CA1081896A - Copolyesters derived from ethoxylated 3,5-dibromo-4- hydroxybenzoic acid - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Flame retardant high molecular weight linear copolyesters are obtained from the condensation product of (a) an aliphatic or alicyclic diol having from 2 to 10 carbon atoms, (b) an aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 12 carbon atoms or lower alkyl esters thereof, and (c) ethoxyl-ated brominated hydroxybenzoic acid of the formula

Description

This invention relates to flame retardant copolyesters.
The use of hydroxybenzo~c acids for the preparation of polyesters and copolyesters is known. For example, U.S. Patent 2,600,376 issued June 17, 1952 to John R. Caldwell shows the preparation of polyesters of m- and p-hydroxybenzoic acid. Copoly-esters are similarly obtained employing hydroxyaromatic dibasic acids, e.g.

2-hydroxyterephthalic acid, in ~S.. Patent 3,887,468 issued June 3, 1975 to Donald T. Bray 6-Oxyethoxy vanillic acid is used for the production of copolyesters in U.S.
10 Patent 3,056,761 issued October 2, 1962 to Wolfgang Grichl and Hans Luckert and 3,288,755 issued November 29, 1966 to W. Griehl et al.
It is also well known to use halogenated (either chlorine or bromine) reactants for the preparation of polyesters and copolyesters having improved flame retardant properties. Numerous halogenated compounds containing hydroxyl and/or carboxyl functionality have been suggested for this purpose. U.S.

. , Patent 3,752,867 issued August 14, 1973 to Yves Merck and Jean Marie Vion ~
for example, discloses fireproof unsaturated polyester resins containing halo- , genated salicyclic acid. Fire-resistant unsaturated polyesters derived from bromine-containing compounds, e.g. 3,5-dibromo-4-hydroxybenzoic acid are also 20 ~disclosed in Japanese Patent 74 11,875.
Even though it is recognized that brominated hydroxy and carboxy compounds are effective flame ret~rdants for polyesters there are serious draw-backs~ associated with the use of such brominated derivatives in the prepara-tion of high molecular weight polyesters useful as fibers and filaments because of the high polymerization temperatures (generally in an excess of 250C and often as high as 320C) required. At these high temperatures most brominated ma~terials tend to decompose and thus impart undesirable discoloration and, in some instances where the decomposition is pronounced, significantly detract from the overall physical properties of the polymer. Brominated compounds have ~ .
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~OB~896 therefore typic~lly been limited to use in the preparation of unsaturated poly-ester resins where much lower reaction temperatures (typically less than 200C) are encountered.
Quite unexpectedly it has been discovered that certain ethoxylated brominated derivatives of p-hydroxybenzoic acid are useful for the preparation of high molecular weight copolyesters. The resulting flame retardant copoly-esters are useful in the formation of fibers and filaments in addition to hav-ing other thermoplastic applications. These brominated derivatives do not in-terfere with polymer formation so that high molecular weight products having inherent viscosities of 0.4 and higher and readily obtained. The resulting copolyesters also exhibit a high degree of thermal and ultraviolet stability.
Thus, the present invention relates to the use of ehtoxylated bromin-ated p-hydroxyben~oic acid for the preparation of high molecular weight co-polyesters. The resulting thermoplastic copolyester compositions are suitable for use as fibers, filaments and for numerous other applications and, in addition to being flame retardant, have excellent physical properties and ex-hibit a high degree of thermal stability and ultraviolet stability.
By one aspect of this invention, a flame retardant copolyester is provided having improved thermal and ultra-violet stability comprising the condensation product of (a) an aliphatic or alicyclic diol having from 2 to 10 carbon atoms, (b) an aliphatic, alicyclic or aromatic dicarboxylic acid hav-ing from 4 to 12 carbon atoms or lower alkyl esters thereof, and (c) ethoxyl-ated brominated hydroxybenzoic acid of the formula ~3r HO~CH2al2o)n-~-c ~OCH2Q12~mOH

~r where n and m are integers from 1 to 3, the etho~lated brominated hydrox~ben-; * - 3 ~: , . : ..: ..
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, _ zoic acid comprising 1 to 30% by weight of the copolyester composition.
By one variant, the copolyester is a high molecular weight crystal-line linear polymer having an inherent viscosity greater than 0.4.
By a further variant (c) is diethoxylated 3,5-dibromo-4-hydroxyben-zoic acid having n = m = 1.
By yet another variant, (b) is terephthalic acid or dimethyltere-phthalate and (c) constitutes 10 to 25% by weight of the copolyester composi-tion.
By other variants, (a) may be ethylene glycoll,4-butanediol, or 1,4-cyclohexanedimethanol.
By a preferred variant, 3,5-dibromo-4-hydroxybenzoic acid diethoxyl-ate of the formula HO H2CHzO>~C OCHzCHzOH

is preferred for the production of useful copolyesters. The ethoxylated brom-inated p-hydroxybenzoic acids are obtained using known reaction techniques.
Conventional ethoxylation and bromination procedures can be employed for their preparation.
The copolyesters contain from 1 to 30% by weight of an ethoxylated brominated p-hydroxybenzoic acid corresponding to the structural formula Br HO~ CH a~ 0)~0 A` _4_ .
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wherein n and m are integers from 1 to 3. Copolyesters obtained with diethoxyl-ated 3,5-dibromo-4-hydroxybenzoic acid, i.e. when n = m = 1, form an especially preferred embodiment of this invention. The ethoxylated dibrominated hydroxy-benzoic acid is readlly reacted into the polyester and capable of withstanding temperatures encountered during final stages of the polymerization so that the resulting copolyester products have good color and physical properties. The ethoxylated brominated hydroxybenzoic acid may be added to the polymerizer as such or prepolymerized and the prepolymer used.
As noted above, the copolyesters will generally contain 1 to 30 weight percent of the ethoxylated brominated material; however, polymers having good physical properties and color and which exhibit a high degree of thermal and ultra-violet stability are obtained when 10 to 25 weight percent, based on the total copolyester composition, ethoxylated brominated p-hydroxybenzoic acid is present. Especially useful copolyesters contain from 10 to 25 weight percent of the 3,5-dibromo-4-hydroxybenzoic diethoxylate.
The ethoxylated brominated hydroxybenzoic acid may be used as such or can be polymerized and the prepolymer used for the preparation of the co-polyester. The prepolymer will contain repeating units of the type ~ ~ ~ OCHzCH
Br where x indicates the number of repeating units and generally ranges between 2 and 200 and, more generally, between 5 and 100. In general, the prepolymer will be treated and charged in the same manner as the monomer. Under the poly-merization conditions the prepolymer generally depolymerizes so that moieties identical to those obtained using the monomer are randomly inserted in the .

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The ethoxylated brominated p-hydrocybenzoic acid or prepolymer can be reacted with a wide variety of aliphatic and alicyclic diols and aliphatic, alicyclic and aromatic dicarboxylic acids or esters to obtain useful high molecular weight thermoplastic copolyesters. Also, it is possible to react the ethoxylated brominated hydroxybenzoic acid or prepolymer thereof with a prepolymer of the diol and dicarboxylic acid, e.g. bis(2-hydroxyethyl)tere-phthalate.
In general, the useful glycols include the aliphatic (branched or straight chain) or alicyclic diols corresponding to the general formula HO-R-OH where R is a bivalent radical containing 2 to 10 carbon atoms. Useful diols include but are not limited to ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, l,10-decanediol, 1,4-cyclohexanedimethanol and the like. Useful dicarboxylic acids and their lower alkyl (Cl-C4) esters include aliphatic (branched or straight-chain), alicyclic and aromatic dicarboxylic acids containing from 4 to 12 carbon atoms and their esters. Such acids include, but are not limited to, terephthalic acid, isophthalic acid, adipic acid, sebacic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, cyclohexanedicarboxylic acid, and the like. Methyl, ethyl, isopropyl and butyl esters of these acids can also be employed for the copolyester preparation. For example, terephthalic acid or dimethyl terephthalate can be used for the preparation of essentially identical linear copolyester products with ethylene glycol, 1,4-butanediol or 1,4-cyclohexanedimethanol and 3,5-dibromo-4-hydroxybenzoic acid diethoxylate.
Mixtures of two or more diols or dicarboxylic acids (esters) can also be em-ployed.
The present invention has particular advantage for the preparation of linear high molecular weight thermop]astic copolyesters ob~ained by the A~ -6 -108~896 ::
reaction of the ethoxylated brominated hydroxybenzoic acid, a diol selected -from the group consisting of ethylene glycol, 1,4-butanediol and 1,4-cyclo-hexanedimethanol and terephthalic acid or a lower alkyl ester thereof. Par-ticularly useful compositions include ethylene glycol/terephthalic acid (ester)/3,5-dibromo-4-hydroxybenzoic acid diethoxylate copolyesters; 1,4-cyclo- -hexanedimethanol/terephthalic acid (ester)/3,5-dibromo-4-hydroxybenzoic acid diethoxylate copolyesters; and 1,4-butanediol/terephthalic acid (ester)t3,5-dibromo-4-hydroxybenzoic acid diethoxylate copolyester. These copolyesters are particularly important for use as engineering plastics and as fibers and filaments and have acceptable physical properties, color, fire resistance, thermal stability and ultraviolet stability. Preferred copolyester composi-tions of this invention are crystalline linear polymers which can be formed into fibers which have a high melt point, tensile strength, elongation and elastic recovery.
Small amounts of other monomers and/or additives can be incorporated i~; into the copolyesters of aspects of this invention to further enhance their - properties. To improve the disperse dyeability, small amounts of dibasic acids e.g. adipic acid, azelaic acid or dimer acid may also be included.
Sulfonated isophathalic acld may be included to improve basic dyeing proper-ties of the copolyester. to enhance the flame retardant properties other brominated materials, e.g. brominated ethoxylated bisphenol A and other aro-matic brominated diols or diacids, can be included in the reactant charge and incorporated into the copolyester. Antimony oxide or various phosphorus-: :

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containing compounds (e.g. triphenyl and tricresyl phosphate) are also useful additi~es for this purpose. Antimony oxide in amounts up to one gram atom per three gTam atoms of bromine have been found to enhance the self-extinguishing properties conferred by the ethoxylated brominated p-hydroxy-benzoic acid. The amounts of such reactants and additives will generally range from 0.1 to 10~ by ~eight of the copolyester and, more preferabl~, constitute 0.3 to 4~ by ~eight .
Conventional polymerization procedures are used for the production of these copolyesters to react the brominated ethoxylated compound ~ith the diol and diacid or its ester. The various procedures employed as well as reaction conditions and catalysts are de$cribed in the art. The pol~erization can be conducted as a batch or semi-continuous process and the reactants may be ¦ charged as such or prepol~mers employed. 3,5-Dibromo-4-hydroxybenzoic acid ethox~late or a prepolymer thereof may be added to the polymerizer at the outset of the reaction or at some intermediate stage but before the finishing step. ~lumerous modifications of the process are possible including ~ariation of the reactants, catalyst, reaction temperature and pressure, ratio of reactants, manner in which the reactants are charged, physical arrangement of the equipment and the like, as will be evident to those s~illed in the art.

The following examples illustrate various aspects of the invention more fully. In these examples, all parts and percentages are reported on a weight , basis unless otherwise indicated.

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` 108~896 EX~LE I
Preparation of 3 5-dibromo-4-hydroxybenzoic acid diethoxylate: One-hundred and thirty-eight parts p-h~drox~benzoic acid was combined with 75 parts glacial acetic acid and heated on a steam bath at 80C with stirrin~
l.hen solution ~as complete 120 parts bromine ~as added drop~.~ise over a period of `~ t~o hours. The reaction.mixture ~-as then cooled and filtered and the solid product.~.ashed ~ith ~.ater until the filtrate ~.as neutral. A 93~ yield of 3 5-dibromo-4-hydroxybenzoic acid (acid value -l 378; neutral equivalent 149) melting at 270-272C with gas evolution ~.as 101 obtained.

Six parts of the 3 5-dibromo-p-hydroxybenzoic acid ~as combined .ith 34 parts ethyl acetate and 0.3 wt. % triethylamine catalyst in a stirred autoclave. The system was purged several times by applying a vacuum to the s)~stem and then breaking ~Yith dl~ nitrogen. The reactor and its contents l~ere then heated to about s5C and ethylene oxide addition begun.
The ethylene oxide ~as charged incrementally in amounts sufficient to achieve a pressure of 25 psig (maximum pressure developed ~as 30 psig). As the pressu~e dropped additional ethylene oxide ~.as charged until 1.95 parts (slight excess due to loss during sampling) e~hylene oxide had been char~ed. lYhen the acid value of the reaction mixture reached 1.0 ~total reaction time 30 hours) the reaction l~as terminated by cooling and venting unreacted ethylene oxide. Upon standing overnight one-half the theoretical amount of the diethoxylate crystallized. This product melted at 106-107C and had zero acid value with a hydroxyl number of 290.
The structure ~as confirmed b)~ nuclear ma~etic resonance spectroscopy.
B~ removing approximately one-half of the ethyl acetate originally present from the mother liquor additional product ~as obtained so that the total yield of 3 5-dibromo-4-hydroxybenzoic acid diethox)~late ~s approximately 90~. .

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~081896 EXA~LE II
~ o prepare a copolyester, 2000 grams dimethyl terephthalate and 1400 gra~s eth)lene gl~col ~ere combined l;ith 0.3 gram zinc ~cetate and reacted at 200C to prepare a prepol)~er, bis(2-hydrox)eth~l)terephtha1ate. After the t1~eoretical amount of methanol (836 mls.) ~;as remo~ed from the reaction mi~tu1-e (about 5 hours) the rcaction ias tenninated by deactivating the catal\st b~ the addition of O.O~eD trisnonylphenyl phosp~ate. The prepol)lTler ~;as reco~ered for subsequent use.

! Fifty grams of the bis(2-hydrox~eth~l)terephthalate prepol)~mer ~.as combined with 14 grams 3,5-dibromo-4-h~drox~benzoic acid diethoxylate and 25 milligrams antimony trioxide catalyst. The reactants l;ere Jnelted under a nitrogen atmosphere by heating at 225C. The te~perature ~.as increased to 290C and a vacuum applied to the system at 275C.
After one hour ~-~hen the temperature ~as 285C the pressure ~-as reduced to 0.25 mmHg and the polymerization completed ~total polyTnerization time 1 3/4 hours). The solid copolyester product containing lO ~t. percent bromine ~as transparent and had an inherent viscosity of 0.44 (determined by dissolving ~ O.l gram sample of the polymer in 20 grams solvent - a mixtur~
of 40 parts s-tetrachloroethane and 60 parts phenol). Inherent viscosit [~3inh is an approximation of intrinsic viscosity, I~lhich is in turn a parameter of average molecular lYeight. It is defined as the natural logarithm of the relative viscosity (flo~Y time of polymer solution/flol~ time of equal volume of solvent) divided by the polymer concentration in grams/dl. The dimensions of ~inh are dl/g. Recommended AS1~1 nomenclature is logarithmic viscosity number. Intr-nsic viscosity ~] or limiting vis number is obt~ined by determining l~]inh at several concentrations, usuall~ 0.05-0.5 g/dl, and extrapolating to zero cgncentration. For most polymer-solvent systems [~]
~1.05-1.1 [~]inhJ and common practice equates [~]inh c=0 5 t~ith [~]. An aver2ge molecular leight is obtained`from the expression [~] = K' ~ a ~ ere K' and a are constants obtained from log-log plots of [~] against molecular ~.eight for kno~n polymers in solution. Compilations of K' and a for various -¦ poI~mer-solvent s~-stems are ~idely a~ailable.

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Fibers and filaments of copolyesters containing the 3,5-dibromo-4-hydroxybenzoic acid diethoxylate are obtained using conventional procedures, e.g. melt extrusion. These copolyester fibers can be orientated by drawing and they can be heat set by heating the elongated fiber. The fibers have ex-cellent physical properties and can be employed in conventional applications and can be used in any state or aggregation such as monofilaments, flocks, yarns, tows or cords. They are readily knitted or woven and can be used in textile applications by themselves or in blends containing 25-65% by weight of the copolyester and 75-35% by weight of another fiber e.g. cotton, nylon or 10another polyester. Extremely useful blends are obtained when the copolyesters of this invention are blended with cotton. Blends with fibers having elastic properties to obtain stretch fabrics can also be prepared.

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10818g6 ¦ EXh ~LE III
Employing a procedure similar to that described in Example II, 37 I grams bis(2-hydroxyethyl)terephthalate prepolymer and 3.8 grams 3,5-dibromo-¦ 4-hydro.~ybenzoic acid dietho.~ylate ~ere polymerized using 40 milligrams S ¦ antimony triacetate catal~st. The resulting copol~ester product contained ¦ 5.5~ bromine and had an inherent viscosity of 0.53. The copolyester had good clarity l~ith essentially no discoloration. The product had good flame retardant properties, thermal stability and ultraviolet stability.

- EXA~LE n~
To a glass pol~merization tube ~ere charged 12.7 grams bis(2-hydroxy-ethyl)terephthalate prepolymer, 25 milligrams antimony trioxide and 5 mls.
ethylene glycol. The ube and its contents ~ere heated in a methyl salicylate bath and 38.4 grams 3,5-dibromo-4-hydroxybenzoic acid diethoxylate then added and heating continued in a diethylene glycol bath. A vac w m ~as then applied 15 and heating continued for an hour~ The highly viscous polymer melt had good color and the copolyester contained 36.5~ by weight bromine upon analysis.
, ~: EXAMPT.F V
A prepolymer of the dietho~ylat~e of Exampl~ I was prepared by polymerizing 100 grams 3,5-dibromo-4-hydroxybenzoic acid diethoxylate using 20 S0 milligrams antimony trioxide catalyst. Polymerization was accomplished by heating the reaction mixture (maximum temperature 248DC) for `r ~ 1 1/2 .
hours. The resulting opaque solid prepolymer contained 45.6% bromine and had a melting point of 259C as determined by differential scanning calorimetr~. A copolyester ~.as prepared by combining the pTepolymer (7 25 grams) with 50 grams bis(2-hydroxyethyl)terephthalate prepol)~er, 10 mls ethylene glycol and 25 milligrams antimony trioxide. The polymerization ~.as conducted for 4 hours at a m~ximum temperature of 274~C. A high molecular ~eight copolyester ~as obtained as evidenced by shattering of the pol)merization tube upon cooling the highly viscous pol~er melt. The 30 co~ol~-ester contained 6.6~ bromine, ha2 good flame retardant properties and exhibited a high degree of thermal and u~traviolet stability.

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To demonstrate the utllity of the products of aspects of this inven-tion copolyesters as prepared above were evaluated for their flammability, thermal stability and stability upon exposure to ultraviolet radiation. Ther-mal stabilities of !
the copolyester products of Examples II and III were determined by therm~l ~ravimetric analysis by heating a sample of each copol~es~er in a nitrogen atmosphere ~ith a flol~ of 70 mls nitrogen per minute ~hile the temperature - was increased at a rate of 10C per minute and observing the temperature at ~hich initial decomposition occurred and thereafter measuring the ~.eight loss due to decomposition as a function of time. These copolyesters had excellent thermal stability. Initial decomposition of the copolyesteTs l~as not observed until the temperature reached 350C.

Flame retardance ~as determined with a General Electric Flammability Index Tester in accordance with the oxygen index test method (ASTM D 2863-70).
The ox~gen index is the minimum concentration of o~ygen in a mixture of ox~;gen and nitrogen that l~ill support combustion of a sample. The higher the ox)-gen index the better the flame retardancy. Sa~ples were prepared by placing 5.5 grams of the copolyester and a 1 x 8 cm. fiberglass strip in a heavy aluminum foil moldand placing on a hot plate until the copolyester ~as melted. After cooling the test specimens were clamped in an upright position at the bottom of a vertical glass chimney and ignited at the upper end with a flame. The,~oxygen/nitrogen mixture was passed through the chimney and if the sample continued to burn the ox)~gen content of the mixture ~as reduced and the process repeated unt~l the mixture no longer supported combustion. The oxygen index rating l.~as then calculated as follows:
(2 Volume) x 100 (2 Volume) ~ ~N2 ~Jolume) A 13 _ r ' ' ~ . ' ' ---` 1081896 ¦ The a~erage of four samples ~as reported. l~'hereas the oxygen indcx of polyethylene terephthalate l.~as 21.1, a copolyester (6.7% Br) obtained in accordance'~.~ith this invention from 3,5-dibromo-4-hydrox)~benzoic acid diethox~late had an oxvgen index of 23.8. Similar improvement in flame retardance is also obtained ~ith polybutylene terephthalate copol~esters having a comparable bromine content. The addition of 0.5 to 2% b~ eight antimony oxide to the copolyesters derived from the ethoxylated brominated h~drox~-benzoic acid, terephthalic acid (or methyl ester) and ethylene gl~col or l,4-butanediol further e3~ances the flame retardant properties of the thel~oplastic products. `

Ultra~iolet stabilit)~;as determined by finely pul~erizing the col-oly-ester and depositing the ~-ol;dcr on glass plates ~;ihose surface ~;as coated ~it~
a thin la~er of non-~ellol~in~ a~esi~e binder. The g]ass plates ~ere then e~posed to ultra~iolet radiation for 50 hours in a Fade-O-~eter. At thc cnd of this period the samples ~;ere visuall~ examined for discoloration and assigTned visual index numbers from 1 to 5 ~higher numbers indicting increased discoloration). Copolyester products ~6.5 l~t. % Br) obtained in accordance ~ith this invention from both the'3,5-dibromo-4-hydroxybenzoic acid dietho~;late monomer and a prepol~mer thereof ~Example V) had index , ratings of 2. This compared favorably l.ith the pol~eth~lene terephthalate control containing no flame retardant additive l~hich had an index ratin~ of 1. Copolyesters having the same t~eight percent bromine but obtained using other aromatic brominated flame retardant add;tives, namely 2~5-dibromoterephthalic acid and 1,4-di(2-hydroxyethoxy)-2,5-dibromoben~ene shoied appreciably more discoloration and ~;ere assigned index ratings of 4.
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Copolyesters obtained by aspects of the present invention may be treated in accordance with known procedures for working, handling and modifying polyester thermoplastic materials. While the copolyesters may be used with-out further compounding, known additives e.g. stabilizers, lubricants, plasti-cizers, delusterants, dyes, pigments, antistatic agents and the like may be incorporated therein. These copolyesters may also be blended with other poly-mers and the like. Additives may be incorporated using conventional mixing equipment e.g. a Banbury mixer, revolving drum or sigma blade mixer and they generally do not require special processing or handling. They may be mixed with the copolyester in dry form or dispersed or dissolved in suitable solvents.In some instances, it may be advantageous to prepare a master batch o~ the var-ious additives for blending with the copolyester. The incorporation of additives and modifying agents is most advantageously accomplished by melt blending. In this way the additives are readily and uniformly dispersed in the copolyester.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flame retardant copolyester having improved thermal and ultra-violet stability comprising the condensation product of (a) an aliphatic or alicyclic diol having from 2 to 10 carbon atoms, (b) an aliphatic, alicyclic or aromatic dicarboxylic acid having from 4 to 12 carbon atoms or lower alkyl esters thereof, and (c) ethoxylated brominated hydroxybenzoic acid of the formula where n and m are integers from 1 to 3, said ethoxylated brominated hydroxybenzoic acid comprising 1 to 30% by weight of the copolyester composition.

2. The copolyester of Claim 1 in the form of a high molecular weight crystalline linear polymer having an inherent viscosity greater than 0.4.

3. The copolyester of Claim 1 wherein (c) is diethoxylated 3,5-dibromo-4-hydroxybenzoic acid having n = m = 1.

4. The copolyester of Claim 3 wherein (b) is terephthalic acid or dimethylterephthalate and (c) constitutes 10 to 25% by weight of the copoly-ester composition.

5. The copolyester of Claim 4 wherein (a) is ethylene glycol.

6. The copolyester of Claim 4 wherein (a) is 1,4-butanediol.

7. The copolyester of Claim 4 wherein (a) is 1,4-cyclohexanedi-methanol.