US2892817A - Copolyamides from alpha-amino-acids and process for producing same - Google Patents

Description

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United States Patent COPOLYAMIDES FROM ALPHA-AMINO-ACIDS AND PROCESS FOR PRODUCING SAME No Drawing. Application March 28, 1955 Serial No. 497,463

. 6 cla ms. 01. 260-78) This invention relates to a new process for producing copolyamides. More particularly the invention is concerned with a new process for producing copolyamides from alpha-aminoacids and epsilon-caprolactam.

Heretofore, alpha-amino acid copolyamides having good solubility properties have been prepared by copolymerizing the N-carboxyanhydrides or other derivatives, such as esters, and the like, of the alpha-primary-aminocarboxylic acids containing at least one hydrogen on the alpha-carbon. However, these alpha-amino acid polyamides have not been completely satisfactory for the manufacture offibers and filaments since they generally exhibit poor response to aqueous processing treatments and are highly resistant to the most commonly used dyes.

Many of the alpha-amino acid copolyamides produced heretofore are deficient in water sensitivity and dyeability, i.e relative ease of water absorption and power of retention of dyestuffs, which detracts from their commercial utility. For maximum commercial utility, it is imperative that a film-or fiber-forming material be well and easily dyed with a variety of dyestuffs. Similarly, for conversion of the fibers or filaments to fabrics, involving as it does sizing, weaving, knitting, etc., water sensitivity is necessary, if the material is to be handled on existing installed equipment.

In the past, in making alpha-amino acid copolyamides, it has been generally thought in the art to be infeasible to incorporate alpha-amino acids per se in in high polymers. Accordingly, all prior art processes make use of some-derivative of the alpha-amino acid, such as the N-carbonanhydride. Heretofore, caprolactam has been polymerized in the presence of epsilon-aminocaproic acid. However, polycaprolactam was the product obtained and no polymer modification occurred. Alpha-aminoacids cannot be polymerized by themselves since they do not directly dehydrate to polyamides but rather, have a tendency to dimerize and as a result, diketopiperazines are formed... Accordingly, it has heretofore not been considered feasible to copolymerize caprolactam and alphaaminoacids without employing a derivative of the alphaaminoacids. Therefore, there has been a desire to provide a process for manufacturing copolyamides which are capable of being formed into fibers, filaments, films, ribbons, bristles, and the like, directly from alpha-aminoacids without first having to manufacture a derivative thereof.

It is a primary object of the present invention to provide a new process for producing fiber-forming copolyamides from caprolactam and alpha-aminoacids without the necessity of employing a derivative of the alpha-amino Another object of the invention is to prepare copolyamides having improved dye-receptivity. Still another object of the present invention is to provide a new process for producing fiber-forming copolyamides which have increased moisture pickup and retention characteristics and which produce more flexible fibers and filaments than copolyamides produced heretofore. Other objects and advantages of the instant invention will in 2,892,817 Patented June 30, 1959 part appear and will in part be apparent from the description thereof hereinafter.

In accordance with this invention is has unexpectedly been found that polymers or copolyamides can be made from epsilon caprolactam and alpha-aminoacids without employing a derivative of the latter by using a large excess of the caprolactam and employing a reaction temperature within certain defined limits.

The reaction mixture of the instant invention should contain at least 70% by weight of the mixture of caprolactam. Unless a large excess of caprolactam is employed, one is not able to use the alpha-aminoacid per se. The temperature of the reaction is critical and should be In the range of to 250 C. Alpha-aminoacids are comparatively unstable to heat and consequently, they should not be heated at elevated temperatures, except for very short periods of time. During the polymerization reaction, the acids should not be heated above the necessary reaction temperature. While the reaction temperature may vary from 100 C. to 250 C., it is preferred to operate in the range of C. to 225 C., particularly when producing fiber-forming copolyamides.

The copolyamides of the present invention can be conveniently prepared by polymerizing the epsilon-caprolactam and alpha-aminoacid in an inert atmosphere, such as nitrogen, and the like, with or without the aid of a polymerization catalyst. The alpha-aminoacids are only slightly soluble in the epsilon-caprolactam but solution occurs as the reaction proceeds. Complete solution usually occurs in A2 to 5 hours and thereafter the heating is continued in order to form the high molecular weight polymers which are desirable for the formation of fibers and filaments. Generally, a total reaction time of 3 to 6 hours is sufiicient. However, less than 3 hours or more than 6 hours may be employed, depending upon the final molecular weight desired.

The alpha-aminoacids contemplated in the practice of the present invention are those having the general formula:

wherein R is hydrogen or an alkyl group containing from 1 to 5 carbon atoms. Examples of alpha-aminoacids having the above formula are glycine, leucine, alanine, norleucine, alpha-aminoisovaleric acid, alpha-aminoalpha-ethyln-butyric acid, alpha-amino-alpha-isobutylpropionic acid, alpha-amino-alpha-isopropylpropionic acid, etc.

The preparation of the copolyamides of the instant invention in reality takes place in two stages although it is not necessary to isolate any product but the finally desired copolyamide. In the so-called first step or stage the epsilon-caprolactam reacts with the alpha-aminoacid to form a polyamide having an average molecular weight equal to at least the sum of the molecular weights of the acid and caprolactam. This is evidenced by the fact that the alpha-aminoacid, insoluble in caprolactam, gradually goes into solution as the reaction progresses. Thereafter, in the so-called second stage the heating is continued causing the conversion of the non-fiber-forming copolyamide of the first stage into the fiber-forming high molecular weight copolyamide. This is evidenced by the increase in viscosity of the melt in the reaction vessel. The heating is continued, at the temperatures mentioned hereinbefore, until the polymerization reaction has proceeded to the point to give the desired molecular weight in the product, which is determinable by standard viscosity measurements.

While the reaction involved in the present new process proceeds satisfactorily at atmospheric pressure, sub-atmospheric or super-atmospheric pressures may be employed, if desired. In many instances, it is desirable to subject the hot reaction mass to reduced pressure during at least a portion, usually the later stages, of the polymerization. By so doing, water and any other low molecular weight volatile by-products of the reaction which may be present, as well as unreacted monomers, such as the excess caprolactam, may be largely removed. Pressures in the range of 10 to 100 mm. of mercury are satisfactory for this purpose. In addition, a stream of inert gas may be passed through the reaction mass while it is under reduced pressure in order to facilitate the removal of volatile materials.

As mentioned above, the process of the present invention is preferably conducted in an inert atmosphere since when operating at high temperatures, and particularly about 200 C. or more, the polymerizing mixture is susceptible to oxidation by air, or even traces of oxygen. Oxidation causes darkening and degradation of the polymer and accordingly, it is important to exclude oxygen from the reaction vessel when any color in the final product will be detrimental, such as in the preparation of fiber-forming copolyamides. Where color is not a factor, nitrogen or other inert gas need not be employed. The exclusion of oxygen as accomplished by sweeping out the reaction vessel with nitrogen or other inert gas, prior to the initiation of the reaction, and maintaining the oxygen-free atmosphere by passing a continuous stream of the inert gas through the reaction chamber during the polymerization. ert gas assists in the removal of any undesirable volatile by-product which may be present. Althought any inert gas, such as helium and argon, may be employed, it is preferred to use nitrogen for economical reasons. However, ordinary commercial nitrogen is not satisfactory because it contains traces of oxygen which interfere with normal operation. The nitrogen should be purified to a maximum content of 0.005% oxygen.

Upon completion of the polymerization process, the copolyamide formed may be drawn into filaments immediately or it may be cooled and ground to any convenient size for storage. The molten polymer may be cooled by quenching in water and the resultant product ground to the desired size and dried.

The copolyamides produced in accordance with the process of the present invention have recurring structural units represented by the formula:

wherein R is the same as defined above in connection with the general formula representing the alpha-aminoacids useful in the practice of the present invention, and x and y represent the average number of such groups in the polymer chain. Generally, the group x, derived from the caprolactam, will comprise from 70 to 99% by weight of the polymer molecule and the group y, derived from the alpha-aminoacid, will comprise from 1 to 30% by weight of the polymer molecule.

The copolyamides of this in ention are all capable of being spun into continuous filaments, from which staple fibers can be made, if desired. The spinning may be carried out in a number of ways. For example, the copolyamide may be dissolved in a suitable solvent therefor and the resultant solution extruded through a spinneret into a coagulating bath. Thereafter the coagulated filaments are washed, if desired or necessary, and continuously collected on a suitably revolving drum or spindle, or the like. Instead of using a coagulating bath, the extruded solution may be passed through a heated chamber where the solvent is removed by evaporation. In view of the properties of the copolyamides produced in accordance with the instant new process, it is possible to spin the molten copolyamides directly without the addition of any As pointed out above, the stream of insolvent of plasticizer. A mass of the molten polymer may be touched with a rod and upon drawing the rod away, a filament is formed. The filament may then be caught on a revolving drum or reel. In this manner a continuous filament may be drawn from the molten mass until the latter is exhausted. The cross-section of the filaments thus obtained can be regulated by controlling the temperature of the molten mass and the rate of reeling. The higher the temperature and the more rapid the rate of reeling, the finer will be the filament.

Continuous filaments may also be produced by extruding the molten polymer through a spinneret and continuously collecting the extruded filament on a rotating drum. The fineness of the filaments may be controlled by controlling the temperature of the molten polymer, the amount of pressure applied during spinning, the size of the orifice in the spinneret and the rate of reeling.

Filaments produced from the copolyamides of this in vention have the ability to accept a very high degree of permanent orientation under stress. By the application of moderate stress at ordinary temperatures these filaments can be instantly elongated or cold-drawn. The filaments can be cold-drawn as much as several times their original lengths. These cold-drawing operations may be carried out on filaments, which have been allowed to cool fully and solidify, or the cold-drawing may follow the formation of the filaments directly as one part of a continuous process.

In the cold-drawing operation any suitable apparatus and process may be used. For example, the filaments may be wound from one roller to another with the second roller rotating at a higher speed than the first roller. For example, the second roller may be rotated at a speed up to about four or five times that of the first roller. If desired, cold-drawing may be effected by employing a snubbing pin. This process of cold-drawing differs from the stretch-spinning known to the artificial fiber art in that it may be carried out very rapidly and completely in the total absence of any solvent or plasticizer.

The term cold-drawing, as employed herein, includes, in addition to drawing filaments at temperatures as low as 0 C., warming the filaments to facilitate stretching, for example, by passing the filaments through warm or hot water or steam before and/or during the cold-drawing operation, or drawing the filaments at any temperature below the melting point thereof.

For a more detailed description of the present invention, reference is had to the following specific examples which are merely intended to be illustrative and not limitative. In the examples all parts and percent are by weight unless otherwise indicated.

Example I A mixture containing 2 parts of l-leucine and 8 parts of epsilon-caprolactam was placed in a reaction vessel. The reaction vessel was flushed with oxygen-free nitrogen and continuing the nitrogen introduction, the mixture was heated for one hour at 222 C. A slightly viscous and yellow solution was obtained. The heating was continued at 222 C. for another three hours with nitrogen introduction. A melt was obtained which had a melt viscosity of approximately 200 poises. The melt crys tallized on cooling. The copolyamide or polymer obtained had a softening point of C. and a melting point of C. The polymer contained 12.19% nitrogen or 6.19% l-leucine. Filaments were obtained upon drawing a glass rod from the polymer melt.

Example 11 A mixture containing 0.5 part of glycine and 4.5 parts of epsilon-caprolactam was placed in a reaction vessel and the vessel flushed with oxygen-free nitrogen. With continued nitrogen introduction the mixture was heated to 177 C. As the heating continued, gradual solution of the glycine occurred with solution being complete after one hour. The heating was continued at 177 C. for another five hours at the end of which time the melt obtained had a melt viscosity of 500 poises. Elastic filaments were obtained from the melt upon drawing a glass rod therefrom. The molten polymer or melt crystallized upon cooling and the crystalline polymer had a melting point of 126 C. Upon analysis, it was found that the polymer contained 12.96% nitrogen or 9.33% glycine.

Example III A mixture containing one part of alpha-aminoisobutyric acid and 9 parts of epsilon-caprolactam was heated at 222 C. for 4 hours, during which time complete solution of the insoluble acid occurred. Upon continued heating with nitrogen introduction, the melt viscosity of the reaction mass increased to about 500 poises. A light-colored polymer was obtained which had a crystalline melting point of 202204 C. Filaments were formed from the polymer.

Example IV A mixture containing one part of dl-alpha-alanine and 9 parts of epsilon-caprolactam was heated at 222 C. with nitrogen introduction. The dl-alpha-alanine dissolved in one hour. The mixture was heated at 222 C. for an additional five hours whereupon a polymer was obtained having a melt viscosity of 200 poises. Upon cooling the melt, a light yellow crystalline polymer was obtained which had a melting point of 180 C. Soft flexible filaments were obtained from the melt upon drawing a glass rod therefrom.

The products produced in accordance with the instant process can be used in the preparation of fibers and filaments for use in the textile field, for example, in the preparation of knitted, woven, and pile fabrics. In addition, the fibers and filaments so produced have improved dyeing characteristics, as well as increased moisture pickup capacity and moisture retention capacity. This latter property is particularly desirable in Wearing apparel wherein the general wearing comfort of the garment is inherent in moisture pick-up capacity. In addition, filaments and fibers produced from the copolyamides of the instant invention have increased susceptibility to wooltype dyestufis which is obviously advantageous when they are blended with wool fibers. Further, the fibers and filaments have improved stress-strain characteristics and thereby are more flexible.

Copolyamides produced by the process of the present invention are useful in the film-forming art. Solutions thereof may be extruded through an elongated slot into a coagulating bath containing a non-solvent for the copolyamidc. By variation in the size and shape of the orifices through which the polymer is extruded, rods, sheets, ribbons, and other shaped articles can be prepared.

The polymers or copolyamides produced in accordance with the present invention may be molded and otherwise shaped under heat and/or pressure. For example, the polymer may be rolled into thin sheets useful as wrapping material. Irregular shapes may be cast or pressed in suitable molds. The copolyamides obtained by the practice of this invention are also useful in the production of coating compositions, lacquers, and the like. Numerous other advantages of the instant invention will be apparent to those skilled in the art.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A process for preparing linear copolyamides from which filaments having the ability to accept a high degree of permanent orientation upon being cold drawn can be formed which comprises the steps of forming a mixture of epsilon-caprolactam and an alpha-aminoacid having the formula:

wherein R is selected from the group consisting of hydrogen and alkyl groups containing from 1 to 5 carbon atoms, said caprolactam comprising from to 99% by weight of the mixture, heating said mixture in the presence of an inert gas to a temperature in the range of 100 to 250 C. to react the epsilon-caprolactam with the alpha-aminoacid and thus to form a non-fiber-forming copolyamide having an average molecular weight equal to at least the sum of the molecular weights of the caprolactam and the acid, and thereafter continuing the heating within said temperature range and in the presence of the inert gas until the non-fiber-forming copolyamide is converted into a fiber-forming high molecular weight copolyamide.

2. The process as defined in claim 1 wherein the alphaamino-acid is l-leuoine.

3. The process as defined in claim 1 wherein the alpha-amino-acid is glycine.

4. The process as defined in claim 1 wherein the alpha-am-ino-acid is alanine.

5. The process as defined in claim 1 wherein the alpha-amino-acid is alpha-aminoisobutyric acid.

6. A high molecular weight linear copolyamide from which filaments having the ability to accept a high degree of permanent orientation upon being cold drawn can be formed and comprised of recurring structural units of the formula:

wherein R is selected from the group consisting of hydrogen and alkyl groups containing from 1 to 5 carbon atoms, and wherein x is 70 to 99% by weight of the polymer molecule, and y is 1 to 30% by weight of the polymer molecule.

References Cited in the file of this patent UNITED STATES PATENTS 2,293,388 Hanford Aug. 18, 1942 2,356,516 Ha'gedorn Aug. 22, 1944 2,636,877 Coleman Apr. 28, 1953 OTHER REFERENCES Serial No. 323,512, Hagedom (A.P.C.), published April 20, 1943.

Claims (1)

1. A PROCES FOR PREPARING LINEAR COPOLYAMIDES FROM WHICH FILAMENTS HAVING THE ABILITY TO ACCEPT A HIGH DEGREE OF PERMANENT ORIENTATION UPON BEING COLD DRAWN CAN BE FORMED WHICH COMPRISES THE STEPS OF FORMING A MIXTURE OF EPSILON-CAPROLACTAM AND AN ALPHA-AMINOACID HAVING THE FORMULA