Features of copolymerization of vinylidene fluoride with tetrafluoroethylene using ammonium persulphate

Polymer Science U.S.S.R. Vol. 28, No. 5, pp. 1062-1071, 1986 Printed in Poland

0032-3950/86 $10.00+ .0~ ~ Pergamon Journals Ltd.

FEATURES OF COPOLYMERIZATION OF VINYLIDENE FLUORIDE WITH TETRAFLUOROETHYLENE USING AMMONIUM PERSULPHATE* L. YA. MADORSKAYA,V. P. BUDTOV, G. A. OTRADINA, T. G. MAKEYENKO, YE. Yu. KHARCHEVA a n d N. N. LOGINOVA Okhtinsk "Plastpolimer" Science-Production Association

(Received 11 August 1984) The authors have investigated the copolymerization of vinylidene fluoride with tetrafluoroethylene using ammonium persulphate in conditions of emulsifier-free copolymeriza. tion (in absence and presence of a molecular mass regulator) and also in the conditions of the emulsion process in presence of such a regulator. It is assumed that on the conditions considered the process occurs both in the micelles of the emulsifier and in the solid polymer particles formed on fall out from solution of the oligomeric radicals or coagulation of the unstable particles protected by surfactant oligomers. On emulsifier-free copolymerization as in the conditions of the emulsion process copolymers form with a bimodal molecular mass distribution. It has been established that the molecular mass regulator prevents passage of the chain transfer reaction to the polymer present in the solid phase by reducing the fraction of the high molecular mass component of the molecular mass distribution.

TIlE GROWING practical significance of copolymers based o n vinylidene fluoride ( V D F ) accounts for the increased v o l u m e of research in the field of copolymerization o f V D F . However, extremely little w o r k has been done o n the relationship of the kinetic p a r a m e t e r s of the c o p o l y m e r i z a t i o n process with the molecular characteristics of such copolymers although such comprehensive investigations provide reliable i n f o r m a t i o n o n the specific features of the process. The present w o r k reports the results of study of the kinetic patterns of copolymerization of V D F with tetrafluoroethylene (TFE) in a n a q u e o u s m e d i u m c o m b i n e d with d e t e r m i n a t i o n of the M D of the copolyrners formed. VDF and TFE were copolymerized in an aqueous medium at a constant pressure of 2 MPa. The monomer ratio in the polymerization medium during the process was kept constant by using the compensation method [1]. The composition of the initial polymerization monomer mixture provided VDF and TFE copolymers with constant composition (70 moleT. VDF and 30 mole TFE) checked by tbe methods of IR spectroscopy and NMR. The concentration of ammonium persulphate (AP) used as initiator was varied within the limits 2.2 x 10-3 to 7 x 10-3 mole/1. In the first series of experiments copolymerization was carried out in presence of a fluorinated surfactant (F-SA) and a molecular mass regulator ( M M R ) - a primary alcohol the concentration of which was constant at 6 x 10- a mole/1. * Vysokomol. soyed. A28: No. 5, 952-959, 1986.

1062

Copolymerization of V D F with TFE

1063,

In the following two experimental series we studied copolymerization of VDF and TFE without an F-SA both in presence of an M M R (series 2) and in its absence (series 3). The MDs of the VDF and TFE copolymers was determined by the GPC method using the KhZh-1303 liquid chromatograph provided with three columns of macroporous glass of pore sizes 250, 1200 and 2000 A. As eluent we chose DMAA, temperature of analysis 25°C. The molecular masses of the VDF and TFE copolymer were calculated by the principle of the universal calibration, the suitability of which for this copolymer was verified earlier [2]. As calibration standards we used the Waters polystyrene standards with M ranging from 10 × 103 to 2"7 x 106. In this region of M values for the set of chromatographic columns used a linear calibration function was observed. Figure 1 presents the typical curves of the distribution over the eluation volume of the three samples of the V D F and T F E copolymers obtained in each of the three series of experiments. It will be seen that all the copolymer samples both obtained with an F-SA (curve 1) and with emulsifier-free copolymerization in presence of an M M R (curve 2) or without it (curve 3) have an M D of a bimodal character: the curves contain two distinctly separated c o m p o n e n t s - h i g h molecular (I) and low molecular (II). For e a c h of the M D components of the copolymer studied we calculated the magnitudes ~ , , Mw and -~z of the molecular masses by separating the distribution curves over the eluation volume into two components. It was assumed that the peak of component I is symmetrical. (The assumption may introduce an error into the determination of the molecular masses of the components I and II not exceeding 10~). It was found that the polydispersity of Mw/M~ of both M D components does not depend on the specific conditions of synthesis of the V D F and T F E copolymers on exposure to AP and is 1.6+0.1 for the first component and 2.0+0.3 for the second. Emulsion copolymerization of VDF and TFE. It is known [3] that for emulsion polymerization occurring with fiocculation of the polymer particles the rate of the process in the steady state is described by the equation v = dM/dt = ke~ [I] °s,

where ce is the concentration of emulsifier; [I] is the concentration of the initiator; x is the reaction order for the emulsifier; and k is the rate constant. From the data presented (Fig. 2, curve 1) it will be seen that copolymerization of V D F and T F E on exposure to AP in presence of an F-SA and M M R practically from the start proceeds at a constant rate and over the whole concentration range of the initiator half order of the rate of the process for the initiator is observed (Fig. 3a). The dependence of the reaction rate in the steady state on the concentration of the emulsifier is of a more complex character. As may be seen from Fig. 3b, in the region of F-SA values from 2.06x 10 -a to 4.0x 10 - s mole/1, the copolymerization rate o f V D F and T F E depends linearly on the concentration of the emulsifier. Further rise in the concentration of the F-SA did not increase the rate of the process. Such a change in the character of the dependence of the rate of the process on the concentration of the emulsifier in emulsion copolymerization using a water-soluble initiator is evidently associated with the appearance of polymolecular layers of emulsifier on the surface of the latex particles [4] with rise in their concentration. This assumption is well con-

1064

L. YA. MADORSKAYAet al.

sistent with the fact t h a t the absence o f d e p e n d e n c e o f the rate on the c o n c e n t r a t i o n o f emulsifier in the case o f w a t e r - e m u l s i o n c o p o l y m e r i z a t i o n o f V D F a n d T F E u n d e r the influence o f A P is, in fact, o b s e r v e d at c o n c e n t r a t i o n s o f emulsifier exceeding the critical c o n c e n t r a t i o n for micelle f o r m a t i o n (for the F - S A c h o s e n it is 6.6 × 10- 3 mole/l.). The M , values o f the first a n d s e c o n d M D c o m p o n e n t s f o u n d for the e m u l s i o n s a m p l e s o f the V D F a n d T F E c o p o l y m e r s differ b y an o r d e r o f m a g n i t u d e . C h a r a c t e r i stic o f b o t h M D c o m p o n e n t s is the r e l a t i o n typical o f r a d i c a l p o l y m e r i z a t i o n between the m a g n i t u d e 1 / M . a n d the c o n c e n t r a t i o n o f i n i t i a t o r to the degree 0-5 (Fig. 4, curve 1)

w(vet)'loZ.x3 Q,g

12

7

2

o

80

qO

35

55

qs

2

Vel ~counts

zt

6

Tt'me , hr

FIG. 1

FIG. 2

FIG. 1. Curves of the distribution over the eluation volume Vet of the VDF and TFE copolymer obtained during emulsion copolymerization with an MMR (1), without emulsifier with an MMR (2) and without an MMR (3). FIG. 2. Kinetic curves of the copolymerization of VDF and TFE on exposure to AP in presence of emulsifier and MMR (1), without emulsifier with MMR (2) and without MMR (3).

5O

30

I,/

r" IO

..i~:

×~

x~×

I

:3

A l~"

b

30

,,it

I

[

I

13

4

6

8

[z]°c lo-:O.oldz.) °5

I

I

I

Lt

8

c~ 7o-~ moZelZ.

FIG. 3. St eady copolymerization rate of VDF and TFE as a function of the concentration of: a :initiator in conditions of the emulsion process with an MMR (1), without emulsifier with MMR (2) and without MMR (3); b - a s a function of the concentration of emulsifier.

1065

Copolymerization of VDF with TFE

with no relation between the M of both M D components and the concentration of emulsifier. As it turned out, the fraction of the first component depended neither on the concentration of the initiator nor on that of the emulsifier and was , - ~ 3 5 + 5 ~ for all the samples studied (Fig. 5, curve 3). The value of the Jl~'w/_A~,ratio close to 2 for the second M D component and also the value of the _/l~z[Jl~w ratio of 1.5+0.1 indicate that the low molecular mass M D component of the copolymer formed is t h e result of the classical probabilistic process reflecting the statistical character of attachment of the monomers and termination of the radicals.

z/scz,zz)

80, ~

3

7

7o

qOI

I 5

' 7[I]°~ ' lO~Z(mol°'e/l.s) I

FIe. 4

x

----L-. 3

I

1

x

2

5 [ ] 10,%oIe/l FIG. 5

Fie. 4. Dependence of the magnitude 3~t~~ of the first and second MD components of the VDF and TFE copolymer obtained in conditions of the emulsion process with an MMR (l), without emulsifier with an MMR (2) and without an MMR (3). Fw,. 5. Relative content of first MD component of VDF and TFE copolymer as a function of the concentration of initiator in conditions of emulsion copolymerization with an MMR (I), without emulsifier with an MMR (2) and without an MMR (3). The bimodal character of the M D of the V D F and T F E copolymers obtained during the aqueous emulsion process on exposure to AP indicates its heterophasic character. Evidently, the reactions of initiation and growth of the polymer radicals proceed not only in the F-SA micelles but also in the aqueous phase. This is promoted by the comparatively high solubility of V D F in water (1 g/1. at 70°C and a pressure 1.6 M P a ) and the use of the water-soluble initiator AP. As is known, on such initiation the polymer particles formed may be stabilized by the surfactant oligomers (SAO) appearing on interaction of the ion-radicals of initiator and m o n o m e r [4, 5]. These polymer particles are colloid-unstable and aggregate until the charge density on their surface existing through the ionized terminal groups becomes sufficiently great to ensure their stabilization. Consequently the stability of the polymer particles stabilized by the SAO must be considerably less than of the particles stabilited by the F-SA. It may be assumed that they as a result of flocculation are also the source of formation in the polymerization medium of the solid polymer phase. In fact as shown by the electrographic films of the latex particles of V D F and T F E copolymers obtained for a different concentration of F-SA (Fig. 6) flocculation of the individual particles is observed not only

1066

L. YA. MADORSKAYA et aL

F : o . 6. E l e c t r o n o g r a p h i c films o f the latexes o f the V D F a n d T F E c o p o l y m e r o b t a i n e d in t h e c o n d i t i o n s of the e m u l s i o n process at a c o n c e n t r a t i o n o f F-SA 2.2 x 10 - 3 (a) a n d at 10.2 × 10 -3. (b) mole/l. 2 × 10 4 × .

Copolymerization of VDF with TFE

1067

for low concentrations of F-SA but also at concentrations far exceeding the critical concentration for micelle formation. Thus, it may be assumed that in aqueous emulsion copolymerization of VDF and T F E under the influence of AP the process occurs both in the emulsifier micelles and in the solid polymer particles formed on precipitation from the solution of the oligomer radicals or coagulation of the unstable particles protected by the SAO. Naturally, the growth and termination reactions of the molecular chains growing in the micelles and solid polymer particles will be characterized by different rates and consequently the MD of the copolymer formed must be bimodal. From the concepts of the occlusion theory it may also be assumed that the solid polymer phase in which the rate of the termination reaction of the growing chains sharply falls is responsible for the appearance of the first M D component of the VDF and T F E copolym~rs [6, 7]. Emulsifier-free eopolymerization oJ VDF and TFE. Figure 3a, curve 2, shows the dependence of the rate of emulsifier-free copolymerization of VDF and TFE in an aqueous medium in presence of an MMR on the conccntration of AP. In this case, as with emulsion copolymerization of these comonomers, half order reaction on initiator is observed. However, the absolute values of the copolymerization rate proved to be considerably lower than for the emulsion process (cf. angle of slope of curves 1 and 3 in Fig. 2). Emulsifier-free copolymerization on initiation by AP, as is known [8], must be regarded as a special case of the emulsion process in which only the SAOs perform the role of stabilizer of the growing polymer particles. The low efficacy of an SAO as emulsifier as compared with an S-FA is confirmed by the fact that on emulsifier-free copolymerization higher proneness of the polymer particles to coagulation is observed; the VDF and TFE copolymer formed in these conditions practically does not require additional coagulation and is released from the polymerization medium by the usual filtration. The MD of the VDF and T F E copolymer obtained on emulsifier-free copolymerization on exposure to AP and in presence of an M M R is also bimodal and for both MD components linear dependence of 1/3~r,, on the concentration of initiator to the degree 0.5 is traced. The content of the high molecular weight MD components does not depend on the concentration of the initiator and is 30 + 5 °/o, i.e. about the same as in the samples obtained in presence of an F-SA (Fig. 5). The value -~/w of the first MD component does not differ from that in the emulsion samples of the copolymer (Fig. 4) and is equal to (1.2+0.2)x 106 while the corresponding value for the low molecular mass MD component is ~ 1"5 times less. This may be connected with the fact that because of the low efficacy of the SAO coagulation of the growing particles begins at a lower M value of the copolymer. The absence of an M M R in the polymerization medium on emulsifier-free copolymerization of VDF and T F E substantially alters the kinetics of the process. With increase in the concentration of initiator from 2.48 x 10 -a to 6-2 × 10 -a mole/1, only insignificant rise in the rate is observed at the initial stage of the process itselfbefore formation of 6-7 wt. ~ copolymer in the reaction medium. On establishing

1068

L. YA. MADOgSKAYAet al.

steady conditions the dependence of the rate of the process on the concentration of initiator is absent (Fig. 3a, curve 3) and the rate of copolymerization is far lower both as compared with the rate of emulsifier-free copolymerization and of the emulsion process in presence of an M M R (Fig. 2). Since in the experimental conditions the concentration of the monomers remains constant throughout the process increase in the concentration of the initiator must lead not only to enhancement of the role of the initiation reaction but also (in absence of emulsifier and MMR) to recombination of the water-soluble oligomeric radicals with each other. Evidently, with rise in the concentration of initiator the reactions leading to death of the active radicals in certain conditions become competitive in relation to the growth reactions of the polymer chain which finds expression in the absence of a relation between the initial AP concentration and the rate in the steady state on emulsifier-free copolymerization of VDF and TFE in absence of an MMR. In fact, one may propose a very simple scheme of the process including the breakdown of initiator kba, the growth reaction kg with formation of oligomeric OL" radicals and the recombination reaction of the primary I" radicals with the oligomers kr

El] ~b, jr] [I]+[M]

k,' [OL']

k8 [OL'] + [M] ~ K'] [I'] + [OL'] ~ [R']

+ [R']

G

k-k'[P]

where G is the recombination product of the primary radicals with the oligomers, [R'] is the concentration of macromolecular radicals; kt is the rate constant of the reaction of termination of the macroradicals when the polymer is obtained with the concentration [P]; kg is the growth rate constant. Using the usual notions for radical polymerization we obtain the following relations:

k; [M] [I] + k,[I']

[OL'] = kba[I ]

(1)

kg[M] [I'] - k,[I'] JOE'] = kg MO"

(2)

The equation for the rate of the process will have the form

w=kg[M]4

.lk, M [OL']

~

(3)

The joint solutions of equations (1)-(3) gives the following expression for the rate of the process: w= ~

x/2k', [M] [I']'- k,[I]

The concentration of the primary radicals is determined from the relation

(4)

Copolymerization of VDF with TFE

1069

ks

Then for a low concentration of the initiator kbafI] [I']=-k'~ [M1

(6)

w--- k~EM] kt'- 0.s ~kbdEi ]

(7)

At a high initiator concentration

[I']=k~[I] + kg[M] zk e [MJ w=

kg[M]

2

(8)

2k~ f /kgkg '

(9)

i.e. at high concentrations of initiator the rate of the process does not depend on its concentration. The M D of the V D F and T F E copolymer obtained on emulsifier-free copolymerization in absence of an M M R is also bimodal. The M values of both M D components are practically equal to the corresponding M values of the copolymers obtained in conditions of an emulsion process with no relation between the M value and the concentration of initiator and with rise in the content of the first component from 20 to 7 5 ~ with increase in the concentration of AP f r o m 2 × 10 -3 to 3 × 10 -3 mole/l. The findings also contain information on the topochemistry of the reaction proceeding in presence of an MMR. As shown on emulsifier-free polymerization the introduction of an M M R influences the M of the second M D component and leads t o a substantial (more than 2 times) fall in the fraction of the first M D component. This suggests that the formation of the macromolecules with large M occurs in the solid phase not only as a result of the non-termination growth of the polymer chains but also as a result of the course of the chain transfer reaction to the polymer in the solid phase with the participation of the primary radicals of the initiator. This is confirmed by the following experiment. The VDF and TFE copolymer dispersed in an aqueous AP solution (concentration 3 x 10-s mole/l.) was heated with agitation for 5 hr at 70°C both in presence of an MMR ([MMR] =5 x 10-3 mole/L) and without it. Then the polymer was filtered off, washed to neutrality of the washing waters and dried to constant weight after which the viscosity of the melt was determined at 220°C and with a 10 kg load on the IIRT-2M instrument. It was found that the copolymer heated in the solution of initiator in absence of an MMR has a viscosity of the melt 1.5 times greater than the initial. In the specimen heated in similar conditions but with an MMR the viscosity of the melt practically did not change. In addition, the eopolymer heated in absence of an MMR partially lost solubility whereas the other specimen remained fully soluble. The observed differences in the behaviour of the samples of the VDF and T F E copolymers after heating are evidently associated with passage of the reaction of cross-

1070

L. YA. MADORSKAYAet al.

linking by the scheme CH2 - CF2 ~ +-S(),~ HS--O,+ ~ CH - CF2 ~ --,crosslinking which is due to the reaction of transfer of the active centre to the polymer. The radicals formed from the M M R both through the termination reaction CH2 - CF2 + RCH2OH-, ~ CH2 - CF2H + R(~HOH, and the chain transfer reaction with the participation of the primary radicals of the initiator HSO, + RCH2OH--,H2SO, + R(~HOH, are less active than the primary S04 radicals and axe evidently not capable of detaching a hydrogen a t o m from the polymer chain. Thus, fall in M of the copolymer formed observed on introducing an M M R into the polymerization system is due to appreciable suppression of the reaction of chain transfer to the polymer (Fig. 5). It may be assumed that the high moleculax mass M D component also differs from the second low molecular one not only in the absolute value of M but in the degree of branching. The fact that the introduction of the M M R reduces the fraction of the first M D component of the copolymer obtained on emulsifier-free copolymcrization to values corresponding to the fraction of the first component of the copolymer obtained in the emulsion process indicates that the role of the chain transfer reaction to the polymer is quite appreciable. The investigation carried out helped to establish the cause of the formation o f the bimodal M D in V D F and T F E copolymcrs obtained with use of AP and also gave some information on the topochemical features of the process. It may be stated that the question of obtaining a copolymcr with a unimodal M D is at the same t i m e a question of choosing a highly effective emulsifer capable of preventing the process of partial flocculation and coagulation of the growing polymer particles and also a question of choosing an M M R corresponding in quality and quantity. Translated by A. CROZV

REFERENCES 1. French Pat. 1480062, 1967 2. V. P. BUDTOV and G. A. OTRADINA, Tez. Dokl. II Vsesoyuz. simpoz, po zhidkostnoi khromatografii (Summaries of Reports of Second All-Union Symposium on Liquid Chromatography). p. 48, OIKhF, Akad. Nauk SSSR, Chernogolovka, 1982 3. V. I. YELISEYEVA and A. Z. ZUIKOV, Vysokomol. soyed. A19: 2617, 1977 (Translated in Polymer Sci. U.S.S.R. 19: 11, 3021, 1977) 4. V. I. YELISEYEVA, S. S. IVANCHEV and S. I. KUCHANOV, Emul'sionnaya polimerizatsiya i eye primeneniyc v promyshlennosti (Emulsion Polymerization and its Uses in Industry). p. 27, Khimiya, Leningrad, 1976 5. V. N. PAVLYUCHENKO and S. S. iVANCHEV, Usp. Khim. 50: 715, 1981

1071

Alternating copolymerization of piperylene and ethylene

6. G. P. GLADYSHEV and V. A. POPOV, Radikal'naya polimerizatsiya pri glubokikh stepenyakh prevrashcheniya (Radical Polymerization for Deep Degrees of Conversion). p. 72, Nauka, Moscow, 1974 7. R. M. FITCH and J. TSAY, J. Polymer Sci. BS: 703, 1970 8. F. K. HANSEN, J. Polymer Sci. Polymer Chem. Ed. 16: 1953, 1978

Polymer Science U.S.S.R. Vol. 28, No. 5, pp. 1071-107~, 1986 Printed in Poland

0032-3950/86 $10.00+.00 © Pergamon Journals Ltd.

STUDY OF ALTERNATING COPOLYMERIZATION OF PIPERYLENE AND ETHYLENE IN PRESENCE OF COMPLEX ORGANOMETAL CATALYSTS* L. A. MYAGKOVA,YE. N. KROPACHEVA, M. V. ESKINA and A. S. KHACHATUROV Lebedev All-Union S~nthetic Rubber Research Institute (Received 15 August 1984) The authors have studied the alternating copolymerization of piperylene and ethylene under the influence of the catalytic systems TiCI4-CH3COC~Hs-(iso-C4Hg)aAI and [(CH3)3SiO]VOC12-(iso-C,Hg)aA1. It was established that both catalytic systems give alternating copolymers of piperylene with ethylene consisting to 53-73 % of 1,4-trans units and to 27-47 ~o of 1,2-trans units. THE PATENTS [l, 2] give information on the formation of piperylene copolymers with ethylene of composition 1 : 1 under the influence of catalysts containing titanium or vanadium compounds but not on the character of the alternation of the monomers and the microstructure of the piperylene units. It was found by 1H and 13C N M R that the piperylene copolymers with ethylene obtained by us consist of 1,4-trans and 1,2-trans units arranged in a different sequence [3]. The present investigation was concerned with the ways of obtaining alternating piperylene copolymers with ethylene under the influence of the catalytic systems TiCl4acetophenone-(iso--C4H9)aA1 (A) and [(CHa)3SiO]VOCI2-(iso-C,H9)aA1 (B) and the relationship of their structure with the different parameters of the copolymerization process. Copolymerization of pipcrylene with ethylene was carried out in an atmosphere of dry argon in a thermostatted reactor fitted with agitator and and pipe union for sampling in toluene solution at the temperature -30°C. The interaction of TiCI, with acetophenone was carried out at room * Vysokomol. soyed. A28: No. 5, 960-963, 1986.,