Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2003-01-31
2004-07-06
Sellers, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C525S523000, C558S394000
Reexamination Certificate
active
06759503
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to aromatic amines, more particularly to N-cyanoethylated ortho-toluenediamine and N-cyanoethylated meta-toluenediamine, a process for making them, and their use as epoxy curing agents.
It is known to use amines, such as aliphatic or aromatic amines, for the curing of epoxy resins. See, e.g., “Handbook of Epoxy Resins” by H. Lee and K. Neville, McGraw Hill Book Co., 1967. The aromatic amines currently available provide high Tg, good fracture toughness and excellent chemical resistance for adhesive and composite applications, but suffer from several shortfalls. Aromatic amines typically used as epoxy curatives, such as methylenedianiline (MDA) and diethyltoluenediamine (DETDA), are usually considered to be highly toxic. In addition, the potlife of such aromatic amines is of an insufficient duration to consider the amines to be latent curatives. MDA and DETDA, for example, have very long potlives of up to 12 to 24 hours, but do not provide a potlife of several days, which is desired in a latent curing agent. Moreover, such aromatic amines cannot be used with solid epoxy resins for powder coating applications.
The epoxy industry has employed many types of curative blends in an attempt to maximize the desired application properties, but in most cases at the expense of other properties. Additives such as accelerators, tougheners, reactive diluents and non-reactive diluents are employed to maximize a desired property but again to the deterioration of other properties. A number of good references are available on this subject including: Lee and Neville's, “Handbook of Epoxy Resins,” cited above, and W. R. Ashcroft, “Curing Agents for Epoxy Resins,” in B. Ellis (ed.). “Chemistry and Technology of Epoxy Resins,” Blackie Academic and Professional, London (1993), pp. 37-73.
Others in the epoxy industry have developed novel amines in attempting to optimize curative properties. For example, Japanese Patent 2963739 (1999) describes the use of substituted-N-phenyl-1,3-propanediamines as liquid epoxy curatives which do not B-stage during cure and thus yield a fully cured epoxy resin. The substituted-N-phenyl-1,3-propanediamines described therein are represented by the following chemical formula:
where R is hydrogen, lower alkyl group, lower alkoxyl group or halogen. Although the method of synthesis of these curatives is not disclosed, other references teach methods for synthesizing aromatic amines.
For example, European Patent 0 067 593 (1982) describes the cyanoethylation of para, meta, and ortho phenylenediamine to generate 3,3′-(p,m or o-phenylenedi-imino)-dipropanenitrile:
EP 0 067 593 teaches the use of water as the solvent and concentrated hydrochloric acid as the catalyst to obtain the dicyanoethylated product.
Elderfield et al., 68 J. Amer. Chem. Soc. 1262 (1949), describes the synthesis of &bgr;-p-anisidinopropionitrile by boiling p-anisidine and acrylonitrile in acetic acid.
Cookson et al., “The Cyanoethylation of Amines and Arsines,” J. Chem. Soc. 1949, pp. 67-72, describes the cyanoethylation of aniline by heating to 150° C. a mixture of aniline and acrylonitrile in the presence of excess acetic acid in an autoclave to generate 2-cyanoethylaniline and bis-2-cyanoethylaniline. The reference further describes the reaction of diphenylamine and acrylonitrile in an excess of acetic acid using a catalytic amount of fine copper powder to generate diphenyl-2-cyanoethylamine.
Braunholtz et al., “The Preparation of Bis(2-cyanoethyl) Derivatives of Aromatic Primary Amines, and Their Conversion into 1:6-Diketojulolidines,” J. Chem. Soc., 1952, pp. 3046-3051, describes the cyanoethylation of aniline, m-toluidine, p-toluidine, p-anisidine and p-chloroaniline in an excess of acetic acid.
Braunholtz et al., “The Preparation of Bis(2-cyanoethyl) Derivatives of Aromatic Primary Amines, and Their Conversion into 1:6-Diketojulolidines. Part II,” J. Chem. Soc., 1953, pp. 1817-1824, describes the cyanoethylation of several different aromatic primary monoamines in an excess of acetic acid using various metal catalysts to selectively generate mono and di-cyanoethylated derivatives.
All references cited herein are incorporated herein by reference in their entireties.
BRIEF SUMMARY OF THE INVENTION
The invention provides cyanoethylated toluenediamines, processes for synthesizing them, compositions containing them and methods for using them to cure epoxy resins. In preferred embodiments, the cyanoethylated toluenediamines are represented by the following formula:
where the nitrogen atoms are ortho or meta to each other on the aromatic ring.
With regard to the present invention and throughout the specification and claims the terms “cyanoethyl toluenediamine(s)”, “cyanoethylated toluenediamine(s)”, “N-(cyanoethyl) toluenediamine(s)” and “N-(cyanoethylated) toluenediamine(s)” are used interchangeably.
DETAILED DESCRIPTION OF THE INVENTION
The most preferred cyanoethylated toluenediamines of the invention are suitable for use as epoxy resin curing agents. Cyanoethylated toluenediamines where the nitrogen atoms are ortho or meta to each other on the aromatic ring have been found to be particularly suitable for this purpose. Thus, the most preferred cyanoethylated toluenediamines of the invention are cyanoethylated products of ortho-toluenediamine represented by the following Formulas I-IV:
and cyanoethylated products of meta-toluenediamine represented by the following Formulas V-VII:
Formulas I-IV above are the cyanoethylated products of ortho-toluenediamine (OTD). Formulas I-II are based on 2,3-toluenediamine (TDA) and Formulas III-IV are based on 3,4-TDA. A commercial isomer mix of OTD is typically 60/40 2,3-TDA/3,4-TDA. Using commercial grade OTD therefore leads to cyanoethylated isomer mixtures.
Formulas V-VII above are the cyanoethylated products of meta-toluenediamine (MTD). Formula V is based on 2,6-TDA and Formulas VI and VII are based on 2,4-TDA.
Cyanoethylated products of OTD are prepared by reacting OTD with acrylonitrile (ACN) at elevated temperature in the presence of an acid and a protic solvent (e.g., water) for a period of time adequate for reaching the desired extent of conversion to the cyanoethylated product. Cyanoethylated products of MTD are prepared by reacting MTD with ACN at elevated temperature in the presence of an acid and a protic solvent (e.g., water) for a period of time adequate for reaching the desired extent of conversion to the cyanoethylated product. The following equation illustrates a preferred cyanoethylation reaction of the invention.
In the preparation of cyanoethylated OTD, either the pure compounds 2,3-TDA or 3,4-TDA, or isomer mixtures, such as 60/40 2,3-TDA/3,4-TDA, can be reacted with ACN. In fact, any blend or mixture of the TDA isomers may be used. The preferred reactant mixture comprises commercial grade OTD.
In the preparation of cyanoethylated MTD, either the pure compounds 2,4-TDA, 2,6-TDA, or isomer mixtures such as 80/20 2,4-TDA/2,6-TDA can be reacted with ACN. Any blend or mixture of the TDA isomers can be used. The preferred reactant mixture comprises commercial grade MTD.
The molar ratio of reactants, moles of OTD and/or MTD to moles of ACN, can vary from about 10:1 to about 1:10. The molar ratio used will affect the rate of reaction and the product distribution, but as the final product is purified, the final product quality is unaffected. To maximize yield and efficiency, the desired molar ratio is from 0.95:1.0 to about 1.0:2.0 with the optimum being about 1.0:1.2.
The cyanoethylation reaction is conducted using at least one acid catalyst. The acid catalyst can be any mineral, carboxylic, super or supported acid, including but not limited to hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, propionic acid, para-toluenesulfonic acid, triflic acid (trifluoromethanesulfonic acid) and Nafion® super acid catalyst from DuPont, which is a bead-form strongly acidic resin, i.e., a copolymer of tetrafluoroethylene and perfluoro-3,6-dioxa-4-methyl-7-octenesulfonyl fluoride, converted
Cush Tammy Lynn
Starner William Edward
Air Products and Chemicals Inc.
Leach Michael
Sellers Robert
LandOfFree
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