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The effect of gamma-neutron radiation on the electrical conductivity and dipole segmental relaxation of polystyrene
yr.. I. K N I z ~ I X and S. D. M A l a C C a
576
that the main factors in formation and decay of the active centres of polymerization in the VO(OCsHs)a-AI(C~H~)~C1 catalyst system (the number, order and rate constants of the reactions) have been assessed correctly. According to the proposed reaction scheme and the values of the constants, the main cause of loss of activity of the VO(OC~H~)3-AI(C2H6)2CI system is decay of active centres by chain termination.
Translated by E. O. PHrLLrPs REFERENCES 1. I. N. ANDREYEVA, L. C. VARFOLOMEYEVA, V. M. ZAPLETNYAK, V. L. MAKSIMOV, A. V. STAFEYEV, B. I. SAZHIN and O. K. KHARITONOVA, Plast. massy, No. 5, 23, 1970 2. O. K. I~HARITONOVA, R. Ye. PROKOF'EVA, V. L. MAKIRMOV, A. V. STAFEEY, V. M. ZAPLETNYAK a n d B. I. SAZHIN, Vysokomol. soyed. B14: 28, 1972 (Not translated in Polymer Sci. U.S.S.R.)
THE EFFECT OF GAMMA-NEUTRON RADIATION ON THE ELECTRICAL CONDUCTIVITY AND DIPOLE SEGMENTAL RELAXATION OF POLYSTYRENE* YE. I. KI~'IZHNIK a n d S. ]). MAMCHICH I n s t i t u t e of Nuclear Research, Ukr.S.S.R. Academy of Sciences
(Received 9 January 1975) The specific volume resistance p~, the dielectric properties and the gel fraction of polystyrene irradiated in a nuclear reactor have been investigated. I t was found t h a t dependence of p~ a n d t a r J m a x i m u m on radiation dosage is represented b y curves containing extrema. I t was found that the constant characterizing the inereaso iu p~ over the dosage range of ~ 4 0 - - 8 1 0 Mrad is greater than the value usually obtained for fl-irradiation. Some reduction in the relaxation time distribution parao meter was noted at 17 a n d 200 Mrad and the reduction was greater at 806 Mrad.
THe. study of irreversible radiation-electrical effects in PS, which is one of t h e more radiation resistant polymers, has been carried out up to the present time over a limited range of dosages, temperatures, frequencies and times of stay under the applied voltage [1-5]. In view of existing experimental evidence t h a t transfer of energy (LTE) influences radiation effects in PS substantially [6-8], * Vysokomol. soyed. A18: No. 3, 505-508, 1976.
Effect of gamma-neutron radiation on electrical conductivity of PS
577
a r b i t r a r y transfer of results from one form of radiation to another is obviously n o t always justified for PS. F o r this reason it seemed of interest to study the action, of gam m a-neut ron irradiation on PS by means of electrical methods and to analyse the results in conjunction with results obtained in other investigations. The specimens used were discs of thickness N 1 man and diameter ~ 40 mm, cut from t~0hnical PS sheet (~/v~2"3 × 105, density 1.03 g/cm 3 [8]). X-ray analysis of the original PS specimens, carried out in a ]:)RD-1 apparatus, showed an intense halo (which is a characteristic feature of amorphous polymers) in the region of 20~ 18°. The specimens were irradiated in a vertical channel of a VVR-M reactor at Tra d ~--.4 0 - - 5 0 °. The dose rate, determined by the non-equilibrium method [9], was 0.02-0.07 Mrad/sec, and the contribution of neutrons to the total dosage absorbed by the PS was about 0.7 [8]. The methods of measurement of the electrical characteristics (specific volume resistance, pv, dielectric loss tan g and dielectric constant e) are described in reference [10], and of the physicochemical characteristics, namely the quantity of gel fraction and the radiation yield of crosslinkages G(x), in refere n o e [8].
Dependence of Pv on dosage. Figure 1 shows t h a t over the range of dosages D = 0 - 8 1 0 Mrad the curve of pv-~q~(D) contains a well defined minimum. I t is known t h a t in irradiation of PS in air the nature of the action of the radiation is dependent on the ratio of the contributions of radiation induced oxidation and crosslinking [11]. Here the thickness of the specimen and the dose rate play i m p o r t a n t parts. I t has been suggested [12] t h a t in the surface layers of PS irradiated in the presence of oxygen, the free radicals from peroxides and hydroperoxides, which subsequently decompose to form low-molecular polar fractions. Since pv during a time of application of voltage of rv ~ 10a sec at T _~20° is often determined b y the polarization (not residual) current [11], the presence of an oxidized layer can increase the dielectric loss of the whole specimen considerably, a n d Pv, which is inversely proportional t o the dielectric loss factor ~", falls. I n order to equalize the effect of atmospheric oxygen irradiation of the PS specimens was carried out at various dose rates. Thus the falling section of the curve of the dependence of Pv on dosage (Fig. 1) was obtained at a dose rate of ~ 0.02 Mrad/sec, b ut in the region of increase in Pv the dose rate was considerably higher ( ~ 0 . 0 7 Mrad/sec). Consequently for specimens irradiated to dosages o f 33 and 120 Mrad the lengths of the periods of irradiation and the depths of t h e oxidized surface layer were approximately the same (according to reference [14] the depth of the oxidized surface layer of PS irradiated under similar conditions was between 30 and 110/~). However the fraction of gel which characterizes the density of the network, is 0.83 at 120 Mra~l, but at 33 Mrad it is only 0.40. Thus radiation oxidation has a predominating effect on the value of Pv, p ro bab ly up to 40-50 Mr~l. At high dosages radiation crosslinking is evidently predominant. At high crosslinking densities, which obviously bot h shorten the free passage o f the charge carrier as a result of increased cubic contraction and also increase
Y~.. I. K~zzzrsn~ and S. D . ~f~Mo~zcz~
578
the potential barrier to passage of an ion b y "pushing apart" of neighbouring molecules as a result of formation of intermolecular linkages, the mobility of t h e charge carriers (ions) can be reduced considerably. Therefore p~ increases considerably. Comparison of the results of our investigations with those of reference [!5], where the variation in p ~ during irradiation with electrons from 9°Sr was studied, shows that the critical dosage Dcr, at which increase in ps begins, has approximately the same value ( ~ 4 0 Mrad). Above this dosage the dependence o f log ps on log D is linear both in our experiments and in reference [ 15], i.e. p~= aD x, where a is a constant. The increase in the constant K, which characterizes the rate of increase in ps with increase in dosage, from 0.5 in reference [15] to 2.2 in the present work, can be explained b y a substantial increase in the radiation ,hm.cm 8
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1
,,I
,
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FIG. 2
Fio. I. Dependence of the specific volume resistance p~ (1), tan Sm~ (2) at f=400 Hz aud the quantity of gel fraction (3) of samples of PS on radiation dosage. Fxo. 2. Dependence of p~ on temperature: time of application of voltage 300 see (1, 3) and 15 sec (2, 4) at dosages of 806 (1, 2) and 0 Mrad (3, 4). yield of crosslinkages G(x) from 0.05 in/~-irradiation [11] to 0.151 in our experiments with gamma-neutron radiation [8]. The greater efficiency of cross]inklng of PS b y gamma-neutron radiation (LTE _~8.0 keV//Lm according to reference [ 16] ) in comparison with fl-radiation (LTE -~ 0.2 keV/pm [ 11]), i.e. the role of L T E is possibly connected with the occurrence of competing kinetic reactions of different order, occurring within and outside the track. These reactions are excitation of molecules, which is a first order reaction, and the second order deactivation of the excited molecules, and when there is overlapping of spurs the second-
Effect of gamma-neutron radiation on electrical conductivity of PS
579
order reaction is accelerated. Thus the observed L T E effect is caused more b y the slow reaction of deactivation of excitation. Furthermore the higher radiation yield of crosslinkages in our experiments, in comparison with reference [15], could also be explained b y the substantially greater thickness of the specimens (in reference [15] specimens of thickness -~0.05 mm were used) and higher dose rates. Dependence of Pv on temperature. The pv-T curves at different r v both for samples irradiated to 806 M_rad and the original samples (according to known evidence [13]), have three characteristic temperature regions with different types of dependence of Pv on T and ~v (Fig. 2). Over the entire range of temperatures studied Pv of radiation-cross]inked PS is higher than Pv of the original material measured at the same zv. The formation of intermoleeular crosslinkages, which is known [17, 18] to bring about a reduction in tan 5 at a certain frequency w, and can lead, as was stated above, to increase in Pv determined after a time rv=0.1/co sec from the moment of application of a constant voltage. This explains the increase in pv at temperatures close to and below Tg. Reduction in the mobility of the kinetic units involved in the dipole-segmental process of establishment of dipole polarization, as a result of cross]inking of the polymer, causes the region of the pv minimum to be displaced toward higher temperatures. For example at vv= 15 sec the temperatures of the Pv minima are 84 ° and 100 °, and at ~ v : 3 0 0 sec at ~ 7 8 ° and 97 ° for untreated and irradiated specimens respectively (Fig. 2). The higher values of Pv of radiation cross]inked PS in the region above T~ in comparison with the original polymer is evidently brought about b y reduction in the average length of the free passage of the charge carrier (an ion) because of the cubic contraction resulting from crosslinking. From the experimental results presented in Fig. 2 it is not possible to detect any appreciable change in the apparent energy of activation for electrical conductivity in the temperature region above Tg. The dependence of tan ~ on temperature and frequency. The fact that in t h e given region of temperatures (20-150 °) and frequencies (40-2× 104 Hz) there is no appreciable dipole-group loss in atactic PS, is attributable, as was suggested in reference [19], to the rather large molecular forces due to interaction of the benzene rings, as a result of which almost no orientation of dipolar groups occurs in an electrical field. The dependence of tan 5max in dipole-segmental relaxation on dosage (Fig. 1) shows, like the dependence of Pv on dosage discussed above, the competing action of the two processes of radiation oxidation and radiation cross]inking. At dosages of 17 and 33 Mrad the first of these processes obviously predominates and the dielectric constant increment eo--e ~ (~o and e~ are the dielectric constants in a constant field and in a field of infinitely high frequency) increases. The value of tan 5max=(eo--~)/2.~eo-~ also increases. At dosages of 120 and 200 Mrad however the network density reaches a very considerable
580
Y~.. I. K~ztr~iK and S. D. M_Aa~CHIOTr
v a l u e (see above) a n d the crosslinkiug process predominates. I n these circumstances the i n c r e m e n t falls and, as would be expected, t a n Jmax also decreases
I17, 18]. On the basis of measurement of e and tan J of untreated PS and of PS irradiated to various dosages the distribution parameter of relaxation times ~Lwas calculated (according to the Fuoss-Kirkwood theory [20]) for dipole-segmental relaxation at 130 °, for PS irradiated to various dosages Dosage, Mrad 0 17 120 200 806 A 0-56 0-49 0.54 0.49 0.37 T h e decrease in A, which characterizes t h e b r e a d t h o f the s p e c t r u m of relaxation times, a t a dosage of 17 Mrad (in comparison with the original PS), is in s a t i s f a c t o r y a g r e e m e n t with the decrease in ~ as a result of oxidative degradation o f P E [21]. T h e fact t h a t ~ falls substantially as the n e t w o r k density increases (dosage of 806 Mrad) is in good a g r e e m e n t with the narrowing o f the s p e c t r u m o f r e l a x a t i o n times o f dipole-segmental in h a r d e n e d epoxide resins (in comparis o n w i t h the resins before hardening) [22]. T h u s our results s u p p o r t the conclusion of t h e a u t h o r s of reference [23], t h a t the effect of increase in s t r u c t u r a l i n h o m o g e n e i t y (i.e. lowering o f the distribution p a r a m e t e r ~)is stronger for crosslinl~ing t h a n for degradation. Trwnslat~ by E. O. pwrr,T.Tps
REFERENCES
1. 2. 3. 4. 5. ~. 7. 8. 9. 10. 11. 12. 23.
A. BR0CKES, Z. Phys. 149: 357, 1957 T. NAKAI and T. SAKAKIBARA, Electr. Engng. Japan 8: 163, 1963 V. ADAMETS, Elektrichestvo, No. 4, 76, 1964 L. HEYNE and O. HAUSER, Kolloid-Z. und Z. Polymere 205: 39, 1965 V. K. MATVEYEV, S. E. VAISBERG and V. L. KARPOV, Vysokomol. soyed. U: 2666, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 12, 3032, 1969) W. W. PARglNSON, C. D. BOPP, D. BINDER and J. E. WHITE, J. Phys. Chem. 69: 828, 1965 A. B. ZVEREV, Ya. I. LAVRENTOVICH and A. M. KABAKCHI, Khimiya vysokikh energii 3: 453, 1969 Yo. I. KNIZHNIK, L. Ya. NECHIPORUKand Ya. I. LAVRENTOVIffH, Plast. massy, No. 3, 21, 1975 M. B. FIVEISKII, Yu. S. LAZURKIN and M. A. MOKUL'SI~II~ Atomnaya energiya 9: 32], 1960 Ye. I. KNIZHNIK and S. D. MAMCHICH, Vysokomol. soyed. A l l : 1666, 1969 (Translated in Polymer Sci. U.S.S.R. 11: 8, 1887, 1969) A. CHARLESBY, Yadernye izlucheniya i polimery (Atomic Radiation and Polymers). Foreign Literature Publishing House, 1962 (Russian translation) Ye. Ye. BARONI, Vysokomol. soyed. 3: 960, 1962 (Translated in Polymer Sci. U.S.S.R. 3: 7, 759, 1962) B. I. SAZHIN (Ed.), Elektricheskie svoistva polimerov (Electrical Properties of Polymers). Izd. "Khimiya", 1970
Reaction of WCls with alcohols
581
14. A~ A. BELIKOVSKII, Dissertation, 1968 15. J. H. COLEMAN and D. BOHM, J. Appl. Phys. 3: 828, 1953 16. Ya. I. LAVRENTOVICH and A. M. KABAKCHI, Sb. Radiatsionnaya khiraiya polimercy (Collected papers. Radiation Chemistry of Polymers). p. 285, Izd. "Nauka", 1966 17. O. P. MINHAILOV and L. V. KRASNER, Vysokomol. soyed. A9: 213, 1967 (Translated in Polymer Sei. U.S.S.R. 9: 1, 233, 1967) 18. Ye. S. BUDNIKOVA, Ye. Yo. SIROTKINA, V. P. LOPATINS]KII and R. M. KESSENIKH, Vysokomol. soyed. A l l : 931, 1969 (Translated in Polymer Sci. U.S.S.R. l h 1969) 19. G. P. iYHgH~ILOV and T. I. BORISOVA, Uspekhi khimii 3~ 864, 1961 20. R. FUOSS and J. KIRKWOOD, J. Amer. Chem. Soc. 63: 385, 1941 21. G. P. MIKHAILOV and T. I. BORISOVA, Zh. tekh. fiz. 23: 2159, 1953 22. E. SCHLOSER, Plaste und Kautsehuk, No. 9, 652, 1968 23. V. K. MATVEYEV, S. E. VAISBERG and V. L. KARPOV, Plast. massy, No. 11, 42, 1971
REACTION OF WCls WITH ALCOHOLS AND THE ACTIVITY OF THE RESULTING CATALYSTS IN POLYMERIZATION OF CYCLOPENTENE* V. A. KHODZHEMIROV, V. A. YEVDOKIMOVA a n d V. M. CHEREDNIOHENKO L. Ya. Karpov Physicochemioal Research Institute
(Received 15 January 1975) I t is shown that the activity of the three component soluble catalyst system WCle + ROH + AI(CtH5)nCla-n in ring opening polymerization of eyclopentene increases as the electron accepter properties of the organoaluminitun compound increases, and as its reducing power decreases. It was found from the electronic absorption spectra and elementary analysis that when WC16reacts with an excess of ethanol ethoxyehlorides of five valcnt tungsten are formed. From phenol under comparable conditions phenoxychlorides of six valent tungsten are obtained and the degree of substitution of phcnoxyl groups for chlorine ions is not more than three. IT WAS s t a t e d in reference [1] t h a t in ring opening p o l y m e r i z a t i o n of cyclop e n t e n e u n d e r t h e influence o f t h e c a t a l y t i c s y s t e m WCle+I~OI-I+AI(C~Hs)2C1, t h e solubility a n d a c t i v i t y of t h e c a t a l y s t is d e p e n d e n t s u b s t a n t i a l l y on the molar r a t i o of alcohol to WC16. Bearing this in m i n d we h a v e studied the reaction o f WC16 w i t h e t h a n o l a n d phenol a n d also i n v e s t i g a t e d the effect of the reducing a n d a c c e p t e r properties o f the o r g a n o a l u m i n i u m c o m p o u n d on p o l y m e r i z a t i o n o f cyclopentene. * Vysokomol. soyed. A18: No. 3, 509-514, 1976.
576
that the main factors in formation and decay of the active centres of polymerization in the VO(OCsHs)a-AI(C~H~)~C1 catalyst system (the number, order and rate constants of the reactions) have been assessed correctly. According to the proposed reaction scheme and the values of the constants, the main cause of loss of activity of the VO(OC~H~)3-AI(C2H6)2CI system is decay of active centres by chain termination.
Translated by E. O. PHrLLrPs REFERENCES 1. I. N. ANDREYEVA, L. C. VARFOLOMEYEVA, V. M. ZAPLETNYAK, V. L. MAKSIMOV, A. V. STAFEYEV, B. I. SAZHIN and O. K. KHARITONOVA, Plast. massy, No. 5, 23, 1970 2. O. K. I~HARITONOVA, R. Ye. PROKOF'EVA, V. L. MAKIRMOV, A. V. STAFEEY, V. M. ZAPLETNYAK a n d B. I. SAZHIN, Vysokomol. soyed. B14: 28, 1972 (Not translated in Polymer Sci. U.S.S.R.)
THE EFFECT OF GAMMA-NEUTRON RADIATION ON THE ELECTRICAL CONDUCTIVITY AND DIPOLE SEGMENTAL RELAXATION OF POLYSTYRENE* YE. I. KI~'IZHNIK a n d S. ]). MAMCHICH I n s t i t u t e of Nuclear Research, Ukr.S.S.R. Academy of Sciences
(Received 9 January 1975) The specific volume resistance p~, the dielectric properties and the gel fraction of polystyrene irradiated in a nuclear reactor have been investigated. I t was found t h a t dependence of p~ a n d t a r J m a x i m u m on radiation dosage is represented b y curves containing extrema. I t was found that the constant characterizing the inereaso iu p~ over the dosage range of ~ 4 0 - - 8 1 0 Mrad is greater than the value usually obtained for fl-irradiation. Some reduction in the relaxation time distribution parao meter was noted at 17 a n d 200 Mrad and the reduction was greater at 806 Mrad.
THe. study of irreversible radiation-electrical effects in PS, which is one of t h e more radiation resistant polymers, has been carried out up to the present time over a limited range of dosages, temperatures, frequencies and times of stay under the applied voltage [1-5]. In view of existing experimental evidence t h a t transfer of energy (LTE) influences radiation effects in PS substantially [6-8], * Vysokomol. soyed. A18: No. 3, 505-508, 1976.
Effect of gamma-neutron radiation on electrical conductivity of PS
577
a r b i t r a r y transfer of results from one form of radiation to another is obviously n o t always justified for PS. F o r this reason it seemed of interest to study the action, of gam m a-neut ron irradiation on PS by means of electrical methods and to analyse the results in conjunction with results obtained in other investigations. The specimens used were discs of thickness N 1 man and diameter ~ 40 mm, cut from t~0hnical PS sheet (~/v~2"3 × 105, density 1.03 g/cm 3 [8]). X-ray analysis of the original PS specimens, carried out in a ]:)RD-1 apparatus, showed an intense halo (which is a characteristic feature of amorphous polymers) in the region of 20~ 18°. The specimens were irradiated in a vertical channel of a VVR-M reactor at Tra d ~--.4 0 - - 5 0 °. The dose rate, determined by the non-equilibrium method [9], was 0.02-0.07 Mrad/sec, and the contribution of neutrons to the total dosage absorbed by the PS was about 0.7 [8]. The methods of measurement of the electrical characteristics (specific volume resistance, pv, dielectric loss tan g and dielectric constant e) are described in reference [10], and of the physicochemical characteristics, namely the quantity of gel fraction and the radiation yield of crosslinkages G(x), in refere n o e [8].
Dependence of Pv on dosage. Figure 1 shows t h a t over the range of dosages D = 0 - 8 1 0 Mrad the curve of pv-~q~(D) contains a well defined minimum. I t is known t h a t in irradiation of PS in air the nature of the action of the radiation is dependent on the ratio of the contributions of radiation induced oxidation and crosslinking [11]. Here the thickness of the specimen and the dose rate play i m p o r t a n t parts. I t has been suggested [12] t h a t in the surface layers of PS irradiated in the presence of oxygen, the free radicals from peroxides and hydroperoxides, which subsequently decompose to form low-molecular polar fractions. Since pv during a time of application of voltage of rv ~ 10a sec at T _~20° is often determined b y the polarization (not residual) current [11], the presence of an oxidized layer can increase the dielectric loss of the whole specimen considerably, a n d Pv, which is inversely proportional t o the dielectric loss factor ~", falls. I n order to equalize the effect of atmospheric oxygen irradiation of the PS specimens was carried out at various dose rates. Thus the falling section of the curve of the dependence of Pv on dosage (Fig. 1) was obtained at a dose rate of ~ 0.02 Mrad/sec, b ut in the region of increase in Pv the dose rate was considerably higher ( ~ 0 . 0 7 Mrad/sec). Consequently for specimens irradiated to dosages o f 33 and 120 Mrad the lengths of the periods of irradiation and the depths of t h e oxidized surface layer were approximately the same (according to reference [14] the depth of the oxidized surface layer of PS irradiated under similar conditions was between 30 and 110/~). However the fraction of gel which characterizes the density of the network, is 0.83 at 120 Mra~l, but at 33 Mrad it is only 0.40. Thus radiation oxidation has a predominating effect on the value of Pv, p ro bab ly up to 40-50 Mr~l. At high dosages radiation crosslinking is evidently predominant. At high crosslinking densities, which obviously bot h shorten the free passage o f the charge carrier as a result of increased cubic contraction and also increase
Y~.. I. K~zzzrsn~ and S. D . ~f~Mo~zcz~
578
the potential barrier to passage of an ion b y "pushing apart" of neighbouring molecules as a result of formation of intermolecular linkages, the mobility of t h e charge carriers (ions) can be reduced considerably. Therefore p~ increases considerably. Comparison of the results of our investigations with those of reference [!5], where the variation in p ~ during irradiation with electrons from 9°Sr was studied, shows that the critical dosage Dcr, at which increase in ps begins, has approximately the same value ( ~ 4 0 Mrad). Above this dosage the dependence o f log ps on log D is linear both in our experiments and in reference [ 15], i.e. p~= aD x, where a is a constant. The increase in the constant K, which characterizes the rate of increase in ps with increase in dosage, from 0.5 in reference [15] to 2.2 in the present work, can be explained b y a substantial increase in the radiation ,hm.cm 8
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i
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10 FIG. 1
1
,,I
,
i
i i
1oo 1ooo BosaBe, Mrad
I
I
I
170 150 130 lfO
I
90
I
70
I
T,°C
50
FIG. 2
Fio. I. Dependence of the specific volume resistance p~ (1), tan Sm~ (2) at f=400 Hz aud the quantity of gel fraction (3) of samples of PS on radiation dosage. Fxo. 2. Dependence of p~ on temperature: time of application of voltage 300 see (1, 3) and 15 sec (2, 4) at dosages of 806 (1, 2) and 0 Mrad (3, 4). yield of crosslinkages G(x) from 0.05 in/~-irradiation [11] to 0.151 in our experiments with gamma-neutron radiation [8]. The greater efficiency of cross]inklng of PS b y gamma-neutron radiation (LTE _~8.0 keV//Lm according to reference [ 16] ) in comparison with fl-radiation (LTE -~ 0.2 keV/pm [ 11]), i.e. the role of L T E is possibly connected with the occurrence of competing kinetic reactions of different order, occurring within and outside the track. These reactions are excitation of molecules, which is a first order reaction, and the second order deactivation of the excited molecules, and when there is overlapping of spurs the second-
Effect of gamma-neutron radiation on electrical conductivity of PS
579
order reaction is accelerated. Thus the observed L T E effect is caused more b y the slow reaction of deactivation of excitation. Furthermore the higher radiation yield of crosslinkages in our experiments, in comparison with reference [15], could also be explained b y the substantially greater thickness of the specimens (in reference [15] specimens of thickness -~0.05 mm were used) and higher dose rates. Dependence of Pv on temperature. The pv-T curves at different r v both for samples irradiated to 806 M_rad and the original samples (according to known evidence [13]), have three characteristic temperature regions with different types of dependence of Pv on T and ~v (Fig. 2). Over the entire range of temperatures studied Pv of radiation-cross]inked PS is higher than Pv of the original material measured at the same zv. The formation of intermoleeular crosslinkages, which is known [17, 18] to bring about a reduction in tan 5 at a certain frequency w, and can lead, as was stated above, to increase in Pv determined after a time rv=0.1/co sec from the moment of application of a constant voltage. This explains the increase in pv at temperatures close to and below Tg. Reduction in the mobility of the kinetic units involved in the dipole-segmental process of establishment of dipole polarization, as a result of cross]inking of the polymer, causes the region of the pv minimum to be displaced toward higher temperatures. For example at vv= 15 sec the temperatures of the Pv minima are 84 ° and 100 °, and at ~ v : 3 0 0 sec at ~ 7 8 ° and 97 ° for untreated and irradiated specimens respectively (Fig. 2). The higher values of Pv of radiation cross]inked PS in the region above T~ in comparison with the original polymer is evidently brought about b y reduction in the average length of the free passage of the charge carrier (an ion) because of the cubic contraction resulting from crosslinking. From the experimental results presented in Fig. 2 it is not possible to detect any appreciable change in the apparent energy of activation for electrical conductivity in the temperature region above Tg. The dependence of tan ~ on temperature and frequency. The fact that in t h e given region of temperatures (20-150 °) and frequencies (40-2× 104 Hz) there is no appreciable dipole-group loss in atactic PS, is attributable, as was suggested in reference [19], to the rather large molecular forces due to interaction of the benzene rings, as a result of which almost no orientation of dipolar groups occurs in an electrical field. The dependence of tan 5max in dipole-segmental relaxation on dosage (Fig. 1) shows, like the dependence of Pv on dosage discussed above, the competing action of the two processes of radiation oxidation and radiation cross]inking. At dosages of 17 and 33 Mrad the first of these processes obviously predominates and the dielectric constant increment eo--e ~ (~o and e~ are the dielectric constants in a constant field and in a field of infinitely high frequency) increases. The value of tan 5max=(eo--~)/2.~eo-~ also increases. At dosages of 120 and 200 Mrad however the network density reaches a very considerable
580
Y~.. I. K~ztr~iK and S. D. M_Aa~CHIOTr
v a l u e (see above) a n d the crosslinkiug process predominates. I n these circumstances the i n c r e m e n t falls and, as would be expected, t a n Jmax also decreases
I17, 18]. On the basis of measurement of e and tan J of untreated PS and of PS irradiated to various dosages the distribution parameter of relaxation times ~Lwas calculated (according to the Fuoss-Kirkwood theory [20]) for dipole-segmental relaxation at 130 °, for PS irradiated to various dosages Dosage, Mrad 0 17 120 200 806 A 0-56 0-49 0.54 0.49 0.37 T h e decrease in A, which characterizes t h e b r e a d t h o f the s p e c t r u m of relaxation times, a t a dosage of 17 Mrad (in comparison with the original PS), is in s a t i s f a c t o r y a g r e e m e n t with the decrease in ~ as a result of oxidative degradation o f P E [21]. T h e fact t h a t ~ falls substantially as the n e t w o r k density increases (dosage of 806 Mrad) is in good a g r e e m e n t with the narrowing o f the s p e c t r u m o f r e l a x a t i o n times o f dipole-segmental in h a r d e n e d epoxide resins (in comparis o n w i t h the resins before hardening) [22]. T h u s our results s u p p o r t the conclusion of t h e a u t h o r s of reference [23], t h a t the effect of increase in s t r u c t u r a l i n h o m o g e n e i t y (i.e. lowering o f the distribution p a r a m e t e r ~)is stronger for crosslinl~ing t h a n for degradation. Trwnslat~ by E. O. pwrr,T.Tps
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Reaction of WCls with alcohols
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REACTION OF WCls WITH ALCOHOLS AND THE ACTIVITY OF THE RESULTING CATALYSTS IN POLYMERIZATION OF CYCLOPENTENE* V. A. KHODZHEMIROV, V. A. YEVDOKIMOVA a n d V. M. CHEREDNIOHENKO L. Ya. Karpov Physicochemioal Research Institute
(Received 15 January 1975) I t is shown that the activity of the three component soluble catalyst system WCle + ROH + AI(CtH5)nCla-n in ring opening polymerization of eyclopentene increases as the electron accepter properties of the organoaluminitun compound increases, and as its reducing power decreases. It was found from the electronic absorption spectra and elementary analysis that when WC16reacts with an excess of ethanol ethoxyehlorides of five valcnt tungsten are formed. From phenol under comparable conditions phenoxychlorides of six valent tungsten are obtained and the degree of substitution of phcnoxyl groups for chlorine ions is not more than three. IT WAS s t a t e d in reference [1] t h a t in ring opening p o l y m e r i z a t i o n of cyclop e n t e n e u n d e r t h e influence o f t h e c a t a l y t i c s y s t e m WCle+I~OI-I+AI(C~Hs)2C1, t h e solubility a n d a c t i v i t y of t h e c a t a l y s t is d e p e n d e n t s u b s t a n t i a l l y on the molar r a t i o of alcohol to WC16. Bearing this in m i n d we h a v e studied the reaction o f WC16 w i t h e t h a n o l a n d phenol a n d also i n v e s t i g a t e d the effect of the reducing a n d a c c e p t e r properties o f the o r g a n o a l u m i n i u m c o m p o u n d on p o l y m e r i z a t i o n o f cyclopentene. * Vysokomol. soyed. A18: No. 3, 509-514, 1976.