Patent Publication Number: US-3875257-A

Title: Brominated bisphenol A diethanol polyformal

Description:
United States Patent Musser et al.  
 1451 Apr. 1, 1975 BROMINATED BISPHENOL A DIETHANOL [56] References Cited POLYFORMAL UNITED STATES PATENTS 3,114,732 12/1963 VOl&#39;l 131361161 260/52 3,650,663 3/1972 B 1 s 179 Inventors: Harry Musse&#34; Wmsm&#34; 3,809,681 5/1974 M gi/6M1. 260/52 k b th f Jae Son 0 o Kmgspon Tenn Primary E.\&#39;ammerl-larold D. Anderson Assignee: Eastma K d k C Assistant Examiner-Edward Woodberry Rochester, NY.  
 [57] ABSTRACT Disclosed is a brominated bisphenol A diethanol polyformal comprised of recurring units of the structure Filed: Nov. 30, 1973 Appl. No.: 420,494  
 Related US. Application Data Continuation-impart of Ser. No. 281,259, and a continuation-impart of Ser. No. 365,773.  
 where n is l or 2. This polyformal can be formed into a moldable or fiber-forming composition comprising an admixture of from 75 to 98 weight percent polyester and from 25 to 2 weight percent of the polyformal. The admixture of the polyester and the polyformal Cl 260/860 8/DIG 260/DIG&#39; 24 can, depending on the precise conditions of time, tem- Int. perature and pressure f -m in whole or in part a co- Field of Search 260/52, 860, 51 R; 8/21 C, polymer of blocks of polyester and blocks of polyfor- 8/179, D]G 4 mal. The admixture, the block copolymer or a combination of the two can be formed into useful articles.  
  16 Claims, No Drawings BROMINATED BISPHENOL A DIETHANOL POLYFORMAL This application is a continuation-in-part of our copending application Ser. No. 281,259, filed Aug. 16, 1972, entitled BROMINATED BISPHENOL A DIE- Tl-IANOL POLYFORMAL, now US. Pat. No. 3,809,681 and our copending application Ser. No. 365,773, filed May 31, 1973, and now abandoned, entitled BROMINATED BISPHENOL A DIETHANOL POLYFORMAL COPOLYMER.  
  This invention broadly relates to a polyformal of brominated bisphenol A diethanol and formaldehyde. In a first embodiment, this invention relates to the brominated bisphenol A diethanol polyformal itself. In a second embodiment, this invention relates to a composition formed by admixing the brominated bisphenol A diethanol polyformal with a polyester. In a third embodiment, this invention relates to a composition of a block copolymer formed from the admixture.  
  The use of textile fibers and molded objects of synthetic polymers has increased tremendously over the last several decades. The increase in the use of synthetic polymers for preparing synthetic fibers has resulted in large part from the desirable combination of properties that can be achieved in a textile article by using synthetic fibers or blends of natural and synthetic fibers.  
  Although synthetic fibers exhibit many desirable properties, one undesirable property of many synthetic fibers is a lack of flame retardancy. Several years ago the desirability of flame retardant fabrics began&#39;to be recognized. At this time, synthetic fibers were regarded as satisfactory from the flame retardancy standpoint if they exhibited even a moderate degree of flame retardancy. Later, higher standards of flame retardancy for certain finished goods became desirable. These standards required more than a moderate degree of flame retardancy. Still later, federal legislation created the current standards of flame retardancy. These standards require a great deal of flame retardancy for certain types of finished goods, such as childrens sleepwear. Pursuant to this legislation a test was established, often called the Childrens Sleepwear Test,&#34; to determine lO-CHz-CHathe acceptability of fabrics for childrens sleepware. Thus, the current standard of flame retardancy has now caused many textile fibers to be regarded as commercially unsatisfactory for childrens sleepwear because, even though the fabric exhibits a substantial degree of flame retardency, the fabric will not pass the Children s Sleepwear Test. Consequently, because of the present flame retardancy standards, a fabric which exhibits additional flame retardancy often means the difference between being passing and failing the Childrens Sleepwear Test and consequently the difference between the fiber being commercially acceptable and commercially unacceptable.  
  The published prior art that applicants are aware of is German Pat. No. l,252,413, Polish Pat. No. 48,893, German Pat. No. 1,149,899, German Pat. No. 1,001,819, Japanese Pat. No. 71/3174, Japanese Pat. No. 71/10101, Dutch Pat. No. 70/15991, British Pat. No. 1,115,611, British Pat. No. 1,206,171, US. Pat. No. 2,968,646, US. Pat. No. 2,568,658, US. Pat. No. 2,587,442, US. Pat. No. 3,234,167, US. Pat. No.  
 3,234,168, US. Pat. No. 3,294,742, US. Pat. No. 3,334,152, US. Pat. No. 3,367,990, US Pat. No. 3,395,118 and US. Pat. No. 3,524,901.  
  The unpublished prior art that applicants are aware of is the knowledge by others in this country, before the invention thereof by the applicants, of a textile fiber, hereinafter called the diethanol fiber, formed from a polymer of terephthalic acid, ethylene glycol and tetrabromobisphenol A diethanol having the formula The tetrabromobisphenol A diethanol polyformal containing fibers of this invention, hereinafter called the polyformal fibers, are patentably distinguishable over the diethanol fibers of the prior art because the polyformal fibers exhibit an unobviously high degree of flame retardancy over the diethanol fibers.  
  The tetrabromobisphenol A diethanol polyformal copolymer, hereinafter called the polyformal copolymer, is thought to be patentable over the polymer of terephthalic acid, ethylene glycol and tetrabromobisphenol A diethanol, hereinafter called the diethanol polymer, because the amorphous polyformal copolymer exhibits an unobviously low crystallization temperature upon heating and an unobviously high crystallization temperature upon cooling from the melt.  
  The tetrabromobisphenol A diethanol polyformal is thought to be patentable because of the unobviously high flame retardancy of the polyformal fibers and be cause of the unobvious crystallization temperature properties of the polyformal copolymers.  
  Broadly speaking, the brominated bisphenol A diethanol polyformal of the first embodiment of this invention, hereinafter called the polyformal, can be described as a polymeric composition having repeating units of the structure wherein n is 1 or 2. Broadly, the inherent viscosity of the polyformal can be in the range of 0.03 to 1.0. In another aspect of this invention the inherent viscosity of the polyformal can be in the range of 0.05 to 0.30.  
  In a preferred aspect n is 2 and both bromine atoms are in the ortho position with regard to the oxygen atom. Both bromine atoms can be in the meta position with regard to the oxygen atom.  
  Broadly speaking, the admixture of the brominated bisphenol A diethanol polyformal and polyester of the second embodiment of this invention can be described as a moldable or fiber-forming composition comprising an admixture of A. based on the weight of the composition, from to 98 weight percent polyester, and  
 B. based on the weight of the composition, from 25 to 2 weight percent of the brominated bisphenol A diethanol polyformal described above.  
  In a preferred aspect of this embodiment, (A) is from to 92 weight percent and (B) is from 20 to 8 weight percent.  
  In another preferred aspect of this embodiment the polyester is poly(ethylene terephthalate), poly(tetramethylene terephthalate) or poly( l ,4- cyclohexylenedimethylene terephthalate). Poly(tetramethylene terephthalate) is an especially preferred polyester.  
  Textile fibers can be formed from the admixture of the second embodiment. Broadly speaking, the polyformal copolymer of the third embodiment can be described as a moldable or fiber-forming copolymer having an inherent viscosity in the range of 0.30 to 1.0 comprised of A. based on the weight of the composition, from 75 to 98 weight percent blocks of a polyester, and  
 H CH2 B. based on the weight of the composition, from to 2 weight percent blocks of the polyformal described above having an inherent viscosity of 0.03 to 1.0.  
  In a preferred aspect of this embodiment, (A) is from 80 to 92 weight percent and (B) is from 20 to 8 weight percent.  
 In still another preferred aspect of this embodiment the polyester is poly(ethylene terephthalate) or poly(- tetramethylene terephthalate). Poly(ethylene terephthalate) is an especially preferred polyester.  
  Textile fibers can be formed from the copolymers of the third embodiment. In a preferred aspect the polyester is poly(ethylene terephthalate).  
  In this invention the admixture or copolymer can contain minor amounts of other materials which alter selected properties of the polymer. These materials can be introduced into the polyesters either as a comonomer or a physical blend. Specifically the polyester can be modified with a comonomer that imparts basic dyeability to textile fibers.  
  The usefulness of the polyformal is that the polyformal can be admixed or copolymerized with a polyester to form the admixture or polyformal copolymer and useful flame retardant articles, such as molded objects and fibers, can be prepared from the admixture or polyformal copolymer.  
  The polyformal can be admixed with the polyester by several methods well known in the art. One suitable method includes mixing together pellets of each polymer. The polyformal can be copolymerized with the polyester by several methods well known in the art. One suitable method includes melt extruding or melt spinning an admixture of pellets of the polyformal and the polyester.  
  The usefulness of the admixture of the polyformal and the polyester is that the admixture can be prepared into useful flame retardant articles, such as molded objects and fibers.  
  The admixture can be used to prepare useful flame retardant articles by techniques well known in the art. For example, the admixture can be melt spun, drawn, heatset and processed into textile fibers according to conventional methods well known in the art. Additionally, the admixture can be injection molded into useful molded objects using conventional processes and apparatus.  
  The usefulness of the polyformal copolymer is that the copolymer can be prepared into useful flame retardant articles, such as molded objects and fibers.  
  The polyformal copolymer can be used to prepare useful flame retardant articles by techniques well known in the art. For example, the polyformal copolymer can be melt spun, drawn, heatset and processed into textile fibers according to conventional methods well known in the art. Additionally, the polyformal copolymer can be injection molded into useful molded objects using conventional processes and apparatus.  
  The polyformal of this invention can be prepared by a process comprising contacting in a solvent, under polymerization conditions and in the presence of a suitable acid catalyst, formaldehyde and brominated bisphenol A diethanol corresponding to the structure where n is l or 2.  
  The solvent useful in this process can comprise a solvent that is inert with regard to the reactants. Although 5 many conventional solvents can be used, benzene, toluene and hexane are preferred because of their cost and availability.  
  The pressure used for the polymerization reaction can vary widely. Pressures higher than atmospheric can be used but water removal is, of course, more difficult at elevated pressures. Pressures lower than atmospheric can be used, but low pressures are to some extent undesirable because low pressures will tend to allow the formaldehyde to escape from the inert solvent. Atmospheric pressure is preferred because of the ease of creation as well as the minimization of undesirable side effects.  
  The temperature used for the polymerization reation can also vary widely. Temperatures above about C. can be used but are to some extent undesirable because the formaldehyde will tend to escape from the polymerization solvent. In a preferred embodiment the temperature is about l00-l10C. In this embodiment the reaction mixture can be heated at reflux to azeotropically remove the water created by condensation of the formaldehyde and the brominated bisphenol A diethanol.  
  The acid catalyst of this invention can be a variety of catalysts that function as proton donors to catalyze the polymerization reaction. Examples of acids that could be used include p-toluenesulfonic acid, sulfuric acid, trifluoromethanesulfonic acid, methanedisulfonic acid, camphorsulfonic acid, perchloric acid, and sulfonated resins.  
  In this invention the formaldehyde can be in various forms such as paraformaldehyde or gaseous formaldehyde. Paraformaldehyde is preferably used because of its ease in handling, lack of color forming impurities, and its ability to form high molecular weight polyformals. When paraformaldehyde is used the acid catalyst not only functions as a proton donor to catalyze the polymerization reaction, but, in addition, functions to depolymerize the paraformaldehyde.  
  The contact between the brominated bisphenol A diethanol and formaldehyde can be preferably effected by merely stirring a solution of the formaldehyde and brominated bisphenol A diethanol in the solvent. If desired, other contacting procedures well known in the art could be used, such as packed towers, bubble towers and the like.  
  After polymerization is complete, isolation of the polyformal can be accomplished by techniques well known in the art such as removal of the solvent or pre-&#39; cipitation in a nonsolvent, such as methanol.  
  The brominated bisphenol A diethanol that is condensed with formaldehyde can be prepared by condensing one mole of brominated bisphenol A with 2 moles of ethylen oxide to form one mole of brominated bisphenol A diethanol. This reaction is well known in the art and is disclosed in Canadian Pat. No. 663,542.  
  The thermal stability of the polyformal may be increased by acetylation of hydroxy end groups, if desired.  
  Other methods for preparing the polyformal are disclosed in US. Pat. No. 2,968,646.  
  The polyesters useful in this invention can be derived from aliphatic or alicyclic diols containing 2 to carbon atoms. Examples of such diols include ethylene glycol; diethylene glycol; 1,2-propylene glycol; 2,4- dimethyl-2-ethylhexane-l 3-diol; 2-ethyl-2-butyl-1 ,3 propanediol; 1,4-butanediol; 1,5-pentanediol 1,6- hexanediol; 1,10-decanediol; l,4-cyclohexanediol; l,4- cyclohexanedimethanol and 2,2,4,4-tetramethyl-l,3- cyclobutanediol. Ethylene glycol, l,4-butanediol and l,4-cyclohexanedimethanol are preferred diols. Copolyesters may be prepared using two or more of the above diols. Two or more dicarboxylic acids or diols may be used to give copolyesters or block polymers.  
  The polyesters useful in this invention can be derived from aliphatic, alicyclic, or aromatic dicarboxylic acids having 3 to 40 carbon atoms. Examples of such acids include adipic; azelaic; sebacic; l ,4- cyclohexanedicarboxylic; terephthalic; isophthalic and l,4-naphthalic. Terephthalic acid is preferred. It will be understood that the corresponding esters of these acids are included in the term dicarboxylic acid. Copolyesters may be prepared using two or more of the above dicarboxylic acids or esters thereof.  
  The polyformal copolymer can optionally contain other materials such as phosphorus and/or antimony to improve the flame retardance of articles prepared from the polyformal copolymer.  
  In addition, the polyformal copolymer can contain antioxidants, ultraviolet stabilizers, thermal stabilizers, nucleating agents, plasticizers, fillers, glass fibers, pigments lubricants and other additives.  
  To reduce the spinning temperature of the admixture of the polyformal and the polyester, a processing aid also may be blended with the polyformal and polyester.  
  The presence of synergists, such as phosphorus and- /or antimony, further improves the flame resistance of articles prepared from the admixture of the polyformal and the polyester.  
  In addition to antimony compounds and brominated additives, the articles prepared from the admixture of the polyformal and the polyester can contain antioxidants, ultraviolet stabilizers, thermal stabilizers, nucleating agents, plasticizers, fillers, glass fibers, pigments, lubricants and other additives.  
  In one particularly preferred embodiment of the invention the polyformal is blended with poly(tetramethylene terephthalate). In this embodiment, other additives can be added to the poly(tetramethylene terephthalate) such as antioxidants, pigments, fillers, plasticizers, and reinforcing agents such as glass fibers or asbestos. A composition of about 16 weight percent polyformal, about 5 weight percent antimony trioxide and about 20 weight percent glass fiber gives especially desirable results because objects molded of the composition are quite strong and pass even the most stringent flammability tests.  
  The polyformal copolymer of this invention can be prepared in accordance with several methods.  
  According to one method, the polyformal may be dry blended with the polyester and the blend subjected to melt extrusion and/0r melt spinning. During either of these operations, the hydroxyl-terminated polyformal can be caused to react with the polyester by glycolysis, thus producing the polyformal copolymer. If the inherentviscosity of the polyformal is lower than that of the initial polyester, the inherent viscosity of the polyformal copolymer will be less than that of the initial polyester. Although the precise conditions of time, temperature and pressure necessary to form the polyformal copolymer vary depending on the particular polyester, poly(ethylene terephthalate) and the polyformal will react to form the polyformal copolymer when held within a temperature range of 260 to 300C. for from 2 to 5 minutes at a pressure of 0.1 to 760 mm. Some polyesters such as poly(l,4-cyclohexylenedimethylene terephthalate) will react very little or not at all with the polyformal and remain essentially as an admixture with the polyester.  
  According to another method, the hydroxylterminated polyformal may be melt blended with polyester polymer or prepolymer and allowed to equilibrate at a temperature which is in the range of about 240-300C. and above the melting point of the polyester. The subsequent application of reduced pressure permits removal of glycol and formation of a higher molecular weight block polymer.  
  According to still another method, the polyformal may be charged to a reaction vessel containing the dialkyl ester of a dibasic acid, glycol, and conventional polyester catalyst and built into the polyester as it is being formed. The application of reduced pressure and elevated temperatures with subsequent removal of excess glycol gives high molecular weight block polymers of polyester and polyformal according to techniques {well known in the art.  
  The following examples are intended to illustrate but not limit the invention.  
  In this disclosure, the inherent viscosities are determined at 25C. in 60/40 phenol/tetrachloroethane at a concentration of 0.50 g./ 100 ml. All samples are vacuum dried at l 00C. overnight prior to spinning or molding.  
  The oxygen index test is described in MODERN PLASTICS, March 1970, p. 124.  
 EXAMPLE 1 This example describes the preparation ofthe brominated bisphenol A diethanol polyformal.  
  In a l,000-ml., three-neck flask fitted with a mechanical stirrer, Dean-Stark trap, and condenser are placed 400 g. (0.633 mole) of tetrabromobisphenol A diethanol and 460 ml. of benzene. The reaction mixture is heated at reflux for 2 hours during which time the tetrabromobisphenol A diethanol dissolves. The solution temperature is then decreased to 65C. and 20.6 g. (0.650 mole) of percent paraformaldehyde and 2.0 g. of p-toluenesulfonic acid are added. After the reaction mixture is allowed to stir at 65C. for 90 minutes, the temperature is increased to reflux and the water (11.4 ml., 0.633 mole) is azeotropically removed. This requires approximately 3 /2 hours. After the mixture is cooled to room temperature, 0.5 ml. of 15 M ammonium hydroxide is added with vigorous stirring to neutralize the catalyst. The slightly viscous benzene solution is then coagulated by slow addition to 8 liters of methanol. The resultant white powder is washed with 500 ml. of methanol and dried overnight at 50C. under a nitrogen sweep and a vacuum of 17 in. of mercury. The polymer has an inherent viscosity of 0.12 and a softening point of 80C.  
 EXAMPLE 2 This example describes the preparation of a fiber of a copolymer of a polyester and the brominated bisphenol A diethanol polyformal.  
  Granules of poly(ethylene terephthalate) having an inherent viscosity of 0.60 are dry blended with granules of tetrabromobisphenol A diethanol polyformal having an inherent viscosity of 0.15 to give a mixture containing 8 percent by weight of polyformal. Fibers are spun at 270C. The fibers are drawn in water at 68C. and then in superheated steam for an overall draw factor of 4.0. After being heatset in a relaxed state for minutes at 145C., the fibers have the following properties: 2.5 den./fil., 3.6 g./den. tenacity, 33 percent elongation, 44 g./den. elastic modulus, and a 234C. flow point at 0.2 g./den. load. A tube knitted from these fibers shows no yellowing after 40 hours exposure in a carbon-arc Fade-Ometer. The knit fiber also passes the Children&#39;s Sleepwear Test (DOC FF 3-71 The fibers in the knitted sample show no loss in bromine content after 10 laundry cycles in accordance with AATCC Text Method 61-1969, Number IIIA. Another sample shows no loss in bromine content after dry cleaning cycles in accordance with AATCC Test Method 132-1969. The knitted samples dye well and exhibit desirable light fastness.v  
  Analysis of the polymer of the fiber shows the polyester and polyformal have reacted to form a polyformal copolymer under the particular conditions of melt spinning. Under other conditions of time, temperature, and pressure the polyester and polyformal might not form the polyformal copolymer or only a portion of the polyester and polyformal might combine to form the polyformal copolymer. Long times and high temperatures tend to favor the formation of the polyformal copolymer.  
 EXAMPLE 3 This example describes the preparation of a molded object of an admixture of a polyester and the brominated bisphenol A diethanol polyformal.  
  Poly(tetramethylene terephthalate) having an inherent viscosity of 1.5 is placed in a large evaporating dish, and a solution of methylene chloride containing two antioxidants, Goodrite 3114 and dilauryl thiodipropionate (DLTDP), is added to the polyester. The mixture is slurried and the methylene chloride allowed to evapbars. The bars have an oxygen index of 27 as compared to 21 for the control poly(tetramethylene terephthalate). The bromine content of the bars does not decrease during aging for 1 month in an oven at C. The bars exhibit no discoloration during molding or during exposure to ultraviolet light in a carbon-arc Fade-Ometer for 40 hours.  
 EXAMPLE 4 This example describes the preparation of a fiber of an admixture of a polyester and the brominated bisphenol A diethanol polyformal.  
  Poly( 1 ,4-cyclohexylenedimethylene terephalate) having an inherent viscosity of 0.86 is dry blended with tetrabromobisphenol A diethanol polyformal (inherent viscosity 0.12) to give a mixture containing 10 percent by weight of polyformal. The blend is spun at 290C. to give white fibers. The fibers are drawn in water at 68C. and then in superheated steam for an overall draw factor of 3.8. After being heatset in a relaxed state at C. for 5 minutes, the fibers have the following properties: 3.2 den./fil., 2.7 g./den. tenacity, 21 percent elongation, 33 g./den. elastic modulus, and a 260C. flow point at 0.2 g./den. load. The fibers exhibit improved resistance to burning, resistance to yellowing during 40 hours in a carbon-arc Fade-Ometer, and no significant loss of bromine during 15 dry cleaning treatments.  
 EXAMPLE 5 This example describes the preparation of fibers of a copolymer of a polyester and the brominated bisphenol A diethanol polyformal.  
  A blend of the poly( ethylene terephthalate) used in Example 2 and 20 percent tetrabromobisphenol A diethanol polyformal is melt spun at 260C. into nondiscolored fibers. The drafted, heat-set fibers have the following properties: 2.4 den./fil., 3.4 g./den. tenacity, 21 percent elongation, 42 g./den. elastic modulus, 240C. flow point at 0.2 g./den. load. The fibers show further improved resistance to burning compared to the fibers in Example 2, no yellowing during 40 hours in a carbon-arc Fade-Ometer, and no significant loss of bromine during 15 dry cleaning treatments.  
 EXAMPLE 6 This example illustrates preparation of the polyformal copolymer.  
  Poly(ethylene terephthalate) powder with an inherent viscosity of 0.66 and tetrabromobisphenol A diethanol polyformal with an inherent viscosity of 0.09 (number average molecular weight 3800) are dried under vacuum at 100C. overnight. The dry polymers are mechanically blended together to give 12 percent by weight polyformal and extruded at 265C. with a 1% inch Modern Plastics Machinery single screw extruder. The resultant white poly(ethylene terephthalate)/polyformal pellets have an inherent viscosity of 0.53. Gel permeation chromatography indicates equilibration of the polyester and polyformal to give the polyformal copolymer.  
 EXAMPLE 7 This example illustrates that the polyformal retains its integrity and is present as a block after the polyformal is melt extruded.  
  29 grams of the copolymer from Example 6 are placed in 100 ml. of 1N KOH in ethanol and the mixture allowed to stir for 30 minutes at reflux. The resultant hydrolyzed polymer is then subjected to extraction in the following manner: The solution is filtered through a 350-ml. medium fritted glass funnel and the white residue air dried overnight. The residue is then added to 300 ml. of distilled water and stirred for 30 minutes during which time most of the residue dissolves. The aqueous solution containing small amounts of white solid is then extracted with 300 ml. of benzene. The benzene solution is washed once with distilled water, dried, and the benzene removed by evaporation. The clear, glassy residue is then analyzed by nuclear magnetic resonance spectroscopy and shown to be tetrabromobisphenol A diethanol polyformal. The polymer has an inherent viscosity of 0.09, which is identical to that of the polyformal initially blended with poly- (ethylene terephthalate).  
 EXAMPLE 8 This example illustrates that the polyformal copolymer retains its integrity and is present as a block under polycondensation reaction conditions.  
  Ninety-seven grams of dimethyl terephthalate, 62 g. of ethylene glycol, and 8 g. of tetrabromobisphenol A diethanol polyformal (I.V. 0.09) are heated with continuous stirring under a nitrogen atmosphere for 1 hour at 200C. in the presence of a polyester catalyst mixture consisting of 14 ppm. Mg, 49 ppm. Mn, ppm. Ti, and 247 ppm. Sb salts. The temperature is raised to 225C. for an additional hour. The temperature is then increased to 270C., and 88 ppm. phosphorus as the acid phosphate is added. A vacuum is gradually applied to the reaction mixture and held for 1 hour at 0.1 mm. Hg. The inherent viscosity of the resultant polymer is 0.60. The polymer is hydrolyzed and analyzed in a manner identical to Example 7. The yield of polyformal is 70 percent with an inherent viscosity of 0.07.  
 EXAMPLE 9 275C. at 20C./min., then cooled at a rate of 20C./min.  
  Listed below are different scanning calorimetry (DSC) results for these polymers.  
 Sample Heating Cooling Tg(C.) Tc&#39;(C.) Tm(C.) Tc(C.)  
 Polyformal copolymer (4% Br) 81 139 253 221 Diethanol copolymer -Continued Sample Heating Cooling Tg(C.) TC&#39;(C.) Tc(C.)  
 Tm(C.)  
 Tm Crystalline melting point Tg Glass transition temperature Tc Crystallization temperature on heating Tc Crystallization temperature on cooling From the above data it can be observed that the polyformal copolymer has an appreciably lower Tc on heating (crystallizes more readily) and a higher Tc on cooling (crystallizes sooner) than the diethanol polymer. Because the diethanol polymer crystallizes more slowly than the polyformal copolymer, longer heatsetting times will be required in processing. Also, because of the slower crystallization rate of the diethanol copolymer, more shrinkage is produced during heatsetting of fibers; and consequently, orientation of the fiber is lower, giving lower tenacity.  
 EXAMPLE 10 This example describes the high crystallization temperature upon cooling for a polyformal admixture as compared to the diethanol polymer.  
  Using procedures similar to those of Examples 6 and 13, a polyformal copolymer and a diethanol polymer are prepared using dimethyl terephthalate and 1,4- butanediol to form the polyester component.  
  The polymers are heated under nitrogen about 20C. above their melting points to remove previous thermal history, rapidly cooled, then heated back to 245C. at 20C./min., then cooled at a rate of 20C./min. DSC results for these polymers are presented below.  
 Sample Heating Cooling Tc&#39;(C.) Tm(C.) Tc(C.)  
 Polyformal admixture (6.8% Br) 222 187 Diethanol copolymer (6.8% Br) 68 212 166 Tm Crystalline melting point Tc Crystallization temperature on heating Tc Crystallization temperature on cooling In spite of the quenching treatments, advantageously the polyformal admixture apparently had crystallized completely since it did not crystallize further (no lo) on the subsequent heating step as did the copolyester. Also, on the following cooling step, the diethanol polymer did not crystallize until an appreciable lower temperature had been reached.  
 EXAMPLE 1 1 Sample Heating Cooling Tg(C.) Tc (C.) Tm(C.) TC(C.)  
 Polyformal admixture Br) 85 145 270 206 Diethanol copolymer Tm Crystalline melting point Tg Glass transition temperature Tc Crystallization temperature on heating To Crystallization temperature on cooling EXAMPLE 12 230C. and a vacuum of 0.5 mm. applied for 45 minutes. The temperature is again increased to 275C. for an additional 5 minutes. The resulting low melt viscosity polymer has an inherent viscosity of 0.17. After grinding to pass a 3-mm. screen, the prepolymer is subjected to solid phase polymerization under 0.1 mm. vacuum for 1 hour at 180C., 1 hour at 210C. and 14 hours at 230C. The resultant off-white diethanol polymer has an inherent viscosity of 0.51.  
 The diethanol polymer is then spun into fiber,-  
 drafted, and heatset as in Example 2. Knit fabrics of this fiber contain 7.7 weight percent bromine by analysis and failed the Children&#39;s Sleepwear Test (DOC FF 3-71) three out of six times when a flat-lock seam is sewed with a silicon-lubricated thread.  
  A knit fabric of the polyformal copolymer of this invention prepared as described in Example 2 and containing only 4.0 percent bromine passes the above Childrens Sleepwear Test out of 10 times.  
 EXAMPLE 13 This example illustrates the preparation of fibers from the diethanol polymer and the comparative flammability of fibers from a polyformal copolymer and fibers from the diethanol polymer.  
 259 g. (1.35 moles) dimethyl terephthalate 167 g. (2.70 moles) ethylene glycol 22.1 g. (0.035 mole) tetrabromobisphenol A diethanol The above ingredients and a standard Ti, Sb, Mn poly(ethylene terephthalate) catalyst system are placed in a 1,000-ml. flask equipped with a stirrer, a short distillation column and an inlet for nitrogen. The mixture is stirred at 195C. in a nitrogen atmosphere until the ester interchange is completed (90 minutes). The temperature is then increased to 230C. and held for 15 minutes. The temperature is again increased to 275C. and a vacuum of 0.5 mm. is applied for 45 minutes. A pale yellow polymer with an inherent viscosity of 0.51 is obtained.  
  Children&#39;s Sleepwear Test (Federal Government Standard DOC FF 3-71) Children&#39;s Sleepwear Test&#34; Failures/Samples Avg. RFT, Fiber composition l.V. Tested Sec.  
 Diethanol polymer (4% Br) .47 3/8 10.4 Polyformal copolymer Samgles (5-6 oz./ycl.) were seamed (flat-lock seams) with silicone lubricated Pillage residual flame time.  
  As noted above, the samples of the polyformal copolymer fiber pass the test 10 out of 10 times while the samples of the diethanol polymer fiber pass the test only 5 out of 8 times.  
  The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.  
 We claim:  
  1. A moldable or fiber-forming composition consisting essentially of an admixture of A. based on the weight of the composition, from to 98 weight percent polyester, said polyester being the condensation product of at least one aliphatic or alicyclic diol containing 2 to 40 carbon atoms and at least one aliphatic, alicyclic or aromatic dicarboxylic acid or ester thereof having 3 to 40 carbon atoms and B. based on the weight of the composition, from 25 to 2 weight percent of a polymer having an inherent viscosity in the range of 0.03 to 1.0 consisting essentially of recurring units of the structure where n is l or 2, said inherent viscosity being determined at 25C in 60/40 phenol/tetra chloro ethane at a concentration of 0.50 g./ 100 m1.  
  2. The composition of claim 1 wherein (A) is from to 92 weight percent and (B) is from 20 to 8 weight percent.  
  3. The composition of claim 2 wherein n is 2 and both bromine atoms are in the ortho position with regard to the oxygen atoms.  
  4. The composition of claim 3 wherein the polyester is poly(ethylene terephthalate), poly(tetramethylene terephthalate) or poly( l ,4-cyclohexylenedimethylene terephthalate).  
  5. The composition of claim 4 wherein the polyester is poly(tetramethylene terephthalate). 6. A textile fiber consisting essentially of an admixture of 4. based on the weight of the admixture, from 75 to 98 weight percent polyester, said polyester being where n is l or 2, said inherent viscosity being deter- -mined at 25C in 60/40 phenol/tetra chloro ethane at 55 a concentration of 0.50 g./l ml.  
 where n is l or 2, said inherent viscosity being determined at 25C in 60/40 phenol/tetra chloro ethane at a concentration of 0.50 g./ 100 ml.  
 7. The fiber of claim 6 wherein (A) is from so to 92 weight percent and (B) is from 20 to 8 weight percent.  
 8. The fiber of claim 7 wherein n is 2 and both bromine atoms are in the othro position with regard to the oxygen atom.  
 9. A copolymer having an inherent viscosity of at least 0.35 consisting essentially of A. based on the weight of the composition, from 75 to 98 weight percent blocks of a polyester, said polyester being the condensation product of at Q-CHz-CHz-O least one aliphatic or alicyclic diol containing 2 to carbon atoms and at least one aliphatic, alicyclic or aromatic dicarboxylic acid or ester thereof 40 having 3 to 40 carbon atoms, and  
 B. based on the weight of the composition, from 25 to 2 weight percent blocks of a polyformal having an inherent viscosity in the range of 0.03 to 1.0 consisting essentially of recurring units of the structure 10. The copolymer of claim 9 wherein (A) is from 80 to 92 weight percent and (B) is from 20 to 8 weight percent.  
  11. The copolymer of claim 10 wherein n is 2 and both bromine atoms are in the ortho position with regard to the oxygen atom.  
  12. The copolymer of claim 11 wherein the polyester is poly(ethylene terephthalate) or poly(tetramethylene terephthalate).  
 CH2 O CH2 13. A textile fiber formed from a copolymer having an inherent viscosity of at least 0.35, the copolymer consisting essentially of A. based on the Weight of the copolymer, from to 98 weight percent blocks of a polyester, said polyester being the condensation product of at least one aliphatic or alicyclic diol containing 2 to 40 carbon atoms and at least one aliphatic, alicyclic or aromatic dicarboxylic acid or ester thereof having 3 to 40 carbon atoms, and  
 B. based on the weight of the copolymer, from 25 to 2 weight percent blocks of a polyformal having an inherent viscosity in the range of 0.03 to 1.0 consisting essentially of recurring units of the structure q), -o k 0 CH2 CH2 o Cla- Q. Br Ha r 0 0 CH2 CH2 0 CH2 ter is poly(ethylene terephthalate). II S =1