Cyanate ester based thermoset compositions

Details Cyanate ester based thermoset compositions Cyanate ester based thermoset compositions

1998-03-23

2001-02-27

Niland, Patrick D. (Department: 1773)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S100000

Reexamination Certificate

active

06194495

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to cyanate ester based compositions. This invention further relates to curable and cured compositions, useful in applications wherein excellent dielectric and thermal properties are desired.
BACKGROUND OF THE INVENTION
Cyanate esters have been used as curable resins with desirable electrical and thermal properties. As such, they have found utility as matrix resins in a number of industrial applications. Such applications include printed circuit boards, antenna coatings, structural composites, encapsulating resins, matrix resin for abrasives, and adhesives. Chemistry and applications of cyanate esters are discussed in “The Chemistry and Technology of Cyanate Esters” by I. A. Hamerton ® 1994 Blackie Academic & Professional, an imprint of Chapman & Hall and references therein.
Cyanate ester resins, as described in U.S. Pat. No. 3,553,244, are produced by reacting a phenolic compound with cyanogen halide. Such cyanate esters, upon curing, are known to form hard thermoset matrices through cyclotrimerization of the cyanate ester groups. The cyclotrimerization produces symmetrical aryloxytriazine rings which serve as the crosslink sites in the thermoset matrix. The cure of these resins is accelerated by heating, or alternatively by using catalysts such as those described in U.S. Pat. Nos. 4,330,658, 4,330,669, 4,785,075, and 4,528,366. Curable compositions containing partially cured cyanate ester prepolymers are also known and are described in U.S. Pat. No. 4,740,584. Such partial curing produces cyanate ester-containing aryloxytriazine resins that can be further cured through the cyclotrimerization of the remaining cyanate ester moieties. Blends of cyanate ester prepolymers are described in U.S. Pat. Nos. 4,110,364 and 4,371,689. Blends of cyanate esters with thermoplastic polymers are disclosed in U.S. Pat. Nos. 4,157,360, 4,983,683, and 4,902,752.
Many of the aforementioned compositions however are not flame retardant and their use in electrical applications, where flame retardancy is critical, is limited. Flame retardant cyanate ester blends are described in Japanese Patent Nos. 05339342 and U.S. Pat. No. 4,496,695, which describes blends of cyanate esters and brominated epoxies, or polyphenylene ether (PPE), cyanate esters and brominated epoxies. Epoxy resins however are known to have inferior electrical properties relative to cyanate esters, and the corresponding cyanate ester-epoxy blends do not have optimal electrical properties.
These issues have been addressed by preparing blends of brominated cyanate esters as disclosed in U.S. Pat. Nos. 4,097,455 and 4,782,178. Blends of cyanate esters with the bis(4-vinylbenzylether)s or brominated bisphenols are also described in U.S. Pat. Nos. 4,782,116, and 4,665,154. Blends of cyanate esters with brominated poly(phenylene ether)s, polycarbonates or perbromobenzylacrylates are disclosed in Japanese Patent No. 08253582.
However, curable compositions comprising cyanate esters are still sought, and there is still a need for curable compositions that can have electrical applications.
SUMMARY OF THE INVENTION
The present invention provides curable compositions comprising (a) a compound selected from the group consisting of a cyanate ester, a cyanate ester prepolymer, and mixtures thereof; (b) a cyanate ester-free aryloxytriazine, and (c) a catalyst. The present compositions provide the desired flame retardant properties (UL-94 flammability of V-1 or better) which are useful in electrical applications.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment of the present invention is provided a composition where the cyanate ester is represented by the structure of Formula I
A
1
—(OCN)
n
  Formula I
wherein A
1
is a C
6-200
aromatic or mixed aromatic-aliphatic hydrocarbon radical containing a member or members selected from the group consisting of oxygen, nitrogen, halogen, sulfur, phosphorus, boron, silicon, hydrogen, and mixtures thereof, and “n” represents an integer from about 1 to about 10. In a preferred embodiment of this invention n represents an integer from about 2 to about 5, and most preferably from about 2 to about 3. Typical of this type are the cyanate ester compounds wherein n=2. Illustrative examples of cyanate ester compounds are bis(4-cyanatophenyl)methane bis(3-methyl-4-cyanatophenyl)methane, bis(3-ethyl-4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, 1,1-bis(4-cyanatophenyl)ethane, 2,2-bis(4-cyanatophenyl)propane, 2,2-bis(4-cyanatophenyl)1,1,1,3,3,3-hexafluoropropane, di(4-cyanatophenyl)ether, di(4-cyanatophenyl)thioether, 4,4-dicyanatobiphenyl, 1,3-bis(4-cyanatophenyl-1-(1-methylethylidene))benzene, 1,4-bis(4-cyanatophenyl-1-(1-methylethylidene))benzene and resorcinol dicyanate. Also useful are cyanate esters of Formula I wherein n>2. Examples of such materials include the cyanate ester of phenol formaldehyde novolak, cyanate ester of phenol dicyclopentadiene novolak, 1,1,1-tris(4-cyanatophenyl)ethane.
Cyanate ester prepolymers that can be used in the present invention are prepolymers produced by partial curing of the cyanate ester in the presence or absence of a catalyst. A typical example of such a cyanate ester prepolymer is partially cured bis(3,5-dimethyl-4-cyanatophenyl)methane, sold under the tradename AroCy M-20 by Ciba. A detailed description of cyanate ester and cyanate ester prepolymers can be found in “The Chemistry and Technology of Cyanate Esters” by I.A. Hamerton® 1994, Blackie Academic and Professional, a n imprint of Chapman and Hall, which is incorporated herein by reference.
The cyanate ester-free aryloxytriazine component useful in the present invention is represented by Formula II:
wherein A
2
is a C
6-200
aromatic or alternatively a mixed aromatic-aliphatic hydrocarbon radical, alternatively containing a member or members selected from the group consisting of oxygen, nitrogen, halogen, sulfur, phosphorus, boron, silicon, and mixtures thereof, such that at least one A
2
is aromatic and each A
2
i free of cyanate ester groups. Preferred cyanic acid ester-free triazine resins useful in the present invention include tris(triphenoxy)-1,3,5-triazine, and substituted derivatives thereof such as tris(2,4,6-tribromophenoxy)-1,3,5-triazine, tris(2-allylphenoxy)-1,3,5-triazine, tris(4-allylphenoxy)-1,3,5-triazine, tris(2-methoxy-4-allylphenoxy)-1,3,5-triazine, tris(4-vinylphenoxy)-1,3,5-triazine. In applications requiring UL-94 V-0 flame retardancy, the use of brominated triazines such as tris(2,4,6-tribromophenoxy)-1,3,5-triazine is preferred. The level of incorporation of brominated triazines typically falls in the range from about 10% to about 30% by weight of the total composition.
Catalysts, as used in the present invention, include a compound selected from the group consisting of carboxylate salts, phenols, alcohols, amines, urea derivatives, imidazoles, and metal chelates. Preferred catalysts include octoate, carboxylate, or acetylacetonate salts of zinc, cobalt, copper, manganese, iron, nickel, or aluminum.
It is understood that a catalyst includes low molecular weight or polymeric entities, and as such includes thermoplastics and elastomers. In another embodiment of the present invention, the catalyst is a phenolic compound. Phenolic compounds particularly useful in the present invention are represented by Formula III:
A
3
—(OH)
m
  Formula III
wherein A
3
is C
6-1000
aryl, optionally substituted with aryl, C
1-20
alkyl, alkoxy, aryloxy, carboxy, thio, sulfonyl, containing optionally a member or members selected from the group consisting of oxygen, nitrogen, halogen, sulfur, phosphorus, boron, silicon, hydrogen, and mixtures thereof, and “m” represents an integer from about 1 to about 200, and preferably from about 1 to about 5.
Typical compounds represented by structures of Formula III include alkylphenols such as nonylphenol, or dinonylphenol, octylphenol, 3(2-hydroxyphenyl)propionic acid, 3(2-hydroxyphenyl)propanol, 2-methoxy-4-allylphenol, 2-allylphenol and bisphenols including 2,2-b

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