Cyclopolymerization and Polymers with Chain-Ring Structures

21

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Thermally Stable Polyimides from Pyrrole Dicarboxylic Acid Anhydride Monomers R. W. STACKMAN Celanese Research Company, Summit, ΝJ 07091

Arylene-bis-(pyrrole dicarboxylic acid anhydrides) were prepared by the condensation of two moles of d i ethyl diacetyl succinate with one mole of aromatic diamine, followed by hydrolysis and dehydration. Condensation of these novel dianhydrides with various aromatic diamines resulted in the formation of poly (amic acids) which were further condensed to poly imides. If the diethyl diacetyl succinate and aromatic diamine were reacted in equimolar quantities an N-(amino aryl) pyrrole diester was formed which can be further condensed to give polyimide directly. The initially prepared poly (amic acids) lose water in the range of 150-230°C to form the polyimide which shows thermal stability up to 400°C. Heating of the N-(amino aryl) pyrrole diester monomer under vacuum at 200-250°C was found to be sufficient for conver sion to the polyimide. These pyrrole derivative monomers therefore are easily obtained from rela tively inexpensive starting materials and appear to offer promise of being an attractive route to ther mally stable polymers at reasonable cost. Aromatic polyimides possess outstanding thermal s t a b i l i t y as w e l l as being unusually high m e l t i n g , i n t r a c t a b l e and i n s o l u b l e (1). Polyimides are prepared e i t h e r by polyamide s a l t techniques, by condensation o f dianhydrides with d i isocyanates (2) o r by r e a c t i o n of an aromatic diamine with a dianhydride t o give a poly(amic a c i d ) followed by dehydration to give the polyimide. The polyimides from a v a r i e t y of d i amines have been reported and the dianhydride u n i t has been v a r i e d widely ( 1 ) . T h i s r e p o r t deals with polyimides prepared from n o v e l dianhydrides c o n t a i n i n g a b i s p y r r o l e s t r u c t u r e . Dicarboxy p y r r o l e s were f i r s t reported i n the l i t e r a t u r e many years ago (3). These compounds are prepared by the 0097-6156/82/0195-0273$06.00/0 © 1982 American Chemical Society

Butler and Kresta; Cyclopolymerization and Polymers with Chain-Ring Structures ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

274

POLYMERS WITH CHAIN-RING STRUCTURES

r e a c t i o n of e t h y l d i a c e t y l s u c c i n a t e with an amine i n g l a c i a l a c e t i c a c i d as shown by the f o l l o w i n g equation:

II II .. HO A r. HOAc C H 0-C-CH-ÇH-C-0-C H + RNH > H C-C C-CH II II 0 0 o

C

o

Q 3

c

0

I'll _ _ « C H-0C-C-C-C0C Ho

o

* J i l lj H B H3C-C

1

0

*

1 3

3

Ν

i By extending t h i s r e a c t i o n t o the use o f aromatic d i amines one can o b t a i n t e t r a c a r b o x y l i c a c i d s which may be subsequently converted t o the dianhydride by the f o l l o w i n g series of reactions: 0

C

o

c

CH Q,

3

3

H C ok=^ HOAc "5"2

II C H 0C-ÇH-CH-C-0C H +H N-R-NH 2**^ « 2 * 0C-C1 * v y \J C—CH 3 H 3C-0 o

CH

5

^ C - 0 C

2

H

2

5

o

5

0

u

0

0

0

N~R~N C-0C H 2

ck C H

NaOH

χ

HC1.

3

N-R-N

C H

3

5

3

? C-OH 0

9

I

i

II -C-OH CH

0

CH

0

s0

κ 0

The dianhydrides may then be r e a c t e d with aromatic diamines to g i v e a poly(amic a c i d ) which i s converted t o the p o l y imide .

(Τ

N-R-N, CH,

0+H N-R ' -NH„—> • -R ' -N-C 731V o

>

HOC-^/ II

Ο",


in OH

ϊ

STACKMAN

Thermally Stable Polyimides

275

One m o d i f i c a t i o n o f t h i s procedure has been t o react the e t h y l d i a c e t y l succinate with diamine on an equimolar b a s i s t o give an Ν(aminophenyl)pyrrole d i e s t e r which can then undergo f u r t h e r condensation t o give the polyimide directly. C H -(Lc-CH-CH-§-OC H 2

2

CH,-C 3 n

C>OL,

+H N-R-NH 2

2

Discussion Synthesis o f b i s ( p y r r o l e ) monomers. The condensation of e t h y l d i a c e t y l succinate with amines t o give d i a l k y l e s t e r s of Ν s u b s t i t u t e d p y r r o l e s proceeds i n near q u a n t i t a t i v e y i e l d s t o the b i s ( d i c a r b o e t h o x y dimethyl p y r r o l e ) . The c o n d i t i o n s f o r t h i s r e a c t i o n a r e the same as those used by e a r l i e r workers t o prepare mono dicarboxy p y r r o l e d e r i v a t i v e s 03-8). Upon c o o l i n g of the a c e t i c a c i d r e a c t i o n s o l u t i o n the product, b i s p y r r o l e d e r i v a t i v e , c r y s t a l l i z e s out and i s recovered i n s u f f i c i e n t p u r i t y t o be used without f u r t h e r p u r i f i c a t i o n . Attempts t o hydrolyze the b i s ( d i c a r boethoxy p y r r o l e ) d e r i v a t i v e s i n aqueous NaOH proved unsuccessful due t o the h i g h degree o f i n s o l u b i l i t y . I f , however, the h y d r o l y s i s was begun i n a l c o h o l i c media, the r e a c t i o n progressed q u i t e r a p i d l y to give the b i s ( d i carboxy p y r r o l e ) . Anhydride formation has been accomplished by r e f l u x i n g the t e t r a a c i d i n a c e t i c anhydride. Here again, the product i n high p u r i t y can be obtained merely by c o o l i n g the r e a c t i o n mixture. As can be seen from Table I , the y i e l d s o f the v a r i o u s b i s p y r r o l e monomers are a l l very h i g h , even though no e f f o r t s were made t o optimize the y i e l d s f o r these syntheses.


276

POLYMERS WITH CHAIN-RING

STRUCTURES

The m e l t i n g p o i n t s of some of the d e r i v a t i v e s are summarized i n Table I I . Other analyses performed on these samples (NMR, I n f r a r e d , Elemental Analyses) are a l l c o n s i s t e n t with the proposed s t r u c t u r e s . P o l y i m i d e s . The p r e p a r a t i o n of the polyimides proceeds through poly(amic a c i d ) i n t e r m e d i a t e s . The poly(amic a c i d ) can be i s o l a t e d p r o v i d i n g the temperature of the condensation i s p r o p e r l y c o n t r o l l e d . At 50°C the s t r u c t u r e formed i s almost e n t i r e l y poly(amic a c i d ) w h i l e at the s o l v e n t r e f l u x temperature almost 100% polyimide i s formed. The presence of the amic a c i d i s a l s o c l e a r l y shown by i n f r a r e d and TGA curves. F i g u r e 1 shows the weight l o s s of the amic a c i d s t r u c t u r e at 150-230°C. F i f t e e n percent of the weight of the sample i s l o s t during t h i s p e r i o d . T h i s l o s s appears t o be of two types, p o s s i b l y from s o l v e n t l o s s as w e l l as dehydration. Although q u a n t i t a t i v e estimates have not been made, i t appears as though i n c e r t a i n samples, a p o r t i o n of the weight l o s s corresponds to the t h e o r e t i c a l l o s s f o r water i n the c y c l i z a t i o n (5% f o r Sample 34b). DSC scans of the poly(amic a c i d ) show a broad endotherm at 160-175 C which probably corresponds with a r i n g c l o s u r e to the imide. A f t e r that p o i n t decomposition can be seen past 400 C. P r e p a r a t i o n of the polymer at a h i g h e r temperature (160 C) gives almost e x c l u s i v e l y p o l y i m i d e . The r e s u l t s of p o l y m e r i z a t i o n s u s i n g s e v e r a l dianhydrides and diamines are summarized i n Table I I I . Departure from the t h e o r e t i c a l carbon and hydrogen analyses (Table IV) f o r samples C and D probably i n d i c a t e s incomplete c y c l i z a t i o n of the imide s t r u c t u r e . No f r e e amic or c a r b o x y l i c a c i d f u n c t i o n a l i t y i s found i n the IR s p e c t r a of these samples. The TGA curves (Figures 2 & 3) show l i t t l e or no i n i t i a l weight l o s s up to 400 C. As i s common f o r aromatic polyimides these polymers are a l l brown to g o l d i n c o l o r and are s o l u b l e i n 97% H 2 S O 4 . Inherent v i s c o s i t i e s as shown i n Table IV are low, being l e s s than 0.5 d l / g . , i n d i c a t i n g low molecular weight. While f i l m s could be prepared from the poly(amic a c i d s ) , which were converted to polyimides on heat treatment (200-250 C f o r s e v e r a l h o u r s ) , they were very b r i t t l e and broke on h a n d l i n g . T h i s i s not s u r p r i s i n g i n view of the low inherent v i s c o s i t y (- (0.01)

80%

96%

87%

0.175

-—- (0.08)

93%

94%

95%

0.10

82%

100%

98%

0.10

- < ( ^ o - ( Ô ) - (0.05)

--

(0.05)

92%

100%

70.2%

0.10

(0.05)

95%

98%

95%

0.10

- < Ô > — S0 -(0.05)

87%

95%

98%

2

TABLE I I PROPERTIES OF PYRROLE DERIVATIVES

i»3 0

X

CH„

c-x R

Ν CH

ESTER 140-143

0

-C-X u 0

X (MPT)°C ACID 225-230(DECO) 220-225 DECO

-0r

ANHYDRIDE

194-204 MELT/I DECOMP

210(230 DECO) 84-85^

-270 (DECO)

-310°(DECO)


Figure 1. Thermogravimetric analysis of typical polyamic acid.

ATMOSPHERE-AIR

e

HEATING RATE 30 C/MIN.

to 00 Butler and Kresta; Cyclopolymerization and Polymers with Chain-Ring Structures ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

21.

279

Thermally Stable Polyimides

STACKMAN

T A B L E PREPARATION

Ο

Χ

σ

E X N O .

I I I O F

C H

3

C H

C H

3

C H

R

=

R

POLYIMIDES

β

3

0

3

SOLVENT

1

A

N , N -

T E M P . , ° C

CONV.,%

160

89

150

96

130

98

130

87

DIMETHYL ACETAMIDE Β

DIMETHYL FORMAMIDE

C

N , N DIMETHYL ACETAMIDE

D

N , N DIMETHYL ACETAMIDE

r— TABLE I V PROPERTIES Polyimide

Analysis Analysis ( 5 % Wt. Loss )

OF POLYIMIDES Composition Calculated

Ex No,

I.V. dl/g

A

0.29

470°C

76. 4

4.5

Β

0.38

455

63. 4

C

0.48

440

D

0. 38

420

a

0.1%

a

Cone,

of Polyimides Found

Ν

Ç

H

8.93

76.5

5.72

8.87

3.7

7.41

62.8

4.1

7.23

72. 7

4.3

8.48

68

4.35

8.05

70. 5

4.2

11.58

67.7

5.42

C

Η

Ν

10.4

i n 99% I^SO^


Figure 2. Thermogravimetric analysis of polyimides, heating rate 30°C/min.

W ce

Ο H

§

H

ce

ο

5

1

Ο

ï

S

H

2§

w *»

ce

*

Cyclopolymerization and Polymers with Chain-Ring Structures

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