sulphonyl fluoride copolymer

Tetrafluoroethylene/sulphonylfluoride copolymer

867

imidazole is a p e n u l t i m a t e m e c h a n i s m ; by m e a n s of a m e t h o d where a large excess o f a c o m o n o m e r is used it is possible not ordy to d e t e r m i n e the p r o p a g a t i o n m e c h a n i s m , but also to achieve a m a j o r simplification, o f the process of calculating the c o p o l y m e r i z a tion c o n s t a n t s for the p e n u l t i m a t e model.

Translated by R. J. A. I'-~ENDRY REFERENCES 1. K. L. PETRAK, J. Polymer Sci., Polymer Letters 16: 393, 1978 2. L.A. TATAROVA, I. S. MOROZ~OVA, T. G. YERMAKOVA, V. A. LOPYREV, N. F. KEDRINA and I. S. YENIKOLOPYAN, Vysokomol. soyed. 22:112, 1982 (Not translated in Polymer Sci. U.S.S.R.) 3. L. I. ANDREYEVA, V. Yu. BARANOVSKII and V. A. KABANOV, Vestnik MGU, seriya 2, Khimiya 27: 417, 1986 4. E. R. MAYO and F. M. LEWIS, J. Amer. Chem. Soc. 66: 1594, 1944 5. M. FINEMAN and D. D. ROSS, J. Polymer Sci. 5: 259, 1950 6. T. KELEN and F. T-UDOS, J. Macromolec. Sci. Chem. 9: 1, 1975 7. L. P. MAKHNO, T. G. YERMAKOVA, Ye. S. DOMNINA, L. A. TATAROVA, G. G. SKVORTSOVA and V. A. LOPYREV, U.S.S.R. Pat. 464584; Byull. izobr., No. 11, 66, 1975 8. C.~U. PITTMAN and T. D'ARCY ROUNSEFFELL, Computers in Polymer Sci, p. 146, N.Y., 1977 9. D. R. BURFIELD and A. M. SAVARIAR, Europ.'Polymer J. 16: 1003, 1980 10. V. JAACKS, Makromolek. Chem. 161: 161, 1972 11. D. R. BURFIELD and A. M. SAVARIAR, J. Polymer Sci. Polymer Letters 20: 515, 1982

PolymerScienceU.S.S.R.Vol. 31, No. 4, pp. 867-875, 1989 Printedin Poland

0032-3950/89 $10.00+.00 © 1990PergamonPress pie

STRUCTURE AND PROPERTIES OF SOLUTIONS OF TETRAFLUOROETHYLENE / SULPHONYL FLUORIDE COPOLYMER * V. P. BUDTOV, V. M. BELYAYEV, G. A. OTRADINA a n d N. A. DOMNICHEVA Okhtinsk Production Association "Plastpolimer"

(Received 2 October 1987) A method of preparing solutions of tetrafluoroethylene/sulphonyl fluoride copolymer is worked out, the MM is determined, and the structure of the copolymer maeromolecules is studied. In DMAA this copolymer behaves as a polyelectrolyte. Stable molecular aggregates are formed even at the solvent boiling point. The copolymer is fractionated, and the correlation between the sedimentation coefficient, the viscosity, and the MM is found. The degree of branching of the high molecular fractions is calculated. * Vysokomol. soyed. A31: No. 4, 786-792, 1989.

868

V.P. BUDTOVet al.

THs wide development o f m e m b r a n e technology has led to increased interest in studying the ionomeric materials used for this purpose. The copolymer o f tetrafluoroethylene with sulphonyl fluoride m o n o m e r (FSF) has attracted special interest because o f its high chemical and thermal stability [1, 2]. The structure o f this material in the solid state has been studied previously [3, 4]. However, solutions o f this polimers and its M M have not been studied, although these characteristics are determirting factors in processing the polymer to produce components, artd can also serve as a basis for artalysis and control o f the production processes for its production. The p o o r solubility o f the p o l y m e r was the first i m p o r t a n t complicating factor, and the second, third, and fourth were the presence o f aggregates in solution, polyelectrolyte swelling o f the macromolecules, and the liability o f the macromolecules to branching. This has naturally led to considerable difficulties in the m e t h o d o f a p p r o a c h , the surm o u n t i n g o f which is in itself all important problem. The method of obtaining the FSF is described by Gladkikh et al. [5]. Two FSF specimens of equivalent mass, i.e. ~ 1030 were studied. The MM of the monomer was 449. The FSF dissolves only in certain fluorinated solvents at high temperature [6]. On the other hand, in its hydrolysed form (only this form of FSF is discussed in this article) it becomes partly soluble in a number of highly polar solvents, i.e. DMSO, DMFA, and DMAA. The best solvent is DMAA with addition of 19/0 water. This best solvent effect obtained on adding an insoluble substance is known in the literature. Since, as we observed, even in this solvent complete dissolution was not observed with all the specimens, it was important to standardize the conditions of preparing the solutions. The FSF was dissolved by boiling in the given solvent at 164°C for 1.5-2 hr under reflux.

%,/c,,-,,,/kS

0"6- ~

,, .

# Q

×".-.--~

_

0"# 0.2' ?

=

•

0 8-

.------~x-

'

._ o - - ~ . - - - o - - ~ - - o = I

I

4

2

8

6

.x

7

5.

I

c, kg/mS

8

FIG. 1. Reduced specific viscosity as a function of the concentration of FSF solution in DMAA at 25°C (1, 2, 5, 7) or 135°C (3, "4, 6, 8) at an initial concentration c=4'3 (1, 3) or 8.8 kg/m 3 (2, 4), and also for DMAA with addition of LiBr to 0.01 molar in a solution of specimen 1 (5, 6) or specimen 2 (7, 8). The viscosity of the diluted solutions was measured in a viscometer with a suspended level, tke DMAA flow time being 100 see. In view of the poor solubility of the polymer and the observation of aggregates (see below) the properties of the solutions in some degree depend on the concentration at which the polymer is dissolved. We selected an initial solution concentration of 8.8 kg]m 3.

Tetrafiuoroeth2~lene/sulphonyl fluoride copolymer

869

The value of the reduced specific viscosity #hp/Cis increased on drecreasing the polymer concentration in solution (Fig. 1), which is typical of aqueous solutions of polyelectrolytes. Similar effects were observed in ionized solutions such as DMAA [7]. Addition of a monovalent salt (NaI or LiBr) suppresses the polyelectrolyte swelling effect, and is most effective with LiBr. In the subsequent tests solutions of FSF in DMAA containing 0.01 molar LiBr were used.

r~p/C 4

40

80

120 T °

Fio. 2. Reduced specific viscosity as a function of the temperature of the solution of FSF in DMAA. Co= 3.0 kg/m 3.

Figure 2 shows the reduced specific viscosity of the FSF solution in DMAA as a function of temperature, for an initial concentration co = 3.0 kg/m 3. The relation between V~p/cand T is generally expressed in the form of a smooth curve with saturation (passage from a poor to a good solvent [8]). In our case a sharp increase in Vsp/c with increase in T is observed, which indicates rupture of the supermolecular formations. In this connection, the method of birefringence in a stream was used to evaluate the degree of molecular dispersion of the solutions. Figure 3 shows the values of the birefringence An as a function of the shear stress g0/-7/o), where g is the velocity gradient and r/o is the solvent viscosity. In order to obtain a solution having molecular dispersion the solutions prepared were centrifuged. It was found that solutions of some of the initial specimens contained a gel-like fraction in concentrations up to 20~, which did not pass into solution. The specimens were fractionated at various temperatures in a centrifuge. On centrifuging a 5% solution in the preparalive rotor of the G-170 centrifuge the least soluble fraction 1 was separated at 70°C and a provisional speed of 10* rpm, Fractions 2 and 3 were separated at 50 and 20°C and speeds of 2 × 104 and 3 × I0" rpm respectively, The polymer fractions were vacuum dried at 60°C to constant weight. The sedimentation measurements were carried out on a G-120 centrifuge (made by MOM, Hungary) at 120°C and a rotor speed of 3 x 10" rpm. The concentration effects of the sedimentation factors S were allowed for in the usual way [8]. A Soviet KhZh-1303 chromatograph was used for GPC of the FSF solutions. The GPC method used and the column characteristics are described bY Madorskaya et aL [9]. The chromatograms of the soluble parts of FSF specimen 2 and the individual fractions of this specimens are shown in Fig. 4. The molecular characteristics of the FSF studied are shown in Table 1.

Structure o f solutions. T h e plots o f An against g ( q - r/0) in Fig. 3 for the original specim e n s show m a r k e d non-linearity. This m e a n s that there are anisotropic colloidal structures in the F S F solution. It is i n t e r e s t i n g to n o t e that i n the case o f specimen 1 a u n i q u e r e l a t i o n An-,,g(r/-r/o ) is o b t a i n e d for solutions o f different ionic strength. This indicates that a d d i t i o n o f a salt does n o t change the s t r u c t u r e o f the particles [10]. U s i n g the theory which applies to the h y d r o d y n a m i c b e h a v i o u r o f artisodiametric p a t t i -

870

V.P. BUDTOVet al.

cles [10] it is possible to evaluate [11] the MM of such formations from the degree of I-

[x-

An (g)/ distortion of the plot of An against g. For this, the initial slope of the plot of L An g / ( g ) , _ , o ] against g2 was calculated. Knowing this, it is possible to calculate the Particle

AnglOS

~,/'I

2

/>/

.

O,g

1.5

g(rl-rlo),

kg.rn'1.sec"2

Fxo. 3. Birefringeneeas a function of shear stress gQ/-~7o) for specimens 1 (1), 2 (2), and 2, fraction 3 (3). relaxation time : = 2 (1 - 4,

\

O)

)a'-*O

g2

The quantity z is connected with the MM by the equation x =N M ( t / - ~°/)

(2)

RTe

This is used to calculate the MM of the anisodiametric particles M,. This value is given in Table 1. It must be noted here that the MM determined in th;s way is the MM of the large particles themselves in solution, i.e. of aggregates. In the case of the fractions of this specimen having the lowest molecular weight the relation between An and g is linear, which indicates molecular dispersion of the solutions. TABLE1. MOLECULAR Specimen, No. 1

2 2, fraction 3

CHARACTERISTICS OF ~

[q] × lOa"m3/kg 25° 135 ° 4.4 5.1 2"4

8.6 11.2 6.6

FSF SPEC'n~NS

I

.[A~ x 1029 ,

30 20 5

ms

M , × I0 -~

30 7

Tetrafluoroethylene/sulphonyl fluoride copolymer

871

Table 1 gives the values of the optical anisotropy A7 of the solutions studied. This value is very high, i.e. greater than that for flexible chain polymers by a factor of about 10-100, for example in the case of the copolymex of vinylidene fluoride with tetrafluoroethylene [12].

a

2o

I 10

b

2o

l

CJ,ma/k9 x

c

2

x 10 d

0.05

I

I

10 10

o

I

I

20 Cs°'s, mole

Fio. 4 FIo. 5 Fzo. 4. Distribution curves for elution volume V for the soluble part of specimen 2 (a) and its fractions 1 (b), 2 (c), and 3 (d). FiG. 5. Values of [~/]as a function of c~"°'5 for specimen 1, dissolved in DMAA with addition of NaI (1) or LiBr (2). Accordingly, the results obtained indicate colloidal dispersion of the FSF solutions. By means of special fractionation tests (temperaure + a centrifugal field) it was possible to obtain FSF fractions forming solutions having molecular dispersion. Polyelectrolyte swelling. As follows from the data of Fig. 1, the value of tl,p/e is inversely related to the solution concentration. The relation between qsp/e and e for different concentrations of salt G added to a FSF solution in D M A A was measured. In itself determination of [r/] in the case of polyelectrolyte swelling is not always a problem which can be clearly solved, since extrapolation to c--*0, in the case of considerable electrostatic swelling is not as a rule very reliable. In view of this, the relation between tl,p/c and c was used for analysing the relation between [r/] and ca at the minimum concentration of the test solution 0.5 kg/m 3.

872

V.P. BUDTOVet at.

Figure 5 shows the relation between [;1] and c~"°'s . Similar relations between ~hp/c and e and [q] and e~ are typical of chain polyelectrolytes [t3], Irt fact, it is known that the intrinsic viscosity It/] = [r/]0~3, where [r/J0 is the value of the intrinsic viscosity in a 0-solvent, and 0~is the macromolecule swelling factor. The quantity ~3 is connected with the excluded volume factor z by the Fiksman relation ~2 = t + 2z

(3)

In the given case there is no difference between ~ as determined fiom the macromolecule dimensions and from It/]. In the case of polyelectrolytes, modem theories [14, 15] give z=CmM !

o+

,

(4)

where Cmis a constant and fl0 is the excluded volume of a segment determined by conventiollal polymer-solvent interaction. It can be seen from the relation between It/] and c~-°'5 given in Fig. 5, that in the case of the salt LiBra fairly good linear relation obtains between these quantities. In the case of a solution containing NaI the relation between [q] and c~-°'s is stronger. This is associated with the lower effectiveness of NaI in screening the interaction of the charges along the chain. As a consequence of the stronger polyelectrolyte swelling a change in the value of the Kuhn segment on variation of the salt [14, 15] is possible, which should lead to the observed laws. Accordingly, analysis of these data shows that the FSF macromolecule s are fairly flexible and high molecular polyelectrolytes. The value of It/] extrapolated to cs~0 has a comparatively low value: (1.5-2-5) × x 10 -2 m3/kg. Thi~ indicates that the DMAA is a poor solvent. Determination of M M and the degree of branching. The MM of the fractions were determined by approximation to sedimentation equilibrium [8]. The measurements were made in a six-sector capillary type cell. The Archimedean multiplier, equal to (1-vpo) =0.I, was determined by a pycnometric method (where v is the specific partial volume and Po is the solvent density). The provisional velocity of measurement was 1 × 104 rpm. The hydrodynamic characteristics and the measured values of the mean number average M,, the mean weight average M,¢ and the z-mean Mz MM are given in Table 2. Itcan be seen that the value of M s of the fractiorts studied lies within the range 0.5-5.0 × x 106, which is close to the minimum values of the quantity M,, as determined by the birefringence method. This indicates specific agreement of the data obtained by the different methods, and the existence of a continuous transition in MM from a solution having molecular dispersion to a colloidal solution. It was shown above that the value of It/] is inversely related to the salt concentration, and that when the salt concentration is high the polymer is deposited in the residue. In,view of this, it is reasonable to assume that the solvent used is ideal for the given system. According t o d a t a on the hydrodynamic characteristics and the MM for the third (having molecular dispersion) fraction, it is possible to establish the traditional Mark-

Tetrafluoroethylene/sulphonyl fluoride copolymer

873

K u h n - H o u w i n k relation for S and It/l, S=2"5 x 10-2M °'5,

[t/] =6.8 x 10-*M °5

(5)

The values obtained for the coefficients are typical of flexible chain polymers in a 0-solvent. The value of the Kuhn segment is 60 ~ at the value of the factor K, obtained. A method involving the combination of two "fractionating parameters" [8, 16] was used for qualitative assessment of the branching, i.e. sedimentation and GPC. In accordance with this method, using the integral distribution with respect to S an.d the elution volume II, a relation between log S and Vcan be constructed, using the values of S and Vfor the same integral distribution fractions. Irr the case of branched specimens this relation between log S and V must be described by the relation (for a constant number o f branches m) log S = Ksv(l - b) C2 V - log Bsv, (6) where Ksv is a constant for the given system, and b and C2 are coefficients in the relations

S= K s M l-b,

logM = C 1 - C 2 V

(where Ks, C1 and C, are constants). The quantity Bsv depends on the degree of branch-

2"0

-IC/.

~b xC

~d 1"4

tO

08 D

I 26

I 22

I

18 K counf

FIo. 6. Log S as a function of Vfor the soluble part part of specimen 2 and its fractions in DMAA at m values of 0 (1), 10 (2), 20 (3), 40 (4), 70 (5) and 100 (6) or at values of M× 10-6=2 (7), 4.1 (8), 6.9 (9), and 11.9 (10). The points refer to the soluble part as a whole (a) and to fractions 1 (b), 2 (c) a n d 3 (d).

V.P. BUDTOVet al.

874 TABLe2. HYDRODYNAMICA N D

M O L E C U L A R CHARACTERISTIC.q~

OFTHESOLUBLePARTA N D

THE tRACTION

OF F S F SPECIMEN 2

Fraction number 3 2 1

[r/] × 10a, m3/kg 25*

5"1 2"4 8"0 6"4

S~

Mwtx

Svedberg x l 0 ~s 135° units w 11"9 28"7 8"6 6'6 8"0 12"8 33"8 10"0 44"0 12"6

M~?x x 10 - s

8"0 50"0

Mmx

MB$.. X

xl0-S × I0 -s 1"9 0.4 3"1 7.5

6.0 1"2 7"0 12"0

Mw?x × I0 -s

Mz~× × I0 -s

9"0 1-7 11.0 16.0

50"0 6"0 30"0 45"0

Mw

m

4"7 40 0 3"5 30 2"I 70

4"2

* Soluble part. t Measured by approximation to ~limentation equilibrium. : Calculated from xdin~ntation constant distribution curves and corrected for branching of the macromolecules.

ing, and with increase in the branching number m the value of Bsv is decreased. The quantity Bsv=hG c1-~)/3b where h and G are branching factors [8], allowing for the increase in S and the decrease in [r/] with increase in m for the same value of MM. When the value of MM is constant and m is variable the relation between S and V is log h V log S = Ksv + 3bC2 log G

(7)

Assuming that b f 0 . 5 and h--G 1/3 [8] the coefficient of proportionality between log S and Vin (6) and (7) is equal to 0.5 (72. The value o f h was calculated from the equation h - ' = 0"385(1 +2m)°'2s [

1-6 I

~/i~J

(8)

Figure 6 gives log S as a function of V for solutions of fractions and the soluble part of the original specimen 2. It is found that in the case Of fraction 3 (linear macromolecules) C2 =9-22 and C1 = 10.58, which is close to the expected values. The values of Bsv for trifunctional branching units having different MM were calculated. In the case of the mean values of S for fractions 1 and 2 the values of Msv are calculated with correction for branching. The values obtained are given in Table 2. These values of Msv are close to the values of Ms obtained by art absolute method. Consequently, the previous proposals are true for FSF solutions. In the case of macromolecules of fractions 1 and 2 it is found that m--70 and 30 branches respectively. The branching density (number of branches per unit degree of polymerization) is equal to 4 x 10- 3, which is close to the corresponding values for the copolymer of vinylidene fluoride and tetrafluoroethylene [12, 171. The method used provides a means of evaluating both the true distribution with respect to MM and the same distribution corrected for branching of the macromolecules. The values of the mean MM calculated from these curves are shown in Table 2. The values of Mw and M~, as determined by independent methods, are in fairly good agreement with the calculated values. The polydispersity of the soluble part of specimen 2 is equal to five. Translated by N. STANDBN

TetradIuoroethylene/sulphonyl fluoride copolymer

875

REFERENCES 1. Yu. A. PANSHIN, S. G. MALKEVICH and Ts. S. DUNAYEVSKAYA, Ftoroplasty (Fluoroplastics), Moscow, 1978 2. Ionoobmennye ftorpolimernye membrany, primenyayemye v protsesse khlorshchelochnogo elektroliza. Set. Proizvodstvo i primeneniye polimerizatsionnykh plastmass. Obzor. informatsiya (Ion Exchange Fluoro-polymer Membranes Used in Alkaline Fluoride Electrolysis. Series Production and Applications of Polymerized Plastics, Review of Information) 42 pp., Moscow, 1983 3. W. J. HSU and T. D. GIERKE, J. Membr. Sci. 13: 307, 1983 4. H. W. STAKWEATHEW, Macromolevules 15: 320, 1982 5. S. N. GLADKIKH, S. M. TIMASHEV, G. G. CHUVILEVA, A. L ANDREYEVA and N. A. DREIMAN, Zh. fiz. khim. 6: 916, 1982 6. G. H. CAIN and M. J. COVITCH, J. Eiectrochem. Soc. 131: 1350, 1984 7. D. HARWOOD and J. FELLERS, Macromolecules 12: 693, 1979 8. S. R. RAFIKOV, V. V. BUTOV and Yu. B. MONAKOV, Vvedenie v fizikokhimiyu rastvorov polimerov (Introduction to the Physical Chemistry of Polymer Solutions). p. 328, Moscow, 1978 9. L. Ya. MADORSKAYA, V. N. BUDTOV, G. A. OTRADINA, Ye. Yu. KHARCHEVA and N. N. LODINOVA, Vysokomol. soyed. 28: 952, 1986 (Translated in Polymer Sci. U.S.S.R. 28: 5, 1062, 1986) 10. A. PETERLIN and H. STUART, .l. Phys. 112: 129, 1939; 113: 663, 1939 11. V. P. BUDTOV, N. A. DOMNICHEVA and N. Ye. YAVZINA, Kolloid. zh. 35: 451, 1975 12. G. A. OTRADINA, V. P. BUDTOV, N. N. DOMNICHEVA, L. N. VESELOVSKAYA, T. G. MALKEVICH and T. G. MAKEYENKO, Vysokomol. soyed. A21: 572, 1979 (Translated in Polymer Sci. U.S.S.R. 21: 3, 627, 1979) 13. J. SKOLNICK and M. FIXMAN, Macromolecules 10: 944, 1977 14. J. NODA, T. TSUGA and M. NAGASAWA, J'. Phys. Chem. 74: 710, 1970 15. T. ODIJK and A. HOWART, J. Polymer Sci. Polymer Phys. Ed. 16: 627, 1978 16. V. P. BUDTOV, Ye. L. PONOMAREVA and V. M. BELYAYEV, Vysokomol. soyed..4,22: 2152, 1980 17. S. I. KOGAN, G. A. OTRADINA, V. P. BUDTOV and V. M. BELYAYEV, Vysokomol. soyed. 26: 1170, 1984