Gas diffusion in fluoro-polymers before and after irradiation

Gas diffusion in fluoro-polymers

3129

13. B. I. SREZNEVSKII, ZhRFKhO 14: 420, 1882 14. R'. P. KHARITONOV and V. A. KRIVTSOV, Organosilikatnyye materialy v teplofiz icheskikh issledovaniyakh (Organosihcates in Thermal Investigations). Izd. "Nauka", 1975 15. Yu. I. ALE~SEYEV, V. L. KOROLEV and V. P. KNYAZH1TSKII, Materialy tret'yego Vsesoyuznogo simpoziuma po goreniyu i vzryvu (Proceedings of the Third All-Union Sumposium on Combustion and Explosion). Izd. "Nauka", 1972 16. N. GRASSI, Khimiya protsessov dostruktsii polimerov (Chemistry of Polymer Degradation). Izd. inostr, lit., 1959 17. YUZO OKHI and SHUNICHI TSUGE, Combust. Sci. and Technol. 9: 4, 1973

Polymer Science U.S.S.R. Vol. 20, pp. 3129-3135. (~) Pergamon Press Ltd. 1979. Printed in Poland

0032-3950178/1201-3129507.50/@~

GAS DIFFUSION IN FLUORO-POLYMERS BEFORE AND AFTER IRRADIATION* N. S. TIKHOMIROVA, YU. M. MALINSKII a n d V. L. K~-gPOV L. Ya. Karpov Scientific Research Institute of Physical Chemistry Scientific Research Association "Plastpolymer"

(Received 24 February 1978) A study was made of diffusion and solubility of argon in polytrifluoroethylen, and a copolymer of tetrafluoroethylene and vinylidene fluoride before and after irradiation (in a vacuum of 10-5 torr) with various doses of ssCo y-radiation. Fluoropolymer films were prepared from solutions with subsequent removal of solvent. Diffusion was measured manometrically. Temperature dependences of permeability P, diffusion D and solubility of argon in fluoro-polymers a, were measured. It was established that the fluoro-polymers studied are similar to PVC as regards activation energy of diffusion, enthalpy and entropy of solution of gases and Do values. Irradiation of films produces an extremal solubility coefficient and minimum P and D values on the dose curve in the region of 200-300 Mrad, which is evidence of competing processes of structure formation, degradation, amorphization and unsaturation taking place in fluoro-polymers. THIS s t u d y is concerned with the diffusion of m o n a t o m i c gases in a tetrafluoroe t h y l e n e - v i n y l i d e n e fluoride c o p o l y m e r a n d in polytrifluoroethylene ( P T F E ) b e fore a n d after ionising radiation; there is c o m p a r a t i v e l y little i n f o r m a t i o n available [1, 2] on diffusion constants in non-irradiated a n d irradiated fluoroplastics. F l u o r o - p o l y m e r s were dissolved in powder form in previously distilled acetone; solution c o n c e n t r a t i o n was 7 wt. °/o for the c o p o l y m e r a n d 3 wt. % f o r * Vysokomol. soyed. A2@:No. 12, 2791-2796, 1978.

~130

1~. S. TIKHOMmOVAd od.

t h e trifluoroethylene polymer. Solutions were filtered through glass filters No. 2 a n d placed in glass rings with a cellophane base. At the top the rings were covered with filter paper and were placed on strictly horizontal balancing platforms. Film formation took place in Mr under a vacuum cabinet at room temperature. T h e films were dried to constant weight in a vacuum drier equipped with controlled heating. The thickness of copolymer films was 120-130 a m and polytrifluoroethylono films, 300/an. The films were irradiated (6°Co) in a vacuum of 10 -5 tort in glass ampoules with a constant dose rate of 0.75 Mrad~hr. The permeability constant P of fluoroplastics, diffusion constant D and the solubility constant a of helium and argon were measured in films at different temperatures before and after irradiation ~asing a pressure gauge on an apparatus previously described [3].

Iog Do -!

,

7

-3 -5

*5

-7 I

5

I0

15

E4 , /wa//mole FIG. 1. Relation between log Do and the activation energy of diffusion of srgon in polymers: 1--copo]ymer; 2--polytrifluoroethylene; 3--PVC; 4--PTFE; 5--

polyamide 54/10; 6--methylol polyamide; 7--PE. Results of measuring P, D and a in fluoro-polymers for helium and argon at
Gas diffusion in fluoro-polymers

3lZl

gives the heat and entropy of solution of argon in other polymers [3]. These values are the highest in the copolymer and the polymer of trifluoroethylene a n d lowest in P T F E . Comparatively high values of AS for these fluoro-polymers indicate a relatively high chain flexibility. A proportional variation of AH and AS is observed in the polymer series shown in Table 2 on transition from one polymer to another [3]. Highest values of AS a n d AH are observed for the copolymer and lowest in the series mentioned for P T F E . Since the energy of interaction of molecular chains depends on the posia

~1.0

.

~

1o

~I0

I

I

I

100

50

1-51

ix

Do~e~Mf~2d

2O0

b O~

\\\\\ // ':,Z '-5 i

j//t

-F "I: l-

oN

" 20O

\\b(/

/jJ #00

Dose, M/,ad

8OO

Fie. 2. Relation between c~nstants of permeability (1), diffusion (2) and solubility (3) of argon in polytrifluoroethylene (a) and a copolymer (b) and the dose of irradiation. tion, configuration and therefore, the number of micro-states of the system, tJao proportionality observed in the variation of mixing enthalpy and entropy c o n f o r m s to the established rule. Table 2 also shows results in the literature [4] concerning the molecular cohesion of PE, PVC and P T F E , which characterize the degree of interaction be-

3132

1~. S. T r g ~ o ~ o v A

et al.

tween the chains in these polymers. These results are not availal)lo for polymers containing hydrogen fluoride. Since, however, these polymers are similar to PVO in D Oand E~ values it may be assumed that the value of molecular cohesion is in the region of 2000-3000. When studying gas diffusion in a number of polymers [3] it was shown that values of log Do and ED are linked with the linear relation log Do = - 9 . 0 + 0 . 7 2

ED

18 °

17 0 14 °

lO

/

z

3 e#eg

:Fzo. 3. Relation between the relative peak height of diffraction for polytrifluoroethyleno and dose: 1--non-irradiated sample; 2--sample irradiated with a dose of 400 Mrad; 3-800 Mrad. Results o b t a i n e d during t h e diffusion of argon in polymers containing h y d r o gen fluoride are also shown on this straight line (Fig. 1). This suggests t h a t energies of molecular interaction o f p o l y m e r chains m a y be e v a l u a t e d qualitat i v e l y f r o m t h e D Ovalue: low values of D Ocorrespond t o m a x i m u m values o f E ~ . TABLE

1. P E R M E A B I L I T Y OF FILMS, D I F F U S I O l q AlqD S O L U B I L I T Y OF GASES I N F L U O R O - P O L Y MERS AT D I F F E R E N T T E M P E R A T U R E S

Material

;opolymer

] 'TFE

T, oK

298 333 368 298 333 368

J

Helium

mS/m2P X 1017,See D X 10u, m/Pa m2/see 2"3 8"8 28.5

!

-

1.1 2.0 4-0

Argon crX 10L ma/m~/Pa 2.10 4.40 7.10

P X 1017 m~/m s see, m/Pa

0.1 0"9 4.1 0-2 1.7 6.9

D × 10 xt,

a × l O 6,

m~/see

ma/m~/Pa

6'1 1.6 2.0 1-6 4-8 12.0

0.16 0.56 2.05 0,13 0.36 0.57

! ]

I

W h e n polymers containing h y d r o g e n fluoride are exposed t o ionising radiat i o n fluorine a n d h y d r o g e n atoms are separated, macromolecules undergo breakd o w n a n d intermolecula~ crosslinking takes place, which is preceded b y t h e sep a r a t i o n of C - - H and C - - F bonds [5]. These processes result in a v a r i a t i o n o f all diffusion "constants. During irradiation with a dose o f 500 Mrad the eoeffieienb

Gas diffusion in fluoro-polymers

3133

o f diffusion of argon measured at 368°K decreases ~ 3 times in the trifluoroethylene polymer, while the solubility constant is almost doubled (Fig. 2a). More intensive changes take place in the copolymer with this dose tha~ in the trifluoroTABLE 2.

COEFFICIENTS AND

Materials

Copolymer Trifluoroethylene polymer PVC PE Polyamide 54/10 --NH[(CH,)sC0" "NH(CH2)6NC0" •(CH,),CO]NH-Methylol polyamide 2/10 --N(CH~) 5COl CH~OH PTFE

OF DIFFUSION ~S

Do,

VALUES FOR

ACTIVATION ENERGIES

OF D I F F U S I O N

AND

AH

ARGON--POLYMER SYSTEMS

D × 10n, Do*× 101., m2/sec m~/soc 1"14 1"60

2.75 1"1

0-44 2"40

66 0.38x l0 s

0"04

ED,

cal/mole 2000 3300

Molecular cohesion at 5 A [4] cal m m

zIH, kcal/ /mole

AS at 20° a n d 760 tort, kcal/ /mole.deg

10"27 7"50

+16"15 +8"35

3500 120,000

2600 1000

7.90 5"50

+7.41 +4.70

810

6100

5800

6.00

+ 2-52

0"07

5300

6100

5800

5"40

+1"91

0"13

3"20

5200

1"60

- - 1"84

* Pre-exponential factor in the Arrhenius equation.

ethylene polymer, thus producing a five fold variation in constants P, D and (Fig. 25). A reduction in the rate of diffusion of argon in the fluoroplastics examined with an increase in the dose of radiation is explained b y the effect of structural network formed during irradiation as a result of intermolecular crosslinking [5]. Network formation reduces polymer chain mobility. The motion of gas molecules inside the polymer with these bonds is due to overcoming a highe¢ potential barrier t h a n before the formation of bonds. The activation energj of diffusion of argon in fluoro-polymers irradiated by comparatively high doses therefore • increases, compared with initial values: for the copolymer there is a 1.8 fold increase with a dose of 1400 Mrad, for the trifluoro-ethylene polymer, a 1.2 fold increase with a dose of 700 Mrad (Table 3). The Do value also increases, but much more considerably t h a n ED. We also observed this for argon-irradiated polyamide and polyethylene systems [1]. There is a linear relation between log D e and ED for the diffusion of a r g o n through irradiated polymers and fluoro-polymers

3134

N , S. T I ~ o ~ r a o v A

et

al.

log D0-- 10"5+ 0"7ED with the relation derived for a system of gas-non-irradiated polymers [3, 6]. A variation in solution entropy of argon in fluoro-polymers during irradiation is evidence of intensive irreversible processes of radiolysis in polymers, similar t o processes described for P E and polyamides [1]. For a eopolymer the AS valu~ o f the system decreases b y one order of magnitude with a dose of 1400 Mrad (Table 3). This is because, as a result of a reduction in chain flexibility, the probability of exchange here and there between atoms of the gas adsorbed and polymer chain segments also decreases. For trifluoroethylene polymers this effect has n o t been observed probably because the entropy of the system was measured after irradiation with a dose of 700 Mrad, at which processes of breakdown and t h e formation of unsaturation [5] in fluoro-polymers (as well as intermolecular crosslinking) considerably increase the solubility of gases in the polymer (Fig. 2). as

2~CTIVATIONENERGY OF DIFFUSIOI~ 9 ENTHALPY AND ENTROPY OF SOLUTIONS ARGOI~ IN POLYMERSCONTAININGFLUORINEBEFORE AND AFTER IRRADIATION

T A B L E 3.

Material Copolymer Polytrifluoroethylene

Dose, Mrad

E., kcal/mole

0 1400 0 700

2-0 3.7 3.3 3.9

D o × 101~, m2/sec

AH, kcal/mole

2"75 5"0 l'l 7"60

10"3 4"8 7"5 5"1

OF

AS, kcal/mole. "deg 16.7 1.8 1.4 2.0

I t was established b y studies using X-ray diffraction in a copolymer and a polymer of trifluoroethylene that the crystalline component decreases with the dose of irradiation and practically disappears with doses of the order of 10~ Mrad (Fig. 3). Amorphization also increases the solubility of gases in the polymer. The processes indicated therefore have a competing effect on mixing entropy. An after-effect is observed in irradiated fluoroplastie films, similar to the effect previously established for the diffusion of monatomic gases in P E and polyamidea [1]. After heating irradiated polymer films containing fluorine values of P and D of argon show a considerable reduction, compared with corresponding values before heating. For example, constants P and D of argon through polytrifluoroethylene films, irradiated with a dose of 700 Mrad (at 25°C) were as follows before heating: P ~ 0 . 2 2 × 10 -I7 ma/m2/sec, m/Pa, D~-0.62 × 10 -11 m2/sec and after heating for I hr at 70°C:P~0.045 x lO-17m3/m2/see.m/Pa, D : 0 . 2 4 × 10 - u m2/see. The cause of reduced P and D values of argon as a result of heat treatment o f irradiated films is the existence in these films of free radicals, the interaction o f which (to form new crosslinks) is accelerated on increasing temperatura.

Organo -siloxytitanium trichlorides

313~

Results of investigation therefore show that polytrifluoroethylene and t h e copolymer are similar to PVC as regards the activation energy of diffusion, Do, heat and entropy of solution of argon before and after exposure to ionising radiation; in the dose range of 10~ Mrad maximum a and mirdmum P and D are observed as a result of competing processes of radiolysis. By heating irradiated films possible after-effects of radiolysis can be eliminated. Translated by E. S~M~RE REFERENCES 1. N. S. TIKHOMIEOVA, Yu. M. MALINSKII and V. L. KARPOV, Vysokomol. soyed. 9, 1960 (Not translated in Polymer Sci. U.S.S.R.) 2. A. G. SAVIN, S. E. VAISBERG and V. L. KARPOV, Plast. massy, ~To. 2, 3, 1972 (Not translated in Polymer Sci. U.S.S.R.) 3. N. S. TIKHOMIROVA, Yu. M. MALINSKII and V. L. KARPOV, Vysokomol. soyed. 2: 221, 1960 4. V. S. KT.IMENKO, V. A. KARGIN and A. I. KITAIGORODSKH, Zh. fiz. khimii 27:: 1217, 1953 5. N. I. ROL'SHAKOVA, N. S. TIKHOMIROVA, V. L SERENKOV, G. I. Z/tTJKIND a n d N. N. PRIDATCHINA, Vysokomol. soyed. A I 6 : 1931, 1974 (Translated in Polymer S c i . U.S.S.R. 16: 8, 2216, 1974) 6. R. M. BARRER and G. SKIRROW, J. Polymer Sei. 3: 549, 1948

Polymer Science U.S.S.R. Vol. 20, pp. 3135-3144. ( ~ Pergamon Press Ltd. 1979. Printed in Poland

0032-~950/78/1201-3135507.50/@~

PHYSICAL AND CHEMICAL P R O P E R T I E S A N D ACTIVITY OF ORGANO-SILOXYTITANIUM TRICHLORIDES IN POLYMERIZATION OF ETHYLENE* Yu. A. SA~OALOV, A. I. IL'YASOVA, N. I. PUCHKINA and K. S. MINSKER I n s t i t u t e of Chemistry, Bashkir Branch of the U.S.S.R. Academy of Sciences

(Received 27 February 1978) A s t u d y was made of physical and chemical properties (heat stability, hydrolysis, reduction with aluminium alkyl) and activity in polymerization of ethylene o f a number of siloxytitanium trichlorides obtained by catalytic reaction of polysiloxanes with TiCI~. I t was shown t h a t siloxy groups of the initial t i t a n i u m compound are contained b y centres of polymerization of ethylene. The a c t i v i t y of siloxytitanium trichlorides with aluminium alkyl in polymerization of ethylene decreases with an increase of the length of the siloxane radical. Kinetic parameters of polymerization in the presence of the catalysts studied were calculated. * Vysokomol. soyed. A20: No. 12, 2797-2804, 1978.