1. A branched polyolefin characterized by: one or more of ethylene and 1-hexene are used as polymerization monomers, one or more of cobaltocene serving as a reducing agent and silver trifluoromethanesulfonate serving as an oxidizing agent are used as chemical regulation and control auxiliaries, and alpha-diimine nickel catalyst and methylaluminoxane MAO cocatalyst are used for preparing the branched polyolefin by a coordination polymerization method.

2. A branched polyolefin according to claim 1, characterized in that: the structure of the branched polyolefin is regulated through an oxidation-reduction process.

3. A branched polyolefin according to claim 2, characterized in that: the regulation and control through the oxidation-reduction process specifically comprises the steps of regulating and controlling by using cobaltocene as a reducing agent, regulating and controlling by using silver trifluoromethanesulfonate as an oxidizing agent or regulating and controlling by using cobaltocene as a reducing agent and regulating and controlling by using silver trifluoromethanesulfonate as an oxidizing agent.

4. A process for the preparation of a branched polyolefin as claimed in claim 1, which process comprises:

the method comprises the following specific steps:

1) after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, respectively dissolving a methyl aluminoxane MAO cocatalyst and an alpha-diimine nickel catalyst in a toluene solvent under the conditions of normal pressure ethylene atmosphere and water bath to respectively obtain a methyl aluminoxane MAO cocatalyst toluene solution and an alpha-diimine nickel catalyst toluene solution, then adding the toluene solvent and the methyl aluminoxane MAO cocatalyst toluene solution into the polymerization reaction device, and stirring at the rotating speed of 600 r/min;

2) adding the alpha-nickel diimine catalyst toluene solution into the polymerization reaction device in the step 1), initiating polymerization reaction and timing, and adding an oxidant silver trifluoromethanesulfonate toluene solution before initiating polymerization reaction or adding no oxidant silver trifluoromethanesulfonate toluene solution before initiating polymerization reaction;

3) after the polymerization reaction is finished, acidifying ethanol by adopting hydrochloric acid with the mass concentration of 5%, adding the ethanol into the polymerization reaction, quenching the polymerization reaction, separating out a polyethylene product after the polymerization reaction is quenched, washing the polyethylene product for multiple times by using ethanol, and finally, putting the polyethylene product into a 40 ℃ normal-pressure oven and a negative-pressure oven for drying to constant weight to obtain a branched polyolefin product.

5. The process for the preparation of branched polyolefins according to claim 4, characterized in that: in the step 1), 1-hexene is added into a polymerization reaction device.

6. The process for the preparation of branched polyolefins according to claim 4, characterized in that: in the step 2), cobaltocene is firstly dissolved in a toluene solution to obtain a cobaltocene toluene solution, then the cobaltocene toluene solution and the alpha-diimine nickel catalyst toluene solution in the step 1) are premixed and injected into the polymerization reaction device in the step 1), polymerization reaction is initiated and timed, and an oxidant of silver trifluoromethanesulfonate toluene solution is added or no oxidant of silver trifluoromethanesulfonate toluene solution is added in the polymerization reaction.

7. The process for the preparation of branched polyolefins according to claim 6, characterized in that: in the step 2), the mass ratio of the reducing agent cobaltocene to the alpha-diimine nickel catalyst is 0.1-1.5, and the mass ratio of the oxidizing agent silver trifluoromethanesulfonate to the alpha-diimine nickel catalyst is 0.1-1.5.

8. The process for the preparation of branched polyolefins according to claim 4, characterized in that: the polymerization reaction conditions in the step 2) are as follows: the reaction temperature is 20 ℃, the molar ratio of aluminum in the methylaluminoxane MAO cocatalyst to nickel in the alpha-diimine nickel catalyst is 600-1800, and the concentration of 1-hexene is 0.1-0.6 mol/L.

9. The process for the preparation of branched polyolefins according to claim 4, characterized in that: the alpha-nickel diimine catalyst in the step 1) is ArN ═ c (me) -NAr, Ar ═ 2,6- (i-Pr)₂C₆H₃。

Background

With the continuous development of the polyolefin industry, the demand of people for polyolefin materials with diversified properties is also increasing. Among these, the realization of controlled preparation of polyolefin products is naturally a major concern of researchers. However, the main control means at present focus on the adjustment of the catalyst ligand or the control of the external reaction conditions of the polymerization reaction. And the polymerization performance of the nickel catalyst is regulated and controlled by means of a chemical auxiliary agent. Early researchers proposed the concept of redox control, and then, by adjusting the electron density of the active center of the rhodium complex, the hydrogenation rate of cyclohexene by the reduced rhodium complex was increased by 16 times compared with the ground state. The oxidant is also utilized to realize the change of the metallic valence state of the ferrocene serving as the ligand of the titanium catalyst, realize the adjustment of the selectivity of the catalyst and really realize the regulation and control of the polymer chain structure through the redox switch. In recent years, researchers have also focused on the control of the redox of nickel diimine catalysts to achieve a chain structure that is not involved in olefin polymerization. Thereby realizing the controllable preparation of the polyolefin product.

The nickel perylene diimine catalyst controlled by redox 'on-off' has important significance on the controllable preparation of high-end polyolefin products. It can regulate and control the catalytic performance of catalyst by regulating the valence state of active metal center and eliminate the dependence on external reaction condition. In addition to the regulation and control of catalytic performance by using the reducer dicyclopentadiene reduced nickel catalyst to adjust the offset of the charge of the metal active center of the nickel perylene diimine catalyst (BIAN) in situ, researchers creatively realize the redox regulation and control of a polyethylene chain structure by using a photochemical control method. In the course of the study of the redox control of the nickel naphthalimide catalyst Cat B. Cobaltocene is widely used as a good reducing agent. Subsequent researches find that the silver trifluoromethanesulfonate serving as a corresponding oxidizing agent can be easily switched between an oxidation state and a reduction state of a target substance with a reducing agent cobaltocene. However, no report is found in the related research on the performance change of ethylene homopolymerization or ethylene/1-hexene copolymerization catalyzed by a catalytic system after adding silver trifluoromethanesulfonate, which is an oxidant, into a cobalt-cobaltocene reduction and naphthalocyanine diimine nickel catalyst reduction system.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a preparation method for preparing branched polyolefin by redox regulation, which can broaden the types of branched polyolefin products to a certain extent and can be used as a new regulation and control means to effectively regulate and control the polymerization performance of a chain walking catalyst to a certain extent.

The technical scheme adopted by the invention is as follows:

a branched polyolefin

The branched polyolefin of the invention takes one or more of ethylene and 1-hexene as polymerization monomers, and takes cobaltocene (CoCp) as a reducing agent₂) And one or more of silver trifluoromethanesulfonate (AgOTf) serving as an oxidant is used as a chemical regulation auxiliary agent, and the branched polyolefin is prepared by using an alpha-diimine nickel catalyst (Cat. B) and a methylaluminoxane MAO cocatalyst through a coordination polymerization method.

The structure of the branched polyolefin is regulated through an oxidation-reduction process.

The regulation and control through the oxidation-reduction process specifically comprises the steps of regulating and controlling by using cobaltocene as a reducing agent, regulating and controlling by using silver trifluoromethanesulfonate as an oxidizing agent or regulating and controlling by using cobaltocene as a reducing agent and regulating and controlling by using silver trifluoromethanesulfonate as an oxidizing agent. The alpha-nickel diimine catalyst is regulated and controlled through the oxidation-reduction process, the activity of the alpha-nickel diimine catalyst is changed, the structure and the performance of the prepared branched polyolefin are further regulated and controlled, and the branched chain of the branched polyolefin, the melting point of the branched polyolefin, the molecular weight of the branched polyolefin and the stress-strain tensile property of the branched polyolefin product are changed.

Preparation method of branched polyolefin

The method comprises the following specific steps:

1) after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, respectively dissolving a methyl aluminoxane MAO cocatalyst and an alpha-diimine nickel catalyst in a toluene solvent under the conditions of normal pressure ethylene atmosphere and water bath to respectively obtain a methyl aluminoxane MAO cocatalyst toluene solution and an alpha-diimine nickel catalyst toluene solution, then adding the toluene solvent and the methyl aluminoxane MAO cocatalyst toluene solution into the polymerization reaction device, and stirring at the rotating speed of 600 r/min;

2) adding the alpha-nickel diimine catalyst toluene solution into the polymerization reaction device in the step 1), initiating polymerization reaction and timing, and adding an oxidant silver trifluoromethanesulfonate toluene solution before initiating polymerization reaction or adding no oxidant silver trifluoromethanesulfonate toluene solution before initiating polymerization reaction;

3) after the polymerization reaction is finished, acidifying ethanol by adopting hydrochloric acid with the mass concentration of 5%, adding the ethanol into the polymerization reaction, quenching the polymerization reaction, separating out a polyethylene product after the polymerization reaction is quenched, washing the polyethylene product for multiple times by using ethanol, and finally, putting the polyethylene product into a 40 ℃ normal-pressure oven and a negative-pressure oven for drying to constant weight to obtain a branched polyolefin product.

In the step 1), 1-hexene is added into a polymerization reaction device.

In the step 2), cobaltocene is firstly dissolved in a toluene solution to obtain a cobaltocene toluene solution, then the cobaltocene toluene solution and the alpha-diimine nickel catalyst toluene solution in the step 1) are premixed and injected into the polymerization reaction device in the step 1), polymerization reaction is initiated and timed, and an oxidant of silver trifluoromethanesulfonate toluene solution is added or no oxidant of silver trifluoromethanesulfonate toluene solution is added in the polymerization reaction.

In the step 2), the mass ratio of the reducing agent cobaltocene to the alpha-diimine nickel catalyst is 0.1-1.5, and the mass ratio of the oxidizing agent silver trifluoromethanesulfonate to the alpha-diimine nickel catalyst is 0.1-1.5.

The polymerization reaction conditions in the step 2) are as follows: the reaction temperature is 20 ℃, the molar ratio of aluminum in the methylaluminoxane MAO cocatalyst to nickel in the alpha-diimine nickel catalyst is 600-1800, and the concentration of 1-hexene is 0.1-0.6 mol/L.

The alpha-nickel diimine catalyst in the step 1) is ArN ═ c (me) -NAr, Ar ═ 2,6- (i-Pr)₂C₆H₃。

The branched polyolefin is prepared by an alpha-diimine nickel catalyst under the catalysis of MAO, and the flexible regulation and control of the performance of the branched polyolefin product are realized by adjusting the reaction equivalent of adding a reducing agent cobaltocene and an oxidizing agent silver trifluoromethanesulfonate into the polymerization reaction and other conditions. The nickel diimine catalyst is used for preparing branched polyolefin by catalytic polymerization by a chain walking mechanism, so that the chain structure of a polyethylene product is more flexibly controlled. The invention has simple polymerization process and adjustable proportion of ethylene and 1-hexene comonomer in the copolymerization process. The catalyst/cocatalyst ratio in the polymerization reaction process, the addition equivalent of the reducing agent cobaltocene or the oxidizing agent silver trifluoromethanesulfonate can be adjusted. The properties of the resulting branched polyolefins also vary within certain limits.

The phase transition temperature, molecular weight, branching degree, tensile property and the like of the branched polyolefin prepared by the invention are all regulated and controlled within a certain range by adding the reducing agent cobaltocene and the oxidizing agent silver trifluoromethanesulfonate. And the branched chain structure of the branched polyolefin can realize regular change in a certain range under the regulation and control of cobaltocene as a reducing agent with different equivalent weights.

The invention has the beneficial effects that:

1. the ethylene/1-hexene copolymerization process is simple, and the coordination polymerization process of the catalyst promoter MAO and the olefin monomer in a polymerization reaction system is carried out by a 'chain walking' catalyst. Branched polyolefin products with different properties can be obtained by redox regulation of a reducing agent cobaltocene and an oxidizing agent silver trifluoromethanesulfonate, wherein the properties comprise the weight average molecular weight, the melting point temperature, the branching degree, the tensile property and the like of the branched polyolefin products.

2. The branched polyolefin prepared by the method has obvious effect of redox regulation and control on the performance, and the weight average molecular weight of the product is 9.78 multiplied by 10⁴g/mol to 16.55X 10⁴g/mol, the melting point temperature is-10.69-57.94 ℃, the branching degree is 71 branches/1000C-101 branches/1000C, the tensile property strain is 185-1808%, and the product performance (such as the product weight average molecular weight, the melting point temperature, the branching degree and the tensile property strain) is adjustable in a certain range.

Drawings

Fig. 1 is a process scheme for preparing branched polyolefins using an α -diimine nickel catalyst (ArN ═ c (Me) -NAr) NiBr2 and redox control corresponding thereto, wherein Me ═ ismethyl；An＝acenaphthene；Ar＝2,6-(i-Pr)₂C₆H₃。

FIG. 2 is a graph showing the variation of catalyst activity, wherein FIG. 2(a) shows the variation of catalyst activity after adding different equivalents of cobalt (II) as a reducing agent to a nickel diimine catalyst/MAO polymerization system; FIG. 2(b) is a graph showing the trend of catalyst activity changes after different equivalents of silver trifluoromethanesulfonate oxidant was added to a nickel diimine catalyst/MAO polymerization system.

FIG. 3 is a graph showing the melting point trend of branched polyolefin, wherein FIG. 3(a) is a graph showing the melting point trend of branched polyolefin obtained by adding different equivalents of cobalt (Co) as a reducing agent to a nickel diimine catalyst/MAO polymerization system; FIG. 3(b) is a graph showing the trend of melting point changes of branched polyolefins obtained by adding different equivalents of silver trifluoromethanesulfonate, which is an oxidant, to a nickel diimine catalyst/MAO polymerization system.

FIG. 4 shows the molecular weight and molecular weight distribution trends of branched polyolefins prepared with reduced nickel alpha-diimine catalyst/MAO catalyst system for different reaction durations.

FIG. 5 is a diagram showing the trend of activity change of a catalyst system in the process of adding different equivalent amounts of a reducing agent cobaltocene and an oxidizing agent silver trifluoromethanesulfonate into an alpha-nickel diimine catalyst/MAO catalyst system to catalyze ethylene homopolymerization or ethylene/1-hexene copolymerization; FIG. 5(a) is a diagram showing the trend of catalyst activity change in the ethylene homopolymerization process at different Co: Ni: Ag ratios;

FIG. 5(b) is a diagram showing the variation trend of catalyst activity in ethylene/1-hexene copolymerization process under different Co: Ni: Ag ratios.

FIG. 6 is a distribution diagram of the branched chains of branched polyolefins prepared with different equivalents of the reducing agent cobaltocene added to the nickel alpha-diimine catalyst system.

FIG. 7 is a graph of stress-strain tensile properties of branched polyolefin products prepared by homopolymerization of ethylene with different equivalents of cobaltocene as a reducing agent and silver trifluoromethanesulfonate as an oxidizing agent added in an alpha-nickel diimine catalyst/MAO catalyst system. The experimental conditions for each sample are shown in table 1:

TABLE 1 CoCp₂Catalyzing ethylene homopolymerization and ethylene/1-hexene copolymerization by Cat.B catalytic system in presence of AgOTf

^aThe reaction conditions were 0.0025mmol of cat. b, 600 of Al/Ni, 20 ℃ of T, and 30or 45min of reaction time.^bActivity 10⁵g polymer/(mol Ni·h).

Detailed Description

The present invention is described in more detail below with reference to the drawings and examples, but the present invention is not limited thereto, and it will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements are also considered to be within the scope of the present invention. Those not described in detail in this specification are within the skill of the art.

The catalyst and the corresponding operation flow of the embodiment of the invention are shown in figure 1;

example 1:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 44.00mL of toluene and 2mL of MAO toluene solution with the concentration of 1.5mol/L are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at 20 ℃, and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent. Injecting 2.0mL of cobaltocene toluene solution with the concentration of 0.0025mol/L into 2.0mL of alpha-nickel diimine catalyst toluene solution with the concentration of 0.0025mol/L for premixing, then injecting all the mixed solution into a polymerization reaction device, initiating polymerization reaction and timing, when the polymerization reaction time length reaches 15min, adding 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) into the polymerization reaction, quenching the polymerization reaction, and precipitating a polyethylene product after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

In specific implementation, the invention also performs experiments on the conditions of cobaltocene with different equivalent weights, the activity condition of the catalyst after the corresponding polymerization reaction system, the melting point condition of the prepared branched polyethylene and the branch distribution condition of the branched polyolefin: in FIG. 2(a), the activity of the catalyst changes when different equivalents of cobaltocene are added into the catalyst system, and it can be seen that the activity of the catalyst gradually decreases with the increase of the equivalents of cobaltocene. FIG. 3(a) shows that the melting point of the resulting branched polyethylene gradually increases with the addition equivalent of cobaltocene. FIG. 6 shows that as the equivalent weight of cobaltocene increases, the methyl content of the obtained branched polyethylene increases and the content of long-chain branches decreases.

Example 2:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 44.00mL of toluene and 2mL of MAO toluene solution with the concentration of 1.5mol/L are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at 20 ℃, and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent. After 2.0mL of toluene solution of silver trifluoromethanesulfonate with a concentration of 0.0025mol/L was injected into the polymerization reactor, 2.0mL of toluene solution of catalyst with a concentration of 0.0025mol/L was injected into the polymerization reactor to initiate polymerization and to measure the time. And when the polymerization reaction time is 15min, adding 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) into the polymerization reaction, quenching the polymerization reaction, and precipitating a polyethylene product after quenching the polymerization reaction. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

In specific implementation, the invention also performs experiments on the conditions of different equivalent amounts of silver trifluoromethanesulfonate and the corresponding activity conditions of the catalyst after polymerization reaction system, the melting point conditions of the prepared branched polyethylene, and the branch distribution conditions of the branched polyolefin: in fig. 2(b), the activity of the catalyst changes when different equivalent amounts of silver trifluoromethanesulfonate are added into the catalytic system, and it can be seen that the activity of the catalyst does not change obviously and regularly with the increase of the equivalent amount of silver trifluoromethanesulfonate. FIG. 3(b) shows that the melting point of the resulting branched polyethylene gradually decreases with increasing equivalent of silver trifluoromethanesulfonate.

Example 3:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 42mL of toluene, 2mL of MAO toluene solution with the concentration of 1.5mol/L and 3.79mL of 1-hexene are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at the temperature of 20 ℃, and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent; injecting 2.0mL of cobaltocene toluene solution with the concentration of 0.0025mol/L into 2.0mL of catalyst toluene solution with the concentration of 0.0025mol/L for premixing, then injecting all the catalyst toluene solution into a polymerization reaction device, initiating polymerization reaction and timing, and injecting 2.0mL of silver trifluoromethanesulfonate toluene solution with the concentration of 0.0025mol/L into a reaction system for continuous reaction at the 5 th minute of polymerization reaction. When the reaction time is 15min, 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) is added into the polymerization reaction, the polymerization reaction is quenched, and a polyethylene product is precipitated after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

Example 4:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, under the conditions of normal pressure ethylene atmosphere and water bath at the temperature of 20 ℃, 38.21mL of toluene, 2mL of MAO toluene solution with the concentration of 1.5mol/L and 3.79mL of 1-hexene are added into the polymerization reaction device and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent. Injecting 2.0mL of cobaltocene toluene solution with the concentration of 0.0025mol/L into 2.0mL of catalyst toluene solution with the concentration of 0.0025mol/L for premixing, and then injecting all the catalyst toluene solution into a polymerization reaction device to initiate polymerization reaction and timing. 2.0mL of a toluene solution of silver trifluoromethanesulfonate having a concentration of 0.0025mol/L was injected into the reaction system at the time of the 10 th minute of the progress of the polymerization reaction to continue the reaction. When the reaction time is 15min, 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) is added into the polymerization reaction, the polymerization reaction is quenched, and a polyethylene product is precipitated after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

Example 5:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 42.00mL of toluene and 2mL of MAO toluene solution with the concentration of 1.5mol/L are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at 20 ℃, and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent. Injecting 2.0mL of cobaltocene toluene solution with the concentration of 0.0025mol/L into 2.0mL of catalyst toluene solution with the concentration of 0.0025mol/L for premixing, and then injecting all the catalyst toluene solution into a polymerization reaction device to initiate polymerization reaction and timing. 2.0mL of a toluene solution of silver trifluoromethanesulfonate having a concentration of 0.0025mol/L was injected into the reaction system at the time of the 10 th minute of the progress of the polymerization reaction to continue the reaction. When the reaction time reaches 30min, 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) is added into the polymerization reaction, the polymerization reaction is quenched, and a polyethylene product is precipitated after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

Example 6:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 42.00mL of toluene and 2mL of MAO toluene solution with the concentration of 1.5mol/L are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at 20 ℃, and are fully mixed at the rotating speed of 600r/min, so that ethylene is fully dissolved in the toluene solvent. Injecting 2.0mL of cobaltocene toluene solution with the concentration of 0.0025mol/L into 2.0mL of catalyst toluene solution with the concentration of 0.0025mol/L for premixing, and then injecting all the catalyst toluene solution into a polymerization reaction device to initiate polymerization reaction and timing. 2.0mL of a toluene solution of silver trifluoromethanesulfonate having a concentration of 0.0025mol/L was injected into the reaction system at the 15 th minute of the progress of the polymerization reaction to continue the reaction. When the reaction time reaches 45min, 3mL of hydrochloric acid acidified ethanol with the mass concentration of 5% (5 wt%) is added into the polymerization reaction, the polymerization reaction is quenched, and a polyethylene product is precipitated after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

Comparative example 1:

after the polymerization reaction device is subjected to anhydrous and anaerobic treatment, 46.00mL of toluene solvent and 2.0mL of methylaluminoxane MAO cocatalyst toluene solution with the concentration of 1.5mol/L are added into the polymerization reaction device under the conditions of normal pressure ethylene atmosphere and water bath at the temperature of 20 ℃, the toluene solvent and the methylaluminoxane MAO cocatalyst toluene solution are fully mixed at the rotating speed of 600r/min, ethylene is fully dissolved in the toluene solvent, 2.0mL of alpha-nickel diimine catalyst toluene solution with the concentration of 0.0025mol/L is added into the polymerization reaction device, polymerization reaction is initiated and timed, when the reaction time reaches the end of 15min, 3mL of hydrochloric acid with the mass concentration of 5 percent (5 weight percent) is taken and added into the polymerization reaction, the polymerization reaction is quenched, and a polyethylene product is separated out after the polymerization reaction is quenched. Washing the separated polyethylene product with 95% ethanol for multiple times, and drying in a normal pressure oven and a negative pressure oven at 40 deg.C to constant weight to obtain the final product.

FIG. 4 is a graph showing the change in molecular weight of the branched polyethylene obtained in comparative example 1 at different reaction times of 5 to 45min, and it can be seen that the molecular weight increases overall with the increase in reaction time. The mechanical properties are shown in fig. 7, curve a, where the sample reaches the yield point relatively quickly, followed by strain hardening.

The invention implements different tests:

in fig. 5(a), the catalytic activity of the catalyst in the ethylene homopolymerization process changes under different Co to Ni to Ag ratios, and it can be seen that the catalytic activity in the redox regulation process is within the range between the basic state catalytic activity and the reduced state catalytic activity, thereby proving the effectiveness of the redox regulation. FIG. 5(b) is a diagram showing the variation trend of catalyst activity in ethylene/1-hexene copolymerization process under different Co: Ni: Ag ratios.

FIG. 7 is a graph of stress-strain tensile properties of branched polyolefin products prepared by homopolymerization of ethylene with different equivalents of cobaltocene as a reducing agent and silver trifluoromethanesulfonate as an oxidizing agent added in an alpha-nickel diimine catalyst/MAO catalyst system. The mechanical properties of example 1 are shown in FIG. 7, curve C, where the test bars did not reach yield point and the stress rose rapidly with strain. The mechanical properties of example 1 are shown in FIG. 7, curve E, where the test bars reach the yield point relatively quickly and fracture occurs. The mechanical properties of example 5 are shown in FIG. 7, curve F, where the resulting sample stress rises faster with strain. The mechanical properties of example 6 are shown in curve J in fig. 7, which shows that the sample has higher strain and lower stress compared with the sample obtained in example 5, and the other curves in fig. 7 are graphs of the stress-strain tensile properties of branched polyolefin products prepared by adding different equivalent amounts of reducing agent cobaltocene and oxidizing agent silver trifluoromethanesulfonate into the alpha-diimine nickel catalyst/MAO catalyst system to catalyze the ethylene homopolymerization.

The branched polyolefin prepared by the method has obvious effect of redox regulation and control on the performance, and the weight average molecular weight of the branched polyolefin prepared by the method can be 9.78 multiplied by 10⁴g/mol to 16.55X 10⁴The g/mol range is regulated, the melting point temperature can be regulated and controlled within the range of-10.69 ℃ to 57.94 ℃, the branching degree can be regulated and controlled within the range of 71branches/1000C to 101branches/1000C, and the tensile property strain can be regulated and controlled within the range of 185 percent to 1808 percent.