GB1565042A - Preparation of block copolymers and products therefrom - Google Patents

Description

(54) PREPARATION OF BLOCK COPOLYMERS AND PRODUCTS THEREFROM (71) We, THE DOW CHEMICAL COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, of Midland, County of Midland, State of Michigan, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention provides an improved process for the preparation of block copolymers which permits the inclusion of monomers which are generally considered unsuitable for anionic polymerization, and block copolymers containing such monomers.

According to one aspect of the present invention there is provided a process for the preparation of a block copolymer, which process comprises contacting a polymer chain, which has been prepared by anionic polymerization and the ends of which are terminated with a primary or secondary thiol group, with a free-radical polymerizable monomer under free-radical polymerization conditions whereby a block copolymer comprising at least one anionically polymerized block and at least one free-radical polymerized block is obtained.

Monomers which are polymerizable by free-radical initiation suitable for the practice of the present invention include; for example, p-chlorostyrene, bromostyrene, acrylonitrile, methacrylonitrile and acrylates and methacrylates.

In the free-radical polymerization in accordance with the invention, many free-radical polymerization initiating compounds may be employed or alternatively free radicals may be generated by heating in the absence of a peroxide compound or other free-radical generating compound.

The free-radical generating compounds which can be employed in this invention include organic, inorganic peroxides and azo compounds. The term "organic peroxides" is meant to include the hydro-peroxides, unless otherwise stated, and to encompass compounds containing from 4 to 40 carbon atoms per molecule, inclusive. The organic peroxides can also be substituted with non-peroxy members such as halogen, hydroxy radicals, ether and/or ester linkages.

The free-radical polymerization in accordance with the invention may be carried out in solution suspension, bulk or emulsion techniques.

In a preferred aspect, the thiol terminated polymer is one which has been prepared by contacting the living polymer with a sulfur compound (as hereinafter defined).

By the term "sulfur-compound" is meant elemental sulfur and alkyl episulfides, the episulfides being of the formula:

wherein R is hydrogen, C1-18 alkyl or an aromatic group containing only hydrogen ana carbon.

Such compounds include; for example, ethylene sulfide, propylene episulfide, dodecylene episulfide, and phenyl episulfide.

According to a further aspect the process of the present invention comprises providing an anionically polymerizable monomer or mixtures thereof, polymerizing the monomer of mixtures thereof anionically to provide polymer chains having at least one active or living end, contacting said polymer chains with a sulfur compound (as hereinafter defined) in a quantity at least sufficient to react with said polymer chain living ends, to thereby terminate the ends with a primary or secondary thiol group, characterized by contacting the thiol terminated polymer chains with a free-radical polymerizable monomer and initiating free radical polymerization to thereby provide a block copolymer comprising at least one anionically polymerized block and at least one free-radical initiated block.

Solvents normally used in anionic polymerization can be employed in accordance with the present invention.

Suitable organolithium compounds which can be used for the anionic polymerization correspond to the formulaRLi)x,wherein R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical and x is an integer from 1 to 4, inclusive. The aliphatic and cycloaliphatic radicals can be saturated or contain olefinic unsaturation. The R in the formula has a valence equal to the integer, and preferably contains from 1 to 20 inclusive, carbon atoms, although it is within the scope of the invention to use higher molecular weight compounds. The preferred compound is n-butyllithium.

Another desirable variety of lithium initiators are the difunctional lithium compounds such as are described in our U.K. Patent specification No 1,499,467.

Lithium compounds are used with particular benefit, however, other known alkali metal anionic polymerization initiating systems may be used if desired.

The amount of catalyst or initiator used in the preparation of block copolymers by anionic polymerization can vary over a wide range but will generally be at least 0.00001 mole of the organolithium compound per 100 moles of the total monomers to be polymerized in the process. The upper limit for the amount of organolithium used depends primarily upon catalyst solubility and the desired molecular weight of the polymer resulting from the polymerization. A preferred effective catalyst level is from 0.005 to 1 mole of organolithium per 100 moles of total monomers charged to the polymerization zone.

A wide variety of block copolymers may be readily prepared by the process of the present invention. Such polymers may have homopolymer blocks, copolymer blocks or a mixed block copolymer wherein one of the blocks may be a homopolymer and one or more of the blocks being copolymer.

According to a further aspect of the present invention there is provided a block copolymer of ABA configuration in which each A represents a random copolymer of styrene and acrylonitrile or represents a polymer of bromostyrene and B is a conjugated diene elastomer block.

Particularly desirable block copolymers in accordance with the present invention are an ABA copolymer of butadiene and a random copolymer of styrene and acrylonitrile. By the term "random copolymer" is meant one wherein the sequence of styrene and acrylonitrile does not have a precise mathematical relationship. Beneficially, the block B is a homopolymer of butadiene or isoprene having a molecular weight of 30,000 to 500,000 and preferably 40,000 to 80,000, the A block containing 95 to 50 parts by weight styrene and 5 to 50 parts by weight of acrylonitrile, the A block having a weight average molecular weight of from 3,000 to 100,000 and preferably 5,000 to 20,000 molecular weight units, as determined by gel permeation chromatography.

Another desirable block copolymer of the ABA configuration is a block copolymer of butadiene or isoprene with bromostyrene wherein the block B has the hereinbefore delineated molecular weight limitations and block A is a bromostyrene block having a weight average molecular weight of 5,000 to 200,000 and beneficially from 10,000 to 50,000 molecular weight units, the molecular weight being determined by gel permeation chromatography. Polymers prepared in accordance with the present invention beneficially can be employed for a variety of applications by selection of the desired blocks. Thermoplastic elastomers are readily prepared as well as thermoplastics, polymeric surface active agents, emulsifiers, and vulcanizable elastomers. Thermoplastic elastomers, thermoplastics and rubbers prepared in accordance with the present invention are readily fabricated by conventional fabricating techniques such as solvent casting, compression molding, injection molding, extrusion, melt spinning and like fabrication techniques to provide a wide variety of useful articles including fibers, films, compression moulding, it ejection mouldings, and the like. Block polymers in accordance with the present invention may be compounded with pigment, fillers, stabilizers, dyes and the like in conventional plastic or elastomer processing procedures.

The invention is further illustrated by the following examples.

Example 1 An agitated, nitrogen-purged flask was charged with 50 grams of butadiene dissolved in 450 milliliters of dry benzene. 14.3 Milliequivalents of n-butyllithium in benzene was added and the temperature of the reaction mixture maintained by means of a water bath at a temperature of from about 50 to 55"C. Polymerization was completed in about thirty minutes. A 20 milliliter portion of the reaction mixture was withdrawn from the vessel by a syringe and injected into a 100 milliliter nitrogen-purged flask which contained 0.15 milliliter of tetrahydrofuran. The mixture of polybutadiene solution and tetrahydrofuran was cooled to about 5"C and 0.16 milliliter of propylene sulfide added. The resulting mixture was stirred for about 12 minutes and 0.1 milliliter of glacial acetic acid was added to the mixture and the mixture diluted with about 60 milliliters of methanol. On addition of methanol, a precipitate formed. The precipitate was separated by filtration and dried overnight at room temperature under vacuum. The product was 2 grams of polybutadiene with a mercaptan cap or end group. A second 20 milliliter portion of the reaction mixture was similarly treated with the exception that 0.13 milliliter of ethylene sulfide was employed in place of propylene sulfide to provide an ethylene sulfide terminated polybutadiene weighing about 2 grams. A 1/10 gram portion of the propylene sulfide terminated polybutadiene was mixed with 10 milliliters of styrene monomer and 5 milliliters of ethylbenzene. The mixture was divided into two portions and each portion was placed in a glass ampoule. Both ampoules were heated to 125"C, one ampoule for a period of one hour and the remaining ampoule for three hours. At the end of that time, the ampoules were cooled, the contents removed and analyzed by gel permeation chromatography. The weight of the polymer sample recovered showed that at the end of one hour heating, 7.5 weight percent of the styrene polymerized and the sample heated for three hours resulted in 22.5 weight percent polymerized styrene. Gel permeation chromatography chromatograms indicated the presence of some mercaptan capped polybutadiene in the sample which had been heated for one hour. No indication of the mercaptan capped polybutadiene was present in the sample which had been heated for three hours. Similar results were obtained with the ethylene sulfide terminated polybutadiene. A portion of the polybutadiene solution which was uncapped was terminated with glacial acetic acid and subsequently subjected to the same polymerizing condition, that is, 125"C for one hour and for three hours in the presence of styrene and on examination using gel permeation chromatography, the peak corresponding to the polybutadiene appeared generally unchanged. The foregoing demonstrate clearly that the sulfide-terminated polymers exhibit a strong tendency to form block copolymers. The block copolymers prepared were of the AB configuration.

Example 2 A quantity of bis[4-(1-phenylethenyl)phenyl]-ether (0.4 gram) in 30 milliliters of dry benzene was mixed with 2.36 milliequivalents of secondary butyl lithium at room temperature for a period of three hours to form oxydi-4,1-phenylene bis(3-methyl-1phenylpentylidene)-bis(lithium). To the reaction vessel was added two milliliters of isoprene, and the reaction mixture heated for about 5 minutes at 60"C, thereby solubilizing the suspension of the bislithium compound. The resulting solution was then charged to a one-liter nitrogen purged flask which contained 40 grams of butadiene dissolved 450 milliliters of dry benzene. A water bath having a temperature between about 50 and 55"C was employed to maintain the temperature of the reaction mixture. Polymerization of the butadiene proceeded for about 55 minutes and the reaction vessel and mixture cooled in an ice bath. A solution of one-half milliliter of propylene sulfide and two milliliters of tetrahydrofuran were added to the vessel with agitation. The viscosity of the reaction mixture appeared to decrease somewhat and then increase rapidly. Fifteen minutes after the addition of the propylene sulfide, one milliliter of glacial acetic acid was added to terminate any active anions. The yield of the dimercaptan capped polybutadiene was quantitative. The capped polybutadiene had an inherent viscosity of 0.79 deciliter per gram when measured in toluene at 0.15 gram of polymer per one-hundred milliliters of toluene at a temperature of 25"C. Eight grams of the capped polybutadiene were mixed with 21 grams of bromostyrene, 0.2 gram of azobisisobutyrolnitrile and 37 grams ethylbenzene. The resulting mixture was placed in a nitrogen purged, closed, stainless steel tube and heated to 70"C and maintained at that temperature for period of six hours. The polymer was recovered by dissolving reaction mixture in benzene and precipitation in methanol. Upon molding of the resultant thermoplastic elastomeric polymer, the tensile strength at rupture was 1620 pounds per square inch (123 kg/sq cm) with an ultimate elongation of 520 percent.

Example 3 A block copolymer was prepared in the following manner. A dry toluene solution containing 0.26 gram of bis[4-(1-phenylethenyl)phenyl] ether in 20 milliliters of toluene was mixed with 1.5 milliequivalents of sec-butyllithium at room temperature for a period of 65 minutes.

The reaction mixture was a toluene dispersion of oxydi-4,1-phenylene bis)3-methyl-1- phenylpentylidene)-bis(lithium). To the toluene dispersion was added 1.3 milliliters of isoprene and the mixture heated to 600C for a period of 5 minutes. The dispersion became a solution as the isoprene was added to the bislithium compound. The resulting solution of the solubilized bislithium compound was charged to a one-liter nitrogen purged flask which contained 450 milliliters of dry toluene having dissolved therein 40 grams of butadiene. The butadiene solution in the reaction flask was previously treated with 0.31 milliequivalent of sec-butyllithium for the purpose of removing active impurities such as oxygen and moisture which are known to interfere with the polymerization reaction. The charged one-liter flask was positioned in a water bath maintained at a temperature of about 55" for a period of about 90 minutes. At the end of the 90 minute period, polymerization was assumed complete. The one-liter flask and contents were placed in an ice bath for a period of about 10 minutes. At the end of this period of time, the temperature of the reaction mixture as determined by the use of a thermocouple in the flask was about 30"C. A one-half milliliter portion of purified propylene sulfide and a 2 milliliter portion of purified tetrahydrofuran were added to the flask. Twenty minutes after the addition of the propylene sulfide and tetrahydrofuran, 0.12 milliliter of glacial acetic acid was added to the flask to terminate the active lithium sites. The reaction mixture contained a dimercaptan capped polybutadiene and the solution was maintained at about room temperature overnight. The following morning, 33 milliliters of styrene, 12.5 milliliters of acrylonitrile and 1.63 grams of azobisisobutyrolnitrile were added to the reaction mixture in the one-liter flask. The reaction mixture was then heated to 700C for a period of five hours with continuous stirring. At the end of this period, a polymeric product was separated from the reaction mixture, 57 grams of a thermoplastic elastomeric polymer was recovered. A portion of the polymer was molded and the tensile strength at break was determined to be 1124 pounds per square inch (78.7 kg/sq cm). The elongation at break was 460 percent. A compression molded film was analyzed employing infrared spectroscopy. The analysis indicated that the polymer contained about 16.7 weight percent styrene, 6.4 weight percent acrylonitrile, and about 76.9 percent butadiene.

WHAT WE CLAIM IS: 1. A process for the preparation of a block copolymer, which process comprises contacting a polymer chain, which has been prepared by anionic polymerization and the ends of which are terminated with a primary or secondary thiol group, with a free-radical polymerizable monomer under free-radical polymerization conditions whereby a block copolymer comprising at least one anionically polymerized block and at least one free-radical polymerized block is obtained.

2. A process as claimed in claim 1 in which the thiol terminated polymer has been prepared by contacting the living polymer with a sulfur compound (as hereinbefore defined).

3. A process as claimed in claim 2 in which the sulfur compound is ethylene sulfide, propylene episulfide, dodecylene episulfide, or phenyl episulfide.

4. A process as claimed in any one of the preceding claims in which the free-radical polymerizable monomer is p-chlorostyrene, bromostyrene, acrylonitrile, methacrylonitrile, an acrylate or a methacrylate.

5. A process as claimed in any one of the preceding claims in which free-radicals are generated in the free-radical polymerization by the action of heating.

6. A process as claimed in any one of claims 1 to 4 in which free-radicals are generated in the free-radical polymerization by a free-radical generating compound selected from organic peroxides, inorganic peroxides and azo compounds.

7. A process for the preparation of a block copolymer substantially as hereinbefore described in any one of the Examples.

8. A process for the preparation of a block copolymer, the steps of the process comprising providing an anionically polymerizable monomer or mixtures thereof, polymerizing the monomer or mixture thereof anionically to provide polymer chains having at least one active or living end, contacting said polymer chains with a sulfur compound (as hereinbefore defined) in a quantity at least sufficient to react with said polymer chain living ends, to thereby terminate the ends with a primary or secondary thiol group, contacting the thiol terminated polymer chains with a free-radical polymerizable monomer and initiating freeradical polymerization to thereby provide a block copolymer comprising at least one anionically polymerized block and at least one free-radical initiated block.

9. A block copolymer which has been prepared by a process as claimed in any one of the preceding claims.

10. A block copolymer of ABA configuration in which each A represents a random copolymer of styrene and acrylonitrile or represents polymer of bromostyrene and B is a conjugated diene elastomer block.

11. A block copolymer as claimed in claim 10 in which B is a homopolymer of butadiene or isoprene having a molecular weight of 30,000 to 500,000, and each A block contains 95 to 50 parts by weight styrene and 5 to 50 parts by weight of acrylonitrile and has a weight average molecular weight of from 3,000 to 100,000 as determined by gel permeation chromatography.

12. A block copolymer as claimed in claim 11 in which each A block has a molecular weight of from 5,000 to 20,000.

13. A block copolymer as claimed in claim 10 in which B is a homopolymer of butadiene or isoprene having a molecular weight of 30,000 to 500,000, and each A is a bromostyrene block having a weight average molecular weight of 5,000 to 200,000 as determined by gel permeation chromatography.

14. A block copolymer as claimed in claim 14 in which each A block has a molecular

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   90 minutes. At the end of the 90 minute period, polymerization was assumed complete. The one-liter flask and contents were placed in an ice bath for a period of about 10 minutes. At the end of this period of time, the temperature of the reaction mixture as determined by the use of a thermocouple in the flask was about 30"C. A one-half milliliter portion of purified propylene sulfide and a 2 milliliter portion of purified tetrahydrofuran were added to the flask. Twenty minutes after the addition of the propylene sulfide and tetrahydrofuran, 0.12 milliliter of glacial acetic acid was added to the flask to terminate the active lithium sites. The reaction mixture contained a dimercaptan capped polybutadiene and the solution was maintained at about room temperature overnight. The following morning, 33 milliliters of styrene, 12.5 milliliters of acrylonitrile and 1.63 grams of azobisisobutyrolnitrile were added to the reaction mixture in the one-liter flask. The reaction mixture was then heated to 700C for a period of five hours with continuous stirring. At the end of this period, a polymeric product was separated from the reaction mixture, 57 grams of a thermoplastic elastomeric polymer was recovered. A portion of the polymer was molded and the tensile strength at break was determined to be 1124 pounds per square inch (78.7 kg/sq cm). The elongation at break was 460 percent. A compression molded film was analyzed employing infrared spectroscopy. The analysis indicated that the polymer contained about 16.7 weight percent styrene, 6.4 weight percent acrylonitrile, and about 76.9 percent butadiene.

   WHAT WE CLAIM IS: 1. A process for the preparation of a block copolymer, which process comprises contacting a polymer chain, which has been prepared by anionic polymerization and the ends of which are terminated with a primary or secondary thiol group, with a free-radical polymerizable monomer under free-radical polymerization conditions whereby a block copolymer comprising at least one anionically polymerized block and at least one free-radical polymerized block is obtained.
2. 2. A process as claimed in claim 1 in which the thiol terminated polymer has been prepared by contacting the living polymer with a sulfur compound (as hereinbefore defined).
3. 3. A process as claimed in claim 2 in which the sulfur compound is ethylene sulfide, propylene episulfide, dodecylene episulfide, or phenyl episulfide.
4. 4. A process as claimed in any one of the preceding claims in which the free-radical polymerizable monomer is p-chlorostyrene, bromostyrene, acrylonitrile, methacrylonitrile, an acrylate or a methacrylate.
5. 5. A process as claimed in any one of the preceding claims in which free-radicals are generated in the free-radical polymerization by the action of heating.
6. 6. A process as claimed in any one of claims 1 to 4 in which free-radicals are generated in the free-radical polymerization by a free-radical generating compound selected from organic peroxides, inorganic peroxides and azo compounds.
7. 7. A process for the preparation of a block copolymer substantially as hereinbefore described in any one of the Examples.
8. 8. A process for the preparation of a block copolymer, the steps of the process comprising providing an anionically polymerizable monomer or mixtures thereof, polymerizing the monomer or mixture thereof anionically to provide polymer chains having at least one active or living end, contacting said polymer chains with a sulfur compound (as hereinbefore defined) in a quantity at least sufficient to react with said polymer chain living ends, to thereby terminate the ends with a primary or secondary thiol group, contacting the thiol terminated polymer chains with a free-radical polymerizable monomer and initiating freeradical polymerization to thereby provide a block copolymer comprising at least one anionically polymerized block and at least one free-radical initiated block.
9. 9. A block copolymer which has been prepared by a process as claimed in any one of the preceding claims.
10. 10. A block copolymer of ABA configuration in which each A represents a random copolymer of styrene and acrylonitrile or represents polymer of bromostyrene and B is a conjugated diene elastomer block.
11. 11. A block copolymer as claimed in claim 10 in which B is a homopolymer of butadiene or isoprene having a molecular weight of 30,000 to 500,000, and each A block contains 95 to 50 parts by weight styrene and 5 to 50 parts by weight of acrylonitrile and has a weight average molecular weight of from 3,000 to 100,000 as determined by gel permeation chromatography.
12. 12. A block copolymer as claimed in claim 11 in which each A block has a molecular weight of from 5,000 to 20,000.
13. 13. A block copolymer as claimed in claim 10 in which B is a homopolymer of butadiene or isoprene having a molecular weight of 30,000 to 500,000, and each A is a bromostyrene block having a weight average molecular weight of 5,000 to 200,000 as determined by gel permeation chromatography.
14. 14. A block copolymer as claimed in claim 14 in which each A block has a molecular

    weight of from 10,000 to 50,000.
15. 15. A block copolymer as claimed in any one of claims 11 to 14 in which B has a molecular weight of from 40,000 to 80,000.
16. 16. A shaped article comprising a block copolymer as claimed in any one of claims 9 to c