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
1999-12-20
2001-12-11
Lipman, Bernard (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...
C525S192000, C525S332800, C525S332900, C525S342000
Reexamination Certificate
active
06329467
ABSTRACT:
BACKGROUND OF THE INVENTION
Tire rubbers which are prepared by anionic polymerization are frequently coupled with a suitable coupling agent, such as a tin halide, to improve desired properties. Tin-coupled polymers are known to improve treadwear and to reduce 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.
U.S. Pat. No. 5,486,574 discloses dissimilar arm asymmetric radical or star block copolymers for adhesives and sealants. U.S. Pat. No. 5,096,973 discloses ABC block copolymers based on butadiene, isoprene and styrene and further discloses the possibility of branching these block copolymers with tetrahalides of silicon, germanium, tin or lead.
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 coupling the rubber with both a tin halide and a silicon halide. For instance, such 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. It is highly preferred for coupled polymer to be asymmetrically coupled with a tin halide and a silicon halide. Asymmetrical tin coupling also normally leads to improve the cold flow characteristics. Asymmetrical coupling in general also leads to better processability and other beneficial properties.
The coupled rubbery polymers of this invention are comprised of (1) tin atoms having at least three polydiene arms covalently bonded thereto and (2) silicon atoms having at least three polydiene arms covalently bonded thereto. It is highly preferred for the coupled rubbery polymer to be asymmetrically coupled wherein at least one of the polydiene arms bonded to the tin atoms has a number average molecular weight of less than about 40,000, wherein at least one of the polydiene arms bonded to the silicon atoms has a number average molecular weight of less than about 40,000, wherein at least one of said polydiene arms bonded to the tin atoms has a number average molecular weight of at least about 80,000, wherein at least one of said polydiene arms bonded to the silicon atoms 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 asymmetrically tin-coupled rubbery polymer is within the range of about 2 to about 2.5.
This invention more specifically discloses a coupled rubbery polymer which is particularly valuable for use in manufacturing tire tread compounds, said coupled rubbery polymer being comprised of (1) tin atoms having at least three polydiene arms covalently bonded thereto and (2) silicon atoms having at least three polydiene arms covalently bonded thereto.
The subject invention further 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 (1) tin atoms having at least three polydiene arms covalently bonded thereto, wherein at least one of said polydiene arms bonded to the tin atoms has a number average molecular weight of less than about 40,000, wherein at least one of said polydiene arms bonded to the tin atoms has a number average molecular weight of at least about 80,000 and (2) silicon atoms having at least three polydiene arms covalently bonded thereto, wherein at least one of said polydiene arms bonded to the silicon atoms has a number average molecular weight of less than about 40,000, wherein at least one of said polydiene arms bonded to the silicon atoms 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 coupled rubbery polymer is within the range of about 2 to about 2.5.
This invention also reveals a process for preparing an asymmetrical 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 and a silicon halide to the polymer cement in a separate reaction vessel to produce the asymmetrically coupled rubbery polymer, wherein said asymmetrical 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 or a salt of a cyclic alcohol thereto subsequent to the time at which the tin-coupled rubbery polymer is coupled. Sodium mentholate is a representative example of a salt of a cyclic alcohol which is preferred for utilization in stabilizing the coupled rubbery polymers of this invention.
DETAILED DESCRIPTION OF THE INVENTION
Virtually any type of rubbery polymer prepared by anionic polymerization can be coupled in accordance with this invention. In fact, the techniques of this invention can be used to asymmetrically couple virtually any type of rubbery polymer synthesized by anionic polymerization. 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 cha
Feng Yi
Halasa Adel Farhan
Hsu Wen-Liang
Pearson Charles John
Lipman Bernard
Rockhill Alvin T.
The Goodyear Tire & Rubber Company
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