Polyethylene wax with ultralow molecular weight, high crystallinity and narrow molecular weight distribution and preparation method thereof

Abstract

The invention relates to the technical field of polyethylene wax preparation, in particular to polyethylene wax with ultralow molecular weight, high crystallinity and narrow molecular weight distribution and a preparation method thereof.The preparation method comprises the steps that under the conditions that the temperature ranges from 60 DEG C to 180 DEG C and the pressure ranges from 0.5 MPa to 5.0 MPa, ethylene is introduced into a reaction device, an organic solvent is continuously added to serve as a medium, and the polyethylene wax with the ultralow molecular weight, the high crystallinity and the narrow molecular weight distribution is obtained; and adding alkyl aluminum halide and alkoxy titanium to carry out high-temperature solution polymerization reaction, and after the reaction is ended, cooling and drying to obtain the polyethylene wax. The polyethylene wax prepared by the invention has the characteristics of ultralow molecular weight, high crystallinity and narrow molecular weight distribution, and the molecular weight and the molecular weight distribution can be effectively adjusted in various modes, such as adjustment of substituent groups on phenyl or polymerization reaction conditions; meanwhile, compared with polyethylene wax in the prior art, the polyethylene wax produced by the process has remarkable advantages.

Description

Technical Field

[0001] The invention relates to the technical field of polyethylene wax preparation, in particular to a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution and a preparation method thereof. Background Art

[0002] Polyethylene wax is a thermoplastic polymer made from polyethylene through a specific process. Its molecular weight is between 1,000 and 10,000, its melting point is generally between 90°C and 120°C, and it has waxy physical properties. Polyethylene wax is solid at room temperature, but becomes liquid when heated. It is easily soluble in aromatic hydrocarbons, halogenated hydrocarbons, and aliphatic hydrocarbon solvents. It is not easy to decompose or oxidize, and it can resist corrosion by chemicals such as acids and alkalis. In addition, polyethylene wax shows good compatibility with a variety of polymers and other materials, so it is widely used in many fields such as film manufacturing, coatings, lubricants, ink additives, and plastic modification.

[0003] In terms of production, polyethylene wax can be prepared through several different processes: ethylene cracking, purification from ethylene polymerization byproducts, and ethylene polymerization. Among them, polyethylene wax produced by ethylene polymerization stands out because of its more concentrated molecular weight and melting range distribution, highly adjustable product properties and stable quality, which makes it very suitable for the production of high-quality, diversified high-end wax products. The advantage of this production process is that it can better control the characteristics of the final product and meet the specific requirements of polyethylene wax for different applications.

[0004] In the prior art, such as CN201280041261, CN107325207, CN111154017, and CN200480017722, some preparation methods of polyethylene wax are disclosed, but there are still many defects: (1) Narrow melting point range: The melting point of polyethylene wax is usually concentrated between 90-120°C, which means that its stability at higher temperatures is limited. For applications that need to withstand higher temperature environments, such as high-temperature processing or long-term use under high temperature conditions, this material may soften, deform, or even melt. (2) Insufficient thermal stability and oxidation resistance: Although polyethylene wax has certain chemical stability, it may undergo slow oxidative degradation under long-term high temperature, resulting in performance degradation. Especially when exposed to oxygen and ultraviolet rays, this degradation process will accelerate, affecting the service life and performance of the product. (3) Uneven molecular weight distribution: Polyethylene wax produced by traditional production processes often has the problem of wide molecular weight distribution, which may lead to poor consistency and repeatability of the product. Uneven molecular weight distribution will affect the physical properties of the material, such as melt index, viscosity, etc., and further affect the processing performance and quality of the final product. The above defects limit the large-scale use of polyethylene wax.

[0005] Therefore, developing a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution has good application prospects and market value. Summary of the invention

[0006] The first aspect of the present invention provides a method for preparing a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, the preparation method comprising: introducing ethylene into a reaction device under the conditions of a temperature of 60 to 180°C and a pressure of 0.5 to 5.0 MPa, continuously adding an organic solvent as a medium, adding an alkyl aluminum halide and an alkoxy titanium to carry out a high-temperature solution polymerization reaction, and after the reaction is terminated, cooling and drying to obtain the polyethylene wax.

[0007] In some preferred embodiments, the reaction apparatus is repeatedly vacuumed and replaced by ethylene for 3-5 times at 130-180° C. in advance, and then ethylene is introduced and the exhaust pressure is adjusted to 0 MPa.

[0008] In some preferred embodiments, the organic solvent includes at least one of toluene, xylene, cyclohexane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, n-decane, n-heptane, benzene, and chlorobenzene.

[0009] In some preferred embodiments, the titanium alkoxide has any of the following structural formulas;

[0010]

[0011] In some preferred embodiments, the molecular formula of the alkyl aluminum halide is Et 3 Al 2 Cl 3 or R n AlX 3-n , wherein R is an alkyl group, X is a halogen atom, and n is 1, 2 or 3.

[0012] In some preferred embodiments, the molar ratio of the alkyl aluminum halide to the alkoxy titanium is 1:(50-1000).

[0013] In some preferred embodiments, the polymerization reaction time is 10 to 60 minutes.

[0014] The second aspect of the present invention provides a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, which is obtained by the above preparation method.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The polyethylene wax prepared by the present invention has the characteristics of ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, and the molecular weight can be effectively adjusted in a variety of ways, such as adjusting the substituents on the phenyl group or the polymerization reaction conditions; at the same time, the molecular weight distribution of the polyethylene wax produced by this process is narrower than that of some polyethylene waxes in the prior art, such as free radical polymerization polyethylene wax, Ziegler-Natta polyethylene wax, and metallocene polyethylene wax, which shows that the present invention has obvious advantages in the field of polyethylene wax preparation;

[0017] (2) The preparation process of the present invention has the advantages of being more economical and easily available. Compared with relatively expensive metallocene catalysts, the new process has the characteristics of being easy to obtain, low cost, and resistant to moisture and air. 3 Al 2 Cl 3 As a co-catalyst, the operation is simpler, which reduces complicated protective measures and operation steps, reduces the difficulty of operation and improves production efficiency;

[0018] (3) Compared with other non-cyclopentadienyl catalysts, the preparation process of the present invention has higher polymerization activity and can achieve a more suitable molecular weight, and can more accurately control the molecular weight, which makes the produced polyethylene wax more advantageous in performance, thereby greatly broadening its application range. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The reaction devices used in the embodiments of the present invention are all high-pressure batch reactors, model WZ-100N-2010-1002.

[0021] Example 1

[0022] This embodiment provides a method for preparing a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, comprising:

[0023] (1) The reaction device was repeatedly evacuated and replaced with ethylene at 150°C for 3 times in advance, and then ethylene was introduced and the exhaust pressure was adjusted to 0 MPa;

[0024] (2) Under the conditions of a temperature of 60° C. and a pressure of 1 MPa, ethylene was introduced into the reaction apparatus, and 28.0 mL of an organic solvent was continuously added as a medium, and 1 mL of an alkyl aluminum halide was added. When the temperature of the reactor reached 100° C., 1 mL of alkoxytitanium was quickly added, and the reaction was carried out at a pressure of 1 MPa for 20 min to perform a high-temperature solution polymerization reaction;

[0025] (3) After the reaction is terminated, the mixture is cooled and poured into acidified ethanol having a volume ratio of concentrated hydrochloric acid to ethanol of 1:9 to terminate the reaction. The mixture is washed with ethanol and dried in vacuum to obtain the polyethylene wax.

[0026] The organic solvent is toluene which has been dehydrated and deoxygenated by reflux of metallic sodium.

[0027] The alkyl aluminum halide is 0.6 mol / L Et 3 Al 2 Cl 3 Hexane solution.

[0028] The titanium alkoxide is catalyst Z6.

[0029] The specific implementation methods of Examples 2 to 16 are the same as those of Example 1, and the differences are shown in Table 1.

[0030] Table 1

[0031]

[0032] As shown in Table 1, the present invention aims to prepare polyethylene wax with specific properties, and the catalyst activity directly affects the polymerization efficiency and product quality. The data in Table 1 provide an important basis for determining the optimal process conditions such as alkyl aluminum halide concentration, organic solvent type and reactor temperature. For example, selecting a suitable Et 3 Al 2 Cl 3 concentration (such as 0.6 mol / L), toluene as an organic solvent, and controlling the reaction temperature at 100°C can help improve the catalyst activity, thereby improving the production efficiency and quality of polyethylene wax and achieving target properties such as ultra-low molecular weight, high crystallinity, and narrow molecular weight distribution.

[0033] The activity comparison of different alkyl aluminum halides further proves that the Et 3 Al 2 Cl 3 The advantage of this polymerization system is that compared with the alkyl aluminum halides that may be used in other prior arts, it can better play a catalytic role, which is also an important feature of the preparation process of the present invention. It helps to reduce production costs and improve product performance, thereby making the invention more competitive in the field of polyethylene wax preparation and laying the foundation for its large-scale industrial production and application.

[0034] Examples 17-19

[0035] The specific implementation methods of Examples 17-19 are the same as those of Example 3, and the differences are shown in Table 2; the specific implementation methods of Examples 20-27 are the same as those of Example 19, and the differences are shown in Table 2; the specific implementation methods of Example 28 are the same as those of Example 20, and the differences are shown in Table 2; the specific implementation methods of Example 29 are the same as those of Example 21, and the differences are shown in Table 2; the specific implementation methods of Example 30 are the same as those of Example 22, and the differences are shown in Table 2; the specific implementation methods of Example 31 are the same as those of Example 23, and the differences are shown in Table 2; the specific implementation methods of Example 32 are the same as those of Example 24, and the differences are shown in Table 2; the specific implementation methods of Example 33 are the same as those of Example 25, and the differences are shown in Table 2; the specific implementation methods of Example 34 are the same as those of Example 26, and the differences are shown in Table 2.

[0036] The weight average molecular weight, number average molecular weight and PDI (polymer dispersibility index) were tested using Agilent PL-GPC220 high temperature gel permeation chromatograph according to GB / T 27843-2011 standard: solvent l, 2,4-trichlorobenzene, test temperature 150°C, solvent flow rate 1mL / min, sample mass concentration 1.0g / L, and polystyrene as the standard sample.

[0037] The melting point (Tm) and crystallinity (Xc) of the sample were determined as follows:

[0038] The measurement was performed using a differential scanning calorimeter. Accurately weigh 4.0-7.0 mg of sample and place it in the differential scanning calorimeter at 20 °C min -1 The temperature was raised to 160°C at a rate of 10°C·min and kept at this temperature for 3 min to eliminate the thermal history. -1 The temperature was cooled to -80°C at a cooling rate of 10°C / min, then kept at -80°C for 10 min, and then heated at 10°C / min -1 The temperature was raised to 160°C at a heating rate of 1.5°C. During the whole process, the crystallinity data was obtained from the cooling curve, and the glass transition temperature and melting point of the polymer were obtained from the second heating curve. By analyzing the melting peak area, the formula Xc = ΔH / ΔH was used. 0 *100% calculated sample crystallinity, where the melting enthalpy of polyethylene ΔH 0 The instrument used in the measurement process is a TA Instruments Q200 differential scanning calorimeter.

[0039] The density is determined using a multifunctional electronic density meter, model XF-120S, produced by Shanghai Lichen Bangsi Instruments. The specific operation is as follows: First, place a polyethylene wax sample without bubbles on the top weighing area of ​​the density balance, and press the 'SAMPLE' key after the indication stabilizes. At this time, the screen displays 'LO'. Subsequently, transfer the sample to the tray inside the balance, and after the indication stabilizes again, press the 'SAMPLE' key again to obtain the density value of the polyethylene wax sample. This determination method is accurate and fast, and can provide important data support for subsequent process research and performance evaluation of polyethylene wax.

[0040] The testing of weight average molecular weight, number average molecular weight, PDI, melting point, crystallinity and density of polyethylene wax is of great significance. Molecular weight related indicators affect physical and processing properties, ensuring its stable performance in applications such as plastic modification and ink addition; melting point and crystallinity determine thermal properties and microstructure, which are crucial to processing temperature, application range, hardness, lubrication, film properties, etc.; density is related to molecular structure, affecting compatibility, dispersion and sedimentation in plastic modification, coatings and inks, etc. These tests provide key basis for understanding characteristics, optimizing applications and controlling quality, and are important indicator parameters when polyethylene wax is applied.

[0041] Table 2

[0042]

[0043]

[0044] Table 3

[0045]

[0046] Analysis of the data in Table 2-3 shows that the alkoxytitanium catalyst of the present invention exhibits many advantages when catalyzing the polymerization of ethylene with polyethylene wax. 3 Al 2 Cl 3 , good activity, the prepared polyethylene wax has stable molecular weight and high crystallinity.

[0047] Table 4 shows the relevant parameters of common polyethylene waxes available on the market.

[0048] Table 4

[0049]

[0050] As shown in Table 4, the molecular weight distribution of the polyethylene wax produced by the present invention is narrower than that of polyethylene wax on the market. Compared with traditional metallocene catalysts, the reaction temperature and ethylene pressure of this catalyst have a significant effect on the polymerization activity and molecular weight, and no hydrogen is required to adjust the molecular weight; compared with non-metallocene catalysts, it has higher activity and can achieve higher and more accurately controlled molecular weight. The molecular weight can also be adjusted by adjusting the substituents on the phenyl group or the polymerization reaction conditions.

[0051] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, characterized in that: The preparation method comprises: introducing ethylene into a reaction device under the conditions of a temperature of 60 to 180°C and a pressure of 0.5 to 5.0 MPa, continuously adding an organic solvent as a medium, adding an alkyl aluminum halide and an alkoxy titanium to carry out a high-temperature solution polymerization reaction, and after the reaction is terminated, cooling and drying to obtain the polyethylene wax.

2. The preparation method according to claim 1, characterized in that: The reaction device was repeatedly evacuated and replaced by ethylene at 130-180°C for 3-5 times in advance, and then ethylene was introduced and the exhaust pressure was adjusted to 0 MPa.

3. The preparation method according to claim 1, characterized in that: The organic solvent includes at least one of toluene, xylene, cyclohexane, n-hexane, cyclohexane, methylcyclohexane, ethylcyclohexane, n-decane, n-heptane, benzene and chlorobenzene.

4. The preparation method according to claim 1, characterized in that: The titanium alkoxide has any of the following structural formulas; 5. The preparation method according to claim 1, characterized in that: The molecular formula of the alkyl aluminum halide is Et3Al2Cl3 or R n AlX 3-n , wherein R is an alkyl group, X is a halogen atom, and n is 1, 2 or 3.

6. The preparation method according to claim 1, characterized in that: The molar ratio of the alkyl aluminum halide to the alkoxy titanium is 1:(50-1000).

7. The preparation method according to claim 1, characterized in that: The polymerization reaction time is 10 to 60 minutes.

8. A polyethylene wax with ultra-low molecular weight, high crystallinity and narrow molecular weight distribution, characterized in that: Obtained by the preparation method according to any one of claims 1 to 7.

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