Biphenylene end-capped polyquinoline and polyimide resins afford low void content graphite-reinforced composites with good initial properties. However, with both resins, rapid degradation occurs during oxidative isothermal aging at elevated temperatures. The degradation is not observed during isothermal aging under a nitrogen atmosphere which suggests that the biphenylene end-cap (or the resulting crosslink/chain extension structures) is not particularly thermooxidatively stable. The nature of the thermooxidative instability is currently under investigation

Alston, W. B.

Droske, J. P.

Stille, J. K.

English

NASA Technical Reports Server

N86-11267
ALL-AROMATIC BIPHENYLENE ENO-CAPPEO POLYQUINOLINE
AND POLYIMIDE MATRIX RESINS
John P. Droske_ and John K. Stllle
Colorado State University
William B. Alston
National Aeronautics and Space Administration
Lewis Research Center
A promising approach to the processing of thermally 'stable polymers is the use
of oligomeric pre-polymers containing reactive end-groups which undergo crosslinking/
chain extension during processing and post-cure. Unfortunately, end-capped pre-
polymers generally afford processed materials which show lower retention of proper-
ties for extended periods at high temperatures than would be expected had an all-
aromatic, high molecular weight polymer been employed. Since the decreased thermo-
oxidative stability is partly attributable, in some cases, to the use of aliphatic
reactive end-groups (ref. l), end-groups which afford more thermally stable structures
are desired.
Biphenylene is an especially attractive reactive end-cap for high performance
composite resins due to its all-aromatic structure. Biphenylene undergoes thermolysis
above 350oc to afford tetrabenzocylooctatetraene (tetraphenylene), aromatic polymer,
or stable aromatic compounds depending on the reaction conditions (ref. 2 and fig. l).
Thus, any structure formed as a result of the thermolysis of a biphenylene unit in a
thermally stable polymer would be expected to maintain the all-aromatic character and
high temperature performance of the polymer. The temperature necessary for the ring
opening reaction can be lowered by the addition of appropriate transition metal
catalysts, such as (NBD Rh Cl) 2 and (PPh3)2 Ni(CO)2 which are known to open strained
cyclic hydrocarbons by an oxidative addition mechanism (ref. 3).
RESULTS AND DISCUSSION
Neat Resin Properties
Of the various polyquinolines that have been prepared (ref. 4), the ether-ether
linked polyquinoline showed the greatest promise as a laminating resin due to its
good solubility in common organic solvents (e.g. CHCl3) and its relatively low
TPresent Address: Department of Chemistry
University of Wisconsin-Stevens Point
91
https://ntrs.nasa.gov/search.jsp?R=19860001800 2020-03-23T06:26:17+00:00Z
Tg (266°C). We envisioned that the use of an oligomeric ether-ether linked poly-
quinoline would give a most processable thermoplastic resin, which could be converted
to a thermosetting resin with a high Tg after processing by reaction of the bipheny-
lene end-groups. Since it is desirable to use the least amount of the biphenylene
end-cap possible (functionalized biphenylenes are only prepared with considerable
difficulty), a series of biphenylene end-capped oligomeric polyquinolines having
various degrees of polymerization were prepared.
The neat resins containing 2.5 wt% (Ph3P)2Ni(CO) , were melt pressed into thin
films at 325 ° under 5000 lb. load for 15 minutes. All2films after processing were
insoluble (24 hours in CHCI3) and had Tg's of 235 °- 243°C. Young's modulus above Tg
increased by an order of magnitude due to the crosslinking (Table l). It was sur-
prising that the Tg as well as the mechanical properties above Tg after processing
were independent of the degree of polymerization and thus, the concentration of
biphenylene end-caps. The results suggested that a limited and approximately equal
amount of crosslinking was occurring in each of the three samples. As a control
phenyl end-capped polyquinolines offal_= II and I_F= 22 were prepared and melt p_o-
cessed in the presence of the Ni ° catalyst under the same conditions. The b-F= II
material had very poor film qualities whereas the I}l_'= 22 material processed into a
good quality, transparent film. However, both samples after processing were com-
pletely soluble in CHCl3 and showed no increase in Tg indicating that no cross-
linking/chain extension-occurred in the absence of the biphenylene end-cap.
Thermal gravimetric analysis of melt pressed film samples of biphenylene end-
capped polyquinoline (b-F= 22) containing 2.5 wt% (PPh3) 2 Ni(CO) 2 showed breaks in
air and nitrogen of 535°C and 570°C, respectively. These values are comparable to
those obtained with film samples of high molecular weight polyquinolines cast from
solution. However, oxidative isothermal aging at 300°C for lO0 h showed 3% weight
loss for the melt pressed film of biphenylene end-capped polyquinoline whereas the
high molecular weight polyquinoline film showed 0% weight loss during the same aging.
Composite Properties
Graphite-reinforced composites were prepared from biphenylene end-capped poly-
quinoline of D--F= 22. This degree of polymerization was considered to be an optimum
of processability with a minimum incorporation of the biphenylene end-cap since no
gains were realized when a lower degree of polymerization polyquinoline (containing
a corresponding higher concentration of the biphenylene end-cap) was used. Pre-pregs
were prepared by brus_-coating a chloroform solution o_ the polymer onto either
unidirectional Celion" - 6000 graphite fiber or Celion _ - 3000 graphite cloth. When
the Ni ° catalyst was used, processing was effected at 625°F (330°C) under 1500 psi
for 2 hours. The uncatalyzed laminates were processed at 735°F (3gl°C) •under 2000
psi for 3 hours, the higher temperature being necessary to effect the uncatalyzed
ring opening of biphenylene. In both cases high quality void-free laminates were
prepared but due to the relatively flexible polymer backbone and the moderate degree
of crosslinking attributable to the biphenylene end-cap, thermoplastic breaks during
room temperature interlaminar shear were observed. Furthermore, only 25% of the
initial room temperature interlaminar shear strength was retained after oxidative
aging at 650°F (343°C) for 50 h, even though the composite weight loss was only
two percent during the aging.
92
Using th_ PMR (polymerization of monomer reactants) approach (ref. 5). unidirec-
tional Celion _ - 600_graphite fiber w_s impregnated with a methanolic solution of
the diester of 3, 3', 4, 4' - benzophenonetetracarboxylic dianhydride, oxydianiline,
and 2-aminobiphenylene in a calculated stoichiometry to give I_-= 4.8915 (FMW =
3000). The pre-preg showed desirable tack and drape. The pre-preg was staged at
r o o o "i o o o
N N N N
I. o o j o o
4.8915
400°F (204°C) for l hour and processed at 735°F (39l°C) under 1500 psi for 3 hours.
(The Ni° catalyst was not used since it was insoluble in the methanolic monomer
solution.) The resultant 9-ply laminates were of high quality and had low void
content but showed thermoplastic breaks during interlaminar shear testing even
though the Tg of the composite (337°C) was well above the test temperature (316°C).
In an effort to increase the crosslink density, 3, 5 and lO mole % of the oxydiani-
line monomer was replaced with the appropriate amount of the triamine, 3, 3', 5' -
triaminobenzophenone. Composites in which 3 and 5 mole % of the diamine was re-
placed with the triamine showed sufficient crosslink density as evidenced by true
thermoset breaks during interlaminar shear testing at 600°F (316°C, Table 2).
However, photomicrographs of the composites after oxidative isothermal aging at
600°F for 50 h showed the presence of voids. Polymide composites isothermally aged
at 650°F (343°C) under a nitrogen atmosphere for 71 h did not show degradative void
formation.
CONCLUSION
Biphenylene end-capped polyquinoline and polyimide resins afforded low void
content graphite-reinforced composites with good initial properties. However, with
both resins, rapid degradation occurred during oxidative isothermal aging at elevated
temperatures. The degradation was not observed during isothermal aging under a
nitrogen atmosphere which suggests that the biphenylene end-cap (or the resulting
crosslink/chain extension structures) are not particularly thermooxidatively stable.
The nature of the thermooxidative instability is currently under investigation.
93
REFERENCES
I •
.
.
.
5.
Alston, W. B.: Characterization of PMR-15 Polyimide Resin Composition in
Thermooxidatively Exposed Graphite Fiber Composites. NASA TM-81565, 1980
and Proc. of the 12th SAMPE National Technical Conference, October, 1980.
a•
b.
C.
a.
b.
C.
d.
Lind•w, D. F.; Friedman, L.
Friedman, L.; Rabideau, P. W.
Friedman, L.; Lind•w, D. F.
J. Am. Chem. Soc. 1967, 8__99,1271.
J. Or9. Chem. 1968, 33, 451•
J. Am. Chem. Soc. 1968, go, 2324.
Cassar, L.; Eaton, P. E.; Halpern, J. J. Am. Chem. Soc. 1970, 9_22,3515.
Gassman, P. G.; Reitz, R. R. J. Am. Chem. Soc. 1973, 95, 3057.
Bishop, K. C. Chem. Rev. 1976, 76, 461.
Stille, J. K.; Lau, K.S.Y. Accounts of Chemical Research 1977, lO, 434.
Stille, J. K. Macromolecules 1981, 14, 870.
Serafini, T. T.; Delvigs, P.; Alston, W. B.: PMR Polyimides - Review and Update.
NASA TM-82821, 1982 and Proc. of the 27th National SAMPE Symposium and
Exhibition, May, 1982.
340°C
30 h
CeDa
aso°c
3--5se©
Figure I. The products of the pyrolysis of biphenylene
under various conditions.
94
Table
Wt %
DP biphamylene
3 23
11 7.5
22 3,5
22* 0
ephenyl qmd-cep
I. Biphenylene End-Capped Polyquinoline.
Neat Resin Processing
32b"°C, 500 psi, 15 rain; (Ph3P)2Ni(CO) 2
Tg (°C) Tg (°C) ATg Solubility E' above Tg
before procmsing after processing _ (CHCl:_,24h) (dynes/cm 2 @T°C)
153 235 +82 26% .....
212 243 +31 i 1.4 x 108
(285-335°C)
232 243 +11 i 1.0 x 108
(291-330°C)
232 232 0 0
Table 2. Biphenylene End-Capped Polyimide/CelionR-6000
Unidirectional Graphite Composite.
H2N" 0 "NHe
H,N (mole %)
POST-CURE
Tg I°C,TMA) I LSS
after pc RT 600°F
Ipsll
% wt loss
48 h/6OO°F
150 h/600°F 331 14370 7098pc • 1.4
14h / 650°F 3 2 S 12261 7316 pc
47h / 600°F 328 13294pc 6842pc 1.2
10 43h/60_F 310 9628pc • 5422pc • 1.7
• Thermoplastic break
95


All-aromatic biphenylene end-capped polyquinoline and polyimide matrix resins

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