A high-temperature stable, optically transparent, low dielectric aromatic polyimide is prepared by chemically combining equimolar quantities of an aromatic dianhydride reactant and an aromatic diamine reactant, which are selected so that one reactant contains at least one Si(CH3)2 group in its molecular structure, and the other reactant contains at least one -CF3 group in its molecular structure. The reactants are chemically combined in a solvent medium to form a solution of a high molecular weight polyamic acid, which is then converted to the corresponding polyimide

Pratt, J. Richard

St.clair, Anne K.

St.clair, Terry L.

English

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National Aeronautics and 
Space Administration 
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20546 
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NOTICE 
The invention disclosed in this document resulted from research in 
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https://ntrs.nasa.gov/search.jsp?R=19900017640 2020-03-11T17:48:49+00:00Z
AROMATIC PULYlMlOES CONTAINING A DIMETHYLSILANE-LINKED DlAMlNE 
AWARDS ABSTRACT 
MASA Case No. LAR 141 98-1 
Because of their outstanding thermal stability, low density, resistance to 
radiation, toughness and flexibility, linear aromatic polyimides are being used 
increasingly for applications in space. Polyimides are also being exploited by the 
electronics industry as film and coating materials in the production of advanced 
microelectronic circuitry. To be useful as a film or coating material for microelectronics 
applications, a polymer must be an excellent insulator and have a low dielectric 
constant. The lower the dielectric constant of the candidate polymer, the more 
efficient the circuit. The dielectric constant of commercially available, state-of-the-art 
polyimide film presently used for electronics applications ranges from about 3.2 to 4.0 
at 10 GHz depending upon moisture content. It is an object of the present invention 
to provide polyimides which possess dielectric constants in the range of about 2.5 to 
2.8 at 10 GHz, which afford a much improved circuit system. The need exists also for 
high-temperature, highly optically transparent or colorless film and coating materials 
for applications on large space components such as solar cells, space mirrors, thermal 
control coating systems, antennae and many others. Commercial polyimide film is 
known for its bright yellow color, and it is not efficient in its transmission of solar 
energy. Accordingly, another object of the present invention is to provide polyimides 
which are highly opticially transparent and therefore are significantly more efficient than 
currently used materials for these applications. 
By the present invention, the foregoing objects and advantages are attained and 
the disadvantages of the prior art are obviated by providing novel linear aromatic 
polyimide films and coatings which contain a dimethylsilane linkage in the dianhydride 
portion and at least one trifluoromethyl group in the diamine portion of the polymer 
chain. 
The novelty of the present invention resides in the provision of an aromatic 
polyimide which is high-temperature stable and optically transparent, while having low 
dielectric properties. 
L A R - 1 4 1 9 8 - 1  
S e r i a l  No. 0 7 / 4 4 9 , 2 1 0  
F i l e d  D e c e m b e r  1 2 ,  1 9 8 9  
P r i n t  F i g u r e  L$ .i 1-e - 
LAR 14198-1 -1 - PATENT APPLICATION 
AROMATIC POLYlMlDES CONTAINING A 
DIMETHYLSILANE-LINKED DlANHYDRlDE 
Oriain of the Invention 
5 
The invention described herein was jointly made in the performance 
of work under a NASA Contract and by Government employees and is 
subject to the provisions of Section 305 of the National Aeronautics and 
Space Act of 1958, as amended, Public Law 85-568 (72 Stat. 435; 42 USC 
10 2457). 
Backaround of the Invention 
1. Field of the Invention 
-
The present invention relates generally to high-temperature stable 
polyimides. It relates particularly to aromatic polyimides which contain 
dimethylsilane in the dianhydride and -CF, groups in the diamine portion of 
the polymer chain. 
20 
2. Description of the Related Art 
-
Because of their outstanding thermal stability, low density, resistance 
to radiation, toughness and flexibility, linear aromatic polyimides are being 
25 used increasingly for applications in space. Polyimides are also being 
exploited by the electronics industry as film and coating materials in the 
production of advanced microelectronic circuitry. 
To be useful as a film or coating material for microelectronics 
applications, a polymer must be an excellent insulator and have a low 
30 dielectric constant. The lower the dielectric constant of the candidate 
polymer, the rnore efficient the circuit. The dielectric constant of 
commercially available, state-of-the-art polyimide film presently used for 
Inventors: (1) Anne K. St. Clair (3) Terry L. St. Clair 
Address: 17 Roberts Landing Drive 17 Roberts Landing Drive 
Poquoson, VA 23662 Poquoson, VA 23662 
ss: 0 ss: 
Employer: NASA Langley Research Center 
(2) J. Richard Pratt 
46 Valmore Drive 
Poquoson, VA 23662 
ss: -
Employer: At time invention conceived PRC Kentron 
Initial Evaluator: Paul M. Hergenrother 
Serial No.: 0'77449,210 
Filed: December 1 2, 1989 
LAR 141 98-1 -2- PATENT APPLICATION 
electronics applications ranges from about 3.2 to 4.0 at 10 GHz depending 
upon moisture content. It is an object of the present invention to provide 
polyimides which possess dielectric constants in the range of about 2.5 to 
2.8 at 10 GHz, which afford a much improved circuit system. 
5 The need exists also for high-temperature, highly optically transparent 
or colorless film and coating materials for applications on large space 
components such as solar cells, space mirrors, thermal control coating 
systems, antennae and many others. Commercial polyimide film is known 
for its bright yellow color, and it is not efficient in its transmission of solar 
10 energy. Accordingly, another object of the present invention is to provide 
polyimides which are highly optically transparent and therefore are 
significantly more efficient than currently used materials for these applications. 
Summarv of the Invention 
By the present invention, the foregoing objects and advantages are 
attained and the disadvantages of the prior art are obviated by providing 
novel linear aromatic polyimide films and coatings which contain a 
dimethylsilane linkage in the dianhydride portion and at least one 
20 trifluoromethyl group in the diamine portion of the polymer chain. 
Brief Descri~tior~ of the Drawinq 
For a more complete understanding of the present invention, including 
25 its objects and attending advantages, reference should be made to the 
Detailed Description of the Preferred Embodiments, which is set forth below. 
This detailed description should be read together with the accompanying 
drawing, wherein the sole Figure is a reaction scheme outlining the 
preparation of polyimides according to the present invention which contain a 
30 dimethylsilane linkage in the dianhydride portion and at least one 
trifluoromethyl group in the diamine portion of the polymer chain. 
LAR 14198-1 -3- PATENT APPLICATION 
Descri~tion of the Preferred Embodiments 
Referring now to the reaction scheme set forth in the drawing, polymer 
grade dimethylsilane-containing dianhydride (SiDA) is combined with an equal 
5 molar portion of polymer grade trifluoromethyl-containing aromatic diamine in 
an amide-type solvent and the mixture is stirred until a high molecular weight 
polyamic acid is formed. The reaction is carried out at ambient temperature 
in a closed vessel. The polyamic acid solution is applied to a substrate in 
the form of a thin film or coating and thermally converted to the polyimide 
10 by heating to 250°C-300°C. 
In Table 1 some properties of the polymers of the present invention are 
compared with those of a commercial polyimide, DuPont Kapton H@film. The 
silicon and fluorine-containing films of the present invention possess 
significantly lower dielectric constants (2.5-2.8) compared to  apto on@ film. 
15 They are also significantly more optically transparent than the commercial 
film. The polymers of this invention are found to display at least 90% 
transparency at 500 nm compared to 30% for Kaptonm film measured by 
UV-visible spectroscopy on 0.50 mil thick film samples. 
TABLE I Properties of SiDA Films 
- .  ---I 
Polymer Diamine Physical Appearance 
Ar 
Dielectric Constant (1 mil thick) at lOGHz 
SiDA + 4.4'-6F Essentially Colorless 2.64 
SiDA + 3-BDAF @ O S C ( C F ~ ) ~ @ O ~ $  
SiDA + DABTF 
Pale yellow /colorless 
Pale yellowlcoloriess 
Bright yellow 
LAR 14198-1 -5- PATENT APPLICATION 
Although the aromatic dianhydride actually employed contains only one 
dimethylsilane unit, more than one dimethylsilane unit should produce similar 
results. Although the aromatic diamines actually employed contain one or 
two -CF3 groups, the use of more that two -CF3 groups should produce 
5 similar advantageous results. 
Although the polyimides of the present invention were synthesized with 
a dimethylsilano unit in the dianhydride and -CF3 groups in the diamine 
portion of the polymer, similar results should be obtained by locating the 
dimethylsilane unit in the aromatic diamine and incorporating one or more 
10 -CF, groups in the dianhydride portion of the polymer. 
SPECIFIC EXAMPLES 
Example I 
15 To a dry vessel was added 1.8146 g (0.0035 m) of polymer grade 
recrystallized 2,2-bis[4(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF) 
(mp 162°C) and 12.2 g dry dimethylacetamide (DMAc). After the diamine 
had dissolved, 1.2333 g (0.0035 m) of polymer grade recrystallized 
bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA) (mp 172°C) was 
20 added at once to the stirring diamine/DMAc solution. Stirring was continued 
for a period of eight hours until all dianhydride had dissolved and a viscous 
light yellow solution was obtained. The resulting polyamic acid had a 
solution inherent viscosity of 1.21 dl/g at 35°C. The solution was capped 
with dry nitrogen and refrigerated until used for film casting. 
25 A film of the SiDA + 4-BDAF polyamic acid was prepared by casting 
the solution (15% solids by weight) onto a soda-lime glass plate in a dust- 
free chamber at a relative humidity of ten percent. The solution was spread 
by an aluminum blade with the gap set so as to ensure a final film thickness 
of 1.0 mil or 0.5 mil. The polyamic acid film was thermally converted to the 
30 corresponding polyimide by heating in a forced air oven for one hour each 
at 100°, 200" and 300°C. The resulting polyimide film was removed from the 
glass plate after cooling to room temperature by immersion in water. The 
LAR 14198-1 -6- PATENT APPLICATION 
apparent glass transition temperature of this polymer measured by 
thermomechanical analysis was 237°C. The dielectric constant of the SiDA + 
4-BDAF film was found to be 2.56 at 10 GHz. 
5 Example II 
Using tho same method and conditions as described in Example I of 
the present invention, equimolar amounts of 2,3-bis[4(3-aminophenoxy)- 
phenyl]hexafluoropropane (3-BDAF) (mp 133°C) and SiDA were dissolved in 
DMAc to form a polyamic acid having an inherent viscosity of 0.80 dllg. The 
10 resulting polyimide film had an apparent glass transition temperature of 
196°C and a dielectric constant of 2.66 at 10 GHz. 
Example Ill 
By the same method and conditions described in Example I of the 
15 present invention, equimolar amounts of 2,2-bis(4-aminophenyI)hexafluoro- 
propane (4,4'-6F) (mp 194°C) and SiDA were dissolved in DMAc to form a 
polyamic acid having an inherent viscosity of 0.63 dllg. The resulting 
polyimide film had an apparent glass transition temperature of 300°C and a 
dielectric constant of 2.64 at 10 GHz. 
20 
Example IV 
By the same method and conditions described in Example I of the 
present invention, equimolar amounts of 3,5-diaminobenzotrifluoride (DABTF) 
(mp 183°C) and SiDA were dissolved in DMAc to form a polyamic acid 
25 having an inherent viscosity of 0.48 dllg. The resulting polyimide film had 
an apparent glass transition temperature of 267°C and a dielectric constant 
of 2.75 at 10 GHz. 
The foregoing specific Examples are merely exemplary and are not 
30 to be considered as exhaustive, but only to illustrate the invention without 
serving as limitations thereon. 
LAR 14198-1 -7- PATENT APPLICATION 
What is claimed as new and desired to be secured by Letters Patent 
of the United States is: 
LAR 14198-1 -7 PATENT APPLICATION 
AROMATIC POLYIMIDES CONTAINING A 
DIMETHYLSILANE-LINKED DlANHYDRlDE 
Abstract of the Disclosure 
A high-temperature stable, optically transparent, low dielectric aromatic 
polyimide is prepared by chemically combining equimolar quantities of an 
aromatic dianhydride reactant and an aromatic diamine reactant, which are 
selected so that one reactant contains at least one Si(CH,), group in its 
10 molecular structure, and the other reactant contains at least one -CF, group 
in its molecular structure. The reactants are chemically combined in a 
solvent mediuni to form a solution of a high molecular weight polyamic acid, 
which is then converted to the corresponding polyimide. 



Aromatic polyimides containing a dimethylsilane-linked dianhydride

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