The N-CYCAP polyimides utilize a (2,2) paracyclophane endcap that polymerizes and does not generate volatile gases during the cure process. These polyimides have both high glass temperatures (390 C) and an onset of decomposition in air of 560 C. Thermal oxidative stability (TOS) weight loss studies show that replacing 25 percent by weight of the paraphenylene diamine in the polymer backbone with metaphenylene diamine improves the weight loss characteristics. N-CYCAP neat resin samples performed better than PMR-II-50 when exposed at 343 and 371 C in air for up to 1000 hours. Preliminary composite studies show that both PMR-II-50 and N-CYCAP have better thermal stability when fabricated on T-40R. Higher isothermal aging temperatures of longer aging times are needed to determine the differences in TOS between composite samples of PMR-II-50 and N-CYCAP polyimides

Schverman, Marla A.

Sutter, James K.

Waters, John F.

English

NASA Technical Reports Server

NASA Technical Memorandum 104341
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Long Term Isothermal Aging
and Thermal Analysis of
N-CYCAP Polylmldes:
-i
/ames K. Sutter and John E Waters
Lewis Research Center
Cleveland, Ohio
:i
and
Maria A. Schverman
Xavier University
Cincinnati, Ohio
Prepared for the
i:
@
High Performance Materials Symposimat the Polymer Technology Conference
sponsored by the American Chemical Soeiety
Philadelphia, Pennsylvania, June 3-5, 1_:
https://ntrs.nasa.gov/search.jsp?R=19910015972 2020-03-19T18:01:58+00:00Z

LONG TERM ISOTHERMAL AGING AND THERMAL ANALYSIS OF
N-CYCAP POLYIMIDES
James K. Sutter and John F. Waters
NASA Lewis Research Center
Cleveland, Ohio
and
Marla A. Schverman
Xavier University
Cincinnati, Ohio
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SUMMARY
N-CYCAP polymides utilize a [2.2] paracyclophane endcap that polymerizes and
does not generate volatile gases during the cure process. These polymides have both
high glass transition temperatures (390 °C) and an onset of decomposition in air of
560 °C. Thermal oxidative stability (TOS) weight loss studies show that replacing
25 percent by weight of the paraphenylene diamine in the polymer backbone with meta-
phenylene diamine improves the weight loss characteristics. N-CYCAP neat resin sam-
ples performed better than PMR-II-50 when exposed at 343 and 371 °C in air for up to
i000 hr. Preliminary composite studies show that both PMR-II-50 and N-CYCAP have
better thermal stability when fabricated on T-40R. Higher isothermal aging tempera-
tures of longer aging times are needed to determine the differences in TOS between
composite samples of PMR-II-50 and N-CYCAP polyimides.
INTRODUCTION
A major research goal at the NASA Lewis Research Center is the development of
new polymer matrix resins for high temperature applications. A prominent resin used
to replace metallic components in aircraft engines where temperatures can reach
300 °c is PMR-15 (structure i). Another resin being considered for even higher tem-
perature environments is PMR-II-50 (structure 2). Both of these polymers contain the
nadic carboxylic acid ester as a monomer in an addition curing polyimide. Vannucci
and Malarik (ref. I) have demonstrated that the nadic endcap is the weak link in both
of these addition curing polyimides.
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One objective when developing high temperature resins is to replace the nadic
acid ester endcap with an endcap that is more thermally stable. These new resins
should maintain similar processing conditions to those of PMR-15 and PMR-II-50 when
formulated to similar molecular weights. One newly developed resin system contains a
paracyclophane imidized endcap, termed N-CYCAP (amiNe substituted _Clophane Addition
Polyimides). The resin system formulated from 4-amino[2.2]paracyclophane contains a
strained ring system as the site of addition crosslinking. N-CYCAP polyimides con-
tain fewer carbon-carbon single bonds, have increased aromatic ring content, and emit
no volatiles during the cure cycle (ref. 2).
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EXPERIMENTAL
All monomers and solvents were used as-received. All thermal analyses were
recorded on either an Omnitherm 35050 Thermal Analysis System or an Omnitherm
Advantage II Thermal Analysis System at a scan rate of i0 °C/min. Thermomechanical
analyses were carried out with a DuPont Instruments 943 TMA on postcured neat resin
disks. Differential scanning calorimetry was carried out on imidized molding powders
in a DuPont Instruments DSC cell under ambient air.
Compression molding (i000 psi) was performed in a circular hardened steel die
with brass plungers. The charged die was placed in a press preheated to the process
temperature, and the ramp rate of the die was approximately 20 °C/min. All polymer-
ized specimens were cooled to room temperature under pressure. Isothermal weight
loss studies were conducted in triplicate on neat resin samples, all cut to the same
size (5.1 mm x 5.1 mm x 1.8 mm), at 343 and 371 °C in a forced hot air oven under
i atmosphere flowing air.
Prepregs were prepared by filament winding the respective fibers and by applying
approximately a 50 percent by weight solution of monomers in chloroform. Laminates
were processed using a simulated autoclave technique at 200 psi as in Vannucci et al.
(ref. i).
RESULTS AND DISCUSSION
N-CYCAP polyimides were formulated from a variety of aromatic diamines and
dianhydrides. Some of the most thermal stable resins were formulated from 4-amino
[2.2] paracyclophane, hexafluoro dianhydride (HFDA), paraphenylene diamine (p-PDA),
and metaphenylene diamine (m-PDA). Samples of molding powders from these monomers
were compression molded at 316, 343, 371, and 398 °C. The cure cycle of these
polyimides was identical to that of the corresponding PMR-II powders with similar
molecular weights. Typically, the N-CYCAP polyimides were compression molded into
void-free neat resins on the first attempt.
2
The cyclophane endcapped polyimides polymerize vigorously and their exotherms
were studied for samples with formulated molecular weights (FMW) of 1886 and 6030
(fig. i). These molding powders correspond to polyimides with n values of 2
and i0 where the weight percent of the cyclophane endcap is 24 and 7.5, respectively.
The differential scanning calorimetry (DSC) experiments showed two exotherms for all
N-CYCAP polyimides. The temperatures at which these exotherms began to occur were
250 and 350 °C.
[2.2] Cyclophane containing polymers were studied previously (ref. 3). The bond
cleavage in N-CYCAP polyimides during curing of the resins leads to crosslinked
polymers with high glass transition temperatures and excellent thermal oxidative
stability. The glass transition temperatures (T_) of air-postcured (16h) N-CYCAP
polyimides were reported previously to be as high as 353 °c (ref. 2). The effect of
a nitrogen postcure was examined for N-CYCAP polyimides. The highest T obtained
g
after nitrogen postcuring was 390 °C (table I).
Thermal oxidative weight loss studies (TOS) compared the neat resin stabilities
of N-CYCAP to PMR-II-50 (fig. 2 and table II). The neat resins were aged at 343 and
371 °C in air. The effects of postcuring in different environments were also studied
to determine the stabilities of the neat resins postcured in air versus nitrogen
(ref. 4). All neat resins were aged at 343 °C for i000 hr. Resins aged at 371 °C
for 600 hr or more decomposed and could not be weighed accurately.
The TOS study performed at 343 °C clearly demonstrates the excellent stability
of N-CYCAP resins containing metaphenylene diamine (m-PDA) (fig. 2). The sample
containing 25-percent m-PDA lost only 10.5 percent of the resins total weight after
i000 hr. This neat resin specimen performed better than any other sample in both the
343 and 371 °C aging studies. The best PMR-II sample lost 14.6 percent of its weight
after the same period of time. This ranking was also observed when the resins were
nitrogen postcured before the 343 °C aging study began (fig. 2). The N-CYCAP sample
containing 25-percent m-PDA that was nitrogen postcured at 371 °C and aged at 343 °C
in air lost 24.2 percent of its weight while the best PMR-II sample lost
28.5 percent.
Weight loss studies at 371 °C follow a similar trend to the studies at 343 °C.
Because of a rapid degradation of all resins tested at 371 °C, the best weight com-
parison can be seen after aging for 250 hr. After 250 hr the resins cracked and
deteriorated quickly. The N-CYCAP resin containing 25-percent m-PDA lost only
7.4 percent of its weight while the best PMR-II sample lost 19.5 percent. The com-
parison of the best N-CYCAP resin (with 25-percent m-PDA) and the best PMR-II sample
after 500 hr of aging at 371 °C in air follows the trend observed after 250 hr of
aging. Wherein N-CYCAP lost 19.4 percent of its weight, the PMR-II-50 resin lost
37.9 percent of its weight after 500 hr.
Preliminary studies were performed to determine the long-term thermal stability
and initial mechanical property of N-CYCAP and PMR-II-50 matrix resins on two types
of graphite fiber composites. The results of these studies are shown in tables III
and IV. The 343 °C isothermal aging study shows that the N-CYCAP and PMR-II-50
composites were comparable. All composites made from T-40R fiber were more stable
than those fabricated from T650-42 fiber. The isothermal test temperature appears
to have not been high enough to determine significant differences in the thermal
stability of N-CYCAP and PMR-II-50 resins. The composites were tested for flexural
and interlaminar shear strength (ILSS) and are shown in table IV. The N-CYCAP
3
composites performed better than the PMR-II-50 composites in the ILSS test at 343 °C
whereas the PMR-II-50 composites performed better in the 343 °C flexural tests.
CONCLUSIONS
Resins and composites fabricated from N-CYCAP and PMR-II-50 were tested for
their long-term thermal stability. N-CYCAP neat resins containing metaphenylene
diamine and paraphenylene diamine performed better than the PMR-II-50 neat resins in
the 343 and 371 °C TOS studies. N-CYCAP exhibited high T's (390 °C). Composite
studies show that both N-CYCAP and PMR-II-50 have better t_ermal stability when
fabricated on T-40R graphite fiber. Higher isothermal aging temperatures of longer
aging times are needed to determine differences in these resin systems.
REFERENCES
i. Vannucci, R.D.; and Malarik, D.C.: Autoclave Cured Composites for 371 °C
(700 OF) Applications. HiTEMP Review 1989, NASA CP-I0039, 1989,
pp. 15-1 to 15-8.
2. Sutter, J.K.; and Waters, J.W.: Long Term Isothermal Aging and Thermal Analysis
of N-CYCAP Polymides. HITEMP Review 1990, NASA CP-10051, 1990, pp. 4-1 to 4-9.
3. (a) Meyers, R.A.; Hamersma, J.W.; and Green, H.E.: Paracylophane Units:
Versatile Segments for Polymer Chain Crosslink formation. Polymer Letters,
Vol. i0, 1972, pp. 685-689. (b) Chang, D.M.; and Marvel, C.S.: Aromatic Poly-
ethers, Polysulfones, and Polyketones as Laminating Resins. VII. Polymers
with [2.2]-p-Cyclophane units. J. Polym. Sci Polym. Chem., Ed., Vol. 13, 1975,
pp. 2507-2515. (c) Upshaw, T.A.; and Stille, J.K: [2.2] Paracyclophane End-
Capped Polyquinoline Prepolymers: Synthesis, Processing, and Thermal Proper-
ties. Polym, Mater. Sci. Eng. Proc., vol. 59, 1988 pp. 553-557.
4. Bowles, K.J.: Thermo-Oxidative Stability Studies of PMR-15 Polymer Matrix
Composites Reinforced with Various Continuous Fibers. SAMPE Proc. Vol. 35,
Book I, G. Janicki, V. Bailey, and H. Schjelderup, eds.,) 1988, pp. 147-161.
TABLE I. - RESIN GLASS TRANSITION TEMPERATURES
Resin s
PMR-II-50
N-CYCAP, n = 6
N-CYCAP, n = i0
N-CYCAP, n = I0
with 25 percent m-PDA
No
postcure
Postcure
in air at
370 °C
Postcure
in nitrogen
at 371 °C
Postcure
in nitrogen
at 400 °C
Glass transition temperature, °C
301
267
323
319
365
339
353
35O
387
336
357
342
408
390
382
365
SAil resins were cured for 2 hr at 371 °C.
TABLE II. - RESIN THERMAL OXIDATIVE WEIGHT LOSS STUDIES
Resin a
PRM-II-50
N-CYCAP, n = i0
(i00 percent p-PDA)
N-CYCAP, n = i0
25 percent m-PDA
Postcure
environment
Air
Nitrogen
Air
Nitrogen
Air
Nitrogen
Aging time,
hr
25O 500
Weight loss, percent
19.5
16.8
13.2
14.4
7.4
10.7
37.9
32.5
30.0
30.2
19.4
21.7
aAll resins were tested in 1 atm air; postcure
temperature, 371 °C.
TABLE III. - i000 HR ISOTHERMAL AGING at 343 °C
Resin
N-CYCAP
N-CYCAP, 25 percent m-PDA
PMR-II-50
PRM-II-50, 25 percent m-PDA
Composite weight loss, percent
T40R fiber
5.8±0.9
3.8±0.6
3.3±1.3
3.4±0.4
T650-42 fiber
6.5±0.5
7.2±0.2
6.7±1.3
7.6±1.6
TABLE IV. - FLEX STRENGTH and ILSS of COMPOSITES TESTED at 343 °C
N-CYCAP
Resin a
N-CYCAP, 25 percent m-
PDA
Fiber
T40R
T650-42
T40R
T650-42
Flex strength,
ksi
59.3±3.0
47.3±2.0
PMR-II-50
PMR-II-50,
25 percent m-PDA
T40R
T650-42
T40R
T650-42
69.6±4.1
81.2±2.6
87.7±7.9
75.4±2.1
ILSS,
ksi
4.48±0.2
5.35±0.1
5.11±0.5
3.50±0.18
4.09±0.12
4.62±0.11
4.67±0.67
T t
g
o c
376
338
360
330
386
372
351
385
.2
0
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-.2
- /
t I I I I I
7',
p %
_'..,./ Cyclophane
content
in endcap,
n wt%
2 24
____-- 10 7.S
• I I I I
50 100 150 200 250 300 350 400 450 500
Tempemlure, °C
Figure 1.--DSC of N-CYCAP polylmldes.
Resin
N-CYCAP
(25 percent m-PDAI
N-CYCA
(100 percent p-PDA
PMR-II-7$
PM R-II-50
Air poMcured (16 hr at 371 °C)
Nttrogon postcumd (24 hr at 398 °C)
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0 5 10 15 20 25 30 35
Weight loss, percent
Figure 2.--Realn TOS after 1000 hours at 343 _C.
N/ A
National/_ronau_c._ and Report Documentation Page
Space Administration
1. Report No. 2. Government Accession No. 3. Recipienfs Catalog No.
NASA TM -104341
5. Report Date4. Title and Subtitle
Long Term Isothermal Aging and Thermal Analysis of
N-CYCAP Polyimides
7. Author(s)
James K. Sutter, John F. Waters, and Maria A. Schverman
9. Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135 - 3191
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546 - 0001
6. Performing Organization Code
8. Performing Organization Report No.
E -6115
10. Work Unit No.
505 - 10-50
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsc, ing Agency Code
15. Supplementary Notes
Prepared for the High Performance Materials Symposium at the Polymer Technology Conference sponsored by
the American Chemical Society, Philadelphia, Pennsylvania, June 3-5, 1991. James K. Sutter and John F.
Waters, Lewis Research Center. Maria A. Schverman, Xavier University, Cincinnati, Ohio. Responsible person,
James K. Sutter, (216) 433-3226.
16. Abstract
N-CYCap polyimides utilize a [2.2] paracyclophane endcap that polymerizes and does not generate volatile gases
during the cure process. These polyimides have both high glass transition temperatures (390 °C) and an onset of
decomposition in air of 560 °C. Thermal oxidative stability (TOS) weight loss studies show that replacing 25 percent
by weight of the paraphenylene diamine in the polymer backbone with metaphenylene diamine improves the weight
loss characteristics. N-CYCAP neat resin samples performed better than PMR-II-50 when exposed at 343 and 371 °C
in air for up to 1000 hours. Preliminary composite studies show that both PMR-II-50 and N-CYCAP have better
thermal stability when fabricated on T-40R. Higher isothermal aging temperatures of longer aging times are needed to
determine the differences in TOS between composite samples of PMR-II-50 and N-CYCAP polyimides.
17. Key Words (Suggested by Author(s))
Polyimides
Thermosetting resins
Polymers
High temperature
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Unclassified
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Unclassified - Unlimited
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Long term isothermal aging and thermal analysis of N-CYCAP polyimides

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