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Thermoanalytical studies of polymeric compounds as viscous additives to lubricants
Petrol. Chem, U. S. S. R. Vol. 30, No. 3, pp. 181-186, 1990 Printed in Great Britain
0031-6458/90 $10.00+.00 © 1991 Pergamon Press plc
THERMOANALYTICAL STUDIES OF POLYMERIC COMPOUNDS AS VISCOUS ADDITIVES TO LUBRICANTS* T. KH. AKCHURINAand S. S. EFENDIYEVA Institute of Chemistryof Additives,AzerbaidzhanAcademyof Sciences,Baku (Received 22 June 1989)
The present paper generalizes the results of thermoanalytical investigations of copolymers of isobutylene and alkylmethacrylate with the vinylaromatic and carbocyclic compounds synthesized in [1-3] as thermally more stable viscous additives compared with the polyisobutylene and polyalkylmethacrylate currently used. The investigations carried out aid the solution of problems such as determination of the thermal stability of polymeric compounds as a function of their composition, molecular weight, molecular weight distribution, etc., establishment of these indices for copolymers, study of the mechanism of thermal degradation of polymeric compounds, etc.
EXPERIMENTAL Thermal analysis, consisting of thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) of specimens, was carried out on a Paulik-Paulik-Erdei OD-102 derivatograph under dynamic heating conditions in the 20-500"C temperature range. Preliminary experiments showed that the optimum heating rate for obtaining reliable results and reducing the test time is 5 deg/min. The specimens weighed 0.1 g, and aluminium oxide was used as ethanol.
RESULTS AND DISCUSSION Thermal analysis of most of the polymeric compounds investigated showed that, during heating, the main process of their thermal decomposition is preceded by an initial section characterized by a comparatively small weight loss (2-10%) at relatively low temperatures. The existence of this section can be attributed to the presence in the polymeric compound of volatile low-molecular fractions, and also weak or defective chemical bonds. Assessment of the thermal stability of copolymers from the temperatures at which the degree of decomposition amounts to _>10% [4] without taking account of the given section can produce considerable error. In such cases, we have suggested a criterion for assessing the thermal stability of polymeric compounds: temperature TR, obtained by projecting on to the abscissa axis the point of intersection of a tangent drawn towards the TG curve at the point of the maximum rate of * Neftekhimiya30, No. 4, 545-550. 181
182
T. KH. AKCHURINAand S. S. EmZ~rDIYEVA
MW
17000
2
1,~00~
aO0~ I
260
f
J
I
~
280
I
I
300
'
;~ZO
J
~
340
,I
I
I
I.I
280
300 t,'c
FIo. 1. TG and D T G curves o f e o p o l y m e r of deeylmethaerylate with styrene (MW 15000, e o m o n o m e r ratio 90:10 (wt.%)).
weight loss with a line drawn parallel to the abscissa axis through the point corresponding to the start of weight loss. The points on the TG curve, corresponding to the start and the maximum rate of weight loss, are determined on the basis of the DTG curve (Fig. 1). By way of example, Table 1 presents thermoanalytical data for polydecylmethacrylate and copolymers of decylmethacrylate with dicyclopentadiene. From this it follows that, in the case of compounds characterized by small weight loss of the initial section of decomposition (2%), the value of parameter TR almost coincides with Tm~. Parameter Tm~ was similar to the temperatures marking out the process of evaporation from the effective thermal transformations calculated by the Adoni method [5]. In the case of great weight loss on the initial section of decomposition of the polymeric compound, the TR values are correspondingly displaced towards higher temperatures compared with parameter 7"1o~. Generalizing the above, it can be noted that temperature TR is not connected with the possible presence of defective chains, weak chemical bonds, and low-boiling fractions, or with evaporation of the polymer, which precedes its thermal breakdown. Thus TR is a direct indicator of the resistance of the polymeric compound to temperature effects and to a certain extent comprises a criterion of thermal stability. TABLE l. THERMODYNAMICDATAOF POLYDECYLMETHACRYLATEANDCOPOLYMERSOF DECYLMETHACRYLATEWITHSTYRENE Molecular weight of copolym©r
~0000 tt000 14000 15000 ~7000 14000
14000 14000 ~t 000
Decyl-
First stage of degradation
methacryhteJ styrene ratio, wt.¢~
temperature range, 'C
90:10 90:10 90:t0 90:t0 90:t0 80:20 70 : 30 60:40
t30-290 165-272 145-267 140-260 120-232 240-252 255-265 210-258
weight loss, %
r~,
t0 290 6 287 6 280 6 270 5 265 t 294 2 292 2 293 Polydecyhnethacrylate
rso ~ ,
E, U/moic
TR, "c
333 325 322 3t2 308 332 325 330
207,9 197,9 t84,9 t70,3 158,2 206,7 204,6 205,0
300 295 284 279 27t 295 294 294
t66'1
264
3t0 I
,I
Thermoanalyticalstudies of polymericcompoundsas viscous additivesto lubricants
183
Parameter TR correlates well with the average activation energy of thermal decomposition (Table 1) and can be recommended for rapid assessment of the thermal stability of polymeric compounds. The error of the method for determining parameter TR in the limit amounts to 3 deg. Thermal analysis of the polymeric compounds investigated by us, carried out in oxidizing (air) and inert (argon) atmospheres, showed that the criteria used in the work for assessing the resistance of these compounds to thermal effects (TR, ?'50~, E) characterize their thermal stability in both atmospheres [6]. Data of thermal analysis of compounds, obtained by studying them in an air atmosphere, are given in this article. Thermoanalytical data of the investigated copolymers of decylmethacrylate with styrene [7] (CP-I), dicyclopentadiene [6] (CP-II), and indene (CP-III) and also copolymers of isobutylene with (z-methylstyrene (CP-IV) and dicyclopentadiene [8] (CP-V) are presented in Table 2. Analysis of the given data makes it possible to conclude that for all the cases investigated there is an identical dependence of thermal stability of copolymers on their molecular weight and composition. With increasing molecular weight, the resistance of the copolymers to temperature effects decreases. The introduction of up to 20% styrene, dicyclopentadiene or indene units into a polydecylmethacrylate or polyisobutylene macromolecule leads to an increase in the stability of the copolymer, and a further increase in the content of comonomer units has no positive effect on copolymer stability. Hence the amount of styrene, indene or dicyclopentadiene units in polydecylmethacrylate or polyisobutylene can vary from 10 to 20% depending on the requirements concerning the resistance of the viscous additive. Comparison of thermoanalytical data for decylmethacrylate and isobutylene homopolymers with data for corresponding copolymers of similar molecular weight indicates greater thermal stability of the latter, which substantiates the rationality of carrying out copolymerization processes in order to produce additives ensuring increased viscosity and temperature properties of oils thickened by them. A comparative assessment of the thermal stability of the polymeric compounds investigated with equal molecular weights and comonomer ratios in the case of copolymers showed that they can be placed in the following order of thermal stability: CP-IV > CP-I > CP-V > CP-II > CP-III = polyisobutylene > polydecylmethacrylate. To broaden the procedural possibilities of thermal analysis, it was of interest to use it in determining the molecular weight of polymeric compounds. For this it was necessary to find the mathematical dependence of the thermoanalytical parameters of the polymer on its molecular weight. The results of analysis showed that with a high degree of correlation there is a linear dependence of parameter TR and in some cases also parameter TDTGmax on the molecular weight (MW) of the polymeric compound. Thus, for example, as can be seen from Fig. 2, there is a linear dependence of the parameters investigated on the molecular weight of the copolymers, the dependence being fulfilled most accurately for parameter TR. Using the least-squares method [9], empirical equations expressing the dependence of thermoanalytical parameters on the molecular weight of the polymeric compound were obtained. Thus, for copolymers of decylmethacrylate with styrene the equation has the following form: M--85 000-250 TR and for polyisobutylene
184
T. K}~. AKCHURINA and S. S. E~NDIYEVA
TABLE 2. THERMOANALYTICAL DATA OF POLYMERIC COMPOUNDS INVESTIGATED Molecularweight ] of ¢cl~l~nncr Comonomer x 10-3 ratio,wt.q,, Tt0~, "C TR,"C T~t, "C E, kJ/mole
Decylmethacrylate-styrenecopolymer t0 tl 14 t5 17 t4 t4 t4
90 t0 90 t0 90 t0 90:t0 90 t0 80 20 70 30 60 40
290 287 280 270 265 294 292 293
300 293 287 279 271 295 294 294
333 325 322 3t2 308 332 325 330
207,9 t97,9 t84,9 t70,3 t58,2 206,7 204,6 205,0"
t3 8 t0 t4 17 20 t4 t3 t4
95:5 90:t0 90:10 90:t0 90:t0 90:t0 85:t5 80:20 70 : 30
Decylmetlmcrylatc--dicyclopentadien e copolymer 252 265 274 280 269 275 254 267 248 252 240 242 260 270 267 273 253 260
299 317 3t5 302 296 290 307 319 30t
10 8 t0 t3 t6 t0 8
95:5 90:t0 90:t0 90:t0 90:t0 85 : t5 80 : 20
Decylmethacryhte-indenecopolymer 247 250 260 278 25t 275 252 260 255 255 265 282 290 250
300 3t3 330 305 300 3t3 332
t87,3 t96,6
295
158,2
378 373 372 374 372 373 375
262,4 249,3 2t4,6 2tt,3 t62,7 259,t 255,8
392 380 376 396 393
2t9,7 193,3 t86,2 202,8 200,3
t87,4 168,3:
t73,9 158,2
t85,2
Polydecylmethacrylate [
i0
250
I
260
[
Isobutylene -a-methylstyrene copolymer
25
332 327 302 295 250 330 330
t0 t2 15 t0 7,5
90 90 90 90 90 80 70
2,5 6 10 t0 8,8
90 : 10 90:10 90 : t0 80 : 20 70 : 30
300 265 281 288 286
-
278
6
t0 t0 t0 t0 10 20 30
336 327 305 298 266 332 330
Isobutylene-dicyclopentadienecopolymer 3t0 293 289 299 297
Polyisobutylene
10
[
[
280
]
358
]
179,1
M = 18700 - - 6 2 5 T R or
M = 3t7400 -- 850rw~ T h e m equations m a k e it possible to calculate the molecular weight o f the corresponding p o l y m e r i c c o m p o u n d s from the thermoanalytical parameters. The average deviation o f values
Thermoanalytical studies of polymeric compounds as viscous additives to lubricants
185
drnld~ DTG
I00
60
20
2OO
rR
~'00 t, °C
l=IO.2. Dependence of parameters Tl0%(1), Ts0,~ (2), and TR (3) on molecular weight MW of decylmethacrylate-styrenecopolymers(comonomerratio 90:10 (wt.%)). of the molecular weight of the polymeric compounds investigated, calculated by means of the given equations, amounts to +1-9. There is good agreement between data from determining the molecular weight of polymers by the method proposed and by viscometry, and the relative divergence of molecular weight values determined by these methods does not exceed 5 rel.%. The thermoanalytical investigations carded out showed that the shape of the DTG curve peak makes it possible in a number of cases to form some idea of the molecular weight distribution of the polymeric compound: the presence of two or several peaks on its DTG curve may indicate the presence of polymers of different molecular weight. The DTG curves of the polymeric compounds also make it possible in a number of cases to follow the change in the mechanism of their thermal breakdown, for example on transition from homopolymer to copolymer [6]. To compare the results of assessing the thermal stability of polymeric compounds by thermoanalytical methods with the methods widely used in practice, thermal breakdown of the polymers investigated was carried out in a solution of turbine oil L by the standard procedure of heating 5% solutions of polymers at 200"C for 12 hr. Test results showed that with increasing molecular weight of the copolymers their breakdown resistance decreases. The reduction in stability of copolymers with increase in their molecular weight is due to more difficult movement of macromolecules in the oil solution, on account of which rupture of the chemical bond of the main chain of copolymers is more likely. Compared with a homopolymer, the stability of the copolymers investigated in thickened oils as a function of the copolymer composition changes in the following way. An increase in the content of comonomer units in the copolymer to 20% leads to an increase in the stability of the latter. Further increase in the amount of comonomer units (to 30 and 40%) has no effect on increase in copolymer stability. Consequently, the results of thermoanalytical investigations of polymeric compounds as viscous additives to lubricants correlate with data on the fall in viscosity of their solutions during heating. Thus the investigations of polymeric compounds as viscous additives to lubricants showed
186
T. KH. AKCHURINAand S. S. EFENDIYEVA
that methods of thermal analysis present wide-ranging possibilities in the field of further development of corresponding theoretical studies and are also fairly accurate rapid methods for assessing the thermal characteristics of the given additives in wide temperature ranges.
SUMMARY The synthesis and investigation of viscous additives based on different polymeric compounds are of considerable scientific and practical interest owing to the need to develop high-quality thickened oils of different designation with increased viscosity and temperature properties.
REFERENCES 1. A.M. KULIYEV, Z. A. SADYKHOV and A. M. LEVSHINA, Azerb. Khim. Zhurn., 6, 41, 1962. 2. A.M. KULIYEV, Z. A. SADYKHOV and A. M. LEVSHINA, Azerb. Neft. Khoz-vo, 3, 33, 1963. 3. A.I. AKHMEDOV, Z. A. SADYKHOV, A. I. LEVSHINA, et al., Uch. Zap. AGU ira. S. M. Kirova, Set. Khim., 75, 1972. 4. K.D. JEFFREYS, Brit. Plastics, 36, 188, 1963. 5. Z. ADONYI, Chem. Eng., 10, 320, 1966. 6. A.I. AKEIMEDOV, S. M. GUSEIN-ZADE, A. M. LEVSH1NA et al., Neftekhimiya 27, No. 4, 563, 1987. 7. A.I. AKHMEDOV, T.Kh. AKCHURINA, A. M. LEVSHINA et al., Khimiya i Tekhnologiya Topliv i Masel, 4, 33, 1984. 8. T. Kh. AKCHURINA, A. I. AKHMEDOV, S. M. GUSEINZADE and A. M. LEVSHINA, Khimiya i Tekhnologiya Topliv i Masel, 6, 45, 1975. 9. L.M. BATUNER and Ye. M. POZIN, Matematicheskiyemetody v khimicheskoi tekhnike (Mathematical Methods in Chemical Engineering), p. 665, Khimiya, Leningrad, 1968.
0031-6458/90 $10.00+.00 © 1991 Pergamon Press plc
THERMOANALYTICAL STUDIES OF POLYMERIC COMPOUNDS AS VISCOUS ADDITIVES TO LUBRICANTS* T. KH. AKCHURINAand S. S. EFENDIYEVA Institute of Chemistryof Additives,AzerbaidzhanAcademyof Sciences,Baku (Received 22 June 1989)
The present paper generalizes the results of thermoanalytical investigations of copolymers of isobutylene and alkylmethacrylate with the vinylaromatic and carbocyclic compounds synthesized in [1-3] as thermally more stable viscous additives compared with the polyisobutylene and polyalkylmethacrylate currently used. The investigations carried out aid the solution of problems such as determination of the thermal stability of polymeric compounds as a function of their composition, molecular weight, molecular weight distribution, etc., establishment of these indices for copolymers, study of the mechanism of thermal degradation of polymeric compounds, etc.
EXPERIMENTAL Thermal analysis, consisting of thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) of specimens, was carried out on a Paulik-Paulik-Erdei OD-102 derivatograph under dynamic heating conditions in the 20-500"C temperature range. Preliminary experiments showed that the optimum heating rate for obtaining reliable results and reducing the test time is 5 deg/min. The specimens weighed 0.1 g, and aluminium oxide was used as ethanol.
RESULTS AND DISCUSSION Thermal analysis of most of the polymeric compounds investigated showed that, during heating, the main process of their thermal decomposition is preceded by an initial section characterized by a comparatively small weight loss (2-10%) at relatively low temperatures. The existence of this section can be attributed to the presence in the polymeric compound of volatile low-molecular fractions, and also weak or defective chemical bonds. Assessment of the thermal stability of copolymers from the temperatures at which the degree of decomposition amounts to _>10% [4] without taking account of the given section can produce considerable error. In such cases, we have suggested a criterion for assessing the thermal stability of polymeric compounds: temperature TR, obtained by projecting on to the abscissa axis the point of intersection of a tangent drawn towards the TG curve at the point of the maximum rate of * Neftekhimiya30, No. 4, 545-550. 181
182
T. KH. AKCHURINAand S. S. EmZ~rDIYEVA
MW
17000
2
1,~00~
aO0~ I
260
f
J
I
~
280
I
I
300
'
;~ZO
J
~
340
,I
I
I
I.I
280
300 t,'c
FIo. 1. TG and D T G curves o f e o p o l y m e r of deeylmethaerylate with styrene (MW 15000, e o m o n o m e r ratio 90:10 (wt.%)).
weight loss with a line drawn parallel to the abscissa axis through the point corresponding to the start of weight loss. The points on the TG curve, corresponding to the start and the maximum rate of weight loss, are determined on the basis of the DTG curve (Fig. 1). By way of example, Table 1 presents thermoanalytical data for polydecylmethacrylate and copolymers of decylmethacrylate with dicyclopentadiene. From this it follows that, in the case of compounds characterized by small weight loss of the initial section of decomposition (2%), the value of parameter TR almost coincides with Tm~. Parameter Tm~ was similar to the temperatures marking out the process of evaporation from the effective thermal transformations calculated by the Adoni method [5]. In the case of great weight loss on the initial section of decomposition of the polymeric compound, the TR values are correspondingly displaced towards higher temperatures compared with parameter 7"1o~. Generalizing the above, it can be noted that temperature TR is not connected with the possible presence of defective chains, weak chemical bonds, and low-boiling fractions, or with evaporation of the polymer, which precedes its thermal breakdown. Thus TR is a direct indicator of the resistance of the polymeric compound to temperature effects and to a certain extent comprises a criterion of thermal stability. TABLE l. THERMODYNAMICDATAOF POLYDECYLMETHACRYLATEANDCOPOLYMERSOF DECYLMETHACRYLATEWITHSTYRENE Molecular weight of copolym©r
~0000 tt000 14000 15000 ~7000 14000
14000 14000 ~t 000
Decyl-
First stage of degradation
methacryhteJ styrene ratio, wt.¢~
temperature range, 'C
90:10 90:10 90:t0 90:t0 90:t0 80:20 70 : 30 60:40
t30-290 165-272 145-267 140-260 120-232 240-252 255-265 210-258
weight loss, %
r~,
t0 290 6 287 6 280 6 270 5 265 t 294 2 292 2 293 Polydecyhnethacrylate
rso ~ ,
E, U/moic
TR, "c
333 325 322 3t2 308 332 325 330
207,9 197,9 t84,9 t70,3 158,2 206,7 204,6 205,0
300 295 284 279 27t 295 294 294
t66'1
264
3t0 I
,I
Thermoanalyticalstudies of polymericcompoundsas viscous additivesto lubricants
183
Parameter TR correlates well with the average activation energy of thermal decomposition (Table 1) and can be recommended for rapid assessment of the thermal stability of polymeric compounds. The error of the method for determining parameter TR in the limit amounts to 3 deg. Thermal analysis of the polymeric compounds investigated by us, carried out in oxidizing (air) and inert (argon) atmospheres, showed that the criteria used in the work for assessing the resistance of these compounds to thermal effects (TR, ?'50~, E) characterize their thermal stability in both atmospheres [6]. Data of thermal analysis of compounds, obtained by studying them in an air atmosphere, are given in this article. Thermoanalytical data of the investigated copolymers of decylmethacrylate with styrene [7] (CP-I), dicyclopentadiene [6] (CP-II), and indene (CP-III) and also copolymers of isobutylene with (z-methylstyrene (CP-IV) and dicyclopentadiene [8] (CP-V) are presented in Table 2. Analysis of the given data makes it possible to conclude that for all the cases investigated there is an identical dependence of thermal stability of copolymers on their molecular weight and composition. With increasing molecular weight, the resistance of the copolymers to temperature effects decreases. The introduction of up to 20% styrene, dicyclopentadiene or indene units into a polydecylmethacrylate or polyisobutylene macromolecule leads to an increase in the stability of the copolymer, and a further increase in the content of comonomer units has no positive effect on copolymer stability. Hence the amount of styrene, indene or dicyclopentadiene units in polydecylmethacrylate or polyisobutylene can vary from 10 to 20% depending on the requirements concerning the resistance of the viscous additive. Comparison of thermoanalytical data for decylmethacrylate and isobutylene homopolymers with data for corresponding copolymers of similar molecular weight indicates greater thermal stability of the latter, which substantiates the rationality of carrying out copolymerization processes in order to produce additives ensuring increased viscosity and temperature properties of oils thickened by them. A comparative assessment of the thermal stability of the polymeric compounds investigated with equal molecular weights and comonomer ratios in the case of copolymers showed that they can be placed in the following order of thermal stability: CP-IV > CP-I > CP-V > CP-II > CP-III = polyisobutylene > polydecylmethacrylate. To broaden the procedural possibilities of thermal analysis, it was of interest to use it in determining the molecular weight of polymeric compounds. For this it was necessary to find the mathematical dependence of the thermoanalytical parameters of the polymer on its molecular weight. The results of analysis showed that with a high degree of correlation there is a linear dependence of parameter TR and in some cases also parameter TDTGmax on the molecular weight (MW) of the polymeric compound. Thus, for example, as can be seen from Fig. 2, there is a linear dependence of the parameters investigated on the molecular weight of the copolymers, the dependence being fulfilled most accurately for parameter TR. Using the least-squares method [9], empirical equations expressing the dependence of thermoanalytical parameters on the molecular weight of the polymeric compound were obtained. Thus, for copolymers of decylmethacrylate with styrene the equation has the following form: M--85 000-250 TR and for polyisobutylene
184
T. K}~. AKCHURINA and S. S. E~NDIYEVA
TABLE 2. THERMOANALYTICAL DATA OF POLYMERIC COMPOUNDS INVESTIGATED Molecularweight ] of ¢cl~l~nncr Comonomer x 10-3 ratio,wt.q,, Tt0~, "C TR,"C T~t, "C E, kJ/mole
Decylmethacrylate-styrenecopolymer t0 tl 14 t5 17 t4 t4 t4
90 t0 90 t0 90 t0 90:t0 90 t0 80 20 70 30 60 40
290 287 280 270 265 294 292 293
300 293 287 279 271 295 294 294
333 325 322 3t2 308 332 325 330
207,9 t97,9 t84,9 t70,3 t58,2 206,7 204,6 205,0"
t3 8 t0 t4 17 20 t4 t3 t4
95:5 90:t0 90:10 90:t0 90:t0 90:t0 85:t5 80:20 70 : 30
Decylmetlmcrylatc--dicyclopentadien e copolymer 252 265 274 280 269 275 254 267 248 252 240 242 260 270 267 273 253 260
299 317 3t5 302 296 290 307 319 30t
10 8 t0 t3 t6 t0 8
95:5 90:t0 90:t0 90:t0 90:t0 85 : t5 80 : 20
Decylmethacryhte-indenecopolymer 247 250 260 278 25t 275 252 260 255 255 265 282 290 250
300 3t3 330 305 300 3t3 332
t87,3 t96,6
295
158,2
378 373 372 374 372 373 375
262,4 249,3 2t4,6 2tt,3 t62,7 259,t 255,8
392 380 376 396 393
2t9,7 193,3 t86,2 202,8 200,3
t87,4 168,3:
t73,9 158,2
t85,2
Polydecylmethacrylate [
i0
250
I
260
[
Isobutylene -a-methylstyrene copolymer
25
332 327 302 295 250 330 330
t0 t2 15 t0 7,5
90 90 90 90 90 80 70
2,5 6 10 t0 8,8
90 : 10 90:10 90 : t0 80 : 20 70 : 30
300 265 281 288 286
-
278
6
t0 t0 t0 t0 10 20 30
336 327 305 298 266 332 330
Isobutylene-dicyclopentadienecopolymer 3t0 293 289 299 297
Polyisobutylene
10
[
[
280
]
358
]
179,1
M = 18700 - - 6 2 5 T R or
M = 3t7400 -- 850rw~ T h e m equations m a k e it possible to calculate the molecular weight o f the corresponding p o l y m e r i c c o m p o u n d s from the thermoanalytical parameters. The average deviation o f values
Thermoanalytical studies of polymeric compounds as viscous additives to lubricants
185
drnld~ DTG
I00
60
20
2OO
rR
~'00 t, °C
l=IO.2. Dependence of parameters Tl0%(1), Ts0,~ (2), and TR (3) on molecular weight MW of decylmethacrylate-styrenecopolymers(comonomerratio 90:10 (wt.%)). of the molecular weight of the polymeric compounds investigated, calculated by means of the given equations, amounts to +1-9. There is good agreement between data from determining the molecular weight of polymers by the method proposed and by viscometry, and the relative divergence of molecular weight values determined by these methods does not exceed 5 rel.%. The thermoanalytical investigations carded out showed that the shape of the DTG curve peak makes it possible in a number of cases to form some idea of the molecular weight distribution of the polymeric compound: the presence of two or several peaks on its DTG curve may indicate the presence of polymers of different molecular weight. The DTG curves of the polymeric compounds also make it possible in a number of cases to follow the change in the mechanism of their thermal breakdown, for example on transition from homopolymer to copolymer [6]. To compare the results of assessing the thermal stability of polymeric compounds by thermoanalytical methods with the methods widely used in practice, thermal breakdown of the polymers investigated was carried out in a solution of turbine oil L by the standard procedure of heating 5% solutions of polymers at 200"C for 12 hr. Test results showed that with increasing molecular weight of the copolymers their breakdown resistance decreases. The reduction in stability of copolymers with increase in their molecular weight is due to more difficult movement of macromolecules in the oil solution, on account of which rupture of the chemical bond of the main chain of copolymers is more likely. Compared with a homopolymer, the stability of the copolymers investigated in thickened oils as a function of the copolymer composition changes in the following way. An increase in the content of comonomer units in the copolymer to 20% leads to an increase in the stability of the latter. Further increase in the amount of comonomer units (to 30 and 40%) has no effect on increase in copolymer stability. Consequently, the results of thermoanalytical investigations of polymeric compounds as viscous additives to lubricants correlate with data on the fall in viscosity of their solutions during heating. Thus the investigations of polymeric compounds as viscous additives to lubricants showed
186
T. KH. AKCHURINAand S. S. EFENDIYEVA
that methods of thermal analysis present wide-ranging possibilities in the field of further development of corresponding theoretical studies and are also fairly accurate rapid methods for assessing the thermal characteristics of the given additives in wide temperature ranges.
SUMMARY The synthesis and investigation of viscous additives based on different polymeric compounds are of considerable scientific and practical interest owing to the need to develop high-quality thickened oils of different designation with increased viscosity and temperature properties.
REFERENCES 1. A.M. KULIYEV, Z. A. SADYKHOV and A. M. LEVSHINA, Azerb. Khim. Zhurn., 6, 41, 1962. 2. A.M. KULIYEV, Z. A. SADYKHOV and A. M. LEVSHINA, Azerb. Neft. Khoz-vo, 3, 33, 1963. 3. A.I. AKHMEDOV, Z. A. SADYKHOV, A. I. LEVSHINA, et al., Uch. Zap. AGU ira. S. M. Kirova, Set. Khim., 75, 1972. 4. K.D. JEFFREYS, Brit. Plastics, 36, 188, 1963. 5. Z. ADONYI, Chem. Eng., 10, 320, 1966. 6. A.I. AKEIMEDOV, S. M. GUSEIN-ZADE, A. M. LEVSH1NA et al., Neftekhimiya 27, No. 4, 563, 1987. 7. A.I. AKHMEDOV, T.Kh. AKCHURINA, A. M. LEVSHINA et al., Khimiya i Tekhnologiya Topliv i Masel, 4, 33, 1984. 8. T. Kh. AKCHURINA, A. I. AKHMEDOV, S. M. GUSEINZADE and A. M. LEVSHINA, Khimiya i Tekhnologiya Topliv i Masel, 6, 45, 1975. 9. L.M. BATUNER and Ye. M. POZIN, Matematicheskiyemetody v khimicheskoi tekhnike (Mathematical Methods in Chemical Engineering), p. 665, Khimiya, Leningrad, 1968.