FR3037065A1 - POLYMERIZABLE COMPOSITION FOR ELECTRIC MACHINE, AND CORRESPONDING METHOD - Google Patents

Abstract

A polymerizable composition (120) for an electric machine is provided. The polymerizable composition (120) comprises: (A) from about 10 percent by weight to about 30 percent by weight of a polyfunctional cyanate ester; (B) about 25 percent by weight to about 60 percent by weight of a first difunctional cyanate ester, or a prepolymer thereof; (C) about 10 percent by weight to about 30 percent by weight of a second difunctional cyanate ester, or a prepolymer thereof, and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride. A corresponding method is also proposed.

Description

The present invention relates generally to polymerizable compositions comprising cyanate ester resins. More particularly, the present invention relates to cyanate ester resin compositions for encapsulating components of an electric machine. Thermosetting resins are commonly used as electrically insulating encapsulating (eg encapsulating) materials for electrical machines. Thermosetting resins such as cyanate ester resins have advantages because of their mechanical properties, their thermal stability and their chemical resistance. However, when these materials are used at high temperatures, their performance may not be satisfactory and they are likely to cause significant thermal degradation even after short periods of use. Prior art encapsulating materials may further induce cracking and produce excessive heat at the operating temperature of the electrical machines. Thus, it may be desirable to improve the thermal conductivity as well as the mechanical properties of the cyanate ester resins used in encapsulating materials. Advanced materials for dissipating the heat generated in electrical machines are also desirable, particularly in alternators used in aeronautics and other aerospace applications. Therefore, electrically insulating encapsulating materials are needed which can be used at high temperatures and effectively dissipate the heat generated by the electrical machines. In addition, improved methods for encapsulating components of an electric machine are also desirable. The present invention proposes to meet these needs. According to one embodiment, the present invention relates to a polymerizable composition for an electric machine. The polymerizable composition comprises: (A) from about 10 percent by weight to about 30 percent by weight of a polyfunctional cyanate ester having the structure (I) y R + Ar1-OCN (I) wherein "n" is an integer equal or greater than 1, Y has a structure (i) or (ii): (i) * R2-Ar2-OCN, or Ar2-OCN, Ar 'and Are are independently at each occurrence a C5-C30 aromatic radical, R 1 and R 2 are independently at each occurrence a C 1 -C 3 aliphatic radical or a C 3 -C 20 cycloaliphatic radical and * represents the binding site; (B) about 25 percent by weight to about 60 percent by weight of a first difunctional cyanate ester with structure (II), or a prepolymer thereof (II) NCO-Ar3-R3-Ar3 -OCN, where Ar 'is a C5-C30 aromatic radical, R3 is a bond or a C1-C2 aliphatic radical; (C) about 10 weight percent to about 30 weight percent of a second difunctional cyanate ester of structure (III), or a prepolymer thereof (NCO-Ar4-R5) -Ar4-OCN where Ar4 is a C5-C30 aromatic radical and R5 is a C3-C10 aliphatic radical; and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride. One embodiment consists of a polymerizable composition for an electric machine. The polymerizable composition comprises: (A) about 14 percent by weight to about 18 percent by weight of a polyfunctional cyanate ester having the structure (I) y R + Ar1-OCN (I) where "n" is an integer equal or greater than 1, Y has a structure (i) or (ii): (i) R2-Ar2-OCN or Ar2-OCN, Ar 'and Are are independently at each occurrence a C5-C30 aromatic radical, Ri and R2 are independently each occurrence a C1-C3 aliphatic radical or a C3-C20 cycloaliphatic radical and * represents the bonding site; (B) from about 32 percent by weight to about 40 percent by weight of a first difunctional cyanate ester of structure (II), or a prepolymer thereof (II) NCO-Ar3-R3-Ar3-OCN, Wherein Ar3 is a C5-C30 aromatic radical, R3 is a bond or a C1-C2 aliphatic radical; (C) about 18 percent by weight to about 22 percent by weight of a second bifunctional cyanate ester with structure (III), or a prepolymer thereof (III) NCO-Ar4-R5-Ar4- OCN 5 where Ar4 is a C5-C30 aromatic radical and R5 is a C3-Clo aliphatic radical; (D) about 18 percent by weight to about 22 percent by weight of a thermally conductive filler comprising boron nitride; and (E) about 5 percent by weight to about 15 percent by weight of a hardener, the hardener comprising a thermoplastic polymer, a reactive cyanate ester, or a combination thereof. According to a second aspect, the present invention relates to a method for encapsulating a component of an electrical machine, comprising: applying, in contact with the component, an encapsulating material comprising a polymerizable composition and a polymerization of the composition polymerizable, the polymerizable composition comprising: (A) from about 10 percent by weight to about 30 percent by weight of a polyfunctional cyanate ester having the structure (I) y R + Ar1-OCN (I) wherein "n" is an integer equal to or greater than 1, Y has a structure (i) or (ii): R 2 -Ar 2 -O CN or Ar 2 -O CN, Ar 3 and Ar 3 are independently at each occurrence a C 5 -C 30 aromatic radical R 1 and R 2 are independently each occurrence a C 1 -C 3 aliphatic radical or a C 3 -C 20 cycloaliphatic radical and * represents the binding site; (B) about 25 percent by weight to about 60 percent by weight of a first difunctional cyanate ester with structure (II), or a prepolymer thereof (II) NCO-Ar3-R3-Ar3 -OCN, where Ar3 is a C5-C30 aromatic radical, R3 is a bond or a C1-C2 aliphatic radical; (C) about 10 percent by weight to about 30 percent by weight of a second bifunctional cyanate ester with structure (III), or a prepolymer thereof (III) NCO-Ar4-R5-Ar4- OCN 15 where Ar4 is a C5-C30 aromatic radical and R5 is a C3-Clo aliphatic radical; and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride.

The invention will be better understood from the detailed study of some embodiments taken by way of nonlimiting examples and illustrated by the appended drawings in which: FIG. 1 represents a stator comprising the polymerizable composition according to one embodiment of the present invention 25; and FIG. 2 is a graph illustrating the evolution of the thermal conductivity as a function of the increase in boron nitride concentration according to one embodiment of the present invention.

As explained in detail below, the present invention relates to compositions for encapsulating components or gluing windings of an electric machine. More particularly, the invention relates to cyanate ester resin compositions for encapsulating components in an electric machine. An approximation vocabulary, used herein throughout the specification and claims, can be used to modify any quantitative representation that can vary in a permissible manner without causing a change in the basic function to which it relates. Thus, a value modified by one or more terms such as "about" and "substantially" is intended to be limited to the precise value mentioned. In some cases, the approximation vocabulary may correspond to the accuracy of an instrument for measuring the value. Here and throughout the description and claims, range boundaries may be combined and / or replaced by each other; unless the context or formulation is opposed, these ranges are identified and include all subintervals contained therein. In the following description and claims, unless the context or wording is opposed, the definite and indefinite articles include plural forms. For the purposes of this specification, the term "or" is not intended to be exclusive and refers to the presence of at least one of the components cited and, unless the context clearly precludes it, covers cases where a combination of the components mentioned may be present. As used herein, the term "aromatic radical" refers to a matrix of at least one valence atoms constituting at least one aromatic group. The valence atom matrix of at least one, constituting at least one aromatic group, may comprise hetero atoms such as nitrogen, sulfur, selenium, silicon and oxygen or may be composed of exclusively carbon and hydrogen. As used herein, the term "aromatic radical" includes, but is not limited to, phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene and biphenyl. As indicated, the aromatic radical contains at least one aromatic group. The aromatic group is invariably a cyclic structure with 4n + 2 "delocalized" electrons, "n" being an integer equal to or greater than 1, as illustrated by phenyl groups (n = 1), thienyl groups (n = 1) furanyl groups (n = 1), naphthyl groups (n = 2), azulenyl groups (n = 2), anthracenyl groups (n = 3) and others. The aromatic radical may also include non-aromatic components. For example, a benzyl group is an aromatic radical, which includes a phenyl ring (the aromatic group) and a methylene group (the non-aromatic component). Likewise, a tetrahydronaphthyl radical is an aromatic radical comprising an aromatic group (C6H3) fused with a non-aromatic component - (CH2) 4-. For convenience, the term "aromatic radical" is defined herein as encompassing a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, haloaromatic groups, conjugated dienyl groups, and the like. alcohols, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example, carboxylic acid derivatives such as esters and amides), amine groups, nitro groups and the like. For example, the 4-methylphenyl radical is a C7 aromatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Likewise, the 2-nitrophenyl group is a C 6 aromatic radical comprising a nitro group, the nitro group being a functional group. The aromatic radicals include halogenated aromatic radicals such as 4-trifluoromethylphenyl, hexafluoroisopropylidenebis (4-phenyl-1-yloxy) (ie -OPhC (CF3) 2PhO-), 4-chloromethylphenyl-1-yl, 3-trifluorovinyl-2-thienyl, 3-trichloromethylphenyl (i.e., 3-CCl3Ph-), 4- (3-bromoprop-1-yl) phen-1-yl (i.e. 4-BrCH2CH2CH2Ph-) and the like . Other examples of aromatic radicals include 4-allyloxyphen-1-oxy, 4-aminophen-1-yl (ie, 4-H2NPh-), 3-aminocarbonylphenyl-1 (ie, NH 2 COOPh-), 4- benzoylphen-1-yl, dicyanomethylidenebis (4-phen-1-yloxy) (i.e. -PhC (CN) 2 PhO-), 3-methylphenyl-1-yl, methylenebis (4-phenyl-yloxy) ( namely -OPhCH2PhO-), 2-ethylphen-1-yl, phenylethenyl, 3-formyl-2-thienyl, 2-hexyl-5-furanyl, hexamethylene-1,6-bis (4- phen-1-yloxy) (ie -OPh (CH2) 6PhO-), 4-hydroxymethylphen-1-yl (ie, 4-HOCH2Ph-), 4-mercaptomethylphenyl-1-yl (ie, 4-HSCH2Ph- ), 4-methylthiophen-1-yl (ie, 4-CH3SPh-), 3-methoxyphen-1-yl, 2-methoxycarbonylphenyl-1-yloxy (eg methyl salicyl), 2- nitromethylphenyl-1-yl (ie 2-NO2CH2Ph), 3-trimethylsilylphenyl-1-yl, 4-t-butyldimethylsilylphenyl-1-yl, 4-vinylphenyl-1-yl, vinylidenebis (phenyl) and the like. The term "C3-C10 aromatic radical" embraces aromatic radicals containing at least three but not more than 10 carbon atoms. The aromatic radical 1-imidazolyl (C3H2N2-) represents a C3 aromatic radical. The benzyl radical (C7H7-) represents a C7 aromatic radical. For the purposes of the present description, the term "cycloaliphatic radical" refers to a radical having a valence of at least one and comprising an atomic matrix which is cyclic but which is not aromatic. As defined herein, a "cycloaliphatic radical" does not contain an aromatic group. A "cycloaliphatic radical" may include one or more non-cyclic components. For example, a cyclohexylmethyl group (the ring of atoms that is cyclic but not aromatic) and a methylene group (the non-cyclic component). The cycloaliphatic radical may include hetero atoms such as nitrogen, sulfur, selenium, silicon and oxygen OR may be composed exclusively of carbon and hydrogen. For convenience, the term "cycloaliphatic radical" is defined herein to cover a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example, carboxylic acid derivatives such as esters and amides), amine groups, nitro groups and the like. For example, the 4-methylcyclopent-1-yl radical is a C 6 cycloaliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Likewise, the 2-nitrocyclobut-1-yl radical is a C 4 cycloaliphatic radical comprising a nitro group, the nitro group being a functional group. A cycloaliphatic radical may comprise one or more halogen atoms, which may be Identical or different Halogen atoms include, for example, fluorine, chlorine, bromine and iodine. Cycloaliphatic radicals having one or more halogen atoms include 2-trifluoromethylcyclohex-1-yl, 4-bromodifluoromethylcyclooctyl, 2-chlorodifluoromethylcyclohex-1-yl and hexafluoroisopropylidene-2,2. -bis (cyclohex-4-yl) (ie -C6HioC (CF3) 2 C6H10-), 2-chloromethylcyclohex-1-yl, 3-difluoromethylenecyclohex-1-yl, 4-trichloromethylcyclohex-1-yloxy 4-bromodichloromethylcyclohex-1-ylthio, 2-bromoethylcyclopent-1-yl, 2-bromopropylcyclohex-1-yloxy (e.g.

CH3CHBrCH2C6H10O-) and the like. Other examples of cycloaliphatic radicals include 4-allyloxycyclohex-1-yl, 4-aminocyclohex-1-yl (i.e., H2NC 6E1-10), 4-aminocarbonylcyclopent-1-yl (ie, NH2C005H8-), 4-acetyloxycyclohex-1-yl, 2,2-dicyanoisopropylidenebis (cyclohex-4-yloxy) (ie -OC6FlioC (CN) 2C6E1100-), 3-methylcyclohex-1-yl, methylenebis (cyclohex-4-yloxy), OC6H10CH2C6H10O-), 1-ethylcyclobut-1-yl, cyclopropylethenyl, 3-formyl-2-tetrahydrofuranyl, 2-hexy-5-tetrahydrofuranyl, hexamethylene-1,6-bis (cyclohex-4-yloxy) ) (ie -O C6E110 (CH2) 6C6E1100-), 4-hydroxymethylcyclohex-1-yl (ie, 4-HOCH2C6H10-), 4-mercaptomethylcyclohex-1-yl (ie, 4-HSCH2C6H10-), 4-methylthiocyclohex-1-yl (ie, 4- CH3SC6H10-), 4-methoxycyclohex-1-yl, 2-methoxycarbonylcyclohex-1-yloxy (2-CH3OCOC6H10O-), 4-nitromethylcyclohex-1-yl ( namely NO2CH2C6H10-), 3-trimethylsilylcyclohex-1-yl, 2-t-butyld imethylsilylcyclopent-1-yl, 4-trimethoxysilylethylcyclohex-1-yl (ie (CH3O) 3SiCH2CH2C6H10-), 4-vinylcyclohexen-1-yl, vinylidenebis (cyclohexyl) and the like. The term "C 3 -C 10 cycloaliphatic radical" embraces cycloaliphatic radicals containing at least three but not more than 10 carbon atoms. The cycloaliphatic radical 2-tetrahydrofuranyl (C4H70-) represents a C4 cycloaliphatic radical. The cyclohexylmethyl radical (C6FliiCH2-) represents a C7 cycloaliphatic radical.

As used herein, the term "aliphatic radical" refers to a matrix of at least one valence atoms consisting of a linear or branched, non-cyclic, matrix of atoms. The aliphatic radicals are defined as having at least one carbon atom. The matrix of atoms comprising the aliphatic radical may comprise heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen or may be composed exclusively of carbon and hydrogen. For convenience, the term "aliphatic radical" is defined herein as covering, as part of the "linear or branched non-cyclic atom matrix", a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example, carboxylic acid derivatives). such as esters and amides), amine groups, nitro groups and the like. For example, the 4-methylpent-1-yl radical is a C 6 aliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 2-nitrocyclobut-1-yl radical is a C 4 aliphatic radical comprising a nitro group, the nitro group being a functional group. An aliphatic radical may be a haloalkyl group which has one or more halogen atoms, which may be the same or different. The halogen atoms include, for example, fluorine, chlorine, bromine and iodine. Aliphatic radicals having one or more halogen atoms include alkyl halides such as trifluoromethyl, bromodifluoromethyl, chlorodifluoromethyl, hexafluoroisopropylidene, chloromethyl, difluorovinylidene, trichloromethyl, bromodichloromethyl, bromoethyl, and the like. , 2-bromotrimethylene (eg -CH2CHBrCH2-), and the like. Other examples of aliphatic radicals include allyl, aminocarbonyl (ie -CONH 2), carbonyl, 2,2-dicyanoisopropylidene (ie -CH 2 C (CN) 2 CH 2 -), methyl (i.e. -CH3), methylene (ie -CH2-), ethyl, ethylene, formyl (ie -CHO), hexyl, hexamethylene, hydroxymethyl (ie -CH2OH), mercaptomethyl (ie -CH2SH), methylthio (ie -SCH3), methylthiomethyl (ie -CH2SCE13), methoxy, methoxycarbonyl (ie, CE13000-), nitromethyl (ie -CH2NO2), thiocarbonyl trimethylsilyl (i.e. (CH 3) 3 Si), t-butyldimethylsilyl, 3-trimethyloxy-silylpropyl (i.e. (CE130) 3 SiCH2CH2CH2-), vinyl, vinylidene and the like. In another example, a C 1 -C 10 aliphatic radical contains at least one but not more than 10 carbon atoms. A methyl (i.e., CH 3 -) group is an example of a C 1 + aliphatic radical. A decyl group (i.e., CH 3 (CH 2) 9 -) is an example of a C 10 aliphatic radical. As explained in detail below, some embodiments of the invention relate to a polymerizable composition for an electric machine. The polymerizable composition comprises: (A) from about 10 percent by weight to about 30 percent by weight of a polyfunctional cyanate ester of structure (I) Ar1-OCN (I) wherein "n" is an integer equal to or greater than at 1, Y has a structure (i) or (ii) (i) R2-Ar2-OCN, or (ii) * Ar2-OCN Ar 'and Ar2 are independently at each occurrence a C5-C30 aromatic radical, R and R2 are independently each occurrence a C1-C3 aliphatic radical or a C3-C20 cycloaliphatic radical and * represents the linking site; (B) about 25 percent by weight to about 60 percent by weight of a first difunctional cyanate ester with structure (II), or a prepolymer thereof (II) NCO-Ara-R3-Ar3 -0CN where Ar3 is a C5-C30 aromatic radical, R3 is a bond or a C1-C2 aliphatic radical; (C) about 10 percent by weight to about 30 percent by weight of a second difunctional cyanate ester with structure (III), or prepolymer thereof (III) NCO-Ar4-R5-Ar4 -OCN I) NC ° where Ar4 is a C5-C30 aromatic radical and R5 is a C3-C10 aliphatic radical; and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride. The term "polyfunctional cyanate ester" as used herein refers to a material having three or more cyanate ester functional groups. The term "bifunctional cyanate ester" as used herein refers to a material having two functional groups of cyanate esters. Non-limiting examples of polyfunctional cyanate esters include phenol novolac cyanate ester, dicyclopentadiene modified novolac cyanate ester, 1,2,3-tris (4-cyanatophenyl) propane or combinations thereof. -this. In certain embodiments, the polyfunctional cyanate ester comprises a structure of formula (VII) or (VIII): OCN OCN OCN (VIII) NCO OCN OCN (VIII) OCN Non-limiting examples of polyfunctional cyanate esters Primaset® PT30, Primaset® PT15, or combinations of these are available from Lonza. In some embodiments, the amount of polyfunctional cyanate ester in the polymerizable composition is from about 10 percent by weight to about 30 percent by weight. In some embodiments, the amount of polyfunctional cyanate ester in the polymerizable composition is from about 12 percent by weight to about 22 percent by weight. In some embodiments, the amount of polyfunctional cyanate ester in the polymerizable composition is from about 14 percent by weight to about 18 percent by weight. In some embodiments, the first bifunctional cyanate ester comprises a structure of formula (IV): ## STR2 ## wherein Ar 'is a C 5 -C 30 aromatic radical. In certain embodiments, the first bifunctional ester comprises a structure of formula (IX): ## STR1 ## A non-limiting example of a suitable difunctional cyanate ester ester is Primaset® LECY, marketed by Lonza. The amount of first bifunctional cyanate ester in the polymerizable composition is from about 25 percent by weight to about 60 percent by weight. In some embodiments, the amount of first bifunctional cyanate ester in the polymerizable composition is from about 30 percent by weight to about 50 percent by weight. In some embodiments, the amount of the first bifunctional cyanate ester in the polymerizable composition is from about 32 percent by weight to about 40 percent by weight. In one embodiment, the second bifunctional cyanate ester comprises a prepolymer of a bifunctional cyanate ester of formula (V): (V) NCO-Ar4-R4-Ar4-OCN wherein Ar4 is a C5-aromatic radical C30 and R4 is a C3-C20 aliphatic radical. The term "prepolymer" as used herein refers to a monomer or a plurality of monomers reacted to take an intermediate molecular weight state. This material is amenable to further polymerization by reactive groups to take a high molecular weight state. In this way, mixtures of reactive polymers with unreacted monomers may also be called prepolymers. The term "prepolymer" and the term "polymer precursor" are sometimes used interchangeably. In one embodiment, the second bifunctional cyanate ester comprises a prepolymer of a bifunctional cyanate ester of formula (VI): CH 3 NCO-Ar4-C-Ar4-OCN (W) CH3 where Ar4 is a C5-C30 aromatic radical. . In one embodiment, the second bifunctional cyanate ester comprises a prepolymer of a bifunctional cyanate ester of formula (X): ## STR1 ## A non-limiting example of a suitable second difunctional cyanate ester is Primaset® BA3000, marketed by Lonza. In one embodiment, the amount of second bifunctional cyanate ester in the polymerizable composition is from about 10 percent by weight to about 30 percent by weight. In addition, the amount of second bifunctional cyanate ester in the polymerizable composition may be from about 15 percent by weight to about 25 percent by weight. In some embodiments, the amount of the second difunctional cyanate ester in the polymerizable composition is from about 18 percent by weight to about 22 percent by weight.

The polymerizable composition further comprises a thermally conductive filler. The thermally conductive filler comprises boron nitride. In some embodiments, the thermally conductive filler is added at different dose levels depending upon several requirements of the polymerized composition (especially thermal conductivity, viscosity, or toughness). In some embodiments, the thermally conductive filler is present in the polymerizable composition in an amount of from about 5 percent by weight to about 25 percent by weight. In some embodiments, the thermally conductive filler is present at about 15 percent by weight to about 25 percent by weight. In some embodiments, the thermally conductive filler is present in an amount of from about 18 percent by weight to about 22 percent by weight. The polymerizable composition may further comprise a hardener, the hardener comprising a reactive cyanate ester, a thermoplastic polymer or a combination thereof. The hardener may be present at about 5 percent by weight to about 15 percent by weight. The term "reactive cyanate ester" as used herein means a material comprising cyanate ester moieties, which is capable of reacting with one or more of the polyfunctional cyanate ester, the first difunctional cyanate ester, and the second bifunctional cyanate ester. A non-limiting example of a suitable reactive cyanate ester is the Primaset® HTL 300 marketed by Lonza.

In one embodiment, the thermoplastic polymer comprises a polyimide. In certain embodiments, the polyimide comprises structural units of formula (XI): wherein R 6 is a C 3 -C 10 aliphatic radical, a C 5 -C 30 aromatic radical or combinations thereof. A non-limiting example of suitable polyimide is P84®, marketed by Evonik. The crosslinking reaction of cyanate ester resins at high temperatures can be controlled by a choice of suitable catalysts. In some embodiments, the polymerizable composition may further comprise a suitable catalyst. Without being bound by any theory, it is believed that in the absence of a sufficient amount of catalyst the polymerizable composition may react quickly when raised to high temperatures and the corresponding reaction rate may be greater than the rate heat dissipation, which leads locally to hot spots and thermal runaway. In some embodiments, the reaction temperature can be lowered and the reaction rate can be controlled by selecting a suitable chemical composition of the catalyst and controlling the amount of catalyst used. Non-limiting examples of suitable catalysts are carboxylates or metal chelates.

In some embodiments, non-limiting examples of suitable catalyst are acetylacetonates of zinc, copper, cobalt, manganese, iron, aluminum or combinations thereof. In some embodiments, the catalyst comprises copper acetylacetonate, cobalt acetylacetonate, aluminum acetylacetonate, or combinations thereof. In some embodiments, cocatalysts constituting an active hydrogen source (eg, alkylphenols) may also be used. In some embodiments, the catalyst may be present in the polymerizable composition in an amount of from about 10 parts per million (ppm) to about 150 ppm. In one embodiment, the polymerizable composition may further include additional additives such as stabilizers, additional hardeners, and the like.

The polymerizable composition can be polymerized by any suitable method. In some embodiments, the polymerizable composition can be polymerized by heating the composition. In some embodiments, a temperature of about 18 ° C to about 400 ° C may be employed for the polymerization. In some embodiments, a temperature of about 100 ° C to about 300 ° C may be employed for the polymerization. The time required for the polymerization may vary depending on the final application; for example, it may depend on the thickness of the molded article or laminate. In some embodiments, a sufficient amount of time for the polymerization of the composition may be from about 2 hours to about 12 hours. In embodiments where the polymerized composition is used in the form of molded articles (such as those made by resin transfer molding, compression molding, or injection molding), laminates, glued articles, or the like. As encapsulating materials, it may be desirable to apply pressure during the hot polymerization step. In some other embodiments, microwaves, high frequencies, ionizing radiation, electron beams or combinations thereof can be used to perform the polymerization step. Without being bound by any theory, it is believed that the polyfunctional cyanate ester, after crosslinking, has the desired thermal stability and thermal properties. By mixing the first difunctional cyanate ester with the polyfunctional cyanate ester, a thermally stable resin can be obtained, the resin having a glass transition temperature greater than 280 ° C. Moreover, the first difunctional cyanate ester, mixed with the polyfunctional cyanate ester, provides the desired viscosity for the transformation. However, the polymerized composition formed after the crosslinking of the polyfunctional cyanate ester and the first bifunctional cyanate ester is ordinarily rigid and may be susceptible to cracking during the thermal cycle. Hardeners such as the second difunctional cyanate ester are added to improve the mechanical properties of the composition while preserving the viscosity of the polymerizable composition and the desired thermal stability. The hardener can react with the cyanate resins and form a homogenous cross-linked structure with longer chains to provide heat resistance and thermal stability. In some embodiments, as discussed above, additional hardeners may be added to the composition to improve the toughness, the hardener comprising a reactive cyanate ester, a thermoplastic polymer, or a combination thereof.

The thermal conductivity of the polymerized composition can be further enhanced to provide, for electrical machines, a heat-conductive and mechanically-resistant encapsulation (encapsulation) composition for high temperatures. In some embodiments, boron nitride is added to increase the thermal conductivity of the polymerized composition. Without being bound by any theory, it is believed that even if the boron nitride filler increases the thermal conductivity of the polymerized composition, the toughness of the composition obtained may in some cases be reduced. In some cases of this type, to improve the toughness of the polymerized composition, an additional hardener (eg, a reactive cyanate ester or a thermoplastic polymer) may be added. The additional hardener can improve the breaking strength. In some embodiments of the present invention, to formulate a polymerized composition having the desired properties, five base materials may be blended which include a polyfunctional cyanate ester, a first bifunctional cyanate ester, a second bifunctional cyanate ester a heat-conductive filler (such as boron nitride) and a hardener (such as a thermoplastic polymer or a reactive cyanate ester). Without being bound by any theory, it is believed that by controlling the relative amounts of polyfunctional cyanate ester, the first difunctional cyanate ester, the second difunctional cyanate ester, a thermally conductive filler (such as boron nitride). ) and a hardener (such as a thermoplastic polymer or a reactive cyanate ester), the desired combination of properties (such as thermal stability, thermal conductivity, flexural strength, toughness, rupture and viscosity). For example, as described above, a certain minimum amount of the polyfunctional cyanate ester is desirable to achieve the desired thermal stability. Likewise, the amount of the first bifunctional cyanate ester can be controlled in the polymerizable composition so that the polymerizable composition has a sufficiently low viscosity to be converted. In some embodiments, the polymerizable composition may be substantially solvent-free and the first bifunctional cyanate ester may provide the desired viscosity characteristics. In addition, the amount of the second difunctional cyanate ester can be controlled in the polymerizable composition to provide the desired mechanical properties in the polymerized composition. As indicated above, an appropriate amount of thermally conductive filler may be added to further enhance the thermal conductivity of the composition. However, the addition of boron nitride may reduce the toughness of the composition, which may be restored by providing a controlled amount of a hardener such as a thermoplastic polymer or a reactive cyanate ester. In one embodiment, the polymerizable composition has a viscosity and the corresponding polymerized composition has thermal and mechanical properties favorable to the final application (for example, as a coating material for an alternator stator). The term "polymerized composition" as used herein covers partially as well as completely polymerized compositions. In one embodiment, the polymerizable composition has a viscosity of less than about 5000 centipoise at a temperature of about 100 ° C. In some embodiments, the polymerizable composition has a viscosity of less than about 4000 centipoise (cP) at a temperature of about 100 ° C. In some embodiments, the polymerizable composition has a viscosity of less than about 3000 centipoise (cP) at a temperature of about 100 ° C.

As a contribution to the improvement of thermal stability, it is desirable in some embodiments that the polymerized composition has a glass transition temperature of at least about 280 ° C. In some embodiments, the polymerized composition from the polymerizable composition has a glass transition temperature of at least about 300 ° C. As indicated, a thermally conductive filler (such as boron nitride) is added to enhance the thermal conductivity of the polymerized composition. In some embodiments, the polymerized composition has a thermal conductivity of about 0.75 W / m.K to about 1.2 W / m.K. In some other embodiments, the polymerized composition has a thermal conductivity greater than 1 W / m.K. After the thermal cycle, the polymerized composition may also be characterized by flexural strength and fracture toughness. In one embodiment, the polymerized composition has a flexural strength greater than 55.16 MPa (8000 psi). In some embodiments, the polymerized composition has a flexural strength of about 58.6 MPa to about 75,85MPa (8500-11,000 psi). In some embodiments, the polymerized composition has a fracture toughness of about 1.2 MPa.m-12 to about 1.6 MPa.m-12. Non-limiting examples of suitable applications for the polymerizable composition include encapsulation, gluing, insulation, lamination or combinations thereof. In some embodiments, the polymerizable composition can be used to encapsulate components of an electric machine. Non-limiting examples of suitable components include stators, coils, core sheets, notch covers, notch wedges or combinations thereof. The electrical machine may be selected from a motor, an alternator, a transformer, a toroidal core, an inductor and combinations thereof. In some embodiments, an alternator stator includes the polymerized composition obtained from the polymerizable composition. FIG. 1 schematically represents a stator 100 impregnated with the polymerizable composition 120. As illustrated in FIG. 1, the polymerizable composition 120 and the polymerized composition obtained can fill all the interstices and spaces present between the stator windings 110.

In one embodiment there is also provided an electrically insulating encapsulating material having a polymerized composition obtained from the polymerizable composition. In some cases, the encapsulating material can provide: (1) the desired thermal stability at a temperature above 250 ° C through the use of the polyfunctional cyanate ester and a thermally conductive filler (boron nitride) ); and (2) processability for the impregnation process through the use of the first bifunctional cyanate ester to preserve the viscosity, and the choice of a suitable exothermic catalyst to minimize thermal runaway heat as much as possible . In addition, in some embodiments, the encapsulating material can be thermally stable and can effectively dissipate heat generated by electrical machines operating at elevated temperatures. The property of high temperature stability and heat dissipation may be useful, for example, in applications in alternators. The alternator requires heat reduction with maximum power output, especially when used in aeronautics and other aerospace applications. The encapsulating material may also be suitable for use in electric motors and transformers. In some of these cases, the encapsulating material can provide the desired resistance to shock and vibration and the exclusion of moisture and corrosive agents during high speed vibrations.

A method for encapsulating an electric machine component is also provided. The method comprises the application, in contact with the component, of an encapsulation material comprising a polymerizable composition described above. The term "application" as used herein refers to the impregnation of one or more components of the electrical machine with the polymerizable composition using an appropriate technique, for example pressure impregnation OR impregnation. under vacuum. For example, in some embodiments, the method may include placing a stator in a mold. An encapsulation composition may be impregnated into the stator cavity by application of a pressure such that the encapsulation composition fills all gaps and interstices present in the stator components (such as interstices between stator coils). The method further comprises heating the component to polymerize the polymerizable composition in the presence or absence of vacuum. An example of such a process is provided by the vacuum and vacuum impregnation process, in which an entire component of an electric machine is placed in a pressure vessel under a high vacuum which expels air and air. other trapped gases. The polymerizable composition is introduced into the pressure vessel and the entire vessel is pressurized, usually to at least 620 kPa (90 psi) or more to achieve full penetration into the machine components. The assembly can be fired at high temperatures to polymerize the polymerizable composition. In some embodiments, the polymerizable composition is polymerized at a temperature of about 120 ° C to about 250 ° C. EXAMPLES Materials: BA3000, PT-30, LECY and Primaset HTL-300 were purchased from Lonza. Polyimide P84 NT2 was purchased from Evonik, and PTX60P boron nitride was purchased from Momentive. All resin mixtures were made in plastic cups (resin cups) designed to serve in a high speed planetary centrifugal mixer equipped to evacuate. The boron nitride feedstock and the thermoplastic hardeners were dried for at least 24 hours at 150 ° C in a vacuum oven and were removed from the oven before the feeds.

Process for preparing a catalyst solution: A solution of copper (II) acetylacetonate was prepared by adding 0.300 g of Cu (acac) 2 in 10.0 g of nonylphenol. The resulting copper (II) acetylacetonate solution was poured into an oversized bottle and sonicated for 60 minutes at 50 ° C.

Details of the Polymerization Process: Polymerization Program: A series of formulations contained in various metal molds and trays was polymerized in a programmable oven according to the following protocol: 1) Heating at 120 ° C from room temperature and holding at 120 ° C for 3 hours. 2) Heating at 165 ° C and holding for 2 hours. 3) Heating at 250 ° C and maintaining for 4 to 6 hours.

In another possible process, the first step was omitted and the sample was heated directly to a temperature of 150 ° C to 165 ° C to completely gel the material and carry out most of the polymerization prior to polymerization. final at high temperature. The following ASTM methods were used to determine: 1) flexural strength (D790); 2) bending deformation (D790); fracture toughness (D5045); 4) the glass transition temperature or Rg by AMD (E1540); and 5) thermal conductivity (E1540) measured at 250 ° C. Viscosity measurements were performed as follows: The viscosity of the resin formulation was tested using a Brookfield DV-II + programmable viscometer with a Thermosel temperature controller. In a disposable sample chamber (model # HT-2DB) were charged 17.5 grams (+/- 0.5 grams) of resin formulation preheated (at 50 ° C), gently brewed after warming up to ensure homogeneity. A Thermosel chuck from the SC4 series has been placed inside the sample chamber already inserted into the Thermosel temperature controller. The viscosity was measured at a rotational speed of 6 rpm and a temperature of 100 ° C. After 15 minutes of equilibration under these conditions, the viscosity was recorded. EXAMPLE 1 Mixtures of PT30, LECY, BA3000 and Boron Nitride (BN) BA3000 is placed for about 1 hour at 75 ° C in an oven to facilitate transfer to a resin cup. The resin cup is loaded with BA3000, LECY and PT-30 and heated in an oven for 15 to 30 minutes. The constituents are then stirred for 4 minutes, then manually stirred to ensure that the entire BA3000, possibly undissolved, is distributed throughout the well and then stirred again for 4 minutes. After cooling the resin mixture on bench for 15 to 20 minutes, copper acetylacetonate in nonylphenol (50 ppm copper acetylacetonate relative to the resins) is added to the resin mixture and stirred for a further period of time. 30 seconds. Dry boron nitride is added to the above resin and catalyst mixture and stirring is performed for 30 seconds. The stirring is continued under vacuum for another 3.5 minutes to complete and the homogeneous mixture is degassed. Just after brewing, samples for thermal conductivity tests and mechanical tests are prepared by pouring the mixture into molds and / or simple disposable trays previously treated with Frekote. The remainder of the resin is stored at 4 ° C pending viscosity measurements and as a reserve for possible additional controls. Table 1 details the different mix samples and their composition. In Table 1, Sample No. 1 is the comparative example without PT30 or any hardener. Table 2 presents the data for samples 2 to 12 (mixtures with BN load) compared to comparative sample 1 (no-load mixture of BN).

Table 1: Composition of the various blends No. BA 3000% by weight LECY PT 30 BN P84% by weight% by weight% by weight% by weight 1 38.7 38.7 - 22.5 - 2 19, 4 38.7 19.4 22.5 - 3 31.0 31.0 1'5 22.5 - 4 19.4 38.7 1, .5 22.5 3.9 5 19.4 34.8 1 , .5 22.5 7.7 6 20.6 41.2 20.6 17.5 - 7 20.6 37.1 16.5 17.5 8.2 3037065 29 8 20.6 41.2 20, 6 17.5 - 9 20.0 36.0 16.0 20.0 8.0 10 20.0 39.9 20.0 20.0 - 11 21.8 39.3 17.5 12.5 8, 7 12 21.2 38.2 17.0 15.0 8.5 Table 2: Properties of the various mixtures No. Viscosity Cp at 100 ° C Tg (° C) Flexural strength (MPa) TR TB d deformation sample (Mpa.m "2) (W / mK) 1 - 292 2 1625 312 58.9 1.6 1.241 1.08 3 - 308 59.98 1.61 1.287 4 - - 59.25 1.65 1.349 5 5000 - 64.9 1.83 1.483 6 2150 - 61.64 1.83 1.23 7 1200 - 65.94 1.99 1.266 0.7 8 600 - 64.12 2.05 1.074 0.56 9 2400 311 66.86 2.25 1.433 0.82 10 1100 314 62.81 1.90 1.234 0.77 11 450 - - - - 0.55 12 700 - - - - 0.62 EXAMPLE 3 Mixtures of PT30, LECY, BA3000, nitride of bo re 5 and thermoplastic polyimide (P84) BA3000 is placed for about 1 hour at 75 ° C in an oven to facilitate transfer to a resin cup. The resin cup is loaded with BA3000, LECY and PT-30 and heated in an oven for 15 to 30 minutes. These constituents are then stirred for 4 minutes, then manually stirred to ensure a distribution, throughout the bucket, of the possibly undissolved BA3000, and again stirred for 4 minutes. Thermoplastic polyimide P84 is then added to the resin mixture above and stirred for 30 seconds. After cooling the resin mixture and P84 hardener on bench for 15 to 20 minutes, copper acetylacetonate in nonylphenol (50 ppm copper acetylacetonate relative to the resins) is added to the resin mixture and stirred for another 30 seconds. The dry boron nitride is added to the resin mixture and stirred for 30 seconds. The stirring is continued under vacuum for another 3.5 minutes to complete and the homogeneous mixture is degassed. Just after brewing, samples for thermal conductivity tests and mechanical tests are prepared by pouring the mixture into molds and / or simple disposable trays previously treated with Frekote. The remainder of the resin is stored at 4 ° C pending viscosity measurements and as a reserve for possible additional controls. Table 1 details the different mix samples and their composition.

Table 2 presents the data for samples 4, 5, 7, 9, 11 and 12 (mixtures with P84 formulations) compared to comparative samples 2, 3, 6, 8 and 10 (mixtures without hardener P84). Various mixtures comprising PT30, LECY, BA300, P84, with a variable concentration of BN, are compared in Table 2. In Table 1, samples 11, 12, 7 and 8 show a concentration, from strong (such as 12.5, 15, 17.5 and 20% by weight), BN in the mixture with an approximately invariable amount of hardener P84. As the BN concentration increases from 12.5 to 20% by weight, the concentration of other constituents, including P84, decreases proportionately. The thermal conductivity (0.55, 0.62, 0.7, 0.82) and the viscosity (450, 700, 1200, 2400 cP at 100 ° C) of the mixture increase with the increase in the concentration of the mixture. BN. The data is also shown in Figure 2 which shows an improvement in the thermal conductivity of the mixture related to the increase in boron nitride concentration. The use of a hardener such as thermoplastic polyimide in the blend (eg, the blend of PT30, LECY, BA3000, BN and P84 - samples 4, 5, 7, 9, 11 and 12) improves the property toughness compared to the hardener-free mixture (eg a mixture of PT30, LECY, BA3000 and BN - samples 2, 3, 6, 8 and 10). A comparison of samples reveals that the hardener P84 enhances the mechanical strength of the material, particularly the fracture toughness (TR) (Table 2). The fracture toughness increases from 1.07 (Sample No. 8) to 1.27 Mps.m1 / 2 (Sample No. 7) to 17.5% by weight of BN, and from 0 to 8.2 % by weight the P84 concentration of the samples. Similarly, the fracture toughness (TR) increases from 1.23 (Sample No. 10) to 1.43 (Sample No. 9) Mps.m1 / 2 for 20% by weight of BN by increasing from 0 to 8.0% the P84 concentration of the samples. EXAMPLE 4 Blends of PT30, LECY, BA3000, BN and Primaset HTL-300 BA3000 is placed for about 1 hour at 75 ° C in an oven to facilitate transfer to a resin cup. The resin cup is loaded with BA3000, LECY, PT-30 and HTL-300 (15% by weight) and heated in an oven for 15 to 30 minutes. The components are then stirred for 4 minutes, then manually stirred to ensure that the entire BA3000, if not undissolved, is distributed throughout the well and again stirred for 32 minutes. After bench cooling for 15 to 20 minutes, copper acetylacetonate in nonylphenol (50 ppm copper acetylacetonate relative to the reactive resins) is added and stirred for a further 30 seconds. The dry boron nitride is added and stirred for 30 seconds. The vacuum is then made in the mixer; the stirring continues, under vacuum, for another 3.5 minutes to complete and the homogeneous mixture is degassed. Just after brewing, samples for thermal conductivity tests and mechanical tests are prepared by pouring the mixture into molds and / or simple disposable trays previously treated with Frekote. The remainder of the resin is stored at 4 ° C pending viscosity measurements and as a reserve for possible additional controls. The result of the mechanical tests for the HTL-300 mixtures is shown in Table 3. The viscosity increases (from 1900 cP to 6500 cP at 100 ° C) for the HTL-300 formulations as shown in Table 3, especially for samples Nos. 13, 14, 15, 18, 16 and 17. The viscosity increases substantially when the HTL-300 concentrations are sufficiently high to improve the various mechanical properties. Therefore, the HTL-300 mixture can be used in applications where low viscosity values are not essential. Table 3: Various properties of a mixture containing HTL-300 Sample No. BA LEC Y PT BN% HTL Viscosity Cp at 100 ° C Tg (° C) Bending Strength Defor- mation TR 300 0 30 weight -300 (Mps.-m-2) 13 19.4 38.7 15.5 22.5 3.9 1900 314 57.57 1.55 3037065 33 14 19.4 34.8 15.5 22 , 5 7.7 2300 318 53.2 1.65 1.272 15 19.4 31.0 15.5 22.5 11.6 2500 318 55.35 1.85 1.305 16 19.4 27.1 15.5 22 15.5 4300 - 59.28 1.82 1.299 17 19.4 23.2 15.5 22.5 19.4 6500 - 54.5 1.62 1.319 18 19.4 31.0 15.5 22 , 5 11.6 2400 - 62.28 1.94 1.198

Claims (20)

REVENDICATIONS1. A polymerizable composition for an electric machine, comprising: (A) about 10 percent by weight to about 30 percent by weight of a polyfunctional cyanate ester having the structure (1) (I) NCO-Ar1-R1-fY-R1- 1 --- Ar1-OCN where "n" is an integer equal to or greater than 1, Y has a structure (i) or (ii): * R2-Ar2-OGN or * Ar2-0CN Arl and Are are independently at each occurrence of a C 5 -C 30 aromatic radical, R 1 and R 2 are independently at each occurrence a C 1 -C 3 aliphatic radical or a C 3 -C 20 cycloaliphatic radical and * represents the binding site; (B) about 25 percent by weight to about 60 percent by weight of a first bifunctional cyanate ester with structure (II), or a prepolymer thereof (II) NCO-Ara-R3-AP-OCN where Ara is a C 5 -C 30 aromatic radical, R 3 is a bond or a C 1 -C 2 aliphatic radical; (C) about 10 percent by weight to about 30 percent by weight of a second difunctional cyanate ester with structure (III), or a prepolymer thereof (III) NCO-Ar4-R5-Ar4-O-CN 3037065 Wherein Ar4 is a Cs-C30 aromatic radical and R5 is a C3-C10 aliphatic radical; and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride. The polymerizable composition of claim 1, further comprising about 5 percent by weight to about 15 percent by weight of a hardener, the hardener comprising a thermoplastic polymer, a reactive cyanate ester, or a combination thereof. The polymerizable composition of claim 1, wherein the thermoplastic polymer comprises a polyimide. The polymerizable composition according to claim 1, wherein the hardener comprises a polyimide having structural units of formula (XI): the radical R6 being a C3-C10 aliphatic radical, a C5-C30 aromatic radical or combinations of them. 20 The polymerizable composition of claim 1, wherein the polyfunctional cyanate ester comprises a phenol novolac cyanate ester, a dicyclopentadiene modified novolac cyanate ester, a 1,2,3-tris (4-cyanatophenyl) propane, or combinations of these. Mt rc (XI) 3037065 36 Polymerizable composition according to claim 1, wherein the first bifunctional cyanate ester comprises a structure of formula (IV): NCO-Ara-CH-Ara-OCN (CH3 1-v) where Ara is a C5 aromatic radical -C3o. The polymerizable composition of claim 1, wherein the second bifunctional cyanate ester comprises a prepolymer of a bifunctional cyanate ester of formula (V): ## STR1 ## wherein Ar 4 is a C 5 -C 30 aromatic radical and R 4 is a C 3 -C 20 aliphatic radical. The polymerizable composition of claim 1, wherein the second bifunctional cyanate ester comprises a prepolymer of a bifunctional cyanate ester of formula (VI): ## STR3 ## wherein Ar 4 is a C 5 -C 30 aromatic radical. The polymerizable composition of claim 1 comprising from about 25 ppm to about 150 ppm of a catalyst. The polymerizable composition of claim 9, wherein the catalyst comprises copper acetylacetonate, cobalt acetylacetonate, aluminum acetylacetonate, or combinations thereof. The polymerizable composition of claim 1, wherein the polymerizable composition has a viscosity of less than about 5000 centipoise at 100 ° C. 3037065 37 The polymerizable composition of claim 1, wherein a polymerized composition obtained from the polymerizable composition has a thermal conductivity of about 0.75 W / m.K to about 1.2 W / m.K. 5 The polymerizable composition of claim 1, wherein a polymerized composition obtained from the polymerizable composition has a glass transition temperature equal to or greater than 280 ° C. An electric machine having a polymerized composition obtained from the polymerizable composition of claim 1, the electrical machine being selected from a motor, an alternator, a transformer, a toroidal core, an inductor and combinations of those -this. An electrically insulating encapsulating material comprising the polymerizable composition of claim 1. 16. Alternator stator comprising a polymerized composition obtained from the polymerizable composition according to claim 1. 17. A polymerizable composition for encapsulating an electrical machine component, comprising: (A) about 14 weight percent to about 18 weight percent of a polyfunctional cyanate ester having the structure (I) NCO-Ar1-R1 Wherein "n" is an integer equal to or greater than 1, Y has a structure (i) or (ii): ## STR2 ## ii) * Ar2-0CN, Ar and Are are independently at each occurrence a C5-C30 aromatic radical, III and R2 are independently at each occurrence a C1-C3 aliphatic radical or a C3-C20 cycloaliphatic radical and represents the binding site (B) about 32 percent by weight to about 40 percent by weight of a first difunctional cyanate ester with structure (II), or a prepolymer thereof (T) NCO-Ara -R3-Ar3-0CN where Ara is a Cs-C30 aromatic radical, R3 is a C1-C2 aliphatic bond or radical, (C) about 18 percent by weight to about 22 percent by weight of a second bifunctional cyanate ester with structure (III), or a prepolymer thereof (III) NCO-Ar4-R5-Ar4-OCN wherein Ar4 is a Cs-C30 aromatic radical and R5 is a C3-Clo aliphatic radical ; (D) about 18 percent by weight to about 22 percent by weight of a thermally conductive filler comprising boron nitride; and (E) about 5 percent by weight to about 15 percent by weight of a hardener, the hardener comprising a thermoplastic polymer, a reactive cyanate ester, or a combination thereof. 18. A method for encapsulating a component of an electrical machine, comprising: applying, in contact with the component, an encapsulating material having a polymerizable composition, the polymerizable composition comprising: 3037065 (A) about 10 to one hundred percent by weight to about 30 percent by weight of a polyfunctional cyanate ester having the structure (I) (I) NCO-Ar1-111-4Y-R1-1-Ari-OCN where "n" is an integer equal to or greater than 1, Y has a structure (i) or (ii) * R2-Ar2-OCN, or * Ar2-OCN, Ar1 and Are are independently at each occurrence a C5-C30 aromatic radical, R1 and R2 are independently at each occurrence a C 1 -C 3 aliphatic radical or a C 3 -C 20 cycloaliphatic radical and * represents the binding site; (B) about 25 percent by weight to about 60 percent by weight of a first bifunctional cyanate ester with structure (II), or a prepolymer thereof (II) NCO-Ara-R3-A13-0CN where Ar3 is a Cs-C30 aromatic radical, R3 is a bond or a C1-C2 aliphatic radical; (C) about 10 percent by weight to about 30 percent by weight of a second difunctional cyanate ester of structure (III), or a prepolymer thereof (III) NCO-Ar4-R5-Ar4-CN where Ar4 is a C5-C30 aromatic radical and R5 is a C3-Clo aliphatic radical; and (D) about 5 percent by weight to about 25 percent by weight of a thermally conductive filler comprising boron nitride; and polymerizing the polymerizable composition. 3037065 40 The method of claim 18, wherein the polymerizable composition comprises about 5 percent by weight to about 15 percent by weight of a hardener, the hardener comprising a thermoplastic polymer, a reactive cyanate ester, or a combination thereof. this. The method of claim 18, wherein the polymerizable composition is polymerized at a temperature of about 120 ° C to about 250 ° C.