Preparation method of high-heat-resistance low-dielectric thermotropic liquid crystal polyester containing large-volume side group

Abstract

The invention discloses a high-heat-resistance low-dielectric thermotropic liquid crystal polyester containing a large-volume side group and a preparation method thereof. The preparation method comprises the following steps: respectively carrying out acetylation reaction on a monomer 6-hydroxy-2-naphthoic acid and bisphenol AP with a mixture of acetic anhydride and 1-methylimidazole, and then recrystallizing and refining; and adding the refined 6-acetoxy-2-naphthoic acid monomer, the refined acetylated bisphenol AP monomer, terephthalic acid and zinc acetate into a container, heating, carrying out melt polycondensation reaction, after the reaction is finished, cooling the product, crushing, and drying, so as to obtain the high-heat-resistance low-dielectric thermotropic liquid crystal polyester containing the large-volume side group. The low-dielectric thermotropic liquid crystal polyester material is prepared by introducing a bisphenol monomer containing a large-volume side group in a melt polymerization manner; the dielectric constant and dielectric loss of the liquid crystal polymer are greatly reduced, the melting point of the liquid crystal polyester can be improved, and the prepared liquid crystal polymer has excellent insulating property and thermal property and can meet the application requirement under 5G high frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, and in particular to a high-heat-resistant and low-dielectric type I thermotropic liquid crystal polyester containing bulky side groups and a preparation method thereof. Background Art

[0002] Thermotropic liquid crystal polymers (TLCPs) are a class of polymer compounds that can exist in a liquid crystal phase under certain conditions. They are currently considered the most suitable insulating substrate material for printed circuit boards used in high-frequency communications. TLCPs exhibit excellent heat and corrosion resistance, low moisture absorption, outstanding dimensional stability, and extremely low dielectric constant and dielectric loss. With the advent of the 5G era, dielectric materials with as low dielectric constants and dielectric loss as possible are required to reduce signal transmission loss and signal delay during high-frequency communications. The relationship between a material's dielectric constant and polarity can be expressed using the Debye equation, as shown in Equation (1-1).

[0003] Among them, D k is the dielectric constant of the material, N is the dipole density, which reflects the density of the material; other α e is the electronic polarizability, α d is the ionic polarizability, μ 2 / 3Tk b is the molecular polarizability.

[0004] There are three common methods for reducing the dielectric constant of polymers: (1) introducing fluorine atoms into the polymer molecular chain to reduce the polarization of the molecular chain and thus reduce the dielectric constant of the polymer; (2) introducing bulky structures or macromolecular chain side groups (such as CH3, benzene rings, etc.) through physical or chemical methods to increase the free volume of the polymer and reduce the material density to reduce the dielectric constant of the polymer. The dielectric constant of a material is closely related to its density (the number of molecules per unit volume). Reducing the material density can significantly reduce its dielectric constant; (3) blending other materials with lower dielectric constants to reduce the dielectric constant of the blend, such as polytetrafluoroethylene (PTFE), glass fibers, and glass microspheres.

[0005] Method (1) introduces fluorinated monomers into polymer segments to reduce the dielectric constant and dielectric loss of the material. However, the chemical inertness and strong electronegativity of fluorinated monomers may lead to low polymerization efficiency, requiring reliance on highly active catalysts or extreme conditions, increasing process complexity and energy consumption. In addition, the molecular chain order of liquid crystal polyesters (such as nematic or smectic) is crucial to dielectric properties, but the introduction of fluorinated groups may destroy the regularity of the liquid crystal phase, resulting in fluctuations in the dielectric constant and loss.

[0006] The prior art CN112080291A discloses "Liquid crystal polymer film for 5G communication flexible copper-clad laminate and its preparation method", which provides a method for preparing a low-dielectric liquid crystal polymer by blending polytetrafluoroethylene with a liquid crystal polymer; polytetrafluoroethylene is prepared with a liquid crystal polymer through physical blending. Although a composite material with a lower dielectric constant and dielectric loss can be prepared, the simple physical blending method makes it easy for polytetrafluoroethylene to be unevenly dispersed during subsequent processing, resulting in difficulty in accurately controlling the quality of the liquid crystal polymer product.

[0007] In response to the above problems, the present invention provides a high-heat-resistant, low-dielectric thermotropic liquid crystal polyester containing large-volume side groups and a preparation method thereof. The low-dielectric thermotropic liquid crystal polyester material is prepared by melt polymerization by introducing a large-volume side-group aromatic monomer. The melting point of the liquid crystal polyester is increased by introducing a bisphenol aromatic monomer, thereby giving the material high heat resistance, which can effectively avoid the various problems caused by simple blending. In addition, the present invention can effectively reduce the dielectric constant of the liquid crystal polymer and further improve the heat resistance to meet the high-frequency and high-speed usage requirements of 5G. The low-dielectric thermotropic liquid crystal polymer of the present invention has excellent dielectric properties and processing properties, and can be used in mobile phone antennas, high-frequency connectors and other fields. Summary of the Invention

[0008] The purpose of the present invention is to provide a highly heat-resistant, low-dielectric thermotropic liquid crystal polyester containing large-volume side groups and a preparation method thereof. By introducing a bisphenol monomer containing large-volume side groups into the liquid crystal polymer, the dielectric constant of the liquid crystal polymer can be effectively reduced. At the same time, the heat resistance of the polymer can be further improved to meet the high-frequency and high-speed usage requirements of 5G.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] In an embodiment of the present invention, the bulky side group repeating structural unit is selected from one or more of the following: bisphenol AP, bisphenol A, bisphenol fluorene BHPF, 1,3,4-thiadiazole biphenyl, and 5-tert-butylisophthalic acid.

[0011] A method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups comprises the following steps:

[0012] (1) Acetylation reaction is performed on monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP with a mixture of acetic anhydride and 1-methylimidazole, and after the acetylation reaction is completed, the acetylated monomers are recrystallized multiple times to remove excess acetic anhydride, and the obtained acetylated monomers are filtered and washed in ice water and then recrystallized and purified to obtain 6-acetoxy-2-naphthoic acid monomer (ANA) and acetylated bisphenol AP monomer (BPAP), respectively;

[0013] (2) melt polycondensing the purified 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) at a molar ratio of 50-80:10-25:10-25, applying a negative pressure environment to the reaction vessel using a vacuum pump, and after 2 minutes, opening a nitrogen cylinder and introducing nitrogen to remove all air from the reaction system;

[0014] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250-255°C for melt polycondensation reaction, react for 3-4 hours, raise the temperature to 280-285°C, react at 280-285°C for 2-3 hours, continue to raise the temperature to 300-310°C for 1-1.5 hours, at which time the melt has viscosity and acetic acid no longer distills out, reduce the stirring speed, turn off the nitrogen, turn on the vacuum pump to draw a vacuum degree of 2000 Pa, and simultaneously raise the temperature to 340-345°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the said thermotropic liquid crystal polymer containing large-volume side groups with high heat resistance and low dielectric constant.

[0015] Preferably, in step (1), the acetic anhydride accounts for 2.2 to 2.4 times the total molar number of monomer hydroxyl groups; and the 1-methylimidazole accounts for 300 to 350 ppm of the total weight of the monomers.

[0016] Preferably, in step (2), the molar ratio of the 6-acetoxy-2-naphthoic acid monomer (ANA), the acetylated bisphenol AP monomer (BPAP) and terephthalic acid (TPA) is 50-80:10-25:10-25.

[0017] Preferably, in step (1), the acetylation reaction is carried out under the following conditions: heating to 150-160° C. and then maintaining the temperature for 1-2 hours.

[0018] Preferably, in step (2), the zinc acetate accounts for 400 to 450 ppm.

[0019] Preferably, in step (2), the nitrogen is introduced for 5 minutes at a time and repeated 3 to 4 times to remove all air from the reaction system.

[0020] The present application also claims protection for a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, which is prepared by the above-mentioned preparation method of the thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups.

[0021] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0022] 1. The present invention introduces a bisphenol monomer AP containing a bulky side group to prepare a low-dielectric thermotropic liquid crystal polyester material by melt polymerization, which can effectively avoid various problems caused by simple blending. At the same time, the introduction of the bisphenol monomer increases the melting point of the liquid crystal polyester, giving the material high heat resistance.

[0023] 2. The present invention significantly reduces the dielectric constant and dielectric loss of existing liquid crystal polymers while further improving the thermal stability of the polymer. The resulting liquid crystal polymer has excellent insulation and thermal properties, meeting the application requirements of 5G high frequencies.

[0024] 3. The low-dielectric thermotropic liquid crystal polymer of the present invention has excellent dielectric properties and processing properties, and can be applied to fields such as mobile phone antennas and high-frequency connectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be made based on these drawings without paying any creative work.

[0026] Figure 1 This is a dielectric property curve of the high-heat-resistant and low-dielectric thermotropic liquid crystal polyester with bulky side groups according to Example 1 of the present invention;

[0027] Figure 2 This is a TGA graph of the high-heat-resistant and low-dielectric thermotropic liquid crystal polyester with bulky side groups according to Example 1 of the present invention;

[0028] Figure 3 This is a POM diagram of the high-heat-resistant and low-dielectric thermotropic liquid crystal polyester with bulky side groups according to Examples 1 to 7 of the present invention;

[0029] in, Figure 3 , Figure (a), Figure (b), Figure (c), Figure (d), Figure (e), Figure (f), and Figure (g) correspond to Examples 1 to 7, respectively. DETAILED DESCRIPTION

[0030] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0031] The present invention is further described below with reference to the following examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific applications. The implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] See attached Figure 1 -Attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0034] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0035] (2) Refined 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) were added to a three-necked flask at a molar ratio of 80:10:10 and 400 ppm of zinc acetate. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0036] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0037] Example 2

[0038] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0039] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0040] (2) Refined 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) in a molar ratio of 75:12.5:12.5 and 400 ppm of zinc acetate were added to a three-necked flask. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0041] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0042] Example 3

[0043] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0044] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0045] (2) Refined 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) were added to a three-necked flask at a molar ratio of 70:15:15 and 400 ppm of zinc acetate. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0046] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0047] Example 4

[0048] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0049] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0050] (2) Refined 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) in a molar ratio of 65:17.5:17.5 and 400 ppm of zinc acetate were added to a three-necked flask. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0051] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0052] Example 5

[0053] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0054] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0055] (2) Refined 6-acetoxy-2,0-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) were added to a three-necked flask at a molar ratio of 60:20:20 and 400 ppm of zinc acetate. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0056] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0057] Example 6

[0058] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0059] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0060] (2) Refined 6-acetoxy-20-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) in a molar ratio of 55:22.5:22.5 and 400 ppm of zinc acetate were added to a three-necked flask. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0061] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0062] Example 7

[0063] See attached Figure 3 This embodiment provides a method for preparing a thermotropic liquid crystal polyester with high heat resistance and low dielectric constant containing bulky side groups, comprising the following steps:

[0064] (1) A mixture of monomers 6-hydroxy-2-naphthoic acid (HNA) and bisphenol AP, respectively, with acetic anhydride accounting for 2.2 times the total molar number of hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers was heated to 150° C. and then kept at this temperature for 1 hour for acetylation reaction. After the acetylation reaction, the acetylated monomers were recrystallized multiple times to remove excess acetic anhydride. The obtained acetylated monomers were filtered and washed in ice water for recrystallization and purification to obtain 6-acetoxy-20-naphthoic acid monomers (ANA) and acetylated bisphenol AP monomers (BPAP), respectively.

[0065] (2) Refined 6-acetoxy-20-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) were added to a three-necked flask at a molar ratio of 50:25:25 and 400 ppm of zinc acetate. A vacuum pump was used to apply a negative pressure environment to the reaction vessel. After 2 minutes, the nitrogen cylinder was opened and nitrogen was introduced for 5 minutes at a time. This was repeated 3 times to remove all air from the reaction system.

[0066] (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250°C for melt polycondensation reaction, react for 3 hours, raise the temperature to 280°C, react at 280°C for 2 hours, and continue to raise the temperature to 300°C for 1 hour. At this time, the melt has viscosity and acetic acid no longer distills out. At this time, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polymer containing large-volume side groups.

[0067] Comparative Example 1

[0068] This comparative example is carried out on the basis of the above-mentioned Example 1, and the similarities with the above-mentioned Example 1 are not repeated here.

[0069] In this comparative example, the molar ratio of 6-hydroxy-2-naphthoic acid, biphenol, and terephthalic acid is 80:10:10.

[0070] Comparative Example 2

[0071] This comparative example is carried out on the basis of the above-mentioned Example 3, and the similarities with the above-mentioned Example 3 are not repeated here.

[0072] In this comparative example, the molar ratio of 6-hydroxy-2-naphthoic acid, biphenol, and terephthalic acid is 70:15:15.

[0073] Comparative Example 3

[0074] This comparative example is carried out on the basis of the above-mentioned Example 5, and the similarities with the above-mentioned Example 5 are not repeated here.

[0075] In this comparative example, the molar ratio of 6-hydroxy-2-naphthoic acid, biphenol, and terephthalic acid is 60:20:20.

[0076] Comparative Example 4

[0077] This comparative example is carried out on the basis of the above-mentioned Example 7, and the similarities with the above-mentioned Example 7 are not repeated here.

[0078] In this comparative example, the molar ratio of 6-hydroxy-2-naphthoic acid, biphenol, and terephthalic acid is 50:25:25.

[0079] Comparative Example 5

[0080] This comparative example is carried out on the basis of the above-mentioned Example 1, and the similarities with the above-mentioned Example 1 are not repeated here.

[0081] In this comparative example, the molar ratio of the purified 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) is 45:27.5:27.5.

[0082] Comparative Example 6

[0083] This comparative example is carried out on the basis of the above-mentioned Example 1, and the similarities with the above-mentioned Example 1 are not repeated here.

[0084] In this comparative example, the molar ratio of the purified 6-acetoxy-2-naphthoic acid monomer (ANA), acetylated bisphenol AP monomer (BPAP), and terephthalic acid (TPA) is 85:7.5:7.5.

[0085] Comparative Example 7

[0086] This comparative example is carried out on the basis of the above-mentioned Example 1, and the similarities with the above-mentioned Example 1 are not repeated here.

[0087] In this comparative example, the molar ratio of the purified 6-acetoxy-2-naphthoic acid monomer (ANA) to p-acetoxybenzoic acid was 50:50.

[0088] Comparative Example 8

[0089] This comparative example is carried out on the basis of the above-mentioned Example 2, and the similarities with the above-mentioned Example 2 are not repeated here.

[0090] In this comparative example, the molar ratio of the purified 6-acetoxy-2-naphthoic acid monomer (ANA) to p-acetoxybenzoic acid was 60:40.

[0091] Comparative Example 9

[0092] This comparative example is carried out on the basis of the above-mentioned Example 3, and the similarities with the above-mentioned Example 3 are not repeated here.

[0093] In this comparative example, the molar ratio of the purified 6-acetoxy-2-naphthoic acid monomer (ANA) to p-acetoxybenzoic acid was 70:30.

[0094] The reaction equation of the above embodiment is shown in the following equation (1):

[0095]

[0096] The reaction equations of Comparative Examples 1 to 4 are shown in the following equation (2):

[0097]

[0098] The reaction equations of Comparative Examples 7 to 9 are shown in the following equation (3):

[0099]

[0100] The low dielectric thermotropic liquid crystal polymers containing bulky side groups obtained in Examples 1 to 7 and Comparative Examples 1 to 9 were subjected to melting point tests and dielectric property tests. The test results are shown in Table 1.

[0101] Table 1

[0102]

[0103] As can be seen from Table 1, the introduction of bisphenol AP monomer can significantly reduce the dielectric constant and dielectric loss. With the increase of bisphenol AP monomer content, the dielectric constant of the copolyester shows an overall downward trend. The reduction in dielectric constant can be attributed to the stacking effect of the large benzene ring side groups of the bisphenol AP monomer. The presence of benzene ring side groups greatly increases the stacking density of the copolyester molecular chain structure, thereby increasing the free volume of the copolyester and thus reducing the dielectric constant. At the same time, compared with Cases 7 to 9, the introduction of bisphenol AP monomer in the embodiment can significantly increase the melting point of the polymer, improve its thermal stability, and make the liquid crystal polyester have certain high temperature resistance. Through the above method, we can prepare a high-temperature resistant and low-dielectric liquid crystal polyester containing large-volume side groups.

[0104] The test methods for the above performances are as follows:

[0105] (1) Melting point: The melting point is measured by DSC. The temperature is raised from room temperature to 380°C at a heating rate of 20°C / min, and then the temperature is lowered to room temperature at a rate of 20°C / min after being kept at this temperature for 3 minutes. The test sample is kept at room temperature for 3 minutes and then heated to 380°C again at a rate of 20°C / min to obtain the second melting curve of the liquid crystal polyester. The melting peak of the curve is selected as the melting point.

[0106] (2) Determination of logarithmic viscosity: The solvent is pentafluorophenol; 0.050 g of a sample of liquid crystal copolyester is weighed into a clean and dry 50 ml conical flask, and then 50 ml of pentafluorophenol is added thereto. The flask is covered with a stopper and placed in an 80°C shaker to dissolve for 8 hours to completely dissolve the sample. The solution is then filtered using a No. 2 sand core funnel into another clean and dry 25 ml volumetric flask and placed in the above water bath at a constant temperature for 1 hour. The outflow time t of the pure solvent and the solution is measured using an Ubbelohde viscometer (capillary diameter 0.63 mm) in a 60°C water bath. 溶剂 and t 溶液; Then use formula (2-1) to calculate IV:

[0107]

[0108] (3) Dielectric constant and dielectric loss measurement: The measurement was carried out at room temperature using a vector network analyzer. The test sample was a resin sheet with a thickness of 1 mm and the measurement frequency was 2.5 GHz.

[0109] In summary, the present invention introduces bisphenol monomers containing large side groups to prepare low-dielectric thermotropic liquid crystal polyester materials by melt polymerization, which can effectively avoid various problems caused by simple blending; the present invention greatly reduces the dielectric constant and dielectric loss of existing liquid crystal polymers, while further improving the melting point of the polymer and having good high-temperature resistance. The prepared liquid crystal polymer has excellent insulation and thermal properties, which can meet the application requirements under 5G high frequency; the low-dielectric thermotropic liquid crystal polymer of the present invention has excellent dielectric properties and processing properties, and can be used in mobile phone antennas, high-frequency connectors and other fields.

[0110] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations 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 patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a thermotropic liquid crystal polymer with high heat resistance and low dielectric constant containing bulky side groups, characterized in that: The steps include: (1) acetylation reaction is performed on monomers 6-hydroxy-2-naphthoic acid and bisphenol AP with a mixture of acetic anhydride and 1-methylimidazole, and after the acetylation reaction is completed, the acetylated monomers are recrystallized multiple times to remove excess acetic anhydride, and the obtained acetylated monomers are filtered and washed in ice water and then recrystallized and purified to obtain 6-acetoxy-2-naphthoic acid monomers and acetylated bisphenol AP monomers, respectively; (2) melt polycondensing the purified 6-acetoxy-2-naphthoic acid monomer, acetylated bisphenol AP monomer, and terephthalic acid in a molar ratio of 50-80:10-25:10-25, applying a negative pressure environment to the reaction vessel using a vacuum pump, and after 2 minutes, opening a nitrogen cylinder and introducing nitrogen to remove all air from the reaction system; (3) Continue to introduce nitrogen, turn on the mechanical stirring device, raise the temperature to 250-255°C for melt polycondensation reaction, react for 3-4 hours, raise the temperature to 280-285°C, react at 280-285°C for 2-3 hours, continue to raise the temperature to 300-310°C for 1-1.5 hours, at which time the melt has viscosity and acetic acid no longer distills out, reduce the stirring speed, turn off the nitrogen, turn on the vacuum, and simultaneously raise the temperature to 340-345°C and maintain for 30 minutes before stopping the reaction; after the reaction is completed, wait for the product to cool, crush it and dry it, and after drying, obtain the high heat-resistant and low dielectric thermotropic liquid crystal polyester containing large-volume side groups.

2. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (1), the acetic anhydride accounts for 1.0 to 5.0 times the total molar number of monomer hydroxyl groups; and the 1-methylimidazole accounts for 100 to 1000 ppm of the total weight of the monomers.

3. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: The bulky side-group aromatic monomers are one or more of the following: bisphenol AP, bisphenol A, bisphenol fluorene BHPF, 1,3,4-thiadiazole biphenyl, and 5-tert-butylisophthalic acid.

4. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (2), the molar ratio of the 6-acetoxy-2-naphthoic acid monomer, the acetylated bisphenol AP monomer and the terephthalic acid is 50-80:10-25:10-25.

5. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (1), the acetylation reaction is carried out under the following conditions: heating to 150-160° C. and then maintaining the temperature for 1-2 hours.

6. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (2), the zinc acetate accounts for 400 to 450 ppm.

7. The method for producing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (3), the conditions for the melt polycondensation reaction are: reaction at 250°C for 3 to 4 hours, reaction at 280°C to 285°C for 2 to 3 hours, reaction at 300°C to 310°C for 1 to 1.5 hours, and vacuum reaction at 2000 Pa at 340°C to 345°C for 30 minutes.

8. The method for preparing a high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups according to claim 1, wherein: In step (3), the bulky side group-containing liquid crystal polyester is taken out for dielectric properties and DSC testing, wherein the dielectric constant is between 2.7 and 3.0, and the dielectric loss is 1.6×10 -3 ~3.0×10 -3 The melting points of the polymers are all greater than 345°C and the molecular weight distribution is narrow.

9. A high heat-resistant and low dielectric thermotropic liquid crystal polyester containing bulky side groups, characterized in that: The low dielectric thermotropic liquid crystal polymer containing bulky side groups is prepared by the preparation method of any one of claims 1 to 8.

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