JPH04218504A - Method for increasing molecular weight of syndiotactic polypropylene - Google Patents

Abstract

PURPOSE:To readily increase the mol.wt. of polypropylene having a substantially syndiotactic configuration with a reduced amount of radiations. CONSTITUTION:A method for increasing the mol.wt. of polypropylene having a substantially syndiotactic configuration by the irradiation of radiations in the absence of oxygen. The polypropylene is preferably heated after the irradiation of the radiations. The polypropylene having the substantially syndiotactic configuration can be irradiated with the radiations in the melted state. The polypropylene having the substantially syndiotactic configuration is preferably a polypropylene in which a diffraction line is not observed in a spacing of lattice planes of approximately 7.1Angstrom by X-ray diffraction method.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for increasing the molecular weight of syndiotactic polypropylene. Specifically, the present invention relates to a method for increasing the molecular weight of polypropylene having a substantially syndiotactic structure by partial crosslinking.

0002

BACKGROUND OF THE INVENTION Isotactic polypropylene is inexpensive and has a relatively good balance of physical properties, and is used for various purposes. On the other hand, the existence of syndiotactic polypropylene has been known for a long time. However, the conventional method of low-temperature polymerization of vanadium compounds with a catalyst consisting of ether and organoaluminum has poor syndiotacticity and is said to have elastomeric properties. It was hard to say that it expressed his characteristics.

[0003] On the other hand, J. A. It was discovered for the first time by Ewen et al. that polypropylene with good tacticity, with a syndiotactic bentad fraction exceeding 0.7, can be obtained using a catalyst consisting of a transition metal compound having an asymmetrical ligand and aluminoxane (J
．． Am. Chem. Soc. , vol. 11
0, 6255-6256 (1988)). This syndiotactic polypropylene with good stereoregularity has an excellent balance of rigidity and impact resistance, and is at a level that can be fully used for conventional isotactic polypropylene applications. There were problems in that only polymers with small molecular weights and narrow molecular weight distributions could be obtained, resulting in poor moldability.

0004

[Problem to be solved by the invention] To solve this problem, it is useful to widen the molecular weight distribution, and for this purpose, it is possible to achieve the objective by using a mixture of catalysts containing different transition metals. Although it is possible, there are problems such as poor catalytic activity.

[0005] On the other hand, isotactic polypropylene can be crosslinked by irradiation with radiation to obtain a branched polymer, which is said to have good moldability (
JP-A-62-121704), isotactic polypropylene has a high rate of decrease in molecular weight when irradiated with radiation, and irradiation with a small amount of radiation, for example, several Mrad, does not increase the molecular weight (for example, Jo
Urnal of Applied Polymer
Science vol. 11,705 (1967
). ).

[0006] Accordingly, an object of the present invention is to provide a method for easily increasing the molecular weight of polypropylene having a substantially syndiotactic structure with a small radiation dose.

[0007]

[Means for Solving the Problems] The present inventors solved the above-mentioned problems, conducted extensive research into increasing the molecular weight of polypropylene having a substantially syndiotactic structure, and completed the present invention.

That is, the present invention is a method for increasing the molecular weight of syndiotactic polypropylene, which is characterized in that polypropylene having a substantially syndiotactic structure is irradiated with radiation in the absence of oxygen.

In the present invention, polypropylene having a substantially syndiotactic structure includes not only a homopolymer of propylene having a syndiotactic structure but also a copolymer of propylene and other olefins.

Catalysts used for producing syndiotactic polypropylene include those listed in J. A. Ewen
An example is a catalyst consisting of a transition compound having an asymmetric ligand and aluminoxane described in the literature of et al.
Even if the catalyst has a different structure, it can be used as long as it can produce polypropylene having a syndiotactic pentad fraction of 0.7 or more.

Examples of the transition metal compound having an asymmetrical ligand include isopropyl (cyclopentadienyl-1-fluorenyl) hafnium dichloride, or isopropyl (cyclopentadienyl-1-fluorenyl) described in the above-mentioned literature.
Examples include fluorenyl) zirconium dichloride. In addition, as aluminoxane, the following formula (I)

[
0012

[Chemical formula 1] or formula (II)

[0013]

[Formula 2] (In these formulas, R is a hydrocarbon residue having 1 to 3 carbon atoms, n
is an integer from 1 to 50. ) are exemplified, and in particular, methylaluminoxane in which R is a methyl group and n is 5 or more, preferably 10 or more is used.

The ratio of aluminoxane used to the above transition metal compound is 10 to 1,000,000 times by mole, usually 50 times
~5000 times the mole.

There are no particular limitations on the propylene polymerization conditions, and a solvent polymerization method using an inert medium, a bulk polymerization method or a gas phase polymerization method substantially free of an inert medium can also be used. Generally, the polymerization temperature is -100 to 200 DEG C., and the polymerization pressure is normal pressure to 100 kg/cm2. Preferably -100 to 100°C, normal pressure to 50k
g/cm2.

In the present invention, the preferable molecular weight of the polypropylene having a substantially syndiotactic structure to be irradiated with radiation is generally about 0.1 to 5 as the intrinsic viscosity measured in a tetralin solution at 135°C. A value of 2.0 or less is preferable.

In the case of a propylene homopolymer, the degree of syndiotacticity is 0.6 or more as a syndiotactic pentad fraction, preferably 0.7 or more. If the syndiotactic pentad fraction is less than 0.6, the properties as a crystalline polypropylene will not be sufficient and the physical properties will be poor, which is not preferable. In addition, in copolymers of propylene and other olefins, a peak observed at about 20.2 ppm in the 13C-NMR absorption spectrum measured with a 1,2,4-trichlorobenzene solution using tetramethylsilane as a reference. 0 of the peak intensity whose intensity is attributed to all methyl groups of the propylene unit
．． It is 3 or more, preferably 0.5 or more. This value is 0.
If it is less than 3, the physical properties will be poor, which is not preferable.

Examples of α-olefins other than propylene used in the copolymerization with propylene include ethylene and optionally branched α-olefins having 4 to 20 carbon atoms. In particular, butene-1, pentene-1,
hexene-1, octene-1,4-methylpentene-1
is preferred. The amount of these α-olefins is preferably 20% by weight or less, particularly preferably 10% by weight or less, based on propylene.

In the present invention, radiation irradiation is performed in the absence of oxygen, ie, under vacuum or in an inert gas atmosphere such as nitrogen, helium, or argon. If radicals still exist after irradiation, it is preferable to hold the irradiated syndiotactic polypropylene in the absence of oxygen for a sufficient period of time to eliminate the radicals.

Examples of radiation include γ rays, electron beams,
X-rays are preferably used, and when electron beams are used, it is preferable to reduce the thickness of the syndiotactic polypropylene before irradiating. The dose during irradiation is 0.1-5
0 Mrad, usually about 1 to 10 Mrad is sufficient. Note that both gamma ray and electron beam irradiation are carried out industrially, and gamma rays are usually carried out in batches because it takes time, but with electron beams, a conveyor is installed below the electron beam irradiation equipment and the Place the polymer and irradiate it.

In the present invention, radiation irradiation is carried out at a relatively low temperature, preferably below 100°C, particularly preferably below 50°C, under such conditions that radicals remain in the polymer after irradiation, and then heated after irradiation. is preferable.

The heating temperature is preferably higher than the irradiation temperature but lower than the melting point of syndiotactic polypropylene, and is usually 80° to 140°C.

[0023] The heating time depends on the heating temperature; the higher the temperature, the shorter the heating time. Typical heating times are about 5 minutes to about 5 hours. As a guideline for the heating temperature and heating time, the temperature and time are sufficient to annihilate radicals, for example, 10
The objective can be achieved by heating for 1 hour at 0°C.

[0024] By heat treatment after radiation irradiation,
The reduction in molecular weight of the polypropylene that occurs when handling syndiotactic polypropylene in which radicals are present in the presence of oxygen can be avoided.

In the present invention, it is preferable that the syndiotactic polypropylene to be irradiated with radiation in the absence of oxygen has a low degree of crystallinity. Here, syndiotactic polypropylene with a low degree of crystallinity means that substantially no diffraction lines are observed at a lattice spacing of about 7.1A when measured by X-ray diffraction. Substantially no diffraction lines are observed means, for example, that Cu-K is used as an X-ray source.
This means that when α rays are used and observed in the range of 5 to 50 degrees as 2θ, only about 1/5 or less of the maximum intensity peak of the observed diffraction image is observed.

If a strong diffraction line is substantially observed at a spacing of about 7.1A, the effect of increasing the molecular weight is small.

[0027] The syndiotactic polypropylene having a low degree of crystallinity as described above is irradiated with radiation at an irradiation temperature of preferably 80°C or lower, more preferably 50°C or lower, particularly preferably 30°C or lower, and after the irradiation. It is preferable to perform the heat treatment under conditions such that a sufficient amount of radicals remain in the syndiotactic polypropylene, and then heat treatment. The heating temperature at this time is the same as the heating temperature described above. Note that this does not mean that the molecular weight will not increase even if radiation is irradiated under conditions where crystallization is advanced, but that it is more effective than the above conditions.

In the present invention, it is also a preferred embodiment that the syndiotactic polypropylene is irradiated with radiation in the molten state in the absence of oxygen. Here, the molten state means that it is not substantially in a crystalline state, and is a state in which no sharp peak reflecting the crystal structure is observed when an X-ray diffraction spectrum is measured.

The temperature during radiation irradiation may be any temperature at which the crystallization rate of the molten syndiotactic propylene is sufficiently slow, and does not necessarily need to be maintained at a temperature higher than the melting point of the syndiotactic polypropylene. Preferably 30
Temperatures of 0° to 60°C, particularly preferably 180° to 80°C are employed.

As described above, by irradiating molten syndiotactic polypropylene with radiation, it is possible to mold it without heating or cooling after irradiation. Therefore, the radicals present in the syndiotactic polypropylene in a molten state do not react with oxygen, so that the molecular weight does not decrease.

[0031]

[Examples] The present invention will be explained in more detail below with reference to Examples and Comparative Examples. However, these examples are for illustrating the invention, and
It is not a restriction.

Example 1 Isopropylcyclopentadienyl-1-fluorene synthesized according to a conventional method was lithiated, reacted with zirconium tetrachloride, and the reaction product was recrystallized to obtain isopropyl(cyclopentadienyl-1-fluorene). 0.2 g of 1-fluorenyl) zirconium dichloride and methylaluminoxane manufactured by Toyo Akzo Co., Ltd. (degree of polymerization 16.1) 30
g and propylene were charged into an autoclave having an internal volume of 200 liters, and polymerization was carried out at 20° C. for 2 hours at a polymerization pressure of 3 kg/cm 2 -G. The polymerization mixture was treated with methanol and methyl acetoacetate at 30°C, washed with an aqueous hydrochloric acid solution, and then filtered to obtain 5.6 kg of syndiotactic polypropylene. This polypropylene is 13C
- Syndiotactic pentad fraction 0 according to NMR
．． 935, and the intrinsic viscosity (hereinafter abbreviated as η) measured in a tetralin solution at 135°C is 1.45, the ratio of the weight average molecular weight and number average molecular weight measured in 1,2,4-trichlorobenzene (hereinafter MW/ MN) was 2.2.

This polypropylene was sealed in a glass tube under degassing, and γ-rays were irradiated at 2 Mrad/hr to 3 Mra at 20°C.
d irradiation and then heating at 100° C. for 1 hour. The powder after heating had a η of 1.58 and a MW/MN of 3.1.

[0034] For polypropylene before irradiation, 230°C,
Shear rate 100mm/sec. The die swelling is 1.19, and the shear rate is 6 mm/
sec. The take-up speed is 8.2 mm/sec. The melt tension was 12.5.

Furthermore, the polypropylene after irradiation had a die swelling of 1.60 and a melt tension of 16.5 g under the same conditions, which were significantly improved compared to before irradiation. Comparative Example 1 In Example 1, the sealed tube was broken without heat treatment after radiation irradiation and η was measured, and it was 1.38, and the MW
/MN was 2.12.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the γ-ray irradiation was carried out in air. η was 1.18 and MW/MN was 2.1.

Example 2 The polypropylene obtained in Example 1 was melt-pressed at 200°C to form a 1 mm sheet, which was then placed in water at 0°C and quenched. At this time, the rate of temperature decrease was measured by a sensor inserted into the center of the sheet and found to be 250° C./min, and the X-ray diffraction spectrum of the molded product is shown in FIG. The surface spacing is 7.
No diffraction line is observed at 1A (12.5° in 2θ). This sheet was sealed in a glass tube under degassing and irradiated with γ rays at 2 Mrad/hr for 3 Mrad at 20°C. When the sheet was taken out and η was measured, it was 1.53, which was MW/MN.
was 2.9. Some sheets were heated at 100°C for 1 hour. The polypropylene after heating had a η of 1.64 and a MW/MN of 3.5. Under the same conditions as Example 1, the die swelling was 1.75 and the melt tension was 17.
．． It was 6g.

Example 3 The same procedure as in Example 1 was performed except that a sheet obtained by cooling for 30 minutes after molding (the X-ray diffraction spectrum of the molded product is shown in FIG. 2) was used. The one heat-treated after irradiation had η of 1.47. Furthermore, the die swelling under the same conditions as in Example 1 was 1.50.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the γ-ray irradiation was performed in air. η was 1.27 for the sample without heating after irradiation, and 1.29 for the sample that was heated. Ta.

Example 4 The sheet obtained in Example 2 was irradiated with an electron beam of 5 Mrad under a nitrogen stream using an electron beam irradiation device (EPS-750 manufactured by Nissin High Voltage Co., Ltd.). 100℃ under nitrogen after irradiation
The mixture was heated for 1 hour. η after heating was 1.84. Under the same conditions as Example 1, the die swelling was 2.08 and the melt tension was 17.6 g.

Example 5 The polypropylene obtained in Example 1 was placed in a sealed tube and heated under degassing.
Heating to 30°C, then 2 Mrad/gamma radiation at 140°C.
It was irradiated with 6 Mrad for hr. After cooling, the polypropylene was taken out and η was measured, and it was 1.67, indicating that M
W/MN was 4.2. In addition, according to the X-ray diffraction spectrum at 140° C. of the polymer molded under the same conditions, no sharp peaks were observed and only a broad diffraction spectrum was observed.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the γ-ray irradiation was carried out in air, and η was 0.85.

Example 6 The same procedure as in Example 1 was performed except that γ-ray irradiation was performed at 160° C., which is higher than the melting point of the polymer, and η was 1.69 and MW/MN was 4.6. .

Comparative Example 5 Isotactic pentad fraction is 0.940, η is 1
．． 43. When commercially available isotactic polypropylene having a MW/MN of 5.8 was irradiated with γ-rays in the same manner as in Example 1, η was 1.08.

Comparative Example 6 The polymerization method of Example 1 was repeated at 0° C. using 1,2 ethylene bistetrahydroindenyl zirconium dichloride in place of isopropyl (synchropentadienyl-1-fluorenyl) zirconium dichloride as a transition metal catalyst component. Polymerization is carried out, and the isotactic pentad fraction is 0.8.
When γ-rays were irradiated in the same manner as in Example 1 using isotactic polypropylene having a polypropylene 95, η of 1.23, and MW/MN of 2.2, η was 0.98.

[0046]

Effects of the Invention As is clear from the above results, the molecular weight of polypropylene having a substantially syndiotactic structure can be easily increased by irradiating it with radiation in the absence of oxygen and then heating if desired. Ru. In addition, the obtained polymer has large die swelling and melt tension, and is particularly characterized by good processability into blow molding, sheets, films, etc.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an X-ray diffraction spectrum of a syndiotactic polypropylene molded product used in Example 2.

FIG. 2 is a diagram showing an X-ray diffraction spectrum of a syndiotactic polypropylene molded product used in Example 3.

Claims (4)

[Claims] 1. A method for increasing the molecular weight of syndiotactic polypropylene, which comprises irradiating polypropylene having a substantially syndiotactic structure with radiation in the absence of oxygen. 2. The method according to claim 1, wherein the radiation treatment is followed by heat treatment. 3. The polypropylene having a substantially syndiotactic structure has substantially no diffraction lines observed at a lattice spacing of about 7.1 A when measured by X-ray diffraction. Method. 4. The method according to claim 1, wherein the polypropylene having a substantially syndiotactic structure is irradiated in a molten state.