Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-11-07
2001-07-24
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S271000, C525S314000, C525S316000
Reexamination Certificate
active
06265484
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to tapered block copolymers of monovinylarenes and conjugated dienes and methods of preparation of these tapered block copolymers.
BACKGROUND OF THE INVENTION
There has developed in the polymer field, and especially in the packaging and related industries, a need for thermoplastic polymers that can be formed into colorless, transparent articles having good impact strength and ductility. There are needs for polymers which are useful as single components as well as for use in blends with other commonly used polymers to make articles with improved properties. The polymers satisfying these needs should be suitable for use with conventional extrusion, injection and blow molding equipment and also suitable for use in other methods of forming plastics into containers, tubes, films, fibers, and the like. Polystyrene, high impact polystyrene, branched block copolymers, and the like have been developed to meet these criteria with various degrees of satisfaction.
Much effort has been directed to the preparation of substantially transparent block copolymer resins with a variety of block structures produced by a variety of monomer addition sequences and a variety of coupling agents. Desirable properties and an economic advantage can be obtained by blending some monovinylaromatic-conjugated diene copolymers with polystryene polymers. However, because blueness of blends of monovinylaromatic-conjugated diene copolymers with polystyrene polymers cannot be predicted by rule of mixtures behaviors, getting a desirable combination of properties can be a complicated task. Sometimes relatively colorless monovinylaromatic-conjugated diene copolymers give blends with high blueness when blended with colorless general purpose polystyrene.
Blueness of articles formed from various copolymers and blends of copolymers with other polymers is a longstanding problem in applications where colorless materials which also have good impact strength and ductility are desirable. Specific examples include materials for water and food containers.
SUMMARY OF THE INVENTION
It is an object of this invention to provide novel resinous tapered block copolymers of vinyl-substituted aromatic hydrocarbons and conjugated dienes from which can be made articles with low blueness and acceptable impact strength and ductility.
It is another object of this invention to provide novel resinous tapered block copolymers of vinyl-substituted aromatic hydrocarbons and conjugated dienes suitable for use in blends with polymers of styrene, particularly blends from which can be made articles that exhibit low blueness and acceptable impact strength and/or ductility. Further, it is an object to provide novel resinous tapered block copolymers of vinyl-substituted aromatic hydrocarbons and conjugated dienes which can be used in smaller amounts than some of the other commonly used resinous polymodal monovinyl substituted aromatic-conjugated diene block copolymers in blends with polymers of styrene to achieve similarly low blueness levels and good impact strength and/or ductility in articles made from the blends.
A further object of this invention is to provide novel processes for making resinous tapered block monovinylaromatic/conjugated diene copolymers, including copolymers suitable for use in blends.
In a first embodiment of the invention, copolymers are prepared under solution polymerization conditions in a reaction zone by:
(a) charging a monovinylaromatic monomer and an initiator in the presence of a randomizer and allowing polymerization to occur until essentially no free monomer is present; thereafter
(b) charging an initiator and a monovinylaromatic monomer and allowing polymerization to occur until essentially no free monomer is present; thereafter
(c) charging a mixture of monovinylaromatic monomer and conjugated diene monomer and allowing polymerization to occur until essentially no free monomer is present; and thereafter
(d) charging the reaction mixture with a coupling agent.
In a second embodiment of the invention, copolymers are prepared in the same manner as those of the first embodiment, except that additionally, after step (c) and preceeding step (d), a second separate charge of a mixture of monovinylaromatic monomer and conjugated diene monomer is made and allowed to polymerize until essentially no free monomer is present before charging the reaction mixture with a coupling agent.
DETAILED DESCRIPTION OF THE INVENTION
We have discovered novel monovinylaromatic/conjugated diene tapered block copolymers which can be used neat or blended with polymers of styrene to produce resins which can be formed into articles with low blueness and advantageous impact properties and/or ductility.
The polymers of this invention are characterized as resinous non-rubbery block copolymers of at least one conjugated diene with at least one monovinylarene, having at least one random-tapered block and are prepared so that, when the choice of coupling agent permits, at least a portion of the final product is of a branched, coupled character.
The polymers prepared according to this invention contain from about 55 to about 95, preferably from about 60 to about 90, more preferably from about 65 to about 85, weight percent of copolymerized monovinyl aromatic monomer based on the weight of total monomers employed. Correspondingly, the inventive copolymers contain from about 45 to about 5, preferably from about 40 to about 10, and more preferably from about 35 to about 15 weight percent copolymerized conjugated diene monomer based on the total weight of monomers in the copolymer.
The coupled portions of the resinous polymodal block copolymers of this invention have terminal polymonovinylarene blocks on the extending arms of each linear or radial copolymer molecule, and further contain at least ones internal tapered block of monovinylarene and conjugated diene. The resinous copolymeric polymodal products also contain portions of linear uncoupled block copolymers of poly(monovinylarene)-poly(conjugated diene); the linear uncoupled block copolymer content is considered to be an important portion of the resinous product with respect to its overall properties.
Components
The process of this invention can be carried out using as an initiator 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 alkyl metal cation. Mixtures of organoalkali metal compounds can be used. The presently preferred initiators are alkylmonolithium compounds, especially n-butyllithium or sec-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. Each of the charges containing conjugated diene in the same sequence of charges may be the same, but is not necessarily the same, conjugated diene monomer or mixture of conjugated diene monomers. The presently preferred conjugated diene monomer is 1,3-butadiene.
The monovinylaromatic monomers which can be used contain 8 to 12 carbon atoms and include styrene, alpha-methylstyrene, 4-methylstyrene, 3-methylstyrene, 2-methylstyrene, 4-ethylstyrene, 3-ethylstyrene, 2-ethylstyrene, 4-tert-butylstyrene, 2,4-dimethylstyrene and condensed aromatics such as vinyl napthalene and mixtures thereof. Each of the charges containing monovinylaromatic monomer in the same sequence of charges may be the same, but is not necessarily the same, monovinylaromatic monomer or mixture of monovinylaromatic monomers. The presently preferred monovinylaromatic monomer is styrene.
Examples of polar compounds which can be advantageously employed as randomizers 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
Farrar, Jr. Ralph C.
Moczygemba George A.
Stacy Nathan E.
Trepka William J.
Mullis Jeffrey
Owen Polly C.
Phillips Petroleum Company
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