A major goal in the field of high temperature polymers was to prepare aromatic polyimides that can be easily fabricated with the required thermal and physical properties for aerospace applications. Recent research was directed to achieve polyimides that are: soluable in a common organic solvent; melt-processable; and thermally curable without the evolution of volatile by-products. A monomer, N-phenyl 3,4-dimethylene pyrrolidine, that can be modified to form a bis (exocyclodiene) I for the preparation of polyimides by the Diels-Alder process was developed. Preparation of high temperature polymeric materials by Diels-Alder polymerization that will maintain their integrity and toughness during long exposure time at elevated temperature is sought

Ottenbrite, Raphael M.

Smith, Joseph G.

Yoshimatsu, Akira

English

NASA Technical Reports Server

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9 7 6 0 %  
77 PREPARATION OF 81S[4-(3,4 OIMETHYLENE-PYRROLIDYL). PHENYL] METHANE AS A HIGH T€MPERATURE REACTIVE OLIGOMER 
Raphael M. Ot tenbr i t e ,  Joseph G .  Smith and 
Ak i ra  Yoshimatsu 
Department of Chemistry 
V i r g i n i a  Commonwealth Un ive rs i t y  
Richmond, V i rg in ia  23284 
INTRODUCTION 
A major goal i n  the  f i e l d  of h igh temperature po ly -  
mers has been t o  prepare ardmatic polyimides t h a t  can be 
e a s i l y  fabr ica ted  with the  required thermal and phys ica l  
proper t ies fo r  aerospace appl icat ions.  Recent research 
has been d i rec ted  t o  achieve polyimides t h a t  are: 
a)  so lub le  i n  a comnon organic so lvent  
b) me1 t-processable 
c )  thermal ly  curable wi thout the evo lu t i on  o f  vo la-  
The me l t  p rocessab i l i t y  of polyimides can be enhanced 
by lowering t h e  f low temperature using syn the t i c  tech- 
niques such as t h e  incorporat ion of a ry l -e the r  and meta- 
phenylene l inkages i n  the polymer backbone. 
An approach by Har r i s  (Z), t o  o b t a i n  phenylated 
polyimides invo lves  the  Diels-Alder po lymer iza t ion  o f  
phenylated biscyclopentadienones w i t h  bismaleimides. The 
problem w i t h  t h i s  process i s  t h a t  dur ing  the react ion,  
carbon monoxide i s  produced subsequent t o  the  D ie ls -A lder  
addi t ion.  Furthermore, a t  temperatures of >300°C dehydro- 
genation, as w e l l  as o ther  decomposition processes, occurs 
t o  y i e l d  a polymer w i t h  l ess  s o l u b i l i t y .  
We have developed a unique monomer, N-phenyl-3,4-di- 
methylenepyrrol id ine,  t h a t  can be modi f ied t o  fo rm a 
bis(exocyc1odiene) I f o r  the preparation o f  poly imides by 
the Diels-Alder process ( 3 ) .  This bis(exocyc1odiene) does 
undergo Die ls-Alder  reac t i on  wi th  bismaleirnides 11 w i thou t  
the evo lu t ion  o f  gaseous by-products. The o b j e c t i v e  of 
t h i s  research i s  t o  prepare high temperature polymeric 
mater ia ls  by Die ls-Alder  polymerization t h a t  w i l l  mainta in  
t h e i r  i n t e g r e t i t y  and toughness dur ing long exposure t i m e  
a t  elevated temperature. 
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EXPERIMENTAL 
S vn t he s i s B I S [ 4 - (3.4 - Dime thy  1 enepyr r o  1 i dy 1 ) pheny 1 ] - 
methane 
T h e  synthes is  of phenyl methane was c a r r i e d  out by 
react i n g 4.4 ' -methyl e nedi ami  ne 2.3- b i s - 
(bromomethyl )-1,3-butadiene. During the  reac t ion ,  the 
f l a s k  was covered w i t h  f o i l  t o  avoid l i g h t  catalyzed 
polymerizat ion o f  the diene group o f  the s t a r t i n g  m a t e r i a l  
and Product. N sweep appeared t o  h e l p  r e t a r d  the oxida- 
t i o n  of the p&duct. The product,. bis(3,4-dimethylene- 
p y r r o l  i dy l )a ry lene ,  was very r e a c t i v e  and r e a d i l y  under- 
goes s e l f  D ie ls-Alder  addi t ion.  Since these dienes have 
poor s o l u b i l i t y  i n  organic solvents and poor s t a b i l i t y ,  
attempts t o  p u r i f y  these monomers were not  successful. 
of 
a r y l  enes w i  t h 
Sel f D i  e l  s-A1 der React i on o f  B i  s[ 4- ( 3,4-dime thy1 enepyrro- 
'l i d y l  )ph eny lJ  methane 
Dimer izat ion which can r e s u l t  from a Diels-Alder 
reac t i on  between t w o  exocycl ic dienes was observed i n  the 
case of N-phenyl-3,4-dimethylenepyrrolidine. To evaluate 
the s t a b i l i t y  of these bisdiene compounds, bis[4-(3,4-di- 
methy lenepyr ro l idy l )  phenyl J methane (5% monomer i n  C D C l  ) 
was heated a t  50°C and followed by 1H NMR spectroscopj. 
Af ter  heat ing a t  50°C f o r  7 h, new m u l t i p l e t  s ignals 
appeared a t  6 2-3 region w i t h  decreasing endo protons o f  
the exocycl ic diene a t  6 5.5 region, It i s  estimated t h a t  
the reac t i on  r a t i o  by s e l f  Diels-Alder was 20-30% under 
model compound preparation cond i t ions  and 2-3% under 
condi t ions of polymerization based on the i n t e g r a t i o n  of 
the 1H NMR spectra. 
B i s r4 - ( 3.4 -d i me t h v l  
so l  u t i on which contained equimol a r  amounts o f  b i  s[ 4- (3,4- 
dimethyl  enepyrro l  i d y l  )-phenyl ]methane J and b i smal eimi de 
I 1  i n  s o l u t i o n .  Af ter standing overnight,  the  prepolymer 
s o l u t i o n  became a gel. The polymer g e l  was washed w i t h  
chloroform and acetone, and then d r i e d  i n  vacuo. -- 
f i l m s  were prepared by cas t ing  the prepolymer 
s o l u t i o n  onto a clean glass surface. The glass p la tes 
were h e l d  a t  room temperature overn ight  t o  a l low the 
so lvent  t o  evaporate. The f i l m s  were then heated a t  120°C 
f o r  12 h t o  g i ve  transparent f l e x i b l e  polymer f i l m s .  
These f i l m s  were heated another 12 h a t  1 5 O O C .  
RESULTS AND DICUSSION 
Cop01 yme r i za t i  on B i s [ 4 - ( 3,4- d i  met hy 1 eneFyr r o l  i dy 1 1 
methane 1 wi th  Bismaleimide 11 
It was observed tha t  bisL4-(3,4-dimethylenepyrrol i d y l  
phenylldethane reacts  very r a p i d l y  w i th  bismaleimide by 
D ie ls -A lder  add i t ion .  However, t h i s  r e a c t i o n  i s  slower i n  
a c i d i c  so lvents ,  such as t r i f l u r o a c e t i c  acid,  due t o  the 
p ro tona t ion  o f  the  ni t rogen i n  the p y r r o l i d i n e  r i ng .  The 
po lymer iza t ion  o f  bis[4- (3,4-dimethylpyrrol i d y l  )methane 
w i th  bismaleimide was followed by 1H NMR spectoscopy. A t  
50°C i n  tr i  f 1 uoroacetic acid,  eompl e t e  polymerizat ion 
could be achieved w i th in  48 h. Tho po lymer izat ion y i e l d  
was est imated t o  be 92% based on the i n t e g r a t i o n  o f  1H NMR 
spectrum. 
The 1H NMR peak height decreases f o r  the  bisdiene 
protons and the polymer backbone proton area increases 
dur ing  the  react ion.  The new methylene protons on the 
cen t ra l  r i n g  due t o  the Die ls-Alder  add i t ion ,  i s  consis- 
t e n t  w i t h  the  decreasing exocyc l ic  diene peak. Conse- 
quent ly ,  i t  i s  considered t h a t  the D ie ls -A lder  reac t ion  i s  
the predominant process i n  t h i s  polymerizat ion.  The 
inherent  v i s c o s i t y  determined dur ing the  polymerizat ion 
w a s  p l o t t e d  against  the 1H NKR s ignal  he igh t  due t o  the 
newly foi-med methylene protons (Figure 1). I t  appears 
o f  
! 
. 
4 0.16 
e 
t ha t ,  a f t e r  format ion o f  oligomer dimer3 and t r imers  
w i t h i n  the f i r s t  3 h, the elongat ion of the:polymer chain 
takes place as i nd i ca ted  by t h e  increasing v i s c o s i t y  w i t h  
time. 
The E f f e c t  o f  Mole R a t i o , o f  Monomer on F i l m  Proper t ies  
A f t e r  determining the monomer concentrat ion o f  
b i sL4- ( 3,4-dime thy1 enepyrrol i d y l  )phenyl ]methane concent r a  - 
t i o n  by 'H NMR spectrum, the bismaleimide comonomer was 
added t o  the s o l u t i o n  t o  make the prepolymer so lu t ion .  
The polymer f i l m s  were then prepared from t h i s  prepolymer 
so lu t i on .  Shown i n  Table I are  the f i l m  p roper t i es  which 
were found t o  depend on the mole r a t i o  of both monomers. 
The a d d i t i o n  o f  20-30% less  bismaleimide I1 than bisdiene 
I made good f l e x i b l e  f i l m s .  Th is  observation might be 
expla ined by the  f a c t  t h a t  t he  20-30% o f  the bisdiene may 
be undergoing a s e l f  Diels-Alder process t h a t  was de- 
sc r ibed e a r l i e r .  
I 
Table 1: The Effect &Mole Ratio of Monomers on Film 
Proper ties 
Mole Ratio Solution Viscosity Film Property 
(1) 
.I 
1.0 1.0 nonv'kcous brittle 
1.0 0.9 nonviscous britt le 
1.0 0.8 viscous -> gel flexible 
1.0 0.7 viscous -> gel flexible 
1.0 0.6 nonviscous britt le 
solvents. 
r i g i n a l  polymer f i l m  was inso luab le  i n  organic 
Hot concentrated s u l f u r i c  a c i d  was used as a 
solvent f o r  f i v e  d i f f e r e n t  polymer f i l m s  which had d i f f e r -  
en t  cu r ing  temperatures a f t e r  cas t i ng  (Table 2 ) .  The 
polymer f i l m s  t h a t  were t reated a t  temperatures above 
120°C were n o t  so lub le  i n  hot H SO4. This decreased 
s o l u b i l i t y  may be due t o  a c r o s s l h k i n g  r e a c t i o n  taking 
place i n  the polymer f i l m  a f t e r  hea t ing  a t  h igh  tempera- 
tu res  and/or ox ida t i on  of  the p y r r o l i d i n e  r i n g  t o  the 
aromatic py r ro le .  
. 
_.. 
Table 2: Solubility of the Polymer Film in Concentrated 
H2S04 
I Curing Temperature ( C) Solubility 
25 
50 
120 
160 
200 
P 
P 
i 
1 
1 I 
Thermal Analysis 
The thermal , s t a b i l i t y  and decomposition temperature 
o f  the polymer f i l m s  were analyzed by TGA. The measure- 
ments were c a r r i e d  out  i n  N and a i r  atmosphere, respec- 
t i v e l y .  The polymer f i l m  w?s thermal ly  s t a b l e  w i t h  on ly  
10% weight l oss  a t  357°C and 20% weight l o s s  occurred a t  
413°C i n  n i t rogen.  The thermal data o f  the polymer f i l m  
are tabu la ted  i n  Table 3. On the o ther  hand, TGA p l o t s  i n  
a i r  showed d i f f e r e n t  behavior. T.here t w o  p la teau regions 
i n  the TGA curve were observed. The second r a p i d  weight 
loss occurred above 400°C and was i n d i c a t i v e  o f  t o t a l  
decomposition o f  the polymer backbone. The f i r s t  moderate 
weight loss  occurred a t  much lower temperatures (239°C). 
Table 3: Thermal Properties of Polymer Film 
Atmosphere I 20% wt. loss 
nitrogen 
air 
357 413 
239 385 
Acknowledgement: The authors wish t o  thank the NASA 
Langley f o r  the f i a n c i a l  support of t h i s  research and the 
s c i e n t i f i c  discussions held wi th  N. Johnston, T. S i n c l a i r  
and P. Hergenrother. 
References 
1. a )  M i  t t a l  , K.L., "Polyimides: Synthesis, Character- 
i z a t i o n ,  and Appl icat ion",  New York: Plenum Press, 
1984. 
b) Cassidy, P.E., "Thermally S tab le  Polymers: Synthesis 
and Properties", New York: Marcel Dekker, Inc., 
1980. 
c )  Hergenrother, P. and T.L. S t .  C l a i r ,  "Proceeding of 
Second In te rna t i ona l  Conference on Polyimides", i n  
E l l e n v i l l e ,  New York, 1985. 
2. Harr is ,  H., "Polyimides: Synthesis, Character izat ion 
and Application", ed., K.L. M i t t a l ,  p 3, New York: 
Plenum Press, 1984. 
3 - 1  n&ba-L-  ". .., y c c L . , y I  i t e ,  R.M. and P.V. Alston, 3. Hetero. Chem., - -
10, 785, (1973) 
322 (1975).  4 
b) m t e n b r i t e ,  R.M. and P.V. A ls ton,  3. Org. Chem., 40, - - -  
4 .  Chen, H I K . ,  Disser ta t ion work, "Synthesis and 
Character izat ion of N-phenyl-3,4-dirnethyl enepyrrol i d i  ne 
polymers". 
5. Becker, E.D., "High Resolut ion FiKR", New York: Academic 
Press, 1969. 
6. Ot tenbr i te ,  R.H., Polymer Bu l l . ,  - 6, 225 (1981). 


Preparation of bis(4-(3,4 dimethylene pyrrolidyl) phenyl) methane as a high temperature reactive oligomer

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