Polymerization of epichlorohydrin caused by BF3 etherate

P O L Y M E R I Z A T I O N OF E P I C H L O R O H Y D R I N CAUSED BY BF8 ETHERATE * YA. I. F,STR12qand S. G. EWrELIS Associated Branch of Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 13 June 1968)

Ilq THE earlier p a p e r [1] we r e p o r t e d on t h e k i n e t i c s o f t h e p o l y m e r i z a t i o n o f e p i c h l o r o h y d r i n ( E C H ) a n d glycidic alcohol n i t r a t e caused b y gaseous B F a. I n p r a c t i c e liquid B F s complexes are generally u s e d as c a t a l y s t s , p a r t i c u l a r l y its d i e t h y l e t h e r a t e ( D E B F ) . I t was desired to s t u d y kinetic changes in t h e react i o n caused b y p a r t i c i p a t i o n o f t h e e t h e r in order to o b t a i n f u r t h e r d a t a r e g a r d i n g t h e p o l y m e r i z a t i o n m e c h a n i s m . T h e m o n o m e r was E C H . EXPERIMENTAL Rextctants: The monomer (ECH), solvent (methylene chloride) and BF s were purified and proportioned as in [1], The diethyl etherate of BFs (DEBF) was prepared directly in the thin-walled glass bulb by successively freezing equimolecular amounts of BFs and dry diethyl ether from the vapour phase. In some cases +the ether was placed in an ampoule cor~taining a solution of the monomer, in which case only BFs was frozen in the bulb. The excess ether was measured out into an ampoule in the experiments conducted with an excess of ether. BFa di-(isopropyl)etherate was prepared in the same way as DEBF. Triethyloxoniumfluoroborate (C2Hs)s O+BF-4 was obtained from the diethyl etherate of BFs and epichlorohydrin using the Meerwein [2] method. The purified and vacuum-dried salt was measured out into the thin-walled bulbs under argon. The calorimetric measuring procedure, and the methods used in separating and analysing the reaction products were the same as those described previously.

DISCUSSION OF RESULTS

The polymerization of ECH in the presence o f DEBF proceeds more slowly t h a n w i t h BFa, a n d so t h e m a i n m e a s u r e m e n t s were carried o u t a t 0 to - - 4 0 °. I t is seen f r o m Fig. 1 t h a t t h e kinetic curves are n o t S - s h a p e d , a n d t h e r e is r a p i d s a t u r a t i o n , w i t h o u t a n y i n d u c t i o n period. F i g u r e 2 shows t h e initial r a t e s o f p o l y m e r i z a t i o n (w0) a n d t h e p o l y m e r yield ( ~ ) p l o t t e d a g a i n s t t h e initial c o n c e n t r a tions o f m o n o m e r (lVI0) a n d c a t a l y s t (Co). I t was f o u n d t h a t in t h e e a r l y stages t h e r e a c t i o n is a p p r o x i m a t e l y second order ( ~ 1 . 8 ) w i t h r e s p e c t t o m o n o m e r , a n d t h e relationship b e t w e e n w o a n d Co c a n n o t be described b y a p o w e r law. * Vysokomol. soyed. A l l : No. 5, 1133-1139, 1969. 1286

Polymerization of epichlorohydrin caused by BFs etherate

1287

TABLE 1. POLYMERIZATI01~" O:F ECH CAUSED BY DEBF AT 0 ° (Co-----2"5× I0 -~, M o = 2 " O mole/L)

Time 20 sec 42 ,, 600 ,,

Yi~d,%

Mol. wt.

23'1 24.6 29.2

450 450 480

Time

Yield,~o

Mol. wt.

53.0 73.0 78.0

470 470 495

7620 sec 24hr 48 hr

T h e r e is a t e n d e n c y for increase in w 0 t o stop as Co rises. T h e yield of polymerization p r o d u c t s (a~) is m u c h lower t h a n in the presence of gaseous B F 3. Figure 2b shows t h a t if Co ~ 0 . 2 × 10 -2 mole/1. Wo and a~ t e n d to zero, as also in the presence

#o

#

. i 30

2

ls 10

f

1 I

IO0

I

300 Time, sec

I_

500

FI(~. 1. Characteristic kinetic curves of the polymerization of ECH caused by DEBF at --20 °, M0-~l'0 mole/1.; Co, mole/L× 10s: •--0"5; 2--1-17; 3--1.7 and 4--3-1. of BF3. T h e f r a c t u r e d line in Fig. 2b shows the relation o f wo to Co for the polymerization caused b y B F 8 o b t a i n e d on e x t r a p o l a t i n g the Arrhenius curve for ke~ t o - - 2 0 ° [1]. I n t h e presence of D E B F the reaction r a t e is several times lower t h a n with B F 3. I t m a y be shown t h a t the relationships described a b o v e for the polymerization of E C H in the presence o f D E B F are observed only w i t h slow initiation of the reaction. One would certainly e x p e c t t h a t p a r t i c i p a t i o n of the e t h e r would prim a r i l y affect the rates of initiation and termination. W i t h " s p o n t a n e o u s " init i a t i o n when the whole of the c a t a l y s t is rapidly c o n v e r t e d to active centres the initial r a t e is correctly described b y the expression w0=kpCoM ~ where k~ is the r a t e of p r o p a g a t i o n [1]. T h e m o d e r a t e r e d u c t i o n in t h e rate of initiation caused b y ether p a r t i c i p a t i n g in the reaction c a n n o t in this case reduce w 0 as would a rise in the r a t e of termination. A fall in the r a t e of initiation to a value commensurable with the r a t e of t e r m i n a t i o n would result in S-shaped kinetic

1288

YA. I. ESTRIN and S. G. ENTELIS

curves, as was shown in [1]. F u r t h e r r e d u c t i o n in the r a t e of initiation would lead to loss of the S-shapes t o g e t h e r with a m a r k e d reduction (of several orders) in w 0.

/%ki

A t the same time with slow initiation, when the expression w 0 - - - - - - C 0 ~ ~ kpkt is correct, (here/~i and/¢t are the rates of initiation and t e r m i n a t i o n [1]) a n y change in the rates of initiation or t e r m i n a t i o n should be reflected in corresponding changes in w 0.

~Z

O

I'0

/

~ I0

b

- I.o

0'6

0"6 "~ oo i

30

0"2 ~ I'0

2'0

~ 2

0.2

•

l.O

3'0

"~

2"0

3"0

Co , [0~, molefl.

Mo , mole/l.

FTG. 2. Initial rate (w0) and maximum yield ( ~ ) vs. initial concentration of monomer (a) and catalyst (b). Polymerization temperature -- 20°, C~----1.i7 × 10 -3 mole/1. (a); Me= 1.0 mole/1. (b). I t is therefore clear t h a t a change in w 0 a m o u n t i n g to several orders due to the addition of e t h e r would be possible only with slow initiation. Seeing t h a t the p o l y m e r yield is lower with D E B F t h a n with B F a we assume t h a t t h e role of chain t e r m i n a t i o n m u s t be greater in t h e presence o f D E B F . H o w e v e r , w h e n the reaction was carried out a t 0 ° for a long t i m e (up to two days) b y t h e ampoule m e t h o d it was f o u n d t h a t the rapid stage in the reaction was followed b y a slow one in which the yield is increased to values exceeding t h a t obt a i n e d in the p o l y m e r i z a t i o n with B F a (see Table 1). I t is therefore not the e t h e r t h a t is the real cause of chaifi t e r m i n a t i o n : m o s t p r o b a b l y the e t h e r reacts with t h e active centre to f o r m a new a n d considerably less reactive active centre.* W e assume t h a t t h e following sequence o f reactions takes place on adding D E B F to t h e m o n o m e r solution. T h e first stage is p r o b a b l y B F 3 exchange bet w e e n D E B F a n d monomer:

CH2 BF,.

(C,H,)~0+0~

CHs ~KB F , . O/

CH

\

-t- (C,H,),O

(I)

CH

* In viev of this e® in Fig. 2 should be taken to mean the yield of polymer at the end of the rapid stage,

Polymerization of epichlorohydrin caused by BFa etherato

1289

This rapid reaction is common to any ethers whether cyclic or acyclic in complexing reactions with B F s [3-6]. The equilibrium constant K is determined by the relative basicity of the ethers. Unfortunately the basicity of a-oxides with respect to B F a has not been determined owing to the instability of their complexes with B F 3. The reactions of initiation and chain propagation are probably not unlike the corresponding reactions without the ether: CH~ BF3" O

/

\

CH~

CH I R

--~ BFs--O--CH2--CH--O

R

\

(II)

CH t R

CH..

+ 0

R

+/

i

CH i R

CH~ (O--CH2--CH)~--O|

CH2

ki -

/ + O\

CH~ (IIl)

\

CH I R

H

R

CH ] R

I R

There must also be a termination reaction t h a t is first-order with respect to active centres and zero order with respect to monomer with a rate constant of k 0 [1]. In the presence of ether the process m a y be complicated by the following reactions resulting in the formation of acyclic internal oxonium salts: CH ~

C~H6

/

-

BFs" O

\

+/

+ (C2H5)~0-~BF3--O--CHr-CH--O I \ CH R C~H5

(IV)

i

R

~+/

CH~

+/

C2H5

CH +(C~Hd0 kot ~0--CH~--CH--0

R

I R

(v)

\C~H5

The acyclic trialkyloxonium ions formed in reactions IV and V m a y then react with monomer: C~H5

CH~

+/

~ O--CH2--CH--O

1

R

.

+ O

\

CI-I~

/

C~H5

\

CH

i

R

k'l ~ O--CH2--CH--OC2H5 / R

--*

+/

+ C2H50 \

(vi)

CH

i

R

* The nature of the termination processes will be the subject of the next report. ¢ ka is the rate of deactivation.

1290

YA. I. ESTRIN and S. O. E~rELm

giving rise to the formation of new active centres. I f k'l<
K - - c~° "JE°

(1)

co~ .~

taking into consideration that c~=Co--C~o and CoM=Eo, then (CoM)~+ g ~ o c ~ g M o C

o= O .

(2)

Hence: KMo

K2Mo~

.....

2-+X/--i- +~iVtoUo

c°M=-

(3)

(the --sign before the root has been omitted, as CMocannot be a negative value). Rearranging equation (3) we have:

Co

/~o/' /

4Co

1\).

(4)

In a case where 4C0

~o<1

(5)

we m a y assume that 4C° 2C0 1 q - - ~ ; ~ 1 - ~K1V[o ---

(6)

and then

coM=Eo~Co.

(7)

Since the C0fl~0 ratio in our experiments was approximately 0.01-0.03, condition (5) must be satisfied" if K > 0 . 1 . Therefore if condition (5) is fulfilled, the rapid establishment of a state of equilibrium will mean that practically all the B F 3 is bound in a complex with monomer, while the ether remains "free".

Polymerization of epichlorohydrin caus~d by BFs otherate

1291

Let us derive the equation for the rate of change in the number of active centres (cyclic internal oxonium salt) in accordance with reactions (II) and (V) taking the termination reaction into consideration:

dn

M

(8)

--dt = kic .lVI--ktn-- kdnE

where n is the number of active centres. Using the condition of the semi-stationary state with respect to active centres, i.e. taking dn/dv equal to zero, and taking (7) into account, the number of active centres at the start of the reaction will be:

kiCo~o no--~]gt_~_~dCO

(9)

Then the initial rate of polymerization:

Wo- - (d ~ l & )~=M =~pnJIo= kp~iC~°~

(]0)

kt+ kdCO " Equation (10) agrees with the observed square-law variation relating w o to M~ and presupposes that the dependence of w o on Co will become very slight as Ca rises.

/0

~

2 J

I

I

!

2

3

t.l,,ole

FIG. 3. Plots of Mo/W 2 o vs. 1/(Co)eftfor Mo=l'0 mole/1.: 1-- --38°; 2-- --20 °. Equation (10) m a y be rearranged in a form more convenient for graphic analysis: We

k i b p kikp. Co . 1

(11)~ 1

Figure 3 shows the curves obtained for - - v s . - when ]Ko=l.O mole/l. Wo (Co)o~ [(Co),~=Co--0.2 ×10 -2 mole/1.]. From the slope of these straight lines we find kt//ci/cp, i.e. l/heft is the reciprocal of the effective rate of polymerization with BF~

1292

YA. I. ESTRI~ and S. G. E~rr~ms

in the absence of ether. The sections cut off on the ordinate axis correspond to the value of kd/ki'/~p. The found values of kpbi//~t are 1.5 and 0.36 1)/mole~.sec at --20 and --38 ° respectively. The values o f / ~ extrapolated to the temperatures indicated above are 2.0 and 0.87 1.2/mole~.sec. respectively [1]. The lower values of/~i/~p/kt found for the polymerization with D E B F compared with the k ~ values found by extrapolation m a y be attributed to the inexactitude of the assumptions made in deriving equation (10). I n the first place the equilibrium (I) m a y not be established instantaneously. Secondly, if the equilibrium constant is between 0.1 and 0.01, C0~----E0~C0. At the same time the relationship between Co ~ and C0 m a y be regarded as approximately linear, i.e. equation (10) will remain correct if a correction factor, q:C~o/Co is introduced. Any other assumptions regarding the ratio of the rates of exchange, initiation and termination result in expressions contrary to the experimental findings. In particular the assumption that the equilibrium (I) is slowly established results in an equation where the order with respect to monomer is higher t h a n second. It was desired to verify certain consequences arising from the proposed scheme. A. I f the original amount of ether differs from the amount of B F 3, and if there is a smM1 excess of ether, equation (10) m a y be replaced by another of similar form:

]$P'~i~0~0

(12)

where Co represents the initial concentration of B F 3, and E o the total initial concentration of ether. According to (12) a rise in E 0 (CO remaining constant) must lead to reduction in w0. This is in fact shown by the data in Table 2. I t will be seen that the participation of ¢he ether in termination reactions is reflected in the yield and molecular weight of the polymerization products. B. The kinetics of the reaction are little influenced by whether the catalyst is a BFa.O(CaH~) 2 complex, or whether the B F 3 and (CzHs)~O are introduced separately in equimolecular amounts. I t was in fact found that when BFa was introduced into a monomer solution containing an equimolecular amount of diethyl ether the initial rate was rather higher (10-30% higher) than with the complex, though the kinetics curves for the rest of the process are similar The causes of this difference m a y be the same as those for the lower values of kikp/k t compared with ke~ (see above). C. The acyelic trialkyloxonium ion emerging in reactions IV and V is similar in structure to the triethyloxonium ion. One would therefore expect the catalytic activity of the triethyloxonium salt to be low. I t was found, however, t h a t at 0 ° triethyloxoniumfluoroborate (TEOFB) initiated the polymerization of E C H s o slowly that the rate of heat evolution was considerably below the sensitivity range

Polymerization of epichlorohydrin caused by BF 8 etherate

1293

o f t h e calorimeter. I t w a s possible t o s t u d y t h e p o l y m e r i z a t i o n of E C H in t h e presence of T E O F B o n l y a t t e m p e r a t u r e s a b o v e 35 ° b y t h e calorimetric m e t h o d ; t h e results are g i v e n in T a b l e 3. D. B y using as c o m p l e x i n g a g e n t a n e t h e r t h a t w a s i n a c t i v e in r e s p e c t to o x o n i u m ions a n d h a d lower b a s i c i t y t h a n B F 3 we o b t a i n e d higher r a t e s a n d yields t h a n w i t h D E B F . I t w a s f o u n d t h a t t h e c o m p l e x BFs.(iso-CsHT)20 a t - - 3 8 ° results in t h e s a m e r a t e of p o l y m e r i z a t i o n as t h a t o b s e r v e d w i t h gaseous BFa (by e x t r a p o l a t i o n ) a n d m o r e o v e r t h e yield of p o l y m e r is t h e s a m e as w i t h BFz. W e k n o w t h a t d i i s o p r o p y l e t h e r does n o t r e a c t w i t h TEOF:B (in c o n t r a s t to d i m e t h y l ether) [2] a n d h a s ~ 30 t i m e s lower b a s i c i t y in r e s p e c t to B F 3 t h a n d i e t h y l e t h e r [3]. T h e e q u a l i t y of t h e r a t e s a n d yield of p r o d u c t s in t h e p o l y m e r i z a t i o n caused b y B F 3 a n d its c o m p l e x w i t h (iso-CaI-IT)~O shows firstly t h a t t h e r e is r a p i d e s t a b l i s h m e n t of e x c h a n g e equilibrium b e t w e e n e t h e r a t e a n d m o n o m e r TABLE

2.

I~OLYMERIZATION OF ECH EXCESS

CAUSED B Y OF

DEBF

IN P R E S E N C E

OF A N

ETHER

(Me= 1"0 mole/l,, Co=3"1 × 10 -2 mole/L, --20 °) Eo × 10L mole/1. 3.1 6-2 9'3

Wo× 103 mole/1. found 8.6

5.5 2.0

~,~o

Mol. wt.

calculated* 8.8 5.0 3.4

40 "9 35"8 14'9

390 410 320

* wo was calculatedfrom (12) taking the previouslyfound ratios of the rate constantsinto consideration. TABLE 3. POLYMERIZATIONOF ECH CAUSED BY TRIETHYI-OXONIUMFLUO:ROBORATE (TEOFB) (Me= 1"0 mole/1.) Co × 102,

mole/1. 0.86 0.82 0.84 1.24 2-18

Temperature, oC 0 35 48.5 48.5 48 "5

ws × 103, mole/1., see Very little ~0.3 0.43 0.47 0.70

Yield,*% 62-8 56'6 44'9 63"4 83"5

Mol. wt. 415 430 440 440 535

* The yield was determinedafter keepingthe ampoule for 13-19 days at roomtemperatureon completionof the reaction. a n d secondly t h a t a r e d u c t i o n in t h e r a t e can only be due to " q u a s i - t e r m i n a t i o n " t h r o u g h i n t e r a c t i o n o f t h e cyclic o x o n i u m ion w i t h t h e acyclic ether. To all app e a r a n c e s d i i s o p r o p y l e t h e r t a k e s p r a c t i c a l l y no p a r t in this reaction.

1294

T.I.

BORISOVA et al.

We may therefore assume that the proposed scheme satisfactorily describes the polymerization of ECtt in the presence of the diethyl etherate of boron fluoride. In the polymerization of ECtt with DEBF, and also with BF3, chain transfer through monomer is an important factor in addition to the initiation reaction and chain propagation and termination, a s irrespective of Co and 1Y[0 the molecular weights of the reaction products are in the range 400-500. CONCLUSIONS

(1) The kinetics of the polymerization of epichlorohydrin caused by the diethyl etherate of boron fluoride in methylene chloride have been investigated. (2) It has been shown that the polymerization mechanisms can only comply with a scheme of slow initiation. (3) A scheme has been proposed whereby exchange equilibrium between the monomer and ether complexes with BF 3 is rapidly established, and the ether participates in a "quasi-termination" reaction. (4) It has been shown that with triethyloxoniumfluoroborate the polymerization of epichlorohydrin proceeds at an appreciable rate only at temperatures above 35 °. Translated by R. J. A. HENDRY

REFERENCES 1. Ya. I. ESTRIN and S. G. ENTELIS, Vysokomol. soyed. A I 0 : 2589, 1968 2. H. MEERWELN, S. HINZ, P. HOFMANN, E. KRONIG and E. PFEIL, P r a k t . Chem. 147: 257, 1937 3. H. E. W I R T H and P. J. FLICK, J. Phys. Chem. 66: 2277, 1962 4. A. C. RUTENBERG, A. A. PALKO and $. S. DRURY, J. Amer. Chem. Soe. 85: 2703, 1963 5. A. C. RUTENBERG, A. A. PALKO and J. S. DRURY, J. Phys. Chem. 68: 976, 1964 6. A. C. RUTENBERG, A. A. PALKO and J. S. DRURY, J. Phys. Chem. 69: 527, 1965

DIELECTRIC CONSTANTS OF POLYMERS IN THE GLASSY STATE* T. I. Boamovx, G. P. ~K~AmOV (dec.) and M. 1~. KOTON Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences (Received 17 June 1968)

~k STUDY of dipole polarization relaxation of polymers of variable structure made it possible to establish certain structural properties with which an increased dielectric constant of a polymer in the glassy state is associated. * Vysokomol. soyod. A l l : No. 5, 114001144, 1969.