s y s t e m , * This value is more precise than that published earlier [2].
B. G. BELEN'KAYA et al.
642
h a v i n g t h e s a m e dielectric c o n s t a n t , w e r e selected in this case for t h e isodielectrie plots. T h e dielectric c o n s t a n t of t h e s y s t e m w a s e v a l u a t e d for v a r i o u s c o n v e r s i o n s b y t h e a d d i t i v i t y s c h e m e in w h i c h t h e 8 o f its c o m p o n e n t s w h i c h h a d b e e n g i v e n -lot ;÷an o~ i
•
-Iogfan~ 5.0
2
-logc
3 o.2 o., ~Slo9tM1o
Y'zo. 2
l~a. 3
Fie. 2. Determination of the order of the reaction with respect to the initiator for 3.5 mole/1. monomer in CHIC12; log [M]0/[M] ratios: 1--0.2; 2--0.4; 3--0.6; 4--0-8. l~ko. 8. The determination of the order of reaction in CHIClj with respect to the monomer; c--18-37X 10 -s mole/l. Dielectric constant: 1--10.6; 2--11.4; 3--12-2; 4--13.6. a b o v e w e r e considered. T h e l o g a r i t h m i c d e p e n d e n c e o f t h e isodielectric c o n s t a n t s ket on t h e initial m o n o m e r c o n c e n t r a t i o n is i l l u s t r a t e d in l~ig. 3. One c a n see i t t o b e a b u n d l e o f c u r v e s for v a r i o u s ~ v a l u e s w h i c h indicates a change o f -lo9 ~an ct -lo
a
9 ~an ( r
6.4(
¢8-
6'0
5.~
5"6
5"Z
2
5.0
5"2
2"0
b
"i
1
I
i
2.z/-
I
I
2.8 -1o9 c
I
o.!
r
T
I
I,
I
O.Z+os[M.To-
FIe. 4. Determination of the order of reaction: a--with respect to the initiator; b--with respect to the monomer; CHsNOI as solvent. Dielectric constant: 1--38.65; 2--38.75.
Cationic polymerization of fl-proplolactone
643
the reaction order with respect to the monomer when its concentration increases. One gathers from these results t h a t the order (evaluated from the tan ~ of the curves in Fig. 3) changes from --~ to --2 as [M]o increases from 1 to 6.2 molefl. [2Vl]o kc+ log [M] -- 2.3[M]~ t
(2)
Equation (2) was verified in a series of experiments in which nitromethane was used as the solvent. The latter has a larger dielectric constant (ea¢=38), so t h a t one can approximate the conditions in the initial process stages to isodielectric ones. Figure lc and d show the kinetic curves of a process in which the component concentrations were varied, while Fig. 4 shows the logarithanio dependence of ket on the initial components concentrations. The order of the reaction with respect to the initiator, like in methylene chloride, equalled 3]2, and with respect to the monomer ranged from --½ to --2, depending on its concentration (Fig. 4). Equation (2) thus described the P L polymerization in solvents differing in polarity. The process rate differences are due in the examined systems to the effect of e on kef. In our earlier work [1] we had examined the cationic polymerization kinetics of lactones over ionic associates in the shape of triplet ions: (q+) 0
(X) 0
'0
(P+)
0
0
0
~C---O=C ~ C =O+,~C+ + O=C
0
-~- ~ ;== O=C (CH2)n
~ o (a-) 0 0 I1÷ I K~' I
(Y)
0 II
~ C---O=C~ ~-~ CC=+0A+- ~~ I (Q)
0 II
0 I[
A-
0
0 0 I1. /I ~---~ (~---O=C\
/I --i-O=C\II
K T X , I ~ - ~ - - ~ KTA
(CH*)n
(CHz)n
(P)
(CH,z)n
0 II
C+A-+C ~
A- ~ C+A -
(Tx)
(TA)
Where the triplet ions Tx were the reactive centres, the process will be described b y the equation: T X~ A log [M]° kpKTc ( I + K T c ) t [M] =
+
+
+.,
KxK1 [M]o
(3)
in Iwhich k~ is the chain propagation constant on ion triplets under the condi-
644
B.G.
BELEN'KAYA e$
al.
tion t h a t the main portion of the growing chains exists as paired ions Y, and b y equation T
X
[~]- kpKTKxc
log [M]°
-]-
A
(KaKI[M]i-KTKxC)* , ~ ~ t KaK1 [M]0
(4)
where the main proportion of the growing chains exists as paired ions P. I n the ease of K~c<
7.T ~ r X .
~ p ~ x T t~
log ~
K~K~M~t
log [M]0
kpKTKxC
[M]--
x ~L jo T X ~ *
,t
K~ K 1[M]o
(5)
(6)
These equations describe the reaction kinetics for two different states of the main proportion of growing chain ends. These states, which are extremes, can change from one into the other and form an intermediate series of systems in which the extreme states are presented as different specific weights. The portion of states P will obviously increase as the initial monomer concentration increases. The order of the reaction with respect to [M]0 will change in this case from --½ to ~2.
The comparison of equations (5) and (6) with the experimentally found eqn. (2) showed them to be identical. For low monomer concentrations will apply: T X kpKT K~K'-~ - - , ~ KxK1
(7)
and for large ones, T
X
K =-K"-- kpKTKx ~ k~K1
(8)
Our analysis of the process kinetics in the range of low and higher monomer concentrations shows the polymerization in these two systems to have slightly differing mechanisms which are characterized by having a different reaction order with respect to the monomer, but also different constants K. The comparison of eqn. (7) and (8) naturally leads to the assumption t h a t firstly constants K' and K " must have differing dependences on e, and secondly t h a t the activation energies of the two examined processes must differ. The K' and K " dependences on the dielectric constant of the medium, D, are reproduced in l~ig. 5, which also contains the dependence of an averaged constant which was calculated for a medium concentration of the monomer. The points belonging to the largest D values belong to system PL-CHaNO 2. The fact that the points are easily connected by straight lines confirms the above.. conclusion about the identity of the mechanisms of the PL polymerization i~
Cationic polymerization of fl-propiolactone
645
these two solvents. The results also show that the extent to which K depends on e increases on changing from K " to K'. The analytical shape of the K' and K " dependences on e according to Fig. 5 is: 26 log K ' = - - 1 . 6 8 ~ - - - for [M]0=l mole/1. 55 log K"----3.53-~- - - for [M]o=6.2 mole/1. The activation energies of the two systems are 91.5 a n d 103.5 kJ/mole f o r [lY[]0= 1.0 and 6.2 mole/1, respectively.
,~,cm2/ohrn.equig I'0
30
0'5
25 ....
I
6
.=
lg
I
8
20
m//D
FIG. 5
30 l/0 OxlO~, rnole/l.
FIG. 6
:FIG. 5. T h e d e p e n d e n c e o n t h e dielectric c o n s t a n t o f t h e m e d i u m of c o n s t a n t s : 1--K'; 2--K"; 3 - - a v e r a g e c o n s t a n t K . Fzc. 6. T h e
electroconductance
of
polymerization a t 20°C.
system
PL-(C2Hs)=OHSbF~-CHzCI=
The examined mechanism of the P L polymerization over SbF~ shows the ion triplets to be chiefly responsible for the process kinetics. This idea is supported b y the anomalous dependence of the equivalent eleetroconductance on dilution (Fig. 6). The comparison of the results reported here with those of earlier work [1, 2] shows the SbCl~ and SbF~ counter ions differently affect the P L polymerization at 20°C; their behaviour is practically identical in the CL polymerization at 50°C. Although the latter process is more alkaline, the transition to the triplet range takes place approximately in the same concentration range as with P L and the reason appears to be the concentration difference of the initiator as well as that of the process temperature in these two processes. Translated by K . A. ALLEN
~}46
S . P . RUDOBASHTAet a~. REFERENCES
1. B. G. BELEN'KAYA, Ye. B. LYUDVIG and A. I. LEVENKO, Vysokomol. soyed. A20: 559, 1978 (Translated in Polymer Sei. U.S.S.R. 20: 3, 1978) 2. Ye. B. LYDAVIG and A. K. KHOMYAKOV, Dokl. Akad. Nauk SSSR 201: 877, 1971 3. B. G. BELEN'KAYA and Ye. B. LYUDVIG, Dokl. Akad. Nauk SSSR 224: 583, 1975
PolymerScienceU.S.S.R. Vol. 20, pp. 646-653. ~ ) PergamonPress Ltd. 1979.Printed in Poland
POLYMER
MEMBRANES
0032-$950178/0301-0646507.50/0
AND
TO WATER
THEIR
PERMEABILITY
VAPOUR*
S. P. RUDOBASHTA, V. ~[. DMITRIEV a n d A. N. PLANOVSgn Chemical Engineering Institutes, Tambov and Moscow
(Received 17 May 1977) The diffusion equilibria and the mass transport of water vapour through poly~mide 6, 12 and through PVC films have been studied and the results analysed. The isothermal concentration dependences of the mass transport coefficients were obtained by stationary and non-stationary methods; these agreed well. Equations have been formulated for the gas phase permeability and mass transport coefficients using the partial kinetic parameters for stationary conditions. A zonal method of calculating the moisture sorption kinetics by a hygroscopic material tightly packed in a polymer film are explained by using mass transport data. T H E h e r m e t i c p a c k i n g o f chemicals, foods, p h a r m a c e u t i c a l s a n d o t h e r p r o d u c t s , a s well as o f i n s t r u m e n t s a n d m a c h i n e r y , t o p r e s e r v e t h e i r quality, is t o d a y o f g r e a t i m p o r t a n c e . N o n - p o r o u s p o l y m e r films are u s e d all o v e r t h e world for t h i s p u r p o s e . T h i s m a k e s it v i t a l to k n o w t h e m e c h a n i s m o f t h e w a t e r v a p o u r p e r m e a t i o n o f t h e s e m a t e r i a l s as well a s t h e kinetics o f this process. T h e r e are v a r i o u s w a y s in w h i c h a g a s o f v a p o u r can p e r m e a t e a m e m b r a n e ; t h e s e d e p e n d on t h e s t r u c t u r e of t h e l a t t e r . A m a t e r i a l w i t h a c a p i l l a r y p o r o u s z t r u c t u r e will p r o d u c e t h e t r a n s p o r t o f t h e gas or v a p o u r b y t h e p h e n o m e n a w h i c h t ~ k e place in t h e pores [1], while a n o n - p o r o u s m a t e r i a l will give rise to a migration by molecular,diffusion. T h e m a s s t r a n s f e r t h r o u g h a n o n - p o r o u s m e m b r a n e is t h e result o f a sequence o f t h e following e l e m e n t a r y acts: a diffusion (molecular or t u r b u l e n t ) o f t h e d i s t r i b u t e d c o m p o u n d f r o m t h e b u l k o f t h e m e d i u m to t h e surface o f t h e m e r e * Vysokomol. soyed. A20: No. 3, 572-578, 1978.