JPH01126306A - Production of olefin polymer - Google Patents

Abstract

PURPOSE:To obtain a polymer having excellent transparency and rigidity, high stereoregularity and bulk density in high activity, by previously polymerizing an alpha-olefin in the presence of a compound catalyst and then polymerizing the alpha-olefin. CONSTITUTION:0.001-30wt.% based on total polymerization amount of 3- methylbutene-1 or a mixture of 3-methylbutene-1 and >=3C olefin is previously polymerized usually at >=50 deg.C in the presence of a catalyst consisting of (A) a solid catalytic component comprising Mg[e.g. MgCl2 or Mg(OCH3)Cl], Ti[e.g. TiCl4 or Ti(OC4H9)4, a halogen and an electron donative compound (e.g. ethyl acetate or ethyl oleate) as essential components and (B) an organometallic compound (e.g. triethylaluminum) of a metal of group I-III of the periodic table and then >=3C olefin is polymerized along or copolymerized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing olefin polymers. Specifically, a specific α-olefin is prepolymerized, and then an α-olefin such as propylene is main-polymerized to produce an α-olefin polymer with excellent transparency and rigidity, as well as stereoregularity and bulk density. Concerning the method of obtaining activity.

[Conventional technology]

Conventionally, titanium trichloride or a titanium-containing solid catalyst component with a magnesium compound as a carrier was used to prepare α-
Prior to polymerizing olefins, it is well known to prepolymerize small amounts of alpha-olefins at relatively low temperatures.

[Problem that the invention seeks to solve]

Japanese Patent Publication No. 2111-F discloses a method of obtaining a titanium-containing solid catalyst component supported on a magnesium compound and an organoaluminum compound. However, with this method the transparency of propylene polymers can hardly be improved.

On the other hand, in Japanese Patent Publication No. 43-321730, after prepolymerizing a catalyst consisting of titanium trichloride and an organoaluminum compound with a small amount of 3-methylbutene-7, A method of obtaining a propylene copolymer with good transparency by copolymerizing an α-olefin was also disclosed in Japanese Patent Application Laid-Open No. 2003-120002. ;/
2011 also discloses that a catalyst consisting of titanium trichloride and an organoaluminum compound is mixed with a small amount of 3-methylbutene
A method for obtaining a compound powder after prepolymerization in 1 is proposed.

However, although these methods improve the physical properties of the propylene polymer, they use titanium trichloride, which has low polymerization activity, as a catalyst component.

Therefore, a step for removing catalyst residue after polymerization is essential, and this method cannot be said to be industrially fully satisfactory.

Therefore, it is desired to develop a method for producing a polymer that simultaneously has these various effects through polymerization using a solid catalyst component containing magnesium, titanium, halogen, and an electron-donating compound as essential components.

[Means for solving problems]

As a result of intensive studies to solve the problems of the prior art, the present inventors have developed a catalyst consisting of an organoaluminum compound and a catalyst component whose essential components are magnesium, titanium, halogen, and an electron-donating compound. -Methylbutene-11 Preferably, 3-methylbutene-1 and 3 carbon atoms
The present inventors have discovered that a propylene polymer with excellent transparency and rigidity, good stereoregularity, and bulk density can be obtained by prepolymerizing with a mixture of other α-olefins of 0 to 0, and have arrived at the present invention. .

That is, the gist of the present invention is to provide a catalyst consisting of a solid catalyst component (b) whose essential components are magnesium, titanium, halogen, and an electron-donating compound, and an organometallic compound of metals from groups 1 to 2 of the periodic table. In the presence of 3-methylbutene-11
Alternatively, there is a method for producing an olefin polymer, which comprises prepolymerizing a mixture of 3-methylbutene-7 and an olefin having 3 or more carbon atoms, and then homopolymerizing or copolymerizing the olefin having 3 or more carbon atoms.

The present invention will be explained in detail below.

The solid catalyst component in the present invention) includes at least a magnesium compound, a titanium compound, and an electron-donating compound,
Further, if necessary, a composite containing all conventionally known magnesium, titanium, halogen, and electron-donating compounds obtained by contacting and reacting temporarily or stepwise with an auxiliary agent such as a silicon compound or a halogenating agent. Solids are used.

Specifically, (1) A method of reacting a dialkoximer, magnesium, a titanium compound, and an electron-donating compound in any order, and then washing as appropriate with a liquid hydrocarbon. (2) A method of reacting a dialkoximer, magnesium, a titanium compound, and an electron-donating compound. A method of contacting and reacting in any order and then washing as appropriate with liquid hydrocarbon (
3) After reacting an organomagnesium compound with a reaction product of water, alcohol, phenol or silanol, a titanium compound and an electron-donating compound in any order,
It is produced by a method such as washing with a liquid hydrocarbon as appropriate.

Furthermore, during these reactions, silicon compounds, /S rogene compounds, alcohols, or inert solids, e.g.
Sio2, Al2oz, polypropylene, polyethylene, poly-3methylbutene-71poly-qmethylpentene-/, TiO2, B2O3, CaC03, etc. may be added.

The solid catalyst component (4) is preferably -General NiM
g(OR')z-nxn C In the formula, R1 represents a furkyl group, an aryl group, or an aralkyl group, X is a halogen, n
indicates O≦n≦ko. ), a magnesium compound represented by the general formula Ti(OR2)mX4-mX4-m (wherein R
2 represents an alkyl group, an aryl group, or an aralkyl group, X represents )10, and m represents O≦m≦q. ) is a composite solid containing magnesium, titanium, halogen, and an electron donating compound obtained by reacting a titanium compound and an electron donating compound.

Specifically, the magnesium compound represented by the general formula ME (OR') z -n xn includes MgCl
2, MJI (OCH3) Ct, M,! 1l (QC2H
,)Ct, M#(QC8H7)CL%Mi(OC4H
*')CL s MJi'(OCgHs)Ct, Mj
'(OCH3)2, MJ1(OQtHs)z, MJ9(
OCsHy)z, MS(QC:,H,)2, MII(O
CsHs)z, 111L9(OCH2CsHs)
z, MJil (QC2H,) (OC4H11), Mli
F (OC1H5) (QC, H,), MJ (○C4H9)
(OCsHs), 111L9 (OC6H4CHz)
It's a good idea to win second place. These can also be used in combination.

In addition, as carrier raw materials, organomagnesium compounds, MJilOlMy(oH), M#(OH)C't,
M, 9 carbonate, W salt of organic acid, 1 silicate
, MJ9 aluminate, etc. can also be used.

°- As a titanium compound represented by the general formula Ti(OR2)mx, -0, specifically, TiCl2, TiB
r,,TiI,,Ti(OCH3)CL3,T1(
oc2H,)cz3,'I'i (QC,H,)CL3
,'I'1(QC6H,)CA3,Ti(OCH3)2
Ct.

'ri(oc2a,)2cz,,Ti(QC,Ho)2
Ct2,'ri(QC,H,)2ct2,Ti(o(R
3), Ct, Ti (○C, H,)3CL, Ti
(0(!.

Ho)3Ct, Ti(QC,H,)3C2,Ti(O
CH3), Ti (QC2H8) Ti (OC4H*)
a, Ti(QC, R5), etc. In addition, the general formula Ti(OR2)mX4-LXz-7 (wherein R3 is an alkyl group, an aryl group, or an aralkyl group, and X is)) rogene, and t represents O≦t≦3. ) can also be used. These may be used in combination.

Examples of the electron-donating compound generally include phosphorus-containing compounds, oxygen-containing compounds, sulfur-containing compounds, nitrogen-containing compounds, and the like. Among these, oxygen-containing compounds are preferred.

Examples of oxygen-containing compounds include ethers, esters, ketones, and acid anhydrides.

Preferably, ethyl acetate, methyl propylate, ethyl acrylate, ethyl oleate, ethyl stearate,
Ethyl phenylacetate, methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, methyl toluate, ethyl toluate, furovir toluate, butyl toluate, methyl ethyl benzoate, ethyl ethyl benzoate, ethyl xylene carboxylate , methyl anisate, ethyl anisate 1. Esters of carboxylic acids such as methyl ethoxybenzoate, ethyl ethoxybenzoate, ethyl cinnamate, diethyl phthalate, dibutyl phthalate, diisobutyl phthalate, dihexyl phthalate, dioctyl phthalate or r-butyl lactone. Examples include cyclic esters and acid anhydrides such as maleic anhydride and phthalic anhydride. Also, 5i-OR', Si-○○OR' or 8
A silicon compound having an i-NR double bond (in the formula, R4 represents a hydrocarbon group having 1 to 20 carbon atoms) is also preferably used.

The composition of the titanium-containing solid catalyst component is No. Rodan/
Titanium (molar ratio) is /-! ;000. Electron-donating compound/titanium (molar ratio) is 0. / -t, titanium/magnesium (mole ratio) is in the range of 0.0 /~i, o, titanium content (weight qb) in the solid catalyst component is in the range of 0.07-20, preferably no. ratio) is 3 to ioo,
Electron-donating compound/titanium (molar ratio) is 0.3 to 3, titanium/magnesium (molar ratio) is 0.02 to O, S;
The titanium content (wt%) in the solid catalyst component is 0. /~10
within the range of

Preferably, the organometallic compound (6) of a metal in Group To4 of the periodic table includes a compound represented by the general formula h1n3 x, -j. In the above formula, R5 is the carbon number l-
20 hydrocarbon groups are shown, with aliphatic hydrocarbon groups being particularly preferred. X represents halogen, and j represents the number of 3. Specific examples of the organoaluminum compound include triethylaluminum, tripropylaluminum, tributylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminium monochloride, etc., but trialkylaluminum is preferably used. Organoaluminum compounds containing one or more A/ atoms bonded via 0 or N atoms can also be used.

Furthermore, dialkyl aluminum hydride, dialkyl aluminum alkoxide, alkylaluminium sesquialkoxide, etc. can also be used.

The electron-donating compound C) used as necessary is selected from the group of electron-donating compounds used in the production of the titanium-containing solid catalyst component, but preferably aromatic carboxylic acid esters, 5i- These include silicon compounds containing 0-C bonds, silicon compounds containing At-0-8i-C bonds, and the like.

The prepolymerization is carried out using the solid catalyst component (b) and the periodic table No. 1-1.
3-methylbutene-11 or 3-methylbutene-11 or 3-methylbutene-/ and carbon number 3-2
α-olefin of θ, preferably propylene, butene-
l.

This is carried out by contacting a mixture with hexene-11 octene-1 and the like. where 3-methylbutene-1
If the prepolymerization is carried out with only 3-methylbutene-l, the polymerization rate of 3-methylbutene-l is very low, so it is usually necessary to lengthen the prepolymerization time, and the activity of the propylene polymerization that follows also tends to decrease. is 3-methylbutene-
It is more preferable to carry out prepolymerization with a mixture of 7 and other α-olefins having 3 to -0 carbon atoms, since the prepolymerization time can be shortened and the activity of the subsequent propylene polymerization will not be significantly reduced.

The composition of the mixture is 3-methylbutene-7/other α-olefin (molar ratio) of 0.0/~10000.
Preferably o, t Ni0001, preferably /-1
The range is 00. The temperature of prepolymerization is usually θ~100℃,
Preferably the temperature is 20 to 0°C, more preferably over 0°C, and the amount of prepolymerization is usually the solid catalyst component (A).
/ /i 0.0 / - / 001 s Selected from the range of 0.00 / - 30% by weight based on the total polymerization amount. Outside this range, the effects of the present invention cannot be obtained sufficiently, which is not preferable.

There is no particular restriction on the proportion of each catalyst component used during prepolymerization, but
Usually, the molar ratio of the titanium pair in the catalyst component (G) to the metal in the component (C) and the electron donating compound of the component (C) is i:oJNt
o:o N/(7, preferably l:O,S~3:O~
Selected to be 3.

After the prepolymerization, the polymer-containing solid catalyst component is washed with an inert hydrocarbon or is subjected to the main polymerization of olefin without washing.

Polymerizable olefins include ethylene, propylene,
Examples thereof include butene-1% 3-methylbutene-11-methylpentene-7, and preferred α-olefins having 3 or more carbon atoms, particularly propylene. In addition to homopolymerization, commonly known random or block copolymerization can also be suitably applied. For example, it is particularly suitable when applied to block copolymerization because the balance between rigidity and impact resistance is improved.

The usage ratio of each catalyst component is the ratio of titanium in (to catalyst component) to (
The molar ratio of the metal of component (g)) to the electron-donating compound of component (C) is selected to be 1:3 to 0:0, preferably 1:0 to 200:3 to 0.

Polymerization reactions include butane, pentane, hexane, heptane,
This is carried out in the presence or absence of a solvent such as an inert hydrocarbon such as toluene or a liquefied α-olefin. The temperature is e
The temperature is o-ioo°C, preferably 0 to 90°C, and the pressure is not particularly limited, but is usually selected from within the range of atmospheric pressure to 100 atm.

Further, hydrogen can also be present in the polymerization system as a molecular weight regulator.

In addition, means commonly used for homopolymerization and copolymerization of α-olefins can also be applied to the present invention.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited by these embodiments unless it departs from the gist thereof.

In addition, on the voice stream side, the catalytic efficiency (shown as CE) is the amount of ill-combined polymer produced (9) in the solid catalyst component, and the polymerization activity (shown as K) is the α-olefin pressure per hour. t kg/d per solid catalyst component (Aty
This is the amount of polymer produced (19). Isotactic index (denoted as II) is the amount (% by weight) remaining after extraction with boiling n-hebutane in a modified Soxhlet extractor for a period of time. Bulk density (expressed as ρB).

The unit (Jil/cc) was measured according to JIS-47. Melt flow index (MFI,!-
) was measured according to ASTM-D-123g.

Transparency evaluation was performed using press molding at 270°C with a perforation thickness of 1! I held a 1wII press film 10 crn away from my eyes and looked at the clarity of the scenery behind the film when I looked through it. Here, those that appear clearly are marked as ○, and those that appear blurry are marked as Δ. The stiffness is the first yield strength y s (
kg/d) and flexural modulus (kg/d), and the first yield strength YS is determined in accordance with ASTM D63g-7- by a tensile test of a dumbbell piece punched from a press sheet with a thickness of θ. Flexural modulus is ASTM D-790-A
Measured according to &.

Example 1 Preparation of solid catalyst component Commercially available Mg(QC2H,)2 was reacted at S/30°C for 1 hour in an OO flask equipped with a stirrer and a thermometer under a seal of purified N2. Thereafter, the temperature was lowered to 1000C, and a toluene solution of phenol powder I was added dropwise. After dropping, raise the temperature 1
The reaction was carried out at 30° C. for 1 hour to obtain a slurry-like reaction product as a yellow solid.

After adding 7 ml of purified toluene A' to this, -2
TiC242j at -20°C,
V1 was added. After the addition, the temperature was gradually raised to 0° C., then ethyl benzoate/J9 was added, and the temperature was maintained for 1 hour. Thereafter, it was washed with purified toluene to obtain a solid product.

Then TiC4,l: J f/ , ethyl benzoate i
, 3 g was added and the solid product was treated for 1 hour at gθ°C. After that, purified toluene -〇〇-
A solid catalyst component (ulg) was obtained by washing with water 9 times. The Ti content in this solid was 2.1% by weight.

忤) Pre-polymerization purification Into a /l induction stirring autoclave which was sufficiently purged with argon, under a 1 argon seal, 0, sg mmol of triethylaluminum was added at room temperature, and then liquid 3-methylbutene-/, yisg and liquid propylene were added. I prepared 1. Next, the temperature was raised to 50° C., and the solid catalyst component/l obtained in Example/(A) was added to carry out prepolymerization for 20 minutes. Thereafter, the mixture was washed three times with 200 ml of purified normal hexane at room temperature to obtain a prepolymerization catalyst component.

This prepolymerization catalyst component contained solid catalyst component (A)/I equivalent type polymer 3077.

(C) Polymerization of propylene Purified Triethyl M aluminum 1. O mmol, methyl paramethylbenzoate 0.3
Add mmol and further increase H, ft/, Okg/c at room temperature.
d, and 700 g of liquid propylene was charged.

Then, the temperature was raised to 70°C, and the prepolymerization catalyst component obtained in the above step) was added as a solid catalyst component (g), and the temperature was raised to 70°C.
Polymerization was carried out for 1 hour.

Thereafter, excess propylene was purged to obtain powdered polypropylene cob. Catalyst efficiency CE is / 9.3ooy
-pp/g-cat, and the polymerization activity was t, SO. The pB of the obtained polymer was 71/cc, I
I is 97. Flathead, MFI was 3.0. The transparency evaluation of this product is ○, and the first yield strength YS is 3tr.
o ky/crls flexural modulus is i r, i o o
It was tcg/crl. Table 1 shows various measurement results.
summarized in.

Example 6 (6) Prepolymerization In (B) of Example 1, the amount of propylene charged was 3
Example 1 except that the prepolymerization time was changed to g and po minutes.
Prepolymerization was carried out in the same manner as in (B).

The obtained prepolymerization catalyst component contained 2 g of solid catalyst component (4) and 2 l of comb polymer.

(C) Polymerization of propylene Propylene was polymerized in the same manner as in Example 1 (C) except that the prepolymerization catalyst component obtained in Example 2 (B) was used, and the catalyst efficiency cE = ttr. ooo 1
-pp/y-cat, polymerization activity=l, 00. II=9
7.0chi, ρB=0. 6I/cc, MFI
= 3. It was tl.

Various measurement results are shown in Table-7.

Example 3 (B) Prepolymerization 0) of Example 1, except that in (B) of Example 1, the temperature and time of prepolymerization were changed to 0.degree. C. and 1 hour, respectively.
Prepolymerization was carried out in the same manner as above. The obtained prepolymerization catalyst component contained a solid catalyst component and a polymer.

(C) Polymerization of propylene Propylene was polymerized in the same manner as in Example 1 (C) except that the prepolymerization catalyst component obtained in Example 3 (B) was used, and the catalyst efficiency CE = 1 Zuoo!
j-pp/y-cai, polymerization activity=3KO1II=
97.0chi, ρB=0. 'll, 1/cc s M F
I = J, 2.

Various measurement results are shown in Table-1.

Example V 03) Prepolymerization Prepolymerization was carried out in the same manner as in (g) of Example 1, except that in (b) of Example 1, the prepolymerization time was changed to 3 minutes. The obtained prepolymerization catalyst component is solid catalyst component (A) 7
It contained 1 g of polymer.

(C) Polymerization of propylene Propylene was polymerized in the same manner as in Example 1 (C) except that the prepolymerization catalyst component obtained in Example &03) was used, and the catalyst efficiency CE=/A, Co. 001-p
p/I-Cat, polymerization activity K = S'IO.

II=? if%, pB = 0.11! ;i/cc,
M F I = q, 2.

Various measurement results are shown in Table-/.

Example! 0) In (6) of Prepolymerization Example/, the seven polymers at the time of prepolymerization were changed to 3-
Prepolymerization was carried out in the same manner as in Example 1 (Φ) except that only methylbutene-7 was used and the prepolymerization time was t-/hour. The obtained prepolymerization catalyst component was a solid catalyst component (4:i,
It contained 20g of the polymer.

(C) Propylene polymerization example Propylene polymerization was carried out in the same manner as in Example 1 (C) except that the prepolymerization catalyst component obtained in Φ) was used, and the catalyst efficiency CE = / 26o o y -p
p/g-cat, polymerization activity = 9 AJ%, ρB = 0. IIl, fi/c
c, MFI=31 g.

Various measurement results are shown in Table-1.

Example 6 (g) Production of solid catalyst component In the same manner as in Example 1, commercially available MIICt, tuJ,
1ilr was collected and purified normal decane 2S- and coethylhexanol 23. ! ml f was added, and the temperature was raised while stirring, and the reaction was carried out at 130° C. for 2 hours.

I got it.

TiCt, 3 (Itl
It was added dropwise over a period of 1 hour. After dropping, the temperature was gradually raised to 76C after q hours.

Diisobutyl phthalate 2, g 9r at iio°C
was added and reacted at the same temperature for 2 hours.

Next, this material was heat filtered to collect the solid part, and TiCt
43 u! After suspending in r fir, the temperature was raised to 100C and reacted at 110C for 1 hour. Thereafter, the solid catalyst component (
4)3. Ir was obtained.

The T1 content of this product is 3. It was heavy fk chi.

(B) Example/using the solid catalyst component obtained in Prepolymerization Example 6 (g)
Prepolymerization was carried out in the same manner as in CB) to obtain a prepolymerization catalyst component. This prepolymerization catalyst component is solid catalyst component (A)/
, g of the polymer 2011 was contained.

(C) Polymerization of propylene In Example 1 (C), the prepolymerization catalyst component obtained in Example & CB) was used, and in place of methyl paramethylbenzoate, phenyl) IJ ethoxysilane 0.0
5 mmol was used, and H2woθ, J kg
/ (Propylene was polymerized in the same manner as in Example/(C) except that it was changed to -14, and powder polypropylene 2301
! 'l got it. What is the catalyst efficiency CE? 009-p
p/g-Cat, polymerization activity is lO, and ρ
B is 0. lI! ; 9/cc, II is 97, Tachi,
MFI was lO0 evening. The transparency evaluation of this product is ○, and the first yield strength YS is 3: lkQ/(-d,
The flexural modulus was /7.200kq/ad.

Comparative Example 1 (g)) Pre-polymerization Purification N-hexane/f was placed at room temperature under a N2 seal in a /1 induction stirring glass autoclave which had been sufficiently purged with N2.
d.) Diethyl aluminum 1. λmi9 The solid catalyst component (4)/i obtained in Example 1 was added. After that, 2! ; Keep at ℃ and add propylene gas at 3℃.
Prepolymerization was carried out by flowing for a minute. After the prepolymerization was completed, normal hexane/20- was added, and the entire amount was transferred to a 200-bar flask that had been sufficiently purged with purified N2, and used for the main polymerization. The prepolymerization catalyst component obtained here contained ions of solid catalyst component (A)/g of civoripropylene.

(C) Polymerization of propylene Polymerization of propylene was carried out in the same manner as in (C) of Example 1, except that the prepolymerization catalyst component obtained in Comparative Example 1 was used, and the catalyst efficiency CE = / 9 t 0 0 ,9
'-pp/I-Cats polymerization activity = 440, I
I=Tari, Kochi, ρB=0. 'l 7
fj/ccMF I = '1.2.

Various measurement results are shown in Table-/.

The evaluation of the transparency of this item is Δ because it looks blurry.
Yes, the first yield strength YS is. 330kfl/cr
l, the flexural modulus is /j/0 01c9/(-1
It was 71.

From the above results, a polymer with excellent transparency and rigidity can be obtained by main polymerization using a prepolymerization catalyst component prepolymerized with 3-methylbutene-1 or a mixture of 3-methylbutene-1 and propylene. [Effects of the Invention] According to the method of the present invention, not only a propylene polymer with excellent transparency and rigidity and high bulk density can be obtained, but also with high polymerization activity and stereoregularity. Therefore, a process for removing catalyst residues and non-quality polymers after polymerization becomes unnecessary, which is also advantageous from an industrial perspective.

Claims (7)

[Claims] (1) In the presence of a catalyst consisting of a solid catalyst component (A) whose essential components are magnesium, titanium, halogen, and an electron-donating compound and an organometallic compound (B) of a metal from Groups I to III of the periodic table, An olefin polymer characterized in that 3-methylbutene-1 or a mixture of 3-methylbutene-1 and an olefin having 3 or more carbon atoms is prepolymerized, and then an olefin having 3 or more carbon atoms is homopolymerized or copolymerized. Production method. (2) The method according to claim 1, characterized in that a mixture of 3-methylbutene-1 and propylene is prepolymerized. (3) Electron-donating compound (
C)
The method described in section. (4) The method according to claim 1, characterized in that the temperature of the prepolymerization exceeds 50°C. (5) The amount of polymerization in the prepolymerization is 0 per 1 g of solid catalyst component (A)
．． 2. The method according to claim 1, wherein the amount is 0.01 to 100 g. (6) The method according to claim 1, wherein the amount of polymerization in the prepolymerization is 0.001 to 30% by weight of the total amount of polymerization. (7) The solid catalyst component (A) has the general formula Mg (OR^1)
Magnesium compound represented by _2-nXn (wherein R^1 represents an alkyl group, aryl group, or aralkyl group, X represents a halogen, and n represents 0≦n≦2), general formula Ti (OR^2) _mX_4_-_m (in the formula R
^2 represents an alkyl group, an aryl group, or an aralkyl group, X represents a halogen, and m represents 0≦m≦4. 2. The method according to claim 1, characterized in that it is obtained by reacting a titanium compound represented by () and an electron-donating compound.