DICARBOXYLIC ACID AZOMETHINES AND HIGH GLASS TRANSITION TEMPERATURE POLYESTER PRODUCTS PRODUCTED THEREFROM

Abstract: This invention is directed to acid terminated azomethine oligomers formed by reacting aromatic dialdehydes of aromatic diketones with amino-carboxylic acid compounds. These oligomers may be reacted with epoxy resins to produce polymer material having high glass transition temperatures.

Description: This invention relates to acid terminated azomethine oligomes which may be reacted with epoxy resins to produce polymeric materials with high glass transition temperatures. Azomethines are compounds containing a ( C=N-) repeating unit in their backbone. More particularly, this invention is directed to carboxyterminated, aromatic azomethine oligomes formed by reacting aromatic dialdehydes or aromatic diketones with particular amino-carboxylic acid compounds. Both low and high molecular weight azomethine polymers (commonly termed Schiff-base polymers) have been described in literature and various patents. Generally, these azomethine polymers are made by reacting aromatic dialdehydes with aromatic diamines. The preparation of low molecular weight polyazomethines by solution polymerization has been described by Delman et al in Macromol Sci. Chem. A1. (1) 147-148 (67). U.S. Patents 3,516,970; 3,516,971 and 3,526,611 described the synthesis by melt polymerization of high molecular weight Schiff-base polymers. The high molecular weight azomethine polymers are taught as being highly insulating and thermally stable, i.e., capable of withstanding high temperatures for sustained periods of time without undergoing significant degradation or phase change. They have thus been suggested for aerospace applications requiring polymers having high temperature stability. While the carboxy terminated azomethine oligomers of this invention are of relatively low molecular weight, we have found that they have good thermal stability and high melting points. It is known in the art that carboxy functional materials may be reacted with epoxy resins to form thermoplastic and thermoset materials. We have now found that the carboxy terminated aromatic azomethine oligomers of this invention, when reacted with epoxy resins, produce polyester materials with high glass transition temperatures. Such high glass transition temperature polyesters would be useful in applications requiring materials having good thermal stability and relatively high melting points. According to the present invention there is provided a carboxy terminated aromatic azomethine oligomer having the formula: HOOC-(R') n -Y-N=(R)C-X-C(R)=N-Y-(R') n -COOH. wherein X is a phenylene group, each R is H or an alkyl group having 1-5 carbon atoms, and the -C(R)N- groups are linked through X at the 1.3 or 1.4 positions, Y is a pyridine group, n is 0 or 1, R' is an amide group, ester group or an ether group, and the azomethine group and the HOOC-(R') n - group are linked through Y at the meta or para position. This invention is also directed to the polyester products produced by reacting epoxy resins and the acid terminated aromatic azomethine oligomers described above. Advantageously, the high melting oligomers of this invention, when reacted with epoxy resins, form high glass transition temperatures polyesters which are suitable for use as, for example high temperature adhesives, composites, and potting compounds. The azomethines, containing two carboxyl groups, are formed by reacting aromatic diketones or aromatic dialdehydes with amine compounds having a carboxyl group in about a 1:2 molar ratio. Each of the reactants for forming these acid terminated azomethines will be discussed in greater detail. As is well known in the art, if R is an alkyl group, this compound is an aromatic diketone or, if R is hydrogen, this compound is an aromatic dialdehyde. Preferably, R of this compound is hydrogen, since the aldehyde group is more reactive with an amine group than is the ketone group. These azomethine oligomers can be reacted in accordance with the invention with epoxy resins to form thermoplastic and thermosetting polyesters. Oligomers formed from compounds wherein the CRO groups are linked through the phenyl group X at the 1.3 positions, as compared to the 1.4 positions, yield polyesters having increased flexibility. On the other hand, oligomers formed from compounds wherein the CRO groups are at the 1.4 positions of X, as compared to the 1.3 positions, yield polyesters having higher glass transition temperatures. It is preferred, in order to form high glass transition temperature polyesters, to thus employ the oligomers formed from the 1.4 position compounds. Exemplary of the aromatic diketones and aromatic dialdehydes which may be employed to form the oligomers of this invention are terephthaldicarboxaldehyde, isophthaladehyde, and diacetylbenzene with terephthaldicarboxaldehyde being most preferred. Mixtures of suitable aromatic diketones and/or aromatic dialdehydes, may also be used in forming the oligomer of this invention. The amine compounds to form the oligomers of this invention contain a terminal carboxyl group and are selected from compounds having the formula: H₂N-Y-(R') n -COOH, wherein Y is pyridine group, n is 0 or 1. R' is a group as specified below, and the H₂N group and the COOH group are linked through Y at the 1.3 or 1.4 positions. The hydrogens of the pyridine group may be substituted by methyl, methoxy, and/or chloro groups. Preferably, at most, only one or two of the hydrogens of the pyridine group are substituted. When n is 0, the amine and carboxyl groups are linked directly to the pyridine group. When n is 1, the amine group is linked directly to the pyridine group and the carboxyl group is linked to the pyridine group through a group R'. This group is defined as an alkylene group preferably having 1-5 carbon atoms such as methylene, propylene and butylene, an amide group, an ester group or an ether group. The use of the group R' in the amine compound used to form the azomethine oligomer results in increased flexibility in the polyesters formed by reacting these oligomers with epoxy resins. Linking the amine and carboxyl groups through Y at the 1,3 positions, as compared to the 1,4 positions, results in azomethine oligomers which form polyesters having increased flexibility. On the other hand, linking the amine group and the carboxyl group through Y at the 1,4 positions, results in polyesters having higher glass transition temperature. It is preferred, in order to form high glass transition temperature polyesters, to thus employ the oligomers formed from 1,4 position compounds. As would be apparent to those skilled in the art, mixtures of the amino-carboxylic acid compounds may also be employed. In forming the oligomers of this invention, the aromatic and the amine compounds are reacted in about a 1:2 molar ratio under conditions wherein the CRO groups of aromatic compound and the amine group of amine compound react. By reacting these compounds in about a 1:2 molar ratio, all of the CRO groups will be reacted. While it is not generally necessary, the amine compound may be employed in the reaction mixture in a slight excess of this ratio, e.g., in about 1:2-2.2 molar ratio, so as to insure that these compounds are reacted in about 1:2 molar ratio and thus all of the CRO groups of aromatic compound will be reacted. Generally in forming the oligomer, the compounds are dissolved separately in suitable solvents and then the solutions are mixed and heated to an elevated temperature. generally between about 90°-200°C, more preferably between about 170°-200°C, whereafter the compounds react to form the oligomer. This azomethine product generally separates out in a crystalline form which can be easily recovered from the solvent. Exemplary of solvents which may be employed for making the oligomer in this manner include ethanol, acetone, dimethyl formamide and dimethyl acetamide. Catalysts, while not generally being required to catalyze this reaction, particularly when employing dialdehydes as aromatic compound may be employed. Exemplary of such catalysts are p-toluene sulfonic acid, phosphoric acid and sulfuric acid. The oligomers of this invention are particularly useful in making high glass transition temperature polyester products such as adhesives, composites, and potting compounds, by reacting the oligomers with epoxy resins. If the oligomers of this invention are reacted with diepoxide materials, high glass transition temperature thermoplastic polyesters are formed. When reacted with epoxies having more than two epoxide groups per molecule, the dicarboxylic acid oligomers of this invention produce high glass transition temperature thermosets. Epoxy resins which may be reacted with the dicarboxylic acid azomethine oligomers of this invention include, but are not limited to, those having, on average, two or more epoxide groups per molecule. A large number of such polyepoxide resins are known to those skilled in the art. Exemplary of such polyepoxide resins are those derived from a dihydric phenol or dihydric alcohol and an epihalohydrin. Examples of epihalohydrins are epichlorohydrin, epibromohydrin and epiiodohydrin with epichlorohydrin being preferred. Dihydric phenols and dihydric alcohols are exemplified by resorcinol, hydroquinone, Bisphenol A, p,p'-dihydroxy benzol phenone, p,p'-dihydroxy phenyl, p,p'-dihydroxy diphenyl ethane, bis-(2-hydroxy naphtha) methane, 1,5-dihydroxy naphthaline, ethylene glycol, propylene glycol, 1,4-butane diol, hydrogenated Bisphenol A, 1,4-cyclohexane diol, 1,3-cyclopentane diol, cyclohexane dimethanol, and the like. These polyepoxide resins, as is well known in the art, are made in the desired molecular weights by reacting the epihalohydrin and the diols in various ratios, or by reacting a dihydric phenol with a lower molecular weight polyepoxide resin. Other polyepoxide resins are the glycidyl polyethers of Bisphenol A. Examples of commercially available epoxy resins of the type described above and useful in this invention to form, e.g., composites, include Epon 828, available from and a trademark of Shell Chemical Company (Houston, Texas). Mixtures of the epoxy resins may also be employed as the epoxy resin reacted with the dicarboxyl azomethine oligomers to form the polyesters of this invention. While some polyepoxide resins have been discussed as exemplary for use in forming the polyester product of this invention, their disclosure is not to be considered limiting to the epoxy resin. Other epoxides will be apparent to those skilled in the art. Generally, in forming the polyester resins of this invention, the epoxy resin and the oligomer of this invention are reacted in about a 1-5:1 ratio of epoxide to acid groups, more preferably in about a 1-2:1 ratio of epoxide to acid group. However, this ratio is not meant to be limiting to this invention. The optimal ratio would depend on the application and type of composition being formed and selection of such a ratio would be within the skill of one in the art. The epoxy resin and azomethine may be reacted by any number of conventional techniques for such reactions, which optimal technique would be dependant on the particular reactants and product formed. For example, the azomethine and epoxy resin may be simply mixed together and heated to react the materials and form the polyester. This invention will be further understood by referring to the following example. The diacids can be formed by the following procedure. Terephthaldicarboxaldehyde (13.4g) is dissolved in 100 ml ethanol and 15 ml dimethylformamide. In a separate flask 27.6g 6-amino nicotinic acid is dissolved in 100 ml ethanol and 15 ml dimethylformamide. Both the above solutions are mixed at 50°C; yellow color appears immediately and within a few minutes the product separates at light yellow crystals. Two grams of the above acid are mixed with 4g of bisphenol-A diglycidyl either and the mixture is heated to obtain a homogeneous solution. The solution is placed in an aluminum pan and is heated at 170°C for one hour. The cured sample has softening point of 142°C.

Claims: A carboxy terminated aromatic azomethine oligomer having the formula: HOOC-(R') n -Y-N=(R)C-X-C(R)=N-Y-(R') n -COOH. wherein X is a phenylene group, each R is H or an alkyl group having 1-5 carbon atoms, and the -C(R)N- groups are linked through X at the 1.3 or 1.4 positions, Y is a pyridine group, n is O or 1, R' is an alkylene group amide group, ester group or an ether group, and the azomethine group and the HOOC-(R') n - group are linked through Y at the meta or para position. An azomethine oligomer according to Claim 1, wherein said -C(R)N- groups are linked through X at the 1,4 position. An azomethine oligomer according to Claim 1 or 2, wherein R' is selected from the group consisting of C₁-C₅ alkylene groups. An azomethine oligomer according to any one of claims 1 to 3, wherein at most two hydrogens of said pyridine group are substituted by methyl, methoxy or chloro. An azomethine oligomer according to any one of the preceding claims, wherein the azomethine group and the HOOC -(R') n - group are linked through Y at the para positions. A Polyester products having high glass temperatures and being formed by reacting: I. epoxy resin, and II. carboxy terminated aromatic azomethine oligomers as claimed in any one of the preceding claims. Polyester products according to Claim 6, wherein epoxy resin is selected from diepoxide resins. Polyester products according to Claim 6, wherein said epoxy resin is selected from epoxy resins having, on average, at least three epoxide groups per molecule.

Inventors: CHATTHA, MOHINDER S.
Applicants: FORD FRANCE SOCIETE ANONYME, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1986
Main classification: C07C251
IPC codes: C08G59, C07D213