Polydienes and polydiene copolymers having poly(alkylene oxide) grafts and their use in the manufacture of tire components

Abstract

1. A tire tread comprising a vulcanization residue of a vulcanizable composition comprising: (i) a poly(alkylene oxide)-grafted polydiene or polydiene copolymer; (ii) a natural or synthetic elastomer; (iii) a silica filler; and (iv) a curative, wherein the poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprises a sulfur or methacrylate bond between the polydiene or polydiene copolymer chain and the poly(alkylene oxide) chain.

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention are directed to the preparation of poly(alkylene oxide)-grafted polydienes and polydiene copolymers and the use of these polymers in the manufacture of tire components, particularly silica-filled tire components. [Background technology]

[0002] In the technical field of tire construction, silica is often used as a reinforcing filler because it increases mechanical strength and reduces rolling resistance. However, the use of silica as a reinforcing filler can be problematic because silica is generally incompatible with tire rubber and tends to agglomerate. The latter is thought to affect the tire's ability to resist wear and abrasion. Therefore, there is a need to increase the compatibility between silica and other components of rubber compounds, especially rubber components. Summary of the Invention

[0003] One or more embodiments of the present invention provide a tire tread comprising a vulcanization residue of a vulcanizable composition, the vulcanizable composition comprising (i) a poly(alkylene oxide)-grafted polydiene or polydiene copolymer, (ii) a natural or synthetic elastomer, (iii) a silica filler, and (iv) a curative, wherein the poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprises a sulfur or methacrylate linkage between the polydiene or polydiene copolymer chain and the poly(alkylene oxide) chain.

[0004] Yet another embodiment of the present invention provides a method for preparing a poly(alkylene oxide)-grafted polydiene or polydiene copolymer, the method comprising: (i) providing a polydiene or polydiene copolymer; (ii) providing an end-functionalized poly(alkylene oxide); (iii) combining the polydiene or polydiene copolymer with the end-functionalized poly(alkylene oxide) in a solvent; and (iv) reacting the polydiene or polydiene copolymer with the end-functionalized poly(alkylene oxide) in the presence of a free radical initiator, thereby forming the poly(alkylene oxide)-grafted polydiene or polydiene copolymer, comprising a polydiene or polydiene copolymer having one or more poly(alkylene oxide) chains grafted thereto. DETAILED DESCRIPTION OF THE INVENTION

[0005] Embodiments of the present invention are based, at least in part, on the discovery of methods for preparing poly(alkylene oxide)-grafted polydienes and polydiene copolymers and their use in the manufacture of silica-filled tire components, such as treads. In particular embodiments, the polymers are poly(ethylene glycol)-grafted poly(styrene-co-butadiene) copolymers. It has been unexpectedly discovered that silica-filled tire components, such as treads, prepared using these grafted copolymers exhibit an advantageous balance of rolling resistance and dry handling, as indicated by the dynamic mechanical properties of the vulcanizates.

[0006] Preparation of grafted copolymers In one or more embodiments, poly(alkylene oxide)-grafted polydienes and polydiene copolymers (e.g., poly(ethylene glycol)-grafted poly(styrene-co-butadiene) copolymers), sometimes referred to as PEG-grafted polydienes or copolymers or simply grafted polymers, are prepared by combining a polydiene or polydiene copolymer (e.g., poly(styrene-co-butadiene) copolymer) with end-functionalized poly(ethylene glycol) in a suitable solvent or liquid medium in the presence of a free radical initiator.

[0007] Reaction conditions time As proposed above, a polydiene or polydiene copolymer (e.g., a poly(styrene-co-butadiene) copolymer) is combined with an end-functionalized poly(alkylene oxide) in the presence of a free radical initiator in a suitable solvent or liquid medium, sometimes collectively referred to as a reaction mixture. The end-functionalized poly(alkylene oxide) is believed to react with vinyl units on the polydiene or polydiene copolymer to form a grafted polymer. After the reaction, the reaction mixture is optionally quenched, and the grafted polymer is then isolated from the other components of the reaction mixture.

[0008] According to one or more embodiments of the present invention, the reactants are combined (i.e., the polydiene and / or polydiene copolymer is combined with the end-functionalized poly(alkylene oxide)) and maintained in a reaction mixture for at least 10 hours, in other embodiments at least 12 hours, and in other embodiments at least 15 hours, before isolating the grafted polymer. In these or other embodiments, the reactants are combined (i.e., the polydiene and / or polydiene copolymer is combined with the end-functionalized poly(alkylene oxide)) and maintained in a reaction mixture for from about 10 to about 25 hours, in other embodiments from about 12 to about 20 hours, and in other embodiments from about 15 to about 17 hours, before isolating the grafted polymer.

[0009] Temperature and reaction conditions In one or more embodiments, the reaction mixture in which the end-functionalized poly(alkylene oxide) is reacted with the polydiene or polydiene copolymer to form the graft polymer may be maintained at a temperature sufficient to activate the free radical initiator. In one or more embodiments, the reaction mixture is maintained at a temperature of from about 65 to about 100°C, from about 70 to about 98°C in other embodiments, or from about 80 to about 95°C in other embodiments.

[0010] In one or more embodiments, the reaction mixture is maintained under an inert atmosphere, for example, under a nitrogen blanket in a sealed vessel. As will be appreciated by those skilled in the art, the pressure at which the reaction mixture is maintained will increase as the temperature of the reaction mixture increases.

[0011] Solid concentration In one or more embodiments, the reaction mixture for reacting the terminally functionalized poly(alkylene oxide) with the polydiene or polydiene copolymer to form the grafted polymer comprises a solvent or liquid medium, as described above, and may be characterized by a solids concentration of less than 20 wt. % of the polymerization mixture, less than 18 wt. % in other embodiments, and less than 15 wt. % in other embodiments. In one or more embodiments, the reaction mixture comprises from about 8 to about 20 wt. % of solids, from about 10 to about 18 wt. % in other embodiments, and from about 11 to about 15 wt. % of solids, based on the total weight of the polymerization mixture.

[0012] Polydienes and polydiene copolymers The polydiene or polydiene copolymer to be grafted in accordance with embodiments of the present invention is generally characterized as comprising one or more mer units derived from the polymerization of a diene monomer and, optionally, one or more units derived from the polymerization of a vinyl aromatic monomer. In certain embodiments, the grafted polymer is a polydiene copolymer comprising mer units derived from a diene monomer and a vinyl aromatic monomer. In one or more embodiments, the grafted polymer is a poly(styrene-co-butadiene) copolymer.

[0013] Polydienes or polydiene polymers may be characterized by their molecular weight, which may include the number average molecular weight (Mn), weight average molecular weight (Mw), and peak molecular weight (Mp). As will be understood by those skilled in the art, molecular weights can be determined by gel permeation chromatography (GPC) using appropriate calibration standards. For purposes of this specification, GPC measurements use polystyrene standards and polystyrene Markovnik constants unless otherwise specified.

[0014] In one or more embodiments, the polydiene or polydiene copolymer has an Mp greater than 160 kg / mol, greater than 170 kg / mol in other embodiments, and greater than 180 kg / mol in other embodiments, sometimes referred to as the base Mp. In these or other embodiments, the polydiene or polydiene copolymer has an Mp less than 280 kg / mol, less than 260 kg / mol in other embodiments, and less than 250 kg / mol in other embodiments. In one or more embodiments, the polydiene or polydiene copolymer has an Mp of from about 160 to about 280 kg / mol, from about 170 to about 260 kg / mol in other embodiments, and from about 180 to about 250 kg / mol.

[0015] In one or more embodiments, the polydiene or polydiene copolymer has an Mn, sometimes referred to as the base Mn, greater than 130 kg / mol, greater than 140 kg / mol in other embodiments, and greater than 150 kg / mol in other embodiments. In these or other embodiments, the polydiene or polydiene copolymer has an Mn less than 300 kg / mol, less than 280 kg / mol in other embodiments, and less than 260 kg / mol in other embodiments. In one or more embodiments, the polydiene or polydiene copolymer has an Mn of from about 130 to about 300 kg / mol, from about 140 to about 280 kg / mol in other embodiments, and from about 150 to about 260 kg / mol.

[0016] In one or more embodiments, the polydiene or polydiene copolymer has a Mw, sometimes referred to as the base Mw, greater than 180 kg / mol, greater than 190 kg / mol in other embodiments, and greater than 200 kg / mol in other embodiments. In these or other embodiments, the polydiene or polydiene copolymer has a Mw less than 500 kg / mol, less than 450 kg / mol in other embodiments, and less than 400 kg / mol in other embodiments. In one or more embodiments, the polydiene or polydiene copolymer has a Mw of from about 180 to about 500 kg / mol, from about 190 to about 450 kg / mol in other embodiments, and from about 200 to about 400 kg / mol.

[0017] Polydienes or polydiene copolymers produced according to aspects of the present invention may be characterized by their vinyl content, which can be described as the number of unsaturations in the 1,2 microstructure relative to the total unsaturation within the polymer chain. As will be understood by those skilled in the art, vinyl content can be determined by NMR analysis. In one or more embodiments, the polydienes or polydiene copolymers contain greater than 10%, greater than 20%, and greater than 35% vinyl in other embodiments. In these or other embodiments, the polydienes or polydiene copolymers contain less than 80%, less than 60%, and less than 46% vinyl in other embodiments. In one or more embodiments, the reactive polymers contain from about 10 to about 80%, from about 20 to about 60% in other embodiments, and from about 35 to about 46% vinyl in other embodiments.

[0018] Polydienes or polydiene copolymers produced according to aspects of the present invention may be characterized by bound styrene content, which refers to the weight percent of vinyl aromatic monomer incorporated into the polydiene copolymer. As will be understood by those skilled in the art, bound styrene (i.e., styrene incorporated into the polymer) can be determined by reference to the relative weights of vinyl monomers contained in the polymerization mixture to the diene monomer. Alternatively, bound styrene can be determined by NMR analysis. In one or more embodiments, the polydiene or polydiene copolymer comprises a vinyl content greater than 5 wt%, greater than 8 wt% in other embodiments, and greater than 10 wt% in other embodiments. In these or other embodiments, the reactive copolymer comprises a vinyl content less than 50 wt%, less than 35 wt% in other embodiments, and less than 20 wt% in other embodiments. In one or more embodiments, the reactive copolymer comprises a vinyl content of from about 5 to about 50 wt%, from about 5 to about 20 wt% in other embodiments, from about 8 to about 15 wt% in other embodiments, and from about 10 to about 20 wt% in other embodiments.

[0019] End-functionalized poly(alkylene oxide)s In one or more embodiments, the end-functionalized poly(alkylene oxide) grafted onto the polydiene or polydiene copolymer according to embodiments of the present invention comprises one or more mer units derived from the polymerization of alkylene oxide monomers and also comprises a terminal functional group that will react with the vinyl units of the polydiene or polydiene copolymer under appropriate conditions, as described herein.

[0020] In one or more embodiments, the alkylene oxide monomers from which the poly(alkylene oxide) chains of the end-functionalized poly(alkylene oxide) are formed may be selected from ethylene oxide and propylene oxide. In certain embodiments, the chains are polyethylene oxides, which are also sometimes referred to as polyethylene glycol, ethylene glycol, PEO, or PEG chains.

[0021] Poly(alkylene oxide) chains, sometimes referred to as poly(alkylene oxide) groups, are characterized by the number of mers (also referred to as repeat units) in the chain. In one or more embodiments, the poly(alkylene oxide) chain contains from about 5 to about 55 repeat units, in other embodiments from about 8 to about 50, and in other embodiments from about 10 to about 45 repeat units. In one or more embodiments, the poly(alkylene oxide) group contains fewer than 25 repeat units, in other embodiments fewer than 20 repeat units, in other embodiments fewer than 15 repeat units, in other embodiments fewer than 12 repeat units, and in other embodiments fewer than 10 repeat units.

[0022] In one or more embodiments, the chain length of the poly(alkylene oxide) group can vary depending on whether the group is associated with a poly(alkylene oxide) having a terminal thiol group or a poly(alkylene oxide) having a terminal methacrylate group. For example, when the poly(alkylene oxide) group is attached to a terminal thiol group, the number of repeating units can be from about 30 to about 55, in other embodiments from about 35 to about 50, and in other embodiments from about 40 to about 45 repeating units. On the other hand, when the poly(alkylene oxide) group is associated with a poly(alkylene oxide) having a terminal methacrylate group, the number of repeating units can be from about 5 to about 20, in other embodiments from about 7 to about 15, and in other embodiments from about 8 to about 12 repeating units.

[0023] In these or other embodiments, the poly(alkylene oxide) chain may be characterized by its molecular weight. In one or more embodiments, the poly(alkylene oxide) chain has a number average molecular weight (Mn) of about 250 to about 5000 g / mol, in other embodiments about 400 to about 2500 g / mol, and in other embodiments about 500 to about 2000 g / mol. In one or more embodiments, the poly(alkylene oxide) group has an Mn of less than 1500, in other embodiments less than 1250, in other embodiments less than 1000, in other embodiments less than 750, and in other embodiments less than 500 g / mol.

[0024] In one or more embodiments, the molecular weight of the poly(alkylene oxide) group can vary depending on whether the group is associated with a poly(alkylene oxide) having a terminal thiol group or a poly(alkylene oxide) having a terminal methacrylate group. For example, when the poly(alkylene oxide) group is associated with a terminal thiol group, the Mn can be from about 1000 to about 5000, in other embodiments from about 1500 to about 3000, and in other embodiments from about 1700 to about 2250 g / mol. On the other hand, when the poly(alkylene oxide) group is associated with a poly(alkylene oxide) having a terminal methacrylate group, the Mn can be from about 250 to about 1500, in other embodiments from about 400 to about 1000, and in other embodiments from about 450 to about 750 g / mol.

[0025] As noted above, end-functionalized poly(alkylene oxide)s comprise terminal functional groups that will react with vinyl units of a polydiene or polydiene copolymer. In one or more embodiments, the functional groups comprise methacrylate groups, and the end-functionalized poly(alkylene oxide)s may be referred to as methacrylate-terminated poly(alkylene oxide)s or poly(alkylene oxide) methacrylates. In other embodiments, the functional groups comprise thiol groups, sometimes referred to as sulfanyl groups, and the end-functionalized poly(alkylene oxide)s may be referred to as thiol-terminated poly(alkylene oxide)s or poly(alkylene oxide) thiols.

[0026] In one or more embodiments, the methacrylate group may be defined by the formula -OC(O)-C(CH)=CH. In other words, a terminally functionalized poly(alkylene oxide) containing a terminal methacrylate group can be defined by the formula R-OC(O)-C(CH)=CH, where R is a poly(alkylene oxide) group. Poly(alkylene oxide) polymers functionalized with terminal methacrylate groups are commercially available. For example, a methacrylate-end-functionalized poly(ethylene oxide) polymer having a molecular weight of about 550 g / mol can be purchased from Creative PEGWorks under the trade name PSB-2162, or a polymer having a molecular weight of about 500 g / mol can be purchased from Sigma Aldrich.

[0027] In one or more embodiments, the thiol group may be defined by the formula -SH. In other words, a terminal-functionalized poly(alkylene oxide) containing a terminal thiol group can be defined by the formula R-SH, where R is a poly(alkylene oxide) group. Poly(alkylene oxide) polymers functionalized with terminal thiol groups are commercially available. For example, a thiol-end-functionalized poly(ethylene oxide) polymer having a molecular weight of about 2000 g / mol can be purchased from Creative PEGWorks under the trade name PLS-605, or a thiol-end-functionalized poly(ethylene oxide) polymer having a molecular weight of about 2000 g / mol can be purchased from LaysanBio.

[0028] In one or more embodiments, the end-functionalized poly(ethylene oxide) polymers used in the present invention are monofunctional, meaning that the polymer contains only one functional group at one end of the polymer chain. In these or other embodiments, the poly(ethylene oxide) chain is linear and the other end of the chain is capped, meaning that the other end of the chain contains, for example, an alkyl unit forming an alkoxide end group (i.e., -OR). For example, the poly(alkylene oxide) end of the chain that is not tethered to a functional group may contain a methyl group and thus may be referred to as a methoxypoly(alkylene oxide).

[0029] Amount of reactants The amount of end-functionalized poly(alkylene oxide) combined with the polydiene or polydiene copolymer in the reaction mixture to form the grafted polymer may be quantified based on the molar ratio of the number of moles of end-functionalized poly(alkylene oxide) to the number of moles of polydiene or polydiene copolymer. Alternatively, the amount of end-functionalized poly(alkylene oxide) combined with the polydiene or polydiene copolymer in the reaction mixture to form the grafted polymer may be quantified based on the relative weight of end-functionalized poly(alkylene oxide) to the weight of polydiene or polydiene copolymer. In either case, the amount of end-functionalized poly(alkylene oxide) reacted with the polydiene or polydiene copolymer may depend on the reactivity of the end-functionalized poly(alkylene oxide). Poly(alkylene oxide)s having terminal thiol groups have been observed to be more reactive than poly(alkylene oxide)s having terminal methacrylate groups. Thus, in one or more embodiments, a larger excess of poly(alkylene oxide) having terminal methacrylate groups may be added.

[0030] In one or more embodiments, when the end-functionalized poly(alkylene oxide) comprises methacrylate groups, the molar ratio of moles of end-functionalized poly(alkylene oxide) to moles of polydiene or polydiene copolymer can be from about 30:1 to about 50:1, in other embodiments from about 33:1 to about 45:1, and in other embodiments from about 35:1 to about 42:1.

[0031] In one or more embodiments, when the end-functionalized poly(alkylene oxide) contains a thiol group, the molar ratio of moles of end-functionalized poly(alkylene oxide) to moles of polydiene or polydiene copolymer can be from about 1:1 to about 10:1, in other embodiments from about 1.3:1 to about 8:1, and in other embodiments from about 1.5:1 to about 6:1.

[0032] In one or more embodiments, when the end-functionalized poly(alkylene oxide) includes methacrylate groups (e.g., a poly(alkylene oxide) having an Mn of about 500), the relative weight of end-functionalized poly(alkylene oxide) to the weight of polydiene or polydiene copolymer may be from about 10 to about 20 parts by weight, or in other embodiments from about 12 to about 18 parts by weight, or in other embodiments from about 14 to about 16 parts by weight of end-functionalized poly(alkylene oxide) per 100 parts by weight of polydiene or polydiene copolymer.

[0033] In one or more embodiments, when the end-functionalized poly(alkylene oxide) contains thiol groups (e.g., a poly(alkylene oxide) having an Mn of about 2000), the relative weight of end-functionalized poly(alkylene oxide) to the weight of polydiene or polydiene copolymer may be from about 1 to about 15 parts by weight, or in other embodiments from about 2 to about 12 parts by weight, or in other embodiments from about 3 to about 11 parts by weight of end-functionalized poly(alkylene oxide) per 100 parts by weight of polydiene or polydiene copolymer.

[0034] Free Radical Initiators As indicated above, a free radical initiator is used to promote the reaction between the polydiene or polydiene copolymer and the end-functionalized poly(alkylene oxide). In one or more embodiments, the free radical initiator is soluble in the reaction mixture and is activated upon heating. In one or more embodiments, the free radical initiator is activated upon heating to temperatures consistent with the reaction temperatures outlined above.

[0035] In one or more embodiments, the free radical initiator is an azo compound such as, but not limited to, azobisisobutyronitrile (i.e., 2,2′-azobis(2-methylpropionitrile)) (also known as AIBN), 1,1′-azobis(cyclohexanecarbonitrile), 2,2′-azobis(2,4-dimethylvaleronitrile), and dimethyl-2,2′-azobis(2-methylpropionate).

[0036] As one of ordinary skill in the art will readily recognize, the amount of free radical initiator that can be used will depend on the nature of the free radical initiator, and one of ordinary skill in the art can readily determine, with undue experimentation, the appropriate amount to use. In one or more embodiments, the amount of free radical initiator present in the reaction mixture can be quantified relative to the end-functionalized poly(alkylene oxide). For example, if the free radical initiator is AIBN, in one or more embodiments, the amount of free radical initiator present in the reaction mixture is from about 0.05 to about 0.5, in other embodiments from about 0.07 to about 0.3, and in other embodiments from about 0.1 to about 0.2 parts AIBN per 100 parts end-functionalized poly(alkylene oxide).

[0037] Reaction medium As noted above, the reaction mixture includes a solvent, which may also be referred to as a reaction medium. In one or more embodiments, at least one of the polydiene or polydiene copolymer, the end-functionalized poly(alkylene oxide), and the grafted polymer product is soluble in the solvent. In one or more embodiments, each of the polydiene or polydiene copolymer, the end-functionalized poly(alkylene oxide), the free radical initiator, and the grafted polymer product is soluble in the solvent.

[0038] Useful solvents include, but are not limited to, hydrocarbons with low or relatively low boiling points, such as aromatic hydrocarbons, aliphatic hydrocarbons, and cycloaliphatic hydrocarbons. Non-limiting examples of aromatic hydrocarbons include benzene, toluene, xylene, ethylbenzene, diethylbenzene, and mesitylene. Non-limiting examples of aliphatic hydrocarbons include n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, isopentane, isohexane, isopentane, isooctane, 2,2-dimethylbutane, petroleum ether, kerosene, and mineral spirits. Non-limiting examples of cycloaliphatic hydrocarbons include cyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane. Mixtures of the above hydrocarbons can also be used.

[0039] antioxidants In one or more embodiments, an antioxidant can be introduced into the reaction mixture after the grafting reaction, optionally after the addition of the quenching agent discussed below, or in combination with the quenching agent. Exemplary antioxidants include 2,6-di-tert-butyl-4-methylphenol (also known as BHT).

[0040] As one of ordinary skill in the art will appreciate, the effective amount of antioxidant can vary depending on the nature of the antioxidant, and one of ordinary skill in the art can readily determine an appropriate amount using undue experimentation. For example, when BHT is used, the amount of antioxidant introduced into the reaction mixture can be from about 0.1 to about 1.0, or in other embodiments from about 0.5 to about 0.7, parts by weight of AIBN per 100 parts of end-functionalized poly(alkylene oxide).

[0041] Quenching the reaction After reaction of the polydiene or polydiene copolymer with the end-functionalized poly(alkylene oxide), the reaction mixture may be quenched to deactivate the reactivity caused by the free radical initiator. In one or more embodiments, the quenching agent may include a protic compound, including, but not limited to, an alcohol, a carboxylic acid, an inorganic acid, water, or a mixture thereof.

[0042] As one skilled in the art will appreciate, an excess amount of quenching agent can be effectively used.

[0043] Desolvation of grafted polymers Following the grafting reaction and the optional introduction of the quenching agent and the optional introduction of the antioxidant, the grafted polymer product can be separated from the solvent, which may be referred to as desolventization. In other words, as described above, the grafting reaction occurs in an organic solvent, and during the desolventization step, the organic solvent is separated from the resulting grafted polymer.

[0044] In certain embodiments, desolventization involves hot water and / or steam coagulation. For example, the reaction mixture containing the grafted polymer can be combined with steam or a hot water stream. The heat associated with the steam or hot water stream volatilizes the solvent and any other volatiles in the reaction mixture. The polymer product is then dispersed in the aqueous phase, for example, in the form of polymer crumbs. The nature and size of the polymer crumbs can generally be manipulated by the introduction of mechanical energy (e.g., in the form of a mixer).

[0045] In one or more embodiments, the polymer crumbs are temporarily stored in water as a crumb dispersion until the subsequent drying step described below. The crumb dispersion is generally a mixture of polymer particles or crumbs and water. The polymer particles, sometimes referred to as coagulated polymer, are generally macroscale, having dimensions of at least greater than 1 millimeter. This crumb dispersion may be contained in a vessel, for example, a conventional reactor vessel, such as a continuous stirred tank reactor.

[0046] In one or more embodiments, the polymer crumbs may be further processed to remove residual solvent and dry the polymer (i.e., separate the polymer from the water). In the practice of the present invention, the polymer may be dried using conventional techniques, which may include one or more of filtration, squeezing, and heating. After desolventization and drying, the volatile content of the dried polymer may be less than 2.0% by weight of the polymer, less than 1.0% by weight in other embodiments, and less than 0.5% by weight in other embodiments.

[0047] In other embodiments, the grafted polymer product can be desolventized by using a devolatilizer, which is an extruder-type device that can operate in conjunction with heat and / or vacuum. In yet other embodiments, the reaction mixture can be directly drum dried. In yet other embodiments, the reaction product can be dried by heating it on a heated mill.

[0048] Regardless of the method used to desolvent and dry the grafted polymer, the finished polymer product may be referred to as a dried polymer. The dried polymer can be shaped or otherwise manipulated into bales using conventional techniques.

[0049] Graft polymer properties In one or more embodiments, the grafted polymer may be characterized by the weight percent of poly(alkylene oxide) associated with the grafted polymer. As will be understood by one of ordinary skill in the art, this weight percent can be determined by NMR analysis. In one or more embodiments, the grafted polymer comprises greater than 1 weight percent, in other embodiments greater than 2 weight percent, and in other embodiments greater than 3 weight percent poly(alkylene oxide). In one or more embodiments, the grafted polymer comprises from about 1 to about 10 weight percent, in other embodiments from about 1.3 to about 8 weight percent, and in other embodiments from about 1.5 to about 7.5 weight percent poly(alkylene oxide).

[0050] In one or more embodiments, the grafted polymer may be characterized by the number of poly(alkylene oxide) grafts (i.e., poly(alkylene oxide chains)) associated with the entire grafted polymer. As will be understood by one of ordinary skill in the art, this can be determined by NMR analysis. In one or more embodiments, the number of grafts associated with the grafted polymer may be greater than 1, in other embodiments greater than 2, and in other embodiments greater than 3, and in other embodiments greater than 4. In one or more embodiments, the number of grafts associated with the grafted polymer may be from about 1 to about 12, and in other embodiments from about 2 to 16. The number of grafts may be about 10, and in other embodiments, about 3 to about 9. In one or more embodiments, the number of grafts may vary depending on the nature of the end-functionalized poly(alkylene oxide). For example, when the end-functionalized poly(alkylene oxide) has terminal thiol groups, the number of grafts may be about 1 to about 6, in other embodiments, about 1.3 to about 7, and in other embodiments, about 1.5 to about 5. On the other hand, when the poly(alkylene oxide) has terminal methacrylate groups, the number of grafts may be about 2 to about 10, in other embodiments, about 3 to about 8, and in other embodiments, about 4 to about 6.

[0051] In one or more embodiments, when the grafted polymer is synthesized by reacting a terminally functionalized poly(alkylene oxide) containing a terminal methacrylate with a polydiene or polydiene copolymer, the grafted polymer may be characterized as comprising a methacrylate graft (also referred to as a linkage) between the polydiene or polydiene copolymer and the poly(alkylene oxide) chain. In these embodiments, when the grafted polymer is synthesized by reacting a terminally functionalized poly(alkylene oxide) containing a terminal thiol group with a polydiene or polydiene copolymer, the grafted polymer may be characterized as comprising a sulfur graft (also referred to as a linkage) between the polydiene or polydiene copolymer and the poly(alkylene oxide) chain.

[0052] Industrial Applicability In one or more embodiments, the grafted polymers of the present invention may be used in compounding vulcanizable rubber compositions that may be useful, for example, in preparing tire components. Rubber compounding techniques and the additives used therein are generally described in The Compounding and Vulcanization of Rubber, Rubber Technology (2002). nd This is disclosed in "Ed. 1973."

[0053] Generally speaking, these vulcanizable rubber compositions include a vulcanizable rubber component, a reinforcing filler, and a curative or curative system. These compositions may also optionally include metal activators, resins, and processing oils, as well as various other components that may conventionally be included in these vulcanizable rubber compositions.

[0054] In one or more embodiments, the grafted polymers of the present invention may form all or part of the rubber component of the vulcanizable composition, i.e., the rubber component may include other vulcanizable rubbers, sometimes referred to as elastomeric polymers or simply elastomers.

[0055] Other elastomers in rubber components Rubber compositions can be prepared by using the polymers of the present invention alone or together with other elastomers (i.e., polymers that can be vulcanized to form compositions with rubbery or elastomeric properties). Other elastomers that may be used include natural and synthetic rubbers. Synthetic rubbers are typically obtained from the polymerization of conjugated diene monomers, copolymerization of conjugated diene monomers with other monomers such as vinyl-substituted aromatic monomers, or copolymerization of ethylene with one or more α-olefins and, optionally, one or more diene monomers.

[0056] Exemplary elastomers include natural rubber, synthetic polyisoprene, polybutadiene, polyisobutylene-co-isoprene, neoprene, poly(ethylene-co-propylene), poly(styrene-co-butadiene), poly(styrene-co-isoprene), poly(styrene-co-isoprene-co-butadiene), poly(isoprene-co-butadiene), poly(ethylene-co-propylene-co-diene), polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber, epichlorohydrin rubber, and mixtures thereof. These elastomers can have a myriad of macromolecular structures, including linear, branched, and star structures.

[0057] The rubber composition may contain fillers, such as inorganic and organic fillers. Examples of organic fillers include carbon black and starch. Examples of inorganic fillers include silica, aluminum hydroxide, magnesium hydroxide, mica, talc (hydrated magnesium silicate), and clay (hydrated aluminum silicate). Carbon black and silica are the most common fillers used in tire manufacturing. In certain embodiments, a mixture of different fillers may be advantageously used.

[0058] For purposes of this specification, the poly(alkylene oxide)-grafted polydiene or polydiene copolymer is considered part of the rubber component of the vulcanizable composition. In one or more embodiments, the vulcanizable composition comprises from about 40 to about 70 weight percent, in other embodiments from about 45 to about 65 weight percent, and in other embodiments from about 50 to about 60 weight percent rubber, based on the total weight of the vulcanizable composition. In one or more embodiments, the rubber component comprises from about 30 to about 100 weight percent, in other embodiments from about 50 to about 90 weight percent, and in other embodiments from about 60 to about 80 weight percent poly(alkylene oxide)-grafted polydiene or polydiene copolymer, based on the total weight of the rubber component. In these or other embodiments, the rubber component comprises greater than 50 weight percent, in other embodiments greater than 60 weight percent, in other embodiments greater than 70 weight percent, and in other embodiments greater than 80 weight percent poly(alkylene oxide)-grafted polydiene or polydiene copolymer, based on the total weight of the rubber component.

[0059] In one or more embodiments, carbon blacks include furnace blacks, channel blacks, and lamp blacks. More specific examples of carbon blacks include super abrasion furnace blacks, medium super abrasion furnace blacks, high abrasion furnace blacks, high speed extrusion furnace blacks, fine furnace blacks, semi-reinforced furnace blacks, medium processed channel blacks, hard processed channel blacks, conductive channel blacks, and acetylene blacks.

[0060] In certain embodiments, the carbon black has a viscosity of at least 20 m 2 / g, in other embodiments, at least 35 m 2The carbon black may have a surface area (EMSA) of 1 / g, where the surface area value can be determined using the cetyltrimethylammonium bromide (CTAB) technique per ASTM standard D-1765. The carbon black may be in pelletized or non-pelletized flocculent form. The preferred form of the carbon black may depend on the type of mixing equipment used to mix the rubber compound.

[0061] The amount of carbon black used in the rubber composition may be up to about 50 parts by weight per 100 parts by weight of rubber (phr), with about 5 to about 40 phr being typical.

[0062] Some commercially available silicas that can be used include Hi-Sil™ 215, Hi-Sil™ 233, and Hi-Sil™ 190 (PPG Industries, Inc.; Pittsburgh, Pa.) Other suppliers of commercially available silica include Grace Davison (Baltimore, Md.), Degussa Corp. (Parsippany, NJ), Rhodia Silica Systems (Cranbury, NJ), and JM Huber Corp. (Edison, NJ).

[0063] In one or more embodiments, silica can be characterized by its surface area, which is a measure of its reinforcing properties. The Brunauer, Emmett, and Teller (BET) method (described in J. Am. Chem. Soc., 1939, vol. 60, 2 pp. 309-319) is an accepted method for determining surface area. The BET surface area of ​​silica is generally 450 m 2 / g. A useful range of surface area is from about 32 to about 400 m 2 / g, about 100~250m 2 / g, and about 150 to about 220 m 2 / g is an example.

[0064] The pH of the silica is generally from about 5 to about 7, or slightly above 7, or in other embodiments, from about 5.5 to about 6.8.

[0065] In one or more embodiments, when silica is used as a filler (alone or in combination with other fillers), a coupling agent and / or shielding agent may be added to the rubber composition during mixing to enhance the interaction of the silica with the elastomer. Useful coupling agents and shielding agents are disclosed in U.S. Patent Nos. 3,842,111, 3,873,489, 3,978,103, 3,997,581, 4,002,594, 5,580,919, 5,583,245, 5,663,396, 5,674,932, and 5,675,941. ,684,171, 5,684,172, 5,696,197, 6,608,145, 6,667,362, 6,579,949, 6,590,017, 6,525,118, 6,342,552, and 6,683,135, which are incorporated herein by reference.

[0066] As indicated above, the grafted polymers of the present invention are particularly advantageous in vulcanizates (e.g., tire treads) containing silica fillers. In one or more embodiments, these vulcanizates are prepared from rubber compositions containing greater than 50 parts by weight, greater than 65 parts by weight in other embodiments, and greater than 80 parts by weight of silica per 100 parts by weight of rubber. The useful upper range may be limited by the high viscosity imparted by the silica. In one or more embodiments, these vulcanizates are prepared from rubber compositions containing from about 70 to about 120 parts by weight, from about 80 to about 115 parts by weight in other embodiments, and from about 85 to about 110 parts by weight of silica per 100 parts by weight of rubber. Typically, silica is used in combination with a coupling agent and / or a shielding agent, with the amount of coupling agent and / or shielding agent being from about 4% to about 20% based on the weight of the silica used.

[0067] In one or more embodiments, silica is used in combination with carbon black. The amount of carbon black used in combination with silica can be quantified based on the weight ratio of carbon black to silica. In one or more embodiments, the weight ratio of carbon black to silica is from about 0.1:1 to about 1:1, in other embodiments from about 0.15:1 to about 0.8:1, and in other embodiments from about 0.2:1 to about 0.5:1.

[0068] A number of rubber curing agents (also called vulcanizing agents) may be used, including sulfur or peroxide-based cure systems. Curing agents are described in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 20, pp. 365-468, (3 rd Ed.1982), especially Vulcanization Agents and Auxiliary Materials, pgs.390-402, and AYCoran, Vulcanization, Encyclopedia of Polymer Science and Engineering, (2 nd Ed. 1989), which are incorporated herein by reference. The vulcanizing agents may be used alone or in combination.

[0069] Other components typically used in rubber compounding may also be added to the rubber composition. These include accelerators, accelerator activators, oils, plasticizers, waxes, antiscorch agents, processing aids, zinc oxide, tackifying resins, reinforcing resins, fatty acids such as stearic acid, peptizers, and antidegradants such as antioxidants and antiozonants. In certain embodiments, the oils used include those conventionally used as extender oils, as described above.

[0070] All components of the rubber composition can be mixed using standard mixing equipment, such as a Banbury or Brabender mixer, an extruder, a kneader, and a two-roll mill. In one or more embodiments, the components are mixed in two or more stages. In the first stage (often referred to as the masterbatch mixing stage), a so-called masterbatch (typically containing the rubber component and filler) is prepared. To prevent premature vulcanization (also known as scorch), vulcanizing agents may be omitted from the masterbatch. The masterbatch may be mixed at an initiation temperature of about 25°C to about 125°C and an extrusion temperature of about 135°C to about 180°C. Once the masterbatch is prepared, vulcanizing agents may be introduced and mixed into the masterbatch in a final mixing stage, which is typically performed at a relatively low temperature to reduce the chance of premature vulcanization. Optionally, an additional mixing stage, sometimes referred to as a remill, can be used between the masterbatch mixing stage and the final mixing stage. When the rubber composition contains silica as a filler, one or more remill stages are often used. Various ingredients, including the polymers of the present invention, may be added during these remills.

[0071] Mixing procedures and conditions particularly applicable to silica-filled tire compounds are described in U.S. Patent Nos. 5,227,425, 5,719,207, and 5,717,022, and European Patent No. 890,606, all of which are incorporated herein by reference. In one embodiment, an initial masterbatch is prepared by including polymer and silica in the substantial absence of coupling and shielding agents.

[0072] Rubber compositions prepared from the polymers of this invention are particularly useful for forming tire components such as treads, subtreads, sidewalls, body ply skims, bead fillers, etc. In one or more embodiments, these tread or sidewall compounds may comprise from about 10% to about 100% by weight, in other embodiments from about 35% to about 90% by weight, and in other embodiments from about 50% to about 80% by weight of a polymer of this invention, based on the total weight of rubber in the compound.

[0073] When rubber compositions are used in tire manufacturing, they can be processed into tire components according to conventional tire manufacturing techniques, including standard rubber molding, molding, and curing techniques. Typically, vulcanization is accomplished by heating the vulcanizable composition in a mold, which can be heated to, for example, about 140°C to about 180°C. The cured or crosslinked rubber composition, also referred to as a vulcanizate, is the sulfur-cured residue of the rubber composition (i.e., the vulcanizable composition) and generally comprises a three-dimensional polymer network that is thermoset. Other components, such as fillers and processing aids, can be uniformly dispersed throughout the crosslinked network. Pneumatic tires can be made as discussed in U.S. Patent Nos. 5,866,171, 5,876,527, 5,931,211, and 5,971,046, which are incorporated herein by reference. [Example]

[0074] In order to demonstrate the practice of the present invention, the following examples have been prepared and tested. However, these examples should not be construed as limiting the scope of the invention. The claims shall define the invention.

[0075] Polymer Example 1: SBR (Control) A nitrogen-purged, jacketed steel reactor was charged with approximately 20 wt. % butadiene / hexane mixture, approximately 33 wt. % styrene / hexane mixture, and enough anhydrous hexane to make 10 pounds of a 15 wt. % solution of total monomers in hexane (1.5 wt. % styrene, 13.5 wt. % butadiene). The reactor was charged with n-butyllithium (1.6 M in hexane, 0.714 mmol per 100 grams of monomer), followed by 2,2-bis(2'-tetrahydrofuryl)propane (1.6 M in hexane, 0.30 equivalents relative to Li), and the jacket temperature was set to 140°F. The batch temperature peaked at 189.6°F after 24 minutes. After an additional 30 minutes, the polymerization was quenched by adding the poly(styrene-co-butadiene) (SBR) polymer cement dropwise into a bucket containing approximately 8 L of isopropyl alcohol (IPA) and 15 g of 2,6-di-tert-butyl-4-methylphenol (BHT). The polymer was allowed to solidify and then drum-dried. The polymer was analyzed by NMR to determine the mole percent of bound styrene and vinyl based on diene units. The results of this test are reported in Table I.

[0076] Polymer Example 2: SBR-g-PEGM500 A batch of SBR cement was prepared as described in Example 1, except that the polymerization was quenched by adding isopropyl alcohol (1 equivalent relative to Li) to the reactor. Thirty minutes after termination, an end-functionalized poly(ethylene oxide) having an average Mn of 500 g / mol, i.e., methoxypoly(ethylene glycol) monomethacrylate (also referred to as poly(ethylene glycol) methyl ether methacrylate) (PEGM500), which had been destabilized by stirring over dry basic alumina, was added to the reactor, followed by a free radical initiator, i.e., 2,2'-azobis(2-methylpropionitrile) (AIBN) (0.1 equivalent relative to PEGM500, dissolved in toluene). The reactor temperature was set at 176°F. The amounts of SBR and PEGM 500 introduced into the reactor are provided in Table I. After allowing the reaction to proceed overnight, the reaction mixture (i.e., polymer cement) was added dropwise to approximately 8 L of isopropyl alcohol (IPA) and 15 g of 2,6-di-tert-butyl-4-methylphenol (BHT). The polymer was allowed to coagulate and then drum-dried. The polymer was analyzed by NMR to determine the bound styrene, mole percent vinyl, and weight percent ethylene oxide. The results of this test are reported in Table I.

[0077] Polymer Examples 3-4: SBR-g-PEGM500 The same procedure as in Example 2 was followed, except that the jacket temperature was set at 200°F for the overnight reaction. The resulting polymer was similarly isolated and analyzed. The results of the tests are reported in Table I.

[0078] [Table 1]

[0079] Polymer Examples 5-8: SBR-g-PEGSH SBR was prepared in a manner similar to that of Example 1, and the dried polymer was introduced into four dry 750 mL glass bottles. The bottles were then sealed with rubber septa, purged with nitrogen, and approximately 450 mL of toluene was added. The polymer was allowed to dissolve overnight. A terminally functionalized poly(ethylene oxide) with an average Mn of approximately 2000 g / mol, i.e., methoxypoly(ethylene glycol) monothiol (also referred to as poly(ethylene glycol) methyl ether thiol (PEG-SH)), was added as a solid to each bottle along with AIBN as a toluene solution. The amounts of SBR, PEG-SH, and AIBN introduced into each bottle are reported in Table II. After stirring the bottles overnight in an 80°C water bath, each bottle was quenched with 3 mL of IPA / BHT solution (approximately 0.1 g BHT / 1 mL of IPA solution), poured into an IPA bucket containing BHT (approximately 8 liters of IPA), coagulated, and drum-dried. The polymer was analyzed by NMR to determine the mole percent of bound styrene, vinyl, and weight percent ethylene oxide. The results of this test are reported in Table II.

[0080] [Table 2]

[0081] Rubber Examples 9 to 16 Silica-filled vulcanizable compositions were prepared using the polymers prepared in Examples 1-8 above, using the rubber formulations and mixing sequences provided in Table III. These rubber formulations demonstrated rubber compounds useful for tire tread manufacturing. As shown in Table III, the mixing procedure was a three-step mixing procedure, including a masterbatch mixing step, a "remill mixing step," and a final mixing step. The various mixing steps were performed in a Brabender mixer. During the preparation of the masterbatch, the mixer was operated at 50 rpm, and a peak composition temperature of 160°C was reached. At that point, the composition was dropped from the mixer and allowed to cool to less than about 90°C. At this point, the composition was reintroduced into the mixer along with the ingredients identified for the "remill stage," and mixing continued at 50 rpm, achieving a peak composition temperature of approximately 160°C. The composition was again dropped from the mixer and allowed to cool to less than about 90°C. The composition was then reintroduced into the mixer along with the ingredients identified for the "final mix stage," and a final mixing step was performed at 40 rpm, achieving a peak composition temperature of approximately 100°C.

[0082] As can be seen from Tables III and IV, the type of SBR used in each example varied according to the polymer from the example above. The particular SBR (i.e., the polymer from the sample above) is specified in Table IV along with the results of the dynamic testing performed on the rubber compound or the resulting vulcanizate.

[0083] [Table 3]

[0084] For the data in Table III, the dynamic rheological properties of the vulcanizates (e.g., tan δ and G') were obtained from temperature sweep studies conducted over the range of about -80°C to about 80°C and 10 Hz, and strain sweep studies conducted over the range of 0.05 to about 7.5% strain in 0.25% increments.

[0085] [Table 4]

[0086] Various modifications and alterations that do not depart from the scope and spirit of this invention will be apparent to those skilled in the art. This invention is not to be duly limited to the illustrative embodiments set forth herein.

Claims

1. (i) a poly(alkylene oxide)-grafted polydiene or polydiene copolymer; and (ii) a natural or synthetic elastomer; and (iii) a silica filler; and (iv) a curing agent, wherein the poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprises a sulfur or methacrylate linkage between the polydiene or polydiene copolymer chain and the poly(alkylene oxide) chain.

2. 2. The tire tread of claim 1, wherein said polydiene or polydiene copolymer chains are poly(styrene-co-butadiene).

3. 3. Tire tread according to claim 1 or 2, wherein the poly(alkylene oxide) chains are poly(ethylene oxide) chains.

4. Tire tread according to any one of claims 1 to 3, wherein the poly(alkylene oxide) chains have a molecular weight of from about 250 to about 5000 g / mol.

5. Tyre tread according to any one of claims 1 to 4, wherein the poly(alkylene oxide) chains have a molecular weight of less than 1000 g / mol.

6. Tyre tread according to any one of claims 1 to 5, wherein the poly(alkylene oxide) chain has less than 20 repeat units.

7. Tire tread according to any one of claims 1 to 6, wherein said poly(styrene-co-butadiene) is characterized by a vinyl content of more than 20%.

8. The tire tread of any one of claims 1 to 7, wherein said poly(styrene-co-butadiene) is characterized by a bound styrene content of from about 20 to about 50 weight percent.

9. The tire tread of any one of claims 1 to 8, wherein said poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprises from about 1 to about 10 weight percent poly(alkylene oxide).

10. Tire tread according to any one of claims 1 to 9, wherein said vulcanizable composition comprises more than 50 parts by weight of silica per 100 parts by weight of rubber.

11. The tire tread of any one of claims 1 to 10, wherein the tire tread comprises a rubber component, the rubber component comprising more than 50% by weight of the poly(alkylene oxide)-grafted polydiene or polydiene.

12. 1. A process for preparing a poly(alkylene oxide)-grafted polydiene or polydiene copolymer, said process comprising: (i) providing a polydiene or polydiene copolymer; (ii) providing an end-functionalized poly(alkylene oxide); (iii) combining the polydiene or polydiene copolymer with the end-functionalized poly(alkylene oxide) in a solvent; (iv) reacting the polydiene or polydiene copolymer with the end-functionalized poly(alkylene oxide) in the presence of a free radical initiator, thereby forming a poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprising a polydiene or polydiene copolymer having one or more poly(alkylene oxide) chains grafted thereto.

13. The method of claim 12 , wherein the end-functionalized poly(alkylene oxide) is a thiol end-functionalized poly(ethylene oxide).

14. 14. The method of claim 12 or 13, wherein the end-functionalized poly(alkylene oxide) is a methacrylate end-functionalized poly(ethylene oxide).

15. The method of any one of claims 12 to 14, wherein the polydiene or polydiene copolymer chain is poly(styrene-co-butadiene).

16. The method of any one of claims 12 to 15, wherein the poly(alkylene oxide) chain is a poly(ethylene oxide) chain.

17. 17. The method of any one of claims 12 to 16, wherein the poly(alkylene oxide) chains have a molecular weight of from about 250 to about 5000 g / mol.

18. 18. The method of any one of claims 12 to 17, wherein the poly(alkylene oxide) chains have a molecular weight of less than 1000 g / mol.

19. The method of any one of claims 12 to 18, wherein the poly(alkylene oxide) chain has less than 20 repeat units.

20. 20. The method of any one of claims 12 to 19, wherein the poly(styrene-co-butadiene) is characterized by a vinyl content of greater than 20%.

21. 21. The method of any one of claims 12 to 20, wherein the poly(styrene-co-butadiene) is characterized by a bound styrene content of from about 20 to about 50 weight percent.

22. The method of any one of claims 12 to 21, wherein the poly(alkylene oxide)-grafted polydiene or polydiene copolymer comprises from about 1 to about 10 weight percent poly(alkylene oxide).

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