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
1995-04-26
2001-03-27
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S332700, C525S351000
Reexamination Certificate
active
06207764
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions containing halogenated elastomers, particularly elastomeric interpolymers containing isobutylene and para haloalkyl-substituted styrene, crosslinking agents and thiosulfate accelerators.
BACKGROUND OF THE INVENTION
Halogenated copolymers of isobutylene and up to about 4 mole % of isoprene (butyl rubber) are well known polymeric materials whose vulcanizates offer some outstanding properties not possessed by many other diolefin based elastomers. Articles prepared from many cured halogenated elastomers offer improved resistance to oils and greases as well as resistance to oxygen and ozone degradation. Butyl rubber vulcanizates exhibit good abrasion resistance, excellent impermeability to air, water vapor, and many organic solvents, as well as resistance to aging and sunlight. These properties render these materials ideal candidates for one or more applications such as water hoses, organic fluid hoses, components in tire construction, gaskets, adhesive compositions and various molded articles.
More recently, new halogenated elastomeric interpolymers have been discovered which offer many of the same properties as halogenated butyl rubber, but are even more ozone and solvent resistant and are more readily curable. These materials are the halogenation product of random copolymers of a C
4
to C
7
isoolefin, such as isobutylene, and a para-alkyl styrene comonomer wherein at least some of the alkyl substituent groups present in the styrene monomer units contain halogen.
These copolymers and their method of preparation are more particularly disclosed in U. S. Pat. No. 5,162,445, the complete disclosure of which is incorporated herein by reference.
The aromatic halomethyl groups present in such copolymers permit facile crosslinking to be accomplished in a variety of ways, including by means of zinc oxide or promoted zinc oxide curing systems normally used to cure halogenated butyl rubber.
Some of these promoted zinc oxide crosslinking systems, however, give serious precure problems.
U. S. Pat. No. 5,373,062 discloses halogenated elastomer compositions featuring a promoted zinc oxide crosslinking agent and a bismuth carboxylate scorch inhibitor.
It is an object of this invention to provide halogenated elastomer compositions which cure quickly, but without serious precure problems, and achieve a high level of crosslinking.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved promoted curing system for halogenated elastomers has been discovered wherein the curing system contains a crosslinking agent and an accelerator material containing one or more groups of the formula
—S—SO
2
—OM
attached to a hydrocarbon radical, an organic bridging group or a polymer, and M is a monovalent metal, the equivalent of a multivalent metal, a monovalent ion derived by the addition of a proton to a nitrogenous base or the equivalent of a multivalent ion derived by the addition of two or more protons to a nitrogenous base.
Halogenated elastomer compositions containing these crosslinking agents and accelerator materials cure quickly to a high state of cure, and avoid problems of precure.
DETAILED DESCRIPTION OF THE INVENTION
The halogenated elastomer present in the compositions of this invention include chlorinated or brominated butyl rubber, chlorinated or brominated interpolymers of a C
4
to C
7
isolefin and a para-alkyl styrene, mixtures thereof or mixtures of one or both of these elastomers with vulcanizable diene elastomers such as natural or synthetic cis-polyisoprene, polybutadiene, butadiene-styrene copolymers or elastomeric copolymers of ethylene, propylene and up to 10 mole % of a non-conjugated diene (known as EPDM rubber).
The halobutyl rubbers can be based on chlorinated or brominated copolymers of isobutylene with up to about 4 mole % of isoprene. These elastomers generally have a number average molecular weight within the range of about 50,000 up to about 500,000 and may be prepared by polymerization and halogenation methods well known in the art such as disclosed in U.S. Pat. Nos. 2,940,960 and 3,099,644, the disclosures of which are incorporated herein by reference.
Halogenated interpolymers based on a C
4
to C
7
isoolefin, such as isobutylene, and a para-alkylstyrene, such as para-methylstyrene, are also now known in the art as evidenced by the aforementioned U.S. Pat. No. 5,162,445.
More preferred materials are the halogenation product of a random copolymer of a C
4
to C
7
isoolefin, such as isobutylene, and a para-alkylstyrene comonomer wherein at least some of the alkyl substituent groups present in the styrene monomer units contain halogen. Preferred materials may be characterized as isobutylene interpolymers containing the following monomer units randomly spaced along the polymer chains:
wherein at least about 5 mole % of the comonomer units present in the polymer chain are of the structure of formula 2, R and R′ are independently hydrogen or C
1
to C
4
alkyl, R″ is independently hydrogen, C
1
to C
4
alkyl or X, and X is bromine or chlorine, and wherein the interpolymer is otherwise substantially free of any halogen in the polymer backbone chain.
With reference to isobutylene as the isoolefin comonomer, these interpolymers are inclusive of:
a) copolymers consisting of isobutylene and a monomer having the structure of formula 2 wherein R″ is hydrogen or C
1
to C
4
alkyl, e.g., copolymers of isobutylene and a monohalo-substituted para-alkylstyrene;
b) terpolymers comprising isobutylene and a mixture of monomers having the structure of formulas 1 and 2 wherein R″ is hydrogen or C
1
to C
4
alkyl, e.g., terpolymers of isobutylene, a para-alkylstyrene and a monohalo-substituted para-alkylstyrene;
c) terpolymers comprising isobutylene and a mixture of monomers having the structure of formula 2 wherein, with respect to a major proportion of the formula 2 monomer, R″ is hydrogen or C
1
to C
4
alkyl and, with respect to a minor proportion of said formula 2 monomer, R″ is bromine or chlorine, e.g., terpolymers of isobutylene, a mono-halo substituted para-alkylstyrene and a di-halo substituted para-alkylstyrene; and
d) tetrapolymers comprising isobutylene and a mixture of monomers having the structure of formulas 1 and 2 wherein, with respect to major proportion of the formula 2 monomer, R″ is hydrogen or C
1
to C
4
alkyl and, with respect to a minor proportion of said formula 2 monomer, R″ is bromine or chlorine, e.g., tetrapolymers of isobutylene, a para-alkylstyrene, a monohalo-substituted para-alkylstyrene and a dihalo-substituted para-alkylstyrene.
As stated above, these halogenated interpolymers are prepared using a copolymer of a C
4
to C
7
isoolefin and a para-alkylstyrene as the halogenation substrate. Interpolymers having the composition (a), (b), (c) or (d) above will be produced as a function of the severity of the halogenation reaction. For example, mild halogenation will tend to yield interpolymers of the characteristics of (b), stronger halogenation will yield interpolymers of the characteristics of (a) or (d) and the strongest halogenation will yield terpolymers having the characteristics of (c).
The most preferred elastomers used in the compositions of the present invention are random elastomeric brominated terpolymers comprising isobutylene and para-methylstyrene (PMS) containing from about 0.5 to about 20 mole % PMS, more preferably from about 2 to about 15 mole % PMS, wherein up to about 60 mole % of the PMS monomer units contain a mono-bromomethyl group. These elastomeric copolymers generally exhibit a number average molecular weight in the range of from about 50,000 to about 250,000, more preferably from about 80,000 to about 180,000. From about 5 up to about 60 mole % of the total PMS monomer content of the terpolymer contains a mono-bromomethyl group with essentially no bromination occurring in the polymer backbone or in the aromatic ring. The bromine content of these terpolymers generally ranges from about 0.1 to
Henderson Christopher
Monsanto Company
Morris Louis A.
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