Thermal transformations of compounds modelling major fragments of network polymers, based on oligo- and polycarbodiimides

Thermal transformations of compounds

87

2. V. V. KORSHAK, S. "V. VINOGRADOVA, I. P. STOROZHUK et aL Authors' cert. No. 622, 823 (U.S.S.R.) Publ. in Bull. Inventions, No. 33, 1978 3. A. GORDON and R. FORD, Sputnik khimika, Mir. 437, 1976 4. V. L SOKOLENKO and V. T. DOROFEYEV, Authors' cert. No. 595, 289 (U.S.S.R.), Publ. in Bull. Inventions, 8, 91, 1978 5. S. GAVRIL'YAK and S. NEGAMI, V kn. Perekhody i relaksatsionniye yavleniya v polimerakh (In: Transformations and Relaxational Phenomena in Polymers). p. 193, (Ed. by R. Baier), Mir, Moscow, 1963

Polymer Science U.S.S.R.Vol.26, No. 1, pp. 87-95, 1984 Printedin Poland

0032-3950184$10.00+.00 © 1985 Pergamon Press Ltd.

THERMAL TRANSFORMATIONS OF COMPOUNDS MODEIJ,ING MAJOR FRAGMENTS OF NETWORK POLYMERS, BASED ON OLIGO- AND POLYCARBODIIMIDES* V. A. PANKRATOV, V. M. LAKTIONOV, A. I. AKHMEDOV, P. N. GRIBKOVA, S.-S. A. PAVLOVA, YA. M. BILALOV,

S. V. VINOCRADOVAand V. V. KORSHAK A. N. Nesmeyanov Institute of Elemento-Organic Compounds, U.S.S.R. Academy of Sciences (Received 20 November 1982)

The thermal, thermo-oxidative and thermohydrolytic stability of diphenylcarbodiimide, the cyclic dimer of diphenylcarbodiimide, hexaphenylisomelamine and hexaphenylmelamine, which model major fragments of network polymers based on oligo- and polycarbodiimides were studied over the 250-550° temperature range. Gaseous, liquid and solid products of the decomposition of these compounds were identified. It was established that under thermolysis conditions in a vacuum, the stabilities of the model compounds were almost the same, whilst hexaphenylmelamine displayed the highest stability towards thermo-oxidation and thermohydrolysis arid diphenylcarbodiimide, the least. The results obtained permit recommendation of ways of performing directed crosslinking of linear polymers with carbodiimide groups in the chain, in order to obtain the most thermally stable systems.

APPRECIABLEthermal and fire resistance [1, 2] is characteristic of aromatic oligo- and polycarbodiimides, synthesized by catalytic deearbonylation of diisocyanates. Crosslinking of these polymers [3] was observed at temperatures above 150Q, due to the presenee of reactive - N = C = N groups, which finally result in the formation of heterounit * Vysokomol. soyed. A26: No. 1, 79-85, 1984.

88

V . A . PANKRATOVet al.

network polymers. Linear polymerization (I). dimerization (II) and trimerization (III) o f carbodiimide groups [3-5] have the greatest value in crosslinking processes. . . . . N=C.-=N . . . . I

II

il

R

I

I

n

I1 /\

1

.....C--N . . . . . . . . N

~ III

N~C----N . . . . . . . .

N

....N = C - - N ....

Y

/

N ....

N

I

N

\

F r o m I R spectroscopic data [3, 6] on oligo- and polycarbodiimides, preheated to 1500) the presence o f dimeric (1690) and trimeric (1640 c m - 1 ) fragments was found, the thermal stabilities o f which are naturally dissimilar. Linear carbodiimide polymerization proceeds in specific anionic catalytic conditions at low temperatures [5], consequently the f o r m a t i o n o f crosslinked structures is less likely on account o f this process, with heat treatment o f the oligo- and polycarbodimides. I n order to explain the influence o f a heterounitary structure and the contribution o f each type o f unit to the overall thermal stability o f crosslinked polymers based on oligo- and polycarbodiimides, we studied the thermal, thermo-oxidative and t h e r m o hydrolytic stability in the 250-550 ° temperature range o f c o m p o u n d s simulating the major structural elements o f these polymers• As examples, we chose diphenylcarbodiimide (DPC), its dimer ( D D P C ) , the trimer o f diphenylcarbodiimide-hexaphenylisomelamine ( H P I M ) and its isomer, hexaphenylmelamine ( H P M ) ; so far as is k n o w n [7, 8] under defined conditions H P I M is isomerized to H P M . The structmes and some properties of the model c o m p o u n d s are given in Table 1. All the model compounds were synthesized by known methods [7-11]. Purification of DPC was carried out by triple distillation in a vacuum and of HPIM, DDPC and HPM by double recrbstallization from suitable solvents (see Table 1). The degradation of model compounds was ca-:icd out in glass anapoules, volume 12 ml, in isothermal heating conditions for 1 hr at each temperature (batch weight of sample, ca, 20 rag). Ampoules for thermal degradation studies were evacuated to 0.133 Pa and sealed. For thermo-oxidative degradation studies, the ampoules were previously evacuated (0.133 Pa) and then filled with pure dry oxygen to a pressure of 17.65 kPa, but for thermohydrolysis filled with water vapour (ca. 2'3 kPa), whilst cooling the ampoule under vacuum. Analysis of the gaseous degradation products of model compounds was carried out on a LKhM-8MD chromatograph, using parallel columns (l= 1 m) with SKT brand carbon in 0.25-0.50 mm granules (H2, CO, 02, CH4 analysis) and Porapak S + 10 ~ PEI (CO2 analysis). The absolute chromatographic calibration was carried out with the pure individual gases (katharometer detector, helium carrier gas). The precision of analysis in the chosen regime was not < 1-3 ~ relative. Liquid and solid products of degradation were identified on a Finnigan coupled gas chromatograph-mass spectrometer (glass column, 3 mm diameter, 1"5 m long filled with Chromaten N - A W + 5 ~ E-301), using an

Thermal transformations of compounds

89

EVM to process the results. The relative amounts of liquid and solid degradation products were determined by solution of the residues after de~adation in 0.5 ml acetone and by chromatography on a 1 m long column, filled with Chromaton N-AW + 5 ~ E-301, on an LKhM-8MD chromatograph, programming the temperature from 35 to 250 ° at a rate of 8 deg/min (x.aporizer block temperature 300 °, katharometer at 250 ° helium carrier).

TABLE 1. STUDIES ON MODEL COMPOUNDS

Melting point, °C Compound

Structural formula

experimental

Typical IR

literature

spectral absorption, cm- t

iJi;C . . . . . . .

Ph--N=~ :~N--Ph

141/200 Pa (b.p)

119-121/60 Pa [9]

2130-2145 (N = C = N)

196'5-197'5 (benzene : hep-

196 [ll]

1640+5 ( C = N )

t

tane 1 : 3)

292 5 293 0 [7]

ph\ /Ph N

302"5-303"0 (nitrobenzene)

HPIM Ph--N PhN

HPM

I

NPI~ II /\

N-Ph

N NPh

•-

•

1530_+ 5 (C-N) (in triazole ring)

/\ N N Ph \ , / ~ " ( , \ N / P h ~;h / N N \Ph

DDPC :':~ -2.-c=NP~ ! T ;"~.:T ( : - - ~ - P h

162.0-163'5 (benzene : alcohol=l : 1

162-163 [101

1690_+10 ( C = N )

Since, a c c o r d i n g to gas c h r o m a t o g r a p h i c analysis, after heating at 250 ° for 1 hr, D D P C c o m p l e t e l y split to d i p h e n y l c a r b o d i i m i d e , a n d the c o m p o s i t i o n a n d a m o u n t o f gaseous p r o d u c t s o f the t h e r m o h y d r o l y s i s o f D D P C a n d D P C at 400 ° coincide, we c o m p l e t e l y e x c l u d e d D D P C f r o m further c o n s i d e r a t i o n . T h e s t u d y o f the t h e r m o d e g r a d a t i o n o f D P C , H P I M a n d H P M in a v a c u u m in the 250-550 ° range showed the c o m p l e t e absence o f gaseous p r o d u c t s o f d e c o m p o s i t i o n , except traces o f H2 a n d CH~ which are always f o r m e d in cleavage o f o r g a n i c c o m p o u n d s a b o v e 400 ° . M o r e o v e r , d u r i n g t h e r m a l d e g r a d a t i o n , with all the m o d e l c o m p o u n d s v a r i o u s a m o u n t s o f benzene, benzonitrile, aniline, indole, d i p h e n y l a m i n e , diphenylc a r b o d i i m i d e a n d 9 H - c a r b a z o l e were identified. A s an example, Fig. 1 shows c h r o m a t o g r a m s o f the d e g r a d a t i o n p r o d u c t s f r o m D P C , H P I M a n d H P M at 500 °. A t r a n s f o r m a t i o n o f p a r t o f the s a m p l e into H P M was characteristic for D P C a n d H P I M i.e. i s o m e r i z a t i o n o f H P I M to H P M occurred, a n d D P C initially cyclotrimerized to H P I M a n d then it isomerized. T h e source o f the d i p h e n y l a m i n e in the d e c o m p o s i t i o n p r o d u c t s is c o n s i d e r e d to be H P M .

90

V.A. PANKRATOVet al.

(.) I N II DPC

--'¢"

~

HPIM

_

J ~"~

~"%~/ ~-~

A+ ~.___2_.,:--%_~I_/?-N

HPM The increase of the diphenylamine content in passing from DPC to HPM (Fig. 1) also serves as an indirect confirmation of the above scheme of transformations and decompositions of the model compounds at elevated temperatures. The main products of decomposition of DPC in a vacuum is aniline, whilst it is formed in rather small amounts in the decomposition of HPM (see Fig. 1). The temperature regions for oxygen absorption and evolution of CO and CO2 during thermo-oxidative degradation are different for the various model compounds (see Table 2). Absorption of oxygen by DPC begins at 300° and for HPIM and HPM it occurs at 250 and 375 ° respectively. In the thermo-oxidative process, evolution of CO and CO2 was observed simultaneously with oxygen absorption. Moreover, COa up to 500 ° is the predominant gaseous product of thermo-oxidation, amounting to 0.306, 0.447 and 0.131 mole/mole of DPC, HPIM and HPM, respectively, at 400 °. It is characteristic that in spite of the fact that the initial oxidation temperature for HPIM is 50 ° higher than for DPC, the latter is more stable at higher temperatures than is HPIM (see Fig. 2a). HPM has the greatest thermo-oxidative stability up to 400 °, and DPC undergoes the least degree of oxidative degradation at temperatures above 450 °. The amount of CO in the thermo-oxidation of the model compounds increases continuously with temperature (Fig. 2b), hence for DPC there is a practically linear increase in it with a temperature rise from 350 to 550 °, whilst for HPIM and HPM the initially observed appreciable increase in the quantity of CO in the decomposition products (350-450 ° for HPIM and 400-450 ° for HPM) is changed, with a reduced CO production rate at higher temperatures.

Thermal transformations of compounds

91

In contrast from thermodegradation, a decrease in the diphenylamine content of products from D P C and H P I M is noted in thermo-oxidative degradation, which may be explained both by its oxidation and also by the reduced isomerization of H P I M to H P M , in the presence of oxygen. 3

1o 7

3

7

0

FIG. 1. Chromatograms of liquid and solid decomposition product~ of DPC (a), HPIM (b) and HPM (c), in a vacuum at 500° 1 - benzene, 2 - benzonitrile, 3 - aniline, 4 - not identified, 5 - indole, 6 - diphenyl, 7 - diphenylamine, 8 - diphenylcarbodiimide, 9 - 9H-carbazole. On the whole, the quantitative composition of the liquid and gaseous oxidation products f r o m the model compounds is the same as for thermolysis in a vacuum, with the sole difference that the aniline content increases and phenol formation is noticed. The only gaseous products of thermohydrolysis of the model compounds is CO2 (Table 2). D P C and H P I M (Fig. 3) have the least stability to steam at a high temperature. Their decomposition begins at a temperature below 250 ° at the same time as H P M begins to decompose, evolving CO~, only at 400 °. The maximum amount of CO,

92

V.A.

PANKRATOV

et aL

TABLE 2. COMPOSITION OF GASEOUS PRODUCTS OF THERMAL ( a ) , THERMO-OXIDATIVE (b) AND THERMOHYDROLYTIC (C) DEGRADATION OF MODEL COMPOUNDS OVER ] HR HEATING AT EACH TEMPERATURE Gaseous

products,

mole/mole*

Relative

amount

Degradation T °

of type

CO2

CO

adsorbed oxygen*

Diphenylcarbodiimide 250

300

350

400

450

500

550

a

-

--

b

-

-

--

c

0.281

-

-

a

-

-

-

b

0.004

-

0"042

c

0.375

--

--

a

-

-

-

b

0.021

0.009

0.115

c

0.444

-

--

a

-

--

--

b

0.306

0.078

0-555

c

0.561

-

-

a

-

-

-

b

0.345

0-166

1.000

c

0.582

--

-

-

-

-

b

0.350

0.248

1.000

c

0.451

-

-

-

-

-

b

0.284

0.316

c

0.515

-

a*

a*

1.000 -

Hexaphenylisomelamine 250

300

350

375

400

450

500

a

-

-

-

b

-

-

-

c

0.044

-

-

a

-

-

-

b

-

-

-

c

0.166

-

-

a

-

-

-

b

0"055

0.013

0-124

c

0.333

-

-

a

-

-

0.291

b

0.398

0.085

c

0.452

-

-

a

-

-

0.326

b

0.447

0.112

c

0.515

-

-

a

-

--

-

b

0.461

0.166

1.000

c

0.531

-

-

--

--

--

0'425

0"194

1'000

a t b

Thermal transformations of compounds Gaseous

Degradation

T°

products,

93

mole/mole*

Relative a m o u n t of

type

COz

CO

adsorbed oxygent

Hexaphynylisomelamine c a b c

550

0.503 _ 0-367 0.487

I I~

-_ 0.223

i

]i

_

1'000

--

Hexaphenylamine 300

350

375

a

-

-

-

b

--

-

--

c

--

--

--

a

--

--

--

b

--

--

c

.

a b

--

-

0.003

-

C

400

.

a b c a b c as b c a b c

450

500

550

0.131 0.003 . 0.351 0.073 . 0.412 0.124 . 0.429 0.319

.

.

.

-.

.

0.012 .

0.090 -. . 0.222 . . 0.245 . . 0.311 -

.

.

.

0.154 0'326 1.000 1.000 -

* F o r c o m p a r a t i v e r e s u l t s , t h e a m o u n t o f g a s e o u s d e g r a d a t i o n p r o d u c t s w e r e c a l c u l a t e d f r o m t h e a n a l y t i c a l results in mole/mole diphenylcarbodiimide or per { mole HPIM or HPM. t T h e r a t i o o f Oz a b s o r b e d to its o r i g i n a l c o n t e n t in t h e s y s t e m , c a l c t d a t e d f r o m t h e f o r m u l a [ O 2 ] v - [O2]t/[O2]v w h e r e [O2]v is t h e t o t a l a m o u n t o f 0 2 i n t r o d u c e d i n t o t h e a m p o u l e in moles; [ 0 2 ] , is t h e a m o u n t o f u n r e a c t e d 0 2 in m o l e s . ~t T r a c e s o f C H 4 a n d H2 w e r e f o u n d in the g a s e o u s d e g r a d a t i o n p r o d u c t s .

a t 550 °, w a s 0 . 3 1 9 m o l e / m o l e f o r H P M , 0.515, 0.487 evolution

mole/mole, r e s p e c t i v e l y .

whilst for DPC and HPIM,

thc values were

Judging from the nature of the curves for CO2

( F i g . 3), t h e t h e r m o h y d r o l y s e s

of D P C

and HPIM

mechanism; however, on the whole the stability of HPIM

proceed

by the same

t o t h e r m o h y d r o l y s i s is h i g h e r

than that of DPC. The major part of the liquid thermohydrolysis products from DPC are aniline and a very small amount

of benzene but benzonitrile, diphenylamine

and

9H- carbazole are completely absent. The content of aniline and diphenylamfi~e in the decomposition

products of HPIM

a r e t h e s a m e as w i t h t h e r m o l y s i s i n a v a c u u m , t h e

m a i n p r o d u c t o f H P M t h e r m o h y d r o l y s i s is d i p h e n y l a m i n e . E v i d e n t l y , s t e a m a t e l e v a t e d temperatures

suppresses trimerization

of diphenylcarbodiimide;

t i o n o f i s o m e l a m i n e t o t h e u s u a l f o r m is o b s e r v e d .

however, isomeriza-

94

V.A. PANKRATOVet al.

Therefore, if the stabilities of the model compounds are similar under vacuum thermolysis conditions (the formation of solid and liquid degradation products are noted at a temperature above 400°), then the thermo-oxidative stabilities of the cyclotrimerization products of diphenylcarbodiimide, hexaphenylisomelamine and hexaphenylmelamine are appreciably higher than that of the original monomer. Also, under thermohydrolysis conditions, H P M begins to decompose at 400 °, i.e. 150 ° higher than the - N = C = N linkage in the earbodiimide and isomelamine rings.

a

05

b

0.1

0.1 !

300

. ,,I

,,

,..~

500.T °

850

I

I

#50

FIG. 2

T

550 T °

_

~

-J.---...-

300

500 T °

FIG. 3

FIG. 2. Quantity of CO2 (a) and CO (b) formed during degradation of DPC (1), HPIM (2), and HPM (3) in the presence of oxygen, in relation to temperature. Here and in Fig. 3, the amounts of CO2 or CO are given in moles per 1 mole DPC or per ~ mole HPIM and HPM. FIG. 3. Quantity of CO2, formed during degradation of DPC (I), HPIM (2) and HPM (3) in saturated water vapour, in relation to temperature. F r o m the results obtained on thermal, thermo-oxidative and thermohydrolytie degradation of compounds simulating major fragments of linear and network polymers, based on oligo- and polycarbodiimides, it may be concluded that the increase in thermal stability of these polymers can be achieved by structure formation under conditions which provide preferably for polycyelotrimerization of the carbodiimide linkages. Translated by C. W. CAPP

REFERENCES 1. D.L. BERNARD and A. J. DOMENY, Germ. Pat. 1,802,082, Chem. Abstr. 71: No. 14, 62063, 1969 2. A. LA SPINA, J. VOGEL, H. PIECHOTA and R. SCHLIEBS, Germ. Pat. 2,100,621, Chem. Abstr. 77: No. 24 (I), 153186, 1972 3. L. M. ALBERINO, W. J. FARRISSEY and A. A. R. SAYIGH, J. Appl. Polymer Sci. 21: 1999, 1977 4. T. W. CAMPBELL and K. C. SMELTZ, J. Org. Chem. 28: 2069, 1963 5. G. J. ROBINSON, J. Polymer Sci. 2: 3901, 1964

Thermo-oxidative degradation of m-carborane containing polyamide

95

6. L. M. ALBERINO, W. J. FARRISSEY and A. A. R. SAYIGH, Polymer Preprints 15: 77, 1974 7. V. A. PANKRATOV, S. V. YINOGRADOVA, V. V. KORSHAK, S. N. KUZNETSOV and L. I. MITINA, VINITI, Dep. No. 5844-81, 1974 8. S. V. LINDEMAN, V. Ye. SHKLO'VER, Ya. T. STRUCHKOV, S. N. KUZNETSOV and V. A. PANKRATO¥, Kristallografiya 27: 65, 1982 9. T. W. CAMPBELL, J. J. MONAGLE and V. S. FOLDI, J. Amer. Chem. Soc. 84: 3673, 1962 10. R. RICHTER, Chem. Ber. 101: 174, 1968 11. M. BUSCH, G. BLUME and E. PUNGS, J. Prakt. Chem. 79: 5t9, 1909

Polymer Science U.S.S.R. Vol. 26, No, 1, pp. 95-98, 1984 Printed in Poland

0032-3950/84 $10.00+ ,00 © 1985 Pergamon Press Ltd.

THE EFFECT OF RED PHOSPHORUS ON THE THERMO-OXIDATIVE DEGRADATION OF AN m-CARBORANE CONTAINING POLYAMIDE* V. V. KORSHAK, N. I. BEKASOVA, L. G. KOMAROVA,

G. A. KATS and L. I. KOMAROVA A. N. Nesmeyanov Institute of Elemento-Organic Compounds, U.S.S.R. Academy of Sciences. (Received 22 December 1982) The effect on its stability towards thermo-oxidation of adding finely dispersed red phosphorous to a m-carborane containing polyamide has been studied. It was shown that adding 3 ~ of red phosphorus to the polyamide film enabled the formation of thermostable structures at relatively low temperatures. Also, the oxygen index is increased from 16"1 for the initial polyamide to 21.1 for polyamide to which 3 % of red phosphorus has been added.

IT is well known [1, 2] that the introduction of a m-carborane containing fragment into a

polyamide chain causes a notable increase in the thermal stability in an inert atmosphere or in a vacuum. However, on heating polyamides with m-carboranedicarboxylic acid in air, even at 250--300 °, an increase is noted in the sample weight, of up to 20-33 y. at 450-550 °, on account of the reaction of the carborane nucleus with oxygen in moist air. It is known from the literature, that introduction of red phosphorus into some classes of polymers causes an increase in the oxygen index [3, 4]. In this connection, it was of interest to us to study the influence of such an effective flame inhibitor as red phosphorus on the thermo-oxidative stability of poly-p, p'-diphenylene-m-carboranylene dicarbamide. * Vysokomol. soyed. A26: No. 1, 86-88, 1984.