JPH02173014A - Random propylene copolymer and its production - Google Patents

Abstract

PURPOSE:To obtain the title copolymer improved in heat sealability and blocking resistance by copolymerizing propylene with an alpha-olefin in the presence of a catalyst prepared from a specified Hf compound and an aluminooxane. CONSTITUTION:Propylene is copolymerized with a 4-20C alpha-olefin such as 1- butene at 40-100 deg.C in the presence of a catalyst containing an Hf compound having, as ligands, a polydentate coordination compound ion to which at least two groups selected from cycloalkadienyl groups dn derivatives thereof are bonded through lower alkylene groups and an aluminooxane in an amount to give 10<-8>-10<-2>g Hf atoms/l and 10<-4>-10<-1>g Al atoms/l. In this way, a random copolymer comprising 90-99mol.% propylene units, 1-10mol.% 4-20C alpha-olefin units and having an intrinsic viscosity of 0.5-6dl/l as measured in decalin at 135 deg.C and satisfying 90<m.p.[Tm]<155-3.5 (100-P) (where P is the amount (mol.%) of polyene), a weight-average MW/number-average MW of below 3.5 and a content of boiling trichloroethylene-insolubles <=5wt.% can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a novel propylene random copolymer and a method for producing the same. The present invention particularly relates to a novel propylene-based random copolymer with excellent heat-sealing properties and anti-blocking properties, and a method for producing the same.

Technical background of the invention and its problems Polypropylene has excellent physical properties, so
It is used for a wide range of purposes. For example, polypropylene is widely used as a packaging film, but since polypropylene has a relatively high melting point, in order to improve heat-sealability at low temperatures in this type of application, propylene is generally mixed with ethylene or carbon atoms with 4 to 20 carbon atoms. α−
It is used as a propylene/α-olefin copolymer by copolymerizing olefins.

Conventionally known packaging films made of propylene/α-olefin copolymers have superior transparency and scratch resistance compared to films made of low-density polyethylene, but they still have poor heat sealability at low temperatures. However, the development of a propylene/α-olefin copolymer with excellent heat sealability at low temperatures is desired.

It is known that in order to improve the heat sealability of the propylene ψα-olefin random copolymer described above, it is sufficient to increase the copolymerization amount of ethylene or α-olefin having 4 to 20 carbon atoms with respect to propylene. There are, but
If the copolymerization amount of ethylene or α-olefin having 4 to 20 carbon atoms is increased, the resulting propylene/α-
Olefin copolymers have a large amount of solvent soluble content, resulting in poor blocking resistance and poor rigidity.

In order to obtain a propylene/α-olefin random copolymer with excellent heat sealability, blocking resistance, and rigidity at low temperatures, it is necessary to have a low melting point despite the small amount of α-olefin copolymerized. Propylene α
- The emergence of olefin random copolymers is necessary.

Conventionally, olefin polymerization catalysts consisting of titanium or vanadium compounds and organic aluminum compounds have been used to produce propylene/α-olefin random copolymers, but in recent years, zirconium compounds have been used as new Ziegler-type olefin polymerization catalysts. Catalysts consisting of and aluminoxane have recently been proposed.

JP-A No. 58-19309 describes the following formula % formula % [where R is cyclopentadienyl, C1 to C6 alkyl, halogen, Me is a transition metal, Ha
N is a halogen] and a transition metal-containing compound represented by the following formula %)) [where R is methyl or ethyl and n is 4 to 2
In the presence of a catalyst consisting of a linear aluminoxane represented by the number 0] or a cyclic aluminoxane represented by the following formula [where R and n are the same as above], ethylene and A method is described in which one or more α-refines of C-C12 are polymerized at a temperature of 150°C to 200°C. The publication states that in order to adjust the density of the resulting polyethylene, the polymerization of ethylene should be carried out in the presence of small amounts of up to 10% by weight of somewhat long-chain α-olefins or mixtures. .

JP-A-59-95292 describes a linear aluminoxane represented by the following formula, [where n is 2 to 40, and R is C1-C6] and a linear aluminoxane represented by the following formula [where n and R The definition is the same as above] An invention relating to a method for producing a cyclic aluminoxane represented by The publication describes, for example, methylaluminoxane and titanium or zirconium bis(
It is stated that when olefins are polymerized by mixing them with a cyclopentadienyl compound, 25 million g or more of polyethylene can be obtained per 1 g of transition metal per hour.

JP-A No. 60-35005 describes the following formula [where,
R is C-CI O alkyl and R is R1 or combined to represent 10-] is first reacted with a magnesium compound, then the reaction product is chlorinated, and A method for producing a polymerization catalyst for olefins by treatment with a compound of TIV, Zr or Cr is disclosed. The publication states that the above catalyst is particularly suitable for the copolymerization of a mixture of ethylene and C-012 α-olefin.

JP-A-60-35006 discloses that two or more different transition metal mono- or tricyclopentadienyl or derivatives thereof (a) and aluminoxane (b) are used as a catalyst system for producing a reactor blend polymer. ) combinations are disclosed. In Example 1 of the same publication, ethylene and propylene were polymerized using bis(pentamethylcyclopentadienyl)zirconium dimethyl and aluminoxane as catalysts, and the number average molecular Jlit was 15,300.
It is disclosed that a polyethylene having a weight average molecular weight ff of 136,400 and a propylene content of 3.4% was obtained. In addition, in the same Example 2, ethylene,
Polymerize propylene and create a number-average molecule! 2,200, weight average molecular weight 11.900 and a toluene soluble portion containing 30 mol% propylene component and number average molecular weight 3.000,
A number average molecule f consisting of a toluene insoluble portion containing a weight average molecular weight of 7,400 and a propylene component of 4.8 mol%
f12,000, weight average molecular weight 8,300 and 7.
A blend of polyethylene and ethylene-propylene copolymer containing 1 mol% propylene component is obtained. Similarly, in Example 3, molecular weight distribution (Mw/Mn) 4.
A blend of LLDPE and ethylene-propylene copolymer is described, consisting of a soluble portion of 57 and a propylene component of 20.6% and an insoluble portion with a molecular weight distribution of 3.04 and a propylene component of 2.9 mol%.

JP-A No. 60-35007 discloses that ethylene alone or together with an α-olefin having 3 or more carbon atoms is used with metallocene and the following formula [where R is an alkyl group having 1 to 5 carbon atoms, and n is 1 in the presence of a catalyst system comprising a cyclic aluminoxane represented by A method for polymerization is described.

According to the description in the same publication, the polymer obtained by this method has a weight average molecular weight of about 500 to about 1.4 million 1, and a molecular weight distribution of 1.5 to 4.0.

In addition, JP-A-60-35008 discloses that by using a catalyst system containing at least two kinds of metallocenes and aluminoxane, polyethylene having a wide molecular weight distribution or ethylene and α-olefin of 03 to C1o can be combined. It is described that polymers are produced. The publication states that the above copolymer has a molecular weight distribution (My/I'ln) 2
It is described what to do with ~50.

Furthermore, JP-A-61-130314 discloses that polypropylene with a high degree of isotacticity can be obtained by polymerizing propylene in the presence of a catalyst system consisting of a sterically fixed zircon-chelate compound and aluminoxane. Are listed.

Furthermore, J,Am,Chem,Soc,, 109.6
544 (1987), ethylenebis(indenyl)
When propylene is polymerized in the presence of a catalyst system consisting of hafnium dichloride or its hydride and aluminoxane, high molecular weight isotactic polypropylene is produced, and its molecular weight distribution (IVw/Fi[n) is 2.1 to 2.
．． It is stated that it is 4 and narrow.

On the other hand, Japanese Patent Application Laid-Open No. 63-142005 discloses that M
It is described that stereoblock polypropylene having v/Mn of 5.0 to 14.9 can be obtained. The propylene obtained here is a rubbery polymer with a short isotactic chain length.

The present inventors have discovered that by copolymerizing propylene and an α-olefin having 4 to 20 carbon atoms in the presence of an olefin polymerization catalyst consisting of a specific hafnium compound and aluminoxane, the molecular weight distribution is narrow and α-olefin is copolymerized. - Despite the small amount of olefin copolymerized, conventionally known propylene/α-
Propylene α has a lower melting point compared to olefin copolymers.
- It was discovered that an olefin copolymer could be obtained, and the present invention was completed.

Purpose of the Invention The present invention aims to solve the problems in the prior art as described above, and has a narrow molecular weight distribution and α
- A propylene/α-olefin random copolymer that has a low melting point despite having a small amount of copolymerized olefin, and has excellent heat sealability, blocking resistance, and rigidity, and a method for producing the same. is intended to provide.

Summary of the Invention The propylene/α-olefin random copolymer according to the present invention is a propylene random copolymer consisting of a structural unit (a) derived from propylene and a structural unit (b) derived from an α-olefin having 4 to 20 carbon atoms. A copolymer, (A) the structural unit (a) in an amount of 90 to 99 mol%,
and the structural unit (b) is present in an amount of 1 to 10 mol%, and (B) has an intrinsic viscosity [η] measured in decalin at 135 ° C.
is in the range of 0.5 to 6 dll/g, and (C) melting point [To+
1 is in the range of 90<Tm<155-3.5 (100-P) (wherein P is the propylene component content (mol%) in the copolymer), and (D) gel permeation・Weight average molecular weight (Mw) and number average molecular weight (Mn) measured by chromatography
) (My/Mn) is less than 3.5, and (E) the amount of boiling trichlorethylene insoluble matter is 5% by weight or less.

In addition, the present invention: The method for producing a propylene ψα-olefin random copolymer comprises: In the presence of a hafnium compound having a coordinating compound as a ligand, and (B) a catalyst formed from an aluminoxane, propylene and a carbon atom having 4 carbon atoms
~20 α-olefins at a temperature of 40 to 100°C, the resulting copolymer contains 90 to 99 mol% of the structural unit (a) derived from propylene, and the structural unit (a) derived from α-olefin It is characterized in that it is copolymerized so that the structural unit (b) is present in an amount of 1 to 10 mol%.

DETAILED DESCRIPTION OF THE INVENTION The propylene/α-olefin random copolymer and the method for producing the same according to the present invention will be specifically explained below.

The propylene/α-olefin random copolymer according to the present invention is a random copolymer of propylene and an α-olefin having 4 to 20 carbon atoms. In this propylene/α-olefin random copolymer, the structural unit (a) derived from propylene is present in an amount of 90 to 99 mol%, preferably 92 to 98 mol%, and the structural unit derived from α-olefin (b) is desirably present in an amount of 1 to 10 mol%, preferably 2 to 8 mol%. The structural unit (a) derived from propylene in the copolymer is 90
If it is less than mol%, the blocking resistance and rigidity of the copolymer tend to be poor. On the other hand, if it exceeds 99 mol %, the melting point of the copolymer will be high and the heat sealability will tend to be poor.

The α-olefins having 4 to 20 carbon atoms used in the present invention include 1-butene, ■-pentene, ■-hexene,
-Methyl-1-pentene, 3-methyl-■-pentene,
1-octene, ■-decene, l-dodecene, 1-tetradecene, ■-hexadecene, ■-octadecene, 1-eicosene, etc. are used. Among these, 1-butene is particularly preferred.

Further, the propylene/α-olefin random copolymer according to the present invention has an intrinsic viscosity [η] of 0.5 to 6 dll/g, preferably 1 to 5 dll, as measured in decalin at 135°C.
/g range is desirable. This intrinsic viscosity is 0.
If it is less than 5 dD/g, the blocking resistance and rigidity of the copolymer tend to deteriorate, which is undesirable, while if it exceeds 6 dD/g, it tends to have poor moldability, which is not preferred.

Furthermore, the propylene-α-olefin random copolymer according to the present invention has a melting point [
Tm] is 90<Tm<155-3.5 (100-P), preferably 100<Ti<150-3.5 (100-P) (where P is the content of propylene component in the copolymer (mol% ) is within the range of ).

The melting point T1 of such a propylene φα-olefin random copolymer and the propylene component content P in the copolymer
A schematic relationship with mol% is shown as straight line A in FIG.

In addition, in FIG. 1, the relationship between the melting point Ti of the conventionally known propylene/α-olefin random co-combination and the propylene component content P mol % is also shown as a straight line B.

As is clear from FIG. 1, the melting point of the propylene/a-olefin random copolymer according to the present invention is the same as that of the conventionally known propylene/α-olefin copolymer when the amount of copolymerized α-olefin is the same. It is 10 to 20°C lower than the melting point of the random copolymer. Therefore, the film obtained from the propylene/α-olefin random copolymer according to the present invention has excellent heat sealability particularly at low temperatures.

Furthermore, since the copolymerized amount of α-olefin exhibits excellent heat sealability, it also has excellent blocking resistance and, moreover, excellent rigidity.

In addition, in the present invention, using a differential scanning calorimeter (DSC),
200% propylene/α-olefin random copolymer
℃ for 5 minutes, then cooled to 20℃ at a rate of 10℃/min, then left at 20℃ for 5 minutes, and then heated from 20℃ to 200℃ at a rate of 10℃/min. The temperature of the maximum endothermic peak (Ti) was taken as the melting point of the propylene/α-olefin random copolymer.

Furthermore, gel permeation chromatography of the propylene/α-olefin random copolymer according to the present invention
The molecular weight distribution (Mv /Mn) determined by (GPC) is
Less than 3.5, preferably 3.0 or less, particularly preferably 2.5
It is in the following range. As described above, the propylene/α-olefin random copolymer according to the present invention has a narrow molecular weight distribution and has excellent blocking resistance from this point as well.

The My/l1li'In value was determined as follows in accordance with "Gel Vermeation Chromatography J" written by Takeuchi and published by Maruzen.

(1) Using standard polystyrene with a known molecular weight (manufactured by Toyo Soda ■, monodisperse polystyrene), calculate the molecular weight M and its G.
P C (Got Permeation Chrom
atograph) count n1, molecule ff1M
A correlation diagram calibration curve of E V (ElutlonvolurAe) is prepared. The concentration at this time is 0.02% by weight.

(2) Take a GPC chromatograph of the sample using GPC7TFJ determination, calculate the number average molecular weight M and weight average molecular weight Mw in terms of polystyrene using the above (1), and calculate Mv 7
Find the Mn value. Sample preparation conditions and GP
The C measurement conditions are as follows.

[Sample Preparation] (a) Disperse the sample in an Erlenmeyer flask together with 0-dichlorobenzene solvent to a concentration of 0.1% by weight.

(b) Heat the Erlenmeyer flask to 140°C and stir for about 30 minutes to dissolve.

(c) Subject the solution to GPC.

[GPC measurement conditions] It was conducted under the following conditions.

(a) Equipment Manufactured by Waters (150cm^L
C/GPC) (b) Column manufactured by Toyo Soda (GMH
Type) (c) Sample amount 400 μg (d) Temperature 140°C (e) Flow rate 1 ml/min The melting point was measured using Perkin Elmer-7 type DSC.
Using the device, sample quantity 2.5 mg and heating rate 1
Measured at 0°C/min.

The propylene-α-olefin random copolymer according to the present invention desirably has a soluble amount in boiling n-pentane of 3% by weight or less, preferably 2% by weight or less, and more preferably 1% by weight or less.

Furthermore, it is desirable that the propylene/α-olefin random copolymer according to the present invention has an insoluble portion in boiling trichlorethylene of 5% by weight or less, preferably 3% by weight or less, and more preferably 1% by weight or less.

To determine the amount of boiling trichlorethylene insoluble matter and boiling n-pentane soluble matter, put 3 g of a finely ground sample into a thimble filter paper, extract with a Soxhlet extractor using 180 ml of solvent for 5 hours, and dry the extracted residue to a constant weight with a vacuum dryer. The weight was determined by drying the sample and calculating the weight difference from the original sample.

The propylene/α-olefin random copolymer according to the present invention as described above is composed of (A) a polypropylene group in which at least two groups selected from cycloalkagenyl groups or substituents thereof are bonded via a lower alkylene group; In the presence of a hafnium compound having a coordinating compound as a ligand, and (B) a catalyst formed from an aluminoxane, propylene and a carbon atom having 4 carbon atoms
~20 α-olefins at a temperature of 40 to 100°C, the resulting copolymer contains 90 to 99 mol% of the structural unit (a) derived from propylene, and the structural unit (a) derived from α-olefin It can be produced by copolymerizing the structural unit (b) so that it is present in an amount of 1 to 10 mol%.

The catalyst component [A] used in the present invention is a cycloalkagenyl group or a substituted product thereof, specifically, at least two groups selected from the group consisting of an indenyl group, a substituted indenyl group, and a partially hydrogenated product thereof. It is a hafnium compound whose ligand is a polydentate compound in which groups are bonded via lower alkylene groups. The following compounds can be exemplified as the hafnium compound.

Ethylenebis(indenyl)dimethylhafnium, ethylenebis(indenyl)diethylhafnium, ethylenebis(indenyl)diphenylhafnium, ethylenebis(indenyl)methylhafnium monochloride, ethylenebis(indenyl)ethylhafnium monochloride, ethylenebis(indenyl)methyl hafnium monopromide, ethylene bis(indenyl) hafnium compound lide, ethylene bis(indenyl) hafnium compound lide, ethylene bis(4,5,8,7-tetrahydro-1-indenyl) dimethyl hafnium, ethylene bis(4, 5,6,7-tetrahydro-1-indenyl)methylhafnium monochloride, ethylenebis(4,5,8,7-tetrahydro-1-indenyl)
Hafnium dichloride, ethylene bis(4,5,6,7-titrahydro-indenyl) hafnium dichloride, ethylene bis(4-methyl-1-indenyl) hafnium dichloride, ethylene bis(5-methyl-1-indenyl) hafnium dichloride, Ethylenebis(6-methyl-1-indenyl)hafnium dichloride, Ethylenebis(7-methyl-1-indenyl)hafnium dichloride, Ethylenebis(5-methoxy-1-indenyl)hafnium dichloride, Ethylenebis(2,3-dimethyl) -1-indenyl) hafnium dichloride, ethylenebis(4,7-simethyl-1-indenyl)hafnium dichloride, ethylenebis(4,7-simethoxy-1-indenyl)
Hafnium dichloride.

The catalyst component [B] used in the method of the invention is an aluminoxane. As the aluminoxane used as a catalyst component, the oxyorganoaluminum compound represented by the general formula (I) or the -format (II) is preferably a hydrocarbon group such as a methyl group, preferably a methyl group or an ethyl group, and particularly preferably a methyl group or an ethyl group. is a methyl group, and m is an integer of 2 or more, preferably 5 or more. Examples of the method for producing the aluminoxane include the following method.

(1) Compounds containing adsorbed water, salts containing water of crystallization, such as magnesium chloride hydrate, copper sulfate hydrate, aluminum sulfate hydrate, nickel sulfate hydrate, monochloride
A method of adding trialkylaluminium to a suspension in another hydrocarbon medium such as cerium hydrate and causing a reaction.

(2) A method in which water, steam, or ice is directly applied to trialkylaluminium in a medium such as benzene, toluene, ethyl ether, or tetrahydrofuran.

Note that the aluminoxane may contain a small amount of organometallic component.

In the hafnium compound as described above, the concentration of the hafnium atoms in the polymerization reaction system is usually 10-8 to 10 ghum atoms/f! , preferably in an amount of 10-7 to 10-3 gram atoms/Ω.

Further, the above aluminoxane is used in an amount of 10-4 to 10-1 gram atoms/g, preferably 5X10-' to 5X10-2 gram atoms/g, in terms of aluminum atoms in the reaction system. This is desirable.

The polymerization temperature is usually 40 to 100°C, preferably 45 to 9°C.
It is desirable that the temperature is 5°C, more preferably in the range of 50 to 90°C.

The polymerization of olefins as described above is usually carried out in a gas phase or a liquid phase. In liquid phase polymerization, an inert hydrocarbon may be used as a solvent, or the olefin itself may be used as a solvent.

Hydrocarbon media specifically include butane, isobutane, pentane, hexane, octane, decane, dodecane,
Aliphatic hydrocarbons such as hexadecane and octadecane,
Alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, and cyclooctane, aromatic hydrocarbons such as benzene, toluene, and xylene, and petroleum fractions such as gasoline, kerosene, and kerosene are used.

The polymerization pressure is usually from normal pressure to 100 kg/cd, preferably from normal pressure to 50 kg/c, and the polymerization can be carried out in any of the batch, semi-continuous and continuous methods. The molecular weight of the polymer can be controlled by hydrogen and/or polymerization temperature.

Effects of the Invention According to the present invention, a novel propylene/α-olefin random copolymer has a narrower molecular weight distribution and a lower melting point even with a small α-olefin content compared to conventionally known propylene/α-olefin random copolymers. A copolymer and a method for producing the same are provided, and this copolymer has excellent heat-sealability, as well as excellent blocking resistance and rigidity.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 (Preparation of methylaluminoxane) PolyIller Coa+iun, 29.180
(198g).

(Synthesis of ethylene bis(indenyl) hafnium dichloride) Bis(indenyl)ethane (Bill, Soc, Chlm,
, 2954 (1967)) and 50 ml of THF, and heated to -30~ while stirring.
Cooled to -40°C. To this, n-Bu Ll (1
, 6M solution) was added dropwise and then heated to -30°C.
After stirring for 1 hour, bis(indenyl)ethane was anionized by naturally raising the temperature to room temperature. Add THF60 to another 200 ml glass flask purged with nitrogen.
ml and cooled to below -60°C, HrC1!
6.7g was added gradually. Thereafter, the temperature was raised to 60°C and stirred for 1 hour. The anionized ligand was added dropwise to the mixture, stirred at 60°C for 2 hours, and then filtered through a glass filter. The filtrate was concentrated to an initial volume of 115 ml at room temperature. This operation precipitates a solid. The precipitated solid was filtered through a glass filter, washed with hexane/ethanol, and dried under reduced pressure to obtain the target compound.

(Polymerization) 500 ml of toluene, 3 moles of propylene, 0.1 mole of l-butene, and i milligram atoms of methyladalminoxane (calculated in terms of Afi atoms) were charged into a 2 g stainless steel autoclave which had been sufficiently purged with nitrogen at room temperature. Thereafter, the temperature inside the polymerization system was raised to 45°C, 1.25 x 10 Z rmol of ethylenebis(indenyl)hafnium dichloride was added, and the temperature was raised to 45°C.
Polymerization was carried out for 5 hours. Polymerization was stopped by adding methanol to the polymerization system.

The resulting polymer slurry was poured into a large amount of methanol, recovered by filtration, and the catalyst component was removed with an isobutyl alcohol/hydrochloric acid solution. After that, 8
When dried under reduced pressure overnight at 0°C with 11 g of 200-300 mm, the -butene content was 2.2 mol%, and the temperature was 135°C.
The [η] measured in decalin is 3.02 d#/g, the melting point by DSC is 124°C, the amount of boiling trichlorethylene insolubles is 0% by weight, and the boiling n-pentane solubles amount is 0.5% by weight. 3% by weight, My
5 g of polyv-27./Mn of 2.41 was obtained.

Example 2 Polymerization was carried out in the same manner as in Example 1, except that the amount of ■-butene charged was 0.25 mol. The ■-butene content was 5.6 mol%, and [η ] is 2.
95d#/g, melting point is 116°C, boiling trichlorethylene insoluble content is 0% by weight, boiling n-pentane soluble content is 0.4% by weight, My/Mn is 2.
．． 29.1 g of polymer No. 33 was obtained.

FIG. 1 is a diagram showing the relationship between propylene content and melting point of a random copolymer.

In FIG. 1, the straight line A shows the relationship between the propylene content and melting point of the propylene W random copolymer according to the present invention; It shows the relationship between the propylene content and melting point of the copolymer.

FIG. 2 is a flowchart for producing a propylene copolymer.

Agent, Patent Attorney, Picture Book, Shunbetsu

Claims (1)

[Scope of Claims] 1) A structural unit (a) derived from propylene and a structural unit (b) derived from an α-olefin having 4 to 20 carbon atoms.
), wherein (A) the structural unit (a) is in an amount of 90 to 99 mol%,
and the structural unit (b) is present in an amount of 1 to 10 mol%, and (B) has an intrinsic viscosity [η] measured in decalin at 135 ° C.
is in the range of 0.5 to 6 dl/g, and (C) the melting point [Tm] measured by differential scanning calorimeter is 90<Tm<155-3.5(100-P) (where P is a copolymer (D) Weight average molecular weight (@M@w) and number average molecular weight (@M@w) measured by gel permeation chromatography.
A propylene-based random copolymer characterized in that the ratio (@M@w/@M@n) to M@n) is less than 3.5, and (E) the amount of boiling trichlorethylene insoluble matter is 5% by weight or less. Combined. 2) (A) A hafnium compound whose ligand is a polydentate compound in which at least two groups selected from cycloalkadienyl groups or substituents thereof are bonded via a lower alkylene group, and (B) In the presence of a catalyst formed from aluminoxane, propylene and a carbon atom
-20 α-olefins at a temperature of 40 to 100°C, the resulting copolymer contains 90 to 99 mol% of the structural unit (a) derived from propylene, and has a structure derived from α-olefins. A method for producing a propylene random copolymer, which comprises copolymerizing the unit (b) so that it is present in an amount of 1 to 10 mol%.