Abstract:
This invention relates to polyester polyether segmented copolymers wherein the polyether segment contains a certain amount of heterocyclic ring repeat units, for example, the hydantoin ring. These polyester polyether segmented copolymers are useful in the production of fibers, films or other extrusion moldings where elastomeric properties are desirable.

Description:
BACKGROUND OF THE INVENTION 
     In the textile and allied fields where elastomeric properties are desired in certain products and end uses, rubber has long been used. For many applications, natural or synthetic rubber falls short because of undesirable aesthetics or insufficient physical properties. In many instances it must be covered with other materials, natural or synthetic, for use in garments. Therefore much effort has gone into the development of materials which have the desirable elastic properties of rubber but not the undesirable aesthetic or physical properties mentioned above. Much of this work has evolved around the incorporation of long-chain &#34;soft segments&#34; into polymers made up of varying proportions of more easily crystallized thermoplastic &#34;hard segments&#34;, resulting in segmented copolymers which are thermoplastic, elastomeric, and capable of being extruded into filaments, fibers or other desired shapes. 
     Charch and Shivers reported the use of polyester ether condensation block copolymers (&#34;Part II; Elastomeric Condensation Block Copolymers&#34;, Charch and Shivers, Textile Research Journal, 1959, p. 536.) which are capable of being shaped into fibers, their compositions being based primarily on the use of poly (oxyethylene oxyterephthalogyl) as the hard segment and poly (oxyethylene) as the soft segment. The low glass transition temperature, resultant extensibility, reactive difunctionality and economy explain this soft segment&#39;s extensive use in various other studies; however, its susceptability to room temperature recrystallization at high molecular weights, even as part of a block copolymer, adversely effects elastic properties and limits useful molecular weights to less than 1500. 
     In constructing segmented copolymers which have sufficiently rapid hardening rates to allow satisfactory handling after extrusion, it has been found necessary to have certain percentages of specific dicarboxylic acids in the hard and soft segments and certain percentages of specific low molecular weight diols in the hard segment. For instance it is reported essential in U.S. Pat. No. 3,763,109 that at least about 70 mole % of the dicarboxylic acid in the polymer be terephthalic acid and at least about 70 mole % of the low molecular weight diol in the polymer be 1,4-butane diol. Also, at least about 70 mole % of the low molecular weight diol in the hard segment must be 1,4-butane diol. Further the sum of the percentages of the carboxylic acid in the hard and soft segments which is not terephthalic acid and the low molecular weight diol in the hard segment which is not 1,4-butane diol can not exceed about 30 mole %. Copolyesters having fewer 1,4-butylene terephthalate units than assured by the foregoing requirements do not have sufficiently rapid hardening rates for satisfactory handling after extrusion. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a thermoplastic segmented copolyester polyether consisting essentially of a multiplicity of randomly occurring intrachain segments of long-chain (soft segments) and short-chain (hard segments) ester units, said long-chain ester units being represented by the following structure: ##STR1## where L is a divalent radical remaining after removal of terminal hydroxyl groups from poly (oxyalkylene) glycols having at least 1 nitrogen containing ring per molecule, a carbon to nitrogen ratio of from about 3/1 to about 350/1, and a molecular weight between 200 and 8,000, and R is a divalent radical remaining after the removal of the carboxyl groups from a dicarboxylic acid having a molecular weight of less than 300. 
     Short-chain ester units are represented by the following structure: ##STR2## where E is a divalent radical remaining after removal of hydroxyl groups from a low molecular weight diol having 2 to 15 carbon atoms per molecule and a molecular weight between 50 and 250, and R is the divalent radical described for (a) above. 
     The introduction of a foreign repeat unit in the backbone of a crystallizable soft segment, such as a polyether, has an effect on the soft segment crystallization process. Such a foreign unit must be stable to processing temperatures and must not be so rigid as to reduce the mobility (raise the glass transition temperature) of the soft segement itself. The foreign unit should be nonreactive during the synthesis of the segmented thermoplastic elastomer and should be present in the concentration of at least 1 unit per polyether molecule. The long-chain ester unit, or soft segment, of the elastomeric copolymer is preferably about 40-70% by weight of the copolyester. 
     The polyether soft segment of the present invention may be represented by the following structures: ##STR3## In (c), the unit X is placed near the center of the polyether chain and may be one foreign unit or a series of foreign units covalently linked together. In (d), the unit X is one or more foreign repeat units as in (c) but these units are placed along the length of the linear polyether chain. 
     In both formulas (c) and (d), X is a nitrogen containing heterocyclic ring giving the polyether soft segment a carbon to nitrogen ratio of from about 3/1 to about 350/1 and a molecular weight between 200 and 8,000. The sum of m plus n is within the range of 5 to 180, and x in formula (d) has a maximum value of 10. 
     The nature of X is such that it may covalently enter the polyether chain to influence crystallization. Covalent links to the polyether in (c) or (d) may be the amide link or the imide link, both of which are capable of withstanding high temperature processing. These links, the polyester units themselves, and the foreign unit(s) X in (c) or (d) form the soft segment. 
     The introduction of the repeat unit X into the poly(oxyethylene) chain, where X is greatly different from poly(oxyethylene), disrupts chain regularity and suppresses the melting point of the soft segment preventing crystallization at room temperature. This allows the use of higher molecular weight polyethers, or stated differently, lower mole percentage of the soft segment. The lower mole percentage of soft segment increases the melting point of the copolymer due to higher mole percentage of the hard segment. The ratio of weight percent of the short chain ester units to long-chain ester units is preferably between 60 to 40 and 30 to 70. Also a more regular chain is obtained which may result in better separation of the hard and soft phases. Better phase separation results in a higher tenacity, a lower glass transition temperature for the soft segment and an improved elastomeric performance. 
     DETAILED DESCRIPTION 
     The term &#34;foreign repeat unit&#34; as applied to the soft segments of this invention refers to heterocyclic, nitrogen containing, rings which may covalently link (as amide or imide) along the soft segment chain as described previously. Representative units are: 1,3-divalent-5,5-dialkylhydantoin (including alkyl groups connected in a cyclic fashion to the 5,5 positions); 2,5-divalent-1,3,4-triazole; 2,5-divalent-1,3,4-oxadiozole; 2,-5-divalent-1,3,4-thiadiazole; 1,3-divalent-1,2,4-triazolidine-3,5-dione; 4,5-divalent-1,2-isothiazole; 4,5-divalent-1,2-oxazole; 4,5-divalent-1,3-diazole; 2,5-divalent-1,3-oxazole; 2,4-divalent-imidazole; divalent (N position) hypoxanthine; and 2,5-divalent-1,3-thiazole. 
     The term &#34;long-chain ester units&#34; as applied to units in the copolymer chain refers to the reaction product of a long-chain glycol with a dicarboxylic acid. Such &#34;long-chain ester units&#34;, which are repeating units in the copolyesters of this invention, correspond to formula (a) above. The long-chain glycols are polymeric glycols having terminal hydroxy groups and a molecular weight above about 400 and preferably about 1,000 to 3,000 for (c). The long-chain glycol used to prepare the copolyesters of this invention are poly(oxyalkylene) glycols having foreign repeat units represented by formulas (e) and (f). ##STR4## 
     These poly(oxyalkylene) glycols have carbon to nitrogen ratios between about 3/1 and about 350/1, molecular weights between 200 and 8,000, m plus n is within the range of 5 to 180, and x in formula (f) has a maximum value of 10. In a preferred embodiment, the poly (oxyalkylene) glycols have carbon to nitrogen ratios between about 8.5/1 and about 23/1 and molecular weights between 450 and 8,000. Representative long-chain glycols are poly(oxyethylene) glycol, poly (oxypropylene)glycol, poly(oxymethylethylene) glycol, poly(oxytetramethylene) glycol, and coolymers of ethylene oxide and 1,2-propylene oxide. 
     The term &#34;short-chain ester units&#34; as applied to units in the copolymer chain refers to low molecular weight compounds for polymer chain units having molecular weights less than about 500. They are made by reacting a low molecular weight diol (below about 250) with a dicarboxylic acid to form ester units represented by formula (b) above. 
     Included among the low molecular weight diols which react to form the short-chain ester units are a cyclic, alicyclic, and aromatic dihydroxy compounds. Preferred are diols with 2 to 15 carbon atoms such as ethylene, propylene, 1,4-butane, pentamethylene, 2,2-dimethyl trimethylene, hexamethylene, and decamethylene glycol, dihydroxycyclohexane, cyclohexane dimethanol, resorcinol, hydroquinone, 1,5-dihydroxy naphthaline, etc. Especially preferred are aliphatic diols containing 2 to 8 carbon atoms. Equivalent ester-forming derivatives of diols are also useful (e.g. ethylene oxide or ethylene carbonate can be used in place of ethylene glycol). The term &#34;low molecular weight diols&#34; as used herein should be construed to include such equivalent ester-forming derivatives; provided however, that the molecular weight requirement pertains to diol only and not to its derivatives. 
     Dicarboxylic acids which are reacted with the foregoing long-chain glycols (L in formula a) and low molecular weight diols (E in formula b) to produce the copolyesters of this invention are aliphatic, cycloaliphatic, or aromatic dicarboxylic acids of a low molecular weight, i.e., having a molecular weight of less than about 300. The term &#34;dicarboxylic acids&#34; as used herein, includes equivalents of carboxylic acids having 2 functional carboxyl groups which perform substantially like dicarboxylic acids in reaction with glycols and diols in forming copolyester polymers. These equivalents include esters and ester-forming derivatives, such as acid halides and anhydrides. The molecular weight requirement pertains to the acid and not to its equivalent ester of ester-forming derivative. Thus, an ester of a dicarboxylic acid having a molecular weight greater than 300 or an acid equivalent of a dicarboxylic acid having a molecular weight greater than 300 are included provided the corresponding acid has a molecular weight below about 300. The dicarboxylic acids can contain any substituent groups or combinations which do not substantially interfere with the copolyester polymer formation and use of the polymer of this invention. 
     Aliphatic dicarboxylic acids, as the term is used herein, refers to the carboxylic acids having 2 carboxyl groups each attached to a saturated carbon atom. If the carbon atom to which the carboxylic acid group is attached is saturated and is in a ring, the acid is cycloaliphatic. Aliphatic or cycloaliphatic acids having conjugated unsaturation often can be used provided they are thermally stable at polymerization temperatures and do not undergo homopolymerization. 
     Aromatic dicarboxylic acids, as the term is used herein, are dicarboxylic acids having 2 carboxyl groups attached to a carbon atom in an isolated or fused benzene ring. It is not necessary that both functional carboxyl groups be attached to the same aromatic ring and where more than 1 ring is present, they can be joined by aliphatic or aromatic divalent radicals or divalent radicals such as --O-- or --SO 2  --. 
     Representative aliphatic and cycloaliphatic acids which can be used for this invention are sebasic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, adipic acid, glutaric acid, succinic acid, carbonic acid, oxalic acid, azelaic acid, dimethylmalonic acid, allylmalonic acid, 4-cyclohexene-1,2-dicarboxylic acid, 2-ethyl suberic acid, 2,2,3,3-tetramethyl succinic acid, cyclopentane dicarboxylic acid, decahydro-1,5-naphthalene dicarboxylic acid, 4,4&#39;-bicyclohexyl dicarboxylic acid, decahydro-2,6-naphthalene dicarboxylic acid, 4,4&#39;-methylene bis (cyclohexane carboxylic acid), 3,4-furan dicarboxylic acid, and 1,1-cyclobutane dicarboxylic acid. Preferred aliphatic acids are cyclohexane-dicarboxylic acids and adipic acid. 
     Representative aromatic dicarboxylic acids which can be used include terephthalic, phthalic and isophthalic acids, dibenzoic acid, substituted dicarboxylic acids with two benzene nuclei such as Bis (p-carboxyphenyl) methane, p-oxy(p-carboxyphenyl) benzoic acid, ethylene-Bis (p-oxybenzoic acid), 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, phenanthrene dicarboxylic acid, anthracene dicarboxylic acid, 4,4&#39;-sulfonyl dibenzoic acid, and c 1  -c 12  alkyl and ring substitution derivatives thereof, such as halo, alkoxy, and aryl derivatives. Hydroxy acids such as (β-hydroxy ethoxy) benzoic acid can also be used provided an aromatic dicarboxylic acid is also present. 
     Aromatic dicarboxylic acids are a preferred class for preparing the copolester polymers of this invention. Among the aromatic acids, those with 8 to 16 carbon atoms are preferred, particularly the phenylene dicarboxylic acids, i.e., terephthalic, phthalic and isphthalic acids. 
     Polymers described herein can be made conveniently by a conventional ester interchange reaction such as that described in detail to U.S. Pat. No. 3,763,109. Other special polymerization techniques, for example interfacial polymerization, may prove useful for preparation of specific polymers. Both batch and continuous methods may be used for any stage of copolyester polymer preparation. Polycondensation of prepolymers can also be accomplished in the solid phase by heating divided solid prepolymer in a vacuum or in a stream of inert gas to remove liberated low molecular weight diol. This method has the advantage or reducing degradation because it must be used at temperatures below the softening point of the prepolymer. 
     Although the copolyesters of this invention possess many desirable properties it is advisable to stabilize certain of the compositions to heat or ultraviolet radiation, and this can be done by incorporating stabilizers into the polyester compositions. Satisfactory stabilizers comprise phenols and their derivatives, amines and their derivatives, compounds containing both hydroxyl and amine groups, hydroxyazine, oximes, polymeric phenolic esters and salts of multivalent metals in which the metal is in its lower valent state. 
     The properties of these copolyesters can be modified by the incorporation of various conventional inorganic compounds such as titanium dioxide, carbon black, silica gel, alumina, clays, and chopped fiberglass. 
    
    
     All parts, proportions, and percentages disclosed herein are by weight unless otherwise indicated. The following examples further illustrate the invention. 
     EXAMPLES 
     The following ASTM methods are employed in determining the properties of the polymers prepared in the examples which follow. All methods are carried out at 65° C. and 60 RH rather than 70° C. and 65 RH specified by ASTM. 
     
         ______________________________________Tenacity at Break       D2657-2Elongation at Break     D2657-72Stress Decay            D2731-72Tensile Recovery        D2731-72______________________________________ 
    
     Relative viscosity is determined in three different solution concentrations, 1% and less, of polymer in solvent consisting of 60 parts by weight of phenol and 40 parts by weight of tetrachloroethane in a Ubbelohde viscometer at 25°±1° C. The intrinsic viscosity is then determined as the intercept of a plot of ##EQU1## 
     Thermal data was collected on a DuPont 990 termal analysis system using the differential thermal analysis cell and the differential scanning calorimeter cell. 
     EXAMPLE 1 
     The segmented copolymers of this invention may be prepared using prepolymers represented by formula (c), one example of which is Dantocol DHE-20, with a molecular weight of 1,000 and available from Glyco Chemical Company. Other such prepolymers are available with molecular weights of 400 to 2500. The prepolymer is prepared generally according to procedures disclosed in British Pat. No. 1,260,972. For example, 128 g (1 mole) 5,5-dimethylhydantoin may be melted at 200° C. in a round flask fitted with a stirrer and gas inlet and outlet tubes. The melt is stirred vigorously while ethylene oxide is introduced for 2 hours resulting in a weight gain of 88 g (2 mole ethylene oxide). The temperature is gradually reduced to 120° C. and the product is fractionally distilled under vacuum, the major fraction distilling at 205° C. to 210° C. at 1.5 mm mercury. The product is allowed to crystallize and is purified by recrystallization from isopropyl alcohol with the addition of petroleum ether. Further ethoxylation of the 1,3-di(β-hydroxyethyl)-5,5-dimethylhydantoin is achieved by the addition of ethylene oxide under pressure in the presence of a basic catalyst such as NaOH. 
     EXAMPLE 2 
     Another type of polyether prepolymer, which is represented by formula (d), may be prepared as follows: Bis-1,3-(2-hydroxyethyl)-5,5-dimethylhydantoin (181 g, 0.82 mole) is placed in a round bottom flask fitted with a reflux condenser, a mechanical stirrer and a dropping funnel containing 207.2 g (about 1.64 mole) thionyl chloride. Benzene (300 ml) is added to the reaction flask, which is then stoppered and the thionyl chloride is added with stirring at such a rate as to complete addition in 2 hours. The reaction mixture is stirred overnight at room temperature, then refluxed at 50° C. until evolution of SO 2  and HCL is complete and again cooled to room temperature. The mixture is poured onto 1 kg ice and washed with ether to give an ether solution which in turn is washed, first with water and then with 5% NaHCO 3  solution. The ether solution is dried, filtered and the ether removed leaving a liquid residue. The crude product is vacuum distilled at 11 mm mercury with the major portion collected at 195° to 197° C. Redistillation at 2 mm mercury gives the product, Bis-1,3-(2-chloroethyl)-5,5-dimethylhydantoin which melts at 80° C. 
     To 200 g (0.2 mole) Glyco Chemical&#39;s DHE-20 (hydantoin polyether of M n  about 1,000) in 200 ml tetrahydrofuran is added 0.4 mole sodium naphthalenide, 200 ml dimethoxyethane and the sodium salt of the hydantoin polyether forms as a precipitate. At this point 34.4 g (0.136 mole) of the Bis-1,3-(2-chloroethyl)-5,5-dimethylhydantoin prepared above is added as a solution in 100 ml tetrahydrofuran. After stirring overnight the tetrahydrofuran and dimethoxyethane solvents are removed by distillation and replaced with 300 ml hexamethyl phosphorus triamide. This mixture is refluxed for 6 hours at 80° to 90° C. under dry nitrogen, cooled to room temperature and 38 g dry methyl alcohol is added, followed by 25.5 g acetic acid as a 5% aqueous solution. Vacuum evaporation is used to remove the water and other low-boiling solvents, followed by vacuum distillation to remove the hexamethylphosphorus triamide. The remaining polymer product is represented by the formula ##STR5## where the sum of m and n is 20 and x is 2. Other variations of this prepolymer may be prepared by using hydantoin polyethers of other or mixed molecular weights instead of the DHE-20 used in this example. 
     EXAMPLE 3 
     Synthesis of a segmented copolymer which is 50% by weight hard segment and 50% by weight soft segment is carried out as follows: dimethylterephthalate (200 g, 1.03 moles) and 1,4-butane diol (129.95 g, 1.442 moles) are added to a 1 kg resin kettle equipped with a mechanical stirrer, a nitrogen inlet tube, a thermocouple connected to a Barber-Coleman recorder, and a dual partial condenser of which the lower column is heated to 100° C. by a circulating oil bath and the upper column is heated at 70° C. by a circulating hot water bath. Mounted above the dual partial condenser is an automatic liquid dividing distillation head with a high speed condenser. This system is continuously purged with nitrogen and is heated using a heating mantle at 120° C. Upon reaching this temperature, low speed stirring is started. When the temperature of the reaction mixture reaches 125° C. the catalyst, tetra-butyltitanate (200 mg, 0.10 wt %), is added in 10 ml hexane. The ester interchange reaction begins at 130° to 135° C. and the reaction temperature is increased slowly over a 60-minute period to 160° to 165° C. after which the nitrogen purge is discontinued and a vacuum cycle is started. At this stage at least 80% of the theoretical amount of methanol is distilled. The pressure during the vacuum cycle is reduced very slowly to 175 mm and is maintained at this level for 15 minutes. The pressure is then further reduced to 70 mm for 45 minutes, by which time the theoretical amount of methanol has distilled. At this point the ester interchange product is poured quickly into a 1 kg polymerization kettle containing Ionox 330 (1.0 wt. %) and hydantoin polyester prepolymer of a molecular weight about 1,000) 200 g, 0.20 moles), as prepared and described in Example 1, and the mixture is cooled under a nitrogen blanket to room temperature. Polymerization is started using a Dowtherm boiler to melt the ester interchange product, and when melting is complete a vacuum cycle is started and maintained for 1 hour below 0.1 mm. The polymer is then extruded and quenched in cold water followed by vacuum drying and grinding. 
     Elemental analysis of the 50/50-hard/soft segment copolymer is given in the following table. 
     
         ______________________________________       Theoretical for% Element   50/50 Copolymer Found______________________________________Carbon      59.6            61.0Hydrogen    7.0             7.0Nitrogen    1.4             1.1______________________________________ 
    
     Thermal analysis provided the following data: 
     
         ______________________________________Parameter______________________________________Melting Range-Hard Segment                   165-180° C.Recrystallization Range 140-150° C.Heat of Fusion          43.48 in.sup.2 /gGlass Transition Temperature                   -64° C.______________________________________ 
    
     Molecular weight data regarding this polymer system was gathered by measuring solution viscosities, recording gel permeation chromatography curves, and by analyzing nuclear magnetic resonance spectra. 
     An average intrinsic viscosity of 1.42 was observed. 
     Gel permeation chromatography indicates a Gaussian distribution of molecular weights with a polydispersity ratio in the range of 2 to 2.8. 
     Nuclear magnetic resonance spectra display signals expected for the polymer backbone and allow the calculation of a number average molecular weight for the soft segment. The ratio of the signal generated by the methyl protons at the 5-position of the hydantoin ring (located at 1.37δ) to the signal assigned to the methylenes of the polyether (located at 3.63δ) suggest a number average molecular weight of 1,050, demonstrating the maintenance of the soft segment integrity during polymerization. 
     Average data from chemical analysis of several preparations as described in this example are given in the following table: 
     
         ______________________________________       Ester Interchange                   Polycondensation       Product     Product______________________________________Methyl Esters, meq/kg         132           3Acid Number, meq/kg         28            8% Tetrahydrofuran         4.4           0.11% Butane diol 1.3           9.5______________________________________ 
    
     Polymer structural characterization by nuclear magnetic resonance data, and corroborated by chemical thermal analyses described in this example, define the repeat unit structure as expected. The hard and soft segment repeat units are illustrated below along with the assigned chemical shifts. 
     
         ______________________________________ ##STR6##Hard Segment ##STR7##Soft SegmentNMR Signal   Chemical Shift Line Shape______________________________________a            1.37           Singletb            1.97           Multipletc            3.63           Singlet*d            4.47           Multiplete            8.13           Singlet______________________________________ *This signal is flanked by additional signals of much lower intensity which are assigned to methylenes adjacent to ester groups and to the hydantoin ring. 
    
     The dried polymer is melt-spun using a piston driven extruder giving a 6 filament, 100 denier elastic yarn, which is then exposed to one of a variety of heat treatments and/or stressing operations. For example, a sample spun at 1200 mpm exhibited the following physical characteristics after being drawn over a hot pin at 70°-80° C. at a draw ratio of 2.0. 
     
         ______________________________________Tenacity at Break       1.05 g/dElongation at Break     250%Stress Decay            18.7%Tensile Recovery        90%______________________________________ 
    
     EXAMPLES 4 THROUGH 10 
     Copolymer compositions similar to that described in Example 3 and using identical polymer synthesis techniques are prepared with the exception that the molecular weight of the hydantoin-containing segment prepolymer (HPOE) is varied. Thermal properties of the resulting elastomers are given in the following table. 
     
         ______________________________________ExampleNo.    HPOE --M.sub.n             Copolymer T.sub.m °C.                          Copolymer T.sub.rc °C.______________________________________4       400       126          --5       600       159          1096       800       172          1427      1000       178          1468      1200       184          1519      1500       195          15310     2000       208          160______________________________________ 
    
     EXAMPLES 11 THROUGH 15 
     Copolymer compositions similar to that described in Example 3 and using identical polymer synthesis techniques are prepared with the exception that the weight percent of the hard segment to the soft segment is varied. Thermal properties of the resulting elastomers are given in the following table. 
     
         ______________________________________Example No.      % Hard:Soft  T.sub.m °C.                             T.sub.rc °C.______________________________________11         60/40        208       16512         45/55        164       10813         40/60        164       10714         35/65        158       9015         30/70        158       90______________________________________ 
    
     Copolymer compositions similar to those described in Example 3 through 15 may be prepared in like manner except for the hydantoin polyether prepolymer prepared and described in Example 2 may be substituted for that prepared and described in Example 1. 
     EXAMPLE 16 
     Dimethyl terephthalate (180 g, 0.927 mole), ethylene glycol (143.8 g, 2.32 mole) and manganese benzoate (89.4 mg, 0.03 mole%) are added to a 1 kg resin kettle equipped as in Example 3. The system is continuously purged with nitrogen and is heated in a heating mantle to 120° C., where stirring is started. When the temperature of the reaction mixture reaches 170° C., methanol is distilled and collected. The mixture is allowed to react for about 70 additional minutes. At this time, 100% of the theoretical amount of methanol has been distilled and the temperature of the reaction mixture is 220° C. The ester interchange product is then cooled to 180° C. where antimony tributyrate (210 ml, 0.05 mole %) and triethylene glycol phosphate (250 ml, 50 ppm) is added. After the ester interchange product cools to 170° C., it is rapidly poured into a 1 kg polymerization kettle containing hydantoin poly (oxyethylene) prepolymer of number average molecular weight about 1000 (120 g, 0.12 mole), and Ionox 330 (1.0 wt.%) as thermal stabalizer. The polycondensation is started using a Dowtherm boiler to melt the ester interchange product, and when melting is complete, a vacuum is started and maintained for 3 hours below 0.1 mm Hg. The polymer is then extruded and has an I.V. of 0.8, a melting point of 220° C. and a temperature of recrystallization of 132° C. 
     EXAMPLE 17 
     Dimethyl terephthalate (120 g, 0.62 mole), dimethyl isophthalate (30 g, 0.16 mole), 1,4-cyclohexane dimethanol (156 g, 1.08 mole) and hydantoin polyether (184 g, 0.18 mole) are added to a 1 kg resin kettle equipped as in Example 3. The system is continually purged with nitrogen and is heated with a heating mantle to 120° C. where low speed stirring is started. When the temperature of the reaction mixture reaches 125° C., the catalyst, tetra-butyltitanate (0.16 ml, 0.10 wt %) is added. The ester interchange reaction begins at 190° to 195° C. and when 90% of the theoretical amount of methanol product has been distilled, the ester interchange product is poured into a polymerization vessel containing 1.0 wt % Ionox 330, a thermal stabilizer, and cooled to a room temperature under nitrogen. An additional 0.16 ml of tetra-butyltitanate is added to the polymerization vessel before the ester interchange product is melted using a dimethylphthalate boiler. When the melting is complete, a programmed vacuum cycle is started and maintained for 1 hour and 15 minutes below 0.1 mm Hg. The polymer is then extruded and has an I.V. of 0.74, a T m  of 247° C., and a T rc  of 165° C. The polymer is ground, dried and spun into yarn at 275° C. from a hydraulic, piston driven Chemtex spinning apparatus. The undrawn yarn has a denier of 74, a tenacity of 0.63 g/d and an elongation at break of 258%. The yarn is drawn at 400 mpm with draw ratios of 2.0:1 and 3.5:1 and exhibits the following physical properties. 
     
         ______________________________________          DR 2.0:1  DR 3.5:1______________________________________Denier           28          31Tenacity (g/d)   1.5         1.8Elongation (%)   65.5        52.9Stress Decay (%)1st cycle        52.3        50.45th cycle        39.5        37.0Tensile Recovery (%)1st cycle        72.0        72.05th cycle        62.0        61.0______________________________________ 
    
     A similar copolyester may be prepared in like manner except dimethylphthalate is substituted for dimethyl isophthalate. 
     The effect of the foreign unit present in the polyester is best illustrated by preparing two copolymers as described in example III above, one containing a 50% by weight of a hydantoin poly (oxyethylene), HPOE, number average molecular weight about 1200, and one containing 50% by weight of poly (oxyethylene) number average molecular weight about 1300, POE, without the foreign unit, but with a similar number average molecular weight. 
     Melt spinning each into 50/6 yarn and analysis by differential scanning calorimetry from room temperature to 300° C. shows: 
     The scan of the POE containing copolymer exhibits an ill-defined endotherm at 48° C. corresponding to the melting point of the soft segment, followed by an endotherm at 156° C. corresponding to the melting point of the hard segment. Cooling the sample results in exotherms at 122° C. and 30° C. corresponding to the recrystallization of the hard and soft segments respectively. When a sample of the POE containing copolymer is annealed at 136° C. for 30 minutes followed by room temperature annealing for 3 days, phase separation apparently is enhanced and thus allows for more efficient crystallization of both segments. This phenomenon is manifested in differential scanning calorimetry endotherms which are more clearly defined than before annealing. 
     The differential scanning calorimetry scan from room temperature to 300° C. of the HPOE containing copolymer exhibits only one endotherm, a multiplet at about 170° C. which corresponds to the melting point of the hard segment. Cooling the sample to room temperature results in only one exotherm, at 138° C., corresponding to the recrystallization of the hard segment. Even after annealing the sample as above, no melting or recrystallization of the soft segment is observed as evidenced by the lack of a second endotherm or exotherm. The effect is to render the soft segment totally amorphous at or above room temperature, thus allowing for a greater degree of soft segment mobility. Maximum mobility allows maximum elastomeric performance since any crystallization of the soft segment reduces its entropy and thereby reduces the rubber elasticity of these copolymers. 
     Crystallization of the HPOE containing copolymer can be induced by annealing the sample just below the melting point of the hard segment (160° C. for 15 minutes) followed by annealing of the sample below room temperature (-17° C. for 5 days). A poorly defined endotherm corresponding to the soft segment melting is observed at 5° to 10° C. followed by hard segment melting at 170° C. Recrystallization of the hard and soft segments is observed at 138° C. and -15° C. respectively. 
     In essence the presence of a foreign unit (for example, a hydantoin unit) has the effect of depressing the melting point of the soft segment from about 48° C. to a more useful temperature in terms of elastomeric properties, that is, below room temperature.