FR2624124A1 - DIAMINE-FREE IMIDE GROUP POLYMERS AND PROCESSES FOR THEIR PREPARATION - Google Patents

Abstract

New thermally stable polymers containing imide groups. More precisely, these polymers are obtained by reaction, at a temperature ranging from 50 DEG C to 300 DEG C, between: a) an N, N'-bismaleimide, b) an acrylate reactant consisting especially of a novolac epoxy(meth)acrylate, c) an imidazole compound, and d) a chlorinated or brominated epoxy resin, the latter being taken by itself or mixed with an unchlorinated or unbrominated resin.

Description

dans laquelle
les symboles Y, identiques ou différents, représentent chacun un atome d'hydrogène, un radical néthyle ou un atome de chlore ;
le symbole A représente un radical divalent choisi dans le groupe constitué par les radicaux : cyclohexylènes ; phénylènes ; méthyl-4 phénylène-1,3 ; méthyl-2 phénylène-1,3 ; méthyl-5 phénylène-1,3 diéthyl-2,5 méthyl 3 phénylène-1,4 ; et les radicaux de formule

dans laquelle T représente un lien valentiel simple ou un groupement

et les symboles X, identiques ou différents, représentent chacun un atome d'hydrogène, un radical méthyle, éthyle ou isopropyle
- (b) un réactif acrylate consistant
* soit (bi) dans un (méthy)acrylate d'époxy novolaque répondant à la formule générale

dans laquelle
les symboles R1 et R2, identiques ou différents, représentent chacun un atone d'hydrogène ou un radical méthyle
n est un nombre positif se situant dans l'intervalle allant de 0,1 à8;;
* soit dans le mélange du composé (bi) précité avec au plus 30 t en poids, par rapport au poids au mélange (bl) + (b2), d'un composé (b2) de formule générale

dans laquelle
le symbole R3 représente un atome d'hydrogène ou un radiacl méthyle
le symbole B représente un radical organique trivalent dérivé d'un hydrocarbure aliphatique saturé linéaire ou ramifié ayant de 1 à 20 atomes de carbone et pouvant renfermer un ou plusieurs ponts oxygène et une ou plusieurs fonctions hydroxyles
et (c) un composé imidazole.POLYMERS WITH IMIDED GROUPS
DIAMINE-FREE AND PROCESSES FOR THEIR PREPARATION
In the French version 87/09000 filed by the Applicant on June 23, 1987, polymers with imide groups have been described and claimed which comprise the reaction product, at a temperature ranging from 500C to 3O00C, between
- (a) an N, N'-bis-.aleimide of formula

in which
the symbols Y, which may be identical or different, each represent a hydrogen atom, a nethyl radical or a chlorine atom;
the symbol A represents a divalent radical chosen from the group consisting of radicals: cyclohexylenes; phenylenes; 4-methyl-1,3-phenylene; 2-methyl-1,3-phenylene; 5-methyl-1,3-phenylene-2,5 diethyl-methyl 3-phenylene-1,4; and the radicals of formula

in which T represents a simple valential link or a grouping

and the symbols X, identical or different, each represent a hydrogen atom, a methyl, ethyl or isopropyl radical
- (b) a consistent acrylate reagent
* or (bi) in a (methy) novolak epoxy acrylate corresponding to the general formula

in which
the symbols R1 and R2, identical or different, each represent a hydrogen atom or a methyl radical
n is a positive number in the range from 0.1 to 8 ;;
* either in the mixture of the abovementioned compound (bi) with at most 30 t by weight, relative to the weight in the mixture (bl) + (b2), of a compound (b2) of general formula

in which
the symbol R3 represents a hydrogen atom or a methyl radiacl
the symbol B represents a trivalent organic radical derived from a linear or branched saturated aliphatic hydrocarbon having from 1 to 20 carbon atoms and which may contain one or more oxygen bridges and one or more hydroxyl functions
and (c) an imidazole compound.

 One of the advantages linked to the implementation of the invention in accordance with the aforementioned French application lies in the fact that it makes it possible to obtain, from a single N, Nt-bis-maleimide and a (meth) acrylic ester of epoxy resin, polymers which are homogeneous and perfectly suitable, when they appear as prepolymers, for the production of prepreg intermediate articles (used in the preparation of laminates in particular) using technique of impregnating fibrous materials using a solution of prepolymer in a solvent.

 It has now been found, and this is what constitutes the object of the present invention, that specific properties can be brought to the polymers described in the aforementioned French application by the addition, in their preparation medium, of '' a chlorinated or tanned epoxy resin, the latter being taken alone or as a mixture with a non-chlorinated or non-brominated epoxy resin; this measure provides excellent combustion resistance for the polymers which are prepared in this way.

More specifically, the present invention relates to polymers with imide groups which comprise the reaction product, at a temperature ranging from 500C to 3000C, between
- (a) an N, N'-bis-maleimide corresponding to formula (I) and to the definitions given above
- (b) an acrylate reagent consisting either in the compound (bi) or in the mixture (bl) + (b2) which have been defined above; and
- (c) an imidazole compound, said polymers containing imide groups being characterized in that the reaction medium which serves to prepare them further contains an epoxy resin (d) consisting either in a chlorinated or brominated epoxy resin (dl), or in mixing the resin (dl) with a non-chlorinated or non-brominated epoxy resin (d2).

 By chlorinated or brominated epoxy resin (dl) is meant an epoxy resin which has an epoxy equivalent weight of between 100 and 500 and which consists of a glycidic ether obtained by reacting a chlorinated derivative with epichlorohydrin. brominated on the aromatic nucleus (s) derived from a polyphenol chosen from the group formed by: the family of bis (hydroxyphenyl) alkanes such as bis (4-hydroxyphenyl) -2.2 propane, bis (4-hydroxyphenyl) methane, bis (4-hydroxyphenyl) methyl-phenyl-methane, bis (4-hydroxyphenyl) tolyl-methanes; resorcinol; hydroquinone; pyrocatechol; 4,4'-dihydroxy diphenyl and the condensation products of the above-mentioned phenols with an aldehyde.

 By non-chlorinated or non-brominated epoxy resin (d2) is meant an epoxy resin which has an epoxy equivalent weight also between 100 and 500 and which consists of a glycidic ether obtained by reacting a polyphenol with epichlorohydrin. non-chlorinated or non-brominated chosen from the group of the above-mentioned phenols.

The expression "epoxy equivalent weight", which appears above, can be defined as being the weight of resin (in grams) containing an epoxy function

 Preferably, and this applies both to the resin (dl) and to the resin (d2) which can be used in admixture with the resin (dl), an epoxy resin having an epoxy equivalent weight included between 150 and 300. As for the physical characteristics of this resin, they range from those of low-viscosity liquid resins (approximately 2 10 Pa s at 250C) to those of pasty resins whose melting point is of the order of 600C.

 Most preferably, an epoxy resin (d) is used in the present invention, consisting either of a resin (dl) belonging to the family of glycidic ethers of bis (hydroxyphenyl) alkanes, brominated on aromatic rings, which has been mentioned above at About the detailed definition of the resin (dl), either in the mixture of such a resin (dl) with a resin (d2) belonging to the family of glycidic ethers of bis (hydroxyphenyl) alkanes, non-brominated.

 The amount of epoxy resin (d) represents 2% at 20 t and preferably 3 t to 15 t of the weight of the bis-imide mixture (a) + acrylate reagent (b).

 It was found that the amount of chlorine or bromine provided in the polymers according to the invention by the epoxy resin (d) is likely to influence certain properties of the cured polymers obtained, in particular the properties in terms of thermal stability and those in matter adhesion of polymers on metals such as for example copper. The best results are obtained when this quantity of chlorine or bromine provided by the epoxy resin (d), expressed by the percentage by weight of elemental chlorine or elemental bromine relative to the weight of the overall bis-imide mixture (a) + acrylate reagent (b) + epoxy resin (d), represents at most 6 t; this amount of chlorine or bromine is preferably in the range from 1 & to t. The amount of chlorine or bromine can easily be adjusted to the desired value by using epoxy resins (dl) (used in amounts representing 2 to 20 t and preferably 3 to 15 t of the weight of the bis-imide + reactant mixture acrylate) having a greater or lesser chlorine or bromine content and / or starting from mixtures of chlorinated or brominated epoxy resins (dl) with non-chlorinated or non-brominated epoxy resins (d2).

By way of specific examples of bis-imides (a) of formula (I), mention may be made in particular of the compounds indicated in French application 87/09000, that is to say - N, N '- metaphenylene- bis-maleimide, - N, N'-parapbenylene-bis-maleinide, - NDN'-4,4'-diphenylmethane-bis-maleimide, - N, N'-4, 4'-diphenylether-bis-maleimide , - N, N '-4,4' -diphenylsulphone-bis-maleimide, - N, N'-cyclohexylene-1,4-bis-maleimide, - N, N '-4,4' -diphenyl- 1.1 cyclohexane-bis-maleimide, - N, N'-4,4'-diphenyl-2,2 propane-bis-maleimide, - N, N '-4,4' -triphenylmethane-bis-maleimide, - N, N'-methyl-2 phenylene-1,3-bis-maleimide, - N, N'-methyl-4 phenylene-1,3-bis-maleimide, - N, N'-methyl-5 phenylene-1,3-bis-maleimide,
These bis-maleimides can be prepared according to the methods described in American patent US-A-3,018,290 and the English patent.
GB-A-1,137,290. N, N-4,4'-diphenylmethane-bis-maleimide is preferably used for the implementation of the present invention.

 Novolak epoxy (meth) acrylates (bl) of formula (fui) are, as indicated in the aforementioned French application, known products, some of which are commercially available. They can be prepared by reacting (meth) acrylic acid with an epoxy resin of novolak type, the latter being the reaction product of epichlorohydrin and phenol / formaldehyde polycondensates (in formula (II) given above R2 is then a hydrogen atom) or cresol / formalin polycondensates (in formula (II) R2 is then a methyl radical). These oligomeric polyacrylates (b1) of formula (II) and a process for preparing them are described, for example, in American patent US-A-3,535,403.

 As specific examples of compounds (b2) of formula (III) which can be used alongside the epoxy novolak (meth) acrylate (b1), mention may be made in particular, as indicated in the above-mentioned French application, of the (meth) acrylic esters of polyols such as 1,2-butanetriol tri (meth) acrylate, 1,2,6-hexanetriol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, tri (meth) pentaeryl thritol acrylate.

 Preferably used, for the implementation of the present invention, the (meth) acrylates of novolak epoxy (bowl) of formula (II) in which R1 and R2 represent a hydrogen atom and n is a positive number se lying in the range from 1 to 5, these compounds being taken alone or as a mixture with at most 25% by weight, relative to the weight of the mixture (bi) + (b2), of a compound (b2) consisting in trimethylolpropane triacrylate.

The quantities of N, N'-bis-imide (a) and of acrylate reagent (b) are chosen, as indicated in the aforementioned French application, so that the ratio r
number of maleimide groups provided by bis-imide (a)
number of acrylic double bonds provided by the reagent (b) is in the range ranging from 1.7 / 1 to 10/1 and, preferably, ranging from 2/1 to 8/1. It should be understood that the expression "acrylic double bonds provided by the reagent (b)" designates all of the groups CH2 = CR1 provided by the compound (bl) more optionally all of the groups CH2 = CR3 provided by the compound (b2).

dans laquelle R4, R5, R6 et R7 identique ou différents, représentent chacun : un atome d'hydrogène, un radical alkyle ou alcoxy ayant de 1 à 20- atomes de carbone, vinyle, phényle, nitro, R6 pouvant former avec
R7 et les atomes de carbone auxquels sont liés ces radicaux un cycle unique comme par exemple benzénique
Corme exemples spécifiques de composés imidazole, on peut citer en particulier : l'imidazole ou glyoxaline, le méthyl-1 imidazole, le méthyle2 inidazole, le diméthyl-1,2 imidazole, le vinyle imidazole, le vinyl-l méthyl-2 imidazole, le benzimidazole. The imidazole compound (c) corresponds to the general formula

in which R4, R5, R6 and R7, which may be identical or different, each represent: a hydrogen atom, an alkyl or alkoxy radical having from 1 to 20 carbon atoms, vinyl, phenyl, nitro, R6 can form with
R7 and the carbon atoms to which these radicals are linked a single ring such as for example benzene
As specific examples of imidazole compounds, mention may in particular be made of: imidazole or glyoxaline, 1-methyl imidazole, methyl2 inidazole, 1,2-dimethylimidazole, vinyl imidazole, vinyl-1 methyl-2 imidazole, benzimidazole.

The imidazole compound is used in catalytic amounts. Depending on the nature of the imidazole compound and according to the desired polymerization rate at the implementation stage, the imidazole compound is used at a rate, expressed in number of moles of compound (c) per 100 g of bis-imide (a) , lying, as indicated in the aforementioned French application, in the range going from 0.15 10 to 6.10 -and, preferably, going from 0.3.10-3 to 4.10 3
The general conditions for putting the present invention into practice are those described in French application 87/09000 and recalled below.

 The polymers according to the invention can be prepared in bulk by direct heating of the bis-imide (a), of the acrylate reagent (b), of the imidazole compound (c) and of the epoxy resin (d) at least up to the obtaining a homogeneous liquid mixture. The temperature can vary depending on the physical state of the compounds present, but it is generally between 500 ° C. and 3000 ° C. It is advantageous to bring and maintain the starting compounds in a state of intimate mixture before and during heating using, for example, good agitation. Preferably, the imidazole compound (c) is added initially to the well-stirred mixture of reagents (a), (b) and (d) so as to allow its rapid dispersion. When this compound is particularly active, to avoid its encapsulation in the polymer network generated, it is desirable to add it to a solvent compatible with the reaction medium; it has been found that it could be advantageous to use one of the polar organic liquids which is discussed below as the solvent.

 The preparation of the polymers according to the invention can also be carried out by heating the mixture of reactants within an organic diluent which is liquid in at least part of the range 500 ° C. to 3000 C. Among these diluents, mention may be made of in particular aromatic hydrocarbons such as xylenes and toluene, halogenated hydrocarbons such as chlorobenzenes, polar solvents such as dioxane, tetrahydrofuran, dibutyl oxide, dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone, dimethylacetamide, methylglycol , methyl ethyl ketone and cyclohexanone. Polymer solutions or suspensions can be used as they are for many uses; the polymers can also be isolated, for example by filtration, optionally after precipitation using an appropriate non-solvent.

 it should be understood that the properties of the polymers according to the invention can vary to a large extent depending in particular on the exact nature of the reagents used, the proportions of reagents chosen and the precise temperature conditions adopted in the range mentioned above. As regards the polymers obtained, these can be hardened polymers, insoluble in the usual polar solvents such as for example the liquids mentioned in the preceding paragraph and which do not exhibit any significant softening below the temperature at which they start. to degrade.

 However, these polymers can also be in the form of prepolymers (P) soluble in polar organic solvents such as, for example, those mentioned above and having a softening point at a temperature below 2000 ° C. (in general this point of softening is between 500 and 1500 C). These prepolymers can be obtained in bulk by heating the mixture of reactants until a homogeneous or pasty product is obtained at a temperature generally between 500 and 1800 C for a period which can range from a few minutes to a few hours, this the duration being shorter the higher the temperature adopted.

Before subjecting the mixture of reagents to heating, it is also advantageous here to carry out a prior intimate mixture thereof by stirring. There also exists a preferred method for using the imidazole compound (c) and this is that indicated above with regard to the direct preparation of cured polymers. The preparation of the prepolymers can also be carried out in suspension or in solution in a diluent which is liquid in at least part of the range 500 - 180C
The prepolymers (P) can be used in the liquid mass state, a simple hot casting sufficient for the shaping and the production of molded objects. They can also, after cooling and grinding, use them in the form powders which lend themselves remarkably to compression coiling operations, possibly in the presence of fillers and the state of powders, spheres, granules, fibers or flakes. In the form of solutions, the prepolymers (P) can be used for the production of prepreg intermediate articles, the reinforcement of which can be made up of fibrous materials (in the form of simple fibers, woven or nonwoven webs) based on silicate or aluminum or zirconium oxide, carbon, graphite, boron, asbestos or glass. These prepolymers (P) can also be used for the production of cellular materials after incorporation of a blowing agent such as for example azodicarbonamide.

 In a second stage, the prepolymers (P) can be hardened by heating to temperatures of the order of 3000 C, generally between 1500 and 2500 C; additional shaping can be carried out during hardening, possibly under vacuum or under super-atmospheric pressure, these operations can also be consecutive.

 According to a preferred embodiment of the present invention, the operation is carried out in two stages, the first stage consisting in heating the mixture of the reactants between 500 ° C. and 1800 ° C. to form a prepolymer (P), the second stage consisting in hardening the prepolymer (P), after having given it the desired shape, by heating to temperatures of the order of 3000 C.

However, in accordance with an even more preferred embodiment of the present invention, the operation is carried out in two stages, using, in the first stage, as indicated in the above-mentioned French application, a process for the continuous preparation of the prepolymer (P) consisting to be introduced individually into a screw extruder mixer
- on the one hand bis-imide (a) in the divided solid state, and
- on the other hand, the group of reagents constituted by the acrylate reagent (b) in the liquid or molten state, the imidazole compound (c) in the solid state or in solution and the epoxy resin (d) in the state liquid, the various reagents of this group can themselves be introduced on their side together or separately.

The expression "screw extruder mixer" is intended to denote an apparatus which does not have a dead zone during the progression of the material. Apparatus of this kind which can comprise one or more screws are described in the work of EG FISHER-Extrusion of Plastics (Interscience Publisher 1964) pages 104 to 108. These mixers can comprise two endless screws intermeshing one in the other and turning in the same direction; a device of this type more particularly equipped for the preparation of alkaline terephthalates is described in French patent FR-A-1 462 935. Another variety of mixers which can be used is constituted by devices comprising an endless screw with interrupted thread simultaneously performing a rotational movement and an oscillatory movement in the direction of the axis, housed in an envelope comprising teeth which cooperate with the interrupted fins of the screw. Devices of this type are described in French patents
FR-AI 184 392, 1 184 393, 1 307 106 and 1 369 283.

 For reasons of convenience of implementation, it is preferred to use bis-imide (a) in the form of particles whose dimensions range from 0.1 to 5 mm. Their introduction into the mixer can be adjusted by devices known for this use, such as screws or dosing scales.

 The acrylate reagent (b) is supplied in the liquid state in the mixing zone. Its introduction can be carried out by means of a metering pump. The reagent (b) is supplied at one or more points located downstream from the bis-imide supply zone (a).

 The imidazole compound (c) can be incorporated in the solid state with the acrylate reagent (b). However, it is preferred to incorporate, with the acrylate reagent, the imidazole compound (c) in the form of a solution in a polar solvent such as those which have been mentioned above. Its introduction into the mixer can also be carried out at any other point in the mixing zone located downstream of the bis-imide feeding zone (a).

 As for the epoxy resin (d), it is introduced into the mixer in the liquid state at one or more points also located downstream of the bis-imide feed zone (a).

 Preferably, the acrylate reagent (b), the imidazole compound (c) and the epoxy resin (d) are introduced together in the form of a mixture at one or more points located downstream of the feed zone of the bis-imide ( at).

 Maintaining the kneading zone at the chosen temperature of between 500 ° C. and 1800 ° C. and preferably between 1300 ° C. and 1600 ° C. is generally obtained by controlled heating of the envelope of the screw or of the worms of the apparatus. With regard to the envelope, the heating can be exerted in a uniform manner over its entire length, but it is also possible to have several contiguous heating zones ensuring the temperature of the mixing zone, for example increasing in the direction of progression of the material. Upstream of the first point of introduction of the reagent (b), (c) or (d), it is preferred that the temperature be situated in the range 20 - 1300 C.

 The residence time of the products in the mixing zone can vary to a certain extent depending on the bis-imide (a) used, the temperature adopted and the quantities of reagents used. Generally, it is of the order of 1 to 30 minutes. At the outlet of the mixer, it is possible to adjust the softening point of the prepolymer (P) by heating the latter in an oven under given temperature and duration conditions.

 The polymers according to the invention are useful in fields of industry which require materials endowed with good mechanical and electrical properties as well as a great chemical inertness at temperatures of 2000 to 3000 C. As examples, they are particularly suitable good for making prepreg intermediate items. The prepreg articles can be used for the production of parts having various shapes and functions in many industries such as aeronautics. These parts, called laminates, which can be parts of revolution, are obtained by plating several layers of prepreg on a form or a support. Prepregs can also be used as reinforcements or as a means of repairing damaged parts.

 The following examples are given by way of illustration, but not limitation.

EXAMPLE 1
Example which describes a polymer according to the invention prepared by a continuous process.

 The apparatus used is a BUSS laboratory kneader known under the name "Ko-kneader" type PR 46. This kneader comprises an endless screw formed of a shaft comprising interrupted helical threads, the interruptions forming separate fins; it is driven by an appropriate mechanism. The screw is housed in a body comprising three contiguous double-walled coaxial cylindrical envelopes; the inner wall of the kneading body has teeth-shaped projections. The screw is subjected to a rotational movement and simultaneously to an oscillatory movement in the direction of its axis, which creates an exchange of material in two directions.

 In the first envelope, water is circulated at 200C and in the other two, a fluid heats to 1550C. The screw rotation speed is 60 revolutions / minute.

 In the first part of the mixer (corresponding to the first envelope), N, N'-4,4'-diphenylmethane-bis-maleimide is introduced via a metering balance at the rate of 1200 g / h; bis-maleimide is introduced in the form of grains whose average size is of the order of 0.25 mm.

 In the second part of the mixer (corresponding to the second envelope), the following is introduced, in the form of a mixture, the assembly: acrylate reagent + imidazole solution in N-methylpyrrolidone containing 25% by weight of imidazole + brominated epoxy resin , at a rate of 495.4 g / h.

 The dosage of the reagents is such that: the bis-maleimide represents 78 t of the weight of the bis-maleimide + acrylate reagent assembly; imidazole represents 0.05 t of the weight of the bis-maleimide + acrylate reagent assembly and the brominated epoxy resin represents 10 t of the weight of the bis-maleimide + acrylate reagent assembly.

 The acrylate reagent consists in the mixture based on approximately 80% by weight of a novolak epoxy diacrylate of formula (II) in which R1 = R2 = H and n is a number between 2 and 4 and 20 5 weight of trimethylolpropane triacrylate; this reagent is commercially available under the trademark EBECRYL 629 and from the company UCB and it has approximately 0.5 free acrylic double bond per 100 g of reagent.

The brominated epoxy resin used here results from the condensation of tetrabrominated bisphenol A and epichlorohydrin. It has a bromine content of 20% by weight and an epoxy equivalent weight of 220. It is commercially available under the registered trademark ARALDITE from the company CIBA, type
LY 8047. The amount of bromine provided by the epoxy resin, expressed as the percentage by weight of elementary bromine relative to the weight of the overall bis-imide composition + acrylate reagent + epoxy resin, is equal to 1.82.

 The average residence time of the material in the mixer is around 6 minutes 30 seconds. At the outlet of the device, a prepolymer is collected, the softening point of which is around 530C. This prepolymer brought to 1600C for 15 minutes has a softening point of 750C. It is soluble in solvents such as for example N-methylpyrrolidone, dimethylformamide or mixtures of these solvents with solvents with a lower boiling point such as methyl isobutylketone.

 With a first part of the prepolymer obtained, prepregs and copper-ply laminates with 6 plies (6 layers of prepregs) are prepared. With this in mind, a prepolymer solution at 50% by weight in N-methylpyrrolidone is used to coat a glass fabric manufactured by the company PORCHER under the reference 7628 whose grammage is 200 g / m2 and having undergone a treatment with gamma-aminopropyltriethoxysilane (silane A 1100 from UNION CARBIDE). The impregnated fabric contains 35 g of prepolymer per 65 g of fabric; it is dried in a ventilated atmosphere at 1300C for 5 minutes. Then cut 6 squares (15 x 15 cm) which are stacked with a copper foil 35 µm thick placed on one of the outer faces of the stack and the assembly is placed between the trays a press under the following conditions - pressure: 40 105 Pa, - heating of the press plates: 15 minutes at 1500C, then 45 minutes at 2000C.

 During the lamination operation, a creep rate of the polymer is observed of around 20% by weight. After an additional heat treatment at 2350C for 4 hours, the adhesion of copper is examined on the prepared 6-ply laminate: this adhesion, measured with a dynamometer by pulling copper at 900 angles (according to MIL P 55 617 B standard with a traction speed of 55 mm / min), is of the order of 15 N / cm; this value is maintained after aging for 1000 hours at 2000C.

 With a second part of the prepolymer obtained previously, prepregs and laminates comprising 6 plies are prepared under the conditions described above (note that no copper foil is used here). After post-curing at 2350C for 4 hours, combustibility measurements are carried out using the UL 94 vertical test (thickness of the laminate-based test pieces: 0.8 mm; the combustion time is given in seconds after conditioning of 48 hours, at 230C and under 50 t of relative humidity; the classification is established on the average of 10 results: 5 test pieces and 2 tests on each test piece) - combustion time: 3 s - classification: VO.

Claims (10)

1) Polymers with imide groups which comprise the reaction product, at a temperature ranging from 500C to 3000C, between  - (a) an N, N'-bis-maleimide of formula

 in which  the symbols Y, which are identical or different, each represent a hydrogen atom, a methyl radical or a chlorine atom  the symbol A represents a divalent radical chosen from the group consisting of radicals: cyclohexylenes; phenylenes; 4-methyl-1,3-phenylene; 2-methyl-1,3-phenylene; 5-methyl-phenylene-1,3, 2,5-diethyl-methyl 3-phenylene-1,4; and the radicals of formula

 in which T represents a simple valential link or a grouping

 and the symbols X, identical or different, each represent a hydrogen atom, a methyl, ethyl or isopropyl radical  - (b) a consistent acrylate reagent  * or (bl) in a (methy) novolak epoxy acrylate corresponding to the general formula

  in which  the symbols R1 and R2, identical or different, each represent a hydrogen atom or a methyl radical  n is a positive number in the range from 0.1 to S ;;  * either in the mixture of the abovementioned compound (bowl) with at most 30 t by weight, relative to the weight in the mixture (bl) + (b2), of a compound (b2) of general formula

 in which  the symbol R3 represents a hydrogen atom or a methyl radiacl  the symbol B represents a trivalent organic radical derived from a linear or branched saturated aliphatic hydrocarbon having from 1 to 20 carbon atoms and which may contain one or more oxygen bridges and one or more hydroxyl functions  and (c) an imidazole compound, said polymers containing imide groups being characterized in that the reaction medium which serves to prepare them further contains an epoxy resin (d) consisting either of a chlorinated or brominated epoxy resin (dl), or in mixing the resin (dl) with a non-chlorinated or non-brominated epoxy resin (d2). 2) Polymers according to claim 1, characterized in that the bis-maleimide (a) of formula (I) is N, N'-4,4'-diphenylmethanebis-maleimide. 3) Polymers according to any one of claims 1 or 2 characterized in that the acrylate reagent (b) is chosen from the group formed by the novol epoxy (meth) acrylates (b1) of formula (I1) in which R1 and R2 represent a hydrogen atom and n is a positive number in the range from 1 to 5, these compounds being taken alone or in a mixture with at most 25 t by weight, relative to the weight of the mixture (bowl ) + (b2), of a compound (b2) consisting of trimethylolpropane triacrylate. 4) Polymers according to any one of claims 1 to 3, characterized in that the imidazole compound (c) corresponds to the general formula

 in which R4, R5, R6 and R7, identical or different, each represent: a hydrogen atom, an alkyl or alkoxy radical having from 1 to 20 carbon atoms, vinyl, phenyl, nitro, R6 can form with R7 and the carbon atoms to which these radicals are linked a single cycle, for example a benzene ring. 5) Polymers according to claim 4, characterized in that the imidazole compound (c) is chosen from the group formed by imidazole or glyoxaline, 1-methylimidazole, 2-methylimidazole, 1,2-dimethylimidazole , vinyl-l imidazole, vinyl-1 methyl-2 imidazole and benzimidazole. 6) Polymers according to any one of claims 1 to 5, characterized in that one uses - as epoxy resin (dl): an epoxy resin which has an epoxy equivalent weight between 100 and 500 and which consists in a glycidic ether obtained by reacting with epichlorohydrin a chlorinated or brominated derivative on the aromatic nucleus (s) derived from a polyphenol chosen from the group formed by: the family of bis (hydroxyphenyl) alkanes such as bis (4-hydroxyphenyl) -2,2 propane, bis (4-hydroxyphenyl) methane, bis (4-hydroxyphenyl) methyl-phenyl-methane, bis (4-hydroxyphenyl) tolyl- methane; resorcinol; hydroquinone; pyrocatechol 4,4 'dihydroxy diphenyl; and the condensation products of the above-mentioned phenols with an aldehyde - optionally, as epoxy resin (d2): an epoxy resin which has an epoxy equivalent weight also between 100 and 500 and which consists of a glycidic ether obtained by reacting with epichlorohydrin a non-chlorinated or non-brominated polyphenol selected from the group of the above-mentioned phenols. 7) Polymers according to any one of claims 1 to 6, characterized in that on the one hand the amounts of N, N'-bis-imide (a) and of acrylate reagent (b) are chosen so that The report  number of maleimide groups provided by bis-imide (a)  number of acrylic double bonds provided by the acrylate (b) is in the range from 1.7 / 1 to 10/1, and on the other hand the rate of imidazole compounds (c), expressed in number of moles of compound (c) per 100 g of bis-imide (a), lies in the range from 0.15 10 3 to 6.10-3 8) Polymers according to any one of claims 1 to 7, characterized in that on the one hand the amount of epoxy resin (d) represents 2% to 20% of the weight of the bis-imide mixture (a) + acrylate reagent ( b), and on the other hand the amount of chlorine or bromine provided by the epoxy resin (d), expressed by the percentage by weight of elemental chlorine or elemental bromine relative to the weight of the overall bis-imide mixture (a) + acrylate reagent (b) + epoxy resin (d), represents at most 6%. 9) Polymers according to any one of claims 1 to 8, characterized in that they are in the form of hardened polymers insoluble in the usual polar organic solvents and having no significant softening below the temperature at which they begin to degrade. 10) Polymers according to any one of claims 1 to 8, characterized in that they are in the form of thermosetting prepolymers (P) soluble in the usual polar organic solvents and have a softening point at a temperature below 2000C.