WO1995018164A1

WO1995018164A1 - Triblock copolymers of alkylene oxides and hydrocarbons and polyurethanes prepared therefrom

Info

Publication number: WO1995018164A1
Application number: PCT/US1994/014905
Authority: WO
Inventors: Johan A. Thoen; Thomas H. Kalantar; Daniel P. Green
Original assignee: The Dow Chemical Company
Priority date: 1993-12-29
Filing date: 1994-12-23
Publication date: 1995-07-06

Abstract

Described herein is a triblock copolymer of the formula A-B-A wherein A is a poly(alkylene oxide) or poly(alkylene sulfide) group and B is a polymeric hydrocarbon group with a molecular weight in the range of from 1.000 to 25.000, wherein the A blocks comprise from 5 to 50 percent by weight of the copolymer, as well as polyurethane polymers prepared therefrom. Also disclosed is a process for the preparation of a functional triblock copolymer which comprises the sequential steps of: (1) polymerizing a conjugated 1,3-diene under reaction conditions sufficient to form a polydiene dianion; (2) contacting the polydiene dianion with an alkylene oxide or alkylene sulfide, in an amount and under reaction conditions sufficient to provide a block segment comprised of at least two repeat units derived from the alkylene oxide or alkylene sulfide on each end of the polymer; and (3) contacting the product of step (2) with a proton-donating compound under reaction conditions sufficient to provide a terminal hydroxyl or thiol group on each end of the copolymer.

Description

TRIBLOCK COPOLY ERS OF ALKYLENE OXIDES AND HYDROCARBONS AND POLYU RETHANES

PREPARED THEREFROM

This invention relates to functional hydrocarbons and, more particularly, to functional polybutadienes and polyurethanes prepared therefrom.

It is known to prepare functional polybutadienes by polymerizing butadiene in the presence of a lithium- or sodium-containing initiator, and then contacting the resulting dianion with ethylene oxide to produce a functional polybutadiene as shown, for example, in U.S. Patent 4,866, 120. Such materials are known to react with polyisocyanates to form polyurethane materials, although the physical properties and thermal processing characteristics of the resulting polyurethane may be less than desirable.

In one aspect, this invention is a triblock copolymer of the formula A-B-A wherein each A block is a poly(alkylene oxide) or poly(alkylene sulfide) group and B is a polymeric hydrocarbon group with a molecular weight in the range of from 1 ,000 to 25,000, wherein the A blocks comprise from 5 to 50 percent by weight of the copolymer.

In a second aspect, this invention is a process forthe preparation of a functional triblock copolymer which comprises the sequential steps of:

(1 ) polymerizing a conjugated 1 ,3-diene under reaction conditions sufficient to form a polydiene dianion; (2) contacting the polydiene dianion with an alkylene oxide or alkylene sulfide, in an amount and under reaction conditions sufficientto provide a block segment comprised of at least two repeat units derived from the alkylene oxide or alkylene sulfide on each end of the polymer; and

(3) contacting the product of step (2) with a proton-donating compound under reaction conditions sufficientto provide a terminal hydroxyl or thiol group on each end of the copolymer.

In a third aspect, this invention is a polyurethane polymer prepared by the reaction of the copolymer of the first aspect of the invention and at least one polyisocyanate.

It has been discovered that the copolymers of the invention are useful as an isocyanate-reactive compound in processes for the preparation of pόlyurethane/urea polymers and, when so used, advantageously provide a polyurethane with increased resistance to hydrolysis and weatherability, relative to polyurethanes prepared from polyether and polyester polyols. In addition, polyurethanes prepared with the copolymer of the invention and difunctional isocyanates and chain extenders have been discovered to advantageously provide a thermoplastic material with improved thermal processing characteristics (such as melt flow), less phase separation, and improved physical properties, such as tensile strength, tear strength, and elongation, relative to thermoplastic materials prepared from functionalized polydienes which do not contain terminal block segments of an alkylene oxide or alkylene sulfide. By contrast, hydroxy-terminated polydienes with only one alkylene oxide group per end group may not be useful in certain polyurethane applications because they have poor compatibility with the polyisocyanate and/or chain extenders used in such reactions. For example, when reacted neat with difunctional isocyanate in the presence of additional difunctional active hydrogen-containing materials, the hydroxy-terminated polybutadiene tends to undergo gross phase separation and forms relatively low molecular weight polyurethane polymers. Accordingly, the thermal processing characteristics and physical properties of such product would be less than desirable.

The triblock copolymer of the first aspect of the invention may be prepared by contacting a polymeric hydrocarbon dianion with an alkylene oxide or alkylene sulfide, in an amount and under reaction conditions sufficient to provide a block segment comprised of at least two repeat units derived from the alkylene oxide or alkylene sulfide on each end of the polymer; and then contacting the resulting block copolymer with a proton-donating compound under reaction conditions sufficientto provide a terminal hydroxyl orthiol group on each end of the copolymer. The process of the second aspect of the invention is directed to a method for the preparation of such copolymers wherein the "B" block is a polydiene.

The polymeric hydrocarbon dianion ("polymeric dianion") used to prepare the copolymer of the first aspect of the invention may be prepared by any of several methods. For example, the polymeric dianion may be a polydiene dianion prepared by polymerizing a con- jugated 1 ,3-diene in the presence of an initiator compound at a suitable temperature and pressure. For this method, the polydiene dianion is most preferably polybutadiene. The term "polydiene" as used herein refers to a polymer of a conjugated 1,3-diene. An alternative method is to contact a functionalized hydrocarbon polymer with sodium, potassium, a hydroxide, alkoxide, or hydride of either, or a mixture thereof, to obtain a polymeric dianion. The term "functionalized hydrocarbon polymer" as used herein means a hydrocarbon polymer with the following terminal groups: hydroxyl (-OH), thiol (-SH), primary amine (-NH₂), secondary amine (-NHR, wherein R is a Cι_₂o organic moiety), sulfonic acid (-S0₃H), and carboxyl (-COOH), or combinations thereof. The particular dianion species generated will, of course, depend on its method of preparation. For example, a dihydroxy-terminated polymer will form a dialkoxide; a dithiol-terminated polymerwill form a dithiolate, and so forth. Examples of suitable hydrocarbon polymers include polyethylene, poly(isobutylene), and polydienes. Most preferably, the hydrocarbon polymer is polybutadiene.

If the dianion is prepared by polymerizing a conjugated 1,3-diene in the presence of an initiator compound, suitable initiator compounds include alkali metal compounds which are preferably sodium- or lithium-containing organic compounds, or mixtures of sodium- or lithium-containing organic compounds and alkali metal alkoxides or aryloxides. Most preferably, the polymerization process is carried out as described in copending application "A Process For The Preparation Of Polyfunctional Polydienes," by Johan Thoen et al., describes certain sodium salts and alkali metal alkoxides and aryloxides.

Suitable conjugated 1 ,3-dienes which are useful in the preparation of the polydiene dianion include any 1 ,3-diene containing 4 to 12 carbon atoms, preferably 4 to 8 carbon atoms. Examples of suitable compounds include 1,3-butadiene; isoprene; myrcene; 2,3-dimethyl-1,3-butadiene; 1 ,3-pentadiene; 2-methyl-3-ethyl-1,3-butadiene; 2-methyl-3-ethyl-1 ,3-pentadiene; 2-ethyl-1 ,3-pentadiene; 1,3-hexadiene; 2-methyl- -1,3-hexadiene, 1,3-heptadiene; 3-methyl-1,3-heptadiene; 1,3-octadiene; 3-butyl- -1 ,3-octadiene; 3,4-dimethyl-1 ,3-hexadiene; 3-n-propyl-1 ,3-pentadiene; 4,5-diethyl- -1 ,3-octadiene; phenyl- 1 ,3-butadiene; 2,3-diethyl-1 ,3-butadiene; 2,3-di-n-propyl-

-1 ,3-butadiene and 2-methyl-3-isopropyl-1 ,3-butadiene. Among the dialkylbutadienes, it is preferred that the alkyl groups contain from 1 to 3 carbon atoms. Of the above monomers, 1 ,3-butadiene, isoprene, myrcene, 2,3-dimethyl-1 ,3-butadiene and 1 ,3-pentadiene are preferred, with 1 ,3-butadiene being particularly preferred. The 1 ,3-conjugated dienes may be polymerized alone, or in a mixture with each other to form copolymers. In addition, the above compositions may contain amounts of other anionically polymerizable monomers such as styrene, α-methylstyrene, and stilbene. However, when employed, such comonomers are preferably employed i n an amount such that they comprise less than about 50 weight percent of the polydiene dianion, more preferably less than about 20 weight percent. The copolymer of the invention is prepared by reacting a polymeric dianion with an alkylene oxide or alkylene sulfide, wherein the alkylene oxide or alkylene sulfide is employed in an amount sufficient to provide terminal block segments comprising at least two repeat units derived from the alkylene oxide or alkylene sulfide. In the process of the second aspect of the invention, the polymeric dianion is a polydiene dianion. Suitable alkylene oxides and alkylene sulfides include ethylene oxide, ethylene sulfide, propylene oxide, 1,2- or

2,3-butylene oxide, or mixtures thereof. For example, if the polymeric dianion is reacted with ethylene oxide, the block segment is of the formula: -(CH₂-CH₂-0)_x-, wherein x is a number from 2 to 20. Preferably, the alkylene oxide or sulfide is used in an amount sufficientto provide a block segment on each end of the polymer with an average number of repeat units of at least about 2, more preferably at least about 4, most preferably at least about 10; and is preferably no greater than about 20, and more preferably no greater than about 15.

If the process to add the terminal block segments is carried out using a solution of dianion which has not been previously functionalized, as in the process of the second aspect of the invention, the alkylene oxide or alkylene sulfide may simply be combined with the solution at a temperature of less than about 40°C and slowly heated to a temperature in the range of from 80°C to 130°C to obtain polymerization. If the process is carried out using a polymeric hydrocarbon dianion prepared from a hydrocarbon polymer which has been previously functionalized (to provide a terminal hydroxyl group, for example), the process to add the terminal block segment of alkylene oxide or alkylene sulfide may be carried out under any suitable reaction conditions typically employed for the polymerization of alkylene oxide or alkylene sulfide in the presence of an initiator compound, with the functionalized hydrocarbon polymer serving as the initiator. For example, the functionalized hydrocarbon polymer may first be contacted with sodium, potassium, or a hydroxide, alkoxide, or hydride thereof, or a mixture thereof, to obtain a polymeric dianion. Thereafter, any water generated by such procedure is preferably removed from the reaction mixture so that it is present in an amount of less than about 200 ppm, so that it will not initiate with the alkylene oxide or alkylene sulfide to any great extent. The solution of polymeric dianion may then be combined with the alkylene oxide or alkylene sulfide and heated to obtain polymerization. Preferably, however, the process is carried out at a temperature in the range of from 80°C to 130°C, more preferably in the range of from 90°C to 120°C.

Thereafter, the product containing terminal block segments is contacted with a proton-donating compound under reaction conditions sufficient to provide a terminal hydroxyl orthiol group on each end of the copolymer. In the process of the second aspect of the invention, the product containing terminal block segments is the product of step (2). Examples of such compounds include HCI or glacial acetic acid. If terminal amine end groups are desired, amine-terminated copolymers may be prepared by reductive amination of the hydroxy- or thiol-terminated copolymer, or by reaction with acrylonitrile, followed by a reduction step. Sulfonic acid-terminated (-SO3H) copolymers may be prepared by the oxidation of a thiol-terminated copolymer. If carboxylic acid end groups are desired, carboxyl-terminated copolymers may be prepared by reacting the hydroxy- or thiol-terminated copolymer with an acryiate ester, followed by a hydrolysis step, and so forth.

If the copolymer contains unsaturation, it is preferably hydrogenated under standard conditions and in the presence of a suitable catalyst in order to hydrogenate such groups. Any suitable hydrogenation catalyst may be used, but generally preferred are noble metal catalysts such as platinum, palladium, or ruthenium on activated carbon or transition metals such as nickel on kieselguhr. The temperature of the hydrogenation reaction is preferably in the range of from 50°C to 300°C, and is preferably less than about 100°C. The duration of the reaction may vary, for example, from 6 to 24 hours, or longer, depending on the specific reactants, temperature and pressure. The reaction pressure may vary from 15 psig to 2,500 psig.

The copolymer of the first aspect of the invention and the copolymer prepared by the process of the second aspect of the invention have an internal polymeric hydrocarbon block "B" which has a molecular weight which is preferably in the range of from 1 ,000 to 25,000, but is more preferably less than about 3,000. The "A" blocks derived from the alkylene oxide or alkylene sulfide preferably comprise at least about 5 percent, more preferably at least about 10 percent, most preferably at least about 15 percent; and is preferably no greater than about 30 percent, and more preferably no greater than about 25 percent by weight of the copolymer.

In a third aspect, this invention is a polyurethane polymer prepared by the reaction of the copolymer of the first aspect of the invention and at least one polyisocyanate. Any reaction mixture used to prepare the polyurethane should contain from 1 to 99 percent by weight of the copolymer. Suitable isocyanates include aromatic, aliphatic and cyclo-aliphatic diisocyanates and combinations thereof. Representatives of these types are m-phenylene diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, hexamethylene- -1 ,6-diisocyanate, tetramethylene-1 ,4-diisocyanate, cyclohexane-1 ,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 4,4'-biphenylene diisocyanate and other diisocyanates disclosed in U.S. Patent 4,731 ,416, column 5, lines 13-37. Also suitable are isocyanate- -terminated prepolymers such as those prepared by reacting an excess of stoichiometry of a diisocyanate with a polyol. Aromatic diisocyanates such as tolylene diisocyanate, 4,4'-methyldiphenyl diisocyanate and polymethylene polyphenyl isocyanate and liquid forms thereof (such as carbodiimide-modified MDI) are preferred, with diphenylmethane-

-4,4'-diisocyanate (MDI) being most preferred. The polyisocyanate is preferably used in an amount such that the "index", or ratio of isocyanate groups to active hydrogen groups in the reaction mixture to prepare the polyurethane is at least 0.60: 1.00, more preferably at least 1.00: 1.00; and is preferably no greater than 2.00: 1.00, more preferably no greater than 1.20: 1.00.

In addition, the reaction mixture to prepare the polyurethane may also contain chain extenders which, if a thermoplastic polymer is to be prepared, are preferably mostly difunctional. The term "chain extender" as used herein means any compound having 2 or 3 pendant or terminal hydroxyl or primary or secondary amine groups and an equivalent weight of less than about 500. Preferably, the chain extender is difunctional. Examples of chain extenders include aliphatic (straight- or branched-chain) diols ortriols, cycloalkane diols or triols, or cycloalkane dialkanols or trialkanols, having from 2 to 10 carbons in the chain. Examples of such include ethylene glycol, 1,3-propanediol, 1 ,4-butanediol, 1 ,3- and 1,5-pentanediol, 1 ,2- and 1 ,6-hexanediol, 1 ,2-propanediol, 1,3- and 2,3-butanediol, 3-methylpentane-1 ,5-diol, 1 ,9-nonanediol, 2-methyloctane-1 ,8-diol, 1,2-, 1 ,3- and

1 ,4-cyclohexanedimethanol, 1 ,2-, 1 ,3-, and 1 ,4-cyclohexanediol, 1,3-cyclobutanediol and 1,3-cyclopentanediol, as well as mixtures of two or more of such diols. Trifunctional extenders such as glycerol and trimethylol propane can also be employed. Preferably, the chain extender is 1 ,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, ethylene glycol, and diethylene glycol, or mixtures thereof.

The polyurethane may be prepared by any suitable method, depending on the type of material to be prepared, using the copolymer of the invention as a "polyol", or high equivalent-weight isocyanate-reactive component. Optionally, other types of polyols, such as polyether or polyester polyols, may be employed in combination with the copolymer of the invention. For example, thermoset elastomers may be prepared by hand-casting or reaction injection molding (RIM) techniques; polyurethane foams may be prepared by combining the reactants in the presence of a suitable blowing agent; thermoplastic polyurethanes may be prepared by combining the reactants in either a "one-shot" technique, where the reactants are fed directly into an extruder or mixing head, or by the preparation of isocyanate-functional prepolymers which are then reacted with a chain-extruder; and polyurethane sealants may be prepared from lower equivalent weight isocyanate- and/or active hydrogen-functional prepolymers. In addition, suitable urethane catalysts may also be employed in the preparation of such compositions. The compositions of the invention can also incorporate various additives such as fillers, fiberglass, antioxidants, pigments, fire retardants, plasticizers, reinforcing agents and wax lubricants commonly employed in the art in such compositions. If the polyurethane is a thermoplastic polyurethane, preferably it is thermally processable at a temperature of less than about 215°C. The thermal processability, tensile strength (and elongation), and tear strength of the polyurethane polymer may be evaluated by the following test methods, respectively: ASTM D-638, ASTM D- 1938, and ASTM D-1238. The hydrolytic stability of a polyurethane elastomer may be tested by soaking the elastomer in water at 70°C for one week, and then testing its tensile strength and tear strength using the procedures set forth above. The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are given by weight.

Example 1 - Preparation Of Polyethylene Oxide-Polybutadiene-Polyethylene Oxide Triblock Copolymer Butadiene was added to a reactor vessel containing 1 ,200 ml of a mixture of anhydrous cyclohexane and tetrahydrofuran (THF) (9/1 volume/volume ratio) at about 15°C. To that was added a predetermined amount (10 to 40 mL, according to the desired molecular weight) of a previously prepared THF solution of sodium napthalenide (1 N solution), mixed with potassium t-butoxide. The molar ratio of Na: K was 1 : 1. The green-blue color changed to a deep red color and an exothermic reaction occurred. A reaction temperature of 30°C was reached within a few minutes, after which the reactor contents were cooled to take a sample from the reactor for analysis. The molecular weight of the polybutadiene was determined using a gel permeation chromatography technique and ¹ H-NMR was used to determine the microstructure (percentage of repeat units containing a pendant vinyl group). To the solution of the polybutadiene anion was added a predetermined amount of anhydrous ethylene oxide. The temperature was raised to 35°C for 30 minutes and subsequently to 90°C to complete the polymerization. After 4 to 8 hours, the mixture of polymer in solvent was cooled to room temperature and protonated with glacial acetic acid. The acetate salt was removed by filtration and the solvent was evaporated at 80^CC under reduced pressure. The product was analyzed by ¹ H-NMR to determine the percent ethylene oxide content in the polymer. The weight ratio of ethylene oxide blocks to polybutadiene was 44/100. The average molecular weight (M_n) was 11,661, and the polydispersity index (M_w/M_n) was 1.21. The vinyl content (percentage of 1 ,2-polybutadiene units) of the polydiene block copolymer was 58.7 percent.

Example 2 - Preparation Of Polyethylene Oxide-Butadiene-Polyethylene Oxide A-B-A Triblock Copolymers. Butadiene (100 g) was added to a reactor vessel containing 1,200 g of a mixture of anhydrous cyclohexane and tetrahydrofuran (9: 1 volume/volume ratio) at 1 1°C. A THF solution of sodium napthalenide (1.0 molar) mixed with potassium-tert-butoxide (1.0 molar) was then added. The green-blue color changes to deep red color and an exothermic reaction occurs. A reaction temperature of 48°C was reached within a few minutes. The reaction mixture was cooled to 1 1 °C. A sample was taken from the reactor for analysis. The number average molecular weight of the polybutadiene was determined by gel permeation chromatography (using polybutadiene standards) to be 6,441. M_w/M_n was determined to be 1.18. The vinyl content in the polybutadiene was determined by 'H-NMR to be 53 percent.

Ethylene oxide (6 g) dissolved in 10 mL THF was added to a 600 mL portion of the polybutadiene solution prepared above. The red color of the polybutadiene solution disappeared quickly, indicating the reaction with the ethylene oxide was occurring. The temperature of the mixture was increased to 80°C and maintained there for 60 minutes. The product was neutralized with dilute HCI, washed with water and dried over MgS0 . The solvent was evaporated at 80°C under reduced pressure. The product was analyzed by ¹³C-NMR to determine the average ethylene oxide cap block length. The average cap block length for the product was 2.3 ethylene oxide units per end block.

Example 3 - Polymerization Of Polythylene Oxide End Blocks Onto Hydroxy-Functional Polybutadiene A. Preparation of Dianion: To a round-bottomed flask was added hydrogenated hydroxyl-terminated polybutadiene (available from Nippon Soda) dissolved in toluene and a stoichiometric amount (relative to the hydroxyl groups of the polybutadiene) of potassium hydroxide, to prepare a bis-potassium salt. The flask was fitted with a reflux condenser and Dean Stark trap, and the solution was refluxed for between 5 hours and 2 days until sufficient water was removed such that the final solution contained no more than 200 ppm water.

Toluene was stripped from the solution, and the resulting dianion was dissolved in anhydrous tetrahydrofuran (THF). The vinyl content of the dianion was about 90 percent. B. Polymerization of Ethylene Oxide End Blocks: Into a dry Parr reactor was added a 20 weight percent solution of the bis-potassium salt prepared above in THF, and the solution was cooled to 0°C. The desired amount of ethylene oxide was distilled into the reactor, and the solution was stirred between 50^CC and 100°C while the extent of reaction was monitored by the drop of pressure inside the reactor. Once the reaction was complete, the reaction was quenched with a 10-fold excess of water dissolved in THF. The product mixture was carefully washed sequentially with dilute aqueous hydrochloric acid and saturated aqueous sodium chloride to wash out the potassium salts. The organic layerwas dried over anhydrous sodium sulfate and concentrated in vacuo to yield a polyethylene oxide/hydrogenated polybutadiene/polyethylene oxide triblock copolymer.

Example 4 - Preparation of Polyethylene Oxide-(Hydrogenated-Polybutadiene)-Polyethylene Oxide Triblock Copolymer Using Aluminum-Porphyrin Catalyst Into a dry, 600 mL Parr reactor was added 6.1489 (10.0 mmol) of tetraphenylporphyrin. The reactor was evacuated and repressurized with 1 atmosphere of dry nitrogen. Toluene (300 mL) was added to the reactor and the solution was stirred for 30 minutes. Triethylaluminum (10.00 mL, 1.00 M, 10.0 mmol, 1.00 equivalent) was added via syringe and the reactor contents were stirred for 1 hour. Hydrogenated, hydroxytelechelic polybutadiene (95 g, Mn = 1990, 50 mmol, 5 equivalent (available from Nippon Soda) dissolved in lOO mL of toluene was added and the reaction mixture was cooled to -5°C. Ethylene oxide (24 g. 545 mmol, 54.5 equivalent) was distilled into the reactor, and the solution was stirred at 80°C for 14 hours. The reaction mixture was quenched with a 0.25 mL of water dissolved in THF, filtered through a Celite™ filter aid, and carefully washed sequentially with dilute aqueous hydrochloric acid, 1.0 N sodium hydroxide solution and saturated aqueous sodium chloride. The organic layer was dried over anhydrous sodium sulfate and concentrated in vacuo to yield polyethylene oxide-(hydrogenated-polybutadiene)-polyethylene oxide triblock copolymer (1 13 g, 95 percent yield).

Example 5 - Preparation of Polyurethane Polymer The hydroxytelechelic polyethylene oxide-polybutadiene-polyethylene oxide triblock copolymer polyol produced in Example 4 (M_n = 2,355, f(oH) = 1.90, 16 weight percent EO) (15.91 g), and 1 drop commercial dibutyltin dilaurate catalyst were dissolved in 200 mL dry tetrahydrofuran and the solution heated to reflux. Molten purified monomeric MDI (8.901 g) was added. After 1 hour, 1 ,4-butanediol (2.44 g) was added. After 18 hours, the solution was cast into a 36 mil film, with ultimate tensile strength 3,400 psi, ultimate elongation 580 percent, and tear strength 230 lb/inches. The elastomer showed melt flow beginning at 200°C, without macrophase segregation, as shown by the clarity of the melt flow strand.

Claims

I . A triblock copolymer of the formula A-B-A wherein each A block is a poly(alkylene oxide) or poly(alkylene sulfide) group and B is a polymeric hydrocarbon group with a molecular weight in the range of from 1 ,000 to 25,000, wherein the A blocks comprise from 5 to 50 percent by weight of the copolymer.

5 2. The copolymer of Claim 1 wherein the polymeric hydrocarbon group is polybutadiene.

3. The copolymer of Claim 1 wherein each A block is a poly(alkylene oxide) group.

4. The copolymer of Claim 3 wherein each A block is a poly(ethylene oxide)

10 9^r0LJP-

5. The copolymer of Claim 1 wherein each A block is a poly(alkylene sulfide) group.

6. The copolymer of Claim 1 wherein the molecular weight of the A block is less than 3,000.

15 7. The copolymer of Claim 1 wherein the A blocks comprise at least 10 percent by weight of the copolymer.

8. The copolymer of Claim 1 which contains terminal amine groups.

9. The copolymer of Claim 1 which contains terminal carboxyl groups.

10. The copolymer of Claim 1 wherein the A blocks comprise no greater than 20 25 percent by weight of the copolymer.

I I . A process for the preparation of a functional triblock copolymer which comprises the sequential steps of:

(1) polymerizing a conjugated 1 ,3-diene under reaction conditions sufficientto form a polydiene dianion; 25 (2) contacting the polydiene dianion with an alkylene oxide or alkylene sulfide, in an amount and under reaction conditions sufficient to provide a block segment comprised of at least two repeat units derived from the alkylene oxide or alkylene sulfide on each end of the polymer; and

(3) contacting the product of step (2) with a proton-donating compound under 30 reaction conditions sufficient to provide a terminal hydroxyl orthiol group on each end of the copolymer. ^~

12. The process of Claim 1 1 wherein the conjugated 1 ,3-diene is butadiene.

13. The process of Claim 1 1 wherein the polydiene dianion is reacted with an alkylene oxide in step (2).

35 14. The process of Claim 13 wherein the alkylene oxide is ethylene oxide.

15. The process of Claim 1 1 wherein the molecular weight of the polydiene dianion is less than 3,000.

16. The process of Claim 1 1 wherein the alkylene oxide or alkylene sulfide is employed in an amount sufficientto provide terminal block segments which comprise at least 10 percent by weight of the copolymer.

17. The process of Claim 16 wherein the alkylene oxide or alkylene sulfide is employed in an amount sufficient to provide terminal block segments which comprise at least 15 percent by weight of the copolymer.

18. The process of Claim 1 1 wherein the alkylene oxide or alkylene sulfide is employed in an amount sufficient to provide terminal block segments which comprise no greater than 25 percent by weight of the copolymer.

19. A polyurethane polymer prepared by the reaction of at least one polyisocyanate and a triblock copolymer of the formula A-B-A wherein A is a poly(alkylene oxide) or poly(alkylene sulfide) group and B is a polymeric hydrocarbon group with a molecular weight in the range of from 1,000 to 25,000, wherein the A group comprises 5 to 50 percent by weight of the copolymer.

20. The polyurethane polymer of Claim 19 wherein the polyisocyanate is

4,4'-methyldi phenyl diisocyanate, or carbodiimide-modified 4,4'-methyldiphenyl diisocyanate.