Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-08-02
2001-06-12
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S217000, C524S100000, C524S494000, C524S612000, C528S422000, C528S423000
Reexamination Certificate
active
06245841
ABSTRACT:
BACKGROUND 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.
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 aryloxytriazine rings which serve as the crosslink sites in the thermoset matrix. The cure of these resins is effected by heating, particularly in the presence of 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 cyanate ester prepolymers are also known and are described in U.S. Pat. No. 4,740,584. Such prepolymers comprise cyanate ester-containing aryloxytriazine residues 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 applications, where flame retardancy is critical, is limited. Such applications include electrical applications such as printed circuit boards. Flame retardant cyanate ester blends are described in Japanese Patent No. 05339342 and U.S. Pat. No. 4,496,695, which describe blends of cyanate esters and brominated epoxies, or poly(phenylene 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 pentabromobenzylacrylates are disclosed in Japanese Patent No. 08253582.
In European Patent Application 0889096 curable compositions are described comprising a) a cyanate ester compound; b) a monovalent, non-polymeric phenolic compound having no more than 36 carbon atoms; c) an alloy of polyphenylene ether and polystyrene; d) a flame retardant not reactive with the cyanate ester compound; and e) a metal catalyst. The application teaches the use of an alloy of high molecular weight polyphenylene ether with polystyrene. The examples exhibit significant phase separation in the cured state, which can lead to non-uniform thermal and dielectric performance. The application also teaches that addition of PPE-polystyrene alloy to a cyanate ester resin causes significant reductions in its Tg. Such reductions in thermal performance are undesirable since lower Tgs of the cured composition lead to poorer dimensional stability during processing steps, such as soldering, and reduce the high temperature dielectric performance and reliability.
Therefore, there is still a need for curable compositions comprising cyanate esters with optimal thermal performance, flow, flame retardancy and electrical properties.
SUMMARY OF THE INVENTION
This need is satisfied by the present invention which provides curable compositions comprising: (a) at least one compound selected from the group consisting of cyanate esters and cyanate ester prepolymers, (b) a flame retardant which is substantially toluene soluble and substantially free of hydroxy residues in the cured state, (c) a curing catalyst. In a preferred embodiment the invention comprises (a) at least one compound selected from the group consisting of cyanate esters and cyanate ester prepolymers, (b) a cyanate ester-free aryloxytriazine, and (c) a curing catalyst. The present compositions provide the desired balance of properties particularly useful in electrical applications.
DETAILED DESCRIPTION OF THE INVENTION
In the compositions of this invention the cyanate ester is represented by the structure of Formula I
wherein A
1
is a C
6-1000
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, and hydrogen, 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 is equal to 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, di(4-cyanato-2,6-methylphenyl)thioether, di(4-cyanato-2-t-butyl-3-methylphenyl)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 cyanated thermoplastic polymers produced by cyanation of free hydroxyl residues of a thermoplastic polymer. Such cyanation may be carried out, for example, by reaction of the hydroxyl groups of a thermoplastic polymer with a cyanogen halide preferably in the presence of a basic compound such as triethylamine. Useful thermoplastic polymers include for example poly(2,6-dimethyl-1,4-phenylene ether) (PPE).
Also useful are cyanate esters of Formula I wherein n is greater than 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. It is within the scope of the invention to employ mixtures of two or more different cyanate esters.
Cyanate ester prepolymers that can be used in the present invention contain free cyanate ester groups and may be produced by partial curing of the cyanate ester resin in the presence or absence of a catalyst. A typical example of such a cyanate ester prepolymer is the partial reaction product of bis(3,5-dimethyl-4-cyanatophenyl)methane, sold under the tradename AroCy® M-20 by Ciba. A detailed description of cyanate esters and cyanate ester prepolymers can be found in “The Chemistry and Technology of Cyanate Esters” by I. A. Hamerton© 1994, Blackie Academic and Professional, an imprint of Chapman and Hall, which is incorporated herein by reference. It is within the scope of the invention to employ mixtures of two or more different cyanate ester prepolymers, and mixtures of one or more cyanate ester prepolymers with one or more cyanate ester-containing compounds which are not prepolymers.
Flame retardants suitable for use in embodiments of the present jo invention are substantially toluene-soluble and are substantially free of hydroxy residues in the cured state. Substantial solubility of the flame retardant in toluene allows for preparation of homogeneous solutions of compositions of the invention which generally enables m
Pan Yiqun
Yeager Gary William
Brown S. Bruce
General Electric Company
Johnson Noreen C.
Niland Patrick D.
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