PROCESS FOR THE PREPARATION OF POLAYMIDES BY AMIDE-ESTER INTERCHANGE

Abstract: Melt-processable polyamides are prepared smoothly and rapidly by interchange of diesters of dicarboxylic acids with diamines in a solventless melt phase process.

Description: Process for the Preparation of Polyamides by Amide-Ester Interchange BACKGROUND OF TF.E INVENTION Polyamides, useful as molding resins and as film and fiber formers, are maQe commercialiy by react ing a diacid or diacid precursor with a diamine. In one process a diacid is initially reacted with a diamine in an aqueous media to form a solid polyammonium salt which precipitates from the reaction mixture. The solid is then heated successively in an autoclave reactor under pressure to control explosive initial dehydration and subsequently under reduced pressure to effect conversion of the polyammonium salt to a polyamide. This requires expensive equipment and very careful process control in order to optimize heat and mass transfer. The high me - solid salt which intially can't b sirrec undergoes almost explosive dehydration as the reactor temperature is increase. The solid salt is converted to a mobile liquid which increases in viscosity as additional water is removed as high pressure steam. An alternate approach to the use of autoclaves consists o dispersing the polyammonium salts in highly polar solvents and e rectinc dehyaration and solubilization by elevating the temperature of the solution. This process eliists the need for autoclaves jut invokes the use or very special high boiling solvents. The product must ultimately be recovered from solution as a solid. The expensive, high boiling, polar and frequently toxic solvents must be completely removed from the product and be very efficiently recycled to control manufacturing costs. In still another version, the acids may be first converted to diacid chloride derivatives which can be reacted in solution or interfacially with diamines at relatively low temperatures to yield polyamides. Very corrosive hydrogen chloride is produced as a b roduct of this reaction. The by-product acid must be completely removed from the solution or dispersion of polymer and the poìxmGr must be separated from the reaction solvent. Again the solvent must be efficiently recycled. The process of the present invention on the other hand is smooth and rapid, and it is widely applicable, being limited, apparently, only by the ultimate nature of the final product, which must be melt processable, i.e., it must have a melting point below the thermal decomposition temperature. In practice, this excludes only a relatively few polyamides, namely, high melting materials such as polyamides containing units derived from p-phenylene iamine, or m-phenylene diamine and aromatic diacids, such as isophthalic and teraphthalic acids, or polyamides derived from the 4,4'dicarboxylic acid of diphenyl, and the like. In general, subject to the foregoing recuirement that the ultimate product be melt processakle, the dibasic acid diester should be a diaryl ester o a dicarboxylic acid con tailing 5 carbon atc.s and above, i.e., giutaric, adipic, sebacic acid etc. The di-primary amines should include those of 4 carbon atoms and above, i.e., tetramethylene, pentamethylene, hexamethylene diamine, etc. The novel products or- the process are also features of the invention, many of them being transparent, tough, ant soivent-resistant. SUMMARY OF THE INVENTION According to the present invention, there is provided a process for the preparation of a melt processable polyamide by ester-amide interchange, said process comprising heating in the substantial absence of a solvent a mixture of at least one diaryl ester of a dicarboxylic acid having at least 6 carbon atoms and at least one diprimary amine having at least A carbon atoms at 2 temper- ature above the melting point o said polyamide under enolic compound removing conditions until formation of said polyamide is substantially complete. Polyamiaes made by the process are unusually tough and generally <RTI ID=2.34> transparent, and they do not dissolve in conventional solvents, giving them unusual and beneficial properties, e.g., as wrappings for food. DETAILED DESCRIPTION OF THE INVENTION Illustratively, useful diaryl esters of dicarboxylic acids suitable for use in the process of the present invention are diphenolic esters derived from phenolic compounds, e.g., a monohydric phenol, including phenol itself, and alkyl-or halo-substituted phenols, such as o-,m-, and p- cresols, and o- and p-chlorophenol, and the like, and a dicarboxylic acid, e.g., one having at least 5 carbon atoms, such as the aliphatic diacids like glutaric acid, adipic-acid, azeleic acid, 1,12-dodecane dicarboxylic acid, and others, of up to about 30 inclusive carbon atoms and the aromatic diacids, such as phthalic, isophthalic and terephthalic acid. The acids must be higher boiling than phenol to facilite synthesis. General not suitable, because they do not produce melt-processaDle polyamides, are combinations of diphenclic esters cf aromatic dicarboxylic acids with aromatic diamines. A preferred family of diesters are diphenolic esters of terephthalic acid, isophthalic acid, and mixtures thereof. As examples or- di-primary amines, particularly useful in the process are those of the general formula H2N-R-NH2 wherein R is bivalent straight chain, branched or cyclic alkylene or arylene. of such grcups optionally interrupted with carbony 1, amino, sulfur-containing groups, and the like, with a total carbon content of the order of 4 to 3d carbon atoms. Illustrative examples are 1,4tetramethylene diamine, 1,6-hexamethylene diamine, 1,12diaminododecane, bis(4-2minocyclohexyl)methane, mixtures thereof, and the like. Generally unsuitable are di-primary aromatic diamnes, such as m-phenylene diamine and p-phenylene diamine, which have a general tendency to produce polyamides which are so high melting as to be notmelt-processable, especially when reacted with isophthalates and terephthalates. In general, the process is carried out by charging the mixture intro a reaction vessel and heating the reactants until they are melted. The ester-amide interchange reaction occurs smoothly and rapidly at temperatures in the range of from about 135 C., to about 3500C., and pressures from atmospheric down to about 15 torr. The reactor should permit removal of the byproduct phenolic compound as it is produced. Temperatures in the above mentioned range readily permit removal by distillation of the usual byproducts, e.g., phenol, o-cresol, p-chlorophenol, and the like. An alternate polymerization and polymer recovery process consists of heating the mixture until the appropriate interchange has occurred without removal of the pheolic by-products. Polymer recovery may be effected b means of anti-solvent addition to precipitate the polymer. The polymers are recovered in conventional ways and they may be molded in any desired shape and are useful as structural and engineering materials to replace metal. tarts, in electrical appliances, as lenses, safety shields, instrument windows and in food wrapping. The are used in many other waysknown for such polymers. DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is further described in the examples which follow. These examples are illustrative embodiments of the invention, and are not to be constured in limitation thereof. Polymeric products were thermally characterized by glass transition temperature (Tg) and crystal melting point (tun) as determined with a Perkin-Elmer DSC-2 instrument at a scanning rate of 200C/mi. The relative degree of polymerization was estimated by determining intrinsic viscosities in G 40:60 tetrachloroethane:phenol mixture at 300C.and reported as deciliters/gram. EXAMPLE 1 A 500-ml 3-necked round bottomed glass flask was fitted with a glass paddle stirrer, a nitrogen blanket inlet and a reflux condenser with side take off arm. A mantle was used to supply heat. To the vessel was added 190.8 g. of diphenyl isophthalate and 73.8 g. of 1,6-hexamethylenediamine. The mixture was heated during 40 minutes from 190 C. to 2530C. at less than atmospheric pressure and a total of 84 grams of is- tillate (phenol) was collected. The transparent polymeric hexamethylene isophthalamide solidified in the reaction flask; it was amorphous, and it did not dis solve in chloroform. EX IPLE 2 The general procedure of Example 1 was repea- ted, using 119 c. of l,6-hexamethylenediamine and 310 g. of asphenyl isophthalate. This reaction was conducted in two stages. The first phase of the reaction was stopped at the pre-polymer stage. The product could be readily poured from the reaction flask. Its glass transition temperature (Tg) was 78 C. A portion of tis pre-polymer was further polymerized at 2850C. under a r-Zc Cr about 1mm. o rercury. "ere was thus obtains a high molecular weight polyamide, Tg., 1160C., and having an intrinsic viscosity, (I.V.), of 0.83 dl/g. EXAMPLE 3 The general procedure of Example 2 was repeated, substituting a 1:1 molar mixture of diphenyl terephthalate and diphenyl isophthalate for the diphenyl isophthalate. The high molecular weight product had a Tg of 1270C., and an IV of.1.34 dl/g. EXEMPLE 4 The general procedure of Example 2 was repeated, substituting 1,12-diaminododecane for the 1,6-hexamethylenediamine. The high molecular weight product had a Tg of 86 C., and an IV of 0.86 dl./g. EXAMPLE 5 The general procedure of Example 2 was repeated, substituting a 0.7:0.3 molar mixture of 1,6-hexamethylenediamine and bis(4-aminocyclohexyl)methane for the l,6-hexanemethylenediamine. The high molecular weight product had a Tg of 1550C., and an IV of 0.85 dulls. EXAMPLE 6 The reaction apparatus was the same as described in Example 1. The charge of raw materials was 74.6 grams of diphenyl adipate and 29.4 grams of 1,6hexamethylene diamine. The reaction mixture was heated to 1950C for a period of 40 minutes without the removal of any of the bn rocuc, phenol. A portion of the polymer solution was then poured into rapidly stirred methanol to effect precipitation or the polymer. The precipitation polymer was washed several times with additional methanol, filtered and dried. The polymer recovered in this manner was characterized by determining the crystal melting point to be 2500C.and the IV was 0.69 dl/g. The polyamide in the remaining reaction mixture was isolated by removal of phenol at elevated tem?er2ture under reduced pressure. This portion of the hexamethylene adi- pamide (6,6-nylon) polymer had a crystal melting point of 2500C and an IV of 0.78 dl/g. This example illustrates two different isolation procedures for the same polymerization process. EXAMPLE 7 A mixture of 16.0 g (0.054 moles) of diphenyl adipate and 5.0 g (0.057 moles) of 1,4-diaminobutane were placed in a side arm test tube equipped with a mechnical stirrer and a nitrogen blanket. The test tube was heated in an oil bath to 140"C.2n held there 45 minutes. The temperature was then raised to 180 C.and held there for 20 minutes. Finally the temperature was raised to 2950C.and the by-product phenol removed slowly under reduced pressure. The resulting crystalline polymer gave a Tm - 2890C. and an IV - 0.80 do/5. The foregoing detailed description will suggest many variations to those skilled in this art. For example, di-orthocresyl terephthalate and di-para-chlorophenyl terephthalate can be substituted for the diphenyl terephthalate. Diphenyl adipate can be substituted for diphenyl terephthalate. And tetramethylenediamine can be substituted for the l,6-hexamethylenediamine. All such variations are within the full scope of the appended claims.

Claims: CLAIMS: 1. A process for the preparation of a meltprocessable polyamide by ester-amide interchange, said process comprising heating in the substantial absence of a solvent a mixture of at least one diaryl ester of a dicarboxylic acid having at least 6 carbon atoms and at least one diamine having at least 4 carbon atoms, at a temperature above the melting point of said polyamide under phenolic compound removing conditions until formation of said polyamide is substantially complete. 2. A process according to Claim 1, wherein the tester of the dicarboxylic acid is selected from the group consisting of a diaryl terephthalate, a diaryl isophthalate and a mixture thereof. 3. A process according to Claim 2, wherein the diaryl terephthalate is diphenyl terephthalate. 4. A process according to Claim 2, wherein the diarvl isophthalate is diphenyl isophthalate. r. A process according to Claim 1, in which the diaryl ester is diphenyl adipate. 6. A process according to Clal: 1, where diamine is selected from the group consisting of 1,6-hexamethylenediamine, 1, 12-diaminododecane, bis (4-aminocyclo- hexyl) methane and mixtures cf any of the foregoing. 7. A process according to Claim 1, comprising heating a mixture of diphenyl adipate and 1,4-diaminobutane under the conditions described. 8. A polyamide prepared by the process of Claim 1. 9. A polyamide prepared by the process of Claim 2. 10. A polyamide prepared by the process of Claim 3. 11. A polyamide prepared by the process of Claim 4. 12. A polyamide prepared by the process of Claim 5. 13. A polyamide prepared by the process of Claim 6. 14. A polyamide prepared by the process of Claim 7.

Inventors: FOX, DANIEL WAYNE, SHAFER, SHELDON JAY
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1984
Main classification: C08G69
IPC codes: C08G69