An ethylene-propylene copolymer elastomer containing long ethylene chain segments and preparation method thereof

Abstract

The present invention discloses an ethylene-propylene copolymer elastomer containing long ethylene chain segments and a preparation method. The mass proportion of the rubber phase in the olefin elastomer is less than 80wt%. The ethylene unit proportion of the elastomer is greater than 20%, and the number average sequence length of the ethylene in the elastomer is greater than 3. The elastomer obtained by the present invention has a longer average ethylene sequence length. Compared with traditional toughened and modified polypropylene, the present invention replaces traditional ethylene-propylene rubber with an ethylene-propylene copolymer with a high block content. The polyethylene shell of the former has a very low glass transition temperature. The high block content ethylene-propylene copolymer is used as a compatibilizer, which greatly improves its compatibility with polypropylene. The prepared polypropylene material has better low-temperature toughness and better meets the requirements of industries such as automobiles and home appliances.

Description

Field of the Invention

[0001] The present invention relates to the technical field of preparation of ethylene-propylene copolymer elastomers, in particular to an ethylene-propylene copolymer elastomer containing long ethylene chain segments and a preparation method thereof. Background Art

[0002] Polypropylene (PP) is one of the most widely used commodity plastics due to its excellent mechanical properties, including heat resistance, high strength, processability, and low cost. Due to its excellent properties, PP is widely used in industries such as automotive, home appliances, engineering, and electronics.

[0003] However, due to the high regularity of its molecular structure, polypropylene has poor impact resistance, which is more pronounced in low-temperature environments. This greatly limits its use in many applications. Currently, the main industrial solution to this problem is to improve the mechanical properties of polypropylene by adding nucleating agents and rubber phases to polypropylene through physical blending.

[0004] The introduction of the rubber phase improves the impact properties of heterophasic polypropylene to a certain extent. However, the transformation of polypropylene from a homogeneous structure to a heterophasic structure affects the overall performance of the material due to the poor compatibility between the phases. In order to produce polypropylene products with excellent performance, researchers have made many attempts, including improving the production process of elastomers. Currently, it is generally recognized that the decisive factor affecting the performance of heterophasic polypropylene is the difference in compatibility between the phases, so the compatibilization of heterophasic polypropylene has become a hot research direction for the toughening of polypropylene.

[0005] Currently, to improve the compatibility between the phases in heterophasic polypropylene, the main method in the prior art is to change the block content and segment structure in the dispersed phase. CN 104356324 discloses a propylene / α-olefin block interpolymer. During the reaction process, a chain shuttling agent is added to the reaction mixture so that the resulting polymer molecule includes two or more blocks. CN 103641862 discloses a method for preparing a crystalline ethylene-propylene copolymer. A metallocene complex is used as a main catalyst, and methylaluminoxane or isobutyl-modified methylaluminoxane is used as a cocatalyst to copolymerize and prepare an ethylene-propylene crystalline copolymer with a block-type comonomer sequence distribution. CN 115558195 discloses a high-impact copolymerized polypropylene resin with both high fluidity and rigidity. The impact copolymerized polypropylene has an ethylene structural unit mass content of 16-25%, a rubber phase mass content of 30-40%, and a simple supported beam notched impact strength of greater than 50 kJ / m at room temperature. 2 However, the impact performance loss at low temperature is large, and the simple supported beam notch impact strength at -20℃ is only 8KJ / m 2 . Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies of the prior art and provide an ethylene-propylene copolymer elastomer containing long ethylene segments and a method for preparing the same. The technical solution of the present invention is as follows:

[0007] According to the first aspect of the present invention, the present invention provides an ethylene-propylene copolymer elastomer containing long ethylene chain segments, wherein the mass proportion of the rubber phase in the elastomer is less than 80wt%; the molar fraction of ethylene units in the elastomer is greater than 50%, and the number average sequence length of ethylene in the elastomer is greater than 3.

[0008] In a preferred embodiment of the present invention, the number average sequence length of ethylene in the elastomer is preferably greater than 4.99, more preferably greater than 8.72.

[0009] In a preferred embodiment of the present invention, the rubber phase component in the elastomer is a soluble fraction separated by xylene fractionation according to GB / T24282-2021.

[0010] In a preferred embodiment of the present invention, the number average sequence length of ethylene is the average length n of continuous ethylene units calculated from the NMR characterization results. E .

[0011] In a preferred embodiment of the present invention, in the sequence distribution of the elastomer, the content of the ternary sequence EEE consisting of three consecutive ethylene units E is greater than 20%, preferably greater than 36%, more preferably greater than 50%.

[0012] In a preferred embodiment of the present invention, in the sequence distribution of the elastomer, the sum of the contents of the ternary sequences EPE and PEP consisting of ethylene units E and propylene units P is less than 50%, preferably less than 35%, more preferably less than 18%, and even more preferably less than 10.5%.

[0013] A prominent feature of the elastomer provided by the present invention is its significantly higher block copolymer content than commercial products. It is well known that the block copolymer component is a key factor in improving the compatibility between multiple phases. Good compatibility between multiple phases significantly enhances the toughening effect of the elastomer, which plays a key role in improving the compatibility of heterophasic polypropylene.

[0014] According to a second aspect of the present invention, the present invention provides a method for preparing the above-mentioned ethylene-propylene copolymer elastomer containing long ethylene chain segments, which comprises the following steps:

[0015] Two reactants (mixed gases) containing different molar ratios of ethylene and propylene are provided to a polymerization reactor by periodic switching to carry out copolymerization of ethylene and propylene. The reaction temperature is controlled at 50 to 90° C. and the reaction pressure is controlled at 1 to 100 bar to obtain the ethylene-propylene copolymer elastomer containing long ethylene chain segments.

[0016] In a preferred embodiment of the present invention, the frequency of periodic switching of the two reactants having different molar ratios of ethylene and propylene is 5-90 times / hour.

[0017] In a preferred embodiment of the present invention, the ethylene content of the reactants ranges from 2% to 98%, with the remainder being propylene. Furthermore, preferably, the molar percentage difference in ethylene content between the two reactants is no less than 30%.

[0018] In a preferred embodiment of the present invention, before switching to a mixed gas with a different E / P ratio, the remaining raw material gas from the polymerization reaction carried out under the mixed gas with the current E / P ratio must be completely evacuated.

[0019] Compared with existing technologies, the present invention offers the following advantages: It utilizes dynamic switching polymerization technology to produce an ethylene-propylene copolymer elastomer containing a relatively high number of long ethylene sequences and exhibiting low xylene solubles. Due to its unique segment structure, this elastomer exhibits excellent compatibility with polypropylene, significantly enhancing its toughening effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the accompanying drawings are provided only for a better understanding of the present invention and should not be construed as limiting the present invention.

[0021] Figure 1 A schematic diagram of the polymerization process for preparing ethylene-propylene copolymer elastomers containing long ethylene chain segments is shown. DETAILED DESCRIPTION

[0022] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0023] Preparation of polymers

[0024] The polymerization process is gas phase polymerization of ethylene and propylene.

[0025] like Figure 1As shown, the gas-phase polymerization stage is carried out by alternating between two ethylene-propylene gas mixtures in different ratios. The polymerization atmosphere is switched at a predetermined frequency to achieve the desired polymer properties during the gas-phase polymerization in the fluidized bed reactor. Hydrogen can also be introduced to control molecular weight. The polymerization is carried out in a gas-phase fluidized bed reactor. The fluidized bed reactor operates at a reaction temperature range of 65-90°C and a pressure range of 1-30 bar. The average residence time during the ethylene copolymerization stage is 10-100 minutes.

[0026] Example 1

[0027] Sodium chloride, catalyst, co-catalyst and electron donor were added to the 1.5L stirred tank R1. Then the gas phase copolymerization stage was started. The gas phase polymerization stage was carried out by alternating switching between two ethylene propylene gas mixtures with different proportions. The E / P ratios of the mixed gases were 3:1 and 1:3 respectively. The switching frequency was set to 40 times / hour, that is, the mixed gas switching operation was performed every 1 minute 30 seconds. Every two switching operations constituted a complete switching cycle. One switching cycle refers to the cycle of switching from the first mixed gas to the second mixed gas and then switching back to the first mixed gas. The total reaction residence time is 60 minutes. Before switching the gas, a vacuum pump was used to evacuate the residual gas in the kettle before the next stage of gas intake. The gas phase reaction temperature was 70°C and the pressure was 5 bar. After the gas phase copolymerization was completed, the product was obtained by cyclone separation.

[0028] The average sequence length of the ethylene segment is 8.73, the content of the ternary EEE sequence is 50.3%, and the ethylene content is 62.2%. The impact strength of the blend with homopolymer polypropylene (elastomer addition is 30wt%) at room temperature is 31.8kJ / m 2 , and the flexural modulus is 903 MPa. Compared with Comparative Example 1, the average sequence length of the ethylene segment is increased by 113.4%, and the content of the ternary EEE sequence is increased by 90.5%.

[0029] Example 2

[0030] Sodium chloride, catalyst, co-catalyst and electron donor were added to the 1.5L stirred tank R1. Then the gas phase copolymerization stage was started. The gas phase polymerization stage was carried out by alternating switching of two ethylene propylene gas mixtures with different proportions, and the E / P ratios of the mixed gases were 3:1 and 1:3 respectively. The switching frequency was set to 20 times / hour, that is, the mixed gas switching operation was performed every 3 minutes, and every two switching operations constituted a complete switching cycle, in which one switching cycle refers to the cycle of switching from the first mixed gas to the second mixed gas and then switching back to the first mixed gas, and the total reaction residence time is 60 minutes. Before switching the gas, a vacuum pump was used to evacuate the residual gas in the kettle before the next stage of gas intake. The gas phase reaction temperature was 70°C and the pressure was 5 bar. After the gas phase copolymerization was completed, the product was obtained by cyclone separation.

[0031] The average sequence length of the ethylene segment is 6.20, the content of the ternary EEE sequence is 33.1%, and the ethylene content is 56.7%. The impact strength of the blend with homopolymer polypropylene (elastomer addition is 30wt%) at room temperature is 23.1kJ / m 2 , and the flexural modulus is 858 MPa. Compared with Comparative Example 1, the average sequence length of the ethylene segment is increased by 51.6%, and the content of the ternary EEE sequence is increased by 25.4%.

[0032] Comparative Example 1

[0033] Sodium chloride, catalyst, co-catalyst, and electron donor were added to a 1.5 L stirred tank R1. The gas-phase copolymerization stage was then initiated. A gas-phase copolymerization reaction was first conducted with an E / P ratio of 3:1 for the mixed gas. After 15 minutes of reaction, the residual gas in the reactor was evacuated using a vacuum pump. A gas-phase copolymerization reaction was then conducted with an E / P ratio of 3:1 for another 15 minutes. The reaction was terminated and the product was obtained by cyclone separation.

[0034] The average sequence length of the ethylene segment is 4.09, the content of the ternary EEE sequence is 26.4%, and the ethylene content is 56.3%. The impact strength of the blend with homopolymer polypropylene (elastomer addition is 30wt%) at room temperature is 10.1kJ / m 2 , the bending modulus is 738Mpa.

[0035] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An ethylene-propylene copolymer elastomer containing long ethylene chain segments, characterized in that: The average sequence length of the ethylene segments in the elastomer is 8.73, the content of the ternary EEE sequence is 50.3%, and the ethylene content is 62.2%; the mass proportion of the rubber phase is less than 80%; The ethylene-propylene copolymer elastomer containing long ethylene chain segments is prepared by the following method: The gas-phase polymerization stage was carried out by alternating switching between two ethylene-propylene mixtures with different ratios, with the E / P ratios of the mixtures being 3:1 and 1:3, respectively. The switching frequency was set at 40 times per hour, meaning a gas mixture switching operation was performed every 1 minute 30 seconds. Every two switching operations constituted a complete switching cycle, where one switching cycle refers to the period of switching from the first gas mixture to the second gas mixture and then back to the first gas mixture. The total reaction residence time was 60 minutes. Before switching gases, a vacuum pump was used to evacuate the residual gas in the reactor before proceeding to the next stage of gas intake. The gas-phase reaction temperature was 70°C and the pressure was 5 bar. After the completion of the gas-phase copolymerization, the product was obtained by cyclone separation.

2. The ethylene-propylene copolymer elastomer containing long ethylene chain segments according to claim 1, characterized in that: The rubber phase in the elastomer is a soluble fraction separated by xylene fractionation.

3. The ethylene-propylene copolymer elastomer containing long ethylene chain segments according to claim 1, characterized in that: The average sequence length of the ethylene segment is the average length of the continuous ethylene units calculated from the NMR characterization results. n E .

4. The ethylene-propylene copolymer elastomer containing long ethylene chain segments according to claim 1, characterized in that: In the sequence distribution of the elastomer, the sum of the contents of the ternary sequences EPE and PEP consisting of ethylene units E and propylene units P is less than 50%.

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