CA1131846A

CA1131846A - Copolyetherester based on ethylene oxide-capped poly(propylene oxide) glycol and branching agent

Info

Publication number: CA1131846A
Application number: CA348,362A
Authority: CA
Inventors: Guenther K. Hoeschele
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1979-03-28
Filing date: 1980-03-25
Publication date: 1982-09-14
Also published as: BR8001749A; DE3011561A1; GB2048907A; NL182731B; ES490018A0; SE8002380L; FR2452504A1; ES8106165A1; JPS63178132A; JPH0343304B2; SE440785B; KR830002015B1; KR830002005A; NL182731C; AU522486B2; NL8001817A; JPH0115532B2; JPS5728153A; GB2048907B; JPS55147546A

Abstract

ABSTRACT OF THE DISCLOSURE
A copolyetherester composition is derived from terephthalic acid or ester forming equivalents thereof, 1,4-butanediol, an ethylene oxide-capped poly(propylene oxide) glycol and a branching agent having a functionality of 3-6. The ethylene oxide-capped poly(propylene oxide) glycol has an ethylene oxide content of from about 15-35 weight percent and a number average molecular weight ranging from about 1500-2800. The branching agent is present in the copolyetherester in a concentration of from about 1.5-6.0 equivalents per 100 moles of terephthalic acid or ester forming equivalent thereof. The copolyetherester composition contains from about 25-48 weight percent buty-lene terephthalate units and has a melt index at 230°C of less than about 50 grams per 10 minutes. The copolyether-ester compositions can be injection moled or extruded into various shaped articles, e.g., hose, with ease and exhibit good physical properties, e.g., good low temperature properties and high strength.

Description

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TITLE
Copolyetherester Based on Ethylene Oxide-Capped ~y(propylene o _de) Glycol and Branching Agent B~CKGROUN~ O~ 'rHE I~ENTION
Thermoplastic copolyetheresters can be des-cribed a.s copolymers consisting of recurring long chain and short chain ester units joined through ester linkages. The long chain ester units are formed by esterification of a dicarboxylic acid with a polyether glycol, the short chain ester uni-ts by esterification of a dicarboxylic acid with a low molecular weight dlol.
Relatively soft copolyekheresters (hardness <40D) based on poly(tetramethylene oxide) glycol (PTMEG) in which butylene terephthalate is the principal short chain ester unit are known. These polymers have good physical properties but do not process as well as desired in high-speed injection molding or extrusion operations due to their rate of hardening. One can improve hardening rates of the polymer by using during its preparation higher molecular weight PTMEG but this results in impairment of low temperature properties of the polymer. Replacing PTMEG with poly(propylene oxide) glycol (PPG) or poly(ethylene oxide) glycol does not yield acceptable polymer products because of the low reactivity of the foxmer and the excessive water sensitivity of the lattex. In the case of PPG, phasing during the melt condensation (inhomogeneity of the polymerization mass because of incompatibility of shor-~and long chain ester units) is also a problem. Phasing can lead to nonrandomized ~olymer compositions having inferior physical properties. It is desirable to obtain a copolyetherester having both goo~ physical properties and processing characteristics.

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SUM~tARY OF THE INVEWTION
A novel copolyethere~ter composition has been discovered that has good physical properties, low moisture sensitivity , processes wel:l and is economical to produce. More specifically, the copolyetherestex composition of this invention is der:ived from terephthal~
ic acid or its ester-forming equivalent, 1,4-butaner.~iol, ethylene oxide-capped poly(propylene oxide) glycol, and a branching agent havlng a functionality of 3-6, said ethylene oxide-capped poly(propylene oxide) glycol having an ethylene oxide content of from about 15--35 weight percent and a number average molecular weight I ranging fxom about 1500-2800, and said branching agent beinr.~ present in a concentration of from about 1.5-6.0 equivalents per 100 moles of terephthalic acld or ester-forming equivalent thereof; and said copolyetherester composition containing from about 25-48 weight percent 1,4-butyl~ne terephthalate units and having a melt i.ndex at 230C of less than about 50 grams per 10 minutes.
Preferably, the ethylene oxide content of the ethylene oxide-capped poly(propylene oxide) glycol i5 from about 20-30 weight percent and the number average molecular weight i5 from about 1900-2500. The concen-txation of branching agen~ is preferably from 2O5-5.5 equivalents per 100 moles of terephthalic acid or ester-forming-equivalent.
~ETAI~ED D CRIPTION OF THE INVENTION
The copolyetheresters of the present invention are prepared rom terephthalic acid , or its ester-forming equivalent, such as dimethyl terephthalate, : 1,4-butanediol, and ethylene oxide capped poly(propylene oxide) glycol having an ethylene oxide content o~ from about 15-35 weight percent and a number average molecu-lar weight o~ from about 1500-2800. Furtherr the copolyetherester composition must contain a branching agent having a functionality of 3-~ in a concentration of from about 1.5-6.0 equivalents per 100 moles of terephthalic acid or ester-forming equivalent. The copolye-therester composition must contain Erom about 25-48 weight percent 1,4-butylene terephthalate units and is urther characterized by a melt index of less than about 50 g/10 min at 230C.
The ethylene oxide-capped poly(propylene oxide) g~ycol can be prepared by condensatlon of propylene oxide with propylene glycol or water in the presence of a basic `catalyst to form a poly(oxypropylene) homopolymer which is then reacted with ethylene oxide to obtain the copoly~er.
The ethylene oxide content of the ethylene oxide-capped poly(propylene oxide) gLycol must be between about 15-35 weight percent because at higher ethylene oxide contents the resulting copolyetheresters exhibit excessive water swell while at lower ethylene oxide levels phasing occurs during the melt conden-sation polymerization. Also, it ls necessary thatthe glycol have a number average molecular weight ~f from about 1500 to 2800 because at a lower molecular weight the hardening rate of the resulting copolyether-ester is unsatisfactory and at a higher molecular weight process dif~iculties during the polymer prep-aration such as phasing are encountered. Further, in order to obtain a copolyetherester composition having acceptable pxocessing characteristics and physical properties it is necessary that the melt lndex be below the limit specified because lower molecular weight polymers are difficult to process at the high process temperature required to melt the copolyetherester and they exhibit lower tensile and tear strength. In addition, it is essential that the copolyatherester composition contain a branching - ~3~

agent having a functionality o 3-5. The branching agent can be represented by the formula (HO)aX(COOH)b wnere X is a polyfunctional radical, a = 0-6, b = 0-4, and ~he sum of a ~ b = 3-6, and it has a molecular weight of from abou~ 92-3000. It is necessary to the success of the present invention that the branching agent be present in the amount defined.
When the branching agent is present in amounts of less than 1.5 equivalen-ts,it becomes increasingly difficult to achieve a high degree of polymerization without excessive polymer degradation during the melt - condensation polymerization~ At concentrations above 6.0 equivalents the p~ysical properties of injection molded parts are seriol-sly impaired.
Terephthalic acid or its ester forming equivalent and the ethylene oxide-capped poly(pro-pylene oxide) glycol are incorporated into the copoly-etherester in substantially the same molar proportions as are present in the reaction mixture. The amount of 1,4-butanediol actually incorporated corresponds to the difference between the moles of terephthalic acid and the capped poly(prop~lene oxide) glycol present in the reaction mixture.
The copolyetheresters described herein are made by a conventional ester interchange reaction in the presence of the branching agent. Preferably, an antioxidant is incorporated into the copolyether-ester, usually added before polymerization with the monomers. If desired, a photostabilizer can also be added along with the antioxidant.
The preferred procedure for preparing the copolyetherester composition involves heating the dimethyl ester of terephthalic acid with the ethylene oxide-capped poly(propylene oxide) glycol :
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~t31~6 ancl a molar excess of l,~-butanediol in -the presence of branchinq agen~ at a concentration of erom 1.5-6.0 equivalents per lO0 moles of teraphthalic acid or ester-forming equivalen~. The reac~ion is conducted S in the presence of a catalyst such as tetrabutyl titanate at about 150--260C and a pressure o~
O.05-0.5 MPa, preferably ambient pressure, whi.le distillins off methanol formed by the ester inter-change. This procedure results in the formation of a low molecular weight prepolymer which can be carried to a high molecular weight copolyetherester by dis-tillation of 1,4-butanediol. The second process stage is known as polycondensation. Additional ester interchange occurs during this polycondensation which serves to increase the molecular weight and to randomi~e the arrangement of the long and short chain ester units.
Best results are usually ob~ained if this final dis-tillation or polycondensation is run at less than about 670 Pa, preferably less than about 250 Pa, and about 20 200-280C, preferably about 230-260C, for less than about 2 hours, e.g., about 0.5 l.S hours. If desired, solid phase polymerization can be employed to achieve the final molecular welght of the copolyetherester by isolating intermediate molecular weight polymer from

2~ the melt polycondensation in small particle size form and heating the solid polymer particles under vacuum or in a stream of an inert gas, In all instances, the polycondensation reaction should be continued until the copolyetherester has a melt index at 230C of less than about 50 g/10 minutes.

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The branching agent has the general formula (HO)aX(COOH)b and has a molecular weight of about 92-3000. Y is a polyfunctional radical and a - 0-6, b = 0-4 and the sum of a + b mus~ be 3-6. In more detail, the branching agen~ may be a polyol having

3-6 hydroxyl ~roups, a polycarboxylic acid having 3 or 4 carboxyl groups or a hydroxy acid having a total of 3-6 hydroxyl and carboxyl groups.
Representative polyols that function as branching agants that can be used include glycerol, trimethylol propane, pentaery~hritol, 1,2,6-hexane-triol,sorbitol, 1,1,4,4-tetra~is(hydroxymethyl)-cyclohexane, tris(2-hydroxyethyl)isocyanurate, and dipentaerythritol. In addition to those low molecular weight polyols, higher molecular weight polyols (MW 400-3000), particularlytriols derived by con-densin~ alkylene oxides having 2-3 carbons, e.g., ethylene oxidel propylene oxide with polyol initiators, which have 3-6 carbons, e.g., glycerol, can also be used as branching agents.
Representative polycarhoxylic acids that can be used as branching agents include hemimellitic or trimellitic acid, trimesic acid, pyromellitic acid, 1,1,2,2-ethanetetracarboxylic acid, 1,1,2-ethanetri-carboxylic acid, 1,3,5-pentanetricarboxylic acid, and 1,2,3,4~cyclopentanetetracarboxylic acid. Although the acids may be used as such, pre~erably they are used in the form of their lower alkyl esters or as their cycllc anhydrides in those instances where cyclic anhydrides can be ~rmed.
Representative hydroxy acids that can be used as branching agents include malic acid, citric acid, tartaric acid, 3-hydroxyglutaric acid, mucic acid, trihydroxyglutaric acid, and 4-(beta hydroxyethyl) phthalic acid.

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Preferably, branching agents in which a is 3 or 4 and b is O or b is 3 or 4 and a is O are preferred. Especially preferred branching agents include trimellitic anhydride, trimesic acid, oxy-propylated triols (optionally capped with ethyleneoxide) havin~ molecular weight of 400-3000 and tris(2-hydroxyethyl) isocyanurate.
Usually, an antioxidant is added to the composi~ion in an amount of up to 2 percent by weight of the copolyetherester. Generally, the amount of antloxidant that is added to and incorporated in the copolyetherester is from about 0.1-1~ by weight of the copolyetherester. The antioxidants can be added with the monomers prior to the formation of the copoly-etherester polymer or, if desired, they can be addedto the molten polymer after pol~merization has been completed. Preferably, the antioxidant is added with the monomers before polymeriza-tion is initiated. Both arylamine and phenolic antioxidants can be used, with ~he phenolics being preerred for non-discoloring compositions. A preferred arylamine antioxidant is

4,4'-bis(~,~-dimethylbenzyl~diphenylamine. Preferred phenolic antioxidants are amide-containing phenolic antioxidants of the type described in U.S. 3,584,047 to Dexter. Preferred amide-containing phenolics are N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy hydrocinnamamide~ and ~J,N'-trimethylenebis(3,5~di-tert-butyl-4~hydroxyh~drocinnamamlde) or mixtures thereof.
Properties of these copolyetherester compos-itions can be modified by lncorporation of variousconventional organic fillers, such as carbon black, ;~ silica gel, alumina, clays and chopped fiber glass.
Improvement is light stability occurs by the addition ~i of small amounts of pigments or the incorporation of '~:

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a light stabilizer, such as ul~raviolet light absorbers.
The addition of hindered amine photostabilizers, such as bls(l,2,2,6,6-pentamethyl-4-piperidinyl) n-butyl-(3,5-di-tert-butyl-4-hydroxybenzyl)malona-te, usually S in amounts of rom 0.05-1.0% by weight of the copoly etherester, are particularly useful in preparing compositions having resistance to photodegradation.
The polymers of thls invention can be processed by most prscedures which are used for thermo-plastics. Because of their melt viscosity, melt sta-bility and rapid hardening rate, they are suitable for injection molding, compression molding and extrusion.
The polymers are useful for forming a variety of goods, including molded articles, films, tubing, hose and wire covers, where their excellent low temperature propertles and resistance to oil is particularly beneficial in many end uses. In finely divided form, the polymers are suitable for rotational molding and powder coating. The polymers can be oriented by drawing to pro~vTide oriented fQrms such as films and fibers. The polymers can be blended with a wide range of other polymers and are particularly useful as impact modifiers in engineering plastics.

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The following ASTM methods are employed in determining the properties of the pc~lymers prepared in the examples which follow:
Modulus at 100~ elongation,l Mlt)o D 412 Modulus at 300~ elonga-tion, M3t)0 D 412 Modulus at 500% elongatlon, M5()0 3 412 Tensile at Break, TB D 412 Elongation at Break,l E3 D 412 Haxdness, Shore D and Shore A D 2240 Melt Index D 1238 Split Tear3 D 470 Tear Resistance, Die C D 624 Clash Berg torsional stiffness D 1043 Fluids Resistance D 471 _____~__ ____ ________________~_____ 1 - Cross-head speed 50.8 cm/min.
2 ~ 2160 g load~ drying conditions: 1 hr. at 135C/
27 Pa 3 - Modified by use of 3.81 x 7.62 cm sample with 3.81 cm cut on the long axid of the sample. This con-figuration avoids "necking down" of the sample at the point of tearing. Cross-head speed 127 cm/min.
The following catalyst is used in preparing the copolyetheresters oE the examples:
Catalyst To 425 parts of anhydrous 1,4-butanediol in a round bottom flask is added 23.32 parts of tetra-butyl titanate. The mixture is agitated at 50C for 2-3 hours until the small amount of solids originally present disappears.
The following procedure is used for the preparation of the copolyetherester compositions of this invention.
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E~PLE 1 . _ _ A.) The followiny materials are placed in an agitated flask fitted fox distillation:
ethylene oxide ~EO)-capped poly(propylene S oxide) glycol (PPG) ~number average molecular weight 2200, EO content 26.3 wt. ~) 39 parts dimethyl tereph~halate 20 paxts 1,4~butanediol 15 parts trimellitic anhydride (TMA) 0.25 parts*
Antioxidant A 0.12 parts Antioxidant B 0.12 parts Light Stabilizer A6 0.3 parts Catalyst 2.4 parts ________________ * 3.78 equivalents/100 moles terephthalic acid.
4 - N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide)

5 - N,N'-trimethylenebis(3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide)

6 - Bis(1,2,2,6,6-pentamethyl-4-piperidinyl) n-butyl-(3,5-di-tert.-butyl-4-hydroxybenzyl)malonate.
~ A stainless steel stirrer with a paddle cut -~ to conform with the internal radius o~ the flask is positioned about 1/8 in. from the bottom of the flask and agltation is started. The flask is placed in an oil bath at 160C, agitated for five minutes and then the catalyst is added. Methanol distills from the reaction mixture as the temperature is slowly raised to 250C over a period of one hour. When the temper-~; ature reaches 250C, the pressure is gradually reduced - to 133 Pa within 20 minutes. The polymerization mass is agitated at 250C/133 Pa for 56 minutes. Then the polycondensation polymerization is discontinued by releasing the vacuum under nitxogen and the resulting :
:

3~ ~ ~ti viscous molten product is scraped from the flask in a nitrogen (water and o~ygen free) atmosphere and allo~,~ed to cool. The resultlng polymer has a melt index of 15.0 g/lQ min. measured at 230C.
B.) The procedure described above for Example l-A is repeated except that (1) an EO-capped PPG having a number average molecular weight of 2400 and an EO
content of 17.9~ and (2) 0.33 parts TMA (5.0 equivalents/
100 mole terephthalic acid) is used. The resulting polymer has a melt index of 13.5 g/10 min. measured at 230C.
.) Fox control purposes the procedure described above for Example l-A is repeated except that the following EO-capped poly(propylene oxide) glycols and amounts of TMA are used:
Control Control Polymer I Polymer II
EO content, ~ 8.5 50.7 Molecular Weight 2120 1920 20 T~A, parts 0.35 0.2 T~, equiv./100 moles terephthalic acid 5.28 4.24 Mel~ index (230C), - g/10 min. 12.0 14.1 In spite of the higher TMA level used ~or the preparation of Contxol Polymer I, a 40~ longer poly-condensation cycle is necessary to achieve a comparable degree of polymerization.
For measuring the physical properties of the four polymer compositions, 1.0 mm slabs are prepared by compression molding of dry, shredded polymer at 210C; the testing data are summarized in Table I.

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Table I
Control Con~rol Polymer Polymer Polymer Polymer lA :LB I II
E0 content of polyether ol~col, ~ 26.3 17.9 8.5 50.7 ~pprox. short chain es~er unlts, ~ < - - -31 trans-Appearance of melt <-translucen~ ~ opaque lucent Mloo~ MPa 5.9 5.9 5.2 5.9 MPa 84 8.3 __~ 8.5 M500, MPa 10.5 :L0.4 -- 10.4 TB, MPa 15.0 11.2 7.3 13.9 B' 1030 560 280 860 Split tear, kN/m 7~4 6.3 5.6 7.7 Hardness, Durometer A 85 85 84 85 % Volume increase,wa~er/3d/24C1.8 1.4 0.5 15.0 It is evident :Erom the data sun~arized in Table I that only Polymers lA and lB exhibit a satis-factory combination of acceptable physical properties and moisture sensitivity. Control Polymer I has poor physical properties because of incompatibility (so-calLed "phasing") of long chain and short chain ester units in the melt, thus preventing the randomization of the long and short chain ester units in the polymer.
Control Polymer II, on the other hand, exhibits excessiv2 water swell and moisture sensitivity because of the hydrophilic nature of polyether glycol.

' ~ 12 EX~MPLE 2 The procedure described above Eor Example lA
is repeated excep~ that -the following EO-capped poly(pro-pylene oxide) glycols are used:
Control S Pol~mex 2 Polymer III
EO content of poly(propylene oxide) glycol, ~ 26.9 26.7 Molecular Weight 1836 3130 The physical properties of the resulting polymers ater compression molding are shown in Table II.
Table II
Control Poly~er 2 Polvmer III
Melt index at 230C, g/10 min. 11.5 . 15.5 15 Appearance of melt translucent opaque Mloo, MPa 5.5 5.3 M300' MPa 7~8 7.6 M500' MPa 10.5 ---TB, MPa 14.7 7.9 EB, 1050 370 Tear resistance, Die C, kN/m 63 38 Because of the high molecular weight of the ~: polyether glycol used for the preparation of Control Polymer III, melt phasing during the synthesis is taking place which has an adverse effect on polymer properties such as tensile strength and tear resistance.
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~4 The procedure described above for Example lA
is repeated except the leng-th o~ the polycondensation cycles are varied resulting in different melt index grades of polymer. The physical properties of the resulting polymers are shown in Table III.
Tab_e III
- Polymer~ ontrol Polymer 3A 3B_ 3C _IV V
Melt index as 23GC, gllO min. 16.2 28 49.5 95* 165*
Mloo, MPa 6.0 5.9 5.9 5.9 6.0 M300' MPa 8.5 8.1 8.1 7.9 8.5 M500' MPa 10.3 9.5 9.4 9.1 ___ TB, MPa 14.6 13.4 12.4 10.4 8.6 B' 920 1000 940 700 400 Tear ~esistance, Die C, kN/m 62 57 47 42 33 When Example 3 is repeated without ~he use of a branching agent such as ~MA, the minimum melt index (measured at 230C) achievable after very long poly-condensation cycles is 73 g/10 minutes.
It is evident ~rom the data of Table III that the high melt index Control Polymers IV and V are deficient in respect to tensile strength and tear ; resistance when compa~ed with the properties of the pol~mers of this invention. Furthermore, the Control Polymers are difficult to process by injection ~
molding or ex~rusion because o their very low melt viscosity at the high processing ~ature o~ 200-220C.
:~ _________ _____ ~__ _ __________~____ * 324 g load used, melt index calculated for 2160 g lcad by multiplying by a factor of 2160/324.

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EXl~MP~E
The proceduxe described abo~e for Example 1 is repeated except that the following amounts o~ T~L~
are ~mployed:
TMA Content of Polymer (equi~. Melt Index Amoun~ of /100 moles tere- at 230C
TMA (par~s~ ~lallc acid~
Polymer 4A 0 . 25 3 . 78 ~0. 7 Polym~r 4B 0. 40 6 . 0 25 . O
Co~trol Polymer VI 0.50 7.5 16.5 The three copolyether~stexs are i~jection molded on a "3 oz. Van Dorn* Injection Molder" under the following conditions:
Barrel Temperature, C
Rear 177 Center 193 Front & Nozzle 202 Ram Pressure, MPa 77 20 Injectio~ Ti~e, sec. 20 ~,, ~ Mold Closet Time~ ~ec. 25 ; ~ , ~ Cycle Time, sec. 50 . .
Mold Temperature~ C 24 The stress-strain properties of injection lded dumbbells (thickness 1.87 mmj prepared from the three polymer compositions of this example are tabulated in Table rv TABLE rv Control Polymer_4A Polymer 4B Pol~ner VI
' ~ MLoo9 MPa 9.0 9O8 __ ~; TB, MPa 10.7 10.5 9.9 EB~ % 140 110 77 Above data show that because of the high degre of branching, Control Pol ~ er VI is deficient in respect to its elastomeric properties compared to the performance of Pol ~ er 4A and 4B.
* denotes trade ~ark .. . .. . ~ . . ... ......... . .

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:' A.) The procedure described above for Example lA is repeated except the following starting materials are used.
5 E0 capped PPG ~number average mole-cular weight 2400, ~O content 17.9~) 57.2 parts dimethyl terephthalate 38.7 parts 1,4-butanediol 24.0 parts T~A 0.4 parts*
10 Antioxidant A 0.2 parts Antioxidan~ B 0.2 parts Catalyst 3.5 parts * 2.1 e~uiv.~100 moles B.) The procedure described immediately above for Example 5A is repeated except that 0.53 parts (2.1 equivalents/100 moles) of branching agent tris(2-hydroxy-ethyl) isocyanurate is used instead o~ 0.4 parts TMA.
C.) The procedure described above for Example SA is repeated except that 1.25 parts (2.1 equivalents/100 moles) of a branching agent which is a triol prepared by oxypropylating glycerol and having a number average molecular wei~ht of about 600 is used instead of 0.4 parts TMAo The physical properties of the three polymer compositions measured on compression molded 1 mm slabs are tabulated in Table V.
Tab~e V
Poly~er 5A _olymer 5B Polymer 5C
Short chain ester unit content, % 39.0 39-0 39.0 Melt index at 230C, g/10 ~in. 25.0 6.5 11.0 Mloo, MPa 9.1 7.7 8.0 M300' ~Pa 10.5 10.5 10.3 TB,l~Pa 15.3 17.4 13.9 EB' % 730 810 700 Split tear, kN/m 6.5 8.2 7.0 Hardnes~, Durometer A 89 90 89 ~3~ t~

TABLE V (Continued) ___ Pol~mer 5A ~y~ SB ~y___ 5C
% Volume Increase H20/3 days/24C 0.6 0.7 0.7 ASTM #3 oil/7 days/100C 25 24 27 Clash Berg Torsional Modulus, MPa 24C 17.8 18.4 17.5 -45~C 20.5 21.2 19.7 -56C 37.8 40.5 38.0 ;

Claims

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1. A copolyetherester composition derived from terephthalic acid or its ester-forming equivalents, 1,4-butanediol, an ethylene oxide-capped poly(propylene oxide) glycol and a branching agent having a function-ality of 3-6, said ethylene oxide-capped poly(propylene oxide) glycol having an ethylene oxide content of from about 15-35 weight percent and a number average molec-ular weight ranging from about 1500-2800, and said branching agent being present in a concentration of from about 1.5-6.0 equivalents per 100 moles of tere-phthalic acid or ester-forming equivalent thereof;
and said copolyetherester composition containing from about 25-48 weight percent 1,4-butylene terephthalate units and having a melt index at 230°C of less than about 50 grams per 10 minutes.

2. A copolyetherester composition of Claim 1 wherein the ethylene oxide content of the ethylene oxide-capped poly(propylene oxide) glycol is from about 20-30 weight percent.

3. A copolyetherester composition of Claim 2 wherein the number average molecular weight of the ethylene oxide-capped poly(propylene oxide) glycol is from about 1900-2500.

4. A copolyetherester of Claim 3 containing 2.5-5.5 equivalents per 100 moles of terephthalic acid of a branching agent.

5. A copolyetherester of Claim 3 wherein the branching agent is trimellitic anhydride.

6. A copolyetherester of Claim 3 containing up to 2 weight percent antioxidant.

7. A copolyetherester of Claim 6 containing the antioxidant N,N'-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamamide) or N,N'-trimethylene-bis(3,5-di-tert-butyl 4-hydroxyhydrocinnamamide) or mixtures thereof.

8. A copolyetherester of Claim 3 containing the photostabilizer bis(l,2,2,6,6-pentamethyl-4-piperidinyl) n-butyl-3,5-di-tert-butyl-4-hydroxybenzyl)-malonate.