NASA Contractor Report 178413 

DEVELOPMENT OF AN IMPACT- AND 

SOLVENT-RESISTANT THERMOPLASTIC - -- - COMPOSITE MATRIX - PHASE IV 

C. B. Delano 

Acurex Corporation 

Aerotherm Division 

520 Clyde Avenue 

P.O. Box 7040 

Mountain View, California 94039-7040 

(NASA-CR-178413) DEVELOPHENT OF AN IHPACTAND SOLVEIT-RESISThBT TEIZBMOPLASTIC COHPOSnE 118 p HATRIX, PHASE 4 (Acurex Corp.) CSCL 11D Unclas 

N 88-1 41 45 

G3/24 01 14269 

co, 

September 1987 

National Aeronautics and 

Space Admnistration 

Lanaky Resewch Center 

Harnpton, Virginia 23665-5225 
NASA Contractor Report 178413 

DEVELOPMENT OF AN IMPACT- AND SOLVENT-RESISTANT 

THERMOPLASTIC COMPOSITE MATRIX -- PHASE IV 

C. B. Delano 

Acurex Corporation 

Aerotherm Division 

520 Clyde Avenue 

P.O. Box 7040 

Mountai n View, Cali forni a 94039 

Contract No. NAS1-16808 

September 1987 

NASA 

National Aeronautics and 

Space Admi ni st ration 

Langley Research Center 

Hampton, Vi rgi ni a 23665 
FOREWORD 

This report was prepared by Acurex Corporation for the National 

Aeronautics and Space Administration, Langley Research Center, under contract 

NAS1-16808. 

Use of commercial products or names in this report does not constitute 

official endorsement of such products or manufacturers , either expressed or 

implied by the National Aeronautics and Space Administration. 

The work was conducted from September 1985 to September 1987. 

Future aerospace vehicles may require the use of graphite composites 

with a favorable combination of properties including impact resistance. 

Thermoplastic resins provide composites with high-impact resistance. However, 

the solvent resistance of most thermoplastics is poor. Program effo ts were 

directed towards the optimization of a solvent-resistant thermoplast c 

polyimi de that would be amenable to the fabrication of hi gh-qual i ty 

composites. 

Mr. Paul Hergenrother was the NASA technical monitor. The Materials 

Development Department of Aerotherm Division of Acurex Corporation performed 

the work on this contract. Mr. C. B. Delano was the program manager and 

Mr. C. J. Kiskiras provided technical assistance. 

PEECEDLNO PAGE BLANK NOT FILMED 

iii 
TABLE OF CONTENTS 

Page 

ii i 

Section 

FOREWORD . . . . . . . . . . . . . . . . . . . . . . SUMMARY . . . . . . . . . . . . . . . . . . . . . . . ix 

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1 

1.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . 1.2 PRIOR EFFORTS . . . . . . . . . . . . . . . . . . . 1.3 PRESENT EFFORTS . . . . . . . . . . . . . . . 1 

2 

4 

2 OBJECTIVE . . . . . . . . . . . . . . . . . . . . . . . 11 

3 RESULTS AND DISCUSSION . . . . . . . . . . . . . . . . . 13 

3.1 POLYMER SELECTION . . . . . . . . . . . . . . . . . 13 

3.1.1 Synthesis . . . . . . . . . . . . . 3.1.2 Moldings of .High-Molecular-Weight Polymers . . . . 3.1.3 Annealing Studies . . . . . . . . . . . . 3.1.4 Testing .... .. . . .. ... .... .... 3.1.5 Selection . . . . . . . . . . . . . . . . . . . . 

13 

23 

33 

35 

50 

3.2 MOLECULAR WEIGHT/MELT FLOW OPTIMIZATION STUDIES . . 51 

3.2.1 Flow Properties . . . . . . . . . . . 3.2.2 BTDA/BAC/m-PDA Polymers . . . . . . . . . . 3.2.3 BTDA/BAC/2,4-DAT Polymers . . . . . . . . . . . . 3.2.4 Barcol Hardness Testing of Polymers . . . . . . . 

52 

54 

56 

66 

3.3 COMPOSITE PROPERTIES AND SELECTION OF THE FINAL 

POLYIMIDE COMPOSITION . . . . . . . . . . . . . 3.4 SCALE-UP AND PROPERTIES OF THE SELECTED POLYMER . . 69 

73 

CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . 79 

4.1 NEAT RESINS . . . . . . . . . . . . . . . . . . . 4.2 MOLECULAR WEIGHT/MELT FLOW PROPERTIES . . . . . 79 

79 

EXPERIMENTAL e 83 

REFERENCES e e 87 

APPENDIX A -- FAILURE TEMPERATURE UNDER COMPRESSION LOAD 89 

APPENDIX B -- TMA FLOW TEST METHOD DEVELOPMENT 93 

APPENDIX C -- END CAPPING OF BTDA/BAC/m-PDA POLYMER WITH 

PHTHALIC ANHYDRIDE . . . . . . . . . . . 101 
Figure 

1 

2 

3 

4 

10 

11 

12 

13 

14 

15 

16 

17 

LIST OF ILLUSTRATIONS 

Resin shrinkage and smooth prepregs . . . . . . . . . . . Weight percent flexible segment versus Barcol 

hardness . . . . . . . . . . . . . . . . . . . . . . . . 

Inherent viscosity/stoichiometry studies with the 

BTDA/HDA/m-PDA polymer . . . . . . . . . . . . . . . . . 

Inherent viscosity/reaction sol ids content studies with 

the BTDA/HDA/m-PDA polymer . . . . . . . . . . . . . . . Inherent viscosity versus percent solids . . . . . . . . DSC anal ysi s of BTDA/HDA/m-PDA pol ymer . . . . . . . . . 

DSC curves of BTDA/BDA/m-PDA polymer . . . . . . . . . . TMA curves for BTDA/BAC/m-PDA polymer . . . . . . . . . . TMA curves for BTDA/BDA/m-PDA and BTDA/HDA/m-PDA 

polymers . . . . . . . . . . . . . . . . . . . . . . . . 

Press flow areas of polysulfone and polyetherimide . . . 

Comparison of the flow properties of the BTDA/BAC/m-PDA 

polymer to polyetherimide . . . . . . . . . . . 

TMA flow curves of BTDA/BAC/2,4-DAT polymers . . . TMA flow curves of BTDA/BAC/2,4-DAT polymer blends 

TMA flow curves of BTDA/HDA/E,4-DAT polymers . . . . . . 

Inherent viscosity versus TMA flow property 

re1 ationshi p . . . . . . . . . . . . . . . . . . . . . . Tg normalized inherent viscosity versus TMA flow 

property . . . . . . . . . . . . . . . . . . . . . . . . Inherent viscosity -- press flow relationship . . . . . . 

vi 

Page 

5 

7 

18 

20 

21 

28 

32 

43 

44 

53 

55 

57 

58 

62 

64 

65 

67 
LIST OF TABLES 

Tab1 e 

1 

- Page 

8 

Glass transition temperature and Barcol hardness of 

molded polymer samples . . . . . . . . . . . . . . . . . 2 Molding studies of the three candidate polymers 

at 303°C . . . . . . . . . . . . . . . . . . . . . . . . 26 

Comparison of DSC properties of unmolded polyimide 

powders . . . . . . . . . . . . . . . . . . . . . . . . . 3 

29 

4 DSC data for varying molecular weight BTDAIHDAlm-PDA 

polymers . . . . . . . . . . . . . . . . . . . . . . . . 31 

34 

36 

Barcol hardness of candidate polymers . . . . . . . . . . Physical property changes of heat treated specimens . . . 

Summary of average compression test results on the three 

candidate polymers . . . . . . . . . . . . . . . . . . 37 

8 Fracture energies of the three candidate polymers . . . . 40 

9 Dry- and water-boiled properties of the three candidate 

polymers . . . . . . . . . . . . . . . . . . . . . . . . 41 

10 Stressed aircraft fluid and paint stripper resistance of 

the three candidate polymers . . . . . . . . . . . . . . 46 

11 Sixteen-hour unstressed weight gains of various 

compositions in paint strippers . . . . . . . . . . . . . 48 

Twelve-day unstressed weight gains of compositions in 

paint strippers . . . . . . . . . . . . . . . . . . . . . 

Properties of varying molecular weight BTDA/BAC/2,4-DAT 

polymers . . . . . . . . . . . . . . . . . 

Properties of BTDA/BAC/2,4-DAT polymer blends . . 

12 

49 

13 

59 

14 60 

15 Properties of various molecular weight BTDA/HDA/2,4-DAT 

polymers . . . . . . . . . . . . . . . . . . . . . . 63 

16 Glass transition temperature and Barcol hardness of 

mol ded polymers . . . . . . . . . . . . . . . . . . . . . 68 

Carbon fabric composite properties of polyimide 

compostions . . . . . . . . . . . . . . . . . . . . . . . 17 

70 

18 Composite processing parameters and resin Tg . . . . . . 71 

vi i 
LIST OF TABLES (Concluded) 

Table Page 

19 Properties of the BTDA/HDA/BAC/2,4-DAT polyimide . . . . 76 

- 

20 Mechanical properties of BTDA/HDA/BAC/2,4-DAT 

polymer . . . . . . . . . . . . . . . . . . . . . . . . . 77 

viii 
1 

c 

1 

1 

1 

1 

P 

8 

I 

1 

4 

3 

E 

I 

I 

1c 

I 

8 

I 

selected for mlecu 

Reducing the 

stoichiometric imba 

insoluble material. 

SUMMARY 

This 18-month follow-on Phase IV effort primarily addressed tailoring 

the melt viscosity properties of aliphatic-aromatic polyimides to give readily 

processable prepregs for manufacture of high-quality composites. 

Since 93°C tensile testing of the polyimide from 3,3',4,4'- 

benzophenonetetracarboxylic dianhydride with 196-hexanediamine and 

- rn-phenylenediamine indicated during Phase I11 that shear yielding had 

occurred, initial efforts on this follow-on program were directed toward 

reducing the amount of the linear aliphatic portion of the polyimide. 

Substitution of the 1,6-hexanediamine with both 1,4-butanediamine and 

1,3-bis(aminomethyl) cyclohexane gave the expected improvements in Barcol 

hardness at 93°C. The polyimide from the latter aliphatic diamine was 

ar weighthelt viscosity optimization efforts. 

molecular weight of the candidate polyimide by 

ance or end capping with phthalic anhydride led to 

Numerous unsuccessful attempts were made to find reaction 

conditions to eliminate formation of the insoluble material obtained upon 

evaporation of the solvent (m-cresol) - from polymers prepared using 

97.5 percent stoichiometry. Polymer from clear solutions isolated with 

methanol provided material with low pressure flow properties. However, 

redissolution of this same material in cresol and evaporation of the cresol 

gave a material that did not flow well. 

ix 
By substituting 2,4-diaminotoluene for the - wphenylenediamine in the 

polyimide, low-pressure flow properties were obtained. The expected direct 

relationship between melt viscosity and molecular weight was obtained for the 

polyimi de from 3,3 I ,4 ,4' -benzophenonetetracarboxyl i c dianhydri de with 

2,4-diami notol uene and 1,3-bi s (ami nomethyl )cyclohexane or lS6-hexanediami ne. 

Polymers containing the 2,4-diaminotoluene were found to be soluble in 

chloroform, whereas polymers with - nrphenylenediamine were not soluble. Since 

the objective of this follow-on effort was good melt processability, polymers 

containing the 2,4-diaminotoluene were used in the remaining efforts. 

Polymers with an inherent viscosity of 0.55 dl/g were selected for 

prepregging and composite fabrication studies. This inherent viscosity 

represents a Brookfield viscosity of approximately 33 Pa-S at 20 percent 

solids in Tcresol. 

phthalic anhydride end-capped polymers was used to achieve this Brookfield 

viscosity in solutions used for prepregging. Zero void composites were 

readily fabricated from these solutions by pressing solventless prepregs to 

selected thicknesses at elevated temperature and less than 6.9 MPa pressure. 

Blending of polymer solutions prepared from synthesis of 

Composite flexural strengths in excess of 698 MPa (100 ksi) were 

obtained with carbon-fabric composites at room temperature and 93°C from two 

polyimide compositions. 

failure mode from composites tested previously and is probably due to improved 

compression properties of the matrix resin. 

These excellent values are attributed to a change in 

X 
ABSTRACT 

Polyimides from BTDA with - m-phenylenediamine and three aliphatic 

diamines were prepared in - m-cresol and characterized. 

included compression strength and modulus, stressed solvent resistance, and 

melt-flow tests. Efforts to reduce the molecular weights of these polymers 

by either stoichiometric imbalance or phthal i c anhydride end cappi ng produced 

opacity in the polymer moldings when the stoichiometry was less than 

99 percent . allows clear polymer moldings to be obtained at all stoichiometries by end 

capping or stoichiometric imbalance. 

studies, carbon fabric composites were prepared from three polyimide 

compositions containing BTDA, 2,4-diaminotoluene and two aliphatic diamines. 

Flexural strengths of two of the resins were in excess of 689 MPa (100 ksi) 

at both room temperature and 93OC. The polyimide from BTDA, 

1,6-hexanedi ami ne, 1,3-bi amin in om ethyl )cyclohexane and 2,4-diaminotoluene was 

selected for scale-up and neat resin characterization tests. 

polymer was 233OC. 

Characterization tests 

Use of 2,4-di ami not01 uene in place of the - m-phenylenedi ami ne 

After melt-flow/molecular-weight 

The Tg of this 

xi 
SECTION 1 

INTRODUCTION 

This report describes an 18-month follow-on effort conducted to develop 

improved thermoplastic resins for application in composite structures for 

aerospace vehicles. 

Section 1.2 briefly summarizes prior efforts,l,2 and Section 1.3 describes our 

approach to the follow-on effort. 

1.1 BACKGROUND 

Section 1.1 describes the advantages of such a system, 

The successful development of impact- and solvent-resistant 

thermoplastic systems for glass and graphite composites is particularly 

attractive from the standpoint of their potential low-cost and streamlined 

manufacturability. Hypothetically, thermoplastics only require simple heating 

and cooling cycles for component manufacture, whereas thermosets require more 

precise, and possibly extended, heating schedules which must be consistent 

with the cure chemistry. 

High modulus (matrix properties), excel lent processabil ity, and solvent 

resistance (high crosslink density) are some of the attractive features of 

thermosets, which are currently the preferred matrices for graphite 

composites. Furthermore, since the B-staged epoxy resins are liquids, 

excellent fiber collimation is achievable in the prepregs. The response of 

graphite composites to low-speed impact has been of concern for a number of 

years. Kevlar, glass, and other fibers are used with graphite fibers to 

1 
prov de more impact-resistant compos tes. Such "hybrids" compromise initial 

mechanical properties (modulus, compressive strength) to provide improved 

impact properties. Thermoplastics, on the other hand, offer impact resistance 

not attainable with conventional thermosets (excludes new toughened systems). 

Aircraft design requires lifetime prediction of their components. Any 

material which exhibits environmental degradation will compromise the design 

safety margins for the selected component. Conventional thermosets absorb 

moisture which lowers their performance, especially at elevated temperatures. 

The sensitivity of existing thermoplastics to aircraft fluids and other 

solvents may preempt their serious consideration in aircraft components. 

Therefore, Acurex proposed resistance to aircraft solvents as the starting 

point for the program effort. Exposure to fuel, deicing fluids, and hydraulic 

fluids are serious concerns. 

being examined by a number of investigators. 

strippers on composites may not be required. 

1.2 PRIOR EFFORTS 

Methods to remove paint from composites are 

If successful, use of paint 

The Acurex approach is based on the development of polymers with rigid 

crystallizable segments interconnected with soft or flexible, energy-absorbing 

segments. 

chains and provide high-modulus and solvent resistance. 

The rigid segments can act as physical crosslinks between polymer 

The interconnecting 

soft segments provide impact resistance and melt processibility. 

The excellent common solvent resistance under stress of three 

polyaliphatic-aromatic heterocyclics (two polyimides and polybentimidazole) 

verified the soft-rigid segment approach to obtaining solvent-insensitive 

polymers. The polyimide from 3,3' ,4,4'-benzophenonetetracarboxylic 

dianhydride (BTDA) with 1,8-octanediamine (ODA), and - m-phenylenediamine 

(m-PDA) was selected as the best candidate from the first-year Phase I effort. 

2 
The second-year Phase I1 efforts continued to show promise for this polymer. 

However, due to opacity developed in the molded polymer with 1-hr treatment at 

316°C (600"F), 1,6-hexanediamine (HDA) was substituted for the ODA since that 

composition remains clear with the cited thermal treatment. 

noted that these selections were based on a number of factors which are 

consistent with current understanding of composite resins, e.g., good tensile 

properties of the bulk resin. 

CR 172285.1 

It should be 

These efforts are described in NASA 

Methods to produce carbon-fiber prepregs which would produce 

high-qual ity composites from the selected polyimide were addressed in the 

third-year Phase 111 effort. Amenability to fiber impregnation using 

conventional equipment was addressed in depth. Other Acurex efforts suggested 

that low-solids content varnishes of polyphenylquinoxaline and polysulfone can 

be used to prepare carbon-fiber prepregs and composites. 

of the Phase I11 effort, it was determined that low-solids content cresol 

solutions of the high-molecular weight BTDA/HDA/m-PDA polyimide provided 

composites with incompletely impregnated fiber bundles. 

these 6.9 MPa processed composites, however, was void free. Excellent fiber 

bundle impregnation was achieved by the use of monomers and prepolymers to 

produce >50 percent solids content impregnating varnishes. With the fiber 

bundles filled, the resin content at the prepregs surface was reduced and 

high-pressure molding of such prepregs did not always produce void-free 

composites. 

for more resin on the prepreg surface. 

volume, thermoplastic prepregs made by this method should be completely smooth 

and dense for the fabrication of quality composites. 

In the first months 

The interply resin in 

Voids were most evident in the interply regions suggesting a need 

It was concluded that high-fiber 

3 
Conditions were developed for the production of smooth and dense 

prepregs using high pressures (13.8 MPa). 

prepreg at atmospheric pressure with varying thermal, squeegeeing, and 

smoothing schedules invariably led to a high-melt viscosity varnish which, 

after final volatile removal, required high pressures for final perfecting of 

the prepreg. 

prepregs at lower pressures. However, commercial prepregs are not currently 

produced with vacuum treatment. 

Numerous attempts to produce the 

Processing the prepregs under vacuum and heat provided perfected 

The need to use the preimidized aliphatic diamine prepolymer in 

prepregging varnishes was also established to reduce the moisture sensitivity 

of the prepregs. The melt viscosity requirements of 100 percent solids neat 

resins to produce perfected prepregs needed additional study. The 

uncontrolled molecular weight growth that generally occurs in condensation 

polyimides will not be amenable to reproducible prepreg production or 

low-pressure composite processing. 

controlled flow properties, 

Injection-moldable thermoplastics have 

The BTDA/HDA/m-PDA polyimide (neat resin) is moldable at 0.69 MPa and 

temperatures as low as 260OC. 

must be capable of being molded at a far lower pressure than 0.69 MPa to 

provide prepreg which can be molded into composites at 0.69 MPa due to the 

restriction of the resin's flow by the fibers. 

NASA CR 172568.2 The shortcoming of resins with low-flow properties is shown 

in Figure 1. 

and use of resins with lower melt viscosities is required. 

1.3 PRESENT EFFORTS 

However, it became evident that the neat resin 

These efforts are described in 

Final smoothing of the prepreg must occur after volatile removal 

Present efforts concerned optimization of the melt flow properties of 

the polyimide to obtain low-void composites, a subject prior efforts had not 

4 
R 0 

c 

ch P, 

c 

E 

Y 

m 

aJ 

L 

P 

aJ 

L 

P 

U 

c 

(d 

L 

t 

v) 

a 

L 

a 

5 
addressed. Melt viscosity is directly related to the polymer's molecular 

weight and therefore molecular weight tailoring of the candidate polyimide to 

achieve lower melt viscosity was the approach taken. 

The room temperature strengths of unannealed composite and neat resin 

specimens from the BTDA/HDA/m-PDA polyimide were excellent. However, strength 

loss appeared to be more rapid for the polyimide at elevated temperatures than 

state-of-the-art 177°C curing epoxy systems. This loss of properties at 

elevated temperatures is attributed to shear yielding. 

Initial efforts on the present program addressed substitution of the 

HDA with two alternative aliphatic diamines. 

flexible aliphatic segment, for example, from HDA to 1,4-butanediamine (BDA), 

was expected to lead to improved elevated temperature composite strengths. 

1,3-Bis(aminomethyl)cyclohexane (BAC) was also selected for investigation. 

Reducing the length of the 

As noted in Figure 2, plotting Barcol hardness values against the 

percent by weight of the linear aliphatic portion of numerous polymers shows 

the validity of the approach (assumes a relationship between Barcol hardness 

and compression strength) . is treated as a rigid backbone segment. The polymer compositions are 

indicated in Table 1. 

also given in Figure 2 and Table 1. 

The cyclohexane ring in the BTDA/BAC/m-PDA polymer 

Glass transition temperatures (Tg) of the polymers are 

The improvement in Barcol hardness of the BTDA/BDA/m-PDA and 

BTDA/BAC/m-PDA polymers over the BTDA/MDA polymer is apparent. 

improvement is attributed to the use of m-PDA in the polymers and in the case 

of the BTDA/BAC/m-PDA polymer, use of the 1,3 isomer of the bis(aminomethy1) 

cyclohexane which would also give a "meta" effect. The Barcol hardness of an 

Acurex-prepared MY720/DDS sample is 553 and the BTDA/BAC/m-PDA polymer has 

almost this hardness, suggesting that it holds potential to provide excellent 

This 

6 
h 

I 

\/BAC-~-PDA = Barcol hardness 

r 

= Glass transition 

temperature 

BTDA/BDA/m-PDA 

‘!/8 BTDA/H DA/m- PDA 

I 

u 175 1 Y 

0 

\\ 

’Y9 t125 

\ 

\ 

\ 

m3 

L 

\ 

5 

100 I I I I 

(0 

co 

F: 

2 50 n 

k 

40 

- 

I v 

cn 

cn 

al 

c 

30 m 

c 

7 

0 

V 

L 

m 

m 

20 

10 

0 

10 20 30 40 

Weight percent (CH2)x in polyimide 

Figure 2. Weight percent flexible segment versus Barcol hardness 

7 
I. 

Table 1. Glass transition temperature and Barcol hardness 

of molded polymer samples 

Number 

1 

2 

3 

4 

5 

6 

7 

8 

8A 

9 

10 

11 

Polymer Composi tiona 

BTDA with MDA 

BTDA with BDA 

BTDA with HDA 

BTDA with ODA 

BTDA with DDA 

BTDAb with BAC and m-PDA 

BTDAb with BDA and m-PDA 

BTDAb with HDA and m-PDA 

BTDA with HDA and m-PDA 

BTDA with ODA and m-PDA 

BTDA and PMDA with HDA 

BTDA and PMDA with ODA 

TgD OC 

29 6 

160 

127 

113 

89 

24 1 

22 2 

19 6 

200 

17 6 

117 

111 

aBTDA = Benzophenonetetracarboxyl i c dianhydride 

BMDA = Pyromellitic dianhydride 

MDA = 4,4'-methylenediani 1 i ne 

BDA = lD4-bUtanediamine 

HDA = lD6-hexanediamine 

ODA = lD8-octanediamine 

DDA = lD12-dodecanediamine 

BAC = lD3-Bis(aminomethy1 )cyclohexane 

m-PDA = m-phenylenediamine 

bBTDA from the Chriskev Company 

Barcol Hardness 

RT 93°C 140°C 

Test Test Test 

40 

36 

21 

15 

6 

50 

46 

42 

38 

38 

15 

17 

31 

30 

12 

0 

0 

45 

40 

35 

26 

21 

0 

0 

32 

19 

0 

0 

0 

39 

33 

30 

18 

13 

0 

0 

8 

1 

I 

I 

I 

I 

I 

s 

i 

8 

I 

1 

I 

8 
I 

1 

I 

I 

1 

I 

I 

I 

1 

s 

1 

1 

1 

1 

composite strengths. 

efforts were conducted on the BTDA/BAC/m-PDA polyimide after 

from initial efforts on the present program. 

As a consequence, molecular weighthe1 t 

m 

n 

1 

1 

4 9 

vi scosi ty 

t was selectee, 
SECTION 2 

OBJECTIVE 

The overall objective of this program is the development of new 

thermoplastic laminating resin(s) that can be used with glass or graphite 

fibers to provide impact- and solvent-resistant composites for potential use 

on aerospace vehicles. These composites must have mechanical properties 

equivalent to state-of-the-art 177°C (350°F) curing epoxy systems. Although 

several routes can be pursued to improve the impact strength of composites 

(such as increasing the strain-to-failure capability of the reinforcement) 

this effort specifically pertains to resin development. Even though the 

tensile strength and tensile modulus of the reinforcement are considered to be 

the dominant contributors to impact strength of composites, the matrix also 

plays an important role by transferring load and dissipating stress. 

Target properties for the polymers are listed below. 

Amenable to impregnation of a reinforcement using conventional 

equipment 

Long prepreg shelf life at ambient conditions (>6 months) 

Acceptable processi bi 1 i ty [maximum curl ng temperature of 316°C 

(600"F), maximum curing pressure of 0.69 MPa (100 psi), maximum 

time at final temperature of 1 hr, insensitive to heatup rate, and 

no volatile evolution] 
e Thermoformability (thermoform flat-sheet stock to desired 

configurations at maximum temperature and pressure of 316°C and 

0.69 MPa, respectively; ability to undergo thermoforming process 

twice) 

Acceptable mechanical properties over temperature range of -54' to 

93°C (-65" to 200°F) after environmental exposure (humid aging and 

long-term aging at 93°C) 

Resistant to airplane fluids and solvents (under stress) 

Impact resistance and damage tolerance 

12 
SECTION 3 

RESULTS AND DISCUSSION 

This section has been divided into subsections which deal with 

different key aspects of the development effort. Initial efforts were 

directed toward selection of the best of three candidate polymers based on a 

number of tests. 

Selection. 

flow optimization studies. These studies ensued and are described in 

Section 3.2, Molecular Weight/Melt Flow Optimization Studies. Composite 

efforts are described in Section 3.3. 

These efforts are described in Section 3.1, Polymer 

The BTDA/BAC/m-PDA polymer was selected for molecular weighthelt 

3.1 POLYMER SELECTION 

3.1.1 Synthesis 

Initial efforts required preparing three polymers in sufficient 

quantity and molecular weight to select the one with the best balance of 

properties for further evaluation. The three polymers were from BTDA and 

m-PDA with three aliphatic diamines, BDA, HDA, and BAC. These efforts are 

described below. 

Monomers 

BDA, HDA, and 2,4-diaminotoluene (2,4-DAT) were used in the as-received 

condition from materials which had been successfully polymerized in the past. 

The wPDA was d i s t i l l e d a t 0.3 mn Hg at llO°C. 

and the four fractions analyzed by gas chromatography. 

The BAC was vacuum distilled 

The first fraction had 

13 
an obvious low boiling contaminate. 

the same low boiling contaminate which was not removed by the simple 

distillation. 

contaminate. 

obtained from the polymerizations discussed below, this small amount of 

contaminate does not appear to limit molecular weight growth. 

The last three fractions had a trace of 

If required, a column could be used to possibly remove this 

However, as evidenced by the inherent viscosities (IVs)* 

BTDA was initially used in the as-received condition from the Chriskev 

Company. A subsequent lot of this material had the distinct odor of acetic 

anhydride. 

at 180°C prior to use. 

Therefore, subsequent lots were treated overnight in a vacuum oven 

BTDA from the Chriskev Company is imported from Japan and is chemically 

dehydrated compared to thermal dehydration used on Gulf Chemical 'st material . It is reported to be purer than the Gulf material and free of triacid. 

anhydride assay by aniline titration is 98.6 percent. 

1 4 percent is tetraacid. 

Its 

The remaining 

As discussed in the next section, initial difficulty in obtaining 

v scous cresol solutions of the polymer from BTDA with BDA and m-PDA prompted 

distillation of the BOA and gas chromatographic analysis of the various 

fractions. 

160.0° to 160.8"C, the last two cuts were nearly chromatographically pure and 

were combined. This higher purity BDA also failed to provide viscous cresol 

solutions of polymer. 

The as-received BDA was of good purity and after distillation at 

As discussed below, there is a significant difference in the 

polymerizability of BTDA from the two sources. Gulf's BTDA provides high 

All IV's in this report were conducted in cresol at 25.0"C at 0.5 g/100 ml 

concent rat i on . the present program. 

* 

tNow Alco. Alco also has available high-purity BTDA which was not tested in 

14 
molecular-weight polymers in cresol in 1 to 2 hr at 180°C whereas Chriskev's 

BTDA requires overnight reaction at 180°C to obtain high molecular-weight 

polymers. 

BTD A /BD A /m- P D A Po 1 y me r 

The BTDA/BDA polymer had 

efforts by a standard method wh 

been successful ly prepared during 

ch involved a final reaction cond 

pr i or 

tion of 1 hr 

at 180°C. After four unsuccessful attempts to obtain viscous cresol solutions 

of the BTDA/BDA/m-PDA polymer after 1 hr at 180"C, efforts shifted to the 

BTDA/HDA/m-PDA polymer. 

were developed, and used to prepare the BTDA/BDA/m-PDA polymer. 

The BTDA/BDA/m-PDA polymer was successfully prepared as follows: 

New methods to prepare the BTDA/HDA/m-PDA polymer 

After 

the BTDA was dissolved in cresol at 180"C, the solution was placed in an ice 

bath. A cresol solution of BDA was added to the cold BTDA-cresol solution. 

After 30 min at room temperature, the BTDA/BDA prepolymer was heated for 2 hr 

and 20 min in a 180°C oil bath followed by cooling to room temperature. 

m-PDA-cresol solution was added, adjusting the solution to 10 percent solids 

content. Based on the monomer weights, 99.50 percent of the stoichiometric 

diamine weights had been added. 

oil bath. After 2 hr and 16.5 hr, IVs of aliquots withdrawn from the reaction 

were 0.30 and 0.37 dl/g respectively. The wPDA was then added to the 

polymerization to give' a calculated stoichiometry of 100.20 percent. 

4 more hours of reaction at 180"C, the IV of a sample of the polymer was 

0.48 dl/g. After final addition of wPDA to give a calculated diamine 

stoichiometry of 101.00 percent and 20 hr reaction time at 180"C, the IV of 

the polymer was 1.02 dl/g. The polymerization was viscous and clear at the 

180°C reaction temperature. Additional 24-hr and 48-hr reaction periods at 

180°C produced polymer samples with IVs of 1.22 and 1.31 dl/g, respectively. 

A 

The reaction was then immersed into an 180°C 

After 

15 
A 239g batch of the BTDA/BDA/m-PDA polymer was successfully prepared 

following the procedure described above. After condensation of the BTDA/BDA 

prepolymer for 2 hr at 180°C, a cresol solution of m-PDA was added to give a 

calculated total amine stoichiometry of 100 percent. 

solids content was adjusted to 12 percent and the reaction heated to 180OC. 

After 4 hr at 180°C, the IV of the polymer was 0.53 dl/g. The amine 

stoichiometry was increased to 100.80 percent and, after a 4-hr additional 

reaction at 180"C, the IV of the polymer was 1.05 dl/g. 

The polymerization 

This polymer was isolated by slowly pouring the cresol solution into a 

Waring blender containing methanol. 

30 min in refluxing isopropyl alcohol, filtered, and finally dried 16 hours at 

170°C and 0.1 mm Hg. 

The isolated polymer was stirred for 

This polymer was used to make the moldings required for 

mechanical property determinations and other tests. 

Additional polymer was required so 61g were prepared from the same raw 

materials employed above (a different lot of BTDA). After precondensation of 

the BTDA/HDA prepolymer for 12 hr at 180°C, the amine stoichiometry was 

adjusted with m-PDA to 100.81 percent and the solids content was adjusted to 

15 percent. 

polymer was 0.67 dl/g and 1.32 dl/g, respectively. 

the reaction temperature was very viscous and was diluted to 10 percent solids 

After 4-hr and 8-hr reaction times at 180"C, the IV of the 

The polymer solution at 

prior to isolation in methanol. 

BTD A /HD A /m-P D A P ol ymer 

The reactions described below were conducted on the BTDA/HDA/m-PDA 

polymer after the prel imi nary experiments with the BTDA/BDA/m-PDA polymer 

failed to provide high molecular-weight polymer. 

polymerizations, aliphatic or aromatic diamines added above stoichiometric 

quantities usually resulted in a gel, presumably due to crosslinking 

reactions. 

Based on prior 

16 
As a prelude to attempt to polymerize BTDA with HDA and 

polymerizability of BTDA was tested with HDA. Thus, BTDA with 

m-PDA, the 

a 95 percent 

stoichiometric quantity of HDA, was heated for 1 hr at 180°C in cresol at 

10.69 percent solids. The additions of 1.6 percent HDA and 2.0 percent HDA, 

each followed by a l-hr reaction at 180°C, did not significantly increase the 

viscosity of the hot solution. The further addition of 5 percent HDA followed 

by treatment at 18OOC led to a gel after 15 minutes at temperature. The 

stoichiometry at gelation was about 103.5 percent HDA. This gel is defined as 

a Type A gel which is caused by an addition of excess diamine to the 

polymerization and is probably attributable to interchain crosslinks with 

diamine molecules. 

A 98.00 stoichiometric BTDA/HDA/m-PDA polymer was prepared at 11.71 percent 

solids in cresol. The m-PDA, added as a cresol solution at room temperature, 

was reacted with the BTDA/HDA prepolymer at 180°C for 1 hr and 35 min. The 

BTDA/HDA prepolymer solution was prepared by addition of a HDA-cresol solution 

to the ice-bath-cooled BTDA-cresol solution followed by condensation at 18OOC 

for 1 hr and 15 min. Several aliquots of the reaction mixture were taken for 

further reaction with m-PDA and other diamines to investigate reaction 

conditions required to produce high-rnolecular-weight polymer. 

Reaction conditions, calculated final stoichiometries, and resulting IVs 

are indicated in Figure 3. 

Figure 3. 

The following observations were made from 

0 At 100.5 percent stoichiometric amine, HDA and MDA lead to gel in 

1/3 of the time it takes m-PDA to gel (Figure 3, Blocks D, E, F, 

and G) 

Excess MDA or m-PDA does not necessarily lead to gel (Figure 3, 

Blocks H and I, and the Blocks, J, K, L, M, and N) 

0 

17 
V 

7- 

m 

Jz U 

1 

.C 

SLLCFQQV 

1 

t 

VI 

w-v 

E40 '-Doh EomM mtm3.a m I, 

8aECO 

TZL. 

h 'CW 0- I 

P 

I 

.C 

.r 

0 

E 

h 

w 

.I= n 

- 

e 

I, 

U 0 

E 

L 

W 

0 

p. 

aJ 

L 

3 

m 

LL 

.I18 
0 Excess m-PDA appears to cleave the backbone (Figure 3, Blocks K, L, 

and M); however, overnight reaction lead to a significant increase 

in the IV of one polymer containing excess m-PDA (Figure 3, 

Blocks M and N) 

The study described above raises more questions than it answers, 

particularly in view of the fact that all three gels obtained at about 

100.5 percent stoichiometry were found to be soluble in excess cresol after 

overnight heating at 60°C (Figure 3 blocks D, E, and F). 

defined as a Type B gel. 

soluble polymer and thus become a Type B gel is unknown since most gels in the 

past have been discarded and not tested for slow dissolution in cresol at 

60°C. 

This type of gel is 

As to whether Type A gels can be diluted to obtain 

Results from a second polymerization similiar to the one described 

above are shown in Figure 4. 

Observations from the reactions and samples removed are listed below. 

0 The 100.5 percent amine stoichiometry led to a gel as observed in 

the first study which could be slowly dissolved in cresol at 60°C 

for IV determination (Figure 4, Block E) 

A direct relationship exists between IV and solids content of the 

reaction 

This latter relationship is plotted in Figure 5, and the relationship 

between the percent solids and IVs for the 20 hr at 180°C samples (22 hr 

total reaction time) suggests a second-order reaction. Oi 1 bath temperature 

variation which affects the reaction rate was normalized by placing the 

samples in test tubes in the same stirred oil bath for the overnight reaction. 

Significant increases in the IVs were observed for all of the reactions. The 

attainment of a polymer with an IV of 1.36 dl/g without observing gel was 

19 
rt 

il 

n'l; N m i 

0 

n 

v) 

U 

.C 

v 

0 

v) 

20 
5 10 15 

Percent solids 

Note: 2-hr samples reacted individually with stirring. 

20-hr samples all reacted in same oil bath in 

test tubes without stirring. 

reaction time, see Figure 4.) 

(22-hr total 

Figure 5. Inherent viscosity versus percent solids 

21 
significant. All samples appeared to be in solution at the reaction 

temperature. However, an elastomeric behavior was observed in the cooled 

cresol solutions of the 10, 15, and 20 percent solids reactions. All of the 

reactions were clear up to 15 percent solids. At 20 percent solids, a slight 

haze developed in the second hour of reaction at 180°C and at 23 percent 

solids a heavy opacity developed in the first hour of reaction at 180°C. 

It is noteworthy that prior efforts involved scale-up of the 

99.0 percent stoichiometric amine reaction at 13 percent solids since the last 

1.0 percent amine could not be added without gel formation. 

at 180°C (1 hr at 96.0 percent amine stoichiometry and the last hour at 

99.0 percent stoichiometry) resulted in IVs of about 1 dl/g (HzSO.4). 

understanding that the rate of molecular-weight growth at 180°C is apparently 

slower with the Chriskev BTDA, the 1-hr reaction times at 180°C are obviously 

inadequate, particularly with m-PDA. 

A 2-hr reaction 

With the 

The second study, although key to understanding how to achieve 

high-molecular weight, poses more questions, i.e., can high-molecular-weight 

polymer be made at 98.0 percent amine stoichiometry and high solids content 

reactions? 

A 2479 polymerization of the BTDA/HDA/r-PDA polymer was prepared by 

procedures described above at 15 percent solids. After a 2-hr reaction at 

180°C at 98.50 percent amine stoichiometry, the IV of the polymer was 

0.53 dl/g. 

was adjusted to 99.00 percent and after 12-hr reaction at 180"C, the IV of the 

polymer was 0.90 dl/g. The polymerization was hazy compared to the very clear 

solution obtained on the BTDA/BDA/m-PDA polymer described in the previous 

section. The polymer was isolated as previously described. 

The reaction seemed to be slightly hazy. The amine stoichiometry 

22 
I 

1 

I 

i 

I 

I 

I 

8 

I 

I 

I 

1 

I 

I 

I 

I 

1 

I 

I 

BTDA/BAC/m-PDA P ol ymer 

An 89 polymerization at 99.95 percent amine stoichiometry and 

15 percent solids was carried out as described in the previous sections. 

After 4- and 8-hr reaction times in a 180°C oil bath, the IVs of the 

polymers were 0.41 and 0.44 dl/g, respectively. The stoichiometry was 

adjusted to 101.00 percent with m-PDA followed by heating to 180°C for 

15 hr. After 12 hr at 180"C, the polymerization was viscous but not gelled. 

After 15 hr the polymerization mixture was not stirrable but upon dilution 

to 10 percent solids, it became stirrable again. The IV of the polymer was 

1.85 dl/g after the 15-hr reaction time at 180°C at the 101.00 percent amine 

stoichiometry. 

A 255g polymerization was carried out at 15 percent solids and a total 

amine stoichiometry of 100.99 percent. After a 3-hr reaction at 180"C, the IV 

of the polymer was 0.47 dl/g. 

a polymer with an IV of 0.69 dl/g and after 4 more hours of reaction the IV of 

Additional reaction at 180°C for 3 hr produced 

the polymer was 0.90 dl/g. The polymer was then isolated by the previously 

described procedure. 

3.1.2 Moldings of High-Molecular-Weight Polymers 

Thick Moldings 

Preliminary molding studies on 2g samples in a 5.1 cm2 disk mold 

demonstrated that the three candidate polymers were completely molded at 

6.9 MPa at the temperatures indicated below: 

Compos i ti on Temperature 

BTDA /BDA/m-P DA 

BTD A /HD A /m-PD A 

BTDA /BAC/m-PD A 

316 " C 

288 " C 

343 " c 

23 
Since these initial molding efforts were directed toward mechanical 

property and other tests, other molding conditions were not investigated. The 

polymers were molded with a 10-min hold at the temperatures indicated above to 

produce several moldings. 

Sixty gram samples of each polymer were molded to nominal thicknesses 

of 0.3 cm for GIc testing. The moldings were quartered and two each of the 

opposite quadrants were transmitted to NASA in the "as molded" and "annealed" 

conditions. Annealing studies are discussed in the next section of the 

report. 

Thirty gram samples of each polymer were molded to nominal thicknesses 

of 0.22 cm. These moldings were sectioned into 1.27 cm strips for solvent 

resistance and other tests. 

One hundred gram samples of each polymer were molded to nominal 1.27-cm 

thicknesses for compression testing. 

All of the above moldings appeared to be homogeneous by transmitted 

light and were good quality except for the lOOg molding of the BTDA/BAC/m-PDA 

polymer which had entrapped air bubbles near the center of the molding. Only 

about 10 percent of the area of the molding contained the bubbles. 

Thin Moldings 

Attempts to mold tensile specimens thinner than the other moldings led 

to moldings from all three of the candidate polymers which contained 10 to 

30 percent unmolded areas. These moldings were to have an areal weight of 

approximately 0.2 g/cd, which is a factor of about 5 less than the next 

thicker moldings. Unmolded areas are a direct result of uneven polymer 

distribution in the mold, limited processibility of the polymers and 

accordingly uneven pressure distribution during the molding. 

24 
This problem was studied in some detail, even though moldability was 

not part of the, decision matrix for selection of the best candidate. 

Perfected prepregs will probably have areal weights of less than 0.2 g/cm2. 

Furthermore, they will contain up to 65 volume percent fibers which will 

further arrest resin flow in the xy plane. 

To investigate the inability of the resin to provide good quality thin 

moldings, unmolded fibrous resins (TGA scans showed that all three resins were 

essentially free of cresol) were placed into a 2.54 cm2 plunger mold at about 

a 45" angle and molding pressure and temperature varied to determine 

conditions necessary to "fill" the mold. The areal weight of completely 

molded specimens was about 0.2 g/cm2. 

relatively high pressures to fill the mold, 

All three candidates required 

The percent molded area for the 6.9 MPa (1000 psi), 303°C processed 

moldings are listed in Table 2. 

and pressure applied for 30 min with hold times in the mold prior to pressure 

application of 0, 10, and 30 min. Thermocouple readings indicated that the 

molding reached the temperature in about 15 min and was approximately 

isothermal for the remainder of the time. Lower pressure moldings, 

i.e., 1.4 MPa (200 psi), gave a smaller percentage molded area, as expected, 

which correlated with the reduced pressure. Thus the 1.4 MPa processed 

moldings had molded areas of about one-fifth of the 6.9 MPa processed 

mol dings. 

The mold was placed into a preheated press 

The percent molded areas indicated in Table 2 show that only one of the 

three candidate polymers "filled" the mold at the 6.9 MPa, 303°C molding 

conditions (BTDA/HDA/m-PDA polymer). 

mold prior to pressure application reduced the flow of the BTDA/HDA/m-PDA 

polymer and gave only a 90 percent molded area. 

Holds of 10 and 30 min in the heating 

Heating the BTDA/BDA/m-PDA 

25 
Table 2. Molding studies of the three candidate polymers at 303°C 

Composition 

BTDA/ BDA/m-PDAa 

~ ~~~~ 

BTDA/HDA/m-PDA 

BTDA/BAC/m-PDA 

Hold Time 

With No 

Pressure 

(min) 

0 

10 

30 

0 

10 

30 

0 

10 

30 

Ti me wi th 

6.9 MPa 

Pres sure 

(mi n) 

30 

30 

30 

30 

30 

30 

30 

30 

30 

Estimated Clear 

Molded Area 

(%I 

80 

70 

60 

100 

90 

90 

70 

70 

70 

aTwo batches of polymer were tested with the same results 

obtained for both batches. Cresol IV's of the two 

batches were 1.05 and 1.32 dl/g 

T ._? 

i' 

26 

I 

I 

I 

1 

I 

I 

I 

1 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
I 

I 

I 

I 

I 

1 

1 

I 

I 

1 

I 

I 

I 

I 

I 

1 

1 

I 

I 

polymer prior to pressure application also led to reduced flow areas. 

BTDA/BAC/m-PDA polymer gave constant flow areas with 0, 10, and 30 min holds 

prior to pressure application. 

The 

Prior program efforts2 with the BTDA/HDA/m-PDA 

polymer showed reduced flow with increasing molding temperature. 

DSC Analysis of Molded and Unmolded Polymers 

DSC analysis of molded and unmolded portions of the disks as well as 

virgin polymer and other moldings was carried out in an attempt to understand 

why reduced flow areas were observed with hold times at temperature prior to 

pressure application. 

polymer in three conditions: 

for 1 hr at 316°C after molding for 10 min at 288°C. 

reheat of the DSC sample (heated to 425"C), which was molded 10 min at 288°C. 

The Tg transition is evident, as well as a high-temperature exotherm which is 

Figure 6 provides DSC curves* of the BTDA/HDA/m-PDA 

as prepared, molded 10 min at 288"C, and heated 

The fourth curve is a 

nearly eliminated with molding and completely eliminated by treatment to 

425°C. The exotherm associated with melt of the powder isolated from a cresol 

solution with methyl alcohol has been previously noted. It was concluded from 

inspection of numerous DSC traces that high temperatures (425°C) eliminate 

the exotherm, and fusion under pressure and temperature conditions also 

eliminates the exotherm. 

molding, does not eliminate the exotherm. The origin of the exotherm is 

unknown. 

Fusion alone, as evidenced by good clarity of the 

Table 3 summarizes the data on selected as-prepared polyimides. The 

suggestion that the peak exotherm temperature is a basic characteristic of the 

polymer's composition is noted. 

sample No. 48-83, isolated with methyl alcohol, has the same peak exotherm 

For example, the BTDA/BDA/m-PDA polymer, 

All DSC, TGA and other thermal analyses in this report were conducted at 

15"C/min unless noted otherwise 

* 

27 
iB8.86.C 

4 

I 250 I 300 1 . ------l--+, 350 400 

200 

-i.50 ! 

150 

Temperature ('Cl 

Curves from top to bottom are: 

Curve 1 = As prepared fibers, AH = 40.4 J/g Curve 2 = Molded 10 min at 288', AH = 1.0 J/g 

Curve 3 = Above plus 1 hr at 316'C, AH = 0.9 J/g 

Curve 4 = Reheat of sample which gave Curve 2 

Tgs shown are onset temperatures 

Figure 6. DSC analysis of BTDA/HDA/m-PDA polymer 

28 

I 

1 

I 

1 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

1 

I 

I 
I 

I 

1 

I 

I 

Composi ti on 

BTDA/BDA/m-PDA 

BTDA/HDA 

BTDA/HDA/m-PDA 

BTDA/ODA 

BTDA/ODA/m-PDA 

(50/50 wt pct) 

BTDA/BAC/m-PDA 

Table 3. Comparison of DSC properties of unrnolded polyimide powders 

Exotherm 

Sample No. Tg (onset), 'C Onset, 'C Peak, 'C bH, J/g 

43-54 226 36 5 389 29 

43-83 223 376 39 7 38 

43-83 Poor definition 

from cresol of event 37 0 39 6 3 

Reheat of 

cresol sample 217 None None None 

78- 134 134 308 336 22 

(reheat) 123 None None None 

338-85 16 1 342 36 7 22 

(reheat) 192 None None None 

43-50 20 1 342 364 39 

338-438 110 320 349 57 

(reheat) 106 None None None 

65-107 190 342 36 1 32 

43-69 24 1 336 36 2 65 

from cresol None None None None 

I 

I 

I 

I 

I 

I 29 
temperature as the polymer isolated by heating the cresol solution for 1 hr at 

250°C. 

The peak exotherm temperature and AH values were determined for a series 

of varying molecular weight BTDA/HDA/m-PDA polymers. The detai 1 s of this study 

are presented in Table 4. The peak exotherm temperatures show essentially no 

variation with molecular weight and the AH values show only a slight increase 

with molecular weight. 

from cresol at room temperature with methyl alcohol. They were then treated 

for the same time with fresh methyl alcohol at 6OoC, and finally vacuum dried 

together overnight at 200°C and 0.1 mn Hg. It can be tentatively concluded 

from this study that the DSC exotherm is a basic property of the polymer when 

isolated as fibers from the cresol reaction medium. How it varies with method 

of isolation, trace cresol, crosslinking, branching, and/or other possible 

vari ab1 es is not known . 

All of the samples were initially isolated individually 

Another phenomenon was observed with the BTDA/BDA/m-PDA polymer which 

was not observed from BTDA/HDA/m-PDA or BTDA/BAC/m-PDA polymers. DSC analysis 

of the fused portion of the test disks molded at 252", 280", and 303°C with no 

hold time gave a Tg which was about 20°C lower than the unfused or unmelted 

portion of the disk. 

425°C gave a final Tg for the polymer which was essentially the same as the 

as-prepared and unfused polymers. 

is shown in Figure 7, which shows the DSC curves of the as-prepared polymer, 

the polymer after fusion for 30 min at 28OoC, and the latter polymer reheated 

after the first DSC analysis. The fused portion of the BTDA/BDA/m-PDA polymer, 

which was held for 30 min at 303°C at atmospheric pressure followed by 

application of 6.9 MPa pressure for 30 min, gave a Tg onset temperature at 

220°C suggesting that thermal history influences the Tg. 

Reheating the DSC specimens which had once been heated to 

This behavior was repeated several times and 

30 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 
I 

I 

I 

I 

I 

I 

I 

I 

" 

L 

W 

E 

2, 

0 

n 

e 

0 

0. 

I 

E 

\ 

4 

n 

I 

\ 

e 

n 

7 

z 

c, 

r 

rn 

61 

3 

L 

Q 

3 

V 

W 

0 

E 

m 

r 

>r L 

Q 

> 

L 

0 

cc 

fe 

c, 

Q 

TI 

0 

v, 

.r 

7 

F 

.C 

n 

. 

d 

61 

(6 

I- 

- 

n 

- 

(6 

c, 

Q 

(3 

0 

v, 

n 

W u-- -. 

on 

E 

c,(d 

9" Y 

W 

W 

v) 

r 

0 

I n 

E 

L 

aJ 

r 

c, 

0 

X 

w 

0 

P -I 0 u 

r 

OW 

aJL 7aJ 

nn 

E€ 

(63 

mz 

ObbW cu mmwmle . . *I 

0000 4 

(UNcuNNcu 

O1 

m I 

31 
ll. 

U 

10 

B 

0.00 

375.63'C 

39.99J,'g 

U 

10 

B 

222. eeoc 

0.007 

2 

I 

I 

1 I .--I 

150 - 2cio 250 300 350 400 450 

Temperature ('C) 

Curves from top to bottom are: 

Curve 1 = As prepared fibrous material 

Curve 2 = Fused portion of 30 min at 280°C, 

6.9 MPa processed disk 

Curve 3 = Reheat of sample which gave Curve 2 

Tgs shown are onset temperatures 

Figure 7. DSC curves of BTDA/BDA/m-PDA polymer 

32 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 
3.1.3 Annealing Studies 

Prior efforts showed that the room temperature and elevated temperature 

Barcol hardnesses of several polymers were increased with 24-hr treatment at 

140°C. For example, the hardness of the BTDA/HDA/m-PDA polymer increased from 

32 to 38 at room temperature with this treatment. 

Small moldings of all three candidates when treated at or above their 

Tgs expanded in the z or mold plunger direction with concurrent shrinkage in 

the xy directions. Furthermore, a molding of the BTDA/HDA/m-PDA polymer was 

intentionally reduced in thickness from 2.31 to 1.71 mn with a corresponding 

increase in its area by treating it for 6 hr at 222°C under 0.4 MPa pressure 

and cooling under that pressure. With a single heat treatment to 300"C, the 

polymer cube essentially returned to its original dimensions. 

The three candidate polymers were then heat treated for 16 hr at 20°, 

30", and 50°C below their Tgs. Barcol hardness measurements were made on the 

samples at room temperature, 93" and 140°C and a second time at room 

temperature at the end of the elevated temperature tests. 

are presented in Table 5. 

These measurements 

Only minor benefits to the hardness of the majority of the samples are 

observed from various heat treatments shown in Table 5. The BTDA/HDA/m-PDA 

polymer shows slight improvement over the as-molded values with the 16-hr heat 

treatments at 20" and 30°C below Tg (176 and 166"C, respectively). The 

increase in hardness at 93°C with different polymer compositions is important. 

The BTDA/BAC/m-PDA polymer with its hardness of 45 at 93°C and 38 at 140°C 

shows excellent retention of the room temperature value. 

the value of the control sample at 14OOC. 

It is nearly twice 

33 
Table 5. Barcol hardness of candidate polymers 

Start 

45 

48 

46 

46 

37 

44 

45 

36 

42 

50 

49 

50 

50 

Composition End 

48 

48 

42 

44 

39 

43 

45 

41 

45 

49 

50 

51 

50 

BTDA/BDA/m-PDA 

38 

41 

40 

40 

30 

35 

35 

27 

35 

42 

46 

45 

45 

BTDA/ HDA/m- PDA 

Cont rolb 

30 

35 

34 

31 

20 

29 

29 

23 

20 

38 

35 

39 

38 

BTDA/BAC/m-PDA 

Heat 

Treatment 

Temperaturea 

("C) 

None 

202 

192 

17 2 

None 

176 

166 

146 

N/A 

None 

221 

211 

191 

Test Temperature 

-T 

93°C 1 140°C 

BSamples dried for 2 hr at 12O'C and cooled in a dessicator 

Samples treated 16 hr at the 

bControl sample was reported in NASA CR 172568. 

prior to starting experiment. 

indicated temperature 

Heat-treated sample previously gave a value of 38 at room 

temperature and 18 at 140'C. 

34 
Other variables associated with the specimens during heat treatment 

were measured and are listed in Table 6. All samples lost weight with heat 

treatment which was usually accompanied by a reduction in the sample's volume. 

The volumes of the BTDA/HDA/m-PDA polymer samples after the 146' and 166OC 

treatments were not reduced. The slight thickness increase observed with heat 

treatment is probably related to dimension changes observed when the polymers 

are heat treated above their Tg, as previously discussed. Thickness increase 

is clearly associated with shrinkage in other sample dimensions to give the 

observed reduction in volume. All of the moldings were heat treated for 16 hr 

at 30°C below the Tg of polymer. 

3.1.4 Testing 

The three candidate polyimides were tested for the compressive 

properties , fracture energies , suscepti bi 1 i ty to moisture (water boi 1 ) and 

stressed solvent resistance. These tests, which are described below, were 

conducted on moldings prepared and annealed as described in the previous 

section. 

Compression Properties 

Moldings of the three candidate polymers were sent to Delsen Testing 

Laboratories, Inc., Glendale, California, for specimen preparation and 

compression properties determination per ASTM D695-85. 

obtained from each molding for three replicates per test condition. The 

compression properties of the three candidates were obtained at room 

temperature, 93OC, and 93OC after 24-hr water boil. A summary of the test 

results is provided in Table 7. Table 7 also gives the percent moisture 

weight gain after 24-hour water-boiled specimens. 

Nine specimens were 

The compression properties obtained by extensometer on the three 

candidates suggest good potential as composite matrices. The BTDA/BAC/m-PDA 

35 
Table 6. Physical property changes of heat treated specimens 

Heat 

Treatment Thickness Wei ght Vol ume 

Tempe rat u rea I n c reas e Loss Change 

Composi t i on ("C) (%) 0) (%) 

BTDA/BDA/m-PDA 

202 0.2 0.30 -0.22 

192 0.1 0.31 -0.19 

172 None 0.30 -0.12 

- 

BTDA/ HDA/m- PDA 

176 0.1 0.21 -0.17 

166 0.1 0.19 +0.04 

146 0.1 0.15 +0.02 

BTDA/BAC/m-PDA 

221 0.1 0.34 -0.37 

211 0.2 0.33 -0.34 

191 0.2 0.32 -0.18 

- . 

Speci f i c 

Gravity 

of Heat - 

Treated 

Specimen 

(g/cc) 

1.3807 

1.3808 

1.3791 

1.3609 

1.3584 

1.3596 

1.3377 

1.3370 

1.3359 

36 
v) 

al 

C, 

L 

0 

L 

.In 

2! 

.C In 

VI 

aJ 

L 

n 

E 

0 

E 

0 

c, 

c 

c 

I-wrco -u,- d 0 I- -m43 y-! '91 

mu, mu, mu, 

-- 

r-* Nul u,* om 

ea mm er- . . ?'4 ?3 Y Y Y 

._ N4Cu 

Y YY 

VI 

i 

*r 

0 

W 

VI 

V aJ 

0 

L 

b, 

c, 

n 

c 

*C 

n 

r L 

I * 

cu 

al 

L 

n 

c, 

V 

m 

QI 

0 

.. 

0, 

c, 

0 

z 

37 
polymer had a modulus at room temperature of 4.85 GPA, the BTDA/HDA/m-PDA 

polymer a modulus of 3.92 GPa, and the BTDA/BDA/m-PDA polymer a modulus of 

4.37 GPa. These compression moduli values are higher than familiar 

engineering thermoplastics cited in the 1986-87 Modern Plastics Encyclopedia. 

For example, polyamide-imide is seen to have a compression modulus of 

1.9-3.1 GPa, polyetherimide a modulus of 2.9 GPa, and polysulfone a modulus of 

2.7 GPa. 

with expectation and with the Barcol hardness values discussed in the previous 

The high compression moduli of the program polymers is consistant 

sections. 

Stress at proportional limit (end of Hookean elasticity) is excellent 

for all three polymers at room temperature. This value would be expected to 

be important in predicting compression fatigue properties of the candidate 

resins. The proportional limit stress of the BTDA/BAC/m-PDA polymer is 

somewhat lower than the other two polymers at room temperature but is clearly 

superior at 93°C. 

Previous* compression properties determination by strain gage on the 

BTDA/HDA/m-PDA polymer by Acurex are consistent with the room temperature 

values reported by Delsen. 

for the BTDA/HDA/m-PDA polymer at 93°C is much higher than the 100 MPa value 

However, the compression yield strength of 132 MPa 

measured previously at 82°C on this polymer. An increase in elevated 

temperature Barcol hardness is also observed for the composition tested in 

Table 7 over previously measured values, (See Table 1, entries 8 and 8A.) 

Tensile Properties 

Quality moldings were not prepared from the three candidates as 

planned, because of their marginal flow properties. Due to schedule 

constraints, polymer selection was made without these values. Because of 

their high inherent viscosities (-1.0 dl/gm), it is expected that all three 

38 
polymers, if completely molded, would have tensile properties equal to or 

better than those previ ously2 determi ned for the BTDA/HDA/m-PDA polymer. 

Fracture Toughness Properties 

Moldings sent to NASA-Langley were sectioned and Krc values determined 

for specimens in the as-molded condition as well as specimens given the 

annealing schedule previously described. These values are given in Table 8. 

GI~ was estimated from compression moduli results given in Table 7 and an 

assumed Poisson's ratio of 0.35 for all three polymers. 

The three polymers show a slight increase in KI~ and Glc values with 

increasing Tg and decreasing linear aliphatic weight percent content. 

trend is opposite to expectation. 

This 

Relevant to program goals, the values are 

acceptable. 

Dry- and Water-Boiled Properties 

The three polymers were subjected to thermal mechanical analysis (TMA) 

for Tg determination and Tg shift due to moisture exposure. 

measurements were used for dry Tg determination and failure temperature under 

compression load (FTUCL). (See Appendix A for the effect of moisture on 24-hr 

water-boiled specimens. 1 These results are presented in Table 9 with inherent 

viscosity, Barcol hardness, and 50-day chloroform weight-gain values. The 

samples had nominal dimensions of 0.2 cm X 0.6 cm X 0.6 cm. 

Expansion 

Expansion coefficient determination on the polymers by TMA was not 

straightforward. Heating the as-molded annealed samples the first time lead 

to shrinkage in the xy dimensions with a corresponding growth in the thickness 

or z dimension. The cooling curve was not superimposable on the heating 

curve. Several reheats of the same specimen were required to obtain near 

superposition of the heating and cooling curves and to bring the glassy 

39 
'able 8. Fracture energies of the three candidate polymers 

Composi tion 

BTDA/BDA/m-PDA 

As molded 

Heat treated 

16 hr at 192'C 

BTDA/ HDA/m-P DA 

As molded 

Heat treated 

16 hr at 166'C 

BTDA/ BAC/m- PDA 

As molded 

Heat treated 

16 hr at 211'C 

~~ 

2.43 (2220) 

2.43 (2220) 

2.16 (1970) 

2.12 (1930) 

2.72 (2480) 

2.78 (2540) 

b GI0 

J/m2 (in-lb/inZ) 

1193 (7.8) 

1193 (7.8) 

1044 (6.81, (8.l)C 

1002 (6.5) 

1337 (8.7) 

1403 (9.2) 

acornpact tension prepared and tested by NASA Langley 

bVal ues calculated usi ng compression modul i from 

CValue calculated from tensile modulus obtained on 

Research Center 

Table 7 using GI~ = K~~z/E(l-vz) 

prior program (485,000 psi 12 

40 
In 

L 

a 

0 

E" 

c 

n 

W 

c, 

rb 

-0 

.lU 

S 

rb 

V 

In 

aJ 

L) 

elL 

n 

aJ 

0 L 

n 

U 

aJ 

i 

a, 

c, 

rb 

L 

-0 

r 

I8 

I 

. 

09 

aJ 

7 

n 

e 

a 

a 

0 

E 

0 

ln 

ln 

al 

L 

F 

.C 

n 

E 

s 

L 

aJ = 

c 

aJ 

L 

c, 

4 

L 

E 

W 

c, 

W 

L 

a 

a 

x 

a 

c 

v 

l2 

w 

2 

u 

z 

0 

41 
expansion coefficient near the Tg to about 1/3 of the value for the melt 

expansion coefficient. 

Figure 8 provides an example of the behavior of the BTDA/BAC/m-PDA 

polymer on the first and fifth heating and cooling cycles. 

1.1 percent of its weight during the first three cycles and 1.2 percent of its 

thickness. 

fifth cycles. 

BTDA/HDA/m-PDA polymers. 

polymers. 

curves. 

The polymer lost 

It lost essentially no weight or thickness during the fourth and 

Similar behavior was observed for both the BTDA/BDA/m-PDA and 

Figure 9 provl'des the last heating cycles for these 

Tg's were obtained from the intercept of the glassy and melt 

Expansion coefficients are given in the figures. 

FTUCL temperatures under the 0.3 MPa (450 psi) load were determined on 

dry and 24-hr water-boiled samples. The shift, due to water boil, in all 

three polymers is about 30OC. The weight gains for the three polymers is 

between 1.6 and 1.8 percent which is about a factor of 3 less than values 

obtained with epoxy resin based on MY720.3 

Fifty-day chloroform absorption values are also provided in Table 9. 

The BTDA/HDA/m-PDA polymer which showed a weight gain of 4.8 percent is 

slightly lower than previously observed; however, 1-hr heat treatments at 

316°C reduced these previous values to about 2 percent weight gain. 

BTDA/BDA/m-PDA and BTDA/BAC/m-PDA polymers show about a three-fold improvement 

over the BTDA/HDA/m-PDA polymer in Table 9 with weight gains of 1.5 percent. 

The values provided in Table 9 suggest adequate performance for all three 

polymers relevant to the 93°C wet performance sought in the program. 

Stressed Solvent Resistance Properties 

Both the 

The three candidates were immersed in deicing fluid, hydraulic fluid, 

and two paint strippers under stress. 

with a small flexural specimen which was clamped in a three-point bend fixture 

The stressed condition was achieved 

42 
8 

8 

20 - 

0- 

-20 

ORIGINAL PAGE IS 

OE POOR QUAJJm 

~3i?.Om/m*c i 

B 

1 

R 

1 

- 

E 

I 

a 

0) 

C 

.c 

u 

m 

m 

C 

4 0 

m 

C 

E 

4 

a 

ilc 

E 

It 

i 

0 

E 

1 

40 4 

4 

20 i 

-I 

04 

-201 

-40 4 

4 

-601 

I 

J 

-4 

50 100 150 200 250 300 350 

Temperature ('C) 

(a) BTDA/BAC/m-PDA -- first cycle 

(b) BTDA/BAC/m-PDA -- fifth cycle 

Figure 8. MA curves for BTDA/BAC/m-PDA polymer 

4 3, 
i I I I 50 100 150 20 0 250 300 350 -20+ . 

Temperature ('C1 

(a) BTDA/BDA/m-PDA 

1 

i 

i 

~ 

j 

j 

I 

40 - 

20 - 

07 

-20+--.---.-l--------~--.-- 

0 50 100 i50 200 250 300 31 

Temperature I'C) 

(b) BTDA/HDA/m-PDA 

0 

Figure 9. MA curves for BTDA/BDA/m-PDA and BTDA/HDA/m-PDA polymers 

44 
to a 0.127 cm (0.047 in) deflection over a 3.81 cm (1 50 in) span. This 

deflection was calculated to produce a 34.5 MPa (5000 psi) tensile stress on 

the tensile side of the test coupon for a specimen wh ch was 0.203 cm 

(0.080 in) thick with a modulus of 3.45 GPa (500,000 psi). The candidates had 

nominal thicknesses of 0.215 cm (0.085 in) and moduli as indicated in Table 7. 

Consequently, test specimen thickness and modulus variance from the design 

condition produced slightly higher or lower tensile stresses than the 

calculated 34.5 MPa (5000 psi) value. 

The paint strippers were of two types: a nonacid stripper (CEE BEE 

A-254) and an acid stripper (Inland Chemical AP-561A). They were obtained 

from the United Airlines repair facility at the San Francisco airport and are 

in current use. Plans are to slowly convert to the acid stripper for its 

greater acceptability from environmental considerations (employee health, 

disposal, etc.). 

specifications for use on their respective aircraft. 

thought to be methylene chloride-phenol and methylene chloride-formic acid. 

However, the latter composition, upon evaporation, has the sweet odor of 

phenol. The strippers are used to remove the urethane paint and the epoxy 

primer from aluminum. 

to prevent exposure. United Airlines currently removes paint from composites 

by hand sanding; however, a number of new methods are being investigated for 

this application, i.e., plastic media blasting. 

Both meet the McDonnell Douglas CSDl and Boeing D6-17487 

The compositions are 

Windows and composite wing fairings are no doubt masked 

The results of the stressed aircraft fluid and paint stripper tests are 

given in Table 10. All three candidates passed the 30-day exposure to 

hydraulic and deicing fluids based on a pass/fail criterion. All three 

candidates showed weight gains and did not completely return to their original 

45 
I ! 

46 

. 

L 

r 

s 

m EO 

zz 

am I 

-3aJ 
original flat condition. The 7-day recovery deflections of all specimens 

shows less than 0.0012 cm (0.005 in) or 10 percent permanent deflection. 

Exposure to both paint strippers led to failure of all three candidates 

in less than 16 hr. 

chloroform resistance of the candidates. 

solvent effects of phenol or formic acid with the methylene chloride. 

This result was unexpected, due to the excellent 

It is likely due to the combined 

This result prompted collection of polymer samples from a number of 

compositions for test in the two paint strippers. Since these samples had 

varying weights, percent weight gains only indicate resistance or attack and 

do not allow for a comparison between compositions. 

in the stressed-solvent tests described above were all close to the same 

dimensions. 

The three polymers tested 

Results of the tests on the collected samples are given in Table 11. 

The best compositions are either crystalline or crosslinked. 

showed no weight gain in the 16-hr tests. 

cyanate (NC) resinO4 Tests were continued for 12 days for samples which 

showed no surface attack by the paint strippers in the 16-hr tests. The 

12-day exposed samplebs were then allowed to stand out under ambient conditions 

to see if they would return to their original weights. 

presented in Table 12. 

One composition 

It was a highly crosslinked novolac 

These data are 

It is concluded that solvation differences between paint strippers 

exist and depend on the specific composition of the paint stripper. 

12-day exposed Kapton film results point out this difference. 

Kapton after 16-hr exposure in both paint strippers showed weight gains of 

about 30 percent and no surface attack. 

liquification of the Kapton sample in the nonacid paint stripper but had no 

The 

Samples of 

However, 12-day exposure led to 

47 
Table 11. Sixteen-hour unstressed weight gains of various 

compositions in paint strippers 

Composi tiona 

aODA = 1,8-octanediamine 

PBI = polybenzimidazole 

TAB = 3,3' ,4,4'-tetraaminobiphenyl 

PMDA = pyromellitic dianhydride 

NMA = methylnadic anhydride 

DDS = 4,4'-diaminodiphenyl sulfone 

NC = novolac cyanate 

DGA = diglycidylaniline 

48 

Program Resins 

BTDA/ BDA/m-PDA 

As molded, annealed 

After 1 hr at 316°C 

BTDA/HDA/m-PDA 

As molded, annealed 

After 1 hr at 316°C 

BTDA/ BAC/m-PDA 

As molded, annealed 

After 1 hr at 316°C 

Prior program resins 

BTD A/O D A/ m- P D A 

PBI from TAB with 

sebacic acid 

PMD A/O D A 

Miscellaneous thermoplastics 

Kapton 

U1 tern 

Mi scel laneous thermosets 

EPON 828/NMA 

DG A/ Ton ox 

MY720/DDS 

NC 

Mi scel laneous composites 

Ry to n/ car bon 

Pee k/carbon 

Nonacid 

Paint Stri pper 

23 

14 

215 

223 

123 

45 

61 

242 

4 

32 

Di ssol ved 

51 

0 

0.2 

0 

8 

3 

- 

Acid 

Paint Stri pper 

43 

10 

240 

16 1 

49 

43 

36 

Di ssol ved 

4 

27 

Dissolved 

Lost 

1 

0.2 

0 

11 

4 
~~ ~~ ~~~~ ~~~ ~~ ~~~ 

Tab1 e 12. Twel ve-day unstressed wei ght gal ns of compositions i n pai nt 

st ri ppers 

Composi ti ona Nonacid Paint Stripper Acid Paint Stripper 

BTDA/ BDA/m-PDA 

(after 1 hr at 316'C) 

PMDA/ODA 

Kapton 

MY 720/DDS 

NC 

Ry t o n /c a r bo n 

Peek/carbon 

BTDA/ BDA/m-PDA 

(after 1 hr at 316°C) 

PMDA/ODA 

Kapton 

MY720/DDS 

NC 

Ry ton / ca r bon 

Peek/carbon 

12-Day Weight Gain (%I 

19 3 

25 

Li qu 

1.6 

0 

13 

11 

fied 

164 

19 

28 

3.2 

1.1 

12 

5 

Weight Gain After 2 days at 

Ambient Condition (%I 

82 

11 

-- 

0.7 

-0.7 

1.4 

3.6 

aODA = 1,8-octanediamine 

PBI = polybenzimidazole 

TAB = 3,3' ,4,4' -tet raami nobi phenyl 

PMDA = pyromell i tic dianhydride 

NMA = methylnadic anhydride 

DDS = 4,4'-diami nodi phenyl sul fone 

NC = novolac cyanate 

DGA = diglycidylaniline 

49 

58 

9 

10 

0.7 

0 

2.1 

0 
further influence on the sample in the acid stripper. The term liquification 

means the sample lost its dimensions but did not dissolve. 

Relevant to program goals, the three polymers demonstrated good 

resistance to hydraulic and deicing fluids and chloroform. 

efforts suggest that resistance to acetone will be even better than the 

chloroform resistance. Short time exposure (1 to 2 hr) to paint strippers 

which contain a combination of chlorinated and acidic solvents may be 

acceptable but overnight exposure must not occur. 

In view of the 2-day recovery test results indicated in Table 12 which 

Prior program 

show the presence of residual paint stripper in most of the polymers, it can 

be concluded that paint strippers should not be used on crosslinked or 

crystal line polymers without prior extensive testing. Structural composites 

should show 100 percent recovery of properties after intentional or accidental 

exposure to aircraft fluids and paint strippers. Paint stripper reformulation 

is probably required to achieve this goal. 

3.1.5 Selection 

The BTDA/BDA/m-PDA and BTDA/BAC/m-PDA polymers are superior to the 

BTDA/HDA/m-PDA polymer in compression properties and resistance to paint 

stripper. 

same without clear benefit for use of one over the other two. The 

BTDA/BDA/m-PDA polymer is slightly more resistant to paint stripper than the 

BTDA/BAC/m-PDA polymer, particularly after 1-hr heat treatment at 316OC. The 

BTDA/BDA/m-PDA polymer is less moldable than the BTDA/BAC/m-PDA polymer . This 

moldability rating is subjective and based on a seemingly better ability of 

the BTDA/BAC/m-PDA polymer to give thi n moldings than the BTDA/BDA/m-PDA 

The remainder of the tests show the three polymers to be about the 

polymer. 

50 
The polymers used for the characterization tests had inherent 

viscosities close to 1 dl/g in cresol. As demonstrated in subsequent sections 

of this report, the poor moldability of the three candidates at low pressure 

was due to their high molecular weight. 

with the characterization tests, the BTDA/BAC/m-PDA polymer was recommended 

for the molecul ar-wei ght/mel t flow optimi zation studies. 

3.2 MOLECULAR WEIGHT/MELT FLOW OPTIMIZATION STUDIES 

Based on this premise in combination 

The objective of this effort was to increase flow properties of the 

selected polymer by controlling (reducing) its molecular weight. 

Stoichiometric imbalance (excess BTDA) and end capping with phthalic anhydride 

were investigated. As a point of reference which assumes complete reaction 

(which is not likely for second-order polymerizations), the BTDA/BAC/m-PDA 

polymer with a 10,200 MW would result from an amine stoichiometry of 

96.0 percent (DP = 49) and a polymer with a 20,400 MW would result from an 

amine stoichiometry of 98.0 percent (DP = 99). 

The polymer from BTDA with BAC and m-PDA was selected for investigation 

with NASA's verbal approval obtained on 7/9/86. Molecular-weight tailoring 

efforts demonstrated that the BTDA/BAC/m-PDA polymer had very limited 

potential to provide low-molecular-weight polymers with the desired flow 

properties. 

groups in the m-PDA, the resulting polymers were produced in both low and high 

molecular weights with flow properties as expected. Telecom with the NASA 

technical representative on 12/1/86 lead to verbal approval to proceed with 

substitution of the m-PDA in the BTDA/BAC/m-PDA polymer with 

2,4-diaminotoluene (2,4-DAT). The balance of work in the program was carried 

out with the BTDA/BAC/2,4-DAT polyimide. 

When a methyl group is placed ortho to one or both of the amine 

51 
3.2.1 Flow Properties 

Optimizing the flow properties of the selected polymer required a flow 

test be used to monitor progress of these efforts. Three tests were conducted 

on the different molecular-weight levels of the polymer investigated. 

Molding Tests 

This test was described in Section 3.1.2. For the molecular-weight 

tailoring efforts, the pressure was reduced from 6.9 MPa (1000 psi) to 

1.45 MPa (210 psi). The 5.07 cm2 (1 in21 mold was loaded with 0.5g fibrous 

polymers at a 45" angle as previously described. Completely molded specimens 

would have an areal weight of 0.1 g/cm2. All tests were conducted for 30 min 

at 303OC. 

TMA Flow Test 

The developed TMA flow test is a penetration test wherein a sample is 

placed under a weighted probe and subsequently heated. The resulting curves 

are normalized to 100 percent penetration to allow samples of varying 

thicknesses to be compared. Further description of this technique is provided 

in Appendix B. Unless otherwise noted, flow curves given in this section of 

the report were conducted at 0.20 MPa (28 psi). 

Press Flow Test 

Acurex compares the melt flow properties of resins by placing a weighed 

sample in a press equipped with an accumulator which applies a constant force 

to the sample. The area of the resulting disk obtained after a prescribed 

time is related to the melt viscosity of the polymer, 

calibratable. Figure 10 shows the areas of 0.5g disks of polysulfone (UDEL 

P1700) and polyetherimide (ULTEM P1000) pressed for 5 min with 95 Kg (210 lb) 

force at the indicated temperatures. Inherent viscosities of the two polymers 

The procedure is 

52 
100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

9 

8 

7r 

6 

5 

4 

3 

2 

1 I I I I I I 

240 260 280 300 320 340 360 380 

Temperature, OC 

Figure 10. Press flow areas of polysulfone and polyetherimide 

53 
in cresol were 0.488 and 0.543 dl/g, respectively. 

were 187" and 217"C, respectively (DSC inflection points). 

3.2.2 BTDA/BAC/m-PDA Polymer 

The Tg's of the polymers 

Experiments with both phthalic anhydride end-capped and imbalanced 

stoichiometry were carried out on the title polymer. 

stoichiometries of less than 99.0 percent, opacity developed during the 

polymerizations. 

stoichiometry. That is, reactions with only 95 percent of the amine have more 

With both approaches, at 

The degree of opacity is directly related to the 

opacity than higher amine percentages. Brief treatment of the opaque polymers 

at 429°C resulted in volatile loss (foaming) and a clear polymer. Opacity was 

eventually traced to the "crystal 1 ine" nature of the intermediates formed, 

This is discussed in some detail in Appendix C and summarized below. 

End-capping experiments with phthalic anhydride (PA) at 97.5 percent 

BTDA stoichiometry (BTDA = 0.975 mole, amines = 1.000 mole, PA = 0.050 mole) 

lead to only one polymer with excellent flow properties. 

of this polymer are compared to the flow properties of polyetherimide in 

Figure 11. 

BTDA/BAC/m-PDA polymer were 0.086 MPa (12.5 psi), 0.20 MPa (28 psi), and 

0.90 MPa (130 psi). 

pressures were used. 

brittle, its flow properties were consistent with program goals: 

The flow properties 

Flow pressures used for the three flow curves for the 

For the polyetherimide, only the 0.086 MPa and 0.90 MPa 

A1 though the BTDA/BAC/m-PDA polymer was somewhat 

a polymer 

which flowed at low pressure. The flow properties of this polymer were in 

distinct contrast to other 97.5 percent stoichiometric compositions described 

in Appendix C and the 100 percent stoichiometric composition described in 

Appendix B. The polymer with the desired flow properties was isolated from a 

clear cresol solution by quenching in methanol. 

54 
h 

W 

aJ 

01 

c 

m 

S 

V 

r 

0 

u) 

v 

.r 

-IE o 

Temperature ('Cl 

(a) BTDA/BAC/m-PDA polymer 

1 

O/ 

-50 

-60 4 -701 -eo 

0.086 MPa 

0.90 MPa 

-10 OI 

-20 - 

-30 - 

-40 - 

0 50 100 150 20 0 250 300 350 400 4 

Tomper8ture I'C) 

-50 - 

-60 - 

-70- 

-eo - 

-90 - 

-100 

(b) Polyetherimide 

4 

c 

0 

Tomper8ture I'C) 

(b) Polyetherimide 

Figure 11. Comparison of the flow properties of the BTDA/BAC/m-PDA polymer 

to polyetherimide 

55 
Polymers isolated by evaporation of the cresol exhibit an endotherm at 

about 350°C and flow properties representing the presence of crystallinity. 

It was known that this behavior is attributable to the BTDA/m-PDA/BTDA 

segments in the polymer since the BTDA/BAC polymer did not exhibit a 

high-temperature endotherm. The program approach dictated that good flow 

properties must be exhibited by the polymer after evaporation of a suitable 

prepreggi ng sol vent. 

Consequently, the synthesis of clear polymers which did not have a 

high-temperature endotherm were required before the molecular weighthelt flow 

properties would be optimum. Efforts then focused on this aspect of the 

end-capping efforts. 

It was found that when BTDA is condensed with an aromatic diamine at a 

2 to 1 stoichiometry at 15 percent solids in cresol, both crystalline and 

amorphous adducts can be obtained, When the aromatic diamine is m-PDA, a 

precipitate is formed after only a few minutes reaction at 180°C. 

4,4'-methylenediani 1 i ne, a clear solution is obtained; however ,upon cresol 

evaporation, an opaque solid is obtained. When either 2,6- or 

2,4-diaminotoluene is condensed with the BTDA, evaporation of the cresol at 

180°C from the clear solution leads to clear amorphous adducts. 

With 

A 96 percent amine stoichiometric BTDA/BAC/2,4-DAT polymer was clear 

upon evaporation of the cresol from the reaction mixture. In addition, the 

1-hr at 329°C treated sample showed no high-temperature endotherm. 

3.2.3 BTDA/BAC/2 ,4-DAT Polymers 

Clear, amorphous BTDA/BAC/2,4-DAT polymers were obtained from 90, 96, 

97, 97.5, 98, 98.5, and 100 percent stoichiometries. TMA flow curves, IVs, 

and other properties of these polymers, as well as blends of selected 

polymers, are provided in Figures 12 and 13 and Tables 13 and 14. TMA flow 

56 
10 

! 

0 

- 10 

-20 

- 

b4 - -30 

aJ 

ol 

-40' lz 

u 

.rl 

v) 

C 

-60. .rl 

n 

-70. 

-80- 

-90 - 

-100- 

Temperature ("C) I I 

327OC 377OC 

Figure 12. TMA flow curves of BTDA/BAC/2,4-DAT polymers 

57 

0 

Press flow temperature: 

Areas indicated on samples tested 
h 

bp 

Y 

c1 

m 

c 

m 

r 

0 

C 

0 

m 

C 

0 

E 

3 

.,-i 

.A 

IO _I-- -- .- ___ 

I 

0; I 

-10 I 

-20 i 

I 

I 

-30 4 

-30 J 

I 

-50 4 

i 

-60 

I 

-70 -I 

, I 

-BO 

-90 i 

_- I I -7 

- 1 0 0 Ll---r-------' 0 50 100 I50 20G 250 300 350 

Temperature ("C) 

2 

/ 4.0 cm 

I 

i 

! 

, 

1 

i 

I 

1 

I 

I 

I 

I 

I 

2 

2 

8.1 cm 

7.9 cm 

! 

9.7 Cm2 i 

--TT 

' 400 450 500 

377OC 

Press flow temperature: 

Areas indicated on samples tested 

a 

Figure 13. TMA flow curves of BTDA/BAC/2,4-DAT polymer blends 

58 
v) 

L 

W 

E 

>, 

0 

n 

IU 

n 

I 

d 

N 

\ 

0 

U 

\ 

U 

tc, 

r 

07 

Y 

.L 

m 

n 

m 

.r 

P 

L 

(0 

s 

u 

W 

F 

c 

i2 

m 

E 

h 

L 

4 

> 

YO 

v) 

a.3 

c, 

L 

aJ 

n 

0 

L 

n 

*r 

m 

4 

W 

4 

I- 

- 

n 

,,I I 

I 

I 1 

n 

0 

0 

W 

03 

CT) 

N 

fm 

N 

N 

d 

(u 

m 

d 

N 

03 

d 

N 

d 

d 

(u 

9 

N 

m 

N 

In 

0 

? 

Q\ 

m 

r( 

. N 

m 

0'. 

e 

h 

ao. 

0 

co 

r( 

d. 

0 

d 

co 

9 

a> I 

oa L -1 

WW 

59 
v) 

U 

c 

aJ 

7 

n 

L 

z, 

0 

n 

II 

d 

(u 

\ 

0 

m 

\ 

c3 

Icc 

0 

v) 

aJ 

c, 

L 

0 

L 

ii 

F 

d 

.) 

a 

a 

m 

-r 

8 

n 

f 

aJ 

ta 

I7 

n 

0 co 0' 

Q: . 91 W l-l co 4 rn 

0 

0 

Y 

Grl m r- tn d~ 

c, 

c 

0 

U 

.rn 

.lt 

L ala 

tax 

I-z 

z2 

l-l In co rl rl 

m In tn m W 

m m 3m 

u, 0 In u, In h co W W W 

m m m m m 

m 

0 0 0 0 0 

m W * m*m W *r- e e 

W In * 

m W 

d d 

cu m * 

cu N N N d 

r- l-l co 

m m d 

N 

b co 

0 N 

N N N N 

m a a aL 

LaJ 

aJ WE 

a I L L a 

E E E Ez, 

c *- a- a 2;s 

l-l N m d In 

60 

- l-l 

N 

m 

0 

U 

K 

ta 

rN 

4 

0 

aJ 

L 

aJ 

3 

. 

e 

v) 

L 

aJ 

E 

a 

0 

0- 

7 

2 

c, aJ 

E 

0 

z 

V 

0 

c, 

v) 

c, 

c 

6, 

V 

L 

a, 

W 

m 

-0 

c 

a 

In 

rce 

0 

a 

al 

c, 

.C 

.r 

n 

.r 

.- 

a 

0 
curves, IVs, and other properties of the BTDA/HDA/2,4-DAT polymers are given 

in Figure 14 and Table 15. Press flow areas determined at 327 and 377°C are 

indicated in some of the figures. For a reference point in each of the three 

figures, the TMA flow curve of polyetherimide has been included (dashed line). 

Figure 15 provides a plot of the inherent viscosities of different molecular 

weight levels and polymer blends of the BTDA/BAC/2,4-DAT and the 

BTDA/HDA/2,4-DAT polymer. The relationship indicated in Figure 15 shows that 

the inherent viscosities of the BTDA/BAC/2,4-DAT polymers are directly related 

to the polymer's flow properties as measured by the TMA flow test at 0.20 MPa 

(28 psi) pressure. A one-tenth increase in inherent viscosity value leads to 

about a 30°C increase in the 50 percent flow temperature. Normalizing the 

50 percent flow temperature by subtracting the Tg from the 50 percent flow 

temperature provides the results given in Figure 16. The normalized data for 

the two polymers show that Tg values essentially account for the differences 

observed in the 50 percent flow temperatures for the two compositions in 

Figure 15. Thus, for a given inherent viscosity polymer, the 50 percent TMA 

flow temperature can be estimated if the polymers' Tg is known. 

The normalized values for polysulfone, polyetherimide, and blends of 

BTDA/2,4-DAT/BAC and HDA polymers have been added to Figure 16. The 

50 percent TMA flow temperatures for these polymers is less than 50°C above 

their Tgs but should be about 90'C above their Tgs to fit within the data for 

the BTDA/2,4-DAT/al i p hat i c di ami ne polymers. 

The press flow method of characterizing the flow properties of the 

polymers shows that polysulfone and polyetherimide are approximately equal to 

the flow properties of the BTDA/HDA/2,4-DAT polymers. Flow properties 

obtained at 327" and 377°C are plotted against inherent viscosities in 

61 
8 

I 

mGINAL PAGE IS 

a mR QUALITY; 

04 r ____) 

I 

-10' 

I 

-20 4 

Note: See Table 15 for 

flow curve numbers -30 4 

-p, 

+ 

350 

/6.7 'i. c 

400 450 500 

u 

I 

I 

I 

I 

c 

Temperature ("C) 

327OC 377'C . 

Press flow temperature: 

Areas indicated on samples tested 

Figure 14. TMA flow curves of BTDA/HDA/2,4-DAT polymers 

62 
v) 

*r 

aJ 

3 

L 

4 

F 

3 

0 

aJ 

c 

v) 

3 

0 

L 

2 

cc 

0 

ln 

4 

aJ 

4 

I7 

n 

Y 

v) 22 19 

LL 

CLU 

c, 

EW 

aJaJ 

VU 

Lao 

E -r u 

nz- I 

mm ON 

I I mol 

I *I *I 

I-ln Gf 

mbmcublno 

mmwcummm 

4NmmoOm4 

NI- 

. . . . . 

v) 

UaJ 

x 

63 
1.0 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

BTDA/HDA/2,4-DAT Polymers 

- BTDA/BAC/2 ,4-DAT Polymers 

x Blends of 0.127 with 0.735 IV Polymers 

0 Blends of 0.321 with 0.735 IV Polymers 

I /- 

/- 

250 300 350 400 

0.2 MPa (28 psi) 50% flow temperature (OC) 

Figure 15. Inherent viscosity versus TMA flow property relationship 

64 
L 

h 

0 

n 

c 

a 

In 

L 

h 

0 

n 

c 

Qkh 

OON 

. lld . .. 

b,b, 0 

NN \\+ 

eo 0 

oc Im VI \\u 

e< c 

!-+e 

mmm 

no 

IOX 

a 

VI 

L 

O+ 

0 

In 

cu 

0 

0 

cu 

0 

In 

4 

0 

0 

4 

0 

Ln 

>, 

c, 

L 

aJ 

P 

0 

L 

P 

3 

0 

G 

f 

L 0 J V c, ul Q .r 

L w aJ 

n c, E E 

aJ aJ 

!- L 

!- *r 

2 bp 

0 

Ln L 

0 

c 

c" 

65 
Figure 17. 

polymers at both temperatures as expected. 

The BTDA/BAC/2,4-DAT polymers flow less than the BTDA/HDA/2,4-DAT 

Interpretation of either flow test relevant to obtaining quality 

composites was needed at this juncture. Thus, if a 5 or 10 cm2 press flow 

area was required to process prepregs at 100 psi then an inherent viscosity 

and temperature could be specified. Similar reasoning applies to the TMA flow 

test. The two flows are related. This is seen in Figures 12 through 14 where 

between a 5 to 10 cm2 press flow area was obtained on the polymers at 

approximately the 50 percent TMA flow temperature. 

Acurex-developed unidirectional polysulfone, carbon fiber prepregs from 

the early 1970s provide the following consolidation specifications. 

260"C, 0.69 MPa, 5 min for flat composites 

287"C, 1.04 MPa, 5 min for deep draw, 0.25-cm-thick cross-plied 

stock 

The indicated processing temperatures are seen from Figure 10 to be 

equivalent to about 9.0 and 12 cm2 press flow areas at 1.45 MPa and can be 

used as the basis of selection for processing the candidate compositions. 

Results presented in Figure 17 show that a BTDA/BAC/ZS4-DAT polymer with an IV 

of 0.5 dl/g would have a press flow area of 10 cm* at 377°C. 

selection of a polymer with an IV of 0.55 dl/g for a good balance between 

toughness and processability was recommended to NASA. 

BTDA/BAC/2,4-DAT and BTDA/HDA/2,4-DAT polyimides would have better flow 

properties, the loss in Barcol hardness discussed in the next section did not 

seem to justify this selection. 

3.2.4 Barcol Hardness Testing of Polymers 

Initial 

Although blends of the 

Barcol hardness of selected moldings were measured at room temperature, 

93°C and 140°C. These values are tabulated in Table 16. The values for the 

66 
377°C test temperature 

50 

30 

(v 

E 

V 

(CJ 

6, 

L 

(CJ 

m 

s 10 

0 

v) 

v) 

W 

L 

P 

5 

3 

Inherent vi scosi ty 

BTDA/HDA/2,4-DAT Polymers 

BTDA/BAC 2,4-DAT Polymers 

X Blends of .127 with .735 IV Polymers 

0 Blends of .321 with .735 IV Polymers 

i= Blends of BTDA/2,4-DAT/HDA and BAC Polymers 

327°C test temperature 

50 c 

.1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 3 

Inherent viscosity 

Figure 17. Inherent viscosity -- press flow relationship 

67 

‘t 

Polysul fone 

Pol yether imide 
Table 16. Glass transition temperature and Barcol hardness of 

molded polymers 

-- 

Number Polymer Composition 

Polysul f one 

Polyetherimide 

BTDA/BAC/2,4-DAT 

St o i c h i ome t ry : 

98.5% 

99% 

100% 

BTD A/ HD A/ 2,4-DAT 

Stoi chi omet ry: 

97.5% 

98.5% 

B1 ends 

40% BTDA/BAC/2,4-DATa 

60% BTDA/HDA/2,4-DATb 

40% BTDA/BAC/2,4-DATc 

60% BTDA/HDA/2 ,4-DATb 

a0.336 IV polymer 

b0.736 IV polymer 

C0.436 IV polymer 

68 

187 

217 

243 

248 

232 

207 

211 

226 

230 

Barcol Hardness 

RT 

Test 

34 

36 

50 

46 

50 

38 

38 

46 

47 

- 

93°C 

Test 

30 

27 

42 

42 

45 

32 

32 

40 

40 

140°C 

Test 

30 

22 

42 

38 

42 

28 

28 

33 

33 
polyimides with 2,4-DAT are very similar to the values previously obtained 

with m-PDA in Table 1. The blends of the BTDA/2,4-DAT/HDA and BAC polymers 

show values intermediate between the two parent polymers and are close to the 

values obtained on the BTDA/BDA/m-PDA polymer in Table 1. 

3.3 COMPOSITE PROPERTIES AND SELECTION OF THE FINAL POLY IMIDE COMPOSITION 

Carbon fabric composites were fabricated from the BTDA/HDA/2,4-DAT, 

BTDA/BAC/2,4-DAT, and the BTDA/HDA/BAC/2,4-DAT polyimides. Flexural strengths 

and moduli and shear strengths of the composites are listed in Table 17. 

Final prepreg drying conditions, composite molding conditions, and the 

Tgs of the molded resins are provided in Table 18. The carbon fabric used in 

the composites was Celion 3000 (24 x 231, eight harness satin weave. The 

epoxy compatible size was removed with methylene chloride prior to 

impregnation. 

20-percent-solids varnishes to the carbon fabric on Teflon-coated glass to 

give a final resin volume (without cresol) of 40 percent. Cresol removal 

occurred by 20-hr treatment at 100°C in an air circulating oven. 

in the oven, the prepreg was turned over. This treatment was followed by 

0.5-hr treatment at 180°C. Final prepreg drying correlations used for the 

composites are listed in Table 18. 

Impregnation occurred by the all-at-once addition of the 

After 4 hr 

With complete cresol removal, the calculated thickness for 

60-volume-percent fiber, zero-void, and 7-ply composites is 0.25 cm (0.10 in). 

Since the resin solutions had been added to the fabric to provide this fiber 

volume, all of the composites were molded in air to 0.25-cm stops at less than 

6.9 MPa pressure and at the temperatures indicated in Table 18. 

The mechanical strengths of the composites from BTDA/2,4-DAT and HDA or 

HDA and BAC are excellent at both room temperature and 93°C. The 698+ MPa 

69 
Table 17. Carbon fabric composite properties of polyimide compositions 

Flexural Propertiesa 

Strengths 

MPa(ksi)/Modulus, GPa(msi) 

Test Tempera t u re 

("C) 

Short Beamb 

Shear Stren th, 

MPa( ksi 7 

Test Temperature 

("C) 

Composition 1 LEl::tpe 93°C 

807( 117)/59(8.6) 

-- 

400(58)/58(8.4) 

861(125)/59(8.6) 

800(116)/59(8.5) 

BTDA/HDA/2 ,4-DAT 

BTDA/HDA/E ,4-DAT 

BTDA/BAC/2 ,4-DAT 

BTDA/HDA/BAC/E ,4-DAT 

BTDA/HDA/BAC/ES4-DAT 

Ambient 

60(8.6) 

51 (7.3) 

27(3.9) 

59(8.4) 

65(9.2) 

98-113 

98-103 

98-86 

1 98-112 1 98-114 

724 ( 105)/53 (7.7) 

-- 

462 ( 67)/59 (8.5) 

765( 111)/54( 7.8) 

765(111)/56(8.1) 

aASTM D790-84as 2 specimens per test 

bASTM D2344-84, 3 specimens per test 

70 

93°C 

56( 8.0) 

49( 7.1) 

25 ( 3.5) 

50(7.2) 

57(8.2) 
1 

1 

aJ c 

'C)a Y- aJ En Ou'rv 

aJv) 

c,nc 

.I- E 0 

E 

0 

*Ic, 

*r 

v) 

0 

P 

0 

5 

".?? 

000 

wwm 

0 cug3 

mo 

om 

NN 

ECE 

EEE 

*r *r *Icc 

*r *C 

EE 

000000 

OOOmOw 

WWWbW4 NNcumcum 

0 0 0-0 m m mncu a 8 

oocu 

mcum 

cu 

OO.? 

mm 

mm 

cub 

44 

44 

II 

coco 

mm 

0 

0 

0 

a 

0 

c, 

E -3 

E3 

ov 

71 
(loo+ ksi) flexural strengths at 93°C are a significant improvement over the 

551 MPa (80 ksi) flexural strength previously obtained at 82°C on the 

BTDA/HDA/m-PDA composi te.2 This strength improvement is clearly due to a 

change in failure modes. The 698+ MPa failures occurred on the compression 

side of the specimen with fracture of individual fiber tows. 

failure also occurred on the compression side of the test specimen, however, 

fiber tows were pushed away from the specimen surface and were not fractured. 

This change in failure modes is probably due to differences in the 

mechanical properties of the polymers. Although the substitution of m-PDA 

with 2,4-DAT may play a role (restricted rotation around the C-N bond due to 

the presence of the - o-methyl group), the elevated temperature compression 

yield strengths were higher for the BTDA/HDA/m-PDA polymer when prepared from 

the Chriskev BTDA than the Gulf BTDA. 

strength is discussed in Section 3.1.4. 

The 551 MPa 

This difference in compression yield 

The increase flexural properties observed from room to elevated 

temperature testing is contrary to expectation. 

related to thermal stress relief at 93°C of residual cooldown stresses in the 

as-prepared composites. 

with elevated temperature testing is not serious and shows an improvement over 

the 22 and 42 percent strength reduction obtained in the BTDA/HDA/m-PDA resin 

sy s tem. 2 

This increase is no doubt 

The 10- to 15-percent decrease in shear strengths 

Photomicrographs of all of the composites showed that excellent flow 

had occurred during molding. 

however, the composite with the BTDA/BAC/2 ,4-DAT matrix showed numerous 

microcracks in the matrix due to the mismatched coefficients of contraction of 

the fiber and the resin. The microcracked matrix is responsible for the low 

composite strengths seen for this resin system in Table 17. 

All of the composites showed zero void contents, 

72 
A 

prior to 

though the BTDA/BAC/2,4-DAT resin system had been recommended to NASA 

composite testing for scale-up, in view of its poor composite 

properties it was subsequently recommended that the BTDA/HDA/BAC/2,4-DAT 

polyimide be scaled up. It is not clear why the BTDA/BAC/2,4-DAT polyimide 

mi crocracked when tested as a composite mat ri x, however, its higher prepreg 

drying temperatures and composite molding temperatures appear to be 

implicated. 

brittleness is increased by prepreg staging in air versus nitrogen at 

temperatures as low as 288OC (55OOF). Thus, minimum drying cyles at elevated 

temperatures appear to be indicated until further efforts elucidate the 

cause(s) of matrix microcracking. Antioxidants may be needed. 

It was also learned during the above composite efforts that resin 

3.4 SCALE-UP AND PROPERTIES OF THE SELECTED POLYMER 

Synthesis of 4 kg of the selected polymer, BTDA/HDA/BAC/2,4-DAT was 

required for neat resin property determination and transmittal of 3.6 kg as a 

20 percent solids solution to NASA. 

viscosity of 33.8 Pa*s at 25OC in cresol at 20 percent solids. 

Table 18.) 

The selected polymer had a Brookfield 

(See 

The nominal molar fractions of the monomers in the BTDA/HDA/BAC/2,4-DAT 

polymer are: BTDA at 0.5, HDA at 0.125, BAC at 0.125, and 2,4-DAT at 0.25. 

End capping is accomplished with PA and the final stoichiometry contains 

0.5 percent excess anhydrides. For example, synthesis of the 

BTDA/HDA/BAC/2,4-DAT polymer based on 1.00 mole of total amines at 99 percent 

stoichiometry used 0.99 mole BTDA (99 percent), 0.03 mole PA (1.5 percent) 

and 1.00 mole amines (100 percent). 

Scale-up was readily accomplished by a 20-fold multiplication of the 

0.3-mole synthesis which provided the composite properties given in Table 17. 

The procedure is outlined below and further details are given in Section 5. 

73 
, 

The BAC was distilled and the remainder of the ingredients were used in the 

as-received condition. 

175°C just prior to use. 

22 1 flask followed by addition of both aliphatic diamines. 

was added at room temperature to the stirring cresol solution of the amines. 

After 30 min reaction, the aromatic amine and the remainder of the cresol were 

added. The reaction was heated to 183°C with stirring and it was continued 

for 24 hr. Upon cooling to approximately 1OO"C, the solution was made up to 

20 percent solids by the addition of fresh cresol. Samples were removed for 

Brookfield viscosity determination. The 99.0 percent stoichiometric reaction 

was determined to have a viscosity of 71.5 Pa-s at 25OC. 

The BTDA was dried overnight under high vacuum at 

A portion of the cresol was added to a preweighed 

The powdered BTDA 

A second reaction at 97.8 percent stoichiometry produced a polymer 

solution with a viscosity of 15.4 Pa-s at 25°C. 

Semilog extrapolation of the two solution viscosities showed that a 

50/50-weight-percent blend of the two polymer solutions would produce a 

solution with a viscosity of 33.0 Paos at 25OC. Blending followed by stirring 

and warming to approximately 90°C produced three 12 1 containers which had 

solution viscosities of 35.1, 34.1, and 34.8 Pa-s. The majority of the 

polymer solution (4.95 kg of polymer) was shipped to NASA on August 25, 1987. 

The balance of the solution blend was diluted to 10 percent solids with 

chloroform and isolated with methanol to produce 577g of polymer. This 

polymer was molded at 343°C to produce the several moldings required for 

property determinations. 

below the Tg of the polymer). 

The moldings were annealed for 24 hr at 200°C (30°C 

Properties of the neat molded BTDA/HDA/BAC/2.4-DAT polymer are listed 

in Tables 19 and 20. The properties seen in Table 19 for the selected polymer 

are between those for the BTDA/HDA/2 ,4-DAT and BTDA/BAC/2 ,4-DAT polymers. The 

50 percent flow temperature by TMA flow test is 100°C above the Tg. This 

74 
agrees with the values in Figure 16 for this family of polymers. Barcol 

hardness is between those determined for the BTDA/HDA/2,4-DAT and 

BTDA/BAC/2,4-DAT polymers and listed in Table 16. The selected polymer, 

unlike those from nrPDA, is soluble in chloroform and methylene chloride and 

shows no resistance to paint strippers, but good resistance to hydraulic and 

deicing fluids. 

75 
Table 19. Properties of the BTDA/HDA/BAC/2,4-DAT polyimide 

a5000 psi, 14 days 

76 

1. I nherent vi scosi ty 

2. Tg 

DSC (onset) 

DSC (inflection) 

3. Barcol hardness 

RT 

93°C 

140" C 

RT (after above tests) 

4. Specific gravity 

5. TMA flow test 

50% flow temperature 

at 0.20 MPa (28 psi) 

6. Solvent resistance 

Pai nt strippers 

-- Acid 

-- Nonacid 

Deicing fluid (stressedIa 

Skydrol 500B (stressedla 

7. Wet properties (24-hr water boil) 

Dry FTUCL 

Wet FTUCL 

Weight gain 

8. Expansion coefficient 

20°C 

50°C 

90°C 

110°C 

170°C 

240°C (melt) 

Tg 

0.55 dl/g 

228" C 

233°C 

43 

36 

32 

47 

1.333 g/cc 

331°C 

80% dissolved in 16 hr 

60% dissolved in 16 hr 

Pass 

Pass 

231°C intercept 

220°C deviation from 

1 i neari ty 

220°C intercept 

161°C deviation from 

1 i neari ty 

2.5% 
Table 20. Mechanical properties of BTDA/HDA/BAC/2,4-DAT polymera 

c 

Compression Properties (ASTM D 695) 

Stress at Proportional Stress at Yield, Modulus, GPa Strain at Yield 

I 

Limit, MPa (psi) MPa (psi) (psi x 105) (%) 

RT 93 OC RT 93°C RT 93°C RT 93°C 

98.6 75.2 2 14 157 3.82 3.16 9.50 8.57 

(14300) (10900) (31000) (22700) (5.54) (4.58) 

I 

Tension Properties (ASTM D 638) 

Stress at Proportional 

Limit, MPa (psi) 

RT 93OC 

33.0 28.3 

(4790) (4100) 

c I I I 

Stress at Failure Modulus, GPa Strain at 

MPa (psi) (Psi 1 Failure (%) 

RT 93OC RT 93OC RT 93OC 

128 93.7 3.14 2.72 6.68 5.00 

(18600) ( 13600) (4.56) ( 3.95) 

77 
SECTION 4 

CONCLUSIONS AND RECOMMEND AT I ON S 

4.1 RESIN SYNTHESI 

There are differences in the BTDA from two sources pertaining to 

reaction conditions in cresol required to achieve high-molecularweight polymers. 

Cresol condensation of one source of BTDA with diamines provides a 

direct relationship between monomer concentration and IV attained 

(second order reaction). High IVs were attained, however, at lowmonomer concentrations (5 percent) on prior phases of this program 

from another source of BTDA. 

Since the synthesis was readily scaled up to 15 kg of solution 

(3 kg polymer), it is concluded that relatively large batches of 

the polymer can be prepared without difficulty 

Extensive purification of the raw materials is not required. The 

BTDA was dried just prior to use and the BAC was distilled. The 

remainder of the ingredients were used in the as-received 

condition. All are commercially available. 

4.2 RESIN PROPERTIES 

Reducing the linear aliphatic content of the program polyimide 

compositions increases the Tg as well as the Barcol hardness. 
Compression modulus and the stress at the proportional limit are 

also increased with reduced linear aliphatic contents. 

The stressed solvent resistance of the BTDA/m-PDA/BDA, HDA, and BAC 

polymers is excellent in deicing fluid and hydraulic fluids. 

paint stripper compositions used on commercial aircraft, their 

stressed sol vent resistance is unacceptable even though their 

resistance to chloroform is excellent. The action of the phenol or 

other organic acid present in paint strippers in combination with 

the halogenated solvent attacks polyimides as well as all other 

thermosets and thermoplastics tested. 

strippers is required before their use on composites will be 

acceptable. 

The stressed sol vent resistance of the BTDA/HDA/BAC/2,4-DAT polymer 

is excellent in deicing and hydraulic fluids. 

composition is soluble in chloroform, methylene chloride, and two 

paint strippers. Chloroform solubility is no doubt due to use of 

the 2,4-DAT in place of the mPDA in the composition. 

In two 

Reformulation of paint 

This polymer 

BTDA/m-PDA/BDA, HDA, and BAC polymers showed good fracture 

toughness and moisture resistance relevant to the intended 

application in composites. 

4.3 MOLECULAR WEIGHT/MELT FLOW PROPERTIES 

High-molecular-weight BTDA/m-PDA/BDA, HDA, and BAC polyimides and 

BTDA/2,4-DAT/HDA and BAC polyimides readily provide thick moldings at 

6.9 MPa and temperatures less than 100°C above their respective Tgs. 

Thin moldings (0.20 g/cm2) are not successfully prepared by the 

conditions cited above from high-molecular-weight BTDA/m-PDA/BDA, 

HDA, and BAC polyimides or the BTDA/2,4-DAT/HDA and BAC polyimides. 

80 
Low-pressure thin moldings are prepared from the cited polymers 

with reduced molecular weights (IVs of less than -0.6 dl/g). 

Molecular-weight reduction by either stoichiometric imbalance or 

end capping does not provide the expected improvement in melt flow 

properties when the aromatic amine is nrPDA. 

crystallization of intermediates upon evaporation of the solvent 

from the polymer. Isolation of the polymers from clear cresol 

solutions with methanol gives polymers which give the expected melt 

flow properties after molding at 303°C for 30 min. 

When the aromatic diamine used in the polyimides is 2,4-DAT or 

2,6-DATS intermediate crystallization does not occur and the 

expected improvements in melt flow properties are obtained upon 

solvent evaporation, 

Melt viscosities of neat polymers which have the same solution 

viscosities will be very close if not the same. Reproducible 

solution viscosities are achieved by the blending of two polymer 

solutions which, by end capping, have viscosities above and below a 

target viscosity value. This is probably only achievable with 

completely imidized polymers. The prognosis to achieve this high 

degree of me1 t vi scosi ty reproduci bi 1 i ty from PMR approaches is 

poor. This latter approach was studied in detail in Phase 111 

efforts of this program. 

This is due to 

4.4 PREPREGS 

Carbon fabric prepregs were readily prepared from 20 percent solids 

varnishes with good fiber bundle impregnation 

Smoothed prepregs were not required to prepare zero void composites 

due to the good melt flow properties of the resins 

81 
4.5 COMPOSITE PROPERTIES 

0 The 7-ply Celion carbon fabric composites prepared from the 

BTDA/HDA/Z ,4-DAT and BTDA/HDA/BAC/2,4-DAT polyimi des had excel lent 

flexural and good shear properties at room temperature and 93OC. 

(The epoxy size on the carbon fabric had been removed with 

methylene chloride). 

The 7-ply Celion carbon fabric composite prepared from the 

BTDA/BAC/2,4-DAT had poor flexural and shear properties due to 

microcracking of the resin matrix. 

prepreg drying and molding temperatures used in its preparation 

than the two polyimides mentioned above. 

and composite in air may also have played a role in the 

microcracking. 

The composites prepared on this Phase IV effort were readily 

prepared void free with rapid heating and cooling cycles at 

pressures of less than 6.9 MPa. This i s i n distinct contrast to 

Phase I11 composite efforts with polymers in which no control was 

excerci sed over the molecular wei ght of the polymers. 

0 

This may be due to the higher 

Processing the prepreg 

0 

4.6 PROGRAM OBJECTIVES 

With the limited testing conducted on the BTDA/2,4-DAT/aliphatic amine 

polyimides to date, it is concluded that this class of polymers holds 

excellent potential to meet all of the program objectives detailed in 

Section 2, with the exception of stressed resistance to chlorinated solvents 

and paint strippers. The initial composite properties, in particular, are 

most attractive. 

82 
SECTION 5 

EXPERIMENTAL 

Procedure for Study of Reaction and Stoichiometry Conditions to Produce 

Polyimides in Cresol 

Silicone oil in a large crystallizing dish was heated to 180°C on a 

hotplate equipped with magnetic stirring capability. Fifteen grams 

(0.04655 mole) of BTDA was weighed into a 250 ml erlenmeyer flask on an 

analytical balance. A preweighed Teflon-coated magnetic stirring bar and 

150 ml of cresol were added to the flask which was placed in the hot oil bath 

to dissolve the BTDA. 

and 2.7059 (0.02328 mole) HDA was quantitatively washed into the flask with 

small portions of cresol. 

temperature. 

in the 180°C oil bath. 

(0.02328 mole) m-PDA dissolved in 59 cresol was quantitatively transferred 

into the flask. 

in the hot oil bath, cooled to room temperature, and the weight of solution 

determined to be 159.29. 

contained 11.75 percent polymer. 

The flask was cooled in an ice bath to room temperature 

The reaction was allowed to stir for 45 min at room 

This was followed by a 1 hr and 15 min treatment under nitrogen 

After cooling to room temperature, 2.416g 

The reaction was stirred under nitrogen for 1 hr and 20 min 

Based on calculated polymer weight, the solution 

A small sample was removed from the reaction and diluted to 0.5 percent 

by weight polymer in cresol. 

determined at 25°C. 

by evaporating a weighed portion of the solution to dryness in an 

The relative viscosity of the sample was 

The solids content of the viscosity sample was determined 

83 
air-circulating oven for 30 min each at 150' and 225OC. The cresol weightloss from the sample was converted t o m i l l i l i t e r s for calculation of the 

inherent viscosity of the sample. It was 0.46 at 0.5 dl/g at 25OC. 

Aliquots of the reaction were taken and reacted at 180°C with diamines 

and/or cresol added to give selected adjustments to the stoichiometry or 

solids content. 

inherent viscosity determination as described above. 

indicates the reaction conditions and stoichiometries studied. 

Samples were removed from the completed polymerizations for 

Figure 3 of this report 

A second reaction was conducted along the lines described above, 

however, it was at a higher solids content and the m-PDA was not reacted prior 

to taking aliquots for further reactions. Thus, 29.33289 of BTDA 

(0.09103 mole) was dissolved in 9Og of cresol with heat. 

solution was cooled to 14°C and 5.31139 (0.04533 mole) of HDA in 5g of cresol 

was added with rapid stirring. Transfer from the weighing container was 

completed with small portions of cresol. The reaction was heated in a 180°C 

oil bath for 2 hr and 20 min. After cooling to room temperature, 4.43709 

(0.04103 moles) of m-PDA dissolved in 89 of cresol was added. 

The BTDA-cresol 

The weight of 

the solution was 127.49 which represents a solids content of 23.53 percent 

The diamine/BTDA stoichiometry was calculated to be 95.26 percent. As 

discussed above, aliquots of this reaction mixture were diluted with creso 

and/or the stoichiometry adjusted with m-PDA or MDA for further reaction. 

Figure 4 of this report shows the stoichometries and solids contents of 

reaction conditions studied. 

98.5 Percent Stoichiometric BTDA/HDA/2,4-DAT Polymer 

A 2 1 flask equipped with stirrer and nitrogen inlet was weighed and 

set up with heating mantle and stirring motor. 

(0.2500 mole) HDA and 500 ml of cresol was added. BTDA dried at 175OC in a 

To the flask, 29.05409 

84 
vacuum oven overnight was weighed into a 400-ml beaker. The 155.79 

(0.4925 mole) of BTDA and 2.96429 (0.0200 mole) PA were added to the stirring 

cresol solution of HDA at room temperature. Fresh cresol (250 ml) was used to 

transfer the anhydrides into the flask. 

(0.2500 mole) of 2,4-DAT was added. The flask and contents were placed on a 

balance and the total solution weight increased to 1009.8g. After 24-hr 

reaction under a nitrogen blanket at temperatures between 190" and 200°C, the 

To the stirring solution, 30.54259 

flask was cooled, reweighed, and the solution weight brought up again to 

1009.8g. The Brookfield viscosity of the 20 percent solids solution at 25OC 

was determined to be 30.5 Pa*s. 

99.0 Percent Stoichiometric BTDA/HDA/BAC/ZS4-DAT Polymer 

To a preweighed 22 1 flask equipped with stirrer, 248.949 (1.750 mole) 

BAC, 203.21g (1.750 mole) melted HDA and 7 1 cresol were added. To this 

rapidly stirring solution was added 2233.059 (6.930 mole) BTDA and 31.1059 

(0.210 mole) PA from two 4 1 beakers. The BTDA had been dried the previous 

night at 175OC under high vacuum. 

(3.500 mole) of 2,4-DAT was added. The flask with contents was placed on a 

scale and the solution weight increased to 14,3919. After 24 hr of reaction 

with stirring under a nitrogen blanket at temperatures between 185O and 195OC, 

the flask was cooled, weighed, and the solution weight brought up to 14,3919 a 

After 30 min of stirring, 427.609 

second time. The Brookfield solution viscosity at 25OC was determined to be 

71.0 Pa-s. 

85 
I 

1 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

M 

1 

I 

I 

I 

I 

REFERENCES 

1. Delano, C. B., and C. J. Kiskiras, "Development of an Impact- and 

Sol vent-Resistant Thermoplastic Composite Matrix, 'I NASA CR 172285, 

April 1984. 

"Development of an Impact- and 

Solvent-Resistant Thermoplastic Composite Matrix -- Phase I11 ,I' 

NASA CR 172568, June 1985. 

2. Delano, C. B., and C. J. Kiskiras, 

3. 

4. 

Delano, C. B., J. 0. Dodson, and R. J. Milligan, "Extended Flow Life 

Laminating Designs, I' AFML-TR-77-158 (1977). 

Delano, C. B., A. H. McLeod, and C. 3. Kiskiras, "Synthesis of Improved 

Phenolic and Polyester Resins," NASA CR-165180, September 1980. 

PRECEDINO PAGE BLANK NOT FILMED 

A- 
I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

APPENDIX A 

FAILURE TEMPERATURE UNDER COMPRESSION LOAD 

Acurex screens for upper use temperature by placing a cube of resin in 

the TMA and determining the temperature where the expansion curve deviates 

from linearity. With a lOOg weight on the penetration probe, curves similar 

to those indicated in Figure A-1 are obtained. Some resins after water boil 

show a change in slope with water loss above 100°C. This slope change gives a 

deviation from linearity but is not interpreted as failure temperature since 

resin softening may not occur until a much higher temperature is reached. 

Acurex calls this test "failure temperature under compression load" (FTUCL) . Inspection of the curves in Figure A-1 shows that deviation from linearity can 

preceed resin softening by several hundred degrees if the resin system has 

crystallinity. 

provides an intercept temperature which is closer to the heat distortion 

temperature described in ASTM D648. The three curves shown in Figure A-2 show 

Extrapolation of the expansion curve with the softening curve 

the behavior of the crystalline polyimides from PMDA with c6, c8, and C12 

diamines. These three polymers exhibit thermal crystallization. Figure A-3 

shows the behavior of the amorphous polyimides from BTDA with the same three 

diamines. 

reached. Increasing diamine aliphatic chain length in both series of 

polyimides reduces the upper use temperature, The high FTUCL of the polyimide 

from BTDA with isophoronediamine shows the expected result from the use of the 

cycloaliphatic compared to linear diamines. 

Penetration occurs before the glass transition temperature is 
% 

20 

E 

V 

E 

0 .- 

E 20 0, 

E 

0 

.r 

Fa i 1 ure temperature 

under compression 

load (FTUCL) 

(0 

op 

8 

f e 

rA 

pene t ra ti on 

probe Resin 

cube 

Dry 

In te rce p t 

temperature 215OC 

- i 

(0 

168OC \ % E 

Deviation from 

linearity temperature - 

Temperature (OC) 

450 psi 

24-hr waterboiled 

5 20 Intercept 

- temperature 184'C aJ 

V 

0 

VI 

E Devi ation 

1 ineari ty 

.- 

E temperature Y ~ 

Temperature (OC) 

Figure A-1. Procedure for determining upper use temperature 

90 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 
I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

0 100 200 300 400 500 

Temperature ('c) 

Figure A-2. FTUCL curves for PMDA with C6, C8, and C12 diamines 

0 100 200 300 

Temperature (OC) 

Figure A-3. FTUCL curves for BTDA with C6, C8, C12, and isophorone diamines 

91 
APPENDIX B 

TMA FLOW TEST METHOD DEVELOPMENT 

8.1 FIBEROUS POLYMERS 

Prior testing on fiberous polymers utilized a lOOg weight on the DuPont 

TMA expansion probe in combination with DSC cups to contain the po1ymer.l The 

large downward displacement of the probe demonstrated flow or a volume 

collapse of the fiberous polymer near the Tg. 

BTDA/HDA/m-PDA polymer fibers with varying inherent viscosities provided the 

result seen in Figure B-1. Clearly the probe displacement is associated with 

the Tg of the polymers; however, no information on melt properties of the 

polymers is obtained since the fibers are not molten at 200°C, the temperature 

at the end of the downward probe displacement. 

8.2 MOLDED POLYMERS 

Use of this procedure on the 

As discussed below, the test described above gives a good indication of 

the melt flow characteristics of molded polymer specimens. 

obtained on several molded polymer samples at two pressures. Approximately 

0.086 MPa (12.5 psi) pressure was obtained by placing a lOOg weight on the TMA 

expansion probe in combination with the DSC cup on the sample to protect the 

probe. 

the probe with 0.0025-cm (1 mil) thick aluminum foil on the sample to protect 

the probe. The area for the 0.90 MPa pressure was calculated from the probe 

dimensions with no correction for the increased area caused by the thin 

aluminum foil. Use of small, thin-resin specimens, which were typically 

Flow curves were 

A 0.90 MPa (130 psi) pressure was obtained by placing a 4579 weight on 
200 

0- 

-200 - 

a - -400- 

a 

0 

E 

fc -600- 

5 -800- 

E 

r( 0 

n 

e 

0 

r( 

-looo-l 

I n 

0 50 100 is0 200 250 300 350 400 4 

Tompormturo ('Cl 

0 

Note: Inherent viscosities of samples 

Sample I = 0.30 dl/g 

Sample H = 0.37 dl/g 

Sample J = 0.62 dl/g 

Sample G = 1.59 dl/g 

Figure B-1. Low-pressure flow curves of BTDA/HDA/m-PDA fi berous polymers 

I 

I 

'1 

1 

I 

I 

1 

I 

1 

I 

1 

I 

I 

1 

I 

1 

I 

I 

I 94 
0.3 mn to 0.7 mn thick, placed on stainless steel foil prevented the melting 

polymer from contaminating the bottom of the holder and the thermocouple. 

Flow curves for a number of polymer compositions are provided in 

Figures 8-2 through 8-5. Two curves are given in each figure. The top curve 

was obtained at the 0.086 MPa pressure and the bottom curve at the 0.90 MPa 

pressure. FLOW curves for polysulfone (UDEL P1700) and polyetherimide 

(Ultem P1000) are provided in Figure 8-2 for reference to two injection 

mol da bl e po 1 ymers . Figure 8-3 provides flow for the polyimides from BTDA with 

1,6-hexanediamine (HDA) or with 1,8-octanediamine (ODA). The BTDA/ODA polymer 

has a higher flow onset temperature than the BTDA/HDA polymer due to its 

crystallinity. 

17 joules/gram. It crystallized during slow cooldown from its molding 

temperature of 303°C. 

This was a program first. Its Tm is 215°C with a AH of 

Figures B-4 and B-5 provide flow curves for the first three program 

p o 1 yme r s : BTD A /BD A/m-P D A, BTD A /HD A /m- PD A, and BTD A /B AC /m-P D A. 

for all of the polymers presented in Figures B-2 through B-5 show at least two 

features in common. 

the polymer. 

applied pressure. 

the onset temperature of the low-pressure flow curves. 

weight aliphatic-aromatic polyimides, these temperatures are close to the 

polymer decomposition temperatures. 

F 1 ow cu r ve s 

A slight volume decrease is seen near the Tg (or Tm) of 

The magnitude of this volume decrease is directly related to the 

Polymer melt temperatures (PMT) are probably very close to 

With high-molecularBoth of the injection moldable resins (Udel P1700 and Ultem 1000) give 

flow curves at low pressure which are parallel to the higher pressure curves. 

This is in distinct contrast to the behavior of aliphatic-aromatic polyimides 

at the two pressures. 

but flow is induced by high pressure, 

Essentially no useful flow is observed at low pressure, 

95 
w 

m 

0 

C 

c 

0 

C 

0 

C 

a 

-. 

n 

t 

4 

n 

10 

0 

-10 

-20 

-30 

-40 

-50 

-60 

-70 

-80 

-90 

-io0 

IC 

0 

-10 

-20 

-30 

-40 

-50 

-60 

-70 

-a o 

-90 

50 100 150 200 250 300 350 400 4 

Temperature f'C) 

(a) Polysul f one 

Temperature I'Cl 

(b) Polyetherimide 

Note: Top curves are at 0.086 MPa pressure, 

bottom curves are at 0.90 MPa pressure. 

Figure B-2. Flow curves of commercial thermoplastics 

96 
I 

1 

I 

0- 

-10 - 

-20 - c 

ae - -90- 

5 -40- 

rn 

E 

5 

g -50- 

p -60- 

.4 

a 

C 

r( 

0 

-70 - 

-80 - 

-90 - 

I-#-.-I.I-r-I.g- D 50 100 is0 200 2so SO0 350 400 4 

(a) BTDA/1,6-hexanedi ami ne polymer 

-100 

Temperature ('Cl 

0 

Note: Top curves are at 0.086 MPa pressure, 

bottom curves are at 0.90 MPa pressure. 

Figure 8-3. Flow curves of BTDA with two aliphatic diamines 

97 
r 

0 

6 -50- .4 

m 

C 

-60- d 

P 

-70 - 

-BO - 

-90 - 

-100 

0- 

-10- 

-20 - 

# - -30- 

m 

0 

L: 

0 

5 -40- 

s -50- -4 

m 

C 

-60- d 

0 

-70 - 

-a0 - 

-90- 

1-1-1-1-1-*. 

1-I-I-I- 100 160 200 2!iO 300 350 400 -100 ! . I . 1 . 0 50 

Temperature I'D 

(b) BTDA/HDA/m-PDA polymer 

io 

0 

Note: Top curves are at 0.086 MPa pressure, 

bottom curves are at 0.90 MPa pressure. 

Figure B-4. Flow curves of BTDA/BDA/m-PDA and BTDA/HDA/m-PDA polymers 

98 
0- 

-lo{ 

. 

bp -20] 

-30 Y 

8 

P 

5 -40 

6 

-50 

""1 -80 

0 50 io0 150 200 250 300 550 400 4 

Tenpermture PC) 

0 

BTDA/BAC/m-PDA polymer 

Note: Top curve is at 0.086 MPa pressure, 

bottom curve is at 0.90 MPa pressure. 

Figure B-5. Flow curves of BTDA/BAC/m-PDA polymer 

contrast to the behavior of a1 iphatic-aromatic polyimides at the two 

pressures. 

is induced by high pressure. 

Essentially no useful flow is observed at low pressure, but flow 

99 
APPENDIX C 

END CAPPING OF BTDA/BAC/m-PDA POLYMER WITH PHTHALIC ANHYDRIDE 

The efforts described below were all with BTDA/BAC/m-PDA and phthalic 

anhydride (PA) at a BTDA stoichiometry of 97.5 percent. Opacity is developed 

in reactions containing less than 99.0 percent stoichiometry (BTDA = 1.000 

mole, amines = 0.990 mole or BTDA = 0.990 mole, amines = 1.000 mole, PA = 

0.020 mole) and the quantity of opacity developed is directly related to the 

stoichiometry. Reactions at 95 percent stoichiometry have more opacity than 

reactions with 96 percent stoichiometry, etc. 

C.l REACTION CONDITIONS AND OPACITY 

These investigations addressed the issue of reaction conditions and 

opacity. Specifically, do reaction conditions exist which will lead to clear 

polymers at 97.5 percent BTDA stoichiometry? Opacity is developed in the 

reaction (if it develops) with increasing reaction times at 180°C after the 

m-PDA addition and by evaporation of the solvent from clear cresol solutions 

at 180OC. 

with 100 percent BTDA or amine stoichiometries and prepreg staging. At that 

time, prereaction of the aliphatic amine with the BTDA at 180°C prior to the 

m-PDA addition and addition of a small quantity of butanol were found to 

eliminate the opacity developed in the prepregs. 

The latter phenomenon is no doubt the same effect noted last year2 

BTDA and PA were condensed with BAC for 2 hr at 180°C after addition of 

a cresol solution of the BAC in an ice-bath-cooled clear cresol solution of 

YAG< I@ ,~~~i3~~~

10 1 PIRECEDMQ PAGE BUN& NOT FILMED 
the anhydrides. 

divided into portions. 

nominal 15 percent with cresol, N-methylpyrrolidinone (NMP) and butanol. Each 

portion was condensed at 180°C and samples withdrawn with increasing reaction 

time. All of the reactions were heated for 16 hr at 180°C. 

A cresol solution of the mPDA was added to'the reaction and 

The solids content of each portion was adjusted to a 

Opacity developed in the reaction to which NMP had been added within 

30 min in the 180°C oil bath. 

control containing only cresol. 

developed in the reaction containing butanol. Removal of the cresol from the 

samples at 180°C in an air-circulating oven lead to increased opacity over 

that visible in the reaction in the NMP and control samples but very little in 

the butanol samples. Increasing reaction times reduced the opacity in all of 

the samples after cresol removal. 

Only a trace of opacity developed in the 

Slightly more than a trace of opacity 

DSC analysis was conducted on numerous samples and Figures C-1 and C-2 

show four curves for samples obtained from various treatments. 

are given below and are represented in each figure as the top to bottom 

curves, respectively . 

Top curve: 

Second curve: 

Third curve: 

1 hr in 329°C oven 

Fourth curve: 

The treatments 

2-hr reaction plus 2 hr in 180°C oven 

16-hr reaction plus 2 hr in 180°C oven 

16-hr reaction plus 2 hr in 180°C oven and 

Inspection of the DSC curves from the three reactions shows the 

reheat of DSC specimen which gave third curve 

following items: 

There is a high-temperature exotherm evident in the NMP diluted 

reaction in both of the 2- and 16-hr samples. 

persists through a 1 hr at 329°C drying condition but is 

This exotherm 

102 
0.40 

0.20-1 I 

E-0.20 

U 

c 

-0.804 

-I 

-1.00 

339.13-C 

24.42J/g 

i 

219.82OC 

-1.201---7---- . , . , 0 50 100 150 200 250 300 350 400 450 

Temperature ('C) 

(a) Samples from NMP modified cresol reaction 

0.401 

0.20] 

- p 0.00 

\ 

- si -0.204 

r. 

LL 

c, -0.40 

-0.601 

i 

-0.804 

? 

-1.00-( 

i 

-1.201 

0 . 50 

I . 100 1 * 

150 

I ' 

200 , ' 250 , , 300 8 1 350 

7- 

400 450 

Temperature ('Cl 

(b) Samples from cresol reaction 

Figure C-1. DSC curves of BTDA/BAC/m-PDA/PA polymers 

103 
-1 

-4 

-5 

-6 

333.15-C ./' 

I 227.54-C , 

I 

! 

I 

I 

I 

I 

, 

I 

I 

! 

-12&---f--r---7-------- 1 . ' ' ' ' l----I 

200 250 300 350 400 450 0 50 100 150 

Temperature ('Cl 

Samples from butanol modified cresol reaction 

Figure C-2. DSC curves of BTDA/BAC/rn-PDA/PA polymers 

104 
eliminated with 425°C treatment. There is no evidence of an 

endotherm. This reaction had a lot of opacity. 

The 2-hr cresol sample showed an exotherm whereas the 16-hr 

sample did not. Visually, this is consistent with the quantity of 

opacity in the respective samples. Treatment of the 16-hr 

samples for 1 hr at 329°C gave an endotherm at 337°C. 

The butanol diluted samples showed no exotherm or increase in 

opacity upon cresol evaporation. 

endotherm at 333°C. 

Baseline i n s t a b i l i t y a t high temperature seen in the cresol and 

butanol reactions were attributed to continued loss of volatiles 

The cresol and butanol samples have final Tgs close to 227°C 

whereas the NMP sample achieved a Tg of only 220°C 

None of the samples exhibit a distinct Tg until they are heated to 

very high temperatures 

The 329°C treated sample gave an 

Flow curves for the 329°C treated samples are provided in Figure C-3. 

A pressure of 0.90 MPa was used. The curve from the NMP reaction appears to 

initially show better flow characteristics, however, this is lost at higher 

temperatures. Both the cresol and butanol samples show a plateau above the Tg 

with a sharp knee in the melt curve at about 325°C. 

C.2 POLYMERS FROM CRESOL 

The absence of high-temperature exotherm in the butanol-cresol samples 

discussed above prompted investigation on the influence methanol isolation 

might have on the flow properties of such polymers. A 97.5 BTDA stoichiometry 

reaction with phthalic anhydride end capper was carried out for 16 hr at 180°C 

followed by 3 hr at 232°C (refluxing cresol). 

75 percent cresol, 25 percent toluene mixture was 15 percent. 

The solids content in the 

105 
-1o-f OI--\ ~ 

in 

c 

E 

c3 -701 

*C 

Figure C-3. Flow curves of cresol-evaporated samples of 

BTDA/BAC/m-PDA/PA polymer 

Evaporation of the cresol from samples withdrawn from the near-clear reaction 

gave some opacity. The majority of the polymer was isolated with methanol 

vacuum, a molding 

he 

tY 

c-4 

treatment, and after drying for 16 hr at 200°C under high 

was prepared which was visually clear. Small portions of 

molding were redissolved in cresol at 180"C, the latter w 

The DSC curves for the samples indicated below are 

(in the order shown below): 

(1) Fiberous polymer 

the powder and 

th some difficu 

given in Figure 

I 

I 

I 

I 

I 

(2) 

(3) 

Fiberous polymer molded 30 min at 303"C, 6.9 MPa 

Reaction evaporated to dryness and treated for 1 hr at 329°C 

(4) Fiberous polymer dissolved in cresol, treated the same as No. 3 

(5) Molded polymer dissolved in cresol, treated the same as No. 3 

106 
I 

! 

1 

I 

4 

1 

I 

I 

i 

j 

I 

! 

i 

! 

j 

I 

0 50 100 15C 200 253 300 350 400 450 

Temperature ("El 

Figure C-4. DSC curves of BTDA/BAC/m-PDA/PA polymers from 

the same final reaction mixture 

107 
Clearly evident in the polymers from cresol evaporation is an endotherm 

just below to 350°C which was not present in either the neat fiberous polymer 

or the molding. 

Flow curves for Samples 2, 3, 4, and 5 are provided in Figure C-5. 

Curves were obtained at 0.2 MPa (28 psi) pressure. It is clear that the 

excellent flow properties of the molded polymer (Sample 2) were compromised by 

the cresol treatment. This is probably due to crystallinity or other 

phenomena which gave rise to the endotherms seen in the DSC curves of 

polymers in Figure C-4. Flow onset in the cresol-treated polymers is 

50°C higher for all of the cresol-treated polymers than the m 

Samples of the 329°C treated molded polymer, the react 

the fibrous polymer redissolved in cresol were treated for 30 

subsequently for 10 min at 400°C in an air circulating oven. 

lded PO ymer. 

on mixture, and 

min at 350°C and 

Weight losses 

-10 -I 

these 

about 

\L i -looc----;o . I 1 , -------- i 

0 100 150 20 0 250 300 350 400 450 

Temperature (OC) 

Figure C-5. Flow curves of BTDA/BAC/m-PDA/PA polymers 

from the same final reaction mixture 

108 
I 

I 

I 

I 

I 

I 

b 

I 

I 

1 

I 

I 

I 

I 

I 

1 

1 

I 

I 

for the 1 hr at 329°C treated samples through the 10 min at 400°C treatment 

for the polymers were 3.1, 16.5, and 3.5 percent, respectively. The origin of 

the volatile species is not clear, but may include absorbed atmospheric 

moisture, residual unreacted monomers, cresol, and methanol. The onset Tgs by 

DSC after the 350°C treatment were 235"C, 229"C, and 225"C, respectively. 

After 400°C treatment, the values were 235"C, 239"C, and 225"C, respectively. 

The variation in final Tgs is not understood, particularly between the molded 

polymer and the fiberous polymer. 

Flow curves for the three polymers heated at 350" and 400°C are 

provided in Figures C-6 and C-7. 

evaporation show that the 350°C treatment temperature is inadequate to improve 

the flow properties over the beginning 329°C treated samples. 

these two materials show an increase in the endotherms with treatment at this 

temperature. 

properties and loss of the endotherm by DSC analysis. 

decomposition may have occurred with the 400°C treatment. 

of the molded specimen were modified slightly with the thermal treatments as 

noted in the top diagram of Figure C-6. 

curve of the molded polymer. 

C.3 SUMMARY OF FINDINGS 

Both of the polymers isolated by cresol 

The DSC's of 

Treatment of these two polymers at 400°C shows improved flow 

Some amount of polymer 

The flow properties 

Included in this diagram is the flow 

Relevant to program goals, the flow curves of BTDA/m-PDA/BAC polyimides 

obtained by cresol evaporation are probably unacceptable. The flow curves 

suggest that a high-temperature treatment schedule might be devised to 

eliminate the endotherm, however, the program approach required that this can 

be accomplished on the prepreg and not the neat resin. 

It is clear that the opacity developed in the early stages of the 

reaction is related to the increasing concentration of an intermediate or 

109 
I 

-204 

-IO{ O’ 4 

Y I 

nnl d~rl _. . 

treated 

35OoC 

-70 -601 :I , , 

, . I,, , 1. I .s 

450 

-100 

0 50 100 150 200 250 300 350 400 

Temperature ( C) 

(a) Molded polymer 

\L-T- 35OoC 

treated 

\ \ 

\\ 

\\ 1 -BO -f 

-90 4 

-100~ r-’.- ---1 -I-----L=4 

\ 

! 

0 50 100 150 200 250 300 35c 400 450 

Temperature (OC) 

(b) Sample from reaction mixture by cresol evaporation 

Figure C-6. Flow curve variation of BTDA/BAC/m-PDA/PA polymers 

with heat treatment 

110 

t 

I 

1 

I 

1 

I 

I 

I 

I 

I 

1 

1 

I 

1 

I 

1 

1 

I 

I 
-90 4 

-100 i0 - 

treated \ 

35OoC 

treated 

\\ 'u 

50 

, . 100 1 .--l--~-l-------l-----r--- 

150 200 250 300 350 

i; 

400 450 

Temperature (OC) 

Sample from redissolved fiberous polymer by cresol evaporation 

Figure C-7. Flow curve variation of BTDA/BAC/m-PDA/PA 

polymers with heat treatment 

111 
precursor polymer which is insoluble in the cresol. 

conduct polymerization at 20 percent solids and evaporation of clear cresol 

solutions to produce opaque samples suggest this. Reactions at 100 percent 

stoichiometry have a far less tendency to produce opaque samples upon cresol 

loss than do reactions at lower BTDA or amine stoichiometries. Reactions at 

97.5 percent BTDA stoichiometry appear to require longer reaction times than 

100 percent stoichiometric reactions to produce samples which upon cresol 

evaporation do not produce opacity at the same concentration of reactants. 

Since the reaction rate is monomer-concentration dependent, the reason 

extended reaction times are required for the phthalic anhydride end-capped 

polymers is not clear. 

Both the inability to 

Isolations of a few milligrams of cresol insoluable (opacity) material 

from the NMP-modified cresol reaction occurred by repeated overnight settling 

of the particles, decanting, and addition of fresh cresol. 

very complex infrared spectrum (carbonyl region) and no visible melting point 

to 450°C. 

and a AH of 69 joules/gram. Reheat of the sample, which showed about a 

10 percent weight loss through the first heating, gave a curve which had an 

onset Tg of 240°C and no high-temperature exotherm. 

that opacity is a precursor to the final BTDA/BAC/m-PDA composition. The lack 

of an endotherm in the DSC curve suggested that cresol insolubility may not be 

due to crystallinity. 

the polymer, is a direct result of heating cresol solutions of the polymer for 

1 hr at 329°C or higher. 

The powder had a 

DSC analysis showed an exotherm with a peak temperature of 398°C 

This experiment suggests 

The endotherm, which influences the flow properties of 

Cresol appears to be a suitable reaction medium; however, cresol alone 

appears to be an unsuitable prepregging solvent. Further, no cosolvents, such 

as butanol, were found to be useful in eliminating the high-temperature 

112 

I 

I 

‘I 

I 

I 

I 

I 

I 

I 

I 

I 

1 

I 

1 

1 

I 

I 

I 

1 
I 

I 

1 

I 

I 

1 

I 

I 

I 

1 

1 

I 

I 

I 

I 

I 

I 

I 

I 

endotherm which alters the flow properties. 

very effective in removing something from the cresol reaction mixture which 

causes high weight losses upon heating from 325°C to 400°C. 

loss may be cresol , however, after resolvation of the methanol-treated polymer 

with cresol, its weight loss is consistent with expectation -- specifically, 

the same as the starting polymer. 

Methanol treatment appears to be 

This high weight 

113 
2. Government Accession No. 1. Report No. 

NASA CR 172413 I I 

3. Recipient’s Catalog No. 

I 

4. Title and Subtitle 

Developent of an Impact- and Solvent-Resistant 

Thermoplastic Composite Matrix -- Phase IV 

6. Performing Organization Code 

5. Report Date 

September 1987 

7. Author(s1 

C. B. Delano 

9. Performing Organization Name and Address 

Acurex Corporation/Aerotlierm Divisior; 

555 Clyde Avenue, P.O. Box 7555 

f4ounta;n View, California 94035 

13. Type of Report and Period Covered 

8. Performing Organization Report NO. 

10. Work Unit No. 

534-06-23-02 

11. Contract or Grant No. 

N AS 1 - 1G 808 

12. Sponsoring Agency Name and Address 

Iiational Aeronautics and Space Administration 

Langley Research Center 

Hampton , Virginia 236654225 

I 

15. Supplementary Notes 

Con t ra c t o r Report 

14. Sponsoring Agency Code 

Langley Technical lloni tor: P. 11. Hergenrother, NASA-Langley Research Center, 

Hanipton, Vi rgini a 23665 

17. Key Words (Suggested by Author(s)) 

Aliphatic Polyimides 

Physical Properties 

Prep regs 

Composi tes 

blechani cal Properties 

16. Abstract Polyimides from BTDA with m-phenylenediamine and three aliphatic diamines 

were prepared in cresol and characTerized. Characterization tests included 

compression strength and modulus, stressed solvent resistance, and me1 t-flow tests. 

Efforts to reduce the molecular weights of these polymers by either stoichiometric 

imbalance or phthalic anhydride end capping produced opacity in the polymer 

moldings when the stoichiometry was less than 99 percent. Use of 2,4-diaminotoluen 

in place of the m-phenylenediamine allowed clear polymer moldings to be obtained 

at a1 1 stoichiom&ries by end capping or stoichiometriQmbalance. After 

nlel t-flow/molecular-weight studies, carbon fabric comp~ tes were prepared from 

three polyimide compositions containing BTDA, 2,4-diami rtoluene and two 

aliphatic diamines. 

689 MPa (100 ksi) at both room temperature and 93 C. 

1,G-hexanediamine, 1,3-bis(aminomethyl )cyclohexane and 2,4-diaminotol uene was 

selected for scale-up and neat resin characterization tests. 

polymer was 233 C. 

Flexural strengths of two ofothe resins were in excess of 

The polyimide from BTDA, 

The Tg of this 

18. Distribution Statement 

Unclassified -- Unlimited 

Subject kgory 27 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages 

Uncl assi fied Unclassified 124 

22. Price