HK1169430A - Composite of a polymer and surface modified hexagonal boron nitride particles - Google Patents

Description

Composite of polymer and surface modified hexagonal boron nitride particles

Related case number

This patent application is related to commonly owned patent applications filed on the same day as this patent application [ attorney docket numbers CL4388, CL4659, and CL4660 ].

Technical Field

The present invention relates to a polymer composite comprising a polymer and surface-modified hexagonal boron nitride particles dispersed in the polymer. The polymer composite may be used to form a film, which in turn may be used as a substrate for a flexible printed circuit board. The invention also provides a method for preparing the composite material. Suitable polymers include polyimides and epoxies.

Background

U.S.2007/0041918 to Meneghetti et al discloses hexagonal boron nitride treated with a zirconate and which is used in polymers at up to 75 weight percent to produce samples with improved thermal conductivity.

WO 2008/140583 to Sainsbury et al discloses exposure to NH₃Plasma modified BN nanotubes with amine (NH 2). Incorporation into polymers is mentioned.

U.S.6,160,042 to Ishida discloses boron nitride incorporated into epoxy resins surface treated with 1, 4-phenylene diisocyanate.

Mevell et al, chem. mater. "(2007, 19, 6323-.

Epoxies and polyimides are commonly used as components in printed circuit boards. Heat management is an increasing problem due to the increased density of components in electronic circuits. The incorporation of 50 volume% and more hexagonal boron nitride (hBN) particles into the polymer imparts increased thermal conductivity without compromising electrical insulation. Generally, surface treatment of BN particles is required to obtain sufficient dispersion and moldability.

However, even with surface treatments, the high loadings of hBN particles required to improve the thermal conductivity of a given polymer still result in a substantial increase in viscosity with a decrease in processability. This is particularly problematic in the production of base films for flexible printed circuit boards.

Summary of The Invention

The present invention provides a composite material comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the surface-modified hexagonal boron nitride particles comprising hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- - -, halogen, alkyl and substituted or unsubstituted aryl; wherein R is¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or substituted or unsubstituted aryl.

The present invention also provides a method comprising mixing a plurality of surface-modified hexagonal boron nitride particles with a polymer solution comprising a solvent, and extracting the solvent, wherein the surface-modified hexagonal boron nitride particles comprise hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the following structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- - -, halogen, alkyl and substituted or unsubstituted aryl; wherein R is¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or substituted or unsubstituted aryl.

Brief Description of Drawings

Fig. 1 is a schematic structural view of hexagonal boron nitride particles.

FIG. 2a is a photograph of a Transmission Electron Micrograph (TEM) of the edge of hBN (comparative example A) in the as received state.

FIG. 2b is a SMhBN plate edge TEM made according to example 1.

FIG. 3a is a TEM of the basal plane of SMhBN of example 1, as viewed from the platelet edge.

FIG. 3b is a TEM of the SMhBN plate edge of example 1 as viewed from the basal plane.

Detailed Description

In the present invention, a novel treatment of hBN is provided that generates new chemistries on the surface of hBN particles, making them highly compatible with thermoset polymers such as epoxies and polyimides, and provides tough flexible substrates for flexible printed circuit boards.

Whenever a numerical range is provided herein, unless otherwise specifically indicated, the range is intended to include the endpoints of the range.

In one embodiment, the polymer is a thermoset polymer, or uncured (or uncrosslinked) thermosettable polymeric precursor corresponding thereto. When the precursor polymer is subjected to high temperatures, it undergoes a crosslinking reaction (or curing reaction) or imidization reaction that converts the flowable and/or formable polymer into a non-flowable, non-formable polymer. Suitable thermosetting polymers include, but are not limited to, polyimides and cured epoxies. Suitable thermosettable precursor polymers include polyamic acids and epoxy polymers. The curing process may or may not involve the addition of a cross-linking agent. The conversion of certain polymers requires the addition of a crosslinking agent.

The term "flowable" relates to a viscous substance that moves when a shear force is applied. The term "readily formable" refers to a viscous substance that can be formed into a shaped article and hold the shape for a sufficient time so that it can be fixed into that shape by cooling, curing, or imidization. Generally, all of the flowable material is flowable, but not all of the flowable material is flowable. Easily formable substances generally have a higher viscosity than less easily formable but flowable substances.

Polyimides are non-crosslinked thermoplastic polymers that generally decompose before they melt. Polyimides do not exhibit flow at temperatures up to 500 ℃. However, as used herein, the term "thermoset polymer" includes polyimides, while the term "thermosettable polymer" includes polyamic acids.

The present invention provides a thin film having a thickness of less than 500 μm. The film is typically made by, for example, melt casting or solution casting onto the release surface. In one embodiment, the film has a thickness in the range of 10 to 100 μm. In another embodiment, the film has a thickness in the range of 15 to 80 μm. A film that is too thin may exhibit insufficient toughness for use as a substrate for a printed circuit board. A thin film that is too thick may exhibit insufficient flexibility for use as a substrate for a flexible printed circuit board.

The viscosity as described herein was determined at room temperature according to ASTM D2196-05 using a Brookfield viscometer model DV-II +, spindle # 28.

In one aspect, the present invention provides a composition (herein specified SMhBN) comprising hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl and aryl (including substituted aryl); wherein R is¹Is hydrogen, alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -. The substituted phenyl group is bonded to the hBN surface.

It is known that hexagonal boron nitride particles are represented by the structure shown in fig. 1, consisting of a plurality of wafers stacked in layers, providing a high surface area for reaction. The alternating white and black circles represent nitrogen and boron atoms arranged in a hexagonal lattice. The hBN particles used herein are not particle size limited. Typical commercially available hBN particle sizes range from about 0.7 microns, from about 10 to 12 microns, and from about 14 to 15 microns. As the particle size becomes smaller, the particles become more difficult to disperse. On the other hand, with larger particle size formation, the composite film may exhibit undesirable surface roughness.

In one embodiment, the SMhBN has a substituted phenyl concentration in the range of 0.1 to.0 wt.% based on the SMhBN.

In another aspect, the present invention provides a process for preparing SMhBN, said process comprising reacting hexagonal boron nitride particles with a substituted phenyl diazonium chloride in an alcohol/water solution in the presence of metallic iron and dilute HCl, and recovering the reaction product therefrom; wherein the alcohol/water solution has a water concentration of at least 50% by volume; and wherein the substituted phenyldiazonium chloride is represented by the formula

Wherein X is selected from NH₂--、HO--、R²OC(O)--、HSO₃--、NH₂CO- -, halogen, alkyl and aryl (including substituted aryl); r¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl). In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the water/alcohol solution has at least 80% water by volume.

Suitable substituted phenyldiazonium chlorides can be prepared by known methods. For example, the preparation of 4-aminochlorodiazobenzene is described in British patent GB1536320, the preparation of 4-hydroxychlorodiazobenzene is described in "Helvetica Chimica Acta" (English; 68; 1985; 1427-1443) to Grieve et al, and the preparation of 4-carboxydiazobenzene chloride is described in "American chemical Journal" (33; 1905; 417) to Weedon.

In one embodiment, the molar ratio of substituted diazobenzene chloride to hBN in the reaction mixture is in the range of from 0.005: 1 to 0.1: 1. In one embodiment, a molar excess of iron relative to the amount of substituted phenyldiazonium chloride is added. In another embodiment, iron is added in powder form. In another embodiment, the iron powder is less than 1-2mm (10 mesh) in at least one dimension.

The amount of modifier remaining on the hBN surface depends on the surface area of the hBN and the reactivity of the phenyl group. The phenyl group containing an electron donating group (such as amino or alkyl) is more reactive, while the phenyl group containing an electron withdrawing group (such as COOH or OH) is less reactive. The effect of hBN surface area on the absorption of a given phenyl group is shown in table 1:

it has been found that the rate of reaction is controlled by the reactivity and the semi-ideality of the groups and the ease with which the substrate can be reacted. The less reactive hydroxyphenyl group produces less substituted phenyl surface modified hBN than the more reactive aminophenyl group when the starting materials are in the same ratio.

In one embodiment of the process, an excess of iron is present. It is believed that the iron provides a surface on which the reduction of the diazonium salt to a radical occurs. If an excess of iron is present, the reduction reaction can proceed to a higher degree. The excess iron ensures that all diazonium salts are reduced, avoiding the explosion hazard associated with having residual diazonium salts.

The dilute acid reduces the reaction rate of the diazonium salt, thereby reducing the risk of explosion. It has been found that dilute HCl (0.1 to 1.0M in one embodiment, and 0.3 to 0.7M in another embodiment) is desirable for the processes disclosed herein. Due to the relative stability of the diazonium chloride, it is desirable to use HCl to avoid possible explosions.

In one embodiment, the reaction is carried out at room temperature.

In one embodiment of the batch process, an aqueous solution of substituted diazobenzene chloride is mixed with a dispersion of hBN in a water/alcohol mixture. The iron particles were then added to the mixture and stirred for a few minutes, followed by addition of HCl, followed by stirring for an additional about 30 minutes. The concentration of HCl in the reaction mixture does not exceed 0.1M.

In one embodiment, iron particles are removed with a magnet and SMhBN is isolated by filtration and dried.

By mixing alcohol with water, a viscosity suitable for handling and mixing the reaction mixture is obtained. Suitable alcohols include, but are not limited to, C₁To C₆Alkyl alcohols, including methanol, ethanol, and propanol. Alcohol concentrations above 50% by volume have little additional effect on viscosity, but present a safety hazard. The diazonium chloride compositions used herein are naturally unstable, especially when not in solution. The presence of flammable liquids such as alcohols would add undesirable fuel to a fire if a destabilizing event were to occur.

In one embodiment, 50/50 volumes of a mixture of water and alcohol was used as the solvent for the surface modification reaction. In another embodiment, a mixture of 80 vol% water and 20 vol% methanol is used.

In another embodiment, SMhBN is mixed with a polymer to produce a polymer composition comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the surface-modified hexagonal boron nitride particles comprising hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO--、Halogen, alkyl and aryl (including substituted aryl); r¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the polymer comprises polyamic acid. In another embodiment, the polyamic acid is in the form of a solution. In another embodiment, the polymer is a polyimide. In another embodiment, the polymer is an epoxide-containing polymer in liquid or solution form. In another embodiment, the polymer is a cured epoxy resin.

Polyimide chemistry is well known in the art; see, for example, Bryant in "Encyclopedia of Polymer Science and Technology" (DOI10.1002/0471440264.pst272.pub 2). The condensed polyimides are generally obtained by imidization of the corresponding polyamic acids. Suitable polyamic acid compositions include, but are not limited to, polymers prepared by the reaction of equimolar amounts of a diamine and a tetracarboxylic dianhydride (or an acid ester or acid halide ester derivative of a dianhydride) in a suitable solvent. In one embodiment, the anhydride moiety is selected from the group consisting of pyromellitic dianhydride (PMDA), 4, 4-oxydiphthalic anhydride (ODPA), 3, 3 ', 4, 4 ' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 3, 3 ', 4, 4 ' -biphenyl tetracarboxylic dianhydride (BPDA), 2 ' -bis (3, 4-dicarboxyphenyl) 1, 1, 1, 3, 3, 3-hexafluoropropane dianhydride (FDA), and 2, 3, 6, 7-naphthalene tetracarboxylic dianhydride.

Suitable diamines include 1, 4-phenylenediamine (PPD), 1, 3-phenylenediamine (MPD), 4 ' -diaminodiphenyl ether (4, 4 ' -ODA), 3, 4 ' -diaminodiphenyl ether (3, 4 ' -ODA), 1, 3-bis- (4-aminophenoxy) benzene (APB-134), 1, 3-bis- (3-aminophenoxy) benzene (APB-133), 2 ' -bis- (4-aminophenyl) -1, 1, 1, 3, 3, 3-hexafluoropropane (6F diamine), and bis [4- (4-aminophenoxy) phenyl ] ether (BAPE).

The polyamic acid formed can be a homopolymer or a random copolymer (if more than one diamine and/or dianhydride is used for the polymerization). Block copolymers can be formed by initially polymerizing with an excess of a first diamine or a first diacid anhydride, followed by the addition of a different diacid anhydride or diamine, respectively.

Polyamic acids are more highly processable than the corresponding polyimides due to their solubility in a variety of solvents. It is common practice in the art to perform any mixing and shaping operations on the polyamic acid composition, followed by imidization. Polyimides are well known to be highly inert to solvents and high temperatures.

Epoxy chemistry is well known in the art; see, for example, Pham and Marks in "Encyclopedia of Polymer Science and Technology" (DOI10.1002/0471440264.pst 119). "epoxy resin" is a term of art used to refer to cured epoxies. The uncured epoxide has cyclic epoxy groups along the polymer chain. Cured epoxides are cured epoxides in which most of the cyclic epoxy groups have undergone reaction with a curing agent (also referred to as a cross-linking agent) to form cross-links between polymer chains, thereby forming a rigid, substantially inert 3-D network of polymer chains. Suitable uncured epoxy compositions comprise one or more multifunctional or difunctional epoxy resins, an epoxy curing agent, a toughening agent, and a cure accelerator.

Suitable multifunctional epoxy resins include, but are not limited to, epoxy novolacs, cresol novolac epoxy resins, tetraglycidyl ether of diaminodiphenylmethane, triglycidyl tris (hydroxyphenyl) methane, triglycidyl ether of p-aminophenol, naphthalene epoxy resins, triglycidyl derivatives of cyanuric acid, epoxy derivatives of biphenol. Suitable difunctional epoxy resins include, but are not limited to, glycidyl ethers of bisphenol a, bisphenol F, and bisphenol S, as well as reactive diluents such as aliphatic epoxies.

Suitable curing agents for epoxies include, but are not limited to, amines, amides, anhydrides, polyamides, polyamine adducts, organic acids, phenols, and phenolic resins. Phenolic resin curing agents are particularly preferred because of their regulating effect on the viscosity and moisture uptake of the composition, good electrical properties and high temperature mechanical properties. Suitable phenolic resin curing agents include bisphenol a, novalac-type phenol resins, dicyclopentadiene-type phenol, terpene-modified phenol resins, and polyvinyl phenol.

In one embodiment, the epoxy composition further comprises a polymeric toughener having an average molecular weight in the range of 5000-. Suitable polymeric tougheners include, but are not limited to, phenoxy compounds, acrylic acids, polyamides, polycyanates, polyesters, and polyphenylene ethers.

In another embodiment, the epoxy composition further comprises a cure accelerator. Suitable cure accelerators include, but are not limited to, amines, guanidines, imidazoles, triphenylphosphine, triphenylphosphonium tetrafluoroborates, or epoxide adducts thereof.

Uncured epoxies are more highly processable than the corresponding cured epoxies due to their inherent flowability at room temperature or solubility in a variety of solvents. It is common practice in the art to perform any mixing and shaping operations on the uncured epoxy composition followed by curing. It is well known that cured epoxy polymers are highly inert to solvents and high temperatures.

In one embodiment, the polymer composition comprises 30 to 70 wt.% SMhBN. In another embodiment, the polymer composition comprises 40 to 65 wt.% SMhBN. In one embodiment, the average equivalent spherical diameter of the SMhBN is in the range of 0.5 μm to 50 μm. In another embodiment, the average equivalent spherical diameter of the SMhBN is in the range of 0.5 to 25 μm.

It is not necessary to destroy the agglomerated SMhBN. Generally, SMhBN does not readily agglomerate. PT620 is sold by the supplier as agglomerated hBN. In some embodiments, agglomerated SMhBN is preferred for improved thermal conductivity. The SMhBN agglomerates may be soft or hard. By surface modification of PT620 hard agglomerates are formed, suitably agglomerates in the size range 0.5-50 microns. In one embodiment, the SMhBN dispersed in the polymer is characterized by a plurality of particle size distribution peaks characteristic of a so-called multimodal particle size distribution.

Particles having a size of about 1/10 or less of the desired film thickness are suitable for preparing photopatterned films having isotropic, balanced mechanical and thermal properties. Increasing the particle size, causing anisotropy and surface roughness.

In another aspect, the present disclosure provides a method comprising mixing a plurality of surface-modified hexagonal boron nitride particles with a polymer solution comprising a solvent, and extracting the solvent, wherein the surface-modified hexagonal boron nitride particles comprise hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the following structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl and aryl (including substituted aryl); r¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the method further comprises mixing a dispersion of SMhBN in a first organic liquid with a solution of a polymer in a second organic liquid, provided that the first and second organic liquids are miscible and both are solvents for the polymer.

When the polymer is a polyamic acid, suitable organic liquids include, but are not limited to, N '-dimethylacetamide, N' -dimethylformamide, N-methylpyrrolidone, tetramethylurea, dimethyl sulfoxide, and hexamethylphosphoramide.

When the polymer is an epoxy resin, suitable organic liquids include, but are not limited to, acetone, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, carbitol, butyl carbitol, toluene, and xylene.

In one embodiment, the SMhBN is dispersed in the first organic liquid at a solids content in the range of from 20 to 70 wt%. In another embodiment, the solids content is in the range of 30 to 40 wt.%. The dispersion is readily obtained by simple mixing using any mechanical stirrer.

In one embodiment, the first organic liquid and the second organic liquid are both dimethylacetamide (DMAc) and the SMhBN concentration is 30-40%. In this embodiment, the dispersion viscosity is less than 100cp at room temperature. It has been found that a viscosity below 100cp is generally insufficient to obtain uniform mixing of the dispersed SMhBN in the polymer solution. In another embodiment, a masterbatch of 30-40% SMhBN in DMAc is made by adding about 5-20 wt% polymer based on the weight of SMhBN. The presence of the polymer increased the concentration above 100cp and caused the polymer and SMhBN to disperse well into each other, resulting in a masterbatch with a relative SMhBN/polymer concentration in the range of 96/4 to 80/20. The prepared masterbatch is then mixed with other polymer solutions to obtain the final desired concentration of SMhBN in the polymer, i.e. in the range of 30 to 70 wt% based on total solids, in one embodiment in the range of 40 to 65% by weight of total solids. In one embodiment, the polymer is a polyamic acid. In an alternative embodiment, the polymer is an uncured epoxy resin.

The polymer dispersion is made by high shear mixing. Suitable high shear mixers include, but are not limited to, homogenizers (available from Silverson Mechanics Inc, East Long Meadow, MA), blenders, ultrasonic mixers, or roll mills with milling media. The viscosity of the dispersion comprising organic liquid, SMhBN and polymer suitable for high shear mixing may be in the range of 100-2000cp, preferably in the range of 200-1500 cp.

In one embodiment, the second organic liquid may be a liquid polymer, such as a liquid epoxy resin having a relatively low molecular weight and viscosity. Liquid epoxy resins suitable for use in the process are prepared from bisphenol a, bisphenol F, epoxy modified liquid rubbers, epoxy resins derived from polyols such as ethylene glycol, propylene glycol, neopentyl glycol, and the like. Reactive diluents such as allyl glycidyl ether, glycidyl methacrylate and allyl phenyl glycidyl ether can also be used to improve the dispersion of SMhBN. It has been found that the viscosity for high shear mixtures is in the range of 200-1500 cp. The solvent may be used to dilute the dispersion until it is within the viscosity range described above.

In another embodiment, the second organic liquid is selected from N, N '-dimethylacetamide, N' -dimethylformamide or N-methylpyrrolidone and the polymer is dissolved therein at a concentration in the range of 10-30 wt.%, preferably 15-25 wt.%. To achieve miscibility with the first organic liquid when the second organic liquid is a liquid polymer, the liquid polymer is dissolved in the first organic liquid when they are mixed. In one embodiment, the first organic liquid and the second organic liquid are the same. In one embodiment, the first organic liquid and the second organic liquid are both dimethylacetamide (DMAc).

In one embodiment, the dianhydride corresponding to the dianhydride moiety in the polyamic acid SMhBN/polyamic acid dispersion increases the molecular weight of the imidized polymer, desirably improving the mechanical properties of the film. A suitable method is to add the corresponding dianhydride (part of the polyamic acid) in an amount of 10-25 mg, stir the dispersion for ten minutes until the anhydride is completely dissolved in the dispersion, and measure the viscosity of the dispersion. The mixing of the dispersion and the determination of the viscosity of the dispersion is continued with the addition of a small amount of acid anhydride until a dispersion having a viscosity in the range of 60,000-150,000cp and preferably in the range of 75,000-100,000cp is obtained. These viscosities are generally associated with polyamic acid solutions that are suitable for solution casting films followed by imidization into tough, strong polyimide films.

For SMhBN/epoxide dispersions, they preferably have a total solids content of from 40 to 80% by weight, preferably in the range from 50 to 70% by weight. Furthermore, the dispersion viscosity is preferably in the range of 100-2000cp, preferably in the range of 200-1500 cp.

The compositions can be formed into articles such as films or sheets, rods, or other article shapes, and then undergo a transition from a flowable or formable composite to a non-flowable, non-formable composite via curing, imidization, or other means. Depending on the specific characteristics and components of the non-cured composite, it may be desirable to extract at least a portion of the organic liquid to obtain a suitable easily formable composite. Extraction may be achieved by any convenient method, including but not limited to heating in a vacuum oven or air circulation oven, or evaporation on hot rollers by casting.

In one embodiment, the second organic liquid is a liquid polymer and only the first organic liquid undergoes extraction. In one embodiment, the second organic liquid is a solvent for the polymer solution and is also subjected to extraction.

In another aspect, the present invention provides a film having a thickness of less than 500 μm, the film comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, wherein the surface-modified boron nitride particles comprise hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl or aryl (including substituted aryl); wherein R is¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the polymer comprises polyamic acid. In another embodiment, the polyamic acid is in the form of a solution. In another embodiment, the polymer is a polyimide. In another embodiment, the polymer is an epoxide-containing polymer in liquid or solution form. In another embodiment, the polymer is a cured epoxy resin.

In one embodiment, the polymer composition comprises 30 to 70 wt.% SMhBN. In another embodiment, the polymer composition comprises 40 to 65 wt.% SMhBN. In one embodiment, the average equivalent spherical diameter of the SMhBN in the polymer is in the range of from 0.5 μm to 50 μm. In another embodiment, the average equivalent spherical diameter of the SMhBN in the polymer is in the range of from 0.5 to 25 μm. In one embodiment, the SMhBN dispersed in the polymer is characterized by a plurality of particle size distribution peaks characteristic of a so-called multimodal particle size distribution.

In one embodiment, the film further comprises an organic liquid. In one embodiment, the film is easily formable. In an alternative embodiment, the film is not readily formable. Generally, an easily formable film is a precursor to an less easily formable film. In one embodiment, the formable film is first formed and then converted to the non-formable film in a single pass continuous process. In an alternative embodiment, the formable film is made, for example, as a web. The web is passed to a manufacturing machine which forms the easy-to-form film into a complex shape and then causes it to cure or imidize into a less-to-form state while maintaining the complex shape.

In another aspect, the present invention provides a method comprising casting a dispersion of a plurality of surface-modified hexagonal boron nitride particles in a solution of a polymer in a solvent onto a surface, forming the thus-cast dispersion into a viscous liquid film, and extracting the solvent to form a thin film having a thickness of less than 500 μm; wherein the surface-modified hexagonal boron nitride particles comprise hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the following structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl and aryl (including substituted aryl); r¹Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

The term "casting" refers to a process whereby a polymer composition is applied to a surface to form a film. Suitable casting methods include, but are not limited to, adjustable microfilm applicators (doctor blades), wound metering rods (Meyer rods) or slot dies (which are commonly used in large scale production).

A composition suitable for film casting ("casting composition") comprises an organic liquid, a polymer dissolved therein, and a plurality of SMhBN particles dispersed in the polymer. In one embodiment, a casting composition includes a polymer composite comprising a first organic liquid, a second organic liquid miscible in the first organic liquid, a polymer dissolved in at least the first organic liquid or the second organic liquid, and a mixture of a plurality of SMhBN particles dispersed in the polymer. In one embodiment, the polymer is a polyamic acid. In an alternative embodiment, the polymer is an uncured epoxy polymer.

In another embodiment, the first organic liquid and the second organic liquid are the same. In another embodiment, the first organic liquid and the second organic liquid are both DMAc. In an alternative embodiment, the casting composition includes a polymer composite comprising a liquid polymer and a first organic liquid miscible in the liquid polymer, and a mixture of a plurality of SMhBN particles dispersed in the polymer. In another embodiment, the first organic liquid is DMAc. In another embodiment, the liquid polymer is a liquid epoxy polymer.

In one embodiment, the surface onto which the casting composition is cast is selected to provide adhesive contact with the cast film after solvent extraction and to cure or imidize to obtain a multilayer laminate, wherein at least one layer comprises the cured or imidized film. In one embodiment, the casting composition comprises a polyamic acid, and the suitable surface is a polyimide. In another embodiment, the casting composition comprises an epoxy resin, and the suitable surface is a cured epoxy. In another embodiment, the surface is a metal foil surface. In another embodiment, the metal foil is a copper foil.

When the film is cast on a metal foil, the metal surface can be roughened to obtain adhesion. In one embodiment, the casting is performed on the matte side of the electrodeposited copper foil. In an alternative embodiment, casting is performed on the light emitting side of the electrodeposited copper foil, and the foil is used as the release layer. If casting is carried out on a rough surface, but the polymer is not fully cured or imidized, it is also possible to separate the two layers by conventional methods. However, if the polymer is fully cured or imidized, the layers are strongly bonded.

Other materials suitable for use as the release layer include, but are not limited to, polyethylene, polyvinyl chloride, ethylene terephthalate, polyethylene naphthalate, and polycarbonate.

The quality of the film so cast depends on the uniformity of the dispersion in the coating composition, the absence of entrained bubbles, the viscosity of the dispersion, the accuracy with which the cast composition is metered to form a uniform thickness, and the like. The uniformity of the cast composition depends in part on the degree of wetting of the particles by the solvent and resin, and in part on the particle size and degree of agglomeration. Preferably, the particles are dispersed in a moderately viscous resin solution using a high shear mixture. During storage of the low viscosity polymer solution of the dispersion, the particles tend to settle. Suitable epoxy coating compositions have viscosities in the range of 100-2000 cp. Suitable polyamic acid coating compositions have viscosities in the range of 75000-100000 cp. Air bubbles can be removed by vacuum agitation.

In another aspect, the present invention provides a method comprising placing a conductive metal layer on a surface of a polymer composite film having a surface and a thickness of less than 500 μm, the polymer composite film comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the surface-modified hexagonal boron nitride particles comprising hexagonal boron nitride particles, the surface having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group being represented by the following structure, followed by applying pressure or a combination of pressure and heat to achieve adhesion therebetween:

wherein X is a group selected from NH₂--、HO--、R₂OC(O)--、R₂C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl or aryl (including substituted aryl); wherein R is₁Is alkyl or alkoxy, and R₂Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R₁Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the metal is copper. In another embodiment, the copper is in the form of copper foil. In one embodiment, the conductive metal layer is in the form of a conductive via.

In one embodiment, the method further comprises placing an adhesive layer between the polymer composite film and the conductive metal layer.

Other suitable conductive metal layers are suitable including, but not limited to, stainless steel, copper alloys, aluminum, gold, silver, tungsten, nickel, and alloys thereof.

Suitable materials for use in the adhesive layer include, but are not limited to, epoxies, acrylics, phenolics, thermoplastic polyimides, polyetherimides, polyesters, polyamides, polyamide-imides, polyimides, polyetherimides, polyether-ketones, polyether-sulfones, and liquid crystal polymers.

In another aspect, the present disclosure provides a multilayer article comprising a conductive metal layer in adhesive contact with a surface of a polymer composite film having a surface and a thickness of less than 500 μm, the polymer composite film comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the surface-modified hexagonal boron nitride particles comprising hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl and aryl (including substituted aryl); r₁Is alkyl or alkoxy, and R²Is hydrogen, alkyl or aryl (including substituted aryl).

In one embodiment, R¹Is hydrogen. In another embodiment, X is NH₂-or HO- -. In another embodiment, X is NH₂- -. In another embodiment, X is HO- -.

In one embodiment, the metal is copper. In another embodiment, the copper is in the form of copper foil. In one embodiment, the conductive metal layer is in the form of a conductive via. In one embodiment, the multilayer article further comprises an adhesive layer between the polymeric composite film and the conductive metal layer.

The metal layer may be formed of any metal including copper, gold, silver, tungsten, or aluminum. In one embodiment, the metal layer is a copper foil. The copper foil may be formed in any manner known in the art, including plated or rolled copper foil.

In one embodiment, the adhesive layer comprises a thermoplastic polymer. Suitable thermoplastic polymers include, but are not limited to, polyimides prepared by reacting aromatic dianhydrides with aliphatic diamines. Other materials that may be used as the dielectric adhesive layer include polyesters, polyamides, polyamide-imides, polyetherimides, polyether-ketones, polyether-sulfones, and liquid crystal polymers. In an alternative embodiment, the adhesive layer comprises a thermoset polymer. Suitable thermosetting polymers include, but are not limited to, epoxies, phenolics, melamine resins, acrylics, cyanate resins, and combinations thereof. Generally, the adhesive layer has a thickness in the range of 3-35 μm and an in-plane Coefficient of Thermal Expansion (CTE) at 20 ℃ of 25-90ppm/° C.

In one embodiment, the adhesive layer comprises a polyimide having a glass transition temperature of 150-. Generally, the bonding temperature is 20 to 50 degrees above the glass transition temperature. In another embodiment, the adhesive polyimide is synthesized by condensing an aromatic dianhydride with a diamine component comprising 50 to 90 mole percent aliphatic diamine and 1 to 50 mole percent aromatic diamine. In another embodiment, the aliphatic diamine is hexamethylene diamine (HMD) and the aromatic diamine is 1, 3-bis- (4-aminophenoxy) benzene, and the aromatic dianhydride is a combination of 3, 3 ', 4, 4' -benzophenonetetracarboxylic dianhydride (BTDA) and a 3, 3 ', 4, 4' -biphenyltetracarboxylic acid polymer having a glass transition temperature in the range of 150 ℃ to 200 ℃.

In another embodiment, the adhesive is a heat sealable copolyimide comprising from 60 to 98 mole percent of imide repeat units of formula I

And 2 to 40 mol% of further imide recurring units of the formula II

Wherein R is a tetravalent organic carboxylic acid diacid anhydride group selected from the group consisting of pyromellitic dianhydride, 4, 4-oxydiphthalic anhydride, 3, 3 ', 4, 4 ' -benzophenone tetracarboxylic dianhydride, 2 ', 3, 3 ' -benzophenone tetracarboxylic dianhydride, 3, 3 ', 4, 4 ' -biphenyl tetracarboxylic dianhydride, 2 ', 3, 3 ' -biphenyl tetracarboxylic dianhydride, 2 ' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride, bis (3, 4-dicarboxyphenyl) sulfone dianhydride and m-phenylene bis (1, 2, 4-trimellitic) dianhydride; and wherein R ' is a divalent aromatic or aliphatic diamine group selected from the group consisting of p-phenylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, 4 ' -diaminodiphenyl ether, 3, 4 ' -diaminodiphenyl ether, 1, 3-bis (4-aminophenoxy) benzene, 1, 2-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminobenzoyloxy) benzene, 4 ' -diaminobenzanilide, 4 ' -bis (4-aminophenoxy) phenylene ether, and polysiloxane diamine, with the proviso that the imide repeating units of formula (I) are different from the imide repeating units of formula (II).

The conductive metal layer thickness may generally be in the range of 2 to 500 μm, and in one embodiment, the conductive metal layer thickness is in the range of 3 to 35 μm. In one embodiment, the conductive metal layer is a copper foil having a CTE in the range of 15 and 17ppm/° c at 20 ℃.

The conductive layer may be mechanically or chemically pretreated to improve lamination adhesion. Pretreatment commonly used in the art includes, but is not limited to, electroplating; immersion deposition along thin film bonding surfaces of copper, zinc, chromium, tin, nickel, cobalt, other metals, and alloys of these metals. In addition to roughening the surface, the chemical pretreatment also results in the formation of metal oxide groups, which can improve the adhesion between the metal layer and the dielectric multilayer. In one embodiment, pre-treatment is applied to both sides of the metal to enhance adhesion of both sides of the metal.

In one embodiment, the resin-coated foil is prepared by coating a metal foil (preferably a copper foil) with the above-described casting composition. In one embodiment, the casting composition is metered onto a moving copper foil in a continuous process using a combination of a paint roller and a compaction roller. Other suitable coating methods are knife or blade coating, slot or extrusion coating, gravure coating, slide coating and curtain coating. In one embodiment, the coated foil is dried, typically in an oven, to increase the viscosity of the uncured coating, which is partially cured or imidized to form a so-called B-stage composition. In one embodiment, the process is a continuous coating process and the foil coated with the B-stage composition can be wound on a roll for further use. In some embodiments, the first coating is fully cured and the coated foil is then further coated with one or more additional layers.

In one embodiment, the conductive metal layer is formed on the surface of the film by dry plating or wet plating. Dry plating methods known in the art include sputter coating or ion plating. In wet plating, the surface of the cured layer is first roughened with an oxidizing agent such as permanganate, dichromate, ozone, hydrogen peroxide/sulfuric acid, or nitric acid to form an uneven surface ("anchor") to anchor the conductive layer. The conductor is then formed by a combination of electroless and electrolytic plating.

However, the resulting multilayer laminate can be used as a raw material in the production of printed circuit boards. Printed circuit boards are made by applying a photoresist material to a metal surface. In the case of positive photoresists, the circuit pattern is imaged onto the photoresist surface, thereby photopolymerizing the positive photoresist. The imaging may involve coherent and/or non-coherent light sources. One method of imaging is via a phase mask. The photo-polymerized pattern reproduces the circuit to be formed. After imaging, the resin coated foil is contacted with a solvent that dissolves the unpolymerized photopolymer. The resin coated foil thus treated is then subjected to an exposed metal chemical treatment. After chemical removal of the exposed metal, the resin coated foil is then subjected to etching, such as ion beam etching, to remove the photopolymer layer to expose the underlying conductive via pattern, producing a printed circuit board that is now ready to receive electronic components. The printed circuit board so formed may be used as a core layer of a multilayer printed circuit board as described above, or it may still be a single layer printed circuit board. Printed circuit boards can be rigid or flexible depending on the thickness of the coating made from the coating composition, and the nature of its cured or imidized polymer.

In another embodiment, the cured or imidized layer may be drilled with a drill, laser, or the like to form a via or through hole.

Examples

Measuring：

The glass transition temperature (T) of the cured film was determined using a thermomechanical analyzer in accordance with IPC test method No. 2.4.24.5_g) And in-plane Coefficient of Thermal Expansion (CTE). The CTE was measured in a single direction in the plane of the film. The glass transition, modulus and loss modulus of the films were determined using a kinetic mechanical analyzer according to IPC test method No. 2.4.24.4.

The thermal conductivity in the direction perpendicular to the film plane was calculated using this relationship:

thermal conductivity (diffusivity x C)_pX bulk density.

The specific heat (C) of the films was determined by standard methods using Differential Scanning Calorimetry (DSC) using a sapphire standard_p). Thickness t and bulk density ρ (w/{ π r)²T) is based on measurements at room temperature.

Use of the peptide from NETZSCH-Netzsch LFA 447 NanoFlash from GmbH (Selb, Germany)A xenon flash instrument measures thermal diffusivity. Gold layers were sputter coated on both sides of each 1 inch diameter (25.4mm) die cut sample, followed by a graphite layer. The sample thus prepared is placed in a holder cooled by a circulating bath to keep the temperature of the sample constant during the measurement. The flash gain at 1260 was set in the range of 78 to 5000. Pulse widths of 10 and 66ms are used. The detector is a liquid nitrogen cooled IR detector. Each data point represents the average of four samples.

Example 1 and comparative example A：

8.0g of p-phenylenediamine was dissolved in 100mL of deionized water and 57mL of 0.5M hydrochloric acid at room temperature. 5.1g of sodium nitrite dissolved in 50mL of deionized water was added to the solution to prepare the corresponding diazonium chloride. The diazonium salt solution was added to a dispersion containing 25g of hBN (NX1 grade, Momentive Performance Materials, Strongsville, USA) dispersed in 200mL of methanol and 800mL of water. 6.0g of iron powder (325 mesh) was added to the dispersion at room temperature and stirred. After five minutes, 250mL of 0.5M hydrochloric acid was added to the dispersion and stirred for an additional 30 minutes (min). The dispersion was filtered, washed with water, ammonia solution (25cc ammonia solution in one liter of water), then methanol. The product was dried in a vacuum oven at 100 ℃ overnight to yield dry SMhBN.

Thermogravimetric analysis (TGA-10 ℃/min heating rate, air atmosphere) showed that the sample thus prepared contained 2.55 weight percent (wt%) aminophenyl based on the weight of the SMhBN, based on weight loss between 250 ℃ and 600 ℃. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of SMhBN showed cation peaks at m/z 92 and 106. The cationic peak at m/z 92 confirms the presence of-C on the hBN surface₆H₄-NH₂A group. The m/z ion peak at 106 corresponds to the structure-N-C6H 4-NH2, confirming that the aminophenyl group is covalently bonded to the N atom in hBN.

FIG. 2a is a photograph of a Transmission Electron Micrograph (TEM) of the edge of hBN (comparative example A) in the as received state. FIG. 2b is a SMhBN plate edge TEM made according to example 1. The nearly identical appearance of the two samples indicates that there is little or no intervening aminophenyl groups between the hBN wafers. FIGS. 1a and 1b show respectivelyAndthe'd' (0002) pitch of (c).

FIG. 3a is a TEM of the basal plane of SMhBN of example 1, as viewed from the platelet edge. FIG. 3b is a TEM of the SMhBN plate edge of example 1 as viewed from the basal plane. Fig. 3a and 3b show the amorphous coating on the basal plane and no coating on the edges, indicating that the surface modification only occurs on the basal plane.

Examples 2 to 5

The procedure of example 1 was followed except that the amount of p-phenylenediamine (PPD) was varied. The amounts of sodium nitrite, hydrochloric acid and iron vary proportionally to the p-phenylenediamine on a molar basis. The weight loss data measured from TGA (between 250 ℃ C. and 600 ℃ C.) was taken as the amount of aminophenyl grafted onto the hBN surface. The results are shown in Table 2.

Examples 6 to 8

The method of example 1 was used to surface modify different grades of hBN. 4.0g PPD was dissolved in 50mL deionized water and 28.5mL 0.5M hydrochloric acid at room temperature. 2.55g of sodium nitrite dissolved in 50mL of deionized water was added to the solution to prepare the corresponding diazonium chloride. The diazonium salt solution was added to a dispersion containing 25g of a grade of hexagonal boron nitride (NX1, PT120& PT620, Momentive Performance Materials, strong sville, USA) in 100mL of methanol and 400mL of water, respectively. 3.0g of iron powder (325 mesh) was added to each dispersion at room temperature and stirred. After five minutes, 125mL of 0.5M hydrochloric acid was added to each dispersion and stirred for an additional 30 minutes. Each dispersion was filtered, washed with water, an ammonia solution consisting of 25cc of ammonium hydroxide in water, then methanol, and dried in a vacuum oven at 100 ℃. The amount of surface functional groups was determined by thermogravimetric analysis. The results are shown in Table 3.

^*Supplier data

Example 9

The same procedure as reported in example 1 was also followed to graft hydroxyphenyl groups onto the hBN surface. The PPD was replaced with the same amount of p-aminophenol. After the reaction, TGA showed that the SMhBN so produced contained about 0.51 wt% hydroxyphenyl groups based on the total weight of the SMhBN. ToF-SIMS analysis of SMhBN showed cationic peaks at m/z 93 and 107. The cation peak at 93 confirms-C on the hBN surface₆H₄-an OH group. The peak at 107 corresponds to-N-C6H 4-OH confirming that the hydroxyphenyl group is attached to the N atom in hBN via a covalent bond.

Example 10 and comparative example B

A polyamic acid solution was formed by reacting 1.0 mole of 1, 3- (4-aminophenoxy) benzene (134APB) with 0.8 mole of 4, 4 ' -oxy-3, 4, 3 ', 4 ' -diphthalic anhydride (ODPA) and 0.2 mole of pyromellitic dianhydride (PMDA) in a dimethylacetamide (DMAc) solvent at room temperature under a nitrogen atmosphere. The viscosity of the polyamic acid solution thus obtained was 8500cp at a shear rate of 1.40 s-1; the solids content was 19.5% by weight.

Comparative example B

40.0g of the above polyamic acid solution was mixed with 7.8g of hBN as received and the dispersion was stirred at room temperature for 30 minutes. The viscosity of the dispersion was determined using a Brookfield DV-II + type viscometer. The results are shown in Table 4. This composition is consistent with the composition of a cured film comprising 50 wt% resin and 50 wt% hBN.

Example 10

A dispersion similar to the dispersion in comparative example B was prepared using the same amount of polyamic acid, SMhBN in example 1, and the viscosity was measured. The data are summarized in table 4.

Example 11：

30g of SMhBN prepared as in example 1 were mixed with 60g of DMAc using a mechanical stirrer to form a dispersion. 51.3g of the polyamic acid solution of example 10 was added to the SMhBN dispersion and mixed thoroughly using a Silverson homogenizer at 75% rate for four minutes to form a SMhBN/polyamic acid concentrate or masterbatch.

56.51g of the SMhBN/polyamic acid masterbatch thus obtained were mixed with an additional 29.84g of polyamic acid solution for about 20 minutes using a mechanical stirrer to produce a SMhBN/polyamic acid dispersion/solution corresponding to a SMhBN concentration of 55 wt% in the cured film. An aliquot of 25mg ODPA was added to the SMhBN/polyamic acid dispersion/solution. After each addition, the dispersion/solution was mixed for about ten minutes until the solids were completely dissolved. After a total of six ODPA aliquots, 0.70s^-1The dispersion/solution viscosity at shear rate has increased to 77400 cp. The dispersion/solution thus prepared was kept in a vacuum desiccator for 30 minutes to remove entrained air bubbles. The resulting dispersion/solution was cast onto the polyester film surface using a doctor blade with a 0.010 inch (in) opening to produce a 12 "long and 8" wide film. The two-layer film thus obtained was baked at 80 ℃ for thirty minutes in an air circulating oven. The two layers were separated and the SMhBN/polyamic acid film was clamped in a metal frame and baked in an air circulating oven at 100 ℃ for fifteen minutes. The B-staged film thus prepared was then heated to 300 ℃ at a rate of 5 ℃/min in a furnace and held at 300 ℃ for five minutes; then rapidly heated to 375 ℃ and held at 375 ℃ for five minutes to cure. At the end of the five minute wetting, the furnace was shut down and the so treated samples were allowed to cool to room temperature while still in the furnace.

Comparative example C：

An hBN concentrate was prepared by mixing 60g of DMAc with 30g of hBN in as received state (NX1 grade) using a mechanical stirrer. 51.3g of the polyamic acid solution described in example 10 was then added to the dispersion and mixed thoroughly for four minutes using a high shear Silverson homogenizer at 75% rate. 56.51g of the hBN concentrate thus obtained were mixed with 29.84g of the polyamic acid solution for about 20 minutes using a mechanical stirrer to produce a polyamic acid dispersion/solution containing 55 wt% hBN in the cured film. A 25mg aliquot of ODPA was added to the dispersion/solution so prepared and each aliquot was stirred for about ten minutes until the solid was completely dissolved in the dispersion. A total of two aliquots of this ODPA were added to the dispersion/solution such that the viscosity of the dispersion/solution increased to 79200cp at a shear rate of 0.70s "1. The resulting dispersion/solution was degassed, cast into a film, and post-treated in the manner described for the dispersion/solution in example 11.

A polyimide film for control was prepared using the polyamic acid solution in example 10.100 g of the polyamic acid solution and 100mg of ODPA were mixed using a mechanical stirrer for about 10 minutes until all solids were dissolved. The viscosity of the dispersion/solution thus prepared was 72200cp at 0.70 s-1. The same procedure as reported in example 11 was used to prepare and cure the films.

The thermal and mechanical properties of the films prepared in example 11 and comparative example C, as well as the unfilled polyimide film, were determined using thermomechanical analysis and kinetic mechanical analysis. The results are shown in Table 5.

^*Measured by TMA.^**Measured by DMA.

Examples 12 to 14 and comparative example D

The SMhBN in example 1 was mixed with the polyamic acid solution and converted to the polyimide film described in example 1, but with different relative proportions, as shown in table 6. Table 6 shows the CTE of the films thus produced.

Examples 15 to 22 and comparative example D

The SMhBN samples prepared in examples 6-8 were mixed with polyamic acid in a range of ratios according to the method of example 11 to prepare SMhBN/polyimide composite films as listed in Table 7. The thermal conductivity perpendicular to the plane of the film was measured and the results are also shown in table 7.

Example 23

24.8g ODPA was mixed with 4.25g PMDA to form a mixture. The mixture thus formed was slowly added over a period of two hours to a solution of 29.2g of 1, 3- (4-aminophenoxy) benzene (134APB) in 350mL of DMAc to form a 15% polyamic acid solution. After the viscosity reached 10000cp, 11g of SMhBN from example 1 was added and stirred well to obtain a homogeneous dispersion. The polymer viscosity was then raised to 75000 centipoise by slowly adding a small amount of PMDA with constant stirring.

The solution mixture was then degassed under vacuum and cast as a film on a glass plate to produce a film of approximately 12X 12 "size. The thus coated plate was dried on a hot plate set at 100 ℃ for 15 minutes. The film was removed from the hot plate and cooled to room temperature. The film is mounted on the latch frame. The film thus mounted was dried and cured in an oven programmed to raise the temperature from 120 ℃ to 300 ℃ over an hour. The film mounted in the frame was then removed from the oven and immediately placed into a second oven that had been preheated to 400 ℃. The film mounted in the frame was heated in the second oven for five minutes, then removed and cooled on the bench.

The cooled film was removed from the frame and the edges were trimmed to obtain an 8 x 10in sample. The film thus trimmed was then placed between two 12 × 12in (18 μm thick) copper foils. The package thus formed is then inserted into a container made of caulk/aluminum foil, TeflonPFA sheet/copper foil/SMhBN-polyimide composite film/copper foil/TeflonPFA sheet/aluminum foil/caulk in a larger sandwich structure. The sandwich structure thus formed was placed in a vacuum oven between the platens of a hydraulic press set at a temperature of 150 ℃. The hydraulic press was then heated to 350 ℃ and a pressure of 350psi was applied to the platen. The hydraulic press was cooled to 150 ℃, the package was removed from the hydraulic press, and the laminate was removed.

Example 24 and comparative examples E and F

9.0g of poly (o-methylphenyl glycidyl ether) -co-formaldehyde (molecular weight 1080, Aldrich, USA), 0.9g of PKHH Phenoxy resin (Phenoxy Specialties (RockHill, SC, USA)), 0.9g of bisphenol A, 3.6g of DuriteD _ SD-1819 (dicyclopentadiene-phenol adduct, Borden Chemical Inc. (Louisville, KY)) and 0.86g of 2-ethyl-4-methylimidazole were dissolved in 25mL of methyl ethyl ketone to prepare an epoxy resin composition. The epoxide solution thus formed was stirred for 30 minutes at room temperature using a magnetic stirrer.

14.4g of the hydroxyphenyl-grafted SMhBN of example 9 were added to the epoxide solution prepared above and the resulting mixture was stirred at room temperature, followed by four minutes using an ultrasonic probe (Dukane Sonic Welder, equipped with a 1 watt probe and 1/4 "Sonic horn). The dispersion thus obtained is degassed under vacuum. The thus-sonicated dispersion was cast onto a polyester film using a doctor blade with a 0.010in opening. The cast film was dried in an air circulating oven at 50 ℃ for thirty minutes, and the film was peeled from the base polyester film. The dried film was placed on a porous fiberglass/Teflon sheet and cured by heating at 130 ℃ for thirty minutes, at 150 ℃ for ten minutes, and at 170 ℃ for one hour in an air circulating oven.

Comparative example E：

The same film as in example 24 was prepared except that NX1 hBN in the as received state was used.

Comparative example F

Another piece of film was prepared in the same manner, but without any hBN.

Table 8 shows the CTE results for the three films.

Claims (15)

1. A composite comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the surface-modified hexagonal boron nitride (SMhBN) particles comprising hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- - -, halogen, alkyl and substituted or unsubstituted aryl; wherein R is¹Is hydrogen, alkyl or alkoxy, and R²Is hydrogen, alkyl or substituted or unsubstituted aryl.

2. The composite material of claim 1, wherein R¹Is hydrogen and X is NH₂--。

3. The composite material of claim 1, wherein R¹Is hydrogen and X is HO- -.

4. The composite of claim 1, wherein the polymer is a polyamic acid.

5. The composite of claim 1, wherein the polymer is a polyimide.

6. The composite of claim 1, wherein the polymer is a cured epoxy resin composition.

7. The composite of claim 1, wherein the polymer is an uncured epoxy resin composition.

8. The composite material of claim 1, wherein the SMhBN particles have a size in the range of 0.5 to 50 μ ι η.

9. The composite of claim 8, wherein the concentration of SMhBN is 30-70 wt%.

10. A method of making a composite material comprising a polymer and a plurality of surface-modified hexagonal boron nitride particles dispersed in the polymer, the method comprising mixing a plurality of surface-modified hexagonal boron nitride particles with a polymer solution comprising a solvent, and extracting the solvent, wherein the surface-modified hexagonal boron nitride particles comprise hexagonal boron nitride particles having a surface and a substituted phenyl group bonded to the surface, the substituted phenyl group represented by the structure:

wherein X is a group selected from NH₂--、HO--、R²OC(O)--、R²C(O)O--、HSO₃--、NH₂CO- -, halogen, alkyl or aryl, including substituted aryl; wherein R is¹Is hydrogen, alkyl or alkoxy, and R₂Is hydrogen, alkyl or substituted or unsubstituted aryl.

11. The method of claim 10, wherein R¹Is hydrogen and X is NH₂--。

12. The method of claim 10, wherein R¹Is hydrogen and X is HO- -.

13. The method of claim 10, wherein the polymer is a polyamic acid.

14. The method of claim 10, wherein the polymer is an uncured epoxy resin composition.

15. The method of claim 10, wherein the SMhBN particles have a size in the range of 0.5 to 50 μ ι η.