Claims
- 1. A method for the preparation of a block copolymer having the configuration AB(BA).sub.n wherein n is an integer of from 1 to 3 inclusive; A represents a block which is a random copolymer of an alkenyl aromatic monomer and an .alpha.-methylstyrene monomer, wherein the mole ratio of alkenyl aromatic monomer to .alpha.-methylstyrene monomer ranges from 1:0.5 to 1:2.5; B represents a polydiene selected from a group consisting of 1,3-butadiene, isoprene and mixtures thereof where the polydiene contains not over 25 mole percent 1,2 vinyl groups, the polydiene blocks having polymerized therein from 0 to 10 weight percent of a monovinyl aromatic compound, the polydiene blocks being 2 to 98 weight percent and the alkenyl aromatic monomer .alpha.-methylstyrene blocks being from 98 to 2 weight percent of the polymer, the steps of the method comprising polymerizing the diene monomer in a hydrocarbon solvent, and optionally in the presence of the .alpha.-methylstyrene monomer, employing a multifunctional lithium polymerization initiator in the absence of oxygen and moisture at a temperature of from about 40.degree. to 120.degree. C. to provide a living diene polymer block of desired molecular weight dissolved in the hydrocarbon solvent, adding a polar solvent to the hydrocarbon solvent containing the living diene polymer and the .alpha.-methylstyrene monomer, adding .alpha.-methylstyrene monomer if not already present, and then adding continuously the alkenyl aromatic monomer at a rate whereby a random alkenyl aromatic monomer-.alpha.-methylstyrene monomer polymer blocks are polymerized and chemically attached to the polydiene block.
- 2. The method of claim 1 wherein the polydiene is polymerized in the presence of the .alpha.-methylstyrene monomer.
- 3. The method of claim 1 wherein the polydiene is from about 10 to 40 weight percent of the polymer prepared.
- 4. The method of claim 1 wherein the polydiene is from about 55 to 90 weight percent of the polymer prepared.
- 5. The method of claim 1 wherein n is one.
- 6. The method of claim 1 wherein the glass temperature of the polydiene prepared is not greater than -60.degree. C.
- 7. The method of claim 1 wherein the polydiene is 1,3-polybutadiene.
- 8. The method of claim 1 wherein the polydiene is polyisoprene.
- 9. The method of claim 1 wherein the alkenyl aromatic monomer is styrene.
- 10. The method of claim 1 wherein the molecular weight of the block copolymer is from about 5,000 to 500,000 molecular weight units.
- 11. The method of claim 10 wherein the molecular weight of the block copolymer is from about 80,000 to 300,000 molecular weight units.
- 12. The method of claim 1 wherein the ratio of alkenyl aromatic monomer to .alpha.-methylstyrene is from about 1:1 to about 1:2.
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation of application Ser. No. 288,622, filed July 30, 1981, abandoned, which is a continuation of application Ser. No. 169575 filed July 17, 1980, abandoned, which is a continuation-in-part of our co-pending U.S. patent application Ser. No. 95,696 filed Nov. 19, 1979 now abandoned which is a continuation-in-part of our co-pending U.S. patent application Ser. No. 12,539 filed Feb. 15, 1979, now abandoned.
Block copolymers of the configuration AB(BA).sub.n wherein n is an integer of from 1 to 3 inclusive and A represents a random copolymer of an alkenyl aromatic monomer and .alpha.-methylstyrene and B represents a block of a polymer of one or more conjugated dienes, certain block copolymers, for example certain block copolymers of the structure polystyrene-polyisoprene-polystyrene and polystyrene-polybutadiene-polystyrene, show the unique feature that without being vulcanized they have at ambient temperature elastomeric properties including strength properties, comparable to those of conventional vulcanizates and are reversibly plastifiable. They are also good impact plastics if the polydiene content is kept low. The known block copolymers, however, are somewhat deficient in that they either exhibit relatively poor low temperature performance or poor high temperature performance. Known block copolymers having terminal polymer blocks of styrene and .alpha.-methylstyrene show improved high temperature performance in comparison with those with terminal polymer blocks of styrene, but their polydiene center block contains high 1,2-vinyl structure which raised the glass temperature of the polydiene block and thus contributed to poor low temperature properties.
It would be desirable if there were available an improved block copolymer which has a relatively high heat distortion temperature and also exhibits good low temperature properties.
It would be desirable if there were available a method of preparation of such polymers.
It would be desirable if there were available a medium impact resin having a high degree of transparency, good low temperature properties and improved heat distortion.
It would be desirable also if an improved thermoplastic elastomer having desired low temperature and improved heat distortion properties were available.
It would be desirable also if there were available an improved soft thermoplastic resin with good heat distortion and low temperature properties.
These benefits and other advantages in accordance with the present invention are achieved in a block copolymer, the block copolymer having the configuration AB(BA).sub.n wherein n is an integer of from 1 to 3 inclusive (preferably n=1); A represents a block which is a random copolymer of an alkenyl aromatic monomer and an .alpha.-methylstyrene, wherein the mole ratio of the alkenyl aromatic monomer to the .alpha..sub..dbd. methylstyrene ranges from 1:0.5 to 1:2.5 and preferably from about 1:1 to 1:2, B represents a diene polymer selected from a group consisting of 1,3-butadiene, isoprene and mixtures thereof wherein the polydiene contains not over 25 percent mole 1,2 vinyl groups, the polydiene blocks having polymerized therein from 0 to 10 weight percent of an alkenyl aromatic compound, the polydiene blocks being 2 to 98 weight percent and the alkenyl aromatic monomer the .alpha..dbd.methylstyrene blocks being from 98 to 2 weight percent of the polymer.
Also contemplated within the scope of the present invention is a method for the preparation of a block copolymer having the configuration AB(BA).sub.n wherein n is an integer of from 1 to 3 inclusive (preferably n=1); A represents a block which is a random copolymer of an alkenyl aromatic monomer and an .alpha..sub..dbd. methylstyrene, wherein the mole ratio of alkenyl aromatic monomer to the .alpha..sub..dbd. methylstyrene ranges from 1:0.5 to 1:2.5 and preferably from about 1:1 to 1:2, B represents a polydiene selected from a group consisting of 1,3-butadiene, isoprene and mixtures thereof where the polydiene contains not over 25 mole percent 1,2 vinyl groups, the polydiene blocks having polymerized therein from 0 to 10 weight percent of an alkenyl aromatic compound, the polydiene blocks having 2 to 98 percent and the alkenyl aromatic monomer -.alpha..sub..dbd. methylstyrene blocks being from 98 to 2 weight percent of the polymer, the steps of the method comprising polymerizing the diene monomer in a hydrocarbon solvent, and optionally in the presence of at least one .alpha..sub..dbd. methylstyrene monomer, employing a multifunctional lithium polymerization initiator in the absence of oxygen and moisture at a temperature of from about 40.degree. to 120.degree. C. to provide a living diene polymer block of desired molecular weight dissolved in the hydrocarbon solvent, adding a polar solvent to the hydrocarbon solvent containing the living diene polymer and the .alpha..sub..dbd. methylstyrene, adding the .alpha..sub..dbd. methylstyrene if not already present, and then adding continuously the alkenyl aromatic monomer at a rate whereby a random alkenyl aromatic monomer .alpha..sub..dbd. methylstyrene polymer blocks are polymerized and chemically attached to the polydiene block. By the term alkenyl aromatic monomer is meant a monomer of the formula: ##STR1## where n is an integer from 0 to 3, R.sub.1 is an alkyl radical containing up to 5 carbon atoms and R.sub.2 is hydrogen. Preferred alkenyl aromatic monomers include styrene, vinyltoluene, (all isomers alone or in admixture); particularly desirable in paravinyltoluene.
By the term .alpha..sub..dbd. methylstyrene is meant a compound of the above formula wherein R.sub.1 is an alkyl radical containing up to 5 carbon atoms and R.sub.2 is methyl.
The resultant block copolymers may be elastomeric or resinous depending upon the portions of the ingredients selected. Polymers prepared employing low portions of the diene, i.e., 2 to 40 weight percent polydiene, are generally resinous, transparent, and particularly suited for packaging applications where both low temperatures and high temperatures are encountered; for example, frozen foods which are subsequently heated prior to serving. Polymers in accordance with the present invention which contain higher proportions of the polydiene block; for example, from 55 to 98 weight percent polydiene, provide desirable thermoplastic elastomers having a relatively high service temperature and highly desirable low temperature characteristics. Polymers containing from about 40 to 55 weight percent diene are what might be considered soft plastics. The molecular weight of the block copolymer in accordance with the present invention as determined by gel permeation chromatography will vary from about 5,000 to 500,000 molecular weight units. Particularly desirable polymers for most applications have a molecular weight range from about 80,000 to 300,000 molecular weight units. The term "random" as employed in the present invention is not used to mean that the two monomers in the copolymer are alternating in a one to one manner or conform strictly to random statistics. It is employed to mean that extensive block-like structures of polymerized alkenyl aromatic monomer or a polymerized .alpha.-methylstyrene monomer do not exist.
Preferably the polymer blocks B are elastomeric polymer blocks of an unsaturated diene such as butadiene, isoprene or mixtures thereof. It is essential to the present invention that the 1,2-vinyl polydiene microstructure content of the polydiene block be not greater than 25 percent, the 1,2-vinyl content being computed from the infrared spectrum by the method of P. Morero et al., as set forth in Chim. Ind. Milan, 41,758 (1959), and the glass transition temperature (T.sub.g) of these polydienes be not greater than about -60.degree. C. as determined by a Perkin-Elmer differential scanning calorimeter, model DSC2, when a sample is heated at a rate of 20.degree. C. per minute. Block copolymers in accordance with the present invention may be of the linear ABA configuration or the branched configuration such as AB(BA).sub.n. In the preparation of a linear polymer such as of the ABA configuration, a difunctional lithium catalyst is employed whereas in the preparation of the simplest branched polymer having the structure AB(BA).sub.n a multifunctional lithium polymerization initiator is employed. Multifunctional lithium containing initiators are well known in the art as is the use of such initiators in the polymerization of olefinically unsaturated hydrocarbon monomers. Such polymers and initiators are disclosed in the following U.S. Pat. Nos. 3,660,536; 3,663,634; 3,668,263; 3,684,780; 3,725,368; 3,734,973; 3,776,893; 3,776,964; 3,784,637; 3,787,510; 3,954,894; 4,172,100; 4,172,190; 4,182,818; 4,196,153; 4,196,154; 4,200,718; 4,201,729; 4,205,016.
References of record in the parent application include the following U.S. Pat. Nos. 3,265,765; 3,912,793; 3,925,512; 4,089,913 and 4,136,137.
US Referenced Citations (2)
Continuations (2)
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288622 |
Jul 1981 |
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| Parent |
169575 |
Jul 1980 |
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Continuation in Parts (2)
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95696 |
Nov 1979 |
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| Parent |
12539 |
Feb 1979 |
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Patent Grant
4431777
