JP2023091394A - Liquid crystal polymer, rubber composition, and pneumatic tire - Google Patents

Abstract

To provide a liquid crystal polymer that is added to vulcanized rubber and able to increase a peak top value of tanδ of the vulcanized rubber, a rubber composition containing the liquid crystal polymer, and a pneumatic tire including the vulcanized rubber obtained from the rubber composition.SOLUTION: A liquid crystal polymer obtained by reacting a mesogen-group-containing compound having an active hydrogen group and an isocyanate compound has a hydrogen bond ratio between the polymers of 50% or less calculated by FT-IR (ATR method). Preferably, at least one of the mesogen-group-containing compound and the isocyanate compound is a branched compound having a branch structure.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a liquid crystal polymer, a rubber composition containing the liquid crystal polymer, and a pneumatic tire comprising a vulcanized rubber obtained using the rubber composition as a raw material.

In general, tires are used in various driving environments, and are required to improve wet grip performance (hereinafter simply referred to as "WET performance"), which is grip performance on wet road surfaces, for example, in the rain.

Patent Document 1 below describes a technique for improving the WET performance of a pneumatic tire by using, as a raw material, a rubber composition containing at least two types of diene rubbers having a bimodal temperature distribution curve of tan δ as a rubber component. is described.

Further, in Patent Document 2 below, rubber containing a liquid copolymer containing an aromatic vinyl compound and a conjugated diene-containing compound as monomer units and having a weight average molecular weight (Mw) of 1,000 to 50,000 A technique for improving the WET performance of a pneumatic tire by using the composition as a raw material is described.

JP-A-08-27313 JP 2016-117880 A

In order to improve the WET performance of a pneumatic tire, it is important to optimize the loss tangent (tan δ) of the rubber portion (vulcanized rubber) that constitutes the pneumatic tire. In general, WET performance is greatly dependent on tan δ (hereinafter also referred to as “tan δ (0 ° C.)”) near 0 ° C. of the rubber portion constituting the pneumatic tire, and the larger the tan δ (0 ° C.) Excellent wet performance of tires. As a method for increasing tan δ (0 ° C.), for example, increasing the peak top value of tan δ of the rubber portion (when the tan δ peak is bimodal, the peak top value of the peak near 0 ° C.) , tan δ (0° C.) is also increased.

However, it has been found that there is a limit to increasing the peak top value of tan δ of the rubber portion with the technique described in the above patent document. The present invention has been completed in view of the above circumstances, and provides a liquid crystal polymer that is added to a vulcanized rubber to increase the peak top value of tan δ of the vulcanized rubber, and a rubber composition containing the liquid crystal polymer. , and a pneumatic tire comprising a vulcanized rubber obtained by using the rubber composition as a raw material.

The above object can be achieved by the present invention as described below. That is, the present invention provides a liquid crystal polymer which is a reaction product of a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound, wherein the hydrogen bonding ratio between the polymers calculated using FT-IR (ATR method) is It relates to a liquid crystal polymer characterized in that it is 50% or less.

In the liquid crystal polymer, at least one of the mesogenic group-containing compound and the isocyanate compound is preferably a branched compound having a branched structure.

The present invention also relates to a rubber composition containing the liquid crystal polymer described above and a diene rubber, and a pneumatic tire comprising a vulcanized rubber obtained using the rubber composition described above as a raw material.

The liquid crystal polymer according to the present invention is a reaction product of a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound, and the active hydrogen group of the mesogenic group-containing compound and the isocyanate group of the isocyanate compound form a urethane bond. Generated by In general, two or more liquid crystal polymer chains tend to agglomerate with each other through hydrogen bonding of urethane bonds. However, the liquid crystal polymer according to the present invention is designed so that the hydrogen bonding ratio between the polymers calculated using FT-IR (ATR method) is 50% or less. Thus, aggregation of liquid crystal polymer chains can be suppressed.

Here, tan δ is represented by the following formula.
[tan δ] = [G″ (loss modulus)]/[G′ (storage modulus)]
As described above, the liquid crystal polymer according to the present invention is designed so that the hydrogen bonding ratio between the polymers calculated using FT-IR (ATR method) is 50% or less, so the hydrogen bonding of the urethane bond Aggregation of liquid crystal polymer chains via is suppressed. When the aggregation of the liquid crystal polymer chains is suppressed, the storage elastic modulus G' of the liquid crystal polymer alone or the vulcanized rubber compounded with the liquid crystal polymer decreases. As a result, when the liquid crystal polymer according to the present invention is blended into the vulcanized rubber, the storage elastic modulus G′ of the vulcanized rubber decreases, resulting in a tan δ peak top value (tan δ peak is bimodal and If so, the peak top value of the peak closer to 0° C.) can be increased.

In the present invention, when the mesogenic group-containing compound and/or the isocyanate compound, which are raw materials for the liquid crystal polymer, are branched compounds having a branched structure, hydrogen bond formation of urethane bonds possessed by two or more liquid crystal polymer chains is It can be inhibited by steric hindrance of the branched structure of the branched compound. As a result, the hydrogen bonding rate between polymers calculated using FT-IR (ATR method) can be further reduced, and aggregation of the liquid crystal polymer in the vulcanized rubber can be further suppressed. As a result, the storage elastic modulus G' of the vulcanized rubber is further lowered, so that the peak top value of tan δ can be further increased.

A rubber composition containing a liquid crystal polymer and a diene rubber according to the present invention has a large peak top value of tan δ derived from the liquid crystal polymer when vulcanized rubber. Therefore, the pneumatic tire comprising the vulcanized rubber of the rubber composition according to the present invention has improved WET μ (wet coefficient of friction) due to improved hysteresis friction, thereby improving WET performance.

The liquid crystal polymer according to the present invention is a reaction product of a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound, and the hydrogen bond rate between the polymers calculated using FT-IR (ATR method) is 50%. It is characterized by the following.

The hydrogen bonding ratio between liquid crystal polymers is measured using a known FT-IR device, and the absorbance (ABS ^- 1 ), and the absorbance (ABS-2) of the stretching vibration peak (near 1703 cm ⁻¹ ) of the carbonyl group possessed by the urethane bond that is not hydrogen-bonded, it can be calculated from the following formula.
[Hydrogen bond rate (%)] = 100 × (ABS-1) / ((ABS-1) + (ABS-2))

As the mesogenic group-containing compound having an active hydrogen group, for example, a compound represented by the following general formula (1) can be used.

In the above general formula (1), X is an active hydrogen group, R ₁ is a single bond forming part of the adjacent bonding group, -N=N-, -CO-, -CO-O-, or -CH =N—, R ₂ is a single bond forming part of the adjacent bonding group, or —O—, and R ₃ is a single bond forming part of the adjacent bonding group, or a It is an alkylene group. However, those in which R ₂ is —O— and R ₃ is a single bond forming part of the adjacent bonding group are excluded. The “single bond forming a part of the adjacent bonding group” means a state in which the single bond is shared with a part of the adjacent bonding group. For example, in the above general formula (1), when R ₁ is a single bond that forms part of the adjacent bonding group, the single bond R ₁ is shared with the benzene rings on both sides, and the benzene on both sides Forms a biphenyl structure with the ring. Examples of X include OH, SH, NH ₂ , COOH, secondary amine and the like.

As the mesogenic group-containing compound, a compound obtained by adding alkylene oxide and/or styrene oxide to the compound represented by the general formula (1) (hereinafter also referred to as "oxide addition compound") may be used. Alkylene oxide and/or styrene oxide function to lower the temperature at which the liquid crystal phase appears in the liquid crystalline polyurethane polymer. The phase transition temperature (Ti) can be easily designed within a desired temperature range. Alkylene oxides can be used, for example ethylene oxide, propylene oxide, or butylene oxide. The alkylene oxides listed above may be used alone or in combination of multiple types. Styrene oxide may have a substituent such as an alkyl group, an alkoxy group, or a halogen on the benzene ring. As the alkylene oxide, it is also possible to use a mixture of the above alkylene oxide and the above styrene oxide. The amount of alkylene oxide and/or styrene oxide to be added is 4 to 20 mol, preferably 5 to 15 mol, of alkylene oxide and/or styrene oxide per 1 mol of the compound represented by the general formula (1). adjusted to

The compounding amount of the mesogenic group-containing compound, particularly the oxide addition compound is adjusted to 20 to 95% by mass, preferably 30 to 85% by mass, based on the total raw materials for the liquid crystal polymer. When the compounded amount of the mesogenic group-containing compound, particularly the oxide addition compound, is less than 20% by mass, it becomes difficult for the resulting polymer to exhibit liquid crystallinity. If the amount of the mesogenic group-containing compound, particularly the oxide addition compound, exceeds 95% by mass, polymerization by the urethane reaction will be insufficient.

As the isocyanate compound, for example, diisocyanate compounds shown below can be used. Examples of diisocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, and 1,5-naphthalene diisocyanate. , p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, and m-xylylene diisocyanate; ethylene diisocyanate, 1,5-pentamethylene diisocyanate, 2,2,4-trimethylhexamethylene- Aliphatic diisocyanates such as 1,6-diisocyanate, 2,4,4-trimethylhexamethylene-1,6-diisocyanate, and 1,6-hexamethylene diisocyanate; and 1,4-cyclohexane diisocyanate, 4,4′-dicyclo alicyclic diisocyanates such as hexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate; The exemplified diisocyanate compounds may be used singly or in combination of multiple types.

In the present invention, tri- or higher functional isocyanate compounds may be used in combination as the isocyanate compounds (i) and (ii). Examples of tri- or more functional isocyanate compounds include triphenylmethane triisocyanate, tris(isocyanatophenyl)thiophosphate, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, Triisocyanates such as 1,8-diisocyanato-4-isocyanatomethyloctane, bicycloheptane triisocyanate, and tetraisocyanates such as tetraisocyanatosilane.

When the total amount of the mesogenic group-containing compounds constituting the liquid crystal polymer is 100 parts by mass, the proportion of the isocyanate compound is preferably 5 to 70 parts by mass, more preferably 15 to 60 parts by mass. If the amount of the isocyanate compound is less than 5 parts by mass, polymerization by urethane reaction will be insufficient. On the other hand, when the ratio of the isocyanate compound exceeds 60 parts by mass, the amount of the mesogenic group-containing compound in the total raw material of the liquid crystalline polyurethane polymer is relatively small, resulting in deterioration of the liquid crystallinity of the liquid crystalline polyurethane polymer.

The liquid crystal polymer according to the present invention is a reaction product of a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound. It is preferably a branched compound having

The mesogenic group-containing compound, which is a branched compound having a branched structure, includes, for example, a mesogenic group-containing compound (oxide addition compound).

Examples of the isocyanate compound, which is a branched compound having a branched structure, include 2,4,4-trimethylhexamethylene-1,6-diisocyanate and isophorone diisocyanate.

In the liquid crystal polymer according to the present invention, an active hydrogen group-containing compound may be used as a raw material for the liquid crystal polymer in addition to the mesogenic group-containing compound and the isocyanate compound. Active hydrogen group-containing compounds include, for example, polyol compounds and amine compounds. Polyol compounds include, for example, polyether polyol, polyester polyol, polycarbonate polyol, polyester polycarbonate polyol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butane Diol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, 1,4-bis(2-hydroxyethoxy)benzene, trimethylolpropane, glycerin, 1,2,6-hexanetriol, meso-erythritol, pentaerythritol, tetramethylolcyclohexane, methylglucoside, sorbitol, mannitol, dulcitol, sucrose, 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol, diethanolamine, N-methyldiethanolamine, triethanolamine, and the like. Amine compounds include ethylenediamine, tolylenediamine, diphenylmethanediamine, diethylenetriamine, monoethanolamine, 2-(2-aminoethylamino)ethanol, monopropanolamine, and the like. Each active hydrogen group-containing compound listed above may be used alone, or a plurality of types may be mixed and used.

Moreover, when reacting a mesogenic group-containing compound having an active hydrogen group with an isocyanate compound, a urethane polymerization catalyst known to those skilled in the art may be used. Such polymerization catalysts include organic tin catalysts such as dibutyltin dilaurate and tin octylate, triethylenediamine and its derivatives, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N ',N'-tetramethylhexamethylenediamine, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU), bis(N,N-dimethylamino-2-ethyl) ether, bis(2-dimethyl tertiary amine-based catalysts such as aminoethyl)ether; carboxylic acid metal salt catalysts such as potassium acetate and potassium octylate; and imidazole-based catalysts. Among these, the use of dibutyltin dilaurate and its derivatives is preferred.

When a polyfunctional compound is incorporated into the liquid crystal polymer, examples of the polyfunctional compound include compounds having three or more functional groups capable of reacting with active hydrogen groups or isocyanate groups. Specific examples include triols such as glycerin and trimethylolpropane; tetraols such as pentaerythritol; diamines such as 4′-diaminodiphenylmethane (MOCA); aminoalcohols such as diethanolamine, triethanolamine and aminoethylethanolamine;

The liquid crystal polymer according to the present invention is particularly useful for a pneumatic tire, particularly for a rubber composition that is a raw material for a vulcanized rubber constituting a rubber portion of a pneumatic tire. A rubber composition according to the present invention contains a liquid crystal polymer and a diene rubber.

Diene rubbers include natural rubber (NR), polyisoprene rubber (IR), polystyrene butadiene rubber (SBR), polybutadiene rubber (BR), chloroprene rubber (CR), nitrile rubber (NBR) and the like. If necessary, those modified at the ends (eg, modified BR, modified SBR, etc.) or those modified to impart desired properties (eg, modified NR) can be preferably used. As for polybutadiene rubber (BR), in addition to those synthesized using cobalt (Co) catalyst, neodymium (Nd) catalyst, nickel (Ni) catalyst, titanium (Ti) catalyst, and lithium (Li) catalyst, WO2007 -129670 can also be used.

Considering the fuel efficiency of pneumatic tires, the polystyrene-butadiene rubber should have a styrene content of 10 to 40% by mass, a vinyl bond content in the butadiene portion of 10 to 70% by mass, and a cis content of 10% by mass or more. Particularly preferred are those having a styrene content of 15 to 25% by mass, a vinyl bond content in the butadiene portion of 10 to 60% by mass, and a cis content of 20% by mass or more. When the rubber composition according to the present invention is used as a tread rubber portion of a pneumatic tire, it is preferable to use a non-oil-added polystyrene-butadiene rubber rather than an oil-added type.

In addition to the rubber component and the liquid crystal polymer, the rubber composition according to the present invention includes carbon black, silica, a silane coupling agent, an anti-aging agent, a softening agent such as zinc oxide, stearic acid, wax and oil, and a processing agent. Various compounding agents such as auxiliary agents can be blended.

As silica, wet-process silica and dry-process silica can be used, but it is particularly preferable to use wet-process silica containing hydrous silicic acid as a main component.

As the silane coupling agent, a silane coupling agent having reactivity with diene rubber is used. Silane coupling agents that can be used in the present invention include, for example, bis(3-triethoxysilylpropyl) tetrasulfide (eg, "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl) disulfide (eg, Degussa "Si75"), bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilyl) sulfide silanes such as ethyl)disulfide; Protected mercaptosilanes such as 1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane and the like.

Examples of carbon black include carbon blacks commonly used in the rubber industry such as SAF, ISAF, HAF, FEF and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black.

Antiaging agents include aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, and dithiocarbamic acid, which are commonly used for rubber. Antiaging agents such as salt-based anti-aging agents and thiourea-based anti-aging agents may be used singly or in an appropriate mixture.

After the step of mixing compounding agents other than the vulcanization compounding agent, the vulcanization compounding agent is further mixed and dispersed. Examples of vulcanization compounding agents used in the step of mixing vulcanization compounding agents include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization accelerator auxiliaries, and vulcanization retarders. be done.

Sulfur as a sulfur-based vulcanizing agent may be ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, and the like.

As vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, and guanidine-based vulcanization accelerators, which are commonly used for rubber vulcanization. Vulcanization accelerators such as accelerators and dithiocarbamate-based vulcanization accelerators may be used singly or in an appropriate mixture.

The rubber composition according to the present invention includes a rubber component and a liquid crystal polymer, and optionally carbon black, silica, a silane coupling agent, a vulcanization compounding agent, an antioxidant, zinc oxide, stearic acid, wax, oil, and the like. The softening agent, processing aid, etc. are kneaded using a kneader commonly used in the rubber industry, such as a Banbury mixer, a kneader, and a roll.

In addition, the method of blending each of the above components is not particularly limited, and blending components other than vulcanization compounding agents such as sulfur vulcanizing agents and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added. A method of adding each component in an arbitrary order and kneading, a method of adding all the components at the same time and kneading, and the like may be used.

In the present invention, a vulcanized rubber in which the liquid crystal polymer is dispersed in the diene rubber can be produced by mixing the diene rubber and the liquid crystal polymer and then vulcanizing the resulting rubber composition. Since such a vulcanized rubber has a large peak top value of tan δ, WET μ (wet coefficient of friction) increases due to improvement in hysteresis friction, thereby improving WET performance. Therefore, the vulcanized rubber of the rubber composition according to the present invention is particularly useful, for example, as a tread member for pneumatic tires.

Examples and the like that specifically show the configuration and effects of the present invention will be described below.

(Production of mesogenic group-containing compound having active hydrogen group)
In a reaction vessel, BH6 (400 g) as a mesogenic group-containing compound having an active hydrogen group, potassium hydroxide (23 g), and toluene (2400 ml) as a solvent are added and mixed. 10 equivalents were added to BH6, and the mixture was reacted at 120° C. for 3 hours under pressurized conditions (addition reaction). Then, oxalic acid (18 g) was added to the reaction vessel to stop the addition reaction, insoluble salts in the reaction solution were removed by suction filtration, and toluene in the reaction solution was removed by vacuum distillation. , a mesogenic group-containing compound (mesogen diol) having an active hydrogen group represented by the following formula (2) was obtained. The hydroxyl value of mesogen diol is 156.3. Note that the mesogen diol shown in formula (2) is a representative one and may include various structural isomers. n in formula (2) is 5.5 on average.

(Manufacture of liquid crystal polymer)
(Example 1)
1,5-pentamethylene diisocyanate represented by the following formula (3) as an isocyanate compound was blended in a compounding ratio of 22 parts by mass with respect to 100 parts by mass of the mesogen diol represented by the formula (2) produced above, and stirred. The liquid crystal polymer 1 according to Example 1 was produced by mixing at 100° C. while stirring.

(Example 2)
Same as Example 1 except that 1,6-hexamethylene diisocyanate represented by the following formula (4) as an isocyanate compound was blended at a blending ratio of 23 parts by mass with respect to 100 parts by mass of the mesogen diol described in formula (2). A liquid crystal polymer 2 according to Example 2 was produced by the method of .

(Example 3)
2,4,4-trimethylhexamethylene-1,6-diisocyanate represented by the following formula (5) as an isocyanate compound was blended at a compounding ratio of 29 parts by mass with respect to 100 parts by mass of the mesogen diol described in formula (2). A liquid crystal polymer 3 according to Example 3 was produced in the same manner as in Example 1 except for the above.

(Production of mesogenic group-containing compound having active hydrogen group)
In a reaction vessel, BH6 (4230 g) as a mesogenic group-containing compound having an active hydrogen group, potassium hydroxide (19 g), and toluene (5320 ml) as a solvent are added and mixed. 9.9 equivalents were added to BH6, and the mixture was reacted at 120° C. for 2 hours under pressurized conditions (addition reaction). Then, oxalic acid (15 g) was added to the reaction vessel to stop the addition reaction, insoluble salts in the reaction solution were removed by suction filtration, and toluene in the reaction solution was removed by vacuum distillation. , a mesogenic group-containing compound (mesogen diol) having an active hydrogen group represented by the following formula (6) was obtained. The hydroxyl value of mesogen diol is 123.6. The mesogen diol shown in formula (6) is a representative one, and may include various structural isomers. n ^* in formula (6) is an average of 6.45.

(Comparative example 1)
To 100 parts by mass of the mesogen diol represented by formula (6) produced above, 17 parts by mass of 1,5-pentamethylene diisocyanate represented by the above formula (3) as an isocyanate compound was blended and stirred. The liquid crystal polymer 4 according to Comparative Example 1 was produced by mixing at 100° C. while stirring.

The evaluation items in Examples and the like were measured as follows.

<Method for measuring hydrogen bonding rate between liquid crystal polymers>
FT-IR (manufactured by PerkinElmer: Spectrum 100), by the ATR method, the absorbance (ABS-1) of the stretching vibration peak (around 1716 cm ^-1 ) of the carbonyl group of the hydrogen-bonded urethane bond, and The absorbance (ABS-2) of the stretching vibration peak (around 1703 cm ⁻¹ ) of the carbonyl group of the urethane bond that is not hydrogen-bonded was measured. Based on the measurement results, the hydrogen bonding rate was calculated according to the following formula.
[Hydrogen bond rate (%)] = 100 × (ABS-1) / ((ABS-1) + (ABS-2))
Table 1 shows the measurement results of the hydrogen bonding rate.

(Production of rubber compositions of Examples 1 to 3 and Comparative Example 1)
The liquid crystal polymers obtained in Examples 1 to 3 and Comparative Example 1 were mixed with a diene rubber (SBR, trade name: SL563, JSR Corporation) using a lab mixer (product name: Laboplastomill, manufactured by Toyo Seiki Seisakusho). made). In the first step, the compounding procedure is as follows: 100 parts by mass of SBR, 50 parts by mass of silica (trade name: NipSeal AQ, manufactured by Tosoh Silica), a silane coupling agent (bis (3-triethoxysilylpropyl) tetra Sulfide, trade name: Si69, manufactured by Evonik Deguza) 4 parts by mass, zinc oxide (trade name: type 1 zinc oxide, manufactured by Mitsui Mining & Smelting Co., Ltd.) 2 parts by mass, stearic acid (trade name: Lunax S-20, Kao) Co., Ltd.) and 2 parts by mass of an anti-aging agent (trade name: Nocrac 6C, manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) are added and kneaded at 160 ° C. Then, as the second step, the kneaded product 26 parts by mass of each liquid crystal polymer is added to and kneaded at 160 ° C., and in the third step, 1.4 parts by mass of sulfur (rubber powder sulfur 150 mesh, manufactured by Hosoi Chemical Industry Co., Ltd.) is added to the kneaded product, vulcanized Accelerator (trade name: Noccellar CZ (primary vulcanization accelerator), manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) 0.95 parts by mass, and vulcanization accelerator (trade name: Noccellar D (secondary vulcanization accelerator) (manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) was added and kneaded at 90° C., and rubber compositions of Examples 1 to 3 and Comparative Example 1 were obtained.

<Dynamic viscoelasticity measurement>
The rubber compositions of Examples 1 to 3 and the rubber composition of Comparative Example 1 were vulcanized by heating at 160° C. for 20 minutes, molded into a predetermined shape, and used as measurement samples. For each measurement sample, a dynamic viscoelasticity measuring device (product name "Fully automatic viscoelasticity analyzer VR-7110", manufactured by Ueshima Seisakusho Co., Ltd.) was used to measure the storage elastic modulus (E') and the loss elastic modulus (E"), The peak top value of tan δ was determined, and is shown in Table 2 as an index based on the peak top value of tan δ of Comparative Example 1 as 100. The measurement conditions are as follows.
Size of measurement sample: length 40 mm, width 3 mm, thickness 2 mm
Measurement mode: Tensile mode Measurement temperature: 0°C, 60°C
Frequency: 100Hz
Dynamic strain: 0.15%
Table 2 shows the results.

From the results in Table 2, the vulcanized rubbers of the rubber compositions of Examples 1 to 3 have greatly increased tan δ peak top values. Therefore, for example, in a pneumatic tire provided with a vulcanized rubber obtained by using the rubber composition as a raw material as a tread member, WET μ (coefficient of friction in WET) increases due to improvement in hysteresis friction, and WET It can be seen that the performance is improved.

Claims (4)

A liquid crystal polymer that is a reaction product of a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound, wherein the hydrogen bonding ratio between the polymers calculated using FT-IR (ATR method) is 50% or less. A liquid crystal polymer characterized by: 2. The liquid crystal polymer according to claim 1, wherein at least one of the mesogenic group-containing compound and the isocyanate compound is a branched compound having a branched structure. A rubber composition comprising the liquid crystal polymer according to claim 1 or 2 and a diene rubber. A pneumatic tire comprising a vulcanized rubber obtained using the rubber composition according to claim 3 as a raw material.