Diels-Alder cycloaddition copolymers from 1,4,5,8-tetrahydro-1,4;5,8-diepoxyanthracene and anthracene end-capped polyimide oligomers appear, by thermogravimetric analysis (TGA), to undergo dehydration at elevated temperatures. This would produce thermally stable pentiptycene units along the polymer backbone, and render the polymers incapable of unzipping through a retro-Diels-Alder pathway. High resolution solid 13C nuclear magnetic resonance (NMR) of one formulation of the polymer system before and after heating at elevated temperatures, shows this to indeed be the case. NMR spectra of solid samples of the polymer before and after heating correlated well with those of the parent pentiptycene model compound before and after acid-catalyzed dehydration. Isothermal gravimetric analyses and viscosities of the polymer before and after heat treatment support dehydration as a mechanism for the cure reaction

Ahn, Myong-Ku

Meador, Mary Ann B.

Meador, Michael A.

Olshavsky, Michael A.

English

NASA Technical Reports Server

NASA Technical Memorandum 10 1 3 85 
Addition Polymers From 1,4,5 , 8-tetrahydro- 
1,4;5,8-diepoxyanthracene and Bis-dienes 
11: Evidence for Thermal Dehydration 
Occurring in the Cure Process 
Mary Ann B. Meador, Michael A. Olshavsky, Michael A. Meador, 
and Myong-Ku Ahn 
Lewis Research Center 
Cleveland, Ohio 
Prepared for the 
197th National Meeting of the American Chemical Society 
Dallas, Texas, April 9-14, 1989 
(bASA-TE-I 0 1  38% A D C I I I I C  k E C l Y  BEES YBOB 889-  35235 
AliD BIS-DIENB2. 2: EVICENCE E C 6  ' I R E R I A L  
D E E P D B A T I G I  C C C t 6 E I Y G  II T6Y CCEtE EEOCESS ( E A S A )  E p CSCL 1 f C  63/27 0178547 
Y , U , 5 , 8 - % E I B A t i Y  EEC- 1,4; 5 ,  E - D I E E C X  Y AETBRACENE 
Unclas 
https://ntrs.nasa.gov/search.jsp?R=19890005864 2020-03-20T04:51:11+00:00Z
A D D I T I O N  POLYMERS FROM 1,4,5,8-TETRAHYDRO-1,4;5,8-DIEPOXYANTHRACENE 
AND B I S - D I E N E S  11: EVIDENCE FOR THERMAL DEHYDRATION OCCURRING 
I N  THE CURE PROCESS 
Mary Ann B .  Meador, M ichae l  A .  O lshavsky , *  
M ichae l  A .  Meador, and Myong-Ku Ahn** 
N a t i o n a l  A e r o n a u t i c s  and Space A d m i n i s t r a t i o n  
Lewis  Research Cen te r  
C l e v e l a n d ,  O h i o  44135 
SUMMARY 
D i e l s - A l d e r  c y c l o a d d i t i o n  copo lymers  from 1,4,5,8-tetrahydro-l,4;5,8- 
d iepoxyan th racene  and an th racene  end-capped p o l y i m i d e  o l i g o m e r s  appear ,  by  TGA, 
t o  undergo d e h y d r a t i o n  a t  e l e v a t e d  t e m p e r a t u r e s .  T h i s  wou ld  p roduce t h e r m a l l y  
s t a b l e  p e n t i p t y c e n e  u n i t s  a l o n g  t h e  po lymer  backbone, and r e n d e r  t h e  po lymers  
i n c a p a b l e  o f  u n z i p p i n g  t h r o u g h  a r e t r o - D i e l s - A l d e r  pa thway.  
s o l i d  l 3 C  NMR o f  one f o r m u l a t i o n  o f  t h e  po lymer  system b e f o r e  and a f t e r  h e a t i n g  
s o l i d  samples o f  t h e  po lymer  b e f o r e  and a f t e r  h e a t i n g  c o r r e l a t e d  w e l l  w i t h  
t h o s e  of t h e  p a r e n t  p e n t i p t y c e n e  model compound b e f o r e  and a f t e r  a c i d - c a t a l y z e d  
d e h y d r a t i o n .  I s o t h e r m a l  g r a v i m e t r i c  ana lyses  and v i s c o s i t i e s  o f  t h e  po lymer  
b e f o r e  and a f t e r  h e a t  t r e a t m e n t  s u p p o r t  d e h y d r a t i o n  as a mechanism f o r  t h e  cu re  
r e a c t  i o n .  
d N 
d e
W I a t  e l e v a t e d  tempera tu res ,  shows t h i s  t o  indeed  be t h e  case.  NMR s p e c t r a  o f  
H igh  r e s o l u t i o n  
INTRODUCTION 
We r e c e n t l y  r e p o r t e d  t h a t  1,4,5,8-tetrahydro-l,4;5,8-diepoxyanthracene, 1 ,  
forms h i g h  m o l e c u l a r  w e i g h t  D i e l s - A l d e r  a d d i t i o n  copo lymers  w i t h  an th racene  
end-capped p o l y i m i d e  o l i g o m e r s ,  f o r  example, o l i g o m e r  2 ( r e f .  1 ) .  The po lymers  
a r e  s o l u b l e  i n  common o r g a n i c  s o l v e n t s ,  l i k e  N,N-d imethy l formamide and 
N - m e t h y l p y r r o l i d i n o n e ,  b u t  on h e a t i n g  a t  e l e v a t e d  tempera tu re ,  become i n s o l u b l e  
and v e r y  t h e r m a l l y  s t a b l e .  The un ique  the rma l  b e h a v i o r  o f  t h i s  system makes i t  
a good c a n d i d a t e  as a m a t r i x  r e s i n  for h i g h  t e m p e r a t u r e  compos i tes .  
*Case Western Reserve-NASA C o o p e r a t i v e  Aerospace R&D I n t e r n .  
* * I n d i a n a  S t a t e  U n i v e r s i t y ,  T e r r e  Haute,  I n d i a n a  47809 and NASA-ASEE 
Summer F a c u l t y  F e l l o w .  
1 2 
3 
x =  
\ /  / / 0 0 
2 
I t  was suggested  ( r e f .  1 )  t h a t  t h e  polymers, on  h e a t  t r e a t m e n t ,  undergo 
d e h y d r a t i o n .  
a l o n g  t h e  po lymer  backbone, and make i t  i m p o s s i b l e  f o r  t h e  po lymer  t o  u n z i p  by  
a r e t r o - D i e l s - A l d e r  mechanism. D e h y d r a t i o n  was c o n s i s t e n t  w i t h  t h e  degree o f  
w e i g h t  loss r e c o r d e d  w i t h  t h e r m o g r a v i m e t r i c  a n a l y s i s  ( T G A )  o f  t h e  u n t r e a t e d  
po lymers .  However, p r e v i o u s l y ,  we were unab le  t o  o b t a i n  d i r e c t  s p e c t r a l  e v i -  
dence t h a t  such a p rocess  was o c c u r r i n g .  
T h i s  r e a c t i o n  would p roduce h i g h l y  s t a b l e  p e n t i p t y c e n e  u n i t s  
wn DEHYDRATION, cxmn 
I \  I \  - - 
4 3 
I n  t h i s  paper ,  such d i r e c t  ev idence  w i l l  be p r e s e n t e d .  A compar ison  between 
t h e  magic a n g l e  s p i n n i n g  (MAS) l 3C  NMR o f  s o l i d  po l ymer  samples b e f o r e  and 
a f t e r  h e a t  t r e a t m e n t  w i t h  those  o f  s u i t a b l e  model compounds w i l l  be shown. 
C I ~  RESULTS AND DISCUSSION 
Polymer 3 was s y n t h e s i z e d  as p r e v i o u s l y  r e p o r t e d  ( r e f .  1 )  w i t h  some m i n o r  
m o d i f i c a t i o n s .  
endox ide  1 i n  N,N-d imethy l formamide (DMF) w e r e  hea ted  a t  155 " C  under  400 p s i  
n i t r o g e n  f o r  36 h r .  The po lymer  was o b t a i n e d  i n  q u a n t i t a t i v e  y i e l d  as a d a r k  
brown s o l i d  a f t e r  removal  o f  s o l v e n t .  
A one-to-one m i x t u r e  o f  an th racene  end-capped o l i g o m e r  2 and 
MAS l 3 C  NMR o f  po lymer  3 ( f i g .  l ( a ) >  gave n i n e  peaks:  ( a )  a b road  l i n e  
a t  48.32 ppm, ( b )  a b road  m u l t i p l e t  a t  65.50 ppm c o r r e s p o n d i n g  t o  t h e  carbon 
b e a r i n g  two -CF3 groups  ( l ong - range  coup led  t o  t h e  f l u o r i n e s ) ,  ( c )  a peak a t  
80.52 ppm, ( d >  f i v e  a r o m a t i c  peaks a t  110.31, 123.84,  131.68,  138.44, and 
143.90 ppm, and ( e )  a b road  c a r b o n y l  l i n e  a t  164.95 ppm. Most o f  t h e  a r o m a t i c  
2 
peaks ( d ) ,  t h e  c a r b o n y l  peak ( e ) ,  and peak ( c )  can be ass igned  t o  t h e  i m i d e  
o l i g o m e r  c h a i n s .  
w i t h  t h e  s o l u t i o n  l 3 C  NMR o f  b i s - a d d u c t  5 r e p o r t e d  by  H a r t  and coworkers 
( r e f .  2 ) .  I n  a d d i t i o n  t o  a r o m a t i c  peaks,  t h e  spec t rum o f  5 c o n t a i n s  t h r e e  
a l i p h a t i c  peaks a t  47.47,  49.07, and 81.09 ppm b e l o n g i n g  t o  t h e  t h r e e  a l i p h a t i c  
The o t h e r  peak ass ignments  can be made based on compar ison 
b r idgeheads .  Hence, peaks ( a )  and ( c )  can be ass igned  t o  t h e  b r idgeheads  i n  
t h e  po lymer .  
s o l u t i o n  NMR o f  5 show up as one b road  peak a t  48.32 ppm i n  t h e  po lymer . )  
(The two peaks a t  47.47 and 49.07 ppm wh ich  a r e  r e s o l v e d  i n  t h e  
When po lymer  3 i s  hea ted  a t  315 "C f o r  5 h r ,  changes o c c u r  i n  t h e  s o l i d  
'3C NMR spec t rum ( f i g .  l ( b ) ) .  
t o  d i s a p p e a r ,  and a new peak ( f )  a t  53.42 ppm deve lops .  For l o n g e r  h e a t i n g  
t i m e s  or a t  h i g h e r  tempera tu res ,  t h e  ( a >  and ( c )  peaks d i s a p p e a r  c o m p l e t e l y  
( f i g .  l ( c > > ,  l e a v i n g ,  i n  t h e  a l i p h a t i c  r e g i o n ,  o n l y  t h e  new peak ( f )  a t  
53.42 ppm. 
The peaks a t  48.32,  80.52,  and 110.31 ppm b e g i n  
Two p o s s i b l e  e x p l a n a t i o n s  c o u l d  accoun t  f o r  t h e  d i sappearance  o f  t h e  two 
( 1 )  d e p o l y m e r i z a t i o n  ( r e t r o - D i e l s - A l d e r  r e a c t i o n ) ,  or ( 2 )  dehy- b r i dgeheads :  
d r a t i o n .  I n  o r d e r  t o  d i f f e r e n t i a t e  between t h e  two p rocesses ,  t h e  i n h e r e n t  
v i s c o s i t i e s  o f  the  polymer b e f o r e  and a f t e r  h e a t  t r e a t m e n t  w e r e  m o n i t o r e d .  I f  
d e p o l y m e r i z a t i o n  i s  t h e  p r i m a r y  p r o c e s s ,  t h e  v i s c o s i t y  s h o u l d  d r a m a t i c a l l y  
decrease.  I n  c o n t r a s t ,  d e h y d r a t i o n  s h o u l d  r e s u l t  i n  v i r t u a l l y  no change i n  
t h e  v i s c o s i t y .  B e f o r e  h e a t  t r e a t m e n t ,  po lymer  3 had an i n h e r e n t  v i s c o s i t y  o f  
0 .15 ;  a f t e r  h e a t i n g  f o r  5 h r  a t  315 "C, t h e  v i s c o s i t y  o f  t h e  r e s i n  i n c r e a s e d  
t o  0.18.  
The appearance o f  t h e  new peak a t  53.42 ppm c o n f i r m s  t h a t  d e h y d r a t i o n  i s  
o c c u r r i n g .  
b r i d g e h e a d  ca rbon  (53.81 ppm) i n  p a r e n t  p e n t i p t y c e n e  6, t h e  p r o d u c t  o f  a c i d  
c a t a l y z e d  d e h y d r a t i o n  o f  adduc t  5 .  
t i o n  t o  form a more s t a b l e  s t r u c t u r e .  Fo rmat ion  o f  an a r o m a t i c  system by  dehy- 
d r a t i o n  o f  an endox ide  r i n g  has been proposed p r e v i o u s l y  as a c u r e  mechanism 
fo r  o t h e r  such po lymers  ( r e f .  3). However, no ev idence  t h a t  t h i s  was o c c u r r i n g  
was shown. O t h e r  D i e l s - A l d e r  a d d i t i o n  copolymers have been shown t o  a r o m a t i z e  
t h r o u g h  l o s s  o f  ca rbon  monoxide ( r e f .  4 > ,  ca rbon  d i o x i d e  ( r e f .  5 > ,  and hydrogen 
( r e f .  6 ) .  
T h i s  peak cor responds t o  t h e  chemica l  s h i f t  o f  t h e  a l i p h a t i c  
The d r i v i n g  f o r c e  f o r  t h e r m a l l y  a c t i v a t e d  d e h y d r a t i o n  would be a r o m a t i z a -  
3 
A proposed mechanism fo r  d e h y d r a t i o n  i s  shown be low.  I n i t i a l  c l eavage  o f  
one o f  t h e  epox ide  oxygen-carbon bonds i n  3 a f f o r d s  t h e  c o r r e s p o n d i n g  b i r a d i c a l  
7 .  The d r i v i n g  f o r c e  f o r  t h i s  c leavage  would be t h e  r e d u c t i o n  o f  c o n s i d e r a b l e  
s t e r i c  i n t e r a c t i o n s  between t h e  benzene r i n g s  i n  3 .  I n  t h e  second s t e p ,  
1 ,4-hydrogen t r a n s f e r  from t h e  c -br idgehead carbon t o  t h e  oxygen r a d i c a l  c e n t e r  
p roceeds v i a  f o r m a t i o n  o f  a h i g h l y  f a v o r e d  f i v e - c e n t e r  t r a n s i t i o n  s t a t e  t o  p r o -  
v i d e  i n t e r m e d i a t e  8 .  D e h y d r a t i o n  o f  t h i s  i n t e r m e d i a t e  would t h e n  proceed v i a  
e i t h e r  a c o n c e r t e d  or two-s tep  p r o c e s s .  
3 
4 8 
T h e r m o g r a v i m e t r i c  a n a l y s i s  ( T G A )  o f  t h e  c o m p l e t e l y  dehydra ted  po lymer  3 
was r u n  i n  a i r  and n i t r o g e n  ( f i g .  2 ) .  The c u r e d  n e a t  r e s i n  shows no  i n i t i a l  
w e i g h t  loss a t  l o w e r  t e m p e r a t u r e s ,  and has an o n s e t  o f  decompos i t i on  i n  excess 
o f  600 " C  i n  b o t h  a i r  and n i t r o g e n .  
CONCLUSIONS 
C l e a r l y ,  d e h y d r a t i o n  i s  t h e  dominant  c u r e  p rocess  i n  t h i s  po lymer  system. 
T h i s  l eads  t o  a po lymer  wh ich  i s  i n c a p a b l e  of u n z i p p i n g  by  a r e t r o - D i e l s - A l d e r  
mechanism, s i n c e  t h e  r e a c t i o n  produces  a r o m a t i c  p e n t i p t y c e n e  u n i t s  a l o n g  t h e  
c h a i n .  We have proposed a mechanism f o r  d e h y d r a t i o n ,  and have shown d i r e c t  
s p e c t r a l  ev idence  t h a t  t h i s  i s  o c c u r r i n g .  MAS l 3 C  NMR o f  s o l i d  samples i s  a 
v e r y  p o w e r f u l  t e c h n i q u e  i n  p r o b i n g  t h e  r e a c t i o n s  o c c u r r i n g  a t  e l e v a t e d  tempera- 
t u r e s  i n  o t h e r w i s e  i n t r a c t a b l e  po lymer  systems.  We hope t o  use t h i s  as a tool  
t o  b r i n g  new i n s i g h t  i n t o  t h e  c u r e  c h e m i s t r y  o f  o t h e r  such s y s t e m s .  
To deve lop  t h i s  r e s i n  system i n t o  a u s e f u l  h i g h  tempera tu re  m a t e r i a l ,  
opt imum c u r e  c o n d i t i o n s  must  be deve loped,  and f low p r o p e r t i e s  o f  t h e  po lymer  
must  be maximized b y  f o r m u l a t i o n  s t u d i e s ,  w i t h o u t  d e t r i m e n t a l l y  a f f e c t i n g  t h e  
the rma l  s t a b i l i t y .  T h i s  i s  t h e  s u b j e c t  o f  a c u r r e n t  s t u d y .  
4 
REFERENCES 
1 
d 
. 
1.  Meador, M . A . B . :  J. Polym. S c i .  Polym. Chem. Ed., lpBs, 26, 2907-2916. 
2. H a r t ,  H.;  Raju, N . ;  Meador, M.A. ;  and Ward, D.L.: J .  Org. Chem., m, 
- 48, 4357-4360. 
3. Jones, R.J.: U.S. P a t e n t  3,905,941, 1975; O ' R e l l ,  M.K.; Sheppard, C.H.; 
Vaughan, R.H.; and Jones, R.J., NASA CR-134716, 1974. 
4. Dineen, J.M.; J o w e l l ,  E.E. ,  J r . ;  and Volpe, A . A . :  Polym. P r e p r . ,  u, 
282-283. S t i l l e ,  J.K., J. Macromol. Sci.-Chem., m, 3, 1043-1065. 
5. S c h i l l i n g ,  C.L., J r . ;  Reed, J.A.; and S t i l l e ,  J.K.: Macromolecules,  1969, 
- 2, 85-88. 
6. Powe l l ,  D.G.; and Ma th ias ,  L.J. :  Polym. Prep., u, 2, 575-576. 
d 
d 
tb )  
d 
A 
200 100 0 
PPM 
FIGURE 1. - MAS I 3 C  NMR OF POLYMER 3. 
I N G  FOR 5 HR AT 315 OC, tc )  AFTER 
(a)  BEFORE HEATING, tb )  AFTER HEAT- 
HEATING FOR 2 HR AT 350 OC. 
5 
6 
National Aeronautics and 
1. Report No. 
NASA TM-101385 
Report Documentation Page 
2. Government Accession No. 3. Recipient's Catalog No. 
I 
4. Title and Subtitle 
Addition Polymers From 1,4,5,8-tetrahydro-l,4; 5,8-diepoxyanthracene 
5. Report Date 
6. Performing Organization Code and Bis-dienes II: Evidence for Thermal Dehydration Occurring in 
the Cure Process 
7. Author(s) 8. Performing Organization Report No. 
Mary Ann B. Meador, Michael A. Olshavsky, Michael A. Meador, 
and Myong-Ku Ahn 
9. Performing Organization Name and Address 
National Aeronautics and Space Administration 
Lewis Research Center 
Cleveland, Ohio 44135-3191 
12. Sponsoring Agency Name and Address 
E-4442 
10. Work Unit No. 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
Technical Memorandum 
7. Key Words (Suggested by Author@)) 
Addition poly imide 
Thermal stability 
NMR dehydration 
High temperature polymer 
National Aeronautics and Space Administration 
Washington, D.C. 20546-0001 
18. Distribution Statement 
Unclassified - Unlimited 
Subject Category 27 
14. Sponsoring Agency Code 
9. Security Classif. (of this report) 
' ' unclassified 
15. Supplementary Notes 
Prepared for the 197th National Meeting of the American Chemical Society, Dallas Texas, April 9-14, 1989. 
Mary Ann B. Meador and Michael A. Meador, NASA Lewis Research Center; Michael A. Olshavsky, Case 
Western Reserve University-NASA Cooperative Aerospace R&D Intern; Myong-Ku Ahn, Indiana State 
University, Terre Haute, Indiana 47809 and NASA-ASEE Summer Faculty Fellow. 
20. Security Classif. (of this page) 21. No of pages 22. Price' 
Unclassified 8 A02 
16. Abstract 
Diels-Alder cycloaddition copolymers from 1,4,5,8-tetrahydro- 1,4;5,&diepxyanthracene and anthracene end- 
capped polyimide oligomers appear, by TGA, to undergo dehydration at elevated temperatures. This would 
produce thermally stable pentiptycene units along the polymer backbone, and render the polymers incapable of 
unzipping through a retro-Diels-Alder pathway. High resolution solid 13C NMR of one formulation of the 
polymer system before and after heating at elevated temperatures, shows this to indeed be the case. NMR spectra 
of solid samples of the polymer before and after heating correlated well with those of the parent pentiptycene 
model compound before and after acid-catalyzed dehydration. Isothermal gravimetric analyses and viscosities of 
the polymer before and after heat treatment support dehydration as a mechanism for the cure reaction. 


Addition polymers from 1,4,5,8-tetrahydro-1,4;5,8-diepoxyanthracene and Bis-dienes. 2: Evidence for thermal dehydration occurring in the cure process

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