Polyimide foams and their preparation

Described are flexible polyimide foams having enhanced compression fatigue life and softness for use in the manufacture of seat cushions and methods for the production of such foams and precursors therefor. These foams are produced from novel polyimides prepared by reaction of an organic tetracarboxylic acid or derivative thereof, preferably an ester with (a) about 1 to about 50 mol percent of a diester of (i) a primary amino-substituted aromatic carboxylic acid, and (ii) a polymethylene glycol, and (b) at least one aromatic or heterocyclic primary diamine. Foams can be produced having (a) a fatigue life as determined by ASTM test procedure D 3574-81 using foam specimens from three to five inches in thickness of at least 15,000 cycles, or (b) an indentation force deflection as determined by ASTM test procedure D3574-81 on foam specimens of one-inch thickness of less than 40 pounds of force at 25% deflection and less than 180 pounds of force at 65% deflection, or both of (a) and (b).

TECHNICAL FIELD 
This invention relates to new and useful polyimides, and more particularly 
to novel polyimides and polyimide foams having improved properties, to 
novel precursors from which such polyimides and polyimide foams can be 
prepared, and to processes for their preparation. 
BACKGROUND 
A great deal of effort has been devoted to the development of polyimides 
and polyimide foams having useful properties. One promising area of 
application for flexible polyimide foams is as a potential substitute for 
flammable polyurethane foams in aircraft seat cushions and the like, where 
the fire resistance and lightness of polyimides would be of considerable 
advantage. 
Unfortunately, previously known flexible polyimide foams generally suffer 
from either or both of two shortcomings limiting their usefulness for seat 
cushion applications: 
1. Lack of sufficient compression fatigue life, which means that the foam 
prematurely loses its resiliency (ability to return to its original shape) 
after repeated compression during usage. 
2. Lack of sufficient softness which causes the cushion to be stiffer and 
less comfortable than desired. 
THE INVENTION 
This invention provides new and useful flexible polyimides which can 
overcome either or both of the foregoing shortcomings. 
Pursuant to one embodiment there is provided a polyimide foam prepared by 
reaction of an organic tetracarboxylic acid or derivative thereof (e.g., 
salt, acid halide, anhydride or preferably ester thereof) with (a) about 1 
to about 50 mol percent of a diester of (i) a primary amino-substituted 
aromatic carboxylic acid and (ii) a polymethylene glycol, and (b) at least 
one aromatic or heterocyclic primary diamine. These polyimides per se 
constitute an additional embodiment of this invention. 
Another embodiment of this invention involves provision of a foamable 
polyimide precursor comprising an essentially stoichiometric mixture of 
(a) at least one organic tetracarboxylic acid ester, and (b) a mixture of 
at least two primary diamines, one such diamine being about 1 to about 50 
mol percent of a diester of (i) an amino-substituted aromatic carboxylic 
acid and (ii) a polymethylene glycol, and a second such diamine being an 
aromatic or heterocyclic diamine. 
A still further embodiment of this invention involves a method of preparing 
a polyimide foam which comprises reacting an essentially stoichiometric 
mixture of (a) at least one organic tetracarboxylic acid (or derivative 
thereof, preferably an ester), and (b) at least two primary diamines, one 
such diamine being about 1 to about 50 mol percent of a diester of (i) an 
aminosubstituted aromatic carboxylic acid and (ii) a polymethylene glycol, 
and a second such diamine being an aromatic or heterocyclic diamine; and 
heating the reaction mixture to cure it into polyimide foam. When using 
the free tetracarboxylic acid or a salt, acid halide or anhydride thereof, 
a suitable blowing agent should be present in the reaction mixture to 
cause the foam structure to be developed. Use of the ester is preferred as 
this results in the development of the foam structure even without use of 
a blowing agent. 
Yet another embodiment of this invention is a polyimide foam having (a) a 
fatigue life as determined by ASTM test procedure D 3574-81 using foam 
specimens from three to five inches in thickness of at least 15,000 
cycles, or (b) an indentation force deflection as determined by ASTM test 
procedure D3574-81 on foam specimens of one-inch thickness of less than 40 
pounds of force at 25% deflection and less than 180 pounds of force at 65% 
deflection, or both of (a) and (b). For the purposes of this invention, 
failure in the foregoing fatigue life test procedure is either (i) a 
thickness loss of more than 10%, (ii) a loss in indentation force 
deflection at 40% deflection of more than 10%, or (iii) a significant 
visually-perceivable surface cracking. 
The above and other embodiments, features and advantages of this invention 
will become still further apparent from the ensuing description and 
appended claims. 
In the practice of this invention the flexible polyimides are formed by use 
of a combination of primary diamines, one of which is a diester of an 
amino-substituted aromatic carboxylic acid and a polymethylene glycol, and 
a second of which is a different aromatic diamine or a heterocyclic 
diamine. Such diesters may be represented by the general formula: 
EQU H.sub.2 N--ArCOO--R--OOCAr--NH.sub.2 
wherein R is an alkylene group (which may be branched or straight chain) 
and which preferably contains from 3 to 8 carbon atoms, most preferably 
trimethylene; and Ar is an aromatic group which may be composed of one or 
more fused or non-fused benzene rings which in turn may carry suitable 
substituents (e.g., nitro, alkoxy, etc.) in addition to the primary amino 
groups. 
A few exemplary diesters of this type include: 
ethylene glycol-4-aminobenzoic acid diester; 
ethylene glycol-3-aminobenzoic acid diester; 
ethylene glycol-2-aminobenzoic acid diester; 
trimethylene glycol-3-aminobenzoic acid diester; 
trimethylene glycol-2-aminobenzoic acid diester; 
trimethylene glycol-3-amino-2-nitrobenzoic acid diester; 
tetramethylene glycol-3-amino-4-nitrobenzoic acid diester; 
tetramethylene glycol-3-amino-5-nitrobenzoic acid diester; 
tetramethylene glycol-4-amino-2-nitrobenzoic acid diester; 
1,5-pentanediol-4-amino-3-nitrobenzoic acid diester; 
1,6-hexanediol-5-amino-2-nitrobenzoic acid diester; 
neopentyl glycol-4-amino-2-methylbenzoic acid diester; 
1,8-octanediol-4-amino-2-propylbenzoic acid diester; 
1,9-nonanediol-3-amino-4-methylbenzoic acid diester; 
1,10-decanediol-4-(4-aminophenyl)benzoic acid diester; 
and the like. Mixtures of such diesters may be employed. 
A particularly preferred diester of this type is the diester of 
trimethylene glycol (1,3-propanediol) and 4-aminobenzoic acid. 
The other organic diamines with which the foregoing diamino-substituted 
diesters are employed may be represented by the formula: 
EQU H.sub.2 N--R'--NH.sub.2 
wherein R' is an aromatic group containing 5 to 16 carbon atoms and 
containing up to one hetero atom in the ring, the hetero atom being 
nitrogen, oxygen or sulfur. Also included are aromatic groups such as: 
##STR1## 
Representatives of such diamines include: 2,6-diaminopyridine; 
3,5-diaminopyridine; 
3,3'-diaminodiphenylsulfone; 
4,4'-diaminodiphenylsulfone; 
4,4'-diaminodiphenylsulfide; 
3,3'-diaminodiphenylether; 
4,4'-diaminodiphenylether; 
meta-phenylenediamine; 
para-phenylenediamine; 
4,4'-methylene dianiline; 
2,6-diamino toluene; 
2,4-diamino toluene; 
and the like. 
It is also possible and sometimes desirable in the preparation of the 
polyimide precursors of this invention, to include in the reaction mixture 
one or more aliphatic diamines. Such aliphatic diamines are preferably 
alpha-omega diaminoalkanes having the formula: 
EQU H.sub.2 N--(C.sub.2).sub.n --NH.sub.2 (I) 
wherein n is an integer from 2 to 16. Representatives of such diamines 
include 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 
1,6-diaminohexane, etc. 
In place of or in addition to the foregoing aliphatic amines, use can be 
made of aliphatic etherified polyamines of the type polyoxypropylene 
amines having the formula: 
EQU H.sub.2 N--CH(CH.sub.3)CH.sub.2 --[OCH.sub.2 CH(CH.sub.3)].sub.x 
--NH.sub.2(II) 
wherein x varies from 1 to about 5 carbon atoms. 
Other useful primary diamines which may be included in the products of this 
invention include amine-terminated butadienenitrile copolymers having the 
general formula: 
##STR2## 
wherein R is either a phenylene group or an alkylene group, R.sub.1 is 
hydrogen or methyl, and x and y or each independently integers ranging 
from 1 to 25 and n is an integer, preferably below 20. In these copolymers 
it is preferred that butadiene constitute at least 50% by weight of the 
butadiene and nitrile monomer. The nitrile monomer copolymerized with the 
butadiene can either be acrylonitrile or methacrylonitrile. Such 
copolymers generally have low molecular weights, preferably less than 
3,000 to insure that they are sufficiently fluid to react in the formation 
of the polyimide as well as sufficiently fluid so as to be capable of 
foaming. 
Still another type of primary diamines which may be included in the 
products of this invention is the aromatic amino-terminated silicones, 
such as those having the general formula: 
##STR3## 
wherein R is a C.sub.2 to C.sub.6 alkylene group, R.sub.1 and R.sub.2 are 
each independently lower alkyl containing 1 to 3 carbon atoms and n is an 
integer from 1 to 4. 
In the practice of this invention the organic tetracarboxylic acid 
preferably in the form of its diester, most preferably from methanol or 
ethanol, is reacted with the above-referred-to combination of amines to 
form a prepolymer in the form of a consolidated, fragile foam structure, 
which is then subjected to additional heating in order to effect imide 
formation and thereby cure the polymer. When using the tetracarboxylic 
acid ester this operation can be conducted either in the presence or 
absence of an added blowing agent to provide the desired polyimide foam. 
The tetracarboxylic acid esters preferably employed in the practice of this 
invention have the general formula: 
##STR4## 
wherein A is a tetravalent organic group and R.sub.1 to R.sub.4 inclusive 
are independently hydrogen or lower alkyl, most preferably methyl, ethyl, 
or propyl. The tetravalent organic group A is preferably one having one of 
the following structures: 
##STR5## 
wherein X is one or more of the following: 
##STR6## 
Preferred among the tetracarboxylic acid esters are the alkyl esters of 
3,3',4,4'-benzophenone tetracarboxylic acid, most preferably the lower 
alkyl diesters thereof. Mixtures of two or more aromatic esters, most 
preferably predominating in diesters, may be employed, if desired. 
It is also possible, in accordance with this invention, that the 
tetracarboxylic acid derivative employed in the manufacture of the 
polyimide foams be a caprolactam as taught by U. S. Pat. Nos. 4,161,477, 
4,183,838 and 4,183,839, the disclosures of which are incorporated herein 
by reference. As described in those patents, a bis-imide is formed by 
reaction of a tetracarboxylic acid dianhydride with an oxoimine such as 
caprolactam and then reacted with the diamine or diamines to produce the 
desired polyimides. The caprolactam is displaced during the reaction, in 
much the same way as is the ester portion of the tetracarboxylic acid 
ester. 
The relative proportions used in the preparation of the precursors and 
polymers of this invention can be varied. In general, it is preferred to 
employ essentially stoichiometric proportions as between the 
tetracarboxylic acid ester and the combination of primary diamines. 
However, non-stoichiometric mixtures can be used although the excess of 
the reactant present in excess usually does not participate in the 
reaction. As noted above, about 1 to about 50 mol percent (preferably 
about 20 to about 50 mol percent) of the combination of primary diamines 
employed is composed of one or more diesters between an amino-substituted 
aromatic carboxylic acid and a polymethylene glycol. The balance of the 
combination is composed of aromatic or heterocylic diamine(s) with or 
without the addition of still other diamines, for example diamines of the 
type referred to hereinabove in formulas I, II, III and IV, or any mixture 
thereof. Usually the overall combination of amines will contain no more 
than about 10 mol percent of these other diamines. 
In accordance with one preferred form of the invention, use is made of a 
combination of aromatic amines, one of which is a nitrogen heterocyclic 
diamine, preferably 2,6-diaminopyridine and/or 3,5-diaminopyridine, while 
the other is a diamine containing two benzene rings, preferably 
4,4'-methylenedianiline and/or 4,4'-oxydianiline. When using a combination 
of aromatic amines in accordance with this concept, the mol ratio of the 
non-heterocyclic diamine to the nitrogen-containing heterocyclic diamine 
is within the range of 1.0 to 3.0, and preferably 1.5 to 2.8. 
When using a lower alkyl ester of the tetracarboxylic acid, the resulting 
alcohol produced in the reaction as well as the water released during the 
reaction can be used as the blowing agent during polymerization to form 
the desired polyimide foams. Alternatively, use can be made of any of a 
variety of organic or inorganic blowing agents. By use of a solid blowing 
agent such as Celogen TSH, Celogen OT, Celogen AZ 130, Celogen RA, Celogen 
HT 500, Celogen HT 550, sodium bicarbonate, benzenesulfonyl hydrazide, 
boric acid, benzoic acid, and Expandex 5 PT of controlled particle size, 
the homogeneity of the cellular structure of the resulting polyimide foam 
can be more accurately controlled. Preferred for such use are solid 
blowing agents which have been subjected to ball milling or other grinding 
so that the blowing agent is less than 200 microns in diameter, with 98 
percent of the blowing agent particle sizes being less than 150 microns in 
diameter. 
The chemical compositions of the blowing agents identified by trade name 
above follow: 
______________________________________ 
Blowing Agent Chemical Composition 
______________________________________ 
Celogen TSH toluenesulfonyl hydrazide 
Celogen OT p,p'-oxybis(benzenesulfonyl hydrazide 
Celogen AZ 130 
azodicarbonamide 
Celogen RA p-toluenesulfonyl semicarbazide 
Celogen HT 500 
a modified hydrazine derivative 
Celogen HT 550 
hydrazol dicarboxylate 
Expandex 5 PT 5-phenyltetrazole 
______________________________________ 
Variations in the concentration of the blowing agent can be used to achieve 
specific densities and ILD values. Concentrations of up to 10 percent 
based on the weight of the polyimide precursor, and preferably 1 to 5 
percent, can be employed. A concentration of about 2.5 weight percent is 
particularly preferred. 
Hydrated organic compounds of the type referred to in U.S. Pat. No. 
4,621,015 may also be used as blowing agents in the process. 
In the practice of this invention, it is possible to include in the 
reaction mixture various filler and/or reinforcing materials. For example, 
graphite, glass and other synthetic fibers can be added to the composition 
to produce a fiber-reinforced product. Microballons may be added for 
density adjustment, if desired. It is frequently desirable to employ a 
surfactant thereby increasing cellular structure stability and uniformity, 
and increase fatigue resistance and make the foam more flexible and 
resilient. The nature of such surfactants for this use is well known and 
reported in the patent literature. 
Although not necessary, for some applications it is desirable to add a 
suitable quantity of a flame retardant material to the formulation in 
order to still further increase the flame resistance of the resultant 
foam. 
In preparing the precursors of this invention, it is preferred to employ 
the procedures and spray drying techniques described in U.S. Pat. No. 
4,296,208, the disclosure of which is incorporated herein by reference. 
The temperatures at which the precursor is converted to the polyimide foam 
are generally those temperatures used in the reparation of other polyimide 
polymers. As a general rule temperatures ranging from 200.degree. to 
400.degree. C. can be used, with heating rimes from 5 to 60 minutes or 
longer. As those skilled in the art will appreciate, the time for carrying 
out the reaction is somehat dependent upon the reaction temperature, 
higher temperatures nabling the use of shorter reaction times. It is also 
possible to heat to a lower temperature in the first stage of the reaction 
and then to higher temperatures in the later stages. 
Heating can be carried out in a conventional oven if desired. 
Alternatively, the foaming and curing of the precursor into a foamed 
polyimide polymer can be effected by means of microwave heating. In this 
technique, the precursor is exposed for 1 to 120 minutes to radio 
frequencies within the range of 915 to 2450 MHZ, with the power output 
ranging from 1 to 100 kw. The power output to prepolymer weight ratio 
generally falls within the range of 0.1 to 10 kw per kg. 
Having described the basic concepts of the invention, reference is now made 
to the following examples which are provided by way of illustration, but 
not by way of limitation of the practice of the invention. 
The following abbreviations are used in the examples: 
MDA--4,4'-Methylenebisaniline 
DAP--2,6-Diaminopyridine 
TGD--Trimethylene glycol di-p-aminobenzoate 
ATBN--Amino-terminated poly(butadiene-acrylonitrile), (HYCAR 1300X16) 
ODA--4,4'-Oxydianiline 
BTDA--Benzophenone tetracarboxylic acid dianhydride 
BTDE--Benzophenone tetracarboxylic acid, methyl ester 
DC-193--Polysiloxane surfactant (Dow Corning Corporation) 
pcf--Pounds per cubic foot 
IFD--Indentation force deflection as measured by the Indentation Force Test 
of ASTM Test Designation D 3574-81 
All polyimide foams were produced using a two-stage microwave-thermal oven 
procedure. The microwave was a Gerling Moore 5.5 kw microwave cavity 
having two microwave sources, only one of which was used. Low power (one 
source) was 1.5 kw and full power (one source) was 2.75 kw.

Roller fatigue results were measured using the Dynamic Fatigue Test by the 
"Roller Shear at Constant Force" according to ASTM Test Designation D 
3574-81. 
EXAMPLE 1 
Formulation 
[(0.47 mol MDA+0.3 mol DAP+0.25 mol TGD) per mol BTDA]+1.86% DC-193 based 
on the combined weights of the monomers. 
Procedure 
A 5-liter, 3-necked round bottom, glass flask in a heating mantle equipped 
with a stirrer, reflux condenser and thermometer was charged with 1612 g 
(5 mols) of BTDA, 1286 g (40.14 mols) of methanol, and 60 g of water. The 
heater and stirrer were switched on. The solution was milky off-white in 
appearance. After 30 minutes with the temperature at 50.degree. C., the 
heater was switched off and the mixture was stirred for another 19 
minutes. At this point the temperature had reached 71.degree. C. and the 
reaction mixture had turned into a clear, deep amber solution indicating 
completion of the esterification reaction. While stirring the system and 
keeping the temperature between 50.degree. and 65.degree. C., the diamines 
were added using methanol dilution and washes, in the following amounts 
and sequence: 393 g (1.25 mols) TGD; 466 g (2.35 mols) MDA; 164 g (1.50 
mols) DAP. A total of 805 g of methanol was added during these operations 
which occurred over a period of about 2 hours. Next, with the temperature 
of the system at 44.degree. C., 49 g of DC-193 diluted with methanol was 
added, again using a methanol rinse and the system was stirred for another 
2 hours and 15 minutes. 
The reaction solution was spray dried under nitrogen in a Niro Mobile Minor 
spray dryer. In this operation the solution was fed to the dryer over a 
2-hour period with the inlet temperature between 100.degree. and 
110.degree. C., the outlet temperature between 68.4.degree. and 
70.1.degree. C., and the atomizer speed between 28,000 and 34,900 rpm. 
This yielded 3,018 g of polyimide precursor in powder form. The powder was 
sifted through a sieve with 425 micron openings and kept in a sealed 
plastic bag until used. 
Using separate portions of precursor, three polyimide foams were produced. 
In each case, a free-rise foaming procedure was used (i.e., no mold was 
utilized). In one run the foam was produced by microwaving for 5 minutes 
at 1.5 kw and for 10 minutes at 2.75 kw followed by use of a thermal oven 
held at 490.degree. F. for 1 hour and 15 minutes. In another run the 
sample was treated in the microwave for 10 minutes at 2.75 kw followed by 
exposure to 490.degree. F. in a thermal oven for 1 hour and 3 minutes. The 
third sample was produced in the same fashion as the second sample except 
that the time in the thermal oven was 1 hour and 15 minutes. Using trimmed 
sections from the resultant foams, measurements and observations were made 
of their properties. 
Results 
The foams were of very good quality with relatively fine cell structures. 
They were extremely soft, resilient, flexible and non-brittle. The average 
density was 0.49 pcf. 
The IFD (1 inch thick specimen) was 17 pounds of force at 25% deflection 
and 66 pounds of force at 65% deflection. The roller fatigue test (3 inch 
thick specimen) was terminated at 14,000 cycles with little surface damage 
and 15% average thickness loss. The foam had a tensile strength of 11 psi 
and an elongation at break of 28%. 
EXAMPLE 2 
Formulation 
[(0.53 mol MDA+0.3 mol DAP+0.2 mol TGD) per mol BTDA]+1.86% DC-193 based on 
the combined weights of the monomers. 
Procedure 
BTDE was prepared in a 2-liter, 3-necked flask using 386.7 g (1.20 mols) of 
BTDA, 307.6 g (9.60 mols) of methanol and 14.5 g of water during a 45 
minute reaction period with a temperature controlled between 22.degree. 
and 70.degree. C. The diamines were then added to the deep, clear amber 
solution. The following sequence and amounts of addition were used: 127.1 
g (0.64 mol) of MDA; 39.2 g (0.36 mol) of DAP; 75.2 g (0.24 mol) of TGD. 
These additions occurred over a period of about 38 minutes with the 
temperature between 45.degree. and 51.degree. C. Methanol rinses were 
employed. Thereupon the heater was turned on and the mixture stirred for 
23 minutes during which time the temperature increased from about 
40.degree. C. to about 62.degree. C. Next, 11.7 g of DC-193 dissolved in 
methanol was added, again using a methanol rinse. The resultant reaction 
solution was then dried using a vacuum oven with the vacuum adjusted from 
25 to 29 inches of mercury and a temperature of 150.degree. F. The powder 
was sieved and converted into a polyimide foam using a polypropylene mold 
in a 2-stage microwave-thermal oven procedure. The powder was subjected to 
microwaving for 20 minutes at 1.5 kw. In the thermal oven the temperatures 
were 455.degree. F. for 10 minutes, 470.degree. F. for 22 minutes and 
500.degree. F. for 56 minutes. Trimmed sections of the foam were used in 
determining the physical properties described below. 
Results 
The polyimide foam had a density of 0.58 pcf, a tensile strength of 10 psi 
and an elongation of 64% at break. 
EXAMPLE 3 
Formulation 
[(0.34 mol MDA+0.34 mol DAP+0.34 mol TGD) per mol BTDA]+1.87% DC-193 based 
on the combined weights of the monomers. 
Procedure 
BTDE was produced at 23.degree.-70.degree. C. from 387 g (1.20 mols) of 
BTDA, 308 g (9.61 mols) of methanol and 15 g of water. To the resultant 
clear, dark amber solution were added TGD (129 g; 0.41 mol), MDA (81 g; 
0.41 mol) and DAP (45 g; 0.41 mol). The additions were facilitated by use 
of methanol rinses and the temperature of the reaction mixture was 
controlled between 36.degree. and 64.degree. C. over a period of 1 hour 48 
minutes. To the reaction mixture was then added 12.0 g of DC-193 using 
methanol dilution and rinse. The resultant mixture was stirred for about 
1.5 hours. 
The polyimide precursor was isolated in powder form by use of a vacuum oven 
operated generally as in Example 2. The yield of dried polyimide precursor 
was 731 g. Sieved polyimide precursor was converted into polyimide foam in 
a mold by use of the 2-stage microwave-thermal oven procedure. The 
microwave portion of the cycle involved 20 minutes at 1.5 kw. The final 
curing in the oven occurred at 470.degree. F. over a period of 1.5 hours. 
Results 
The polyimide foam had a density of 0.56 pcf. 
EXAMPLE 4 
Formulation 
[(0.72 mol MDA+0.30 mol TGD) per mol BTDA]+1.97% DC-193 based on the 
combined weights of the monomers. 
Procedure 
A methanol solution of BTDE was produced from 818 g (2.5 mols) of BTDA, 641 
g (20.01 mols) of methanol and 31 g of water. The reaction temperature was 
raised from 25.degree. to 72.degree. C. during a reaction period of about 
1 hour. To this solution were added the following ingredients in the 
following sequence: TGD (245 g; 0.76 mol); MDA (355 g; 1.79 mols) and 28 g 
of DC-193. These ingredients were added as methanol solutions and methanol 
rinses were employed. The maximum reaction temperature was 61.degree. C. 
The polyimide precursor was recovered in powdered form by use of a spray 
drying procedure generally as in Example 1 using an inlet temperature 
between 96.degree. and 102.degree. C. an outlet temperature between 
68.8.degree. and 69.7.degree. C. and an atomizer speed ranging from 31,600 
to 32,800 rpm. This resulted in a recovery of 1,515 g of polyimide 
precursor which was stored in a jug until use. Polyimide foams were 
produced using the 2-stage free-rise microwave-thermal oven procedure 
(microwave: 2.75 kw for 15 minutes; thermal oven: 480.degree. F. for 1 
hour 32 minutes). Trimmed sections from the resultant foams were used for 
physical property determinations and observations. 
Results 
The foam was soft, extremely flexible and resilient at room temperature, 
with a non-homogeneous cell structure. It had a density of 0.92 pcf. The 
roller fatigue test (31/8 inch thick specimen) was terminated after 31,866 
cycles with an average thickness loss of 16%, a weight loss of 1.1% and 
some severe cracking. At 14,725 cycles, virtually no damage to the foam 
was observed in the roller fatigue test. 
EXAMPLE 5 
Formulation 
[(0.31 mol TGD+0.71 mol MDA+0.00038 mol ATBN) per mol BTDA]+2.35% DC-193 
based on the combined weights of the monomers. 
Procedure 
The following ingredients were used to produce BTDE: 981 g (3.00 mols) of 
BTDA; 769 g (23.76 mols) of methanol; and 36 g of distilled water. To the 
methanol solution of BTDE was added 1.98 g of ATBN (HYCAR 1300X16, B. F. 
Goodrich Chemical Company) with the temperature of the methanol solution 
at 65.degree. C. Heat was then applied and solution brought to reflux 
temperature for one hour. Then, the other diamines were added by use of 
methanol dilution and rinses in the order of TGD (294 g; 0.92 mol) and MDA 
(425 g; 2.14 mols). A total of 509 g of methanol was used in these 
additions. During the additions the temperatures were maintained between 
50.degree. and 63.degree. C. Finally, 40 g of DC-193 was added together 
with dilution methanol and the solution stirred for an additional 15 
minutes. The polyimide precursor was recovered in powder form by use of a 
spray dryer operated generally as in Examples 1 and 4. The recovery was 
1,878 g. One portion of the precursor was placed in a 260.degree. C. air 
oven for 30 minutes and the resultant foam was subjected to a T.sub.g 
determination by DSC analysis. Polyimide foam was produced in a mold from 
the polyimide precursor powder by use of the 2-stage microwave-thermal 
oven procedure (microwave: 2.75 kw for 20 minutes; thermal oven: 
470.degree. F. for 33 minutes and 480.degree. F. for 1 hour and 11 
minutes). Trimmed sections of the foams were subjected to physical 
property determinations. 
Results 
The foam had a T.sub.g of 242.degree. C., a density of 0.92 pcf, and an IFD 
(1 inch specimen) of 25 pounds of force at 25% deflection and 112 pounds 
of force at 65% deflection. The roller fatigue test (35/8 inch thick 
specimen) was terminated at 21,972 cycles with no weight loss and an 
average thickness loss of 2%. 
EXAMPLE 6 
Formulation 
[(0.31 mol TGD+0.71 mol MDA) per mole BTDA]+1.94% DC-193 based on the 
combined weights of the monomer. Samples were also produced containing 
either zinc borate or alumina trihydrate fire retardants. 
Procedure 
A methanol solution of BTDE was produced from 1,636 g (5.00 mols) of BTDA, 
1,283 g (39.64 mols) of methanol and 60 g of water using the general 
procedure of Example 1. To this solution were added 490 g (1.53 mols) of 
TGD and 709 g (3.57 mols) of MDA. A total of 847 g of dilution methanol 
was used for these additions. Temperatures were controlled during the 
additions to between 49.degree. and 60.degree. C. Then, 55 g of DC-193 was 
added as a methanol solution. The product was spray dried and the 
resultant dry powder sifted through a No. 25 screen. Polyimide foam was 
produced from the polyimide precursor (microwave: 10 minutes at 2.75 kw; 
thermal oven: 1 hour at 475.degree. F.). Into four additional individual 
quantities of the powdered polyimide precursor were mixed various flame 
retardants, as follows: Foam A - 18 g zinc borate powder (Firebrake ZB; 
U.S. Borax & Chemical Company) per 100 g polyimide precursor; Foam B - 18 
g alumina trihydrate powder (SB-632; Solem Industries) per 100 g polyimide 
precursor; Foam C - 18 g alumina trihydrate powder (Akrochem 8.0; Akron 
Chemical Company) per 100 g polyimide precursor, and Foam D - 25 g alumina 
trihydrate powder (SB-136; Solem Industries) per 100 g polyimide 
precursor. Each of these mixtures was converted into a polyimide foam by 
the 2-stage microwave-thermal oven procedure using the following 
conditions: Foam A - microwave: 1.5 kw for 10 minutes; thermal oven: 
475.degree. F. for 63 minutes; Foam B - same as Foam A except 65 minutes 
in the thermal oven; Foam C - microwave: 1.5 kw for 10 minutes; thermal 
oven: 470.degree. F. for 43 minutes and 480.degree. F. for 27 minutes; and 
Foam D - microwave: 1.5 kw for 15 minutes; thermal oven: 475.degree. F. 
for 1 hour and 9 minutes. All foaming operations in this Example were 
conducted without use of a mold. 
Results 
Each of the foams was soft, flexible and resilient. The baseline foam 
(i.e., without added flame retardant) had a density of 1.12 pcf and showed 
an LOI (ASTM D 2863-77) of 32-33. Foam A had a density of 0.71 pcf and 
exhibited an LOI of 41-42. Foam B had a density of 0.77 pcf and exhibited 
an LOI of 38-39. The density of Foam C was 0.73 pcf with an LOI of 37-38. 
Foam D had a density of 0.67 of pcf and exhibited an LOI of 39-40. 
EXAMPLE 7 
Formulation 
[(0.31 mol TGD+0.71 mol ODA) per mole of BTDA]+1.94% DC-193 based on the 
combined weights of the monomers. 
Procedure 
A solution of BTDE in methanol was produced using BTDA (981 g; 3.00 mols), 
methanol (768 g; 23.73 mols) and distilled water (36 g). The diamines were 
added as follows: TGD (294 g; 0.92 mol); and ODA (430 g; 2.14 mols) using 
methanol dilution and washes. During these additions the temperature was 
controlled between 45.degree. and 68.degree. C. Then, 33 g of DC-193 
diluted with methanol was added. During these operations a total of 510 g 
of methanol was added to the system. The reaction mixture was stirred for 
about 3 hours. The polyimide precursor was recovered by use of a spray 
dryer and sieved through a No. 25 screen. Using a mold, the polyimide 
precursor was converted into polyimide foam by exposure for 15 minutes in 
a microwave (2.75 kw power) and 1.5 hours to 475.degree. F. in a thermal 
oven. 
Results 
The foam had a density of 0.92 pcf. The roller fatigue test using a foam 
specimen of 4.5 inches in thickness was terminated at 40,000 cycles with 
very minor damage to the surface, a weight loss of 0.7% and an average 
thickness loss of 3.5%. An 8.3% loss in IFD at 40% deflection was 
incurred. 
EXAMPLE 8 
Formulation 
[(0.31 mol TGD+0.71 mol MDA) per mole BTDA. Samples were also produced 
containing various surfactants and flame retardants. 
Procedure 
A methanol solution of BTDE was formed from 1,636 g (5.00 mols) of BTDA, 
1,282 g (39.61 mols) of methanol and 60 g of water. Diamines added to the 
system were TGD (490 g; 1.53 mols) and MDA (709 g; 3.57 mols). As in the 
above examples, methanol rinses and dilution were employed. To aid in the 
dissolution of the TGD the temperature was raised to 70.degree. C. The 
resin solution was cooled to 40.degree.-45.degree. C. and subdivided into 
weighed portions by pouring into 1,000 mL Erlenmeyer flasks. The following 
additives were measured into the respective resin solutions: 
Solution A: 6.12 g DC-193 and 16.2 g dimethyl methylphosphonate in 484 g of 
resin solution 
Solution B: 6.00 g DC-193 and 15.55 g Antiblaze 1045 phosphate ester 
(Albright & Wilson Inc.) in 503 g of resin solution 
Solution C: 6.45 g DC-193 in 485 g of resin solution 
Solution D: 2.96 g DC-193 in 483 g of resin solution 
Solution E: 3.26 g Zonyl FSN-100 surfactant (duPont) in 475 g of resin 
solution 
Solution F: 2.90 g Arlasolve 200 surfactant (ICI) in 470 g of resin 
solution 
Each of these solutions was reheated to somewhat above 50.degree. C. on a 
hot plate using a magnetic stirrer in order to re-dissolve any 
precipitates that may have formed. These solutions were poured into 
separate aluminum foil lined trays and subjected to drying in a vacuum 
oven at 140.degree. to 150.degree. F. while occasionally breaking up the 
solids from the upper surfaces and emptying the cold trap as needed. The 
respective dried products from the solutions were powdered using a 
household blender operated at the highest speed. The powders were sifted 
through a No. 25 sieve and stored in plastic jugs. In the two-stage 
microwave-thermal oven procedure, the following conditions were used: 
Product A: microwave 15 minutes at 1.5 kw; thermal oven 470.degree. F. for 
1 hour 3 minutes 
Product B: microwave 15 minutes at 1.5 kw; thermal oven 480.degree. F. for 
1 hour 
Product C: microwave 10 minutes at 1.5 kw; thermal oven 470.degree. F. for 
1 hour 6 minutes 
Product D: microwave 15 minutes at 1.5 kw; thermal oven 470.degree. F. for 
61 minutes 
Product E: microwave 15 minutes at 1.5 kw; thermal oven 480.degree. F. for 
67 minutes 
Product F: microwave 15 minutes at 1.5 kw; thermal oven 480.degree. F. for 
62 minutes In each free-rise foaming was employed. 
Results 
Product A: foam density was 0.53 pcf; LOI was 35-36 
Product B: foam density was 0.61 pcf; LOI was 41-42 
Product C: foam density was 0.53 pcf 
Product D: foam density was 0.71 pcf 
Product E: foam density was 0.78 pcf 
Product F: foam density was 0.89 pcf 
EXAMPLE 9 
Formulation 
[(0.72 mol MDA+0.31 mol TGD) per mole BTDA]+2.0% DC-193 based on the 
combined weights of the monomers. 
Procedure 
In this Example, a ten gallon, stainless steel reactor equipped with 
heating or cooling coils supplied by cold or hot running water, a single 
blade impeller and an overhead condenser system was used. The following 
ingredients were charged into the reactor: BTDA (6.543 kg; 20.00 mols), 
methanol (5.126 kg; 158.4 mols), and distilled water (258 g). While 
stirring the solution, its temperature was raised from 80.degree. F. to 
135.degree. F. over a 40 minute period at which time the heating was 
discontinued. The solution was stirred for another 10 minutes during which 
its temperature decreased to 125.degree. F., yielding a clear amber 
solution of BTDE in methanol. The diamines were charged as follows: TGD 
(1.961 kg; 6.12 mols) and MDA (2.825 kg; 14.22 mols) using methanol 
dilution. Then, 227 g of DC-193 was added, again using methanol as a 
solubility aid. In these operations a total of 3.443 kg of methanol was 
introduced into the reactor. The mixture was then heated and stirred for 
about 45 minutes until the temperature reached 55.degree. C. at which 
point the heating was discontinued. The reaction solution was stirred for 
an additional 1 hour and 7 minutes. Portions of the reaction solution were 
dried in a spray dryer. A representative sample of the resultant polyimide 
precursor was foamed in a mold under the following conditions: microwave: 
25 minutes at 2.75 kw; thermal oven: 450.degree. F. for 63 minutes. 
Results 
The polyimide foam had a tensile strength of 19 psi and a density of 1.06 
pcf. The roller fatigue test on a specimen of 4.25 inch thickness was 
terminated at 23,373 cycles with no weight loss and no loss in IFD at 40% 
deflection. The foam sustained a 3% to 4% thickness loss but had cracks 
only at the ends of the roller travel. 
When producing the polyimides of this invention for applications other than 
foams (e.g., for structural applications, adhesives, films, or the like), 
the mixture of diamines may be reacted with the organic tetracarboxylic 
acid or a derivative thereof such as its dianhydride, its acid halides, 
its salts, or its esters. Use of tetracarboxylic acid dianhydrides is most 
preferred for these particular reactions because of their high reactivity. 
It will be understood that various changes and modifications can be made in 
the details of procedure, formulation and use without departing from the 
spirit and scope of the invention.