Aromatic polypyromellitimides based on aromatic diamines with phthalide or phthalimidine side groups

AROMATIC POLYPYROMELLITIMIDES BASED ON AROMATIC DIAMINES WITH PHTHALIDE OR PHTHALIMIDINE SIDE GROUPS * S. V. VI~OGRADOVA, V. V. KORSHXK and Yx. S. VYGODSKII

Institute of Hetero-orga~ic Compounds, U.S.S.R. Academy of Sciences (Received 14 April 1965) POLYPYROM~LLITI~DV,S are probably the most prominent among the various classes of new, heat-resistant polymers obtained by means of the polyeyelization reaction [1, 2]. The polypyromcllitimides have distinctive properties such as high heat resistance and thermal stability, excellent dielectrical properties, which are maintained over a wide range of temperatures, high radiation resistance etc. [3, 4]. The polypyromellitimides described in the literature have been synthesized from aromatic diamines of the type:

H2N~ N H 2

H 2 N ~ R _ _ ~

NH2

where R-~ --,O,S, CH2 or C(CH8)2. We felt that for the synthesis of polypyromellitimides it would be interesting to use other aromatic diamines that would provide the possibility of modification of the polymers, in particular to obtain soluble aromatic polyimides and to impart additional reactivity to them. We selected 3,3-bis-(4-aminophenyl)phthalide (I) and 3,3-bis-(4-aminophenyl)phthalimidine (the imide of anilinephthalein) (II) as the starting diamines:

H2N

NH2

H2N

~ (I)

NH2

[01 (Ill

* Vysokomol. soyed. 8: No. 5, 809-814, 1966. 888

Aromatic polypyromellitimides

889

This choice was based on the fact t h a t synthesis of polyarylates based on bisphenols with similar substituents on the central carbon atom, for example phenolphthalein and its derivatives, has produced polyarylates possessing a valuable combination of physicomechanical properties [6, 7]. DISCUSSION

It is well known t h a t the conditions under which a polycondensation is carried out and the ratio of the reactants have an important bearing on the successful accomplishment of the process. I n order to find the effect of these factors on the synthesis of polypyromellitimides from I and I I we studied the first stage of the reaction of these diamines with pyromellitic anhydride] (PMA) in dimethyl formamide and dimethylaeetamide, with different ratios of the reactants and for different reaction times. The polycondensation was carried out in an Ubbelohde

tokes

76

,

7

,

3

I

,

I

5~120 80

I

100

Time,hn FIG. 1.

Variation in viscosity of the solution during reaction of I with PMA in dimethylacetamidc at a concentration of 12.4°/o.

viscometer at 25 °. The course of the reaction was followed by means of the change in viscosity of the solution. I t was found t h a t the highest viscosity was attained with the reactants in equimolar proportions. With increase in reaction time the viscosity of the solution increased up to a certain limit and then began to fall. I t is seen from Figure 1 t h a t when I is reacted with PMA in dimethylacetamide t h e viscosity of the solution, and hence the molecular weight of the polymer, reaches a maximum after reaction for 5 hours at 25°C. Further increase in the reaction time results in a marked fall in the viscosity of the system. A similar effect was found when the reaction was carried out in dimethylformamide. Whereas the maximal logarithmic viscosity number in this case was 1.7 dl/g after a reaction time of 5 hours,

890

S. V, VINOGRADOVA et al.

after 192 hours it had decreased to 0.8 dl/g. It should be noted however that in general the nature of these solvents had no marked effect on the reaction rate. Thus when I was reacted with PMA at 25 ° in dimethylacetamide, dimethylformamide and dimethylsulphoxide at the same concentration (12.4%) the maximal viscosity was reached in ~ 5 hours. The maximal logarithmic viscosity numbers for the polyamidoacid from I in dimethylformamide, dimethylacetamide and dimethylsulphoxide were 1.7, 1.9 and 1.2 dl/g respectively, and for the polyamidoacid from I I in the same solvents 1.50, 1.60 and 0.87 dJ/g respectively. Bower and Frost [2] and Frost and Kesse [5] have also observed a decrease in the viscosity of polyamidoacids at a certain stage in the reaction, in reactions between PMA and aromatic diamines of the type of (4-aminophenyl)methane. This is evidently due to degradative hydrolysis, similar to the hydrolysis of phthalamic acid, where hydrolysis of the amide bonds is accelerated m a n y times by the catalytic effect of the earboxyl groups in the ortho-position [8]. We also observed considerable reduction in molecular weight in attempts to obtain the polymers in powder form b y precipitating them from solution in the above solvents with absolute benzene, ether or dioxan. In these circumstances the logarithmic viscosity number fell from 1.7-1.9 to 0.4-0.6 dl/g. It is evident t h a t during the process of separation, washing and drying of the polymers in vacuo, which normally takes 1-2 days, hydrolysis brings about considerable degradation of the polymers. We obtained films of the polyamidoacids from I and I I with PMA from solution in dimethylformamide and dimethylacetamide, in vacuo, on a glass substrate. These were readily soluble in dimethylformamide, dimethylacetamide and dimethylsulphoxide, and in mixtures of these solvents with chloroform, tetrahydrofuran, dioxan, benzene and other chlorinated or aromatic solvents.

450

500

550

roe

FIG. 2. Thermogravimetric analysis of polypyromellitimide II. Rate of increase in temperature 300 degrees/hour, pressure 5 × 10-3 ram. The process of cyclization of films based on the aromatic polyamidoacids presents certain difficulties with respect to finding a suitable relationship between the temperature of cyclization, the time of cyclization and film thickness, because of degradative hydrolysis due to moisture in the environment and the

Aromatic polypyromellitimides

891

water liberated during cyclization. The polyamidoacids based on I and I I undergo cyclization fairly well i n vacuo at 120 °, and at 200 ° at a residual pressure of less than 1 mm eyclization is complete in 3 hours. The infrared spectra of specimens of the polymers heated in this way showed the complete absence of the bands characteristic of the COOH-group (1720 cm -1) and > N H - g r o u p (3300, 1680 and 1540 cm -1) of the polyamidoacid, and the appearance of strong bands of the imide group in the 1710 and 1760 cm -1 regions. Our polyimides based on I and II, which contain very large side substituents, remain soluble in solvents such as dimethylformamide, dimethylacetamide and dimethylsulphoxide even at room temperature, in contrast to previously described polypyromellitimides, which are insoluble in organic solvents. The logarithmic viscosity number of polypyromellitimides I and II in dimethylformamide was about 0.4 dl/g. The lower value for the polyimides in comparison with the uncyclized polymers is probably associated firstly with the considerable change in structure of the polymers in passing from the polyamidoacid to the polyimide and the absence of association of the latter with the solvent, and secondly with the possibility of hydrolysis of the polyamidoacid during the cyclization process. We have also cyclized the polyamidoacids based on the above diamincs b y a chemical method, b y means of a mixture of acetic anhydride and pyridine (1: 1). For this purpose the original films were immersed in this mixture for 24 hours and were then rapidly heated (for 1 minute) at 300 ° at a residual pressure of less than 1 ram. The polypyromellitimides based on I and I I have a particularly high heat resistance. Thermogravimetric analysis of these (the rate of increase in temperature for plotting the thermograms was 300°/hour at a residual pressure of 5X 10-3 mm) showed that these polymers do not lose weight up to 450 °. Figure 2 shows a thermogravimetric curve of the polyimide based on II as an example. These polyimides do not melt up to 500 °, and judging b y the thermomechanical curve t h e y do not undergo deformation up to 500 ° (the load on the specimen for plotting the thermomechanical curve was 0.8 kg/cm~). Treatment of aluminium test panels with solutions of the polyamidoacids based on these diamines, with subsequent heat treatment to bring about cyclization gives this coatings with good adhesion to aluminium, which do not break down on prolonged immersion in water. Both the original diamines and the polyamidoacids derived from them are more resistant to the action of light and atmospheric oxygen than diamines such as m- and p-phenylenediamine, benzidine or 4,4'-diaminodiphenyl oxide. For example, the properties of anilinephthalein do not alter on prolonged storage, and a solution of the polyamidoaeid based on this remains almost colourless after several months' storage at room temperature, whereas a solution of the polyamidoacid based on 4,4'-diaminodiphenyl ether, with an excess of the aliamine, darkens after standing for only 400 hours.

892

S. V. Vr~oGRADOVA et al. EXPERIMENTAL

The starting materials I and I I were synthesized by the method of Schwarzenbach a n d Brandenberger [9], according to the scheme: COC1

CC12

COC1

C

H

O C

C

HCI ~

NH, NH, J /

O0 \c / /

NH8

NNH,NH,

O0 \c / ~/N /

C

II

0

C

H

0

o-Phthalyl chloride was prepared b y the method described in. reference [10]. The product was purified b y redistillation at 146-147°/14 m m (reference [10] gives b.p. 131133°/9-10 mm). For the next stage 500 ml of freshly distilled nitrobenzene a n d 100 g of hathydrous A1C1a were placed in a 2 1. flask, the mixture was cooled to 25 ° and 40.6 g of o-phthalyl chloride and 42.48 g of dried, freely dispersed sym-diphenylurea were added. The temperature was raised to 80 ° over the next two hours a n d held at this level for a further 2.5-3 hours. The mixture was then cooled, a mixture of ice a n d hydrochloric acid was added and the nitrobenzene was removed by steam distillation. After removal of the nitrobenzene the residue was ground and again treated b y steam distillation. After the second steam distillation the yield of the product was 60-68 g. For synthesis of I the above product was hydrolyzed with concentrated hydrochloric acid (25 ml of hydrochloric acid to 10 g of product) at 140 ° for 4 hours, in ampoules. The hydrolyzed product was filtered, a n d in order to liberate the diamine aqueous ammonia was added to the filtrate. The precipitated diamine was faltered off and recrystallized several times from ethanol (in the calculated proportion of 50 ml of alcohol to 1 g of diamine). The yield of I was 32% of theory, m.p. 204 ° (reference [11] gives m.p. 202.5-203.2°). For synthesis of I I the product of condensation of o-phthalyl chloride with 8ym-diphenylurea was hydrolyzed with 25% ammonia in an autoclave at 130 ° for 4 hours. Product I I precipitated in the form of large, yellow crystals. These were filtered off and recrystallized several times from ethanol, and dried in vacuo at 120 °. The yield of I I was 30% of theory. Found, %: C 76.01; 75.87; I-I C20HxTlkTaO. Calculated, %: C 76.19; I-I

5.62; 5.40;

5.58; 1~ 13.03; 12.81. N 13.33

Aromatic polypyromellitimides

893

Infrared spectroscopic analysis (Fig. 3) showed that only the groups characteristic of I I are present in the product. The melting point of the imide of a:~ilinephthalein was 243244 °, no increase in melting point having been obtained as a result of the last recrystallization. The melting point found b y us for I I is not in agreement with the published melting point [9], which is given as 313 ° .

I

I

I

i

I

I

I

I

1

I

I

I

I

I

I

'

I

I

1

Vp Cr~-1

FZG. 3. Infrared absorption spectrum of II. Pyromellitic dianhydride was purified by sublimation through silica gel at 225-240 ° a n d a residual pressure less t h a n 1 mm. The sublimed PMA melted at 286-287 ° in agreement with the published melting point (286-287 ° [12]). The solvents, N,N-dimethylacetamide and N,N-dimethylformamide, used for syathesis of the polyamides, were dried over phosphorus pentoxide a n d redistilled in vacuo. The boiling point of the N,N-dimethylformamide was 42.5°/17 mm, an(]. of the N,N-dimethylacetamide 58°/13 m m (water content, 0.03-0.05%). Dimethylsulphoxide was refluxed over calcium hydride and redistilled at 59.2°/4 ram. Preparation of polymers. The polymers were made in a Ubbelohde viscometer with a capillary diameter of 2.0--2.2 mm, calibrated with glycerol at 25 °. The viscometer was charged with 0.0025 mole of the diamine and 10 ml of solvent. After solution of the diamine 0.0025 mole of PMA was added, either in portions or in one addition. The PMA dissolved in a few minutes, with vigorous agitation. The reaction was carried out at 25 ° and the viscosity of the solution was measured at chosen intervals of time. After a t t a i n m e n t of the maximal viscosity the solution was diluted to a concentration of 5-10~o and used for production of films by pouring on to a glass test panel. Films of thickness N 30-60 p were obtained at room temperature in vacuo ( ~ 1 ram). For determination of the logarithmic viscosity n u m b e r of the polymers during the course of the reaction test samples of the solution were removed and diluted to a concentration of 0.5 g/dl. The viscosity was determined at 25 °. I n c o n c l u s i o n we e x p r e s s o u r g r a t i t u d e t o B. V. L o k s h i n for r e c o r d i n g t h e i n f r a r e d s p e c t r a o f t h e p o l y i m i d e s , a n d t o V. S. 1 ) o p k o v for t h e t h e r m o g r a v i metric analyses of the polymers. CONCLUSIONS (1) P o l y a m i d o a c i d s a n d p o l y i m i d e s b a s e d o n p y r o m e l l i t i c d i a n h y d r i d e w i t h 3 , 3 - b i s - ( 4 - a m i n o p h e n y l ) p h t h a l i d e a n d 3 , 3 - b i s - ( 4 - a m i n o p h e n y l ) p h t h a l i m i d i n eh a v e been synthesized. (2) I t w a s f o u n d t h a t p o l y a m i d o a c i d s o f h i g h e s t m o l e c u l a r w e i g h t are o b t a i n e d w h e n the r e a c t a n t s are p r esen t in e q u i m o l a r proportions.

894

L . P . K R x e r v ~ A et al.

(3) The polyamidoacids from the above diamines can be cyclized by heat treatment i n vacuo at temperatures above 120 °. (4) The presence of phthalide or phthalimidine side groups in the polymer molecules results in the production of soluble aromatic polyimides. Translated by E. O. P~ILL~2S REFERENCES 1. 2. 3. 4. 5. 6.

7. 8. 9. 10. 11. 12.

B. P. 903271, 1962; B. P. 903272, 1962 G. M. BOWER and L. W. FROST, J. Polymer Sci. AI: 3135, 1963 Z. AMBORSKI, Ind. Engng. Chem., Product Research and Development 2: 189, 1963 N. W. TODD, Rubber and Plastics Age 45: 1026, 1964 L. W. FROST and J. KESSE, J. Appl. Polymer Sci. 8: 1039, 1964 V. V. KORSHAK, S. V. VINOGRADOVA a n d S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 S. V. VINOGRADOVA, V. v . KORSHAK, S. N. SALAZKIN and S. V. BEREZA, Vysokomol. soyed. 6: 1403, 1964 M. L. BENDER, Y. L. CHOW and F. CHLOUPEK, J. Amer Chem. Soe. 80: 5380, 1958 G. SCHWARZENBACH and M. BRANDENBERGER, ttelv, chim. acta 20: 1253, 1937 Organic Syntheses, Vol. XV, p. 83, J o h n Wiley and Sons, Inc., 1931 M. H. HUBACHER, J. Amer. Chem. Soe. 73: 5885, 1951 W. UTERMARK and W. SCHICKE, Schmelzpunkttabellen orgamscher Verbindungen, Akademie-Verlag, Berlin, 1963

DETERMINATION OF THE TRANSITION TEMPERATURES OF POWDERED POLYMERS BY THE POWDER THERMOMECHANICAL METHOD * L. P. KRAPIVI~A, S. A. ARZEXKOV and I. N. I~xzn~sKAYA Dzerzhinsk Institute of Chloro-organie Products and Acrylates

(Received 14 April 1965)

TEE thermomechanical method suggested by Kargin and Sogolova [1] has become widely used for the study of polymers. For recording thermomechanical curves it is usual to use monolithic specimens obtained from a block of polymer or by compression moulding from a powder. We have shown previously [2] that the physicochemical processes occurring during compression moulding of specimens from a powder can substantially alter the transition temperatures determined by the thermomechanical method. At the present time many polymers are produced in the form of powders, hence the necessity has arisen of determining transition temperatures directly * Vysokomol. soyed. 8: No. 5, 815-820, 1966.