A high temperature semi-interpenetrating polymer network (semi-IPN) was developed which had significantly improved processability, damage tolerance and mechanical performance, when compared to the commercial Thermid.RTM. materials. This simultaneous semi-IPN was prepared by mixing the monomer precursors of Thermid.RTM. AL-600 (a thermoset) and NR-150B2 (a thermoplastic) and allowing the monomers to react randomly upon heating. This reaction occurs at a rate which decreases the flow and broadens the processing window. Upon heating at a higher temperature, there is an increase in flow. Because of the improved flow properties, broadened processing window and enhanced toughness, high strength polymer matrix composites, adhesives and molded articles can now be prepared from the acetylene end-capped polyimides which were previously inherently brittle and difficult to process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to high temperature polymers. It 
relates particularly to a semi-interpenetrating polymer network approach 
to the obtainment of more processable, tougher and more moisture resistant 
high temperature polymers. The systems are particularly adapted to use as 
moldings, adhesives and composite matrices. 
2. Description of the Related Art 
There is a continual search in the art for more processable and damage 
tolerant high temperature polymers for use as moldings, adhesives and 
composite matrices in aerospace and electronic technologies. Materials 
used in these environments must have a variety of desired properties 
including easy processing, good damage tolerance, a high glass transition 
temperature, good mechanical performance, capable of withstanding high 
temperature, low moisture absorption, and resistance to a variety of 
organic solvents. Although polymers exist that exhibit one or more of the 
above properties, these materials are generally deficient in at least one 
other desired property. 
One example of such material is the thermoplastic polyimide, NR-150B2, 
which is commercially available from E.I. Dupont de Nemours and Company 
(Dupont). This material is well known for its good toughness and 
microcracking resistance. In addition, it has unusually high 
thermo-oxidative stability. Unfortunately, it is difficult to process and 
it requires processing temperatures as high as 400.degree. C. 
Another example includes the commercially available Thermid.RTM. materials, 
which are commercially available from the National Starch and Chemical 
Corporation. These materials are acetylene-endcapped polyimides. They 
offer outstanding thermo-oxidative stability, exceptional dielectric 
properties and excellent resistance to humidity at elevated temperature. 
However, these materials are inherently brittle due to their highly 
crosslinked structures and are liable to microcrack in their composites 
when subjected to thermal cycling. Also, despite having the advantage of 
addition-curing, they are actually very difficult to process. This is 
primarily due to their very narrow processing window. Thermid.RTM. MC-600, 
for example, has a gel time of three minutes at 190.degree. C. (A. L. 
Landis and A. B. Naselow, NASA Conference Publication 2385 (1985)). The 
problem becomes exacerbated in composite fabrication, particularly in 
large and/or complex composite parts. Because of the processing 
difficulty, the composite property values for Thermid.RTM. MC-600 are 
lower than expected. The National Starch and Chemical Corporation product 
data sheet number 26283 reports the values of 195 and 148 ksi for the 
unidirectional flexural strengths tested at 25.degree. C. and 316.degree. 
C., respectively, and interlaminar shear strengths of 12 and 8 ksi at 
25.degree. C. and 316.degree. C., respectively. The desired values are 250 
and 150 ksi for the 25.degree. C. and 316.degree. C. flexural strengths 
and 14 and 8 ksi for the 25.degree. C. and 316.degree. C. interlaminar 
shear strengths. 
This processing problem was well recognized in the early stages of the 
material's development. Several approaches have been attempted to improve 
the processability of Thermid.RTM. MC-600. The first approach was to 
incorporate difunctional or monofunctional acetylene-terminated reactive 
diluents into the material (A. L. Landis and A. B. Naselow NASA Conference 
Publication 2385 (1985)). This approach had limited success due to the 
lack of a common solubility between the preimidized oligomer and the 
diluent. 
Grimes and Reinhart (U.S. Pat. No. 4,365,034) took another approach, 
recognizing that the processing problem was related to the fast cure rate 
of the acetylene-terminated material. They added a chemical inhibitor to 
retard the rate of cure so that the oligomer remains in the fluid state 
for an extended period of time thereby increasing the processing window. 
Some examples of this inhibitor include hydroquinone, maleic acid, 
glutaric acid, or bis(.beta.-naphthyl)para-phenylene diamine. However, 
whether such an approach indeed facilitates the fabrication of high 
quality composite materials was not demonstrated. 
To improve the resin flow, Landis and Naselow (NASA Conference Publication 
2385 (1985)) developed an isoamide version of Thermid.RTM. MC-600, which 
is now known as Thermid.RTM. IP-600. Despite the markedly improved resin 
flow, the resulting composite showed relatively low levels of mechanical 
properties (unidirectional flexural strengths of 130 and 78 ksi at 
25.degree. C. and 288.degree. C. and interlaminar shear strengths of 7 and 
5 ksi at 25.degree. C. and 288.degree. C., respectively). 
Recently, Landis and Lau (U.S. Pat. No. 4,996,101) extended the isoamide 
modification concept to the development of a semi-interpenetrating polymer 
network (semi-IPN). They prepared a sequential semi-2-IPN by combining a 
thermoplastic polyisoimide with a thermosetting imide or isoamide oligomer 
which contains an acetylene-terminated group. They assert that the 
isoamide modification can, by theory, improve the composite processing and 
thereby produce better quality composite materials than the present 
state-of-the-art materials. Unfortunately, they did not demonstrate the 
improved composite properties for these semi-2-IPNs. The absence of a 
showing of the composite mechanical properties makes the utility of this 
technology questionable. It is doubtful that the isoamide modification 
can, in practice, significantly improve the processability. The reason is 
as follows: the isoamide undergoes an isoimide-imide isomerization. This 
isomerization reaction induces a melt-flow transition which is responsible 
for the improved resin flow. However, the isomerization reaction takes 
place rapidly and occurs at a relatively low temperature. Thermid.RTM. 
IP-600, for example, shows a sharp melt-flow transition peak at 
148.degree. C. in the Rheometrics.RTM. rheology-temperature curve. This is 
illustrated in FIG. 1. This transition is due to the isoamide-imide 
isomerization. This interpretation is supported by the appearance of 
another transition peak occurring at 188.degree. C. due to the melt-flow 
of the imide formed from the isoamide. Thermid.RTM. MC-600 has the same 
transition peak at 188.degree. C. The cure temperature for Thermid.RTM. 
based composites is usually 250.degree. C. At this critical cure 
temperature, Thermid.RTM. IP-600 has already gelled, the gel temperature 
being 220.degree. C. Thus, the enhanced flow resulting from the isoamide 
modification will not significantly affect the composite fabrication. This 
may explain why low values were obtained for the composite mechanical 
properties formed from Thermid.RTM. IP-600. 
Egli and St. Clair (U.S. Pat. No. 4,695,610) have also prepared chemically 
compatible semi-2-IPNs from thermoplastic polyimide sulfones and 
thermosetting acetylene-endcapped polyimide sulfones. However, none of 
these prior art products have the desired combination of properties set 
forth herein above. 
It is believed that the processing difficulty of the Thermid.RTM. materials 
is directly related to the fundamental nature of the curing chemistry. 
According to the proposed cure mechanism (Goldfarb, Lee, Arnold, and 
Helminiak, NASA CP 2385 (1985)) the curing of an acetylene-terminated 
oligomer proceeds stepwise and can be broadly divided into two distinct 
stages. The reaction sequence is shown by the following reaction scheme. 
##STR1## 
In stage one, the reaction site is an acetylene-terminated group, which is 
marked in the rectangular area at the top of the reaction equation. This 
reacting group is relatively sterically unhindered and is ready to react 
with another acetylene-terminated group of a different molecule. The 
addition reaction occurs very rapidly via a free radical mechanism. In a 
very short period of time, six to seven molecules are added to form a 
cluster, which has six to seven arms and a conjugated polyene moiety 
embedded in the center of the cluster. At this stage, the material is in 
the solid state. The reaction essentially stops until a higher curing 
temperature is applied. 
The fast reaction rate of the stage one reaction is responsible for the 
narrow processing window of an acetylene-terminated oligomer. This entraps 
any residual solvent and air. As a result, the cured neat resin, 
composite, and adhesive joint contain voids and cracks which result in 
poor mechanical performance. 
Another important factor contributing to the poor mechanical performance, 
particularly elevated temperature mechanical properties, is a lack of high 
degree of crosslinking. The crosslinking reaction occurs in stage two. The 
reacting group is the conjugated polyene marked in the rectangular area in 
the middle of the reaction scheme. Since this reaction site is buried in 
the center of a cluster, it is extremely difficult sterically for the 
polyene to interact with another molecule of the polyene. Consequently, a 
very high processing temperature is required to effect the crosslinking 
reaction. 
The novelty of the present invention lies in the concept that if stage one 
of the reaction is slowed down and stage two is accelerated, a 
well-consolidated composite will result. The semi-IPN reaction system of 
the present invention is designed to exploit this concept. 
An object of the present invention is to prepare a tough, processable 
semi-IPN from a thermosetting and a thermoplastic polyimide. The semi-IPN 
reaction system is so designed to undergo chain extension below 
300.degree. C., whereby the flow and the reaction rate are decreased and 
the processing window is broadened and, upon heating above 300.degree. C., 
the flow is increased and crosslinking occurs at a rate which allows for 
the formation of a void-free polymer network. 
Another object of the present invention is to form an unconventional 
simultaneous semi-interpenetrating network from a thermoplastic monomer 
precursor solution and a thermosetting monomer precursor solution. 
Another object of the present invention is to improve the processing of 
Thermid.RTM. AL-600. 
Another object of the present invention is to improve the processing of 
NR-150B2. 
Another object of the present invention is to prepare molding compounds, 
adhesives, and polymer matrix composites from the semi-interpenetrating 
network. 
SUMMARY OF THE INVENTION 
A high temperature semi-interpenetrating polymer network (semi-IPN) was 
developed which had significantly improved processability, damage 
tolerance, and mechanical performance, when compared to the unmodified 
acetylene-endcapped polyimides known commercially as Thermid.RTM.. The 
improved processability is attributed in part to the broadening of the 
processing window and enhanced resin flow at the critical processing 
temperatures above 300.degree. C. This was accomplished by a two step 
process. In the first step, the monomers slowly underwent linear chain 
extension below 300.degree. C. This reaction was slow enough to allow the 
volatiles from the solvent and the reaction to escape, increasing the 
flow, and broadening the processing window. In the second step, the resins 
were heated above 300.degree. C., causing an increase in molecular 
mobility and flow which allows for the formation of a composite having 
improved damage tolerance and mechanical properties. For example, the 
fracture energy for the semi-IPN was 603 j/m.sup.2 as compared to 93 
j/m.sup.2 for Thermid.RTM. LR-600. 
The simultaneous semi-IPN was prepared using a non-conventional synthetic 
method where the monomer precursors of a thermoset were mixed with the 
monomer precursors of a thermoplastic and allowed to randomly react upon 
heating. In the present invention, the thermosetting polyimide monomer 
solution was Thermid.RTM. AL-600, which is commercially available from the 
National Starch and Chemical Corporation. The thermoplastic polyimide 
monomer precursor solution is commercially available from E.I. Dupont de 
Nemours and Company (Dupont) under the name NR-150B2. 
These semi-IPNs are useful as molding compounds, adhesives, and polymer 
matrix composites for the electronics and aerospace industries.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In high performance semi-IPN synthesis, one or more easy-to-process, but 
brittle thermosetting polyimides are combined with one or more tough, but 
difficult-to-process linear thermoplastic polyimides to form a semi-IPN 
polyimide which has a combination of several desirable properties. These 
properties include easy processability, damage tolerance, good mechanical 
performance, and good thermo-oxidative stability. This is achieved by 
controlling factors such as: (1) selection of constituent polymer 
components; (2) composition variation of the constituent materials; and 
(3) processing parameters. 
The selection of the constituent thermosetting and thermoplastic polyimides 
is based primarily on their processing and property compatibility. Of 
particular importance are solubility in a common organic solvent and 
compatible cure cycles. In addition, these polymers must have comparable 
glass transition temperatures (Tgs) of .+-.50.degree. C. coupled with 
similar mechanical performance and thermo-oxidative stability. These 
qualifications are met in the present invention. 
The thermosetting polyimide, Thermid.RTM. AL-600, is a solution containing 
the following monomeric precursors: 
##STR2## 
In this solution, 2 moles of BTDE are combined with 1 mole of APB and 2 
moles of APA. These precursors form an acetylene-terminated oligomer which 
then crosslinks to give a highly crosslinked polyimide when heated. 
The thermoplastic polyimide portion of the semi-IPN was prepared from a 
monomeric mixture of the following three compounds: 
##STR3## 
This polyimide precursor solution in N-methyl pyrrolidinone (NMP) is 
commercially available from Dupont under the name NR-150B2. In this 
solution, 6FTA is present in a stoichiometric quantity with respect to the 
total of PPD and PMD. The molar ratio of PPD to MPD is about 95:5. 
Although this mixture exists in NMP, there are other polyimide precursor 
solutions available from Dupont which are in ethanol. These systems are 
marketed under the trademarks NR-150B2 S2X to NR-150B2 S10X. When 
polymerized, this thermoplastic polyimide contains the following repeat 
unit: 
##STR4## 
The composition of these materials significantly affects many aspects of 
the processing, properties, and morphology of the semi-IPN. For example, 
by increasing the concentration of the thermosetting component, there is 
an increase in the processability and performance of the semi-IPN but a 
decrease in the toughness characteristics. Although the weight ratio of 
the thermoset to the thermoplastic can be varied from 95:5 to 5:95, the 
ratio between 80:20 and 20:80 is preferred. The ratio of 80:20 gave the 
best overall balance of processing, performance, and cost effectiveness. 
The semi-IPN of the present invention exhibits significantly improved 
processability over the prior art. The curing reaction of the prior art 
involves two steps or stages. In the first stage, there is a very rapid 
free-radical initiated addition reaction through the acetylene-terminated 
group leading to a linear polyene structure. This reaction takes place at 
a relatively low temperature (200.degree. to 250.degree. C.). The second 
stage involves a very slow crosslinking reaction of the conjugated double 
bond in the polyene to yield a highly crosslinked structure. This reaction 
occurs at a very high temperature (e.g. 371.degree. C.). The present 
invention designed a reaction system to achieve that the reaction rate for 
the first stage was decreased and the second stage was accelerated. A 
retarded stage one reaction broadens the processing window and allows the 
volatiles to escape. Also, increasing the rate of stage two increases the 
degree of crossslinking and, thus, improves the elevated temperature 
mechanical properties. 
These objectives were achieved through a change in the flow properties of 
the prior art. This was made possible by the presence of a thermoplastic 
component, that exhibited poor flow in the low temperature region and good 
flow in the high temperature range. Thus, its presence decreases the flow, 
slows down the reaction rate and broadens the processing window of the 
prior art, during the low temperature curing stage. Also, in the high 
temperature region, its presence increases the flow, molecular mobilities 
and rate of the crosslinking reaction. This provides a high temperature 
system having both improved processability and thermal mechanical 
performance, compared to the unmodified prior art. Furthermore, if the 
thermoplastic used has good toughness, its presence also enhances the 
toughness related properties, including fracture toughness, impact 
resistance, and microcrack resistance. 
To illustrate how the presence of a thermoplastic component alters the 
rheological properties of the prior art, FIG. 2 shows the rheological 
properties of a semi-IPN prepared from a Thermid.RTM. AL-600 and NR-150B2 
monomeric precursor solution. The sample preparations and rheological 
characterization are detailed in the examples. For a meaningful comparison 
of the rheological properties, the constituent materials were also 
prepared and characterized along with the semi-IPN sample under an 
identical condition. Their rheological properties are also shown in FIG. 
2. Thermid.RTM. AL-600 had two large transition peaks at 140.degree. C. 
and 210.degree. C., respectively. As a result, this material exhibited 
excessive flow in the low temperature region (140.degree.-200.degree. C.). 
The opposite is true for the NR-150B2 material. This material did not melt 
and its viscoelasticity behaved like a solid. FIG. 3 shows the 200.degree. 
C. isothermal curing curve for this material. 
Interestingly, when the cure temperature was raised above 200.degree. C., 
the NR-150B2 began to flow rapidly and stayed in a fluid state throughout 
the rheological measurements for up to 430.degree. C. (see FIG. 4). 
Conversely, the Thermid.RTM. AL-600 material rapidly gelled (gel 
temperature 220.degree. C.) and became a rigid solid at temperatures above 
260.degree. C. This behavior is also seen in the 250.degree. C. isothermal 
curing curve shown in FIG. 4. There was a dramatic increase in moduli 
(three to four orders of magnitude) just within 1 0 minutes at 250.degree. 
C. 
In the semi-IPN, the presence of the NR-150B2 material decreased the flow 
of the Thermid.RTM. AL-600 in the temperature range of 140.degree. C. to 
200.degree. C. This provided synergistic flow properties for the semi-IPN. 
In the higher temperature region (200.degree. C.-400.degree. C.), the 
presence of the NR-150B2 material increased the flow of the Thermid.RTM. 
AL-600 (see FIGS. 2 and 4). The increased flow at 250.degree. C. and 
316.degree. C., which were the cure temperatures used in the present 
invention, is particularly important. As a result, the improved 
processability has provided high quality composites. This is demonstrated 
in the examples. The composite property values obtained in this invention 
were significantly higher than those reported by the National Starch and 
Chemical Corporation and Landis, as mentioned previously. A unidirectional 
flexural strength of 279 ksi and interlaminar shear strength of 20.7 ksi 
were obtained for the semi-IPN matrix resin of the present invention when 
tested at room temperature. In fact, these values mark the first time a 
high level of composite mechanical properties have been reported in the 
open literature for the Thermid.RTM.-based materials. This is remarkable 
in view of the fact that these materials have been under experimental and 
developmental evaluation and modification for the past 20 years. 
In the present invention, the simultaneous synthetic method is preferred, 
because it offers easier processing, better performance, and less phase 
separation, as compared to the sequential approach. In the conventional 
method, an uncrosslinked preimidized oligomer is crosslinked with a 
monomer precursor of NR-150B2. The constituent thermosetting and 
thermoplastic polymers are formed independently without any chemical 
interference between the precursors of the two polymer components. 
The synthetic method employed in making the present semi-IPN was 
non-conventional. This method involved mixing the monomers of the 
thermosetting component with the monomers of the thermoplastic component 
and allowing them to react randomly to form a simultaneous semi-IPN. There 
is an inter-reaction between the monomers of the thermoset and the 
thermoplastic which results in a semi-IPN which is significantly different 
in chemical structure and properties from those prepared by conventional 
methods. The reaction is illustrated by the following scheme. 
##STR5## 
Some of the products formed have the chemical structures shown below: 
##STR6## 
and other acetylene-terminated imide oligomers. 
The non-conventional synthetic method is very attractive because it uses 
low viscosity, low molecular weight starting materials. These starting 
materials are soluble in a low-boiling solvent. The use of a low-boiling 
solvent enables ease of solvent removal during the product manufacturing. 
The semi-IPN polyimide of this invention is useful as a composite matrix 
and as an adhesive and molding compound for long-term applications in the 
range from 200.degree. C. to 316.degree. C. as in aerospace structural 
components and especially in electronic technologies. 
The following are examples which illustrate the preparation and use of 
semi-IPNs for applications such as advanced composites, structural 
adhesives, and molding articles. These examples are merely illustrative 
and intended to enable those skilled in the art to practice the invention 
in all of the embodiments flowing therefrom, and do not in any way limit 
the scope of the invention as defined in the claims. 
EXAMPLES 
Example 1 
Rheological Characterization 
The following is the procedure used to determine the rheological properties 
of the semi-IPN systems and their constituent materials. A sample powder 
was prepared by precipitation into water in a high speed blender. The 
solids were collected, washed with water, and dried at room temperature 
for one week. No heat treatment was given to the dried powder prior to the 
rheological measurements. This was done to study their thermal transitions 
in the low temperature region. For solid materials, such as Thermid.RTM. 
IP-600, Thermid.RTM. MC-600, and Thermid.RTM. FA-700, the commercial 
products were used as received. Rheological measurements were performed on 
a Rheometrics.RTM. System 4 rotary rheometer equipped with a parallel 
plate test fixture. A sample disc of 2.50 cm in diameter was prepared by 
molding approximately 0.7 g of material at room temperature under a 
pressure of 5,000 psi. The resulting sample disc was approximately 1.5 mm 
in thickness. The sample discs were always stored inside the decicator 
before use. During measurement, the plates and the test sample were 
enclosed in a heated chamber purged with dry nitrogen. In the isothermal 
experiment, the test chamber was always pre-warmed to the test temperature 
before loading the sample. In the dynamic experiment, the test chamber was 
prewarmed to 110.degree. C., followed by temperature scans from 
110.degree. C. to 450.degree. C. at a rate of 2.degree. C./min. In both 
cases, the initial (first) measurement was taken after the sample was 
subjected to oscillatory shear under the initial test temperature for 
approximately three minutes. In addition to a dynamic run, isothermal 
measurements were also made at 135.degree. C., 200.degree. C., and 
250.degree. C., respectively. 
A dynamic motor was used to drive the upper plate to oscillate continuously 
at a fixed frequency of 10 rad/sec. The bottom plate, which remained 
stationary during the measurement, was attached to a torque transducer 
which recorded forces. The strain (oscillatory amplitude) level was 
adjusted manually in accordance with the changing stiffness of the 
reactive resin system during measurement. The levels of strain were 
selected to assure that the measurements were performed within the 
material's linear viscoelastic response range and, at the same time, 
adequate torque values were generated without slippage. Each experiment 
was repeated at least twice to ensure its reproducability. The recorded 
cyclic torque values were separated into in-phase and out-of-phase 
components, and the corresponding storage (G') and loss (G") moduli and 
the tan .delta. values were calculated by the Rheometrics.RTM. Data 
Acquisition and Analysis package. 
Example 2 
Preparation of semi-IPN of Thermid.RTM. NR-150B2 
This semi-IPN was prepared by the non-conventional synthetic method which 
was generally discussed supra. 
To 138.6 g of a Thermid.RTM. AL-600 monomeric precursor solution (75 weight 
percent solids in ethanol as supplied by the National Starch and Chemical 
Corporation) was added 42.6 g of an NR-150B2 monomeric precursor solution 
(61.1 weight percent solids in ethanol obtained from Dupont) and 38.0 g of 
anhydrous ethanol. The mixture was stirred at room temperature for one 
hour to yield a homogeneous, viscous dark black solution, which contained 
about 59 weight percent solids. The Thermid.RTM. AL-600 and NR-150B2 
monomeric precursors were present in approximately 80 and 20 weight 
percent, respectively. 
Example 3 
Neat Resin Preparation 
To prepare a neat resin, the solution of Example 2 was concentrated at 
100.degree. C. under vacuum (30 inches Hg) for two hours and then staged 
at 200.degree. C. for one hour in air to afford a black molding powder. 
About 15.00 g of this molding powder was compression molded at 250.degree. 
C. for one hour and at 316.degree. C. for another hour under 2500 psi 
pressure. The material was removed from the press when the mold 
temperature reached 177.degree. C. This process yielded a neat resin which 
had a density of 1.32 g/cc and showed no detectable voids or defects by a 
visual inspection. 
The as cured neat resin was used to prepare compact tension testing 
specimens for fracture energy evaluation. However, for the other test 
specimen preparations, the resin was post-cured at 316.degree. C. for 16 
hours in air. To make a meaningful comparison of the properties, the neat 
resins of Thermid.RTM. LR-600 and NR-150B2 were also prepared and tested 
along with the semi-IPN material under identical conditions. There was one 
exception, in that the NR-150B2 neat resin had an additional curing at 
350.degree. C. for one-half hour in order to increase the molecular 
weight. Table 1 compares the physical and mechanical properties of these 
three neat resins. 
TABLE 1 
______________________________________ 
Neat Resin Properties 
Semi-IPN 
Thermid .RTM. 
AL-600 Thermid .RTM. 
Property and NR-150B2 
LR-600 NR-150B2 
______________________________________ 
.sup.a Glass Transition 
320 290 352 
Temperature, .degree.C. 
.sup.b Fracture Energy, 
603 93 2555 
G.sub.1c, J/m.sup.2 
.sup.c Temperature at 
490 460 515 
5% weight loss 
by TGA in Air 
.sup.d Moisture 
-- 0.3 0.6 
Absorption, % 
______________________________________ 
.sup.a By TMA 
.sup.b Per ASTM E399 
.sup.c At a heating rate of 2.5.degree. C./min 
.sup.d Two weeks in water at room temperature 
Example 4 
Composite Fabrication 
For advanced composite applications, the resin solution from example 2 was 
used to prepare a prepreg tape by passing unsized Celion.RTM. 6000 
graphite fibers (available from BASF A.G.) through a dip tank and onto a 
12-inch diameter multiple speed drum winder wrapped with release paper. 
This produced a wet prepreg (10 inches by 75 inches) having smooth, good 
tack, and drape characteristics by visual inspection. The tape was dried 
on the rotating drum at room temperature for ten hours, removed from the 
drum, cut into 3 inch by 6 inch plies and then staged at 150.degree. C. 
for one-half hour in air. Twelve plies were stacked unidirectionally, 
placed in a cold matched metal die and then inserted into a press which 
was preheated to 250.degree. C. A thermocouple was attached to the matched 
die to determine the temperature. When the die temperature reached 
250.degree. C., 500 psi pressure was applied. The composite was cured one 
hour at 250.degree. C. and one hour at 316.degree. C. under 500 psi 
pressure and then removed from the press, when the die temperature reached 
177.degree. C. The composite was postcured at 316.degree. C. in air for 16 
hours. This resulted in a high quality composite, as no voids, cracks, or 
defects were detected by ultrasonic C-scan. The composite was then 
machined into various specimens for testing. For comparison purposes, 
Celion.RTM. 6000 graphite fiber-reinforced composites were also fabricated 
from Thermid.RTM. AL-600 and Thermid.RTM. LR-600 and tested under the same 
conditions as the semi-IPN material. The unidirectional composite 
properties of the semi-IPN and the constituent materials are given in 
Table 2. 
TABLE 2 
__________________________________________________________________________ 
Unidirectional Composite Properties 
Semi-IPN.sup.d 
Thermid .RTM. AL-600 
Thermid .RTM. 
Thermid .RTM. 
Thermid .RTM. 
Thermid .RTM. 
Property and NR-150B2 
Al-600.sup.d 
LR-600.sup.d 
MC-600.sup.f 
IP-600.sup.g 
__________________________________________________________________________ 
.sup.a Glass Transition 
290 and 330 
-- -- -- -- 
Temperature, .degree.C. 
Density, g/cm.sup.3 
1.58 1.50 1.50 -- -- 
.sup.b Flexural 
Strength, Ksi 
25.degree. C. 
279 -- -- 195 130 
232.degree. C. 
206 -- -- 148.sup.e 
78.sup.h 
.sup.b Flexural 
Modulus, Msi 
25.degree. C. 
15.0 -- -- 15.0 -- 
232.degree. C. 
14.5 -- -- 12.0.sup.e 
-- 
.sup.c Interlaminar 
Shear Strength, 
Ksi 
25.degree. C. 
20.7 9.6 9.6 12.1 7.3 
232.degree. C. 
14.0 4.5.sup.e 
-- 8.0.sup.e 
5.0.sup.h 
__________________________________________________________________________ 
.sup.a By TMA 
.sup.b Per ASTM D790 
.sup.c Per ASTM D2344 
.sup.d Reinforced with Celion .RTM. 6000 graphite fibers 
.sup.e Tested at 316.degree. C. 
.sup.f Reported by the National Starch and Chemical Corporation Product 
Data Sheet number 26283, reinforced with Hercules HTS .RTM. graphite 
fibers, postcured for 4 hours at 343.degree. C., and then 4 hours at 
371.degree. C. 
.sup.g Reported by Landis and Naselow NASA Conference Publication 2385 
(1983) 
.sup.h Tested at 288.degree. C.