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Study of ionization ageing of polystyrene films using infrared spectroscopy
STUDY OF IONIZATION AGEING OF POLYSTYRENE FILMS USING INFRARED SPECTROSCOPY* l~. A. BAGIROV, V. P . !~AT.IN, YE. Y i . VOLCttENKOV a n d YIy. N . GAZAI~YAN Institute of Physics, Azerb. S.S.R. Academy of Sciences
(Received 16 October 1968)
D y i n g the preparation and use of products with polymer insulation air inclusions may form in which ionization processes may take place, resulting in irreversible change of the physical and chemical properties of the polymer (ionization or electrical ageing). Studies have therefore been published in recent years dealing with the effect of electric discharges in gas on polymer dielectrics [1-3]. It was established that as a result of the action of electric discharges in polymers, the following main processes take place: crosslinking (formation of a three-dimensional structure), involving the formation after electrical ageing of the insoluble residue of a gel fraction, breakdown of molecular chains, resulting in a reduction in the thickness and weight of the polymer, oxidation, etc. This paper describes some of the characteristics of ionization ageing of polymers investigated by IR spectroscopy. EXPERIMENTAL A n industrial polystyrene (PS) film, prepared b y the Kuskov chemical works b y bulk polymerization of amorphous polystyrene with a n average molecular weight of 90,000, was examined. The average thickness of the PS film was 20 g. The PS film was exposed to electric discharges at room temperature and atmospheric pressure in a special plane test cell wl~ich consists of a n earthed metal electrode for fastening the film, a n air gap and a glass plate with a metal coating, the latter being a high potential electrode. The thickness of the glass plate h = 1.8 m m was equal to the thickness of the air gap. Commercial frequency current was supplied to the electrodes. Ionization ageing was carried out at voltages on the cell (ageing voltage) Uag = 7 - 1 1 kVe~f. The Uag value, which corresponds to the inception of charge ignition was determined from the current-voltage characteristic of the cell using previously described methods [4]; it was about 6 kV. PS film was electrically aged both in air a n d in nitrogen, purified from oxygen. To explain the function of ozone in electrical ageing, PS film was stored in ozone obtained in a Siemens ozonizer. I R spectra were observed in a n IKS-14 spectrophotometer using LiF a n d NaC1 prisms. To study variation of I R spectra with electrical ageing time, the PS film was removed from time to time from the test cell and the spectrum of same part of the film spectrophotometrically recorded. * Vysokomol. soyed. A l l : No. 10, 2323-2329, 1969. 2643
2644
M.A. BAGIROVet aL
In view of the fact that during electrical ageing the surface layer of the polymer breaks down and consequently the background considerably increases, log Ib/I was used as tho measure of Lr~tensity of IR absorption bands, where I is the maximum transition of the band and Ib is background transmission. The gel fraction formed by electrical discharges was obtained by filtration of a solution of PS film in benzene. A mosaic of gel pieces in vaseline paste, fixed between KBr (LiF) was used to observe the IR spectra of gel fraction. RESULTS AND DISCUSSION
I t has been noted [5] t h a t in the I R spectra 05 a PS film subjected to electrical discharges in air changes occur which suggest the appearance of new groups and compounds. Absorption bands of hydroxyl (OH) (3300-2800 cm-X), C = O carbonyl (1720 cm -1) and ethers (1290 cm -x) appear. Increased absorption in the 1600-1500 cm -x region characterizes structures in which the phenyl ring is conjugated with a double bond ( C = O or C----C). A slight increase ia absorption near 1360 cm -x, Superimposed on the band at 1370 cm -x of the initial polystyrene, m a y be due to an increase in the number of methyl groups, CH 8 (1367 em -x) with a possible effect of symmetrical bond-stretching vibrations of NO2 (1365 cm-X). The spectrum of a PS film stored in ozone only (Fig. 1) also shows the appearance of new bands, which in m a n y ways are similar to the absorption bands observed after electrical ageing of PS films in air. It should be noted that bands of hydroxyl and nitro-groups do not occur in I R spectra of PS films subjected to the action of ozone only. The earbonyl band increases both during electrical ageing and by the effect of pure ozone only. I R spectra of PS films subjected to electrical ageing in purified nitrogen do not indicate any changes at all. I t m a y thus be assumed t h a t the main changes in the chemical structure of PS films during electrical ageing are due to the presence of oxygen in the zone of electrical discharge. Erosion. With increased duration of electrical discharge in oxygen the intensity of initial I R absorption bands of PS film decreases. We found that the variation of the band intensity at 1450, 1027, 906, 760 cm -x of the PS films depends on the ageing time. With longer ageing times the band intensity continuously and linearly decreases and the rate of reduction is about the same. A typical variation of the intensity of these bands is shown in Fig. 2 (for the band at 760 cm-X). With a higher voltage across the cell, the rate of band intensity reduction increases. Assuming that the reduction in band intensity is due to polymer erosion b y electrical discharge, it m a y be concluded from Fig. 2 that erosion of polymers, the ageing voltage remaining the same, increases with higher ageing voltage. 'The constant rate of polymer erosion under the action of electrical discharge has been noted previously [2] from measurements of the thickness and weight of the polymer during electrical ageing. Oxidation. The dependence of oxidation shown b y the carbonyl band at 1720 cm-X was studied both in relation to ageing time and ozonization time. ,Corresponding results are shown in Fig. 3.
Study of ionization ageing of polystyrene films using infrared spectroscopy
2645.
0
cz
¢D ~,.=~
._
.
I
S Lq
°~
/
¢9
,=
~=r=,
f
[,.~ uo]~dJosqV
•
2646
M. A. BAO:I~OV et cd.
This Figure indicates t h a t oxidation during ozonization fairly quickly reaches saturation. This m a y be explained by the surface nature o£ ozone ageing of polystyrene as a consequence of limited diffusion o£ ozone into the polymer. After
0"511
of 2 I
f5
25 Time, hi,
d5
~5
FIG. 2. Relative optical density variation (in relation to the initial value) of the band at 760 cm -1 of a PS film with ionization ageing time and different voltages across the cell: •--7; 2--9; 3--11kV. oxidation o f the surface layer (section of rapid increase in absorption intensity of C = O groups) further oxidation takes place v e r y slowly since ozone molecules now oxidize the deeper layers of polymer (section where the absorption intensity of C = O groups increases slowly). • I n the interpretation of kinetic curves of oxidation b y electrical discharge a t ten tio n should be given bot h to the established surface nat ure of oxidation
2 0"~ X~
~
0.#5 I
I
I
I
2O
qO
#0
80
T i m e ~ hr
Fro. 3. Optical density variation of the band at 1720 cm -1 (C =O group) with ageing time under the action of ozone and electrical discharge and different voltages across the cell: /--ozone; 2--7; 3--9; 4--11 kV.
Study of ionization ageing of polystyrene films using infrared spectroscopy 2647 and the fact that as C----O groups form, t h e y are eliminated as a result of the surface erosion of PS films by discharge. Owing to the simultaneous effect of these two processes--oxidation and ,erosion--a dynamic equilibrium is established after a certain time between the number of C = O groups formed and the number eliminated from the polymer (section of saturation on curves of Fig. 3). From the constant rate of erosion, the ageing voltage remaining the same, the appearance of the m a x i m u m on curves of oxidation m a y be explained. Let us make an approximate mathematical calculation. Equations for the variation with time of the number of oxidized units and units eliminated as a result of erosion, take the form
dnl
d~-=v;
dn2 k dt (n--nl--n~)'
where n is the number of units of the surface layer capable of taking part in oxidation or erosion, n 1 is the number of eliminated units, n2 is the number of oxidized units, ]c is the oxidation constant, v is the rate of erosion, which is constant for a given test cell and for given ageing frequencies and voltages. Solving these equations jointly and taking into account the initial conditions n 1 (0)----n2 (0)----0, we obtain: nl-~vt; n2~n~-v/k) × (1--e-~t)--vt. When v----0 (if there is no erosion) n2-~n (1--e-kt), i.e. oxidation increases but does not, so far, cover the whole accessible layer. When there is erosion (v~0) the dependence n ~ f (t) reaches a maximum. The time of appearance of the m a x i m u m can be found by putting the first derivative with respect to time equal to zero according to n2.
With k constant, the higher the rate of erosion, the sooner the m a x i m u m is reached, i.e. the time in which the m a x i m u m appears should decrease with higher ageing voltage, as observed experimentally. With the increase of ageing voltage the degree of oxidation decreases, since the rate of erosion increases. It should be noted t h a t this calculation is fairly approximate and does not describe the whole dependence of oxidation on electrolytic ageing time, for in the initial equations the fact is ignored that not only surface layer molecules take part in erosion and oxidation but also polystyrene molecules, which are in deeper layers and are gradually involved in electrical ageing as the surface layer is eroded. I t has been noted t h a t the saturation section of the curves (Fig. 3) is formed as a result of the equilibrium of processes of eliminating the oxidized layer and oxidation of deeper layers (Fig. 3). Gel formation. I t has been noted [2, 3] t h a t by the electrical discharge in air an insoluble residue--a gel fraction--is formed in the PS film. This is in
2648
M. A. BAGIROV e~ a~. ..2. v
~D
C,
j
(-
cD
0
eD
uo!,~dJosqv
Study of ionization ageing of polystyrene films using infrared spectroscopy
2649
agreement with the view that PS is a polymer which can be crosslinked by irradiation. Crosslinking during irradiation m a y occur both through carbon and oxygen bridges. We found that the amount of gel fraction formed during electrical ageing in air considerably exceeds the amount formed during ageing in nitrogen. Even during ageing in the atmosphere of commercial (1.5-2% 02) nitrogen from which oxygen had not been eliminated, the content of the gel fraction was always less than 1.5% of the overall weight of the polymer (approximately one order lower t h a n for ageing in air). In pure nitrogen the amount of gel was too low to be measured. I n the zone of electrical discharge from oxygen, ozone is rapidly formed which m a y cause erosslinking in PS film. In fact, after storing the PS film in pure ozone, the gel was formed in about the same proportion as during ageing in air. The II~ spectra of the ozone gel and gel made by electrical discharge in air (Fig. 4) are about the same. Absorption bands in the 1740-1560 cm -1 range point to the presence of various kinds of carbonyl groups and double bonds. Bands at 1950, 1878, 1790, 1070, 1025, 965, 908, 844, 760, 708 cm -1 obviously represent the initial polystyrene [6]. Bands at 1278, 1190-1140 em -~ belong to ester and keto ester bridges. It should be noted t h a t the range of absorption at 3600-3000 cm -~, attributed to OH groups, was not observed with the ozone gel. Thus, according to the I R spectra, PS gel from electrical ageing represents macromoleeules of the initial polystyrene with a large number of polar groups containing oxygen, which are connected by ether and keto ether (i.e. oxygen) bridges. According to the time of action of electrical discharges, the proportion of gel rapidly becomes constant (not more t h a n 12°/0 of the overall weight of the PS film). Surface nature of electrical ageing. It can be assumed that all the main processes of electrical ageing of polymers are localized in a relatively thin surface layer. This assumption is supported by the facts as follows: 1. The absorption intensities of new bands formed in the PS film by discharge become constant after a certain time, whereas the intensitites of initial bands slowly decrease during ageing. 2. The weight of the insoluble gel fraction, increasing as electrical ageing continues, rapidly becomes constant but only represents a small proportion of the total weight of the film (12% during ageing in air). I f we assume that the density of gel is equal to the density of the initial film and that the whole aged surface layer is formed of gel, the thickness of this layer, according to the ageing voltage, varies from 0.7 to 2/~. In proportion to the elimination of the aged surface layer, as a consequence of gas liberation or evaporation of electrical discharge, deeper and deeper polymer layers are aged. As a result, the thickness and weight of the polymer decrease.
2650
E . A . DZHAVADYANeta/. CONCLUSIONS
(1) A s t u d y was made of the variations in the I R spectra of a polystyrene film under the action of electrical discharge in air and nitrogen. (2) During electrical ageing in air a large number of groups containing oxygen is formed. The dependence of absorption variation of C----O groups was examined according to the duration of electrical discharge. (3) I t was found t h a t the intensities of the initial bands of the I R spectra 0f PS decrease evenly at a constant rate as electrical ageing continues, and the rate of reduction increases with higher voltage. (4) I R spectroscopic results indicate t h a t crosslinking by electrical discharge in a medium containing oxygen occurs by oxygen bridges. (5) I t was deduced from the experimental results t h a t ionization ageing of polymers is a surface phenomenon. Translated by E. S~.~m~
REFERENCES
1. A. V. MEATS and R. STANETT, Trans. IEE, Power Appar. and Systems, No. 1, 48, 1964 2. S. N. KOIKOV, V. A. PARIBOK and A. K. TSTI{IN, Sb. Proboi dielektrikov i poluprovodnikov (Break down Of Dielectrics and Semiconductors). p. 301, Izd. "Energiya", 1964 3. S. A. ABASOV, M. A. BAGIROV, N. V. ~LIMOVA and V. P. MAT.IN, Izv. AN Azerb. SSR, ser. fiz.-tekhn, i matem, nauk, No. 3, 137, 1965 4. Yu. V. FILIPPOV and Yu. M. YEMEL'YANOV, Zh. fiz. khimii 34: 1083, 1960 5. M. A. BAGIROV, Ye. Ya. VOLCHENKOV and V. P. MALTN, Sb. Materialy nauehnoi konferentsii molodykh uchenykh i aspirantov (Scientific Conference of Young Scientists and Post-Graduates). p. 129, AN Azerb. SSR, 1966 6. Sb. Fizika polimerov (Physics of Polymers). Izd. inostr, lit., 1960
KINETICS AND MECHANISM OF CATIONIC POLYMERIZATION OF CYCLIC ETHERS WITH POLYESTER ADDITIVES* E. A. DZIt~.VADYA_N,B..4. ROZENBERG and N. S. YENIKOLOPYAN Branch of the Iastitute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 11 November 1968)
COPOnYMERS containing units with ester and ether groups can obviously be obtained by the copolymerization of corresponding cyclic ethers and lactones [1-3]. However, because of the limited selection of monomers, this method is very restricted. At the same time it is known t h a t polyesters, including those * Vysokomol. soyed. All: No. 10, 2330-2336, 1969.
(Received 16 October 1968)
D y i n g the preparation and use of products with polymer insulation air inclusions may form in which ionization processes may take place, resulting in irreversible change of the physical and chemical properties of the polymer (ionization or electrical ageing). Studies have therefore been published in recent years dealing with the effect of electric discharges in gas on polymer dielectrics [1-3]. It was established that as a result of the action of electric discharges in polymers, the following main processes take place: crosslinking (formation of a three-dimensional structure), involving the formation after electrical ageing of the insoluble residue of a gel fraction, breakdown of molecular chains, resulting in a reduction in the thickness and weight of the polymer, oxidation, etc. This paper describes some of the characteristics of ionization ageing of polymers investigated by IR spectroscopy. EXPERIMENTAL A n industrial polystyrene (PS) film, prepared b y the Kuskov chemical works b y bulk polymerization of amorphous polystyrene with a n average molecular weight of 90,000, was examined. The average thickness of the PS film was 20 g. The PS film was exposed to electric discharges at room temperature and atmospheric pressure in a special plane test cell wl~ich consists of a n earthed metal electrode for fastening the film, a n air gap and a glass plate with a metal coating, the latter being a high potential electrode. The thickness of the glass plate h = 1.8 m m was equal to the thickness of the air gap. Commercial frequency current was supplied to the electrodes. Ionization ageing was carried out at voltages on the cell (ageing voltage) Uag = 7 - 1 1 kVe~f. The Uag value, which corresponds to the inception of charge ignition was determined from the current-voltage characteristic of the cell using previously described methods [4]; it was about 6 kV. PS film was electrically aged both in air a n d in nitrogen, purified from oxygen. To explain the function of ozone in electrical ageing, PS film was stored in ozone obtained in a Siemens ozonizer. I R spectra were observed in a n IKS-14 spectrophotometer using LiF a n d NaC1 prisms. To study variation of I R spectra with electrical ageing time, the PS film was removed from time to time from the test cell and the spectrum of same part of the film spectrophotometrically recorded. * Vysokomol. soyed. A l l : No. 10, 2323-2329, 1969. 2643
2644
M.A. BAGIROVet aL
In view of the fact that during electrical ageing the surface layer of the polymer breaks down and consequently the background considerably increases, log Ib/I was used as tho measure of Lr~tensity of IR absorption bands, where I is the maximum transition of the band and Ib is background transmission. The gel fraction formed by electrical discharges was obtained by filtration of a solution of PS film in benzene. A mosaic of gel pieces in vaseline paste, fixed between KBr (LiF) was used to observe the IR spectra of gel fraction. RESULTS AND DISCUSSION
I t has been noted [5] t h a t in the I R spectra 05 a PS film subjected to electrical discharges in air changes occur which suggest the appearance of new groups and compounds. Absorption bands of hydroxyl (OH) (3300-2800 cm-X), C = O carbonyl (1720 cm -1) and ethers (1290 cm -x) appear. Increased absorption in the 1600-1500 cm -x region characterizes structures in which the phenyl ring is conjugated with a double bond ( C = O or C----C). A slight increase ia absorption near 1360 cm -x, Superimposed on the band at 1370 cm -x of the initial polystyrene, m a y be due to an increase in the number of methyl groups, CH 8 (1367 em -x) with a possible effect of symmetrical bond-stretching vibrations of NO2 (1365 cm-X). The spectrum of a PS film stored in ozone only (Fig. 1) also shows the appearance of new bands, which in m a n y ways are similar to the absorption bands observed after electrical ageing of PS films in air. It should be noted that bands of hydroxyl and nitro-groups do not occur in I R spectra of PS films subjected to the action of ozone only. The earbonyl band increases both during electrical ageing and by the effect of pure ozone only. I R spectra of PS films subjected to electrical ageing in purified nitrogen do not indicate any changes at all. I t m a y thus be assumed t h a t the main changes in the chemical structure of PS films during electrical ageing are due to the presence of oxygen in the zone of electrical discharge. Erosion. With increased duration of electrical discharge in oxygen the intensity of initial I R absorption bands of PS film decreases. We found that the variation of the band intensity at 1450, 1027, 906, 760 cm -x of the PS films depends on the ageing time. With longer ageing times the band intensity continuously and linearly decreases and the rate of reduction is about the same. A typical variation of the intensity of these bands is shown in Fig. 2 (for the band at 760 cm-X). With a higher voltage across the cell, the rate of band intensity reduction increases. Assuming that the reduction in band intensity is due to polymer erosion b y electrical discharge, it m a y be concluded from Fig. 2 that erosion of polymers, the ageing voltage remaining the same, increases with higher ageing voltage. 'The constant rate of polymer erosion under the action of electrical discharge has been noted previously [2] from measurements of the thickness and weight of the polymer during electrical ageing. Oxidation. The dependence of oxidation shown b y the carbonyl band at 1720 cm-X was studied both in relation to ageing time and ozonization time. ,Corresponding results are shown in Fig. 3.
Study of ionization ageing of polystyrene films using infrared spectroscopy
2645.
0
cz
¢D ~,.=~
._
.
I
S Lq
°~
/
¢9
,=
~=r=,
f
[,.~ uo]~dJosqV
•
2646
M. A. BAO:I~OV et cd.
This Figure indicates t h a t oxidation during ozonization fairly quickly reaches saturation. This m a y be explained by the surface nature o£ ozone ageing of polystyrene as a consequence of limited diffusion o£ ozone into the polymer. After
0"511
of 2 I
f5
25 Time, hi,
d5
~5
FIG. 2. Relative optical density variation (in relation to the initial value) of the band at 760 cm -1 of a PS film with ionization ageing time and different voltages across the cell: •--7; 2--9; 3--11kV. oxidation o f the surface layer (section of rapid increase in absorption intensity of C = O groups) further oxidation takes place v e r y slowly since ozone molecules now oxidize the deeper layers of polymer (section where the absorption intensity of C = O groups increases slowly). • I n the interpretation of kinetic curves of oxidation b y electrical discharge a t ten tio n should be given bot h to the established surface nat ure of oxidation
2 0"~ X~
~
0.#5 I
I
I
I
2O
qO
#0
80
T i m e ~ hr
Fro. 3. Optical density variation of the band at 1720 cm -1 (C =O group) with ageing time under the action of ozone and electrical discharge and different voltages across the cell: /--ozone; 2--7; 3--9; 4--11 kV.
Study of ionization ageing of polystyrene films using infrared spectroscopy 2647 and the fact that as C----O groups form, t h e y are eliminated as a result of the surface erosion of PS films by discharge. Owing to the simultaneous effect of these two processes--oxidation and ,erosion--a dynamic equilibrium is established after a certain time between the number of C = O groups formed and the number eliminated from the polymer (section of saturation on curves of Fig. 3). From the constant rate of erosion, the ageing voltage remaining the same, the appearance of the m a x i m u m on curves of oxidation m a y be explained. Let us make an approximate mathematical calculation. Equations for the variation with time of the number of oxidized units and units eliminated as a result of erosion, take the form
dnl
d~-=v;
dn2 k dt (n--nl--n~)'
where n is the number of units of the surface layer capable of taking part in oxidation or erosion, n 1 is the number of eliminated units, n2 is the number of oxidized units, ]c is the oxidation constant, v is the rate of erosion, which is constant for a given test cell and for given ageing frequencies and voltages. Solving these equations jointly and taking into account the initial conditions n 1 (0)----n2 (0)----0, we obtain: nl-~vt; n2~n~-v/k) × (1--e-~t)--vt. When v----0 (if there is no erosion) n2-~n (1--e-kt), i.e. oxidation increases but does not, so far, cover the whole accessible layer. When there is erosion (v~0) the dependence n ~ f (t) reaches a maximum. The time of appearance of the m a x i m u m can be found by putting the first derivative with respect to time equal to zero according to n2.
With k constant, the higher the rate of erosion, the sooner the m a x i m u m is reached, i.e. the time in which the m a x i m u m appears should decrease with higher ageing voltage, as observed experimentally. With the increase of ageing voltage the degree of oxidation decreases, since the rate of erosion increases. It should be noted t h a t this calculation is fairly approximate and does not describe the whole dependence of oxidation on electrolytic ageing time, for in the initial equations the fact is ignored that not only surface layer molecules take part in erosion and oxidation but also polystyrene molecules, which are in deeper layers and are gradually involved in electrical ageing as the surface layer is eroded. I t has been noted t h a t the saturation section of the curves (Fig. 3) is formed as a result of the equilibrium of processes of eliminating the oxidized layer and oxidation of deeper layers (Fig. 3). Gel formation. I t has been noted [2, 3] t h a t by the electrical discharge in air an insoluble residue--a gel fraction--is formed in the PS film. This is in
2648
M. A. BAGIROV e~ a~. ..2. v
~D
C,
j
(-
cD
0
eD
uo!,~dJosqv
Study of ionization ageing of polystyrene films using infrared spectroscopy
2649
agreement with the view that PS is a polymer which can be crosslinked by irradiation. Crosslinking during irradiation m a y occur both through carbon and oxygen bridges. We found that the amount of gel fraction formed during electrical ageing in air considerably exceeds the amount formed during ageing in nitrogen. Even during ageing in the atmosphere of commercial (1.5-2% 02) nitrogen from which oxygen had not been eliminated, the content of the gel fraction was always less than 1.5% of the overall weight of the polymer (approximately one order lower t h a n for ageing in air). In pure nitrogen the amount of gel was too low to be measured. I n the zone of electrical discharge from oxygen, ozone is rapidly formed which m a y cause erosslinking in PS film. In fact, after storing the PS film in pure ozone, the gel was formed in about the same proportion as during ageing in air. The II~ spectra of the ozone gel and gel made by electrical discharge in air (Fig. 4) are about the same. Absorption bands in the 1740-1560 cm -1 range point to the presence of various kinds of carbonyl groups and double bonds. Bands at 1950, 1878, 1790, 1070, 1025, 965, 908, 844, 760, 708 cm -1 obviously represent the initial polystyrene [6]. Bands at 1278, 1190-1140 em -~ belong to ester and keto ester bridges. It should be noted t h a t the range of absorption at 3600-3000 cm -~, attributed to OH groups, was not observed with the ozone gel. Thus, according to the I R spectra, PS gel from electrical ageing represents macromoleeules of the initial polystyrene with a large number of polar groups containing oxygen, which are connected by ether and keto ether (i.e. oxygen) bridges. According to the time of action of electrical discharges, the proportion of gel rapidly becomes constant (not more t h a n 12°/0 of the overall weight of the PS film). Surface nature of electrical ageing. It can be assumed that all the main processes of electrical ageing of polymers are localized in a relatively thin surface layer. This assumption is supported by the facts as follows: 1. The absorption intensities of new bands formed in the PS film by discharge become constant after a certain time, whereas the intensitites of initial bands slowly decrease during ageing. 2. The weight of the insoluble gel fraction, increasing as electrical ageing continues, rapidly becomes constant but only represents a small proportion of the total weight of the film (12% during ageing in air). I f we assume that the density of gel is equal to the density of the initial film and that the whole aged surface layer is formed of gel, the thickness of this layer, according to the ageing voltage, varies from 0.7 to 2/~. In proportion to the elimination of the aged surface layer, as a consequence of gas liberation or evaporation of electrical discharge, deeper and deeper polymer layers are aged. As a result, the thickness and weight of the polymer decrease.
2650
E . A . DZHAVADYANeta/. CONCLUSIONS
(1) A s t u d y was made of the variations in the I R spectra of a polystyrene film under the action of electrical discharge in air and nitrogen. (2) During electrical ageing in air a large number of groups containing oxygen is formed. The dependence of absorption variation of C----O groups was examined according to the duration of electrical discharge. (3) I t was found t h a t the intensities of the initial bands of the I R spectra 0f PS decrease evenly at a constant rate as electrical ageing continues, and the rate of reduction increases with higher voltage. (4) I R spectroscopic results indicate t h a t crosslinking by electrical discharge in a medium containing oxygen occurs by oxygen bridges. (5) I t was deduced from the experimental results t h a t ionization ageing of polymers is a surface phenomenon. Translated by E. S~.~m~
REFERENCES
1. A. V. MEATS and R. STANETT, Trans. IEE, Power Appar. and Systems, No. 1, 48, 1964 2. S. N. KOIKOV, V. A. PARIBOK and A. K. TSTI{IN, Sb. Proboi dielektrikov i poluprovodnikov (Break down Of Dielectrics and Semiconductors). p. 301, Izd. "Energiya", 1964 3. S. A. ABASOV, M. A. BAGIROV, N. V. ~LIMOVA and V. P. MAT.IN, Izv. AN Azerb. SSR, ser. fiz.-tekhn, i matem, nauk, No. 3, 137, 1965 4. Yu. V. FILIPPOV and Yu. M. YEMEL'YANOV, Zh. fiz. khimii 34: 1083, 1960 5. M. A. BAGIROV, Ye. Ya. VOLCHENKOV and V. P. MALTN, Sb. Materialy nauehnoi konferentsii molodykh uchenykh i aspirantov (Scientific Conference of Young Scientists and Post-Graduates). p. 129, AN Azerb. SSR, 1966 6. Sb. Fizika polimerov (Physics of Polymers). Izd. inostr, lit., 1960
KINETICS AND MECHANISM OF CATIONIC POLYMERIZATION OF CYCLIC ETHERS WITH POLYESTER ADDITIVES* E. A. DZIt~.VADYA_N,B..4. ROZENBERG and N. S. YENIKOLOPYAN Branch of the Iastitute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 11 November 1968)
COPOnYMERS containing units with ester and ether groups can obviously be obtained by the copolymerization of corresponding cyclic ethers and lactones [1-3]. However, because of the limited selection of monomers, this method is very restricted. At the same time it is known t h a t polyesters, including those * Vysokomol. soyed. All: No. 10, 2330-2336, 1969.