GB2167423A - Propylene-based block copolymers and process for preparing same - Google Patents

Abstract

A propylene/branched alpha -olefin block copolymer comprising propylene and a branched alpha -olefin having 5 to 12 carbon atoms, prepared using a catalyst comprising (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor, said block copolymer: (a) comprising 5-95% by weight of said propylene and 95-5% by weight of said branched alpha -olefin having 5 to 12 carbon atoms; (b) having an intrinsic viscosity of 0.5 to 10 dl/g (in decalin at 135 DEG C); (c) having at least one melting point not lower than 145 DEG C among melting points measured by a differential scanning calorimeter (DSC); and (d) having a modulus of flexural rigidity of 8,000 to 15,000 kg/cm<2> (according to ASTM D-747-70). -

Description

SPECIFICATION Propylene-based block copolymers and process for preparing same BACKGROUND OF THE INVENTION The present invention relates to a block copolymer comprising propylene and a branched a-olefin having 5 to 12 carbon atoms.

Heretofore, in order to improve the heat- and impact-resistance of propylene-based polymers, there has been proposed a method in which an ethylene-4-methyl-1-pentene copolymer or a propylene-4-methyl-1-pentene copolymer is used to obtain a material well balanced in heat- and impact-resistance, as disclosed in Japanese Patent Laid Open Nos. 137116/1980 and 81326/1981. According to such a prior art method, although impact resistance is improved, there is a drawback in point of heat resistance, especially the heat distortion temperature is low.

Moreover, since those copolymers are random copolymers, the proportion of amorphous polymers produced becomes large, causing problems such as reactor fouling, for example.

Blending homopolymers with each other may be a solution to the above problem, but with blending it is difficult to obtain a homogeneous dispersion and heat deterioration of polymer is apt to occur at the time of blending.

SUMMARY OF THE INVENTION According to the present invention, there are provided propylene-based block copolymers having superior thermal properties as compared with homopolymers of the constituents monomers and their mixtures, as well as a process for preparing them.

Although some polymer mixtures have superior thermal properties, their optimum mixing range is extremely narrow and high temperatures are required for mixing, thus easily causing deterioration of polymers and making a uniform dispersion difficult.

Particularly, the present invention provides propylene-based block copolymers capable of overcoming the above drawbacks, having a high rigidity over a wide composition range, a high heat resistance, especially a high heat distortion temperature, and with little by-production of amorphous polymers, as well as a process for preparing such copolymers.

According to the present invention there are provided crystalline block copolymers having superior thermal properties, obtained by a block copolymerization of propylene and a branched a-olefin having 5 to 12 carbon atoms. Firstly, the present invention resides in a block copolymer comprising propylene and a branched a-olefin having 5 to 12 carbon atoms, prepared using a catalyst and having the following characteristics (a) to (d), said catalyst comprising (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor:: (a) the proportion of the propylene is 5-95 wt.% and that of the branched C5-C12 a-olefin is 95-5 wt.%; (b) having an intrinsic viscosity (in decalin at 135"C) of 0.5-10 dl/g; (c) at least one of melting points measured by a differential scanning calorimeter (DSC) is not lower than 145"C; and (d) having a modulus of flexural rigidity (ASTM D-747-70) of 8,000-15,000 kg/cm2.

Secondly, the present invention resides in a process for preparing a propylene/branched aolefin block copolymer having the following characteristics (a) to (d) by copoiymerizing propylene with a branched a-olefin of C5 to C12 in the presence of a catalyst comprising (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor, said copolymerization involving a first polymerization stage and a second polymerization stage, the first polymerization stage being carried out at a temperature not higher than 50"C and the second polymerization stage being carried out at a temperature not lower than 50"C in a substantial absence of the monomer used in the first polymerization stage:: (a) the proportion of the propylene is 5-95 wt.% and that of the branched C5-C12 a-olefin is 95-5 wt.%; (b) having an intrinsic viscosity (in decalin at 135"C) of 0.5-10 dl/g; (c) at least one of melting points measured by a differential scanning calorimeter (DSC) is not lower than 145"C; and (d) having a modulus of flexural rigidity (ASTM D-747-70) of 8,000-15,000 kg/cm2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Block Copolymer (a) Composition The block copolymer of the present invention is a crystalline block copolymer comprising propylene and a branched C5-C12 a-olefin and having a stereospecific structure.

Its composition is in the range of 95/5 to 5/95, preferably 95/5 to 40/60, more preferably 90/10 to 70/30, in terms of propylene/branched C5-C12 a-olefin weight ratio.

If the propylene content of the copolymer exceeds 95 wt.%, the heat distortion temperature of the copolymer becomes equal to that of polypropylene and thus becomes low, and if the propylene content is less than 5 wt.%, the heat distortion temperature of the copolymer becomes about the same as that of poly-4-methyl-1-pentene and there is not obtained a copolymer having a high heat distortion temperature.

(b) Intrinsic Viscosity The intrinsic viscosity [iji of the copolymer of the present invention is in the range of 0.5 to 10 dl/g, preferably 1 to 5 dl/g, as measured in decalin at 135"C. If it is lower than 0.5, it is difficult to effect molding of the copolymer because of a too low melt viscosity, and also when it exceeds 10 it is difficult to effect molding because of a too high melt viscosity and extremely poor flow property.

(c) Melting Point The copolymer of the present invention is a crystalline propylene-based block copolymer. One block is formed by propylene, usually melting in the range of 100" to 170"C, while the other block is formed by a branched C5-C12 a-olefin, melting in the range of 100" to 250"C.

The melting point referred to herein means the position of a melting peak obtained by measurement using a differential scanning calorimeter (DSC).

At least one of the above melting points must be not lower than 145"C, or else the heat distortion temperature of the copolymer will become lower, which is not desirable.

(d) Modulus of Flexural Rigidity The modulus of flexural rigidity of the copolymer of the present invention is in the range of 8,000 to 15,000 kg/cm2 as a value measured according to ASTM D-747-70. If it is less than 8,000 kg/cm2, the copolymer will be soft and have a low heat distortion temperature, and a modulus of flexural rigidity exceeding 15,000 kg/cm2 is not desirable because the copolymer will become very fragile aithough the rigidity is high.

(B) Copolymerization (a) Catalyst The catalyst used in the present invention comprises a combination of (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor. Examples of the solid material are those obtained by supporting titanium compounds on inorganic solid carriers by a known method.As examples of inorganic solid carriers are mentioned metal magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide and magnesium chloride; double salts, double oxides, carbonates, chlorides and hydroxides each containing magnesium atom and a metal selected from silicon, aluminum and calcium; as well as those obtained by treating or reacting these inorganic solid carriers with oxygen-containing compounds, sulfur-containing compounds, hydrocarbons, halogen-containing substances, siiiconcontaining compounds, nitrogen-containing compounds or phosphorus-containing compounds.

Examples of oxygen-containing compounds are alcohols, aldehydes,.ketones, ethers, carboxylic acids and derivatives thereof. As sulfur-containing compounds, thiophene and thiols are preferred. As hydrocarbons, aromatic hydrocarbons are preferred, example of which include durene, anthracene and naphthalene. As halogen-containing substances, halogenated hydrocarbons are preferred, examples of which include 1,2-dichloroethane, n-butyl chloride, t-butyl chloride and pdichlorobenzene. Preferred examples of silicon-containing compounds are tetraethoxysilane, vinyltriethoxysilane and allyl-triethoxysilane. Examples of nitrogen-containing compounds are acid amides, amines and nitriles, with benzoic acid amide, pyridine and benzonitrile being particularly preferred.Examples of phosphorus-containing compounds are phosphates and phosphites, with triphenyl phosphite, triphenyl phosphate, tri-n-butyl phosphite and tri-n-butyl phosphate being particularly preferred.

As other preferred examples of the solid material used in the present invention, mention may be made of reaction products of organomagnesium compounds, e.g. Grignard compounds, and titanium compounds. As examples of organomagnesium compounds are mentioned those of the general formulae RMgX, R2Mg and RMg(OR) wherein each R is an organic radical and X is halogen, and other complexes thereof, as well as those obtained by modifying these organomagnesium compounds with other organometallic compounds such as, for example, organosodium, organolithium, organopotassium, organoboron, organocalcium and organozinc.

As examples of the titanium compound used in the present invention are mentioned halides, alkoxyhalides, oxides and halogenated oxides, of titanium. More concrete examples include tetravalent titanium compounds such as titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monoethoxytrichlorotitanium, diethoxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisopropoxytrichlorotitanium, diisopropoxydichlorotitanium, and tetraisopropoxytitanium; titanium trihalides obtained by reducing titanium tetrahalides with hydrogen, aluminum, titanium or organometallic compounds; as well as trivalent titanium compounds such as compounds obtained by reducing tetravalent alkoxytitanium halides with organometallic compounds. Among these titanium compounds, tetravalent titanium compounds are particularly preferred.

The following systems are typical examples of the solid material used in the invention: MgO RX-TiCI4 (Japanese Patent Publication No. 3514/76), MgO-AICI3-TiCI4 (Japanese Patent Laid Open No. 134789/79), Mg-SiCI4-ROH-TiCI4 (Japanese Patent Publication No. 23864/75), MgCI2-AI (OR)3-TiCI4 (Japanese Patent Publication Nos. 152/76 and 15111/77), MgCI2-aromatic hydrocarbons-TiCI4 (Japanese Patent Publication No. 48915/77), MgCI2-SiCI4-ROH-TiCI4 (Japanese Patent Laid Open No. 106581/74), Mg(OOCR)2-Al(OR)3-TiC14 (Japanese Patent Publication No.

11710/77), MgCI2-RX-TiCI4 (Japanese Patent Laid Open No. 42584/77), Mg-POCI3-TiCI4 (Japanese Patent Publication No. 153/76), MgCI2-AIOCI-TiCI4 (Japanese Patent Publication No.

15316/79), RMgX-TiCI4 (Japanese Patent Publication No. 39470/75), MgCI2-CH2=CHSi (OR)3 P(OR)3-ROR-TiCI4 (Japanese Patent Laid Open No. 71608/85) and MgCI2-CH2=CHSi(OR)3-O(OR)3- TiCI4) (Japanese Patent Laid Open No. 129203/84).

As examples of the organometallic compound (2) used in the present invention are mentioned organometallic compounds of Group I-IV metals in the Periodic Table which are known to be a component of Ziegler catalysts. Particularly, organoaluminum compounds and organozinc compounds are preferred.More concrete examples are organoaluminum compounds of the general formulae R3AI, R2AiX, RAIX2, R2AIOR, RAI(OR)X and R3AI2X3 wherein Rs, which may be the same or different, are each an alkyl or aryl group having 1 to 20 carbon atoms and X is a halogen atom, as well as organozinc compounds of the general formula R2Zn wherein Rs, which may be the same or different, are each an alkyl group having 1 to 20 carbon atoms, such as, for example, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminum chloride, ethylaluminum dichloride, diethylaluminum ethoxide, ethylaluminum sesquichloride, diethylzinc, and mixtures thereof.

The amount of the organometallic compound used in the present invention is not specially limited, but usually it is in the range of 0.1 to 1 ,000 moles per mole of the titanium compound.

As examples of the electron donor (3) used in the present invention, mention may be made of carboxylic acid esters, ethers, ketones, alcohols and silicic acid esters. Above all, silicic acid esters such as tetraethoxysilane, monophenyltriethoxysilane and monophenyltrimethoxysilane are preferred.

The amount of the electron donor used in the present invention is not specially limited, but usually it is in the range of 0.01 to 10 moles, preferably 0.1 to 5 moles, per mole of the organometallic compound.

(b) Branched a-Olefin of C5 to C12 As examples of the branched a-olefin of C5 to C12 used in the invention, mention may be made of 3-methyl-1-butene, 3,3-dimethyl-1-butene, 3-cyclohexyl-1-butene, 3-phenyl-1-butene, 4 methyl-1-pentene, 4,4-dimethyl- 1 -pentene, 3-methyl- 1 -pentene, 3-methyl- 1 -hexene, 3,5,5-trime thyl-1-hexene, 3-ethyl- 1 -heptene, 3,7-dimethyl- 1 -octene, 4,6,6-trimethyl- 1 -heptene, allylcyclopentane, allylocyclohexane, 2-allylnorbornene, allylbenzene, allyltoluene and allylxylene. Above all, 4methyl-1-pentene is particularly preferred.

(c) Block Copolymerization The manufacturing process for the block copolymer of the present invention comprises at least two steps which are a first step (A) for producing the branched C5-C12 a-olefin block portion and a second step (B) for producing the propylene block portion. The order of execution of the steps (A) and (B) is not specially limited, but it is desirable to execute the step (A) first. A preferred manufacturing process for the block copolymer will be described below.

In step (A), the branched C5-C12 a-olefin is polymerized in the presence or absence of a solvent. Examples of the solvent which may be used are saturated aliphatic hydrocarbons such as butane, pentane, hexane and heptane, aromatic hydrocarbons such as benzene, toluene and xylene, and aliphatic hydrocarbons such as cyclopentane and cyclohexane.

A bulk polymerization using the branched C5-C12 a-olefin itself as solvent.

The polymerization temperature is not higher than 50"C, preferably 20 to 50"C. If the polymerization temperature is outside this range, the heat resistance of the resulting polymer will not be improved.

The polymerization time is not specially limited, usually it is in the range of 1 to 1,000 minutes, preferably 5 to 300 minutes.

The adjustment of molecular weight can be done to some extent by changing polymerization conditions such as the polymerization temperature and the catalyst mole ratio, but the addition of hydrogen into the polymerization system is more effective for this purpose.

Then, the branched a-olefin remaining in step (A) is removed by a suitable method such as purging or distillation and thereafter there is performed polymerization of propylene in step (B).

The polymerization of propylene is conducted in vapor phase in the presence of an inert solvent or using propylene itself as solvent. As an inert solvent there may be used the same solvent as that used in step (A).

As to polymerization conditions in step (B), the temperature is not lower than 50"C, preferably 50 to 900C, and the polymerization time, which is not specially limited, is usually in the range of 1 to 1,000 minutes, preferably 5 to 300 minutes. Polymerization temperatures outside this range will result in a decreased polymerization rate of a deteriorated stereospecificity of the resulting copolymer.

The adjustment of molecular weight can be done more effectively by the addition of hydrogen.

If necessary, a preliminary polymerization may be performed using propylene prior to the polymerization of step (B). In this case, it is conducted for 5 to 120 minutes at a temperature of 20 to 50"C. By this treatment, particle properties of the resulting polymer are improved.

The following examples are given to illustrate the present invention more concretely, but it is to be understood that the invention is not limited thereto. Measuring methods for various values in those examples will first be described below.

(1) Melting Point A sample (about 10 mg) is set to a differential scanning calorimeter (SSC/580) DSC 20, a product of Seiko Denshi Kogyo K.K:) and is held at 260"C for 5 minutes, then the temperature is reduced to 40"C at a rate of 100C/min and the sample is held at this temperature for 5 minutes.

Thereafter, the temperature is raised at a rate of 10C/min and a peak position during heat-up is measured as a melting point.

(2) Heat Distortion Temperature A sample prepared by a press sheet method is measured for heat distortion temperature at a load of 4.64 kg/cm2 in accordance with ASTM D-648-70, using a heat distortion tester manufactured by Toyo Seiki K.K.

(3) Modulus of Flexural Rigidity Measured according to ASTM D-747-70 using an Olsen type rigidity measuring apparatus manufactured by Toyo Tester Kogyo K.K.

(4) Branched a-Olefin Content With a calibration curve prepared in advance using an infrared spectroscopic method and '3C-NMR, the content is measured infrared-spectroscopically. For example, where 4-methyl-l- pentene is used as the branched a-olefin, its content is measured from Ag74/A920 ratio ["A" representing an absorbance ratio at the wave number (cm t) of small numerals] and the calibration curve.

(5) n-Heptane Extraction Residue Residue (wit.%) after extraction of a powdered copolymer in boiling n-heptane for 7 hours using a Soxhlet's extractor.

Example 1 (a) Preparation of Solid Catalyst Component 10g (105 mmol) of anhydrous magnesium chloride, 1.84 mi (8.8 mmol) of vinyltriethoxysilane and 1.2 ml (4.6 mmol) of triphenyl phosphite were placed in a stainless steel pot having an internal volume of 400 ml and containing 25 stainless steel balls each 1/2 inch (12.7mm) in diameter, and ball-milled for 6 hours in a nitrogen atmosphere at room temperature, thereafter 0.34 g (2 mmol) of diphenyl ether was added, followed by further ball milling for 16 hours in a nitrogen atmosphere. 5 g of the resultant solid powder and 20 ml of titanium tetrachloride were charged into a round-bottomed 200 ml fiask and stirred for 2 hours in a nitrogen atmosphere at 100"C. Then, to remove excess titanium tetrachloride, the reaction mixture was washed with hexane until titanium tetrachloride was no longer recognized in the washing. Subsequent drying under reduced pressure afforded a solid catalyst component containin 26 mg/g of titanium.

(b) Polymerization A stainless steel 3-liter autoclave equipped with an induction stirrer was purged with nitrogen and then charged with 750 ml of 4-methyl-1-pentene, then 2.5 mmol of triethylaluminum, 1.4 mmol of phenyltriethoxysilane and 50 mg of the solid catalyst component prepared above. Then, hydrogen was introduced to give its partial pressure in vapor phase of 0.05 kg/cm2 and thereafter the temperature was raised to 50"C with stirring. Polymerization of 4-methyl-1-pentene was allowed to take place for 15 minutes.

Thereafter, 4-methyl-1-pentene was purged to the exterior of the polymerization system and 1,500 ml of hexane was introduced, then hydrogen was also introduced to give its partial pressure in vapor phase of 0.05 kg/cm2 and the temperature of the polymerization system was raised to 70"C. Propylene was introduced continuously to maintain the total pressure at 7 kg/cm2.G, while polymerization was allowed to take place for 15 minutes.

Thereafter, excess propylene was discharged, followed by cooling, then the contents were taken out and dried to obtain 86 g of a white polymer. This is a total amount of products including amorphous polymer.

Catalytic activity ws 74,000 g.copolymer/g.Ti and the amount of amorphous polymer soluble in the polymerization solvent was 4.8 wt.%.

Properties of the copolymer thus obtained are as shown in Table 1.

Table

First Stage Second Stage Example Monomer Hydrogen Temp. Time Monomer Hydrogen Temp. Time Partial Partial Pressure Pressure kg/cm C min. kg/cm C min.

1 4-methyl-1- 0.05 50 15 Propylene 0.05 70 15 pentene 2 " " " 120 " " " 20 3 " " " " " " " 5 4 " " " 300 " " 50 3 5 " 0 " 120 " " 70 25 6 .l 0.05 " 60 II " | " .l 10 7 Propylene .. 45 30 4-methyl-1- " 50 90 pentene 8 4-methyl-1- " 50 20 Propylene " 70 20 pentene 9 " " " 30 " " " 35 Table 1 (continued)

Polymer Solvent- Catalytic Intrinsic n-Heptane 4-Methyl Example Yield Soluble Activity Viscosity Extraction 1-Pentene Polymer g.copolymer/ Residue Content g wt.% g.Ti dl/g wt.% wt.% 1 86 4.8 74,000 2.5 93.8 12.5 2 132 5.7 102,00 2.8 91.6 22.5 3 74.7 5.8 58,000 3.1 93.6 41.0 4 63 6.0 48,000 2.7 90.4 89.6 5 119 6.4 92,000 3.4 92.3 18.5 6 139 4.0 107,000 2.1 91.2 34.0 7 92.6 2.9 71,000 2.2 91.3 20.0 8 63 5.9 95,500 2.5 90.2 18.5 9 101 8.4 51.800 2.7 89.2 16.4 Table 1 (continued)

Melting Modulus Heat Example Point of Flexural Distortion Rigidity Temperature C kg/cm C 161 1 11,300 123 157.5 2 240 11,200 128 152.5 3 10,500 4 156 9,900 87 240 5 158 11,500 129 151.5 6 151.5 11,200 124 239 7 159 11,400 126 159 8 10,700 125 239 9 11,600 124 239 Example 2 Using the catalyst prepared in Example 1, polymerization was performed in the same way as in Example 1 except that the polymerization time of 4-methyl-1-penetene and that of propylene were set to 120 and 20 minutes, respectively. Results are as set out in Table 1.

The copolymer thereby obtained was hot-pressed to form a film, which was then measured for IR spectrum. Results are as shown in the accompanying drawing.

When fractionation was performed using a decalin/butylcarbitol system, it was impossible to separate propylene units and 4-methyl-1-pentene units.

Examples 3-6 The procedure of Example 1 was repeated except that the polymerization conditions were changed as shown in Table 1. Results are as set forth in Table 1.

Example 7 Polymerization was conducted in the same was as in Example 1 except that as the first stage of polymerization there was performed polymerization of propylene at 45"C for 30 minutes and as the second stage of polymerization there was conducted polymerization of 4-methyl- 1-pen- tene at 50"C for 90 minutes. Results are as set forth in Table 1.

Comparative Examples 1 and 2 Using the catalyst prepared in Examples 1, a homopolymerization of propylene and that of 4methyl-1-pentene were conducted. Polymerization conditions and results are as shown in Table 2.

Comparative Examples 3 and 4 Using the catalyst prepared in Example 1, copolymers having 4-methyl-1-pentene contents of 3 wt.% and 97 wt.% were prepared. Polymerization conditions and properties of the copolymers are as shown in Table 2.

Table 2

First Stage Second Stage Comparative| Monomer |Hydrogen |Temp.|Time| Monomer |Hydrogen |Temp.|Time Example Partial Partial Pressure Pressure kg/cm | C |min.| |kg/cm | C |min.

1 Propylene 0.05 70 60 2 |4-methyl-| " | 50 | " | - | - | 1-pentene 3 " " " 5 Propylene 0.05 70 60 4 " " " 90 Propylene " 50 3 (Partial Pressure 1kg/cm) 5 " " 70 15 Propylene " " 60 Polypropylene (Comparative Example 1)/ 6 Poly 4-methyl-1-penten (Comparative Example 2) = 40/10 (weight ratio) blend Table 2 (continued)

Polymer Solvent- Catalytic Intrinsic n-Heptane Comparative Yield Soluble Activity Viscosity Extraction Example Polymer g.copolymer/ Residue g wt.t g.Ti dl/g wt.% 1 220 1.0 161,000 1.6 98.0 2 25.3 5.9 20,000 2.9 95.3 3 136 3.8 105,000 1.9 96.2 4 42 7.9 32,000 3.0 93.7 5 108 14.8 83,000 2.1 91.3 6 | - | - | - | 1.8 | Table 2 (continued)

4-Methyl-1- Melting Modulus Heat Comparative pentene Point of Flexural Distorsion Example Content Rigidity Temperature wt.% C kg/cm C 165 1 - 12,000 120 2 - 10,000 81 164.5 3 3 11,000 120 4 97 10,000 82 159 5 19 11,600 122 239 164.8 6 20 11,500 124 239 Comparative Example 5 Using the catalyst prepared in Example 1, polymerization was conducted in the same way as in Example 1 except that the first stage polymerization was performed at 70"C for 15 minutes and the second stage polymerization at 50"C for 60 minutes.In the resulting copolymer there was contained 19 wt.% of 4-methyl-1-pentene. The amount of amorphous polymer soluble in the polymerization solvent was 14.8% and thus extremely large as compared with that in Example 2. Other properties are as shown in Table 2.

Example 8 (a) Preparation of Solid Catalyst Component 10 g of anhydrous magnesium chloride and 0.5 ml of 1,2-dichloroethane were placed in a stainless steel pot having an internal volume of 400 ml and containing 25 stainless steel balls each 1/2 inch (12.7mm) in diameter, and ball-milled for 16 hours in a nitrogen atmosphere at room temperature. 5 g of the resulting solid powder and 20 ml of titanium tetrachloride were charged into a round-bottomed 200-ml flask and stirred for 2 hours in a nitrogen atmosphere at 100"C. Then, to remove excess titanium tetrachloride, the reaction mixture was washed with hexane until titanium tetrachloride was no longer recognized in the washing. Subsequent drying under reduced pressure afforded a solid catalyst component containing 13.2 mg/g of titanium.

(b) Polymerization Polymerization was performed in the same way as in Example 1 except that the solid catalyst component just prepared above was used. Properties of the resultant copolymer are as set forth in Table 1.

Example 9 (a) Preparation of Solid Catalyst Component 9.5 g of a reaction product obtained by heat-reaction at 300"C for 4 hours of 40 g magnesium oxide and 133 g aluminium trichloride, and 1.7 g of titanium tetrachloride, were placed in a stainless steel pot having an internal volume of 400 ml and containing 25 stainless steel balls each 1/2 inch (12.7mm) in diameter, and ball-milled for 16 hours in a nitrogen atmosphere at room temperature. The resultant solid powder contained 39 mg/g of titanium.

(b) Polymerization Polymerization was performed in the same way as in Example 1 except that the solid catalyst component just prepared above was used. Properties of the resultant copolymer are as shown in Table 1.

Comparative Example 6 40 g of polypropylene (the one obtained in Comparative Example 1) and 10 g of poly-4methyl-1-pentene (the one obtained in Comparative Example 2) were kneaded for 5 minutes in a nitrogen atmosphere at 260"C using a plastograph manufactured by Toyo Seiki K.K. to obtain a blend. Properties of this blend are as shown in Table 2.

BRIEF DESCRIPTION OF THE DRA WINGS The accompanying drawing illustrated IR spectrum of a film formed by hot pressing from the block copolymer of the present invention obtained in Example 2 (the numerals in the drawing represent wave number, cm 1).

Claims (12)

1. A propylene/branched a-olefin block copolymer comprising propylene and a branched aolefin having 5 to 12 carbon atoms, prepared using a catalyst comprising (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor, said block copolymer: (a) comprising 5-95 /O by weight of said propylene and 95-5% by weight of said branched aolefin having 5 to 12 carbon atoms; (b) having an intrinsic viscosity of 0.5 to 10 dl/g (in decalin at 135"C); (c) having at least one melting point not lower than 145"C among melting points measured by a differential scanning calorimeter (DSC); and (d) having a modulus of flexural rigidity of 8,000 to 15,000 kg/cm2 (according to ASTM D747-70).

2. A copolymer as set forth in Claim 1, wherein said a-olefin is 4-methyl-1-pentene.

3. A process for preparing a propylene/branched a-olefin block copolymer by copolymerizing propylene with a branched a-olefin having 5 to 12 carbon atoms in th presence of a catalyst comprising (1) a solid material containing at least magnesium and titanium, (2) an organometallic compound and (3) an electron donor, characterized by performing a first-stage polymerization at a temperature not higher than 50"C and performing a second-stage polymerization at a temperature not lower than 50"C in a substantial absence of monomer used in the first-stage polymerization, said block copolymer:: (a) comprising 5-95% by weight of said propylene and 95-5% by weight of said branched aolefin having 5 to 12 carbon atoms; (b) having an intrinsic viscosity of 0.5 to 10 dl/g; (c) having at least one melting point not lower than 145"C among melting points measured by a differential scanning calorimeter (DSC); and (d) having a modulus of flexural rigidity of 8,000 to 15,000 kg/cm2 (according to ASTM D 747-70).

4. A process as set forth in Claim 3, wherein said first-stage polymerization is for producing said a-olefin block and said second-stage polymerization is for producing said propylene block.

5. A process as set forth in Claim 4, wherein said first-stage polymerization is carried out by polymerizing said a-olefin in the presence or absence of solvent, then unreacted a-olefin is removed and thereafter said second-stage polymerization is carried out under introduction of propylene in the presence or absence of a solvent.

6. A process as set forth in any one of Claims 3 to 5, wherein said first-stage polymerization is carried out at a temperature of 20 to 50"C.

7. A process as set forth in any one of Claims 3 to 6, wherein said second-stage polymerization is carried out at a temperature of 50 to 90"C.

8. A process as claimed in Claim 3, substantially as hereinbefore described with particular reference to the Examples.

9. A process as claimed in Claim 3, substantially as illustrated in any one of the Examples.

10. A block copolymer when prepared by the process claimed in any one of Claims 3 to 9.

11. A block copolymer as claimed in Claim 1, substantially as hereinbefore described with particular reference to the Examples.

12. A block copolymer as claimed in Claim 1, substantially as illustrated in any one of the Examples.