National Aeronautics and 

Space Administration 

Wshington, D.C. 

20546 

Reply to Attn of: NOTICE 

The invention disclosed in this document resulted from research in 

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owned by NASA and is, therefore, available for licensing in 

accordance with the NASA Patent Licensing Regulation (14 Code of 

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Address all inquires and application for license forthis invention 

to NASA Patent Counsel, Langley Research Center, Mail Code 279, 

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from the above address, 
TOUGH HIGH PERFORMANCE SIMULTANEOUS 

SEMI-INTERPENETRATING POLYMER NETWORK 

AWARDS ABSTRACT 

NASA Case No. LAR 14339-1 

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 asrospace 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. 

The present invention is a semi-interpenetrating polyimide network and methods 

for making and using the same are disclosed. The semi-IPN system comprises a high 

performance thermosetting polyimide having an acetylene-terminated group acting as 

a crosslinking site and a high performance linear thermoplastic polyimide having the 

following repeating unit: 

The polymer is made by combining low viscosity precursors and low molecular 

weight polymers of the thermosetting and thermoplastic polyimides and allowing them 

to react in the immediate presence of each other to form a simultaneous 

semi-interpenetrating polyimide network. 

The novelty of the present invention resides in the provision of a high 
temperature system having significantly improved processability and damage tolerance 

while maintaining excellent thermo-oxidative stability, mechanical properties and 

resistance to humidity, when compared with the commercial high temperature resin, 

Thermid 600. This material is particularly adapted for use as a molding, adhesive, and 

advanced composite matrix for aerospace structural and electronic applications. 

Inventor: Ruth H. Pater 

Address : 106 Tuckahoe Trace 

Employer: NASA LaRC 

Initial Evaluator: Terry L. St. Clair 

Filed: November 2, 1989 

Serial No.: 071430,470 
LAR 14339-1 -1 - PATENT APPLICATION 

A TOUGH HIGH PERFORMANCE SIMULTANEOUS 

SEMI-INTERPENETRATING POLYMER NEWORK 

Cross-Reference 

5 

This application is related to co-pending patent application serial 

number , filed , entitled A Tough High 

Performance Composite Matrix. 

10 Origin of the lnvention 

The invention described herein was made by an employee of the United 

States Government and may be manufactured and used by or for the 

Government for governmental purposes without the payment of any royalties 

15 thereon or therefor. 

Backqround of the Invention 

1. Field of lnvention 

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 

25 moldings, adhesives and composite matrices. 

2. Description of the Related Art 

There is a continual search in the art for more processable and damage 

30 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 
LAR 14339-1 -2- PATENT APPLICATION 

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, 

5 these materials are generally deficient in at least one other desired property. 

For instance, the well-known and commercially available 

acetylene-terminated Thermid Polyimide series offers outstanding 

thermo-oxidative stability, exceptional dielectric properties and excellent 

resistance to humidity at elevated temperature. It is also addition-curable. 

10 However, it is inherently brittle due to its highly crosslinked structure. 

Despite having the advantage of addition-curing, this system is actually 

difficult-to-process. This is primarily due to the fact that this system has a 

very narrow processing window. (Thermid MC-600, for example, has a geltime of three minutes at 190°C.) The problem becomes exacerbated when 

15 the resin is used to fabricate composites, particularly large area laminated 

structures. 

Conversely, NR-150B2, which is available from E. I. DuPont de 

Nemours and Company, is well-known for its outstanding toughness and 

microcracking resistance, in addition to its unusually high thermo-oxidative 

20 stability. However, this material also has a major drawback. It is difficult to 

process and requires a high processing temperature such as 400°C. 

St. Clair et al., (US. 4,695,610) and others have developed 

semi-interpenetrating polymer networks (semi-IPNS) of high temperature 

systems. However, none of these prior art products have the desired 

25 combination of properties set forth hereinabove. 

Summary of the Invention 

Accordingly, a primary object of this invention is to provide an improved 

30 high temperature polymer having the combination of easy processing, 

damage tolerance and excellent moisture resistance. This primary object and 

other objects and benefits are achieved by making a semi-IPN comprising a 
LAR 14339-1 PATENT APPLICATION 

high performance thermosetting polyimide having an acetylene terminated 

group acting as a crosslink site and a high performance linear thernioplastic 

polyimide having the following repeating unit: 

Especially beneficial results are obtained when the high performance 

linear thermoplastic polyimide comprises a mixture of the following 

compounds: 

15 

wherein R, is a trivalent aryl radical and R, is hydrogen or alkyl; and 

25 H2N - H, - NH2, 

wherein R, is a divalent aryl radical. 

Excellent results are achieved when the high performance linear 

thermoplastic polyimide comprises a mixture of the following three 

compounds: 

30 
LAR 14339-1 

0 0 

I I l I 

HO-C C-HO 

I I I l 

0 0 

PATENT APPLICATION 

15 

especially when compound (a) is present in a stoichiornetric quantity, and the 

molar ratio of compound (b):compound (c) is about 95:s. 

A number of additional, especially-preferred embodiments are found in 

the following Detailed Description of the invention. 

20 

Brief Description of the Drawinq 

The single Figure is a schematic depiction of a semi-IPN synthesis. 

25 Description of the Preferred Embodiments 

The concept of the high performance semi-IPN synthesis is shown in 

the drawing. One or more easy-to-process, but brittle thermosetting 

polyimides are combined with one or more tough, but difficult-to-process 

30 linear thermoplastic polyirnides to form a semi-IPN polyirnide having a 

combination of several desirable properties, including easy processability, 

damage tolerance, good mechanical performance and good thermo-oxidative 
LAR 14339-1 -5- PATENT APPLICATION 

stability. In the present invention, the combination of desired properties is 

achieved by controlling factors which include (1) careful selection of 

constituent polymer components, (2) composition variation of the constituent 

materials, (3) processing parameters and (4) thermodynamic and chemical 

5 kinetics variables to control the phase morphology and phase stability. Each 

of these factors is discussed in detail in the following paragraphs. 

The selection of the constituent thermosetting and thermoplastic 

polyimides is based primarily on their processing and property compatibility. 

The processing parameters considered of particular importance are solubility 

10 in a common organic solvent and compatible cure cycle. Further, these 

polymers must have comparable glass transition temperatures (+50°C), 

mechanical performance, and therrno-oxidative stability. 

The semi-IPN of this invention comprises a polyimide which contains an 

acetylene terminated group acting as a crosslinking site and an NR-150B2 

15 polyimide. The NR-150B2 polyimide precursor solution in N-methylpyrrolidone 

(NMP) solvent is obtained from E. I. Dupont de Nemours and Company 

(hereafter Dupont). The polyimide precursor solutions in ethanol solvent 

under the trademarks NR-150B2 S2X to NR-15082 S2X10 are also obtained 

from DuPont. The NR-15082 polyimide can also be prepared as set forth 

20 in U.S 4,3,959,350, according to the following reaction: 
LAR 14339-1 PATENT APPLICATION 

0 0 

I I 

/ \ 

5 + H~NGNH* - t 

HO-C C-HO 

I l I I 

O 

H2N 

0 

PPD MPD 

NR-150B2 Polyimide 

20 The linear thermoplastic polyimide prepared from 6FTA and an aromatic 

diamine or a diamine mixture comprising two or more aromatic diamines 

according to the following reaction equation has utility to the present 

invention: 
LAR 14339-1 PATENT APPLICATION 

0 0 

I I 

H2N- R .--NH2 

A 

no-c C-MO 

I I I I 

0 0 

15 wherein R is a divalent aryi radical. 

Several thermosetting acetylene-terminated aromatic polyimides are 

considered compatible with an NR-15082 polyirnide and, therefore, can be 

used in this invention. These include (1) Thermid LR-600 having the 

20 following chemical formula: 

(2) Thermid AL-600 which comprises the following monomeric precursors: 
LAR 14339-1 -8- PATENT APPLICATION 

(3) Thermid MC-600 represented by the formula: 

(4) Thermid FA-700 having the following formula: 

and finally, Thermid IP-600 which has a general formula shown below: 

wherein n = 1 to 30. 

All of the above thermosetting polyimides are commercially available 

30 from National Starch and Chemical Corporation (Bridgewater, New Jersey). 

The composition of the constituent thermosetting and thermoplastic 

polyimides significantly affects many aspects of the processing, properties 
LAR 14339-1 -9- PATENT APPLICATION 

and morphology of the semi-IPN. It has been found that increasing the 

concentration of the thermoset component increases the processability and 

performance of the semi-IPN, but at a cost of decreasing toughness 

characteristics. While the weight ratio of the acetylene-terminated polyimide 

5 to NR-150B2 can be varied from 95:5 to 5:95, the ratio between 80:20 to 

20:80 is preferred. However, the ratio of 80:20 is particularly preferred 

because this composition offers the best overall balance of processing, 

performance and cost effectiveness. 

The synthesis of the present semi-IPN can proceed in two major ways: 

10 simultaneous and sequential. In the former, the uncrosslinked 

acetylene-terminated prepolymers are combined with the monomer precursors 

of the NR-15052. With application of heat, the acetylene-terminated 

prepolymers are allowed to crosslink in the immediate presence of the 

NR-15052 polyimide undergoing simultaneous linear chain extension. This 

15 synthesis can lead to a network in which one polymer interlocks with the 

other, forming permanent entanglements at the interfacial regions of the two 

polymer systems. The resulting physical crosslinki ng provides synergistic 

properties. This synthesis is designed so that the constituent polymers are 

formed independently without any chemical interference between the 

20 precursors of the thermosetting and thermoplastic polyimides. The sequential 

method involves a process in which one polymer is synthesized andlor 

crosslinked in the immediate presence of the other which has been 

prepolymerized. There are two sequential semi-IPNs: semi-1-IPN and 

semi-2-IPN. The former is prepared by polymerizing a linear polymer in a 

25 precrosslinked network. The reverse sequence results in a semi-2-IPN. In 

this invention, the simultaneous method is preferred, because it offers easier 

processing, better performance and less phase separation, as compared with 

the sequential approach. There is yet another synthetic method which is 

non-conventional, This method involves mixing the monomers of the 

30 thermosetting component with the monomers of the thermoplastic component 

and allowing the monomers to react randomly to form a simultaneous 

semi-IPN. The inter-reaction between monomers of the thermoset and 
LAR 14339-1 -1 0- PATENT APPLICATION 

thermoplastic occurs, which results in a semi-IPN significantly different in 

chemical structure and properties from those prepared by the previous 

met hods. 

As discussed earlier, one of the disadvantages of the Thermid system 

5 is that it exhibits an extremely small processing window. The problem is 

unexpectedly resolved by the present semi-IPN synthesis for the following 

reason. According to a proposed mechanism, the polymerization proceeds 

via a free radical propagation of an acetylene group to form a linear 

conjugated polyene, which then acts as a crosslink site for the subsequent 

10 crosslinking reaction. The curing reaction is extremely sensitive to any 

stearic hinderance surrounding the reaction sites. When a long polymeric 

chain (NR-150B2) is in the immediate vicinity of the crosslink site, as in the 

case of the present semi-IPN synthesis, the kinetics of the acetylene reaction 

is expected to slow down considerably, thus, broadening the processing 

15 window. Consequently, the semi-IPN of the present invention exhibits 

improved processability over the Thermid material. For a different reason, 

the present semi-IPN system is also anticipated to have easier processing 

compared to the pure NR-15082. The Thermid material has excessive flow 

whereas the NR-150B2 system exhibits limited flow. The combination would 

20 then provide a material having a flow intermediate between the constituent 

polymer systems. 

A method to control the phase morphology and phase stability has been 

investigated. It involves the addition of 0.1 to 5 weight percent of 

3-aminophenyl acetylene into the NR-150B2 monomer precursors. To this 

25 mixture the preimidized acetylene-terminated prepolymers are added. The 

concept involves lightly end-capping the NR-150B2 with an acetylene group 

to form an acetylene end-capped NR-15082 polyimide. Through the common 

acetylene end group, the acetylene end-capped NR-15082 is then crosslinked 

with the acetylene-terminated polyimide to give a graft copolymer upon 

30 heating. An example of this synthesis is shown below. 

LAR 14339-1 -1 2- PATENT APPLICATION 

Because of chemical bonding between the constituent polymers, the 

resultant graft copolymer exhibits less phase separation and better long term 

phase stability, as compared with the physically crosslinked semi-IPNs 

prepared by the previous methods. 

5 The semi-IPN polyimide of this invention for adapted to use as a 

composite matrix, and as an adhesive and molding compound for long-term 

applications in the 200°C to 31 6OC in aerospace structural components, 

especially in electronic technologies. 

The following are examples that illustrate preparation and use of the 

1 0 semi-IPNs for applications in advanced composites, structural adhesives and 

molding articles. However, it is to be understood that the examples are 

merely illustrative and iqtended 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. 

15 

EXAMPLES 

Example 1 

20 Preparation of Semi-IPN of Thermid LR-600 and NR-150B2 

This semi-IPN was prepared by the simultaneous synthetic method 

generally described previously. In this synthesis, an acetylene-terminated 

polyimide crosslinks in the immediate presence of an NR-150B2 polyimide 

undergoing simultaneous linear chain extension to afford a simultaneous 

25 semi-IPN. It is possible that transimidization reaction occurs between the 

amic acid of the Thermid system and the monomer precursors of the 

NR-15052 material. This would result in a material somewhat similar to the 

material prepared in Example 2 but different from that made in Example 3. 

Thus, it is of interest to compare their properties. Such a synthesis is 

30 described in the following. To 104.0 g of a Thermid LR-600 solution (50 

percent by weight of an amic acid, in NMP) was added 27.0 g of an 

NR-150B2 monomer precursor solution (48 percent solid content in NMP) and 
LAR 14339-1 -1 3- PATENT APPLICATION 

45.0 g of freshly distilled NMP. This mixture was stirred at room temperature 

for one hour, resulting in a viscous dark brown solution containing about 37 

weight percent solids in which the Thermid LR-600 amic acid and NR-15082 

monomeric materials were present in 80 and 20 weight percent, respectively. 

5 For a molding application, the solution was poured into distilled water 

and blended using a mechanical blender. The precipitated solids were 

filtered, dried at 100°C for two hours under vacuum and staged at 204°C for 

one-half hours to afford a black molding powder. About 15.61 g of the 

molding powder was compression molded at 250°C for one hour and at 

10 316°C for another hour under 2500 psi pressure, and then removed from the 

press when the mold temperature reached 177°C. This gave a neat resin 

having dimensions of 3.2 cm by 3.2 cm by 1.0 cm and a density of 1.34 

glcc. The surfaces of the neat resin showed no voids, cracks or defects, 

and thus it was accepted for compact tension specimen preparation without 

15 further post curing. However, for other test specimen preparations, the resin 

was post-cured at 31 6OC for 16 hours in air. In order to compare properties, 

the neat resins of the constituent materials, namely Thermid LR-600 and 

NR-150B2, were also prepared and tested along with the semi-IPN material 

under identical conditions, except that the NR-150B2 specimen had an 

20 additional curing at 350°C for one-half hour. Table 1 summarizes the 

physical and mechanical properties of the semi-IPN. The neat resin 

properties of the constituent materials are given in Table 5. 
LAR 14339-1 -1 4- PATENT APPLICATION 

TABLE 1 

Neat Resin Properties of Semi-IPN of 

Thermid LR-600 and NR-150B2 

5 

Property 

aGlass Transition Temperature,OC 278 and 325 

10 b Fracture Energy, G,,, Jm2 283 

"Temperature at 5% wt loss by TGA in Air 465 

dMoisture Absorption, % 0.4 

"By TMA; 

15 b~er ASTM E 399; 

"At a heating rate of 2.5OC/min; 

d two weeks in water at room temperature. 

Example 2 

Preparation of semi-IPN of Thermid AL-600 and NR-15QB2 

This semi-IPN was prepared by the non-conventional synthetic method 

25 which was generally discussed supra. 

A 59 weight percent resin solution in ethanol was obtained by stirring 

at room temperature a mixture of 138.6 g of a Thermid AL-600 monomeric 

precursor solution (75 weight percent solids in ethanol), 42.6 g of an 

NR-150B2 monomeric precursor solution (61 .I weight percent solids in 

30 ethanol) and 38.0 g of anhydrous ethanol. This yielded a viscous dark black 

solution in which the Thermid AL-600 and NR-150B2 monomeric precursors 

were present in amounts of approximately 80 and 20 percent, respectively. 
LAR 14339-4 -1 5- PATENT APPLICATION 

To prepare a molding, the solution was concentrated at 100°C for two 

hours under vacuum (30 in Hg) and then staged at 200°C for one hour in 

air. Following the cure cycle of Example 1, a neat resin was obtained which 

had a density of 1.32 g/cc and showed no detectable voids or defects. The 

5 physical and mechanical properties of this neat resin listed in Table 2 were 

determined in Example 1. 

TABLE 2 

Neat Resin Properties of Semi-IPN of 

Thermid AL-600 and NR-150B2 

Property 

15 

"Glass Transition Temperature,OC 320 

b Fracture Energy, G,,, J/m2 603 

'Temperature at 5% wt loss by TGA in Air 490 

d Moisture Absorption, % - - 

"By DSC; see Table 1 for footnotes b through d. 

Example 3 

Preparation of Semi-IPN of Thermid MC-GOO and NR-150B2 

This synthesis follows a conventional simultaneous method in which the 

transirnidization reaction described in Example 1 is unlikely to occur, because 

30 a fully preimidized prepolymer is used in this synthesis, rather than an amic 

acid as used in Example 1. 
LAR 14339-1 -1 6- PATENT APPLICATION 

To a solution of 12.3 g of the NR-150B2 solution described in Example 

2 was added a mixture of 30.0 g of Thermid MC-600 yellow powder in 60 

rnl of freshly distilled NMP. Because the Thermid MC-600 powder was not 

readily soluble in NMP at room temperature, the mixture was warmed and 

5 stirred at 50°C for one hour, resulting in a highly viscous gray material. It 

appeared that there were some insoluble materials present in the solution; 

and the solution was difficult to stir using a stirring bar, because of its high 

viscosity. Such a viscous material was concentrated at 176OC for two hours 

under vacuum (30 in Hg). To reduce its flow and to eliminate the residual 

10 solvents, the material was further treated at 200°C for one-half hour under 

vacuum (30 in Hg). Approximately 14.5 g of the gray molding powder was 

used to prepare a molding following the cure cycle of Example 1. This 

afforded a neat resin with a density of 1.37 g/cc. No voids or were seen on 

the surfaces of this neat resin, the properties of which are shown in Table 

15 3. 

TABLE 3 

Neat Resin Properties of Semi-IPN of 

Thermid MC-600 and NR-150B2 

Property 

"Glass Transition Temperature,OC 329 

b~racture Energy, G,,, J/m2 48 1 

Temperature at 5% wt loss by TGA in Air 490 

'~oisture Absorption, % . - 

See Table 2 for all footnotes. 

30 
LAR 14339-1 -1 7- 

Example 4 

Preparation of Semi-IPN of Thermid FA-700 and NR-150B2 

A 20 weight percent resin solution in NMP was prepared by stirring at 

room temperature a mixture of 52.0 g of Thermid FA-700 powder, 27.1 g of 

the NR-150B2 solution described in Example 1, and 264.0 g of freshly 

distilled NMP. As in Example 3, the resin solution was concentrated to 

afford a molding powder which was subsequently compression molded. This 

formed a neat resin with a density of 1.32 glcc. Other properties of this 

resin are presented in Table 4. 

TABLE 4 

Neat Resin Properties of Semi-IPN of 

Thermid FA-700 and NR-150B2 

Property 

"Glass Transition TemperatureSoC 335 

b Fracture Energy, G,,, J/m2 306 

'Temperature at 5% wt loss by TGA in Air 522 

d Moisture Absorption, % - .

See Table 2 for all footnotes. 
LAR 14339-1 -1 8- PATENT APPLICATION 

TABLE 5 

Neat Resin Properties of Constituent Materials 

Property 

- 

Thermid" 

LR-600TM 'NR-1502~~ 

(National Standards) (DuPont) 

"Glass Transition Temperature,"C 290 

b Fracture Energy, G,, J/m2 93 

"Temperature at 5% wt loss by TGA in Air 460 

dMoisture Absorption, % 0.3 

See Table 1 for footnotes a through d; e prepared by the present inventor. 

Example 5 

Preparation of Celion 6000/Semi-lPN of Thermid LR-600 and NR-15OB2 

For advanced composite applications, the resin solution from Example 

1 was used to prepare a prepreg tape by passing a single tow of unsized 

Celion 6000 graphite fiber through a dip tank and onto a 12-inch diameter 

multiple speed drum winder wrapped with release paper. This produced a 

23.0 cm by 190 crn wet prepreg having a smooth and good tack and drape 

characteristics. The tape was dried on the rotating drum at room 

temperature for 16 hours, and then removed from the drum and cut into 7.6 

cm by 15.2 crn plies. Twelve plies were tacked unidirectionally and staged 

at 150°C for one hour. The staged lay-up was placed in a cold matched 

metal die. This was then inserted into a press preheated to 250°C. A 

thermocouple was attached to the matched die to determine the temperature. 

When the die temperature reached 250 C, 500 psi pressure was applied. 

The composite was cured one hour at 250°C and one hour at 316OC under 
LAR 14339-1 -1 9- PATENT APPLICATION 

500 psi pressure, and then removed from the press when the die 

temperature reached 177°C. The composite was then postcured at 316'C 

in air for 16 hours. The ultrasonic C-scan of the composite showed no 

detectable voids or defects, and thus it was submitted for test specimen 

5 preparations. As a control, a Celion 6000TThermid LR-600 composite system 

was also prepared and tested under the identical conditions for the semi-IPN 

material described above. 

The cured control material, however, showed considerable voids 

detected by the ultrasonic C-scan method. Only the area showing relatively 

10 fewer voids was used for test specimen preparation. 

Tables 6 and 11 show the composite properties for the semi-IPN as 

well as the control material, respectively. 
LAR 14339-1 PATENT APPLICATION 

Table 6 compares the physical and mechanical properties of the 

semi-IPN and its constituent material. 

TABLE 6 

Unidirectional Composite Properties of 

Semi-IPN of Thermid LR-600 and NR-150B2dd 

10 

Property 

"Glass Transition Temperature, "C 312 

Density, g/cm3 

b Flexural Strength, Ksi 

b~lexural Modulus, Msi 

25°C 

232°C 

"Interlaminar Shear Strength, Ksi 

25 "By TMA; 

b~er ASTM 0790; 

"Per ASTM D2344; 

d~einforced with Celion 6000 graphite fibers. 
LAR 14339-1 -21 - PATENT APPLICATION 

Example 6 

Preparation of Celion 6000/Semi-IPN of Thermid AL-600 and NR-150B2 

5 A 59 weight percent resin solution in ethanol from Example 2 was used 

to prepare a prepreg tape (25.4 cm by 190 cm). The wet prepreg exhibited 

smooth and good tack and drape characteristics by a visual inspection. It 

was dried at room temperature for ten hours and then staged at 150°C for 

one-half hour in air. The staged lay-up was cured as in Example 5. This 

10 resulted in a high quality composite, as no voids or defects were detected 

by ultrasonic C-scan. The composite was postcured at 31 6OC for 16 hours 

in air and then machined into various specimens for testing. 

Table 7 shows the physical and mechanical properties of this composite. 

TABLE 7 

Unidirectional Composite Properties of Semi-IPN 

of Therrnid AL-600 and NR-15082~ 

Property 

20 

"Glass Transition Temperature, OG 290 and 330 

Density, g/cm3 1.58 

b~lexural Strength, Ksi 

25°C 279 

232°C 206 

b~lexural Modulus, Msi 

25OC 15.0 

232°C 14.5 

"Interlaminar Shear Strength, Ksi 

25°C 20.7 

232°C 14.0 

See Table 6 for all footnotes. 
LAR 14339-1 -22- PATENT APPLICATION 

Example 7 

Preparation of Celion 6000/Semi-IPN of Thermid MC-600 and NR-15082 

5 As in Example 5, the resin solution (21 percent by weight of solids in 

NMP) from Example 3 were used to yield a prepreg having an area of 23 

cm by 190 cm. During the drying process described in Example 5, this 

prepreg disunited into many pieces. Each piece had a width of about 

0.6 cm. This made the composite lay-up difficult. Despite this difficulty, a 

10 high quality composite (7.6 cm by 15.2 cm by 0.2 cm) was obtained following 

the cure cycle of Example 5. 

The physical and mechanical properties for this composite are listed in 

Table 8. 

TABLE 8 

15 Unidirectional Composite Properties of 

Semi-IPN of Thermid MC-600 and NR-150B2d 

- - -- 

Property 

"Glass Transition Temperature, OC 

Density, g/cm3 

b Flexural Strength, Ksi 

25°C 

232°C 

bFlexural Modulus, Msi 

232'6 

"Interlaminar Shear Strength, Ksi 

See Table 6 for all footnotes. 
LAR 14339-1 -23- PATENT APPLICATION 

Example 8 

Preparation of Celion 6000/Semi-IPN of Thermid FA-700 and NR-15062 

As in Example 5, the resin solution (20 weight percent solids in NMP) 

5 from Example 4 was used to impregnate Celion 6000 graphite fibers. The 

resulting prepreg behaved in a manner similar to that of Example 7. The 

cured composite was essentially void-free, except that one corner of the 

composite showed some voids. The composite properties for this system are 

given in Table 9. 

10 

TABLE 9 

Unidirectional Composite Properties of 

Semi-1PN of Therrnid FA-600 and NR-150~2~ 

15 Property 

"Glass Transition Temperature, OC 31 5 

Density, g/cm3 1.58 

b~lexural Strength, Ksi 

25°C 264.1 

232°C 1 85.1 

b~lexural Modulus, Msi 

25°C 14.4 

232°C 14.1 

"Interlaminar Shear Strength, 

25°C 17.3 

See Table 6 for all footnotes. 

30 
LAR 14339-1 -24- PATENT APPLICATION 

Example 10 

Preparation of Cross-Plv Composites 

To make a realistic assessment of composite microcracking behavior, a 

5 cross-ply composite having a [0,90,0]s lay-up was fabricated for the semi-IPN 

of Thermid LR-600 and NR-150B2 and Thermid LR-600 as a control. The 

fabrication of the cross-ply cqmposites follows the same procedure as their 

unidirectional counterparts described in Example 5. Here, AS-4 graphite 

fibers were used, instead of Celion 6000 graphite fibers which were used for 

10 the unidirectional composites. Specimens (1.5 cm by 0.6 cm by 0.13 cm) 

were machined from the cross-ply composites and were subjected to thermal 

cycling. The temperature was varied from -156 to 288OC with a total time 

of 15 minutes for each cycle. Liquid nitrogen was used as a cooling agent. 

After 1000 and 1500 thermal cycles, the unpolished surfaces were examined 

15 by scanning electron microscopy (SEM) at 100 and 2000X magnifications. 

Also, the specimens were immersed in water at room temperature for 1 year 

to determine the amount of water penetrated into the cracks and absorbed 

by the matrix. 
c- u f 

0) I- 0 44 

E 

. - -8 8 

21.z 

("aO&"n 
LAR 14339-1 -26- PATENT APPLICATION 

TABLE 11 

Unidirectional Composite Properties of Constituent Materials 

5 Property 

Thermid Thermid Thermid 

AL-600" MC-600b lla-600' 

Glass Transition Temperature,OCa 

Density, g/cc 

Flexural Strength, Ksi 

10 25°C 

31 6°C 

Flexural Modulus, Msi 

25°C 

31 6°C 

15 Interlaminar Shear Strength, Ksi 

25°C 

31 6OC 

"Prepared and tested by the present invention using the same cure cycle as 

20 the Semi-IPN materials; b~eported by National Starch ' and Chemical 

Corporation, reinforced with Hercules HTS fibers and postcured four hours 

at 343°C and four hours at 37I0C; 'Reported by A. L. Landis and A.B. 

Naselow NASA CP 2385 (1983); d~ested at 288°C. 

What is claimed as new and desired to be secured by Letters Patent of 

the United States is: 
LAR 14339-1 PATENT APPLICATION 

A TOUGH HIGH PERFORMANCE SIMULTANEOUS 

SEMI-INTERPENETRATING POLYMER NETWORK 

Abstract of the Disclosure 

5 

A semi-interpenetrating polyimide network and methods for making and 

using the same are disclosed. The semi-IPN system comprises a high 

performance thermosetting polyimide having an acetylene-terminated group 

acting as a crosslinking site and a high performance linear thermoplastic 

10 polyimide having the following repeating unit: 

The polymer is made by combining low viscosity precursors and low 

20 molecular weight polymers of the thermosetting and thermoplastic polyimides 

and allowing them to react in the immediate presence of each other to form 

a simultaneous semi-interpenetrating polyimide network. Provided is a high 

temperature system having significantly improved processability and damage 

tolerance while maintaining excellent thermo-oxidative stability, mechanical 

25 properties and resistance to humidity, when compared with the commercial 

high temperature resin, Thermid 600. This material is particularly adapted 

for use as a molding, adhesive and advanced composite matrix for 

aerospace structural and electronic applications. 
Print Figure 

i 
NASA Case No. LAR 14339-1 

RUTH H. PATER ET AL 

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