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,ti .". 1 -. ; ,.5 / .<>#' x 

NASA CASE NO. LAR 14538-1 

PRINT FIG. 1 

NOTICE F227 

The invention disclosed in this document resulted from research in aeronautical and 

space activities performed under programs of the National Aeronautics and Space 

Administration. The invention is owned by NASA and is, therefore, available for licensing 

in accordance with the NASA Patent Licensing Regulation (14 Code of Federal 

Regulations 1245.2). 

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to grant 

licenses to commercial concerns. Although NASA encourages nonexclusive licensing to 

promote competition and achieve the widest possible utilization, NASA will provide the 

necessary incentive to the licensee to achieve early practical application of the invention. 

Address inquiries and all applications for license for this invention to NASA Patent 

Counsel, Langley Research Center, Code 143, Hampton, Virginia 236655225. 

Serial No.: 071736,880 

Filed: 07-26-91 LaRC 

[NASA-Case-LA@-f 453W A PROCESS FOR N92-11203 

PREPARING AN ASSEMBLY 0% AN WKTZCLE AND A 

PQLYIMIDE b:HI&W RESISTS UZrSCl4SIOidAL CHAf\lGE, 

DELWHPNAVIQM, AND DEk!D&BIFJG WHEN EXPOSEE TO UncP as 

CHANGES f M TEMPERATURE Patent Appl icat ion F1J27 0050981 
AWARDS ABSTRACT 

A PROCESS FOR PREPARING AN ASSEMBLY OF AN ARTICLE AND A 

POLYIMIDE WHICH RESISTS DIMENSIONAL CHANGE, DELAMINATION, AND 

DEBONDING WHEN EXPOSED TO CHANGES IN TEMPERATURE 

NASA Case No. LAR 14538-1 

Polyimides have higher coefficients of thermal expansion (CTE) than 

metals, ceramics, and glasses. By lowering the CTEs of polyimides, 

there is an increase in their usefulness for aerospace and 

electronic applications where dimensional stability is a 

requirement. The CTEs of polyimides have been lowered in the past 

by linearizing the polymer molecular structure or by controlling 

the orientation of the polyimide film. 

By the present invention, an assembly of an article and a low CTE 

polyimide is prepared. The assembly resists dimensional change, 

delamination, and debonding when exposed to changes in temperature. 

A polyamic acid solution was prepared by adding a metal ioncontaining additive to the solution. The low CTE polyimide is 

combined with the article to form the assembly. 

The novelty of this invention resides in the preparation of an 

assembly of an article and a polyimide which resists dimensional 

change, delamination, or debonding when exposed to temperature 

changes. This is accomplished by lowering the CTE of the polyimide 

so it more closely matches that of the article by incorporating a 

metal ion-containing additive into the polyamic acid solution. The 

additives which were used with the soluble polyimide could not be 

used in polyamic acid solutions because they caused the polymer to 

gel. The use of a polyamic acid solution eliminates the step of 

having to form the imide and redissolve it prior to use. 

Inventors: ' Diane M. Stoakley Anne K. St.Clair 

Address : 8 Ruth Dr. 17 Roberts Landing Dr. 

Poquoson VA 23662 

ss: 

Poquoson, VA 23662 

SS: 

Employer: NASA LaRC NASA LaRC 

Initial Evaluator: Terry L. St.Clair 

Serial No.: 071736,880 

Filed: 07-26-91 
LAR 1 4538-1 -1 - PATENT APPLICATION 

A PROCESS FOR PREPARING AN ASSEMBLY 

OF AN ARTICLE AND A POLYlMlDE WHICH RESISTS 

DIMENSIONAL CHANGE, DELAMINATION, AND DEBONDING WHEN 

EXPOSED TO CHANGES IN TEMPERATURE 

5 

Cross Reference to Related Cases: 

This application is related to co-pending patent application serial no. - 

, filed , entitled "A Process for Preparing an Assembly of an Article 

10 and a Soluble Polyimide which resists Dimensional Change, Delamination, and 

Debonding when Exposed to Changes in Temperature". 

Ori~in of the lnvention 

15 The invention described herein was made by employees of the United 

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

Government for governmental purposes without the payment of any royalties 

thereon or therefor. 

20 Backaround of the lnvention 

- 1. Field of the Invention 

This invention relates to polyimides which have a low coefficient of 

25 thermal expansion (CTE). More particularly, it relates to the preparation of an 

assembly of an article and a polyimide which resists dimensional change, 

delamination and debonding when exposed to changes in temperature. 
LAR 14538-1 -2- PATENT APPLICATION 

- 2. Descriotion of the Related Art 

Polyimides have become widely used as high performance polymers as 

a result of their excellent thermal stability and toughness. However, polymers 

5 in general, including polyimides, have higher CTEs than metals, ceramics, and 

glasses. Lowering the CTE of polyimides would increase their usefulness for 

aerospace and electronic applications where dimensional stability is a 

requirement. 

The CTEs of polyimides have been lowered in the past by linearizing the 

10 polymer molecular structure or by controlling the orientation of the polyimide 

film. Numata et al. (Polymer Enrrineerina and Science, 28, (4), 906 (1988)) 

lowered the CTE by synthesizing a linear polyimide. By employing polyimides 

prepared from pyromellitic dianhydride (PMDA) or 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and aromatic diamines that contain only 

15 benzene or pyridine rings in para-positions without flexible linkages, they have 

synthesized polyimides with CTEs from 20-0.4 ppmI0C. Numata and Miwa 

(Polvmer, 30, (60), 1 170 (1 989)) found that the CTEs of uniaxially stretched 

polyimide films with rigid and flexible molecular chains were lower than their 

non-oriented counterparts. 

20 By the present invention, an assembly of an article and a polyimide with 

a low CTE is prepared. The assembly resists dimensional change, 

delamination, and debonding when exposed to changes in temperature. The 

CTEs have been reduced by incorporating a metal ion-containing additive into 

a polyamic acid solution. St. Clair et al. (U.S. 4,284,461), Taylor et al. (U.S. 

25 4,311,615) and Stoakley and St. Clair ("Lanthanide-Containing Polyimides" 

Recent Advances in Polvimide Science and Technoloav, W.D. Weber and M.R. 

Gupta, Eds., Society of Plastics Engineers, New York, 1987, pp 471 -479) used 

these additives to alter the adhesive, electrical, and magnetic properties of 

polyimides. 

30 Accordingly, it is the object of the present invention to prepare an 
LAR 14538-1 -3- PATENT APPLICATION 

assembly of an article and a polyimide which resists dimensional change, 

delamination, and debonding when exposed to temperature changes by forming 

a low CTE polyamic acid solution which is imidized. 

Another object of the invention is to reduce the CTE of the polyimide by 

5 incorporating a metal ion-containing additive into the polyamic acid solution so 

it more closely matches the CTE of the article. 

Other objects and advantages of the invention will become apparent to 

those skilled in the art upon consideration of the accompanying disclosure. 

10 

Summary of the Invention 

An assembly of an article and a low CTE polyimide film or coating is 

prepared. The assembly resists dimensional change, delamination or 

15 debonding when exposed to changes in temperature. An article is provided. 

A polyamic acid solution was prepared by reacting equimolar quantities of an 

aromatic diamine and an aromatic dianhydride in a solvent medium. A metal 

ion-containing additive was added to the solution. Examples of this additive 

are: TbCI,, DyCI,, ErCI,, TmCI,, AI(C,H,O,),, and Er,S,. The polyamic acid 

20 solution was imidized to yield a low CTE metal ion-containing polyimide film, 

which is then combined with the article to form the assembly. 

The article selected for the assembly is: a solar concentrator, antennae, 

solar cell arrays, second surface mirrors, precision solar reflectors, electronic 

circuit boards, or any other item known to those skilled in the art. A precision 

25 solar reflector is the preferred article for this application. 

A polyamic acid solution was prepared at a concentration of 10-15 
LAR 1 4538- 1 -4- PATENT APPLICATION 

weight percent. An equimolar quantity of an aromatic diamine was reacted with 

an aromatic dianhydride in a solvent medium. A metal ion-containing additive 

was added to the solution at a concentration of 4-30 weight percent. Erbium 

chloride gave the most effective results for this application. 

5 A thin-film assembly for a solar reflector is prepared. The metal ioncontaining polyamic acid solution is poured onto a glass, metal, or other surface 

having the shape of the reflector. The resin is spun-cast to a thickness of 0.5 

to 5.0 mils and heated to produce a low CTE polyimide film. The film is 

removed from the surface and combined with a reflecting article and protective 

10 topcoat to form the assembly. 

An article is either coated with or embedded into the metal ion-containing 

polyamic acid solution or bonded to the low CTE polyimide substrate. The 

article is also attached to the polyimide substrate by surface-treatment to form 

the assembly. In cases where the article is coated with or embedded into the 

15 polyamic acid solution, thermal imidization is used to form the polyimide. 

Thermal irnidization was performed by heating the solution to about 100°C - 

300°C. 

A polyimide substrate is formed either thermally or chemically prior to the 

attachment of an article. Chemical imidization is performed by reacting the 

20 polyamic acid solution with acetic anhydride and pyridine, recovering the 

precipitate, and heating under pressure to fuse the imide powder. The article 

is bonded to the polyimide substrate with a polyimide-based adhesive or by 

surface treatment. 
LAR 1 4538-1 -5- PATENT APPLICATION 

Brief Descri~tion of the Drawinas 

Figure 1 is a schematic showing a preferred embodiment of the present 

invention where the low CTE polyimide is used as a substrate. 

Figure 2 is a schematic showing an article which is coated with a low 

5 CTE polyimide to form an assembly. 

Figure 3 is a schematic showing the formation of an assembly by 

embedding an article into the low CTE polyimide. 

Figure 4 is a schematic showing an article attached to a low CTE 

polyimide substrate with an adhesive. 

10 

Description of the Preferred Embodiments 

15 A solution of a metal ion-containing polyamic acid resin, which yielded 

a polyimide having a low coefficient of thermal expansion (CTE), was prepared 

at 10-1 5% solids. An equimolar quantity of 3,3',4,4'-benzophenone 

tetracarboxylic dianhydride (BTDA) or 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) was added to a stirred solution 

20 of 4,4-oxydianiline (4,4'-ODA) or 1,3-bis(aminophenoxy)benzene (APB) in a 

polar organic solvent such as N,N-dimethylacetamide (DMAc). The resulting 

polyamic acid solution was stirred at room temperature for approximately 242 

hours. A metal ion-containing additive was added at a concentration range of 
LAR 14538-1 -6- PATENT APPLICATION 

approximately 4-30 weight percent either before the addition of the monomers, 

immediately following the addition of the dianhydride or after the polyamic acid 

polymerization was completed. 

The metal ion-containing polyamic acid solution was cast as a film on 

5 soda-lime glass plates using a doctor blade set to obtain a cured film thickness 

of approximately 0.025 mm (1 mil). The film was placed in a low humidity box 

overnight and then imidized by heating in a forced air oven for 1 hour each at 

1 00°, 200°, and 300°C. The film was removed from the glass plate by soaking 

in water. 

10 Although the dianhydrides, BTDA and GFDA, and the diamines, 4,4'-ODA 

and APB, were used in the polyamic acid polymerization, other dianhydrides 

and diamines employed in the preparation of polyamic acids or polyimides may 

be used in the present invention. 

The solvent medium for the polyamic acid was DMAc. However, other 

15 solvents known to those skilled in the art such as: N,N-dimethylformamide, 1- 

methyl-2-pyrrolidinone, and dimethyl sulfoxide may be used in the preparation 

of polyamic acids. 

The metal ion-containing additives of this invention included the chlorides 

of the following lanthanides: terbium (TbCI,), dysprosium (DyCI,), erbium 

20 (ErCI,), holmium (HoCI,), and thulium (TmCI,). An additional lanthanidecontaining additive used was erbium sulfide (Er,S,). One other metal ioncontaining additive used was aluminum acetylacetonate (AI(C,H,O,),). Each 

additive reduced the CTE and it was found that ErCI, gave the best results. 
LAR 1 4538-1 PATENT APPLICATION 

The data is shown in Tables I and II. 

Table I. Coefficients of Thermal Expansion 

of Metal Ion-Containing BTDA/4,4'-ODA Films 

Additive % Additive Tg by TMA, "C CTE ppmPC 

BTDA/4,4'-ODA 

Control 0.0 281 39.1 

TbCI, 11.3 297 27.4 

10 DyCI3 11.4 292 26.3 

ErCI, 11.6 302 17.0 

TmCI, 11.6 31 4 19.5 

Er2S, 17.1 303 24.5 

Al(C5H702)3 11 .1 295 27.8 

15 
LAR 1 4538-1 PATENT APPLICATION 

Table II. Coefficients of Thermal Expansion 

of Metal Ion-Containing GFDNAPB Films 

It was also found that increasing the concentration of the metal ioncontaining additive resulted in a decrease in the CTE. Table Ill gives these 

results. 
LAR 1 4538- 1 -9- PATENT APPLICATION 

Table Ill. Effect of TbCI, Concentration on 

Coefficient of Thermal Expansion 

15 There were many additional metal ion-containing additives that were 

found not to be useful for this application. These additives were: holmium 

acetate, erbium N-phenylphthalamate, erbium acetylacetonate, tin chloride, 

terbium fluoride, dysprosium fluoride, lutetium fluoride, silver nitrate, gadolinium 

acetate, holmium sulfide, erbium acetate, cerium acetylacetonate, neodymium 

20 acetylacetonate, samarium acetylacetonate, terbium acetylacetonate, 

praseodymium nitrate, neodymium nitrate, samarium nitrate, holmium nitrate, 

Coefficient of 

Thermal Expansion 

ppmPC 

39.1 

Additive 

mole Tbt3: 

mole polymer 

BTDA/4,4'-ODA 

Control 

% Additive 

0.0 

1:lO 

1 :4 

1 :2 

4.5 

11.3 

22.6 

33.3 

27.4 

21 .O 
LAR 1 4538-1 -1 0- PATENT APPLICATION 

erbium nitrate, thulium nitrate, ytterbium nitrate, europium chloride, gadolinium 

sulfide, terbium sulfide, dysprosium sulfide, terbium iodide, thuluim iodide, and 

dysprosium bromide. Some of these additives caused the polyamic acid 

solution to gel while others, although they made good films, were not effective 

5 in lowering the CTE. It is for this reason that the additives listed in Tables I and 

II gave unexpected results. 

A low CTE polyimide substrate is prepared by pouring the metal ioncontaining polyamic acid solution into a mold, drying then imidizing by heating 

for one hour each at 100°, 200°, and 300°C. Another method of forming the 

10 substrate is to slowly add the metal ion-containing polyamic acid solution to a 

stirred mixture of acetic anhydride and pyridine. The imide precipitate is 

recovered, washed with water, and dried. The imide powder is poured into a 

mold and fused by heating under pressure to form the polyimide substrate. 

An article is provided to form an assembly with the polyimide. Examples 

15 of this article are: a solar concentrator, antennae, solar cell arrays, second 

surface mirrors, precision solar reflectors, or electronic circuit boards. Other 

articles known to those skilled in the art can also be used. A metal ioncontaining polyamic acid solution was prepared. The solution is used to coat 

the article, to embed the article, or to form a substrate to which the article is 

20 bonded. For example, a circuit board is coated by either spraying, dipping, or 

brushing with the polyamic acid solution. The solution is imidized by heating 

for 1 hour each at 1 00°, 200°, and 300°C in a forced air oven. The coated 

article is resistant to delamination when exposed to temperature changes. 
LAR 14538-1 -1 I- PATENT APPLICATION 

In another example, the polyarnic acid solution is cast into a mold. The 

circuit board is embedded into the solution prior to imidizing. After imidizing, 

the resulting assembly is resistant to debonding. 

As another example, an article is attached to a polyimide substrate 

5 formed from the polyamic acid solution. The solution is imidized by heating and 

the article is attached to the substrate with a polyimide-based adhesive. The 

resulting assembly is resistant to dimensional change, debonding, and 

delamination when exposed to changes in temperature. 

In yet another example, an assembly for a solar reflector is prepared. 

10 The metal ion-containing polyamic acid solution is poured onto a glass, metal, 

or other surface having the shape of the reflector. The resin is spun-cast to a 

thickness of 0.5 to 5.0 mils and heated to produce a low CTE polyimide film. 

The film is removed from the surface and combined with a reflecting article and 

protective topcoat to form the assembly. 

15 

EXAMPLES 

20 Preparation of the 15% solids polyarnic acid solution of BTDA/4,4'-ODA 

was conducted at room temperature by dissolving 60.079 (0.30 mole) of 4,4'- 

ODA in 948 ml DMAc. After the diamine was dissolved, 96.679 (0.30 mole) 

BTDA were added and stirred. After three hours, the polyamic acid solution 
LAR 1 4538-1 -1 2- PATENT APPLICATION 

was clear yellow with an inherent viscosity of 1.49 dllg when measured at 0.5% 

solids in DMAc at 35OC. A film of this control resin was cast on a glass plate 

at a 15 mil blade gap and left in a low humidity film box overnight. This tack 

free film was then cured by heating in a forced air oven for one hour each at 

5 100°, 200°, and 300°C. The resulting film had a glass transition temperature 

of 281°C. The CTE of this yellow control film was determined to be 39.1 

ppmI0C over the temperature range of 70-1 10°C. 

To 10.459 of the 15% solids BTDA/4,4'-ODA stock resin was added 

0.1 99g (0.00075 moles) TbCI, in 2ml DMAc. This mixture was stirred at room 

10 temperature for several hours, resulting in a milky white resin. A film of this 1 :4 

TbCI,:BTDA/4,4'-ODA resin was cast on a glass plate using a 15 mil blade gap. 

It was placed in a low humidity film box overnight and cured like the control 

film. The resulting hazy yellow film had a Tg of 297OC and a CTE of 27.4 

ppmJ0C. 

15 Example 2 

The process of Example 1 was repeated using 0.2029 (0.00075 moles) 

DyCI,. The resulting 1 :4 DyCI,:BTDA/4,4'-ODA film was a hazy amber film with 

a Tg of 292OC and a CTE of 26.3 ppmPC. 

20 

Example 3 

The process of Example 1 was repeated using 0.2059 (0.00075 moles) 
LAR 1 4538-1 -1 3- PATENT APPLICATION 

ErCI,. The resulting 1 :4 ErC13:BTDA/4,4'-ODA film was a hazy amber film with 

a Tg of 302°C and CTE of 17.0 ppmPC. 

5 

The process of Example 1 was repeated using 0.2069 (0.00075 moles) 

TmCI,. The resulting 1 :4 TmCI,:BTDA/4,4'-ODA film was a hazy yellow film 

with a Tg of 31 4°C and CTE of 19.5 ppmI0C. 

The process of Example 1 was repeated using 0.0809 (0.0003 moles) 

TbCI,. The resulting 1 :I 0 TbC13:BTDA/4,4'-ODA film was a slightly hazy yellow 

film with a CTE of 33.3 ppmI0C. 

15 

Example 6 

The process of Example I was repeated using 0.3989 (0.0015 moles) 

TbCI,. The resulting 1 :2 TbC13:BTDA/4,4'-ODA film was a hazy amber film with 

20 a CTE of 21.0 ppmI0C. 
LAR 1 4538- 1 PATENT APPLICATION 

The process of Example 1 was repeated using 0.1959 (0.0006 moles) 

AI(C,H,O,),. The resulting 1 :5 AI(C,H,O,),:BTDA/4,4'-ODA film was a 

5 transparent amber film with a coefficient of thermal expansion of 27.8 ppmI0C. 

To 37.98309 of DMAc, 0.501 0g (0.001 82 moles) TmCI, were added. 

10 The mixture was stirred at room temperature for approximately 112 hour, then 

2.66039 (0.0091 moles) APB were added. Stirring was continued until the 

diamine was dissolved. After dissolution of the diamine, 4.0830g (0.0091 91 

moles) 6FDA were added and stirring was continued for approximately 19 

hours. 

15 A film of this resin was cast at 18 mils thickness on a glass plate and 

placed in a low humidity film box overnight. The resin was cured by heating in 

a forced air oven for one hour each at 1 00°, 200°, and 300°C. The resulting 

peach colored 1:5 TbCI,:GFDA/APB film had a CTE of 35.7 ppmI0C as 

compared to 51.0 ppmI0C for the colorless control 6FDAJAPB film. 

20 

Exam~le 9

An article 15 (of Figure 3) is attached to a low CTE polyimide substrate 
LAR 1 4538- 1 -1 5- PATENT APPLICATION 

prepared from the metal ion-containing polyamic acid solution as in Example 

1. The solution is poured into a mold and the article is embedded in the 

solution 16 (of Figure 3). The assembly is imidized by heating for 1 hour each 

at 100°C, 200°C, and 300°C in a forced air oven. The article is resistant to 

5 debonding when exposed to changes in temperature. 

Example 10 

An article 15 (of Figure 4) is attached to a low CTE polyimide substrate 

10 10 (of Figure 4) prepared from the metal ion-containing polyamic acid solution 

as in Example 1. The solution is poured into a mold and is imidized by heating 

for 1 hour each at 100°C, 200°C, and 300°C in a forced air oven. The article 

is attached to the substrate by bonding it with an adhesive 17 (of Figure 4). 

The article is resistant to debonding when exposed to changes in temperature. 

15 

Example 11 

A circuit board 13 (of Figure 2) is coated with a metal ion-containing 

polyamic acid solution 14 (of Figure 2) as in Example 1. The coating is applied 

20 to the circuit board by spraying, brushing, dipping, or any other method known 

to those skilled in the art. The coating is imidized by heating for 1 hour each 

at 100°C, 200°C, and 300°C in a forced air oven. The coated article 14 (of 

Figure 2) is resistant to delamination when exposed to changes in temperature. 
LAR 14538-1 -1 6- 

Example 12 

PATENT APPLICATION 

A thin-film assembly for a solar reflector (Figure 1) is prepared. A metal 

ion-containing polyamic acid solution as in Example 1 was prepared. The 

5 solution is poured onto a glass, metal, or other surface which has the shape of 

the reflector. The solution is spun-cast to a thickness of 0.5 to 5.0 mils and 

heated to 100° to 300°C in a forced air oven. The resulting substrate 10 (of 

Figure 1) is removed from the surface and is metallized with a highly reflecting 

metal layer 11 (of Figure 1) such as silver, aluminum, or chromium. The metal 

10 layer is applied at a thickness between 10 and 2000 A using a surface 

treatment such as vapor deposition or sputtering. A clear protective topcoat 12 

(of Figure 1) is applied at 0.1 to 1.0 mil thickness to prevent tarnishing. The 

layers of the assembly are resistant to dimensional change, debonding, or 

delamination upon exposure to changes in temperature. 

15 

The above examples are considered to be illustrative of the invention 

and there may be modifications and variations in the metal ion-containing 

additive, the polyimide, or the article that will be apparent to those skilled in the 

art without departing from the spirit and scope of the invention as set forth 

20 herein. It is therefore to be understood that the invention may be practiced 

ot hewise than as specifically described and claimed herein. 

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

of the United States is: 
LAR 1 4538-1 --&- PATENT APPLICATION 

A PROCESS FOR PREPARING AN ASSEMBLY 

OF AN ARTICLE AND A POLYlMlDE WHICH RESISTS 

DIMENSIONAL CHANGE, DELAMINATION, AND DEBONDING WHEN 

EXPOSED TO CHANGES IN TEMPERATURE 

Abstract of the Disclosure 

An assembly of an article and a polyimide composition is prepared. The 

assembly resists dimensional change, delamination, or debonding when 

10 exposed to changes in temperature. An article is provided. A polyamic acid 

solution which yields a polyimide having a low coefficient of thermal expansion 

(CTE) was prepared. Equimolar quantities of an aromatic diamine and an 

aromatic dianhydride were reacted in a solvent medium to form a polyamic acid 

solution. A metal ion-containing additive was added to the solution. Examples 

15 of this additive are: TbCI,, DyCI,, ErCI,, TmCI,, AI(C,H,O,),, and Er,S,. The 

polyamic acid solution was imidized and is combined with the article to form the 

assembly. 
FIGURE I 

FIGURE 2 

FIGURE 3 

FIGURE 4