Nuclear Instruments and Methods 199 (1982) 427-430 427 North-Holland Publishing Company

INVESTIGATION OF PARAMAGNETIC CHARACTERISTICS OF LADDER AND PARTLY-LADDER POLYCHINONS

D.K. SALTIBAEV, G.A. EGEMBERDIEVA and Z.A. SHISKHKINA Institute of Chemical Sciences of the Kazakh SSR Academy of Sciences, 480100, Alma-Ata, USSR

L.A. VASILEVSKAYA and S.P. PIVOVAROV Institute of Nuclear Physics of the Kazakh SSR Academy of Sciences, 480082, A lma-A ta, USSR

It was shown that for doses of y-irradiation ~0.5 X 105 Mrad and reactor irradiation up to ~ 5 x 1019 n / c m z and heated up to 500°C the investigated samples of the ladder polymers practically did not change their characteristics.

1. Introduction

Amorphous and polycrystal polymers exhibit unique properties and are more and more widely used in technology. These materials are of consid- erable interest for creating new construction materials for nuclear energetics [1].

The ladder and partly-ladder polychinons possess the majority of the specific properties characteristic of polyconjugated systems [2]. A common property of all of these is paramagnetism of the polyconjugated systems; the origin and na- ture of this has been very much investigated by different authors [3].

The results of paramagnetic characteristics studies of some polychinons, their changes after thermal treatment and irradiation in the active zone of a WWR-K reactor at 70°C and by 6°Co y-rays temperature up to 300°C are given in this paper.

The EPR polychinon spectra were taken by means of 3 cm and 10 cm radiospectrometers. In most cases the spectra observed represent the su- perposition of narrow and wide signals with close g-factors, fig. 1. Only for polychinons based on phentiazin and carbazol have single symmetric signals been observed. Analysis of line shape made by the linear anamorphosis method for these sam- ples showed that the signal is a mixture of Lorentzian and Gaussian lines whose width be- tween the points of maximum slope is in the range of 4- ! 2 G and hardly varies with frequency change. Integral intensity of the signals corresponds to

(b)

Fig. 1. Diphenyl (a) and carbazol (b) based EPR polychinons spectra. (Scale is different).

paramagnetic centres (PMC) concentration 1017

102o sp/g, table 1.

2. Results and discussion

Investigation of thermal effect on these poly- mers has shown that the PMC growth with tem- perature increase is characteristic of the majority of polychinons studied, fig. 2. This shows that thermal treatment of the polymers results not only in the destruction of their macro-molecules but also that the structuring and inclination of the hard products of destruction carbonization is char- acteristic of most polychinons. Carbonization of

0167-5087/82/0000-0000/$02.75 © 1982 North-Holland vii. RADIATION EFFECTS

428 D.K. Saltibaev et al. / Paramagnetic characteristics

Table I Paramagnetic characteristics of ladder and partly-ladder polychinons

Sample Polychinon 2x H 1 A HI EPR-signal no structure 3-cm 10-cm shape

range (G) range (G) AH 2 (G)

N PMC concentration (g - I )

1 2 3 4 5

1 ] ~ / - \ ~ ~ / - ~ c . . ~ c.~[ 5.2±0.5 complicat. 5.6x 1018 ~ c ~ - - A H 2 = 35.7

V ~ c

O O

? o

2 ~ f / ' ~ c - . . . y T - ~ , c..~ 5.8--+0.5 6.5±0.5 complicat. 5.9× 10 TM

< Q - ~ c H 2 ~ c " ~ " ~ c ~ , , AH 2 =35.9 O O

o o

"-..f.-~z 5.0±0.5 complicat. 0.6× 3 1018

J ' ~ z ~"-c~i A H 2 = 34.8 O O

o o

C C •

4 S " J ' ~ / ~ " Go ~ " " c ~ " ~;'~" ~' 4 . 5 ± 0 . 5 ~H2c°mplicat'= 35 .7 1"5)<1018

o ?

5 2 ~) 6.7±0.5 complicat. ~ 1017

o o

6 5.0 ± 0.5 complicat. 4.9 × 1018 AH 2 = 35.9

o o

c c 7 ] ' ~ ~ "~ 5.5±0.5 5.2±0.5 complicat. 7.2)<1018

< ~ o/'v-....v./-~ c ~"~_.J'L--. c .-.~'j A n 2 =35.9

o

8 < ~ ' s j Q ' ~ c Y ' ~ c d , 5.0±0.5 Ac°mplicat'H2 = 35.0 8.9× 10 '~

O O

o o

9 c . c " 6.6±0.5 6.2±0.5 singlet 1.7 )< 1019

o o

10 6.1 ± 0.5 complicat. 6.5 × 1018 o , AH 2 =35.9

o

s ~ c ~ c.Q ~ 102o 11 ,'~ [~..>>'%~ ' N , ' ~ - / ~ C ~ C-/]" 11.6±0.5 11.7±0.5 singlet

o o

D.K, Saltibaev et al. / Paramagnetic characteristics

30

. ")J,g.,,

. - - . . .~- , _ ~ 0 200 4o0 600 ~C

N. /O -/e g-1

200

/5O

/O0

50

/¢./#fe-"

40

I~A A

Fig. 2. Temperature dependence of paramagnetic centres con- centration for polychinons. Digits by the curves correspond to the sample nos. in table 1.

429

50

20

10

J¢ /d: f -i

tl

160

120

80

~0

~0 ~0 120 ¢00 JTiM~adl

g

O

Fig. 3. Concentration change of polychinons paramagnetic centres depending upon the irradiation dose by 6°Co "t-rays. Digits by the curve correspond to the sample nos. in table 1.

hard products of thermal treatment of polymers with conjugated bonds leads, as a rule, to the development of their conjugation system [3]. It seems that the analogous phenomena take place during thermal treatment of our polychinons, and the growth of the PMC concentration observed with temperature increase is a consequence of it. An exception is the behaviour of phentiazin based polychinon containing the nominal N H group in the main chain. The PMC concentration with tem- perature growth at first increases and then begins to decrease (curve 11, fig. 2). This is in good agree- ment with the data of paper [4] in which it is shown that the structuring which takes place dur- ing the thermal treatment of polychinons contain- ing N atoms in the main chain is not accompanied by carbonization.

The dominance of the processes of thermo- oxidizing destruction over those of carbonization is also confirmed by the results of element com- position of hard products of destruction of this type of polychinons [5]. There are some sugges- tions [6] that the irradiation effect on polymers with conjugated bonds provokes changes analo- gous to those taking place during heating, i.e. during radiation treatment of such polymers along with radiolytic destruction processes of further polymerization or polycondensation, structuriza- tion. etc., may take place.

Possibly radiolytic destruction of polychinons as well as thermal destruction occurs in defect sites of their molecular structure. Hard products formed in this process are quite large fragments of macro-

molecules with a more definite system of conjuga- tion than initial polymers. The consequence of this is the observed concentration growth of PMC with irradiation dose increase. 'One can see from the data given in fig. 3 that this is characteristic of all the polychinons studied. The most irradiation re- sistant polymer is phentiazin based polychinon whose characteristics began to change only at very big doses ~ 1019 n,/cm 2 (fig. 4).

For comparison, investigation of one of the irradiation resistant polymer materials - polystirol - was carried out. Considerable irradiation damage was observed in this polymer even at - 1018 n / c m 2.

The change of the thermomechanical character- istics of some polychinons has been also investi-

~ :o- ' : ~~ L i l i . :o-:f ~ " D , o ~ I i ® , A

140 / o 160

/00 120

i

60 80

/0 00

0 IO ts lO s? [0 t9 ~ nleme

Fig. 4. Concentration change of polychinons paramagnetic centres depending upon neutron fluence. Digits by the curves correspond to the sample nos. in table 1.

VII. RADIATION EFFECTS

430 D.K. Saltibaev et al. /Paramagnet ic characteristics

gated. Irradiated by 6°Co y-rays and non-irradia- ted (control) samples of polymers have been ex- posed to heating with simultaneous mechanical

o

.,d

42 %- !

I i ~ I i •

o 200 400 To 600°0

Fig. 5. Thermomechanical curve for phentiazin based poly- chinon.

pressure with constant load 38 g / ram 2. The typical shape of the temperature transformation curve is given in fig. 5. The desending part of the curve is connected with the beginning of sample destruc- tion. The temperature of the beginning of the destruction T o, equal to 510°C for the non-irradia- ted sample of phentiazin based polychinon, does not change after irradiation by 6°Co y-rays.

The observed EPR signal changes may be com- pared with the data of crystallinity of the investi- gated samples. The degree of crystallinity was evaluated by X-ray and NMR methods. Partly- ladder polychinons having less ordered structure show an amorphous phase presence more than ladder polychinons do; this is confirmed by the sharp (4 times) difference of angular scattering intensities of X-rays for phentiazin based ladder and diphenylmethane based partly-ladder poly- chinons. X-ray image comparison of diphenyl- methane based partly-ladder polychinon before irradiation and after 100 Mrad irradiation gives

increased crystallinity as a result of irradiation up to 50% (2 times) whereas X-rays of phentiazin based polychinons do not vary after the same irradiation. The NMR spectrum of our poly- chinons also confirmed the data. These results are in a good agreement with [7] where it is shown that the radiation yield of radicals in an amorphous polymer is greater than in the crystalline one.

3. Conclusion

The data make it possible to suppose the pre- vailing flow in conditions of external effects (heat- ing, y- and reactor irradiation) of reactions leading to perfecting the systems of conjugation of hard products and to draw conclusions on the influence of phase polymer state upon the processes of its irradiation damage.

References

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[2] B.A. Zhubanov and D.K. Saltibaev, Vestnik AN KazSSR 11 (1976) 29.

[3] A.A. Berlin, M.A. Teiderih, B.E. Davydov, V.A. Kargin, G.P. Karpacheva, B.A. Krentsel and G.V. Hutareva, Hirniya sopryazhennyh sistem, M., lzd. Himiya (1972).

[4] B.I. Liogonkii, Doctorskaya dissertatsiya, M., INF AN SSSR (1975).

[5] B.A. Zhubanov, T. Sekei, M. Blango, F. Till and D.K. Saltibaev, Materialy VII. Mezhdunarodnogo Simpoziuma Polykondensatsionnye protsessy, Lodz, PNR, (1979).

[6] Ya.I. Paushkin, T.P. Vishnyakova, A.F. Lunin and S.A. Nizova, Organicheskie polymernye poluprovodniki, izd. Himiya M., (1971).

[7] V.V. Voevodskii, Fizika i himiya elementarnyh protsessov izd. "Nauka" (1960) 350.