The production of fire-resistant resins particularly useful for making laminates with inorganic fibers such as graphite fibers is discussed. The resins are by (1) condensation of an ethylenically unsaturated cyclic anhydride with a bis(diaminophenyl) phosphine oxide, and (2) by addition polymerization of the bisimide so obtained. Up to about 50%, on a molar basis, of benzophenonetetracarboxylic acid anhydride can be substituted for some of the cyclic anhydride to alter the properties of the products. Graphite cloth laminates made with these resins show 800 C char yields greater than 70% by weight in nitrogen. Limiting oxygen indexes of more than 100% are determined for these resins

Fohlen, G. M.

Parker, J. A.

Varma, I. K.

English

NASA Technical Reports Server

SR - r & u r . + V Q  
G/30/81 XR 4 9 276,344 
United States Patent 1191 
Varma et al. 
[111 4,276,344 
[45] Jun. 30, 1981 
1541 PHOSPHORUS-CONTAINING BISIMIDE 
RESINS 
[76] Inventors:. Robert A. Frosch, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Indra K. Varma, 
George M. Fohlen, John A. Parker 
[21] Appl. No.: 175,452 
[22] Filed: Aug. 5, 1980 
[51] Int. c 1 . 3  ................................................ B32B 7/00 
[52] U.S. Cl. .................................... 428/260; 428/367; 
428/408; 428/902; 428/920; 526/262; 528/228; 
528/322 
[58] Field of Search ................ 526/262; 528/228, 322; 
428/260, 367,408, 902, 920 
r561 References Cited 
U.S. PATENT DOCUMENTS 
2,444,536 7/1948 Searle ........................ 260/326.5 FM 
Primary Examiner-James J. Bell 
Attorney, Agent, or Firm-Darrell G. Brekke; John R. 
Manning 
1571 ABSTRACT 
Fire-resistant resins particularly useful for making lami- 
nates with inorganic fibers such as graphite fibers, are 
made by (1) condensation of an ethylenically unsatu- 
rated cyclic anhydride with a bis(diaminopheny1)phos- 
phine oxide, and (2) by addition polymerization of the 
bisimide so obtained. Up to about 50%, on a molar basis, 
of benzophenonetetracarboxylic acid anhydride can be 
substituted for some of the cyclic anhydride to alter the 
properties of the products. Graphite cloth laminates 
made with these resins have shown 800' C. char yields 
greater than 70% by weight in nitrogen. Limiting oxy- 
gen indexes (LOI) of more than 100% have been deter- 
mined for these resins, as per ASTM D 2863-4. 
6 Claims, No Drawings 
- r-" 
https://ntrs.nasa.gov/search.jsp?R=19810018734 2020-03-21T09:36:07+00:00Z
4,276,344 
1 
PHOSPHORUS-CONTAINING BISIMIDE RESINS 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; 42 U.S.C. 2457). 
TECHNICAL FIELD 
This invention relates to addition polyimide resins 
and to fiber or fabric-reinforced composites made from 
them. 
BACKGROUND ART 
Strong light-weight composites can be made by em- 
bedding various types of fibers or fabrics in a resin 
matrix. The polymer used for such a matrix is generally 
an epoxy resin, although several other resins such as 2o 
phenolic, novolac, poly(ether sulfone), poly(pheny1 
sulfone), and bismaleimide resins have also been used 
for certain applications. As fibers or fabrics, carbon and 
graphite products have been quite useful in the compos- 
ite structures. 
The search for flame resistant mate& to form lami- 
nates that can be used with greater safety in places such 
as aircraft cabins, has led to the selection of high tem- 
perature resins such as bismaleimides which have a high 
anaerobic char yield (Scientific & Technological Aero- 
space Reprints, 1976, 14-16, (Abstract N76-25354)), and 
to the inclusion of phosphorus-containing compounds 
either in a mixture with or as an integral part of the resin 
used as matrix. Searle, in US. Pat. No. 2,444,536, dis- 
closes a widely used method for the preparation of 35 
maleimide polymers. As to the use of phosphorus-con- 
taining compounds, Kourtides et al. (Proceedings of the 
Adhesive for Industry Conference, El Segundo, Calif., 
June 24-25, 1980) have shown substantial improvement 
in various properties of certain epoxy resins by prepar- 
ing them with bis(3-aminopheny1)methylphosphine 
oxide or its bisphenol analog, instead of the conven- 
10 
15 
25 
30 
40 
0 
2 
DISCLOSURE OF THE INVENTION 
The objects of this invention have been accomplished 
by the preparation of bisimides containing phosphorus 
in the main chain as well as olefinic endgroups which 
can be thermally polymerized to form resins and lami- 
nates that can be virtually incombustible in pure oxygen 
at 300" C. 
The bisimides are formed by condensation of an un- 
saturated cyclic aliphatic dibasic acid anhydride such as 
maleic anhydride with a bis(aminopheny1)alkylphos- 
phine oxide. Aromatic dianhydrides such as benzophe- 
nonetetracarboxylic acid dianhydride may be incorpo- 
rated into the bisimides to lengthen the ultimate poly- 
meric chain. 
DETAILED DESCRIPTION OF THE 
INVENTION 
The bisimides of the invention are condensation prod- 
ucts of an unsaturated cyclic anhydride with a phos- 
phorus-containing aromatic diamine, as illustrated by 
the following reactions: 
0 (0 
0 II 
The monoimide formed can be converted further to the 
bisimide by reaction with more maleic anhydride. On 
the other hand, it may be condensed with an aromatic 
dianhydride to produce a larger polymerizable mole- 
cule: 
0 0 
tional diamine or phenol monomers or curing agents of 
the art. In summary, however, it can be stated that 
while the introduction of phosphorus into organic poly- 
mers has generally resulted in reduced flammability, 60 
increased adhesion, and better solubility in polar sol- 
vents, none of the resins used in the composite art are 
nonflammable. 
The principal object of the present invention is to 
provide greatly improved new phosphorus-containing 65 
matrix resins that can be used for the fabrication of 
improved graphite fiber or cloth composites, and adhe- 
sives. 
In addition to the maleic anhydride shown in the 
above reactions, there can be used similar unsaturated 
cyclic anhydrides such as dichloromaleic anhydride, 
citraconic anhydride, as well as other substituted maleic 
anhydrides in which the hydrogen atoms have been 
replaced by lower alkyl groups or halogen atoms, pref- 
erably chlorine or fluorine. 
The phosphine oxide component of the bisimides of 
this invention is a bis(aminopheny1) type as shown by 
the formula in reaction I in which R stands for a methyl, 
ethyl or phenyl group. The preferred phosphine oxide, 
that with the methyl group, can be made by the method 
4,276,344 
3 
of Arbuzov et al. [Zh. Obshch. Khim. 18, 2008 (194811 
which involves the reaction of triphenylphosphine with 
methyl iodide, followed by treatment with potassium 
hydroxide, nitration, and reduction of the nitro groups 
to amino groups. 
The process for making bisimides from the com- 
pounds just discussed has been disclosed by Searle (U.S .  
Pat. No. 2,444,536), as mentioned earlier. Reactions I 
and I1 take place preferably in a polar solvent such as 
dimethylformamide and the product is generally iso- 
lated by pouring the reaction mixture in a non-solvent 
liquid. The reactants, i.e. the diamine and the anhydride 
components are used in substantially stoichiometric 
proportions, although an excess of up to 10% of either 
component may be employed if desired. The resulting 
bisimides can be cured at temperatures preferbly within 
the range of 235" to 290" C. The resins produced ac- 
cording to the process just described are suitable for 
many applications in which good adhesion and excel- 
lent resistance to heat, fire, solvents, and chemicals are 
required. In the aerospace industry, the new resins may 
be used as adhesives and as matrix material for fiber- 
reinforced light-weight composites. 
To fabricate one type of composite, preimpregnated 
fabrics are first prepared by coating a graphite cloth, 
e.g. an 8-hamess satin-weave designed as style 133 fab- 
ric, with a solution of a bismaleimide in dimethylform- 
amide, and dried at 160"-170" C. in a ventilated oven for 
15 minutes. The dried prepregs are then stacked (4 or 9) 
plies and pressed between aluminum plates covered 
with a polytetrafluoroethylene release film. The result- 
ing laminate is then cured in a flat platen press at 232" C. 
at a pressure of 125 psi for 95 minutes. Post curing is 
done at 300" C.  for 70 minutes. 
The invention will now be illustrated in operational 
detail by the following examples which are not intended 
to limit its scope as defined in the appended claims. 
EXAMPLE 1 
Bis(3-aminopheny1)methylphosphine oxide, 4.92 g 
(20 mmol), was placed in a flask with dimethylformam- 
ide, 20 ml. This was stirred until a solution was ob- 
tained. Maleic anhydride, 4.312 g (44 mmol), was added 
in two portions over a period of ten minutes and the 
resulting solution was kept stirring overnight at room 
temperature and then for 35 minutes longer at 145"&5" 
C. The bismaleimide produced was precipitated by 
pouring the solution, after cooling, into ice-cold water. 
The product was purified from methanol and petroleum 
ether. Elemental analysis showed the following results: 
C, 61.8%; H, 3.8%; N, 6.9%; P, 7.2%; and 0, 19.2%. 
These values substantially correspond to those calcu- 
lated for the formula C21H505N2P1 namely: C, 62.1%; 
H, 3.7%; N, 6.9%; P, 7.6%; and 0, 19.7%. 
EXAMPLE 2 
In this preparation, benzophenonetetracarboxylic 
dianhydride (BTDA) was substituted for half of the 
maleic anhydride used in Example 1. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
5 5  
4 
results were: C, 63.8%; H, 3.8870; N, 5.7%; and P, 
6.23%. Values calculated for the formula 
C15H32011N4P2: C, 65.24%; H, 3.41%; N, 5.97%; P, 
6.6%; and 0, 18.7%. 
EXAMPLE 3 
Dichloromaleic anhydride, 1.66 g (1 1 mmol), was 
used here with the diamine of Example 1, 1.23 g (5 
mmol). These materials were dissolved separately in 
glacial acetic acid at room temperature and the solu- 
tions were mixed and refluxed gently during 2.5 hours. 
After cooling, the solution was poured in water and the 
precipitated imide was purified from toluene: acetone 
and hexane. Elemental analysis showed: C, 47.02%; H, 
2.23%; N, 5.43%; P, 5.72%; and C1, 25.10%. The value 
calculated for C21HllC1405N2P were C, 46.5%; H, 
2.0%; N, 5.2%; P, 5.7%; and C1, 25.8%. 
EXAMPLE 4 
The diamine of Example 1, 2.46 g (10 mmol), was 
dissolved in dimethylformamide, 10 ml, containing SO- 
dium acetate, 1 g. Citraconic anhydride, 2.85 g (25 
mmol), was then added and the solution stirred for 
about 3 hours. Acetic anhydride, 3 ml, was introduced 
and stirring continued for two hours. After cooling, 
pouring in water, filtering, and recrystallizing from 
methanol and petroleum ether, the imide obtained was 
analyzed to contain: C, 62.27%; H, 4.48%; N, 6.6%; and 
P, 7.18%. Calculated values for C23H1905N~P were: C, 
63.5%; H, 4.3%; N, 6.4%; and P, 7.14%. 
EXAMPLE 5 
The same diamine, 2.46 g (10 mmol), was added and 
the solution stirred for nearly 90 minutes. Citraconic 
anhydride, 1.23 g (11 mmol), was introduced and the 
stirring continued for another 90 minutes. The bisimide 
was precipitated and purified as in Example 4. Analysis 
showed C, 61.3%; H, 4.4%; N, 6.3%; and P, 5.8%. 
Values calculated for C22H1705N2P: C, 62.86%; H, 
4.05%; N, 6.66%; P, 7.38%; and 0, 19.05%. 
EXAMPLE 6 
Still the same amine, 1.23 g, (5 mmol), was dissolved 
in dimethylformamide, 5 ml, containing sodium acetate, 
0.5 g. Citraconic anhydride, 0.615 g (5.5 mmol), was 
added to the solution. After 90 minutes of stirring, di- 
chloromaleic anhydride, 0.915 g (5.5 mmol), was intro- 
duced and stirring was continued for 90 minutes. The 
resulting bisimide was precipitated and purified in the 
usual manner. Elemental analysis showed: C, 54.4%; H, 
3.4%; N, 6.3%; P, 7.0%; 0, 15.9%; and C1, 14.0%. The 
calculated values for C22Hpj05N2PC12 were: C, 
54.09%; H, 3.07%; N, 5.74%; 0, 16.39%; P, 6.35%; and 
Some physical properties of laminates made with the 
new resins and graphite cloth, in the manner already 
described, were determined. On comparison with the 
laminates of the art, and for most contemplated uses, 
these properties were generally satisfactory. Some of 
C1, 14.3470. 
The diamine, of Example 1 ,492  g (20 mmol), was 60 the comparative data is shown in Table 1. 
TABLE 1 again dissolved in the formamide, 20 ml, and maleic anhydride, 2.15 g (22 mmol), added in two portions. 
Tensile Tensile Short Beam Flexural 
Strength Modulus Shear Strength (1 1 mmol), was introduced and stirring was continued E:rt (MN/m*) (GN/mZ) (MN/m2) (MN/m2) 
413 50 37 863 
690 80 75 940 
The solution was stirred for one hour. BTDA, 3.54 g 
overnight. After further stirring at 145"+-5" C. for 50 65 
minutes, the solution was cooled and poured in water. resin 
EPOXY 
The precipitated bismaleimide was purified from me- phenolic 580 73 41 515 
thano1:acetone and petroleum ether. Elemental analysis BismaleimideAi 600 79 70 820 
5 
4,276,344 
6 
TABLE I-continued TABLE 2-continued 
Flame and Heat Resistance of 
Graphite Cloth Laminates 
Cure 
Tensile Tensile Short Beam Flexural 
Component Strength Modulus Shear Strength 
Resin (MN/m2) (GN/m2) (MN/m2) (MN/m2) 5 
BismaleimideB" - - 38 ' 610 ature Time at 800' C. LO1 
Temper- Char Yield 
Resin ("C.) (min.) (% weight) (% volume) 
'made with methvlenedianiline 
Example 4 290 15 58 - 
Example 5 315 30 57 
10 Example6 290 30 52 - 
- 'hade with diaminodiphenylether 
Some Of the mechanical properties Of the T h e  curinn reaimes for the fint Seven resins in the table involved conventional 
laminates made with the resins of the invention may be conditionsdesi&d to optimize the properties reported, for instance, the epoxy resin 
was cured a total of 250-290 minutes at a graduated temperature from 23 to 182' C 
"'Made with diaminodiphenylether 
'The LO1 has been determined on this samole because the resin has the lowst  
altered selectively and favorably by using a different "Made with methylenedianiline 
unsaturated anhydride component and a different phos- 
phe oxide component, as well as mixtures of said 
ponents, all chosen from the substances encompassed by 
15 phosphorus contact and the highest char yieid, thus being both more economical 
and satisfactory. The resins of Example 1 and 4 to 6. which contain more phosphorus 
are expected to show LOIS of e q d  quality. 
the claims. The properties may also be altered some- 
what by varying the processing parameters. 
present invention were measured by submitting lami- 
nates made with the resin and graphite cloth to conven- We claim: 
tional tests, namely thermogravimetric analysis carried 1. A bisimide obtained by the condensation reaction 
out in a nitrogen atmosphere at a heating rate of 10" C. 25 Of a PolWerizable ethylenicW unsaturated cyclic 
anhydride with a phosphorus-containing diamine of the 
formula per minute, and the oxygen index method for measuring 
the flammability of plastics (A.S.T.M. D 2863-74). The 
composites were made in the manner earlier described 
and the results of the tests are compared to those of 3o 
prior art laminates shown in Table 2. 
As these results demonstrate, the heat and fire resis- 
tance of graphite composites made with the resins of 
especially in terms of limit- 
ing oxygen index. 
The flame and heat resistance of a typical resin of the 20 this invention is 
[ H2N@fp(o)R' 
TABLE 2 
Flame and Heat Resistance of 
Graphite Cloth Laminates 
Cure 
Temper- Char Yield 
ature Time at 800' C. 
Resin ("C.) (min.) (% weight) 
EPOXY 180' 200' 38 
Phenolic 245 240 46 
BismaleimideA" to 315 115 50 
- 46 BismaleimideB"' - 
Phenolic-novolak - - 46 
Polyethersulfone - - 40 
Polyphenylsulfone - - 47 
Example 1 270 30 62 
Example 2'" 290 30 70 
Example 3 290 15 65 
in which R stands for a methyl, ethyl, or phenyl group. 
2. The bisimide of claim 1 wherein the anhydride is 
selected from the class consisting of maleic anhydride, 
dichloromaleic anhydride, citraconic anhydride, and 
3. The bisimide of claim 2 wherein up to 50% of the 
40 molar quantity of the cyclic anhydride is replaced by 
4. The bisimide of claim 2 wherein the diamine is 
5. A light weight laminate that comprises inorganic 
45 fibers embedded in a resin formed by the addition poly- 
6. The laminte of claim 5 where the inorganic fibers 
35 
LO1 mixtures thereof. 
41 
46 benzophenonetetracarboxylic acid dianhydride. 
- 
47 bis(3-aminopheny1)methylphosphine oxide. 
50 
54 
52 
- 
> 100 
(% volume) 
merization of the bisimide of claim 1. 
are in the form of a graphite cloth. 
- * * * * *  
50 
55 
60 
65 
. 5. 


Phosphorus-containing bisimide resins

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