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
1999-11-15
2001-08-07
Wu, David W. (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...
C525S314000, C525S332500, C525S339000, C525S099000, C526S340000
Reexamination Certificate
active
06271317
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 tetrahalides, such as tin tetrachloride, thereby coupling the polymer chains together.
The coupling efficiency of the tin coupling agent is dependant 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. The amount of coupling which is attained is also, of course, highly dependent upon the quantity of tin coupling agent employed.
Each tin tetrahalide molecule is capable of reacting with up to four live polymer chain ends. However, since perfect stoichiometry is difficult to attain, some of the tin halide molecules often react with less than four live polymer chain ends. For instance, if more than a stoichiometric amount of the tin halide coupling agent is employed, then there will be an insufficient quantity of live polymer chain ends to totally react with the tin halide molecules on a four to one basis. On the other hand, if less than a stoichiometric amount of the tin halide coupling agent is added, then there will be an excess of live polymer chain ends and some of the live chain ends will not be coupled.
Conventional tin coupling results in the formation of a coupled polymer which is essentially symmetrical. In other words, all of the polymer arms on the coupled polymer are of essentially the same chain length. All of the polymer arms in such conventional tin-coupled polymers are accordingly of essentially the same molecular weight. This results in such conventional tin-coupled polymers having a low polydispersity. For instance, conventional tin-coupled polymers normally having a ratio of weight average molecular weight to number average molecular weight which is within the range of about 1.01 to about 1.1.
SUMMARY OF THE INVENTION
This invention is based upon the unexpected finding that greatly improved properties for tire rubbers, such as lower hysteresis, can be attained by asymmetrically coupling the rubber. For instance, such asymmetrically coupled polymers can be utilized in making tires having greatly improved rolling resistance without sacrificing other tire properties. These improved properties are due in part to better interaction and compatibility with carbon black. The asymmetrical tin coupling also normally leads to improve the cold flow characteristics of the rubbery polymer. Tin coupling in general also leads to better processability and other beneficial properties.
The asymmetrical tin-coupled rubbery polymers of this invention are comprised of a tin atom having polydiene arms covalently bonded thereto. At least one of the polydiene arms bonded to the tin atom will be a low number molecular weight arm having a number average molecular weight of less than about 40,000. It is also critical for the asymmetrical tin-coupled rubbery polymer to have at least one high molecular weight polydiene arm bonded to the tin atom. This high molecular weight arm will have a number average molecular weight which is at least 80,000. The ratio of the weight average molecular weight to the number average molecular weight of the asymmetrical tin-coupled rubbery polymers of this invention will also be within the range of about 2 to about 2.5.
This invention more specifically discloses an asymmetrical tin-coupled rubbery polymer which is particularly valuable for use in manufacturing tire tread compounds, said asymmetrical tin-coupled rubbery polymer being comprised of a tin atom having at least three polydiene arms covalently bonded thereto, wherein at least one of said polydiene arms has a number average molecular weight of less than about 40,000, wherein at least one of said polydiene arms has a number average molecular weight of at least about 80,000, and wherein the ratio of the weight average molecular weight to the number average molecular weight of the asymmetrical tin-coupled rubbery polymer is within the range of about 2 to about 2.5.
This invention also reveals a process for preparing an asymmetrical tin-coupled rubbery polymer which comprises: (1) continuously polymerizing at least one diene monomer to a conversion of at least about 90 percent utilizing an anionic initiator to produce a polymer cement containing living polydiene rubber chains, wherein some of the living polydiene rubber chains are low molecular weight polydiene rubber chains having a number average molecular weight of less than about 40,000, and wherein some of the living polydiene rubber chains are high molecular weight polydiene rubber chains having a number average molecular weight of greater than about 80,000; and (2) continuously adding a tin halide to the polymer cement in a separate reaction vessel to produce the asymmetrically tin-coupled rubbery polymer, wherein said asymmetrical tin-coupled rubbery polymer has a polydispersity which is within the range of about 2 to about 2.5.
The stability of the asymmetrical tin-coupled rubbery polymers of this invention can be improved by adding a tertiary chelating amine thereto subsequent to the time at which the tin-coupled rubbery polymer is coupled. N,N,N′,N′-tetramethylethylenediamine (TMEDA) is a representative example of a tertiary chelating amine which is preferred for utilization in stabilizing the polymers of this invention.
DETAILED DESCRIPTION OF THE INVENTION
Virtually any type of rubbery polymer prepared by anionic polymerization can be asymmetrically tin-coupled in accordance with this invention. The rubbery polymers which can be asymmetrically coupled will typically be synthesized by a solution polymerization technique utilizing an organolithium compound as the initiator. These rubbery polymers will accordingly normally contain a “living” lithium chain end.
The polymerizations employed in synthesizing the living rubbery polymers 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 monomers. It is generally more preferred for the polymerization medium to contain 15 to 20 weight percent monomers.
The rubbery polymers which are asymmetrically coupled in accordance with this invention can be made by the homopolymerization of a conjugated diolefin monomer or by the copolymerization of a conjugated diolefin monomer with a vinyl aromatic monomer. It is, of course, also possible to make living rubbery polymers which can be asymmetrically tin-coupled by polymerizing a mixture of conjugated diolefin monomers with one or more ethylenically unsaturated monomers, such as vinyl aromatic monomers. The conjugated diolefin monomers which can be utilized in the synthesis of rubbery polymers which can be asymmetrically tin-coupled in accordance w
Futamura Shingo
Halasa Adel Farhan
Hsu Wen-Liang
Matrana Barry Allen
Rockhill Alvin T
The Goodyear Tire & Rubber Company
Wu David W.
Zalukaeva Tanya
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