Sulfur-curable rubber composition containing graft copolymer

Abstract

The present invention relates to a sulfur-crosslinkable rubber composition comprising a filler component in an amount ranging from 1 to 350 phr and at least one graft copolymer having a modified diene rubber main chain and one or more oligomer side chains grafted to the modified diene rubber main chain, wherein the oligomer side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, and the monomer composition comprises at least one polar monomer.

Description

[Technical Field]

[0001] The present invention relates to sulfur-crosslinkable rubber compositions, sulfur-vulcanized rubber compositions obtained from the respective sulfur-vulcanizable rubber compositions, and rubber products comprising said sulfur-vulcanized rubber compositions, as well as the use of a graft copolymer having a modified diene rubber backbone and one or more oligomer side chains grafted onto the modified diene rubber backbone in a sulfur-vulcanizable rubber composition to increase the rolling resistance of vehicle tires made from the sulfur-vulcanizable rubber compositions.

[0002] The subject matter of the present invention is defined in the claims. [Background technology]

[0003] Since the beginning of the 21st century, the automotive industry has been one of the industrial sectors facing some of the most fundamental challenges, experiencing multiple disruptive technological advances. Increasing customer awareness of ecological aspects such as emission profiles and resource efficiency is calling for new concepts of mobility. At the same time, there are ever-increasing demands for improved vehicle performance characteristics and stronger overall safety regulations. Meeting these challenges is not just the job of car manufacturers. In fact, some of these aspects are heavily influenced by the properties of a vehicle's tires, making optimizing tire properties a key goal.

[0004] Several relevant properties of pneumatic vehicle tires, such as rolling resistance and wet grip, are closely related to the rubber composition of the tread. Consequently, much research effort has been devoted to optimizing rubber composition properties, with significant progress being made in recent years, such as the replacement of carbon black fillers with silica. Unfortunately, the many different physicochemical properties of vulcanized rubber compositions that are relevant to tire running characteristics cannot be varied independently of one another, resulting in trade-offs: one property cannot be enhanced without adversely affecting another related property. For example, improving wet grip or dry raking typically involves a deterioration in rolling resistance, winter performance, and wear characteristics. As a result, optimizing rubber compositions often involves resolving trade-offs by developing solutions to increase certain parameters without significantly compromising their complementary properties.

[0005] Several concepts for improving the properties of rubber compositions are known from the prior art, such as U.S. Pat. No. 10,273,351 B2, EP 3,103,655 B1, and EP 3,260,304 B1. Due to their fundamental relevance to the properties of rubber compositions, much attention has been paid to optimizing the rubber compounds used in the rubber compositions and the rubber manufacturing processes, as disclosed in, for example, EP 3,109,064 A1, WO 2015,121,224, and U.S. 2013,165,589 A1. Here, the affinity of the rubber compound to the filler material is an important factor, which governs the strength of attractive interactions in the rubber composition and thus affects the mechanical properties of the rubber composition.

[0006] Some of the most widely used rubber compounds in the technical field are typically produced using living anionic polymerization. While this type of polymerization allows for a high degree of functionalization, it typically does not allow for the use of a wide range of monomers. In particular, polar monomers, such as acrylate monomers, cannot be used efficiently in these polymerizations, generally resulting in rubber compounds with low polarity. This is often considered a disadvantage, particularly with regard to filler compatibility, since rubber compounds consisting essentially of non-polar repeating units typically exhibit poor filler compatibility. Summary of the Invention [Means for solving the problem]

[0007] In view of the above background, there has been a long felt need to provide a sulfur-crosslinkable rubber composition which overcomes the respective drawbacks of the prior art rubber compositions and which, after vulcanization, exhibits excellent performance properties, particularly in the trade-off between rolling resistance and wet grip.

[0008] It was a further object of the present invention that the sulfur crosslinkable rubber composition after vulcanization should have beneficial mechanical properties, in particular improved durability due to high stiffness.

[0009] It was a further object of the present invention to provide a sulfur-curable rubber composition that exhibits excellent filler compatibility between the rubber compound and the filler used in the sulfur-curable rubber composition.

[0010] A second object of the present invention is to provide a sulfur-vulcanized rubber composition obtained from each of the sulfur-crosslinkable rubber compositions, a method for producing the sulfur-vulcanized rubber composition, and a rubber product containing the sulfur-vulcanized rubber composition.

[0011] It was also an object of the present invention to provide for the use of certain graft copolymers in sulfur-crosslinkable rubber compositions.

[0012] The above-mentioned objects are achieved by the subject matter of the present invention. In particular, the inventors have discovered that the above-mentioned objects can be achieved when the advantages of living anionic polymerization are combined with the advantages of reversible addition-fragmentation chain transfer (RAFT) polymerization. Herein, a non-polar backbone produced by living anionic polymerization is combined with polar oligomeric side chains produced by RAFT polymerization that are grafted onto the non-polar backbone to produce an improved rubber compound that is highly functionalized and has a high density of polar units, which can be vulcanized to obtain a sulfur-vulcanized rubber composition that exhibits high filler compatibility and has excellent performance properties, particularly good rolling resistance, improved winter performance, and improved durability. DETAILED DESCRIPTION OF THE INVENTION

[0013] The subject matter of the present invention will be explained in more detail below, and preferred embodiments of the present invention will be disclosed. It is particularly preferred to combine two or more preferred embodiments to obtain a particularly preferred embodiment. Correspondingly, sulfur-crosslinkable rubber compositions according to the present invention that define the characteristics of two or more preferred embodiments of the present invention are particularly preferred.

[0014] The present invention provides a filler component in an amount ranging from 1 to 350 phr; and at least one graft copolymer having a modified diene rubber backbone and one or more oligomer side chains grafted to the modified diene rubber backbone, wherein the oligomer side chains are preferably polar oligomer side chains; A sulfur-crosslinkable rubber composition comprising: the oligomer side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, the monomer composition comprising at least one polar monomer; The present invention relates to a sulfur-crosslinkable rubber composition.

[0015] The term "sulfur crosslinkable" is well known to those skilled in the art and defines that the rubber composition of the present invention can be cured in the presence of sulfur, whereby the separate chains of the rubber compound are crosslinked, i.e., interconnected, to obtain a cured or sulfur-vulcanized rubber composition. This process is known as vulcanization, and the resulting product can be used to manufacture a variety of rubber products.

[0016] The rubber composition of the present invention contains 1 to 350 phr of a filler component, which may include one or more filler materials such as silica, carbon black, aluminosilicate, chalk, starch, magnesium oxide, titanium dioxide, rubber gel, graphite, graphene, or carbon nanotubes.

[0017] The unit "phr" as used herein stands for "parts by weight per hundred parts by weight of rubber" and is a standard unit used in the rubber industry to specify the amounts of different components in a rubber composition. Each amount is given as the part by weight of that material relative to the total mass of all high molecular weight rubbers present in the mixture that are solid at ambient conditions and make up 100 phr.

[0018] The rubber composition of the present invention comprises at least one graft copolymer. As used herein, the term "copolymer" is understood to mean a polymer formed from two or more different monomers, i.e., monomers with different chemical structures. The term "graft copolymer" defines that the respective copolymer is obtained by grafting oligomeric side chains onto a main chain in a grafting reaction, thereby modifying the main chain and obtaining a segmented graft copolymer having a main chain and oligomeric side chain branches randomly distributed along the main chain. The main chain may be, for example, a linear or branched main chain. Suitable grafting reactions for obtaining graft copolymers are known to those skilled in the art.

[0019] The graft copolymer used in the rubber composition of the present invention has a modified diene rubber backbone, indicating that a diene rubber was used as the backbone for the grafting reaction. As used herein, the term "diene rubber" refers to a rubber resulting from the polymerization or copolymerization of a diene and / or a cycloalkene and thus containing carbon-carbon double bonds. Exemplary diene rubbers are synthetic polyisoprene, polybutadiene (butadiene rubber; BR), and styrene-butadiene copolymer (styrene-butadiene rubber; SBR).

[0020] The graft copolymer used in the rubber composition of the present invention has one or more oligomer side chains grafted thereto, i.e., at least one oligomer side chain grafted thereto. Although the distinction between polymer and oligomer is not clearly defined, the term "oligomer" indicates that the number of repeating units in the side chain is relatively small, typically in the range of 2 to 400 units. The graft copolymer used in the rubber composition of the present invention is not limited in terms of graft density, but sulfur-crosslinkable rubber compositions in which the graft polymer has an average graft density, expressed as the number of side chains per modified diene rubber main chain, in the range of 1 to 10, preferably 2 to 8, and most preferably 2 to 6.

[0021] In the graft copolymers of the present invention, the oligomeric side chains are obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization of the monomer composition. RAFT polymerization is primarily used in biological applications due to its wide range of solvents and monomers that can be used, allowing the use of polar monomers and the efficient synthesis of highly polar oligomers. The concept of RAFT polymerization itself is known in the art and is disclosed, for example, in EP 3109064 A1.

[0022] Due to the chemical nature of the RAFT agents typically employed in RAFT polymerization, the oligomeric side chains resulting from RAFT polymerization can typically be identified by having an end group attached to the modified diene rubber backbone on one side via a radically reactive functional group, preferably a residue derived from a sulfur atom, and on the other side having an end group having the general structure -CR7R8R9, where R7, R8, and R9 are attached to a tertiary carbon and are independently selected from the group consisting of hydrogen, methyl, phenyl, cyano, and -CO2Et groups.

[0023] Before being grafted onto the modified diene rubber backbone, the oligomer side chains obtained by RAFT polymerization typically contain a radical-reactive functional group capable of reacting with the modified diene rubber backbone in the presence of a radical initiator. For example, the radical-reactive functional group may be a sulfur-containing functional group, preferably a thiol group, or an oxygen-containing functional group, preferably an alcohol group.

[0024] Thus, in another embodiment, a graft copolymer, whether or not produced by RAFT polymerization, can be defined as a graft copolymer having a modified diene rubber backbone and one or more oligomeric side chains grafted to the modified diene rubber backbone, wherein the oligomeric side chains are attached to the modified diene rubber backbone via radically reactive functional groups, preferably residues derived from sulfur atoms, and include end groups having the general structure -CR7R8R9, where R7, R8, and R9 are bonded to tertiary carbons and independently selected from the group consisting of hydrogen, methyl, phenyl, cyano, and -CO2Et groups.

[0025] The oligomer side chains used in the present invention are obtained by polymerization of a monomer composition containing one or more monomers. The inventors have found that in order to achieve the above objectives, it is important that the monomer composition contains at least one polar monomer in order to take advantage of RAFT polymerization and obtain oligomer side chains with the desired polarity.

[0026] As used herein, a polar monomer is an organic monomer containing at least one heteroatom, i.e., at least one atom that is neither carbon nor hydrogen. Preferably, the polar monomer contains at least one C—X bond (X is selected from the group consisting of boron, nitrogen, oxygen, sulfur, fluorine, chlorine, bromine, and iodine), i.e., a chemical bond between carbon and a heteroatom. The polar monomer preferably does not contain a phosphorus atom. Suitable polar monomers are disclosed, for example, in U.S. Patent Application Publication No. 20130165589A1. The chemical bond between the carbon and the heteroatom can be a single bond, a double bond, or a triple bond, and the polar monomer preferably contains an ester or ether functional group. Suitable polar monomers are, for example, acrylates and methacrylates containing additional ester or ether functional groups.

[0027] Consistent with the understanding of those skilled in the art, the term "at least one monomer" is not interpreted as referring to a single molecule of said monomer. Instead, those skilled in the art will understand that the monomer composition comprises multiple monomers of the same chemical structure, such as acrylates or methacrylates. In other words, those skilled in the art will understand that the monomer composition preferably comprises at least 1 wt. %, more preferably at least 2 wt. %, of at least one polar monomer, based on the weight of the monomer composition. As a result of RAFT polymerization of the monomer composition, a polar oligomer is obtained that comprises repeat units derived from the monomers by polymerization, and thus comprises repeat units derived from the polar monomer.

[0028] The use of the sulfur-crosslinkable rubber composition of the present invention, which exhibits high compatibility between the graft copolymer and the filler, can provide excellent performance properties after vulcanization, particularly good rolling resistance and improved durability due to high stiffness.

[0029] The inventors have found that particularly good results are obtained when the oligomer side chain itself contains two or more different repeat units along the chain. Without wishing to be bound by theory, it is believed that different repeat units of different chemical structures in the oligomer chain allow for strong interactions with a wider range of compounds in the rubber composition, such as different filler materials. For example, polar functional groups such as amines may exhibit strong interactions with polar groups, such as hydroxyl groups, on the filler surface, while longer alkyl or phenyl groups may promote van der Waals interactions with non-polar compounds such as carbon black.

[0030] Correspondingly, sulfur-crosslinkable rubber compositions according to the invention are particularly preferred, in which the monomer composition comprises at least two different monomers, the term "different monomers" here again having to be interpreted as meaning monomers of different chemical structure, for example acrylate and methacrylate.

[0031] It has been found that particularly good results are obtained when acrylates and / or methacrylates are used as polar monomers. Therefore, sulfur-crosslinkable rubber compositions in which the monomer composition comprises at least one acrylate or methacrylate monomer are particularly preferred.

[0032] The acrylate and methacrylate monomers used herein are salts and esters of acrylic acid and methacrylic acid, respectively. Suitable acrylate and methacrylate monomers are disclosed, for example, in U.S. Patent Application Publication No. 20130165589A1, and are preferably selected from the list consisting of 2-(dimethylamino)ethyl methacrylate, 3-(dimethylamino)propyl methacrylate, 2-(diethylamino)ethyl methacrylate, or a mixture thereof.

[0033] More specifically, the sulfur-crosslinkable rubber composition according to the present invention is preferred, wherein the monomer composition also contains at least one unsaturated hydrocarbon monomer, preferably an aromatic hydrocarbon monomer having a vinyl moiety, and the monomer composition most preferably contains 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more, preferably 70% by weight or more, most preferably 90% by weight or more, based on the weight of the monomer composition.

[0034] Other suitable unsaturated hydrocarbon monomers are disclosed, for example, in U.S. Patent Application Publication No. 20130165589A1, and the aromatic hydrocarbon monomer having a vinyl moiety is preferably selected from the list consisting of styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, 3-(2-pyrrolidinoethyl)styrene, 4-(2-pyrrolidinoethyl)styrene, and 3-(2-pyrrolidino-1-methylethyl)-2-methylstyrene.

[0035] The ratio of each repeating unit in the oligomer side chain can be advantageously controlled by the concentration of the monomer in the monomer composition. Among them, the sulfur-crosslinkable rubber composition according to the present invention is preferred, and in the monomer composition, the weight ratio of the polar monomer to the unsaturated hydrocarbon monomer is in the range of 10:1 to 1:10, preferably in the range of 5:1 to 1:5, and most preferably in the range of 1:1 to 1:4.

[0036] As indicated above, it has been found to be beneficial for the oligomer side chains to be short compared to the diene rubber, particularly in order to maintain good processability of the graft copolymer. Thus, it is preferred that the oligomer side chains have a weight average molecular weight M in the range of 350 g / mol to 40,000 g / mol. w A sulfur-crosslinkable rubber composition according to the present invention having the formula:

[0037] In the framework of the present invention, the weight average molecular weight M wand the number average molecular weight M of the polymers and oligomers n is determined by gel permeation chromatography (GPC) according to BS ISO 11344:2004 using tetrahydrofuran (THF) as eluent at 40°C.

[0038] In view of the above information, the present inventors have determined that certain structures of the oligomeric side chains are particularly beneficial in the sulfur-crosslinkable rubber compositions of the present invention. In particular, the oligomeric side chains are represented by Formula I: [ka] (wherein R1, R2, and R6 are each independently selected from the group consisting of hydrogen and alkyl groups having 1 to 20 carbon atoms; R3 is a substituted or unsubstituted alkyl chain having 1 to 20 carbon atoms; R4 and R5 are each independently selected from the group consisting of substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms, substituted or unsubstituted cycloalkyl groups having 3 to 20 carbon atoms, and substituted or unsubstituted aryl groups having 6 to 30 carbon atoms; the repeating units are preferably statistically distributed in the oligomer chain; and a and b are each independently an integer in the range of 1 to 400, with the sum of a and b particularly preferably in the range of 2 to 400.) Preferred are sulfur crosslinkable rubber compositions according to the present invention having the general structure:

[0039] As used herein, the term "substituted" means that one or more hydrogen atoms of the respective group have been replaced, i.e., replaced with a specified substituent. Within the framework of the present invention, the substituents are independently selected from the group consisting of alkyl groups having 1 to 20 carbon atoms, cycloalkyl groups having 3 to 20 carbon atoms, and aryl groups having 6 to 20 carbon atoms.

[0040] The substituted or unsubstituted alkyl chain having 1 to 20 carbon atoms as defined above represents a saturated hydrocarbon group attached to both the oxygen atom and the nitrogen atom in formula I.

[0041] It is not necessary to use block copolymers, although they may be preferred for certain applications. Thus, the repeat units are preferably statistically distributed in the oligomeric chain.

[0042] A generalized reaction scheme to arrive at the above-defined oligomeric side chains that can be grafted onto a diene rubber backbone is shown below in Reaction Scheme A), where RI is the radical initiator, CTA is the chain transfer agent used in the RAFT polymerization, and CTA' is the end group derived from the chain transfer agent during the RAFT polymerization. [ka]

[0043] Particularly preferred is a sulfur-crosslinkable rubber composition according to the present invention, wherein in the above formula I), R1, R2, R4, and R5 are each independently selected from the group consisting of alkyl groups having 1 to 10 carbon atoms, preferably 1 carbon atom; R3 is an unsubstituted alkyl group having 1 to 10 carbon atoms, preferably 2 carbon atoms; R6 is hydrogen; a and b are each independently an integer in the range of 2 to 50; and the oligomer side chains preferably have an average value a in the range of 15 to 25, preferably 18 to 23, and an average value b in the range of 2 to 10, preferably 3 to 8.

[0044] It has been found that in some cases, the sulfur-crosslinkable rubber composition according to the present invention may exhibit less favorable properties in certain applications compared to unmodified diene rubber compounds from the standpoint of processability, especially if the increase in polydispersity during the synthesis of the graft copolymer is large. The inventors have found that, in principle, it is preferable to limit the increase in polydispersity, typically expressed as PD or PDI, during the synthesis of the graft copolymer. As will be described in more detail below, it has surprisingly been found that adding a radical initiator during the graft reaction to the reaction mixture in at least two separate steps minimizes the increase in polydispersity during the synthesis. This technical teaching allows for the production of graft copolymers with low polydispersity and ensures good properties.

[0045] The graft copolymer has a ratio M w / M n It has been found that sulfur-crosslinkable rubber compositions according to the present invention are preferred, having a polydispersity, calculated as: 1.0 to 3.0, preferably 1.1 to 2.5, most preferably 1.2 to 2.0, and / or the ratio of the polydispersity of the graft copolymer to the polydispersity of the unmodified diene rubber compound is in the range of 1 to 1.5, more preferably 1.05 to 1.2.

[0046] In a related embodiment, the graft copolymer has a weight average molecular weight M in the range of 350,000 to 900,000 g / mol, preferably in the range of 400,000 to 800,000 g / mol. w The sulfur-crosslinkable rubber composition according to the present invention is preferably

[0047] Although the present invention is applicable to a variety of diene rubber compounds, excellent results have been obtained with a preferred sulfur-crosslinkable rubber composition according to the present invention, in which the modified diene rubber backbone is obtained by living anionic polymerization, and the modified diene rubber backbone is preferably a modified styrene-butadiene rubber.

[0048] Suitable monomers for living anionic polymerization are, for example, 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene, isoprene, 2-phenyl-1,3-butadiene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, 3-(2-pyrrolidinoethyl)styrene, 4-(2-pyrrolidinoethyl)styrene, and 3-(2-pyrrolidino-1-methylethyl)-2-methylstyrene.

[0049] The styrene-butadiene rubber defined as preferred may be either a solution-polymerized styrene-butadiene rubber (SSBR) or an emulsion-polymerized styrene-butadiene rubber (ESBR), and it is also possible to use a mixture of at least one SSBR and at least one ESBR. However, the use of SSBR is preferred. The SSBR used may be end-functionalized.

[0050] It has been found that the properties of the sulfur-crosslinkable rubber composition are affected by the choice of filler material used in the filler component, with excellent results being obtained with silica. Accordingly, the sulfur-crosslinkable rubber composition of the present invention preferably contains a filler component in an amount of 10 to 300 phr, preferably 20 to 250 phr, and the filler component preferably comprises silica and / or carbon black, most preferably silica.

[0051] In the above embodiment, the filler component preferably comprises silica in an amount of 90 wt. % or more, preferably 95 wt. % or more, and most preferably 98 wt. % or more, based on the weight of the filler component. Suitable silicas are known to those skilled in the art and are disclosed, for example, in U.S. Patent Application Publication No. 10,273,351 A1. Particularly preferred are sulfur-crosslinkable rubber compositions according to the present invention, wherein the filler component comprises silica and carbon black in a weight ratio of preferably 100:1 to 1:100, and the filler component preferably comprises at least 0.01 phr of carbon black.

[0052] The sulfur-crosslinkable rubber composition according to the present invention may contain other diene rubber compounds. Exemplary diene rubbers are natural or synthetic polyisoprene, polybutadiene (butadiene rubber; BR), and styrene-butadiene copolymer (styrene-butadiene rubber; SBR).

[0053] The sulfur-crosslinkable rubber composition according to the present invention may contain other typical additives known in rubber compositions, such as plasticizers, aging stabilizers, activators, waxes, mastication aids, processing aids, and binder systems. Typical examples of each additive are disclosed in, for example, U.S. Patent Application Publication No. 10,273,351 A1. The total amount of each additive is typically in the range of 3 to 300 phr, preferably 3 to 200 phr, and more preferably 5 to 150 phr.

[0054] The present invention also relates to a sulfur-vulcanized rubber composition obtained by sulfur vulcanization of the sulfur-crosslinkable rubber composition according to the present invention.

[0055] The vulcanization of sulfur-crosslinkable rubber compositions is carried out in the presence of sulfur and / or sulfur donors, typically with the addition of a vulcanization accelerator, some of which can also function as sulfur donors. Similarly, it may be advantageous to use a vulcanization retarder. Examples of these compounds are known to those skilled in the art and are disclosed, for example, in U.S. Patent Application Publication No. 10,273,351 A1.

[0056] Typically, a vulcanization system or cure package, such as a sulfur source and vulcanization-affecting agents, is added to the prepared sulfur-crosslinkable rubber composition with mixing, followed by optional processing steps. The vulcanization itself is typically carried out at elevated temperatures, the appropriate process parameters for which are well established in the industry.

[0057] In view of the above, the present invention also relates to the use of the sulfur-crosslinkable rubber composition according to the invention for obtaining a sulfur-vulcanized rubber composition by vulcanization.

[0058] Also disclosed is a method for preparing a sulfur crosslinkable or sulfur vulcanized rubber composition, comprising the steps of: providing or producing a diene rubber compound, preferably a solution styrene-butadiene rubber; polymerizing a monomer composition comprising at least one polar monomer in the presence of a RAFT agent to produce an oligomer having a terminal functional group; grafting a polar oligomer onto a diene rubber compound in the presence of a radical initiator in a reaction mixture to produce a graft copolymer having a modified diene rubber backbone and one or more oligomer side chains grafted onto the modified diene rubber backbone, wherein the radical initiator is added to the reaction mixture in at least two separate steps, and the total amount of radical initiator added to the reaction mixture is in the range of 0.1 to 1.0 wt. % based on the weight of the diene rubber compound in the reaction mixture; mixing the graft copolymer with a filler component to obtain a sulfur-crosslinkable rubber composition, and optionally mixing the sulfur-crosslinkable rubber composition with sulfur and / or a sulfur source and then vulcanizing the sulfur-crosslinkable rubber composition to produce a sulfur-vulcanized rubber composition, wherein other ingredients can optionally be added to the mixture to facilitate vulcanization.

[0059] A significant feature of the above method is that the radical initiator during the grafting step is added to the reaction mixture in at least two separate steps, i.e., the grafting reaction is carried out by injecting the radical initiator in at least two separate portions. This means that after the addition of the first portion of radical initiator, the reaction is allowed to proceed for at least several minutes before adding a second or subsequent portion of radical initiator to the reaction mixture. As mentioned above, the inventors have surprisingly found that when the above protocol is used, the polydispersity, i.e., M n M against w It has been found that graft copolymers can be obtained without an undesirable large increase in the ratio of

[0060] Therefore, the above method is preferred in which the ratio of the polydispersity of the graft copolymer to the polydispersity of the diene rubber compound is in the range of 1 to 1.5, more preferably in the range of 1.05 to 1.2.

[0061] Having arrived at the sulfur vulcanized rubber composition of the present invention, the present invention naturally also relates to a rubber article, preferably a vehicle tire, comprising the sulfur vulcanized rubber composition according to the present invention, and to the use of the sulfur-crosslinkable rubber composition according to the present invention or the sulfur vulcanized rubber composition according to the present invention, respectively, in the manufacture of a rubber article, preferably a vehicle tire.

[0062] The sulfur vulcanized rubber composition of the present invention is suitable for a variety of rubber products, such as bellows, conveyor belts, air springs, breaker belts, or shoe soles, but its best application, which makes the most use of its excellent performance characteristics, is in vehicle tires. As used herein, the term "vehicle tire" includes pneumatic and solid rubber tires for all types of vehicles, including, for example, truck and bicycle tires, with pneumatic vehicle tires being particularly preferred.

[0063] Finally, the present invention also relates to the use of a graft copolymer having a modified diene rubber backbone and one or more oligomer side chains grafted to the modified diene rubber backbone in the sulfur-crosslinkable rubber composition according to the present invention, i.e., a sulfur-crosslinkable rubber composition comprising a filler component in an amount of 1 to 350 phr for increasing the rolling resistance of a vehicle tire manufactured from the sulfur-crosslinkable rubber composition, wherein the oligomer side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, the monomer composition comprising at least one polar monomer.

[0064] The present invention will be explained in more detail below through experiments.

[0065] In the first step, the precursor of the oligomeric side chain having formula II) was polymerized using RAFT polymerization. [ka]

[0066] Preparation Example 1 (20% Oligomer): 28 mL of 0.2 M 2,2-azobis(isobutyronitrile) (AIBN) and 5 g of 2-cyano-2-propylbenzodithioate (CPDB) were prepared in a 500 mL round-bottom flask, and 21.7 g of 2-(dimethylamino)ethyl methacrylate, 84.9 g of styrene, and 95 mL of toluene were added. The mixture was then reacted at 80 °C for 30 hours, and the solid was precipitated in the solvent and separated. The separated solid was redissolved in toluene, and 33 g of hexylamine and 2.8 g of a reducing agent were added at room temperature (25 °C), followed by stirring for 30 minutes. The resulting product was then precipitated in cold hexane to prepare the oligomer represented by the following chemical formula II). The successful synthesis of the oligomer of formula II was confirmed by the following: 1 This was confirmed by H-NMR. The average a is 23 and the average b is 3.

[0067] Preparation Example 2 (40% Oligomer): The oligomer of formula II) was prepared by carrying out the same method as in Preparation Example 1, except that 43.3 g of 2-(dimethylamino)ethyl methacrylate and 63.7 g of styrene were added instead. Successful synthesis of the oligomer of formula II) was confirmed by: 1 This was confirmed by H-NMR. The average a is 18 and the average b is 8.

[0068] In the second step, the precursors of the oligomeric side chains were grafted onto the diene rubber backbone.

[0069] Preparation Example 3: 440 g of styrene-butadiene rubber, 2.49 kg of n-hexane, and 5.8 kg of tetrahydrofuran were placed in a 20 L reactor, and the mixture was purged under a nitrogen atmosphere. 330 g of the oligomer solution (20 wt % in tetrahydrofuran) obtained in Preparation Example 1 was added, and the internal temperature of the reactor was adjusted to 90°C. 35.2 g of lauroyl peroxide solution (2.5%) was added to initiate the reaction. After 1 hour, 35.2 g of the solution was added again, and after another hour, 17.6 g of the solution was added again. After 1 hour, a small amount of ethanol was added to stop the reaction, and the reaction mixture was poured into acetone to obtain a rubber, to which an antioxidant was added.

[0070] The styrene-butadiene rubber used in Preparative Example 3 was prepared as described below.

[0071] 5 kg of n-hexane, 211 g of styrene, 769 g of 1,3-butadiene, 0.98 g of 2,2-di(2-tetrahydrofuryl)propane as a polar additive, and 0.25 g of n-butyllithium were placed in a 20 L reactor. The internal temperature of the reactor was adjusted to 60 °C, and the adiabatic reaction was carried out while heating ([DTP]:[active Li] = 1.5:1 mol). After 30 min, 20 g of 1,3-butadiene was added to cap the polymer chain ends with butadiene. The polymerization reaction was then quenched using ethanol, and 33 g of a solution of 30 wt% 2,6-di(alkylthiomethyl)-substituted phenol (Wingstay K) in hexane was added as an antioxidant. The resulting polymerization product was added to hot water (heated with steam) and stirred to remove the solvent, yielding a styrene-butadiene copolymer.

[0072] Preparation Example 4: 440 g of styrene-butadiene rubber, 2.49 kg of n-hexane, and 5.8 kg of tetrahydrofuran were placed in a 20 L reactor, and the mixture was purged under a nitrogen atmosphere. 550 g of the oligomer solution (20 wt % in tetrahydrofuran) obtained in Preparation Example 1 was added, and the internal temperature of the reactor was adjusted to 90°C. 35.2 g of lauroyl peroxide solution (2.5%) was added to initiate the reaction. After 1 hour, 35.2 g of the solution was added again, and after another hour, 17.6 g of the solution was added again. After 1 hour, a small amount of ethanol was added to stop the reaction, and the reaction mixture was poured into acetone to obtain a rubber, to which an antioxidant was added.

[0073] The styrene-butadiene rubber used in Preparation Example 4 was prepared as follows.

[0074] A 20 L reactor was charged with 4 kg of n-hexane, 162 g of styrene, 595 g of 1,3-butadiene, 0.98 g of 2,2-di(2-tetrahydrofuryl)propane as a polar additive, and 0.25 g of n-butyllithium. The internal temperature of the reactor was adjusted to 60 °C, and the adiabatic reaction was carried out while heating ([DTP]:[active Li] = 1.5:1 mol). After 30 min, 20 g of 1,3-butadiene was added to cap the polymer chain ends with butadiene. The polymerization reaction was then quenched using ethanol, and 33 g of a solution of 30 wt% 2,6-di(alkylthiomethyl)-substituted phenol (Wingstay K) in hexane was added as an antioxidant. The resulting polymerization product was added to hot water (heated using steam) and stirred to remove the solvent, yielding a styrene-butadiene copolymer.

[0075] Preparation Example 5: A modified styrene-butadiene copolymer was prepared in the same manner as in Preparation Example 4, except that the oligomer prepared in Preparation Example 2 was used.

[0076] The styrene-butadiene rubber used in Preparative Example 5 was prepared as described for Preparative Example 4.

[0077] Preparation Example 6: Styrene-butadiene rubber prepared as described in Preparative Example 3 was used as the comparative rubber compound.

[0078] Preparation Example 7: Styrene-butadiene rubber prepared as described in Preparative Example 4 was used as the comparative rubber compound. [Example]

[0079] Rubber compositions were prepared from the rubber compounds prepared in Preparation Examples 3, 4 and 5 (according to the present invention; Examples 1, 2 and 3), 6 and 7 (comparative experiments; Comparative Examples 1 and 2).

[0080] The rubber compositions were prepared in a laboratory mixer under standard conditions in two stages using a process conventional in the rubber industry. All ingredients except the vulcanization system (sulfur and vulcanization-influencing substances) were mixed in the first mixing stage (base mixing stage). The vulcanization system was added in the second stage (ready mixing stage) to prepare the final mixture by mixing at 90-120°C. The composition of the samples is shown in Table 1.

[0081] The silica here is Ultrasil VN3 silica provided by Evonik. To ensure good comparison of results, the same set of typical plasticizers, additives, and accelerators was used in all experiments.

[0082] The sulfur-crosslinkable rubber compositions were used to prepare test specimens by vulcanizing them after 20 minutes under pressure at 160° C. These test specimens were used to measure material properties typical in the rubber industry using the test methods specified below. Resilience at 70°C according to DIN 53512 (Resilience 70°C); · Elastic modulus at 200% elongation at RT (M200) according to DIN 53504; Average dynamic storage modulus according to DIN 53513 at 55°C (E' average); Eplexor DKF 55°C (E' average); and Loss factor tangens delta max (tan d(max)) at 55°C as the maximum value of the strain sweep from dynamic mechanical measurements according to DIN 53513.

[0083] Unless otherwise indicated, measurements were made according to the latest version of the technical standards as of June 2018.

[0084] The results obtained for the sulfur crosslinkable and sulfur vulcanized rubber compositions, respectively, are summarized in Table 2 below.

[0085] [Table 1]

[0086] [Table 2]

[0087] From the above data, it is clear to one skilled in the art that excellent rolling resistance can be obtained with the rubber compositions of the present invention, as indicated by the high values of modulus at 70°C and low values of loss factor tan d(max) observed at both graft densities, i.e., two and four oligomers per chain. Furthermore, good values for M200 and E' average were also observed, suggesting that the sulfur-vulcanized rubber compositions of the present invention have excellent mechanical properties, especially improved durability properties and high stiffness. This result suggests that the graft copolymers exhibit excellent filler compatibility. The present application relates to the invention described in the claims, but may also include the following as other aspects. 1. a filler component in an amount ranging from 1 to 350 phr; at least one graft copolymer having a modified diene rubber backbone and one or more oligomer side chains grafted onto the modified diene rubber backbone; A sulfur-crosslinkable rubber composition comprising: A sulfur-crosslinkable rubber composition, wherein the oligomeric side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, the monomer composition comprising at least one polar monomer. 2. The sulfur-crosslinkable rubber composition according to claim 1, wherein the monomer composition comprises at least two different monomers. 3. The sulfur-crosslinkable rubber composition according to 1 or 2 above, wherein the monomer composition contains at least one acrylate monomer or methacrylate monomer. 4. The sulfur-crosslinkable rubber composition according to 2 or 3 above, wherein the monomer composition comprises at least one unsaturated hydrocarbon monomer, preferably an aromatic hydrocarbon monomer having a vinyl moiety, and most preferably comprises 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more based on the weight of the monomer composition, and in the monomer composition, the weight ratio of polar monomer to unsaturated hydrocarbon monomer is preferably in the range of 10:1 to 1:10, more preferably in the range of 5:1 to 1:5. 5. The oligomer side chain has a weight average molecular weight M in the range of 350 g / mol to 40,000 g / mol. w 5. The sulfur-crosslinkable rubber composition according to any one of the above items 1 to 4, which has: 6. The oligomer side chain has Formula I:

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Claims

1. a filler component in an amount ranging from 1 to 350 phr; at least one graft copolymer having a diene rubber backbone and one or more oligomeric side chains grafted to the diene rubber backbone; A sulfur-crosslinkable rubber composition comprising: the oligomer side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, the monomer composition comprising at least one acrylate monomer or methacrylate monomer as the at least one polar monomer, and the monomer composition comprising at least one aromatic hydrocarbon monomer having a vinyl moiety as the at least one unsaturated hydrocarbon monomer; the filler component comprises silica in an amount of 90 wt. % or more based on the weight of the filler component; the monomer composition contains 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more based on the weight of the monomer composition; Sulfur-crosslinkable rubber composition.

2. 2. The sulfur-crosslinkable rubber composition according to claim 1, wherein in the monomer composition, the weight ratio of the polar monomer to the unsaturated hydrocarbon monomer is in the range of 10:1 to 1:

10.

3. The oligomeric side chains have a weight average molecular weight M in the range of 350 g / mol to 40,000 g / mol. ｗ The sulfur-crosslinkable rubber composition according to claim 1 or 2, comprising:

4. The oligomeric side chain has Formula I: 【Chemical 1】 (In the formula, R １ , R ２ , and R ６ are each independently selected from the group consisting of hydrogen and alkyl groups having 1 to 20 carbon atoms; R ３ is a substituted or unsubstituted alkyl chain having 1 to 20 carbon atoms, R ４ and R ５ are each independently selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, the repeat units being statistically distributed in the oligomer chain, and a and b are each independently an integer in the range of 1 to 200. The sulfur crosslinkable rubber composition of any one of claims 1 to 3, having a general structure according to the formula:

5. R １ , R ２ , R ４ , and R ５ are each independently selected from the group consisting of alkyl groups having 1 to 10 carbon atoms; R ３ is an unsubstituted alkyl chain having 1 to 10 carbon atoms, and R ６ is hydrogen, a and b are each independently an integer in the range of 2 to 50, and the oligomer side chains have an average value a in the range of 15 to 25 and an average value b in the range of 2 to 10.

6. The sulfur-crosslinkable rubber composition according to any one of claims 1 to 5, wherein the graft copolymer has an average graft density, expressed as the number of side chains per diene rubber main chain, in the range of 1 to 10.

7. The sulfur-crosslinkable rubber composition according to any one of claims 1 to 6, wherein the graft copolymer has a polydispersity in the range of 1.0 to 3.0, and / or the ratio of the polydispersity of the graft copolymer to the polydispersity of the unmodified diene rubber compound is in the range of 1 to 1.

5.

8. The graft copolymer has a weight average molecular weight M in the range of 350,000 to 900,000 g / mol. ｗ The sulfur-crosslinkable rubber composition according to any one of claims 1 to 7, comprising:

9. The sulfur-crosslinkable rubber composition according to any one of claims 1 to 8, wherein the diene rubber main chain is obtained by living anionic polymerization.

10. The sulfur-crosslinkable rubber composition according to any one of claims 1 to 8, wherein the diene rubber main chain is a styrene-butadiene rubber.

11. The sulfur-crosslinkable rubber composition according to any one of claims 1 to 10, comprising a filler component in an amount of 10 to 300 phr, said filler component comprising silica and carbon black.

12. A sulfur-vulcanized rubber composition obtained by sulfur-vulcanizing the sulfur-crosslinkable rubber composition according to any one of claims 1 to 11.

13. A rubber product comprising the sulfur vulcanized rubber composition of claim 12.

14. A vehicle tire comprising the sulfur vulcanized rubber composition of claim 12.

15. 12. Use of a graft copolymer having a diene rubber backbone and one or more oligomer side chains grafted to the diene rubber backbone in the sulfur-curable rubber composition according to any one of claims 1 to 11, for reducing tan δ at 55°C of a vehicle tire produced from the sulfur-curable rubber composition, wherein the oligomer side chains are obtained by reversible addition-fragmentation chain transfer polymerization of a monomer composition, the monomer composition comprising at least one acrylate monomer or methacrylate monomer as the at least one polar monomer, and the monomer composition comprising at least one aromatic hydrocarbon monomer having a vinyl moiety as the at least one unsaturated hydrocarbon monomer, and the monomer composition comprising 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more based on the weight of the monomer composition.

16. The following steps: - Providing or producing a diene rubber compound; - polymerizing a monomer composition comprising at least one polar monomer in the presence of a RAFT agent to produce an oligomer having a terminal functional group; - grafting a polar oligomer onto a diene rubber compound in the presence of a radical initiator in a reaction mixture to produce a graft copolymer having a diene rubber backbone and one or more oligomer side chains grafted to the diene rubber backbone, wherein the radical initiator is added to the reaction mixture in at least two separate steps, and the total amount of radical initiator added to the reaction mixture is in the range of 0.1 to 1.0 wt. %, based on the weight of the diene rubber compound in the reaction mixture; and - mixing the graft copolymer with a filler component to obtain a sulfur-crosslinkable rubber composition; A method for producing a sulfur-crosslinkable rubber composition, comprising: the monomer composition contains at least one acrylate monomer or methacrylate monomer as the at least one polar monomer, and the monomer composition contains at least one aromatic hydrocarbon monomer having a vinyl moiety as the at least one unsaturated hydrocarbon monomer, and the monomer composition contains 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more based on the weight of the monomer composition, and the filler component contains silica in an amount of 90% by weight or more based on the weight of the filler component.

17. The following steps: - Providing or producing a diene rubber compound; - polymerizing a monomer composition comprising at least one polar monomer in the presence of a RAFT agent to produce an oligomer having a terminal functional group; - grafting a polar oligomer onto a diene rubber compound in the presence of a radical initiator in a reaction mixture to produce a graft copolymer having a diene rubber backbone and one or more oligomer side chains grafted to the diene rubber backbone, wherein the radical initiator is added to the reaction mixture in at least two separate steps, and the total amount of radical initiator added to the reaction mixture is in the range of 0.1 to 1.0 wt. %, based on the weight of the diene rubber compound in the reaction mixture; - mixing the graft copolymer with a filler component to obtain a sulfur-crosslinkable rubber composition; and mixing the sulfur-crosslinkable rubber composition with sulfur and / or a sulfur source to produce a sulfur-vulcanized rubber composition and then vulcanizing the sulfur-vulcanizable rubber composition, optionally adding other ingredients to the mixture to facilitate vulcanization; A method for producing a sulfur vulcanized rubber composition, comprising: the monomer composition contains at least one acrylate monomer or methacrylate monomer as the at least one polar monomer, and the monomer composition contains at least one aromatic hydrocarbon monomer having a vinyl moiety as the at least one unsaturated hydrocarbon monomer, and the monomer composition contains 2-(dimethylamino)ethyl methacrylate and styrene in a total amount of 50% by weight or more based on the weight of the monomer composition, and the filler component contains silica in an amount of 90% by weight or more based on the weight of the filler component.

18. The oligomeric side chain has Formula I: 【Chemistry 2】 (In the formula, R １ , R ２ , and R ６ are each independently selected from the group consisting of hydrogen and alkyl groups having 1 to 20 carbon atoms; R ３ is a substituted or unsubstituted alkyl chain having 1 to 20 carbon atoms, R ４ and R ５ are each independently selected from the group consisting of a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 20 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 30 carbon atoms, the repeat units being statistically distributed in the oligomer chain, and a and b are each independently an integer in the range of 1 to 200.

18. The process of claim 16 or 17, having the general structure:

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