Method for Preparing Modified Conjugated Diene-Based Polymer

Abstract

The present invention relates to a method for preparing a modified conjugated diene-based polymer having excellent physical properties such as tensile properties and viscoelasticity properties with a high modification ratio.

Claims

1. A method for preparing a modified conjugated diene-based polymer, the method comprising: polymerizing a conjugated diene-based monomer in the presence of a catalyst composition comprising a neodymium compound, a first alkylating agent, a second alkylating agent and a halide in a hydrocarbon solvent to prepare an active polymer; and reacting or coupling the active polymer with a modifier, wherein a molar ratio of the neodymium compound to the second alkylating agent is 1:20 to 1:35, and the polymerization is performed at a temperature of 30 to 65° C.

2. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the polymerization is performed at a temperature of 40 to 65° C. for 15 minutes to 3 hours.

3. The method for preparing a modified conjugated diene-based polymer according to claim 1, further comprising: mixing the neodymium compound, the first alkylating agent, the second alkylating agent and the halide at −30 to −20° C. to obtain a mixture; and standing the mixture at −30 to −20° C. for 24 to 36 hours to prepare the catalyst composition, prior to preparing the active polymer.

4. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the catalyst composition comprises the neodymium compound, the first alkylating agent, the second alkylating agent and the halide at a molar ratio of 1:(50 to 200):(20 to 35):(2 to 5).

5. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the catalyst composition comprises the neodymium compound in an amount of 0.01 to 0.50 mmol based on 100 g of the conjugated diene-based monomer.

6. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the neodymium compound is a compound represented by the following Formula 1: ##STR00005## in Formula 1, R.sub.a to R.sub.c are each independently hydrogen or an alkyl group having 1 to 12 carbon atoms, where all R.sub.a to R.sub.c are not hydrogen at the same time.

7. The method for preparing a modified conjugated diene-based polymer according to claim 6, wherein R.sub.a is an alkyl group having 4 to 12 carbon atoms, and R.sub.b and R.sub.c are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms.

8. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the neodymium compound is one or more selected from the group consisting of Nd(neodecanoate).sub.3, Nd(2-ethylhexanoate).sub.3, Nd(2,2-dimethyl decanoate).sub.3, Nd(2,2-diethyl decanoate).sub.3, Nd(2,2-dipropyl decanoate).sub.3, Nd(2,2-dibutyl decanoate).sub.3, Nd(2,2-dihexyl decanoate).sub.3, Nd(2,2-dioctyl decanoate).sub.3, Nd(2-ethyl-2-propyl decanoate).sub.3, Nd(2-ethyl-2-butyl decanoate).sub.3, Nd(2-ethyl-2-hexyl decanoate).sub.3, Nd(2-propyl-2-butyl decanoate).sub.3, Nd(2-propyl-2-hexyl decanoate).sub.3, Nd(2-propyl-2-isopropyl decanoate).sub.3, Nd(2-butyl-2-hexyl decanoate).sub.3, Nd(2-hexyl-2-octyl decanoate).sub.3, Nd(2,2-diethyl octanoate).sub.3, Nd(2,2-dipropyl octanoate).sub.3, Nd(2,2-dibutyl octanoate).sub.3, Nd(2,2-dihexyl octanoate).sub.3, Nd(2-ethyl-2-propyl octanoate).sub.3, Nd(2-ethyl-2-hexyl octanoate).sub.3, Nd(2,2-diethyl nonanoate).sub.3, Nd(2,2-dipropyl nonanoate).sub.3, Nd(2,2-dibutyl nonanoate).sub.3, Nd(2,2-dihexyl nonanoate).sub.3, Nd(2-ethyl-2-propyl nonanoate).sub.3, and Nd(2-ethyl-2-hexyl nonanoate)3.

9. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the catalyst composition comprises the first alkylating agent in an amount of 60 to 150 mol based on 1 mol of the neodymium compound.

10. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the first alkylating agent is one or more selected from the group consisting of methylaluminoxane, modified methylaluminoxane, ethylaluminoxane, n-propylaluminoxane, isopropylaluminoxane, butylaluminoxane, isobutylaluminoxane, n-pentylaluminoxane, neopentylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane, 2-ethylhexylaluminoxane, cylcohexylaluminoxane, 1-methylcyclopentylaluminoxane, phenylaluminoxane, and 2,6-dimethylphenylaluminoxane.

11. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the first alkylating agent is methylaluminoxane, modified methylaluminoxane or a mixture thereof.

12. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the second alkylating agent is one or more selected from the group consisting of diethylaluminum hydride, di-n-propylaluminum hydride, diisopropylaluminum hydride, di-n-butylaluminum hydride, diisobutylaluminum hydride, di-n-octylaluminum hydride, diphenylaluminum hydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride, phenylethylaluminum hydride, phenyl-n-propylaluminum hydride, phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride, phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride, p-tolylethylaluminum hydride, p-tolyl-n-propylaluminum hydride, p-tolylisopropylaluminum hydride, p-tolyl-n-butylaluminum hydride, p-tolylisobutylaluminum hydride, p-tolyl-n-octylaluminum hydride, benzylethylaluminum hydride, benzyl-n-propylaluminum hydride, benzylisopropylaluminum hydride, benzyl-n-butylaluminum hydride, benzylisobutylaluminum hydride, and benzyl-n-octylaluminum hydride, ethylaluminum dihydride, n-propylaluminum dihydride, isopropylaluminum dihydride, n-butylaluminum dihydride, isobutylaluminum dihydride, and n-octylaluminum dihydride.

13. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the second alkylating agent is one or more selected from the group consisting of diethylaluminum hydride, di-n-propylaluminum hydride, diisopropylaluminum hydride, di-n-butylaluminum hydride and diisobutylaluminum hydride.

14. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the catalyst composition comprises the halide in an amount offs 2.1 to 3.0 mol based on 1 mol of the neodymium compound.

15. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the halide is one or more selected from the group consisting of elemental halogen, an interhalogen compound, hydrogen halide, an organic halide, a non-metal halide, a metal halide, and an organic metal halide.

16. The method for preparing a modified conjugated diene-based polymer according to claim 1, wherein the halide is one or more selected from the group consisting of dimethylaluminum chloride, diethylaluminum chloride, methylaluminum dichloride, ethylaluminum dichloride, methylaluminum sesquichloride, ethylaluminum sesquichloride and isobutylaluminum sesquichloride.

Description

EXAMPLES

[0143] Hereinafter, the present invention will be described in more detail according to examples. However, the following examples are merely presented to exemplify the present invention, and the scope of the present invention is not limited thereto.

[0144] [Preparation of Modifier]

[0145] To a solution in which 2 g of ethyl piperidine-4-carboxylate was dissolved in dichloromethane (CH.sub.2Cl.sub.2), 1.77 ml of triethylamine (Et.sub.3N) and 1.62 ml of trimethylsilyl chloride (TMSC1) were added at 0° C., and the mixture thus obtained was stirred at 0° C. for 5 hours. Then, a solvent in the solution obtained was evaporated under a reduced pressure, and the resultant residue was redissolved in hexane and repeatedly filtered with hexane twice. The raw material thus filtered was separated through distillation under a reduced pressure to obtain ethyl 1-(trimethylsilyl)piperidine-4-carboxylate with a structure below, and .sup.1H nuclear magnetic resonance spectrum was observed.

##STR00004##

[0146] .sup.1H NMR(500 MHz, CDCl.sub.3): δ 4.11-4.08(m, 2H), δ 3.13-3.11(m, 2H), δ 2.61-2.54(m, 2H), δ 2.34-2.32(m, 1H), δ 1.74(m, 2H), δ 1.42(m, 2H), δ 1.23-1.22(m, 3H), δ 0.05-0.00(m, 9H).

[0147] [Preparation of Catalyst Composition]

Preparation Example 1

[0148] Under nitrogen conditions, neodymium versatate (NdV, 0.80 mmol) was added to a hexane solvent, and methylaluminoxane (MAO, 80.0 mmol), diisobutylaluminum hydride (DIBAH, 16.0 mmol), diethylaluminum chloride (DEAC, 1.92 mmol) and 1,3-butadiene (16.0 mmol) were injected thereto in order, followed by mixing at −20° C. for 12 hours to prepare a catalyst composition (NdV:DIBAH=1:20). The catalyst composition thus prepared was stored at −30 to −20° C. for 24 hours under nitrogen conditions and then, used.

Preparation Example 2

[0149] Under nitrogen conditions, neodymium versatate (NdV, 0.60 mmol) was added to a hexane solvent, and methylaluminoxane (MAO, 60.0 mmol), diisobutylaluminum hydride (DIBAH, 18.0 mmol), diethylaluminum chloride (DEAC, 1.44 mmol) and 1,3-butadiene (12.0 mmol) were injected thereto in order, followed by mixing at −20° C. for 12 hours to prepare a catalyst composition (NdV:DIBAH=1:30). The catalyst composition thus prepared was stored at −30 to −20° C. for 24 hours under nitrogen conditions and then, used.

Preparation Example 3

[0150] Under nitrogen conditions, neodymium versatate (NdV, 0.40 mmol) was added to a hexane solvent, and methylaluminoxane (MAO, 40.0 mmol), diisobutylaluminum hydride (DIBAH, 14.0 mmol), diethylaluminum chloride (DEAC, 0.96 mmol) and 1,3-butadiene (8.0 mmol) were injected thereto in order, followed by mixing at −20° C. for 12 hours to prepare a catalyst composition (NdV:DIBAH=1:35). The catalyst composition thus prepared was stored at −30 to −20° C. for 24 hours under nitrogen conditions and then, used.

Comparative Preparation Example 1

[0151] Under nitrogen conditions, neodymium versatate (NdV, 1.00 mmol) was added to a hexane solvent, and methylaluminoxane (MAO, 40.0 mmol), diisobutylaluminum hydride (DIBAH, 10.0 mmol), diethylaluminum chloride (DEAC, 2.40 mmol) and 1,3-butadiene (30.0 mmol) were injected thereto in order, followed by mixing at −20° C. for 12 hours to prepare a catalyst composition (NdV:DIBAH=1:10). The catalyst composition thus prepared was stored at −30 to −20° C. for 24 hours under nitrogen conditions and then, used.

Comparative Preparation Example 2

[0152] Under nitrogen conditions, neodymium versatate (NdV, 0.20 mmol) was added to a hexane solvent, and methylaluminoxane (MAO, 20.0 mmol), diisobutylaluminum hydride (DIBAH, 10.0 mmol), diethylaluminum chloride (DEAC, 0.48 mmol) and 1,3-butadiene (4.0 mmol) were injected thereto in order, followed by mixing at −20° C. for 12 hours to prepare a catalyst composition (NdV:DIBAH=1:50). The catalyst composition thus prepared was stored at −30 to −20° C. for 24 hours under nitrogen conditions and then, used.

[0153] [Preparation of Modified or Unmodified Conjugated Diene-Based Polymer]

Example 1

[0154] To a completely dried reactor, vacuum and nitrogen were alternately applied, and to a 15 L, reactor in a vacuum state, 4.2 kg of hexane and 500 g of 1,3-butadiene were injected, and the temperature was elevated to 40° C. The catalyst composition of Preparation Example 1 was added thereto, and polymerization was performed for 60 minutes to prepare an active polymer.

[0155] To the active polymer, a hexane solution including 2.5 g of the modifier compound thus prepared was added, and modification reaction was performed under the same temperature conditions as the polymerization conditions for 60 minutes.

[0156] Then, a hexane solution including 1.0 g of a polymerization quenching agent and a hexane solution including 2.0 g of an antioxidant were added to terminate the reaction and prepare a modified conjugated diene-based polymer.

Example 2

[0157] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the temperature of the reactor was elevated to 50° C.

Example 3

[0158] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the temperature of the reactor was elevated to 60° C.

Example 4

[0159] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Preparation Example 2 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 50° C.

Example 5

[0160] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Preparation Example 3 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 50° C.

Comparative Example 1

[0161] BR1208 (manufacturer, LG Chem, Co.) was used as an unmodified Nd-BR.

Comparative Example 2

[0162] CB24 (manufacturer, Lanxess Co.) was used as an unmodified Nd-BR.

Comparative Example 3

[0163] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Comparative Preparation Example 1 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 50° C.

Comparative Example 4

[0164] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Comparative Preparation Example 1 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 70° C.

Comparative Example 5

[0165] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Comparative Preparation Example 2 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 50° C.

Comparative Example 6

[0166] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the temperature of the reactor was elevated to 70° C.

Comparative Example 7

[0167] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Preparation Example 2 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 70° C.

Comparative Example 8

[0168] A modified conjugated diene-based polymer was prepared by the same method in Example 1 except that the catalyst composition of Preparation Example 3 was used instead of Preparation Example 1, and the temperature of the reactor was elevated to 70° C.

TABLE-US-00001 TABLE 1 Polymerization Catalyst NdV:DIBAH temperature composition molar ratio (° C.) Example 1 Preparation 1:20 40 Example 1 Example 2 Preparation 1:20 50 Example 1 Example 3 Preparation 1:20 60 Example 1 Example 4 Preparation 1:30 50 Example 2 Example 5 Preparation 1:35 50 Example 3 Comparative Unmodified Nd-BR Example 1 Comparative Unmodified Nd-BR Example 2 Comparative Comparative 1:10 50 Example 3 Preparation Example 1 Comparative Comparative 1:10 70 Example 4 Preparation Example 1 Comparative Comparative 1:50 50 Example 5 Preparation Example 2 Comparative Preparation 1:20 70 Example 6 Example 1 Comparative Preparation 1:30 70 Example 7 Example 2 Comparative Preparation 1:35 70 Example 8 Example 3

[0169] [Analysis of Physical Properties of Modified Conjugated Diene-Based Polymer]

Experimental Example 1

[0170] With respect to the polymers prepared in the Examples and the Comparative Examples, physical properties were analyzed according to the methods below, and the results are shown in Table 1.

[0171] (1) Microstructure Analysis

[0172] The cis-1,4 bond content, the trans-1,4 bond content, and the vinyl content in a conjugated diene part were measured by Fourier transform infrared spectroscopy (FT-IR).

[0173] Particularly, after measuring a FT-IR transmittance spectrum of a carbon disulfide solution of a conjugated diene-based polymer prepared at a concentration of 5 mg/mL by using disulfide carbon of the same cell as a blank, each content was obtained by using a maximum peak value (a, base line) near 1,130 cm.sup.−1 of the measurement spectrum, a minimum peak value (b) near 967 cm.sup.−1 which indicates a trans 1,4 bond, a minimum peak value (c) near 911 cm.sup.−1 which indicates a vinyl bond, and a minimum peak value (d) near 736 cm.sup.−1 which indicates a cis 1,4 bond.

[0174] (2) Weight Average Molecular Weight (Mw), Number Average Molecular Weight (Mn) and Molecular Weight Distribution (MWD)

[0175] Each polymer was dissolved in tetrahydrofuran (THF) for 30 minutes under 40° C. conditions, and the resultant solution was loaded on gel permeation chromatography (GPC) and flown. In this case, two columns of PLgel Olexis and one column of PLgel mixed-C (trade name, Polymer Laboratories Co.) were used in combination. Also, newly replaced columns were all mixed bed type columns, and polystyrene was used as a gel permeation chromatography standard material.

[0176] (3) Mooney Viscosity (MV, ML1+4, @100° C.)

[0177] The mooney viscosity (ML1+4, @100° C.) (MU) was measured by using MV2000E of Monsanto Co. using Large Rotor at a rotor speed of 2±0.02 rpm at 100° C. In this case, a specimen used was stood at room temperature (23±3° C.) for 30 minutes or more, and 27±3 g of the specimen was collected and put in a die cavity, and then, Platen was operated, and the mooney viscosity was measured while applying torque.

[0178] (4) Beta Value (β-Value)

[0179] The beta value for each polymer was measured using a rubber process analyzer (RPA2000, AlphaTechnologies Co.).

[0180] Particularly, frequency sweep was performed for each polymer in conditions of 100° C. with strain of 7%. In this case, the frequency was set to 2, 5, 10, 20, 50, 100, 200, 500, 1,000, and 2,000 cpm, and a slope of Log(1/tan delta) vs Log(Freq.) was calculated to obtain the beta value.

[0181] (5) Modification Ratio (%)

[0182] The modification ratio was calculated using a chromatogram obtained from measurement of chromatography. Particularly, each polymer was dissolved in tetrahydrofuran (THF) under 40° C. conditions to prepare a specimen, and each specimen was injected into gel permeation chromatography (GPC), tetrahydrofuran was flown as an eluent to obtain a chromatogram, and from the chromatogram thus obtained, the modification ratio was calculated by Mathematical Formula below.

Modification ratio (%)=[(peak area of modified polymer)/(peak area of unmodified polymer+peak area of modified polymer)]×100

TABLE-US-00002 TABLE 2 Example Comparative Example Division 1 2 3 4 5 1 2 3 4 5 6 7 8 Microstructure cis-1,4 97.3 97.2 97.0 96.7 96.6 96.2 96.3 96.4 96.2 96.7 96.9 96.5 96.3 analysis bond trans- 2.3 2.4 2.4 2.7 2.8 1.8 2.9 3.0 3.0 2.7 2.5 2.7 2.9 1,4 bond Vinyl 0.4 0.4 0.6 0.6 0.6 2.0 0.8 0.6 0.8 0.6 0.6 0.8 0.8 bond GPC Mn (×10.sup.5 3.35 2.96 2.92 2.94 2.91 1.57 2.41 2.40 2.33 2.54 2.88 2.85 2.47 results g/mol) Mw (×10.sup.5 8.80 7.92 7.91 7.93 7.92 7.78 5.92 6.93 6.95 6.96 7.95 7.95 6.92 g/mol) MWD 2.63 2.67 2.71 2.70 2.72 4.96 2.45 2.86 2.98 2.73 2.75 2.78 2.79 (Mw/Mn) Mooney viscosity (MV) 67 56 52 53 51 45 45 46 44 49 60 58 49 Beta value 0.264 0.232 0.219 0.220 0.217 — 0.181 0.183 0.168 0.193 0.190 0.185 0.182 Modification ratio (%) 47 35 27 28 25 — — 13 <5 10 14 10 8

[0183] According to the preparation method of the present invention, in Examples 1-5, using the catalyst compositions having the molar ratio of the NdV (neodymium compound) and the second alkylating agent (DIBAH) of 1:20-1:35, and polymerizing at a temperature in 30-65° C., modified conjugated diene-based polymers having excellent living properties of an active polymer, showing a high modification ratio, and having excellent linearity were prepared.

[0184] Meanwhile, in Comparative Examples 3 and 4, using the catalyst composition of Comparative Preparation Example 1 with a too small amount of the second alkylating agent (DIBAH), in Comparative Example 5 using the catalyst composition of Comparative Preparation Example 2 with an excessive amount of the second alkylating agent (DIBAH), and in Comparative Examples 6-8, using the catalyst compositions of Preparation Examples 1-3 but polymerizing at too high polymerization temperature of 70° C., it was confirmed that the modification ratio was low when compared with that of the Examples.

[0185] [Preparation of Rubber Composition and Analysis of Physical Properties]

Experimental Example 2

[0186] After preparing rubber compositions and rubber specimens using the butadiene polymers prepared in the Examples and the butadiene polymers prepared in the Comparative Examples, tensile strength, 300% modulus, elongation and viscoelasticity properties were measured by the methods below, respectively. The results are shown in Table 2 below.

[0187] Particularly, 70 parts by weight of carbon black, 22.5 parts by weight of a process oil, 2 parts by weight of an antiaging agent (TMDQ), 3 parts by weight of zinc oxide (ZnO), and 2 parts by weight of stearic acid were mixed with 100 parts by weight of each of the polymers to prepare each rubber composition. Thereafter, 2 parts by weight of sulfur, 2 parts by weight of a vulcanization accelerator (CZ), and 0.5 parts by weight of a vulcanization accelerator (DPG) were added to each rubber composition, and gently mixed at 50° C. for 1.5 minutes at 50 rpm and then, a vulcanized mixture compound in a sheet shape was obtained using a roll of 50° C. The vulcanized mixture compound was vulcanized at 160° C. for 25 minutes to prepare a rubber specimen.

[0188] (1) Tensile Properties

[0189] After vulcanizing each rubber composition at 150° C. for t90 minutes, tensile strength (kg.Math.f/cm.sup.2), modulus when elongated by 300% (300% modulus, M-300%, kg.Math.f/cm.sup.2) and elongation when breaking were measured according to ASTM D412.

[0190] (2) Viscoelasticity Properties (Tan δ Value at 60° C.)

[0191] Tan δ properties, that are the major factors of low fuel consumption properties were measured using DMTS 500N of Gabo Co. in Germany at a frequency of 10 Hz, prestrain of 3%, and dynamic strain of 3%, and viscoelasticity coefficients (Tan δ) at 60° C. were measured. In this case, with the increase of the Tan δ value at 60° C., hysteresis loss was decreased, and rotation resistance was excellent, that is, the fuel consumption properties were excellent.

TABLE-US-00003 TABLE 3 Example Comparative Example Division 1 2 3 4 5 1 2 3 4 5 6 7 8 Tensile Tensile 117 114 113 114 113 100 106 106 109 106 106 106 105 properties strength (Index) M-300% 132 128 125 126 124 100 115 119 118 119 120 119 118 Elongation 90 94 96 95 96 100 96 91 96 90 90 90 92 Viscoelasticity Tanδ 151 143 137 138 135 100 116 126 123 125 127 126 124 properties at (Index) 60° C.

[0192] The index value of the tensile properties was calculated by Mathematical Formula 1 below with the value of Comparative Example 1 as 100, and the index value of the viscoelasticity properties were calculated by Mathematical Formula 2 below with the value of Comparative Example 1 as 100.

Index=(measured value/standard value)×100  [Mathematical Formula 1]

Index=(standard value/measured value)×100  [Mathematical Formula 2]

[0193] As shown in Table 3, it was confirmed that if the modified conjugated diene-based polymer prepared by the preparation method of the present invention was processed into a rubber specimen, excellent tensile properties and viscoelasticity properties were shown.

[0194] Particularly, Examples 2, 4 and 5 used the catalyst compositions of Preparation Examples 1 to 3, respectively, Comparative Example 3 used the catalyst composition of Comparative Preparation Example 1, and Comparative Example 5 used the catalyst composition of Comparative Preparation Example 2, with the same polymerization temperature of 50° C.

[0195] As a result, all Examples 2, 4 and 5 showed improved tensile properties and viscoelasticity properties when compared with Comparative Example 3 or 5. Through this, it could be found that though the polymerization temperature was included in the range of the present invention, if the molar ratio of the neodymium compound and the second alkylating agent of the catalyst composition deviated from the range of the present invention, the compounding properties of the modified conjugated diene-based polymer were deteriorated.

[0196] In addition, Examples 1-3 and Comparative Example 6 used the catalyst composition of Preparation Example 1, Example 4 and Comparative Example 7 used the catalyst composition of Preparation Example 2, and Example 5 and Comparative Example 8 used the catalyst composition of Preparation Example 3. However, with respect to the polymerization temperature, Examples 1-5 were polymerized at a temperature of 40° C., 50° C. or 60° C., which is included in the range of the present invention (30 to 65° C.), and Comparative Examples 6-8 were polymerized at 70° C. which is higher than the range of the present invention. In this case, all Examples 1-5 showed markedly improved tensile properties and viscoelasticity properties when compared with Comparative Examples 6-8. Particularly, if the Examples and Comparative Examples using the same catalyst composition were compared, it was clearly confirmed that though the catalyst composition satisfying the molar ratio of the neodymium compound and the second alkylating agent, as defined in the present invention, if the polymerization temperature deviated from 30-65° C., and the deterioration of physical properties was induced.

[0197] As described above, if using a catalyst composition having the molar ratio of a neodymium compound and a second alkylating agent of 1:20 to 1:35 and at the same time, performing polymerization at a temperature of 30 to 65° C. according to the preparation method of the present invention, a modified conjugated diene-based polymer having a high modification ratio and excellent compounding properties may be prepared.