Maleimide-maleamic acid resin solution

Solutions of maleimide resins comprising a mixture of bismaleimides and low but solubilizing amounts of maleamic acids are provided at high solids levels, e.g. at least about 50%. Such solutions which comprise common solvents such as acetone, methyl ethyl ketone and toluene are useful in preparing laminates based on bismaleimide resins.

Disclosed herein are soluble compositions of mixtures of maleimide and 
maleamic acid compounds, solutions of such mixtures, laminates based on 
such compositions as well as methods of making and using such 
compositions, solutions and laminates. 
BACKGROUND OF THE INVENTION 
Bisimide resins, e.g. bismaleimide resins, are advantageously used in 
providing resin matrix composites, e.g. glass or carbon fiber reinforced 
laminates, to achieve enhanced properties such as greater thermal 
stability and lower moisture sensitivity than is possible with other 
composites, e.g. composites based on epoxy or other resins. A common 
bisimide, i.e. bis(4-maleimidophenyl)methane, exhibits poor solubility in 
many organic solvents of choice. Its use in commercial manufacture of 
laminates is facilitated by dissolving the bisimide in N-methyl 
pyrrolidone (not a preferred solvent) and by chain extension by Michael 
addition reaction with diamines. 
Nishikawa, et al., disclose in U.S. Pat. No. 4,460,783 that certain 
aromatic ether bismaleimide compounds such as bis(maleimidophenoxyphenyl) 
propane and the like are highly soluble in desirable solvents such as 
acetone, toluene, methyl ethyl ketone and the like. See also Harvey et al 
in "New Aromatic-Ether Bismaleimide Matrix Resins", ANTEC '86, page 1311. 
It has been discovered that in their purer forms such aromatic ether 
bismaleimides have low solubility. It has been further discovered that the 
solubility of such aromatic ether bismaleimides, as well as other 
bismaleimides generally, can be enhanced by the presence of a solubilizing 
amount of compounds having at least one terminal maleamic acid group. 
Bisimide resins have been preferably prepared with low levels (if any) of 
terminal maleamic acid groups which tend to liberate water from ring 
closing imidization during cure of such resin. Such water can vaporize at 
commonly used fabrication temperatures, tending to generate voids or 
blisters in fabricated articles such as laminates., For instance, Bargain 
in U.S. Pat. No. 3,839,358 discloses that bismaleimides, e.g. 
bis(4-maleimidophenyl)methane, are prepared by reacting a diamine with 
maleic anhydride followed by catalytic cyclodehydration. The bismaleimide 
is purified, i.e. separated from acid-containing species, by washing with 
a basic solution, e.g. aqueous sodium bicarbonate. See also Balme who 
discloses in U.S. Pat. No. 3,975,401 a method for reducing the proportion 
of maleimido-acid (i.e. maleamic acid) groups in the precipitated product 
of cyclodehydration. 
Although such acid groups can liberate water during cure conditions, it has 
been discoverd that low amounts of liberated water can be tolerated in 
many fabrication practices. However, in critical applications it is 
especially desirable that bisimide resins cure with minimal liberation of 
water, e.g. to avoid blisters that can form when laminates of the cured 
bisimide resin are subjected to high temperatures, e.g. as in vapor phase 
soldering. 
An object of this invention is to provide soluble bismaleimide resin 
comprising predominately bismaleimides and low but solubilizing amounts of 
maleamic acids. 
Another object is to provide concentrated solutions of such resins in 
common organic solvents. Yet another object is to provide such solutions 
with desirably long stability, for instance, for days, weeks or even 
longer. 
Still another object is to provide laminates, and methods of making 
laminates, from such resins, especially from solutions that rapidly form a 
viscous thermoplastic resin that allows for minimal resin flow from 
reinforced matrices even during severe curing conditions, e.g. high 
pressure. 
These and other objects of this invention are possible since it has been 
discovered that the addition of minor amounts of maleamic acids can 
greatly enhance the solubility of bismaleimides in common organic 
solvents, affording greatly enhanced utility in fabrication, e.g. of 
laminates, without substantially deleterious effects of liberated water. 
SUMMARY OF THE INVENTION 
This invention provides methods of preparing highly soluble bismaleimidme 
compositions by providing mixtures of such bismaleides and solubilizing 
amounts of maleamic acids. This invention also provides such soluble 
compositions, solutions thereof as well as methods of using such 
compositions and solutions to prepare laminates. Such compositions, and 
solutions thereof, are devoid of other carboxylic acids and anhydrides, 
e.g. acetic acid and/or acetic anhydride which are commonly used as 
dehydrating agents in the preparation of such mixtures. 
DETAILED DESCRIPTION OF THE INVENTION 
The methods of preparing highly soluble bismaleimide compositions according 
to this invention comprise providing a mixture of bismaleimide and a 
solubilizing amount of maleamic acids. Such bismaleimide compositions are 
soluble in a variety of common organic solvents and are conveniently 
characterized as being acetone-soluble as distinguished from the pure 
forms of most bismaleimides which exhibit low, e.g. about 5 weight 
percent, solubility in acetone at about room temperature. 
The methods of this invention can be employed with any of the bismaleimides 
and maleamic acids of the formula: 
##STR1## 
where A is --B--, 
##STR2## 
where B,B' and X are independently --O--, --SO--, --CO--, or 
##STR3## 
R.sub.3 and R.sub.4 being independently hydrogen, C.sub.1 -C.sub.3 alkyl, 
and halogenated C.sub.1 -C.sub.3 alkyl and n ranging from 0 to 6, where 
R.sub.1 and R.sub.2 are independently the maleamic acid group, 
--NHCOCH.dbd.CHCOOH, or the maleimide group, 
##STR4## 
wherein R.sub.1 and R.sub.2 are the same providing a mixture of 
bismaleimide and bismaleamic acid and are different thereby providing a 
maleimide-maleamic acid. As used herein the term maleamic acids includes 
bismaleamic acids and half imidized intermediate referred to as a 
maleimide-maleamic acid. 
In certain preferred embodiments of this invention the mixture comprises 
maleimides derived from bis(aminophenoxyphenyl) propane, i.e. A is 
##STR5## 
In other preferred embodiments of this invention the mixture comprises 
maleimides derived from bis(aminophenyl) methane. 
Although purified bismaleimides and bismaleamic acids generally tend to be 
insoluble in common organic solvents such as acetone, methyl ethyl ketone 
and toluene, compositions comprising mixtures of bismaleimides and 
maleamic acids as specified above have been found to be surprisingly 
soluble in such solvents. Accordingly, this invention also provides novel 
and useful, highly soluble mixtures of bismaleimides and maleamic acids. 
Such mixtures of maleimides and maleamic acids can be prepared from diamine 
precursors by methods generally known in the art and disclosed, for 
instance, in U.S. Pat. Nos. 3,562,223 and 4,460,783, both of which are 
incorporated herein by reference. The mixtures of bismaleimides and 
maleamic acids which desirably are predominately bismaleimides with lesser 
amounts of maleamic acids, e.g. residual bismaleamic acid, can be prepared 
by ring closure imidization of the bismaleamic acid precursor. 
Bismaleamic acid can generally be obtained in substantially pure 
quantities, e.g. at least about 90% bismaleamic acid or higher, say at 
least about 98% purity, by condensation reaction, e.g. in a liquid medium 
such as acetone, of maleic anhydride with a diamine of the formula 
##STR6## 
where A is as defined above. The maleimides can be formed from the 
bismaleamic acid precursor, e.g. suspended in a liquid medium such as 
acetone, by ring closure imidization resulting in the liberation of water. 
This ring closure is desirably effected in the presence of an acid 
anhydride dehydrating agent such as acetic anhydride, a tertiary amine 
ring closing agent such as triethylamine, and a metal acetate catalyst 
such as ferrous acetate, nickel acetate or preferably, for more complete 
imidization, cobalt acetate. The ring closing reaction is readily carried 
out at the reflux temperature of the liquid medium to provide a solution 
comprising predominately the bismaleimide and maleamic acids, i.e. 
residual bismaleamic acid precursor and the half-imidized intermediate. 
Quenching the solution in cold water produces a precipitate mixture of 
bismaleimide and maleamic acids. The mixture can be made to be 
substantially devoid of other carboxylic acid, e.g. which may be occluded 
acid which was formed from the acid anhydride dehydrating agent, by 
washing and/or recrystallization. Such washing, e.g. with water, should be 
with an acidic or at least neutral liquid to avoid excessive 
solubilization of the maleamic acids as may occur when basic liquids are 
used. When washing with basic liquids is desired, contact time should be 
short to avoid excessive solubilization of maleamic acids. Such 
recrystallization may be effected from any common organic solvent, e.g. 
acetone, methyl ethyl ketone, toluene and the like. 
Acetone-soluble mixtures of bismaleimides and maleamic acids can comprise 
about 40 to about 95 parts by weight bismaleimide; the remainder of 100 
parts by weight of such mixture will generally comprise maleamic acids, 
i.e. residual bismaleamic acid and the half-imidized intermediate. More 
preferably, such mixtures will comprise at least about 50 or 60 and up to 
about 85 or at least 80 parts by weight of the bismaleimide. In many cases 
the amount of bismaleamic acid will be from about 1 to less than about 30 
parts by weight, preferably often less than about 10 parts. 
The amount of such maleamic acids is conveniently expressed in terms of 
"acidity" based on maleamic acid groups as a percent of total acidity when 
all of the maleimide and maleamic acid groups are taken as maleamic acid 
groups. When the mixture is prepared from a known amount of bismaleamic 
acid precursor, such acidity is readily determined by titrating a sample 
of the mixture to a neutral end-point with a standard base, e.g. N/20 KOH; 
acidity is determined with reference to the titer of the bismaleamic acid 
precursor. 
Preferably, the ring closing reaction is carried out so that the acidity is 
less than about 40% and under conditions mild enough to prevent the 
formation of substantial amounts of higher molecular weight oligomers. 
More preferably, acidity will be in the range of about 1-20%. In many 
cases where it is desirable to provide a highly soluble maleimide that 
liberates low amounts of water upon curing, it is most preferred that 
acidity be in the range of about 2-15%, e.g. about 3-12%. 
This invention also provides solutions of highly soluble mixtures of 
bismaleimides in common organic solvents such as acetone, methyl ethyl 
ketone and toluene, or mixtures thereof. Such solutions can be provided by 
solvents selected from the group consisting not only of acetone, methyl 
ethyl ketone, and toluene but also of methyl isobutyl ketone, 
tetrahydrofuran, dimethylformamide, dimethylacetamide, dimethylsulfoxide, 
N-methyl pyrrolidone, ethylene dichloride, and xylene and the like or a 
mixture of such solvents. In many cases, the solvent of choice will 
consist essentially of acetone. 
Solutions of bismaleimide resin of this invention are useful in providing 
matrix composites and often desirably comprise from about 40 to about 90 
percent solids of resin mixtures of bismaleimide and maleamic acid. Useful 
resin solutions will generally have a viscosity between 50 and 500 
centipoise, although process requirements may require viscosities outside 
of that range. In many cases it is especially desirable that such 
solutions have a viscosity between about 100 and 200 centipoise. 
When solutions are intended to be used within a short period of time (e.g. 
within minutes or even hours, of dissolution) solutions of such mixtures, 
of at least about 50% by weight or higher, e.g. about 70%, can be 
obtained. However, in many cases, especially with relatively high 
concentrations of such mixtures, e.g. at least about 50% by weight, the 
bismaleimide component of the solution tends to separate over time from 
the solution in substantial quantities resulting in a solution containing 
disproportionately higher amounts of resin having maleamic acid terminal 
groups. Such maleamic acid terminal groups often undergo ring closing 
during cure with the result of liberation of water which may undesirably 
tend to form voids or blisters in composites. 
It has been discovered that separation of bismaleimide compounds from 
solutions can be avoided by providing in the solutions of such mixtures of 
maleimides and maleamic acid a minor amount of a species capable of 
interacting with maleamic acid groups to form amides, esters, etc., or 
with terminal unsaturation. Such species can comprise amines, e.g. 
polyamines. The amount of polyamine present in the solution to provide 
stability can be conveniently expressed in terms of equivalents of amine 
groups and maleamic acid groups, e.g. conveniently expressed in terms of 
the ratio of amine groups to maleamic acid groups. When the polyamine is 
present in solution such that the amount of amine groups is substantially 
less than the equivalent amount of maleamic acid groups, solubility may be 
enhanced but for a shorter period of time than when substantially the 
equivalent amounts are utilized. Moreover, when the polyamine is present 
such that the amount of amine groups is substantially greater than the 
equivalent amount of maleamic acid groups, stability will generally tend 
to be lessened, often with substantially increased viscosity of the 
solution. Such viscous solutions may tend to gel rapidly on heating, 
providing undesirable resin composites. 
Considerable latitude can often be employed in determining such 
equivalence. In many cases it is advantageous to provide solutions where 
the ratio of amine groups to maleamic acid groups is from about 0.5 to 
about 4. To achieve exceptionally long stability, e.g. for days or weeks 
or more, without separation, e.g. by precipitation of a maleimide or 
maleamic acid component of the mixture, and to prevent an undue increase 
in viscosity, it is generally useful to provide polyamine so that the 
amount of amine groups is more nearly the equivalent of maleamic acid 
groups, e.g. where the ratio of amine groups to maleamic acid groups is 
about 0.8 to 2, and most preferably about 0.9 to 1.5. 
The polyamine can comprise a diamine as used in preparing the bismaleimides 
of this invention, i.e. a diamine of the formula 
##STR7## 
where A is described above or where the rings are saturated. 
Alternatively, the polyamine can be another diamine such as alkyl diamine, 
for instance diaminopropane, putrescine, cadaverine, hexamethylene 
diamine, and the like, or a triamine such as triaminononane and the like. 
It has been found that stable solutions that allow the resin to rapidly 
become viscous upon heating are achievable when the polyamine contains 
secondary amines, such as diethylenetriamine, triethylenetetramine, 
tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine. 
Especially desirable resins that become rapidly viscous upon heating are 
provided with polyamines containing at least two secondary amines. 
In one method of forming resin matrix composites, cloth-like layers such as 
glass or carbon fiber cloth (woven or non-woven) is saturated with a 
solution of this invention. Such saturation can be conveniently carried 
out by dipping such cloth into a resin solution. Excess solution can be 
removed by passing the cloth through squeeze rolls. Solvent is removed in 
any convenient manner such as by heating the solution-saturated cloth, 
e.g. in an oven at a temperature oftnn above the boiling point of the 
solvent. The length of time at elevated temperature is desirably short, 
e.g. less than about 10 minutes, but will be sufficiently long to remove 
solvent and promote partial reaction of the resin to a coherent 
thermoplastic state (often called B-staging) providing a dry (e.g. 
solventless but often tacky) resin-impregnated cloth, commonly called a 
"pre-preg". Such resin-impregnated cloth can then be provided in one or 
more layers which can be thermoformed, e.g. heated in a compressed stack 
and cured to provide a laminate by heating for an extended period of time, 
e.g. about an hour or more, at elevated temperatures say between about 
150.degree. and 300.degree. C., preferably at least about 180.degree. C. 
to about 250.degree. C. 
An effective amount of polyamine will also facilitate formation of dry 
resin-impregnated cloth. With low levels of polyamine, the resin will 
often remain molten, e.g. at temperatures of about 200.degree. C., for 
undesirably long times, e.g. 20 minutes or more, even hours without 
reacting sufficiently to form a dry thermoplastic resin. When high levels 
of polyamine are utilized, e.g. substantially higher than about the 
equivalent amount of maleamic acid, the resin generally tends to rapidly 
gel upon heating, providing an undesirable foamy, brittle resin. Desirably 
the polyamine will assist in providing such dry thermoplastic resin in a 
short time, say less than about 10 minutes, preferably on the order of 
about 1 to 2 minutes. The time for formation of such dry thermoplastic 
resin is often correlated with "Dry Rubber Time", a predictive test 
defined more particularly herein in Example 4. 
Some polyamines, e.g. diamines, allow for advantageous Dry Rubber Times, 
e.g. about 3 minutes or less, for solutions that are maintained for a 
short period of time, say about a day or so. However, when such solutions 
are maintained for longer times, e.g. about a week or more, Dry Rubber 
Times tend to increase to undesirable levels, e.g. about 5 minutes to 20 
minutes or more. Advantageously, polyamines having secondary amine groups 
allow for short Dry Rubber Times even when solutions are maintained for 
several weeks. Accordingly, preferred aspects of the inventions disclosed 
herein comprise polyamines having secondary amine groups. 
The solutions of this invention may also comprise a variety of other 
materials that can be useful in providing laminates with desirable 
properties. Such materials may include fillers, such as silica, 
thermoplastics and/or reactants having one or more vinyl, epoxy, or 
cyanate ester groups, as illustrated in U.S. Pat. No. 4,654,407, 
incorporated herein by reference. 
The following disclosure is provided to illustrate specific embodiments and 
aspects of the invention but does not imply any limitation of the scope of 
the invention.

EXAMPLE 1 
This example serves to illustrate the preparation of a soluble mixture of 
bismaleimides and maleamic acids derived from bis(aminophenoxyphenyl) 
propane and its use in preparing solutions according to this invention. 
351 grams of maleic anhydride and 1,012 grams of acetone were heated to 
reflux temperature (about 63.degree. C.) in a 5-liter reaction flask. A 
solution of 693 grams of 2,2-bis[4-(4-amino-phenoxy)phenyl]propane in 
1,350 grams of acetone was metered into the refluxing solution over a 
period of 40 minutes. The reaction mixture was held at 30 minutes at 
reflux temperature to provide essentially 100 percent complete conversion 
to the bismaleamic acid of 2,2-bis[4-(4-amino-phenoxy)phenyl]propane which 
precipitated as a yellow powder. 
The following materials were added to the suspension of bismaleamic acid in 
refluxing acetone: 495 grams of acetic anhydride, 3.375 grams of nickel 
acetate tetrahydrate, and 58.5 grams of triethylamine. The suspension was 
maintained at reflux temperature for about two hours then cooled to 
50.degree. C. The resulting clear solution was stirred into cold water 
yielding a precipitated yellow powder which was washed with water to 
remove solubles, filtered and dried in an air oven at 60.degree. C. to 
constant weight. Analysis by high pressure liquid chromatography indicated 
that the powder comprised about 76 percent of the bismaleimide of 
2,2-bis[4-(4-amino-phenoxy)phenyl]propane and about 5 percent of the 
precursor bismaleamic acid; the balance of the powder is believed to be 
the half-imidized intermediate having both maleimide and maleamic acid 
terminal groups. The powder was dissolved in acetone from 40 to about 60 
percent by weight to provide solutions according to this invention. 
EXAMPLE 2 
This example serves to illustrate the preparation of a soluble mixture of 
bismaleimides and maleamic acids derived from methylene dianiline and its 
use in preparing solutions according to this invention. 
39.6 grams of methylene dianiline, 1.5 grams of benzyl dimethylamine, and 
150 grams of acetone were cooled in a 500 cc flask to about 4.degree. C. A 
solution of 43.1 grams of maleic anhydride in 200 grams of acetone was 
added over about a one hour period. The bismaleamic acid of methylene 
dianiline formed as a yellow precipitate as the mixture was stirred for an 
additional two hours at about 4.degree. C. The bismaleamic acid was 
filtered, rinsed with acetone and dried at 65.degree. C. 
78.8 grams of the bismaleamic acid, 330 grams of acetic anhydride, 3.5 
grams of calcium acetate monohydrate, and 400 grams of acetone were heated 
in a 1-liter flask for about one hour at reflux (about 60.degree. C.). 
Acetone was evaporated until the temperature rose to about 80.degree. C. 
After continuing refluxing at about 80.degree. C. for about 2 hours, the 
reaction mixture was poured into water resulting in a precipitate which 
was washed in water and filtered. Analysis by high pressure liquid 
chromatography indicated that the precipitate comprised about 49% of 
bismaleimide of methylene dianiline and about 34% of bismaleamic acid of 
methylene dianiline; the balance of the precipitate is believed to be the 
intermediate product having both maleimide and maleamic acid terminal 
groups. 
A portion of the mixture was dried for one minute on a hot plate (about 
167.degree. C.) and dissolved in acetone to provide a solution according 
to this invention comprising about 50% solids. After several days a small 
amount of acetone insoluble material precipitated from the 50% solution. 
Another solution according to this invention (about 75% solids in acetone) 
exhibited less stability with substantial amounts of acetone insoluble 
precipitate forming after about several hours. 
The surprising solubility of a mixture of bismaleimide and maleamic acids 
derived from methylene dianiline is further indicated by comparison of 
solubilities of pure materials. As indicated above in the description of 
the formation, the solubility of the bismaleamic acid in acetone is 
extremely low. Moreover, commercially available bismaleimide of methylene 
dianiline (from Aldrich Chemical Company, purity 85%) has a solubility in 
acetone of less than about 10%. 
EXAMPLE 3 
This example serves to illustrate methods of this invention in providing 
bismaleimides with solubilizing amounts of maleamic acids. 
Bismaleimide of 2,2-bis[4-(4-aminophenoxy)phenyl]propane was prepared 
essentially as in Example 1 except that the nickel acetate tetrahydrate 
was replaced with 0.32 g of each of the following cyclodehydration 
catalysts: cobalt acetate tetrahydrate, nickel acetate tetrahydrate, 
ferrous acetate, cupric acetate monohydrate, calcium acetate monohydrate, 
zinc acetate dihydrate, chromium triacetate monohydrate and sodium 
acetate. The results of the following analyses of the resultant yellow 
powder are reported in Table 1: 
(a) the composition as determined by high pressure liquid chromatography 
(HPLC) in terms of the area ratios of bismaleimide, what is believed to be 
the half imidized intermediate and residual bismaleamic acid; 
(b) the "acidity" as determined by titration and reported as a percent of 
the total acidity of the precursor bismaleamic acid; and 
(c) the room temperature solubility in acetone in weight percent. 
The results reported in Table 1 indicate that high solubility of 
bismaleimides is highly dependent on the amount of solubilizing maleamic 
acid and that practice of preferred embodiments of this invention can be 
facilitated by use of a cobalt, nickel or ferrous acetate as a 
cyclodehydration catalyst in the preparation of bismaleimide. 
TABLE 1 
______________________________________ 
Powder 
Catalyst Composition.sup.(1) 
Acidity 
(cation) (BMI/MIMA/BMA) % Solubility 
______________________________________ 
Co 78/15/2 3 &gt;70% 
Ni 72/14/6 6 &gt;70% 
Fe 62/27/6 12 &gt;70% 
Cu 32/21/31 23 &lt;40% 
Ca 30/28/30 35 &lt;40% 
Zn 30/18/33 30 &lt;40% 
Cr 27/27/36 37 &lt;40% 
Na 43/33/13 -- -- 
______________________________________ 
.sup.(1) Reported in terms of HIPLC area ratios of principal components 
(i.e. bismaleimide (BMI), maleimidemaleamic acid (MIMA), and bismaleamic 
acid (BMA). 
EXAMPLE 4 
This example serves to illustrate the stabilizing effect of polyamines on 
solutions of mixtures of bismaleimides and maleamic acids and the effect 
of polyamines on curing of such resins as indicated by Dry Rubber Time. 
Dry Rubber Time provides an indication of relative cure rate especially for 
B-staging and, as specified herein, is a measurement of the time for a 
sample of resin solution to cure to a dry rubbery mass on a uniformly 
heated surface. More specifically, about a 1 cc sample of resin (dry or 
solution) is placed on a 200.degree. C., uniformly-heated cure plate 
(Thermo-Electric Company, Cleveland, Ohio). The solvent rapidly evaporates 
as the solution is continuously spread with a spatula forming a molten 
resin. As the resin reacts to form polymer, thin strings can be pulled 
from the resin mass by the spatula. As the reaction continues, the resin 
mass forms into a coherent dry rubbery mass from which polymer strings 
cannot be drawn. The time at which strings are no longer formed is the 
"Dry Rubber Time". A Dry Rubber Time of "0" indicates almost immediate 
gelation of the solution. 
The Dry Rubber Time for the resin mixture of bismaleimide and maleamic 
acids prepared in Example 1 was determined to be greater than three hours 
(about 10,000 seconds). That is, the test was discontinued after three 
hours when molten resin (at 200.degree. C.) failed to form a coherent 
rubbery mass. 
The addition of polyamine to a solution of such mixture provided 
substantially short Dry Rubber Times. Acetone solutions (about 60% solids) 
of the resin mixture of bismaleimides and maleamic acids and various 
polyamines were prepared as indicated in Table 1 by first dissolving the 
polyamine in acetone, then adding the resin mixture with agitation. The 
amount of polyamine is indicated by the ratio of amine groups to acid 
groups. For instance, the mixture of Example 1 was determined by titration 
to have 0.0362 equivalents of acid groups per 100 grams; and diaminoethane 
has 0.0333 equivaents of amine groups per gram (determined by dividing the 
number of amine groups, i.e. "2", by the molecular weight, i.e. "60"). 
Thus, adding 100 grams of the resin of Example 1 to a solution containing 
0.94 grams of diaminoethane provides a solution where the ratio of amine 
groups to acid groups is determined to be about 0.86. 
The results indicated in Table 2 indicate that polyamine can be 
advantageously added to solutions of soluble resin mixtures of 
bismaleimides and maleamic acids to provide exceptionally long stabiliy of 
such solutions, e.g. up to three weeks and longer. Moreover the results 
indicate that certain polyamines can provide exceptionally low Dry Rubber 
Times, e.g. often less than about 5 minutes less, even after three weeks 
of storage. 
TABLE 2 
______________________________________ 
Dry Rubber Time (seconds) 
1 3 
Polyamine R* As made day 6 days 
weeks 
______________________________________ 
Control-No amine 
-- &gt;10,000 -- -- -- 
1,2-diaminoethane 
0.86 -- 545 -- -- 
1,3-diaminopropane 
0.85 -- 165 230 480 
" 1.28 -- 130 200 260 
1,6-diaminohexane 
0.86 120 190 230 400 
" 1.29 120 260 -- 360 
Triaminononane 
0.87 110 170 450 540 
" 1.20 80 -- -- -- 
" 1.73 0 -- -- -- 
Polypropylene oxide 
0.86 -- -- 1400 -- 
diamine.sup.1 
Methylene dianiline 
0.85 -- 170 -- -- 
" 1.71 -- 100 &gt;1200 -- 
" 3.40 -- 70 &gt;1200 -- 
Bis(aminophenoxy- 
0.86 -- 130 &gt;1200 -- 
phenyl) propane 
Bis(aminophenoxy- 
1.72 70 100 &gt;1200 -- 
phenyl) propane 
Diethylene triamine 
1.05 80 90 225 420 
" 1.21 -- 65 -- -- 
" 1.58 -- 40 -- -- 
" 2.10 -- 0 -- -- 
Triethylene tetramine 
1.13 100 100 120 220 
" 1.20 -- 85 -- -- 
" 2.27 -- 0 -- -- 
Tetraethylene 
1.23 70 85 90 100 
pentamine 
Tetraethylene 
1.85 -- 0 -- -- 
pentamine 
Pentaethylene 
1.07 90 -- -- -- 
hexamine 
Pentaethylene 
1.14 85 -- -- -- 
hexamine 
Pentaethylene 
1.29 80 80 90 100 
hexamine 
Pentaethylene 
1.94 -- 0 -- -- 
hexamine 
Polyethylene imine.sup.2 
(2.56 -- 55 -- 55 
wt. %) 
______________________________________ 
.sup.1 Jeffaminem .TM. D230 (Jefferson Chemical Co.) 
.sup.2 Corcat .TM. P18 (Virginia Chemicals Co.) 
*R: ratio of amine groups to acid groups 
EXAMPLE 5 
This example serves to illustrate the preparation of dry resin-impregnated 
cloth and cured laminates according to this invention. 
65 grams of the resin mixture of bismaleimide and maleamic acids prepared 
in Example 1 was added to a solution of 0.975 grams of triethylene 
tetramine in 35 grams of acetone. (The ratio of amine groups to acid 
groups was about 1.13). The solution was used to saturate glass cloth. The 
solution saturated cloth was placed in an air oven (180.degree. C.) for 
about 5 minutes resulting in a dry resin-impregnated cloth (about 38 
percent by weight resin). A laminate was prepared by placing 8 sheets of 
resin-impregnated cloth between two sheets of copper having a density of 
two ounces per square foot and heating in a press for 2 hours at about 
180.degree. C. and 3450 kPa (500 psi). The laminate was removed from the 
press and post cured at 220.degree. C. for 24 hours. 
The laminate was evaluated in accordance with the procedures of 
MIL-P-13949F and determined to have the following properties: 
______________________________________ 
Water Absorption (23.degree. C., 24 hours) 
0.4% 
Dielectric Constant (at 10.sup.6 cps) 
3.5 
Dissipation Factor (at 10.sup.6 cps) 
0.01 
Copper Peel Strength &gt;60 kPa (9 psi) 
______________________________________ 
The laminate was also floated on molten solder (288.degree. C.) for more 
than 10 minutes. The absence of blistering or delamination illustrate 
exceptional resistance to thermal stress. 
EXAMPLE 6 
This example serves to illustrate preferred embodiments of this invention 
where the properties of laminates are effected by the level of maleamic 
acid in mixtures of bismaleimides. 
Laminates were prepared essentially as in Example 5 from materials 
indicated in Table 3. After the post cure at 220.degree. C. the laminates 
were analyzed for visual signs of delamination as indicated by blisters, 
e.g. caused by steam generated from water liberated from ring closure of 
maleamic acids. As reported in Table 3, the laminate prepared from the 
bismaleimide resin having lower levels of maleamic acid had no visible 
blisters; the laminate prepared from the resin having higher levels of 
maleamic acid was severely blistered. 
TABLE 3 
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Bismaleimide 
Mixture TETA.sup.(1) 
(BMI/MIMA/BMA) (g) Blisters 
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80/12/4 0.975 g None 
41/34/10 1.65 g Severe 
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.sup.(1) TETA: triethylene tetramine 
While specific embodiments of the invention have been described, it should 
be apparent to those skilled in the art that various modifications thereof 
can be made without departing from the true spirit and scope of the 
invention. Accordingly, it is intended that the following claims cover all 
such modifications within the inventive concept.