Degradative processes in solid-phase polycondensation of polyhydrazides

Solid-phase polycondensation of polyhydrazides

3021

Our investigation has thus established a number of correlations concerning the effect of the supermolecular and chemical structure of polycaproamide, which is one of the more important polymeric materials, on the nature of its combination of mechanical properties. Translated by E. O. PHrLLr~S REFERENCES 1. V. V. KORSHAK, T. M. FRUNZE, V. V. KURASHEV, V. I. ZAITSEV and T. M. BABCHINITSER, Vysokomol. soyed. A12: 416, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 2, 475, 1970) 2. G. L. SLONIMSI(II and A. A. ASKADSKII, !~Iekhanika pollmerov, No. 1, 36, 1965 3. A. A. ASKADSKI, Fiziko-khimiya poliarflatov (Physical Chemistry of Polyarylates). Izd. "Khimiya", 1968 4. G. A. DUBOV and V. R. REGEL', Zh. tekh. fiz. 25: 2542, 1955 5. V. I. PAVLOV, A. A. ASKADSKII and G. L. SLONIMSKII, Vysokomol. soyed. A9: 385, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 2, 433, 1967) 6. V. A. KARGIN, T. I. SOGOLOVA and N. Ya. RAPOPORT, Dokl. Akad. Nauk SSSR 163: 1196, 1965 7. G. L. SLONIMSKII, A. A. ASKADSKII and V. K. LOGVINENKO, Mekhanika polimerov, 586, 1967 8. M. V. FROLOV, Vysokomol. soyed. A12: 1523, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 7, 1773, 1970)

DEGRADATIVE PROCESSES IN SOLID-PHASE POLYCONDENSATION OF POLYHYDRAZIDES* V. V. KORS~A~, V. A. KHOMUTOV, G. L. BERESTNEVA a n d I. P. BRAG1NA D. I. Mendeleyev Institute of Chemical Technology, Moscow

(Received 7 December 1971) A comparative analysis has been made of the volatile products of degradation of a poly-l,3,4-oxadiazole and a polyhydrazide obtained by polycondensation of the dihydrazide of 4,4'-dicarboxydiphenyloxide with the diacid chloride of 4,4'-dicarboxydiphenylphthalide, and of compounds modelling their repeating unit, a t ' t e m p e r atures from 200 to 650 °. I t is shown that the presence of uneyclized hydrazide fragments is the cause of breakdown of the polymer at lower temperatures. * Vysokomol. soyed. 15: No. 12, 2662-2668, 1973.

3022

V . V . KORSHAX e~ a/.

SoLID-phase polycondensation, which is used extensively for preparation of heat-resistant heteroeyclie polymers, has been studied to a very small extent. A specific feature of the process has been noted several times, in discussion of the eyclodehydration of polyamidoacids [l], poly-o-oxamides [2] and polyhydrazides [3], namely t h a t a limiting degree of conversion is reached a t each reaction temperature. A previous investigation of the kinetics of polycyclodehydration of polyhydrazides [4] enabled this anomalous behaviour to be a t t r i b u t e d to the effect of increased rigidity of the polymer chain as the number of oxadiazole fragments increases. This is supported b y the experimentally found increase in the a p p a r e n t energy of activation as the degree of conversion increases [2, 5, 6] and the fact t h a t the polymer becomes a glassy-state material as partial cyclization occurs during the course of the reaction [4]. These two facts lead to virtual cessation of the reaction a t different stages of conversion. The presence of a eertain number of uncyclized hydrazide fragments, which are "defective" or "weak" sites in the chain, can give rise to premature, low-temperature degradation. Meanwhile it has been shown t h a t when polyeyelodehydration is carried out a t temperatures above the glass temperature of a poly-l,3,4-oxadiazole, because of the rapid relaxation of internal stresses the kinetic hindrances to the smooth course of the process are removed and the reaction goes practically to completion [5]. I t is extremely unsafe to carry out the reaction under these conditions, however, because of the possibility of the occurrence of degradation reactions, and in each individual case a thorough investigation is necessary. For this reason it became necessary to make a comparative study over a wide range of temperatures, of the degradation of polyhydrazide starting materials, poly-l,3,4-oxadiazoles, intermediate reaction products and model compounds of different chemical structure. EXPERIMENTAL

Etar$ing maSerials. The materials studied were 2,5-diphenyl-l,3,4-oxadiazole (I), m.p. 137.5°; N,N'-dibenzoylhydrazine (II), m.p. 240°; 1,4-bis-(5-phenyl-l,3,4-oxadiazol-2-yl),2benzene (III), m.p. 304°; terephthalic acid dibonzoylhydrazide (IV), m.p. 309-310°; 3,3-bis[4-(5-phenyl-l,3,4-oxadiazol-2-yl-phenyl]phthalide (V), m.p. 241.5-242.5°; the N,N'-dibenzoylhydrazide of 4,4'-dicarboxydiphenyl oxide (VI), m.p. 187-188°; a polyhydrazide (VII), obtained b y polycondensation of equimolar quantities of the dihydrazide of 4,4'-diearboxydiphenyl oxide and the diaeid chloride of 4,4'-dicarboxydiphenylphthalide [7], softening point 220% ~r~ 0"9 dl/g (25 °, 0"5% solution in cresol); a polymer derived from V I I with a degree of cyclization of 50~o (VIII), softening point 265 °, qrea 0"82 dl/g, a n d the poly-l,3,4-oxadiazolo from V I I , softening point 325 °, ~r~ 0"72 dl/g (IX). The polycyclization reaction was carried out under high vacuum at 325 °, using powdered material of the same degree of dispersity. The time for a t t a i n m e n t of a given degree of cyclization was found from the results of a s t u d y of the kinetics of the process [5]. All the model compounds were obtained b y t h e general methods of synthesis of N,N'dibenzoylhydrazine [8] and 2,5-diphenyl-l,3,4-oxadiazole [9]. The model compounds and polymers were identified b y elementary analysis and infrared spectroscopy. Degradation of all the polyrnera and model compounds, previously dried to constant weight under high vacuum, was carried out under identical conditions in an atmosphere of argon, in the enclosed space of a pyrolitie apparatus. F o r gas-chromatographic analysis we used a thermal-conductivity detector, a 2.4 m column filled with P o r o p a k C for separation of Hi, CH,, COs, ethylene, ethane and water, and a 1.2 m cohunn filled with Zeolite Ca& (5 A) for separation of Hs, e l , NI, CH, and CO.

3023

Solid-pha~ polyoondommtion of polyhydrazides

The carrier gas was argon, the temperature of the Porapak C column was 80° and the Zeolite CaA (5 A) column 30°. The flow rates of the carrier gas were 30 and 40 ml/min respootively. DISCUSSION

I t is seen from Fig. 1 that compound I evolves water at 400 °. This could be caused either b y the presence, as an impurity, of dibenzoylhydrazine, which undergoes cyclodehydration at such temperatures, or b y removal of water from the solvated heterocyclic structure. A similar production of water occurs in pyrolysis of the model compounds I I I and V, and of the poly-l,3,4-oxadiazole IX. The water present evidently causes hydrolysis of the 1,3,4-oxadiazole ring, as is shown b y evolution of CO s at 450 °. The reactions involved can be represented as follows:

N ~I

\

N II ~

H,O ~

O

O

0

O II

~----

~H,o N NH8 -. Hi + 1qs

The probability of the occurrence .of hydrolytic decomposition of this t y p e lms been demonstrated in a study of the hydrolysis of poly-[2,5-(4',4"-diphenylphthMido)-l,3,4-oxadiazole] [10]. The authors of that paper.identified the polyhydrszide, 4',4"-dicarboxydiphenylphthalide and hydrazine. At temperatures above 500 ° the products of decomposition of compound I include N s and Hs, and above 550 ° CO and OH 4 are present. At 650 ° acetylene, ethylene and ethane are evolved, indicating breakdown of the benzene ring. I t m a y thus be considered that thermal degradation of 1,3,4-oxadiazole systems begins with hydrolytic scission, which is active in the temperature range of 400-550 °, then hemolytic breakdown processes predominate, which on the basis of our experimental results and of evidence in the literature [11-14] can be represented in the general form as follows: N

N

/

\=,~

Nz + CO +

-I-\_-_/

(2)

0

I t follows from what has been said above, however, that another possible source of nitrogen could be secondary hydrolytic decomposition reactions, e.g.

.

v~-.

,

1

~~ _ ~

iI~ I

. *,,.

I

,

i

,,

,.~

~_

~

~

~

~

~

~

~ n~

0

O

t~

~

~ - w om ~ ~, ~." * ~ "

O

%

•

%

I

I

I

I

I

I

I

I

I

I

I

I

I

i

I

I

I

I

I

I

I

I

I

I

t

I

_

~L~

~

~

1

~

G

I

I

N

I

~

~

~l.

t~

I

I

I

0

0

0

0

0

0

$0~

V . V . KORS~A~ e~ aZ.

hydrolysis of compound II + II

0

II ~

--Z

--

0 N2H4~ NH3--, N~+ H2 [i5]

It is seen from Fig. 2 that under the conditions' of hydrolysis of model

compound ]~hydrazine hydrate begins to decompose to N~ and H, at 200% Finally it is not impossible that N~ is evolved from compound II by the reaction O

0

N

± "-"

,1

N C--
\)-~

(4)

0 The pattern of thermal decomposition is quite different in the case of compound II. In the temperature range of 200-300 ° only water is evolved, which suggests that eyclodehydration occurs appreciably, especially at temperatures above the melting point (239-241°). Above 300 °, however, secondary reactions begin, with formation of COs, Nz and products of the type produced by reactions (1), (3) and (4). A~IO 5

3 ! 200

300

//O0

500 E°C

Fxo. 2. Evolution of nitrogen (1) and hydrogen (2) in pyrolysis of hydrazine hydrate; time of heating in argon at each temperature, 8 min, volume of sample 15/A. The possibility and extent of the occurrence of these reactions are dependent on competing factors~ The kinetics of cyclodehydration and hydrolytic decomposition of the hydrazide groups of dibenzoylhydrazine has already been discussed. Further rise in the pyrolysis temperature results in evolution of CO at 450 ° and the appearance of methane (550°), and ethane and ethylene (650°), the last two being products of decomposition of the benzene ring. This comparative study shows that compound II is considerably less heatresistant than compound I, and the weak, defective point is the hydrazide group, which gives rise to side reactions with the water that is formed. Comparison of the results of pyrolysis of compounds I I - V I shows that they

Sblid-phaBe polycondensation of polyhydrazides

3027

are similar to the results obtained with compounds I - I I . There is only s o m e shift in the temperatures at which the pyrolysis products begin to appear. We compared the shift in the vigorous evolution of water by the different hydrazide models with their melting points, and as a result concluded that thermal cyclodehydration of hydrazides to 1,3,4-oxadiazoles occurs appreciably only in the molten state. Compound

II

M.p., °C Temperature of onset of vigorous evolution of water, °C

239-241 250

IV

Vl

309-310 310

185-186 200

Moreover in the case of the bis-oxadiazole models I I I and V the vigorous evolution of gaseous pyrolysis products occurs at lower temperatures than from model compound I, probably because of decrease in the chemical inertness of the compounds as a result of the increase in molecular weight, as occurs in the series of linear phenylenes [6]. Since among the first materials chosen for study of solid-phase polycondensation were polyhydrazides containing lactone rings [3-5] it was of interest to determine the effect of the lactone ring on their thermal stability. More C02 is evolved b y model V than b y model III. This increased evolution of COs, which occurs at 320-450 °, though small, could be attributed to the presence of a lactone ring. This is in full agreement with the results on thermal degradation of poly-[2,5-(4',4"-diphenylenephthalido)-l,3,4-oxadiazole] obtained in reference [14], where it was concluded that the main source of CO~ is hydrolytic degradation of the 1,3,4-oxadiazole ring, and the 1,3,4-oxadiazole and lactone rings begin to decompose in roughly the same region of temperatures. Consequently the presence of the phthalide ring in a hydrazide chain cannot lead to artefacts in study of the kinetics of polycondensation up to temperatures of 400-425 ° . It is evident t h a t the role of the ]actone ring is exhibited in a different manner. Figure 1 shows t h a t the quantity of N2 produced b y pyrolysis of compound V at 500 ° is greater than the quantity obtained from compound VI, although for the model compounds I and II, and I I I and IV, which do not contain lactone rings the relationship is the other way. Evidently under conditions of heat treatment simultaneously with hydrolytic processes there can occur reactions of the lactone ring, similar to the reaction of 4 ' , 4 " - d i c a r b o x y d i p h e n y l p h t h a l i d e with N2H~.H~SO4 in polyphosphoric acid, reported in reference [7]. This side reaction, involving the ]actone ring, can be represented as follows 0 0 II II ~ _CNHNHC_.// \k

O

(~/\0 •

-C _ .~ NN,_CNHNHC /7---~ +H,O_ 0

0

3028

V . V . KORSHAK e$ al. N--N

0

_ . / x7 - - % --CII C--x Ir 7 - % - - - - C - - - - \~ , /--CNHNH~ ~- H 0 0 C _ O

(-(-.o

o

%..>'\c =/'o o o o o [I it - - - - . ~ II tl _CNHNHC_// \\__C_~// \'x,._CNHNHC--.// \X "/ / 6 ' H NHNC ~ ~"~II ~,.)\ / ~- ~, ~ - ~ / - - ; \ - - ~ =C/ - \ _ /~- ~ x C=o o o/\,d\

_~ C"

C"

o

-H sO -C6H~COOH N~N

,b

\\

C

C //

o-

\\ ----C -- --//

N --N

\x

d : \,,/ \ NNHC . .// . .\x,.. .c . (I \3 c Iii / II--x=/ ,,, ~ ,.

~/\c=o

o

~( \.(/~

",o

c-" /

">

--x=/

Thus this study of the thermal degradation of hydrazide and 1,3,4-oxadiazole models has shown that at temperatures below 400 ° the thermal cyclodehydration process is complicated neither by reactions of the lactone ring nor by hydrolytic decomposition of the 1,3,4-oxadiazole ring. The most vulnerable, defective sites in bringing about thermal polycyclodehydration are however the hydrazide fragments themselves. Hydrolytic breakdown of hydrazide fragments that have resisted cyclization under isothermal conditions at temperatures above 300 ° results in decomposition of such fragments according to reaction (1), with evolution of N2 and C02. It is seen from the results of pyrolysis of polyhydrazide VII and of polymers VIII and IX, with different degrees of cyclization, that as the latter is increased the quantities of water, COz and N2 evolved decrease and the temperatures at which they begin to appear become higher. Consequently on the basis of the present experimental evidence it may be concluded that in the investigation of the kinetics of solid-phase polycyclocondensation of aromatic polyhydrazides to poly-l,3,4-oxadiazoles reported in reference [4], the reaction is described fairly correctly up to ~ 350 °. Translated by E. O. PHILLIPS REFERENCES 1. M. M. KOTON, Vysokomol. soyed. ).13: 1348, 1971 (Translated in Polymer Sei. U.S.S.R. 13: 6, 1513, 1971) 2. L. E. KARDASH, A. Ya. ARDASHNIKOV, V. S. YAKUBOVICIt, C. I. BRAZ, A. Ya.

Aqueous dispersions of rigid chain polymers

3. 4. 5. 6.

7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

3029

YAKUBOVICH and A. N. PRAVEDNIKOV, Vysokomol. soyed. Ag: 1914, 1967 (Translated in Polymer Sci, U.S.S.R. 9: 9, 2160, 1967) V. V. KORSHAK, B. V. LOKSHIN, G. L. BERESTNEVA and I. P. BRAGINA, Vysokomol. soyed. A l l : 2077, 1969 (Translated in Polymer Sci. U.S.S.R, 11: 9, 2372, 1969) V. V. KORSHAK, G. L. BERESTNEVA and I. P. BRAGINA, Dold. Akad. Nauk SSSR 197: 597, 1971 V. V. KORSHAK, G. L. BERESTNEVA and I. P. BRAGINA, Vysokomol. soyed. A14: 1036, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 5, 1154, 1972) N. A. ADROVA, M. P. BESSONOV, L. A. LAIUS and A. P. RUDAKOV, Poliimldy--novyi klass termostoikikh polimerov (Polyimides--A New Class of Heat.Resistant Polymers). p. 45, Izd. "Nauka", 1968 V. V. KORSHAK, S. V. VINOGRADOVA and D. R. TUR, Izv. Akad Nauk SSSR, set. khim., 439, 1969 J. CURTISS, J. KOCH and C. BARTELLS, J. Am. Chem. Soc. 31: 420, 1909 R. STOLLE, J. prakt. Chem. 2: 157, 1904 V. V. KORSHAK, S. V. VINOGRADOVA, D. R. TUR and V. A. KHOMUTOV, Izv. Akad. Nauk SSSR, ser. khim., 2721, 1969 V. V. RODEp E. M. BONDARENK0, V. V. KORSHAK, Ye. S. KRONGAUZ and A. L. RUSANOV, ])old. Akad. Nauk SSSR 171: 355, 1966 V. V. RODE, Ye. M. BONDARENKO, V. V. KORSHAK, Ye. S. KONGRAUZ and A. L. RUSANOV, Dokl. Akad. Nauk SSSR 176: 1089, 1967 J. L. COTTER, G. J. KNIGHT and W. W. WRIGHT, J. Gas. Chromatog. 5: 86, 1967 V. V. RODE, Ye. M. BONDARENKO, V. V. KORSHAK, S. V. VINOGRADOVA and D. R. TUR, Izv. Akad Nauk SSSR, ser. khim., 1509, 1969 L. F. AUDRIETH and B. A. OGG, Khimiya gidrazina (Chemistry of Hydrazine). p. 84, Foreign Literature Publishing House, 1954 (R~ssian translation) V. V. KORSHAK, K. K. M0ZGOVA, D. G. BAL'KOVSKH and V. A. KHOMUTOV, Vysokomol. soyed. B13: 695, 1971 (Not translated in Polymer Sci. U.S.S.R.)

SOME PROBLEMS IN THE USE OF THE THERMOCHEMICAL METHOD FOR THE STUDY OF THE PROPERTIES OF AQUEOUS DISPERSIONS OF RIGID CHAIN POLYMERS* N. V. Mr~Au, ov (dec.) and I. M. ZAGRAYEVSKAYA Moscow Textile Institute

(Received 29 December 1971) In aqueous dispersions of polyurethane obtained by mechanical dispersion in the presence of surface active substances, and also in a system based on polyurethane and polyacrylonitrile obtained by mixing solutions of these polymers in dimethylformamide, adiabatic calorimetry has been used to establish the existence of a surface interaction between the components of the two systems, the reaction being indicated by deviation from additivity in the curves for certain thermodynamic characteristics (heat of solution-composition). * Vysokomol. soyed. A15: No. 12, 2669-2672, 1973.