CA1195464A - Oriented copolyetherester elastomer - Google Patents

Abstract

ABSTRACT
A power transmission belt is formed from an oriented segmented thermoplastlc copolyetherester elastomer containing recurring long chain ester units derived from a dicarboxylic acid and a long chain glycol, and short chain ester units derived from a dicarboxylic acid and a low molecular weight diol.

Description

B S395nbL~aLJ/~ Y''~LY~
A variety of uses exists for elastomeric materials in applications requ~ring hi~modulus and ul~imate s~rength~
Such uses inc~ude power transmiss1on belts o~ the ~lat and V vari~tyO For such use~ ~here must, o-f' course~ remain a slight degree of ~lexi~ilîty within the belt~
In the pa~t~ satis~ac~ory power transmlssioIl be~-ts hav~ been produced utilizing a variety of different elastomers which have been rein~orced with ~i~ers suc~ as nylon/ Elasto~
mers which have not bee~ reinforced do not possess suf~f'icient modulus and strength to be used in power transmission belts except in light duty applicationsO
: The use of such reinf'orced elastomers has presented a problem in that a multl-s~ep sp~ration has been necessary ko produce them. The relnforcing cords have to be surrounded by elastomer and th~.s cannot be accomplished expedientlyO
Thus a need exists for an economical one~step operation ~or producing a material which will be satisfactory ~or use as a poweP transmission belt in heavy duty service~
~
According to this invention it has unexpectedly been ~ound that a ther~oplastic copolyetherester elasto~er can be treated to produce a product having the previously mentioned d~red characteristicsO The copolyetheresker must be stretched ~t least 300% of its origina~ length but not to lts br2aklng point3 at a temperature below its melt~ng point by at least 20F,~ maintalned substantially at that length and ~rou~ht to or mainta~ned at a heatlng se~-t~n~ temperatuxe between about 150 and 20F~ b~lQw l~s melting point~ ~nd kher~a~ter cooled -to a temperature below the heat setking temperature by at ~, . ~

least 100F~ The resulting product has outstanding tensile modulus ~nd streng~h ~or uses such as in a power belt.
Addit~onally, :it still poses~es a minor amount of elasticity so that it ~ay be sllghtly stre~ched i~ necessary. ~y a minor amount o~ elasticity it is meant that lt ha3 an ultimate elongation of at leas~ 40-60~
~ he copolyetherester elast,omer which i~ to be treated by the process of the lnstant inventlon con~ists essentially o~ a multiplicity o~ recurring intralinear long-ehain and short~ch2in units connecke~ he~d~to-tail throu~h ester llnka~es~ sa.id long-chain ester units belng represented by the ~ollowing structure:
O O
~1 11 ~OGO;~CRC-~ ) and said short~chain ester units being represented by the follo~qlng struc~ure.
O O
ODO CRC-~ h~
wherein:
G is a divalent radical remaining after removal o:~
terminal hydroxyl groups from poly(a.l~ylene oxi~e) glycols ~av~ng a carbo~-to-ox~gen ra~o o~ abou~ 2~0~4.3 and molecular we:Lght between about 400 and 6000 R i~ Q dival.ent radlcal rem~,ining a~ter remoYal o~
carboxyl groups ~rom a dlcar~oxylic acld havlng a ~olecular weight less than about 300; and D is a diva.lent radlcal re~alning after removal of . ,. "
;~i hydroxyl groups from a low molecular weight diol having a molecular welght less than about 250~
with the provisos Ghat the short~chain ester unlts constitute about 15-95% by weight, pre~erably 25-90% by weight, of the copolyetherester and, ergo, the long~chaln ester units constitute about 5 to 85% by weightg preferably 10-75% by weight, of the copolyethereste~.
Detailed Description o~ the In~ention The term "long-chain ester units" as applied to units in a polymer chain refers to the reaction product of a long-chain glycol wi~h a dicarboxylic acid. Such "long~
chain ester units'l~ which are a repeating unit in the co~

polyetheresters of this invention, correspond to formula (a) abo~e. The long-chain glycols are polymeric glycols having terminal ~or as nearly terminal as possible) hydroxy groups and a molecular weight ~rom about 400-6000. The long-chain glycols used to prepare the copolyetheresters of this inven~
tion are poly(alkylene oxide) glycols having a carbon-to-oxygen ratio of about 2.0-4.3-Representative long-chain glycols are poly(ethyl-ene oxlde) glycol, poly(l,2- and 1,3-propylene oxide) gly-col, poly(tetramethylene oxide) glycol, random or block co polymers o~ ethylene oxide and l,2-propylene oxide, and ran-dom or block copolymers of tetrahydrofuran with minor amounts of a second monomer such as 3-methyltetrahydro~uran (used in prpportions such that the c~rbon-to oxygen mole ratio in the glycol does not exceed about 4.3~.
The term "short-chain ester units" as applied to units in a polymer chain re~ers to low molecular weighG com-pounds or polymer chain units having mol.ecular welghts less ....

than about 550. They are made by reacting a low molecular weight diol (below about 250) with a dicarboxylic acid to ~orm ester units represented by formula (b~ above.
Included among the low molecular weight diols which react to form short-chain ester units are aliphatic~
cycloaliphatic, and aromatic dihydroxy compounds. Preferred are diols with 2-15 carbon atoms such as ethylene, propylene, tetramethylene~ pentamethylene, 2,2-dimethyltrimethylene, hexamethylene~ and decamethylene glycols, dihydroxy cyclo-hexane, cyclohexane dimethanol, resorcinol, hydroquinone,1,5-dihydroxy naphthalene, etc. Especially preferred are aliphatic diols containing 2-8 carbon atoms. Included a~ong the bis-phenols which can be used are bis(p-hydroxy) diphenyl, bis(p-hydroxyphenyl) methane, and bis(p-hydroxyphenyl) pro-pane. ~quivalent ester-forming derivatives o~ diols are also useful (e.g.~ ethylene oxide or ethylene carbonate can be used in place of ethylene glycol). The term "low molecu-lar weight diols" as used herein should be construed to in-clude such equivalent ester-forming dlerivatives; provided, however, that the molecular weight requirement pertains to the diol only and not to its derivatives.
Dicarboxylic acids which are reacted with the foregoing long chain glycols and low molecular weight diols to produce the copolyesters of this invention are aliphatic, cycloaliphatic, or aromatic dicarboxylic acids of a low molecular weight ? i.eO, having a molecular weight of less than about 300. ~he term "dicarboxylic acids" as used herein, includes equivalents of dicarboxylic acids having two functlonal carboxyl groups which perform substan-tially like dicarboxylic acids in reaction with glycols and diols i ln forming copolyester polymers. Thes!le equlvalents include esters and ester-forming derlvativesl, slllch as acid hal~des and anhydrides. The molecular weight requirement pertains to the acid and not to its equivalent ester or ester-forming derivative. Thus~ an ester of a dicarboxylic acid having a molecular weighk greater than 300 or an acid equivalent of a dicarboxylic acid having a molecular weight greater than 300 are included provided the acid has a molecular weight below about 300. The dicarboxyllc acids can contain any substltuent groups or combinat,ions which do not sub-stantially inter~ere with the copolyester polymer formation and use of the polymer of this invention.
Aliphatic dicarboxyllc acids, as the term is used herein, refers to carboxylic acids having two carboxyl groups each attached to a saturated carbon atom. If the carbon atom to which the carboxyl group is attached is saturated and is in a ring~ the acid is cyclaaliphatic.
Aliphatic or cycloaliphatic aclds havlng conjugated un-saturation often cannot be used because of homopolymeriza-'20 tion. However, some unsaturated acids~ such as maleic acid, can be used.
Aromatic dicarboxylic aclds~ as the term is used herein, are dicarboxylic acids having ~wo 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 one ring is present, they can be joined by aliphatic or aromatic divalent radicals or divalent radicals such as -0~ or -S02-.
` 30 Representative aliphatic and cycloaliphatic acids which can be used for this invention are sebacic acid, 1,3-cyclohexane dicarboxylic acid~ 1,4-cyclohexane dicar-boxylic acid, adipic acid, glutaric acid, succinic acid, carbonic acid, oxalic acid, azelaic acid, diethyl-malonic acid, allylmalonic acld, 4-cyclohexene-1,2-dicarboxylic acid,

2-ethylsu~eric acid~ 292,3,3-tetramethylsuccinic acid~ cyclo-pentanedicarboxylic acid, decahydro-1,5-naphthalene dicar-boxylic acid, 4,4'-bicyclohexyl dicarboxylic acid, deca-hydro-2,6-naphthalene dicarboxylic acid, 4,4 ' -methylenebis-(cyclohexane carboxylic acid), 3,4-~uran dicarboxylic acid, and l,l-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, bi-benzoic acid, substituted dicarboxy compounds wlth two benzene nuclei such as bis(p-carboxyphenyl) methane, p-oxytp-carboxyphenyl) benzoic acid, ethylene-bis(p~oxyben-zoic acid~ naphthalene dicarboxylic acid, 2,6-naphtha~
lene dlcarboxylic acid, 2,7-naphthalene dicarboxylic acid, phenanthrene dicarboxylic acid, anthracene dicarboxylic acid, 4,4i-sulfonyl dibenzoic acid, ~nd~Cl~C12 alkyl and ring substitution derivatives thereo~l such as halo, alkoxy, and aryl derivatives. Hydroxyl acids such as p(~-hydroxy-ethoxy) benzoic acid can also be used providing an aroma'cic dicarboxylic acid is also present.
Aromatic dicarboxylic acids are an especially preferred class for preparing the copolyetherester polymers of this invention. Among the aromatic acids~ those with ~-16 carbon atoms are preferred~ particularly the phenylene dlcarboxylic acids~ i.e., phthalic, terephthalic and iso-phthalic acids and th~ir dimethyl derivatives.
~ 6 --Ik is preferred that at least about 50% of the short se~men~s are ldentical a.nd ~ha~ ~he iden~ica~l se~ments ~orm a homopolymer in the flber-for~ing molecular w~ight range (molecular weight> 5000) having a melting polnt of at least 150C, and preferably greater than 200C. Pol~mer~
meeting these requirements exhibit a useful level of proper~
tles such ~s ten~ile ~trength and tear sk.rength. Polymer melting points are conven~ently determined by differential scanning calorimetry~
The short-chaln ester units wlll constltute about 15-95 weight percent o~ the copol~etherester. The remainder of the copolyetherester will be the long segmentsp ergo the long segment will comprise a~out 5-85 weight percent of the copolyetherester. Cspolyetheresters in which the short~
chain units comprise 25-90 weight percent with 10~75 weight perce~t long~chain units are pre~erred~
The copolyetherester which is preferred is pre-pared from the dlmethyl ester of terephthalic acidJ poly(tet-ramethylene oxide) glycol having a molecular weight of about 600-2000 and 1,4butanediol~
Copolyetherester elastomers described herein are commercially av~ila~le from E.I. du Pont ~e Nemou.rs and Company mder the trade mark ~rrTRE~.
In order to ~orm a power transmission belt the copolyetherester is stretched by conventiQnal means at least 300~ of its original length and pre~erably at least 400% at a temperature below its melting point ~y at least 20F.; it may be stretched to any point short o~ lts breaking point, Obviously, ~he exact leIlgth needed ;Eor a ~3iven use w~ll vary ~O bu~ it should be emphasized th~t to achieve the desired char~cteristic~ the copolyetherester must be stretched at le~st 300~ o~ its origin~l length~ Str~kching by less than 300% or at a te~perature below khe melting point by less ;~ 7 , than 20F. does not produce sufficient orientation of the copolyetherester to give tensile modulus and strength high enough for use in heavy duty applications.
Any temperature from ambient to 20F. below the melting point of the copolyetherester can be used. Prefer-ably, temperatures ranging up to about 60~. below the melting point may be utilized or rnore preferably up to about 16~F. below the melting point.
The copolyetherester elastomers must then be main-talned at substantially this length so that it may be heatsetO Rgain, any conventional method may be used for main-taining it at this length, e.g., clamps.
The stretched copolyetherester elastomer must be brought to a heat setting temperature between about 150 ; and 20F. below its melting point. If the copolyetherester is stretched at a temperature below this range, heat is applied to raise the temperature to the heat setting temperature. On the other hand~ if it is stretched at a temperature within the heat setting range, the stretching and heat setting temperatures may be identlcal and a sepa~
rate step to apply heat is not requlred.
Generally, the heat settinæ operation requires only instantaneous residence tlme within ~he heat settlng tempera-ture range, although the length o~ time at the heat setting temperature is not cri-tlcal. Longer times may be used but ln the interest of economy they are kept as short as possible.
Typicallyg the melting point will be between 3110 and 420F., preferably between 230 a~d 410Fo For the preferred copolyetherester mentloned above a heat settlng temperature of between about 330 and 390F. wlll be u~iliæed.

As a consequence of the orientation resulting from stretching and heat setting the copolyetherester will have much different characteristics t~an prior to these operations.
For instance, the elonga~ion at break for a given slab of copolyetherester will be between about 30 and 120%, prefer~
ably between about 40 and 70%. Prior to the stretching and heat treating the elongation at break would be between about 300 and 900%, preferably between about 500 and 800%.
Physical properties of the oriented copolyether-ester are excellent. Both tensile modulus and strength of the unreinforced oriented polymer are similar to those of conventional elastomers which have fiber or fabrlc reinforcement. Consequently, the oriented copolyetherester is suitable for those applications requiring such reinforce-ment~ such as power transmission belts, but has the advan-tage that the costly fabrication steps to provide the rein-forcement are not required. Another advantage of the oriented polymer relative to its unoriented state is its greater ability to retain its strength at elevated tempera-ture making it more suitable for use at higher temperatures.Furthermoreg it is yet an elastic material possessing low hysteresis. This combination of properties is desirable in materials from which power transmission belts are made because it generally results in low heat buildup and there~
fore a lower operating temperature when the belt is used in heavy duty service. Thus a product has been produced which possesses both high strength and a small degree o~ flexi-bility. The flexibility will permit an elongation ak break of 40 to 60%. Such a product may readily be utilized as a belt for power transmission.

The cooling of the copolyetherester after heating may be e~fected by any desired means; the preferred method would be cooling at room temperature but if desired external refrigeration may be utilized to reach ambient condit~ons.
The pressure needed to keep the copolyetherester at the desired elongation may be supplied by any conventional means such as appropriately sized clamps and it is not released until the temperature has been lowered by at least 100F.
below the heat setting temperature.
Power transm~ssion belts of the oriented copoly-etherester may be made in a number of ways. ~or example, a billet can be molded ~rom the polymer in a conventional manner and the billet oriented by stretchlng, heat setting~
and cool~ng according to the processes of the instant inven tlonO An endless belt is then formed by ~oining the ends o~ a desired length of the copolyetherester so orlented using either a cement or the application of heat in the immediate vicinlty of the ends to ~use them together.
Another method that can be used is to fashion a circular band from the copolyetherester ln a conventional manner and then orient the band. The latter method avoids the necessity of havillg to form a joint in the belt.
The copolyetheresters described herein can be made conveniently by a conventional ester interchange reaction.
A preferred procedure involves heating the dicarboxylic acid, e.g., dimethyl ester of terephthalic acid with a long-chain glycol, e.g., poly~tetramethylene oxide) glycol having a molecular weight of about 600~2~000 and a molar excess of dio], e.g.~ 1~4-butanediol in the presence o~ a catalyst at about 150-260C. and a pressure of 0.5 to 5 atmospheres, ~ ~.0 preferably amblent pressure, while distilling off methanol formed by the ester interchange. ~epending on temperature, catalyst, glycol excess, and equipment, this reaction can be completed within a few mînutes, e.g., 2 minutes to a few hours~ e.g., 2 hours.
Concerning the molar ratio of reackants, at least about 1.1 mole of diol, should be present ,~or each mole of acid, preferably at least about 1.25 mole of diol for each mole of acid. The long-chain glycol should be present in the amount of about 0.0025 to 0.85 mole per mole of dicarboxylic acid, preferably 0.01 to 0.5 mole per mole of acid.
This procedure results in the preparation of a low molecular weight prepolymer which can be carried to the high molecular weight copolyetherester of this invention by the procedure described below. Such prepolymers can also be prepared by a number of alternate esterification or ester i.nterchange processes; for example, the long-chain glycol can be reacted ~lth a high or low molecular weight short-chain ester homopolymer or copolymer in the presence of catalyst until randomization occurs. The short-chain ester homopolymer or copolymer can be prepared by ester inter-change from either the dimethyl esters and low molecular weight diols, as above, or from the free acids with the diol acetates. Alternatively, the short-chain ester copolymer can be prepared by direct esterification from appropriate acids, anhydrides~ or acid chlorides, for example, with diols or by other processes such as reaction of the acids with cyclic ethers or carbonates. Obviously~ the prepolymer might also be prepared by running these processes in the presence of the long-cha~n glycol.

The resulting prepolymer is then carried to high molecular welght by distillation of the excess o~ short-chain diol. This process is known as "polycondensation't.
Additional ester interchange occurs dur~ng this polycondensation which serves to increase the molecular weight and to randomize the arrangement of the copolyether ester units. Best results are usually obtained when this final distillation or polycondensation is run at less than about 5 mm. pressure and about 200-270C. for less than 10 about two hours, e.g., 0.5 to 1.5 hours.
Most practical polymerlzation techniques rely upon ester interchange to compleke the polymerlzation reaction.
In order to avoid excessive hold time at hlgh temperatures wlth pos~ible irrever~ible thermal degradation, a catalyst for the ester interchange reac~lon should he employed.
While a wide varlety of catalysts can be employed, organic kitanates such as tetrabutyl titanate used alone or in combi~
bination with magnesium or calcium acetates are pre~erred.
Complex titanates, such as Mg[HTi(OR)6]2, derlved from 20 alkali or alkaline earth metal alkoxides and titanate esters are also very effective. Inorganic titanates, such as lanthanum tltanate, calcium acetate/antimony trioxide mix~
tures and lithium and magnesium alkoxides are representatlve of other catalysts which can be usedO
The catalyst should be present in the amount of 0.005 to 0.2~ by weight based on total reactants.
Ester interchange polymerizations are generally run in the melt without added solvent, but inert solvents can be used to ~acilitate removal of volatile components 30 from the mass at low temperatures. This technique is es-~ecially valuable during prepolym~r preparation, for example~

by direct esterificatlon. Howeverg certaln low molecular weight diols, for example, butane diol in terphenylg are conveniently removed during high polymerization by azeotropic distillation. Both batch and continuous methods can be used for any stage of copolyetherester polymer preparation. Poly-condensation of prepolymer can also be accomplished in the solld 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 of reducing degradation because it must be used at temperatures below the so~tenlng point o~ the prepolymer.
The dicarboxylic acids or kheir derivatives and the polymeric glycol are incorporated into the final product ln the same molar proportions as are present in the ester interchange reaction mixture. The amount of low molecular weight diol actually incorporated corresponds to the differ~
ence between the moles of diacid and polymeric glycol pres-ent ln the reaction mlxture. When mixtures of low molecular weight diols are employed, the amounts of each diol incor-porated ls largely a function of the amounts of the diolspresent, their boiling points, and relative reactivities.
The total amount of diol incorporated is still the differ-ence between moles of diacid and polymeric glycolO
Most preferred copolyesters which are stabilized by the process of this invention are those prepared from dimethyl terephthalate, 1,4-butanediol, and poly(tetra-methylene oxide) glycol having a molecular weight of about 600-2000 or poly(ethylene oxide) glycol having a molecular weight of about 600-1500. Optionally, up to about 30 mole percent and preferably 5-20 mole percent of the dimethyl ~ ~ ~ r ~ ~ ~

terephthalate in these polymers can be replaced by dimethyl phthalate or dimethyl isophthalate. Other preferred copoly-esters are those prepared from dimethyl terephthalate, 1,4-butanediol, and poly(propylene oxide) glycol having a molecu-lar weight of about 600-1600. Up to 30 mole percent and preferably 10-25 mole percent of the dimethyl terephthalate can be replaced with dimethyl isophthalate or butanediol can be replaced with neopentyl glycol until up to about 30% and preferably 10-25% of the short-chain ester units are derived ~rom neopentyl glycol in these poly(propylene oxide) glycol polymers. The polymers based on poly(tetramethylene oxide) glycol are especially preferred because they are easily prepared, have overall superior physical properties~ and are especially resistant to water.
The most preferred copolyetherester compositions may also conkain up to about 5 weight, percent of an anti-oxidant~ e.g., between about 0.2 a;nd 5 weight percent, preferably between about 0.5 and 3 weight percent. The most pre~erred antioxidants are diaryl amines such as 4,4'-bis(~a-dimethylbenzyl) diphenylamine~ The anti-oxidant may be added during the reactio~ by means of which the copolyetherester is formed. In ~act, it is preferred that an antioxidant be present at any point during the process where the poly(alk~lene oxide) glycol is exposed to elevated temperatures 9 e.gO ~ above about 100C. The antioxidant may~ of course, be introd~ced at any stage in the process and even after preparation of a copolyether-ester is complete.

The properties of the copolyetheresters may also be modified by incorporation of various conventional organic ~illers, such as carbon black, silica gel, alumina, clays and chopped fiber glass.
All parts, proportions and percentages disclosed herein are by weight unless otherwise indicated.
The following Examples fur'cher illustrate the invention:
Example 1 Preparation of Copol~etherester A copolyetherester is prepared by placing the followlng materials in an a~itated flask fitted for dis-tillation.
Polytetramethyleneether glycol;
number average molecular weight about 97538.5 parts 1~4-Butanediol 36.5 parts Dimethyl terephthalate60.0 parks 4,4'-~is(alpha, alpha-dimethylbenzyl) diphenylamine 1.05 parts Catalyst 2.1 parts A stainless steèl stirrer with a paddle cut to conform with the internal rad~us of the flask is positloned 2 about 1~8" from the bottom of the flask and agikation is started. The flask is placed in an oil bath at 160Cv~
agitated ~or five minutes and then the catalyst is added.
Methanol distills from the reaction mi~ture as the tempera-ture is slowly raised to 250Co over a period of one hour.
When the temperature reaches 250C~ ~ the pressure is gradu-a~ly reduced to 0.3 mm Hg within 20 minutes. The polymeriza--tion mass is agitated at 250C.~0.3 mm Hg for 35 minutes~
The resulting viscous molten product is scraped from the flask in a nitrogen (water and oxygen free) atmosphere and

3 allowed to cool-- ~5 The polymer has an inherent viscosity of 1.40 at a concentration of 0.1 g~dcl. in m-cresol at 30C. and a Shore D hardness of 55.
Ex~ç~ 2 through 8 Orlentation of~ ~glyel~-r~hr~
A specimen of the copolyetherester prepared ln Example 1 measuring 1" x 6" is cut from a calendered film of 10-13 mils thlckness. The specimen is stretched 400% at one temperature. After being stretched 400%, the speclmen has a length five times its original length. While the stretching ~orce is retained to maint~ain the elongation at 400%, the stretched specimen is adjusted to a second tempera~
ture which is the heat setting tempe~ature and then ad~usted to a third temperature at which point the specimen ls re-leased ~rom the stretching ~orce.
Examples 2 through 7 in the accompanying Table show the physical properties of the copolyetherester a~ter orientation by use of various stretching~ heat settlng, and release t,emperatures~ Example 8 is outside the scope of the invention in that the specimen is stretched without re ceiving a heat setting treatment. Comparison of Examples 2 through 7 with Example 8 illustrates the beneficial effects of the heat setting treatment on modulus and tensile strength.

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Example 9 Fabrication of a V-Belt A 5 ft. long mold which has been preheated to 300F. is filled by extruding therein the copolyetherester prepared in Example 1. The mold cavi'cy has a cross section perpendicular to its long axis that is trapezoidal in shape, the longer of the parallel sides having a length of .~75"
with both angles adjacent to the longer of the parallel sides being 71 and the distance between the parallel sides being .5g". The mold is cooled to room temperature and the part removed.
The molded part is stretched at room temperature by 4~0% of iks original length. In this operation, the 5 ft. long molded part is stre~ched to a new length of 25 ft.
The stretching force is retained while the stretched part is exposed to hot air for 30 minutes at~a temperature of 350F.
and then cooled to room temperature at which point the stretching f`orce is removed from the oriented part.
A V-belt is ~'ormed by selecting a 3 ft. length of the oriented part and cuttlng the ends at a 45 angle. Both ends of the cut section are brought into contact with a surface heated to l150-550F. for sufficient length of` time to cause melting of the copolyetherester ln the immediate vicinity of the ends. The molten ends are removed from the hot surface and immediately joined by bringing them into contact with each other and holding until the molten mate-rial has solidified. When coole~, the joint is trimmed to remove excess material.

~ i~3 ~

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A power transmission belt of a heat-set oriented product of a copolyetherester elastomer, said copolyether-ester consisting essentially of a multiplicity of recurring long-chain ester units and short-chain ester units joined head-to-tail through ester linkages, said long-chain ester units being represented by the formula I and said short-chain units being represented by the formula II where G is a divalent radical remaining after the removal of terminal hydroxyl groups from a poly(alkylene oxide) glycol having a molecular weight of about 400-6000 and a carbon-to-oxygen ratio of about 2.0-4.3; R is a divalent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300 and D is a divalent radical remaining after removal of hydroxyl groups from a diol having a molecular weight less than about 250;
provided said short-chain ester units amount to about 15-95 percent by weight of said copolyetherester; said elastomer being oriented by the steps of (A) stretching said unoriented copolyetherester product free of fiber or fabric reinforcement by at least 300% of its original length, (B) bringing said stretched copolyetherester product to a temperature between about 150°-20°F below the melting point of said copolyether-ester product, and (C) cooling said copolyetherester product while stretched to a temperature below the temperature of step (B), by at least 100°F and recovering an oriented copoly-etherester product having an elongation at break of about 30-120%.

2. The power transmission belt of Claim 1 wherein said poly(alkylene oxide) glycol is poly(tetramethylene oxide) glycol having a molecular weight of 600-2000, the diol is 1,4-butanediol and the dicarboxylic acid is terephthalic acid.

3. An endless power transmission belt structure comprising a thermoplastic copolyetherester elastomer having an oriented crystalline structure about substantially its entire endless path, said crystalline structure being oriented only along said endless path.

4. An endless power transmission belt structure consisting of a thermoplastic copolyetherester elastomer having an elongated oriented crystalline structure about sub-stantially its entire endless path, said endless path having a length several times its original length prior to elongation, said crystalline structure being oriented along said endless path.

5. The power transmission belt of Claim 1 or Claim 2 wherein the thermoplastic copolyetherester elastomer is a HYTREL? elastomer.

6. The endless power transmission belt structure of Claim 3 or Claim 4 wherein the thermoplastic copolyetherester elastomer is a HYTREL? elastomer.

7. An endless power transmission belt structure consisting of thermoplastic copolyetherester elastomer having an oriented crystalline structure about substantially its entire endless path, said crystalline structure being oriented only along said endless path.

8. An endless power transmission belt structure comprising thermoplastic copolyetherester elastomer having an elongated oriented crystalline structure about substantially its entire endless path, said endless path having a length several times its original length prior to elongation, said crystalline structure being oriented only along said endless path.

9. A method of making an endless power transmission belt structure comprising the steps of providing a unitary member consisting of an unoriented thermoplastic copolyetherester elastomer having a given length and orienting said member by stretching said member only lengthwise by at least 300% of said length, heat setting said stretched member at a temperature of approximately 350°F, and cooling said member while stretched.