Description:FIELD OF THE INVENTION
[0001] The present disclosure relates to functionalized emulsion styrene-butadiene rubber (ESBR), a rubber composition containing the functionalized ESBR and a tire produced using the rubber composition.

BACKGROUND OF THE INVENTION
[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Styrene-butadiene rubber (SBR) is widely utilized in manufacturing tires for automobiles. SBR is synthesized by solution or emulsion polymerization techniques. The solution polymerized styrene-butadiene rubber (SSBR) typically exhibits better rolling resistance and tread wear characteristics in tire treads as compared to the emulsion polymerized styrene-butadiene rubber (ESBR). ESBR compounds generally exhibit very high rolling resistance and poor filler interaction due to the polar characteristics of fillers such as silica. Compared to SSBR, ESBR has limited interaction with polar fillers like silica and leads to poor dispersion of filler. Hence, SSBR is often considered to be preferable to ESBR and is typically more expensive than ESBR.
[0004] In tire rubber compositions, the balance between wear resistance, rolling resistance and traction is critical. Incorporation of functionalized rubbers into tire rubber compositions can improve the tire performance properties. Functionalization of rubber provides the rubber with improved characteristics, often for example in the rubber's ability to interact with the filler added to a tire rubber composition. Functional groups that are known to be useful in rubber include, for example, amino groups, amide groups, hydroxyl groups, sulfide groups, carbonyl groups and so forth. The incorporation of polar functional groups in the SSBR chains is much easier as the process involves anionic polymerization. On the contrary, the introduction of polar functional groups into ESBR chains is very challenging as the process involves free radical polymerization. For this reason, functionalization of ESBR has been much less explored.
[0005] Despite their low cost and other process advantages, the abovementioned limitations and the inability to achieve optimal tire performance properties have thus far prohibited tire manufactures from using ESBR compounds in tire applications. It is therefore desirable to have a functionalized ESBR which overcomes the deficiencies found in the prior art, solving the aforementioned problems. The present disclosure satisfies these needs and provides further related advantages.

SUMMARY OF THE INVENTION
[0006] Aspects of the present disclosure relate to acrylate silane- or methacrylate silane-functionalized emulsion polymerized styrene-butadiene rubbers (ESBR), which can be combined effectively with filler-containing rubber formulations to yield improved properties in rubber articles such as tires. The acrylate silane- or methacrylate silane-functionalized ESBR can be prepared by chemically grafting an acrylate silane or a methacrylate silane onto the butadiene region of ESBR. Reacting ESBR with an acrylate silane or a methacrylate silane will result in an ESBR with a silane functionality (e.g., alkoxy silane or alkylsilyloxy silane functionality) grafted onto the polymer chain. Such a functionalized ESBR is preferred because of its increased ability to interact with the filler of a rubber composition.
[0007] Accordingly, one aspect of the present disclosure is directed to a curable rubber composition comprising an emulsion polymerized styrene-butadiene rubber (ESBR) functionalized with an acrylate silane or a methacrylate silane, and a filler.
[0008] In various embodiments, the acrylate silane can be selected from a compound of formula (I):

Formula (I)
wherein,
R1, R2 and R3 represent, independently of one another, a linear or branched alkyl group, an alkoxy group, or a trialkylsilyloxy group of formula (III) below:

Formula (III)
R, R' and R? represent, independently of one another, a linear or branched C1-C12 alkyl group or an aromatic group; and
R4 represents a linear or branched C1-C12 alkyl group.
[0009] In various embodiments, the methacrylate silane can be selected from a compound of formula (II):

Formula (II)
wherein R1, R2, R3 and R4 are as defined above.
[00010] In various embodiments, the acrylate silane- or methacrylate silane-functionalized ESBR as described herein can be used in a blend with non-functionalized elastomers and/or other types of functionalized elastomers. For example, it is possible to use the acrylate silane- or methacrylate silane-functionalized ESBR in a mixture with a non-functionalized ESBR and/or other types of functionalized elastomers.
[00011] In one particularly preferred embodiment, the curable rubber composition of the present disclosure comprises 1 to 100 phr of an ESBR functionalized with an acrylate silane or a methacrylate silane, 1 to 99 phr of an elastomer other than the functionalized ESBR, and 0 to 200 phr of a filler.
[00012] Another aspect of the present disclosure relates to a cured rubber composition, obtained by curing the curable rubber composition disclosed herein.
[00013] Another aspect of the present disclosure relates to a process for preparing a cured rubber composition usable for the manufacture of tires or tire components. The process can include the steps of:
providing a functionalized ESBR by chemically grafting an acrylate silane or a methacrylate silane onto the butadiene region of ESBR;
combining the functionalized ESBR, an elastomer other than the functionalized ESBR, a filler and, optionally, one or more additives, to form a curable rubber composition; and
blending the curable rubber composition with a vulcanization system, and vulcanizing the resulting composition to form the cured rubber composition.
[00014] Another aspect of the present disclosure relates to a tire or tire component, comprising the cured rubber composition disclosed herein.
[00015] Another aspect of the present disclosure relates to a finished or semifinished rubber article, comprising the cured rubber composition disclosed herein.
[00016] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS
[00017] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[00018] FIG. 1 shows FTIR spectra of (a) ESBR, (b) S-ESBR0.5, (c) S-ESBR1, and (d) S-ESBR2.
[00019] FIG. 2A shows 1H-NMR spectra of ESBR.
[00020] FIG. 2B shows 1H-NMR spectra of TESPMA monomer.
[00021] FIG. 2C shows 1H-NMR spectra of TESPMA grafted ESBR (ESBR-g-TESPMA) produced according to an embodiment of the present disclosure.
[00022] FIG. 3 shows DSC curves of ESBR, S-ESBR0.5, S-ESBR1, and S-ESBR2.
[00023] FIG. 4 is a schematic representation of the reaction between TESPMA grafted ESBR and silica.

DETAILED DESCRIPTION OF THE INVENTION
[00024] The following is a detailed description of embodiments of the present disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[00025] As used herein, the term "phr" refers to parts by weight of the referenced component per 100 parts by weight of total rubber or elastomer in the composition. Such term is commonly used in the rubber compounding art.
[00026] The present disclosure provides acrylate silane- or methacrylate silane-functionalized emulsion polymerized styrene-butadiene rubbers (ESBR), which can be combined effectively with filler-containing rubber formulations to yield improved properties in rubber articles such as tires. The acrylate silane- or methacrylate silane-functionalized ESBR can be prepared by chemically grafting an acrylate silane or a methacrylate silane onto the butadiene region of ESBR. The amount of ESBR units and acrylate silane or methacrylate silane units may vary depending on the desired functionality of the resulting polymer. Typically, the acrylate silane or the methacrylate silane can be used in a range of 0.5 to 3.0 mol percentage with respect to total unsaturation present in the butadiene part of the ESBR. Reacting ESBR with an acrylate silane or a methacrylate silane will result in an ESBR with a silane functionality (e.g., alkoxy silane or alkylsilyloxy silane functionality) grafted onto the polymer chain. Such a functionalized ESBR is preferred because of its increased ability to interact with the filler of a rubber composition.
[00027] Accordingly, one aspect of the present disclosure is directed to a curable rubber composition comprising an emulsion polymerized styrene-butadiene rubber (ESBR) functionalized with an acrylate silane or a methacrylate silane, and a filler.
[00028] In various embodiments, the acrylate silane can be selected from a compound of formula (I):

Formula (I)
wherein,
R1, R2 and R3 represent, independently of one another, a linear or branched alkyl group, an alkoxy group, or a trialkylsilyloxy group of formula (III) below:

Formula (III)
R, R' and R? represent, independently of one another, a linear or branched C1-C12 alkyl group or an aromatic group; and
R4 represents a linear or branched C1-C12 alkyl group.
[00029] The term “alkyl” as used herein refers to a straight-chain or branched-chain alkyl containing from 1 to 12, preferably 1 to 10, and more preferably 1 to 6, carbon atoms. With particular preference the term “alkyl” stands for methyl, ethyl or propyl, etc.
[00030] The term “alkoxy” as used herein refers to an alkyl group attached to an oxygen (-O-alkyl). Exemplary alkoxy groups include, but not limited to methoxy, ethoxy, etc.
[00031] As used herein, the term “aromatic group” refers to a 5- to 7-membered monocyclic aromatic group such as phenyl, or a 8- to 11-membered bicyclic aromatic group such as naphthyl, indenyl or azulenyl. The aromatic group refers furthermore to groups that are substituted by fluorine, chlorine, bromine or iodine atoms or by OH, SH, NH2, N3 or NO2 groups.
[00032] In certain embodiments, the acrylate silane can be selected from:

3-(trimethoxysilyl)propyl acrylate (TMSPA); and

3-(triethoxysilyl)propyl acrylate (TESPA).

[00033] In various embodiments, the methacrylate silane can be selected from a compound of formula (II):

Formula (II)
wherein R1, R2, R3 and R4 are as defined above.
[00034] In certain embodiments, the methacrylate silane can be selected from:

3-(triethoxysilyl)propyl methacrylate (TESPMA);

3-(trimethoxysilyl)propyl methacrylate (TMSPMA); and

3-[Tris(trimethylsiloxy)silyl]propyl methacrylate (TTMSPMA).
[00035] In various embodiments, the acrylate silane- or methacrylate silane-functionalized ESBR can be used in the curable rubber composition in an amount ranging from 1 to 100 phr. Preferably, the amount of the functionalized ESBR is between 1 and 80 phr.
[00036] The acrylate silane- or methacrylate silane-functionalized ESBR as described herein can be used in a blend with non-functionalized elastomers and/or other types of functionalized elastomers. For example, it is possible to use the acrylate silane- or methacrylate silane-functionalized ESBR in a mixture with a non-functionalized ESBR and/or other types of functionalized elastomers. According to embodiments of the present disclosure, the functionalized ESBR as described herein can be used to replace a part of non-functionalized elastomer/other type of functionalized elastomer or to replace it completely in curable or cured rubber compositions specifically designed for tire applications. In one embodiment, the functionalized ESBR as described herein is used to replace a part of non-functionalized ESBR/ other type of functionalized elastomer (e.g., epoxidized NR / epoxidized ESBR/functionalized SSBR, etc.,) in curable rubber compositions specifically designed for tire applications.
[00037] The non-functionalized elastomer (or “elastomer” for simplicity) is a cross-linkable (curable), e.g., vulcanizable, elastomer. The term "elastomer" is often used interchangeably with the term “rubber” or more professional "un-vulcanized rubber". The elastomer can be a natural rubber, a synthetic rubber, a blend of synthetic and natural rubber, or a blend of various synthetic rubbers. Exemplary elastomers that can be used in the curable rubber composition of the present disclosure include, but not limited to, natural rubber (NR), synthetic polyisoprene rubber (IR), polybutadiene rubber (PBD), high vinyl-polybutadiene rubber, styrene-butadiene rubber (SBR), solution-polymerized styrene-butadiene rubber (SSBR), emulsion-polymerized styrene-butadiene rubber (ESBR), nitrile rubber (NBR), hydrogenated nitrile rubber, butyl rubber, halogenated butyl rubbers, liquid rubbers, polynorbornene copolymer, isoprene-isobutylene copolymer, chloroprene rubber, ethylene propylene diene monomer rubber (EPDM), acrylate rubber, fluorinated rubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, styrene-isoprene-butadiene terpolymer, isoprene-butadiene copolymer, hydrogenated styrene-butadiene rubber, styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene/butylene-styrene block copolymer (SEBS), styrene-[ethylene-(ethylene/propylene)]-styrene block copolymer (SEEPS), styrene-isoprene-styrene block copolymer (SIS), isoprene-based block copolymers, butadiene-based block copolymers, styrenic block copolymers, hydrogenated styrenic block copolymers, styrene butadiene copolymers, polyisobutylene, ethylene vinyl acetate (EVA) co-polymers, polyolefins, metallocene-catalyzed polyolefin polymers and elastomers, reactor-made thermoplastic polyolefin elastomers, olefin block copolymer, polyurethane block copolymer, polyamide block copolymer, thermoplastic polyolefins, thermoplastic vulcanizates, ethylene n-butyl acrylate copolymer, ethylene methyl acrylate copolymer, neoprene, polyurethane, ethylene acrylic acid copolymer, ethylene-propylene polymers, propylene-hexene polymers, ethylene-butene polymers, ethylene octene polymers, propylene-butene polymers, ethylene-propylene-butylene terpolymers, and a mixture thereof. It is preferable that the amount of the elastomer in the rubber composition is from 1 to 99 phr.
[00038] As indicated above, the curable rubber composition includes a reinforcing filler to improve technical requirements of tires, such as high wear resistance, low rolling resistance, or wet grip. The functional group(s) of the functionalized ESBR improves the interaction between the rubber and filler and thereby enabling dispersion of the filler to a finer degree to achieve a higher level of reinforcement. Typical fillers include carbon black, silica, aluminosilicates, chalk, titanium dioxide, magnesium oxide, zinc oxide, clay, calcium carbonate, and a mixture thereof. Preferably, silica, carbon clack, or a mixture thereof is used as the filler. Filler(s) are present in the rubber composition in an amount of from 0 to 200 phr. In one embodiment, the filler is silica present in an amount of from 10 to 125 phr. In another embodiment, the filler is carbon black present in an amount of from 0 to 50 phr.
[00039] In various embodiments, the curable rubber composition of the present disclosure can further include a vulcanization system to cause vulcanization (cross-linking) of the unvulcanised elastomer(s). The vulcanization system can include at least one vulcanizing agent, at least one vulcanization accelerator, at least one vulcanization activator, or a mixture thereof. In one embodiment, the vulcanization system is present in the rubber composition in an amount of from 0.5 to 20 phr.
[00040] While any vulcanizing agent known in the art may be used, in preferred embodiments of the present disclosure, sulphur is used. The amount of vulcanizing agent is preferably between 0.1 and 5 phr.
[00041] While any vulcanization accelerators can be used, typical accelerators include but not limited to n-cyclohexyl-2-benzothiazole sulfenamide (CBS), diphenyl guanidine (DPG), tetrabenzylthiuram disulphide (TBzTD), N-Tertiarybutyl-2-benzothiazolesulfennamide (TBBS), N,N-dicyclohexyl-2-benzothiazyl sulfenamide (DCBS), and combination thereof. The vulcanization accelerator can be used in an amount ranging from 0.1 to 6 phr.
[00042] The vulcanization activator can be any activator as would be known to one of skill in the art. Preferably, the activator is selected from zinc oxide, stearic acid, and a combination thereof. In one embodiment, a mixture of zinc oxide and stearic acid is used as the vulcanization activator. The vulcanization activator can be used in an amount ranging from 1 to 8 phr.
[00043] The curable rubber composition of the present disclosure may also include any suitable additives generally used in tire rubber compositions. In one embodiment, the rubber composition includes one or more additives from the group consisting of process oil, antiozonant, antioxidant, anti-reversion agent, resin, coupling agent, stabilizer, masticating agent, adhesion promoter, colorant, homogenizer, and dispersion agent.
[00044] In various embodiments, the rubber composition of the present disclosure further comprises a process oil. Process oil may be included in the rubber composition as extending oil typically used to extend elastomers. Process oil may also be included in the rubber composition by addition of the oil directly during rubber compounding. Suitable process oils include various oils as are known in the art, including aromatic, paraffinic, naphthenic, and low polycyclic aromatic (PCA) oils, such as mild extraction solvates (MES), treated distillate aromatic extracts (TDAE), residual aromatic extract (RAE) oil and heavy naphthenic oils, and vegetable oils such as sunflower, soybean, and safflower oils. Process oil(s) can be used in the range from 3 to 30 phr.
[00045] In one embodiment, the rubber composition can further include at least one anti-reversion agent to prevent reversion, i.e., an undesirable decrease in crosslink density. While any anti-reversion agents may be used, typical anti-reversion agents include but not limited to N-(Cyclohexylthio)phthalimide, zinc salts of aliphatic carboxylic acids, zinc salts of monocyclic aromatic acids, bismaleimides, biscitraconimides, bisitaconimides, aryl bis-citraconamic acids, bissuccinimides, and polymeric bissuccinimide polysulfides (e.g., ?,?’-xylenedicitraconamides). The anti-reversion agent can be present in a range of from 0.5 to 5 phr.
[00046] In one embodiment, the rubber composition further comprises at least one antiozonant. The preferred antiozonant is ozone protecting wax. Preferably, the antiozonant is present in an amount of from 0.1 to 3 phr.
[00047] In one embodiment, the rubber composition further comprises at least one antioxidant. Non-limiting examples of antioxidant include 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine), TMQ (2,2,4-trimethyl-1,2-dihydroquinoline), etc.
[00048] In one embodiment, the rubber composition further comprises at least one resin to impart desirable properties to the rubber composition, including hardness, tear strength, and adhesion to reinforcement, etc. Suitable resins include coumarone type resins, including coumarone-indene resins and mixtures of coumarone resins, phenol resins, and rosins. Other suitable resins include phenol-terpene resins such as phenol-acetylene resins, phenol-formaldehyde resins, terpene-phenol resins, polyterpene resins, and xylene-formaldehyde resins. Further suitable resins include petroleum hydrocarbon resins such as synthetic polyterpene resins; aromatic hydrocarbon resins; aliphatic hydrocarbon resins; aliphatic cyclic hydrocarbon resins, such as dicyclopentadiene resins; aliphatic aromatic petroleum resins; hydrogenated hydrocarbon resins; hydrocarbon tackified resins; aliphatic alicyclic petroleum resins; rosin derivatives; and terpene resins. In one embodiment, the resin is selected from phenol-formaldehyde (PF) resin, resorcinol-formaldehyde (RF) resin, aliphatic resin, and aliphatic cyclic hydrocarbon resins. The amount of resin which is used in the rubber composition is between 1 and 30 phr, and preferably between 1 and 20 phr.
[00049] In some embodiments, the curable rubber composition comprises 1 to 100 phr of an ESBR functionalized with an acrylate silane or a methacrylate silane, 1 to 99 phr of an elastomer other than the functionalized ESBR, and 0 to 200 phr of a filler.
[00050] In some embodiments, the curable rubber composition comprises 1 to 100 phr of an ESBR functionalized with an acrylate silane or a methacrylate silane, 1 to 99 phr of an elastomer other than the functionalized ESBR, 0 to 200 phr of a filler, and 0.5 to 20 phr of a vulcanization system.
[00051] In another aspect, the present disclosure is directed to a process for preparing a cured rubber composition usable for the manufacture of tires or tire components. The process can include the steps of:
providing a functionalized ESBR by chemically grafting an acrylate silane or a methacrylate silane onto the butadiene region of ESBR;
combining the functionalized ESBR, an elastomer other than the functionalized ESBR, a filler and, optionally, one or more additives, to form a curable rubber composition; and
blending the curable rubber composition with a vulcanization system, and vulcanizing the resulting composition to form the cured rubber composition.
[00052] In various embodiments, the curable rubber composition can be produced by mixing the above-mentioned components by using conventional kneaders used in the rubber industry, such as heating rolls, kneaders, Brabender Plasticorder, Banbury mixers and the like. After the masterbatch is formed, it can be blended with a vulcanization system as described above. The vulcanization can be carried out in the usual way by heating the mixture to the vulcanization temperature for a sufficient time. The vulcanization can be carried out at temperatures of 110 to 200° C. The resulting cured composition (vulcanizate) can be used for tire applications such as tire treads, under treads, carcass, side walls, and bead portions. The vulcanizate can be used particularly as rubber for tire treads.
[00053] In various embodiments, the process further includes the step of forming a tire component from the cured rubber composition. The tire component can be selected from one or more of a tire tread, an under-tread, a tire sidewall, a tire inner liner, a bead, a rubber coating for tire belt, and a tire cord.
[00054] In another aspect, the present disclosure is directed to a cured rubber composition, obtained by curing the curable rubber composition disclosed herein.
[00055] In another aspect, the present disclosure is directed to a tire or tire component comprising the cured rubber composition disclosed herein.
[00056] In another aspect, the present disclosure is directed to a finished or semifinished rubber article comprising the cured rubber composition disclosed herein.
[00057] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[00058] The present disclosure is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.
Example 1: Functional modification of ESBR by grafting 3-(triethoxysilyl)propyl methacrylate (TESPMA) equivalent to 1 mol % of butadiene in ESBR
[00059] Grafting of TESPMA onto ESBR was carried out using Azobis isobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. In a five-neck round-bottom flask along with a mechanical stirrer, 50 g of ESBR (0.7082 mol of C=C) was dissolved in 1500 ml of toluene. After that, 0.582 g of AIBN (3.543*10-3 mol) and 6.173 g of TESPMA (2.13*10-2 mol) were dissolved in ESBR solution. The solution was stirred for 8 hr at 80° C under nitrogen atmosphere. After stirring got completed, ESBR-g-TESPMA solution was precipitated in methanol containing 1% BHT (butylated hydroxytoluene) as an inhibitor. Then ESBR-g-TESPMA was washed twice with methanol before putting it in a vacuum oven for drying at 50° C for 24 h.
[00060] The TESPMA grafted ESBR (ESBR-g-TESPMA) rubber contains grafted TESPMA equivalent to 1 mol% of butadiene in ESBR. The corresponding designation given to this ESBR-g-TESPMA is S-ESBR1 where 'S' stands for silyl modification, ESBR stands for emulsion styrene butadiene rubber and 1 stands for 1 mol % of butadiene in ESBR as reaction site for TESPMA grafting.
Example 2: Functional modification of ESBR by grafting TESPMA equivalent to 0.5 mol % of butadiene in ESBR
[00061] Grafting of TESPMA onto ESBR was carried out using Azobis isobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. In a five-neck round-bottom flask along with a mechanical stirrer, 50 g of ESBR (0.7082 mol of C=C) was dissolved in 1500 ml of toluene. After that, 0.291 g of AIBN (1.772*10-3 mol) and 3.09 g of TESPMA (1.065*10-2 mol) were dissolved in ESBR solution. The solution was stirred for 8 hr at 80° C under nitrogen atmosphere. After stirring got completed, ESBR-g-TESPMA solution was precipitated in methanol containing 0.5 % BHT as an inhibitor. Then ESBR-g-TESPMA was washed twice with methanol before putting it in a vacuum oven for drying at 50° C for 24 h.
[00062] The TESPMA grafted ESBR (ESBR-g-TESPMA) rubber contains grafted TESPMA equivalent to 0.5 mol% of butadiene in ESBR. The corresponding designation given to this ESBR-g-TESPMA is S-ESBR0.5 where 'S' stands for silyl modification, ESBR stands for emulsion styrene butadiene rubber and 0.5 stands for 0.5 mol % of butadiene in ESBR as reaction site for TESPMA grafting.
Example 3: Functional modification of ESBR by grafting TESPMA equivalent to 2 mol % of butadiene in ESBR
[00063] Grafting of TESPMA onto ESBR was carried out using Azobis isobutyronitrile (AIBN) as an initiator under nitrogen atmosphere. In a five-neck round-bottom flask along with a mechanical stirrer, 50 g of ESBR (0.7082 mol of C=C) was dissolved in 1500 ml of toluene. After that, 1.164 g of AIBN (7.086*10-3 mol) and 12.346 g of TESPMA (4.26*10-2 mol) were dissolved in ESBR solution. The solution was stirred for 8 hr at 80° C under nitrogen atmosphere. After stirring got completed, ESBR-g-TESPMA solution was precipitated in methanol containing 2% BHT as an inhibitor. Then ESBR-g-TESPMA was washed twice with methanol before putting it in a vacuum oven for drying at 50° C for 24 h.
[00064] The TESPMA grafted ESBR (ESBR-g-TESPMA) rubbers contains grafted TESPMA equivalent to 2 mol% of butadiene in ESBR. The corresponding designation given to this ESBR-g-TESPMA is S-ESBR2 where 'S' stands for silyl modification, ESBR stands for emulsion styrene butadiene rubber and 2 stands for 2 mol % of butadiene in ESBR as reaction site for TESPMA grafting.
Example 4: FTIR analysis of modified ESBR (ESBR-g-TESPMA)
[00065] FTIR analysis was performed using attenuated total reflectance (ATR) mode in the wavenumber range of 4000-400 cm-1 with a resolution of 4 cm-1 to characterize the functional groups of the polymer.
[00066] ATR-FTIR was used to figure out the molecular structure of S-ESBR (ESBR-g-TESPMA), in contrast to ESBR, as shown in FIG. 1. Both ESBR and S-ESBR spectra were shown similar absorption peaks as follows: the peaks between 1425 cm-1 to 1490 cm-1 belongs to the bond vibration of aromatic ring of the styrene unit, the peaks at 690 cm-1 and 970 cm-1 corresponds to C-H bond vibration of the cis-1,4 butadiene and trans-1,4 butadiene units respectively, the peak at 913 cm-1 belongs to the C-H bond vibration of the vinyl unit of butadiene, and C=C bond stretching vibration of butadiene peak is observed at 1639 cm-1. New peaks in S-ESBR spectra were observed at 1085 & 1194, 1170, and 1731 cm-1 due to bond stretching and bending vibration of C – O, Si – O – C, and C = O respectively. It was also observed that the intensity of the new peak increased with increasing grafting content.
Example 5: NMR analysis of pure ESBR
[00067] The NMR spectrum of pure ESBR was captured along with modifier and modified ESBR. In the 1H-NMR spectra of ESBR-g-TESPMA new peaks were appeared at d = 0.7, 1.2, 1.6, 2.2, 2.35, 3.75, and 4.2 for n, l, o, q, r, m, and p respectively, due to grafting of TESPMA onto the ESBR chains, as shown in FIGs. 2A, 2B and 2C. FIG. 2A shows 1H-NMR spectra of pure ESBR. FIG. 2B shows 1H-NMR spectra of TESPMA monomer. FIG. 2C shows 1H-NMR spectra of ESBR-g-TESPMA.
Example 6: DSC analysis of modified ESBR (ESBR-g-TESPMA)
[00068] Differential Scanning Calorimetry (DSC) was used to conduct a thermal study of the copolymers in a TA DSC (Discovery 25) instrument at a heating rate of 10 °C/min from -80 °C to 150 °C while a steady flow of nitrogen was present.
[00069] The thermal properties of S-ESBR were characterized by using DSC. As analyzed by DSC analysis the Tg of S-ESBRs was increased from -57° C (ESBR) to -52.2° C (S-ESBR2) as shown in FIG. 3. The increment in Tg of S-ESBR indicated the existence of grafted chains on the unsaturated place. Which restricted the segmental motion of the polymer chain. The single Tg value of S-ESBR indicated the uniform allocation of TESPMA along with the ESBR main chain. FIG. 3 shows DSC curves of pure ESBR, S-ESBR0.5, S-ESBR1, and S-ESBR2.
Examples 7 to 10: Rubber compositions
[00070] Rubber compositions were prepared according to the ingredients and amounts indicated in Table 1. Composition production was performed under industry standard conditions, as shown in Table 2. In the masterbatch mixing step, ESBR and the functionalized ESBR were added to an internal rubber mixer and mixed for about 2-5 min. Then, process oil and silica were added to the mixer and mixed for 2-6 min. Then, antioxidant, resin, and ozone protecting wax were added to the mixer. Subsequently, all the ingredients were mixed for 5 min. The masterbatch rubber composition was discharged from the mixer and air cooled to room temperature. In the final batch mixing step, the masterbatch rubber composition, sulphur, accelerator and activator were added into an internal rubber mixer or a two-roll open mill rubber machine and mixed for 3 min. The resulting unvulcanized rubber composition was discharged from the mixer and air cooled. Test pieces were produced from each of the compositions by optimal vulcanization under pressure at 160° C, and these test pieces were used to determine the material properties typical for the tire industry. Testing was performed according to ASTM and ISO test methods.

Table-1

Ingredients Example 7
(reference rubber) Example 8 Example 9 Example 10
phr phr phr phr
ESBR 100 90 90 90
S-ESBR0.5
(ESBR-g-TESPMA0.5) - 10 - -
S-ESBR1
(ESBR-g-TESPMA1.0) - - 10 -
S-ESBR2
(ESBR-g-TESPMA2.0) - - - 10
Silica 70 70 70 70
Other chemicals Q.S Q.S Q.S Q.S

Table 2

Masterbatch mixing step Rotor speed (rpm) - 60
Temperature - 140° C
Duration – 5 mins

Final batch mixing step Rotor speed (rpm) - 40
Temperature - 100° C
Duration – 3 mins

Rheological properties
[00071] Moving Die Rheometer (MDR) test at 160 deg. Celsius for 30 minutes: Rheological properties of the rubber compositions were measured and are reported in Table 3.

Table 3
Properties ML
(dNm) MH
(dNm) Delta Torque (?M) TS2
(min) T90
(min)
Example 7
(ESBR) 1.54 12.91 11.37 3.21 11.27
Example 8
(ESBR + S-ESBR0.5) 1.68 13.27 11.59 3.02 11.71
Example 9
(ESBR + S-ESBR1) 1.71 14.35 12.64 3.06 11.54
Example 10
(ESBR + S-ESBR2) 1.74 14.41 12.67 3.21 12.90

In Table 3, curing characteristics of the rubber compounds are listed together with their scorch time (ts2), optimum cure time (t90), minimum torque (ML), maximum torque (MH), and delta torque values. Table 3 indicates that all the compounds comprising the modified ESBR in addition to ESBR have higher MH values than the compound comprising only ESBR, indicating better interaction between ethoxysilyl groups and hydroxyl groups of silica.
Optimum cure time (T90) was also increased with grafting, and this may be due to the ethoxysilyl group, which has a retarding effect. No major change in scorch time (Ts2) was observed.
Payne effect
[00072] To determine the Payne effect of rubber compounds, "Alpha Technology 2000 RPA" was used. In accordance with ASTM D6601, a strain sweep test was done on the samples. During this test, the stain was changed from 0.1% to 100% at 0.5 Hz, while the temperature was kept at 100° C. Payne effect study was conducted to understand filler-filler interaction in the rubber compounds. The elastic modulus of the rubber compound at 0.56 percent strain and 100 percent strain at 0.5 Hz and 100° C were used to estimate the Payne effect (?G' = G'0.560% - G'100%), as indicated in Table 4 below.
Table 4
Payne effect ?G’ (G’0.560% – G’100%) (MPa)
Example 7
(ESBR) 0.19
Example 8
(ESBR + S-ESBR0.5) 0.19
Example 9
(ESBR + S-ESBR1) 0.17
Example 10
(ESBR + S-ESBR2) 0.14

It was observed that ?G’ value was reduced considerably in presence of the modified ESBR (S-ESBR2). Lower value of ?G’ in case of example 10 containing 10 phr of S-ESBR2 along with 90 phr of pure ESBR indicates lower Payne effect and hence, reduced filler-filler interaction as compared to example 7 containing 100 phr pure ESBR.
Mechanical Properties
[00073] As per ASTM D412-96, a sheet of moulded rubber compound was cut into the shape of a dumbbell for testing. We used a Universal testing machine (Instron, USA) at room temperature and a cross-head speed of 500 mm/min to measure the sample's tensile strength, elongation at break, and modulus. Each sample was tried on at least five pieces, and the average results were reported. The impact of varying percentages of grafting of TESPMA on the physical characteristics of rubber are given in Table-5 below.
Table-5

Properties 100% modulus, (MPa) 200% modulus, (MPa) 300% modulus, (MPa) Tensile strength, MPa Elongation at break, (%) RI
M300/M100
Example 7
(ESBR) 2.22 5.30 9.94 18.73 472 4.48
Example 8
(ESBR + S-ESBR0.5) 2.33 5.55 10.59 19.17 454 4.54
Example 9
(ESBR + S-ESBR1) 2.40 5.88 11.22 20.24 456 4.68
Example 10
(ESBR + S-ESBR2) 2.62 6.66 13.12 19.42 393 5.01

Table 5 indicates that the sample comprising only ESBR exhibited inferior mechanical properties as compared with the sample comprising combination of modified ESBR (S-ESBR) and ESBR. This may be attributed to the substantial filler–filler interaction due to the presence of hydroxyl groups on the silica surface, which led to the deterioration in the distribution of silica throughout the rubber matrix. On the other hand, the tensile strength and modulus of the rubber compound were enhanced when S-ESBR0.5, SESBR1 or S-ESBR2 was added. This is because the hydroxyl groups on the silica surface formed a covalent bond with ethoxysilyl groups of the S-ESBRs, and the nonpolar component of S-ESBR was compatible with ESBR. The reinforcing index of compound was improved which contained modified ESBR as compared to the sample comprising only ESBR.
Dynamic mechanical properties
[00074] Dynamic mechanical properties like storage modulus, loss modulus, and tan d were studied with DMA +1000 (METRAVIB, France) in tension mode,
(i) Low temperature sweep from -80° C to 25° C at 10 hertz frequency, dynamic strain of 0.1%
(ii) High temperature sweep from 25° C to 80° C at 10 hertz frequency, dynamic strain of 6%.
Tan d was analyzed by DMA at -15 °C, 0 °C, 25 °C and 60 °C to establish most relevant properties for a tire application: snow traction, wet traction, dry traction and rolling resistance. A finished rubber compound with a higher Tan d value at a temperature of -15 to 25° C has better grip, while a lower Tan d value at a temperature of 60° C shows low rolling resistance.
To determine the effect of the modified ESBR (S-ESBR) used in the ESBR matrix, the Tan d and E’ of different samples were compared at various temperatures. The results are reported in Table 6.
Table-6
Properties Tan d Storage modulus, E’ (MPa) Tg
(° C)
Sample name -15° C 0° C 20° C 60° C -15° C 0° C 20° C 60° C
Example 7
(ESBR) 0.392 0.224 0.155 0.288 201 102 60.1 3.68 -26.6
Example 8
(ESBR + S-ESBR0.5) 0.366 0.225 0.157 0.283 249 119 65.7 3.95 -25.4
Example 9
(ESBR + S-ESBR1) 0.419 0.275 0.186 0.275 327 123 61.2 4.30 -21.0
Example 10
(ESBR + S-ESBR2) 0.449 0.307 0.187 0.253 332 114 58.6 4.58 -16.5

When comparing Tan d values at lower temperature (-15 to 25° C), it was found that the compound of Example 10 containing S-ESBR2 in addition to ESBR had a higher value in comparison to the compound containing only ESBR. As a result, the dry traction, wet traction, and snow traction characteristics of Example 10 were increased by 23 percent, 34 percent, and 14 percent, respectively, in comparison to the reference compound of Example 7. Additionally, compared to the compound of Example 7, the compounds of Examples 8-10 all had lower tan d values at the higher temperature of 60° C. As per the DMA data, the rolling resistance indicator (Tan d @ 60° C) of the compound of Example 10 was decreased by 12.2 percent. On the other hand, it was observed that the compound of Example 10 had higher storage modulus (E’) values than the compound of Example 7.
The above examples demonstrate experimentally that rubber compositions comprising the modified ESBR in addition to ESBR result in a rubber product of significantly improved properties as compared to the rubber compositions comprising only ESBR.

Examples 11 to 14: Rubber compositions
[00075] Rubber compositions were prepared according to the ingredients and amounts indicated in Table 7.
Table-7

Ingredients Example 11
(reference rubber) Example 12 Example 13 Example 14
phr phr phr phr
ESBR 70 60 60 60
NR 30 30 30 30
S-ESBR0.5
(ESBR-g-TESPMA0.5) - 10 - -
S-ESBR1
(ESBR-g-TESPMA1.0) - - 10 -
S-ESBR2
(ESBR-g-TESPMA2.0) - - - 10
Silica 40 40 40 40
Carbon black 30 30 30 30
Other chemicals Q.S Q.S Q.S Q.S

Rheological properties
[00076] Moving Die Rheometer (MDR) test at 160 deg. Celsius for 30 minutes: Rheological properties of the rubber compositions were measured and are reported in Table 8.
Table 8
Properties ML
(dNm) MH
(dNm) Delta Torque (?M) TS2
(min) T90
(min)
Example 11
(ESBR-NR30) 1.22 13.57 12.35 4.03 12.38
Example 12
(ESBR-NR30 + S-ESBR0.5) 1.29 13.97 12.68 3.98 13.85
Example 13
(ESBR-NR30 + S-ESBR1) 1.34 14.0 12.66 4.0 14.46
Example 14
(ESBR-NR30 + S-ESBR2) 1.36 14.40 13.04 4.04 15.53

In Table 8, curing characteristics of the rubber compounds are listed together with their scorch time (ts2), optimum cure time (t90), minimum torque (ML), maximum torque (MH), and delta torque values. Table 8 indicates that all the compounds comprising 10 phr of modified ESBR in addition to 60 phr ESBR and 30 phr NR have higher MH values than the compound comprising only 70 phr ESBR and 30 phr NR, indicating better interaction between ethoxysilyl groups and hydroxyl groups of silica.
Optimum cure time (T90) was also increased with grafting, and this may be due to the ethoxysilyl group, which has a retarding effect. No major changes in scorch time (Ts2) was observed.
Payne effect
[00077] To determine the Payne effect of rubber compounds, "Alpha Technology 2000 RPA" was used. In accordance with ASTM D6601, a strain sweep test was done on the samples. During this test, the stain was changed from 0.1% to 100% at 0.5 Hz, while the temperature was kept at 100° C. Payne effect study was conducted to understand filler-filler interaction in the rubber compounds. The elastic modulus of the rubber compound at 0.56 percent strain and 100 percent strain at 0.5 Hz and 100° C were used to estimate the Payne effect (?G' = G'0.560% - G'100%), as indicated in Table 9 below.
Table 9
Payne effect ?G’ (G’0.560% – G’100%) (MPa)
Example 11 (ESBR-NR30) 0.21
Example 12 (ESBR-NR30 + S-ESBR0.5) 0.20
Example 13 (ESBR-NR30 + S-ESBR1) 0.20
Example 14 (ESBR-NR30 + S-ESBR2) 0.18

It was observed that ?G’ value was reduced considerably in presence of the modified ESBR (S-ESBR2). Lower value of ?G’ in case of example 14 containing 10 phr of S-ESBR2 along with 60 phr of pure ESBR and 30 phr of NR indicates lower Payne effect and hence, reduced filler-filler interaction as compared to example 11 containing 70 phr pure ESBR and 30 phr NR.
Mechanical Properties
[00078] As per ASTM D412-96, a sheet of moulded rubber compound was cut into the shape of a dumbbell for testing. We used a Universal testing machine (Instron, USA) at room temperature and a cross-head speed of 500 mm/min to measure the sample's tensile strength, elongation at break, and modulus. Each sample was tried on at least five pieces, and the average results were reported. The impact of varying percentages of grafting of TESPMA on the physical characteristics of rubber are given in Table-10 below.
Table-10

Properties 100% modulus, (MPa) 200% modulus, (MPa) 300% modulus, (MPa) Tensile strength, MPa Elongation at break, (%) RI
M300/M100
Example 11 (ESBR-NR30) 2.35 5.01 8.71 19.72 546 3.70
Example 12
(ESBR-NR30 + S-ESBR0.5) 2.36 5.33 9.45 19.62 509 4.0
Example 13
(ESBR-NR30 + S-ESBR1) 2.47 5.66 9.97 20.05 513 4.04
Example 14
(ESBR-NR30 + S-ESBR2) 2.42 5.71 10.28 20.51 511 4.25

Table 10 indicates that the sample comprising only 70 phr ESBR and 30 phr NR exhibited inferior mechanical properties as compared with the sample comprising combination of 10 phr modified ESBR (S-ESBR), 60 phr ESBR and 30 phr NR. This may be attributed to the substantial filler–filler interaction due to the presence of hydroxyl groups on the silica surface, which led to the deterioration in the distribution of silica throughout the rubber matrix (Example 11). On the other hand, the tensile strength and modulus of the rubber compounds were enhanced when S-ESBR0.5, SESBR1 or S-ESBR2 were added. This is because the hydroxyl groups on the silica surface formed a covalent bond with ethoxysilyl groups of the S-ESBRs, and the nonpolar component of S-ESBR was compatible with ESBR. The reinforcing index of compound was improved which contained modified ESBR as compared to the compound comprising only 70 phr ESBR and 30 phr NR.
Dynamic mechanical properties
[00079] Dynamic mechanical properties like storage modulus, loss modulus, and tan d were studied with DMA +1000 (METRAVIB, France) in tension mode,
(i) Low temperature sweep from -80° C to 25° C at 10 hertz frequency, dynamic strain of 0.1%
(ii) High temperature sweep from 25° C to 80° C at 10 hertz frequency, dynamic strain of 6%.
Tan d was analyzed by DMA at -15 °C, 0 °C, 25 °C and 60 °C to establish most relevant properties for a tire application: snow traction, wet traction, dry traction and rolling resistance. A finished rubber compound with a higher Tan d value at a temperature of -15 to 25° C has better grip, while a lower Tan d value at a temperature of 60° C shows low rolling resistance.
To determine the effect of the modified ESBR (S-ESBR) used in the ESBR-NR30 matrix, the Tan d and E’ of different samples were compared at various temperatures. The results are reported in Table 11.

Table-11
Properties Tan d Storage modulus, E’ (MPa) Tg
(° C)
Sample name -15° C 0° C 20° C 60° C -15° C 0° C 20° C 60° C
Example 11 (ESBR-NR30) 0.274 0.174 0.151 0.278 155 97.1 61.3 3.92 -33
Example 14
(ESBR-NR30 + S-ESBR2) 0.458 0.280 0.182 0.243 210 82.9 42.2 3.94 -20
When comparing Tan d values at lower temperature (-15 to 25° C), it was found that the compound of Example 14 containing 10 phr S-ESBR2 in addition to 60 phr ESBR and 30 phr NR had a higher value in comparison to the sample containing only 70 phr ESBR and 30 phr NR. As a result, the dry traction, wet traction, and snow traction characteristics of Example 14 were increased by 20.5 percent, 61 percent, and 67 percent, respectively, in comparison to the reference compound of Example 11. This can be attributed due to the increases the Tg by grafting of TESPMA into ESBR chains. Additionally, compared to the compound of Example 11, the compound of example 14 had lower tan d values at the higher temperature of 60° C. As per the DMA data, the rolling resistance indicator (Tan d @ 60° C) of the compound of Example 14 was decreased by 12.6 percent. On the other hand, it was observed that the compound of Example 14 had higher storage modulus (E’) values than the compound of Example 11.
The above examples demonstrate experimentally that rubber compositions comprising the modified ESBR in addition to ESBR and NR result in a rubber product of significantly improved properties as compared to the rubber compositions comprising only ESBR and NR.
Examples 15 to 18: Rubber compositions
[00080] Rubber compositions were prepared according to the ingredients and amounts indicated in Table 12.
Table-12

Ingredients Example 15
(reference rubber) Example 16 Example 17 Example 18
phr phr phr phr
ESBR 30 20 20 20
NR 70 70 70 70
S-ESBR0.5
(ESBR-g-TESPMA0.5) - 10 - -
S-ESBR1
(ESBR-g-TESPMA1.0) - - 10 -
S-ESBR2
(ESBR-g-TESPMA2.0) - - - 10
Silica 40 40 40 40
Carbon black 30 30 30 30
Other chemicals Q.S Q.S Q.S Q.S

Rheological properties
[00081] Moving Die Rheometer (MDR) test at 160 deg. Celsius for 30 minutes: Rheological properties of the rubber compositions were measured and are reported in Table 13.
Table 13
Properties ML
(dNm) MH
(dNm) Delta Torque (?M) TS2
(min) T90
(min)
Example 15
(ESBR-NR70) 0.95 15.56 14.62 4.53 9.19
Example 16
(ESBR-NR70 + S-ESBR0.5) 0.99 16.66 15.67 4.44 9.82
Example 17
(ESBR-NR70 + S-ESBR1) 1.01 16.84 15.85 4.52 10.19
Example 18
(ESBR-NR70 + S-ESBR2) 1.08 16.98 15.90 4.55 10.57

In Table 13, curing characteristics of the rubber compounds are listed together with their scorch time (ts2), optimum cure time (t90), minimum torque (ML), maximum torque (MH), and delta torque values. Table 13 indicates that all the compounds comprising 10 phr of modified ESBR in addition to 20 phr ESBR and 70 phr NR have higher MH values than the compound comprising only 30 phr ESBR and 70 phr NR, indicating better interaction between ethoxysilyl groups and hydroxyl groups of silica.
Optimum cure time (T90) was also increased with grafting, and this may be due to the ethoxysilyl group, which has a retarding effect. No major changes in scorch time (Ts2) was observed.
Payne effect
[00082] To determine the Payne effect of rubber compounds, "Alpha Technology 2000 RPA" was used. In accordance with ASTM D6601, a strain sweep test was done on the samples. During this test, the stain was changed from 0.1% to 100% at 0.5 Hz, while the temperature was kept at 100° C. Payne effect study was conducted to understand filler-filler interaction in the rubber compounds. The elastic modulus of the rubber compound at 0.56 percent strain and 100 percent strain at 0.5 Hz and 100° C were used to estimate the Payne effect (?G' = G'0.560% - G'100%), as indicated in Table 14 below.
Table 14
Payne effect ?G’ (G’0.560% – G’100%) (MPa)
Example 15
(ESBR-NR70) 0.23
Example 16
(ESBR-NR70 + S-ESBR0.5) 0.23
Example 17
(ESBR-NR70 + S-ESBR1) 0.21
Example 18
(ESBR-NR70 + S-ESBR2) 0.19

It was observed that ?G’ value was reduced considerably in presence of the modified ESBR (S-ESBR2). Lower value of ?G’ in case of example 18 containing 10 phr of S-ESBR2 along with 20 phr of pure ESBR and 70 phr of NR indicates lower Payne effect and hence, reduced filler-filler interaction as compared to example 15 containing 30 phr pure ESBR and 70 phr NR.

Mechanical Properties
[00083] As per ASTM D412-96, a sheet of moulded rubber compound was cut into the shape of a dumbbell for testing. We used a Universal testing machine (Instron, USA) at room temperature and a cross-head speed of 500 mm/min to measure the sample's tensile strength, elongation at break, and modulus. Each sample was tried on at least five pieces, and the average results were reported. The impact of varying percentages of grafting of TESPMA on the physical characteristics of rubber are given in Table-15 below.
Table-15

Properties 100% modulus, (MPa) 200% modulus, (MPa) 300% modulus, (MPa) Tensile strength, MPa Elongation at break, (%) RI
M300/M100
Example 15
(ESBR-NR70) 2.35 6.29 11.32 22.23 531 4.82
Example 16
(ESBR-NR70 + S-ESBR0.5) 2.39 6.19 11.48 22.94 527 4.80
Example 17
(ESBR-NR70 + S-ESBR1) 2.69 6.86 12.15 23.34 531 4.52
Example 18
(ESBR-NR70 + S-ESBR2) 2.67 6.81 12.06 23.37 524 4.52

Table 15 indicates that the compound comprising only 30 phr ESBR and 70 phr NR exhibited inferior mechanical properties as compared with the compound comprising combination of 10 phr modified ESBR (S-ESBR), 20 phr ESBR and 70 phr NR. This may be attributed to the filler–filler interaction due to the presence of hydroxyl groups on the silica surface, which led to the deterioration in the distribution of silica throughout the rubber matrix (Example 15). On the other hand, the tensile strength and modulus of the rubber compound were enhanced when S-ESBR0.5, SESBR1 or S-ESBR2 was added. This is because the hydroxyl groups on the silica surface formed a covalent bond with ethoxysilyl groups of the S-ESBRs, and the nonpolar component of S-ESBR was compatible with ESBR.

Dynamic mechanical properties
[00084] Dynamic mechanical properties like storage modulus, loss modulus, and tan d were studied with DMA +1000 (METRAVIB, France) in tension mode,
(i) Low temperature sweep from -80° C to 25° C at 10 hertz frequency, dynamic strain of 0.1%
(ii) High temperature sweep from 25° C to 80° C at 10 hertz frequency, dynamic strain of 6%.
Tan d was analyzed by DMA at -15 °C, 0 °C, 25 °C and 60 °C to establish most relevant properties for a tire application: snow traction, wet traction, dry traction and rolling resistance. A finished rubber compound with a higher Tan d value at a temperature of -15 to 25° C has better grip, while a lower Tan d value at a temperature of 60° C shows low rolling resistance.
To determine the effect of the modified ESBR (S-ESBR) used in the ESBR-NR70 matrix, the Tan d and E’ of different samples were compared at various temperatures. The results are reported in Table 16.
Table-16
Properties Tan d Storage modulus, E’ (MPa) Tg
(° C)
Sample name -15° C 0° C 20° C 60° C -15° C 0° C 20° C 60° C
Example 15
(ESBR-NR70) 0.243 0.169 0.150 0.267 99.2 66.2 43.5 3.55 -36.6
Example 16
(ESBR-NR70 + S-ESBR0.5) 0.263 0.178 0.146 0.257 104 68.0 46.0 3.59 -34.2
Example 17
(ESBR-NR70 + S-ESBR1) 0.260 0.171 0.139 0.253 121 77.6 52.5 3.65 -32.3
Example 18
(ESBR-NR70 + S-ESBR2) 0.394 0.238 0.158 0.252 145 67.8 38.2 4.11 -21.2

When comparing Tan d values at lower temperature (-15 to 25° C), it was found that the compound of Example 18 containing 10 phr S-ESBR2 in addition to 20 phr ESBR, and 70 phr NR had a higher value in comparison to the compound containing only 30 phr ESBR and 70 phr NR. As a result, the dry traction, wet traction, and snow traction characteristics of Example 18 were increased by 5.6 percent, 40.8 percent, and 62 percent, respectively, in comparison to the reference compound of Example 15. This can be attributed due to the increases the Tg by grafting of TESPMA into ESBR chains. Additionally, compared to the compound of Example 15, the compounds of Examples 16-18 all had lower tan d values at the higher temperature of 60° C. As per the DMA data, the rolling resistance indicator (Tan d @ 60° C) of the compound of Example 18 was decreased by 6 percent. On the other hand, it was observed that the compound of Example 18 had higher storage modulus (E’) values than the compound of Example 15.
The above examples demonstrate experimentally that rubber compositions comprising the modified ESBR in addition to ESBR and NR result in a rubber product of significantly improved properties as compared to the rubber compositions comprising only ESBR and NR.
, Claims:1. A curable rubber composition, comprising:
an emulsion polymerized styrene-butadiene rubber (ESBR) functionalized with an acrylate silane or a methacrylate silane, and
a filler.
2. The rubber composition as claimed in claim 1, wherein the acrylate silane is selected from a compound of formula (I):

Formula (I)
wherein,
R1, R2 and R3 represent, independently of one another, a linear or branched alkyl group, an alkoxy group, or a trialkylsilyloxy group of formula (III) below:

Formula (III)
R, R' and R? represent, independently of one another, a linear or branched C1-C12 alkyl group or an aromatic group; and
R4 represents a linear or branched C1-C12 alkyl group.
3. The rubber composition as claimed in claim 1, wherein the methacrylate silane is selected from a compound of formula (II):

Formula (II)
wherein R1, R2, R3 and R4 are as defined above.
4. The rubber composition as claimed in any of claims 1 and 2, wherein the acrylate silane is selected from 3-(trimethoxysilyl)propyl acrylate (TMSPA) and 3-(triethoxysilyl)propyl acrylate (TESPA).
5. The rubber composition as claimed in any of claims 1 and 3, wherein the methacrylate silane is selected from 3-(triethoxysilyl)propyl methacrylate (TESPMA), 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), and 3-[Tris(trimethylsiloxy)silyl]propyl methacrylate (TTMSPMA).
6. The rubber composition as claimed in claim 1, wherein the functionalized ESBR is present in an amount of from 1 to 100 phr.
7. The rubber composition as claimed in claim 1, wherein the acrylate silane or the methacrylate silane is used in a range of 0.5 to 3.0 mol percentage with respect to total unsaturation present in butadiene part of ESBR.
8. The rubber composition as claimed in claim 1, further comprising an elastomer other than the functionalized ESBR.
9. The rubber composition as claimed in claim 8, wherein the elastomer is selected from the group consisting of natural rubber (NR), synthetic polyisoprene rubber (IR), polybutadiene rubber (PBD), high vinyl-polybutadiene rubber, styrene-butadiene rubber (SBR), solution-polymerized styrene-butadiene rubber (SSBR), emulsion-polymerized styrene-butadiene rubber (ESBR), nitrile rubber (NBR), hydrogenated nitrile rubber, butyl rubber, halogenated butyl rubbers, liquid rubbers, polynorbornene copolymer, isoprene-isobutylene copolymer, chloroprene rubber, ethylene propylene diene monomer rubber (EPDM), acrylate rubber, fluorinated rubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, styrene-isoprene-butadiene terpolymer, isoprene-butadiene copolymer, hydrogenated styrene-butadiene rubber, styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene/butylene-styrene block copolymer (SEBS), styrene-[ethylene-(ethylene/propylene)]-styrene block copolymer (SEEPS), styrene-isoprene-styrene block copolymer (SIS), isoprene-based block copolymers, butadiene-based block copolymers, styrenic block copolymers, hydrogenated styrenic block copolymers, styrene butadiene copolymers, polyisobutylene, ethylene vinyl acetate (EVA) co-polymers, polyolefins, metallocene-catalyzed polyolefin polymers and elastomers, reactor-made thermoplastic polyolefin elastomers, olefin block copolymer, polyurethane block copolymer, polyamide block copolymer, thermoplastic polyolefins, thermoplastic vulcanizates, ethylene n-butyl acrylate copolymer, ethylene methyl acrylate copolymer, neoprene, polyurethane, ethylene acrylic acid copolymer, ethylene-propylene polymers, propylene-hexene polymers, ethylene-butene polymers, ethylene octene polymers, propylene-butene polymers, ethylene-propylene-butylene terpolymers, and a mixture thereof.
10. The rubber composition as claimed in claim 8, wherein the elastomer is present in an amount of from 1 to 99 phr.
11. The rubber composition as claimed in claim 1, wherein the filler is selected from the group consisting of carbon black, silica, aluminosilicates, chalk, titanium dioxide, magnesium oxide, zinc oxide, clay, calcium carbonate, and a mixture thereof.
12. The rubber composition as claimed in claim 11, wherein the filler is silica, carbon black, or a mixture thereof.
13. The rubber composition as claimed in claim 11, wherein the filler is silica present in an amount of from 10 to 125 phr.
14. The rubber composition as claimed in claim 11, wherein the filler is carbon black present in an amount of from 0 to 50 phr.
15. The rubber composition as claimed in any of claims 1 to 14, further comprising a vulcanization system.
16. The rubber composition as claimed in claim 15, wherein the vulcanization system is present in the rubber composition in an amount of from 0.5 to 20 phr.
17. The rubber composition as claimed in claim 15, wherein the vulcanization system comprises at least one vulcanizing agent, at least one vulcanization accelerator, at least one vulcanization activator, or a mixture thereof.
18. The rubber composition as claimed in any of claims 1 to 17, further comprising one or more additives from the group consisting of process oil, antiozonant, anti-reversion agent, resin, coupling agent, stabilizer, masticating agent, adhesion promoter, colorant, homogenizer, and dispersion agent.
19. The rubber composition as claimed in any of claims 1 to 18, comprising:
1 to 100 phr of an ESBR functionalized with an acrylate silane or a methacrylate silane;
1 to 99 phr of an elastomer other than the functionalized ESBR; and
0 to 200 phr of a filler.
20. A cured rubber composition, obtained by curing a curable rubber composition comprising an ESBR functionalized with an acrylate silane or a methacrylate silane, and a filler.
21. A process for preparing a cured rubber composition, comprising:
providing a functionalized ESBR by chemically grafting an acrylate silane or a methacrylate silane onto the butadiene region of ESBR;
combining the functionalized ESBR, an elastomer other than the functionalized ESBR, a filler and, optionally, one or more additives, to form a curable rubber composition; and
blending the curable rubber composition with a vulcanization system, and vulcanizing the resulting composition to form the cured rubber composition.
22. The process as claimed in claim 21, further comprising the step of forming a tire component from the cured rubber composition.
23. The process as claimed in claim 22, wherein the tire component is selected from one or more of a tire tread, an under-tread, a tire sidewall, a tire inner liner, a bead, a rubber coating for tire belt, and a tire cord.
24. A tire or tire component, comprising the cured rubber composition as claimed in claim 20.
25. A finished or semifinished rubber article comprising the cured rubber composition as claimed in claim 20.