Hydrogenated branched conjugated diene copolymer, rubber composition and pneumatic tire

Abstract

A pneumatic tire produced by processing a rubber composition including a hydrogenated branched conjugated diene copolymer produced by copolymerizing a branched conjugated diene compound and a vinyl compound to form a branched conjugated diene copolymer and hydrogenating the branched conjugated diene copolymer. The branched conjugated diene compound is represented by formula (1), ##STR00001##
where R.sup.1 is an aliphatic hydrocarbon having 6 to 11 carbon atoms, the vinyl compound is represented by formula (3), ##STR00002##
where R.sup.4 is a hydrogen atom, an aliphatic hydrocarbon group having 1 to 3 carbon atoms, an alicyclic hydrocarbon group having 3 to 8 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms.

Claims

1. A pneumatic tire produced by processing a rubber composition comprising a copolymer of a hydrogenated branched conjugated diene copolymer in a liquid form, a rubber component consisting of a styrene-butadiene rubber, and a carbon black, wherein the hydrogenated branched conjugated diene copolymer is produced by copolymerizing a branched conjugated diene compound and a vinyl compound to form a branched conjugated diene copolymer and hydrogenating the branched conjugated diene copolymer, a copolymerization ratio of the branched conjugated diene compound is 1 to 99% by weight, a copolymerization ratio of the vinyl compound is 99 to 1% by weight, the branched conjugated diene compound is myrcene and farnesene, the vinyl compound is styrene, and the rubber composition includes 20 to 100 parts by weight of the hydrogenated branched conjugated diene copolymer and 1 part by weight or more of the carbon black based on 100 parts by weight of the rubber component consisting of the styrene-butadiene rubber.

2. The pneumatic tire of claim 1, wherein a Mooney viscosity ML.sub.1+4 (130 C.) of the rubber composition to which the hydrogenated branched conjugated diene copolymer is blended is lower compared with a Mooney viscosity ML.sub.1+4 (130 C.) of a rubber composition comprising a polymer having the same weight-average molecular weight as the branched conjugated diene copolymer and prepared by replacing the branched conjugated diene compound by at least one of 1,3-butadiene and isoprene.

3. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer has a weight-average molecular weight of 2,000 to 200,000.

4. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer has a hydrogenation ratio of 10 to 90%.

5. The pneumatic tire of claim 1, wherein the copolymerization ratio of the vinyl compound is 40% by weight or more.

6. The pneumatic tire of claim 4, wherein the copolymerization ratio of the vinyl compound is 40% by weight or more.

7. The pneumatic tire of claim 3, wherein the hydrogenated branched conjugated diene copolymer has a hydrogenation ratio of 10 to 90%.

8. The pneumatic tire of claim 1, wherein the processing comprises forming a tread comprising the rubber composition and vulcanizing an unvulcanized tire comprising the tread.

9. The pneumatic tire of claim 3, wherein the copolymerization ratio of the vinyl compound is 40% by weight or more.

10. The pneumatic tire of claim 1, wherein the rubber composition includes 30 to 70 parts by weight of the hydrogenated branched conjugated diene copolymer based on 100 parts by weight of the rubber component consisting of the styrene-butadiene rubber.

11. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer has a weight-average molecular weight of 3,000 to 100,000.

12. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer has a hydrogenation ratio of 30 to 70%.

13. The pneumatic tire of claim 3, wherein the processing comprises forming a tread comprising the rubber composition and vulcanizing an unvulcanized tire comprising the tread.

14. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer has a glass transition temperature of 80 C. to 110 C.

15. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer is produced by copolymerizing a conjugated diene compound, the branched conjugated diene compound and the vinyl compound to form the branched conjugated diene copolymer and hydrogenating the branched conjugated diene copolymer, the conjugated diene compound is at least one of 1,3-butadiene and isoprene, a copolymerization ratio of the conjugated diene compound is greater than 0% by weight and less than 99% by weight, and the copolymerization ratio of the vinyl compound is less than 99% by weight.

16. The pneumatic tire of claim 1, wherein the hydrogenated branched conjugated diene copolymer is produced by copolymerizing a conjugated diene compound, the branched conjugated diene compound and the vinyl compound to form the branched conjugated diene copolymer and hydrogenating the branched conjugated diene copolymer, the conjugated diene compound is at least one of 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene, a copolymerization ratio of the conjugated diene compound is greater than 0% by weight and less than 99% by weight, and the copolymerization ratio of the vinyl compound is less than 99% by weight.

17. The pneumatic tire of claim 3, wherein the rubber composition includes 30 to 70 parts by weight of the hydrogenated branched conjugated diene copolymer based on 100 parts by weight of the rubber component consisting of the styrene-butadiene rubber.

18. The pneumatic tire of claim 3, wherein the hydrogenated branched conjugated diene copolymer has a hydrogenation ratio of 30 to 70%.

19. The pneumatic tire of claim 3; wherein the hydrogenated branched conjugated diene copolymer has a glass transition temperature of 80 C. to 110 C.

20. The pneumatic tire of claim 4, wherein the processing comprises forming a tread comprising the rubber composition and vulcanizing an unvulcanized tire comprising the tread.

21. The pneumatic tire of claim 4, wherein the rubber composition includes 30 to 70 parts by weight of the hydrogenated branched conjugated diene copolymer based on 100 parts by weight of the rubber component consisting of the styrene-butadiene rubber.

Description

EXAMPLE

(1) The present invention is described by means of Examples, but is not limited to the Examples.

(2) Various chemicals used for synthesis of copolymers and preparation of rubber compositions in Examples and Comparative Examples are collectively shown below. Each chemical was subjected to purification by a usual method, if necessary.

(3) <Various Chemicals Used for Synthesis of Copolymers>

(4) Hexane: Anhydrous hexane available from Kanto Chemical Industry Co., Ltd.

(5) Isopropanol: Isopropanol available from Kanto Chemical Industry Co., Ltd.

(6) THF: Tetrahydrofuran available from Kanto Chemical Industry Co., Ltd.

(7) Myrcene: -myrcene available from Wako Pure Chemical Industries, Ltd.

(8) Farnesene: (E)--Farnesene available from Nippon Terpene Chemicals, Inc. (reagent)

(9) Isoprene: Isoprene available from Wako Pure Chemical Industries, Ltd. Butadiene: 1,3-Butadiene available from Takachiho Chemical Industrial Co., Ltd.

(10) Styrene: Styrene available from Wako Pure Chemical Industries, Ltd.

(11) <Various Chemicals Used for Preparation of Rubber Compositions>

(12) Copolymer: Those synthesized in accordance with the description of this specification

(13) SBR: Tufdene 4850 (S-SBR; Oil is contained in an amount of 50% based on 100 g of SBR solid content; Styrene content: 39% by weight) available from Asahi Kasei Chemicals Corporation

(14) Carbon black: SHOBLACK N220 (Nitrogen adsorption specific surface area (N.sub.2SA): 125 m.sup.2/g) available from Cabot Japan K.K.

(15) Antioxidant: NOCRAC 6C (N-1,3-dimethylbutyl-N-phenyl-p-phenylenediamine) available from Ouchi Shinko Chemical Industrial Co., Ltd.

(16) Stearic acid: Stearic acid available from NOF CORPORATION Zinc oxide: Zinc White Grade 1 available from Mitsui Mining & Smelting Co., Ltd.

(17) Sulfur: Powdered sulfur available from Tsurumi Chemical Industry Co., Ltd.

(18) Vulcanization accelerator: NOCCELER CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) available from Ouchi Shinko Chemical Industrial Co., Ltd.

(19) (A) Hydrogenated Myrcene Copolymers

(20) 1. Synthesis of Copolymers

Preparation Example 1-1 (Synthesis of Copolymer 1)

(21) Into a 3-liter pressure resistant stainless steel vessel having been subjected to drying and replacement with nitrogen, 2000 ml of hexane, 110 g of butadiene, 90 g of styrene, and 0.22 mmol of TMEDA were poured, and further, 35 mmol of n-butyllithium (n-BuLi) was added thereto, followed by 5-hour polymerization reaction at 50 C. After the lapse of five hours, 1.15 ml of 1M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 200 g of Copolymer 1 was obtained. The degree of polymerization (percentage of dry weight/charged amount) was nearly 100%.

Preparation Example 2-1 (Synthesis of Copolymer 2)

(22) Into a 1-liter pressure resistant stainless steel vessel, 200 g of Copolymer 1 obtained above, 300 g of THF and 10 g of 10% palladium carbon were poured, and replacement with nitrogen was carried out, followed by replacing with hydrogen to bring the inside pressure to 5.0 kgf/cm.sup.2 and then reacting at 80 C. After the termination of the reaction, the reaction solution was filtrated to remove the palladium carbon, and the filtrate was subjected to air drying overnight and further drying under reduced pressure for two days. Thus, 200 g of Copolymer 2 was obtained. The degree of hydrogenation was 50%.

Preparation Example 3-1 (Synthesis of Copolymer 3)

(23) Into a 1-liter glass vessel having been subjected to drying and replacement with nitrogen, 500 ml of hexane, 46 g of THF and 45 mmol of n-butyllithium (n-BuLi) were poured, followed by polymerization reaction while adding a mixture of 100 ml of hexane, 150 g of isoprene and 125 g of styrene dropwise into the reaction vessel over two hours. Immediately after completion of the addition of the mixture dropwise, 20 ml of 2M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 275 g of Copolymer 3 was obtained. The degree of polymerization was nearly 100%.

Preparation Example 4-1 (Synthesis of Copolymer 4)

(24) 200 Grams of Copolymer 3 was subjected to processing in the same manner as in Preparation Example 2-1 to obtain 200 g of Copolymer 4.

Preparation Example 5-1 (Synthesis of Copolymer 5)

(25) Into a 1-liter glass vessel having been subjected to drying and replacement with nitrogen, 500 ml of hexane, 46 g of THF and 40 mmol of n-butyllithium (n-BuLi) were poured, followed by polymerization reaction while adding a mixture of 100 ml of hexane, 150 g of myrcene and 125 g of styrene dropwise into the reaction vessel over two hours. Immediately after completion of the addition of the mixture dropwise, 10 ml of 2M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 275 g of Copolymer 5 was obtained. The degree of polymerization was nearly 100%.

Preparation Example 6-1 (Synthesis of Copolymer 6)

(26) 200 Grams of Copolymer 5 was subjected to processing in the same manner as in Preparation Example 2-1 to obtain 200 g of Copolymer 6.

Preparation Example 7-1 (Synthesis of Copolymer 7)

(27) Into a 1-liter pressure resistant stainless steel vessel having been subjected to drying and replacement with nitrogen, 500 ml of hexane, 46 g of THF and 40 mmol of n-butyllithium (n-BuLi) were poured, followed by polymerization reaction while adding a mixture of 100 ml of hexane, 95 g of butadiene, 55 g of myrcene and 125 g of styrene dropwise into the reaction vessel over two hours. Immediately after completion of the addition of the mixture dropwise, 10 ml of 2M isopropanol/hexane solution was added dropwise to terminate the reaction. The obtained reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 275 g of Copolymer 7 was obtained. The degree of polymerization was nearly 100%.

Preparation Example 8-1 (Synthesis of Copolymer 8)

(28) 200 Grams of Copolymer 7 was subjected to processing in the same manner as in Preparation Example 2-1 to obtain 200 g of Copolymer 8.

Preparation Example 9-1 (Synthesis of Copolymer 9)

(29) Processing was carried out in the same manner as in Preparation Example 7-1 except that 95 g of isoprene was used instead of 95 g of butadiene to obtain 275 g of Copolymer 9. The degree of polymerization was nearly 100%.

Preparation Example 10-1 (Synthesis of Copolymer 10)

(30) 200 Grams of Copolymer 9 was subjected to processing in the same manner as in Preparation Example 2-1 to obtain 200 g of Copolymer 8.

(31) 2. Preparation of Rubber Compositions and Tires

Preparation Example 1-2

(32) (1) Copolymer 1 obtained above and the above-mentioned various chemicals for preparation of a rubber composition (except sulfur and vulcanization accelerator) were kneaded at 150 C. for five minutes in a Banbury mixer in accordance with the formulation shown in Table 2, and a kneaded product was obtained. Sulfur and vulcanization accelerator were added to the kneaded product, followed by 12-minute kneading at 170 C. using an open roll to obtain Unvulcanized Rubber Composition 1.
(2) Unvulcanized Rubber Composition obtained in (1) above was subjected to extrusion processing to a shape of a tire tread and molding with other members on a tire molding machine, thus forming an unvulcanized tire. This unvulcanized tire was subjected to 20-minute press-vulcanization at 170 C. in a vulcanizer to obtain a tire. Then, by introducing air in the tire, Pneumatic Tire 1 was obtained.

Preparation Examples 2-2 to 10-2

(33) The respective starting compounds were subjected to processing in the same manner as in Preparation Example 1-2 in accordance with the formulation shown in Table 2 to obtain the respective Unvulcanized Rubber Compositions 2 to 10 and Pneumatic Tires 2 to 10.

(34) 3. Results

(35) <Copolymer>

(36) With respect to the obtained Copolymers 1 to 10, weight-average molecular weight Mw, number-average molecular weight Mn, glass transition temperature Tg, Mooney viscosity and copolymerization ratio (1) were measured by the following methods. The results are shown in Table 1.

(37) (Measurement of Weight-Average Molecular Weight Mw, Number-Average Molecular Weight Mn)

(38) Mw and Mn were measured with an apparatus GPC-8000 Series available from TOSO CORPORATION and a differential refractometer as a detector, and were converted based on standard polystyrene.

(39) (Measurement of Glass Transition Temperature (Tg))

(40) With respect to each copolymer, measurement was carried out using a differential scanning calorimeter (DSC) at a heat-up rate of 10 C./min from an initial temperature of 150 C. to a final temperature of 150 C. to calculate Tg.

(41) (Processability)

(42) With respect to each copolymer, a Mooney viscosity ML.sub.1+4 (130 C.) thereof was measured using a Mooney viscosity tester in accordance with JIS K 6300 Test Method of Unvulcanized Rubber. After pre-heating to 130 C. for one minute, under this temperature condition, a large rotor was rotated and after a lapse of four minutes, the Mooney viscosity ML.sub.1+4 (130 C.) was measured. It is indicated that the smaller the Mooney viscosity is, the better the processability is.

(43) (Copolymerization Ratio (1) of Branched Conjugated Diene Compound (1))

(44) The copolymerization ratio (1) (% by weight) was measured by a usual method using a pyrolysis gas chromatography (PGC). Namely, a calibration curve of a purified branched conjugated diene compound (1) was prepared, and % by weight of the branched conjugated diene compound (1) in the copolymer was calculated using an area ratio of a pyrolyzate derived from the branched conjugated diene compound (1) which was obtained by PGC. In the pyrolysis chromatography, a system comprising a gas chromatograph mass spectrometer GCMS-QP5050A available from Shimadzu Corporation and a pyrolyzer JHP-330 available from Japan Analytical Industry Co., Ltd. was used.

(45) TABLE-US-00001 TABLE 1 Preparation Example 1-1 2-1 3-1 4-1 5-1 6-1 7-1 8-1 9-1 10-1 Copolymer 1 2 3 4 5 6 7 8 9 10 (% by weight) Myrcene 0 0 0 0 55 55 20 20 20 20 Butadiene 55 55 0 0 0 0 35 35 0 0 Isoprene 0 0 55 55 0 0 0 0 35 35 Styrene 45 45 45 45 45 45 45 45 45 45 Hydrogenation ratio (%) 0 50 0 50 0 50 0 50 0 50 Mw 5000 5000 5113 4900 5320 5400 5200 5200 5369 5420 Mn 4800 4900 4789 4800 5120 5332 4905 4720 4880 4920 Mw/Mn 1.0 1.1 1.1 1.0 1.0 1.0 1.0 1.1 1.1 1.1 Tg ( C.) 13.4 14.0 5.1 6.0 20.6 19.0 15.1 16.2 10.1 9.2 Mooney viscosity 43 47 52 59 32 38 37 39 36 40 ML.sub.1+4 (130 C.) Copolymerization ratio (l) 55.0 55.0 20.0 20.0 20.0 20.0 (% by weight) In the Table, indicates that there was no detection. (hereinafter the same)

(46) <Rubber Compositions and Tires>

(47) The following tests were carried out using Unvulcanized Rubber Compositions 1 to 10 and Pneumatic Tires 1 to 10 obtained above. The results are shown in Table 2.

(48) (Processability)

(49) Test pieces of a given size were prepared from each of the above unvulcanized rubber compositions, and a Mooney viscosity ML.sub.1+4 (130 C.) thereof was measured using a Mooney viscosity tester in accordance with JIS K 6300 Test Method of Unvulcanized Rubber. The test piece was pre-heated to 130 C. for one minute and under this temperature condition, a large rotor was rotated and after a lapse of four minutes, the Mooney viscosity ML.sub.1+4 (130 C.) was measured. It is indicated that the smaller the Mooney viscosity is, the better the processability is.

(50) (Grip Performance)

(51) In-vehicle running was carried out on a test course of an asphalt road surface using each pneumatic tire obtained above. A test driver evaluated stability control at steering in ten levels. It is indicated that the larger the value is, the more superior the grip performance is.

(52) (Abrasion Resistance)

(53) Test running was carried out 20 rounds of a test course using each pneumatic tire. A depth of a groove of the tire before and after the running was measured, and assuming that the abrasion resistance index of Pneumatic Tire 1 is 100, the depth of a groove of each pneumatic tire is represented by an index. It is indicated that the larger the value is, the higher and the more superior the abrasion resistance is.

(54) (Bleed Resistance)

(55) A surface of each pneumatic tire was observed and a degree of bleeding of an oily substance was evaluated with naked eyes.

(56) : No bleeding

(57) : Slightly bleeding

(58) X: Vigorously bleeding

(59) TABLE-US-00002 TABLE 2 Preparation Example 1-2 2-2 3-2 4-2 5-2 6-2 7-2 8-2 9-2 10-2 Blending amount (part by weight) SBR 150 150 150 150 150 150 150 150 150 150 Copolymer 1 50 Copolymer 2 50 Copolymer 3 50 Copolymer 4 50 Copolymer 5 50 Copolymer 6 50 Copolymer 7 50 Copolymer 8 50 Copolymer 9 50 Copolymer 10 50 Carbon black 100 100 100 100 100 100 100 100 100 100 Antioxidant 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 Zinc oxide 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 Sulfur 1 1 1 1 1 1 1 1 1 1 Vulcanization accelerator 4 4 4 4 4 4 4 4 4 4 Results of evaluation Mooney viscosity ML.sub.1+4 49.7 49.6 55.2 56.2 42.0 43.3 44.5 41.9 42.6 42.1 (130 C.) Grip performance 5 6 6 7 8 10 8 9 8 10 Abrasion resistance 100 109 101 110 105 104 107 124 118 128 Bleed resistance

(60) As shown in Table 2, in Preparation Examples 5 to 10 in which the myrcene copolymer was blended, the Mooney viscosity is low and processability is improved. As shown, especially in Preparation Examples 6, 8 and 10 in which the hydrogenated myrcene copolymer was blended, processability is good, and also grip performance, abrasion resistance and bleed resistance are good.

(61) (B) Hydrogenated Farnesene Copolymer

(62) 1. Synthesis of Copolymer

Preparation Example 11-1 (Synthesis of Copolymer 11)

(63) Into a 3-liter pressure resistant stainless steel vessel having been subjected to drying and replacement with nitrogen, 2000 ml of hexane, 110 g of butadiene, 90 g of styrene, and 0.22 mmol of TMEDA were poured, and further, 35 mmol of n-butyllithium (n-BuLi) was added thereto, followed by 5-hour polymerization reaction at 50 C. After the lapse of five hours, 1.15 ml of 1M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 200 g of Copolymer 11 was obtained. The degree of polymerization (percentage of dry weight/charged amount) was nearly 100%.

Preparation Example 12-1 (Synthesis of Copolymer 12)

(64) Into a 1-liter pressure resistant stainless steel vessel, 200 g of Copolymer 11 obtained above, 300 g of THF and 10 g of 10% palladium carbon were poured, and replacement with nitrogen was carried out, followed by replacing with hydrogen to bring the inside pressure to 5.0 kgf/cm.sup.2 and then reacting at 80 C. After the termination of the reaction, the reaction solution was filtrated to remove the palladium carbon, and the filtrate was subjected to air drying overnight and further drying under reduced pressure for two days. Thus, 200 g of Copolymer 12 was obtained. The degree of hydrogenation was 50%.

Preparation Example 13-1 (Synthesis of Copolymer 13)

(65) Into a 1-liter glass vessel having been subjected to drying and replacement with nitrogen, 500 ml of hexane, 46 g of THF and 45 mmol of n-butyllithium (n-BuLi) were poured, followed by polymerization reaction while adding a mixture of 100 ml of hexane, 150 g of isoprene and 125 g of styrene dropwise into the reaction vessel over two hours. Immediately after completion of the addition of the mixture dropwise, 20 ml of 2M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 275 g of Copolymer 13 was obtained. The degree of polymerization was nearly 100%.

Preparation Example 14-1 (Synthesis of Copolymer 14)

(66) 200 Grams of Copolymer 13 were subjected to processing in the same manner as in Preparation Example 12-1 to obtain 200 g of Copolymer 14.

Preparation Example 15-1 (Synthesis of Copolymer 15)

(67) Into a 1-liter glass vessel having been subjected to drying and replacement with nitrogen, 500 ml of hexane, 46 g of THF and 40 mmol of n-butyllithium (n-BuLi) were poured, followed by polymerization reaction while adding a mixture of 100 ml of hexane, 150 g of farnesene and 125 g of styrene dropwise into the reaction vessel over two hours. Immediately after completion of the addition of the mixture dropwise, 10 ml of 2M isopropanol/hexane solution was added dropwise to terminate the reaction. After cooling, the reaction solution was subjected to air-drying overnight and then further drying under reduced pressure for two days. Thus, 275 g of Copolymer 15 was obtained. The degree of polymerization was nearly 100%.

Preparation Example 16-1 (Synthesis of Copolymer 16)

(68) 200 Grams of Copolymer 15 was subjected to processing in the same manner as in Preparation Example 12-1 to obtain 200 g of Copolymer 16.

Preparation Example 17-1 (Synthesis of Copolymer 17)

(69) Processing was carried out in the same manner as in Preparation Example 15-1 except that 55 g of farnesene and 95 g of butadiene were used instead of 150 g of farnesene to obtain 275 g of Copolymer 17. The degree of polymerization was nearly 100%.

Preparation Example 18-1 (Synthesis of Copolymer 18)

(70) 200 Grams of Copolymer 17 was subjected to processing in the same manner as in Preparation Example 12-1 to obtain 200 g of Copolymer 18.

Preparation Example 19-1 (Synthesis of Copolymer 9)

(71) Processing was carried out in the same manner as in Preparation Example 17-1 except that isoprene was used instead of butadiene to obtain 275 g of Copolymer 19. The degree of polymerization was nearly 100%.

Preparation Example 20-1 (Synthesis of Copolymer 20)

(72) 200 Grams of Copolymer 19 was subjected to processing in the same manner as in Preparation Example 12-1 to obtain 200 g of Copolymer 20.

(73) 2. Preparation of Rubber Compositions and Tires

Preparation Example 11-2

(74) (1) Copolymer 11 obtained above and the above-mentioned various chemicals for preparation of a rubber composition (except sulfur and vulcanization accelerator) were kneaded at 150 C. for five minutes in a Banbury mixer in accordance with the formulation shown in Table 4, and a kneaded product was obtained. Sulfur and vulcanization accelerator were added to the kneaded product, followed by 12-minute kneading at 170 C. using an open roll to obtain Unvulcanized Rubber Composition 11.
(2) Unvulcanized Rubber Composition obtained in (1) above was subjected to extrusion processing to a shape of a tire tread and molding with other members on a tire molding machine, thus forming an unvulcanized tire. This unvulcanized tire was subjected to 20-minute press-vulcanization at 170 C. in a vulcanizer to obtain a tire. Then, by introducing air in the tire, Pneumatic Tire 11 was obtained.

Preparation Examples 12-2 to 20-2

(75) The respective starting compounds were subjected to processing in the same manner as in Preparation Example 11-2 in accordance with the formulation shown in Table 4 to obtain the respective Unvulcanized Rubber Compositions 12 to 20 and Pneumatic Tires 12 to 20.

(76) 3. Results

(77) <Copolymer>

(78) With respect to the obtained Copolymers 11 to 20, weight-average molecular weight Mw, number-average molecular weight Mn, glass transition temperature Tg, Mooney viscosity and copolymerization ratio (1) were measured by the following methods. The results are shown in Table 3.

(79) (Measurement of Weight-Average Molecular Weight Mw, Number-Average Molecular Weight Mn)

(80) Mw and Mn were measured with an apparatus GPC-8000 Series available from TOSO CORPORATION and a differential refractometer as a detector, and were converted based on standard polystyrene.

(81) (Measurement of Glass Transition Temperature (Tg))

(82) With respect to each copolymer, measurement was carried out using a differential scanning calorimeter (DSC) at a heat-up rate of 10 C./min from an initial temperature of 150 C. to a final temperature of 150 C. to calculate Tg.

(83) (Processability)

(84) With respect to each copolymer, a Mooney viscosity ML.sub.1+4 (130 C.) thereof was measured using a Mooney viscosity tester in accordance with JIS K 6300 Test Method of Unvulcanized Rubber. After pre-heating to 130 C. for one minute, under this temperature condition, a large rotor was rotated and after a lapse of four minutes, the Mooney viscosity ML.sub.1+4 (130 C.) was measured. It is indicated that the smaller the Mooney viscosity is, the better the processability is.

(85) (Copolymerization Ratio (1) of Branched Conjugated Diene Compound (1))

(86) The copolymerization ratio (1) (% by weight) was measured by a usual method using a pyrolysis gas chromatography (PGC). Namely, a calibration curve of a purified branched conjugated diene compound (1) was prepared, and % by weight of the branched conjugated diene compound (1) in the copolymer was calculated using an area ratio of a pyrolyzate derived from the branched conjugated diene compound (1) which was obtained by PGC. In the pyrolysis chromatography, a system comprising a gas chromatograph mass spectrometer GCMS-QP5050A available from Shimadzu Corporation and a pyrolyzer JHP-330 available from Japan Analytical Industry Co., Ltd. was used.

(87) TABLE-US-00003 TABLE 3 Preparation Example 11-1 12-1 13-1 14-1 15-1 16-1 17-1 18-1 19-1 20-1 Copolymer 11 12 13 14 15 16 17 18 19 20 (% by weight) Farnesene 0 0 0 0 55 55 20 20 20 20 Butadiene 55 55 0 0 0 0 35 35 0 0 Isoprene 0 0 55 55 0 0 0 0 35 35 Styrene 45 45 45 45 45 45 45 45 45 45 Hydrogenation ratio (%) 0 50 0 50 0 50 0 50 0 50 Mw 5000 5000 5113 4900 5420 5332 5221 5224 5212 5201 Mn 4800 4900 4789 4800 5210 5320 5198 5187 4742 4753 Mw/Mn 1.0 1.1 1.1 1.0 1.0 1.0 1.0 1.0 1.1 1.1 Tg ( C.) 13.4 14.0 5.1 6.0 21.2 18.8 15.2 14.2 12.1 11.8 Mooney viscosity 43 47 52 59 17 21 23 25 24 26 ML.sub.1+4 (130 C.) Copolymerization ratio (l) 55.0 55.0 20.0 20.0 20.0 20.0 (% by weight)

(88) <Rubber Compositions and Tires>

(89) The following tests were carried out using Unvulcanized Rubber Compositions 11 to 20 and Pneumatic Tires 11 to 20 obtained above. The results are shown in Table 4.

(90) (Processability)

(91) Test pieces of a given size were prepared from each of the above unvulcanized rubber compositions, and a Mooney viscosity ML.sub.1+4 (130 C.) thereof was measured using a Mooney viscosity tester in accordance with JIS K 6300 Test Method of Unvulcanized Rubber. The test piece was pre-heated to 130 C. for one minute and under this temperature condition, a large rotor was rotated and after a lapse of four minutes, the Mooney viscosity ML.sub.1+4 (130 C.) was measured. It is indicated that the smaller the Mooney viscosity is, the better the processability is.

(92) (Grip Performance)

(93) In-vehicle running was carried out on a test course of an asphalt road surface using each pneumatic tire obtained above. A test driver evaluated stability control at steering in ten levels. It is indicated that the larger the value is, the more superior the grip performance is.

(94) (Abrasion Resistance)

(95) Test running was carried out 20 rounds of a test course using each pneumatic tire. A depth of a groove of the tire before and after the running was measured, and assuming that the abrasion resistance index of Pneumatic Tire 11 is 100, the depth of a groove of each pneumatic tire is represented by an index. It is indicated that the larger the value is, the higher and the more superior the abrasion resistance is.

(96) (Bleed Resistance)

(97) A surface of each pneumatic tire was observed and a degree of bleeding of an oily substance was evaluated with naked eyes.

(98) : No bleeding

(99) : Slightly bleeding

(100) X: Vigorously bleeding

(101) TABLE-US-00004 TABLE 4 Preparation Example 11-2 12-2 13-2 14-2 15-2 16-2 17-2 18-2 19-2 20-2 Blending amount (part by weight) SBR 150 150 150 150 150 150 150 150 150 150 Copolymer 11 50 Copolymer 12 50 Copolymer 13 50 Copolymer 14 50 Copolymer 15 50 Copolymer 16 50 Copolymer 17 50 Copolymer 18 50 Copolymer 19 50 Copolymer 20 50 Carbon black 100 100 100 100 100 100 100 100 100 100 Antioxidant 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 Zinc oxide 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 1.4 Sulfur 1 1 1 1 1 1 1 1 1 1 Vulcanization accelerator 4 4 4 4 4 4 4 4 4 4 Results of evaluation Mooney viscosity ML.sub.1+10 49.7 49.6 55.2 56.2 42.0 38.2 45.2 47.5 49.6 50.1 (130 C.) Grip performance 5 6 6 7 8 9 7 8 8 8 Abrasion resistance 100 109 101 110 112 134 112 120 117 128 Bleed resistance

(102) As shown in Table 4, in any of Preparation Examples 15 to 20 in which the farnesene copolymer was blended, the Mooney viscosity is low and processability is improved compared with polymers in which the farnesene copolymer was replaced with butadiene or isoprene being the conjugated diene compound. As shown, especially in Preparation Examples 16, 18 and 20 in which the hydrogenated farnesene copolymer was blended, processability is good, and also grip performance, abrasion resistance and bleed resistance are good.

INDUSTRIAL APPLICABILITY

(103) The present invention can provide a novel branched conjugated copolymer or hydrogenated branched conjugated copolymer being useful for improving processability as a rubber component for a tire, and by using these copolymers, can provide a rubber composition for a tire enhancing both of abrasion resistance and grip performance to a high level and exhibiting excellent processability. Further, in the case of using the hydrogenated branched conjugated copolymer, the rubber composition for a tire inhibiting generation of bleeding can be provided.