Copolymers, Polyblends, and Composites

39 Phthalonitrile Resins

Downloaded by UNIV MASSACHUSETTS AMHERST on October 1, 2012 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/ba-1975-0142.ch039

JAMES R. G R I F F I T H , JACQUES G. O'REAR, and T H E O D O R E R. W A L T O N Naval Research Laboratory, Washington, D . C. 20375

A series of aliphatic diamides with chain lengths of 4-18 carbon atoms terminated with ortho-phthalonitrile units on the amide nitrogen atoms was synthesized. Melting points of the pure compounds were determined. At temperatures above the melting points, these compounds are resinous liquids of moderate viscosity which are similar in appearance and reaction behavior to liquid epoxy resins. At about 170°C, the liquids react to form intensely green, polymeric products which are believed to be poly(phthalocyanines). These polymerized products have useful mechanical properties similar to those of cured epoxy resins, and they are thermally stable well above 200°C.

E

ver since L i n s t e a d a n d co-workers i n v e s t i g a t e d p h t h a l o c y a n i n e s i n t h e 1930's ( 1 ) , there has b e e n some interest i n t h e reaction o f a r o m a t i c o r t h o - d i n i t r i l e s for p o l y m e r i z a t i o n . M a r v e l a n d Rassweiler (2) a n d M a r v e l a n d M a r t i n (3) s t u d i e d the possibilities of p r o d u c i n g h i g h m o l e c u l a r w e i g h t p h t h a l o c y a n i n e s f r o m t e t r a n i t r i l e s s u c h as 3 , 3 ' , 4 , 4 ' - t e t r a c y a n o d i p h e n y l e t h e r . T h e p h t h a l o cyanine f o r m a t i o n apparently progressed to a l i m i t e d extent, a n d a metal-free d e r i v a t i v e w a s f o u n d w h i c h d e c o m p o s e d i n a i r at 3 5 0 ° C . W e felt that steric advantages f a v o r i n g extensive p o l y m e r i z a t i o n w o u l d e n s u e i f t h e p h t h a l o n i t r i l e u n i t s w e r e s e p a r a t e d f a r t h e r a n d p l a c e d at t h e e n d s of a l o n g , flexible m o l e c u l a r c h a i n (see S t r u c t u r e 1 ) . F r e e d o m o f m o v e m e n t

(1)

of t h e r e a c t i n g e n d s s h o u l d a l l o w p r o p e r o r i e n t a t i o n f o r t h e i n c l u s i o n o f a n e n d into t h e p h t h a l o c y a n i n e structure. A t h e r m a l c e i l i n g i n a i r of o n l y 3 0 0 ° C w o u l d n o t p r e c l u d e interest i n s u c h p o l y m e r s since most resins w i t h c o n v e n i e n t u s e p r o p e r t i e s , s u c h as e p o x i e s , h a v e a p r a c t i c a l u s e c e i l i n g o f a b o u t 2 0 0 ° C . 458

In Copolymers, Polyblends, and Composites; Platzer, N.; Advances in Chemistry; American Chemical Society: Washington, DC, 1975.

39.

G R I F F I T H

E T

A L .

Phthalonitrile

459

Resins

Syntheses


S e v e r a l s y n t h e s i s p a t h w a y s s h o u l d l e a d t o s t r u c t u r e s s i m i l a r to S t r u c t u r e 1. A n y n u m b e r of tetraacids (Structure 2 ) c a n be synthesized, a n d b y f o l l o w i n g

(2) the route t h r o u g h the tetraamides, tetranitriles c a n b e synthesized i n p r i n c i p l e . T h i s p l a n d i d n o t a p p e a r attractive because of p u r i f i c a t i o n difficulties w i t h the intermediates a n d the necessity that a l l structures i n the central p o r t i o n b e stable u n d e r the reaction conditions. A n o t h e r p o s s i b i l i t y is t h e d i r e c t p l a c e m e n t o f a f u n c t i o n a l g r o u p , X , o n p h t h a l o n i t r i l e ( R e a c t i o n 3 ). Several attempts to nitrate or halogenate p h t h a l o -

CN

suitable reactions

CN

X

(3)

CN

CN

n i t r i l e w e r e u n s u c c e s s f u l , a n d , a l t h o u g h t h e m e t h o d is a t t r a c t i v e , s u i t a b l e reactants a n d conditions f o r the p l a c e m e n t of a u s e f u l f u n c t i o n a l g r o u p w e r e not f o u n d . T h e nitro group m a y be a c q u i r e d i n the preferred 4 position b y diamide formation a n d dehydration from 4-nitrophthalimide (Reaction 4 ). T h e

Ο

Ο

(4) n i t r o g r o u p is n o t f a v o r a b l e f o r s u b s e q u e n t a t t a c h m e n t o f s t r u c t u r e , b u t i t c a n b e differentially r e d u c e d i n the presence of the t w o reactive nitrile groups to y i e l d 4 - a m i n o p h t h a l o n i t r i l e ( R e a c t i o n 5 ) ( 4 ) . T h e a m i n o g r o u p offers a

(5)

p o i n t o f r e a c t i o n f o r a n u m b e r o f p o s s i b l e c o u r s e s , t h e m o s t d i r e c t of w h i c h is d i a m i d e f o r m a t i o n ( R e a c t i o n 6 ) .


460

COPOLYMERS,

P O L Y B L E N D S , A N D COMPOSITES

Table I.

Compound

η

IV

4


V VI VII

a

VIII

5 6 6 (3 Me) 7

IX X XI XII XIII XIV XV

8 9 10 12 13 14 18

Yield, %

Melting Point, °C

55

300-302

68 73 61

256-259 320-323 203-206

63

227-230

53 63 63 73 71 50 60

255-258 181-183 192-194 163-165 178-181 163-165 163-166

Recryst. Solvent

Empirical Formula

C H -DMF 70:30 DMF DMF MeOH

C20H12N6O2

6

6

C21H14N6O2 C22H16N6O2 C23H18N6O2

6

MeOH-H 0 90:10 CH CN MeOH MeOH CH CN CH CN CH CN CH CN

C23H18N6O2

2

C24H22N6O2 C25H22N6O2 C26H24N6O2 C28H28N6O2 C29H 3θΝβθ2 0 οΗ 2Νβ0 0 4Η4θΝβθ2

3

3

3 3

3

3

3

2

3

Structure:

0 II N C s ^ ^ N ^ N H C (CH )

JOT b

AyV'-Bis(3,4-Dicyanophenyl)

-

2

0 II C N H

^ V ^ C N

t X >

T h e linkage between the two carbonyl groups is — C H 2 C H ( C H 3 ) C H 2 C H — . 2

This affords an example of the general type of structure desired, and, although the amide linkage may not be the most desirable for high thermal stability, this class of phthalonitrile was considered sufficiently promising that a series was synthesized to determine some properties and reaction behavior. Resin

Properties

The 12 diamides listed in Table I were derived from 4-aminophthalonitrile and aliphatic diacid chlorides. These are white, crystalline solids with melting points above 160°C. The melts are syrups with free-flow character istics at the melt temperature; glasses may be obtained in some cases by rapid cooling of the melt to room temperature. A plot of the melting points has the


39.

G R I F F I T H

E T

Alkanediamides

A L .

Phthalonitrile

a

Calculated, %


461

Resins

Found, %

c

H

Ν

C

H

Ν

65.21

3.28

22.83

64.96

3.20

22.75

65.96 66.66 67.31

3.69 4.07 4.42

21.98 21.20 20.48

65.86 66.41 67.47

3.59 4.02 4.44

21.83 21.03 20.40

67.31

4.42

20.48

67.57

4.24

20.42

67.91 68.48 69.01 69.98 70.42 70.84 72.31

4.75 5.06 5.35 5.87 6.11 6.34 7.14

19.80 19.17 18.57 17.49 16.99 16.52 14.88

67.71 68.60 69.05 69.92 70.28 71.04 72.22

4.79 5.12 5.23 5.65 5.97 6.38 7.10

19.74 19.08 18.39 17.35 16.79 16.29 14.75

f a m i l i a r o d d - e v e n z i g - z a g as t h e a l i p h a t i c c h a i n i n c r e a s e s i n l e n g t h , w i t h a plateau beyond C (see F i g u r e 1 ) . i

2

Polymerization W h e n a melt of p h t h a l o n i t r i l e c o n t a i n i n g a suspension of clean c o p p e r f l a k e ( a c t i v a t e d c o p p e r b r o n z e p i g m e n t ) is h e a t e d a b o v e 1 7 0 ° C , a g r e e n t i n t s o o n d e v e l o p s u n i f o r m l y t h r o u g h o u t t h e m e l t i f t h e c o p p e r is e v e n l y d i s t r i b u t e d . A r e a s o f m e l t w h i c h a r e c o p p e r - p o o r d o n o t b e c o m e g r e e n as r a p i d l y as t h o s e w h e r e t h e m e t a l is l o c a t e d , a l t h o u g h t h e c o l o r w i l l d e v e l o p at h i g h e r t e m peratures ( 2 2 0 ° C ) even i n the absence of a d d e d metal. T h e sharp, isolated I R a b s o r p t i o n of t h e nitrile g r o u p at about 2 2 4 0 c m " affords a c o n v e n i e n t measure of the degree of reaction, although the total spectrum has not been u s e f u l as p r o o f t h a t t h e r e a c t i o n is p h t h a l o c y a n i n e f o r m a t i o n . T h e g r e e n c o l o r w h i c h b e c o m e s p r o g r e s s i v e l y d e e p e r w i t h s o l i d i f i c a t i o n o f t h e m e l t is a s t r o n g i n d i c a t i o n t h a t p h t h a l o c y a n i n e f o r m a t i o n is s i g n i f i c a n t . I R s p e c t r a o f u n s u b s t i t u t e d p h t h a l o c y a n i n e s d e p e n d t o s o m e e x t e n t o n c r y s t a l m o d i f i c a t i o n s as w e l l as o n c o m p o s i t i o n a n d s t r u c t u r e ( 5 ) . I n t h e r e s i n c u r e , p h t h a l o c y a n i n e u n i t s should be isolated i n the developing network, a n d the spectral changes w h i c h o c c u r as p h t h a l o n i t r i l e s b e c o m e p h t h a l o c y a n i n e p o l y m e r h a v e n o t so f a r b e e n definitive except w i t h r e g a r d to n i t r i l e d i m i n u t i o n . P r i m a r i l y o n t h e basis of t h e o b v i o u s i n t e n s e c o l o r d e v e l o p m e n t a n d p h y s i c a l c h a n g e s ( l i q u i d -> s o l i d t r a n s i t i o n ) i t is b e l i e v e d t h a t s u b s t i t u t e d p h t h a l o c y a n i n e f o r m s b y R e a c t i o n 7. Decrease i n nitrile I R absorption a n d physical strength development b o t h i n d i c a t e that p o l y m e r i z a t i o n of a p p r o x i m a t e l y 4 8 h r s at 2 2 0 ° C is r e q u i r e d to d e v e l o p t h e p o l y m e r i c n e t w o r k to t h e m a x i m u m extent. T h e h y p o t h e t i c a l cure p r o c e s s is d e p i c t e d i n R e a c t i o n 8. 1

Cured

Polymer

Properties

Properties of the c u r e d phthalonitriles are n o w under investigation, a n d the most interesting properties, t h e t h e r m o - m e c h a n i c a l , w i l l r e q u i r e extensive e v a l u a t i o n . A f t e r f u l l c u r e , p o l y m e r s a p p e a r m u c h t h e s a m e as c u r e d e p o x i e s except that the v e r y deep green color makes the b u l k material appear black.



462

COPOLYMERS,

POLYBLENDS,

A N D COMPOSITES

I 50L-L-J ' » I » » » » L i ι ι 1 I 1 ι ι—ι—Ι Ο

5

10

15

20

NO. OF ALIPHATIC CARBONS (n) Figure 1.

Melting points of diamide resins

S o m e d i f f i c u l t y i n a v o i d i n g b u b b l e s at t h e h i g h c u r e t e m p e r a t u r e s is f r e q u e n t l y e n c o u n t e r e d , a n d a l l ramifications of this p r o b l e m are n o t f u l l y u n d e r s t o o d . M o r e t h a n a s t o i c h i o m e t r i c a m o u n t o f c o p p e r flake i n t h e r e a c t i o n m i x t u r e t e n d s t o c a u s e f o a m i n g , a n d t h e r e is s o m e i n d i c a t i o n t h a t a c o m p o n e n t of t h e atmosphere ( p r o b a b l y o x y g e n ) m a y affect the course of a p o l y m e r i z a t i o n . F o r

Reaction 7.

The phthalocyanine reaction


39.

G R I F F I T H

E T

A L .

Phthalonitrile

463

Resins

example, it w a s occasionally observed that a resin m e l t b e t w e e n cover plates o n a h o t s t a g e w i l l first b e g i n t o t u r n g r e e n n e a r t h e e d g e s e x p o s e d t o t h e atmosphere.


A t 3 0 0 ° C i n a i r , t h e r e is a g r a d u a l w e i g h t loss o f a p p r o x i m a t e l y 2 % / d a y , a n d filings o f a s a m p l e w i l l s l o w l y a c q u i r e a b r o w n i s h t i n t i n s t e a d o f t h e d i s t i n c t g r e e n of t h e o r i g i n a l p o l y m e r . It is n o w u n k n o w n w h e t h e r t h i s d e c o m p o s i t i o n is o c c u r r i n g at t h e p h t h a l o c y a n i n e n u c l e u s , at t h e a m i d e l i n k a g e , o r as a r e s u l t o f u n r e a c t e d o r t h o - d i n i t r i l e i n t h e p o l y m e r i c n e t w o r k . I n s p i t e o f t h i s p r o c e s s , t h e s t r u c t u r a l i n t e g r i t y of t h e p o l y m e r i c m a t e r i a l is r e t a i n e d f o r a n u m b e r of d a y s at t h i s t e m p e r a t u r e .

ι

ο

R

h— R

—

ETC.

CN CN

Reaction 8. •,

Hypothesis for cure of phthalonitrile resins

phthalocyanine nucleus; R , connecting structure, usually hydrocarbon; number (e.g. 2 X 10'·')

X , a large, indefinite

A s u i t a b l e m e a n s to e s t i m a t e t h e m o l e c u l a r w e i g h t o f t h e c u r e d resins is y e t t o b e d e v i s e d . S o l v e n t s s u c h as a c e t o n i t r i l e w i l l s l o w l y l e a c h s o m e s o l u b l e m a t e r i a l f r o m t h e p o l y m e r . A b u l k s a m p l e does n o t i n i t i a l l y a p p e a r soluble i n concentrated sulfuric acid, b u t considerable dissolving w i l l occur o v e r s e v e r a l d a y s . T h i s p r o b a b l y results f r o m d e g r a d a t i o n a t t h e a m i d e l i n k a g e . A l t h o u g h m e c h a n i c a l p r o p e r t y s t u d i e s are n o t c o m p l e t e d , t h e p o l y m e r strength levels are sufficiently h i g h to be u s e f u l i n p r a c t i c a l a p p l i c a t i o n s , p a r t i c u l a r l y t h a t of m a t r i x m a t e r i a l s f o r glass a n d c a r b o n fiber r e i n f o r c e d c o m p o s i t e s . T h e a d h e s i v e p r o p e r t i e s d o n o t a p p e a r as g e n e r a l l y u s e f u l as t h o s e of e p o x i e s ( e x c e p t a b o v e t h e d e c o m p o s i t i o n t e m p e r a t u r e s o f e p o x i e s ) , b u t c o u p l i n g a g e n t s ( s i m i l a r t o t h e a m i n o silanes u s e d i n e p o x y a p p l i c a t i o n s ) w h i c h are d e s i g n e d f o r p h t h a l o n i t r i l e resins s h o u l d i m p r o v e t h e i r s u i t a b i l i t y f o r u s e as m e t a l - t o - m e t a l a d h e s i v e s . Experimental 4-Nitrophthalamide (I). This c o m p o u n d was prepared b y a modified Bogert a n d Boroshek (6) method. C o m m e r c i a l 4-nitrophthalimide (500 g;


464

COPOLYMERS,

POLYBLENDS,

AND

COMPOSITES

2 . 6 0 m o l e s ; m p , 1 9 6 ° - 2 0 0 ° C ) is a d d e d q u i c k l y t o a s t i r r e d s o l u t i o n o f 15.6IV N H O H ( 3 5 0 0 m l ) . W i t h continued stirring, external heating (water bath, 4 5 ° C ) is a p p l i e d u n t i l f r o t h i n g ceases ( 1 h r ) . T h e r e s u l t i n g p r e c i p i t a t e i s c o l l e c t e d , w a s h e d w i t h i c e w a t e r ( 2 X 4 0 0 m l ) , a n d d r i e d t o y i e l d 4 4 0 g o f I as pale y e l l o w crystals. Y i e l d , 8 1 % ; m p , 2 0 0 ° - 2 0 2 ° C ; l i t m p , 2 0 0 ° C (6). 4-Nitrophthalonitrile ( I I ) . 4-Nitrophthalamide was converted into 4-nitrop h t h a l o n i t r i l e b y a m o d i f i c a t i o n of the m e t h o d of Scalera a n d B o u i l l a r d ( 7 ) . 4 - N i t r o p h t h a l a m i d e ( 2 2 0 g ; 1.05 moles) is suspended i n p y r i d i n e ( 8 4 0 m l ) . Into this v i g o r o u s l y stirred suspension, p h o s p h o r u s o x y c h l o r i d e ( 2 2 0 m l ; 2 . 4 0 m o l e s ) is a d d e d a t s u c h a r a t e t h a t t h e r e a c t i o n m a i n t a i n s a t e m p e r a t u r e r a n g e of 6 5 ° - 7 0 ° C d u r i n g t h e 3 0 - m i n a d d i t i o n t i m e . T h e s a m e t e m p e r a t u r e is m a i n tained a n a d d i t i o n a l h o u r b y external heating. T h e resulting mixture is p o u r e d o n t o c r u s h e d i c e ( 3 0 0 0 g ) , a n d t h e i c e m i x t u r e is n e u t r a l i z e d w i t h 1 2 N H C 1 ( 1 5 0 m l ) . T h e p u r p l e s o l i d is c o l l e c t e d b y filtration a n d d r i e d . T h e r e s i d u e is e x t r a c t e d w i t h e t h y l a c e t a t e ( 3 X 7 0 0 m l ) , a n d t h e p u r p l e e x t r a c t is d e c o l o r i z e d w i t h N u c h a r C - 1 9 0 a n d w a s h e d , first w i t h 0 . 4 N N a O H s a t u r a t e d w i t h N a C l ( 3 X 70 ml) and then with water (4 X 70 m l ) . D r y i n g and evapo r a t i o n o f t h e e x t r a c t l e a v e s 9 1 g o f I I as p a l e y e l l o w c r y s t a l s . Y i e l d , 5 0 % ; mp, 142°-144°C; litmp, 138°-139°C (7) and 142°C ( 4 ) .


4

4-Aminophthalonitrile (III). The procedure provides analytically pure III. 4 - N i t r o p h t h a l o n i t r i l e ( 1 0 0 g ; 0 . 5 7 6 m o l e ) is d i s s o l v e d i n p y r i d i n e ( 4 0 0 m l ) . T h e p y r i d i n e s o l u t i o n is a d d e d d r o p w i s e d u r i n g 1 h r t o a s t i r r e d s o l u t i o n of 9 0 % sodium dithionite ( 4 5 7 g; 2.36 moles) and water (2700 m l ) . T h e re s u l t i n g m i x t u r e is s t i r r e d f o r a n a d d i t i o n a l h o u r . T h e n w a t e r ( 9 0 0 m l ) is a d d e d , a n d t h e m i x t u r e is c o o l e d t o 4 ° C . T h e w h i t e p r e c i p i t a t e is c o l l e c t e d and washed with cold water (2 X 4 0 0 m l ) . Recrystallization from water (2700 m l ) l e a d s t o 2 7 . 3 g o f I I I as l i g h t c r e a m c o l o r e d c r y s t a l s . Y i e l d , 3 3 . 1 % ; m p , 1 8 1 ° - 1 8 3 ° C ; C H H - , Ν . ^ analysis: calculated: 6 6 . 9 3 % C , 3 . 4 7 % H , and 2 9 , 5 8 % N , and found: 67.03% C , 3.58% H , and 29.47% N . N,N'-Bis(3,4-Dicyanophenyl) A l k a n e d i a m i d e s ( I V - X V ) . D a t a o n the 12 a l k a n e d i a m i d e s a n a l y z e d i n t h e p r e s e n t s t u d y a r e p r e s e n t e d i n T a b l e I. I n c l u d e d are s t r u c t u r e , m e l t i n g p o i n t , r e c r y s t a l l i z a t i o n s o l v e n t , y i e l d , a n d e l e m e n t a l assays. A l l a r e n e w c o m p o u n d s , a n d a l l w e r e p r e p a r e d b y a p p r o p r i a t e m o d i fication of t h e f o l l o w i n g p r o c e d u r e . N,iV'-Bis(3,4-Dicyanophenyl) Tridecanediamide (XIII). A solution of brassylyl chloride ( 9 . 8 1 g ; 0.035 mole) i n C C 1 ( 2 5 m l ) is a d d e d d r o p w i s e to a s t i r r e d s o l u t i o n o f 4 - a m i n o p h t h a l o n i t r i l e ( 1 0 . 0 g ; 0 . 0 7 0 m o l e ) i n p y r i d i n e ( 2 5 0 m l ) d u r i n g 2 5 m i n . C C 1 ( 2 2 5 m l ) is a d d e d , a n d t h e final m i x t u r e is cooled i n a n i c e bath. T h e resulting w h i t e precipitate is collected, w a s h e d w i t h C C 1 ( 2 X 1 5 m l ) , a n d d r i e d . T h e r e s i d u e is d i s p e r s e d i n w a t e r ( 2 0 0 m l ) , collected, water w a s h e d , a n d d r i e d to y i e l d 15.9 g crude d i a m i d e . Three r e c r y s t a l l i z a t i o n s f r o m a c e t o n i t r i l e ( 3 X 1 6 0 m l ) y i e l d 1 1 . 5 g o f X I I I as a n a l y t i c a l w h i t e c r y s t a l s (see T a b l e I f o r p r o p e r t i e s ) . 4

4

4

Literature Cited 1. 2. 3. 4. 5. 6. 7.

Barrett, P. Α., Dent, C. E., Linstead, R. P., J. Chem. Soc. London (1937) 1719. Marvel, C. S., Rassweiler, J. H., J. Amer. Chem. Soc. (1958) 80, 1196. Marvel, C. S., Martin, M. M., J. Amer. Chem. Soc. (1958) 80, 6600. Drew, H. D. K., Kelley, D. B., J. Chem. Soc. London (1941) 637. Ebert, Jr., Α. Α., Gottlieb, Η. B., J. Amer. Chem. Soc. (1952) 74, 2806. Bogert, M. T., Boroshek, L., J. Amer. Chem. Soc. (1901) 23, 756. Scalera, M., Bouillard, R. E., U.S. Patent 2,525,620 (1950).

RECEIVED March 27, 1974.


Copolymers, Polyblends, and Composites

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