The term high performance as applied to polymers is generally associated with polymers that operate at high temperatures. High performance is used to describe polymers that perform at temperatures of 177 C or higher. In addition to temperature, other factors obviously influence the performance of polymers such as thermal cycling, stress level, and environmental effects. Some recent developments at NASA Langley in polyimides, poly(arylene ethers), and acetylenic terminated materials are discussed. The high performance/high temperature polymers discussed are representative of the type of work underway at NASA Langley Research Center. Further improvement in these materials as well as the development of new polymers will provide technology to help meet NASA future needs in high performance/high temperature applications. In addition, because of the combination of properties offered by many of these polymers, they should find use in many other applications

Hergenrother, Paul M.

English

NASA Technical Reports Server

N91-23039
HIGH PERFORMANCE POLYMER DEVELOPMENT
Paul M. Hergenrother
Materials Division
NASA Langley Research Center
INTRODUCTION
The term high performance as applied to polymers is generally associated with polymers that operate at
high temperatures. This is somewhat misleading since there are many polymers that can be classified as high
performance materials that perform well in a hostile environment where the temperature is not high. For
example, polymeric separation membranes that are resistant to strong chemical action for long periods under
stress at ambient temperature or composite matrices on commercial airplanes that must perform over the
temperature range of -54 to 93°C for tens of thousands of hours under stress can be classified as high
performance polymers. There is no standard definition for high performance polymers because the
requirements and environments for different applications vary significantly. In this paper, high performance
will be used to describe polymers that perform at temperatures of 177°C or higher. In addition to
temperature, other factors obviously influence the performance of polymers such as thermal cycling, stress
level, and environmental effects (e.g. moisture, chemical and electrical action).
In regards to high temperature polymers, the worldwide market in 1988 was estimated at 205 million
pounds with a value of $2.3B (ref. 1). This market is expected to double by the end of this decade. New
applications for existing materials as well as the introduction of new polymers will contribute to this market
increase. High temperature polymers are currently available in many different forms such as adhesives,
coatings, composite matrices, fibers, films, foams, membranes and moldings. They are in use or are being
considered for use in the following representative applications:
o Electronic and microelectronic components (circuit boards, moldings, flexible cables, insulators,
coatings, wire wraps, etc.).
o Gaskets, sealants and tubing.
o
O
Binding systems in brake shoes, abrasive wheels and cutting discs.
Structural resins (adhesives, composite matrices, foams) for aircraft, space vehicles, and military
items.
o Jet engine components (fan blades, flaps, ducting, bushings, cowlings, races, etc.).
o Nuclear reactor components (coolants, insulation,- structural parts).
o Conveyor belts for treating and drying materials.
o Pipes for chemical processing and energy generators.
o Fire-resistant materials (protective clothing).
o Reinforcements (high modulus and high strength fibers and ribbons).
o Ablators (thermal protection systems).
o Automotive components (connecting rods, wrist pins, pistons, switches, electrical components).
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o Household items (nonstickinteriorand decorativeexteriorsurfaceson cookware, irons).
o Medical devices(prostheses,circuitryinbio-implants,dentalinstruments).
o Copier machines (gearsand picks).
This paper willdiscusssome recentdevelopments atNASA Langley inpolyimides,poly(arylcneethers)
and acctylenicterminatedmaterials.Although our work concentrateson the development of technologyfor
aeronauticalapplications,primarilystructuraladhesivesand composites,thesepolymers are potentiallyuseful
inother applications.
DISCUSSION
Polyimides constitute a major class of high temperature polymers with a market value in 1988 of $550M.
Two principal uses of polyimides are films and moldings. Recent work in our laboratory on new polyimides
has been directed towards the development of adhesives, composite matrices, films and moldings. A
polyimide designated LARC-TPI (_.Langley Research Center-_Thermoplastic _Polyimide) as depicted in
structure i was initially prepared in our laboratories in the mid 1970s (refs. 2-5). Since the early work on
LARC-TPI, several advances have been made. For example, the molecular weight of the polymer has been
controlled and the molecules end-capped to provide a form with a lower melt viscosity (better compression
and injection moldability) and better melt stability than high molecular weight unend-capped LARC-TPI.
The properties of LARC-TPI are summarized in Table 1. The excellent retention of adhesive properties at
232°C after 37,000 hours at 232°C in air as well as the preliminary laminate properties are particularly
noteworthy. LARC-TPI has been licensed and is available as a film, powder, and solution. This material
has been successfully developed into a form for injection molding.
An isomeric form of LARC-TPI designated LARC-ITPI and shown in structure 2 has been developed.
(° °,, o o ,,. ®!
0 0 tn
2
The properties of LARC-ITPI are essentially identical to LARC-TPI. The advantage of LARC-I'I_I over
LARC-TPI is the use of a less toxic diamine (m-phenylenediamine) to make the polymer and the potential
of lower cost. LARC-TPI is prepared using 3,3'-diaminobenzophenone, a diamine that exhibited a positive
Ames test (mutagenic).
A polyimide similar in chemical structure to LARC-TPI is polyimidesulfone (PISo2)The carbonyl group
from the diamine portion of the molecule has been substituted with a sulfone group by using
3,3'-diaminodiphenyl sulfone in place of 3,3'-diaminobenzophenone. The sulfone diamine is relatively
inexpensive and is non-mutagenie. The mechanical properties of PISo 2 are similar to those of LARC-TI'I.
150
Anotherpolyimide designated LARC-CPI (._Langley Research Center-Crystalline Polyimide) as depicted
in structure 3 has also received considerable attention in our laboratories. The properties are summarized in
o ,o o oo
3
Table 2. The fracture energy as determined on compact tension specimens was extremely high due to the
generation of new surface area through cracks and yielding as the crack propagated through the specimen.
Films of LARC-CPI have been tmiaxially oriented to give 25°C tensile strength and modulus as high as 448.1
MPa (65 Ksi) and 9.65 GPa (1,400 Ksi) respectively. The adhesive properties in Table 1 are impressive. To
attain high strength at 232°C, the bonds must be annealed to induce crystaninlty in LARC-CPI. Further
work has involved molecular weight control and end-capping to provide a form of LARC-CPI that has better
compression moldability and faster crystallization rates than high molecular weight LARC-CPI (ref. 13). A
controlled molecular weight LARC-CPI has provided adhesive specimens and composites which exhibited
high mechanical properties at temperature as high as 232°C.
In the area of poly(arylene ethers), work in our laboratory has concentrated primarily on the
incorporation of heterocyclic units within the polymer backbone (refs. 14-16). In general, heterocyclic units
in poly(arylene ethers) provides a higher glass transition temperature, higher tensile strength and modulus.
Poly(arylene ethers) containing the following heterocyclic units have been prepared. These polymers
o Phenyl and substituted phenyl imidazole
o Phenylquinoxaline
o Ouinoxaline
o Benzimidazole
o Benzoxazole
o 1,3,4-Oxadiazole
o 1,2,4-Triazole
exhibit a unique combination of properties that classifies them as multipurpose materials. As an example,
the properties of a new poly(arylene ether) containing phenylimidazole units as depicted in structure 4 are
presented in Table 3.
N NH
S
C6H5
4
Several poly(arylene ethers) containing heterocyclic units such as the beazoxazole, oxadiazole,
quinoxaline and triazole are semi-crystalline. CrystaUinity in a polymer generally yields higher modulus and
better solvent resistance than an amorphous polymer.
151
Anotherapproach to the development of high performance/high temperature polymers has involved the
use of the ethynyl or acetylenic group. This group has been placed on the ends of molecules, pendent along
the polymer chain and within the polymer backbone. Upon heating, it undergoes a complex reaction leading
to chain extension, branching and/or crosslinking. In some of our work on ethynyl containing materials, a
blend consisting of a low molecular weight ethynyl terminated aspartimide (brittle component) and an
ethynyl terminated arylene ether oligomer (tough component) was thermally cured to yield a resin that
exhibits attractive neat resin, adhesive and composite properties (refs. 17-18). The chemical composition of
the components in the blend are shown in structures 5 and 6. The blend exhibited good compression
moldability, allowing for the fabrication of neat resin moldings, adhesive specimens and composites at 250°C
under 1.4 MPa (200 psi). The properties of the moldings, adhesive specimens and laminates are given in
Table 4.
O O
HC = C_._N H II ...II__NH __ C _ CH
-_11---N-_CH 2_._ NI i
O O
5
.c-c-@ -o o o
6
CONCLUDING REMARKS
The high performance/high temperature polymers discussed in this paper are representative of the type
of work underway at the NASA Langley Research Center. Further improvement in these materials as well as
the development of new polymers will provide technology to help meet NASA future needs in high
performance/high temperature applications. In addition, because of the unique combination of properties
offered by many of these polymers, they should find use in many other applications.
REFERENCES
. J. M. Weatherall and A. T. Ono, paper presented at Am. Chem. Soc. Div. of Polym. Chem.
Symposium on "Recent Advances in Polyimides and Other High Performance Polymers," San Diego,
CA, Jan. 22-25, 1990.
2. V.L. Bell, B. L. Stump and H. Gager, J. Polym. Sci. Polym. Chem. Ed. 14, 2275 (1976).
3. D.J. Progar and T. L. St. Clair, Natl. SAMPE Tech. Conf. Series 7, 53 (1975).
4. D.J. Progar, V. L. Bell and T. L. St. Clair, O.S. Pat. 4,065,345 (1977) to NASA.
5. A.K. St. Clair and T. L. St. Clair, Sci. Adv. Mall. Proc. Eng. Series 26. 165 (1981).
152
..
o
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10.
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13.
14.
15.
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17.
18.
C. L. Hendricks and T. N. Hale in Welding_ Bonding and Fastening 1984 Sym. Proceedings, NASA
Conf. Publ. 2387 (1985), p. 351.
M. Ohta, S. Tamia, T. W. ToweU, N. J. Johnston and T. L. St. Clair, Sci. Adv. Matl. Proc. Eng.
Series 35, 1030 (1990).
D. J. Progar, T. L. St. Clair and J. R. Pratt in Polyimide: Materials, Chemistry and Characterization
(ed. C. Feger, M. M. Khojasteh and J. E. McGrath) Elsevier Sci. PuN. B. V., Amsterdam, 1989, p.
151.
J. R. Pratt, T. L. St. Clair and D. J. Progar, U.S. Pat. 4,937,317 (1990) to NASA.
P. M. Hergearother, N. T. Wakelyn and S. J. Havens, J. Polgm. Sci.: Pt. A: Pol'fm. Chem. 25, 1093
(1987).
P. M. Hergenrother and S. J. Havens, U.S. Pat. 4,820,791 (1987) to NASA.
P. M. Hergenrother and S. J. Havens, SAMPE J. 24 (4), 13 (1988).
P. M. Hergenrother, M. W. Beltz and S. J. Havens, Sci. Adv. Matl. Proc. Eng. Series 34, 963 (1989).
J. W. Connell and P. M. Hergeurother, Pol'fm. Prepr. 29 (1), 172 (1988).
J. W. Connell and P. M. Hergenrother, IBID 35 432 (1990).
P. M. Hergenrother, J. W. ConneH and P. Wolf, 33rd Intl. Union of Pure and Applied Chemistry
Sym. on Macromolecules, 1990, Session 1.5.2.
J. W. ConneU, P. M. Hergenrother and S. J. Havens, High Perf. Polka. J. 1 (2), 119 (1989).
P. M. Hergenrother, J. W. Cormell and S. J. Havens, U.S. Pat. 4,889,912 (1989) to NASA.
153
Table 1 - Properties of LARC-TPI
Glass transition temperature: ~ 250°C
Densily: 1.33 g/cc
Fracture energy (GIc): - 2600 Jim 2 (15 In ItYin 2)
Unoriented Thin Film ProDarties el 25°_ (dried through 1 hr @ 300°C) 1
Tensile Strength, MPa (Ksi) 13.6 (19.7)
Tensile Modulus, GPa (Ksi) 3.72 (540)
Elongation. % 4,8
Ti/Ti Adhesive Prooerties [RT -* 343°C under 1.4 MPa (200 Psi)]
Test Condition
25°C
232°C
232°C afterlO00 hr@232°C
232°C after lOOO0hr@232oc
232°C after 37000hr@232oc
Tensile Shear Strength, MPa (Psi)
42.6 (6000) 2
13.8 (2000)3
15.2 (2200) 3
24.1 (3500) 3
24.1 (3500) 3
Unidiraclional AS-4 Laminate Pmoertie,q 4, [cured lhrough 1 hour @ 350°C under
~ 2.1 MPa (300 Psi)]
Flexural St., Flexural Mod., Short Beam Shear
Test Temperature, °C MPa (Ksl) GPa (Msi) St., MPa (Ksi)
25 1821 (264) 91.0 (13.2) 124 (18.0)
149 1628 (236) 86.9 (12,6) 81 (11.7)
177 1524 (221) 82.8 (12,0) 71 (10,3)
I Ref. 2
2Rel. 3
3Ref. 6
4Ref, 7
Table 2 - Properties of LARC-CPI °
Glass transition temperature: 222°C
Crystalline melt temperature: 350°C
Melt viscosity at 395°C at angular frequency ol 0.1 rad/sec: 105 Pa.sec (106 poise)
Equilibrium moisture pickup: < 1%
Dielectric constant at 1 MHz: 3.1
Solvent Resistance: Excellent
Fracture Energy (GIc): 6650 J/m 2 (38 in Ib/in 2)
Unoriented Thin Film Tensile Prooertjes (Through 1 hr @ 300°C)
Test Condition Strength, MPa (Ksi) Modulus, GPa (Ksi) Elongation, %
25°C 151.7 (22.0) 4.34 (630) 8.3
25°C after 100 hr soak in 30% 139.9 (20.3) 4.07 (590) 5.0
aq. NaOH
177°C 104.8 (15,2) 3,72 (540) 21.1
2320C 35.8 (5.2) 1,69 (245) 76.1
232°C after 100 hr @ 316°C in air 57.9 (8.4) 2.35 (341) 9.6
Ti/Ti Adhesive Prooerties [RT --_ 400°C under 6.9 MPe (1000 Psi), hold 15 min @ 400°C]
Test Condition Tensile Shear Strength, MPa (Psi)
25°C 43.1 (6250)
25"C alter 1000 hr @ 232°C 49.1 (7120)
177°C 31.1 (4510)
232°C 4.1 (590)
232°C after 1000 hr @ 232°C 18.9 (2740)
232°C afler 100 hr @ 316°C in air 25,3 (3670)
"Ref. 12
154
Table 3 - Properties of Poly(arylene ether Imldazole) 3"
Glass transition temperature: 248°C
Fracture Energy (Gjc): 4000 J/m 2 (22.9 in Ib/in 2)
Unoriented Thin Film Prooerties
Test Temp., °C Tensile St., MPa (Ksi) Tensile Mod., GPa (Ksi)
25 9.8 (14.2) 2.8 (407)
177 5.7 (8.2) 2.1 (306)
200 4.6 (6.6) 1.9 (273)
Ti/Tip,dhesive Properties [RT --_ 300°C under 1.4 MPa (200 psi)]
Test Temperature, °C Tensile Shear Strength, MPa (Psi)
25 33.1 (4810)
93 26.2 (3800)
177 25.5 (3700)
200 21.0 (3050)
"Ref. 15
Elong., %
6.0
6.0
7.5
Table 4 - Properties of Resin from a Blend of Ethynyl Terminated Materials"
Glass transition temperature: 245°C
Fracture Energy (GIc): 675 J/m 2 (3.8 in Ib/in 2)
Tensile St.: 93.1 MPa (13.5 Ksi)
Tensile Mod.: 3,6 GPa (525 Ksi)
Elong. (break): 2,6%
Coef. Therm. Expansion: 36.8 ppm/°C
Ti/Ti Adhesive Prooerties [RT -_ 2500C under 1.4 MPa (200 psi), hold 0.5 hr]
Test Condition Tensile Shear St., MPa (Psi)
25oC 22.8 (3300)
25°C after 650 hr @ 200°C, air 17.9 (2600)
150oc 17.2 (2500)
150°C after 650 hr @ 200°C, air 20.5 (2975)
177oc 8.3 (1200)
177°C after 650 hr @ 200°C, air 18.6 (2700)
Unidirectional AS-4 Laminate Prooerties (cured 1 hr @ 250°C under 1.4 MPa)
Flexural St., MPa (Ksi) Tensile St., MPa (Ksi)
Test Temp., °C [Mod., GPa (Msi)] [Mod., GPa (Msi)]
25oc 1517 (220) [104 (15.1)] 1917 (278)[121 (17.6)]
150 1462 (212( [100 (14.5)] 1737 (252) [139 (20.2)]
177 1359 (197)[97.2 (14.1)]
*Ref. 17
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High performance polymer development

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