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New Industrial Polymers Downloaded from pubs.acs.org by UNIV OF CALIFORNIA SANTA BARBARA on 09/12/18. For personal use only.
Polyaminobismaleimides M . A. J.
MALLET
Rhone-Poulenc, Paris, France F. P.
DARMORY
Rhodia Inc., New York, Ν. Y.
1.
Introduction
Polyimide resins constitute a family of plastics p o s s e s s e d o f d r a m a t i c a l l y s u p e r i o r p r o p e r t i e s when compared t o more c o n v e n t i o n a l plastics. Of particular importance is their ability t o m a i n t a i n u s e f u l me c h a n i c a l properties after extreme t h e r m a l exposures for p r o l o n g e d p e r i o d s o f t i m e . The g e n e s i s o f this attribute is t w o - f o l d -—the h i g h l y a r o m a t i c n a t u r e o f t h e polymer backbone, which c o n f e r s t h e h e a t stability, and t h e imide moiety, which i m p a r t s stiffness t o the macromolecular c h a i n . The facile o x i d a t i o n a t ele v a t e d temperature o f aliphatic polymer systems and t h e n e c e s s i t y for f u s e d r i n g s t o a c h i e v e h i g h r e s i n glass transition temperatures and concomitant e l e v a t e d temperature polymer m e c h a n i c a l s a r e w e l l r e c o g n i z e d and amply documented. Two f u n d a m e n t a l l y different approaches t o t h e m o l e c u l a r a r c h i t e c t u r e o f p o l y i m i d e s can be employed: The historically-first s y n t h e t i c method c o n s i s t s in c o n s t r u c t i n g tractable, h i g h m o l e c u l a r weight p r e c u r s o r s , called p o l y a m i c a c i d s , which a r e i m i d i z e d d u r i n g t h e c u r e c y c l e , w i t h l o s s o f water, t o t h e intractable, insoluble, infusible condensation polyimides. - The more r e c e n t s y n t h e t i c r o u t e p r e i m i d i z e s s h o r t m o l e c u l a r segments, similar i n n a t u r e t o t h o s e o f c o n d e n s a t i o n p o l y i m i d e s . Cure is by p o l y m e r i z a t i o n
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o f t h e r e a c t i v e t e r m i n i o f t h e "prepolymers" w i t h o u t loss of volatiles. These a r e t h e a d d i t i o n p o l y i m i d e s . W h i l e c o n d e n s a t i o n p o l y i m i d e s a f f o r d t h e most heat s t a b l e polymers, they a r e g e n e r a l l y d i f f i c u l t and e x p e n s i v e t o p r o c e s s and a f f o r d v o i d y p a r t s . Epitomical o f the heat r e s i s t a n c e p r o p e r t i e s o f c o n d e n s a t i o n p o l y i m i d e s a r e t h e 20,000+ and 9,000 h o u r s e r v i c e l i v e s o f NOLIMID A380 a d h e s i v e f o r t i t a n i u m bonds a t t e m p e r a t u r e s o f 500° and 575°F, respectively. By c o n t r a s t , a d d i t i o n p o l y i m i d e s a l l o w t h e r e p r o d u c i b l e and f a c i l e p r e p a r a t i o n o f l a r g e and v o i d - f r e e p a r t s a t o n l y a modest s a c r i f i c e i n end a r t i c l e thermal s t a b i l i t y . Polyamino-bismaleimides (PABM's) a r e members o f t h e a d d i t i v e p o l y i m i d e c l a s s of resins. 2.
Polvaminobismaleimide Chemistry
M u l t i t u d e s o f r e s e a r c h e r s have i n v e s t i g a t e d t h e h i g h r e a c t i v i t y o f t h e a c t i v a t e d d o u b l e bonds o f b i s m a l e i m i d e s , as shown below.
M a l e i m i d e d o u b l e bonds can r e a c t b y e i t h e r homolytic or h e t e r o l y t i c s c i s s i o n . I n t h e former c a s e , h o m o p o l y m e r i z a t i o n w i t h a second maleimide group i s observed? i n t h e l a t t e r event, n u c l e o p h i l i c addition i s possible.
NEW
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I r r a d i a t i o n at 240°C, and at reduced pressure, o f 1,4-dimaleimidobenzene affords 50% y i e l d s o f polybismaleimides, which remain unaffected by temperatures as high as 600°C (Ivanov? Russian Patent #164,678). S i m i l a r l y , heating o f 4,4 -dimaleimidodiphenylmethane affords polymers which are heat stable to 460°C. These i n f u s i b l e and i n t r a c t a b l e products s u f f e r from extreme b r i t t l e n e s s , which severely r e s t r i c t s t h e i r p r a c t i c a l u t i l i t y (Sambeth & Grundschober; French Patent #1,455,514). Working i n the area o f elastomers, Kovacic (U. S. Patent #2,818,407? Dec. 31, 1957) reported the Michael addition o f amine capped prepolymers to b i s maleimides. S i m i l a r l y , Sheremeteva and co-workers found that r e a c t i o n o f stoichiometric amounts of b i s maleimides and primary aromatic diamines i n r e f l u x i n g ethanol afforded polymers, which thermally degraded so r a p i d l y that they could not be considered heat resistant. Recent work i n Rhone-Poulenc* s laboratories, summarized i n U. S. Patent #3,562,223 (July 13, 1967), has shown that by j u d i c i o u s s e l e c t i o n o f a b i s maleimide t o aromatic diamine r a t i o between these two r e a c t i o n extremes, i t has proven p o s s i b l e to develop a c l a s s o f polyimide r e s i n s with outstanding physicals and c o n t r o l l e d c r o s s l i n k density. (Figure 1). While side-reactions o f the primary aromatic amine with the maleimide moiety were to be feared, none are i n f a c t observed. Thus, N-butylamine amminolyzes succinimides r e a d i l y i n a modification of the time-honored (1887) Gabriel synthesis o f amino acids? by contrast, a n i l i n e does not react with succinimides, even i n hot DMF. This contrast i n behavior between primary a l i p h a t i c and aromatic amines i s ascribàble to t h e i r v a s t l y d i f f e r e n t b a s i c i t i e s (pK^'s of 3.3 and 9.3, r e s p e c t i v e l y ) . F i n a l l y , maleimides are t r a d i t i o n a l l y prepared by a two-step synthesis (e. g. Searle? U. S. Patent #2,444,536? May 14, 1946). Reaction o f maleic anhydride with an amine at room temperature, i n e i t h e r NMP, DMF or acetone, affords the intermediate maleamic acid, which i s then cyclodehydrated by a c e t i c anhydride at 60°C i n DMF. ,
9.
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c© m x
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3.
Polvaminobismaleimide P r o p e r t i e s
The t h e r m a l r e s i s t a n c e o f p o l y a m i n o b i s m a l e i m i d e s may b e e v a l u a t e d b y t h r e e c r i t e r i a — thermogravim e t r i c a n a l y s i s , t h e r m o p h y s i c a l p r o f i l e , and thermooxidative r e s i s t a n c e . 3.1 Thermocrravimetric A n a l y s i s . F i g u r e 2 shows t h e TGA c u r v e s o b t a i n e d f o r PABM s d e r i v e d from m e t h y l e n e d i a n i l i n e and o x y d i a n i l i n e under a i r and n i t r o g e n atmospheres. I n b o t h c a s e s , scan r a t e s o f 20°F/min were employed. These c u r v e s r e v e a l t h a t : 1
t h e TGA main b r e a k p o i n t , under e i t h e r a i r o r n i t r o g e n , i s 360°C f o r MDA-derived PABM s and 290°C f o r ODA-derived PABM s? u n t i l 500°C, c u r v e s o b t a i n e d i n a i r and n i t r o g e n are i d e n t i c a l ; c h a r y i e l d i s c a . 4 7 % f o r b o t h PABM systems. 1
1
The c o n c l u s i o n t o b e drawn from t h i s i n f o r m a t i o n i s t h a t ODA o r MDA b a s e d PABM s behave almost i d e n t i c a l l y on t h e r m a l exposure. This i s not t o t a l l y unexpected, a s t h e dominant f a c t o r , o r a l t e r n a t i v e l y t h e weak l i n k , i n o x i d a t i v e d e g r a t i o n o f t h e s e 1
9.
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Polyaminobismaleimides
M A L L E T AND DARMORY
polymers i s t h e a l i p h a t i c prepolymer t e r m i n i , are i d e n t i c a l f o r b o t h r e s i n s .
which
3.2 T h e r m o p h y s i c a l P r o f i l e . T y p i c a l 181 E - g l a s s (A-1100 f i n i s h ) PABM l a m i n a t e m e c h a n i c a l s a r e shown i n T a b l e I . Room temperature f l e x u r a l s t r e n g t h and modulus a r e 70,000 p s i and 4,000,000 p s i , r e s p e c t i v e l y . These l a m i n a t e s r e t a i n 70% and 80%, r e s p e c t i v e l y o f t h e i r room temperature f l e x u r a l s t r e n g t h and modulus at 480°P. To a l l o w a more m e a n i n g f u l comparison o f PABM* s w i t h c o m p e t i t i v e r e s i n systems, t y p i c a l room temper a t u r e , 400°F, and 480°F l a m i n a t e f l e x u r a l s t r e n g t h s are t a b u l a t e d below. Percentage f i g u r e s i n parent h e s i s r e p r e s e n t t h e r e t e n t i o n o f room temperature properties. F l e x u r a l Strength a t :
PABM EPOXY NOVOLAC EPOXY SILICONE
R.T.
400OF
480°F
70 70 80 37
60 32 20 20
50 20 15 18
KSI KSI KSI KSI
KSI (85%) KSI (45%) KSI (25%) KSI (55%)
KSI (70%) KSI (30%) KSI (20%) KSI (50%)
3.3 T h e r m o o x i d a t i v e S t a b i l i t y . F i g u r e s 3-6 d e t a i l t h e r e t e n t i o n o f PABM l a m i n a t e (A-1100 f i n i s h ) f l e x u r a l s t r e n g t h and modulus a f t e r extended a g i n g p e r i o d s a t temperature v a r y i n g from 355° t o 480°F. 85% o f i n i t i a l f l e x u r a l s t r e n g t h ( e i t h e r room o r e l e v a t e d temperature) i s m a i n t a i n e d a f t e r 10,000 h o u r s o f a g i n g a t 355°F. U s i n g as l a m i n a t e h a l f - l i f e c r i t e r i o n , 50% r e t e n t i o n o f i n i t i a l f l e x u r a l s t r e n g t h , the f o l l o w i n g v a l u e s a r e o b t a i n e d f o r PABM s : 1
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10,000 h o u r s a t 400°F? and 4,000 h o u r s a t 480°F (CS-290 f i n i s h ) . Comparable 480°F h a l f - l i f e v a l u e s a r e : 2,000 h o u r s f o r F r e i d e l - C r a f t s p h e n o l i c r e s i n s ( s o u r c e : A l b r i g h t and W i l s o n ) ? and 250 h o u r s f o r u n m o d i f i e d p h e n o l i c r e s i n s .
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TABLE I .
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ΡABM/181 Ε-Glass Laminate P h y s i c a l s
POLYMERS
MALLET
A N D DARMORY
Polyaminobismaleimides
Figure 3. Changes in flexural strength during thermal aging at 355°, 390°, and 430°F (180°, 200°, and 220°C)
Figure 4. Changes in flexural strength during thermal aging at 355°, 390°, and 430°F (180°, 200°, and 220°C)
N E WINDUSTRIAL
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Figure 5.
Figure 6.
Changes in flexural strength during thermal aging at 480°F (250°C)
Changes in flexural modulus during thermal aging at 480°F (250°C)
POLYMERS
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MALLET
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AND DARMORY
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Polyaminobismaleimide P r o c e s s i n g
Commercial v a r i a n t s o f p o l y a m i n o b i s m a l e i m i d e r e s i n s have been f o r m u l a t e d t o p r o c e s s s i m i l a r l y t o c o n v e n t i o n a l p h e n o l i c s , e p o x i e s , and p o l y e s t e r s . C o n s t i t u e n t monomers o f t h e f o r m u l a t i o n a r e B-staged t o a degree o f advancement such t h a t c l a s s i c a l r h e o l o g i c a l s t u d i e s on PABM s y i e l d Brabender P l a s t i c o r d e r c u r v e s whose shape i s r e m i n i s c e n t o f t h o s e of phenolics. To f u r t h e r q u a n t i f y t h e s e statements, l e t us n o t e t h a t PABM s have m e l t i n g p o i n t s o f 100-120°C and g e l t i m e s which a r e v e r y temperature dependent. Viscosity i n c r e a s e s from 100 t o 10,000 p o i s e s i n 30 min. a t 150°C and i n 5 min. a t 170°C! In p r a c t i c e , p o l y a m i n o b i s m a l e i m i d e p a r t s a r e p r o c e s s e d on c o n v e n t i o n a l thermoset t r a n s f o r m a t i o n equipment (compression, t r a n s f e r , and i n j e c t i o n molding) a t 350-400°F, i n 5-20 minute c y c l e s , and a t 3,000-15,000 p s i . 1
1
5.
Summary
The p o l y a m i n o b i s m a l e i m i d e r e s i n s we have reviewed e x h i b i t many i n t e r e s t i n g a t t r i b u t e s . these are t h e i r : -
-
Among
r h e o l o g y , comparable t o t h a t o f c l a s s i c a l thermosetting resins? m o l d a b i l i t y a t modest temperatures, i n c o n v e n t i o n a l p r e s s e s , and a t low c o s t ? mechanical p r o p e r t i e s , superior t o those o f s e v e r a l m e t a l s on a w e i g h t b a s i s ? e x c e l l e n t dimensional s t a b i l i t y ? f i r e , r a d i a t i o n , c r y o g e n i c temperature, and s o l v e n t resistance? u t i l i t y i n e l e c t r i c a l , f r i c t i o n , and a b l a t i v e applications.
Taken as a whole, t h e s e f a c t o r s suggest t h a t PABM's w i l l f i l l many 500°P a p p l i c a t i o n s i n t h e a i r c r a f t , a i r compressor, aerospace, automotive, b e a r i n g s , e l e c t r o n i c , e l e c t r i c a l , and n u c l e a r i n d u s t r i e s .
