IE912771A1

IE912771A1 - Heat-curable compositions based on cyanate ester compounds¹and polyimide compounds containing diorganopolysiloxane¹group(s)

Info

Publication number: IE912771A1
Application number: IE277191A
Authority: IE
Original assignee: Rhone Poulenc Chimie
Priority date: 1990-09-07
Filing date: 1991-08-02
Publication date: 1992-03-11
Also published as: PT98872A; KR930702424A; MX174494B; FR2666586A1; AU8519691A; EP0547116A1; CA2088672A1; WO1992004395A1; JPH06504071A; ZA915957B

Description

The present invention relates to heat-curable compositions comprising (A) at least one cyanate ester compound consisting essentially of a polyfunctional aromatic cyanic ester containing at least two cyanate (-O-C-N) groups bonded to an aromatic nucleus, in a prepolymer derived from the said organic ester or in a coprepolymer derived from the said cyanic ester and from a polyamine and (B) at least one elastomer consisting essentially of an N,N'-bismaleimide containing diorganopolysiloxane groups, in a prepolymer derived from the said bismaleimide or in a coprepolymer derived from the said bismaleimide and from a diamine.

The heat-curable compositions in accordance with the present invention may additionally contain an appropriate catalyst and one or more additional polymerisable compounds including especially a conventional bismaleimide, an optionally halogenated epoxy resin, an acrylate reactant or an alkenylphenol, and they may furthermore be used in combination with PATENTS ACT, 1964 COMPLETE SPECIFICATION CONVENTION ' HEAT-CURABLE COMPOSITIONS BASED ON CYANATE ESTER COMPOUNDS AND POLYIMIDE COMPOUNDS CONTAINING DIORGANOPOLYSILOXANE GROUP (S) / j RHONE-POULENC CHIMIE, a French Body Corporate, of 25 Quai Paul Doumer, 92408 Courbevoie Cedex, France. -1IE 912771 HEAT-CURABLE COMPOSITIONS BASED ON CYANATE ESTER COMPOUNDS AND POLYIMIDE COMPOUNDS CONTAINING DIORGANOPOLYSILOXANE GROUP(S1 The present invention relates to heat5 curable compositions comprising (A) at least one cyanate ester compound consisting essentially of a polyfunctional aromatic cyanic ester containing at least two cyanate groups (-O-C-N) bonded to an aromatic nucleus, in a prepolymer derived from the said organic ester or in a coprepolymer derived from the said cyanic ester and from a polyamine and (B) at least one elastomer consisting essentially of a polyimide compound containing one or more diorganopolysiloxane groups in its structure.

It also relates to the cured resins prepared from the said heat-curable compositions. The heatcurable compositions in accordance with the present invention may additionally contain an appropriate catalyst and one or more additional polymerisable compounds including especially a conventional bismaleimide, an optionally halogenated epoxy resin, an acrylate reactant or an alkenylphenol, and they may be additionally used in combination with known reinforcing fillers.

The polyfunctional aromatic cyanic esters are known products which are prepared by reaction between a cyanogen halide and a polyhydroxylated phenol (cf. Patent US-A-3,553,244). These cyanic esters can produce cured resins by a cyclotrimerisation reaction of the cyanate groups giving rise to substituted triazine rings which become organised into a three-dimensional polycyanurate network.

Such polycyanurate resins, which have found many uses in a number of fields of application, have advantageous electrical properties (in particular dielectric characteristics), but have the shortcoming of offering levels of properties which are still insufficient, especially where toughness (the values of Charpy impact and of G1C and K1C need to be improved) and adhesiveness to metal substrates are concerned.

In order to obtain tough resins it has been proposed in the prior state of the art to modify polycyanurate resins by adding to their preparation mixture: plasticisers of high boiling point containing ester groups (cf. Patent US-A-4,094,852), and acrylonitrile-butadiene copolymer (cf. Patent US-A-3,649,714), an elastomer such as natural rubbers, polymers derived from conjugated dienes (such as butadiene and isoprene), polychloroprenes (cf. Patent US-A-4,396,745), or an amorphous thermoplastic polymer such as a polysulphone, a polyarylate or a polyethersulphone (cf. Application EP-A-0,311,341).

However, such polymer mixtures are liable to exhibit a serious lack of heat stability at application temperatures as high as those ranging from 220’C to 300’C.

It has now been found that it is possible to obtain, from polyfunctional aromatic cyanic esters, resins which in the cured state exhibit an excellent compromise of properties, especially where toughness, heat stability and adhesiveness are concerned, by using a modifying agent consisting essentially of a polyimide compound containing one or more diorganopolysiloxane group(s) in its structure.

More precisely, the present invention relates 10 to heat-curable compositions which comprise: (A) - at least one cyanate ester compound chosen from the group made up of: (1) - a monomeric polyfunctional aromatic cyanic ester which has the formula: R-(-O-C-N)n (1) in which: n is an integer ranging from 2 to 5 and R denotes an aromatic organic radical of valency n, containing from 6 to 30 carbon atoms, where the cyanate groups are bonded to the aromatic nucleus (nuclei) of R; (2) - a prepolymer of (1), and (3) - a coprepolymer of (1) and of an aromatic primary polyamine; (B) - at least one elastomeric compound; and optionally: (C) - an appropriate catalyst; the said compositions being characterised in that the constituent (B) consists of at least one compound chosen from the group made up of: (4) - an N,N'-bismaleimide containing diorganopolysiloxane group(s), corresponding essentially to the general formula: in which: - X, which is in an ortho, meta or para position in relation to the carbon atom of the benzene ring which is linked to nitrogen, denotes a single valency bond or one of the following atoms or groups: ll — each of Rx, R2/ R3Z R3, R7 and Rg, which are identical or different, denotes a monovalent hydrocarbon radical chosen from linear or branched alkyl radicals containing from 1 to 12 carbon atoms, it being possible for these radicals to be substituted by one or more chlorine, bromine or fluorine atoms or by a -CN group; a phenyl radical optionally substituted by one or more alkyl and/or alkoxy radicals containing from 1 to 4 carbon atoms or by one or more chlorine atoms; - the symbol x is an integer lying in the range from 2 to 8; - the symbols y and z denote identical or different whole or fractional numbers whose sum lies in the range from 0 to 100; (5) - a prepolymer of (4), and (6) - a coprepolymer of (4) and of an aromatic diprimary diamine.

With regard to the constituent (A), the symbol R of the cyanate ester of formula (I) may denote: (i) - a radical of valency n derived from an aromatic hydrocarbon containing from 6 to 16 carbon atoms, such as, for example, benzene, naphthalene, anthracene or pyrene; (ii) - a radical of valency n derived from a group containing a number of aromatic nuclei linked together by a single valency bond or by an inert atom or an inert divalent group such as, for example, the group of formula: β Zq (III) in which R' denotes a single valency bond or a divalent inert atom or group such as -0-, -S-, a linear or branched alkylene radical containing from 1 to 10 carbon atoms, optionally substituted by one or more chlorine, bromine or fluorine atoms and optionally interrupted by one or more oxygen atoms, -CO-, -S02-, -NR- where R denotes a hydrogen atom, an alkyl radical containing from 1 to 3 carbon atoms, phenyl or cyclohexyl, -C00-, In addition, the various aromatic groups referred to above in paragraphs (i) and (ii) may be substituted by one or more linear or branched alkyl or alkoxy radicals containing from 1 to 4 carbon atoms or by one or more halogen atoms.

The cyanate esters (1) of formula (I) which are employed preferably consist of difunctional compounds which correspond to the formula: (IV) in which: - R' denotes a single valency bond or one of the following atoms or groups: - each of the symbols R, which are identical or different, denotes a substituent chosen from a chlorine, bromine or fluorine atom or a methyl, ethyl, propyl or isopropyl radical, it being possible for two neighbouring RH on the same nucleus to denote together a 6-membered aromatic nucleus; - m is an integer equal to 0 or 1; - a is an integer equal to 0, 1 or 2, it being possible for the symbols a, when more than 2 thereof are present, to be identical or different from each other.

By way of specific examples of preferred difunctional cyanate esters (1) of formula (IV) there may be mentioned in particular: - 1,3- and 1,4-diacyanatobenzene, - 1,3-, 1,4-, 1,6-, 1,8-, 2,6- or 2,7-dicyanatonaphthalene, - 4,4'-dicyanatobiphenyl, - bis (4-cyanatophenyl)methane, - bis(3,5-dimethyl-4-cyanatophenylJmethane, - 2,2-bis(4-cyanatophenyl)propane, - 2,2-bis (4-cyanatophenyl) hexafluoropropane, - 1,l-bis(4-cyanatophenyl)ethane, - bis (4-cyanatophenyl) ether, - bis(4-cyanatophenyl) thioether, - bis(4-cyanatophenyl) sulphone, - bis(4-cyanatophenyl) tetrahydrodicyclopentadiene.

Bis (4-cyanatophenyl)methane, bis(3,5dimethy1-4-cyanatophenyl)methane, 2,2-bis(4-cyanatophenyl)propane or mixtures of these cyanates are very preferably employed for making use of the invention.

The cyanate esters (1) may also be employed in the form of a prepolymer (2) containing symmetrical triazine rings, which is prepared by partial cyclotrimerisation of the cyanate groups by heating the monomeric cyanate ester (1) to a temperature ranging from 130‘C to 220*C for a sufficient period to cyclotrimerise 5 to 75% of the total number of the cyanate groups introduced and, preferably, 15 to 50% of the cyanate functional groups. Such prepolymers (2) have a weight-average molecular mass ranging from 400 to 12000; they can be prepared in the presence of a catalyst which is either acidic such as, for example, an inorganic protonic acid or a Lewis acid, or basic such as, for example, an alkali metal hydroxide, an alkali metal alcoholate or a tertiary amine.

The cyanate esters (1) may also be employed in the form of a coprepolymer (3) derived from (1) and from an aromatic primary polyamine such as preferably an aromatic diprimary diamine chosen from the group made up of: -(3.1)- the species corresponding to the general formula: H2N - A - NH2 (V) in which the symbol A denotes a divalent radical chosen from the group consisting of the following radicals: cyclohexylene, phenylene, 4-methyl-1,3-phenylene, 2-methyl-l,3-phenylene, 5-methyl-l,3-phenylene, 2,5-diethyl-3-methyl-l,4-phenylene and the radicals of formula: in which B denotes a single valency bond or a group: CH2 CH3 - C CK3 - s I! ; H - C / in which: - each of the symbols Rj, R10, Ru and R12, which are identical or different, denotes a methyl, ethyl, propyl or isopropyl radical; - each of the symbols T, which are identical 10 or different, denotes a hydrogen atom or a chlorine atom; - the symbol E denotes a divalent radical chosen from the group made up of the radicals: the general and (3.3) - the species formula: corresponding to (VII) in which: - the amino radicals are in a meta or para position relative to each other; - each of the symbols R13, which are identical or different, denotes a methyl, ethyl, propyl or isopropyl radical.

As specific examples of diamines (3.1) of formula (V) there may be mentioned in particular: - para-phenylenediamine, - meta-phenylenediamine, - 4,4'-diaminodiphenylmethane, - 2,2-bis(4-arainophenyl)propane, - benzidine, - di(4-aminophenyl) ether, and - 4,4'-diaminodiphenyl sulphone. 4,4'-Diaminodiphenylmethane is preferably employed for making use of the present invention.

By way of specific examples of hindered diamines (3.2) and (3.3) of formulae (VI) and (VII) there may be mentioned in particular: - 4,4'-diamino3, 3',5,5'-tetramethyldiphenylmethane, - 4,4'-diamino3, 3',5,5'-tetraethyldiphenylmethane, - 4,4'-diamino-3,5-dimethyl3 ', 5'-diethyldiphenylmethane, - 4,4'-diamino-3,3'-diethyl5,5'-dimethyldiphenylmethane, - 4,4'-diamino15 3,3’,5,5'-tetraisopropyldiphenylmethane, - 4,4'-diamino-3,3'-disopropyl5,5'-dimethyldiphenylmethane, - l,4-bis(4-amino-3,5-dimethylα,α-dimethylbenzyl)benzene, - l,3-bis(4-amino-3,5-dimethyla, a-dimethylbenzyl)benzene, - 1,3-diamino-2,4-diethyl-6-methylbenzene, and - 1,3-diamino-2-methyl-4,6-diethylbenzene.

These hindered diamines can be prepared according to the processes described in British Patent GB-A-852,651 and US Patent US-A-3,481,900. 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 preferably employed for making use of the present invention. The coprepolymers (3) are obtained by reaction of the monomeric cyanate ester (1) and of the diamine, the operation being carried out in a homogeneous liquid medium, optionally by using an appropriate solvent such as ketones, at a temperature ranging from 0’C to 100“C over a period ranging from 1 minute to 1 hour. The proportions of cyanate ester and of diamine are chosen so that the ratio number of cyanate groups -(-O-C-N) / number of NH2 groups lies in the range from 1.1/1 to 10/1 and preferably 15 from 1.5/1 to 5/1.

A constituent (A) consisting of a prepolymer (2) derived from the difunctional cyanate esters (1) of formula (IV) is most especially preferred for making use of the invention.

As indicated above, the constituent (B) of the heat-curable compositions according to the present invention consists of at least one compound chosen from the group made up of an Ν,Μ'-bismaleimidesiloxane (4), a prepolymer (5) derived from (4) and a coprepolymer (6) derived from (4) and from an aromatic diprimary diamine.

With regard to the bismaleimidesiloxanes (4) of formula (II), when y and/or z are greater than 1, these are a compound of polymeric structure and are rarely a single compound but in most cases a mixture of compounds of the same chemical structure, which differ in the number of repeat units in their molecule; this results in an average value of y and/or z which can be an integer or a fraction.

When the preparation of the compositions according to the invention is carried out according to the indications given below, within an organic diluent or solvent, any one of the compounds (4) of formula (II) may be employed.

As suitable bismalelmides there may be mentioned those corresponding to formula (II), in which: 1) X = -O-; Rx = R2 = R3 = R, = R5 = R6 = R7 = R8 = linear alkyl radical containing from 1 to 3 carbon atoms; x = 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 2) X = -O-; Rx = R2 = R3 = R4 R7 = Re = linear alkyl radical containing from 1 to 3 carbon atoms; R3 = Re » phenyl radical; x » 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 3) X = -O-; Rx = R2 = R7 = RB = linear alkyl radical containing from 1 to 3 carbon atoms; R3 - R4 - R5 Re » phenyl radical; x · 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 4) X = -0-; Rx = R2 - R3 = R5 = R7 = Re = linear alkyl radical containing from 1 to 3 carbon atoms; R« = R6 = phenyl radical; x = 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70.

) X - -O-; Rx = R3 - R5 = R7 » linear alkyl radical containing from 1 to 3 carbon atoms; R2 R = R6 = Re = phenyl radical; x = 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70.

As specific examples of suitable bismaleimidesiloxanes (4) there will be mentioned especially: 6) CO CO I I CH =_CH CH3 - (CH2)3 - Si 7) (CH2)3 ch3 Si I CH3 [o] with y + z to 70 Ik co^ xco I * CH____CH θ) (CH2)3 9) When the preparation of the polymers according to the invention is carried out in bulk, the bismaleimides (4) of formula (II) which are employed are preferably those in which the diorganopolysiloxane group contains a plurality of Si-phenyl or Si-(substituted phenyl) bonds. Bismaleimides of this type which are particularly suitable are those belonging to the following groups, classified in increasing order of preference: - bismaleimides nos. 2, 3, 4 and 5, - bismaleimides nos. 7, 8 and 9.

The bismaleimidesiloxanes of formula (II) are compounds which are obtained by reacting maleic anhydride, in the presence of a dehydrating agent, a tertiary amine, an organic diluent and a catalyst, with a diamine containing a diorganopolysiloxane group of formula: in which X, R^, 82, 83, R4, 85, 85, 87, R8, x, y and z have the meanings given above in the case of formula (II). To have more details on these blsmalelmidesiloxanes and on the process for their 5 preparation, reference may be made in particular to the contents of French Patent Application FR-A-2,611,728.

The bismaleimidesiloxanes (4) may also be employed in the form of a prepolymer (5) which is prepared by heating the biemaleimidesiloxane (4), the operation being carried out in bulk or in a liguid diluent which may be a solvent, at a temperature ranging from 50 to 180*C, preferably from 80 to 170“C, for a period ranging from 5 minutes to 2 hours or longer, this period being proportionately shorter the higher the temperature adopted.

The bismaleimidesiloxanes (4) can also be employed in the form of a coprepolymer (6) derived from (4) and from an aromatic diprimary diamine chosen from the group made up of the species (3.1), (3.2) and (3.3) discussed above in connection with the definition of the coprepolymer (3) of the constituent (A). The coprepolymer (6) can be prepared by reacting the bismaleimidesiloxane (4) and the diamine, the operation being carried out in bulk or in a liquid diluent which may be a solvent, at a temperature ranging from 50 to 180’C, preferably from 80 to 170*C, for a period ranging from 5 minutes to 2 hours or longer, so as to obtain a homogeneous liquid mixture. The proportions of bisimide and of diamine are chosen so that the ratio number of moles of bisimide / number of moles of diamine lies in the range from 1.2/1 to 10/1 and preferably 15 from 2/1 to 5/1.

A constituent (B) consisting of a bismaleimidesiloxane (4) chosen from bismaleimides nos. 1 to 9 is most especially preferred for making use of the invention.

The reactivity of the constituents of the heat-curable compositions according to the invention can, if need be, be increased and/or controlled by the addition of a catalyst (C) which may be chosen from the compounds which accelerate and/or control the reactivity of cyanate groups, both during the cyclotrimerisation reaction and during the subsequent crosslinking reaction; as examples of compounds of this kind there may be mentioned in particular: - compounds containing free hydrogen such as, for example, alcohols, phenols, carboxylic acids and primary and secondary amines; - compounds consisting of metal carboxylates, optionally dissolved in nonvolatile functional liquids such as, for example, an alkylphenol or a monoalcohol (cf. US-A-4,604,452 and US-A-4,608,434, the substance of which is introduced here by way of reference); - compounds consisting of chelates, such as metal 10 acetylacetonates, optionally dissolved in an alkylphenol (cf. US-A-4,785,075, the substance of which is also introduced here by way of reference).

The catalysts which are preferred consist of metal acetylacetonates and, in particular, of zinc, copper, manganese or cobalt acetylacetonates.

The quantities of the constituents (A) and (B) in the heat-curable compositions which have just been defined are chosen so as to have, by weight relative to the weight of the combination (A) + (B): - from 50 to 98% and, preferably, from 75 to 95% of constituent (A), and - from 2 to 50% and, preferably, from 5 to 25% of elastomeric constituent (B).

With regard to the optional catalyst (C), depending on its nature and depending on the rate of crosslinking which is desired at the utilisation stage, it is employed when needed in a proportion which is in the range from 0.005 to 10% and preferably ranges from 0.01 to 5% relative to the weight of the overall composition including (A) + (B) + optionally the additional polymerisable compound(s) which will now be discussed in the continuation of this description.

The compositions according to the invention may, in fact, additionally comprise an additive (D) consisting of one or more additional polymerisable compounds chosen from: (7) - an Ν,Ν'-bismaleimide of formula: CO CO co - c - z •co - c - z (VIII) in which: - each of the symbols Z, which are identical or different, denotes H, CH3 or Cl; - the symbol 6 may denote one of the radicals 15 denoted by the symbol A in the formula (V) denoting the species (3.1) of aromatic diprimary diamines; (8) - a chlorinated or brominated epoxy resin; (9) - an unhalogenated epoxy resin; (10) - an alkenylphenol of formula: CH2 - CRk - CH2 v-015 (ix) CH2 - CR14 - CH2 in which: - the symbol H denotes a single valency bond or divalent radical chosen from the group made up of the radicals: - CH2 - ; - CH2 - CH2 - ; CH3 I C CH3 SO - ; and- SO2 - ; - each of the symbols R14, which are identical or different, denotes a hydrogen atom or a methyl radical; - each of the symbols R1S, which are identical 10 or different, denotes a hydrogen atom or a linear or branched alkyl radical containing from 1 to 6 carbon atoms, or a phenyl radical; (11) - an acrylate of general formula: (CH2 - CRis - CO - 0 )------ L (X) P in which: - the symbol Rie denotes a hydrogen atom or a methyl radical; - p denotes an integral or fractional number equal to at least 1 and not exceeding 8; - the symbol L denotes an organic radical of valency p derived from a linear or branched saturated aliphatic residue containing from 1 to 30 carbon atoms and capable of containing one or more oxygen bridges and/or one or more free hydroxyl functional groups, or from an aromatic residue (of aryl or arylaliphatic type) containing from 6 to 150 carbon atoms, consisting of a benzene nucleus which may be substituted by one to three alkyl radicals containing from 1 to 5 carbon atoms or of a number of benzene nuclei, optionally substituted as indicated above, which are joined together by a single valency bond, an inert group or an alkylene radical containing from 1 to 3 carbon atoms, it being possible for the said aromatic residue to contain one or more oxygen bridges and/or one or more free hydroxyl functional groups in various places in its structure, it being possible for the free valency (valencies) of the aromatic radical L to be carried by a carbon atom of an aliphatic chain and/or by a carbon atom of a benzene nucleus.

When a compound (D) (or a mixture of compounds D) is employed to produce the compositions according to the present invention, it represents from 2 to 35%, preferably from 5 to 30%, by weight of the overall composition (A) + (B) + (D) + optionally (C).

As specific examples of bismaleimides (7) of formula (VIII) there may be mentioned in particular: - N,N'-meta-phenylenebismaleimide, - N,N'-para-phenylenebismaleimide, - N,N'-4,4'-diphenylmethanebismaleimide, - N,Ν'-4,4'-diphenyl ether bismaleimide, - Ν,Ν'-4,4'-diphenyl sulphone bismaleimide, - N,N'-1,4-cyclohexylenebismaleimide, - N,N'-4,4'-diphenyl-1,1-cyclohexanebismaleimide, - Ν,N'-4,4'-diphenyl-2,2-propanebismaleimide, - N,N'-4,4'-triphenylmethanebismaleimide, - N,N'-2-methyl-1,3-phenylenebismaleimide, - N,N'-4-methyl-l,3-phenylenebismaleimide, and - Ν,N'-5-methyl-l,3-phenylenebismaleimide.

These bismaleimides can be prepared by the processes described in US Patent US-A-3,018,290 and British Patent GB-A-1,137,290.

N,N'-4,4'-Diphenylmethanebismaleimide, taken by itself or mixed with N,N'-2-methyl-l,3-phenylenebismaleimide, N,N'-4-methyl-l,3-phenylenebismaleimide and/or N,N'-5-methyl-l,3-phenylenebismaleimide is preferably employed for making use of the present invention.

It has been found that the quantity of chlorine or of bromine which may be introduced into the compositions according to the invention by the additive (8) is liable to affect some properties of the cured compositions obtained, especially properties related to heat stability and those related to the adhesiveness of the compositions to metals such as, for example, copper. In this connection, the best results are obtained when this quantity of chlorine or of bromine introduced by the additive (8), expressed as the percentage by weight of elemental chlorine or elemental bromine relative to the weight of the overall mixture of (A) + (B) + optional compound (C) + optional compound (D), represents not more than 8%; this quantity of chlorine or bromine preferably lies in the range from 1 to 6%. The quantity of chlorine or of bromine can be easily adjusted to the desired value by using, for example, epoxy resins (8) which have a higher or lower chlorine or bromine content, or by starting with mixtures of chlorinated or brominated epoxy resins (8) with unhalogenated epoxy resins (9).

A chlorinated or brominated epoxy resin (8) is intended to define an epoxy resin which has an epoxy equivalent weight of between 200 and 2000 and which consists of a glycidyl ether obtained by reacting with epichlorohydrin a derivative which is chlorinated or brominated on the aromatic nucleus (nuclei) originating from a polyphenol chosen from the group made up of: the class of bis(hydroxyphenyl)alkanes such as 2,2-bis (4-hydroxyphenyl)propane, bis (4-hydroxyphenyl)methane, 0 bis (4-hydroxyphenyl)methylphenylmethane, bis (4-hydroxyphenyl)tolylmethanes, resorcinol, hydroquinone, pyrocatechol, 4,4'-dihydroxydiphenyl and products of condensation of the abovementioned phenols with an aldehyde.

The expression epoxy equivalent weight which appears above may be defined as being the weight (in grams) of resin containing one epoxy functional group A chlorinated or brominated epoxy resin which has an epoxy equivalent weight of between 250 and 500 is preferably chosen. An epoxy resin (8) very preferably employed in the present invention consists of a resin belonging to the class of glycidyl ethers of bis(hydroxyphenyl)alkanes, brominated on the aromatic nuclei, discussed above in connection with the detailed definition of the resin (8).

An unhalogenated epoxy resin (9) is intended 10 to define an epoxy resin which has an epoxy equivalent weight of between 100 and 1000 and which consists of a glycidyl ether obtained by reacting with epichlorohydrin a polyphenol which is neither chlorinated nor brominated on the aromatic nucleus (nuclei), chosen from the group of phenols discussed above in connection with the detailed definition of the resin (8).

An unhalogenated epoxy resin which has an epoxy equivalent weight of between 150 and 300 is preferably chosen. An epoxy resin (9) consisting of a resin belonging to the class of glycidyl ethers of bis(hydroxyphenyl)alkanes which are not halogenated on the aromatic nuclei, as discussed above in connection with the detailed definition of the resin (8), is very preferably employed.

By way of specific examples of alkenylphenols (10) of formula (IX) there may be mentioned in particular: - 4,4'-dihydroxy-3,3'-diallylbisphenyl, - bis (4-hydroxy-3-allylphenyl)methane, - bis(4-hydroxy-3-allylphenyl) ether, - 2,2-bis(4-hydroxy-3-allylphenyl)propane or 5 Ο,Ο'-diallylbisphenol A, and - the methyl ether corresponding to any one of the abovementioned alkenylphenols.

As is well known, the alkenylphenols are prepared by a thermal (Claisen) rearrangement of phenol allyl ethers, which allyl ethers are obtained in a manner which is known per se by reacting, for example, phenols and allyl chloride in the presence of an alkali metal hydroxide and solvents.

By way of suitable acrylate reactant (11) there may be mentioned: (11.1) - mono(meth)acrylates corresponding to formula (X) in which: - p = 1, and - L denotes a monovalent organic radical of formula: - ( -CHjCHjO-^—Lx (XI) in which: Lx denotes a linear or branched alkyl radical containing from 1 to 6 carbon atoms, or a phenyl radical; and g is an integer equal to zero, 1, 2, 3, 4 or 5; (11.2) - the di(meth)acrylates corresponding to formula (X) in which: - p = 2, and - L denotes a divalent organic radical of formula: 4-CH2CH2O h-L2-f OCH2CH2), (XII) in which: L2 denotes a linear or branched divalent alkylene radical containing from 2 to 9 carbon atoms and capable of containing one or more oxygen bridges or a radical of formula: in which the symbol U denotes a single valency bond or a group: ?H3 fl -CH2-, -CH2-CH2-, -CH(CH3)CH2-, -C-, -0-, -fj- ; CH3 0 each of the symbols r and s, which are identical or different, denotes an integer equal to zero, 1, 2, 3, 4 or 5; (11.3) - the tri- and tetra(meth)acrylates corresponding to formula (X) in which: - p » 3 or 4, and - L denotes a trivalent or tetravalent organic radical derived from a linear or branched saturated aliphatic residue containing from 3 to 20 carbon atoms and capable of containing one or more oxygen bridges and/or one or more free hydroxyl functional groups; (11.4) - epoxy novolak (meth)acrylates which, while 5 corresponding to formula (X) are here denoted by the following formula: CH? 11 CH? II 5h2 CRl6 CR16 «16 CO 1 io I to 1 1 0 I 1 0 I 1 0 I CH2 |H2 fH2 tHOH CHOH CHOH 1 CH? 1 r ch2 i fH2 Jt (XIII) in which: - the symbol Rie has the meaning given above 10 in connection with the formula (X); - the symbol R17 denotes a hydrogen atom or a methyl radical; - t is a whole or fractional number lying in the range from 0.1 to 7; (11.5) - mixtures of a number of acrylates and/or methacrylates of the same type [(11.1), (11.2), (11.3) or (11.4)] together or mixtures of one or more acrylates and/or methacrylates of the same type with one or more acrylates and/or methacrylates of another type.

By way of specific examples of suitable acrylate reactants (11.1) there may be mentioned in particular methyl mono(meth)acrylates, (monoethoxylated)phenol mono(meth)acrylates and (diethoxylated)phenol mono(meth)acrylates.

By way of specific examples of suitable acrylate reactants (11.2) there may be mentioned ethylene glycol di(meth)acrylates, 1,4-butanediol di(meth)acrylates, 1,6-hexanediol di(meth)acrylates, tripropylene glycol di(meth)acrylates, and di(meth)acrylates of the following diphenols, di(monoor polyethoxylated) or otherwise: 4,4'-dihydroxydiphenylmethane, bisphenol A, 4,4'-dihydroxydiphenyl ether and in particular di(meth)acrylates of di(monoethoxylated) bisphenol A or di(meth)acrylates of di(diethoxylated) bisphenol A) [cf. formula (XII) in which L2 denotes the radical: and r = s = 1 or 2].

By way of specific examples of suitable acrylate reactants (11.3) there may be mentioned in particular 1,2,4-butanetriol tri(meth)acrylates, 1,2,6-hexanetriol tri(meth)acrylates, trimethylolpropane tri(meth)acrylates, pentaerythritol tri(meth)acrylates and pentaerythritol tetra(meth)acrylates.

Epoxy novolak (meth)acrylates (11.4) are known products, some of which are available commercially. They can be prepared by reacting (meth)acrylic acids with an epoxy resin of novolak type, the latter being the product of reaction of epichlorohydrin and phenol/formaldehyde polycondensates [R17 in the formula (XIII) given above is then a hydrogen atom] or of cresol/formaldehyde polycondensates [R17 in the formula is then a methyl radical]. These oligomeric polyacrylates (11.4) and a process for preparing them are described, for example, in US Patent US-A-3,535,403.

By way of specific examples of suitable acrylate reactants (11.4) there may be mentioned in particular epoxy novolak acrylates of formula (XIII) in which Rie and R17 denote a hydrogen atom and t is a whole or fractional number lying in the range from 0.1 to 5.

By way of specific examples of suitable acrylate reactants (11.5) there may be mentioned mixtures of epoxy novolak (meth)acrylates (11.4) with not more than 30% by weight, relative to the weight of the mixture of (11.4) + (11.3), of a triacrylate and/or a trimethacrylate corresponding to the definitions given above in connection with the acrylate reactant (11.3) and in particular mixtures of suitable epoxy novolak acrylates, as just referred to above, with not more than 25% by weight, relative to the weight of the mixture, of a suitable triacrylate and/or trimethacrylate chosen from those just referred to above.

The acrylate reactant (11) which is very preferably employed is taken from the group made up of di(monoethoxylated) bisphenol A di(meth)acrylates, di(diethoxylated) bisphenol A di(meth)acrylates, and epoxy novolak acrylates of formula (XIII) in which R16 and R17 denote a hydrogen atom and t is a whole or fractional number lying in the range from 0.1 to 5, these compounds being taken by themselves or mixed with not more than 25% by weight, relative to the weight of the mixture, of trimethylolpropane triacrylate.

Various adjuvants can also be incorporated in the compositions according to the invention. These adjuvants, which are usually employed and are well known to a person skilled in the art, may be, for example, stabilisers or degradation inhibitors, lubricants or demoulding agents, colorants or pigments, or fillers which are pulverulent or in particulate form, such as silicates, carbonates, kaolin, chalk, powdered quartz, mica or ballotini. Adjuvants which modify the physical structure of the product obtained can also be incorporated, such as, for example, blowing agents or fibrous reinforcing agents such as especially carbon, polyimide or aromatic polyamide fibres, or whiskers.

The curable compositions according to the invention may be the result of simply mixing the constituent (A), the constituent (B) and optionally the additive (D) with, If need be, the catalyst (C) directly at room temperature (23*C).

However, the curable compositions according to the invention are preferably the result of a preliminary reaction involving the various constituents used, and obtained by heating and producing a homogeneous liguid material. The curable compositions according to the invention which are thus obtained will be defined In the following paragraphs by the expression preferred compositions.

More precisely, the said preferred compositions may be prepared by directly heating the constituent (A), the constituent (B) and optionally the additive (D) with, if need be, the catalyst (C) for a sufficient period to obtain a homogeneous liguid mixture; the temperature may vary as a function of the physical state of the compounds present, but is between 40 and 120’C and, preferably, between 50 and 100*C; the time is of the order of 5 minutes to 1 hour or longer.

According to an advantageous operating procedure, employed to prepare the preferred compositions, in a first stage the cyanate ester constituent (A) is brought to a temperature of between 40 and 120 *C and preferably between 50 and 100*C, at which it is in a homogeneous liquid state, the operation being carried out in the absence of the optional catalyst (C). Then, in a second stage, the polyimidesiloxane constituent (B) is added to the liquid medium, which is stirred and kept at a temperature which is identical with or different from that used in the preceding stage, which is also between 40 and 120’C and preferably between 50 and 100’C, the stirring and the temperature being maintained for a sufficient time to obtain a homogeneous liquid mixture (time of the order of 5 minutes to 1 hour or longer).

If it is chosen to make use of the optional catalyst (C), this is introduced in the second stage, preferably in the form of solution in the constituent (B) which is charged. If it is chosen to make use of the additive (D), this can be introduced at any time chosen either during the first stage or during the second stage.

The melt viscosity of the preferred compositions which are thus obtained, measured at 80*C, can be easily adjusted to the desired value of between 0.1 Pa s and 50 Pa s, especially by modifying the nature and the respective proportions of the constituents used and the heating temperature and time.

The operations just described can be carried out not only in the melt but also in the presence of variable quantities of a polar liquid such as, for example, cresol, dimethylformamide, N-methylpyrrolidone, dimethylacetamide, methyl ethyl 5 ketone, dioxane or cyclohexanone.

The preferred compositions can be employed directly in the homogeneous liquid state, for example either for impregnating conductors or for producing mouldings by simple hot casting or by injection, or else for producing adhesives. It is also possible to employ these compositions, after cooling and grinding, in the form of powders, for example to obtain compression-moulded objects, optionally in combination with fibrous or pulverulent fillers. The preferred compositions can also be employed in solution to prepare coatings, adhesive bondings, laminated materials in which the backbone may be in the form of woven or nonwoven sheets, unidirectional components or natural or synthetic staple fibres such as, for example, glass, boron, carbon, tungsten, silicon, polyamideimide or aromatic polyamide filaments or fibres.

The preferred compositions are of very particular interest for obtaining solvent-free preimpregnated intermediate articles. The impregnation of the fibrous material may be carried out by applying conventional techniques such as immersion, blade or curtain coating or impregnation by transfer. The transferrable film and the preimpregnated articles can be employed directly or else can be stored with a view to subsequent use; they retain their properties remarkably in the course of cold storage between 0 and °C. The preferred compositions employed for this application preferably have a melt viscosity of between 2 Pa s and 50 Pa s.

The preimpregnated materials can be employed to produce components of various shapes and functions in many industries such as, for example, in aeronautics. These components, which may be components of revolution, are obtained by laying up a number of layers of prepregs on a form or a support. The prepregs can also be employed as reinforcements or means of repairing damaged components.

However, it is also possible to design components according to the filament winding technique, with or without support, intended for the production of components of revolution, a technique employed especially for making components related to the automobile and aeronautics industries. The preferred compositions used in this technique preferably have a melt viscosity of between 0.1 Fa s and 2 Pa s.

The curable compositions according to the invention can be cured (or crosslinked) by heating to temperatures of between 100 and 250*C for 10 minutes to 25 hours, optionally under pressure. Before crosslinking, in the case of the preparation of the preferred compositions, the latter are in the form of a prepolymer consisting of a single phase; the products resulting from the polyimidesiloxane constituent (B) and optionally from the additive (D) are, in fact, soluble in the product resulting from the polyfunctional cyanate ester constituent (A). During crosslinking, as the reactions involving the -(-O-C-N) groups which are still free progress, a phase separation phenomenon develops and a cured composition is finally recovered which has a two-phase structure consisting of a continuous phase rich in product resulting from the starting cyanate ester, and a disperse phase made up of particles of the order of 0.01 to 1 μΤΛ, rich in product resulting from the starting elastomeric constituent (B).

The examples which follow illustrate how the present invention can be put into practice, no limitation being implied.

A number of checks are made in these examples. Similarly, various properties are measured.

The operating methods and/or the standards according to which these checks and measurements are performed are shown below.

- MELT VISCOSITY OF THE CURABLE COMPOSITION: The melt viscosity as discussed in this specification is the dynamic viscosity of the composition obtained at the time of casting at the end of the process of preparation conducted in bulk by heating the constituents; it is measured at 80°C ± 0.1 °C with a Contraves Rheomat 30 viscometer fitted with a rotor turning at a rate of 13 s'1; its value is given in Pa s.

- SOFTENING POINT OF THE CURABLE COMPOSITION: The softening point is the approximate temperature at which a glass rod 6 mm in diameter can easily sink a few mm into the material.

- CT.ASS TRANSITION TEMPERATURE OF THE CURED COMPOSITION; The glass transition temperature (Tg) corresponds to the abrupt drop in the elasticity modulus as a function of temperature. It can be determined on the graph showing the changes in the elasticity modulus (E) as a function of temperature, changes which are measured by dynamic mechanical analysis with the aid of a Dupont model 982 DMA apparatus at a rate of temperature rise of 3*C/minute. The test specimens are conditioned at EHO (zero equilibrium humidity), that is to say that they are placed in a desiccator over silica gel and dried for 24 hours at room temperature at 0.66-1.33xl02 Pa before the measurements are performed.

- TOUGHNESS OF THE CURED COMPOSITIONS: Charpy impact strength is determined at 20C on unnotched bar-type 80x10x4 mm test specimens conditioned at EHO, according to ASTM standard D 256. The crack propagation energy G1C and the critical stress concentration coefficient K1C are determined on CT (CT compact tension) test specimens according to ASTM standard E 399.

- TEST FOR ADHESIVENESS OF THE CURED COMPOSITION TO STAINLESS STEEL: This is carried out in simple shear according to the ASTM standard D 1002. The curable composition is deposited in the form of a 200-pm-thick film onto the metal substrate and is then crosslinked under pressure.

The value of the stress at failure in shear (6R) is measured.

- EXAMPLE 1 1. - Example of application of the invention: Into a glass reactor fitted with an anchor15 type stirrer are introduced at room temperature 100 g of a 2,2-bis(4-cyanatophenyl)propane prepolymer in which 30% of the cyanate functional groups have been cyclotrimerised; this product Is the one marketed by Hi-Tek Polymers under the name Arocy B30.

Stage 1: the reactor is Immersed in an oil bath preheated to 80*C and its contents are stirred until the charged constituent is completely melted and a homogeneous liquid mass has been obtained. This stage takes 5 minutes and degassing is then carried out at reduced pressure.

Stage 2: the liquid mass obtained is cooled to 60°C and 18 g of the bismaleimidesiloxane which is described in section 2 below and 0.025 g of copper acetylacetonate [Cu(C5H7O2)2] predissolved in the bismaleimidesiloxane are introduced. The reaction mass is kept stirred at 60’C until a homogeneous liquid mixture is obtained. This stage takes 10 minutes. The liquid reaction mass obtained is then cast into a mould preheated to 170’C.

The heat-curable composition thus obtained is flexible and adhesive at room temperature (20’C). It has a softening point close to 0’C. Its viscosity at 80“C is 1 Pa s and its gel time at 170°C is 8 minutes.

With this composition, impregnation of hot melt type (with molten material without solvent) of fibrous materials based, for example, on woven carbon fibre sheets, to produce preimpregnated intermediate articles, is possible in the temperature range from 50 to 100eC.

By immediately casting the heat-curable composition into a mould as indicated above it is possible to prepare sheets 140x100x4 mm in size, which will be subjected to the following baking cycle: minutes at 170°C, minutes between 170 and 225°C, hours at 225*C, and 2 hours between 225 and 25’C.

After demoulding, the sheets based on cured composition are cut up to obtain test specimens of appropriate sizes, on which the following are measured: the glass transition temperature (Tg), the elasticity modulus (E), the unnotched Charpy impact strength (Si) and the values of G1C and of K1C.

The values found are as follows: Tg : 235’C E : at 20°C: 3.0 GPa at 200’C: 1.75 GPa Si : 22 kJ/m2 G1C : 160 J/m2 K1C : 0.66 MPa 7m By way of comparison, the operations described above were reproduced, but without employing any bismaleimidesiloxane. The values of Si and of G1C are reduced by 50%; the elasticity moduli E at 20 and 200eC are increased by 10%.

Tests for adhesiveness to stainless steel were also conducted. The curable composition in accordance with the example is crosslinked at a pressure of 105 Pa according to the abovementioned baking cycle. The values found for the stress at failure in shear (6R) are as follows: 6R: at 20’C : 16 MPa at 200’C : 18 MPa These values are practically unchanged after the tested specimens have been subjected to aging for 1000 hours at 180’C. In the absence of bismaleimidesiloxane the values of the stress at failure in shear are 10 MPa at 20’C and 12 MPa at 200’C. 2. - Description of the process for the preparation of bismaleimide containing diorganopolysiloxane groups, employed in the exainple: This bismaleimide has the following formula: 2.1. - Preparation of the diamine containing a diorganopolysiloxane group from which this bismaleimide is derived: 369 g (0.46 mol) of an alpha,omega10 bis(hydro)diorganopolysiloxane of formula: which has a reaction mass of the order of 802 g are charged into a glass reactor fitted with a central stirrer, a dropping funnel and a reflux condenser, in which a slight overpressure of dry nitrogen is established.

The reactor is then introduced into an oil bath preheated to 55’C and the catalyst is then added. The latter is the Karsted catalyst (complex based on elemental platinum and 1,3-divinyl1,1,3,3-tetramethyldisiloxane ligands); it is in 10 solution in toluene (concentration of 3.5% by weight) and 1.49 cm3 of this catalyst solution are introduced with a syringe; the ratio (weight of elemental platinum introduced/weight of the reaction mass) is 91xl0'6. 137 g (0.92 mol) of meta-allyloxyaniline are 15 then gradually run into the reactor over a period of 60 minutes so as to control the exothermicity of the reaction. Thirty minutes after the end of the addition room temperature is restored. The product obtained, 506 g in weight, is a clear viscous oil, orangy-brown in colour, which has a proton NMR spectrum in accordance with the structure: The molecular mass is of the order of 1100 g Under these conditions the degree of conversion of the reactants introduced is 100% (neither amine nor hydrogenated siloxane oligomer are detected by NMR and infrared analysis) and the weight yield of desired diamine is 100%. 2.2 - Preparation of the bismaleimidediorganopolysiloxane: The following are introduced simultaneously 10 over 10 minutes with the aid of two dropping funnels into a glass reactor fitted with a central stirrer and a reflux condenser, in which a slight overpressure of dry nitrogen is established and which is placed in an oil bath preheated to 55°C: - 20 cm3 of an acetone solution of 28 g (0.025 mol and 0.02 NH2 functional groups) of the diaminesiloxane prepared in section 2.1, - 15 cm3 of an acetone solution of 6.4 g (0.055 mol) of maleic anhydride.

When the additions are finished each funnel is rinsed with 5 cm3 of acetone, which is then added to the reaction mass, kept stirred for a further 15 minutes. 6.1 g (0.06 mol) of acetic anhydride are charged into the dropping funnel which had contained maleic anhydride, and 1.67 g (0.0165 mol) of triethylamine are charged into the other funnel.

These two compounds are then run into the reactor and then 0.3 cm3 of an aqueous solution containing 0.0528 mol of nickel acetate per 100 cm3 of solution is added.

The reaction mixture is kept stirred under 5 reflux for 2 hours 30 minutes. The temperature is then lowered to 20 °C.

The reaction mixture is diluted with 80 cm3 of iced water (5‘C) with energetic stirring and the oily product present is then extracted with 80 cm3 of ethyl acetate. The organic phase obtained is washed three times with 80 cm3 of water to reach pH 6 in the aqueous washes, and is then dried over anhydrous sodium sulphate for 2 hours. After filtering, ethyl acetate is removed from the organic phase by evaporation, this operation being finished under reduced pressure (approximately 70 Pa) at 60*C, and 30.3 g (that is a weight yield of 96% of the theoretical) of an orangybrown viscous product are collected, whose NMR spectrum is consistent with the structure of the desired bismaleimide which was specified at the beginning of this example. The molecular mass is of the order of 1260 g.

- EXAMPLE 2: The operation is performed exactly as indicated in Example 1, but without charging catalyst (copper acetylacetonate) in stage 2.

At the end of stage 2 the liquid reaction mass is cast into a mould preheated to 200°C.

The heat-curable composition thus obtained is flexible and adhesive at room temperature (20*C). It has a softening point close to O’C. Its viscosity at 80’C is 1 Pa s and its gel time at 200’C is 35 minutes.

With this composition, impregnation of hot melt type (with molten material without solvent) of fibrous materials based, for example, on woven carbon fibre sheets, to produce preimpregnated intermediate articles, is possible in the temperature range from 50 to 100’C.

By immediately casting the heat-curable composition into a mould it is possible to prepare sheets 140x100x4 mm in size, which will be subjected to the following baking cycle: 60 minutes at 200’C, minutes between 200 and 250’C, hours at 250“C, and 2 hours between 250 and 25”C.

After demoulding, the sheets based on cured 20 composition are cut up to obtain test specimens of appropriate size, on which the following are measured: the glass transition temperature (Tg), the elasticity modulus (E), the unnotched Charpy impact strength (Si) and the values of 61C and of K1C.

The values found are as follows: Tg : 230’C E : at 20’C: 3.0 GPa at 200*C: 1.75 GPa Si : 23 kJ/m2 GlCs 165 J/m2 K1C: 0.64 MPa Jn - EXAMPLE 3: Into a glass reactor fitted with an anchortype stirrer are introduced at room temperature 75 g of a prepolymer of 2,2-bis(4-cyanatophenyl)propane in which 30% of the cyanate functional groups have been cyclotrimerised; this product is the one marketed by Hi-Tek Polymers under the name Arocy B30.

Stage 1: the reactor is immersed in an oil bath preheated to 80C and its contents are stirred until the charged constituent is completely melted and a homogeneous liquid mass has been obtained. This stage takes 5 minutes and degassing is then carried out under reduced pressure.

Stage 2: the liquid mass obtained is cooled to 60°C and 18 g of the bismaleimidesiloxane which is described in Example 1, 0.025 g of copper acetylacetonate predissolved in the bismaleimidesiloxane and 25 g of di(diethoxylated) bisphenol A diacrylate (product available commercially from UCB under the trademark Ebecryl 150) are introduced. The reaction mass is kept stirred at 60°C until a homogeneous liquid mixture is obtained. This stage takes 10 minutes. The liquid reaction mass obtained is then cast into a mould preheated to 170 °C.

The heat-curable composition thus obtained is flexible and adhesive at room temperature (20*C). It has a softening point close to -10°C. Its viscosity at 80’C is 0.5 Pa s and its gel time at 170*C is 10 minutes.

With this composition, impregnation of hot melt type (with molten material without solvent) of fibrous materials based, for example, on woven carbon fibre sheets, to produce impregnated intermediate articles, is possible in the temperature range from 50 to 100’C.

By immediately casting the heat-curable composition into a mould it is possible to prepare sheets 140x100x4 mm in size, which will be subjected to the following baking cycle: 60 minutes at 170*C, minutes between 170 and 225‘C, hours at 225*C, and hours between 225 and 25*C.

After demoulding, the sheets based on cured 20 composition are cut up to obtain test specimens of appropriate size, on which the following are measured: the glass transition temperature (Tg), the elasticity modulus (E), the unnotched Charpy impact strength (Si) and the values of G1C and of K1C.

The values found are as follows:

Claims

CLAIMS 1. ) X -0-; Rj » R 2 = R 3 = R a = Rj = Rg * R ? » R a = linear alkyl radical containing from 1 to 3 carbon atoms; x s 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. (1) - a monomeric polyfunctional aromatic cyanic ester which has the formula: R-(-O-C-N) n (I) in which: n is an integer ranging from 2 to 5 and R denotes an aromatic organic radical of valency n, containing from 6 to 30 carbon atoms, where the cyanate groups are bonded to the aromatic nucleus (nuclei) of R;

1. Heat-curable compositions which comprise: (A) - at least one cyanate ester compound chosen from the group made up of:

2. Heat-curable compositions according to 10 claim 1, characterised in that with regard to the constituent (A), the symbol R of the cyanate ester of formula (I) may denote: (i) - a radical of valency n derived from an aromatic hydrocarbon containing from 6 to 16 15 carbon atoms, such as, for example, benzene, naphthalene, anthracene or pyrene; (ii) - a radical of valency n derived from a group containing a number of aromatic nuclei linked together by a single valency bond or by an inert 20 atom or an inert divalent group such as, for example, the group of formula: in which R' denotes a single valency bond or a divalent inert atom or group such as -0-, -S-, a linear or branched alkylene radical containing from 1 to 10 carbon atoms, optionally substituted by one or more chlorine, bromine or fluorine atoms (2) - a prepolymer of (1), and

3. Heat-curable compositions according to 15 claim 2, characterised In that the cyanate esters (1) of formula (I) which are employed consist of difunctional compounds which correspond to the formula: (IV) in which: - R' denotes a single valency bond or one of the following atoms or groups: - each of the symbols R, which are (3) - a coprepolymer of (1) and of an aromatic primary polyamine; (B) - at least one elastomeric compound; and optionally: (C) - an appropriate catalyst; the said compositions being characterised in that the constituent (B) consists of at least one compound chosen from the group made up of:

4. (4) - an Ν,Ν'-bismaleimide containing diorganopolysiloxane group(s), corresponding essentially to the general formula: - X, which is position in relation to ring which is linked to valency bond or one of in an ortho, meta or para the carbon atom of the benzene nitrogen, denotes a single the following atoms or groups: II l| S II — each of Rj, Rj, R 3 , R 4 , R 3 , Rj, R 7 and R e , which are identical or different, denotes a monovalent hydrocarbon radical chosen from linear or branched alkyl radicals containing from 1 to 12 carbon atoms, it

5. 9. Process for the preparation of the heatcurable compositions according to any one of claims 1 to 8, characterised in that: - in a first stage the cyanate ester constituent (A) is brought to a temperature of between 40 and 120C and 5 - the symbol L denotes an organic radical of valency p derived from a linear or branched saturated aliphatic residue containing from 1 to 30 carbon atoms and capable of containing one or more oxygen bridges and/or one or more free hydroxyl functional groups, or from an 5 the radicals: CH3 . CH 2 - ; - CH2 - CH 2 - ί - f - ; - 0 - i · S - ί · 50 - i aod · S0 2 - ; CH3 - each of the symbols R 1O which are identical or different, denotes a hydrogen atom or a methyl radical; 5 optionally dissolved in an alkylphenol or a monoalcohol, - compounds consisting of metal acetylacetonates, optionally dissolved in an alkylphenol. 5 2) X = -O-; R x = R 2 = R 3 =» R 4 = R 7 = R a = linear alkyl radical containing from 1 to 3 carbon atoms; R 5 = Re = phenyl radical; x = 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 5 identical or different, denotes a substituent chosen from a chlorine, bromine or fluorine atom or a methyl, ethyl, propyl or isopropyl radical, it being possible for two neighbouring R on the same nucleus to denote together a 6-membered aromatic nucleus; 5 and optionally interrupted by one or more oxygen atoms, -CO-, -S0 2 -, -NR- where R denotes a hydrogen atom, an alkyl radical containing from 1 to 3 carbon atoms, phenyl or cyclohexyl, -C00-, it being possible for the various aromatic groups 10 referred to above in paragraphs (i) and (ii) to be substituted by one or more linear or branched alkyl or alkoxy radicals containing from 1 to 4 carbon atoms or by one or more halogen atoms. (5) - a prepolymer of (4), and 5 the range from 0 to 100;

6. Heat-curable compositions according to (6) - a coprepolymer of (4) and of an aromatic diprimary diamine. 7. (7) - an N,N’-bismaleimide of formula: Z - C lj I - c co. ^co - c - z N - G - N | co/ ^co - c - z (VIII) in which: - each of the symbols Z, which are identical or different, denotes H, CH 3 or Cl; - the symbol G denotes a divalent radical 5 chosen from the group consisting of the following radicals: cyclohexylene, phenylene, 4-methyl1,3-phenylene, 2-methyl-l,3-phenylene, 5-methyl1,3-phenylene, 2,5-diethyl-3-methyl-l,4-phenylene, and the radicals of formula:

7. Heat-curable compositions according to one of claims 1 to 6, characterised in that they 20 additionally comprise an additive (D) consisting of one or more additional polymerisable compounds chosen from:

8. (8) - a chlorinated or brominated epoxy resin;

9. (9) - an unhalogenated epoxy resin;

10. Preferably between 50 and 100*C, at which it is in a homogeneous liquid state, the operation being carried out in the absence of the optional catalyst (C); - then, in a second stage, the polyimidesiloxane constituent (B) is added to the liquid medium which is 15 stirred and kept at a temperature which is identical to or different from that used in the preceding stage, which is also between 40 and 120’C and preferably between 50 and 100*C, the stirring and the temperature being maintained for a sufficient time to obtain a 20 homogeneous liquid mixture; - care being taken that in the case where it is chosen to make use of the optional catalyst (C), the latter is introduced in the second stage, preferably in the form of solution in the charged constituent (B). 25 10. Application of the heat-curable compositions according to any one of claims 1 to 8 to the manufacture: - of adhesives; - of structural components according to the technique either of moulding by simple hot casting or injection moulding, or of filament winding; - of intermediate articles preimpregnated according to 5 the technique of solvent-free impregnation of various fibrous materials. 10 aromatic residue (of aryl or arylaliphatic type) containing from 6 to 150 carbon atoms, consisting of a benzene nucleus which may be substituted by one to three alkyl radicals containing from 1 to 5 carbon atoms or of a number of benzene nuclei, optionally 15 substituted as indicated above, which are joined together by a single valency bond, an inert group or an alkylene radical containing from 1 to 3 carbon atoms, it being possible for the said aromatic residue to contain one or more oxygen bridges and/or one or more 20 free hydroxyl functional groups in various places in its structure, it being possible for the free valency (valencies) of the aromatic radical L to be carried by a carbon atom of an aliphatic chain and/or by a carbon atom of a benzene nucleus. 25 8. Heat-curable compositions according to any one of claims 1 to 7, characterised in that the catalyst (C), when employed, is employed in a proportion which is in the range from 0.005 to 10% and preferably from 0.01 to 5% relative to the weight of the overall composition including (A) + (B) + optionally the additional polymerisable compound(s) (D) . 10 - each of the symbols R 1S , which are identical or different, denotes a hydrogen atom or a linear or branched alkyl radical containing from 1 to 6 carbon a phenyl radical; acrylate of general formula: (CH2 CRjg * CO · 0 ) L (Xj P ato jus j or (11) - an in which: - the symbol R 16 denotes a hydrogen atom or a methyl radical; - p denotes an integral or fractional number equal to at least 1 and not exceeding 8; (10) - an alkenylphenol of formula: in which: - the symbol H denotes a single valency bond or divalent radical chosen from the group made up of 10 in which B denotes a single valency bond or a group: 10 any one of claims 1 to 5, characterised in that the quantities of the constituents (A) and (B) are chosen so as to have, by weight relative to the weight of the combination of (A) + (B): - from 50 to 98% and, preferably, from 75 to 95% of 15 constituent (A), and - from 2 to 50% and, preferably, from 5 to 25% of elastomeric constituent (B). 10 3) X = -0-; R 3 = R 2 = R 7 = R 8 = linear alkyl radical containing from 1 to 3 carbon atoms; R 3 = R^, = R 5 = Rg = phenyl radical; x 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 15 4) X » -O-; Rj « R 2 R 3 R s » R 7 « R e « linear alkyl radical containing from 1 to 3 carbon atoms; R 4 = Rg phenyl radical; x » 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 20 5) X -O-; Rj » R 3 « Rj R 7 - linear alkyl radical containing from 1 to 3 carbon atoms; R 2 R 4 « R e = R 8 ” phenyl radical; x 2, 3 or 4; y + z lies in the range from 0 to 100 and preferably from 4 to 70. 25 5. Heat-curable compositions according to any one of claims 1 to 4, characterised in that the catalyst (C), when employed, is taken from the group made up of: - compounds containing labile hydrogen, consisting of alcohols, phenols, carboxylic acids and primary or secondary amines, - compounds consisting of metal carboxylates, 10 - m is an integer equal to 0 or 1; - a is an integer equal to 0, 1 or 2, it being possible for the symbols a, when more than 2 thereof are present, to be identical or different from each other. 15 4. Heat-curable compositions according to any one of claims 1 to 3, characterised in that, with regard to the constituent (B), the bismaleimidesiloxane (4) is taken from the group made up of the bismaleimidesiloxanes of formula (II) in which: 10 being possible for these radicals to be substituted by one or more chlorine, bromine or fluorine atoms or by a -CN group; a phenyl radical optionally substituted by one or more alkyl and/or alkoxy radicals containing from 1 to 4 carbon atoms or by one or more chlorine 15 atoms; - the symbol x is an integer lying in the range from 2 to 8; - the symbols y and z denote identical or different whole or fractional numbers whose sum lies in

11. A heat-curable composition according to claim 1, substantially as hereinbefore described and exemplified.

12. A process for the preparation of a heatcurable composition according to claim 1, substantially as hereinbefore described and exemplified.

13. A heat-curable composition according to claim 1, whenever prepared by a process claimed in claim 9 or 12.

14. Application according to claim 10, substantially as hereinbefore described and exemplified.