Novel heat-stable imido polymers, well adapted for the production of prepregs, are prepared by copolymerizing (a) at least one N,N'-bisimide with (b) at least one hindered aromatic diprimary diamine, (c) optionally, at least one unhalogenated comonomer other than a bisimide, (d) optionally, an imidazole compound, (e) at least one diamino-s-triazine, and (f) at least one chlorinated or brominated epoxy resin (f1), or N,N'-alkylenebistetrahalophthalimide (f2), or halogenated aromatic compound containing two (meth)-allyloxylated benzene nuclei (f3), or unhalogenated epoxy resin (f4).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to novel imido polymers, and, more 
especially, to novel imido copolymers comprising hindered diamine 
recurring units which have good mechanical and electrical properties and 
which are particularly heat-stable at elevated temperatures. 
2. Description of the Prior Art 
French Patent Application FR-A-2,608,613 describes imido polymers, 
including heat-curable prepolymers, which comprise the product of 
reaction, at a temperature ranging from 50.degree. C. to 300.degree. C., 
between: 
(a) an N,N'-bisimide or a plurality of bisimides of the formula: 
##STR1## 
in which each of the symbols Y, which may be identical or different, is H, 
CH.sub.3 or Cl; and the symbol A is a divalent radical selected from among 
the following: cyclohexylene, phenylenes, 4-methyl-1,3-phenylene, 
2-methyl-1,3-phenylene, 5-methyl-1,3-phenylene and 
2,5-diethyl-3-methyl-1,4-phenylene, and the radicals of the formula: 
##STR2## 
wherein T is a single valence bond or one of the groups: 
##STR3## 
and each of the symbols X, which may be identical or different, is a 
hydrogen atom or a methyl, ethyl or isopropyl radical; 
(b) one or more hindered diprimary diamine(s) selected from among: 
(i) the species corresponding to the general formula: 
##STR4## 
in which each of the symbols R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which 
may be identical or different, is a methyl, ethyl, propyl or isopropyl 
radical; and each of the symbols Z, which also may be identical or 
different, is a hydrogen atom or a chlorine atom; and (ii) the species 
corresponding to the general formula: 
##STR5## 
in which the amino radicals are in a meta or para position relative to 
each other; and each of the symbols R.sub.5, which may be identical or 
different, is a methyl, ethyl, propyl or isopropyl radical; 
(c) optionally, one or more unhalogenated monomer(s) other than a bisimide 
of formula (I) and comprising one or more polymerizable carbon-carbon 
double bond(s); and 
(d) optionally, an imidazole compound. 
One advantage of such imido polymers is provided by the steric hindrance of 
the amine reactant (b), which is responsible for a lower reactivity of the 
constituents of the polymerization mixture when compared with the 
polyaminobismaleimides prepared from unhindered diamines. This lower 
reactivity of the constituents of the polymerization mixture is of special 
interest not only for the production of articles requiring a prepolymer in 
the molten state, but also for the production of articles requiring a 
prepolymer in the form of solution in a solvent. Indeed, the viscosity of 
the prepolymer in the molten state, or that of the solution of the 
prepolymer, changes more slightly and this greatly facilitates the 
processing of the prepolymer, especially in applications requiring a 
working life of a number of hours. 
A second advantage of the imido polymers described in the '613 published 
French application is that such polymers are prepared without requiring 
special precautions from the standpoint of health and safety, given that 
the hindered diamines (b) employed do not present the toxicity hazards 
which are generally associated with unhindered aromatic diprimary amines. 
SUMMARY OF THE INVENTION 
A major object of the present invention is the provision of yet further 
improved imido polymers vis-a-vis those described in said '613 French 
application, said further improved imido polymers differing from the prior 
art by additionally comprising the following two added constituents: 
(1) at least one heterocyclic diprimary diamine selected from among the 
guanamines (or diamino-s-triazines); this constituent enables increasing 
the reactivity of the constituents (a), (b) and optionally (c) of the 
polymerization mixture and, in the case of the molded or shaped objects 
ultimately obtained, results in the provision of properties having high 
values without having to carry out, after the prepolymer has been cured, a 
postcure (or after-bake) stage at a high temperature for a period of time 
ranging from about 10 hours to several tens of hours, depending on the 
temperature which is adopted (it has also been unexpectedly found that 
such high property values are quite close to, and can even be as good as, 
the optimum values attained for these properties when the operation is 
carried out according to the prior art, i.e., in the absence of guanamine 
and indeed conducting a postcure stage); and 
(2) a compound selected from among: a chlorinated or brominated epoxy 
resin); an N,N'-alkylenebistetrahalophthalimide; a product containing two 
phenyl radicals bonded directly via a single valence bond, a divalent 
radical or a bridging atom, in which each phenyl radical is substituted by 
a (meth)allyloxy radical and by at least two chlorine or bromine atoms; 
and unhalogenated epoxy resin; or admixture of two or more than two of the 
above compounds; this constituent enables providing a low coefficient of 
thermal expansion for the final polymers, as well as an excellent 
resistance to combustion, in the case where a halogenated compound is 
employed. 
Another object of the present invention is the provision of improved imido 
polymers comprising the hindered diprimary diamines of the type of those 
of formula (II) containing two hindered 4-aminophenyl radicals, but which 
are bonded together by a divalent group other than --CH.sub.2 --. 
Briefly, the present invention features novel imido polymers which comprise 
the copolymerizates, at a temperature ranging from 50.degree. C. to 
300.degree. C., of: 
(a) at least one N,N'-bisimide having the formula (I) and corresponding 
definitions given above; 
(b) at least one hindered aromatic diprimary diamine; 
(c) optionally, at least one unhalogenated comonomer other than a bisimide 
of formula (I) and containing one or more polymerizable carbon-carbon 
double bonds; and 
(d) optionally, an imidazole compound; 
with the proviso that said at least one hindered aromatic diprimary diamine 
(b) comprises: 
(1) a compound having the general formula: 
##STR6## 
in which each of the symbols R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which 
may be identical or different, is a methyl, ethyl, propyl or isopropyl 
radical; each of the symbols Z, which may be identical or different, is a 
hydrogen atom or a chlorine atom; and the symbol B is a divalent radical 
selected from among: --CH.sub.2 --; 
##STR7## 
(ii) a compound having the general formula: 
##STR8## 
in which the amino radicals are in a meta or para position relative to 
each other; and each of the symbols R.sub.5, which may be identical or 
different, is a methyl, ethyl, propyl or isopropyl radical; 
and with the added proviso that said copolymerizates further comprise: 
(e) at least one substituted guanamine of the formula: 
##STR9## 
in which the symbol R.sub.6 is a linear or branched chain alkyl radical 
having from 1 to 12 carbon atoms such as, for example, a methyl, ethyl, 
propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl or 
dodecyl radical, an alkoxy radical having from 1 to 12 carbon atoms, a 
phenyl radical optionally substituted by 1 to 3 alkyl radicals having from 
1 to 3 carbon atoms, a phenylalkyl radical having from 1 to 3 carbon atoms 
in the alkyl moiety and the benzene nucleus of which may optionally be 
substituted by 1 to 3 alkyl radicals having from 1 to 3 carbon atoms; and 
(f) at least one compound selected from among; 
(f1) a chlorinated or brominated epoxy resin; 
(f2) an N,N'-alkylenebistetrahalophthalimide of the formula: 
##STR10## 
in which each of the symbols U, which may be identical or different, is a 
chlorine or bromine atom; the alkylene radical --C.sub.n H.sub.2 n-- may 
be linear or branched; and n is an integer equal to 1, 2, 3 or 4; 
(f3) a halogenated compound of the formula: 
##STR11## 
in which the symbols U are as defined above; the symbol V is a single 
valence bond, a linear or branched chain alkylene radical --C.sub.n 
H.sub.2n --, with n being equal to 1, 2, 3 or 4, or an oxygen atom; and p 
is an integer equal to 2, 3 or 4; 
(f4) an unhalogenated epoxy resin; and 
(f5) a mixture of two or more of the above-mentioned compounds (f1) to (f4) 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
More particularly according to the present invention, exemplary of the 
above guanamines (e), the following are especially representative: 
2,4-Diamino-6-methyl-1,3,5-triazine; 
2,4-Diamino-6-ethyl-1,3,5-triazine; 
2,4-Diamino-6-butyl-1,3,5-triazine; 
2,4-Diamino-6-nonyl-1,3,5-triazine; 
2,4-Diamino-6-undecyl-1,3,5-triazine; 
2,4-Diamino-6-methoxy-1,3,5-triazine; 
2,4-Diamino-6-butoxy-1,3,5-triazine; 
2,4-Diamino-6-phenyl-1,3,5-triazine; 
2,4-Diamino-6-benzyl-1,3,5-triazine; and 
2,4-Diamino-6-(4-methyl)phenyl-1,3,5-triazine. 
These guanamines are known compounds, certain of which are available 
commercially. The preferred guanamines are 
2,4-diamino-6-methyl-1,3,5-triazine, 2,4-diamino-6-nonyl-1,3,5-triazine, 
2,4-diamino-6-phenyl-1,3,5-triazine and mixtures thereof. 
The amount of the additive (e) generally represents 2% to 30%, and 
preferably 4% to 15%, of the weight of the mixture of bisimide(s) 
(a)+diamine(s) (b)+additive (f)+optionally reactant (c). 
By "chlorinated or brominated epoxy resin (f1)" is intended an epoxy resin 
which has an epoxy equivalent weight ranging from 200 to 2,000 and which 
comprises a glycidyl ether prepared by reacting epichlorohydrin with an 
aromatic derivative which is chlorinated or brominated on the aromatic 
nucleus (or nuclei) and produced from a polyphenol selected from among: 
the bis(hydroxyphenyl)alkanes such as 2,2-bis(4-hydroxyphenyl)propane, 
bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)methylphenylmethane or 
bis(4-hydroxyphenyl)tolylmethanes, resorcinol, hydroquinone, pyrocatechol, 
4,4'-dihydroxydiphenyl, and the products of condensation of the 
abovementioned phenols with an aldehyde. 
By the expression "epoxy equivalent weight" is intended the weight of resin 
(in grams) containing one epoxy functional group 
##STR12## 
A chlorinated or brominated epoxy resin which has an epoxy equivalent 
weight ranging from 250 to 500 is preferred. An epoxy resin (f1) 
comprising a resin derived from the glycidyl ethers of 
bis(hydroxyphenyl)alkanes brominated on the aromatic nuclei, which were 
discussed above in connection with the detailed definition of the resin 
(f1), is especially preferred according to the present invention. 
With regard to the compound (f2) of formula (VI), an 
N,N'-alkylenebistetrabromophthalimide is the preferred. 
N,N'-Ethylenebistetrabromophthalimide is especially preferred according to 
the present invention. 
With regard to the compound (f3) of formula (VII), preferred is a 
bis(allyloxydibromophenyl)alkane of the formula: 
##STR13## 
in which n is an integer equal to 1, 2 or 3. 
2,2-Bis(4-allyloxy-3,5-dibromophenyl)propane is especially preferred 
according to the present invention. 
By "unhalogenated epoxy resin (f4)? is intended an epoxy resin which has an 
epoxy equivalent weight ranging from 100 to 1,000 and which comprises a 
glycidyl ether prepared by reacting epichlorohydrin with a polyphenol 
which is unchlorinated and unbrominated on the aromatic nucleus (or 
nuclei) and selected from among the phenols discussed above in connection 
with the definition of the resin (f1). 
An unhalogenated epoxy resin which has an epoxy equivalent weight ranging 
from 150 to 300 is preferred. An epoxy resin (f4) comprising a resin 
including the glycidyl ethers of bis(hydroxyphenyl)alkanes which are not 
halogenated on the aromatic nuclei and which were discussed above in 
connection with the detailed definition of the resin (f1), is especially 
preferred. 
With regard to the mixtures (f5), preferred is a mixture of two or more of 
the preferred compounds (f1) to (f4) which were referred to above. 
The amount of the additive (f) generally represents 2% to 30%, and 
preferably 3% to 15%, of the weight of the mixture of bisimide(s) 
(a)+diamine(s) (b)+optionally reactant (c). 
It has been established that the amount of chlorine or of bromine which may 
be introduced into the polymers according to the invention by the additive 
(f) is such as to affect certain properties of the cured polymers 
obtained, especially the properties relating to heat stability and the 
adhesiveness of the polymers to metals such as, for example, copper. In 
this respect, the best results are obtained when this amount of chlorine 
or of bromine introduced by the additive (f), expressed as the percentage 
by weight of elemental chlorine or of elemental bromine in relation to the 
weight of the overall mixture of bisimide(s) (a)+diamine(s) (b)+optional 
reactant (c)+additives (e) and (f), represents not more than 8%; this 
amount of chlorine or of bromine preferably ranges from 1 to 6%. The 
amount of chlorine or of bromine can be easily adjusted to the desired 
value by using, for example, epoxy resins (f1) which have a higher or 
lower chlorine or bromine content or by starting with mixtures of 
chlorinated or brominated epoxy resins (f1) with unhalogenated epoxy 
resins (f4), or else by starting with mixtures of compounds (f2) and/or 
(f3) with unhalogenated epoxy resins (f4). 
By way of specific examples of bisimides (a) of formula (I), particularly 
representative are the compounds indicated in French Application 
FR-A-2,608,613, namely: 
N,N'-Meta-phenylenebismaleimide; 
N,N'-Para-phenylenebismaleimide; 
N,N'-4,4'-Diphenylmethanebismaleimide; 
N,N'-4,4'-Diphenyl ether bismaleimide; 
N,N'-4,4'-Diphenyl sulfone bismaleimide; 
N,N'-1,4-Cyclohexylenebismaleimide; 
N,N'-4,4'-(1,1-Diphenylcyclohexane)bismaleimide; 
N,N'-4,4'-(2,2-Diphenylpropane)bismaleimide; 
N,N'-4,4'-Triphenylmethanebismaleimide; 
N,N'-2-Methyl-1,3-phenylenebismaleimide; 
N,N'-4-Methyl-1,3-phenylenebismaleimide; and 
N,N'-5-Methyl-1,3-phenylenebismaleimide. 
These bismaleimides can be prepared according to the processes described in 
U.S. Pat. No. 3,018,290 and British Patent GB-A-1,137,290. According to 
the present invention, N,N'-4,4'-diphenylmethanebismaleimide, either alone 
or mixed with N,N'-2-methyl-1,3-phenylenebismaleimide, 
N,N'-4-methyl-1,3-phenylenebismaleimide and/or 
N,N'-5-methyl-1,3-phenylenebismaleimide is the preferred. 
Exemplary of the hindered diamines (b) of formulae (IV) and (III), 
particularly representative are: 
4,4'-Diamino-3,3'-5,5'-tetramethyldiphenylmethane; 
4,4'-Diamino-3,3',5,5'-tetraethyldiphenylmethane; 
4,4'-Diamino-3,5-dimethyl-3',5'-diethyldiphenylmethane; 
4,4'-Diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane; 
4,4'-Diamino-3,3',5,5'-tetraisopropyldiphenylmethane; 
4,4'-Diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane; 
1,4-Bis(4-amino-3,5-dimethyl-.alpha.,.alpha.-dimethylbenzyl)benzene; 
1,3-Bis(4-amino-3,5-dimethyl-.alpha.,.alpha.-dimethylbenzyl)benzene; 
1,3-Diamino-2,4-diethyl-6-methylbenzene; and 
1,3-Diamino-2-methyl-4,6-diethylbenzene. 
These hindered diamines may be prepared according to the procedures 
described in British Patent GB-A-852,651 and U.S. Pat. No. 3,481,900. 
According to the present invention, 
4,4'-diamino-3,3',5,5'-tetramethyldiphenylmethane, 
4,4'-diamino-3,3',5,5'-tetraethyldiphenylmethane, 4,4'-diamino 
-3,3'-diethyl-5,5'-dimethyldiphenylmethane and mixtures thereof are the 
preferred. 
The amount of N,N'-bisimide(s) (a) and of hindered diamine(s) (b) are 
selected such that the ratio r: 
##EQU1## 
generally ranges from 1.5/1 to 20/1 and, preferably, from 2/1 to 5/1. 
In some cases it may be advantageous to modify the polymers according to 
the present invention by also incorporating a copolymerizable reactant (c) 
and/or an imidazole compound (d). 
As an optional reactant (c) which is suitable, particularly representative 
are the compounds indicated in French Application FR-A-2,608,613, namely: 
(c1) either one or more monomers of the formula: 
##STR14## 
in which the allyloxy or methallyloxy radical is in an ortho, meta or para 
position in relation to the carbon atom of the benzene ring which is 
bonded to nitrogen; 
(c2) a compound comprising a mixture of (i) a monomer of the formula: 
##STR15## 
in which the allyloxy or methallyloxy radical is in an ortho, meta or para 
position in relation to the carbon atom of the benzene ring which is 
bonded to nitrogen, with: (ii) at least one monosubstituted derivative of 
the formula: 
##STR16## 
and optionally with (iii) one or more distributed derivative(s) of the 
formula: 
##STR17## 
In the abovementioned compound employed as reactant (c2), the proportions 
of the various constituents of the mixture of the compounds of formulae 
(IX), (X) and optionally (XI) may vary over wide limits. In general, the 
proportions of the constituents are selected within the following limits 
(expressing the weight percentage of each of the constituents in the 
mixture): at least 30%, and preferably from 50% to 80% of 
N-(meth)allyloxyphenylmaleimide of formula (IX); from 5% to 50% and 
preferably from 10% to 35% of mono-(meth)allyl-substituted derivative(s) 
of formula (X); and from 0% to 20% and preferably from 0% to 15% of 
di-(meth)allyl-substituted derivative(s) of formula (XI), with the sum of 
the constituents in each case having to be equal to 100% by weight; or 
(c3) one or more substituted heterocyclic ring(s). 
It should be appreciated that mixtures (cl +c3) or (c2+c3) may be employed 
as reactant (c). 
With regard to the optional reactant (cl), this advantageously comprises: 
N-(2-Allyloxyphenyl)maleimide; 
N-(3-Allyloxyphenyl)maleimide; 
N-(4-Allyloxyphenyl)maleimide; 
N-(2-Methallyloxyphenyl)maleimide; 
N-(3-Methallyloxyphenyl)maleimide; 
N-(4-Methallyloxyphenyl)maleimide; and mixtures thereof. 
The maleimides of formula (IX) are known compounds which are described in 
European Patent Application EP-A-0,208,634. 
With regard to the optional reactant (c2), the crude product produced by 
the process described in European Patent Application EP-A-0,274,967 is 
preferably employed as the compound containing a mixture of 
N-(meth)allyloxyphenylmaleimide of formula (IX) with one or more 
(meth)allylated substitution derivative(s) of formula(e) (X) and 
optionally (XI). 
With regard to the optional reactant (c3), this is advantageously selected 
from among: vinylpyridines, N-vinylpyrrolidone, allyl isocyanurate, 
vinyltetrahydrofuran and mixtures thereof. 
With regard to the amount of optional reactant (c), this generally 
represents less than 60%, and preferably from 2% to 25%, of the total 
weight of the reactants (a) and (b). 
The optional imidazole compound (d) advantageously has the general formula 
indicated in French Application FR-A-2,608,613, namely: 
##STR18## 
in which each of R.sub.7, R.sub.8, R.sub.9 and R.sub.10, which may be 
identical or different, is a hydrogen atom, an alkyl or alkoxy radical 
having from 1 to 20 carbon atoms, or a vinyl, phenyl or nitro radical, 
with the proviso that R.sub.9 and R.sub.10 may together form, with the 
carbon atoms from which they depend, a single ring member such as, for 
example, a benzene ring, and with the further proviso that R.sub.7 may 
comprise a carbonyl group bonded to a second imidazole ring. 
As specific examples of imidazole compounds (d), particularly 
representative are imidazole or glyoxaline, 1-methylimidazole, 
2-methylimidazole, 1,2-dimethylimidazole, 1-vinylimidazole, 
1-vinyl-2-methylimidazole, benzimidazole and carbonyldiimidazole. 
The optional imidazole compound (d) is employed in catalytic amounts. 
Depending on the nature of the imidazole compound and depending on the 
desired rate of polymerization at the processing stage, the imidazole 
compound is advantageously employed in a proportion which generally ranges 
from 0.005% to 1% by weight relative to the combination of reactants 
(a)+(b)+optionally (c) and preferably ranges from 0.01% to 0.5%. 
It should be appreciated that the proportions of the constituents of the 
polymerization recipe in accordance with the present invention which are 
generally employed are selected within the ranges indicated above such as 
to provide a total number of carbon-carbon double bonds [introduced by 
(a)+optionally (c)+optionally (f3)]and, if appropriate, of epoxy groups 
[introduced by (f1) or (f4)] greater than the total number of amino groups 
[introduced by (b) +(e)]. 
Various adjuvants may be incorporated at various times in the polymers of 
the invention. These adjuvants, which are typical and are well known to 
this art, may be, for example, stabilizers or degradation inhibitors, 
lubricants or demolding agents, colorants or pigments, or pulverulent or 
particulate fillers such as silicates, carbonates, kaolin, chalk, powdered 
quartz, mica or ballotini. It is also possible to incorporate adjuvants 
which modify the physical structure of the product obtained such as, for 
example, blowing agents or fibrous reinforcing agents such as, especially, 
carbon, polyimide or aromatic polyamide fibrils or whiskers. 
The polymers according to the invention may be prepared by direct heating 
of the bisimide(s) (a), of the amine reactant (b) and of the additives (e) 
and (f), optionally in the presence of the reactant (c) and/or of the 
imidazole compound (d), at least until a homogeneous liquid mixture is 
produced. The temperature may vary as a function of the physical state of 
the compounds present, but generally it ranges from 50.degree. C. to 
300.degree. C. It is advantageous to bring and to maintain the starting 
compounds to an intimately admixed state before and during the heating, 
for example with the aid of good stirring. When the reactant (c) and/or 
the imidazole compound (d) is (are) employed, it is (they are) preferably 
added to the well-stirred reaction mixture after the mixture of 
(a)+(b)+(e)+(f) has been melted. When the compound (d) is particularly 
active, and in order to prevent its encapsulation in the polymer structure 
generated, it is desirable to add it in a solvent or diluent which is 
compatible with the reaction mixture; it was found that it could be 
advantageous to employ one of the polar organic liquids which are referred 
to below as a solvent or diluent. 
The preparation of the polymers according to the invention can also be 
carried out by heating the mixture of the reactants in the presence of 
variable amounts of an organic diluent which is liquid over at least a 
part of the range 50.degree. C.-250.degree. C. Among such diluents, 
particularly representative are the aromatic hydrocarbons such as xylenes 
and toluene, halogenated hydrocarbons such as chlorobenzenes, polar 
organic liquids such as dioxane, tetrahydrofuran, dibutyl ether, 
dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, 
dimethylacetamide, cyclohexanone, methyl glycol and methyl ethyl ketone. 
The polymer solutions or suspensions may be employed as such for many 
applications; the polymers may also be isolated, for example by 
filtration, optionally after precipitation by means of an organic diluent 
which is miscible with the solvent employed. 
It should be appreciated that the properties of the polymers according to 
the invention may vary to a great extent, especially as a function of the 
precise nature of the reactants employed, of the proportions of reactants 
which are selected and of the precise temperature conditions which are 
adopted within the abovementioned range. With regard to the polymers 
obtained, these may be cured polymers, insoluble in the usual solvents 
such as, for example, the polar organic liquids mentioned in the preceding 
paragraph, and exhibiting no appreciable softening below the temperature 
at which they begin to degrade. 
However, these polymers can also exist in the form of prepolymers (P), 
soluble in polar organic solvents such as, for example, those referred to 
above and exhibit a softening point at a temperature below 200.degree. C. 
(in general this softening point ranges from 50.degree. C. to 150.degree. 
C.). These prepolymers may be prepared in bulk by heating the mixture of 
the reactants until a homogeneous or pasty product is obtained, at a 
temperature which generally ranges from 50.degree. to 180.degree. C. for a 
period of time which may range from a few minutes to a few hours, this 
period being proportionately shorter the higher the temperature adopted. 
Before the mixture of the reactants is subjected to heating, it is 
advantageous, here too, to mix it thoroughly by stirring beforehand. Here 
again there is a preferred method of using the reactant (c) and/or the 
optional imidazole compound (d), and it is that indicated above in 
connection with the direct preparation of cured polymers. The preparation 
of the prepolymers can also be carried out in the presence of variable 
amounts of a diluent which is liquid over at least a part of the range 
50.degree.-180.degree. C. In this context, the polar organic liquids 
referred to above can be advantageously used as a diluent. 
The prepolymers (P) may be employed in the bulk liquid state, simple hot 
casting being sufficient for shaping and the production of molded 
articles. It is also possible, after cooling and milling, to employ them 
in the form of powders which are remarkably well suited for compression 
molding operations, optionally in the presence of fillers in the form of 
powders, spheres, granules, fibers of flakes. In the form of suspensions 
or of solutions, the prepolymers (P) may be employed for the production of 
coatings and of preimpregnated intermediate articles (prepregs) whose 
reinforcement may comprise fibrous substances based on aluminum or 
zirconium silicate of oxide, carbon, graphite, boron, asbestos or glass. 
These prepolymers (P) may also be employed for the production of cellular 
materials after incorporation of a blowing agent such as, for example, 
azodicarbonamide. 
In a second stage, the prepolymers (P) may be cured by heating them to 
temperatures on the order to 300.degree. C., generally ranging from 
150.degree. to 300.degree. C.; an additional shaping may be carried out 
during the curing, optionally under vacuum or under superatmospheric 
pressure, it also being possible for these operations to be consecutive. 
In a preferred embodiment of the present invention, the operation is 
carried out in two stages, the first stage entailing heating the mixture 
of the reactants to from 50.degree. to 180.degree. C. to form a prepolymer 
(P), the second stage entailing curing the prepolymer (P) after it has 
been shaped as desired, by heating to temperatures on the order of 
300.degree. C., generally ranging from 150.degree. C. to 300.degree. C. 
In another preferred embodiment of the present invention, the operation is 
carried out in two stages, but employing in the first stage a continuous 
process for the preparation of the prepolymer (P), entailing separately 
introducing into a kneader containing an extruder screw: 
(i) on the one hand, the bisimide (a) in the divided solid state; and 
(ii) on the other hand, the several reactants comprising the amine reactant 
(b) and the additive (e) in the solid, liquid or molten state, and the 
additive (f) in the liquid state with, if need be, the reactant (c) in the 
liquid state and/or the imidazole compound (d) in the solid state or in 
solution, it being possible for the various reactants of this group 
themselves to be introduced, for their part, together or separately, 
optionally in the presence of a diluent which is liquid over at least a 
part of the range 50.degree.-180.degree. C. 
By the expression "kneader containing an extruder screw" is intended an 
apparatus which does not have any dead region when the substance is 
advanced forward. Apparatus of this type which may comprise one or more 
screws is described in the text by E.G. Fisher, Extrusion of Plastics 
(Interscience Publishers 1964), pages 104 to 108. These kneaders may 
contain two endless screws meshing intimately with each other and rotating 
in the same direction; an apparatus of this type, equipped more 
particularly for the preparation of alkali metal terephthalates, is 
described in French Patent FR-A-1,462,935. Another variety of kneaders 
which can be employed is apparatus containing an endless screw with 
interrupted flights performing a rotary movement and an oscillating 
movement in the direction of the axis simultaneously, which is housed in 
an enclosure comprising teeth which interact with the interrupted flights 
of the screw. Apparatus of this type is described in French Patents 
FR-A-1,184,392, 1,184,393, 1,307,106 and 1,369,283. 
The polymers according to the invention are of interest to industrial 
sectors which require materials having good mechanical and electrical 
properties, as well as great chemical inertness at temperatures of 
200.degree. to 300.degree. C. For example, they are suitable for the 
manufacture of plate or tubular insulators for electrical transformers, 
supports for printed circuits, and the like. The preimpregnated articles 
can be employed for the production of components having various shapes and 
functions in many fields of application such as, for example, in the 
electrical and electronics industries. These components, deemed laminates, 
which may be articles of revolution, are obtained by arraying a number of 
layers of prepregs onto a form or a support. The prepregs can also be 
employed as reinforcements or as means for repairing damaged components. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific example is given, it being understood that 
same is intended only as illustrative and in nowise limitative. 
EXAMPLE 
The following constituents were introduced at ambient temperature into a 
glass reactor fitted with an anchor-type stirrer; 
(i) 77.5 g (0.216 moles) of N,N'-4,4'-diphenylmethanebismaleimide; 
(ii) 14.5 g (0.047 moles) of 
4,4'-diamino-3,3',5,5'-tetraethyldiphenylmethane; 
(iii) 8 g (0.043 moles) of 2,4-diamino-6-phenyl-1,3,5-triazine (or 
benzoguanamine); and 
(iv) 10 g of a brominated epoxy resin resulting from the condensation of 
tetrabrominated bisphenol A with epichlorohydrin; it had an elemental 
bromine content on the order to 50% by weight and an epoxy equivalent 
weight of 450; it is available commercially under the registered trademark 
Qatrex of the Dow company, type 6410. The amount of bromine introduced by 
the epoxy resin, expressed by the percentage by weight of elemental 
bromine in relation to the weight of the combination of 
bisamide+diamine+copolymerizable monomer (N-vinylpyrrolidone: cf. 
below)+guanamine+epoxy resin, was equal to 4.2%. This resin was introduced 
into the reactor in the form of a solution in 10 g of cyclohexanone. 
The reactor was immersed in an oil bath preheated to 160.degree. C. and the 
mixture was stirred until the ingredients introduced melted completely and 
a homogeneous mass was obtained. The length of time of this stage was 5 
minutes. The molten mixture thus obtained was cooled to 140.degree. C. and 
10 g of N-2-vinylpyrrolidone were introduced, and the entire mass was then 
permitted to react under stirring for 28 minutes. 
A prepolymer which had a softening point close to 80.degree. C. was thus 
obtained. The "softening point" was the approximate temperature at which a 
glass rod 6 mm in diameter could easily penetrate a few millimeters into 
the prepolymer. This prepolymer was soluble in solvents such as, for 
example, N-methylpyrrolidone, dimethylformamide and cyclohexanone. 
Prepregs and 10-ply laminates (10 layers of prepregs) were manufactured 
from a first batch of prepolymer prepared as indicated above. To this end, 
a solution of prepolymer at a concentration of 50% by weight in 
N-methylpyrrolidone was employed to coat a glass fabric manufactured by 
the Porcher company under reference 7628, whose weight per unit area was 
200 g/m.sup.2 and which had been subjected to a treatment with 
gamma-aminopropyltriethoxysilane (Union Carbide silane A 1100). The 
impregnated fabric contained 40 g of prepolymer per 60 g of fabric; it was 
dried for 5 minutes in a ventilated atmosphere at 160.degree. C. 10 
squares (15 .times.15 cm) were then cut therefrom and these were stacked 
with a copper sheet 35 .mu.m in thickness, placed on one of the outer face 
surfaces of the stack, and the assembly was placed between the platens of 
a press under the following conditions: 
______________________________________ 
(a) pressure 40 .times. 10.sup.5 Pa, 
(b) heating of the press platens 
2 hours at 190.degree. C. 
______________________________________ 
No postcure was carried out and the adhesion of the copper to the 10-ply 
laminate was examined directly: this adhesion, measured with a tensometer 
by pulling the copper at an angle of 90.degree. (according to MIL Standard 
P 55 617 B using a pulling speed of 55 mm/min was on the order of 19.0 
N/cm. Under the same conditions, the 10-ply copper laminate manufactured 
from a prepolymer prepared as indicated above but in the absence of 
benzoguanamine resulted in an adhesion on the order of 16.0 N/cm; this 
value could be increased to about 19 N/cm, but on condition of subjecting 
the 10-ply laminate to a postcure at 200.degree. C. for 16 hours. 
Prepregs containing 45% by weight of prepolymer and laminates comprising 5 
plies were prepared from a second batch of prepolymer under the conditions 
described above (it should be noted that no copper sheet was employed 
here) without performing a postcure. Combustibility measurements were 
carried out according to the UL 94 vertical test (thickness of the test 
specimens based on laminate: 0.8 mm; the proportion of resin in the 
laminate was approximately 40% by weight; the combustion time is given in 
seconds after conditioning for 48 hours at 23.degree. C. and 50% relative 
humidity. The classification was established from an average of 10 
results: 5 test specimens and 2 tests on each specimen): 
______________________________________ 
(a) combustion time 3 s; 
(b) classification VO. 
______________________________________ 
Prepregs containing 40% by weight of prepolymer and laminates comprising 22 
plies were prepared from a third batch of prepolymer under the conditions 
described above (no copper sheet was employed here either) without 
performing a postcure in this case either. Measurements of thermal 
expansion coefficient along the Z axis of the laminates were carried out 
(thickness of the laminate-based specimens: 3 mm). These measurements were 
carried out by thermomechanical analysis (TMA), using a Du Pont model 982 
instrument, with a rate of temperature increase of 10 K/min under nitrogen 
atmosphere. The value determined for this coefficient was on the order of 
42.times.10.sup.-6 m m.sup.-1 K.sup.-1. Under the same conditions, the 
22-ply laminate manufactured from a prepolymer prepared in the absence of 
benzoguanamine exhibited a thermal expansion coefficient along the Z axis 
on the order of 60.times.10.sup.-6 m m.sup.-1 K.sup.-1 ; this value could 
be reduced to about 40.times.10.sup.-6 m m.sup.-1 K.sup.-1 but on 
condition of subjecting the 22-ply control laminate to a postcure at 
200.degree. C. or 16 hours. 
Furthermore, the glass transition temperature of the cured polymer which 
was evaluated during the measurements performed by thermomechanical 
analysis, was determined to be equal to 200.degree. C. whereas it was 
150.degree. C. in the absence of benzoguanamine. 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims, including equivalents thereof.