BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates generally to rubber compositions useful for forming articles and more particularly to rubber compositions having covering agents for carbon nano materials.

Description of the Related Art

[0002] Nanomaterials include those materials for which a single unit of the material is between 1 nm and 1000 nm in at least one dimension. It has been found that nanomaterials may often have different optical, electronic, chemical reactivity or mechanical properties compared to similar materials but without nanoscale features.

[0003] The European Commission adopted a definition of nanomaterial as follows: A natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions in in the size range 1 nm - 100 nm. The Commission indicated that by derogation of the above, fullerenes, graphene flakes and single wall carbon nanotubes with one or more external dimensions below 1 nm should be considered nanomaterials.

[0004] Tire designers and those involved in searching for new materials useful for the manufacture of tires and other rubber articles are investigating the use of nanomaterials in rubber compositions. Particular interest is in carbon-based nanomaterials such as graphene and carbon nanotubes. As part of the search, other materials that can improve the use of nanomaterials in rubber compositions are an important field that must be investigated. In other words, those skilled in the art of rubber compositions are searching for materials that can be combined with nanomaterials to improve their effect on the properties of rubber compositions.

[0005] Therefore research continues in the field of nanomaterials and other materials that can be combined with them in rubber compositions to improve the physical properties of the resulting rubber compositions and/or to improve the mixing, handling and processing of the rubber compositions that will be used to form useful products.

SUMMARY OF THE INVENTION

[0006] Particular embodiments of the present invention include rubber compositions and articles made from such rubber compositions, including tires. Such rubber compositions are based upon a cross-linkable rubber composition, the cross-linkable rubber composition comprising, in parts by weight per 100 parts by weight of rubber (phr), 100 phr of a rubber component selected from the group consisting of natural rubber, a synthetic rubber and combinations thereof and between 2 phr and 50 phr of carbon nanotubes.

[0007] A covering agent is also included, the covering agent having a form

X— R ¹ — S _x— R ² — X

wherein R and R are an aliphatic group and may be the same or different, S _x is a polysulfide bridge where x is a number of sulfur atoms in the polysulfide bridge and X is a single phenyl moiety that is fully or partially substituted with a halogen. The rubber composition may also include a sulfur curing system.

[0008] The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of particular embodiments of the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0009] Particular embodiments of the present invention include rubber compositions and articles made from such rubber compositions including, for example, tires made at least in part from such rubber compositions. These rubber compositions include carbon nanotubes and a specific covering agent for the surface of the carbon nanotubes. It has been found that the use of the covering agent in rubber compositions that include carbon nanotubes can provide lowered hysteresis properties in the cured rubber composition which results in reduced rolling resistance in a tire. Reduced rolling resistance provides improved fuel economy.

[0010] The rubber compositions disclosed herein include a highly unsaturated rubber component, carbon nanotubes that act as a reinforcing filler in the rubber composition and a covering agent for at least a portion of the carbon nanotube surfaces. More particularly the covering agent has the form X— R— S _x— R— X, wherein R and R are an aliphatic group and may be the same or different, S _x is a polysulfide bridge where x is the number of sulfur atoms in the polysulfide bridge and X is a fully or partially halogen-substituted phenyl moiety. As noted above, it has been found that the covering agent provides lowered hysteresis properties in the rubber compositions disclosed herein.

[0011] In particular embodiments, the rubber compositions disclosed herein are useful for the manufacture of tire components including, for example, those components found in the tire sidewall, those found in the bead area, those found in the tire crown and for tire treads. Other useful articles that can be formed from such rubber compositions include, for example, as conveyor belts, motor mounts, tubing, hoses and so forth. Particular embodiments of articles formed from such rubber compositions may be limited to at least a portion of the part of tire treads that contact the ground surface and in other embodiments may alternatively include the undertread or base, which is a layer of cushioning rubber under the ground-contacting portion of the tread. Such tread construction is known by those skilled in the art as cap and base construction. Useful tire treads may be manufactured from particular embodiments of the rubber compositions disclosed herein for passenger or light truck tires as well as, for example, heavy truck, aircraft tires, agricultural tires and other tires, both pneumatic and nonpneumatic.

[0012] As used herein,“phr” is“parts per hundred parts of rubber by weight” and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in the composition.

[0013] As used herein, elastomer and rubber are synonymous terms.

[0014] As used herein,“based upon” is a term recognizing that embodiments of the present invention are made of vulcanized or cured rubber compositions that were, at the time of their assembly, uncured. The cured rubber composition is therefore“based upon” the uncured rubber composition. In other words, the cross-linked rubber composition is based upon or comprises the constituents of the cross-linkable rubber composition.

[0015] Embodiments of the rubber compositions that are disclosed herein include a highly unsaturated diene rubber component. Diene elastomers are known to be those elastomers resulting at least in part, i.e., a homopolymer or a copolymer, from diene monomers, i.e., monomers having two double carbon-carbon bonds, whether conjugated or not.

[0016] Generally diene elastomers may be classified as either“essentially unsaturated” diene elastomers or “essentially saturated” diene elastomers. As used herein, essentially unsaturated diene elastomers are diene elastomers resulting at least in part from conjugated diene monomers, the essentially unsaturated diene elastomers having a content of such members or units of diene origin (conjugated dienes) that is at least 15 mol. %. Within the category of essentially unsaturated diene elastomers are highly unsaturated diene elastomers, which are diene elastomers having a content of units of diene origin (conjugated diene) that is greater than 50 mol. %.

[0017] Those diene elastomers that do not fall into the definition of being essentially unsaturated are, therefore, the essentially saturated diene elastomers. Such elastomers include, for example, butyl rubbers and copolymers of dienes and of alpha-olefins of the EPDM type. These diene elastomers have low or very low content of units of diene origin (conjugated dienes), such content being less than 15 mol. %.

[0018] The elastomers useful in the rubber compositions disclosed herein may have any microstructure, such microstructure being a function of the polymerization conditions used, in particular of the presence or absence of a modifying and/or randomizing agent and the quantities of modifying and/or randomizing agent used. The elastomers may, for example, be block, random, sequential or micro- sequential elastomers, and may be prepared in dispersion or in solution; they may be coupled and/or starred or alternatively functionalized with a coupling and/or starring or functionalizing agent.

[0019] Functionalized rubbers, i.e., those appended with active moieties, are well known in the industry. The backbone or the branch ends of the elastomers may be functionalized by attaching these active moieties to the ends of the chains or to the backbone or mid-chains of the polymer. Exemplary functionalizing agents that could be included with the diene elastomers include, but are not limited to, metal halides, metalloid halides, alkoxy silanes, imine-containing compounds, esters, ester-carboxylate metal complexes, alkyl ester carboxylate metal complexes, aldehydes or ketones, amides, isocyanates, isothiocyanates and imines - all of these being well- known in the art. Particular embodiments may include functionalized diene elastomers while other embodiments may be limited to including no functionalized elastomers.

[0020] Particular embodiments of the rubber compositions disclosed herein are limited to those having at least 80 phr of the rubber components being highly unsaturated diene elastomers. Other embodiments are limited to having at least 90 phr or 100 phr of the highly unsaturated diene elastomer components.

[0021] Examples of suitable highly unsaturated diene elastomers include, but are not necessarily limited to natural rubber (NR) and synthetic rubbers such as polybutadienes (BR), polyisoprenes (IR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. Such copolymers include butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene terpolymers (SBIR). Any of these examples or mixtures of these examples are suitable for particular embodiments of the rubber compositions disclosed herein.

[0022] In particular embodiments, useful SBR elastomers may have a bound styrene content of between 1 mol% and 45 mol% or alternatively between 15 mol% and 40 mol% or between 20 mol% and 30 mol%.

[0023] Particular embodiments of the rubber compositions disclosed herein include no essentially unsaturated diene elastomer and/or no essentially saturated diene elastomers. Alternatively particular embodiments may include between 1 phr and 10 phr of such elastomers or alternatively between 1 phr and 5 phr of such elastomers or no more than 10 phr or no more than 5 phr of such elastomers.

[0024] In addition to the elastomers disclosed above, particular embodiments of the rubber compositions disclosed herein further include carbon nanotubes as reinforcement filler. Carbon nanotubes are well known in the industry and are recognized as being an allotrope of carbon and are members of the fullerene structural family. Nanotubes can generally be described as being rolled sheets of graphene and can be classified being single-walled, double-walled or multi-walled. Double and multi-walled nanotubes comprise tubes that are concentrically nested to form the multi-walled nanotubes. Particular embodiments of the rubber compositions disclosed may include single-walled carbon nanotubes, double-walled carbon nanotubes, multi- walled carbon nanotubes and combinations thereof. Other embodiments may be limited to carbon nanotubes having larger diameters that may be found in double-walled or multi-walled nanotubes and thus may explicitly rule out single-walled nanotubes. Other embodiments are limited to just multi-walled nanotubes.

[0025] Nanotubes may generally be thought, for example, of having a diameter or thickness of between about 1 nm to about 100 nm and an average L/D (length to diameter ratio) of between 10/1 and 10,000/1. One method for making nanotubes is chemical vapor deposition at elevated temperature, for example around 700° C, of ethylene on a metal/ceramic catalyst of nanoparticles. Sources of carbon nanotubes include, for example, Arkema, Inc. who markets a nanotube product under the trade name GRAPHISTENGTH C100 that is a multi-walled carbon nanotube having a length of about 1000-10,000 nm, a diameter of about 12-15 nm with about 8% impurities; Nanocyl SA who markets a nanotube product under the trade name NC7000 that is a multi-walled carbon nanotube having a length of about 1500 nm, a diameter of about 10 nm with about 10% impurities; and Cnano Technology Limited who markets a nanotube product under the name FLOTUBE 9000 that is a multi-walled carbon nanotube having a length of about 1000- 10,000 nm, a diameter of about 10-15 nm with about 5% impurities.

[0026] Determination of length and diameter of the nanotubes may be through Transmission Electronic Microscope (TEM) in known manner. The TEM can distinguish the difference of 0.1 nm and a carbon nanotube sample ground into a fine power and ultrasonic ally dispersed in a solvent (such as ethanol) can be examined under the TEM and the length and diameters of the tubes measured. The average diameter is the mean value of all the measured diameters using nm as unit. The average length is determined by the mean value of all the measured lengths.

[0027] Particular embodiments of the rubber compositions disclosed herein may include carbon nanotubes having a diameter, for example, of between 1 nm and 100 nm or alternatively between 5 nm and 100 nm, between 5 nm and 50 nm, between 5 nm and 25 nm, between 8 nm and 50 nm, between 8 nm and 25 nm or between 8 nm and 20 nm. Particular embodiments may further include carbon nanotubes having an L/D ratio, for example, of between 10/1 and 10,000/1 or alternatively between 50/1 and 1000/1, between 90/1 and 1000/1 or between 100/1 and 900/1. [0028] Particular embodiments of the rubber compositions disclosed herein may include between 2 phr and 50 phr of carbon nanotubes or alternatively between 2 phr and 40 phr, between 5 phr and 50 phr, between 10 phr and 50 phr or between 10 phr and 40 phr of carbon nanotubes.

[0029] In addition to the rubber components and the carbon nanotubes components, particular embodiments of the rubber compositions disclosed herein further include a covering agent having a form

X— R ¹ — S _x— R ² — X

wherein R and R are an aliphatic group and may be the same or different, S _x is a polysulfide bridge and X is a fully or partially halogen-substituted phenyl moiety. The halogenated phenyl moiety is interactive with the carbon nanotube surface and the polysulfide bridge provides bonding capability to the rubber components in the rubber compositions through the vulcanization mechanism.

[0030] The aliphatic group may be branched or linear and may include cyclic moieties. Aliphatic groups contain no double or triple carbon-carbon bonds. In particular embodiments, the total number of carbon atoms may range between 1 and 10 or alternatively between 1 and 6, between 1 and 4, between 1 and 2 or just one carbon atom. Particular embodiments include no cyclic moieties and may further include only straight-chained moieties. Examples of suitable aliphatic moieties include methyl, ethyl, propyl and butyl moieties and particular embodiments of the aliphatic group of the covering agent may be limited to just one of these examples or alternatively to any particular selection of these examples. Other suitable examples of the aliphatic group may include isobutyl, isopropyl, cyclohexyl and cyclopentyl moieties and so forth.

[0031] The poly sulfide bridge S _x may have a value of x of between greater than 1 and 8 or alternatively between 2 and 8, between 2 and 6 or between 2 and 4 sulfurs.

[0032] The covering agent further includes the fully or partially halogen-substituted phenyl moiety. The halogenated phenyl moiety is meant to interact with the surface of the carbon nanotubes. It is interesting to note that the covering agent disclosed herein does interact with the surface of carbon nanotubes but it does not interact with the surfaces of other carbon surfaces such as other types of graphene or with carbon black. [0033] The interaction between the covering agent and the carbon nanotubes does not increase the reinforcement properties of the carbon nanotubes in the rubber composition. However, it does surprisingly provide reduced hysteresis in the rubber composition as well as a reduced nonlinearity (NL) index, which is defined as the difference between the complex shear modulus G* measured 1% strain and 100% strain at 23 °C. A lower NL index is indicative of improved rolling resistance.

[0034] The aromatic halogenation may be accomplished with any halogen, and in particular embodiments, the halogen is selected from one or more of F, Cl, Br and I. Particular embodiments of the covering agent include aromatic halogenation with only F. The halogenation may result in between 1 and 5 halogen atoms added to the phenyl moiety with particular embodiments having between 3 and 5 halogen atoms, between 4 and 5 halogen atoms or 5 halogen atoms. A fully halogen-substituted phenyl would include 5 halogen atoms while a partially halogen-substituted phenyl would include between 1 and 4 halogen atoms.

[0035] One example of a suitable covering agent is bis[(pentalfluorophenyl)- methyl]tetra sulfide. A method for making this compound is provided in Example 1.

[0036] Particular embodiments of the rubber compositions disclosed herein may include between 0.1 phr and 15 phr of the covering agent or alternatively between 0.5 phr and 12 phr, between 0.5 phr and 10 phr or between 1 phr and 7 phr. Particular embodiments of the rubber compositions disclosed herein may include the amount of covering agent as a weight percent of the weight of the carbon nanotubes. Such embodiments may include the covering agent in an amount of between 5 wt% and 30 wt% of the weight of the carbon nanotubes or alternatively between 5 wt% and 20 wt%, between 10 wt% and 30 wt%, or between 10 wt% and 20 wt%, the weight percent being that of the weight of the carbon nanotubes. For example, in an embodiment of the rubber compositions disclosed herein having 30 phr of carbon nanotubes, a 20 wt% amount of the covering agent would be 6 phr of the covering agent.

[0037] In addition to the rubber components, the carbon nanotubes components, and the covering agents, particular embodiments of the rubber compositions disclosed herein further optionally include an additional reinforcement filler. Reinforcing fillers are well known in the art and include, for example, carbon blacks and silica. Any reinforcing filler known to those skilled in the art may optionally be used in the rubber composition with the carbon nanotubes. In particular embodiments of the rubber composition disclosed herein, the optional filler is essentially carbon black. In other embodiments, there are no additional reinforcement fillers. For rubber compositions that do include an additional filler, some may be limited to just carbon black and other limited to just silica.

[0038] Carbon black, which is an organic filler, is well known to those having ordinary skill in the rubber compounding field. The carbon black optionally included in particular embodiments of the rubber compositions disclosed herein may range between 0 phr and 15 phr or alternatively between 0 phr and 10 phr or between 0 phr and 6 phr. Low amounts of carbon black may be included to make the rubber composition black. In other embodiments, carbon black may be included in up to 50 wt% of the carbon nanotubes or alternatively, no more than 25 wt% of the carbon nanotubes. For example, in a rubber composition that includes 24 phr of carbon nanotubes, 50 wt% of the carbon nanotubes would be 12 phr of carbon black. If too much carbon black is added, then the improvement NL index and/or hysteresis will be lost. Suitable carbon blacks are not particularly limited and may include, for example, N234, N299, N326, N330, N339, N343, N347, N375, N550, N660, N683, N772, N787, N990 carbon blacks.

[0039] As noted above, silica may also be useful as reinforcement filler with the same ranges for the amount of silica that may be added to particular embodiments as provided above for the carbon black. The silica may be any reinforcing silica known to one having ordinary skill in the art including, for example, any precipitated or pyrogenic silica having a BET surface area and a specific CTAB surface area both of which are less than 450 m /g or alternatively, between 30 and 400 m /g. Highly dispersible precipitated silicas (referred to as "HDS") may be useful in particular embodiments of such rubber compositions disclosed herein, wherein "highly dispersible silica" is understood to mean any silica having a substantial ability to disagglomerate and to disperse in an elastomeric matrix. Such determinations may be observed in known manner by electron or optical microscopy on thin sections. Examples of known highly dispersible silicas include, for example, Perkasil KS 430 from Akzo, the silica BV3380 from Degussa, the silicas Zeosil 1165 MP and 1115 MP from Rhodia, the silica Hi-Sil 2000 from PPG and the silicas Zeopol 8741 or 8745 from Huber.

[0040] As is well known in the art, when silica is added to the rubber composition, a proportional amount of a silane coupling agent is also added to the rubber composition. Examples of suitable silane coupling agents include 3,3'-bis(triethoxysilylpropyl) disulfide and 3,3'-bis(triethoxy-silylpropyl) tetrasulfide (known as Si69).

[0041] In particular embodiments, a combination of carbon black and silica may be useful so long as the total amount of both in combination is within the ranges provided above for carbon black and silica when used alone.

[0042] In addition to the rubber components, the carbon nanotubes components, the covering agents and optionally the additional reinforcing filler, particular embodiments of the rubber compositions disclosed herein further include a sulfur curing system comprising sulfur and one or more accelerators.

[0043] As known by those skilled in the art, sulfur may take the form of free sulfur, insoluble sulfur, soluble sulfur and/or provided by a sulfur donor. Sulfur donors, as known in the art, contribute sulfur to the curing process. An example of a sulfur donor is caprolactam disulfide, which is sold under the trade name RHENOGRAN CLD-80 by Lanxess. In particular embodiments, sulfur may be added in an amount ranging, for example, between 0.3 and 3 phr or alternatively between 0.5 phr and 2 phr or between 0.5 and 1.5 phr.

[0044] Accelerators are well known and typically are chosen from the basic families of accelerators based on their speed of vulcanization: guanidines (medium) such as diphenyl guanidine (DPG); thiazoles (semi-fast) such as 2-mercaptobenzothiazole (MBT) and 2- mercaptobenzothiazyl disulfide (MBTS); sulphenamides (fast) such as N-cyclohexyl-2- benzothiazolesulphenamide (CBS), N,N-dicyclohexyl-2-benzothiazolesulphenamide (DCBS) and N-tert-butyl-2-benzothiazole-sulphenamide (TBBS); thiurams (very fast) such as tetramethylthiuram monosulfide (TMTM); and dithiocarbamates (super-fast) such as zinc dimethyldithiocarbamate (ZDMC) and zinc diethyldithiocarbamate (ZDEC).

[0045] The vulcanization system may further include various known vulcanization activators, such as zinc oxide and stearic acid.

[0046] Other additives can be added to the rubber compositions disclosed herein as known in the art. Such additives may include, for example, some or all of the following: antidegradants, antioxidants, fatty acids, waxes, stearic acid and zinc oxide. Examples of antidegradants and antioxidants include 6PPD, 77PD, IPPD, DAPD and TMQ and may each be added to rubber compositions in an amount, for example, of from 0.5 phr and 7 phr. Zinc oxide may be added in an amount, for example, of between 1 phr and 6 phr or alternatively, of between 1.5 phr and 4 phr. Stearic acid may be added in an amount, for example, of between 1 phr and 4 phr or alternatively between 1 phr and 2 phr. Waxes may be added in an amount, for example, of between 0.5 phr and 5 phr or alternatively between 0.5 phr and 1.5 phr.

[0047] The rubber compositions that are embodiments of the present invention may be produced in suitable mixers, in a manner known to those having ordinary skill in the art, typically using two successive preparation phases, a first phase of thermo-mechanical working at high temperature, followed by a second phase of mechanical working at lower temperature.

[0048] The first phase of thermo-mechanical working (sometimes referred to as "non productive" phase) is intended to mix thoroughly, by kneading, the various ingredients of the composition, with the exception of the vulcanization system. It is carried out in a suitable kneading device, such as an internal mixer or an extruder, until, under the action of the mechanical working and the high shearing imposed on the mixture, a maximum temperature generally between 80° C and 175° C, more narrowly between 130° C and 165° C, is reached.

[0049] After cooling of the mixture, a second phase of mechanical working is implemented at a lower temperature. Sometimes referred to as "productive" phase, this finishing phase consists of incorporating by mixing the vulcanization (or cross-linking) system (sulfur or other vulcanizing agent and accelerator(s)), in a suitable device, for example an open mill. It is performed for an appropriate time (typically between 1 and 30 minutes, for example between 2 and 10 minutes) and at a sufficiently low temperature lower than the vulcanization temperature of the mixture, so as to protect against premature vulcanization.

[0050] The rubber compositions can then be formed into useful articles, including tire components such as the toe guard of a tire, and cured.

[0051] The invention is further illustrated by the following examples, which are to be regarded only as illustrations and not delimitative of the invention in any way. The properties of the compositions disclosed in the examples were evaluated as described below and these utilized methods are suitable for measurement of the claimed properties of the claimed invention.

[0052] The maximum tan delta and complex shear modulus dynamic properties for the rubber compositions were measured at 23° C on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress at a frequency of 10 Hz under a controlled temperature of 23° C. Scanning was effected at an amplitude of deformation of 0.05 to 50 % (outward cycle) and then of 50 % to 0.05% (return cycle) or 1% to 100% back to 1% peak-to-peak. The maximum value of the tangent of the loss angle tan delta (max tan d) was determined during the return cycle. The complex shear modulus G* was determined at 10%, 1% and 100% peak-to-peak strain during the return cycle.

[0053] Dynamic properties (G*60° C and Tg) for the rubber compositions were measured on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress of a constant 0.7 MPa and at a frequency of 10 Hz over a temperature sweep from -80° C to 100° C with the temperature increasing at a rate of 1.5° C/min. The shear modulus G* was captured at 60 °C and the temperature at which the max tan delta occurred was recorded as the glass transition temperature,

Tg-

[0054] Modulus of elongation (MPa) was measured at 10% (MA10) at a temperature of 23 °C based on ASTM Standard D412 on dumb bell test pieces. The measurements were taken in the second elongation; i.e., after an accommodation cycle. These measurements are secant moduli in MPa, based on the original cross section of the test piece.

[0055] The elongation property was measured as elongation at break (%) and the corresponding elongation stress (MPa), which is measured at 23 °C in accordance with ASTM Standard D412 on ASTM C test pieces.

[0056] The invention is further illustrated by the following examples, which are to be regarded only as illustrations and not delimitative of the invention in any way.

Example 1

[0057] This example provides a method for making the covering agent having the halogenated phenyl moiety, particularly Bis[(pentafluorophenyl)methyl]tetrasulfide. Sodium tetrasulfide (40% solution in water, 379.6g, 0.87 mol) was charged to a 2 L three neck reactor equipped with magnetic stir bar, pot thermometer and condenser attached to the Dean-Stark trap set-up. The pot was heated to 110-120 °C to remove about 80% of water, then was cooled down to 80 °C. Toluene (7l2g) was added, and the pot was resumed heating to azeotrope to the rest of water.

[0058] After the pot was cooled to 50 °C, ethanol (430.9g) was added, followed by addition of pentafluorobenzyl bromide (477.6g, 1.83 mol) dropwise while keeping pot temperature between 50 and 60 °C. The resulting viscous reaction mixture was heated at 80 °C for 24-36 h. Another portion of Toluene (7l2g) was added to pot and all ethanol were removed by using Dean-Stark trap while keeping the pot temperature below 120 °C.

[0059] The reaction mixture was cooled to 80 °C, water (823g) was added into the pot. The organic layer was separated, aqueous layer was extracted with toluene (3 x 0.6L). The combined organic layer was dried over anhydrous sodium sulfate, filtered, then concentrated in vacuo. The residue was the product (270g, 63%) as yellow solid.

[0060] The product was:

[0061] The product was confirmed through Fourier Transform Infrared Spectroscopy.

Example 2

[0062] This example demonstrates the effect of the covering agent on carbon nanotubes in rubber compositions. Rubber compositions were prepared using the components shown in Table 1. The amount of each component making up the rubber compositions are provided in parts per hundred part of rubber by weight (phr).

Table 1 - Formulations

[0063] The SBR elastomer was 27 % styrene with an Mn of 118,700 and the butadiene portion having 24% vinyl, 46% trans and 30% cis bonds. The carbon nanotubes for Wl and Fl were GR APHIS TEN GTH C100, those of W2 and F2 were FLOTUBE 9000 and those of W3 and F3 were NC7000. Bis[(pentalfluorophenyl)methyl]tetra sulfide was the covering agent as obtained from Example 1. The sulfur content in the formulations F1-F3 was adjusted to reflect the 15.5 wt% sulfur of the covering agent to make the amount of sulfur in each of the formulations the same, i.e., 1.5 phr sulfur. The accelerator was CBS and the protection system was 6PPD.

[0064] The rubber formulations were prepared by mixing the components given in Table 1, except for the accelerators and sulfur, in a Banbury mixer until a temperature of between 110 °C and 170 °C was reached. The accelerators and sulfur were added in the second phase on a mill. Vulcanization was effected at 150 °C for 25 minutes. The formulations were then tested to measure their properties, the results of which are shown in Table 2.

Table 2 - Physical Properties

[0065] As can be seen from Table 2, the max tan delta decreased and the nonlinearity index decreased with the addition of the covering agent.

Example 3

[0066] This example demonstrates that the covering agent has no effect on different types of graphene different from carbon nanotubes. The rubber formulations were the same as those in Example 2 except the graphene filler replaced the carbon nanotubes. The formulations were prepared in the same manner as those in Example 2. Table 3 - Formulations

[0067] The filler used in formulations W4A, B was a reduced graphene oxide available from Angstron Materials under the trade name PDR, having a density of 1.9 g/cm and a surface area of 830 m /g; in formulations W5A, B was a exfoliated and ball- milled graphite available from XG Sciences under the trade name XGnP-M-l5, having a density of 2.2 g/cm and a surface area of 170 m /g; and in formulations W6A, B was a ball-milled graphite available from

Asbury Carbon under the product number 4124, having a density of 2.1 g/cm and a surface area

2

of 350 m /g. The cured properties of the formulations are shown in Table 4.

Table 4 - Physical Properties

[0068] As can be seen from Table 4, the max tan delta and the nonlinearity index did not change appreciably with the addition of the covering agent, indicating that the covering agent was not effective on these graphene types.

Example 4

[0069] This example demonstrates the effect of the covering agent on other types of rubber components in rubber compositions having carbon nanotubes. The rubber formulations were the same as those in Example 3 except rubber components were changed and only the GRAPHISTENGTH C100 carbon nanotubes were used. The rubber formulations included natural rubber and polybutadiene rubber rather than the SBR. The formulations were prepared in the same manner as those in Example 2.

Table 5 - Formulations

[0070] The cured properties of the formulations are shown in Table 6. It should be noted that the Tg of formulations W8 and F8 were measured by DSC since the sweep under ASTM D5992-96 was between -80° C and 100° C.

Table 6 - Physical Properties

[0071] As can be seen from Table 6, the nonlinearity index decreased with the addition of the covering agent indicating that the covering agent had an effect on the carbon nanotubes. The max tan delta did not reflect a change because the Tg of the mixtures were lower than those formulations provided in Example 2.

[0072] The terms“comprising,”“including,” and“having,” as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The term“consisting essentially of,” as used in the claims and specification herein, shall be considered as indicating a partially open group that may include other elements not specified, so long as those other elements do not materially alter the basic and novel characteristics of the claimed invention. The terms“a,”“an,” and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms“at least one” and“one or more” are used interchangeably. The term“one” or“single” shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as“two,” are used when a specific number of things is intended. The terms “preferably,” “preferred,” “prefer,” “optionally,”“may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention. Ranges that are described as being“between a and b” are inclusive of the values for“a” and“b.”

[0073] It should be understood from the foregoing description that various modifications and changes may be made to the embodiments of the present invention without departing from its true spirit. The foregoing description is provided for the purpose of illustration only and should not be construed in a limiting sense. Only the language of the following claims should limit the scope of this invention.