Future generation aircraft need higher performance polymer matrices to fully achieve the weight savings possible with composite materials. New resins are being formulated in an effort to understand basic polymer behavior and to develop improved resins. Some polymer/curing agent combinations that could be useful are difficult to process. In the area of epoxies, a major problem is that some components have physical properties which make them difficult to utilize as matrix resins. A previous study showed that the use of ultrasonic energy can be advantageous in the mixing of curing agents into a standard epoxy resin, such as MY 720 (Ciba-Geigy designation). This work is expanded to include three novel epoxides

Ficklin, R.

Hodges, W. T.

Pratt, J. R.

St.clair, T. L.

English

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EVALUATION OF EXPERIMENTAL EPDXY MONOMERS
W. T. HODGES, T. !. ST. CLAIR, J. R. PRATT* AND ROBIN FICKLIN*
RASA LANGLEY RESEARCH CENTER
HAMPTON, VA 23665
ABSTRACT
Three experimental epoxy monomers were cured with two isomeric curing
agents and compared to a well documented standard epoxy system. The
experimental epoxy monomers were, the 3,3'- and 4,4'-isomers of
tetraglycidylsulfonyldianiline (TGDDS) and the 3,3'-.isomer of
tetraglycidlymethylenedianiline, (TGMDA). The 3,3'- and 4,4'-isomers of
diaminodiphenylsulfone (DDS) were used as the curing agents with the epoxy
monomers. The standard epoxy monomer used in this study was the
	 r
4,4'-isomer of TGMDA, Araldite MY-720. This standard epoxy monomer was
also cured with both isomers of DDS. All of the systems were mixed
ultrasonically for uniformity of constituents. Neat resin moldings were
cast and cured for each system, and their physical and mechanical
Yr %^perties were compared.
*Miss. Univ. for Women, Columbus, MS 39701
EVALUATION OF EXPERIMENTAL EPDXY MONOMERS
W. T. Hodges*, T. L. St. Clair, J. R. Pratt**, and Robin Ficklin**
NASA Langley Research Center
Hampton, Virginia 23665
For publication to SAMPE Quarterly Journal
*Structures Laboratory, U.S. Army Research and Technology Laboratories
(AVSCOM), Hampton, VA 23665.
"Mississippi University for Women, Columbus, MS 39701.
\: n
►-a
1. Introduction
Future generation aircraft need
higher performance polymer matrices
to fully achieve the weight savings
possible with composite materials.)
New resins are being formulated in an
effort to understand basic polymer
behavior ana to develop improved
resins.2-5 Some polymer/curing
agent combinations that could be
useful are difficult to process. In
the area of epoxies, a major
problem is that some components have
physical properties which make them
difficult to utilize as matrix
resins. A previous study in our
laboratory has shown that the use of
ultrasonic energy can be advantageous
in the mixing of curing a gents into a
standard epoxy resin, such as MY 720
(Ciba-Geigy designation). 6	In the
present study we have expanded this
work to include three novel epoxides.
2. Experimental
Processing and Characterization
Equipment
analyzer, with a heating rate of 5°C/	 r'
min and a penetration load of 15
grams. Thermogravimetric analyses
(TGA) were run on a Perkin Elmer
TGS-2 system with an AR-2 autobalance
and a UU-1 temperature program
controller at a heating rate of
2.5°C/min. Dynamic mechanical
analyses (DMA) were performed on a
DuPont Model 982 DMA unit with a
Model 1090 thermal analyser at a
heating rate of 5°C per minute on a
polymer specimen with 3.34 mm x 6.37
mm x 12.2 mm dimensions.
A DuPont 990 thermal analyser was
used for the differential scanning
calorimetry (DSC) measurements, at a
temperature program of 10°C/min.
Flexural strength and moduli of the
specimens were determined in accord-
ance with ASTM procedure D790 using
an Instron TTC M1 testing machine.
Polymer Synthesis
The experimental epoxy monomers used
are illustrated in Figure 1.
I . ' n
The ultrasonic unit used in the
mixing was a Dukane Model 40A305A
generator with 43A5 transducer and
model 113 horn, rated at 300 watts
output power. Glass transition
temperatures by probe penetration of
cured samples were measured on a
DuPont Model 943 thermomechanical
Figure 1 - Ex p erimental Epoxy
Monomers
The experimental epoxy systems were
compared to a standard epoxy system
based on the 4,4'-tetraglycidyl-
methylenedianiline (TGMDA) monomer.
The experimental epoxides with the
-S02 - bridge were the 3,3'- and 4,4'-
isomers of tetraglycidylsulfonyl-
dianiline MODS) and the 3,3'-isomer
of TGMDA.
The standard TGMDA epoxy system used
in this study was acquired from Ciba-
Geigy Corporation as Araldite MY-720
with an epoxy content7-9 of 971.
The major constituent of MY-720 is
4,4'-TGMDA (Figure 2).
Monomer Synthesis
4,4'-Suifonylbis(N,N-bis(2,3-epoxy-
propyl) ,Janiline, 4,4'-TGDDS
A mixture of bis(4-aminophenyl)-
sulfone (101g, 0.407 mol), 22 ml of
glacial acetic acid, and
epichlorohydrin (400 ml, a 212%
excess) was heated in a 3-neck flask
equipped with a Trubore stirrer for
27 hours at 48-60°C. The solvent and
excess epichlorohydrin were removed
on a flash evaporator for 2 hours at
55 0 . Methyl ethyl ketone (300 ml)
was added, and the resulting solution
was treated with 299g of aqueous 451,
NaOH solution (a 10% excess). The
NaOH solution was added incrementally
during 1 hour while refluxing, and
the reflux was maintained for 1 hour.
On cooling, a small amount of white,	 i
low molecular weight polymer was
removed by filtration, and the pH of
the filtrate was adjusted to 7 with a
small amount of HC1. After drying
with anhydrous MgSO 4 , the methyl
ethyl ketone was removed in vacuo for
2 hours at 57°C. The yield was 114 g
(590); the average epoxy content was
74%.
3,3'-Sulfonylbis[N,N-bis(2,3-epoxy-
propyl)[aniline, 3,3'-TGDDS Modified
Procedure
The bis(3-aminophenyl)sulfone (131 g,
0.528 mol) was dissolved in 550 ml
epichlorohydrin and 30 ml glacial
acetic acid. The mixture was heated
for 30 hours at 55-60°C before the
volatiles were removed in vacuo at
60° for 2 hours. Methyl ethyl ketone
(300 ml) was added and the solution
was treated at once with 262 g of 50%
aqueous NaOH solution (a 100%
excess). A temperature of 50-60°C
was maintained for 2.5 hours before a
white polymer was filtered and
discarded. The filtrate was washed
with water and then with HC1 to
adjust the pH of the aqueous layer
from 14 to 5. After separation of
the layers, the methyl ethyl ketone
solution was dried, and the solvent
was removed on the flash evaporator.
The final heating stage was 0.5 hour
at 78°C. The yield of viscous, amber
oil was 216 g (87%). The epoxy
content was q3b.
C^)
3,3'-MethylenebisIN,N-bis(2,3-epoxy-
propyl)Janiline, 3,3'-TGMDA
3. Results and Discussions
Using a similar procedure as in the
previous examples a sample of this
monomer was prepared from 3,3'-
methylenedianiline and epichlorohy-
drin in aqueous ethanol at reflux for
20 hours; 50% NaOH solution was used
to cyclize the chlorohydrin interme-
diate. After removal of the ethanol
in vacuo, methylene chloride was
added, and the aqueous layer was
neutralized with HC1. The methylene
chloride layer was washed with water
and dried with anhydrous MgSO4 before
the solvent was removed in vacuo to
yield 85 g (9010) of product having an
average epoxy content of 750%.
Polymer Characterization
Apparent glass transition temperature
(Tg) measurements by the penetration
method are listed in Table 1 along
with TGA data. The Tg's for the
systems that were studied ranged from
183°C to 265°C. In the case of the
4,4'-TGDDS cured with 4,4'-DDS, the
lower epoxide equivalent system (6310)
had a Tg , of 213°C, verses 265°C for
the higher epoxide equivalent (74%)
system. The TGA data shows the
temperature at which each sample had
lost 50% of its original weight, when
heated in static air at a 2.50C/min.
The experimental monomers and the
baseline MY-720 resin were cured with
both the 3,3'- and 4,4'-isomers of
DDS. All samples were mixed
ultrasonically until they were
transparent, as described in
reference 6.
Sample Cure
After ultrasonic mixing, the resins
were poured into flat bottomed
aluminum pans 57 mm in diameter. All
samples were placed in an oven and
cured according to the cycle
illustrated in Figure 3.
Weight loss TGA data is illustrated
in Figure 4. All of the systems
showed similar behavior with decompo-
sition beginning around 250°C.
Figure 5 compares the DMA behavior of
each system. All systems showed a
transition around -40°C; however, the
high temperature transitions began at
different temperatures from 150°C to
300°C. DSC curves in Figure 6 show
the exothermic behavior of each cued
material. The presence of an
exotherm indicates that a complete
cure had not occurred. This was
evident in all except two cases.
Eased on previous studies in this
la'^oratory these residual exotherms
are no more than artifacts of the
on gi nail cure.
, M
WMechanical Testing
Flexural strengths (Table 2) were
good in comparison to the standard
system for the experimental polymers,
especially for the 4,4'-TGDDS
systems. Baseline MY-720 strengths
were comparable with those in
reference 6.
As can be seen in Tables 1 and 2,
there is a difference in the
mechanical properties of the two
samples of 4,4'-TGDDS that were cured
with 4,4'-DDS. The sample with the
lower epoxide content exhibited lower
strength and modulus than the sample
made with higher epoxide content.
This may be attributed to a lower
crosslink density in the 63% epoxide
material.
The exceptionally high modulus value
for the 3,3'-TGMDA epoxide cured with
4,4'-DDS can most likely be
attributed to a more complete cure.
This material exothermed severely
during its cure cycle. In one case
the exotherm was so intense that the
sample burned and was discarded.
Excessive curing of crosslinking
systems generally leads to high
moduli with accompanying losses in
strength.
Particularly noteworthy are the
properties obtained from the TGDDS
epoxides. In all cases the moduli
are higher than for the standard
MY-720/4,4'-DDS system. For
structural resins, modulus is very
important. In particular, the
4,4'-TGDDS cured with 3,3'-DDS had a
29% higher modulus and also a 12%
higher flexural strength.
Another structure-property relation-
ship that is evident from Table 1 is
that the 3,3'-epoxide always afforded
a lower glass transition temperature
than the corresponding 4,4'-epoxide.
This was true for the TGMDA and TGDDS
systems.
Conclusions
Three novel epoxides were prepared
and cured with two standard curing
agents. The properties of the
experimental systems compared
favorably to a standard epoxide
system (MY-720/4,4'-DDS). All of the
experimental systems exhibited higher
flexural moduli than the standard.
This is an important property for
structural resins. There were some
differences in glass transition
temperatures with the 3,3'-epoxy
system always having a lower
transition than the corresponding
4,4'-epoxy system. The polymer
decomposition temperatures were all
quite similar.	 In all cases the
ultrasonic mixing technique afforded
very uniform, homogeneous mixtures.
However, during subsequent cures some
systems tended to exotherm more than
others. Result-, of this research
indicate that the 4,4'-TGDDS is a
promising system and is worthy of
additional study because of higher
glass transition temperatures and
good mechanical properties.
References
1. H. L. Eohon, Opportunities for
Composites it Commercial
Transport Structures, NASA CP
2251, November 1982.
2. D. A. Scola and R. H. Pater, The
Properties of Novel Bisimide
Amine Cured Epoxy/Celion 60uu
Graphite Fiber Composites, SAMPE
Journal, Vol. 18, No. 1, pp.
16-23, January/February 1982.
3. J. J. King, R. F. Sellers, and
R. N. Castonguay, New Tough,
High Performance Epoxy Amine
Resin Systems, SAMPE Quarterly,
April 1981, Vol. 12, No. 3, pp.
8-11.
4. D. Crozier, G. Morse and Y.
Tajima, The Development of
Improved Chemical Analysis
Methods for Epoxy Resins, SAMPE
Journal, Vol. 18, No. 5, pp.
17-22, September/October 1982.
5. D. G. Glagow and C. Garthwait,
Exploratory Study of the Effects
of Novel Diamine Curing Agents
and Isocyanate Precursors on the
Properties of New Epoxy and
Urethane Adhesives, NASA
CR-145227, May 1972.
6. W. T. Hodges and T. L. St.
Clair, Ultrasonic Mixing of
Epoxy Curing Agents, SAMPE
Quarterly, Vol. 14, Number 3,
April 1983.
7. N. H. Reinking, U. S. 2,951,822
(1960) to Union Carbide Corp.
8. H. Lee and K. Neville, "Handbook
of Epoxy Resins", Ch. 4,
McGraw-Hill, New York, 1967.
9. H. John and P. Goetzky in "Epoxy
Resins Chemistry and Technology"
(C. May and Y. Tanaka, ed.),
Ch. 11, Marcel Dekker, Inc., New
York, 1973.
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Figure 3 - Cure Cycle for Resin Disks
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Evaluation of experimental epoxy monomers

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