PNEUMATIC TIRE WITH TREAD OF MEDIUM VINYL POLYBUTADIENE/RUBBER BLEND

Abstract: Pneumatic tire¹ having a tread² composed of (A) medium vinyl polybutadiene rubber, (B) low vinyl polybuta­ diene rubber and, optionally, (C) cis 1,4-polyisoprene rubber. In a preferential aspect the medium vinyl polybutadiene is required to be of a type prepared by polymerizing 1,3-­ butadiene with a small amount of divinylbenzene in a hydrocarbon solvent with an alkyl lithium catalyst and in the presence of a polar catalyst modifier.

Description: PNEUMATIC TIRE WITH TREAD OF MEDIUM VINYL POLYBUT ADI ENE /RUBBER BLEND Field of Invention This invention relates to tires. The invention particularly relates to pneumatic rubber tires having a rubber tread composition. Background of the Invention Pneumatic rubber passenger and truck tires are composed of elements which conventionally include a tread of a rubber composition. The tread rubber is sometimes desirably compounded to provide a tire with a relatively low rolling resistance with reasonable wear and traction. Although it is desired to compound the tire's tread composition to reduce the rolling resistance of the tire without substantially degrading the tire's traction features, usually tire traction is often expected to be somewhat sacrificed as may be evidenced by its decrease in wet and dry skid resistance. Various rubber compositions have been prepared for various purposes, some of which have included tire treads, which compose a polybutadiene containing a degree of 1,2monomer configuration, sometimes referred to as vinyl content Representative of such various compositions include those, for example, taught in various patent specifications such as U. S. 3,937,681 relating to a tire tread of polybutadiene containing twenty-five to fifty percent of its monomer units in a 1,2-position, British patent 1,166,832 relating to a tire tread of "high vinyl" butadiene rubber containing at least fifty percent of 1,2-addition, U. S. 4,192,366 relating to a tire tread of polyisoprene and medium vinyl polybutadiene rubbers, U. S. 4,259,218 relating to a composition of "medium vinyl" polybutadiene and blends thereof with natural rubber where such composition is required to contain a certain carbon black, U. S. 3,978,165 relating to a composition, taught to be useful for tire treads composed of (a) "medium vinyl" polybutadiene, (b) polybutadiene and (c) butadiene/styrene rubbers and U. S. 3,827,991, U. S. 4,220,564 and U. S. 4,224,197 relating to combinations of polybutadiene containing at least seventy percent of 1,2-configuration with various other rubbers. Although such rubber compositions are taught to provide various benefits, some for tire treads, it continues to be desirable to provide a pneumatic tire having a rubber tread having an enhanced rolling resistance and/or treadwear commensurate with reasonable traction qualities. Statement and Practice of Invention In accordance with this invention, a pneumatic tire is provided having an outer circumferential tread adapted to be ground contacting where said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber (phr), (A) about 20 to about 90, preferably about 70 to about 25, parts by weight medium vinyl polybutadiene rubber having about a 30 to about 55, preferably about 35 to about 48, percent vinyl content, (B) about 10 to about 60, preferably about 15 to about 50, low vinyl polybutadiene rubber having about a 1 to about 15, preferably about 1 to about 10, percent vinyl content and (C) about 0 to about 50 weight percent cis 1,4-polyisoprene rubber. In the practice of this invention, the medium or low vinyl content of the required polybutadienes refers to the weight percent of monomer content of the polymer in the 1,2-configuration. The low vinyl polybutadiene is generally considered to be what is thought of as a somewhat conventional polybutadiene. The cis 1,4-polyisoprene rubber includes both natural and synthetic rubber. A preferred embodiment of the invention, particularly for tires to be used for somewhat conventional loads and speeds such as passenger vehicle tires, although the embodiment is not necessarily limited to such use, is a pneumatic tire provided with such tread where said tread is a sulfur cured elastomeric composition comprised of (A) about 40 to about SO, preferably about 50 to about 85, phr said medium vinyl polybutadiene rubber, and (B) about 10 to about 60, preferably about 15 to about 50, phr of said low vinyl polybutadiene rubber. An additional preferred embodiment of the invention, particularly for tires to be used for somewhat heavy loads and heavy duty such as truck tires, although the embodiment is not necessarily limited to such use, is a pneumatic tire provided with such tread where said tread is a sulfur cured elastomeric composition comprised of (A) about 20 to about 80, preferably about 25 to about 70, phr of said medium vinyl polybutadiene rubber, (B) about 10 to about 60, preferably about 15 to about 50, phr of said low vinyl polybutadiene rubber and (C) about 10 to about 55, preferably 15 to 50, phr of said cis 1,4-polyisoprene rubber. Such pneumatic tires are conventionally comprised of a generally toroidal shaped carcass with an outer circumferential tread adapted to be ground contacting, spaced beads and sidewalls extending radially from and connecting said tread to said beads. The cis 1,4-polyisoprene rubber typically has a cis 1,4-content of about 96 to about 99 weight percent. The major portion of the low vinyl polybutadiene is of the cis 1,4-configuration. The medium vinyl polybutadiene typically has about 10 to about 40 percent of its monomer units in a cis 1,4configuration and, after allowing for the medium vinyl content (1,2-monomer configuration) the remainder of the polymer is considered to be of monomer units in a trans 1,4-configuration. The medium vinyl polybutadiene, in its unvulcanized state, can typically be additionally characterized by having a ML-4 (1000C.) viscosity in the range of about 40 to about 120. These polybutadienes, particularly those in the higher NL-4 viscosity range, can optionally be individually oil extended before mixing with various rubber compounding materials for ease of processing. If oil extension is used, usually about 10 to about 50 phr of rubber processing oil is used, usually of the aromatic or aromatic/paraffinic oil type, to provide a ML-4 (1000C) viscosity of about 40 - 80. In the practice of this invention, it is intended that both organic solvent solution and aqueous emulsion polymerized 1,3-butadiene can suitably be used for the low vinyl polybutadiene. The invention can be practiced with medium vinyl polybutadiene rubber produced by various processes, such as those already known in the art. However, it is a particularly desirable feature of this invention that a particular type of medium vinyl polybutadiene be used. Although the mechanism, precise physical or chemical property or polymer structure effect is not understood, at least one of or a combination of, depending on the tire and its service conditions, tire properties have been observed to be further enhanced by using such particular medium vinyl polybutadiene. Such enhanced tire properties include at least one of or a combination of rolling resistance, skid resistance and tread wear. Such preferred medium vinyl polybutadiene is of the type prepared by polymerizing 1,3-butadiene with a very small amount of divinyl benzene in a hydrocarbon solvent system, preferably an essentially non-polar aprotic solvent, with an alkyl lithium catalyst, and one or more polar catalyst modifiers to effect the polymer's vinyl content. For further details concerning such type of medium vinyl polybutadiene and a method of preparation, reference may be made to U.S. Patent No. 4,230,841 and such patent is hereby incorporated herein by reference. It should readily be understood by one having skill in the art that said tread portion of the pneumatic tire as well as the rubber or other material in the basic carcass normally also containing reinforcing elements in the tread area, can be compounded by methods generally known in the rubber compounding art, such as mixing the various constituent rubbers with various curing aids, such as accelerators, processing additives, such as oils, resins and plasticizers, fillers, pigments, antioxidants and antiozonants and reinforcing materials such as, for example, carbon black. The tire can be built, shaped, molded and cured by various methods which will be readily apparent to those having skill in the art. In the practice of this invention, the polymer blendtread can be integral with and adhered to various tire carcass substrate rubber compositions. Typically, such a rubber composition is at least one of a butadiene/styrene copolymer rubber, cis 1,4 polyisoprene (natural or synthetic rubber) and 1,4 polybutadiene. Optionally, such a blend, particularly where the tread is in the region of the sidewall area of the tire may contain \ one or more of butyl rubber, halobutyl rubber, such as chlorobutyl or bromobutyl rubber, and ethylene /propylene /conjugated diene terpolymer rubber, polyisoprene and polybutadiene rubber. In the further practice of this invention, the tread can typically be applied in the building of the green tire in which the uncured, shaped tread is built onto the car- cass following which the green tire is shaped and cured. Alternately, the tread can be applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a retread. For further description of this invention, reference is made to the accompanying drawing which is a perspective view of a pneumatic tire having a cut-away portion. Referring to the drawing, the tire 1 comprises the usual ground contacting tread portion 2, carcass containing reinforcing elements such as plies and belt(s) and inner liner 3, spaced bead portion 4 for securing the tire to a rim and connecting sidewalls 5. In particular, the tread portion 2 is shown as having the composite required by this invention of the blend of medium vinyl polybutadiene and low vinyl polybutadiene and, in one embodiment, also containing polyisoprene along with compounding agents. The practice of this invention is further illustrated by reference to the following examples which are intended to be representative rather than restrictive of the scope of the invention. Unless otherwise indicated, all parts and percentages are by weight. EXAMPLE I Pneumatic tires of conventional construction (grooved tread, sidewalls, spaced beads, and supporting fabricreinforced carcass) were built, shaped and cured in a conventional tire mold. The tread was built onto the uncured carcass as a pre-extruded element. The tires were of the P155/80R13 type which indicates that they were belted, radial ply passenger type tires somewhat similar to the drawing in this specification. One tire is identified herein as Control X and another tire identified as Experimental Y. Control tire X had a tread composed of (A) 70 phr butadiene/styrene rubber and (B) 30 phr low vinyl, or conventional, polybutadiene rubber and is intended to represent a somewhat conventional passenger tire tread. Experimental tire Y had a tread composed of (A) 70 phr medium vinyl polybutadiene and (B) 30 phr low vinyl (conventional) polybutadiene. Thus, the medium vinyl polybutadiene replaced the butadiene/styrene rubber of the conventional-type tread rubber. The tires (X and Y) were mounted on rims, inflated and submitted to testing. The test values for the control were normalized to a value of 100 for comparison purposes. The tire with the experimental tread was tested and its test values compared to the values of the control tire and reported relative to the normalized values of 100. Surprisingly, the tire with the experimental tread rubber composition Y exhibited an improved (reduced) rolling resistance while also showing improved (increased) skid resistance as compared to control tire X. This is considered to be an important departure from ordinarily expected results. The tread compositions for tires X and Y were comprised of materials shown in the following Table 1. TABLE 1 Partsl Compound Control (X) Experimental (Y) Butadiene/styrene rubber oil extended (70 parts rubber, 26.25 parts oil) 96.25 -O- Medium vinyl polybutadiene3 rubber, oil extended (70 parts rubber, 26.25 parts oil) -0- 96.25 Polybutadiene rubber4 (1 - 2% vinyl) 30 30 Oil, aromatic 9 9 Antioxidant 3.2 3.2 Wax 3.8 3.8 Stearic acid 2 2 Carbon black 70 70 Sulfur 1.5 1.5 Accelerator 1.2 1.2 Zinc Oxide 4 4 1 - Most amounts rounded to nearest tenth of a part. 2 - Emulsion polymerization prepared SBR, oil extended with typical aromatic rubber processing oil. 3 - Contains 26.25 parts typical aromatic rubber-extending type processing oil containing about 70 percent aroma tics. Polymer contains about 45 percent 1,2- or vinyl, 26 percent cis 1,4 and 31 percent trans-1,4 and was of the type prepared by U.S. patent 4,230,841. 4 - Conventional type polybutadiene rubber. (cis 1,4-) Table 2 illustrates the rolling resistance and wet and dry skid resistance values with the Experimental Tire Y compared to values of Control Tire X normalized to 100. TABLE 2 Measured Values Control X Experimental Y Rolling resistance 100 95 /reduced, Wet skid resistance 100 104 (improved) Dry skid resistance 100 104 (improved) EXAMPLE II Pneumatic tires of conventional construction (grooved tread, sidewalls, spaced beads, and supporting fabricreinforced carcass) were built, shaped and cured in a conventional tire mold. The tread was built onto the uncured carcass as a pre-extruded element. The tires were of the 11R24.5 type which indicates that they were steel belted, radial ply truck type tires somewhat similar to the drawing in this speciffflcation. One tire is identified herein as Control XX and another tire identified as Experimental YY. Control tire XX had a tread composed of (A) 25 phr butadiene/styrene rubber (B) 25¯phr low vinyl, or conventional, polybutadiene rubber and (C) 50 phr cis 1,4-polyisoprene rubber. It is intended to represent a somewhat conventional truck tire tread. Experimental tireYYhad a tread composed of (A) 25 phr medium vinyl polybutadiene (B) 25 phr low vinyl (conventional) polybutadiene and (C) 50 phr cis 1,4-polyisoprene rubber. Thus, the medium vinyl polybutadiene replaced the butadiene/styrene rubber of the conventional-type tread rubber. The tires (XX and Yy) were mounted on rims, inflated and submitted to testing. The test values for the control were normalized to a value of 100 for comparison purposes. The tire with the experimental tread was tested and its test values compared to the values of the control tire and reported relative to the normalized values of 100. Surprisingly, the tire with the experimental tread rubber composition YY exhibited an improved (reduced) rolling resistance while also showing improved (increased) treadwear as compared to control tire XX. This is considered to be an important departure from ordinarily expected results. The tread compositions for tires XX and YY were comprised of materials shown in the following Table 3. TABLE 3 Parts Compound Control (xx) Experimental (y?) Butadiene/styrene rubber,2 oil extended (25 parts rubber, 9.38 parts oil) 34.38 - 0 - 3 Medium vinyl polybutadiene3 rubber, oil extended (25 parts rubber, 9. 38 parts oil) - 0 - 34.38 Polybutadiene rubber (1 - 2% vinyl) 25 25 Cis 1,4-polyisoprene rubber 50 50 Oil, aromatic 4.6 4.6 Antioxidant 3 3 Wax 1.5 1.5 Stearic acid 2.5 2.5 Carbon black 70 70 Sulfur 1 1 Accelerator 0.8 0.8 Zinc Oxide 3 3 1 - Most amounts rounded to nearest tenth of a part. 2 - Emulsion polymerization prepared SBR, oil extended with typical aromatic rubber processing oil. 3 - Contains 9.38 parts typical aromatic rubber-extending type processing oil containing about 70 percent aromatics. Polymer contains about 45 percent 1,2- or vinyl, 26 percent cis 1,4 and 31 percent trans-l,4 and was of the type prepared by U.S. patent 4,230,841. 4 - Conventional type cis 1,4-polybutadiene rubber. 5 -Conventional high cis 1,4-polyisoprene rubber. Table 4 illustrates the rolling resistance and treadwear values with the Experimental Tire YY compared to values of Control Tire XX normalized to 100. TABLE 4 Measured Values Control (XX) Experimental (YY) fk-¯educed Rolling resistance 100 95 improved Treadwear 100 110 (improved) The treadwear was a measure of reduction in tread depth after about 32,000 miles of test on a truck. In these Examples, the rolling resistance was measured by mounting and inflating the on-a-rim tire and allowing it to be turned by a 67 inch diameter dynamometer under about 80 percent of its rated load at a rate equivalent to a vehicular speed of 50 mph and the drag force measured. -The test is believed to be somewhat standard. The skid resistance was a standard test in which the tires (A and B) are mounted on opposite sides of a weighted, drawn trailer at various speeds and brakes of the trailer applied and skid force (peak and slide) measured. The treadwear was compared by actually mounting both control and experimental tires on a vehicle and driving it under controlled conditions, with the position of the tires on the vehicle being periodically positionally rotated. In these Examples, the preferred medium vinyl polybutadiene rubber was used. Such rubber was of the herein before described type prepared by U.S. Patent No. 4,230,841 which was incorporated herein by reference. As taught, the medium vinyl polybutadiene is prepared by polymerizing 1,3butadiene with a very small amount of divinyl benzene in an essentially non-polar aprotic solvent with an alkyl lithium catalyst and at least one polar catalyst modifier. Representative examples of such solvents are pentane, hexane, heptane, octane, isooctane and cyclohexene, of which hexane is preferred. Representative examples of alkyl lithium catalysts are methyl lithium, ethyl lithium, propyl lithium, n-butyl lithium, s-butyl lithium, t-butyl lithium and amyl butyl lithium. The n-butyl lithium is preferred. The amount of catalyst is dependent upon the molecular weight desired for the polymerization. The amount of divinylbenzene can be related to the level of active lithium catalyst. The amount of polar compound is dependent upon the vinyl content desired in the polymer. For example, it is described in said patent that between about 0.10 and 1.0 millimols of active alkyl lithium per hundred grams of butadiene can be used and that a mole ratio of divinylbenzene (DVB) to alkyl lithium can be in the range of about 0.1 to about 0.9. It is preferred that the temperature of the polymerization is maintained substantially constant throughout the polymerization. Various polar modifiers are prescribed, of which the strong catalyst modifiers are exemplified such as mexamethyl phosphoric acid triamide (HMPA), N,N,N',N'-tetramethylethylene diamine (TMEDA), ethylene glycol dimethyl ether (glyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether (tetraglyme). While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims: CLAIMS 1. A pneumatic tire having an outer circumferential tread adapted to be ground contacting, where said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber (phr), (A) about 20 to about 90 parts by weight medium vinyl polybutadiene rubber having about a 30 to about 55 percent vinyl content, (B) about 10 to about 60 low vinyl polybutadiene rubber having about a 1 to about 15 percent vinyl content and (C) about 0 to about 50 weight percent cis 1,4-polyisoprene rubber. A 2. A pneumatic tire having an outer circumferential tread adapted to be ground contacting, where said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber, (A) about 40 to about 90 medium vinyl polybutadiene rubber having about a 30 to about 55 percent vinyl content, and (B) about 60 to about 10 low vinyl polybutadiene rubber having about a 1 to about 15 percent vinyl content. 3. A pneumatic tire having an outer circumferential tread adapted to be ground contacting where said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber, (A) about 20 to about 80 medium vinyl polybutadiene rubber having about a 30 to about 55 percent vinyl content, (B) about 10 to about 60 low vinyl polybutadiene rubber having about a 1 to about 15 percent vinyl content and (C) about 10 to about 55 cis 1,4-polyisoprene rubber. 4. The tire of claim 1 where said low vinyl polybutadiene rubber is selected from the group consisting of hydrocarbon solvent solution polymerized 1,3-butadiene and aqueous emulsion polymerized 1,3-butadiene, the cis 1,4-polyisoprene rubber is selected from the group consisting of natural rubber and synthetic rubber, and where one or more of said rubbers is oil extended with about 10 to about 50 weight percent rubber processing oil before mixing with any of the other of said rubbers. 5. The tire of claim 2 where said low vinyl polybutadiene rubber is selected from the group consisting of hydrocarbon solvent solution polymerized 1,3-butadiene and aqueous emulsion polymerized 1,3-butadiene, the cis 1,4-polyisoprene rubber is selected from the group consisting of natural rubber and synthetic rubber, and where one or more of said rubbers is oil extended with about 10 to about 50 weight percent rubber processing oil before mixing with any of the other of said rubbers. 6. The tire of claim 3 where said low vinyl polybutadiene rubber is selected from the group consisting of hydrocarbon solvent solution polymerized 1,3-butadiene and aqueous emulsion polymerized 1,3-butadiene, the cis 1,4-polyisoprene rubber is selected from the group consisting of natural rubber and synthetic rubber, and where one or more of said rubbers is oil extended with about 10 to about 50 weight percent rubber processing oil before mixing with any of the other of said rubbers. 7. The pneumatic tire of claim 1 where said medium vinyl polybutadiene in its uncured state has a ML4(1000C) in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3 butadiene with a small amount of divinyl benzene in a hydrocarbon solvent system with an alkyl lithium catalyst and in the presence of at least one polar catalyst modifier. 8. The pneumatic tire of claim 2 where said medium vinyl polybutadiene has a ML4(1000C) viscosity in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3 butadiene with a small amount of divinyl benzene in a hydrocarbon solvent system with an alkyl lithium catalyst and in the presence of at least one polar catalyst modifier. 9. The pneumatic tire of claim 3 where said medium vinyl polybutadiene has a ML4(1000C) viscosity in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3 butadiene with a small amount of divinyl benzene in a hydrocarbon solvent system with an alkyl lithium catalyst and in the presence of at least one polar catalyst modifier. 10. The pneumatic tire of claim 4, 5 or 6 where said medium vinyl polybutadiene in its uncured state has a ML4(1000C) in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3 butadiene with a small amount of divinyl benzene in a hydrocarbon solvent system with an alkyl lithium catalyst and in the presence of at least one polar catalyst modifier. 11. The pneumatic tire of claim 7 where said medium vinyl polybutadiene is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in hexane solvent with n-butyl lithium and in the presence of at least one polar catalyst modifier. 12. The pneumatic tire of claim 8 where said medium vinyl polybutadiene is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in hexane solvent with n-butyl lithium and in the presence of at least one polar catalyst modifier. 13. The pneumatic tire of claim 9 where said medium vinyl polybutadiene is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in hexane solvent with n-butyl lithium and in the presence of at least one polar catalyst modifier. 14. The pneumatic tire of claim 4, 5 or 6 where said medium vinyl polybutadiene is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in hexane solvent with n-butyl lithium and in the presence of at least one polar catalyst modifier. 15. The tire of claim 1 where said tread is applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a retread. 16. The tire of claim 2 where said tread is applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a tread. 17. The tire of claim 3 where said tread is applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a retread. 18. The tire of claim 4, 5 or 6 where said tread is applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a retread. 19. The tire of claim 7, 8 or 9 where said tread is applied to a cured tire carcass from which the previous tread has been buffed or abraded away and the tread cured thereon as a retread. 20. A pneumatic tire comprised of a generally toroidal shaped carcass with an outer circumferential tread adapted to be ground contacting, spaced beads and sidewalls extending radially from and connecting said tread to said beads, characterized in that said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber (phr), (A) about 25 to about 70 parts by weight medium vinyl polybutadiene rubber having about a 35 to about 48 percent vinyl content, (B) about 15 to about 50 low vinyl polybutadiene rubber having about a 1 to about 10 percent vinyl content and (C) about 0 to about 50 weight percent cis 1,4-polyisoprene rubber; where the major portion#of said low vinyl polybutadiene rubber is of a cis 1,4-configuration, where said medium vinyl polybutadiene rubber, in its vulcanized state has a ML4(1000C) in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3butadiene with a small amount of divinyl benzene in a hydrocarbon solvent with an alkyl lithium catalyst and in the presence of a polar catalyst modifier; and where said tread is integral with and adhered to a carcass substrate rubber composition of at least one of butadiene/ styrene copolymer rubber, cis 1,4 polyisoprene rubber and 1,4 polybutadiene rubber. 21. A pneumatic tire comprised of a generally toroidal shaped carcass with an outer circumferential tread adapted to be ground contacting, spaced beads and sidewalls extending radially from and connecting said tread to said beads, characterized in that said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber, (A) 'about 40 to about 90 medium vinyl polybutadiene rubber having about a 30 to about 55 percent vinyl content, and (B) about 60 to about 10 low vinyl polybutadiene rubber having about a 1 to about 15 percent vinyl content; where the major portion of said low vinyl polybutadiene rubber is of a cis 1,4configuration, where said medium vinyl polybutadiene rubber, in its vulcanized state has a ML4(1000C) in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in a hydrocarbon solvent with an alkyl lithium catalyst and in the presence of a polar catalyst modifier; and where said tread is integral with and adhered to a carcass substrate rubber composition of at least one of butadiene/styrene copolymer rubber, cis 1,4 polyisoprene rubber and 1,4 polybutadiene rubber. 22. A pneumatic tire comprised of a generally toroidal shaped carcass with an outer circumferential tread adapted to be ground contacting, spaced beads and sidewalls extending radially from and connecting said tread to said beads, characterized in that said tread is a sulfur cured elastomeric composition comprised of, based on 100 parts by weight rubber, (A) about 20 to about 80 medium vinyl polybutadiene rubber having about a 30 to about 55 percent vinyl content, (B) about 10 to about 60 low vinyl polybutadiene rubber having about a 1 to about 15 percent vinyl content and (C) about 10 to about 55 cis 1,4-polyisoprene rubber; where the major portion of said low vinyl polybutadiene rubber is of a cis 1,4-configura- tion, where said medium vinly polybutadiene rubber, in its vulcanized state has a ML4(1000C) in the range of about 40 to about 120 and is of the type prepared by polymerizing 1,3-butadiene with a small amount of divinyl benzene in a hydrocarbon solvent with an alkyl lithium catalyst and in the presence of a polar catalyst modifier; and where said tread is integral with and adhered to a carcass substrate rubber composition of at least one of butadiene/ styrene copolymer rubber, cis 1,4 polyisoprene rubber and 1,4 polybutadiene rubber.

Inventors: HAAS, EDWARD JOSEPH, MONTGOMERY, EDWARD CHARLES, SCRIVER, RICHARD MARTIN, JR.
Applicants: THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1982
Main classification: B60C1
IPC codes: B60C1, C08F236, C08L21, C08L9, C08L7, B60C11