Reinforced polyimide structures are described. Reinforcing materials are impregnated with a suspension of polyimide prepolymer and bonded together by heat and pressure to form a cured, hard-reinforced, polyimide structure

Burns, E. A.

Jones, J. F.

Kendrick, W. P.

Lubowitz, H. R.

Thorpe, R. S.

English

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https://ntrs.nasa.gov/search.jsp?R=19740015012 2020-03-17T14:43:11+00:00Z
United States Patent
LuBowttz £l al.
us] 3,647,529
[45] Mar. 7,1972
[54] REINFORCED STRUCTURAL PLASTICS 156)
[72] Inventors: Hymaa R. Lubowttz, Redondo Beach;
William P. Kmdrfck, Manhattan Beach;
John F. Jones, Torrance; Richard S.
Thorpe, Costa Mesa; Eugene A. Boras,
Pake Verdes Estates, all of Calif.
[73] Assignee: TRW Inc ,^ Redondo Beach, Calif.
[22] Filed: July 10,1967
[21] Appl No.: 651,972
[52] VS.CL 117/161 UN, 117/126 OR, 117/132 B,
260/78 TF
[51] IntCI..
 ; C03c25/00
[58] FMd of Search ...117/126GR, 161 UN, 126 AB;
• . . - = , • 260/78 T F
References Cited
UNITED STATES PATENTS
2,421,024 5/1947 Frosch 260/78 TF
2,944.993 7/1960 Brebner 260/78 TF
3,234,181 2/1966 Olivier 260/78 TF
3,423,431 1/1969 Starr etal 260/78 TF
Primary Examiner—Alfred L. Leayitt
Assistant Examiner—Janyce A. Bell
Attorney—Daniel T. Anderson, James V. Tura and Alan D.
Akers
[57] ABSTRACT
This invention relates to reinforced polyimide structures.
Reinforcing materials are impregnated with a suspension of
polyimide prepolymer and bonded together by heat and pres-
sure to form a cured, hard-reinforced, polyimide structure.
6 CUHBS, No DFMWU|S .
00/18
Onclas
37509
rv
t
1
3,647,529
" REINFORCED STRUCTURAL PLASTICS
Thejinvention described herein was made in the per-
formance of work under a NASA contract and is subject to the
provisions of Section 305 of the National Aeronautics and
Space Act of 1958, Public Law 85-568 (72 state 435; 42
U.S.C. 2457).
Reinforced polyimide structures exhibit outstanding physi-
cal properties in the presence of high temperatures. Where
high strength is necessary at elevated temperatures, for exam-
ple as in leading edges for aircraft or nose cones for space
vehicles, reinforced polyimide structures provide excellent
construction materials. Limitations as to their use, however,
.arise from problems resulting from difficult processing
techniques.
Reinforced polyimide articles are currently produced by im-
pregnating sheets of fibrous material with a polyamide acid
produced by a condensation reaction of an anhydride and a
polyfunctional amihe. Materials impregnated with this polya-
mide acid must be hermetically sealed, refrigerated, and kept
in solution, if final cure is not effected within a short time.
When the final product has been formed, a cure of between 5
and 10 hours is necessary to produce a polyimide from the
polyamide acid. During the cure, special processing is neces-
sary to allow for the escape of appreciable volatile matter,
mainly water. Failure to allow for these volatiles will produce
an inferior structure containing interstitial bubbles and
pockets.
It has now been discovered that reinforced polyimide arti-
cles can be produced using rapid-cure polyimide prepolymers.
Preparation of the polyimide prepolymers and the polyimide
polymers produced therefrom, are discussed in more detail in
copending application Ser. No. 650,625, filed July 3, 1967,
now U.S. Pat. No. 3,528,950. It is to be understood that the
polyimides employed in this invention may be produced from
the amines and anhydrides enumerated therein.
The amines which may be utilized for purposes of this in-
vention to prepare the polyimides include the following:
para-phenylene diamine
m eta-phenylene diamine
4,4'-diamino-diphenyt propane
4,4'-diamino-diphenyl methane
benzidine
4,4'-diamino-diphenyl sulfide
4,4'-diamino-diphenyl sulfone
3,3'-diamino-dipheriyl sulfone
4,4'-diamino-diphenyl ether
1,5-diamino-naphthalene
3,3'-dimethoxybenzidine
 :
2,4-bis (beta-amino-t-butyl) toluene .
bis-(para-beta-amino-t-butyl-pheny)ether
bis-(para-beta-methyl-delta-amino-pentyl)benzene
bis-para-(l,l-dimethyl-5-amino-pentyl)benzene
l-isopropyl-2,4-metaphenylene diamine
m-xylylene diamine
hexamethylene diamine
heptamethylene diamine
octamethylene diamine
nonamethylene diamine
decameth) lene diamine
diamino-prppyl tetramethylene diamine
3-methylheptamethylene diamine
4,4-dimethylheptamethylene diamine
2,11-diamino-dodecane
1,2-bis-(3-amino-propoxy (ethane
2,2-dimethyl propylene diamine
3-methoxy-hexamethylene diamine
3,3'-dimethyl benzidine
2,5-dimethy!hexamethylene diamine
2,5-dimethylheptamethylene diamine
5-methyl-nonamethylene diamine
2,17-diamino-eicosadecane
1,4-diamino-cyclohexane .
1,10-diamino-1,10-dimethy! decane
1,12-diamino-octadecane • •
Triamines such as
1,3.5-triaminobenzene
2,4,6-triamino-s-triazine
1,2.3-triaminopropane
4,4'4"-triaminotriphenyl methane, and
5 4,4'4"-triaminotriphenylcarbinol.
Polyfunctional anhydrides employed in the production of
the polyimide prepolymer according to this* invention are
generally dianhydrides although tri- and tetraanhydrides come
within the scope of this invention. Polyfunctional anhydrides
10 which have been found to be suitable in the practice of this in-
vention are as follows:
pyrpmellitic dianhydride
benzophenone tetracarboxylic dianhydride
2,3,6,7-naphthalene tetracarboxylic dianhydride
'5 3,3',4,4'-diphenyl tetracarboxylic dianhydride
1,2,5,6-naphthalene tetracarboxylic dianhydride
2,2',3,3'-diphenyl tetracarboxylic dianhydride
2,2-bis( 3.4-dicarboxyphenyl (propane dianhydride
3,4,9,10-perylene tetracarboxylic dianhydride
bis( 3,4-dicarboxyphenyl )ether dianhydride
ethylene tetracarboxylic dianhydride
naphthalene-1,2,4,5-tetracarboxylic dianhydride
naphthalene-1,4,5,8-tetracarboxylic dianhydride
decahydronaphthalene-1.4,5,8-tetracarboxylic dianhydride
4,8-dimethyl-l,2,3,5,6,7-hexahydronaphthalene-l,2,5,6-.
tetracarboxylic dianhydride
2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dian-
hydride
2,7-dichloronaphthalene-1.4,5,8-tetracarboxylic dian-
hydride
2,3,6,7-tetrachloronaphthalene-l ,4,5,8-tetracarboxylic di-
anhydride
phenanthrene-1,8,9,10-tetracarboxylic dianhydride
,j cyclopentane-l,2,3,4-tetracarboxylic dianhydride
pyrrp|idine-2,3,4,S-tetracarboxylic dianhydride
pyrazine-2,3,5,6-tetracarbpxylic dianhydride
2,2-bis( 2,3-dicarboxyphenyl (propane dianhydride
1,1 -bis( 2,3-dicarboxyphenyl) ethane dianhydride
4Q I,I-bis< 3,4-dicarboxyphenyl) ethane dianhydride
bis( 2,3-dicarboxyphenyl (methane dianhydride
bis( 3,4-dicarboxyphenyl (methane dianhydride
bis( 3,4-dicarboxyphenyl (sulfone dianhydride
benzenerl ,2,3,4-tetracarboxylic dianhydride
45 . 1,2,3,4-butane tetracarboxylic dianhydride. and
thiophene-2,3,4,5-tetracarboxylic dianhydride.
Reinforced articles of this invention employ polymeric
bonding agents which may be reproduced from any polyimide
which has an end-capping group produced by the reaction of a
SO monoanhydride having the structure '
O
H Jl
55
20
25
30
/%/
J
where R represents hydrogen, or a lower alkyl group, e.g.,
60 methyl, ethyl, propyl, butyl, or amyl.
Preparation of the reinforced polyimide articles is effected
by impregnating reinforcing material with the polyimide
prepolymer resin. After the impregnation, items may be stored
in air for later use without special precautions. Final cure or
65 bonding simply consists of arranging the impregnated rein-
forcement into the desired shape and then applying heat and
pressure, whereupon a hard, strong reinforced article is
formed.
The process in more detail consists of forming a suspension
70 of powdered high molecular weight polyimide prepolymer
resins in a solution of a low molecular weight polyimide
prepolymer dissolved in a solvent. If desired, the soluble por-
tion and viscosity of this suspension may be varied by heating.
Details of the polyimide prepolymers may be obtained from
75 the above-mentioned copending application. When a
3,647,529
10
15
homogeneous suspension or dispersion of the polyimide
prepolymer has been obtained, the mixture is applied to the
reinforcing material. The mature is generally applied by
dipping and wiping or spraying however, other methods of ap-
plication may be equally suitable under certain conditions.
After the suspension has been applied to the reinforcement it
is dried to remove some or all of the solvent, generally at
elevated temperatures to reduce process time. Processing to
the final form comprises bonding by heat and pressure. To ac-
complish this, the impregnated reinforcements are subjected
to state-of-the-art processing procedures, such as pressed
. cure, vacuum bagging, autoclaving, hydroclaving, etc. An ex-
ample of press cure laminates consists of subjecting stacked
plies to elevated temperatures of around 450° to 600° F. and
moderately high pressures of around 1,000 p.s.i. Because the
low molecular weight polyimide prepolymer melts at a lower
temperature to provide a fusable matrix for the high molecular
weight polyimide prepolymer powder, a stepped pressure ap-
plication is necessary, To prevent excessive resin flow, a 200 ...
p.s.i. pressure is initially applied for 30 seconds or more, de-
pending on the thickness of composite. This period of heat
and moderate pressure is sufficient to advance the polyimide
prepolymer so that it can withstand the final processing condi-
tions.
The reinforcing materials may be selected from a wide
variety of materials. The limiting factors on.the reinforcing
materials which can be used are defined by the strength of the
material and its decomposition temperature. Thus materials
which provide little physical strength or decompose at tem-
peratures below the processing temperatures would not be
preferable for reinforcing materials. Materials which are
generally most suitable are carbon, such as carbon or graphite
fibers, whiskers, or crystals; silicates, such as asbestos or fiber
glass; or metals, such as metal turnings, wires, or whiskers. In 35
addition refractory materials, such as fibers, whiskers, or
crystals of borides, carbides, silicides, nitrides, or oxides are
suitable.
In addition to the rapid processing characteristics of these
polyimide reinforced structures they also exhibit outstanding 40
physical properties. The following table shows the results of
several tests using different polyimide.compositions and dif-
ferent reinforcing materials.
TABLE . .
This invention has provided a means for prcylucing rein-
forced articles which utilizes the outstanding mechanici'-^ind
thermal properties of the polyimide resins, but which may be
produced in a fraction of the time that was required previ-
ously. Processing conditions for making reinforced polyimides
have been greatly simplified by the stability of the polyimide
prepolymers described in this invention, the reduced
processing time, and the substantial reduction in the amount
of volatiles expelled.
We claim:
1. A process for preparing a reinforced article which com-
prises impregnating a reinforcing material with a polyimide
prepolymer; said prepolymer obtained by coreacting monoan-
hydride with a mixture of polyfunctional amines and dian-
hydrides; said monoanhydride having the structure
25
30
where R represents a member selected from the group consist-
ing of hydrogen and lower alkyl radicals, and curing by the ap-
plication of heat and pressure to form a reinforced article.
2. A process according to claim 1 wherein the lower alkyl
radical is selected from the group consisting of methyl, ethyl,
propyl, butyl, and amyl.
3. A process according to claim 1 wherein the reinforcing
material is selected from the group consisting of carbons, sil-
icates, carbides, silicides, borides, nitrides, oxides and metals.
4. A reinforced article comprising a reinforcing material
bonded together by a cured polyimide resin wherein said resin
is formed from an end-capped polyimide prepolymer; said
prepolymer having an end-capping group derived from a
monoanhydride having the structure
tolylmlde
high
Tempera- molecular
tore of weight
Reinforcement test, ° C. . fraction
Style 181 E glass
cloth. •
Low alkalinity
carbon cloth
CCA-1 (16«1).
25
315
25
315
10
30
76
75
30
30
• 75
•76
Fleiural
strength.
70.6
78.4
91.7
90.7
89.5
66.2
50.6
46.1
44.2
47.8
. 30.5
Flexural
modulus,
10" p.s.l.
II50
5.4
5.1
4.0
4.0 ,
4.1
4.2 „
2.2 55
3.00
1.4
wherein R represents a member selected from the group con-
sisting of hydrogen and lower alkyl radicals.
5. A reinforced article according to claim 4 wherein the
fibrous reinforcing material is selected from the group consist-
ing of carbon, silicates, borides. carbides, silicides, nitrides,
oxides, and metals.
6. A reinforced article according to claim 4 wherein the
lower alkyl radical is selected from the group consisting of
methyl, ethyl, propyl, butyl, and amyl..
• Specimens aged at 315° C. for 100 hours prior to test.
60
65
70
75


Reinforced structural plastics

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