US3483157A - Method of preventing rearrangement of blocked copolyesters - Google Patents

Description

Dec. 9, 1969 SMITH ETAL 3,483,157

METHOD OF PREVENTING REARRANGEMENT OF BLOCKED COPOLYES'IERS Original Filed July 2, 1962 5 sheets*sheet l PRECIPITANT RECORDER E II [i 5 7 LIGHT SOURCE INCIDENT O"; PHOTO BEAM CELL PRECIPITATION CURVE OF TYPICAL FIBER-FORMING COPOLYESTER PRECIPITATED FROM 60-40 PHENOL-TETRACHLORETHANE WITH METHANOL 90 g 80 5 7O 2 so 5 so 40 0C ml OF PREClPlTANT FIG.2

JAMES G. SM|TH CHARLES J. KIBLER ROGER M. SCHULKEN,JR.

INVENTORS I BYk/WJM M/L H ATTORNEYS Dec. 9, 1 J. 6. SMITH ETAL 3,483,157

METHOD OF PREVENTING REARRANGEMENT OF BLOCKED COPOLYESTERS iginal Filed July 2, 1962 5 Sheets-Sheet 3 ATTORNEYS Burg/m4 NOISSIWSNVELL 5 Sheets-Sheet 4 D 9, W69 J. cs. SMITH ETAL METHOD OF PREVENTING REARRANGEMENT' OF BLOCKED COPOLYESTERS Original Filed July 2, 1962 22018 JOz IhmEEmZ xmIOJo 0 20mm mmmkmmhamoo ATTORN YS NOISSIWSNVHJ. BY

United States Patent M 3,483,157 METHOD OF PREVENTING REARRANGEMENT OF BLOCKED COPOLYESTERS James G. Smith, Charles J. Kibler, and Roger M. Schulken, Jr., Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Original application July 2, 1962, Ser. No. 206,755. Divided and this application Oct. 16, 1967, Ser. No. 720,003

Int. Cl. 008g 51/56, 17/08 U.S. Cl. 26031.2 6 Claims ABSTRACT OF THE DISCLOSURE The rearrangement or randomization of a blocked copolyester may be prevented by treating said blocked copolyester with an arsenic compound.

This application is a division of Smith, Kibler, and Schulken U.S. Ser. No. 206,755, filed July 2, 1962, abandoned in favor of continuing application Ser. No. 678,457, in turn abandoned in favor of continuing application 776,311, now Defensive Publication dated May 27, 1969.

This invention relates to copolyesters derived by the condensation of cisand trans-cyclohexanedimethanol and one or more dicarboxylic aromatic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, etc, modified with one or more of the aliphatic dicarboxylic acids such as succinic, glutaric, adipic, pimelic, sebacic, suberic and the like. More specifically the invention relates to the so called blocked copolyesters of this type in which repeat units of the major components, such as the unit derived from the condensation of terephthalic acid and 1,4-cyclohexanedimethanol, and the repeat units of the minor component, such as the unit derived from the condensation of sebacic acid and 1,4-cyclohexanedimethanol, are not randomly distributed along the polymer chain but occur in large discrete groupings termed blocks. Even more specifically the invention relates to a means and method of preventing the rearrangement or randomization of these repeat units under conditions in which blocked copolyesters are held in the molten state for appreciable periods of time, as in the case in the employment of these compositions in the production of fibers and filaments by the melt spinning process or by the formation of films, sheets and other shaped objects by extruding a molten mass of the copolyester material through a shaping orifice.

For purposes of a clearer understanding of the present invention and the phenomena upon which it depends, a discussion of the essential elements of the problems in the extrusion of blocked copolyester compositions is desirable at this point. As is now known from numerous patent and other disclosures in the technical literature, high melting high molecular weight, linear copolyesters of the fiber and film forming variety have come into prominence in recent years. For example U.S. Patent No. 2,901,466 to Kibler, Bell and Smith, issued Aug. 25, 1959, disclosures such copolyesters which have outstanding value in the production of fibers, filaments, films and other shaped objects. These copolyesters are typical of the compositions dealt with in the present invention.

While the phenomenon of blocking in the production of copolyesters has been recognized by other workers in the field of polymer chemistry, as for example D. H. Coffey and T. J. Meyrich in Proceedings of the Rubber Technological Conference, London (1954), pages 170'- 184, published in 1956, so far as we are aware none of these researchers have recognized the desirability of maintaining the original arrangement of the polymer 3,483,157 Patented Dec. 9, 1969 blocks in a copolymer, and of course have not suggested any means of preventing rearrangement or randomization. To the best of our knowledge and belief the present invention involves the first recognition of this problem and a means for its solution.

Before discussing the specific invention which is the subject of the instant invention it is desirable to discuss two terms which will be employed frequently hereinafter, that is, random copolyester and block copolyester. The concept of random and block polymers has existed for a number of years. Indeed, in the field of vinyl polymers, these terms find frequent usage. It is much less common to find references to block polymers in the field of condensation polymers, such as polyesters or polyamides. A copolyester is, of course, one which is prepared from at least three dilTerent reagents, two of which form the basic polyester and the third (or others) constitutes the modifying agent. The first two are customarily a diol and a dicarboxylic acid or a reactive derivative thereof. The modifying agent can be a diacid (or reactive derivative), a diol, a hydroxy acid, etc.

In a random copolyester, the molecular units derived from the modifying agent or agents are distributed at random in the linear chain of molecular units derived from the principal diacid and diol. Specifically, a polyester prepared from three molecular parts of terephthalic acid, one molecular part of sebacic acid and four molecular parts of 1,4-cyclohexanedimethanol contains two different molecular units, one which can be designated (A) derived from terephthalic acid and 1,4-cyclohexanediamethanol and the other, designated (B), derived from sebacic acid and 1,4-cyclohexanedimethanol, thus:

Since there are three A'groups for every B group in the final polyester, the struture of the random copolyester can be represented by a random linear combination of As and Bs in the ratio of three to one, as for example,

However, the structure of the block copolyester can be represented by a linear combination of As and Bs in which the two groups are collected in clusters or blocks,

such as:

wherein T designates the melting point of the unmodified base polymer, K designates a constant and In designates the natural logarithm. In the case of a block co' polymer, the melting point approaches that of the polyester repeat unit which is present as the major component, since the modifying units, B, are grouped in clusters and each of these clusters behaves as a single molecular unit insofar as its effect on the melting point of the blocked copolyester is concerned.

The blocked copolyesters of the instant invention are prepared from (A) at least one glycol and (B) at least one dibasic acid comprising at least 60 mole percent of an acid having two carboxyl radicals attached to a carbocyclic nucleus having from 6-20 carbons per ring, in which copolyester at least three components are present, one of which can be present as an isomer of one of the other two components, said copolyester, if of the fiberand film-forming type, having a number of average molecular weight between 8,000 to about 100,000, an inherent viscosity in a mixture of 60 percent phenol and 40 percent tetrachloroethane of at least 0.6, such viscosity being calculated from the equation:

wherein 1 is the ratio of the viscosity of a dilute (approximately .25 percent by weight) solution of the polymer in a solvent composed of 60 percent by weight of phenol and 40 percent by weight of tetracholorethane to the viscosity of the solvent itself, and C is the concentration of the polymer in grams per 100 cubic centimeters of the solution, said copolyester having a melting point differential of from 10 C. to 50 C. above the melting point of the corresponding random copolyester.

Block copolyesters of the type referred in the preceding paragraph may be prepared by either one of two methods. The first method is the subject of an application in the name of Charles J. Kibler, Nicholas C. Russin and Alan Bell, Ser. No. 801,705, filed Mar. 25, 1959, entitled Linear Abnormalized Block-Type Copolyesters. now US. Patent 3,117,950. Essentially this process involves first preparing a low molecular weight copolyester and heating this copolyester at a temperature below its melting point so that a conversion of the random copolyester structure to a blocked copolyester occurs. The low molecular weight blocked copolyester is then further polymerized in the solid phase by well known techniques, such as by heating the polymer under vacuum at elevated temperatures until the desired viscosity is reached.

The second method is the subject of an application in the name of James G. Smith and Charles J Kibler, Ser. No. 185,992, filed Apr. 9, 1962, and now abandoned, entitled Block copolyesters, and involves first preparing either a high molecular weight polymer or a low molecular weight copolyester and heating this material in the molten state at a temperature selected from a range whose lower limit is defined by the melting point of the random copolyester prepared and whose upper limit is defined by the melting point of the completely blocked copolyester of the same composition.

As will be apparent to those skilled in the art to which this invention relates, it is highly desirable that the fiberand film-forming copolyesters here dealt with shall maintain their desirable physical properties such as ready dyeability, high impact strength, satisfactory elongation, high melting point, high fiber sticking temperature and high fabric stiffening temperature when such copolyesters are converted into fibers, filaments, films, sheeting, and other shaped objects by the various melt extrusion processes employed for this purpose. The ideal situation with respect to the melt-spinning of fibers and films from such compositions would be to have no change occur in the copolyester structure or arrangement of the molecular blocks but experience has shown that when such composi tions are subjected for any appreciable length of time to the effect of temperatures required to bring them into a molten condition and cause them to be sufficiently fluid to be extrudable a change takes place which involves a rearrangement or randomization of the molecular blocks. In other words, when blocked copolyesters are melt spun or molded a randomization of distribution of the molecular blocks occurs if the polymer is held in the molten state for more than a few minutes. It has been found that the polymeric material of the fibers or molded objects produced under such circumstances consist essentially of the randomized copolyester unless very high speed extruding is employed and that such products suffer an adverse change in those physical properties related to the high melting point of the blocked copolyesters. For example, the fiber sticking temperature and the fabric stiffening tempterature of the textile goods obtained by the normal melt spinning process are found to be much lower than is the case with those textile materials obtained by using copolyesters which have completely retained their blocked molecular pattern or structure. Thus is will be evident that the maintenance of the original molecularly blocked arrangement of the copolyester material during melt spinning or other melt extrusion operation is highly important and in fact critical to the successful employment of this desirable type of material for such purposes.

It is accordingly the principal object of the instant invention to provide a means and method whereby the original arrangement of the molecular blocks of a blocked copolyester may be maintained for substantial periods of time.

Another object is to provide a means and method whereby the original arrangement of the molecular blocks of a blocked copolyester may be maintained for a substantial length of time in the molten state.

A further object is to provide a means of preventing the randomization of the molecular units or blocks of a blocked copolyester of the fiber and film-forming type.

Another object is to provide a blocked copolyester stabilized against randomization or rearrangement of its molecular units or blocks and adapted for the melt spinning of fibers, filaments, films and other shaped objects.

A further object is to provide improved copolyester fibers, films, and other shaped objects having a useful and advantageous combination of physical properties, namely good elongation, high melting point, low solubility, high heat distortion temperature, high fiber sticking temperatures, high fabric stiffening temperature, ready dyeability and the like.

Other objects will appear hereinafter.

These objects are accomplished by the following invention which is based upon the discovery that the catalyst which is employed to catalyze the original condensation reactions involved in production of the copolyester itse'f remains in the polymer substance (because no known practical means is available for its removal) is also an effective agent for rapid conversion of the molecular blocked copolyester to the random structure when the blocked copolyester is held in the molten state for appreciable periods of time. We have also found that when this catalyst is converted into an inactive form its effect thus to produce the randomization structure of the blocked copolyester is very markedly reduced or eliminated.

For example, in the production of copolyesters in accordance with the above description, as by the process described in the Kibler, Bell and Smith US. Patent 2,901,466, the catalyst employed may be a titanium compound and preferably one of the titanium magnesium complexes frequently referred to as a Meerwein complex" as described in John R. Caldwells U.S. Patent 5 2,720,502 issued Oct. 11, 1955. These catalysts have the general formula structures set forth below:

wherein M is an alkali metal, e.g. lithium, sodium, or potassium, M' is an alkaline earth metal such as Mg, Ca or Sr, and R is an alkyl radical containing from 1 to 6 carbon atoms; R can be derived from a lower aliphatic alcohol such as methyl, ethyl, propyl, n-butyl, isobutyl, n-amyl etc. Specific examples of such catalyst are N 4 9)6) 2 s)s)z,

and KH(Ti(OCH Other catalysts which may be employed for this purpose are described in US. Patent to Haslam No. 2,822,348 issued Feb. 4, 1959 as, for example, titanium tetraisopropoxide.

In accordance with the invention we have found that, so far as randomization of the blocked copolyester is concerned, the adverse catalytic effect of the condensation catalyst above referred to can be substantially reduced or eliminated by one of two methods. The first method invoIves the treatment of the blocked copolyester in powdered form with stream at a high temperature selected from the range of 100 to 200 C. for periods ranging from one quarter to twenty hours, depending upon the composition and whether atmospheric or superatmospheric pressures are employed. Under these conditions we have found that the steam converts the catalyst present in the polyester to an inactive form which is believed to be a hydrated titanium oxide. In such form the catalyst is no longer effective in converting the blocked structure of the copolyester to a form in which the random arrangement of the molecular or repeat units occurs. Thus there is provided a very practical and ultilitarian method of so controlling the arrangement of these molecular and repeat units as to enable the treated copolyesters produced in accordance with the invention to be converted into shaped articles by the usual melt spinning or melt extrusion processes without the use of special extrusion techniques or special equipment. Thus the final shaped articles can be formed from polymeric material which has an essentially completely blocked molecular pattern or structure, whereas without the steam treatment described hereinabove the molecularly blocked copolyester would rearrange to the random structure under the temperatures normally employed in melt extrusion processes.

The other method of obtaining the aforesaid advantages involves neutralizing the adverse catalytic influence of the catalyst on the randomization of the blocked copolyester material by treating the blocked copolyester with 0.005-0.5 percent by weight of copolyester of an arsenic compound such as arsenic pentoxide, whereby the condensation catalyst present in the copolyester is a so conerted to an inactive form, probably a molecular complex of titanium and arsenic of unknown chemical structure.

DETERMINATION OF THE EXTENT OF BLOCK- ING OF A POLYESTER The determination of the extent of b ocking of a polyester, in this case a copolyester, is based on the measurement of melting point or solubility in any solvent which will dissolve the maferial to an appreciabe extent. In a randomized copolyester as above described the melting point decreases and the solubility increases in proportion to the amount of the modifying component. For example in the case of the copolyester prepared by a condenzation reaction between dimethyl terephthalate, dimethyl sebacate and 1,4-cyclohexanedimethanol the melting point of the final random copolyester decreases as the amount of the modifying agent, in this case dimethyl sebacate, is increased and the solubility of the final random copolyester increases as the amount of the modifying agent, dimethyl sebacate, increases. In a completely blocked copolyester having the configuration of molecular units as described above, the melting point and solubility of the final blocked copolyester approximate the melting point and solubility of the major unmodified polyester component, in this case, the 1,4-cyclohexanedimethanol terephthalate component.

While the melting point of such copolyesters can be determined by simple and conventional methods, the determination of solubility of the polymer requires a special technique. Specifically, solubility may be determined through determination of the precipitation curve of .the polymer and the method will be described in detail below. In all of the references to solution of the copolyester it is to be understood that the material is dissolved in a solvent composed of 60 parts by weight of phenol and 40 parts by weight of tetrachloroethane and the precipitating solvent employed is methanol.

In the accompanying drawing:

FIGURE 1 is a diagrammatic illustration of an apparatus determining the precipitation curves of a copolyester of the type to which the instant invention relates.

FIGURE 2 shows a typical precipitation curve obtained on a copo'yester composition of the subject invention which was obtained through the use of the apparatus shown schematically in FIGURE 1.

FIGURE 3 is a set of precipitation curves of (A) po'y(1,4-cyclohexylidenedimethylene terephthalate), a typical random copolyester of the fiber and film forming variety containing no second modifying acid, and of other random copolyesters of this type (B), (C), (D), which have been modified by varying amounts of a second modifying acid.

FIGURE 4 is a set of precipitation curves of copolyesters derived from the condensation of terephthalic acid and 1,4-cyclohexanedimethanol and modified with succinic acid in varying amounts (E), (F) before melt-spinning into fibers, and precipitation curves (G), (H) of these same copolyester compositions after they have been subjected to melt-spinning into fibers.

FIGURE 5 is a set of precipitation curves similar to those of FIGURES 3 and 4 and illustrating the effect on a blocked copolyester (Curve F of FIGURE 4) by treatment with steam in accordance with the invention, (1) being the precipitation curve obtained on a sample of yarn which was melt-spun from the blocked copolyester of Curve F after the blocked copolyester had been treated with steam under pressure for one hour at C., (I) being the precipitation curve on a sample of yarn meltspun from a copolymer obtained by the same treatment as applied to the copolyester of Curve F but for only onehalf hour at the same temperature, (K) being the precipitation curve on a sample of yarn melt-spun from a copolymer obtained by treating the same copolyester of Curve F at the same temperature for only an extremely short time of the order of two or three minutes, (H) being the precipitation curve of the same copolyester of Curve F after having been spun into yarn but untreated with steam and (L) being the precipitation curve of a sample of film which had been held in the molten state for four minutes at 280 C. and obtained using the polymer of Curve P which had been treated with steam under pressure for one hour at 150 C.

FIGURE 6 is also a set of precipitation curves illustrating the effect on a blocked copolyester of steam treatment at atmospheric pressure in accordance with the invention, (M) being the precipitation curve of the blocked copolyester which has been subjected to steam treatment for fifteen hours at atmospheric pressure, (N) being the precipitation curve obtained on a sample of the copolyester of Curve M which had been pressed into a film and held in a molten state for four minutes, being the precipitation curve obtained on a sample of film which had been pressed and held in the molten state for four minutes from a blocked copolyester of the same composition as that of Curve M but which had been treated with steam for only six hours and (P) being the precipitation curve obtained on a sample of film which had been pressed and held in the melt for four minutes from a sample of the blocked copolyester of the same composition as that of Curve M, the original polyester having received no steam treatment at all.

The apparatus and experimental procedure used in the determination of the precipitation curves above referred to resemble very closely those described by D. R. Morey and I. W. Tamblyn in J. Applied Physics, volume 16, pages 419-424, 1945. The chief difference is in the solvent and the precipitant used to accommodate the polyester.

The apparatus centers about a square glass cell 1 illuminated by a parallel beam of light from a light source 3 which may, for example, be a 100 watt Bausch and Lomb microscope lamp. The cell is thermostated at 25 C. with a water bath 4 equipped with a stirrer 10 and appropriate windows 5 and 6 for illumination of the cell. The directly transmitted light beam 2 impinges on a photocell 7 the output of which is led to a recorder 8. A variable resistance 9 is provided in the circuit so that the output range of the photocell is accommodated by the range of the recorder.

The polymer to be studied is dissolved in 60:40 phenol: tetrachloroethane at a concentration of 0.05 percent. This solution is placed in the cell, so that the incident beam is completely within the solution. The solution is stirred by stirrer 10 and permitted to come to equilibrium with the temperature of the cell. The recorded output of the photocell now corresponds to 100 percent transmission of the incident beam.

The precipitation curve determination is initiated by starting a mechanical pump, not shown, which delivers one ml. of methanol per minute to the solution in the cell through supply conduit 11. The chart speed of the recorder 8 is /2 inch per minute so that one inch of chart length corresponds to 2 ml. of precipitant. As the precipitant is added, it is rapidly mixed into the solution by the stirrer. Usually, there is no change in transmission of the light during addition of the first few ml. of precipitant. However, eventually a point is reached where the polymer begins to precipitate and produce a haze in solution which reduces the amount of light which is directly transmitted through the solution and as a result the percentage transmission recorded on the recorder begins to decrease. As more and more precipitant is metered in, more and more polymer precipitates and the percentage transmission progressively decreases. Finally all the polymer has precipitated and the percentage transmission reaches a constant low value. The curve traced out by the recorder resembles that shown in FIGURE 2. It can be seen, then, that such a curve is a valuable indication of the relative solubilities of polymers. An insoluble polymer will require very little precipitant to initiate the precipitation; a soluble polymer will require a much greater volume of precipitant to initiate the precipitation.

In the following examples and description we have set forth several of the preferred embodiments of our invention but they are included merely for purposes of illustration and not as a limitation thereof.

The method of preventing randomization of blocked co polyesters in accordance with our invention will be conveniently illustrated by the following examples of typical procedures carried out in accordance therewith.

In order more clearly to illustrate our invention reference is made to the curves of FIGURE 3 which are precipitation curves of random copolyesters as identified above, which copolyesters are precipitated from solutions in 60:40 phenolztetrachloroethane by methanol and illustrating the increasing amount of precipitant required to obtain precipitation of these copolyesters with increasing amounts of the modifying second acid in the copolymer. In all the cases it will be understood that the determination of these precipitation curves is by the method and apparatus to which reference has been made above and as illustrated in FIGURES 1 and 2. Referring now to Curve A of FIGURE 3 this curve was determined from the precipitation of the unmodified base polymer, poly(1,4-cyclohexylidenedimethylene terephthalate) from a .05 percent solution of the polymer in 60:40 phenol tetrachloroethane by methanol.

Curve B of FIGURE 3 was determined by precipitating the copolyester prepared from 1,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and one molar equivalent of succinic acid.

Curve C of FIGURE 3 was determined by precipitating a copolyester prepared from l,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and 1 molar equivalent of sebacic acid.

Curve D of FIGURE 3 was determined by precipitating a copolyester prepared from 1,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and 2 molar equivalents of succinic acid.

This set of curves clearly demonstrates that in the case of a random copolyester the solubility of the copolyester increases as the amount of the second modifying acid in the copolymer is increased. For example the copolymer used in determining Curve D of FIGURE 3 requires approximately 4 times the volume of precipitant to precipitate the polymer than does the unmodified base polymer used in obtaining Curve A of FIGURE 3. Hence, the polyester composition of Curve D is much more soluble than that of Curve A. Similarly the copolyester compositions used in obtaining Curves B and C of FIGURE 3, which have an intermediate amount of modifying acid, have also an intermediate solubility.

Reference is now made to the curves of FIGURE 4. These are precipitation curves of blocked copolyesters and of yarns derived therefrom from solutions of 60:40 phenolztetrachloroethane. Referring now to Curve E of FIG- URE 4, this curve was obtained by precipitating a blocked copolyester prepared from 1,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and one molar equivalent of succinic acid and converted to the molecularly blocked structure by the process of Kibler et al., Ser. No. 801,705, filed Mar. 25, 1959, now US. Patent 3,117,950 entitled Linear Abnormalized Block-Type Copolyesters above referred to. Curve F of FIGURE 4 was obtained by the precipitation of the copolyester prepared from 1,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic'acid and 2 molar equivalents of succinic acid and also converted to the molecular blocked structure by the process of Kibler et al. mentioned above.

Curve G of FIGURE 4 is the precipitation curve of the yarn obtained by melt-spinning the molecularly blocked copolyester represented by Curve E of FIGURE 4.

Curve H of FIGURE 4 is the precipitation curve of the yarn obtained by melt-spinning the molecularly blocked copolyester represented by Curve F of FIGURE 4.

The diiferences between the random copolyesters and the block-type copolyesters, particularly in their behavior, will now be elucidated by a comparison of certain of the curves of FIGURE 3 with those of FIGURE 4. Comparing Curve B of FIGURE 3 and Curve E of FIGURE 4, it can be seen that these two polyesters which have an identical chemical composition show a marked difference in their precipitation curves, the polyester represented by Curve E of FIGURE 4 being much less soluble than that represented by Curve B of FIGURE 3 as is clearly indicated by the smaller volume of methanol required to effect precipitation of the polyester of Curve E than was required in the case of the polyester of Curve B. This difference in solubility is due to the difference in molecular arrangement of the chemical repeat units of the two polyesters. In the' case of the polyester of Curve B of FIG- URE 3, the chemical repeat units are randomly arranged along the length of the polymer molecule. In the case of the polyester of Curve E of FIGURE 4, the chemical repeat units are arranged together in such a manner that the majority of the repeat units due to the modifying acid are grouped in a relatively few clusters or blocks. Each of these blocks behaves as a single modifying entity and as such has a relatively minor efiFect upon the solubility of the copolyester. The solubility characteristics of a copolyester which has been molecularly blocked in this manner tend to resemble those of the completely unmodified polyester present as the major constituent. In this case this major constituent is poly(1,4-cyclohexylidenedimethylene terephthalate). Attention is specifically directed to the close resemblance of the precipitation Curve E of FIG- URE 4 and that of Curve A of FIGURE 3, the latter curve being the precipitation curve obtained on the unmodified base polymer poly(1,4-cyclohexylidenedimethylene terephthalate) When the polymer represented by Curve E of FIGURE 4 is melt spun into a fiber, the blocked structure originally present in the polymer is found to be partially or completely absent in the yarn so obtained. This can be illustrated by an examination of Curve G of FIGURE 4 which, as mentioned above, is the precipitation curve obtained on the yarn melt spun from the copolyester composition represented by Curve E of FIGURE 4. It can be seen that the yarn requires much more precipitant to produce the precipitation Curve G than did the original polymer. It can also be seen that the Curve G of FIGURE 4 resembles very closely that of Curve B of FIGURE 3. Curve B of FIGURE 3 represents the precipitation curve obtained on an essentially random copolyester composition identical to that of Curve E. Hence it must be concluded that the molecularly blocked structure present in the copolyester represented by Curve E of FIGURE 4 is no longer present, or present to a greatly reduced extent, in the melt spun yarn obtained therefrom.

A similar situation can be demonstrated to occur with a polyester of a different composition. Comparing Curve D of FIGURE 3 with Curve F of FIGURE 4 it can be seen that these two polyesters, which again have an identical chemical composition, show a marked difference in their precipitation curves. Again it is concluded that the polyester composition represented by Curve F of FIG- URE 4 has a molecularly blocked chemical structure and consequently requires a much smaller volume of precipitant to generate the precipitation Curve F than does the polyester composition which has a random molecular structure as represented by Curve D.

Again, when the blocked copolyester represented by Curve F of FIGURE 4 is melt spun into a yarn the blocked molecular structure is converted to a random structure. This can be demonstrated by considering Curve H of FIG- URE 4 which is the precipitation curve of the yarn melt spun from the polyester composition represented by Curve F of FIGURE 4. It can be seen that the yarn requires much more precipitant to generate the precipitation curve than does the original polymer.

Still again, the precipitation Curve H of FIGURE 4 closely resembles the precipitation Curve D of FIGURE 3 which is the curve obtained from a random copolyester of the same chemical composition.

It must be concluded then that under the melt spinning conditions normally employed, a molecularly blocked copolyester is generally converted wholly or in part to a random molecular structure unless the processes of the instant invention are employed to slow or stop this molecular rearrangement of the chemical repeat units.

The above discussion of the precipitation curves of FIGURES 3 and 4 is intended to serve primarily as an elucidation of the problem dealt with by the instant invention. The solutions of the problem provided according to the invention will now be discussed by reference to certain specific examples and other description.

As previously indicated, in accordance with one embodiment of our invention the copolyester in powdered or other comminuted form is treated with high temperature steam for a certain period of time during which the activity of the catalyst present in the material to cause randomization of the blocked structure of the copolyester is reduced or eliminated by conversion of the catalyst into an inactive form in which it has reduced tendency, or no tendency, to catalyze randomization. For example employing steam at atmospheric pressure and at C. the powdered copolyester may be steam treated for a period ranging from 1-20 hours. On the other hand, when employing steam at superatrnospheric pressure the temperature may range from 100 to 200 C. for a period ranging from two minutes to two hours. In this connection it should be noted that any treatment of the block copolyester with steam, even for short periods, occasions a degree of stabilization of the copolyester against randomization of the molecular or repeat units thereof. By the same token a more extended steam treatment at the higher temperatures tends more completely to stabilize the polymer against randomization. This will be more fully indicated in the following specific examples of typical steam treatment of blocked copolyesters of the fiber and film forming type in accordance with the invention. In each of these examples the blocked copolyester material treated was in finely divided or powdered form and the polymer was prepared in accordance with the above identified Kibler, Russin and Bell application, Ser. No. 801,705, filed Mar. 25, 1959, now US. Patent 3,117,950 entitled Linear Abnormalized Block-Type Copolyesters. As previously stated, essentially this process involves first preparing a low molecular weight copolyester and heating this copolyester at a temperature below its melting point so that a conversion of the random copolyester structure to a blocked copolyester occurs. The low molecular weight blocked copolyester is then further polymerized in the solid phase by Well known techniques such as by heating the polymer under vacuum at elevated temperatures until the desired viscosity is reached. It will of course be apparent that in these examples we have prepared blocked copolyesters of different chemical constitution by virtue of the modification of the base polymer poly(1,4-cyclohexylidenedimethylene terephthalate) with varying amounts of a second dicarboxylic acid and also with ditferent types of dicarboxylic acids for the second modifying acids.

Example 1.Stabi1ization against randomization of a blocked copolyester by steam treatment at superatmospheric pressure A 100 gram sample of a blocked copolyester prepared from l,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and 2 molar equivalents of succinic acid in powdered form and having a melting point of 264274 C. and an inherent viscosity of 0.95 was placed in a glass lined one-liter autoclave and 10 ml. of water added. After sweeping the autoclave thoroughly with nitrogen, it was sealed and heated to C. The pressure within the autoclave was of course the autogenous pressure of water vapor at that temperature. The temperature Was maintained constant at 150 C. and the pressure remained constant for a period of one hour. The autoclave was then vented to atmospheric pressure and cooled. The final product had a melting point of 260265 C. and an inherent viscosity of 0.82 (Sample A).

A second sample of blocked copolyester of the same composition was treated with steam in the above described manner except that the autoclave was held at 150 C. for 0.5 hour before venting. The product in this case had a melting point of 264267 C. and an inherent viscosity of 0.91 (Sample B).

A third sample of the blocked copolyester of the same chemical composition was treated with steam in the same manner as above described except that the autoclave was vented to the atmosphere at approximately two minutes after the temperature of the autoclave reached 150 C. The final product had a melting point of 262266 C. and an inherent viscosity of 0.88 (Sample C).

Precipitation curves were obtained on these three samples A, B and C and on the untreated original blocked copolyester and these four curves were found to be essentially identical. These three samples and the original untreated copolyester are represented in FIGURE by the single precipitation Curve F.

The original untreated blocked copolyester and the three steam treated samples A, B and C were melt spun into yarn using well known melt spinning techniques. Precipitation curves were obtained on each of the four yarn samples so produced and these precipitation curves are shown in FIGURE 5. Precipitation Curve I was obtained from the yarn melt spun from Sample A which had received one hour of steam treatment at 150 C. Precipitation Curve J was obtained from the yarn melt spun from Sample B which had received 0.5 hour of steam treatment at 150 C. Precipitation Curve K was obtained on the yarn melt spun from Sample C which had received a very short steam treatment at 150 C. Precipitation Curve H was obtained on yarn melt spun from the original unsteamed blocked coployester.

It can be seen from these precipitation curves that the original unsteamed copolyester is converted to a completely random copolyester on melt spinning by comparing Curve H and Curve F of FIGURE 5. It can also be seen that the steam treatment described in this example is eifective in reducing the degree of randomization of the molecular structure by comparing Curves I, J, and K with Curve H as above described.

It can also be seen that there is a direct relationship between the length of time which the polymer samples were steamed at 150 C. and the extent to which they randomized on melt spinning. The sample (A) which received the longest time of steaming showed the smallest amount of randomizing during the spinning procedure while the sample (C) which received the shortest time of steam treatment showed the greatest degree of randomization. Under the conditions described in this example a steam treatment longer than two hours tends to degrade the copolyester used in this example to an excessive degree.

Attention is now called to Curve L of FIGURE 5 which is termed four-minute film. This is a precipitation curve obtained, on a film which was pressed from the steam treated Sample A by the following procedure. A sample of the material under examination was placed between two polished metal plates. These plates were pressed together with a pneumatically operated press, the jaws of which were electrically heated and the temperature thermostatically controlled. This press served to heat the polymer rapidly to the melting point and simultaneously compress it to a film. The film so obtained was held between the plates in a molten state for a period of four minutes at 280 C. The plates containing the film were then removed from the jaws of the press and quenched in cold water. This film was used to obtain the precipitation Curve L of FIGURE 5.

A comparison of the precipitation Curves L, I, and F of FIGURE 5 demonstrates that this four-minute film sample has undergone a slightly greater degree of randomization than has the yarn sample represented by Curve I. This simple test was adopted as a means of measuring the degree to which a blocked copolyester had been stabilized by any of the procedures of the instant invention. It is evident that this four-minute film test occasions the use of more severe conditions than are encountered in normal spinning operations. Consequently it is certain that if a tested polymer shows little or no randomization of its blocked copolyester structure after being subjected lit to this four-minute film test, it may be melt spun under normal melt spinning conditions with little or no destruction of the desirable molecularly blocked structure. Subsequent examples will contain frequent references to this four-minute film test.

Example 2.A large scale steam stabilization of a blocked copolyester The polyester used in this example was prepared from i,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and one molar equivalent of succinic acid and molecularly blocked by the above mentioned procedure of Kibler et al. The material had a melting point of 288294 C. and an inherent viscosity of 0.94.

The powdered material was placed in a large vessel equipped with a stirrer and steam which had been heated to 125 C. was passed over the powder While it was stirred to promote contact with the vapor. The temperature of the powder was C. during this treatment. A sample of the steamed polymer was withdrawn after six hours of steam treatment and tested by the above described 4-minute film test. Steaming was then continued for a subsequent 9 hours making a total of 15 hours in all and at this time discontinued. The final product was also tested by the above described 4-minute film test.

Reference is now made to FIGURE 6 where the various precipitation curves which were determined on the samples mentioned in this experiment are shown. The precipitation Curve M is the curve obtained from the original untreated block copolyester and is identical with that obtained on the block copolyester after 15 hours of steam treatment. Curve N is the precipitation curve determined on the film sample pressed in the 4-minute film test using a sample of the block copolyester which had been treated for 15 hours with steam. It can be seen that this 15 hours of steam treatment effectively prevents the rearrangement of the molecular blocks during the 4-minute film test.

Precipitation Curve 0 was determined using the film obtained in the 4-minute film test on the polyester sample withdrawn after 6 hours of steaming. Precipitation Curve P was obtained on the film pressed in the 4-minute film test using the original blocked copolyester. A comparison of Curves O and P demonstrates that 6 hours of steam treatment was insufficient to prevent the rearrangement of the molecularly blocked copolyester structure and indeed the 6-hour steam treated sample behaved in all respects in a manner very similar to the original blocked copolyester Which had received no steam treatment.

This experiment demonstrates that the steam treatment of a blocked copolyester can be highly effective provided it is continued for a sutficient length of time.

In actual commercial use, the length of time required to effect stabilization of the molecularly blocked copolyesters by treatment with steam, can be greatly shortened by the use of superheated steam. Under these circumstances, the superheated steam is passed through a heated bed of comminuted blocked copolyester for the required length of time and the steam penetrates the polymer pellets and inactivates the catalyst. It is essential in this procedure that a heated bed of polymer be used, otherwise the steam will condense and the temperature of the polymer bed will not rise above 100 C. Under these conditions, the polymer may be treated with steam at atmospheric pressure and temperatures within the range of 100-200 C. This greatly reduces the duration of steam treatment required to stabilize the molecularly blocked structure of the copolyesters. The duration of steam treatment will vary from one hour to twenty hours depending on the particular temperature of the polymer bed, a short time being selected for the high temperature treatment, a long time for the low temperature treatment.

Example 3.Stcam stabilization using superheated steam The polyester used in this example was prepared from 13 1,4-cyclohexanedimethanol, 3 molar equivalents of succinic acid and molecularly blocked by the above mentioned procedure described in the copending application of Kibler, Russin and Bell, Ser. No. 801,705, filed Mar. 25, 1959. The blocked copolyester had an inherent viscosity of 0.78.

The powdered blocked copolyester was placed in a layer approximately three inches deep on the surface of a porous glass plate. The bed of polymer was heated by a furnace to 200 C. and steam superheated by a second furnace to 200 C. was passed through the bed of polymer for 1.5 hours. The final polymer had an inherent It is readily seen that a small value of the precipitation abscissa indicates that the polymer is relatively insoluble. That is, only a small volume of precipitant is needed to reduce the percentage transmission of a solution from 100 percent to 95 percent. On the other hand a large value of the precipitation abscissa indicates that the polymer is relatively soluble, that is, a large volume of precipitant is needed to reduce the percentage transmission from 100 percent to 95 percent. Such a number as the precipitation abscissa therefore is a convenient means of characterizing the precipitation curves of polyester samples under study.

PRECIPITATION DATA ON .05% SOLUTIONS IN 60:40 PHENOL-TETRACHLOROETHANE OF MODIFIED LOCKED COPOLYESTERS FROM CIS- AND TRANS- 1,4-CYCLOHEXANE- DIMETHANOL END TEREPHTHALIC ACID Milliliters of Milliliters of precipitant 1 precipitant l (methanol) (methanol) Milliliters of Milliliters of using using precipitant 1 precipitant l copolyester 2 copolyester 2 (methanol) (methanol) treated treated Copolyester using using with steam with steam composition: original original under under modifying acid Percent copolyester copolyester 2 pressure pressure in mole percent trans- (not (not at 150 C. at 175 C. of total acids isomer steamed) steamed) for y, hour for hour Example:

4 Glutaric 17% 95 18. 9 22. 9 19. 9 19. 1 5. Sebacic 20% 95 20. 6 26. 3 31. 3 21. 2 6 95 28.0 35. 4 39. 4 30. 2 7 Isophthalic 78 33. 8 47. 6 39. 6 39. 2

1 Required to reduce transmission from 100% to 95% (Figure 2). 2 From film pressed at 300 C. and held molten for 4 minutes.

viscosity of 0.75 and was found to retain its molecularly blocked structure on melt spinning.

A similar run was carried out using pellets of blocked copolyester in the shape of rough cubes inch to a side and the steam treatment was performed for six hours at 200 C. The final polymer had an inherent viscosity of 0.70 and was found to retain its molecularly blocked structure on melt spinning.

The following four examples will serve to illustrate that steam treatment of blocked copolyesters to prevent randomization of the molecular repeating units is applicable to a wide range of modified blocked copolyesters of different compositions. In fact, so far as our work indicates, the process is applicable to all copolyesters of this type. The following tabulation indicates the results obtained when four different blocked copolyesters having the indicated compositions were treated with steam in accordance with the invention. Before discussing this tabulation it will be desirable to refer to the indicated phenomena by reference to FIGURE 2 of the drawing which is a precipitation curve of a typical fiber-forming copolyester precipitated from 60:40 phenol tetrachloroethane with methanol. Generally speaking, the precipitation curves obtained on the copolyesters of the subject invention have the same general configuration. For the purposes of describing the invention, therefore, it is sufficient to designate by some means the point at which the polymer being studied begins to precipitate from solution, that is to say, the volume of precipitant necessary to initiate precipitation of the polyester being studied. In practice it is difi'icult to define the exact volume of precipitant needed to just exactly initiate the precipitation of the dissolved polymer. It is therefore expedient to select a particular value of the percentage light transmission and determine what volume of solvent is necessary to precipitate sufificient of the dissolved polymer to give this selected percentage transmission value. In the following examples this has been done and the level of 95 percent transmission has been selected. Referring now to FIGURE 2 of the drawing it can be seen that the indicated point X would designate the number of ml. of precipitant required to precipitate sufficient of the dissolved polymer to reduce the level of transmission from 100 percent to 95 percent. This value, X, is termed the precipitation abscissa.

It will be noted from the above tabulation that in certain instances the sample of copolyester was in the form of a film which had been pressed at a temperature of 300 C. and held molten for four minutes. The film form was employed rather than filament form only because it was a more convenient method of handling the material and determining the effect on the temperatures encountered when the material was brought into a molten condition under temperatures comparable to those employed in the standard melt spinning and melt extrusion procedures.

A comparison of the figures of column 5 with those of column 4 will show that in each of the polymers studied a randomization of the original molecularly blocked structure has occurred when the polyester sample was melted at 300 C. since the solubility, as indicated by the ml. of precipitant required to reduce the percentage transmission from 100 percent to percent, increases after the untreated polyester is melted. Similarly the figures of column 7 when compared With those of column 4 will demonstrate that the steam treatment for /2 hour at 175 C. under pressure serves to essentially completely stabilize the blocked molecular structure of the copolyester. This is shown by the fact that after melting the treated copolyester at 300 C. the volume of precipitant needed to reduce the transmission of a solution of the polymer from percent to 95 percent is approximately the same as that of the untreated material. The steam treatment for /2 hour at C. under pressure is seen to be etfective in some cases but not in others indicating that in some instances this treatment is sufiicient to stabilize the molecularly blocked structure of the polyester but that in many cases a higher temperature than 150 C. within the range of 100-200 C. is needed to effect complete stabilization. It has also been found that steam treatment at the higher temperatures of the order of 190 C. and approaching the upper limit of 200 C. for /2 hour tends toward excessive hydrolytic degradation of the copolyester being treated. We have found that the temperature range of to C. is the preferred temperature range for steam treatment under pressure of the polyesters in accordance with the invention.

As indicated under the general discussion of our invention, prevention of randomization of the molecularly blocked copolyesters can be accomplished without the use of steam by treating the blocked copolyester with a small amount of an arsenic compound such as arsenic pentoxide whereby the catalyst present in the copolyester which catalyzes randomization is converted to an inactive form which is probably a molecular complex of titanium and arsenic, the chemical structure of which is presently unknown. The examples which follow illustrate this general method of neutralizing the catalyst and preventing the undesired randomization. As will be evident, there are several specific methods by which this may be done. In each instance the copolyester was prepared from l,4-cyclohexanedimethanol, 3 molar equivalents of terephthalic acid and 2 molar equivalents of succinic acid and converted to the molecularly blocked copolyester using one of the procedures indicated above and containing as a catalyst titanium tetraisopropoxide of such a concentration that there is present in the polymer 150 pars per million of titanium metal.

Example 8.Stabilization against randomization of a blocked copolyester by arensic compounds The blocked copolyester of the above indicated chemical composition had an inherent viscosity of 0.76 and a precipitation abscissa of 41.8. A sample of this blocked copolyester was subjected to the 4-minute film test and the precipitation abscissa of this film was found to be 72, thus indicating extensive randomization of the blocked copolyester structure on melting.

Ten grams of this blocked copolyester were dissolved with heating in 125 ml. of 'y-butyrolacetone and the hot solution was then poured into 1,000 ml. of ethanol to precipitate the polymer. The precipitated polymer was filtered off and dried and found to have an inherent viscosity of 0.78. This dried precipitated copolyester was subjected to the 4-minute film test and the film was found to have a precipitation abscissa of 68.7. This indicated that the solvent employed, -butyrolactone, had no eitect in stabilizing the molecularly blocked copolyester structure. An identical procedure was followed with a second 10 gram sample except 10 mg. of arsenic pentoxide was added to the solution. After precipitating and drying the polymer had an inherent viscosity of 0.85. This material was subjected to the 4-minute film test and the film sample was found to have a precipitation abscissa of 43, which is essentially identical with that of the original blocked copolyester. This demonstrates that the arsenic pentoxide was effective in deactivating the residual titanium catalyst so that the original molecularly blocked copolyester could be melted and held in a molten condition for at least 4 minutes and still retain the molecularly blocked structure.

Example 9 The above procedure while demonstrating the effectiveness of arsenic pentoxide as a means of stabilizing the blocked structure is difiicnlt to carry out with large samples of polymers. The following example describes a procedure whereby large quantities of polymer may be treated with arsenic pentoxide and thereby stabilize the blocked structure of the polymer.

One thousand grams of blocked copolyester of the same composition as used in Example 8 were slurried with 1,000 ml. of water containing 5 grams of arsenic pentovide dissolved in it. After thorough mixing the slurry was evaporated to dryness on a steam bath with occasional stirring. The final product had an inherent viscosity of 0.80. A sample of the material was subjected to the 4-minute film test and the precipitation abscissa of this film was 41.0, a value essentially identical with that of the original untreated blocked copolyester. This method then is as equally e'ltective as that of Example 8 in providing a molecularly blocked copolyester whose molecular structure is stabilized against rearrangement on melting.

Example 10 The following example illustrates another procedure which is convenient to carrying out on moderately large size samples. It is principally dependent upon the use of a carrier or swelling agent to permit the arsenic compound to penetrate the polymer particles and thereby deactivate the catalyst residue.

The carriers which we have found to be especially efiicacious in our process are those selected from the group consisting or butyl benzoate, o-phenylphenol, chlorinated benzenes, dimethyl terephthalate, biphenyl and fl-methoxyethyl benzoate.

Ten grams of blocked copolyester of the same composition as that used in Example 8 were slurried in ml. of water containing 0.3 gram of dissolved arsenic pentoxide and 3 ml. of B-methoxyethyl benzoate as a carrier. The mixture was stirred and heated on a steam bath for 3.5 hours. The product was filtered, dried and found to have an inherent viscosity of 0.77. A sample of the final product was subjected to the 4-minute film test and the film found to have a precipitation abscissa of 58.4. It can be seen that while this treatment is not as effective as those of Examples 8 and 9 in preventing the' rearrangement of molecular blocks during melting, nevertheless some substantial degree of stabilization of the blocked structure is efiected by this treatment. This is shown by the fact that the precipitation abscissa, after the 4-minute film test, is still considerably less than for the untreated polyester after it has been subjected to the 4-minute film test.

In the examples and the above description and in the claims defining our invention we have employed the term stabilization with reference to prevention of the randomization of the molecular blocks of the copolyester. By this term is to be understood reduction or elimination of the tendency of the molecular repeat units, which are normally arranged in discreet clusters or blocks in the polymer to be converted to a randomly arranged grouping of these units during melting of the blocked copolyester as would be the case in melt spinning of the polymer into filaments or in melt extrusion into other shaped articles.

It will thus be seen from the above examples and description that our invention has solved one of the troublesome problems inherent in employing blocked copolyesters for the preparation of such products as fibers, filaments, films and other shaped objects, that is keeping the desirable blocked structure of the copolyester material intact during those periods during which the material is subjected to heat in melting and subsequent extrusion. Expressed in another way, the present invention enables one to preserve or stabilize the desirable properties of the blocked copolyesters of the type hereinabove specified and to such an extent that they may be employed in the production of fibers, filaments, films and other products of improved properties without deterioration of such properties under the conditions normally encountered in the manufacture of such products.

Although the invention has been described in considerable detail with particular reference to certain proferred embodiments thereof, variations and modifications can be etfected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. The process of stabilizating against rearrangement of the molecular blocks of a high molecular weight, linear blocked copolyester of the fiberand film-forming type derived from the condensation of a member of the group consisting of the cisand transisomers of 1,4- cyclohexanedimethanol and at least one dicarboxylic aromatic acid wherein the carboxy radicals are attached to the aromatic nucleus in a para relationship, said copolyester being modified with at least one saturated aliphatic dicarboxylic acid and having a polymeric molecular structure in which molecular repeating units (A) and (B), in which A corresponds to the repeat unit derived from the condensation of 1,4-cyclohexanedimethanol with the said aromatic acid and B corresponds to the repeat unit derived from the condensation of 1,4-cyclohexanedimethanol with the said modifying dicarboxylic acid, are arranged in clusters or blocks in a regular pattern throughout the polymer and containing a catalyst which catalyzes randomization of the molecular repeating units at the melting temperature of the copolyester, and which is an oxygenated titanium compound selected from the group consisting of the alkoxides of titanium and inorganic complexes derived therefrom and present in an amount corresponding to 50500 parts of titanium metal to a million parts of copolyester., which comprising treating the copolyester in comminuted form with rsenic pentoxide whereby the catalyst is converted into a for min which catalyzation of the randomization of the molecular repeating units of the blocked copolyester is reduced or eliminated.

2. The process of claim 1 in which the dicarboxylic aromatic acid is terephthalic acid.

3. The process of stabilizing against rearrangement of the molecular blocks of a high molecular Weight, linear, blocked copolyester of the fiberand film-forming type derived from the condensation of a member of the group consisting of the cisand transisomers of 1,4-cyclohexanedimethanol and terephthalic acid, said copolyester being modified with at least one saturated aliphatic dicarboxylic acid and having a polymeric molecular structure in which molecular repeating units (A) and (B) in which A corresponds to the repeat unit derived from the condensation of l,4-cyclohexanedimethanol with terephthalic acid and B corresponds to the repeat unit derived from the condensation of 1,4-cyclohexanedimethanol with the said modifying dicarboxylic acid arranged in clusters or blocks in a regular pattern throughout the polymer and containing a catalyst which catalyzes randomization of the molecular repeating units at the melting temperatures of the copolyester and which is an oxygenated titanium compound selected from the group consisting of the alkoxides of titanium and inorganic complexes derived therefrom and present in an amount corresponding to 50-500 parts of titanium metal to a million parts of copolyester, which comprises dissolving the copolyester in gamma-butyrolactone, adding 0.005-0.5 percent by weight of the copolyester of arsenic pentoxide, precipitating the copolyester from the solution by adding ethanol, thereto, and filtering off and drying the precipitated copolyester containing the arsenic compound,

4. The process of stabilizing against rearrangement of the molecular blocks of a high molecular weight, linear, blocked copolyester of the fiberand film-forming type derived from the condensation of a member of the group consisting of the cisand transisomers of 1,4-cycl0hexanedimethanol and terephthalic acid, said copolyester being modified with at least one saturated aliphatic dicarboxylic acid and having a polymeric molecular structure in which molecular repeating units (A) and (B) in which A corresponds to the repeat unit derived from the condensation of 1,4-cyclohexanedimethanol with terephthalic acid and B corresponds to the repeat unit derived from the condensation of 1,4-cyclohexanedimethanol with the said modifying dicarboxylic acid are arranged in clusters or blocks in a regular pattern throughout the polymer and containing a catalyst which catalyzes randomization of the molecular repeating units at the melting temperatures of the copolyester and which is an oxygenated titanium compound selected from the group consisting of the alkoxides of titanium and inorganic complexes derived therefrom and present in an amount corresponding to -500 parts of titanium metal to a million parts of CO- polyester, which comprises slurrying the copolyester in finely divided form with a 0.15 percent aqueous solution of arsenic pentoxide, and evaporating off the water from the slurry, whereby the treated copolyester contains 0.005-5 percent by weight of the arsenic compound.

5. The process of claim 4 in which the slurry contains 1-40 percent, based on the weight of the copolyester, of a carrier selected from the group consisting of B-methoxyethyl benzoate, butyl benzoate, o-phenylphenol, chlorinated benzenes, dimethyl terephthalate and biphenyl.

6. The process of claim 4 in which the slurry contains 1-l0 percent, based on the weight of the copolyester, of e-methoxyethyl benzoate as a carrier.

References Cited UNITED STATES PATENTS 2,437,232 3/1948 Rothrock et a1. 3,068,205 12/1962 Smith 260 MORRIS LIEBMAN, Primary Examiner H. H. FLETCHER, Assistant Examiner US. Cl. X.R.

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