Investigation of the influence of ionizing irradition on the structure of copolymers of ethylene with vinysilanes

114

N . N . Kuz'~IIN et al.

18. 19. 20. 21. 22.

E. EITZER and T. KALKA, High Temp. High Press 3: 53, 1971 E. FITZER and T. KALKA, Carbon 10: 173, 1972 A. BURGAR, E. FIRZER, M. HEIM and B. TERWEISCH, Carbon 13: 149, 1975 G. P. SCHULMAN and W. LOCHTER, J. Macromolec. Sci. Chem. AI: 413, 1967 J. TSUR, V. L. FREILICH and W. LEVY, J. Polymer Sci., Polymer Chem. Ed. 12: 153, 1974 23. V. V. KORSHAK, A. L. RUSANOV, S.-S. A. PAVLOVA, P. N. GRIBKOVA, L. A. MIKADZE, D. A. BOCHVAR, I. V. STANKEVICH and O. B. TOM1LIN, Dokl. AN SSSR 227: 1134, 1975 24. V. V. KORSHAK, S.-S. A. PAVLOVA, P. N. GRIBKOVA, L. A. MIKADZE, A. L. RUSANOV, L. Kh. PLIYEVA and T. V. LEKAYE, Izv. AN SSSR, seriya khimich., 1381, 1977 25. V. V. KORSHAK, S.-S. A. PAVLOVA, P. N. GRIBKOVA, L. A. MIKADZE and A. L. RUSANOV, Izv. AN GrSSR, seriya khimich., 313, 1976

Polymer Science U.S.S.R. Vol. 23, 1%. 1, pp. 114-122, 1981 Printed in Poland

0032-3950/81/010114-09507.50/O 1982 Pergamon Press Ltd.

INVESTIGATION OF THE INFLUENCE OF IONIZING IRRADIATION ON THE STRUCTURE OF COPOLYMERS OF ETHYLENE W I T H VINYLSILANES* N. N. Kuz'MI~, S. A. CItEBANYUK,YU. K. OVCHINNIKOV, S. S. LESHCHENKO, V. L. KARPOV and N. F. BAKEYEV L.

Ya.

Karpov

Physicochemieal Research

Institute

(Received 26 October 1979) Methods of wide- and small-angle X-ray diffraction have been used to carry out a structural investigation of copolymers of ethylene with vinylsilanes, varying the type and amount of organosilicon groups, and the ionizing radiation dose. I t is shown that vinylsilane groups have a marked effect on the paracrystalline component. On increasing the irradiation dose, changes were observed in the fraction of the paracrystalline component and in its degree of disorientation, as well as in the average position of the amorphous halo. I n the light of the experimental results it is concluded t h a t decomposition of organosilicon groups takes place mainly in paracrystaUine component.

IN RECENT years authors have been increasingly interested in the structure of the amorphous component in partially crystalline polymers. Underlying this interst is the fact that it is the structure of the amorphous component that largely determines mechanical properties of the polymers. Branch chain defects or pendants are mainly located in amorphous regions. It was accordingly desired * Vysokomol. soyed. A23: No. 1, 102-109, 1981.

Structure of copolymers of ethylene with vinylsilanes

115

to investigate the extent to which the structure of the amorphous component m a y be influenced by the defects relative to the constitution and amount of the latter. To do so we investigated a series of copolymers of PE with vinylsilanes which satisfied requirements in the present instance, since both the size of vinylsilane units in the series and the amount of these units may be varied. There is also a further reason why copolymers of this type were selected: preliminary tests showed t h a t the incorporation of vinylsilane units has a good influences on the radiation stability of PE, and gives the polymer certain novel properties, which is a matter of independent interest. Thus our aim in the investigation was to carry out samll- and wide-angle X-ray diffraction sutdies of the structure of statistical copolymers of ethylene with vinylsilanes relative to the size and molar concentration of organosilicon groups, and to the ionizing radiation dose. The study objects were copolymers I-IV of ethylene with the following vinylsilanes, having a variety of structures of substituents of vinylsilane units, viz: vinyltriethylsilane --Si--(C2H~)3 (I), vinyltrinonoxysilane --Si--(O--CgH19)a (II), vinyltrimethylsilane Si-- (CHs)3 (III), trimethylsiloxyvinylsilane Si-- [Si-- (O-- CH3)a] (IV). The copolymers were prepared by" radical eopolymerization [5, 6]. The conditions of synthesis of the copolymers provides for a statistical distribution of organosilicon units and for molecular weights in the range 100,000 to 18,000. Copolymer specimens were irradiated ~fith a ~°Co apparatus (dose rate 4 Mrad/hr), in a helium medium at room temperature. The isotropic and the oriented specimens were investigated at room temperature. Structural analyses were carried out with aid of a DRON1.5 (CuK~) type diffractometer provided with an asymmetrical focussing monoehromator, using the transmission exposure method. A KRM-1 device was used to plot the low-angle scattering curves. -

-

I n the light of X-ray analyses of isotropic specimens of the unexposed copo]ymers it is seen t h a t the degree of crystallinity is reduced (Fig. 1), as well as: the size of the crystallites (Table 1), as the amount of vinylsilane units is i n creased. All changes occurring in the structure of the copolymers of interest were evaluated in comparison with the structure of the initial low density PE. It is seen from Fig. 1 t h a t the reduction in the degree of crystallinity as the fraction of organosilicon units increases is most marked in copolymer IV, where the vinylsilane units are the most bulky. ~n the composition range where the degree of crystallinity changes only to an insignificant extent no change in the position of the (110) and (200) crystalline reflections was detectable in any of the copolymers, and it is the latter reflections t h a t determine the base plane parameters of the elementary cell. This is apparently due to the fact t h a t during crystallization bulky vinylsilane units are forced out of crystallites, e.g. in contradistinction to metyl groups in ethylene-propylene copolymers, which cocrystallize and markedly distort the PE crystal lattice [7, 8]. The latter assumption is in line with the conclusion reached in [4] regarding elimination of polymer chain defects from crystallites during crystallization.

116

N . N . KVZ'MI~¢ e$ a/.

In the light of the data on macrodensity (Fig. linity and elementary cell parameters, densities for were calculated. It was found that the density of increases (Fig. lc) in the range of low vinylsilane

lb) and degrees of crystalthe amorphous component the amorphous component concentrations. The results

C

f3 >9/cnt 3

0"88 c¢,,, %

a

1

~ •

087 3

zo

2f

q

i

I 0.85 Gx,mole%

I

1

I

I

I

I

3 oc,mole%

p, g /crn a

°851 0.8/ "

0.85

b 2

~

I

70

I

20

I

30x,mo&%

Fzo. 1. Degree of crystallinity (a), m a c r o d e n s i t y (b) and a m o r p h o u s phase d e n s i t y (c) vs. a m o u n t of vinylsilane units x in copolymers I (1) ; TT (2) ; I I I (3) a n d I V (4).

obtained show that a localized arrangement of vinylsilane units exists in amorphous regions of the copolymers. Further evidence of this is provided by the low angle scattering curves for copolymer II: as the vinylsilane concentration increases, the intensity of the low-ang|e reflection decreases (see Fig. 2). It should be said that the intensity reduction observed for curves 2 and 3 takes place :practically without any alteration in the degree of crystallinity (curve 1 coincides, within the limits of experimental accuracy, with the curve for the initial low density PE). It follows that this reduction in the low angle scattering intensity may be due to increasing similarity of electron densities for crystal-

Structure of eopolymers of ethylene with vinylsilanes

117

line a n d amorphous components on account of increased d e n s i t y of the latter. F u r t h e r reductions in the low angle scattering i n t e n s i t y (curves d, 5 ) are due, in addition, to lower degrees of crystallinity.

Pe/.UrL

~

1 I Z

0.60

i

O.ZO10

30

50

28"

I5

5

:FIG. 2

Z5

20 °

FIG. 3

Fro. 2. Low angle X-ray scattering curves for specimens of copolymer II containing 0"2 (1) ; 0.7 (2); 1.8 (3); 2.8 (4) and 3-6 mole % organosilicon groups (5). FIG. 3. Meridional scattering patterns for oriented specimens of copolymer IV with an irradiation dose of 0 (1), 150 (2), 300 {3) and 550 Mrad (4). I t is seen from Fig. lb, t h a t a discontinuity appears on the curve of d e n s i t y versus composition of copolymer I I I in the range of molar concentrations ~ 12 %, a n d stems, as is clear from the X-ray investigations, from complete amorphization of the copolymer in question. A further increase in the molar concentration of organosilicon units likewise leads to reduced macrodensity which is, apparently, the result of a loosening of molecular packing, although the efficiency of the latter process is lower t h a n in the initial range of copolymer compositions. Thus it was found t h a t an increase in the concentration of vinylsilaue units in the amorphous component of a crystalline polymer leads to increased d e n s i t y TABLE l.

Copolymer

SIZE

Amount of vinylsilane groups, mole %

OF THE COPOLYMER C R Y S T A L I ~ T E S

Crystallite ~' size ~ (110), Copolymer II

IT

0.2 1.8 2.8 3.6 0.6 1.5 2.3

194 180 177 154 190 190 155

III

IV

Amount of I vinylsilane Crystallite size L (ll0), groups, 1 mole % A 1 0.7 180 1.7 133 3.2 138 0-3 1.2 3.8

197 161 149

118

N, N. K~rz'Mn~ eta/.

o f the latter component, whereas an increased amount of vinylsilane units in completely .amorphized copolymer results in reduced density. F r o m analysis of isotropic specimens of the copolymers it is impossible to say precisely what structural changes in the amorphous component take place through incorporation of vinylsilane units in the copoylmers. More information is obtainable from a study of oriented specimens. It is known from work reported in [1, 2] that orientation of the specimens enables scattering due to an amorphousisotropic component to be separated from that due to a paracrystalline component. 20~,,x 21I

el o2

0

LJ

C]

19 J

I

10

16

FIG. 4

22

28 2B °

r

I

I

20

40

60

]

80 ~°

FIG. 5

F~G. 4. X - r a y scattering patterns for specimens of copolymer I V containing 1.7 (1) ; 3-2 (2) and 6.7 mole ~o organosilicon groups (3). FIG. 5. Relation of the amorphous halo at 20max vs. azimuthal orientation angle for specimens of copolymers I V before (1) and after irradiation with 550 Mrad (2).

Specimens underwent uniaxial drawing up to 500% followed by annealing for 8 hr at 90-95 °. X-ray patterns of the oriented specimens of copolymer IV show the presence of two amorphous halos (Fig. 3), the first being at 20max----19"35° (matching the amorphous halo for PE) and the other at 20max----10°. It is known [9] that macromolecuIar defects of the type of pendants or branching influence the position of the amorphous halo at 20max. In the case under eonsideration the position of the amorphous halo relating to P E remains unaltered. In view of this one m a y assume that no vinylsilane units are present in this part of the polymer. The second halo at 10 ° owes its appearance to vinylsilane units, as is indicated, in particular, by the fact that an incrase in the number o f these units leads to increasing intensity of the halo (see Fig. 4). Let us now make a more detailed study of the paracrystalline component o f copolymer IV. As in the case of PE [1, 2] the paracrystalline component is well oriented, and has a somewhat wider texture scattering angle compared with the crystallites. It follows that in determining disorientation of the paracrystMline component relative to the crystallite with which it is associated,

S t r u c t u r e of e o p o l y m e r s o f e t h y l e n e w i t h v i n y l s i l a n e s

119

we must take account of the disorientation angle of the erystallites themselves. To a first approximation this angle m a y be determined as the difference in experimentally obtained integral half-widths of disorientation of paraerystalline and crystalline components. Another quantity characterizing the transitional component, is the position of the amorphous halo at 20max (Fig. 5), which is affected b y the azimuthal orientation angle and is related to the packing density of the macromoleeules. To obtain an average value for 20max we must take account of the fractional contribution of paracrystallites varying as to the value of 20max, which is determined as the area under the amorphous halo S 2 as a function of the azimuthal orientation angle (see Fig. 6b) Calculation of 20av was based on the formula 20 max S~d eP

20~v= ~'~

(1) 20maxdq

It is clear from Fig. 6b that there is a disorientation of 7 ° for the paracrystalline component in the unexposed copolymer IV, whereas the disorientation of the latter component in the low-density P E is the same as in the crystallites, i.e. disorientation of the paracrystalline component is zero with respect to crystallites. This means that vinylsilane units have a marked effect on disorientation of the paracrystalline component in copolymer IV. The value of 20av in the latter copolymer containing 1.3 mole °/o vinylsilane units is considerably lower than in the low-density P E (Table 2). Thus it appears that vinylsilane units in copolymer IV give rise to structural transitions that are reflected in a more marked disorientation function and in a change in 20av for the paracrystalline component. It may therefore be surmised that the vinylsilane units are located TABLE

2.

CHARACTERISTICS

OF

THE

CRYSTALLINE~

PARACRYSTALLINE

AND

AMORPHOUS

C O P O L Y M ~ R COMPONENTS

Irradiation Specimen

T°

dose,

20av

20m ax

26 25

20-80 19.90

19.35 19.35

Ccr

8pc

8a I

35 39

39 36

8a,

Mrad Low-density PE

15 68

Copolymer II

15 15

0 550

31 34

34 28

26 35

20.20 20-35

19.35 19.35

Copolymer IV

15 15

0 550

44 34

24 22

32 44

20.95 20.70

19.60 19-50

Note. co,-- Degree of crystallinity; S~¢, Sat, and So2 are respectively fractions of paracrystaliine a n d amorphous components; 29,, is the mean value of the halo position for the paraerystalline component; 20~,, is the halo position for the amorphous component.

120

N.N. K u z ' ~ e~a/.

in the paracrystalline component and give rise to increased disorientation of the latter. In copolymer IV we considered a case involving organosilicon t h a t were sterically most unfavourable and were practically spherical-shaped with a diameter of 13 A. Let us now turn to copolymer I I containing organosilicon groups with long paraffin tails. It was found t h a t the X-ray patterns have only a single amorphousisotropic halo at 19.6 ° for the copolymer containing 1-8 mole% organosilicon units. The increase in 20rex for the amorphous component compared with P E is apparently due to the influence of paraffin tails, which "heal" defects in the packing of the macromolecules.

Sfpel.un. ,

3

0.75

0.75

b

.1,

0"501~ 2'

O:Z5 I_

20

qO

20

q0

60 ~v°

FIG. 6. i~lrea ~q2below the crystalline (1, 1', 2, 2') and amorphous (3, 3', 4, 4") maxima vs, azimuthal orientation angle ~ for specimens of copolymers II (a) and IV (b) before (1, 2', 3, 4') and after irradiation with 550 Mrad (1', 2, 3', 4). The degree of disorientation of the paracrystalline component (in the case under study relative to crystallites) is practically the same as for low-density t)E and is equal to zero, but the mean position of the amorphous halo at 20av is higher (Fig. 6a, Table 2). Thus in contradistinction to copolymer IV we find that in this case vinylsilane units are located not only in the paracrystMline component, as evidenced by a higher value for 2Say, but also in the amorphous component, which leads also to an increase in 26maxAs has previgusly been noted, ionizing irradiation has a marked effect on copolymer of ethylene and vinylsilane units. An analysis of the gaseous products of radiolysis shows that whereas hydrogen is evolved preferentially in PE under irradiation, the relative amount of hydrogen in the ethylene copolymers decreases as the vinylsilane concentration is increased, and more hydrocarbons and a certain amount of organosilicon compounds are formed. The results of an IR analysis of the initial and the irradiated copolymers show that ionizing irradiation is accompanied by abstraction of substituents

Structure of copolymers of ethylene with vinylsilanes

121

on Si atoms. In copolymer IV there is a reduction in the intensity of the bands .

I

I

I

associated with the vibrations of --Si--CH3 (755, 840, 1250 cm -1) and - - S i - - O - - S i

I

I

I

i

bonds (1100 cm-1). Reduced intensity in the absorption of - - S i - - O - - C bonds is

i observed in copolymer II, and bands appear at 760, 820, 850, 1020 and 1250 cm -1

I

I

and are related to vibrations of --Si--CH3 and --Si--C2H~ groups; there are

I

also bands in the 1060-1100 cm -1 region which may be assigned to vibrations of - - S i - - O R and --Si(CH2)n Si-- groups [10, 11]. This means that ionizing ir-

I

I

radiation has a marked influence on the organosilicon groups. I t can be seen from Fig. 3 that a significant reduction appears for copolymer IV in the intensity of the amorphous halo at 20max: 10°, relating to vinylsilane units, on increasing the irradiation dose to 550 Mrad. The other halo relating to scattering typical for low density PE, does not change its position at 20m~x z 19.35 °, and its intensity is only insignificantly altered. At the same time there is a significant reduction in the disorientation of the paracrystMline component (see Fig. 6b, curves 1', 3') and an increase in 20av is observed. In addition, there was an increase in the degree of crystallinity; the amount of the paracrystalline fraction is reduced. I t should be noted that a similar change in the paracrystalline and crystalline components observed for copoIymer IV as the ionizing radiation dose rises likewise appears in low density PE, but, in the Tatter case~ on raising the temperature. This is attributable to a reversible healing of a number

I

T

I

I

of defects. In the case of copolymer IV, fracture of - - S i - - O - - S i - - bonds occurs, as was noted above, on increasing the irradiation dose to 550 Mrad, and the fracture of these bonds leads, in turn, to,an irreversible reduction in the size of defects in the paracrystalline component. The irradiation of copolymer I I is accompanied by a reduction in 20a~ for the paracrystalline component and in the fraction of the latter, and also in a lower degree of crystallinity. On the other hand there is a marked increase in the amount of the amorphous ]sotropic component; at the same time a slight change in the position of the amorphous halo at 28 . . . . from 19.6 to 19.5 °, is observed. Behaviour of this sort on the part of the paracrystalline and crystalline coral ponents is most probably the result of --Si--O--CgH~9 bond sc]ssion leading

I to loss of the paraffinic tail and to the forma~.ion of a defect that is sterically less favourable for packing of the macromolecules, and is reflected in the structural changes we observed. In view of the experimental results one may conclude that vinylsilane groups

122

:N.N. Kvz'MI~ etal.

a r e m a i n l y c o n c e n t r a t e d in t h e p a r a c r y s t a l l i n e c o m p o n e n t , a n d t h a t all t h e m o r e significant s t r u c t u r a l changes occurring u n d e r t h e ionizing i r r a d i a t i o n t a k e place likewise in p a r a c r y s t a l l i n e regions. I n conclusion it should be n o t e d t h a t the results of this i n v e s t i g a t i o n are all consistent w i t h the f r a m e w o r k o f model concepts d e v e l o p e d [1, 2], w h i c h once a g a i n s u b s t a n t i a t e s t h e d e s i r a b i l i t y a n d t h e n e c e s s i t y of using t h e l a t t e r m o d e l to describe t h e s t r u c t u r e of p a r t i a l l y crystalline p o l y m e r s . Translated by R. J. A. HENDRY REFERENCES

1. Yu. K. OVCHINNIKOV, N. N. KUZMIN, G. S. MARKOVA and N. F. BAKEYEV, Vysokomol, soyod. A20: 1742, 1978 (Translated in Polymer Sei. U.S.S.R. 20: 8, 1959, 1978) 2. N. N. KUZMIN, Yu. K. OVCHINNIKOV, V. D. FEDOTOV, N. A. ABDRASHITOVA, G. S. MARKOVA and N. F. BAKEYEV, Vysokomol. soyed. B20: 548, 1978 (Not translated in Polymer Sci. U.S.S.R.) 3. R. KITAMURY, F. HORII and S. H. I-lYON, J. Polymer Sci., Polymer Phys. Ed. 15: 821, 1977 4. J. MARTINEZ-SALAZAS and F. I. BALTA-CALLEJA, Internat. Symposium on Macromolec. Chemistry, Abstracts of Short Reports, vol. 5, p. 86, Tashkent, 1978 5. S. M. SAMOILOV, S. T. PUDOVIK, M. Sh. YAFAGOV and V. N. MONASTYRSKII, Vysokomol. soyed. A17: 2035, 1975 (Translated in Polymer Sci. U.S.S.R. 17: 9, 2347, 1975) 6. S. M. SAMOILOV, B. R. RATNER, S. D. YANKOVA, G. V. ZAMBROVSKAYA, V. I.

IVANOV and V. N. MONASTYRSKII, Vysokvmol. soyed. A18: 314, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 2, 361, 1976) 7. P" R. EICHORN, J. Polymer Sei. 56: 409, 1962 8. P. R. SWAN, J. Polymer Sei. 56: 409, 1962 9. Ye. M. ANTIPOV, Yu. K. OVCHINNIKOV, A. V. REBROV, G. P. BELOV, G. S. MARKOVA and N. F. BAKEYEV, Vysokomol. soyod. A20: 1727, 1978 (Translated in Polymer Sci. U.S.S.R. 20: 8, 1942, 1978) 10. L. BELLAMY, Infrared Spectra of Complex Molomfles, Izd. "Mir", 1967 11. Spektry i khromatogrammy elomoatoorganieheskikh soyedinenii (Spectra and Chromatograms of Heteroorganic Compounds), No. 1, 2, 1976