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
2000-09-15
2004-02-03
Cain, Edward J. (Department: 1714)
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
active
06686421
ABSTRACT:
BACKGROUND OF THE INVENTION
Tin-coupled polymers are known to provide desirable properties, such as improved treadwear and reduced rolling resistance, when used in tire tread rubbers. Such tin-coupled rubbery polymers are typically made by coupling the rubbery polymer with a tin coupling agent at or near the end of the polymerization used in synthesizing the rubbery polymer. In the coupling process, live polymer chain ends react with the tin coupling agent thereby coupling the polymer. For instance, up to four live chain ends can react with tin tetrachloride thereby coupling the polymer chains together.
The coupling efficiency of the tin coupling agent is dependent on many factors, such as the quantity of live chain ends available for coupling and the quantity and type of polar modifier, if any, employed in the polymerization. For instance, tin coupling agents are generally not as effective in the presence of polar modifiers. In any case, the actual number of live chain ends in the rubbery polymer is difficult to quantify. As a result, there is normally unreacted tin coupling agent left in the polymer cement after the coupling process has been completed.
The free tin coupling agent is then available to react with any active protons present in the polymer cement to form hydrochloric acid. For example, excess tin coupling agent can react with most hydroxyl group containing polymerization shortstops or moisture from the air. The acid generated can then cleave the tin-carbon bonds in the tin-coupled polymer. Undesirable polymer degradation is, of course, the result of the tin-carbon bonds in the rubbery polymer being cleaved. This polymer degradation is normally evidenced by a drop in the Mooney viscosity and molecular weight of the polymer.
SUMMARY OF THE INVENTION
This invention relates to a process for improving the stability of a tin-coupled rubbery polymer which comprises adding styrene to the rubbery polymer prior to the time at which it is coupled, and optionally, subsequently adding a tertiary chelating amine or a metal salt of a cyclic alcohol to the tin-coupled rubbery polymer subsequent to the time at which the tin-coupled rubbery polymer is coupled. Sodium mentholate is a representative example of a metal salt of a cyclic alcohol which is preferred for utilization in the process of this invention.
It is normally preferred to use metal salts of cyclic alcohols in the practice of this invention. This is because, in commercial applications where recycle is required, the use of tertiary chelating amines (such as sodium t-amylate) can lead to certain problems. For instance, sodium t-amylate can react with water to form t-amyl alcohol during steam-stripping in the polymer finishing step. Since t-amyl alcohol forms an azeotrope with hexane, it co-distills with hexane and thus contaminates the feed stream. The use of salts of cyclic alcohols, such as sodium mentholate, solves the problem of recycle stream contamination. The sodium mentholate does not co-distill with hexane or form compounds during steam-stripping which co-distill with hexane. Since the boiling points of the cyclic alcohols generated upon the hydrolysis of their metal salts are very high, they do not co-distill with hexane and contaminate recycle streams. Additionally, such cyclic alcohols are considered to be environmentally safe. In fact, sodium mentholate and menthol (the hydrolyzed product of sodium mentholate) are used as a food additive.
This invention more specifically discloses a process for improving the stability of a tin-coupled rubbery polymer which comprises (1) adding 0.1 phr to about 4 phr of styrene to a living rubbery polymer to produce a styrene capped rubbery polymer, and (2) adding a tin halide to the styrene capped living rubbery polymer to produce the tin-coupled rubbery polymer.
This invention more specifically discloses a process for improving the stability of a tin-coupled rubbery polymer which comprises (1) adding 0.1 phr to about 4 phr of styrene to a living rubbery polymer to produce a styrene capped rubbery polymer, (2) adding a tin halide to the styrene capped living rubbery polymer to produce the tin-coupled rubbery polymer, and (3) adding a tertiary chelating alkyl 1,2-ethylene diamine or a metal salt of a cyclic alcohol to the tin-coupled rubbery polymer.
DETAILED DESCRIPTION OF THE INVENTION
The process of this invention is applicable to virtually any type of tin-coupled rubbery polymer. It is of particular value in the stabilization of rubbery polymers that are free of bound styrene (other than the styrene added to cap the rubbery polymer). For instance, the technique of this invention is of great benefit in the stabilization of tin-coupled polybutadiene rubber, tin-coupled polyisoprene rubber, and tin-coupled isoprene-butadiene rubber. Such tin-coupled rubbery polymers will typically be synthesized by a solution polymerization technique utilizing an organolithium compound as the initiator.
Such polymerizations will normally be carried out in a hydrocarbon solvent which can be one or more aromatic, paraffinic or cycloparaffinic compounds. These solvents will normally contain from 4 to 10 carbon atoms per molecule and will be liquid under the conditions of the polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, methylcyclohexane, isohexane, n-heptane, n-octane, n-hexane, benzene, toluene, xylene, ethylbenzene, diethylbenzene, isobutylbenzene, petroleum ether, kerosene, petroleum spirits, petroleum naphtha, and the like, alone or in admixture.
In the solution polymerization, there will normally be from 5 to 30 weight percent monomers in the polymerization medium. Such polymerization media are, of course, comprised of the organic solvent and monomers. In most cases, it will be preferred for the polymerization medium to contain from 10 to 25 weight percent monomer. It is generally more preferred for the polymerization medium to contain 15 to 20 weight percent monomers.
The tin-coupled rubbery polymers stabilized in accordance with this invention can be made by the polymerization of one or more conjugated diolefin monomers. It is, of course, also possible to make rubbery polymers which can be tin-coupled by polymerizing a mixture of conjugated diolefin monomers with one or more ethylenically unsaturated monomers. The conjugated diolefin monomers which can be utilized in the synthesis of rubbery polymers which can be tin-coupled and stabilized in accordance with this invention generally contain from 4 to 12 carbon atoms. Those containing from 4 to 8 carbon atoms are generally preferred for commercial purposes. For similar reasons, 1,3-butadiene and isoprene are the most commonly utilized conjugated diolefin monomers. Some additional conjugated diolefin monomers that can be utilized include 2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and the like, alone or in admixture.
Some representative examples of ethylenically unsaturated monomers that can potentially be synthesized into rubbery polymers which can be tin-coupled and stabilized in accordance with this invention include alkyl acrylates, such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, and the like; &agr;-olefins, such as ethylene, propylene, 1-butene, and the like; vinyl halides, such as vinylbromide, chloroethene (vinylchloride), vinylfluoride, vinyliodide, 1,2-dibromoethene, 1,1-dichloroethene (vinylidene chloride), 1,2-dichloroethene, and the like; vinyl esters, such as vinyl acetate; &agr;,&bgr;-olefinically unsaturated nitrites, such as acrylonitrile and methacrylonitrile; &agr;,&bgr;-olefinically unsaturated amides, such as acrylamide, N-methyl acrylamide, N,N-dimethylacrylamide, methacrylamide, and the like.
Rubbery polymers which are copolymers of one or more diene monomers with one or more other ethylenically unsaturated monomers will normally contain from about 50 weight percent to about 99 weight percent conjugated diolefin monomers and from about 1 weight percent to about 50 weight per
Halasa Adel Farhan
Henning Steven Kristofer
Hsu Wen-Liang
Johnson Edward Lee
Cain Edward J.
Rockhill Alvin T.
The Goodyear Tire & Rubber Company
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