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Effect of water on the polymerization of tetrahydrofuran
EFFECT OF WATER ON THE POLYMERIZATION OF TETRAHYDROFURAN* A. I. KUZAYEV,G. N. KOMRATOV,G. V. KOROVIlVAand S. G. ElVTELIS Aif-diated Branch of the Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 7 April 1969) I:~ investigations of the kinetics of polymerization of tetrahydrofuran (THF) on the catalyst system THF-BFs-F~-oxide [1], it was found t h a t as the water concentration was increased the polymerization stopped when an equilibrium state was reached. I t was suggested t h a t water acted as a termination agent, and was not a chain transfer agent as had been stated previously [2]. I t was later shown that, with an excess of water in the system during the polymerization of TH_F, water is a termination agent [3].
The effect of water on the polymer yield, its molecular weight and molecularweight distribution (MWD) has been studied in the present work for the polymerization of T H F on the catalyst system B F 3 . T H F ~- the nitrate of glycidyl alcohol (NGA) in 1,2-diehloroethane (DCE). EXPERIMENTAL The method of studying the polymerization kinetics and the purification of TI-IF, NGA, BF3-TI-I_F and DCE have been described previously [1, 4]. The MWD of the polymers were studied b y two methods: fractionation in a column filled with divinylpolystyrene gel and working on the gel-permeability mechanism, and fractionation on silica-gel. I n the first case, T H F was used as a elutriant, and in the second case methylethylketone. Figure 1 shows the relationship between the logarithm of the molecular weight and the volume of elutriant which has flowed through the column. I n the case of fraetionation b y the gel-permeability mechanism, the same relationship holds for all the specimens (curve 1); in the case of fractionation on silica-gel, as the proportion of macromolecules containing two hydroxyl groups is increased, the slope of the relationships becomes less (Fig. 1, curve 2-4). The q u a n t i t y of elutriant thus increases, i.e. fractionation on silica-gel is related to the ease with which the polymer macromolecules are adsorbed.
RESULTS AND DISCUSSION F i g u r e 2 s h o w s k i n e t i c r e l a t i o n s h i p s for t h e p o l y m e r b u i l d - u p d u r i n g t h e p o l y m erization of T H F in the presence of a d d i t i o n of water. The e x p e r i m e n t a l results a r e p r e s e n t e d i n T a b l e 1. It may be seen from Table I and Fig. 2 that the rate of polymerization, the f i n a l p o l y m e r y i e l d a n d i t s m o l e c u l a r w e i g h t fall as t h e c o n c e n t r a t i o n o f w a t e r a d d e d t o t h e s y s t e m is i n c r e a s e d . S i n c e c h a i n t r a n s f e r t o t h e m o n o m e r or s o l v e n t * Vysokomol. soyed. A12: No. 5, 1033-1038, 1970. 1169
A.I. KuzA~e-~vet e2.
1170
does not occur during the polymerization of T H F , the relative constant for chain termination b y water m a y be calculated b y using a modified Mayo equation [5]:
l
1
kt [H O]0
(1)
P kMoio
where/~ is the degree of polymerization at low degrees of conversion,/c t and/¢~ are the constants for termination and chain propagation respectively and t is the polymerization time. Figure 3 shows the linear relationship of equation (1), from which a value of/ct//cp equal to 2.5 could be found. Since the rate constant for chain propagation in the polymerization of T H F at 20°C is 6.75× 10 -a 1./mole.sec [1], k t is equal to 1.7 × 1 0 - 3 1./mole.sec.
3 4"0I 3"5 3"0
A •
ZX
I
60
/00
f40
Vel ,
ml
FIG. 1. Relationship between the logarithm of the molecular weight and the elutriant volume (Vel) during fractionation: 1 --by the gel-permeability mechanism; 2-4--by the adsorption mechanism. OH-group content, wt. ~o: 2--0.44; 3--1.60; 4--2.71. On the other hand, the ratio kt/k p m a y be determined from the logarithmic relationship between the limiting yield and the ratio of the water concentration to the catalyst concentration [3]: this has the form: log (I--~)=
log
[H20]0
(2)
From the linear relationship obtained from equation (2), it was found that kt/kp=0.2, and hence the valae of kt is equal to 3.3X 10 -21./mole.sec. The addition of water to the system was made before the start of the reaction and also during its course. Water was, moreover, added to the catalyst. As m a y be seen from the data shown in Table 1, the w a y in which the water is introduced does not have an appreciable effect on the polymerization of T H F . When the tetrahydrofuranate of boron trifluoride is replaced b y its hydrate, the kinetics
Effect of water on polymerization of t e t r a h y d r o f u r a n
1171
of the polymer build-up remains the same as in the case of additions of water at a r a t e e q u a l t o t h e a m o u n t o f c a t a l y s t ( F i g . 2, c u r v e 2). As noted above, the molecular weight of the polymer decreases as the water c o n c e n t r a t i o n is i n c r e a s e d . W h e n e v e r t h e p o l y m e r i z a t i o n is c a r r i e d o u t w i t h o u t additions of water,/~r w and M n 'increase monotonically during the course of the
¢z,%
//
:--2
f-,-
0.2
30
I0
3
f
0.1
/o
14
f I
I
I
20
I
Time, hp
I
zlO
D
0
I
I
0-05
0-1
[H#]0/[M]0
Fxo. 2 FIG. 3 F I e . 2. Kinetics of polymer build-up at various water concentrations (mole/1.): 1 - 0-02; 2--0.16; 3--0.29; 4--0.81; 20°C; [ T H F ] = 6 . 6 mole/1.; [C]=0-16 mole/1. Solid lines correspond to the introduction of water into the system, and the points to the introduction of BFa hydrate. F i e . 3. Dependence of the degree of polymerization on the ratio [I-I=O]/[THF] at low degrees of conversion and a constant reaction time.
process• The molecular weight changes little during the course of polymerization with considerable additions of water, but the tendency to an increase is still retained (Table 2). With [H,O]o/[C]
1. E F F E C T
OF WATERJOI~ THE YIELD AND 1VIWD OF THE POLYMER
(20°C; [ T H F ] = 6 . 6 mole/1.; [C]=0.16mole/1.)
© ©
0.003 0.02 0.165" 0-17 ~.16
24 214 25 240 30
57"5 46.5 41.4 40.3 40.3
8000 3643 2085 2210 2207
4000 2180 1813 1850 1850
2.0 [0"168# 1.67 0"25 I 1-15 0.29 1.19
* W a t e r a d d e d a f t e r the s t a r t o f the reaction. t W a t e r m i x e d w i t h the c a t a l y s t before being a d d e d to the s y s t e m .
53 96 96 196 172
40.0 19.0 16.7 11"7 6.5
2080 1000
487
1810 1200 860 300 426
l'15 1.16 1.14
1172
A.I. KUZAYEVet al.
end of the reaction aS the polymer yield changes by a small amount. Relationships of this type are shown in Fig. 4. The calculated relationship between _~r a n d the degree of conversion corresponding to the living polymer type of polymerization is also shown in Fig. 4 for comparison. Typical integral MWD curves are shown !
3
3000
2000
1000 i,
20
zlO oc,%
FIG. 4. Change in the molecular weight (/1I,, 2, 3, 4;/l~w, 1) during polymerization with small additions of water: 1, 2-- 0-05; 3 -- 0.03 mole/1.; 4 -- calculated relationship corresponding to the formation of a living polymer. in Fig. 5 for polymers obtained with various concentrations of water. Table 1 gives data about the polydispersity of the polymers at the end of the reaction for various concentrations of water. As m a y be seen from Fig. 5 and Table 1, the polydispersity of the final specimens decreases as the concentration of water in the system is increased. Table 2 shows data about the change in polydispersity during the course of the reaction. TABLE 2. CHANGEIN POLYDISPERSITYDLrRINGREA.OTIOlq (Concentrations: [THF]=6.6; [H,O]=0.29; [C]----0-16mole/1.; 20°C) Yield, wt. %
~w
~.
~w/~:l~
4-5 10-5
968
720 750
1.30
Yield, wt. %
Mw
M"
~/~"
14.6 16.7
1005 1000
792 860
1.26 1.16
We used NGA as cocatalyst in the initiation of the polymerization of THF. T~l~ing into account the presence of water in the system with the introduction of B F 3, one must consider the following equilibrium reactions which lie at the basis of the initiation of polymerization: BFs" T H F -}-N G A ~ BF,. N G A - 5 T H F BFa'TI-IF-}-H.O ~ BF3"H.O-TI-IF ~ BFs'H.O-}-T]tF BFs'I-I20+NGA ~- BFs'NGA'I-I.O ~ BFs'NGA+~.O
(3)
(4) (5)
Effect of water on polymerization of t e t r a h y d r o f u r a n
1173
Reactions (3)-(5) are connected with the capacity of boron trifluoride to form complexes with electron-donor compounds [5]. In whatever form BF3 is introduced into the system, its distribution between the oxygen-containing compounds will be determined by the structure of the latter. Therefore the experimental results obtained in the presence of the complex B F s - T H F with [H20]----[BFa.THF] are the same as the results when BFa" H~O is introduced [6]. During the opening of the oxide ring, the complex BF3"NGA leads to the formation of a trialkyloxonium salt, which Meerwein [6] termed an internal +
trialkyloxonium salt, of the form BFa--O--CH--CH,--O(CH2)4 (I), capable of I
CH2ONO~ effecting the polymerization of THF. In the presence of water, the reactions (4) and (5) also lead to the formation of other types of active centre (AC):
./
HO\
BF30H-4- T H F -~
]
~--
BF.OH
(6)
CH,ONO, II or
H0~--
BF3OH
III
The dialkyloxonium ion of the form I I I is incapable of effecting the polymerization o f T H F [6], since proton transfer from one T H F molecule to another occurs when this ion is attacked by another monomer molecule, because of the high TABLE 3.
DEPENDENCE
O F T H E P R O P O R T I O N O F D I O L S PORM:ED O N T H E C O N D I T I O N S O F
THF (Concentrations: [THF] ~ 6.8; [C] = 0.16 moleL1. ) P O L Y M E R I Z A T I O N OF
Temperature, °C 40 40 40 20 20" 20
[H,O] × l0 s, mole/1,
Yield, wt. %
[OH], wt. %
0'4 0"4 0.4 0"3 25.0 32.0
9"1 17"2 28.0* 58"0* 19.0 15.8
5"25 3"80 2 50 0.44 1"85 2"71
Bromine
F r a c t i o n of
~n
number, g/100 g
diols in polymer
480 640 900 4400 1200 800
3"1 4.3 4"9 0.8
0"50 0.45 0"30 0-25 0"30 0.28
* Polymerization reached a n e q u i l i b r i u m state.
mobility of the hydrogen atom in such a system. It has been postulated [3] that opening of the tetrahydrofuran ring may be effected when the ring is attacked by a water molecule: H0(CH~)4 + H20 -* HO(CH.)~OH BF-30H
t
H
BF3OH
(7)
1174
A.I. KUZAYEVet al.
There should thus be a n accumulation of butandiol in the system, or butandiol should at least be present in quantities commensurate with the concentration of BF 8. We were, however, unable to find derivatives of butandiol from the polymerization of T H F in the presence of water by gas-chromatography with a sensitivity of 0.01 mole/1. The question of the part played by type I I AC in the polymerization of THF, or more accurately the question of the stability of this ion pair, is more complicated. Apart from other factors, the stability of oxonium ions is determined by t h e nucleophilic properties o f the counter-ion, and will be greater the less nucleophilic is the counter-ion [6]. The growth of the polytetrafurane chain to high degrees o f polymerization on AC of this t y p e is therefore reduced in probability because o f the concurrent reaction: ÷
H0~0(CH~)~ ~ THF --* H0w~,0(CH~)40H ~- BFsTHF.
(8)
BFsOH
When water is introduced into the system it interacts with type I AC by the following reactions: _ + jT__H_FHO~wvO(CH2),OH -[- BF,'THF (9-1) B F ~ O (CH8)4 + H~O-- I I ---~ HO~O(CHs)~CH----CHz -}- BFs"H20 (9-2) II As a result of the occurrence of reactions (9-1) and (9-2), the number of AC capable of effecting polymerization decreases during the course of the process, and the rate of polymerization decreases. Since 1 mole of water is used for each mole of AC according to the reactions shown above, the limiting yield of polymer should not change when [H~O]<[C]. However, the polymerization system does not reach an equilibrium condition even with [H20]----0.2-0.3 [C]. T h e products of reaction (9) further-react with active centres, leading to an increase in the molecular weight towards the end of the reaction (Fig. 4). Data about the molecularweight distribution confirms this. Whereas the polydispersity rises during the process if there are no addition of water, in the presence of water the m a x i m u m polydispersity is found at the start of the reaction (Table 2): this is connected with exhaustion of the low molecular weight products formed at the start of the reaction. The formation of polymer diols I by reaction (9-1) has been established by two methods. I n the first method the concentration of hydroxyl groups, the bromine number and the number-average molecular weight were determined, and on the basis of these the portion of products of type I and I I was calculated. The results are shown in Table 3. The second method is based on the ability of silica-gel to separate polymers according to the concentration of hydroxyl groups in them. During elutriation of a polymer, maeromo!eeules which have hydroxyl groups at one end or generally which do not contain hydroxyl groups are washed away first, and then the macromolecular diols. The last two lines in Table 3 give data obtained by fractionation on silica-gel.
Effect of water on polymerization of tetrahydrofuran
1175
I t m a y be seen from Table 3 that although the proportion of diols varies during the course of the reaction, after completion of the process it hardly depends at all on the initial concentration of water in the system. This is an indication that termination reactions given b y equations (9-1) and (9-2) occur in parallel.
oIy// I
O
~
I
Z
l
#
I
I
MnXfO'3
5. Integral MWD curves for polytetrahydrofuran obtained with various water additions, namely: 1--0-81; 2--0.32; 3--0.16; 4--0.03 mole/1. W is the weight fraction of the polymer. FIG.
Since the termination of AC of t y p e II, which m a y be formed according to equation (6), b y a molecule of water should lead to the formation of diols, an increase in the water concentration in the system should be accompanied b y an increase in the proportion of the polymer diols. An increase in the water concentration in the system does not lead, however, to the expected result. The proportion of these propagation centres in the polymerization of T H F is consequently low, despite the fact that the probability of their formation should increase as the concentration of water is increased. It m a y therefore be concluded that the hydroxylcontaining connter-ion is unstable, in agreement with the experimental data and with data in the literature. CONCLUSIONS
(1) A s t u d y has been made of the effect of water on the polymerization kinetics of tetrahydrofuran (THF) in solution in 1,2-dichloroethane in the presence of the catalytic system BFa" T H F + t h e nitrate of glicidyl alcohol. I t has been shown that water is a terminating agent for the propagation of chains. The relative constant for termination b y water has been determined and found to be 2-54-0.8 × 10 -2 1./mole.sec at 20°C. (2) The molecular-weight distribution of the polymer has been studied. I t has been found that the polydispersity of polytetrahydrofuran decreases as the concentration of water in the system is increased. (3) The nature of the end groups of the polymers has been investigated, and suggestions for the termination reaction have been p u t forward. Translated by G. F. lYIODT,E~
1176
T.E. LIPATOVAet al. REFERENCES
10 A. I. KUZAYEV, G. N. KOMRATOV, G. V. KOROVINA and S. G. ENTELIS, Vysokomol. soyed. All: 989, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 5, 1117, 1969) 2. B. A. ROZENBERG, Dissertation, 1964 3. Ye. B. LYUDVIG, Ye. L. BERMAN, V. A. PONOMARENKO and S. S. MEDVEDEV, Dokl. A_N SSSR 182: 108, 1968 4. A. I. KUZAYEV, G. N. KOiYIRATOV,G. V. KOROVINA, G. A. MIRONTSEVA and S. G. ENTELIS, Vysokomol. soyed. All: 443, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 502, 1969) 5. Kationnaya polimerizatsiya (Cationic Polymerization) P. Plesch (Ed.), Izd. "Mir", 1966 (Russian translation) 6. H. MEERWEIN, D. DELFS and H. MORSCHEL,Angew. Chemie 72: 927, 1960
E F F E C T OF T E M P E R A T U R E OF P O L Y U R E T H A N E
ON T H E F O R M A T I O N
NETWORKS FROM OLIGOMERS*
T. E. LIPATOVA, A. YE. ~ESTEROV, V. K. IYASHCHEI~KO and Y r . S. LIPATOV Polymer Chemistry Institute, Ukr. S.S.R. Academy of Sciences (Received 7 April 1969)
WE have previously shown [1, 2] t h a t the process of forming three-dimensional polyurethanes from oligomers has a number of special features which distinguish it from the usual process of obtaining a three-dimensional network from monomers. One of the probable reasons for the appearance of the special features is the strong intermolecular interaction both in the oligomeric systems themselves and also in the polymeric products obtained from them. I t has been shown [3, 4] t h a t the intermolecular interactions m a y change even during the formation of the polyurethanes. Since a change in intermolecular interaction is generally accompanied b y a change in the mobility of the molecular chains, this in its turn should probably have a considerable effect on the process of forming the three-dimensional network structure. I n connection with this, it is of interest to investigate the process of forming the polyurethane network under conditions of different intermolecular-interactions, achieved by varying the temperature conditions under which the process is carried out. * Vysokomol. soyed. A12: No. 5, 1039-1043, 1970.
(Received 7 April 1969) I:~ investigations of the kinetics of polymerization of tetrahydrofuran (THF) on the catalyst system THF-BFs-F~-oxide [1], it was found t h a t as the water concentration was increased the polymerization stopped when an equilibrium state was reached. I t was suggested t h a t water acted as a termination agent, and was not a chain transfer agent as had been stated previously [2]. I t was later shown that, with an excess of water in the system during the polymerization of TH_F, water is a termination agent [3].
The effect of water on the polymer yield, its molecular weight and molecularweight distribution (MWD) has been studied in the present work for the polymerization of T H F on the catalyst system B F 3 . T H F ~- the nitrate of glycidyl alcohol (NGA) in 1,2-diehloroethane (DCE). EXPERIMENTAL The method of studying the polymerization kinetics and the purification of TI-IF, NGA, BF3-TI-I_F and DCE have been described previously [1, 4]. The MWD of the polymers were studied b y two methods: fractionation in a column filled with divinylpolystyrene gel and working on the gel-permeability mechanism, and fractionation on silica-gel. I n the first case, T H F was used as a elutriant, and in the second case methylethylketone. Figure 1 shows the relationship between the logarithm of the molecular weight and the volume of elutriant which has flowed through the column. I n the case of fraetionation b y the gel-permeability mechanism, the same relationship holds for all the specimens (curve 1); in the case of fractionation on silica-gel, as the proportion of macromolecules containing two hydroxyl groups is increased, the slope of the relationships becomes less (Fig. 1, curve 2-4). The q u a n t i t y of elutriant thus increases, i.e. fractionation on silica-gel is related to the ease with which the polymer macromolecules are adsorbed.
RESULTS AND DISCUSSION F i g u r e 2 s h o w s k i n e t i c r e l a t i o n s h i p s for t h e p o l y m e r b u i l d - u p d u r i n g t h e p o l y m erization of T H F in the presence of a d d i t i o n of water. The e x p e r i m e n t a l results a r e p r e s e n t e d i n T a b l e 1. It may be seen from Table I and Fig. 2 that the rate of polymerization, the f i n a l p o l y m e r y i e l d a n d i t s m o l e c u l a r w e i g h t fall as t h e c o n c e n t r a t i o n o f w a t e r a d d e d t o t h e s y s t e m is i n c r e a s e d . S i n c e c h a i n t r a n s f e r t o t h e m o n o m e r or s o l v e n t * Vysokomol. soyed. A12: No. 5, 1033-1038, 1970. 1169
A.I. KuzA~e-~vet e2.
1170
does not occur during the polymerization of T H F , the relative constant for chain termination b y water m a y be calculated b y using a modified Mayo equation [5]:
l
1
kt [H O]0
(1)
P kMoio
where/~ is the degree of polymerization at low degrees of conversion,/c t and/¢~ are the constants for termination and chain propagation respectively and t is the polymerization time. Figure 3 shows the linear relationship of equation (1), from which a value of/ct//cp equal to 2.5 could be found. Since the rate constant for chain propagation in the polymerization of T H F at 20°C is 6.75× 10 -a 1./mole.sec [1], k t is equal to 1.7 × 1 0 - 3 1./mole.sec.
3 4"0I 3"5 3"0
A •
ZX
I
60
/00
f40
Vel ,
ml
FIG. 1. Relationship between the logarithm of the molecular weight and the elutriant volume (Vel) during fractionation: 1 --by the gel-permeability mechanism; 2-4--by the adsorption mechanism. OH-group content, wt. ~o: 2--0.44; 3--1.60; 4--2.71. On the other hand, the ratio kt/k p m a y be determined from the logarithmic relationship between the limiting yield and the ratio of the water concentration to the catalyst concentration [3]: this has the form: log (I--~)=
log
[H20]0
(2)
From the linear relationship obtained from equation (2), it was found that kt/kp=0.2, and hence the valae of kt is equal to 3.3X 10 -21./mole.sec. The addition of water to the system was made before the start of the reaction and also during its course. Water was, moreover, added to the catalyst. As m a y be seen from the data shown in Table 1, the w a y in which the water is introduced does not have an appreciable effect on the polymerization of T H F . When the tetrahydrofuranate of boron trifluoride is replaced b y its hydrate, the kinetics
Effect of water on polymerization of t e t r a h y d r o f u r a n
1171
of the polymer build-up remains the same as in the case of additions of water at a r a t e e q u a l t o t h e a m o u n t o f c a t a l y s t ( F i g . 2, c u r v e 2). As noted above, the molecular weight of the polymer decreases as the water c o n c e n t r a t i o n is i n c r e a s e d . W h e n e v e r t h e p o l y m e r i z a t i o n is c a r r i e d o u t w i t h o u t additions of water,/~r w and M n 'increase monotonically during the course of the
¢z,%
//
:--2
f-,-
0.2
30
I0
3
f
0.1
/o
14
f I
I
I
20
I
Time, hp
I
zlO
D
0
I
I
0-05
0-1
[H#]0/[M]0
Fxo. 2 FIG. 3 F I e . 2. Kinetics of polymer build-up at various water concentrations (mole/1.): 1 - 0-02; 2--0.16; 3--0.29; 4--0.81; 20°C; [ T H F ] = 6 . 6 mole/1.; [C]=0-16 mole/1. Solid lines correspond to the introduction of water into the system, and the points to the introduction of BFa hydrate. F i e . 3. Dependence of the degree of polymerization on the ratio [I-I=O]/[THF] at low degrees of conversion and a constant reaction time.
process• The molecular weight changes little during the course of polymerization with considerable additions of water, but the tendency to an increase is still retained (Table 2). With [H,O]o/[C]
1. E F F E C T
OF WATERJOI~ THE YIELD AND 1VIWD OF THE POLYMER
(20°C; [ T H F ] = 6 . 6 mole/1.; [C]=0.16mole/1.)
© ©
0.003 0.02 0.165" 0-17 ~.16
24 214 25 240 30
57"5 46.5 41.4 40.3 40.3
8000 3643 2085 2210 2207
4000 2180 1813 1850 1850
2.0 [0"168# 1.67 0"25 I 1-15 0.29 1.19
* W a t e r a d d e d a f t e r the s t a r t o f the reaction. t W a t e r m i x e d w i t h the c a t a l y s t before being a d d e d to the s y s t e m .
53 96 96 196 172
40.0 19.0 16.7 11"7 6.5
2080 1000
487
1810 1200 860 300 426
l'15 1.16 1.14
1172
A.I. KUZAYEVet al.
end of the reaction aS the polymer yield changes by a small amount. Relationships of this type are shown in Fig. 4. The calculated relationship between _~r a n d the degree of conversion corresponding to the living polymer type of polymerization is also shown in Fig. 4 for comparison. Typical integral MWD curves are shown !
3
3000
2000
1000 i,
20
zlO oc,%
FIG. 4. Change in the molecular weight (/1I,, 2, 3, 4;/l~w, 1) during polymerization with small additions of water: 1, 2-- 0-05; 3 -- 0.03 mole/1.; 4 -- calculated relationship corresponding to the formation of a living polymer. in Fig. 5 for polymers obtained with various concentrations of water. Table 1 gives data about the polydispersity of the polymers at the end of the reaction for various concentrations of water. As m a y be seen from Fig. 5 and Table 1, the polydispersity of the final specimens decreases as the concentration of water in the system is increased. Table 2 shows data about the change in polydispersity during the course of the reaction. TABLE 2. CHANGEIN POLYDISPERSITYDLrRINGREA.OTIOlq (Concentrations: [THF]=6.6; [H,O]=0.29; [C]----0-16mole/1.; 20°C) Yield, wt. %
~w
~.
~w/~:l~
4-5 10-5
968
720 750
1.30
Yield, wt. %
Mw
M"
~/~"
14.6 16.7
1005 1000
792 860
1.26 1.16
We used NGA as cocatalyst in the initiation of the polymerization of THF. T~l~ing into account the presence of water in the system with the introduction of B F 3, one must consider the following equilibrium reactions which lie at the basis of the initiation of polymerization: BFs" T H F -}-N G A ~ BF,. N G A - 5 T H F BFa'TI-IF-}-H.O ~ BF3"H.O-TI-IF ~ BFs'H.O-}-T]tF BFs'I-I20+NGA ~- BFs'NGA'I-I.O ~ BFs'NGA+~.O
(3)
(4) (5)
Effect of water on polymerization of t e t r a h y d r o f u r a n
1173
Reactions (3)-(5) are connected with the capacity of boron trifluoride to form complexes with electron-donor compounds [5]. In whatever form BF3 is introduced into the system, its distribution between the oxygen-containing compounds will be determined by the structure of the latter. Therefore the experimental results obtained in the presence of the complex B F s - T H F with [H20]----[BFa.THF] are the same as the results when BFa" H~O is introduced [6]. During the opening of the oxide ring, the complex BF3"NGA leads to the formation of a trialkyloxonium salt, which Meerwein [6] termed an internal +
trialkyloxonium salt, of the form BFa--O--CH--CH,--O(CH2)4 (I), capable of I
CH2ONO~ effecting the polymerization of THF. In the presence of water, the reactions (4) and (5) also lead to the formation of other types of active centre (AC):
./
HO\
BF30H-4- T H F -~
]
~--
BF.OH
(6)
CH,ONO, II or
H0~--
BF3OH
III
The dialkyloxonium ion of the form I I I is incapable of effecting the polymerization o f T H F [6], since proton transfer from one T H F molecule to another occurs when this ion is attacked by another monomer molecule, because of the high TABLE 3.
DEPENDENCE
O F T H E P R O P O R T I O N O F D I O L S PORM:ED O N T H E C O N D I T I O N S O F
THF (Concentrations: [THF] ~ 6.8; [C] = 0.16 moleL1. ) P O L Y M E R I Z A T I O N OF
Temperature, °C 40 40 40 20 20" 20
[H,O] × l0 s, mole/1,
Yield, wt. %
[OH], wt. %
0'4 0"4 0.4 0"3 25.0 32.0
9"1 17"2 28.0* 58"0* 19.0 15.8
5"25 3"80 2 50 0.44 1"85 2"71
Bromine
F r a c t i o n of
~n
number, g/100 g
diols in polymer
480 640 900 4400 1200 800
3"1 4.3 4"9 0.8
0"50 0.45 0"30 0-25 0"30 0.28
* Polymerization reached a n e q u i l i b r i u m state.
mobility of the hydrogen atom in such a system. It has been postulated [3] that opening of the tetrahydrofuran ring may be effected when the ring is attacked by a water molecule: H0(CH~)4 + H20 -* HO(CH.)~OH BF-30H
t
H
BF3OH
(7)
1174
A.I. KUZAYEVet al.
There should thus be a n accumulation of butandiol in the system, or butandiol should at least be present in quantities commensurate with the concentration of BF 8. We were, however, unable to find derivatives of butandiol from the polymerization of T H F in the presence of water by gas-chromatography with a sensitivity of 0.01 mole/1. The question of the part played by type I I AC in the polymerization of THF, or more accurately the question of the stability of this ion pair, is more complicated. Apart from other factors, the stability of oxonium ions is determined by t h e nucleophilic properties o f the counter-ion, and will be greater the less nucleophilic is the counter-ion [6]. The growth of the polytetrafurane chain to high degrees o f polymerization on AC of this t y p e is therefore reduced in probability because o f the concurrent reaction: ÷
H0~0(CH~)~ ~ THF --* H0w~,0(CH~)40H ~- BFsTHF.
(8)
BFsOH
When water is introduced into the system it interacts with type I AC by the following reactions: _ + jT__H_FHO~wvO(CH2),OH -[- BF,'THF (9-1) B F ~ O (CH8)4 + H~O-- I I ---~ HO~O(CHs)~CH----CHz -}- BFs"H20 (9-2) II As a result of the occurrence of reactions (9-1) and (9-2), the number of AC capable of effecting polymerization decreases during the course of the process, and the rate of polymerization decreases. Since 1 mole of water is used for each mole of AC according to the reactions shown above, the limiting yield of polymer should not change when [H~O]<[C]. However, the polymerization system does not reach an equilibrium condition even with [H20]----0.2-0.3 [C]. T h e products of reaction (9) further-react with active centres, leading to an increase in the molecular weight towards the end of the reaction (Fig. 4). Data about the molecularweight distribution confirms this. Whereas the polydispersity rises during the process if there are no addition of water, in the presence of water the m a x i m u m polydispersity is found at the start of the reaction (Table 2): this is connected with exhaustion of the low molecular weight products formed at the start of the reaction. The formation of polymer diols I by reaction (9-1) has been established by two methods. I n the first method the concentration of hydroxyl groups, the bromine number and the number-average molecular weight were determined, and on the basis of these the portion of products of type I and I I was calculated. The results are shown in Table 3. The second method is based on the ability of silica-gel to separate polymers according to the concentration of hydroxyl groups in them. During elutriation of a polymer, maeromo!eeules which have hydroxyl groups at one end or generally which do not contain hydroxyl groups are washed away first, and then the macromolecular diols. The last two lines in Table 3 give data obtained by fractionation on silica-gel.
Effect of water on polymerization of tetrahydrofuran
1175
I t m a y be seen from Table 3 that although the proportion of diols varies during the course of the reaction, after completion of the process it hardly depends at all on the initial concentration of water in the system. This is an indication that termination reactions given b y equations (9-1) and (9-2) occur in parallel.
oIy// I
O
~
I
Z
l
#
I
I
MnXfO'3
5. Integral MWD curves for polytetrahydrofuran obtained with various water additions, namely: 1--0-81; 2--0.32; 3--0.16; 4--0.03 mole/1. W is the weight fraction of the polymer. FIG.
Since the termination of AC of t y p e II, which m a y be formed according to equation (6), b y a molecule of water should lead to the formation of diols, an increase in the water concentration in the system should be accompanied b y an increase in the proportion of the polymer diols. An increase in the water concentration in the system does not lead, however, to the expected result. The proportion of these propagation centres in the polymerization of T H F is consequently low, despite the fact that the probability of their formation should increase as the concentration of water is increased. It m a y therefore be concluded that the hydroxylcontaining connter-ion is unstable, in agreement with the experimental data and with data in the literature. CONCLUSIONS
(1) A s t u d y has been made of the effect of water on the polymerization kinetics of tetrahydrofuran (THF) in solution in 1,2-dichloroethane in the presence of the catalytic system BFa" T H F + t h e nitrate of glicidyl alcohol. I t has been shown that water is a terminating agent for the propagation of chains. The relative constant for termination b y water has been determined and found to be 2-54-0.8 × 10 -2 1./mole.sec at 20°C. (2) The molecular-weight distribution of the polymer has been studied. I t has been found that the polydispersity of polytetrahydrofuran decreases as the concentration of water in the system is increased. (3) The nature of the end groups of the polymers has been investigated, and suggestions for the termination reaction have been p u t forward. Translated by G. F. lYIODT,E~
1176
T.E. LIPATOVAet al. REFERENCES
10 A. I. KUZAYEV, G. N. KOMRATOV, G. V. KOROVINA and S. G. ENTELIS, Vysokomol. soyed. All: 989, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 5, 1117, 1969) 2. B. A. ROZENBERG, Dissertation, 1964 3. Ye. B. LYUDVIG, Ye. L. BERMAN, V. A. PONOMARENKO and S. S. MEDVEDEV, Dokl. A_N SSSR 182: 108, 1968 4. A. I. KUZAYEV, G. N. KOiYIRATOV,G. V. KOROVINA, G. A. MIRONTSEVA and S. G. ENTELIS, Vysokomol. soyed. All: 443, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 2, 502, 1969) 5. Kationnaya polimerizatsiya (Cationic Polymerization) P. Plesch (Ed.), Izd. "Mir", 1966 (Russian translation) 6. H. MEERWEIN, D. DELFS and H. MORSCHEL,Angew. Chemie 72: 927, 1960
E F F E C T OF T E M P E R A T U R E OF P O L Y U R E T H A N E
ON T H E F O R M A T I O N
NETWORKS FROM OLIGOMERS*
T. E. LIPATOVA, A. YE. ~ESTEROV, V. K. IYASHCHEI~KO and Y r . S. LIPATOV Polymer Chemistry Institute, Ukr. S.S.R. Academy of Sciences (Received 7 April 1969)
WE have previously shown [1, 2] t h a t the process of forming three-dimensional polyurethanes from oligomers has a number of special features which distinguish it from the usual process of obtaining a three-dimensional network from monomers. One of the probable reasons for the appearance of the special features is the strong intermolecular interaction both in the oligomeric systems themselves and also in the polymeric products obtained from them. I t has been shown [3, 4] t h a t the intermolecular interactions m a y change even during the formation of the polyurethanes. Since a change in intermolecular interaction is generally accompanied b y a change in the mobility of the molecular chains, this in its turn should probably have a considerable effect on the process of forming the three-dimensional network structure. I n connection with this, it is of interest to investigate the process of forming the polyurethane network under conditions of different intermolecular-interactions, achieved by varying the temperature conditions under which the process is carried out. * Vysokomol. soyed. A12: No. 5, 1039-1043, 1970.