A method of preparing block copolymers

Abstract: A method for preparing tapered block copolymers in a polymerization process by charging an initiator and monomers sequentially with one or more charges of first one of the monomers, then with a mixture of the two monomers, and then with one or more charges of the second monomer alternating with one or more charges of the first monomer to produce a polymodal tapered block copolymer. Suitable monomers include conjugated dienes and monovinylaromatic compounds. The copolymers are particularly useful for shrink film packaging applications.

Description: Background of the Invention This invention relates to tapered block copolymers with vinylarene terminal blocks. In another aspect, this invention relates to a method of preparing tapered block copolymers with vinylarene terminal blocks by charging of an organometal initiator and a vinyl-substituted aromatic compound with various sequences of more of the vinyl-substituted aromatic compound, a conjugated diene, and combinations of the two monomers. Polymerization of styrene and butadiene with organolithium initiators to produce block copolymers in which one or more non-elastomeric polymer blocks are bonded to one or more elastomeric polymer blocks has been disclosed. Similarly, styrene and butadiene with terminal tapered blocks have been prepared by sequential charging of initiator and monomers to the polymerization zone to produce block copolymers suitable for manufacture of transparent colorless blister packages. DE-A-3 738 748, comparative example III, discloses a seven-step polymerization, where iniator is added wherein block copolymers without any tapered blocks are produced. There is a continuing need for transparent colorless material suitable for shrink wrap packaging applications. Having better shrinkage properties exhibited at lower temperatures would facilitate the use of block copolymer shrink wrap in packaging applications. Summary of the Invention Thus, it is an object of this invention to provide a novel tapered block copolymer of conjugated dienes and vinyl-substituted aromatic hydrocarbons with improved shrink properties. A further object of this invention is to provide a novel process for making tapered block copolymers. The inventive copolymers are prepared by: (1) charging a monovinylaromatic monomer, a randomizer and an initiator, and allowing essentially complete polymerization to occur; thereafter (2a) charging additional monovinylaromatic monomer and initiator, and allowing essentially complete polymerization to occur; (2b) charging a mixture of monovinylaromatic monomer and conjugated diene monomer, and allowing essentially complete polymerization to occur; (2c) charging additional monovinylaromatic monomer and additional initiator, and allowing essentially complete polymerization to occur; thereafter (3) charging conjugated diene monomer and allowing essentially complete polymerization to occur; and finally (4) introducing a coupling agent, wherein all stages are sequential except that charges (2a), (2b) and (2c) can be made in any order of (2a),(2b) and (2c). Also, optionally, a charge of conjugated diene can be made next preceeding or next succeeding either of charges (2a) or (2b). Detailed Description of the Invention The tapered block character of the polymer is produced by, after the initial charge or charges of monovinylaromatic monomer and initiator, charging with a blend of monovinylaromatic monomer and conjugated diene. This is generally followed by a charge of monovinylaromatic monomer and initiator to give a low molecular weight component. Alternatively (as in Run 5 described hereafter in Table II) the last monovinylaromatic monomer charge and the blend charge can be reversed. Finally, a charge of conjugated diene is introduced. At each stage of charging, polymerization is allowed to continue until essentially no free monomer is present. With each subsequent charge which includes initiator a different molecular weight species will be produced as well as the opportunity for polymerization of part of the charge with each of the existing species. After virtually complete polymerisation of the final monomer charge, the active living linear block copolymers are charged with a polyfunctional coupling agent to allow coupling of each of the living species with each of the other species or with others of the same species to form the desired polymodal tapered block polymers. A typical charging sequence, and the resulting polymers at each stage, is shown in the following table. Typical Charging Sequence 1. initiator₁ tetrahydrofuran and styrene₁ S₁-Li₁ 2. initiator₂ and styrene₂ S₁-S₂-Li₁ S₂-Li₂ 3. butadiene₁ and styrene₃ S₁-S₂-B₁/S₃-Li₁ S₂-B₁/S₃-Li₂ 4. butadiene₂ (optional) S₁-S₂-B₁/S₃-B₂-Li₁ S₂-B₁/S₃-B₂-Li₂ 5. initiator₃ and styrene₄ S₁-S₂-B₁/S₃-B₂-S₄-Li₁ S₂-B₁/S₃-B₂-S₄-Li₂ S₄-Li₃ 6. butadiene₃ S₁-S₂-B₁/S₃-B₂-S₄-B₃-Li₁ S₂-B₁/S₃-B₂-S₄-B₃-Li₂ S₄-B₃-Li₃ 7. Epoxidized Vegetable Oil polymodal tapered block polymers with styrene terminal blocks where S = styrene B = butadiene B/S = tapered block At each stage, polymerization is allowed to continue until essentially no free monomer is present. The third, fourth, sixth and seventh steps shown above in the table of a typical charging sequence are carried out in the absence of additional initiator. Tapered blocks in each of the growing polymer chains present are produced by simultaneously charging with both monomers as in the third step shown above in the table of a typical charging sequence. As can be seen from the intermediate products listed in the typical charging sequence table above, there are at least three distinct polymer chains before coupling. Thus, polymodal block copolymers comprising high, medium and low molecular weight species are produced. The randomizer causes random polymerization of the monovinylaromatic monomer and the conjugated diene, but the diene still enters into the chain faster than the monovinyl substituted aromatic so that the block tapers gradually from a random copolymer block to an esssentially monovinyl substituted aromatic block. The process of this invention can be carried out with any of the organomonoalkali metal compounds of the formula RM wherein R is an alkyl, cycloalkyl or arylcarbanion containing 4 to 8 carbon atoms and M is an alkali metal cation. The presently preferred initiator is n-butyllithium. The conjugated diene monomers which can be used contain 4 to 6 carbon atoms and include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and 1,3-pentadiene and mixtures thereof. Presently preferred is 1,3-butadiene. The monovinylaromatic monomers which can be used contain 8 to 12 carbon atoms and include styrene, alpha-methylstyrene, p-vinyltoluene, m-vinyltoluene, o-vinyltoluene, 4-ethylstyrene, 3-ethylstyrene, 2-ethylstyrene, 4-tertbutylstyrene and 2,4-dimethylstyrene and mixtures thereof. Presently preferred is styrene. The polymerization process is carried out in a hydrocarbon diluent at any suitable temperature in a range of -10° to 150°C, preferably in the range of 0° to 110°C, at pressures sufficient to maintain the reaction mixture substantially in the liquid phase. Preferred hydrocarbon diluents include linear and cycloparaffins such as pentane, hexane, octane, cyclohexane, cyclopentane and mixtures thereof. Presently preferred is cyclohexane. Generally the temperature is such that the resulting polymer is in solution. Small amounts of polar compounds are used in the hydrocarbon diluent to improve the effectiveness of alkylmonoalkali metal initiators such as n-butyllithium and to effect partial randomization of the vinylarene/conjugated diene so as to give a tapered block. Examples of polar compounds which can be advantageously employed are ethers, thioethers (sulfides) and tertiary amines. It is usually preferred to use ethers and sulfides in which the radicals attached to the oxygen or sulfur atoms are hydrocarbon radicals. Specific examples of such polar materials include dimethyl ether, diethyl ether, ethyl methyl ether, ethyl propyl ether, di-n-propyl ether, di-n-octyl ether, anisole, dioxane, 1,2-dimethoxyethane, dibenzyl ether, diphenyl ether, tetramethylene oxide (tetrahydrofuran), dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, di-n-butyl sulfide, methyl ethyl sulfide, dimethylethylamine, tri-n-ethylamine, tri-n-propylamine, tri-n-butylamine, trimethylamine, triethylamine, N,N-di-methylaniline, N-methyl-N-ethylaniline, N-methylmorpholine, and the like. It is to be understood also that mixtures of these polar compounds can be employed in the practice of the present invention. The amount of polar compounds used in admixture with the hydrocarbon diluent is usually in the range of 0.005 to 50 weight percent of the total mixture. Presently preferred are either tetrahydrofuran or diethyl ether. Amounts of tetrahydrofuran to provide from about 0.01 to 10 phm (parts per 100 parts of total monomer), preferably 0.02 to 1.0 phm are suitable. The randomizer is added with the initial monovinylaromatic charge, however, for the additional effect of causing the monovinylaromatic component resulting from each initiator charge to be of relatively narrow molecular weight distribution. Surprisingly, it has been found that superior results are obtained by having a polymodal molecular weight distribution of the total polymer chain lengths as a result of the addition of initiator at least three times and yet having the terminal monovinyl substituted aromatic component portions of the molecules resulting from each initiator addition be of relatively narrow molecular weight distribution. The polymerization is carried out in a substantial absence of oxygen and water, preferably under an inert gas atmosphere. Prior to the coupling step, the reaction mass contains a very high percentage of molecules in which an alkali metal cation is positioned at one end of each polymer chain. Impurities in the feed such as water or alcohol reduce the amounts of monoalkali metal polymer in the reaction mass. After virtually complete conversion of the last monomer added to the polymer, a suitable polyfunctional coupling agent is added. As used here, the term "coupling" means the bringing together and joining, by means of one or more central coupling atoms or coupling moieties, two or more of the living monoalkali metal-terminated polymer chains. A wide variety of compounds for such purposes can be employed. Among the suitable coupling agents are the di- or multivinylaromatic compounds, di- or multiepoxides, di- or multiisocyanates, di- or multiimines, di- or multialdehydes, di- or multiketones, di- or multihalides, particularly silicon halides and halosilanes, mono-, di-, or multianhydrides, mono-, di-, or multiesters, preferably the esters of monoalcohols with polycarboxylic acids, diesters which are esters of monohydric alcohols with dicarboxylic acids, lactones, including combination type compounds containing two or more groups and mixtures. Examples of suitable vinylaromatic coupling agents include divinylbenzene, 1,2,4-trivinylbenzene, 1,3-divinylnaphthalene, 1,3,5-trivinylnaphthalene, and 2,4-divinylbiphenyl. Of these, the divinylaromatic hydrocarbons are preferred, particularly divinylbenzene in either its ortho, meta, or para isomer. Commercial divinylbenzene which is a mixture of the three isomers and other compounds is satisfactory. Epoxidized hydrocarbon polymers such as epoxidized liquid polybutadiene and the epoxidized vegetable oils such as epoxidized soybean oil and epoxidized linseed oil, and epoxy compounds such as 1,2; 5,6; 9,10-triepoxydecane, can be used. Examples of suitable multiisocyanates include benzene-1,2,4-triisocyanate, naphthalene-1,2,5,7-tetraisocyanate, and the like. Commerically available products known as PAPI-1, a polyarylpolyisocyanate having an average of 3 isocyanate groups per molecule and an average molecular weight of about 380 are suitable. The multiimines, also known as multiaziridinyl compounds, such as those containing 3 or more aziridine rings per molecule, are useful. Examples include the triaziridinyl phosphine oxides or sulfides such as tri(1-aziridinyl)phosphine oxide, tri(2-methyl-1-aziridinyl)-phosphine oxide and tri(2-ethyl-3-decyl-1-aziridinyl)phosphine sulfide. The multialdehydes are represented by compounds such as 1,4,7-naphthalenetricarboxyaldehyde, 1,7,9-anthracenetricarboxyaldehyde, 1,1,5-pentanetricarboxyaldehyde, and similar multialdehyde-containing aliphatic and aromatic compounds. The multiketones are represented by compounds such as 1,4,9,10-anthracenetetrone, 2,3-diacetonylcyclohexanone, and the like. Examples of the multianhydrides include pyromellitic dianhydride and styrene-maleic anhydride copolymers. Examples of the multiesters include diethyladipate, triethylcitrate, 1,3,5-tricarbethoxybenzene, and the like. Among the multihalides are the silicon tetrahalides such as silicon tetrachloride, silicon tetrabromide, and silicon tetraiodide; the trihalosilanes such as trifluorosilane, trichlorosilane, trichloroethylsilane and tribromobenzylsilane; and the multihalogen-substituted hydrocarbons, such as 1,3,5-tri(bromomethyl)benzene and 2,5,6,9-tetrachloro-3,7-decadiene, in which the halogen is attached to a carbon atom which is alpha to an activating group such as an ether linkage, a carbonyl group, or a carbon-to-carbon double bond. Substituents inert with respect to lithium atoms in the terminally reactive polymer can also be present in the active halogen-containing compounds. Alternatively, other suitable reactive groups different from the halogens as described above can be present. Examples of compounds containing more than one type of functional group include 1,3-dichloro-2-propanone, 2,2-dibromo-3-decanone, 3,5,5-trifluoro-4-octanone, 2,4-dibromo-3-pentanone, 1,2,4,5-diepoxy-3-pentanone, 1,2, 4,5-diepoxy-3-hexanone, 1,2,11,12-diepoxy-8-pentadecanone and 1,3, 18,19-diepoxy-7,14-eicosanedione. Other metal multihalides, particularly those of tin, lead, or germanium, can be employed as coupling and branching agents. Silicon or other metal multialkoxides, such as silicon tetraethoxide, are also suitable coupling agents. Any effective amount of the coupling agent can be employed. While the amount is not believed to be particularly critical, a stoichiometric amount relative to the active polymer-alkali metal tends to promote maximum coupling as a generality. However, less than stoichiometric amounts can be used for lesser degrees of coupling where desired for particular products of broadened molecular weight. Typically, the total amount of coupling agent is in the range of about 0.1 to 20 phm, presently preferably about 0.1 to 1 phm. Preferred at present is epoxidized vegetable oil. Most preferred is epoxidized soybean oil. At the conclusion of the coupling process, the system is treated with an active hydrogen compound such as water, alcohol, phenols or linear saturated aliphatic mono- and dicarboxylic acids to remove the lithium from the polymer. Preferably, the polymer cement, i.e. the polymer in the polymerization solvent, is treated with terminating agents such as water and carbon dioxide and then antioxidants. The resins are then stabilized with a combination of a hindered phenol and an organophosphite, specifically, octadecyl 3-(3',5'-di-t-butyl-4'-hydroxyphenyl) propionate and tris-nonylphenylphosphite. After stabilization, the hydrocarbon diluent is then flashed off the polymer solution to increase the solids content. The following examples will describe in more detail the experimental process used and the polymodal tapered block copolymers with vinylarene terminal blocks obtained as a result of the process. In charges (1), (2a), (2b) and (2c) referred to in the Summary of the Invention above, the weight percentages of monovinylaromatic monomer as a percent of the total monovinylaromatic monomer charged are from about 35 to about 60, from about 10 to about 35, from about 4 to about 15, and from about 10 to about 40, respectively. More preferably, the weight percentages of monovinylaromatic monomer in charges (1), (2a), (2b) and (2c) as a percent of the total monovinylaromatic monomer charged are from about 38 to about 55, from about 15 to about 29, from about 5 to about 14 and from about 12 to about 36, respectively. Most preferably, the weight percentages of monovinylaromatic monomer in charges (1), (2a), (2b) and (2c) as a percent of the total monovinylaromatic monomer charged are from about 42 to about 50, from about 19 to about 23, from about 7 to about 13, and from about 15 to about 31, respectively. The polymers prepared according to this invention are polymodal, resinous block copolymers and contain from about 55 to 95, preferably 60 to 87, and more preferably 70 to 80, weight percent of polymerized monovinyl substituted aromatic hydrocarbon monomer based on the weight of total monomers employed. The weight ratio of monovinyl substituted aromatic monomer to conjugated diene monomer in charge (2b) is from about 5:1 to about 1:10, preferably from about 1:1 to about 1:2, and more preferably from about 1:0.7 to about 1:1.4. The amount of inititiator in the first initiator charge is from about 0.005 phm to about 10 phm, preferably from about 0.1 phm to about 1.0 phm, and more preferably from about 0.03 phm to about 0.04 phm. The amount of inititiator in the second initiator charge is from about 0.005 phm to about 10 phm, preferably from about 0.1 phm to about 1.0 phm, and more preferably from about 0.03 phm to about 0.04 phm. The amount of inititiator in the third initiator charge is from about 0.01 phm to about 50 phm, preferably from about 0.05 phm to about 10 phm, and more preferably from about 0.07 phm to about 1.0 phm. EXAMPLE I In one run there was prepared a polymodal block copolymer of styrene, 1,3-butadiene monomers and a tapered styrene/butadiene copolymer. While not wishing to be bound by theory, applicants believe the copolymer prepared is comprised primarily of species having at least the following general formulas: where S = polystyrene block polymer taper = random tapered block copolymer of butadiene and styrene B = polybutadiene block x = residual coupling agent This block copolymer was prepared in a six-step sequential charging process as follows. In a first step, cyclohexane, 1.63 phm; tetrahydrofuran, 0.5 phm; n-butyllithium, 0.035 phm; and styrene, 36 phm (where phm is parts per 100 parts total amount) were charged at 50°C to a 7.57ℓ (two-gallon) reactor provided with a stirrer. The temperature peaked at about 95°C while the styrene polymerized substantially adiabatically to completion in about 5 minutes. The pressure was about 2.07 bar (30 psig). Then a second charge of 0.035 phm n-butyllithium, 15.8 phm styrene and 13.2 phm cyclohexane was added to the stirred reactor at 69°C. The polymerization was allowed to proceed substantially adiabatically with polymerization temperature peaking at 80°C. Total reaction tine was 5 minutes. In a third step, 6.9 phm butadiene, 6.9 phm styrene and 13.2 phm cyclohexane were added to the stirred reactor and contents at 68°C. The polymerization was allowed to proceed substantially adiabatically peaking at 91°C. The total reaction time was 10 minutes. In a fourth stop, 0.08 phm n-butyllithium, 16.8 phm stryene and 13.2 phm cyclohexane wore charged to the reactor and contents at 67°C. The reaction proceeded substantially adiabatically peaking at 88°C. Total polymerization time was 5 minutes. In the fifth and final polymerization stop, 17.7 phm butadiene and 6.6 phm cyclohexane were added to the reactor and contents at 84°C. The polymerization was allowed to proceed substantially adiabatically with temperature peaking at 105°C. Pressure was 4.14 bar (60 psig). The total polymerization time was 10 minutes. After polymerization was complete, in a sixth final coupling step, the contents of the reactor were heated to 93°C, and 0.4 phm epoxidized soybean oil was added. This was allowed to react for 15 minutes. A small amount of water and carbon dioxide was added in a post treatment. After 5 minutes a phenolic stablizer, 0.25 phm, and a phosphite stabilizer, 1.0 phm, were added. After another 5 minutes, the polymer solution, 33.2 weight percent concentration, was heated to 176°C. The cyclohexane was removed by flashing at ambient pressure. The isolated polymer, still containing some 15 to 20% residual cyclohexane, was dried further in a vacuum oven. The polymerization product mixture just prior to the final coupling step has the following three species of monoalkali living polymers: where S = polystyrene block taper = random tapered block copolymer of butadiene and styrene B = polybutadiene block Li = active lithium The final polymodal tapered block copolymer is a result of various combinations of each of these three species with itself and with each of the others. Several additional resins wore prepared in which the tapered block location and monomer wore varied following essentially the same polymerization, coupling, and isolation procedure. The runs are shown in Table II. All of the polymerizations were done in a final solvent of approximately 201 phm. Polymerizations were usually initiated at or near 50°C and allowed to proceed adiabatically. Polymerization time was 5 minutes for styrene and 10 minutes for butadiene and butadiene/styrene mixtures. A comparative run in which no tapered blocks were made is shown in Example III. EXAMPLE III Run 6 Step # 1 Tetrahydrofuran 0.5 phm n-Butyllithium 0.035 phm Styrene 37 phm Step # 2 n-Butyllithium 0.035 phm Styrene 16 phm Step # 3 Butadiene 7 phm Step # 4 n-Butyllithium 0.08 phm Styrene 22 phm Step # 5 Butadiene 18 phm Intermediate products of this charging sequence resulted in the following polybutadienyllithium-terminated living molecules: Coupling of this polymer lithium with epoxidized soybean oil and isolation of the resulting polymodal polymer was done in a manner identical to that used for the inventive runs described above. While not wishing to be bound by theory, applicants believe that the resulting polymodal polymer primarily comprised six species from the six possible coupling combinations: where S = styrene block polymer B = butadiene block polymer x = residual coupling agent Shrink Test Procedure The resins to be tested for shrink were extruded as 0.508 mm (20 mil) sheets using a 3.175 cm (1.25") extruder with a 15.24 cm (6") wide die and a 0.0508 cm (0.020") die gap. Samples were die cut from the 0.508 mm (20 mil) extruded sheets and conditioned at 96.1-98.9°C (205-210°F). The samples were stretched by an A.M. Long film stretcher at 96.1-98.9°C (205-210°F) at a rate of 100%/min. The amount of stretch was 2X in the machine direction (MD) and 3X in the transverse direction (TD). A standard test method, ASTM-D2732-70, was used to measure unrestrained linear thermal shrinkage. The specimens were die cut to 6.35 cm X 6.35 cm (2.5" X 2.5") by the normal thickness. Three specimens of each were tested. The test specimens were conditioned at 23° ±2°C and 50 ±5 percent relative humidity for not less than 40 hours prior to testing. The specimens were placed in a free shrink holder. The holder did not restrain the specimens from floating in the bath medium, glycerine. The bath temperature was maintained for 10 minutes. The specimens were then removed from the bath and quickly immersed in water at room temperature. The specimens were set aside to cool for one hour, and then both the machine and transverse linear directions were measured. The percent of free shrinkage for each direction was calculated as follows: where L₁ = initial length of side L₂ = length of side after shrinkage The results of the shrink tests are given in Table III. It can be seen from the shrink test results shown in Table III that all the resins of the invention had greater shrink than the control resin. Shrink was greater in the transverse, cross direction of the extruded sheet. Although all the resins with tapered blocks had better shrink than the control resin, location of the tapered block and monomer ratio affected shrink. It can be noted from the above table that, in general, the greater the amount of butadiene relative to the amount of styrene in the polymodal tapered block copolymer, the better the shrink obtained. The butadiene to styrene monomer weight ratio was the same in the copolymers of Runs 4 and 5, but because of the tapered block being located nearer the terminal polystyrene block, Run 4 exhibited better shrink than Run 5.

Claims: A method of preparing block copolymers by stepwise addition of monomers and, optionally, other components to the polymerization system, wherein in each step the polymerization is allowed to continue until essentially no free monomer is present, characterized in that the respective steps comprise the following charges (1) monovinylaromatic monomer, randomizer and initiator, (2a) monovinylaromatic monomer and initiator, (2b) a mixture of monovinylaromatic monomer and conjugated diene monomer, (2c) monovinylaromatic monomer and initiator, and (3) conjugated diene monomer and finally a coupling agent is added, wherein all stages are sequential except that charges (2a), (2b) and (2c) can be made in any order of (2a), (2b) and (2c). The method of claim 1 wherein step (2b) is carried out after step (2a), and step 2(c) is carried out after step (2b). The method of claim 1 or 2 wherein the total amount of monomers is used at a ratio of 60 to 87 weight percent monovinylaromatic monomer to 13 to 40 weight percent conjugated diene monomer. The method of claim 1 comprising in addition charging additional conjugated diene after polymerization of charge 1 is complete and before the last charge prior to introducing the charge (3) conjugated diene. The method of claim 1 wherein in step (2b) the weight ratio of monovinylaromatic monomer to conjugated diene monomer is about 1 to 1. The method of claim 5 wherein in step (2b) the weight ratio of monovinylaromatic monomer to conjugated diene monomer is from 1 :0.7 to 1 : 1.4. The method of any of the preceding claims wherein in step (1) the monovinylaromatic monomer constitutes from 35 to 60 weight percent, preferably from 38 to 55 weight percent and most preferably from 42 to 50 weight percent, each based on the total monovinylaromatic monomer used. The method of any of the preceding claims wherein in step (2a) the monovinylaromatic monomer constitutes from 10 to 35 weight percent, preferably from 15 to 29 weight percent and most preferably from 19 to 23 weight percent, each based on the total monovinylaromatic monomer used. The method of any of the preceding claims wherein in step (2b) the monovinylaromatic monomer constitutes from 4 to 15 weight percent, preferably from 5 to 14 weight percent and most preferably from 7 to 13 weight percent, each based on the total monovinylaromatic monomer used. The method of any of the preceding claims wherein in step (2c) the monovinalyaromatic monomer constitutes from 10 to 40 weight percent, preferably from 12 to 36 weight percent and most preferably from 15 to 31 weight percent, each based on the total monovinylaromatic monomer used. The method of any of the preceding claims wherein said monovinalyaromatic monomer contains from 8 to 12 carbon atoms and said conjugated diene monomer contains from 4 to 6 carbon atoms. The method of claim 11 wherein said monovinylaromatic monomer is styrene, said conjugated diene monomer is 1,3-butadiene, said initiator is an organomonoalkali metal initiator, preferably n-butyllithium, and said randomizer is tetrahydrofuran. The method of any of the preceding claims wherein said coupling agent is epoxidized soybean oil, the polymerization is carried out in a hydrocarbon diluent, the polymerization is carried out in the substantial absence of oxygen and water at a temperature from -10 to 150°C, after the reaction of the coupling agent a terminating agent and then a stabilizer is added, and after termination with said terminating agent any remaining hydrocarbon diluent is flashed off. The method of claim 13 wherein said terminating agent is water and carbon dioxide and said stabilizer is selected from hindered phenols and organophosphites. The method of claim 1 wherein said coupling agent is epoxidized soybean oil, the polymerization is carried out in a hydrocarbon diluent, additional butadiene is added after step (1) and before the last charge prior to introducing the step (3) butadiene charge, the polymerization is carried out in the substantial absence of oxygen and water at a temperature from -10 to 150°C, after reaction of said coupling agent terminating agents and then antioxidants are added, said terminating agents are water and carbon dioxide, stabilizers selected from hindered phenols and organophosphites are added, and after termination with said water and carbon dioxide any remaining hydrocarbon diluent is flashed off. The use of the block copolymers as obtained in any of claims 1-15 for making shrink films.

Inventors: FARRAR RALPH COLEMAN JR, MOCZYGEMBA GEORGE ANTHONY, TREPKA WILLIAM JAMES, FARRAR, RALPH COLEMAN, JR., MOCZYGEMBA, GEORGE ANTHONY, TREPKA, WILLIAM JAMES
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1990
Main classification: C08F297
IPC codes: C08J5, C08F297