CS243047B1 - Process for the production of tough polymers of propylene and its copolymers with ethylene - Google Patents

Abstract

The invention relates to the production of tough propylene polymers and propylene-ethylene copolymers. Polymerization using titanium-based catalytic systems is carried out at a hydrogen concentration of less than 0.3 mol% in the gas phase of the reactor to achieve a polymer flow index of less than 0.1 g/10 min. The polymer or copolymer is degraded in a controlled manner by adding organic peroxides at a temperature of 190 to 300 °C to a flow index of 2 to 6. A highly tough material with high notch toughness is obtained with reduced formation of atactic portions.

Description

The invention relates to a method for producing tough polymers of propylene and its copolymers with β-ethylene.

Highly isotactic polypropylene has attractive properties such as high stiffness, resistance to thermal stress, abrasion and stress cracking, which allow it to be used in a variety of applications. On the other hand, its biggest disadvantage is its high brittleness at low temperatures.

Various methods have been proposed to improve the low temperature toughness of polypropylene.

It is well known to increase the impact strength of polypropylene by adding polyethylene. American patent US 4,088,714 describes the improvement of the properties of a polypropylene-polyethylene blend after the addition of ethylene-propylene rubber.

US Patent No. 4,365,045 describes a method for preparing a material with a low embrittlement temperature based on a two-stage synthesis of so-called TBC copolymers. In this case, a homopolymer block of polypropylene is prepared in the first stage in direct synthesis, followed by a second stage in which a random copolymer of propylene-ethylene is prepared. The hydrogen concentration in the polymerization reactor is controlled so that the resulting polymer has the desired melt index.

In US Patent 4,061,694, the preparation of a tough polymer is based on a TBC copolymer prepared in a similar manner, but the melt index of this material is in the range of 0.5 to 1.5 g/10 min. The prepared copolymer is further degraded with oxygen-containing compounds so that the melt index of the product is higher than the melt index of the starting material.

With the aim of further increasing toughness, a mixture of TBC - copolymer with ethylene-propylene rubber was also prepared and this mixture was thermally or chemically degraded for a longer period (US 4,375,531).

The disadvantage of these processes is the high formation of atactic polypropylene, especially in the production of copolymers.

A method has now been found for producing tough propylene polymers and propylene-ethylene copolymers by polymerization using titanium-based catalytic systems and controlled degradation initiated by peroxides and mechanochemically, in which the polymerization or copolymerization is carried out at a hydrogen concentration of less than 0.3 mol% in the gas phase of the reactor until a polymer flow index of less than 0.1 g/10 min is achieved at 230 °C and the resulting polymer or copolymer is degraded in a controlled manner by adding organic peroxides at a temperature of 190 to 300 °C to a flow index of 2 to 6 g/10 min.

The actual polymerization according to the invention can be carried out in a discontinuous or continuous manner. The preparation of TBC copolymers, i.e. polymer mixtures prepared directly in the reactor from a polypropylene block and a propylene-ethylene random copolymer, can be ensured by discontinuous polymerization in a single polymerization reactor or continuously in two reactors connected in series. In this case, a polypropylene suspension is prepared in the first reactor, which is continuously pumped into the second reactor, where the propylene-ethylene random copolymer is synthesized.

The polymers of the invention are prepared using a titanium-based catalytic system, which catalytic system consists of:

and/ from a solid component, which may be pure ground titanium chloride, ground mixed crystals of titanium chloride with aluminum chloride, ground pure titanium chloride or ground mixed crystals of titanium chloride with aluminum chloride modified with an organic substance, such as aliphatic and aromatic ethers, alcohols, amines, phosphines, esters of organic acids, heterocyclic compounds and the like.

The solid component may also be titanium chloride supported on a carrier. The carrier may contain, for example, compounds of silicon, magnesium, aluminum, manganese, or an internal polymer material such as polypropylene, polyethylene, and the like may serve as the carrier. Titanium chloride supported on a carrier may be modified with organic compounds, similar to pure titanium chloride or mixed crystals of titanium chloride with aluminum chloride.

b/ components containing an organometallic compound of a metal of groups I to III of the periodic table, such as organometallic compounds of aluminum.

c/ components containing some of the organic compounds of oxygen, nitrogen, phosphorus, sulfur, silicon, such as ethers, glycols, esters of organic acids, amines, siloxanes and the like.

The polymers of the present invention can be prepared in a hydrocarbon solvent such as hexane, heptane, and the like or by gas phase polymerization. The polymers can also be prepared by preparing the polypropylene block in a liquefied propylene environment and the propylene-ethylene random copolymer by gas phase polymerization:

Polymerization or copolymerization is carried out in the preparation of polymers according to the invention at a hydrogen concentration of less than 0.3 mol% in the gas phase of the reactor so that the achieved polymer melt index is less than 0.1 g/10 min at 230 °C.

Ensuring low flow indices of the polymer prepared for controlled degradation allows achieving high toughness of the resulting material and also significantly improves production economics, since a certain reduction in the polymerization activity of the catalytic system at low hydrogen concentrations is more than sufficient to be compensated by a reduction in the production of waste soluble polymer, especially in the preparation of TBC copolymers in a solvent process.

In preparing the polymers according to the invention, polymerization or copolymerization is carried out at a temperature of 50 to 90° C., preferably 65 to 80° C. The polymerization pressure is maintained in the range of 0.5 to 0.4 MPa, preferably 0.8 to 1.5 UPa.

The concentration of ethylene in the gas phase of the reactor is set to a value of 5 to 30 mol%, preferably 15 to 20 mol%.

In the preparation of polymers according to the present invention, it is possible to vary the weight ratio of polypropylene to the propylene-ethylene random copolymer by means of a catalytic activity regulator (for example, some glycols and alcohols can be used as regulators) or by changing the ratio of catalyst residence times in the homopolymerization and copolymerization stages. In this way, it is possible to prepare a polymer with an ethylene content of 2 to 20% by weight,* preferably and with regard to the optimization of mechanical properties, of 7 to 12% by weight, at the used ethylene concentrations in the gas phase of the reactor.

Polymerization can produce a material with a melt index of 0.001 to 0.01 g/10 min, or even a material with a melt index that is not measurable. The fluidity of this material is completely unsuitable for processing into granules and, of course, for application in the field of injection molded products.

However, the melt index can be suitably adjusted by using organic peroxide, the addition of which can increase the melt index to the range of 2 to 6 g/10 min. In AO No. 239 716, the degradation of copolymers with organic peroxide was described, where the melt index of the starting powder was less than 0.5 g/10 min.

The degradation achieves a flow index of 10 to 20 g/10 min depending on the amount of peroxide added.

The present invention relates to such a copolymer material, the initial melt index of which is 0.001 to 0.1 g/10 min. Degradation with organic peroxide achieves a melt index in the range of 2 to 6 g/10 min. The use of organic peroxide is particularly suitable for high molecular weight polypropylene types.

Since organic peroxides have a high initiation efficiency, it is necessary to use a moderation stabilization system that ensures processing stability, long-term thermo-oxidative stability and possibly also stability against UV radiation. For this purpose, sterically hindered phenols, but also sulfides and phosphites and light stabilizers are used.

To achieve a uniform flow index in the final product, it is necessary that degradation occurs throughout the entire volume of the processed material. With the appropriate choice of organic peroxide and stabilization system, it is possible to prepare types with not only good fluidity, but also with appropriate mechanical properties.

For materials where the initial melt index is extremely low (0.001 g/10 min), low values of tensile yield strength and elastic modulus E are achieved, measured by the bending method, but the notch toughness values are very high.

If we use a material with a higher flow index (0.01 g/10 min), then the values of tensile yield strength and impact toughness are improved. The high values of notch toughness are maintained.

The mechanical properties of the product depend not only on the resulting flow index of the material, but are also significantly influenced by the characteristics of the input material (atacticity proportion, ethylene content in the granulate).

Polymer or copolymer degradation can be performed on single-screw or multi-screw extruders, which are designed to ensure the necessary homogeneity of the processed material.

The starting material does not contain any additives. These are added either as a separate stream or together with the peroxide concentrate stream. The temperatures in the extruder range from 190 to 300 °C.

The organic peroxide used as a source of free radicals initiating controlled degradation must meet the conditions of adequate volatility and adequate half-life.

The invention will be illustrated by the following examples. Percentages and parts in the examples are by weight unless otherwise indicated.

Example

A stirred polymerization reactor with a volume of 50 l was charged with 20 l of polymerization grade hexane. After the addition of a catalytic suspension containing 4 g of a solid modified titanium chloride catalyst of commercial type, 3.3 g of diethylaluminum chloride and 35 mg of diethylene glycol dimethyl ether in hexane, the reactor contents were heated to 70 °C. Hydrogen was added to the reactor in such an amount that its concentration in the gas phase of the reactor during the polymerization ranged from 2.0 to 2.5 mol%.

Propylene was then added to increase the reactor pressure to 1.1 MPa. The pressure of 1.1 MPa and the temperature of 70 °C were maintained in the reactor for 2 hours at a stirring speed of 600 rpm. After degassing, the polymer suspension was transferred from the reactor to a stirred 50 l deactivation vessel, where the catalyst was deactivated with 6 l of methanol, while the contents of the vessel were maintained at a temperature of 84 °C for 0.5 hour.

After adding 10 l of distilled water, the lower aqueous-methanolic phase was drained. The hexane suspension of the polymer was cooled to 40 °C and passed into a 50 l pressure filter, where the hexane solution of the etactic polymer was filtered off at 40 °C. The powdered polymer was dried in a stream of nitrogen. A stabilizing mixture consisting of 100 parts of polymer, 0.1 part of phenolic stabilizer (2,6-ditert.butyl-4-methylphenol), 0.1 part of phenolic stabilizer (2,6-dimethyl-4-dodecakis (propenyl) phenol, 0.1 part of secondary sulfur antioxidant (distearylthiodipropionate) was added.

The polymer was granulated in a single-screw extruder with a barrel diameter of 19.1 mm and a length (1) to diameter (D) ratio of 2 D. The screw compression ratio was 4/1. The temperatures in the three adjustable zones of the machine were 220 °C, 250 °C and 200 °C. The screw speed was 45 rpm.

The amount of atactic polymer (APP) was determined by evaporation of an aliquot of the hexane filtrate and was related to the total mass of the produced polymer (PP). From the total mass of the produced polymer and the mass of the solid catalyst, the polymerization activity in g PP . · h”' was calculated. The values of the polymerization parameters and mechanical properties of the prepared polymer are shown in Table 1.

Example 2

The polymerization was carried out similarly to Example 1, except that hydrogen was fed into the reactor in such an amount that its concentration in the gas phase of the reactor was maintained at around 0.1 mol % during the polymerization.

The powdered polymer was mixed with 0.05% organic peroxide after drying and the stabilizers mentioned in Example 1 were added in an amount of 0.1%. This mixture was mixed in a mixer for 5 minutes and then granulated in a single-screw extruder as in Example 1. The resulting product had IT = 2.5 g/10 min. The results obtained are shown in Table 1.

Example 3

The polymerization was carried out similarly to Example 1 except that the hydrogen concentration in the reactor was maintained in the range of 5.5 to 6.0 mol% and the reactor pressure was 0.9 MPa. The total homopolymerization time was 4 h.

This was followed by rapid cooling of the reactor contents to 60 °C and at the same time, ethylene and propylene were dosed so that the resulting pressure in the reactor reached 1.1 MPa and the ethylene concentration in the gas phase of the reactor ranged from 9 to 10 mol% (continuously monitored by chromatographic analysis of the gas phase of the reactor).

The reactor was maintained under these conditions for 1.5 h. After degassing, the polymer suspension was processed similarly to Example 1, except that the temperature in the deactivation vessel was set to 77 °C. The values of the polymerization parameters and mechanical properties of the polymers prepared according to Examples 3-8 are shown in Table 2.

Example 4

Homopolymerization and copolymerization were carried out similarly to Example 3 except that the hydrogen concentration in the gas phase of the reactor was maintained at 0.6 mol%. Post-polymerization processing of the polymer suspension was similar to Example 2 except that the organic peroxide concentration in the polymer was increased to 0.06% and the temperature in the deactivation vessel was set as in Example 3.

Example 5

Both homopolymerization and copolymerization were carried out similarly to Example 3 except that the hydrogen concentration in the gas phase of the reactor was maintained at 0.1 mol%, the ethylene concentration during copolymerization was controlled in the range of 16.0 to 17.0 mol%, and the copolymerization time was reduced to 0.5 h. The postpolymerization treatment of the polymer suspension was similar to Example 4 except that the organic peroxide concentration in the polymer was increased to 0.1%.

Example 6

The polymer was prepared under similar conditions as in Example 3, except that a different solid catalyst was used, hydrogen was fed into the reactor in such an amount that its concentration in the gas phase of the reactor during homopolymerization ranged from 5.8 to 6.3 mol%, and the ethylene concentration during copolymerization was maintained in the range of 20.0 to 21.0 mol%.

Example 7

Homopolymerization and copolymerization were carried out similarly to Example 3 except that the same catalyst was used as in Example 6, the hydrogen concentration in the gas phase of the reactor was maintained at 0.1% molar and during copolymerization the ethylene concentration was maintained at 20.0 to 21.0% molar.

The post-polymerization processing of the polymer suspension was similar to that in Example 5.

Examples

The polymerization preparation was carried out under similar conditions as in Example 7, except that hydrogen was not fed into the system and the copolymerization time was shortened to 0.5 h.

Table 1

1 Example 2 Polymerase activity _g pp . _g ;' _t . h- ¹ 405 280 APP X Share 1.4 0.8 Flow index gPP/10 mlh slat 2 1 0.04 Flow index gPP/10 min granulate 2.4 2.5 Mess trot MPa in tension 34 32 Notch toughness 23 °C 3.2 3.8 kJ . m ² 0 °C 1.7 2.0

Table 2

Example 3 4 5 6 7 8 Polymerization activity of gPP . . h-’ 230 250 240 210 190 155 APP Share % 11.1 7.0 6.1 16.9 8.4 3.9 Index gPP/10 min 5.2 0.6 0.02 5.0 0.01 0.01 powder flow Flow index gPP/10 min. 5.4 4.4 5.9 5.1 5.2 4.7 granulate Ethylene content % 2.5 2.5 3.0 5.0 10.5 , 6.5 in polymer Yield strength MPa 27.7 25.0 23.1 24.6 22.5 18.2 in tension Modulus of elasticity QPa 0.95 0.97 * measured by bending method Notched toughness 0 °C 2.9 5.3 8.5 6.2 unbroken 36.3 kJ . M ² -20 °C 2.3 2.7 5.0 4.1 11.4 8.5

The results show that the process according to this invention achieves a significant reduction in the formation of atactic polypropylene and an increase in notch toughness, especially in ethylene-propylene copolymers.

Claims (1)

SUBJECT OF THE INVENTION Process for producing tough propylene polymers and copolymers of propylene with ethylene by polymerization using titanium-based catalyst systems and controlled degradation initiated by peroxides and mechanochemically, characterized in that the polymerization or copolyaeration leads to a gas concentration of less than 0.3 mol% in the gas phase of the reactor. achieving a polymer flow index of less than 0.1 g / 10 min, and the resulting polymer or copolymer is degraded by controlled addition of organic peroxides at 190-300 ° C to a flow index of 2-6 g / 10 min.