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CN-121717957-B - Modified polyethylene and preparation method and application thereof

CN121717957BCN 121717957 BCN121717957 BCN 121717957BCN-121717957-B

Abstract

The invention relates to the field of high polymer materials, and discloses modified polyethylene, a preparation method and application thereof. The modified polyethylene comprises a polyethylene molecular chain and a vinyl side chain grafted on the polyethylene molecular chain and containing a benzene ring, wherein the vinyl content in the modified polyethylene is 0.6-6/1000C, the benzene ring content is 0.5-5.9/1000C, and the crosslinking density of the modified polyethylene is less than or equal to 9.1 multiplied by 10 ‑4 mol/mL. The modified polyethylene has low crosslinking density while maintaining high vinyl double bond content and high benzene ring content, so that the modified polyethylene can be used for preparing cable insulation materials. Meanwhile, the polyethylene contains higher double bond content, so that the crosslinking performance can be obviously improved under the condition of reducing the dosage of the crosslinking initiator, and the obtained cable is ensured to have excellent heat resistance, electrical performance and mechanical performance.

Inventors

  • Tian Mingce
  • LUO KAIQIANG
  • ZHANG YONGJIE
  • YANG WEI
  • Dai Xiying
  • SUN KAIYUE

Assignees

  • 北京怀柔实验室

Dates

Publication Date
20260512
Application Date
20260226

Claims (11)

  1. 1. The modified polyethylene is characterized by comprising a polyethylene molecular chain and vinyl side chains grafted on the polyethylene molecular chain and containing benzene rings, wherein the content of vinyl groups in the modified polyethylene is 0.6/1000C-6/1000C, the content of benzene rings is 0.5/1000C-5.9/1000C, and the crosslinking density of the modified polyethylene is less than or equal to 4.46 multiplied by 10 -4 mol/mL; the vinyl side chain containing the benzene ring has a structure shown in a formula I: wherein R 1 is a C1-C20 linear or branched alkylene group, and R is H or a C1-C5 linear or branched alkyl group.
  2. 2. The modified polyethylene according to claim 1, wherein the modified polyethylene has a vinyl group content of 1/1000C-6/1000C, a benzene ring content of 0.9/1000C-5.9/1000C, and a crosslinking density of 3.8x10 -4 mol/mL or less.
  3. 3. The modified polyethylene according to claim 1 or 2, wherein the modified polyethylene has a density of 0.910-0.930g/cm 3 ; And/or the modified polyethylene has a melt index of 1-3g/10min at 2.16kg and 190 ℃; and/or the weight average molecular weight of the modified polyethylene is 10000-150000g/mol, and the molecular weight distribution is 4-8.
  4. 4. A process for preparing the modified polyethylene of any one of claims 1-3, characterized in that the process comprises the steps of: Step S1, in the presence of a catalyst and a solvent, mixing diene and divinylbenzene, and then carrying out double decomposition reaction to obtain end group diene containing benzene ring; s2, mixing polyethylene, an initiator and end group diene containing benzene ring to obtain a mixture, and purifying to obtain the modified polyethylene; the initiation temperature of the initiator is T1, and the mixing temperature is T2, wherein T2 is more than or equal to T1; the dosage of the initiator is 0.025-1 weight part, the dosage of the end group diene containing benzene ring is 0.05-1 weight part, and the ratio x of the initiator to the dosage of the end group diene containing benzene ring is 1/5-1/2; the diolefin has a structure represented by formula II: formula II, wherein R 1 is a C1-C20 linear or branched alkylene group, and R is H or a C1-C5 linear or branched alkyl group.
  5. 5. The method of claim 4, wherein the divinylbenzene is selected from at least one of p-divinylbenzene, o-divinylbenzene, and m-divinylbenzene; and/or, the amount of diene used is from 2 to 6 mol relative to 1mol of divinylbenzene; and/or the catalyst is used in an amount of 0.5 to 2 mol% relative to 1mol of divinylbenzene; And/or the condition of the double decomposition reaction comprises that the reaction temperature T is T 0 -10℃≤T≤T 0 , wherein T 0 is the boiling point of the organic solvent under normal pressure, and the reaction time is 3-15h.
  6. 6. The method of claim 4 or 5, wherein the method further comprises adding a quencher after the metathesis reaction to effect the quenching reaction.
  7. 7. The process of claim 6, wherein the amount of quencher is 0.1 to 0.5 mol% relative to 1mol of divinylbenzene.
  8. 8. The method of claim 4 or 5, wherein the initiator is selected from at least one of a peroxide initiator, an azo-type initiator, and a nitroxide initiator.
  9. 9. The method according to claim 4 or 5, wherein the purification method comprises mixing the mixture with a good solvent for polyethylene, adding a poor solvent for polyethylene, standing, filtering, and drying to obtain the modified polyethylene.
  10. 10. The method of claim 9, wherein the temperature of mixing is 100-140 ℃; and/or, the good solvent of the polyethylene is an aromatic hydrocarbon solvent; and/or the poor solvent of polyethylene is selected from at least one of methanol, ethanol and acetone.
  11. 11. Use of a modified polyethylene according to any one of claims 1-3 in a cable.

Description

Modified polyethylene and preparation method and application thereof Technical Field The invention relates to the field of high polymer materials, in particular to modified polyethylene and a preparation method and application thereof. Background High voltage polyethylene (also known as low density polyethylene, LDPE) is used as a key base material for high voltage class cables, the molecular structure of which directly determines the applicable voltage class of the cable. In the cable manufacturing process, the high-pressure polyethylene is required to be converted into crosslinked polyethylene (XLPE) through crosslinking treatment so as to remarkably improve the heat resistance of the material. However, this process suffers from two key problems, firstly, the residual crosslinking aid deteriorates the electrical properties of the cable, and secondly, the low vinyl double bond content (usually. Ltoreq.0.1/1000C) in conventional high pressure polyethylene, resulting in limited crosslinking efficiency. Research shows that the vinyl double bond content in the polyethylene molecular chain can be improved effectively to enhance the crosslinking reaction activity, so that the high crosslinking density is ensured and the dosage of the crosslinking auxiliary agent is reduced. US5539075A discloses that copolymerization of 1, 9-decadiene with ethylene to effect modification of polyethylene, although the vinyl double bond content can be increased, has problems of difficult process control, easy occurrence of crosslinking side reaction, and the like. Therefore, the development of a novel synthesis method of high-pressure polyethylene with high vinyl double bond content becomes an important research direction in the field of current cable materials. Furthermore, if a benzene ring structure is introduced on a branched chain in the molecular design of the novel LDPE with high double bond content, the cooperative promotion of the structure and the performance can be realized, wherein the benzene ring is used as a strong electron acceptor and a steric hindrance group, a large number of deep traps can be introduced in a polymer matrix to effectively restrict and delay the migration of charge carriers, so that the accumulation of space charges is obviously inhibited, the direct-current breakdown strength of the material is improved, and the method is important for developing an insulation technology of an ultra-high voltage direct-current cable. Disclosure of Invention The invention aims to provide modified polyethylene, a preparation method and application thereof, and aims to solve the problem that the conventional high-pressure polyethylene is easy to generate cross-linking side reaction when the double bond content is increased, so that the modified polyethylene cannot be used for cable insulation materials. In order to achieve the above object, according to an aspect of the present invention, there is provided a modified polyethylene, wherein the modified polyethylene comprises a polyethylene molecular chain and a vinyl side chain containing a benzene ring grafted to the polyethylene molecular chain, wherein the modified polyethylene has a vinyl group content of 0.6 to 6/1000C, a benzene ring content of 0.5 to 5.9/1000C, and a crosslinking density of 9.1x10 -4 mol/mL or less. The second aspect of the present invention provides a process for preparing the modified polyethylene described above, wherein the process comprises the steps of: Step S1, in the presence of a catalyst and a solvent, mixing diene and divinylbenzene, and then carrying out double decomposition reaction to obtain end group diene containing benzene ring; s2, mixing polyethylene, an initiator and end group diene containing benzene ring to obtain a mixture, and purifying to obtain the modified polyethylene; the initiation temperature of the initiator is T1, and the mixing temperature is T2, wherein T2 is more than or equal to T1; the amount of the initiator is 0.025-1 part by weight, the amount of the end group diene containing benzene ring is 0.05-1 part by weight, and the ratio x of the initiator to the end group diene containing benzene ring is 1/5-1/2. The third aspect of the invention provides an application of the modified polyethylene in a cable. Through the technical scheme, the modified polyethylene provided by the invention and the preparation method and application thereof have the following beneficial effects: The modified polyethylene provided by the invention has low crosslinking density while keeping high vinyl double bond content and high benzene ring content, can effectively inhibit space charge accumulation, is suitable for preparing cable insulation materials, and can effectively improve the direct current breakdown strength of the materials. Meanwhile, the polyethylene contains high double bond content, so that the crosslinking performance can be obviously improved under the condition of reducing the dosage of the crosslinking initiat