Characterization of model compounds, monomers, resin solutions and cure cycles of PMR-15 polyimide are performed. Successful separation of various reaction products is also accomplished by liquid chromatography. The PMR-15 cure analysis is performed by fourier transform spectroscopy and gas chromatograph - mass spectrometry. Characterization receiving inspection tests for Quality Control are recommended

Hunter, A. B.

English

NASA Technical Reports Server

N86-11272
CHARACTERIZATION METHODOLOGY
FOR PMR-15*
A. B. Hunter
Boeing Aerospace Company
Characterization of model compounds, monomers, resin solutions and cure
cycles of PMR-15 polyimide were performed. Successful separation of various
reaction products were also accomplished by liquid chromatography. The PMR-15
cure analysis was performed by fourier transform spectroscopy and gas chroma-
tograph - mass spectrometry. Characterization receiving inspection tests for
Quality Control are recommended.
INTRODUCTION
Within the aerospace industry polyimides are becoming increasingly important.
One particular polyimide being developed for various uses is PMR-15 as developed
by NASA-Lewis. PMR-15 consists of three monomers
0
- Z-oH
-C-OCH 3
0
0 0 0
HO-,C- 
0 0
A monomethy]
a dimethy]
and
ester referred to as NE;
ester referred to as BTDE;
NH2 O.CH2__NH 2 4,4 - methylenedianiline or MDA.
*Work performed under contract NAS 3-22523.
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https://ntrs.nasa.gov/search.jsp?R=19860001805 2020-03-23T06:25:51+00:00Z
The monomers polymerize under heat by the combining of BTDE and MDA with NE
being an end cap. Final crosslinking occurs through the end cap. The material
is usually received as a graphite prepreg and is then molded into part config-
uration under heat and pressure.
DEVELOPMENT OF METHODOLOGY
The starting materials for this polymer are 1) monomethyl ester of 5-nor-
bornene -2, 3-dicarboxylic acid (NE), 2) Dimethyl ester of 3, 3', 4, 4' -benzo-
phenone-tetracarboxylic acid (BTDE) and 3) 4, 4' - methylenedianiline (MDA).
The two esters are synthesized from their respective anhydrides which are purchased
commercially. The MDA is also purchased commercially. The starting products are
then combined in a methanol solution to form the PMR resin. A suggested route
for the polymerization of the resin system through the cure cycle is the form-
ation of polyamide acid then polyimidization and finally the material becomes
thermally crosslinked. Through the course of the reaction, water, methanol, and
cyclopentadiene are evolved as reaction products.
The resin and starting materials were evaluated by liquid chromatography.
Two modes were used as described below:
Mode Adsorption Reverse Phase
Columns 2 DuPont PSM60 Varian RP MCHIO
Mobile Phase 1: THF:H_O with
0.01% Acetic Acid
Methanol Water
Program Isocratic Gradient
40:60 to 80:20 15 Min.
Detector UV @ 210 and 254 NM UV @ 210 and 254 NM
The isocratic method separates the esters their isomers and reaction products.
(See Figure 1). One difficulty with this method is the MDA remains on the
column and needs to be flushed out periodically to restore baseline. Another
difficulty of the method is during the synthesis of the BTDE a small amount of
triester is formed. The triester elution peak is sometimes poorly resolved with
the NE peaR. However, a quantitation can be made because the NE absorbs at 210 NM
whereas the triester absorbs at both 254 and 210 NM. Figure 2 illustrates two
batches of BTDE comparing a normal cook to one that has been overcooked. Figure 3
illustrates PMR resin with the formation of tetraester. The presence of tetraester
has been correlated with a fall off in mechanical properties. The gradient method
illustrated in Figure 4 separates the MDA from the esters. Although it does not
show the detail of the isocratic method, it does permit quantification of the
MDA. Also with this method a reaction product is detected as the resin ages,
See Figure 5. Thermal analysis studies were also performed. Figure 6 illustrates
a typical differential scanning calorimeter analysis performed in a pressure cell.
One area of interest in the scan is the high temperature exothern occurring at
587K denoting crosslinking taking place. The cure was also followed by infrared
analysis which readily detects the disappearance of the MDA and formation of
imide groups. In addition, the outgassing reaction products were monitored by
152
gas chromatography. Water, methanol and cyclopentadiene were all detected.
Cyclopentadiene was first detected at 423K and as the sample reaches 573K a
discontinuity occurs in the outgassing of cyclopentadiene that seems to correlate
with the exotherm detected by DSC.
A number of methods were investigated to characterize the chemical and
physical changes which occur during this cure cycle. The physical changes were
found to be best characterized by dynamic mechanical analysis (DMA) using the
DuPont compound pendulum method. Typical reAults are show_ in Figure 7. The
first three damping peaks occur at 373K (212_F), 423K (302_F) and 503K (446_F)
and correspond very nicely with (1) the melting of the monomers, (2) the imidi-
zation reaction, and (3) the glass transition of softening and flow of the poly-
imide. The frequency curve, which is a measure of modulus, clearly shows that
the first damping peak corresponds to a decrease in modulus _melting) while the
second corresponds to the increase in modulus due to the imidization reaction.
The third peak shows a frequency and damping relationship typical of the glass
transitio_ in a thermoplastic polymer. During the 30 minute holding period at
522K (480_F) both the damping and the frequency increase slightly which would be
consistent with the completion of the ring closing imidization reaction and the
continued flow of the thermoplastic polyimide. With the resumption of heating
at the end of the 30 minute hol_period, both the damping and the frequency decrease
to a minimum at about 563K (554VF) and then increases as the crosslinking reaction
caused by the thermal decomposition of the nadic ring begins to influence the
flow properties of thermoplastic polyimide. Clearly the 30 minute hold period at
522K (480_F) is the proper point to apply pressure to effect the best possible
consolidation of a composite material since it is just above the glass transition
of the essentially complete polyimide and below the activation temperature for
the crosslinking reaction.
Based on the characterization studies we have identified certain Receiving
Inspection tests for Quality Control. The starting materials are controlled by
liquid chromatography. The resin and prepreg are controlled by liquid chromato-
graphy, infrared analysis and gas chromatography. These tests have successfully
identified non-processable material and materials with low mechanical properties
during this contract.
LIQUID CHROMATOGRAPHY
"_8"I'DEill,__
_E g
--0
A A q-
• 3 s IP
TIME...-.------_
PMR-18 RESIN (R'-7)
1- TETRAESTER PRODUCT
2- BTDA
3- NADIC ANHYDRIDE
4" NA:MDA
Figure 1
153
LIQUID CHROMATOGRAPH
BTDE
BATCHS017
lllt
Figure 2
BATCH 4t82
LIQUID CHROMATOGRAPHY
B ! I MARKER PMR-15
2387 USP-1 BTTE
Figure 3
154
4, I.
i / 7:- --
...--
- fj - .
PMR-15
HPLC OF 67% SOLUTION RESIN - FRESH - UNAGED
Figure 4
, |h "
__ ..,_r-
_._ ....i --%
PMR- 15
HPLC SOLUTION RESIN AFTER 24 HOURS AT 316K(110°F)
Figure 5
155
0E
)
0
_JIk -2
I-
<
UJX -8
-4
-8
-6
S_plm PI_O_-15 LOT-GE5244 R-2
St--e, 13. 22 AS RECO
_°_.,l=/.x. D S C
o
: : : : : , : , ; • . . : - : : : : : : : :/
Roc_.lQn _ 4. ill ,_"
Los Z, 24. el 1/,1, //
S
" :. : "- : : : : : : $ : : : I I I I : : : :
40 I0 120 1QO |00 140 IlO 120 IQO 400 440
TEMPERATURE(°C)
Ftgure 6
8m,plel PXR-15 218/' S'Pt.Y
Size, lll. 7. X S. 3SX._l
,._,. 1._ DI_,'_ o_.. _-u
eo 1;,11
1,080
40 0.8
,..rot _ _ I Y _/\ _'"to.,E
O _UT /_ I I l| _L I X' I C5!"I/kY/i,o io.,
Ik 10
. . .' : ., ,;. : : : : : : : : : : : : : :. : : : t"!"0. _)
AP10
O..20 40 .SO .|0 100 1|0 140. 100 180. 200. t:lO
TIME (MIN)
Ftgure 7
156


Characterization methodology for PMR-15

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