This application claims priority to provisional U.S. Patent Application No. 62/373,602 filed on August 1 1 , 2016.

FIELD OF THE INVENTION

The present invention relates to the field of flame retardants, specifically phosphorous- containing flame retardants for electronic applications such as printed wiring boards.

BACKGROUND OF THE INVENTION

The demand for halogen-free material in the electronics market is forecasted to increase in the upcoming years. There are three reasons for this forecast. The first reason is the unfavorable public perception of halogenaled materials. The second reason is the perceived upcoming regulations on brominated systems. Many manufacturers believe that governments will start regulating brominated flame retardants in laminate systems and companies are trying to outpace possible new regulations. The third reason is that compared to brominated systems, phosphorous-based systems tend to have higher thermal stabilities.

One new application area for halogen- free formulations is mobile devices, particularly smartphones and tablets. The fact that smartphones and tablets are consumer products and are at the mercy of publ ic perception; the use of halogen- free materials is expected to be adopted by large market producers. Given the bullish forecasts for these market segments, developing high performance halogen-free products to sell into these market spaces is necessary.

Importantly, the halogen-free market place is also requiring improvements in the dielectric constant. The dielectric constant requirements are trending lower (Dk < 4.0) along with brominated products replacement and for the same reasons. The reasons include V) increasing battery sizes in mobile devices require smaller printed circuit boards and lowering the dielectric constant supports higher circuit density associated with smaller circuit board format; 2) the circuit boards in mobile devices are also getting thinner and a lower dielectric constant reduces the degrading effects of capacitive coupling between the ground plane and the input circuitry; 3) a lower dielectric constant is often associated with lower (improved) dissipation factor (Df). Improved dissipation factors are already becoming requirements for mobile consumer products. The lowering of both the Dk and the Df often causes the copper peel strength to be degraded, Therefore, halogen-free materials which have lower Dk and Df , but also with favorable copper peel strengths, are desirable. In addition high Tg and high thermal stability is also required to improve circuit reliability.

Some work has been done in the field of epoxy resins, such as in BE627887 which may describe an epoxy resin composition wherein a styrene maleic anhydride copolymer may appear to be used as a crosslinking agent for an epoxy resin. This epoxy resin composition has the severe disadvantage of poor thermal stability, and thus is completely unsuitable to be used in the substrate copper clad laminate of multilayer printed circuit board (PCB).

Addressing the ordinary epoxy resin circuit board (e.g., a FR-4 board), which has the main components of low-brominated or high-brominated epoxy resin prepared with bisphenol A epoxy resin or tetrabromobisphenol A epoxy resin, such may be prepared with addition of a curing agent such as dicyandiamide, a solvent and a catalyst, but such has the disadvantages of a undesirably low glass transition temperature Tg (120-140° C) and poor heat resistance. Some efforts have been made to employ multifunctional epoxy resin to replace difunctional epoxy resin, or to use phenolic resin to replace dicyandiamide, in order to increase curing crosslinking density to improve the glass transition temperature, and improve the heat resistance, but such efforts have not improved the high-frequency electrical properties of board.

For example, U.S. Pat. No. 6,509,414 may have employed styrene maleic anhydride copolymer as a curing agent, tetrabromobisphenol A, tetrabromobisphenol A epoxy resin or their mixture as co-curing agents for FR-4 epoxy resin curing in an attempt to improve the glass transition temperature and thermal stability. But the styrene maleic anhydride copolymer in the composition is brittle, and thus, the prepared prepreg (for preparing printed circuit board) is fairly brittle. A problem arises in cutting a prepreg containing such a composition, in that the resin on the edge of the prepreg is easy to dust, which is sometimes referred to as "mushroom effect", and can bring hidden quality dangers to the processing technology. Furthermore, there are two hydroxy groups having a very large polarity in the tetrabromobisphenol A molecular structure, thus, the introduction of tetrabromobisphenol A deteriorates the dielectric properties of the system to an undesirable extent.

In U.S. Pat. No. 6,667,107, difunctional cyanate ester and its self-polymer, styrene maleic anhydride and its derivative and epoxy resin etc. may have been used to prepare a version of a copper clad laminate composition having a low dielectric constant and dielectric loss angle tangent. In such a copper clad laminate composition, cyanate ester resin and styrene maleic anhydride and its derivatives are attempted to be co-adopted to improve the glass transition temperature of the epoxy resin system, and while it may have suitable dielectric properties of high frequency, the molecular structure of the styrene maleic anhydride copolymer adopted in this system has anhydride groups, which can generate carboxyl groups resulting in poor thermal stability and moisture-heat resistance; as they are adopted in concert with cyanate ester which has poor moisture-heat resistance, and the moisture-heat resistance is further deteriorated.

Addition of epoxy resin may have improved the moisture-heat resistance properties to a certain extent, but the improvement is limited and the problem cannot be eliminated fundamentally, therefore, in a preparation process of PCB, the boards are susceptible to etch of moisture and develop delamination, and the product qualified rate is very low.

Japanese Patent Publication 2003-252958 may disclose a version of biphenyl epoxy resin and active ester composition, which has a suitable dielectric constant and dielectric loss angle tangent after curing. But it is version of bifunctional biphenyl epoxy resin that is adopted, which has a low crosslinking density with the active ester; therefore it has the fundamental

disadvantages of low glass transition temperature and low heat resistance of the cured products.

Japanese Patent Publication 2009-235165 may disclose active ester cured epoxy resin with structural formula Y, and no styrene structure is adopted, and cured product with higher glass transition temperature can be obtained: wherein X is a benzene ring or naphthalene ring, j is 0 or 1, k is 0 or 1, n represents the average repeated unit for 0.25-1.25. But for the application fields with a demand for fiammability performance and demanding requirements for dielectric performance, the use of a separate flame retardant is required which can compromise the dielectric constant. Chinese patent CN 104109347 may have adopted redistributed PPO with phenolic or epoxy end groups in an attempt to improve the dielectric constant. In the formulation, besides the redistributed PPO, a phosphorus-containing active ester resin was used as co-curing agent for biphenyl- or DCPD-epoxy. Since the phosphorus-containing active ester resin has an aliphatic bond increasing the flexibility of chain, and not participating in the curing process, the glass transition temperature of the system is negatively affected.

SUMMARY OF THE INVENTION

It is therefore a feature of the present invention to provide for a need in the industry for an epoxy curing composition, which can now include the unexpected invention of a halogen-free curing agent, and a halogen- free co-curing agent wherein the co-curing agent either has a low dielectric constant in and of itself, or wherein the co-curing agent is chosen such that when the curable epoxy composition is cured the overall cured epoxy composition has a low dielectric constant. The cured epoxy resins of this epoxy curing composition can be employed in electronic applications while maintaining a low dielectric constant, and a low moisture uptake as well as a high glass transition temperature (Tg).

It will be understood herein that in one non-limiting embodiment the expression

"halogen- free curing agent for epoxy resins" can be used interchangeably with "halogen-free curing agent for epoxy resins", "epoxy curing agent", "curing agent for epoxy", "epoxy resin curing agent" and "curing agent", and the like.

There is provided herein in one embodiment a composition comprising (a) at least one epoxy compound; (b) at least one oligomeric aromatic polyester phosphorous-containing curing agent; and, (c) at least one co-curing agent having a dielectric constant less than 4.0, or at least one co-curing agent which results in the cured epoxy composition having a dielectric constant of less than 4.0, and wherein the co-curing agent (c) is other than the curing agent(b).

The term "oligomeric" as used herein comprises a co-polymer of from 2 to about 4 different types of monomer units. A "DOPO" moiety as described herein is understood by those skilled in the art to mean a 9,10-Dihydro-9-Oxa-10-Phosphaphenantrene-10-Oxide compound which has a free valence (indicated by the dashed line in the formula below) to bond with another moiety; such a DOPO moiety can be in one non-limiting example of the formula (I):

Other than in the working examples, or where otherwise indicated, all numbers expressing amounts of materials, reaction conditions, time durations, quantified properties of materials, and so forth, stated in the specification and claims are to be understood as being modified in all instances by the term "about" whether or not the term "about" is used in the expression.

It will be understood that any numerical range recited herein includes all sub-ranges within that range and any combination of the various endpoints of such ranges or sub -ranges, be it described in the examples or anywhere else in the specification.

It will also be understood herein that any of the components of the invention herein as they are described by any specific genus or species detailed in the examples section of the specification, can be used in one embodiment to define an alternative respective definition of any endpoint of a range elsewhere described in the specification with regard to that component, and can thus, in one non-limiting embodiment, be used to supplant such a range endpoint, elsewhere described.

It will be further understood that any compound, material or substance which is expressly or implicitly disclosed in the specification and/or recited in a claim as belonging to a group of structurally, compositionally and/or functionally related compounds, materials or substances includes individual representatives of the group and all combinations thereof. Reference is made to substances, components, or ingredients in existence at the time just before first contacted, formed in situ, blended, or mixed with one or more other substances, components, or ingredients in accordance with the present disclosure. A substance, component or ingredient identified as a reaction product, resulting mixture, or the like may gain an identity, property, or character through a chemical reaction or transformation during the course of contacting, in situ formation, blending, or mixing operation if conducted in accordance with this disclosure with the application of common sense and the ordinary skill of one in the relevant art (e.g., chemist). The transformation of chemical reactants or starting materials to chemical products or final materials is a continually evolving process, independent of the speed at which it occurs. Accordingly, as such a transformative process is in progress there may be a mix of starting and final materials, as well as intermediate species that may be, depending on their kinetic lifetime, easy or difficult to detect with current analytical techniques known to those of ordinary skill in the art.

Reactants and components referred to by chemical name or formula in the specification or claims hereof, whether referred to in the singular or plural, may be identified as they exist prior to coming into contact with another substance referred to by chemical name or chemical type (e.g., another reactant or a solvent). Preliminary and/or transitional chemical changes, transformations, or reactions, if any, that take place in the resulting mixture, solution, or reaction medium may be identified as intermediate species, master batches, and the like, and may have utility distinct from the utility of the reaction product or final material. Other subsequent changes, transformations, or reactions may result from bringing the specified reactants and/or components together under the conditions called for pursuant to this disclosure. In these other subsequent changes, transformations, or reactions the reactants, ingredients, or the components to be brought together may identify or indicate the reaction product or final material.

In describing the products of the instant invention as a reaction product of initial materials reference is made to the initial species recited and it is to be noted that additional materials may be added to the initial mixture of synthetic precursors. These additional materials may be reactive or non-reactive. The defining characteristic of the instant invention is that the reaction product is obtained from the reaction of at least the components listed as disclosed. Non-reactive components may be added to the reaction mixture as diluents or to impart additional properties unrelated to the properties of the composition prepared as a reaction product. Thus for example particulate solids such as pigments may be dispersed into the reaction mixture, before during or after reaction to produce a reaction product composition that additionally comprises the non- reactive component, e.g. a pigment. Additional reactive components may also be added; such components may react with the initial reactants or they may react with the reaction product; the phrase "reaction product" is intended to include those possibilities as well as including the addition of non-reactive components.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a curable epoxy composition, which when cured, has a high glass transition temperature and a high thermal stability as well as a low dielectric constant, wherein the composition comprises the combination of a fully aromatic DOPO- substituted polyester with a low dielectric constant epoxy and/or a low dielectric constant co- curing agent.

The at least one epoxy compound (a) described herein can be any epoxy employed commercially and/or in industry, and preferably is non-halo genated, more preferably is non- brominated, and can optionally have a low dielectric constant. A low dielectric constant as regards the epoxy compound (a) is a value of from about 2.5 to about 5.0, more preferably from about 3.0 to about 4.5 and most preferably from about 3.5 to about 4.0.

The epoxy resins which can be used in the herein described invention include, in one embodiment, an epoxy resin selected from a group consisting of bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, bisphenol AD epoxy resin, phenol novolac epoxy resin, bisphenol A novolac epoxy resin, o-cresol novolac epoxy resin, trifunctional epoxy resin, tetrafunctional epoxy resin, multifunctional epoxy resin, dicyclopentadiene (DCPD) epoxy resin, phosphorus-containing epoxy resin, DOPO-containing epoxy resin, DOPO-HQ containing epoxy resin, p-xylene epoxy resin, naphthalene-based epoxy resin, benzopyran-based epoxy resin, biphenyl novolac epoxy resin, phenol aralkyl novolac epoxy resin, and combinations thereof. The epoxy resins which can be used in the herein described invention include, in one other embodiment, polyepoxides having the following general formula (II):

wherein "R " is substituted or unsubstituted aromatic, aliphatic, cycloaliphatic or heterocyclic group having a valence of "a", where "a" preferably has an average value of from 1 to less than about 8. Examples of the polyepoxide compounds useful in the present invention include the diglycidyl ethers of the following compounds: resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (l,l-bis(4-hydroxylphenyl)-l -phenyl ethane), bisphenol F, bisphenol K, phenol-formaldehyde novolac resins, alkyl substituted phenol-formaldehyde resins, phenol- hydroxybenzaldehyde resins, cresol-hydroxybenzaldehyde resins, dicyclopentadiene -phenol resins, dicyclopentadiene-substituted phenol resins tetramethylbiphenol, and any combinations thereof.

Examples of particular polyepoxide compounds useful in the present invention include a diglycidyl ether of bisphenol A having an epoxy equivalent weight (EEW) between 177 and 189 sold by The Dow Chemical Company under the trademark D.E.R. 330; the halogen-free epoxy- terminated polyoxazolidone resins, phosphorus element containing compounds; cycloaliphatic epoxies; and copolymers of glycidyl methacrylate ethers and styrene.

Preferred polyepoxide compounds include epoxy novolacs, such as D.E.N. 438 or D.E.N. 439 (trademarks of The Dow Chemical Company); cresol epoxy novolacs such as QUATREX 3310, 3410 and 3710 available from Ciba Geigy Epon 164 from Momentive; trisepoxy compounds, such as TACTIX 742 (trademark of Ciba Geigy Corporation of Basel, Switzerland); epoxidized bisphenol A novolacs, dicyclopentadiene phenol epoxy novolacs; glycidyl ethers of tetraphenolethane; diglycidyl ethers of bisphenol- A; diglycidyl ethers of bisphenol-F; and diglycidyl ethers of hydroquinone. In one embodiment, the most preferred epoxy compounds are epoxy novolac resins (sometimes referred to as epoxidized novolac resins, a term which is intended to embrace both epoxy phenol novolac resins and epoxy cresol novolac resins). Epoxy novolac resins (including epoxy cresol novolac resins) are readily commercially available, for example under the trade names D.E.N, (trademark of The Dow Chemical Company), and QUATREX and TACTIX 742 (trademarks of Ciba Geigy).

Preferred compounds of the type mentioned above have epoxy equivalent between 150- 400 and most preferably from 160-300 and molecular weight above 500 and most preferable between 700-2,500.

The polyepoxide useful in the present invention is preferably substantially free (or completely free) of bromine atoms, and more preferably substantially free (or completely free) of halogen atoms.

One non-limiting example of polyepoxides that are useful in the present invention and that are substantially free of halogen atoms are the phosphorus-containing epoxy resins such as those which are the reaction products of an epoxy compound containing at least two epoxy groups and a reactive phosphorus-containing compound such as 3,4,5,6-dibenzo-l,2- oxaphosphane-2-oxide (DOPO), or 10-(2',5'-dihydroxyphenyl)-9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO-HQ).

The amount of epoxy in the curable epoxy compositions described herein, is such that the final formulation of epoxy, any optional phosphorous containing epoxy, compound of the general formula (III) described below, in the amounts described herein, and any other components in the amounts described herein or known to those skilled in the art, is such that the total phosphorous content of the composition is from 1 weight percent to about 5 weight percent, more specifically from about 1.5 to about 4 weight percent, and most specifically 2-3 weight percent Thus, one skilled in the art will formulate the amount of epoxy to be commensurate with such other components so as to have a final phosphorous content as described above. The amount of such phosphorus containing epoxy in the final composition can vary from 10-90 parts, preferably 20-80 parts and most preferably from 30-50 parts based on 100 parts of epoxy resin.

The at least one oligomeric aromatic polyester phosphorous-containing curing agent (b) described herein can in one non-limiting embodiment be a reaction product of a

phosphaphenanthrene-substituted hydroquinone and/or napthaquinone with a dicarboxylic aromatic acid and/or ester.

In one non-limiting embodiment, the oligomeric aromatic polyester phosphorous- containing curing agent (b) is the reaction product of a 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide-substituted hydroquinone and/or napthaquinone with a dicarboxylic aromatic acid and/or ester, such as those the oligomeric aromatic polyester phosphorous-containing curing agents described in U.S. Provisional Patent Application No. 62/254847, the entire contents of which are incorporated by reference herein in their entirety.

As examples of dicarboxylic aromatic acids, mention may be made of terephthalic, isophthalic, dibenzoic, naphthalenedicarboxylic acids, 4,4'-diphenylenedicarboxylic acid, bis(p- carboxyphenyl)methane acid, ethylenebis(p-benzoic acid), l,4-tetramethylenebis(p-oxybenzoic acid), ethylenebis(paraoxybenzoic acid) and 1,3-trimethylene bis(p-oxybenzoic acid). Suitable dicarboxylic aromatic esters can be derived from the aforementioned aromatic dicarboxylic acids.

In one non-limiting embodiment, the oligomeric aromatic polyester phosphorous- containing curing agent (b) can be of the general formula (III):

(III) where X is a bivalent aromatic hydrocarbon group containing from 6 to about 12 carbon atoms, and which includes the non-limting examples of phenylene groups, naphthalene groups, biphenylene groups, etc., which groups may optionally include a substituent bonded to the aromatic ring, such as an alkyl group or alkoxyl group containing up to 6 carbon atoms, and,

wherein Z is selected from the group consisting of a covalent bond, -SO2-, -C(CH ₃ ) ₂ -,

-CH(CH ₃ )-, and -CH ₂ -; p = 0-2; q = 0-2, wherein the wavy lines of each structure of Y indicate the bonds to the O atoms which Y bridges in the general formula (III); and,

R ¹ is selected from H, an alkyl group of from 1 to about 4 carbon atoms, phenyl,

naphthyl, and where R ² is H or -C(=0)R ³ and wherein R ³ is selected from an alkyl group of from 1 to about 4 carbon atoms, an aryl group or alkylaryl group which is selected from phenyl, a - napthyl, beta -napthyl , -cresyl, w-cresyl, /?-cresol group. or a phenyl group, or a napthyl group, or and an aromatic phenol group which is selected from one of a phenol group, -cresol group, w-cresol group, /?-cresol group, -naphthol group, and a -naphthol group, and when R ² is H, R ¹ cannot be phenyl or naphthyl, and, n is >1.

In one non-limiting embodiment herein, the oligomeric aromatic polyester phosphorous- containing curing agent (b) can comprise a mixture of different structures of the general formula (III), e.g., the mixture can comprise wherein at least 50 wt% of the general formula (III) structures, and preferably more than 70 wt% of the general formula (III) structures are such that Y is chosen from moieties (i) and (ii) as noted above, with the remaining different structures of the general formula (III) being such that Y is chosen from the (iii) moiety noted above. In one embodiment herein the at least one oligomeric aromatic polyester phosphorus- containing curing agent (b) of the general formula (III), can be such that R ¹ can be of the general formula:

wherein R ² is as defined above.

In another embodiment herein of general formula (III), R ¹ can be an alkyl of from 1 to about 4 carbon atoms, more specifically selected from methyl or ethyl.

In a more specific embodiment of general formula (III), X can be of the general formula:

In yet another embodiment of general formula (III), Y can be of the formula:

as described above.

In one other embodiment of general formula (III), Y can be of the formula:

In one embodiment herein of general formula (III), the value of the subscript n can be of from 1 to about 100, more specifically from 1 to about 15, and most specifically from 1 to about 7. In one non-limiting embodiment, n can be 1 , provided that R ¹ is DOPO-HQ-acetoxy.

In another embodiment, the at least one oligomeric aromatic polyester phosphorus- containing curing agent (b) can be a phosphorus-containing compound of the general formula (III), such as those having at least three reactive groups per molecule, wherein at least two of the reactive groups is an active ester group. More preferably the oligomeric aromatic polyester phosphorus-containing curing agent (b) of the general formula (III) are those having at least four reactive groups per molecule, while the number of active ester groups is at least three.

It will be understood herein that the compound of the formula (III) as described herein can function as a curing agent (b) for curing the epoxy resin (a), as described herein.

The curing agent(s) (b) for curing epoxy resin (a), can, in conjunction with co-curing agent (c) cure epoxy resins which cured epoxy resins can be employed in any commercial or industrial epoxy application which requires a flame retardant such as the non-limiting example of electronic applicatons while maintaining a low dielectric constant, and a low moisture uptake

(for example, lower than 0.6% after a 1-hour pressure cooker test (PCT) and morst preferably lower than 0.4% after 1-hour PCT) as well as a high glass transition temperature (Tg) (for example, higer than 150°C (as measured by DSC) and most preferably higher than 170°C (as measured by DSC). Advantageously herein, the compound(s) which function as oligomeric aromatic polyester phosphorus-containing curing agent (b) for epoxy resins, when reacted with epoxy resins, can be in the absence of hydroxyl groups, such as secondary hydroxyl groups thus, avoiding the high water absorption and higher dielectric constant of conventional curing systems, which when reacted with epoxy the products therein contain such secondary hydroxyl groups.

In one embodiment, the compound(s) which can be used as the oligomeric aromatic polyester phosphorus-containing curing agent (b) for curing epoxy resin (a) can have a phosphorus content of at least 4 wt-percent. And more preferably, the oligomeric aromatic polyester phosphorus-containing curing agent (b) can have a phosphorus content of at least 6%. The compounds of general formula (III) described herein meet these requirements and are preferably substantially free (or completely free) of bromine atoms, and more preferably substantially free (or completely free) of halogen atoms.

The expression "oligomeric aromatic polyester phosphorus-containing curing agent (b)" can refer to an aromatic ester that can react with epoxy according to the following scheme:

In contrast to a conventional epoxy curing scheme:

wherein R* = R ¹ as defined herein. The amount of the oligomeric aromatic polyester phosphorus-containing curing agent (b), which can be used as the compound for curing at least one epoxy compound (a) herein in the curable epoxy composition described herein will vary depending on the specific epoxy resin and the specific oligomeric aromatic polyester phosphorus-containing curing agent (b) and co-curing agent (c) being employed, as well as specific parameters of processing as are known by those skilled in the art. In one non-limiting embodiment, the amount of oligomeric aromatic polyester phosphorus-containing curing agent (b) which can be used for curing at least one epoxy compound (a) is from about 10 to about 150 parts by weight per 100 parts of the epoxy resin, more specifically from about 30 to about 100 parts by weight per 100 parts of the epoxy resin and most specifically from about 50 to about 70 parts by weight per 100 parts of the epoxy resin. To provide adequate flame retardancy the curable compositions herein will have from 1.0% P to about 5% P in the final composition, more preferably greater than 1.5% P, even more preferably greater than 2.2 % P.

A low dielectric constant as regards the co-curing agent (c) having a low dielectric constant itself is a value of from about 2.0 to about 5.0, more preferably from about 2.0 to about 4.0 and most preferably from about 2.0 to about 3.5.

As stated above, the co-curing agent (c) can itself have a low dielectric contstant as described above and elsewhere herein, e.g., less than 4.0, or more preferably less than 3.5, and can have any of the lower endpoints of dielectric constant described herein for any of the co- curing agents decribed herein, e.g., more than 2.0. However, the co-curing agent (c) can also alternatively, or in combination with the co-curing agent itself having a low dielectric constant, be selected to be a component, which when reacted with the other components of the curable epoxy composition, result in a cured epoxy composition having a low dielectric constant value such as that described above and elsewhere herein, e.g, of less than 4.0 and in one non-limiting embodiment more than 2.0.

The co-curing agent (c) described herein can in one non-limiting embodiment be selected from the group consisting of polymeric hydroxy-terminated polyphenyle oxide compounds, styrenic-maleic ahydride copolymers, low dielectric hydrocarbon resins, cyanate esters, dicyclopentadiene epoxy resins, novolac resins, bismaleimides, polyimides, polyamic acids, fluorinated compounds, organosilicon-containing compounds, benzooxazine resins, polybenzoxazoles, polyquinoxalines, poly(2-alkyl oxazolines), poly(N,N-dialkylacrylamides), poly(caprolactones), polylactides, polystyrenes, polyacrylates, and combinations thereof.

Some examples of polymeric hydroxy-terminated polyphenyle oxide compounds, which can be co-curing agent (c) are selected from the group consisting of phenol-redistributed poly(phenylene oxide) compounds, bisphenol-redistributed poly(phenylene oxide )compounds, dicyclopentadiene-redistributed poly(phenylene oxide) compounds, and combinations thereof.

The redistributed poly(phenylene oxide) compounds as used herein may be derivatives of poly(phenylene oxide) compounds of one of the general formulae (IV) or (V):

(IV) or,

(V) where X ¹ is selected from the group of covalent bond, -SO2-, -C(CH ₃ ) ₂ -, -CH(CH ₃ )- and CH2-; Z ¹ to Z ¹² each independently represents hydrogen or a methyl group, W represents hydroxyl, ethylenyl, phenyl ethylenyl, propylenyl, butenyl, butadienyl or epoxy functional group; and m and n are each an integer greater than or equal to 1.

In one embodiment, the phenol-redistributed poly(phenylene oxide) compounds are of the general formula above wherein X ¹ is -C(CH ₃ ) ₂ -, -CH(CH ₃ )-, -CH ₂ , and

In one non-limiting embodiment, the the co-curing agent (c) is a bisphenol-redistributed (phenylene oxide) compound of the general formula (VI):

wherein X ² is -C(CH ₃ ) ₂ -, -CH(CH ₃ )-, -CH ₂ -, or -SO2-; Y ^J -Y ⁸ each independently represents H or— CH ₃ ; Z ¹³ is hydroxyl, ethylenyl, phenyl ethylenyl, propylenyl, butenyl, butadienyl or epoxy function group; and b >1.

In another embodiment herein the co-curing agent (c) is a dicylopentadiene-redistributed poly(phenylene oxide) compound of the general formula (VII):

(VII) wherein Y ⁹ is H or an alkyl group of from 1 to 4 carbon atoms, c is 1-5, d>c, Y ¹⁰ -Y ¹³ each independently represents H or -C¾, Z ¹⁴ is one of a hydroxyl, ethylenyl, phenyl ethylenyl, propylenyl, butenyl, butadienyl or a epoxy functional group.

In one other embodiment the co-curing agent (c) is a styrenic-maleic ahydride copolymer of the general formula (VIII):

wherein e:f is from about 1 :1 to about 8: 1.

The styrenic-maleic ahydride copolymer co-curing agents (c) can include, for example, copolymers of styrene and maleic anhydride having a molecular weight (M _w ) in the range of from 1,500 to 50,000 and an anhydride content of more than 15 percent. Commercial examples of these materials include SMA 1000, SMA 2000, SMA 3000, SMA 4000, SMA EF-60, and SMA EF-80 having styrene-maleic anhydride ratios of 1 : 1, 2: 1, 3: 1, 4: 1, 6: 1, and 8: 1

respectively, and having molecular weights ranging from 6,000 to 15,000, which are available from TOTAL Cray Valley.

In one other embodiment the co-curing agent (c) is a low dielectric hydrocarbon resin selected from the group consisting of polynorbornene resins, benzocyclobutene resins, polyarylenes, parylenes, polynapthalenes, aliphatic polyolefins and combinations thereof. The low dielectric hydrocarbon resin can have any of the dielectric contstant values as described for the co-curing agent having a low dielectic constant elsewhere herein.

The co-curing agent (c) can also be a cyanate ester, such as a cyanate ester selected from the group consisting of the formulae (IX) - (XIV): where X ³ and X ⁴ each independently represents at least R ⁷ , Ar, S0 ₂ , or O; R ⁷ is selected from the group of -C(CH ₃ ) ₂ -, -C(CH ₃ )-, -CH ₂ -, and substituted or unsubstituted dicylopentadienyl; Ar is selected from the group consisting of substituted or unsubstituted benzene, biphenyl,

naphthalene, phenol novolac, bisphenol A, ester, ring-substituted fluorenones, hydrogenated bisphenol A, bisphenol A, novolac, bisphenol F, and bisphenol F novolac function groups; g is an integer greater than or equal to 1, and Y ¹⁴ represents H or an aliphatic functional group or an aromatic functional group of up to 12 carbon atoms.

Some examples of dicyclopentadiene epoxy resins which can function as the co-curing agent (c) described herein can be those of the general formula (XV):

(XV) where Z is selected from -CH ₃ , -C2H5, -C(CH ₃ ) ₃ , and -H, and h is from 0.5 to 1.5.

The novolac resin which can function as the co-curing agent (c) herein can be a phenolic novolac or a dicyclopentadiene phenolic novolac. Some examples of dicyclopentadiene phenolic novolac resins which can function as the co-curing agent (c) herein are those of the general formula (XVI):

where each Y ¹⁵ is independently H or an alkyl group of from 1 to about 4 carbon atoms, and i is 1-5.

Some suitable examples of bismaleimides which can function as the co-curing agent (c) described herein can be those of the general formula (XVII):

where X ⁵ is alkylene group of from 1 to about 8 carbon atoms, or group.

Other phenolic functional materials which are suitable as co-curing agent (c) include compounds which form a phenolic crosslinking agent having a functionality of at least 2 upon heating. Some examples of these compounds are benzoxazine groups-containing compounds. Examples of compounds which form a phenolic crosslinking agent upon heating include phenolic species obtained from heating benzoxazine, for example as illustrated in the following chemical equation:

wherein "j" is greater than 1, and preferably up to about 100,000; and wherein "R ⁸ " and "R ⁹ " may be, independently and separately, the same or different of a hydrogen, an alkyl group from 1 to about 10 carbon atoms, such as methyl, a 6 to 20 carbon atom aromatic group such as phenyl or a 4 to 20 carbon atom cycloaliphatic group such as cyclohexane.

Examples of the above compounds also include benzoxazine of phenolphthalein, benzoxazine of bisphenol-A, benzoxazine of bisphenol-F, benzoxazine of phenol novolac, and mixtures thereof. A mixture of these compounds may also be used in the present invention. Non- limiting examples of commercial benzoxazines from Huntsman include examples such as Bisphenol A benzoxazine (MT35600) ; Bisphenol F benzoxazine (MT35700) Phenolphthalein benzoxazine (MT35800); Thiodiphenol benzoxazine (MT35900) and, Dicyclopentadiene benzoxazine (MT36000).

The co-curing agent (c) as described herein is used in the present invention in an amount effective to crosslink less than 50 percent of the stoichiometric amount needed to cure the epoxy resin, more preferably less than about 40 % amount needed to cure the epoxy resin and most preferably less than about 35 % amount needed to cure the epoxy resin. The amount of co- curing agent should not reduce the overall phosphorus content in the composition to below 1.5%.

Another embodiment herein is directed to phosphorous-containing epoxy resin curable formulations comprising (i) an epoxy resin or a mixture of epoxy resins, (ii) Compound (III), (iii) the co-curing agent described herein, (iv) optionally, a co-crosslinker, (v) optionally, a curing catalyst, and (vi) optionally, a Lewis acid.

Yet in another embodiment herein there is provided a curable flame-resistant epoxy resin composition comprising (i) a crosslinkable epoxy resin or a blend of two or more epoxy resins having more than one epoxy group per molecule, (ii) the above-noted oligomeric aromatic polyester phosphorus-containing curing agent (b), e.g., Compound (III), (iii) a co-curing agent, e.g.,, a benzoxazine-containing compound, (iv) optionally a co-crosslinker and, (vi) optionally, a curing catalyst to obtain a curable flame resistant epoxy resin composition. Such curable flame resistant epoxy resin compositions may be used to make prepregs, which prepregs may be used to make laminates and circuit boards useful in the electronics industry. The curable epoxy resin composition may also be used to coat metallic foils such as copper foils to make resin coated copper foils for so called build-up technology.

In one embodiment of the present invention, the oligomeric aromatic polyester phosphorus-containing curing agent (b) e.g., compound (III), described herein as well in one embodiment, combinations thereof, may be used, as one component, of a curable (crosslinkable) phosphorus-containing flame resistant epoxy resin composition. In this embodiment, the curable phosphorus-containing flame-resistant epoxy resin composition comprises (i) at least one epoxy resin such as those selected from halogen-free epoxies, phosphorus-free epoxies, and

phosphorus-containing epoxies and mixtures thereof, including, but not limited to DEN 438, DER 330, EPON 164 (DEN and DER are trademarks of The Dow Chemical Company), epoxy functional polyoxazolidone containing compounds, cycloaliphatic epoxies, GMA/styrene copolymers, and the reaction product of DEN 438 and DOPO resins, (ii) the oligomeric aromatic polyester phosphorus-containing curing agent (b) Compound (III), described herein, (iii) a co-curing agent (c); and optionally (iv) at least one co-crosslinker, and optionally one or more of a curing catalyst, a Lewis acid, an inhibitor, and a benzoxazine-containing compound.

In one embodiment herein there are provided compounds, compositions and/or formulations obtainable by reacting, blending or mixing components (a)-(c) to form various ignition resistant compounds, compositions or formulations useful in various applications such as prepregs, laminates, coatings, molding articles and composite products.

The curable epoxy resin compositions prepared according to the present invention, whether made either by reacting a mixture of epoxy (a), curing agent (b), e.g., Compound (III), described herein, co-curing agent (c), may be used to make prepregs, which, in turn, may be used to make laminates and circuit boards useful in the electronics industry. The epoxy curable compositions may also be used to coat metallic foils such as copper foils to make resin coated copper foils for so called build-up technology.

In one embodiment herein, the curable epoxy composition described herein is in the absence of bromine, and more preferably in the absence of all halogen. Any of the curable compositions of the present invention described herein may comprise a curing catalyst. Examples of suitable curing catalyst (catalyst) materials useful in the present invention include compounds containing amine, phosphine, ammonium, phosphonium, arsonium or sulfonium moieties or mixtures thereof. Particularly preferred catalysts are heterocyclic nitrogen-containing compounds.

The catalysts (as distinguished from co-crosslinkers) preferably contain on average no more than about 1 active hydrogen moiety per molecule. Active hydrogen moieties include hydrogen atoms bonded to an amine group, a phenolic hydroxyl group, or a carboxylic acid group. For instance, the amine and phosphine moieties in catalysts are preferably tertiary amine or phosphine moieties; and the ammonium and phosphonium moieties are preferably quaternary ammonium and phosphonium moieties.

Among preferred tertiary amines that may be used as catalysts are those mono- or polyamines having an open-chain or cyclic structure which have all of the amine hydrogen replaced by suitable substituents, such as hydrocarbyl radicals, and preferably aliphatic, cycloaliphatic or aromatic radicals.

Examples of these amines include, among others, l,8-diazabicyclo(5.4.0)undec-7-en (DBU), methyl diethanol amine, triethylamine, tributylamine, dimethyl benzylamine, triphenylamine, tricyclohexyl amine, pyridine and quinoline. Preferred amines are the trialkyl, tricycloalkyl and triaryl amines, such as triethylamine, triphenylamine, tri-(2,3- dimethylcyclohexyl)amine, and the alkyl dialkanol amines, such as methyl diethanol amines and the trialkanolamines such as triethanolamine Weak tertiary amines, for example, amines that in aqueous solutions give a pH less than 10 in aqueous solutions of 1 M concentration, are particularly preferred. Especially preferred tertiary amine catalysts are benzyldimethylamine and tris-(dimethylaminomethyl)phenol.

Examples of suitable heterocyclic nitrogen-containing catalysts include heterocyclic secondary and tertiary amines or nitrogen-containing catalysts which can be employed herein include, for example, imidazoles, benzimidazoles, imidazolidines, imidazolines, oxazoles, pyrroles, thiazoles, pyridines, pyrazines, morpholines, pyridazines, pyrimidines, pyrrolidines, pyrazoles, quinoxalines, quinazolines, phthalozines, quinolines, purines, indazoles, indoles, indolazines, phenazines, phenarsazines, phenothiazines, pyrrolines, indolines, piperidines, piperazines and combinations thereof. Especially preferred are the alkyl-substituted imidazoles; 2,5-chloro-4-ethyl imidazole; and phenyl-substituted imidazoles, and mixtures thereof. Even more preferred are N-methylimidazole; 2-methylimidazole; 2-ethyl-4-methylimidazole; 1,2- dimethylimidazole; and 2-methylimidazole and mixtures thereof. Especially preferred is 2- phenylimidazole.

The amount of curing catalyst used depends on the molecular weight of the catalyst, the activity of the catalyst and the speed at which the polymerization is intended to proceed. In general, the curing catalyst is used in an amount of from 0.01 parts per 100 parts of resin (p.h.r.) to about 1.0 p.h.r., more specifically, from about 0.01 p.h.r. to about 0.5 p.h.r. and, most specifically, from about 0.02 p.h.r. to about 0.5 p.h.r. In one embodiment herein it will be understood herein that parts of resin relates to the parts of curable epoxy resin described herein, i.e., the total amount of the curable composition excluding catalyst, (total grams of epoxy + Compound (III), co-curing agent (c), and any other components present other than the curing catalyst = 100% and then taking 100 grams of this is equal to 100 parts of resin); catalyst is added in above ranges to 100 parts of this total weight amount

Preferably, a Lewis acid is also employed in any of the curable epoxy resin compositions of the present invention described herein, especially when the catalyst is particularly a heterocyclic nitrogen-containing compound.

The Lewis acids useful in the present invention include for example one or a mixture of two or more halides, oxides, hydroxides and alkoxides of zinc, tin, titanium, cobalt, manganese, iron, silicon, aluminum, and boron, for example Lewis acids of boron, and anhydrides of Lewis acids of boron, for example boric acid, metaboric acid, optionally substituted boroxines (such as trimethoxyboroxine), optionally substituted oxides of boron, alkyl borates, boron halides, zinc halides (such as zinc chloride) and other Lewis acids that tend to have a relatively weak conjugate base. Preferably the Lewis acid is a Lewis acid of boron, or an anhydride of a Lewis acid of boron, for example boric acid, metaboric acid, an optionally substituted boroxine (such as trimethoxy boroxine, trimethyl boroxine or triethyl boroxine), an optionally substituted oxide of boron, or an alkyl borate. The most preferred Lewis acid is boric acid. These Lewis acids are very effective in curing epoxy resins when combined with the heterocyclic nitrogen-containing compounds, referred to above.

The Lewis acids and amines can be combined before mixing into the formulation or by mixing with the catalyst in situ, to make a curing catalyst combination.

The amount of the Lewis acid employed is preferably at least 0.1 mole of Lewis acid per mole of heterocyclic nitrogen compound, more preferably at least 0.3 mole of Lewis acid per mole of heterocyclic nitrogen-containing compound.

The curable epoxy compositions of the present invention may optionally have boric acid and/or maleic acid present as a cure inhibitor. In that case, the co-curing agent (c) is preferably a polyamine or polyamide. The amount of cure inhibitor will be known by those skilled in the art.

The curable epoxy compositions of the present invention may also optionally contain one or more additional flame retardant additives including, for example, liquid or solid phosphorus-containing compounds, for example, "EXOLIT OP 930", EXOLIT OP 910 from Clariant GmbH and ammonium polyphosphate such as "EXOLIT 700" from Clariant GmbH, a phosphite, or phosphazenes; nitrogen-containing fire retardants and/or synergists, for example melamines, melem, cyanuric acid, isocyanuric acid and derivatives of those nitrogen-containing compounds; halogenated flame retardants and halogenated epoxy resins (especially brominated epoxy resins); synergistic phosphorus-halogen containing chemicals or compounds containing salts of organic acids; inorganic metal hydrates such as Sb ₂ 0 ₃ , Sb ₃ 0 ₅ , aluminum trihydroxide and magnesium hydroxide such as "ZEROGEN 30" from Martinswerke GmbH of Germany, and more preferably, an aluminum trihydroxide such as "MARTINAL TS-610" from Martinswerke GmbH of Germany; boron-containing compounds; antimony-containing compounds; silica and combinations thereof.

In one embodiment, the phosphazene compounds can function as an optional additive to the compositions described herein and can be those of the general formula (XVIII): (XVIII) where Z ¹⁶ -Z ²¹ each independently represents an alkoxy or aryloxy group containing from 1 and/or 6, up to about 10 carbon atoms.

When additional flame retardants which contain phosphorus are present in the curable epoxy composition of the present invention, the phosphorus-containing flame retardants are preferably present in amounts such that the total phosphorus content of the epoxy resin composition is from 0.2 wt. percent to 5 wt. percent.

The curable epoxy compositions of the present invention may also optionally contain other additives of a generally conventional type including for example, stabilizers, other organic or inorganic additives, pigments, wetting agents, flow modifiers, UV light blockers, and fluorescent additives. These additives can be present in amounts of from 0 to 5 weight-percent and is preferably present in amounts less than 3 weight percent.

In one embodiment, the curable epoxy composition may also contain filler. Some examples of filler, may be those such as, glass fiber, glass fiber having a non-circular cross section such as fiat fiber, carbon fiber, silica fiber, silica- alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, boron fiber, potassium titanate fiber, and further, metal fibrous substances such as stainless, aluminum, titanium, copper and brass.

Particularly, the typical fibrous filler is glass fiber or carbon fiber. On the other hand, the filler may be a powdery filler, such as carbon black, silica, quartz powder, glass bead, glass powder, calcium silicate, kaolin, talk, clay, diatomaceous earth, silicates such as wollastonite, metal oxides such as iron oxide, titanium oxide, zinc oxide and alumina, metal carbonates such as calcium carbonate and magnesium carbonate, metal sulfates such as calcium sulfate and barium sulfate, and in addition, silicon carbide, silicon nitride, boron nitride and various metal powders.

Another example of filler may be plate-like filler such as, mica, glass flake and various metal foils. These inorganic fillers can be used alone or in combination of two or more. When these inorganic fillers are used, they are desirably treated previously with a sizing agent or surface treatment agent, if necessary.

The amount of the inorganic filler in the curable epoxy composition may be from 1 to 50% by weight, preferably from 10 to 45% by weight and most preferably from 20 to 40% by weight.

The curable epoxy compositions described above are useful for making coating formulations, encapsulation, composites, and adhesives, molding, bonding sheets, and laminated plates. The compositions of the present invention can be used to make composite materials by techniques well-known in the industry, such as by pultrusion, molding, encapsulation, or coating. As an illustration, a coating formulation may comprise (i) an epoxy resin, (ii) the oligomeric aromatic polyester phosphorus-containing curing agent (b), e.g., Compound (III), and (iii) a co- curing agent (c) such as an amine or phenolic hardener. The amounts of hardener will be known by those skilled in the art.

The present invention is particularly useful for making B-staged prepregs, laminates, bonding sheets, and resin coated copper foils by well known techniques in the industry.

In one embodiment herein there is provided an article that contains any of the curable epoxy composition(s) described herein, and cured versions of the same. In one embodiment the article herein can be used in lead free soldering applications and electronic devices, e.g., printed wiring board applications, specifically the article can be a prepreg and/or a laminate. In one specific embodiment there is provided a laminate and/or a prepreg that contains any one or more of the curable epoxy compositions described herein. In one other embodiment there is provided herein a printed wiring board, optionally a multilayer printed wiring board, comprising one or more prepreg(s) and/or a laminate (e.g., either uncured, partially cured or completely cured) wherein said prepreg(s) and/or laminate comprise any one or more of the curable epoxy compositions described herein. In one embodiment there is provided a printed wiring board comprising a prepreg and/or a laminate wherein said prepreg and/or laminate comprises any one of the curable epoxy compositions described herein. It will be understood herein that any reference herein to an embodiment of a curable epoxy composition can also be attributed to the cured version of the curable epoxy composition.

Partial curing as used herein can comprise any level of curing, short of complete cure, and will vary widely depending on the specific materials and conditions of manufacture as well as the desired end-use applications. In one specific embodiment, the article herein can further comprise a copper foil. In one embodiment the article can comprise a printed wiring board. In one embodiment there is provided an FR-4 laminate which comprises a prepreg and/or laminate of the invention. In a more specific embodiment there is provided a printed circuit board comprising an FR-4 laminate, wherein the FR-4 laminate comprises a prepreg or laminate of the invention.

In one embodiment herein there is provided a process of making a laminate that contains any of the curable epoxy compositions described herein which process comprises impregnating the respective curable epoxy composition(s) into a filler material, e.g., a glass fiber mat to form a prepreg, followed by processing the prepreg at elevated temperature and/or pressure to promote partial cure to a B-stage and then laminating two or more of said prepregs to form said laminate. In one embodiment said laminate and/or prepreg can be used in the applications described herein, e.g., printed wiring boards.

There is provided herein that any of the curable epoxy compositions described herein are useful for making a prepreg and/or laminate with a good balance of laminate properties and thermal stability, such as one or more of high T _g (i.e. above 150°C), Td of 350°C and above, T ₂ ss of 30 minutes and above, a flame resistance rating of V-0, good toughness, and good adhesion to copper foil. In recent years Td has become one of the most important parameters, because the industry is changing to lead-free solders which melt at higher temperature than traditional tin- lead solders. In one embodiment herein the curable epoxy compositions described herein can be used in other applications, e.g., encapsulants for electronic elements, protective coatings, structural adhesives, structural and/or decorative composite materials in amounts as deemed necessary depending on the particular application.

The following examples are used to illustrate the present invention.

Examples:

Preparative Example 1

Preparation Example: Synthesis of DOPO-HQ-Diacetate-Isophthaloyl-Polyester (compound III) DOPO-HQ (CAS reg # 99208-50-1 ) (73.2 g, 225.7 mmol) and isophthalic acid (25.0 g, 150.5 mmol) were mixed together in a 500 mL of flask, and dried under vacuum for about 30 min. Acetic anhydride (85 mL, 902.8 mmol) was added. Under N ₂ protection, the suspension was heated to 150 °C for 1 h or until all DOPO-HQ was converted to DOPO-HQ-diacetate, and excess acetic anhydride was collected via distillation. The reaction mixture was then heated up to 190-200 °C for 2 h. A homogenous solution formed after ~ 1 h, and generated acetic acid and excess acetic anhydride were collected via distillation. Full vacuum (70-100 mTorr) was applied at 190-200 °C for another 1 h to consume DOPO-HQ-diacetate further and remove left-over acetic acid and acetic anhydride. The reaction mixture was cooled down to room temperature, and the product compound III was a yellow solid. ¾ NMR (300 MHz, Chloroform-i , ppm) δ 8.60-6.81 (multiple H), 2.50-2.22 (multiple H), 1.58 (singlet H). ³¹ P NMR (121 MHz, Chloroform-i , ppm) δ 17.5, 18-19 (multiple peaks). The phosphorus content is 6.9%.

Preparation Example 2: Synthesis of DCPD-r-PPO

PPO (20 g, MW~60,000) was dissolved in 50 mL of toluene at 90 °C under nitrogen protection. SD1842 (dicyclopentadiene phenol novolac from Momentive) (6 g, OH equiv -200) was added, followed by portionwise addition of 6 g of BPO (benzoyl peroxide) during 15 min. The mixture was heated at 90 °C for 3 h. The mixture was allowed to cool to room temperature and was added to methanol to precipitate the product. The dark red precipitate was collected by filtration, washed with sodium carbonate aq solution, water and methanol for multiple times, and then dried under vacuum at 100 °C. The solid was redissolved in MEK, and the insoluble solids were filtered out. The MEK solution was collected and dried to recover the final product DCPD- redistributed PPO (dark red solid, Yield -90%). GPC MW analysis (0.1 mg/niL in THF) reveals a MW-7750.

Preparation Example 3: Synthesis of BPA-r-PPO

PPO (20 g, MW~60,000) was dissolved in 50 mL of toluene at 90 °C under nitrogen protection. 10 g of BPA (bisphenol-A) was added, followed by portionwise addition of 10 g of BPO (benzoyl peroxide) during 15 min. The mixture was heated at 90 °C for 6 h. The mixture was allowed to cool to room temperature and was added to methanol to precipitate the product. The yellow precipitate was collected by filtration, washed with sodium carbonate aq solution, water and methanol for multiple times, and then dried under vacuum at 100 °C. The solid was redissolved in MEK, and the insoluble solids were filtered out. The MEK solution was collected and dried to recover the final product BPA-redistributed PPO (yellow solid, Yield -50%). GPC MW analysis (0.1 mg/mL in THF) reveals a MW-3390.

Table 1 : Materials

Trade Name (Producer) General Information Function

A-l EPON 164 (ex Momentive) Cresol novolac Epoxy resin epoxy

A-2 DEN 438 (ex Dow Chemicals) Phenol novolac Epoxy resin epoxy

A-3 HP 7200H (ex DIC Corporation) DCPD Epoxy resin

(dicyclopentadiene)

epoxy

B Compound III (preparative example 1) Phosphorus- Flame

containing ester in retardant and Preparation Example curing agent 1

C-l SD 1708 (ex Momentive) Phenolic novolac Curing agent

C-2 SD 1842 (ex Momentive) DCPD Curing agent

(dicyclopentadiene)

phenolic novolac

C-3 BPA-cyanate (2,2-Bis(4-cyanatophenyl)propane) Bisphenol-A- Curing agent cyanate

C-4 1 , 1 '-(Methylenedi-4, 1 -phenyl ene)bismaleimide Bismaleimide Curing agent

C-5 SMA EF-60 ( Total Cray Valley) Styrene maleic Curing agent anhydride

copolymer

e:f = 6: l

C-6 DCPD-r-PPO (preparative Example 2) DCPD phenol Curing agent novolac- and filler redistributed PPO

(polyphenylene

oxide)

C-7 BPA-r-PPO (preparative Example 3) Bisphenol-A- Curing agent redistributed PPO and filler C-8 SA90 (ex Sabic) Hydroxyl-ended Curing agent redistributed PPE and filler

C-9 SA9000 (ex Sabic) Vinyl-ended Curing agent redistributed PPE and filler

C-10 Silica (ex Denka) Fused silica Filler

D-l 2-mI (ex Air Products) 2-methyl imidazole Catalyst

D-2 Benzyl peroxide (ex Aldrich) Benzyl peroxide Catalyst

Benzylamino silane (ex Aldrich) N-[3- Coupling

(Trimethoxysilyl)pro agent pyl] aniline

Methyl ethyl ketone (ex Fluka) Butan-2-one Solvent

Dowanol (ex Fluka) 1-methoxy 2- Solvent

propanol

Dimethyl formamide (ex Fluka) N,N- Solvent

Dimethylformamide

Glass Cloth (ex BGF Industries) E-Glass Reinforcing agent

Copper foil (ex Gould Electronics) JTC, 1.0 oz./ft ² Resistance to oxidation in warm and humid environments and for precise etching behavior and others

Example 1-8: Small scale Epoxy Curing Experiments with curing agents of the invention

Samples of compound III were combined with epoxy and co-curing agent (c) and cured on a small scale. Samples were cured using DEN438: EPON164 in 1: 1 ratio, co-curing agent in Table 2 and 0.2 wt% of 2-methyimidazole as catalyst. Total % P was 2.2-2.5%. The epoxy was cured at 195-200 °C for 2-3 hours and post-cured at 210-220 °C for 1 hour. Thermal stability of the samples was studied using DSC and TGA. To prepare varnish castings for Dk and Df measurements, compound III was blended with DEN438: EPON164 in 1 : 1 ratio, co-curing agent in Table 2 and 2-methyimidazole as catalyst. 10"xlO" aluminum foils were coated single-side using the sample-epoxy blend. After coating the foils were air dried followed by "B "-staging at 165 °C (3'50"). The epoxy was peeled from the foil, followed by molding and curing at 200 °C for 2-3 hours and post-curing at 210-220°C for 1 hour. The results are shown in the Table 3:

Table 2: Composition for small scale curing experiments

Table 3: Tg, TGA, Dk and Df results for small scale curing experiments

Discussion: As shown in Table 3, the Examples 2-8 of the present invention have low dielectric constant (Dk) and loss factor (Df) compared to Comparative Example 1. The addition of cyanate ester/bismaleimide (Example 3 and 4) increases the glass transition temperature and lowers Dk and Df most. Redistributed PPO compounds with DCPD phenol novolac or bisphenol-A (Example 5-7) are also good co-curing agents and fillers that lower Dk and Df without impacting the thermal properties. The usage of styrene maleic anhydride copolymer as co-curing agent increases the glass transition temperature (Example 8).

Example 9: Laminate Preparation

The low Dk formulation in Example 5 was further explored for the epoxy laminate application. All the materials information is listed in Table 1. The solids content was maintained at 61 % with the addition of MEK/Dowanol (80/20) solvent mixture. Varnish formulation was prepared therefrom which had phosphorous contents of 2.2 % and the composition contents are shown in Table 4.

Table 4: Epoxy laminate formulation of Example 9

The catalyst addition was carefully controlled by adding small incremental amounts of 2- methylimidazole (2 -ml) solution (20 weight% solids solution in DMF) to obtain an optimum varnish gel time of 300 seconds at 17PC according to IPC-TM-650 test 2.3.18.

A glass fabric (17 inches X 36 inches) was continuously passed through a trough containing the varnish and through squeeze rolls such that a uniform coating was obtained. Sections of the coated fabric were hanged in the hood overnight for slow evaporation of solvent. Prepregs were made by drying the resin coated glass fabric in a preheated air circulated oven at 165°C for 2 '30" (two minutes and thirty seconds), which gave a resin flow less than 20.0%. Also, the resin content was controlled to be over 40 %, which is determined through the difference in weight between the glass fabric and the prepreg. The prepreg gel time was determined by collecting the fusible, thermoplastic resin by crushing the prepreg in a zip-lock bag. The collected resin was placed on the hot-plate at 171°C and the gel time determined.

A circular stack of 4 prepregs with a diameter of 25 mm was placed between disposable aluminum (Al) plates to study the rheological behavior of the B-stage prepreg by electrically heating the resin to 200°C at 5°C/min in an AR2000ex Rheometer. A continuous controlled strain condition within the linear viscoelastic region of the prepreg was maintained along with the normal force control that accounts for volume changes occurring in the resin with change in temperature. Based on rheology curves, the final curing temperature for the laminate was selected above 179°C. Based on the rheology curve, the curing cycle was designed to obtain a good wetting of the glass cloth. A low initial pressure of 10 psi was applied at 103-105°C (the complex viscosity of the prepreg was around 17560 pa-s) and sufficient to wet the glass fabric as studied during the preparation of various experimental epoxy laminates. Subsequently 20 psi pressure was applied at 140°C and the pressure was maintained at 20 psi until 165°C. The pressure was again raised to 50 psi at 165°C and 100 psi once the press reached 175°C. A pressure of 100 psi was applied at 175°C and finally a pressure of 220 psi was applied at 195°C.

Finally, the press was maintained at 220 psi and 195°C isothermally for 90 minutes. The laminate showed a good resin flow and the thickness of the final laminate was close to 1.3 mm (without copper). The laminate was rated as a borderline V-0 with a maximum burn time of 8 seconds by following ASTM D3801-10 standard using an Atlas UL-94 burning chamber (V-0 being the highest possible rating).

The glass transition temperature (Tg) of the multilayer laminate was determined to be 181°C by Dynamic Mechanical Analysis (DMA) in a single-cantilever mode at a ramp rate of 3°C/min. The thermal decomposition temperature of the composite at 5 weight% loss is 398°C as measured by Thermogravimetric Analysis (TGA) at a heating rate of 10°C/min in an inert atmosphere of nitrogen.

Example 10-13: Small scale Epoxy Curing Experiments with DCPD epoxy and curing agents of the invention

Samples of compound I were combined with DCPD epoxy and filling/co-curing agent (c) and cured on a small scale. Samples were cured using DCPD epoxy, filling/co-curing agent in Table 5 and 0.04 wt% of 2-methyimidazole and/or 0.2 wt% benzyl peroxide as catalyst. Total % P was 2.4-3.0%. The epoxy was cured at 200-215 °C for 2-3 hours and post-cured at 210-225 °C for 1 hour. Thermal stability of the samples was studied using DSC and TGA. To prepare varnish castings for Dk and Df measurements, compound I was blended with DCPD epoxy, filling/co- curing agent in Table 5 and 2-methyimidazole and/or benzyl peroxide as catalyst. 10"xl0" aluminum foils were coated single-side using the sample-epoxy blend. After coating the foils were air dried followed by "B"-staging at 165 °C (3'50"). The epoxy was peeled from the foil, followed by molding and curing at 200-215 °C for 2-3 hours and post-curing at 210-225°C for 1 hour. The results are shown in the Table 6:

Table 5: Composition for small scale curing experiments

Table 6: Tg, TGA, Dk and Df results for small scale curing experiments

Discussion: As shown in Table 6, when compound I is used to cure DCPD epoxy, good Dk and Df were observed (Dk < 3.1 and Df < 0.008). A 100% cure can be accomplished with compound I with final P content of 3% (Example 10). This cannot be done with DOPO-BPA since final P content will be 6.8% so other components such as DCPD Novolac have to be introduced resulting in increase of Dk and Df. The addition of redistributed PPE, especially SA9000, lowers Dk and Df (Example 12). Silica is a good filler that improves Dk without impacting the thermal properties (Example 13). Example 14: Laminate Preparation

The low Dk&Df formulation in Example 13 was further explored for the epoxy laminate application. All the materials information is listed in Table 1. The solids content was maintained at 65 % with the addition of MEK/Dowanol (80/20) solvent mixture. Varnish formulation was prepared therefrom which had phosphorous contents of 2.4 % and the composition contents are shown in Table 7.

Table 7: Epoxy laminate formulation of Example 14

A laminate was prepared using the above epoxy varnish. Catalyst (20 wt% 2-MI solution in DMF) level was adjusted to give a gel time between 5-6 minutes. The varnish was applied to glass cloth panels by passing them through a trough containing the varnish then pulled between gapped rollers allowing excess material to flow out leaving a smooth uniform coating. The coated panels, light tan in color, were hung and allowed to air dry overnight evaporating most of the solvent. After drying the four 18 x 30 inch panels were cut into 8.5 inch squares and "B" staged at 165°C for 3 minutes resulting in a resin flow of 4.4%. The finale laminate was prepared using 8 plies of each prepreg placed between 2 sheets of 35μηι copper foil. The stack was then placed between steel plates in a heated press. Temperature and pressure were ramped following a viscosity profile obtained from an AR200ex rheometer using the B staged material. A final pressure of 200 psig at 220°C was applied to the laminate and held for 1 hour 15 min prior to cooling producing a laminate with a resin content of 27.5%. The thickness of the laminate after removal of the copper foil measured 1.2 mm. Test samples were cut to determine FR and thermal properties of the laminate. Following UL94 test protocol the laminate was rated V-0. The Tg of the laminate as determined by DSC was 192°C and 5% weight loss occurred at 423°C approximately 20 degrees higher than unfilled Compound I/Epoxy systems. A test plaque was cut from the laminate for the Pressure Cooker Test (PCT). Water uptake after 1 hour was 0.22% and following the solder bath dip test for 20 seconds at 288°C the test plaque passed with a Condition 5 on the first surface and Condition 2 on the second.

While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the process of the invention but that the invention will include all embodiments falling within the scope of the appended claims.