- Email: [email protected]
Hydrolytic processes of the thermal degradation of isomeric aromatic polyamides
2176
Y~.. P. K~AS~OV et al.
CONCLUSIONS
A comparison has been made of molecular-weight distribution curves of polya r y ~ t e P-8 produced in three different ways: from fractionation data, the Gosting method which uses the sedimentation diagrams of an unfractionated specimen and by adding together all the fractions. The last method, which combines fractionation and sedimentation gives a coefficient very close to t h a t calculated from the figures for the high-speed sedimentation of an unfractionated specimen. Gosting's method of using data on the sedimentation of an unfraetionated specimen is quite suitable for finding the molecular-weight distribution of polyarylates.
Translated by V. ALFO~D
REFERENCES 1. E. W. CHANNEN, Rev. Pure Appl. Chem. 9: 225, 1959 2. S. Ya. FRENKEL', Uspekhi fiz. n a u k 53: 161, 1954 3. V. V. KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 4. G.I. TIMOFEYEVA, L. V. DUBROVINA, V. V. KORSHAK and S. A. PAVLOVA, Vysokotool. soyed. 6: 2008, 1964 5. S. R. RAFIKOV, Vysokomol. soyed. 1: 1558, 1959 6. V. V. KORSHAK, S. A. PAVLOVA, G. I. TIMOFEYEVA, S. V. VINOGRADOVA and V. A. PANKRATOV, Dokl. Akad. Nauk SSSR 160: 119, 1965 7. G. I. TIMOFEYEVA, Dissertation, Moscow, 1965 8. T. SVEDBERG and K. O. PEDERSEN, The Ultracentrifuge, Oxford, 1940 9. L. J. GOSTING, J. Amer. Chem. Soe. 74: 1548, 1952 10. S. Ye. BRESLER, V. V. KORSHAK, S. A. PAVLOVA and P. A. FINOGENOV, Izv. Akad. Nauk SSSR, Otd. khim n a u k 344: 354, 1954
HYDROLYTIC PROCESSES OF THE THERMAL DEGRADATION OF ISOMERIC AROMATIC POLYAMIDES*t YE. :P. KRAS~OV, V. I. LOGV~OVA and L. B. SOKOLOV Vladimir Research I n s t i t u t e of Synthetic Resins
(Received 6 September 1965)
I~ A~ earlier work [1] it was suggested that hydrolytic processes were important in the general pattern of the degradation of isomeric aromatic polyamides at high temperatures. This was based on qualitative and quantitative analyses of * Vysokomol. soyed. 8: N o .
11, 1970-1975, 1966. ~f 4th Report of the series "Thermal degradation of polyamidds".
Thermal degradation of isomeric aromatic polyamides
2177
gaseous and liquid products of the pyrolysis of these polymers. I n particular, C02, H~0 and benzene were found to make up the main part of the volatile products, their composition depending very little on the isomeric form of the phenylene diamine and the dicarboxylic acid. The present paper gives the results of a more detailed experimental study of the hydrolytic processes of thermal degradation of isomeric aromatic polyamides. The principal reasons for these processes have been ascertained, and effective methods are suggested for reducing their significance in the general combination of degradative conversions, thus improving the heat resistance of these polymers. RESULTS AND DISCUSSION
The thermal degradation of isomeric aromatic polyamides prepared from mand p-phenylene diamines and acid dichlorides of iso- and terephthalic acids [2, 3] is accompanied by the formation of a considerable amount of volatile, liquid and solid products. The volatile and liquid products have already been analysed in [1]. The solid products of all these polyamides were analysed by thin-layer chromatography, and the results are given in Table 1. TABLE
1. S O L I D P R O D U C T S O F T H E T H E R M A L D : E G R A D A T I O N O F I S O M E R I C A R O M A T I C P O L Y A M I D E S
in vacuo 5~
Conditions of pyrolysis
~9
Products of pyrolysis
Polyamide temper-
ature, °C Poly-m-phenyleneisophthalamide*
Poly-p-phenyleneisophthalamide Poly-m-phenyleneisophthalamide Poly-p-phenyleneisophthalamide
440
520 510 530
time, .¢~ min
30
60 50 90
10"2
7.5 9.1 6.0
O
m-Phenylenediamine N-m-Aminophenylbenzamide N,N'-di-m -Aminophenyl isophthalamide p-Phenylenediamine N-p-Aminophenylbenzamide m-Phenylenediamine N-m-Aminophenylbenzamide p -Phenylenediamine N-p-Aminophenylbenzamide
* This poly;mer w a s p r e p a r e d b y emulsion polycondensation [3].
36
3"65
56
5"75
8 30
0'80 2"25
7O 4O
5"25 3"60
60 40
5"50 2-4
6O
3-6
2178
Y~.. P. KRASNOVet
al.
Although there is a relation between the qualitative composition of the solid products and the isomeric shape of the polymer-chain unit, the presence of only phenylene diamines and N-aminophenylbenzamides in the solid products of the pyrolysis of all these polyamides nevertheless confirms the conclusion of the previous work, i.e. that degradative conversions on the thermal decomposition of isomeric aromatic polyamides are qualitatively identical. The formation of phenyler/e diamines and l~-aminophenylbenzamides is obviously connected with the hydrolytic mechanism of the thermal degradation of these polyamides, there being two possible ways in which these products could be formed. First of all, phenylene diamine could be formed by hydrolysis of the last amine bond in the polyamine chain, and N-aminophenylbenzamide by hydrolysis of the penultimate amine bond followed by decarboxylation of the fragment formed: CO
/2--% NHC O ~
i
N H ~
N-H' + H20
COOH -> -- N H ~ N H C 0 ~
~NH2 + H 2 N ~ _ ~~ I~TH2
+ H20
z..~ CONH(/~'~ NHs ---.
--CO~
/~NH2+H00C/~ CONH~ / /
--co*, z-~ NH2
Since the hydrolysis of amine bonds followsthe law of chance, a large amount of water must be required for the formation of the quantitiesof phenylene diamines and N-aminophenylbenzamides observed experimentally in the thermal degradation of isomeric aromatic polyamides. The second method of formation could be by the hydrolysisand thermal degradation of the low molecular weight fraction of the polymers. Fractionation showed that for poly-m-phenyleneisophthalamide prepared by polycondensation in dimethylacetamide solution there is 5-6~/o of low molecular weight fraction with a specificviscosityof not more than 0.I for a 0"5~o solutionin concentrated H~S04. V~aen prepared by emulsion polycondensation, this same polymer contains 12-13~/oof this fraction.
Thermal degradation of isomeric aromatic polyamides
2179
To verify the influence of the low molecular weight fraction on the thermal degradation rate and yield of solid pyrolysis products two specimens of poly-mphenyleneisophthalamide were made, with a small amount of low molecular weight fraction. Then we compared the high-temperature behaviour of these and the original specimens. The results are shown in Figs. 1 and 2, and Table 2. ~, rnmHq/hr,
/o,qv
2qO
3 2 x
3
f
2"I
/ 180 1"7
120
J
300
330
3~
3~0
Off
l'q~
I
I
I
I
1"50
1"5#
1"62
1"68
tiT, °~10 -3 FIG. 1
FIG. 2
FTG. 1. Thermal degradation rates of various specimens of poly-m-phenyleneisophthalamide vs. temperature: /--prepared by emulsion polycondensation (specimen 1); 2--by solution polycondensation; 3--specimen 1 after fractionation; 4--specimen 1 after treatment in dimethylformamide. FIG. 2. Log. thermal degradation rates vs. reciprocal temperature for different specimens of poly-m-phenyleneisophthalamide. Notation as for Fig. 1. Analysis shows that the low molecular weight fraction does exert a considerable influence on the thermal degradation of poly-m-phenyleneisophthalamide. But we note that, apart from reducing the yied of solid products and improving the heat resistance of the polymer, after it has been treated in hot dimethylformamide, or the low molecular weight fraction removed b y precipitation from dioxane solution in dimethylformamide with 5% lithium chloride, the degradative conversions do not suffer any particular changes. This is supported b y two facts. First of all, the activation energies of the thermal degradation processes remain practically unchanged after these treatments. Secondly, there is no change in the qualitative composition of the gaseous, liquid and solid products, only the numerical yield altering. When the low molecular weight fractions are removed there is a big drop in the yield of COs b u t that of CO does not alter so much. Formation of COs on the
YE. P. KRASNOV et al.
2180
thermal degradation of polyamides is usually attributed to the hydrolytic mechanism [4-6], while the formation of CO is attributed to a homolytic mechanism [6]. From this it is concluded that, after removal of the low molecular weight fraction, the hydrolytic processes develop to a far smaller extent than in the original specimens. There are two possible mechanisms for the formation of COs on the thermal decomposition of isomeric aromatic polyamides. First of all, the direct decarboxylation of the carboxyl terminal groups of both the high and low molecular weight fractions. The particularly large amount of COs formed is in this case due to the low molecular weight fraction. Calculations showed that where the low molecular weight fraction is 10 wt. %, the yield of COs in direct decarboxylation should be 10 cmS/g of polymer, 0.5 cm3/g being due to the high molecular weight fraction. I f the amount of low molecular weight fraction is reduced to 1 ~/o, the COs yield should fall to 1.3 cm3/g of polymer. TABLE 2. RESULTS
OF THE THERlYIAL DEGRADATION
POLY-m
OF SOME SPECIMENS
De-
Specimen
OF
-PHENYLENEISOPHTHALAMIDE
{E.l
gradation temperatare,
°C
°C Original polymer produced b y emulsion 1.52 polycondensation After fractionation in dioxane from 1.88 solution After t r e a t m e n t in hot dimethylform-: 1-75 amide Original polymer produced b y polycondensation in dimethylaeetamide 1.91 solution
Yield of solid Eaot, kcal/ prod/mole ucts at 440 °,
Yield of COz and CO at 380 °, cmS/g of polymer
%
COs
CO
360
300
33"8
10"2
62'0
1"20
385
315
32 "4
0"6
17"2
0'64
395
315
34"0
2"0
14"2
1"44
375
305
33"8
3"8
31"6
0"72
,
* Ts is the minimum vacuum heat-treatment temperature below which the polymer ceases to be soluble in HsS0 ~
(I h.r).
On the thermal degradation of poly-m-phenyleneisophthalamide (with 1213% low molecular weight fraction) the experimental yield of CO2 at 380 ° was found to be 60 cma/g of polymer. After removing the low molecular weight fraction the CO2 yield fell to 14-17 em3/g (Table 2). The large amounts of CO2 found experimentally in the pyrolysis products of isomeric aromatic polyamides can therefore only be partially attributed to the direct decarboxylation of the low molecular weight fraction.
Thermal degradation of isomeric aromatic polyamides
2181
The second method assumes t h a t the terminal carboxyl and amino groups of the low molecular weight fraction have a catalytic effect in the thermal degradation of these polyamides. As w found in [1], on the pyrolysis of isomeric aromatic polyamides terminal ammonium groups are formed followed by their dehydration to nitriles: + NH a R-- COOH ---~ -- R-- COONH4 - H~O __ R--
-
--CONH~
~ --R--C ~-N÷H~O
--H2O
As a result of this reaction, we get the water necessary for the hydrolysis of the amide bonds. Of course, the rate of this complicated process will largely be determined by the concentration of the terminal amino groups from which the ammonia gas is formed, and that of the carboxyl groups from which the ammonium groups are formed on reaction with this gas. If this is so, the COx yields should be largely dependent on the initial concentration of terminal groups in the original polymer and, where there is a low molecular weight fraction, on its relation to the high molecular weight one. This is quite consistent with the experimental results for the thermal degradation of the original and processed specimens of poly-mphenyleneisophthalamide. According to our calculation, a yield of around 60 cm3/g COs may occur if the system contains approx. 5 ~o water, or if this amount of water is formed in the actual process of thermal degradation. The latter is more likely, since the initial moisture content of the test specimens was not more than 0.3% and considerable quantities of water may be recovered according to the scheme given above. In view of the fact that the low molecular weight fraction has a considerable catalytic effect on the processes of thermal degradation of isomeric aromatic polyamides, an effective method of improving their heat resistance could be its more complete removal. In [1] it was found that the entire complicated combination of degradative conversions of isomeric aromatic polyamides was not exhausted by the processes of the hydrolytic decomposition of the amide bonds. While the COs yields can be lowered 4-5 times by removing the low molecular weight fraction, the COs yields are only halved, which means that this fraction has much less influence on homolytic than on hydrolytic processes. On thermal degradation at high temperatures the polymer radical undergoes deep carbonization with formation of paramagnetic centres giving a narrow ESR signal (6 oersted). It is interesting to note that the formation of paramagnetic centres on thermal degradation, particularly for poly-m-phenyleneisophthalamide, is an exponential function of temperature. The activation energy of the process is 51.5 kcal/mole, which is much more than the activation energy calculated from the formation of gaseous products, 33.8 kcal/mole. Of course, the formation of a system of conjugated bonds is due to processes of a free-radical nature.
2182
Y~. P. KRASNOV et al.
EXPERIMENTAL The characteristics of the specimens of isomeric aromatic polyamides were given in [1]. T h a t article also gave a detailed description of the procedure for analysing the gaseous and liquid products of thermal degradation. TABLE 3. VALI.TES OF R$ FOR PHENYLENEDIAMINES AND N-AMINOPHENYLBElqZAMIDES
Values of R I Compound
ethanol-chloroformammonia gas
ethanol-chloroformtetrahydrofuran
0'71 0'86 0'04 0'57 0'81
0"37 0"54
m -Phenylenediamine N-m-aminophenylbenzamide N,N'-di-m-aminophenylisophthulamide p-Phenylenediamine N-p-aminophenylbenzamide
0"38 0"55
Poly-m-phenyleneisophthalamide prepared b y emulsion polycondensation [3] was treated in hot dimethylformamide in a Soxhlet apparatus. The low molecular weight fraction was also removed b y fraetionating the original polymer b y precipitation in dioxane from a 1% solution in dimethylformamide containing 5% lithium chloride. The solid products of the t h e r m a l degradation were qualitatively and q u a n t i t a t i v e l y analysed b y thin-layer c h r o m a t o g r a p h y [7, 8] over a reinforcing layer of the adsorbant silica gel K S K - g y p s u m . The layer of adsorbant was deposited onto glass plates 13 × 18 em a n d alcoholic solutions of the test mixtures were deposited on the starting line with a finea d j u s t m e n t syringe. The chromatographic analysis was carried out with an ascending solvent flow. The solvents used were a mixture of ethanol-chloroform a n d ammonia gas in the ratio 60:20: 1, a n d a mixture of ethanol-chloroform-tetrahydrofuran in the ratio 15: 100:40. After analysis the plate was removed from the solvent b y drying and developed b y spraying on a 1% solution of p-dimethylaminobenzaldehyde in 1 ~ hydrochloric acid. The experimental conditions for chromatographic separation of the solid products of pyrolysis have been described in more detail in [9]. The results are given in Table 3 for phenylenedlamines and N-aminophenylbenzamides. The solid products of the pyrolysis of isomeri~ aromatic polyamides were identified b y comparing their Rj with t h a t of model compounds in different systems of solvents. I R spectroscopy was also used. The numerical composition of the mixtures of solid products was determined b y thin-layer chromatography, using the method proposed b y Truter and P u r d y in [10]. T h e a u t h o r s a r e g r a t e f u l t o T. A . P o l y a k o v a a n d V. K . V e l y a k o v f o r t h e i r assistance in obtaining some of the experimental results used in the present work.
CONCLUSIONS (1) T h e h y d r o l y t i c d e c o m p o s i t i o n o f t h e a m i d e b o n d s o n t h e r m a l d e g r a d a t i o n of isomeric aromatic polyamides has been studied. The heat resistance of these p o l y m e r s is f o u n d t o d e p e n d l a r g e l y o n t h e i r c o n c e n t r a t i o n o f l o w m o l e c u l a r weight fraction.
Polymeric fraction of thermolysed anthracene containing paramagnetie centres
2183
(2) I t is a s s u m e d t h a t t h e c a r b o x y l a n d a m i n o t e r m i n a l g r o u p s h a v e a c a t a lytic effect on h y d r o l y t i c processes in t h e t h e r m a l d e g r a d a t i o n of these p o l y m e r s . (3) M e t h o d s b a s e d on t h e r e m o v a l o f t h e low m o l e c u l a r w e i g h t f r a c t i o n h a v e b e e n s u g g e s t e d as w a y s of i m p r o v i n g t h e t h e r m a l s t a b i l i t y o f p o l y - m - p h e n y l e n e isophthalamide. Translated by V. ALFORD REFERENCES 1. Ye. P. I { ~ N O V ,
2. 3. 4. 5. 6. 7. 8. 9. 10.
V. M. SA~NOV, L. B. SOKOLOV, V. I. LOGUNOVA, V. K. BELY~LKOV
and T. A. POLYAKOVA, Vysokomol. soyed. 8: 380, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 3, 413, 1966) V. M. SAVINOV and L. B. SOKOLOV, Vysokomol. soyed. 7: 772, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 5, 851, 1966) L. B. SOKOLOV and T. V. KUDIM, Dokl. Akad. Nauk SSSR 158: 1139, 1964 S. STRAUS mad L. WALL, J. Res. Nat. Bur. Standards 60: 39, 1958; 63A: 269, 1959 S. R. RAFIKOV and R. A. SOROKINA, Vysokomol. soyed. 3: 21, 1961 (Not translated in Polymer Sci. U.S.S.R.) Ye. P. KRASNOV, L. B. SOKOLOV and T. A. POLYAKOVA, Vysokomol. soyed. 6: 1244, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 7, 1371, 1966) E. STA_H_L,Diinnschicht-Chromatographie, Springer Verlag, Berlin, 1962 A. A. AKHREM and A. I. KUZNETSOVA, Tonkosloinaya khromatografiya. (Thin Film Chromatography.) Izd. Nauka, 1964 Ye. P. KRASNOV, Dissertation, 1965 S. Y. PURDY and E. TRUTER, Analyst 87: 802, 1962
THE POLYMERIC FRACTION OF THERMOLYSED ANTHRACENE CONTAINING PARAMAGNETIC CENTRES, AS AFFECTING THE LOW-TEMPERATURE HEAT TREATMENT OF ANTHRACENE AND BIANTHRYL* A. A. BERLIN, V. A. GICIGOROVSKAYAa n d V. YE. SKUR2kT Institute of Chemical Physics, Academy of Sciences, U.S.S.R. (Received 8 September 1965) IN [1, 2] we described t h e f o r m a t i o n of p a r a m a g n e t i c p o l y m e r s on h e a t t r e a t m e n t o f a n t h r a c e n e a n d b i a n t h r y l a t 450 ° in t h e absence o f air. W e also described t h e a c t i v a t i o n of this process b y t h e a d d i t i o n o f c a t a l y t i c a m o u n t s of p o l y m e r fract i o n s e p a r a t e d f r o m t h e p r o d u c t s of t h e t w o - h o u r h e a t t r e a t m e n t of a n t h r a c e n e (PMCh) c o n t a i n i n g c o n c e n t r a t i o n o f p a r a m a g n e t i c centres o f ~ l0 is spin/g [2]. * Vysokomol. soyed. 8: No. 11, 1976-1983, 1966.
Y~.. P. K~AS~OV et al.
CONCLUSIONS
A comparison has been made of molecular-weight distribution curves of polya r y ~ t e P-8 produced in three different ways: from fractionation data, the Gosting method which uses the sedimentation diagrams of an unfractionated specimen and by adding together all the fractions. The last method, which combines fractionation and sedimentation gives a coefficient very close to t h a t calculated from the figures for the high-speed sedimentation of an unfractionated specimen. Gosting's method of using data on the sedimentation of an unfraetionated specimen is quite suitable for finding the molecular-weight distribution of polyarylates.
Translated by V. ALFO~D
REFERENCES 1. E. W. CHANNEN, Rev. Pure Appl. Chem. 9: 225, 1959 2. S. Ya. FRENKEL', Uspekhi fiz. n a u k 53: 161, 1954 3. V. V. KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 4. G.I. TIMOFEYEVA, L. V. DUBROVINA, V. V. KORSHAK and S. A. PAVLOVA, Vysokotool. soyed. 6: 2008, 1964 5. S. R. RAFIKOV, Vysokomol. soyed. 1: 1558, 1959 6. V. V. KORSHAK, S. A. PAVLOVA, G. I. TIMOFEYEVA, S. V. VINOGRADOVA and V. A. PANKRATOV, Dokl. Akad. Nauk SSSR 160: 119, 1965 7. G. I. TIMOFEYEVA, Dissertation, Moscow, 1965 8. T. SVEDBERG and K. O. PEDERSEN, The Ultracentrifuge, Oxford, 1940 9. L. J. GOSTING, J. Amer. Chem. Soe. 74: 1548, 1952 10. S. Ye. BRESLER, V. V. KORSHAK, S. A. PAVLOVA and P. A. FINOGENOV, Izv. Akad. Nauk SSSR, Otd. khim n a u k 344: 354, 1954
HYDROLYTIC PROCESSES OF THE THERMAL DEGRADATION OF ISOMERIC AROMATIC POLYAMIDES*t YE. :P. KRAS~OV, V. I. LOGV~OVA and L. B. SOKOLOV Vladimir Research I n s t i t u t e of Synthetic Resins
(Received 6 September 1965)
I~ A~ earlier work [1] it was suggested that hydrolytic processes were important in the general pattern of the degradation of isomeric aromatic polyamides at high temperatures. This was based on qualitative and quantitative analyses of * Vysokomol. soyed. 8: N o .
11, 1970-1975, 1966. ~f 4th Report of the series "Thermal degradation of polyamidds".
Thermal degradation of isomeric aromatic polyamides
2177
gaseous and liquid products of the pyrolysis of these polymers. I n particular, C02, H~0 and benzene were found to make up the main part of the volatile products, their composition depending very little on the isomeric form of the phenylene diamine and the dicarboxylic acid. The present paper gives the results of a more detailed experimental study of the hydrolytic processes of thermal degradation of isomeric aromatic polyamides. The principal reasons for these processes have been ascertained, and effective methods are suggested for reducing their significance in the general combination of degradative conversions, thus improving the heat resistance of these polymers. RESULTS AND DISCUSSION
The thermal degradation of isomeric aromatic polyamides prepared from mand p-phenylene diamines and acid dichlorides of iso- and terephthalic acids [2, 3] is accompanied by the formation of a considerable amount of volatile, liquid and solid products. The volatile and liquid products have already been analysed in [1]. The solid products of all these polyamides were analysed by thin-layer chromatography, and the results are given in Table 1. TABLE
1. S O L I D P R O D U C T S O F T H E T H E R M A L D : E G R A D A T I O N O F I S O M E R I C A R O M A T I C P O L Y A M I D E S
in vacuo 5~
Conditions of pyrolysis
~9
Products of pyrolysis
Polyamide temper-
ature, °C Poly-m-phenyleneisophthalamide*
Poly-p-phenyleneisophthalamide Poly-m-phenyleneisophthalamide Poly-p-phenyleneisophthalamide
440
520 510 530
time, .¢~ min
30
60 50 90
10"2
7.5 9.1 6.0
O
m-Phenylenediamine N-m-Aminophenylbenzamide N,N'-di-m -Aminophenyl isophthalamide p-Phenylenediamine N-p-Aminophenylbenzamide m-Phenylenediamine N-m-Aminophenylbenzamide p -Phenylenediamine N-p-Aminophenylbenzamide
* This poly;mer w a s p r e p a r e d b y emulsion polycondensation [3].
36
3"65
56
5"75
8 30
0'80 2"25
7O 4O
5"25 3"60
60 40
5"50 2-4
6O
3-6
2178
Y~.. P. KRASNOVet
al.
Although there is a relation between the qualitative composition of the solid products and the isomeric shape of the polymer-chain unit, the presence of only phenylene diamines and N-aminophenylbenzamides in the solid products of the pyrolysis of all these polyamides nevertheless confirms the conclusion of the previous work, i.e. that degradative conversions on the thermal decomposition of isomeric aromatic polyamides are qualitatively identical. The formation of phenyler/e diamines and l~-aminophenylbenzamides is obviously connected with the hydrolytic mechanism of the thermal degradation of these polyamides, there being two possible ways in which these products could be formed. First of all, phenylene diamine could be formed by hydrolysis of the last amine bond in the polyamine chain, and N-aminophenylbenzamide by hydrolysis of the penultimate amine bond followed by decarboxylation of the fragment formed: CO
/2--% NHC O ~
i
N H ~
N-H' + H20
COOH -> -- N H ~ N H C 0 ~
~NH2 + H 2 N ~ _ ~~ I~TH2
+ H20
z..~ CONH(/~'~ NHs ---.
--CO~
/~NH2+H00C/~ CONH~ / /
--co*, z-~ NH2
Since the hydrolysis of amine bonds followsthe law of chance, a large amount of water must be required for the formation of the quantitiesof phenylene diamines and N-aminophenylbenzamides observed experimentally in the thermal degradation of isomeric aromatic polyamides. The second method of formation could be by the hydrolysisand thermal degradation of the low molecular weight fraction of the polymers. Fractionation showed that for poly-m-phenyleneisophthalamide prepared by polycondensation in dimethylacetamide solution there is 5-6~/o of low molecular weight fraction with a specificviscosityof not more than 0.I for a 0"5~o solutionin concentrated H~S04. V~aen prepared by emulsion polycondensation, this same polymer contains 12-13~/oof this fraction.
Thermal degradation of isomeric aromatic polyamides
2179
To verify the influence of the low molecular weight fraction on the thermal degradation rate and yield of solid pyrolysis products two specimens of poly-mphenyleneisophthalamide were made, with a small amount of low molecular weight fraction. Then we compared the high-temperature behaviour of these and the original specimens. The results are shown in Figs. 1 and 2, and Table 2. ~, rnmHq/hr,
/o,qv
2qO
3 2 x
3
f
2"I
/ 180 1"7
120
J
300
330
3~
3~0
Off
l'q~
I
I
I
I
1"50
1"5#
1"62
1"68
tiT, °~10 -3 FIG. 1
FIG. 2
FTG. 1. Thermal degradation rates of various specimens of poly-m-phenyleneisophthalamide vs. temperature: /--prepared by emulsion polycondensation (specimen 1); 2--by solution polycondensation; 3--specimen 1 after fractionation; 4--specimen 1 after treatment in dimethylformamide. FIG. 2. Log. thermal degradation rates vs. reciprocal temperature for different specimens of poly-m-phenyleneisophthalamide. Notation as for Fig. 1. Analysis shows that the low molecular weight fraction does exert a considerable influence on the thermal degradation of poly-m-phenyleneisophthalamide. But we note that, apart from reducing the yied of solid products and improving the heat resistance of the polymer, after it has been treated in hot dimethylformamide, or the low molecular weight fraction removed b y precipitation from dioxane solution in dimethylformamide with 5% lithium chloride, the degradative conversions do not suffer any particular changes. This is supported b y two facts. First of all, the activation energies of the thermal degradation processes remain practically unchanged after these treatments. Secondly, there is no change in the qualitative composition of the gaseous, liquid and solid products, only the numerical yield altering. When the low molecular weight fractions are removed there is a big drop in the yield of COs b u t that of CO does not alter so much. Formation of COs on the
YE. P. KRASNOV et al.
2180
thermal degradation of polyamides is usually attributed to the hydrolytic mechanism [4-6], while the formation of CO is attributed to a homolytic mechanism [6]. From this it is concluded that, after removal of the low molecular weight fraction, the hydrolytic processes develop to a far smaller extent than in the original specimens. There are two possible mechanisms for the formation of COs on the thermal decomposition of isomeric aromatic polyamides. First of all, the direct decarboxylation of the carboxyl terminal groups of both the high and low molecular weight fractions. The particularly large amount of COs formed is in this case due to the low molecular weight fraction. Calculations showed that where the low molecular weight fraction is 10 wt. %, the yield of COs in direct decarboxylation should be 10 cmS/g of polymer, 0.5 cm3/g being due to the high molecular weight fraction. I f the amount of low molecular weight fraction is reduced to 1 ~/o, the COs yield should fall to 1.3 cm3/g of polymer. TABLE 2. RESULTS
OF THE THERlYIAL DEGRADATION
POLY-m
OF SOME SPECIMENS
De-
Specimen
OF
-PHENYLENEISOPHTHALAMIDE
{E.l
gradation temperatare,
°C
°C Original polymer produced b y emulsion 1.52 polycondensation After fractionation in dioxane from 1.88 solution After t r e a t m e n t in hot dimethylform-: 1-75 amide Original polymer produced b y polycondensation in dimethylaeetamide 1.91 solution
Yield of solid Eaot, kcal/ prod/mole ucts at 440 °,
Yield of COz and CO at 380 °, cmS/g of polymer
%
COs
CO
360
300
33"8
10"2
62'0
1"20
385
315
32 "4
0"6
17"2
0'64
395
315
34"0
2"0
14"2
1"44
375
305
33"8
3"8
31"6
0"72
,
* Ts is the minimum vacuum heat-treatment temperature below which the polymer ceases to be soluble in HsS0 ~
(I h.r).
On the thermal degradation of poly-m-phenyleneisophthalamide (with 1213% low molecular weight fraction) the experimental yield of CO2 at 380 ° was found to be 60 cma/g of polymer. After removing the low molecular weight fraction the CO2 yield fell to 14-17 em3/g (Table 2). The large amounts of CO2 found experimentally in the pyrolysis products of isomeric aromatic polyamides can therefore only be partially attributed to the direct decarboxylation of the low molecular weight fraction.
Thermal degradation of isomeric aromatic polyamides
2181
The second method assumes t h a t the terminal carboxyl and amino groups of the low molecular weight fraction have a catalytic effect in the thermal degradation of these polyamides. As w found in [1], on the pyrolysis of isomeric aromatic polyamides terminal ammonium groups are formed followed by their dehydration to nitriles: + NH a R-- COOH ---~ -- R-- COONH4 - H~O __ R--
-
--CONH~
~ --R--C ~-N÷H~O
--H2O
As a result of this reaction, we get the water necessary for the hydrolysis of the amide bonds. Of course, the rate of this complicated process will largely be determined by the concentration of the terminal amino groups from which the ammonia gas is formed, and that of the carboxyl groups from which the ammonium groups are formed on reaction with this gas. If this is so, the COx yields should be largely dependent on the initial concentration of terminal groups in the original polymer and, where there is a low molecular weight fraction, on its relation to the high molecular weight one. This is quite consistent with the experimental results for the thermal degradation of the original and processed specimens of poly-mphenyleneisophthalamide. According to our calculation, a yield of around 60 cm3/g COs may occur if the system contains approx. 5 ~o water, or if this amount of water is formed in the actual process of thermal degradation. The latter is more likely, since the initial moisture content of the test specimens was not more than 0.3% and considerable quantities of water may be recovered according to the scheme given above. In view of the fact that the low molecular weight fraction has a considerable catalytic effect on the processes of thermal degradation of isomeric aromatic polyamides, an effective method of improving their heat resistance could be its more complete removal. In [1] it was found that the entire complicated combination of degradative conversions of isomeric aromatic polyamides was not exhausted by the processes of the hydrolytic decomposition of the amide bonds. While the COs yields can be lowered 4-5 times by removing the low molecular weight fraction, the COs yields are only halved, which means that this fraction has much less influence on homolytic than on hydrolytic processes. On thermal degradation at high temperatures the polymer radical undergoes deep carbonization with formation of paramagnetic centres giving a narrow ESR signal (6 oersted). It is interesting to note that the formation of paramagnetic centres on thermal degradation, particularly for poly-m-phenyleneisophthalamide, is an exponential function of temperature. The activation energy of the process is 51.5 kcal/mole, which is much more than the activation energy calculated from the formation of gaseous products, 33.8 kcal/mole. Of course, the formation of a system of conjugated bonds is due to processes of a free-radical nature.
2182
Y~. P. KRASNOV et al.
EXPERIMENTAL The characteristics of the specimens of isomeric aromatic polyamides were given in [1]. T h a t article also gave a detailed description of the procedure for analysing the gaseous and liquid products of thermal degradation. TABLE 3. VALI.TES OF R$ FOR PHENYLENEDIAMINES AND N-AMINOPHENYLBElqZAMIDES
Values of R I Compound
ethanol-chloroformammonia gas
ethanol-chloroformtetrahydrofuran
0'71 0'86 0'04 0'57 0'81
0"37 0"54
m -Phenylenediamine N-m-aminophenylbenzamide N,N'-di-m-aminophenylisophthulamide p-Phenylenediamine N-p-aminophenylbenzamide
0"38 0"55
Poly-m-phenyleneisophthalamide prepared b y emulsion polycondensation [3] was treated in hot dimethylformamide in a Soxhlet apparatus. The low molecular weight fraction was also removed b y fraetionating the original polymer b y precipitation in dioxane from a 1% solution in dimethylformamide containing 5% lithium chloride. The solid products of the t h e r m a l degradation were qualitatively and q u a n t i t a t i v e l y analysed b y thin-layer c h r o m a t o g r a p h y [7, 8] over a reinforcing layer of the adsorbant silica gel K S K - g y p s u m . The layer of adsorbant was deposited onto glass plates 13 × 18 em a n d alcoholic solutions of the test mixtures were deposited on the starting line with a finea d j u s t m e n t syringe. The chromatographic analysis was carried out with an ascending solvent flow. The solvents used were a mixture of ethanol-chloroform a n d ammonia gas in the ratio 60:20: 1, a n d a mixture of ethanol-chloroform-tetrahydrofuran in the ratio 15: 100:40. After analysis the plate was removed from the solvent b y drying and developed b y spraying on a 1% solution of p-dimethylaminobenzaldehyde in 1 ~ hydrochloric acid. The experimental conditions for chromatographic separation of the solid products of pyrolysis have been described in more detail in [9]. The results are given in Table 3 for phenylenedlamines and N-aminophenylbenzamides. The solid products of the pyrolysis of isomeri~ aromatic polyamides were identified b y comparing their Rj with t h a t of model compounds in different systems of solvents. I R spectroscopy was also used. The numerical composition of the mixtures of solid products was determined b y thin-layer chromatography, using the method proposed b y Truter and P u r d y in [10]. T h e a u t h o r s a r e g r a t e f u l t o T. A . P o l y a k o v a a n d V. K . V e l y a k o v f o r t h e i r assistance in obtaining some of the experimental results used in the present work.
CONCLUSIONS (1) T h e h y d r o l y t i c d e c o m p o s i t i o n o f t h e a m i d e b o n d s o n t h e r m a l d e g r a d a t i o n of isomeric aromatic polyamides has been studied. The heat resistance of these p o l y m e r s is f o u n d t o d e p e n d l a r g e l y o n t h e i r c o n c e n t r a t i o n o f l o w m o l e c u l a r weight fraction.
Polymeric fraction of thermolysed anthracene containing paramagnetie centres
2183
(2) I t is a s s u m e d t h a t t h e c a r b o x y l a n d a m i n o t e r m i n a l g r o u p s h a v e a c a t a lytic effect on h y d r o l y t i c processes in t h e t h e r m a l d e g r a d a t i o n of these p o l y m e r s . (3) M e t h o d s b a s e d on t h e r e m o v a l o f t h e low m o l e c u l a r w e i g h t f r a c t i o n h a v e b e e n s u g g e s t e d as w a y s of i m p r o v i n g t h e t h e r m a l s t a b i l i t y o f p o l y - m - p h e n y l e n e isophthalamide. Translated by V. ALFORD REFERENCES 1. Ye. P. I { ~ N O V ,
2. 3. 4. 5. 6. 7. 8. 9. 10.
V. M. SA~NOV, L. B. SOKOLOV, V. I. LOGUNOVA, V. K. BELY~LKOV
and T. A. POLYAKOVA, Vysokomol. soyed. 8: 380, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 3, 413, 1966) V. M. SAVINOV and L. B. SOKOLOV, Vysokomol. soyed. 7: 772, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 5, 851, 1966) L. B. SOKOLOV and T. V. KUDIM, Dokl. Akad. Nauk SSSR 158: 1139, 1964 S. STRAUS mad L. WALL, J. Res. Nat. Bur. Standards 60: 39, 1958; 63A: 269, 1959 S. R. RAFIKOV and R. A. SOROKINA, Vysokomol. soyed. 3: 21, 1961 (Not translated in Polymer Sci. U.S.S.R.) Ye. P. KRASNOV, L. B. SOKOLOV and T. A. POLYAKOVA, Vysokomol. soyed. 6: 1244, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 7, 1371, 1966) E. STA_H_L,Diinnschicht-Chromatographie, Springer Verlag, Berlin, 1962 A. A. AKHREM and A. I. KUZNETSOVA, Tonkosloinaya khromatografiya. (Thin Film Chromatography.) Izd. Nauka, 1964 Ye. P. KRASNOV, Dissertation, 1965 S. Y. PURDY and E. TRUTER, Analyst 87: 802, 1962
THE POLYMERIC FRACTION OF THERMOLYSED ANTHRACENE CONTAINING PARAMAGNETIC CENTRES, AS AFFECTING THE LOW-TEMPERATURE HEAT TREATMENT OF ANTHRACENE AND BIANTHRYL* A. A. BERLIN, V. A. GICIGOROVSKAYAa n d V. YE. SKUR2kT Institute of Chemical Physics, Academy of Sciences, U.S.S.R. (Received 8 September 1965) IN [1, 2] we described t h e f o r m a t i o n of p a r a m a g n e t i c p o l y m e r s on h e a t t r e a t m e n t o f a n t h r a c e n e a n d b i a n t h r y l a t 450 ° in t h e absence o f air. W e also described t h e a c t i v a t i o n of this process b y t h e a d d i t i o n o f c a t a l y t i c a m o u n t s of p o l y m e r fract i o n s e p a r a t e d f r o m t h e p r o d u c t s of t h e t w o - h o u r h e a t t r e a t m e n t of a n t h r a c e n e (PMCh) c o n t a i n i n g c o n c e n t r a t i o n o f p a r a m a g n e t i c centres o f ~ l0 is spin/g [2]. * Vysokomol. soyed. 8: No. 11, 1976-1983, 1966.