CN118290712B - Liquid crystal polymer with low mechanical anisotropy and preparation method and application thereof - Google Patents

Abstract

The application belongs to the technical field of liquid crystal polymers, and discloses a liquid crystal polymer with low mechanical anisotropy, and a preparation method and application thereof. The repeating unit of the liquid crystal polymer has a chemical structure shown in the following formula, wherein X is a rod-shaped structure consisting of rigid groups; y is a non-liquid crystal structure consisting of a flexible chain, a heterogeneous rigid group or a kinking group; z is a chiral group; a. b and c are the molar ratios X, Y and Z respectively, a, b and c are each independently selected from any ratio between 0.1% and 90%, and the sum of a, b and c is 100%. The application combines chiral groups with liquid crystal polymers to prepare novel liquid crystal polymers with cholesteric phase molecule spiral arrangement structures, wherein isotropically arranged liquid crystal molecules realize low mechanical anisotropy of the liquid crystal polymers. After extrusion molding, the material can form preferred orientation of molecules, maintain a certain degree of molecular spiral arrangement and realize low mechanical anisotropy of the material.

Description

Liquid crystal polymer with low mechanical anisotropy and preparation method and application thereof

Technical Field

The present application belongs to the technical field of liquid crystal polymers, and specifically relates to a liquid crystal polymer with low mechanical anisotropy, a preparation method thereof, and an application thereof.

Background Art

Liquid crystal polymers are polymer materials that have liquid crystal properties. At present, commercial liquid crystal polymers are mainly composed of polymers formed by ester bonds connecting aromatic rings through rigid rod-shaped molecular units. When it is cooled from the liquid crystal state to the solid state, the highly oriented arrangement of the molecular chain will be retained, and its expansion coefficient is similar to that of metal materials, and can even be negative. Therefore, there is almost no shrinkage problem in the molding process of liquid crystal polymer products. It has high dimensional stability and high temperature resistance far exceeding that of general engineering plastics. It is known as "super engineering plastics". In addition, the large number of aromatic ring structures in the main chain structure of liquid crystal polymers also give it excellent mechanical properties, outstanding chemical resistance and excellent electrical stability, making it widely used in industries such as aerospace, electronics and defense.

During the extrusion molding process, liquid crystal polymers only need a small amount of shear stress to achieve a highly regular arrangement of molecules. Therefore, the mechanical strength of liquid crystal polymers in the direction of the long axis of the molecule is very high, but in the direction perpendicular to the long axis, the mechanical properties are poor, the brittleness is high, and it is very easy to break; the high mechanical anisotropy seriously limits the application of liquid crystal polymer materials.

There is an urgent need to synthesize liquid crystal polymers with low mechanical anisotropy.

Summary of the invention

The present application provides a liquid crystal polymer with low mechanical anisotropy and a preparation method and application thereof, which solve the problems of poor mechanical properties, high brittleness and easy fracture of existing liquid crystal polymers due to high mechanical anisotropy.

In order to achieve the above objectives, the present application adopts the following technical solutions.

In a first aspect of the present application, a liquid crystal polymer having low mechanical anisotropy is provided, wherein a repeating unit has a chemical structure as shown in the following formula:

Among them, X is a rod-like structure composed of rigid groups;

Y is a non-liquid crystal structure composed of a flexible chain, a heterogeneous rigid group or a kink group;

Z is a chiral group;

a, b, c are the molar proportions of X, Y and Z respectively, a, b, c are independently selected from any proportion between 0.1% and 90%, and the sum of a, b and c is 100%.

In some embodiments, X is selected from the structures shown in formula (1) to (10):

.

In some embodiments, Y is selected from the structures shown in formula (11) to (16):

Wherein, m and n are integers, and m≥0, n≥0.

In some embodiments, Z is selected from the structures shown in formula (17) to (19):

.

In some embodiments,

The structural formula of X is:

The structural formula of Y is:

The structural formula of Z is:

c is selected from 1.37%-5.26%.

In some embodiments, the molecular weight of the liquid crystal polymer with low mechanical anisotropy is greater than 5000, and the glass transition temperature thereof is higher than room temperature.

The second aspect of the present application provides a method for preparing the above-mentioned liquid crystal polymer with low mechanical anisotropy, comprising:

Dissolving monomer 2, monomer 3 and acetic anhydride in a solvent to carry out acetylation reaction; then adding monomer 1 and reacting at 110-130° C.; after the reaction, vacuuming to remove small molecules to obtain a liquid crystal polymer with low mechanical anisotropy;

or:

Mixing monomer 2 and monomer 3 with acetic anhydride, and performing acetylation reaction at 140-150°C; then adding monomer 1, heating the reaction solution to 310-330°C, and vacuuming to remove small molecules after the reaction, thereby obtaining a liquid crystal polymer with low mechanical anisotropy;

Among them, the general structural formula of monomer one is HOOC-X-COOH;

The general formula of monomer two is HO-Y-OH;

The general structural formula of monomer three is HO-Z-OH.

In some embodiments, the solvent is N,N-dimethylformamide or pyridine.

The third aspect of the present application provides an isotropic liquid crystal polymer material in the form of fiber or film, which is prepared by extrusion molding of the above-mentioned liquid crystal polymer with low mechanical anisotropy.

The fourth aspect of the present application provides the application of the above-mentioned isotropic liquid crystal polymer material in 5G antennas, high-frequency communication devices, electronic devices or optical fiber wrapping layers.

The third aspect of the present application provides the use of the above-mentioned liquid crystal polymer with low mechanical anisotropy in liquid crystal polymer fibers and/or liquid crystal polymer films.

Compared with the prior art, the beneficial effects of this application are:

The present application innovatively combines chiral groups with liquid crystal polymers to prepare a new type of liquid crystal polymer with a cholesteric phase molecular spiral arrangement structure, wherein the isotropically arranged liquid crystal molecules achieve low mechanical anisotropy of the liquid crystal polymer.

The liquid crystal polymer material with low mechanical anisotropy of the present application can form a preferred orientation of molecules and maintain a certain degree of molecular helical arrangement after extrusion molding, thereby achieving low mechanical anisotropy of the material while ensuring high strength and regular molecular orientation of the material.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

FIG1 is a texture image of the cholesteric chiral liquid crystal polymer prepared in Example 1 under a polarizing microscope;

FIG2 is a texture diagram of the nematic non-chiral liquid crystal polymer prepared in Comparative Example 1 under a polarizing microscope;

FIG3 is a schematic diagram of the polymer network and arrangement of liquid crystal molecules after the cholesteric liquid crystal polymer and the nematic liquid crystal polymer are stretched and formed;

FIG. 4 is a graph showing the biaxial mechanical strength test of liquid crystal polymers with different chiral molecule contents.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are all open terms, meaning including but not limited to.

In the following description of this embodiment, the term "and/or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and/or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character "/" generally indicates that the associated objects before and after are in an "or" relationship.

In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, c can be single or multiple, respectively.

The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present application are to be construed as specifically disclosing each intermediate value between the upper and lower limits of the scope. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present application. The upper and lower limits of these smaller ranges may be independently included or excluded in the scope.

Unless otherwise specified, the technical/scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

In a first aspect, the present application provides a liquid crystal polymer with low mechanical anisotropy, wherein the repeating unit has a chemical structure as shown in the following formula:

Among them, X is a rod-like structure composed of rigid groups;

Y is a non-liquid crystal structure composed of flexible chains, heterogeneous rigid groups or kink groups;

Z is a chiral group;

a, b, c are the molar proportions of X, Y and Z respectively, a, b, c are independently selected from any proportion between 0.1% and 90%, and the sum of a, b and c is 100%. Preferably, c is selected from 1.37% to 5.26%.

In the present application, X includes a group that cannot rotate freely or has limited rotation in the molecular structure, such as phenyl, cyclohexyl or alkynyl. In the present application, preferably X includes phenyl, cyclohexyl, phenyl and cyclohexyl, phenyl and alkynyl or cyclohexyl and alkynyl.

In the present application, X is preferably a structure represented by formula (1) to (10):

In the present application, Y is a non-liquid crystal structure composed of a flexible chain, a heterogeneous rigid group or a kinked group. Preferably, Y is selected from the structures shown in formulas (11) to (16):

Wherein, m and n are integers, and m≥0, n≥0.

In the present application, Z is a chiral group, and Z is selected from the structures shown in formulas (17) to (19):

In the present application, the liquid crystal polymer with low mechanical anisotropy is preferably

The structural formula of X is:

The structural formula of Y is:

The structural formula of Z is:

c is selected from 1.37% to 5.26%; its structural formula is shown below:

Among them, c is selected from 1.37%-5.26%, and the sum of a, b and c is 100%.

In the present application, it is preferred that the molecular weight of the liquid crystal polymer with low mechanical anisotropy is greater than 5000, and the glass transition temperature thereof is higher than room temperature.

The liquid crystal polymer with low mechanical anisotropy of the present application has a chiral nematic phase temperature range, in which the liquid crystal polymer presents a spiral molecular arrangement and has a cholesteric liquid crystal molecular spiral structure. Due to the isotropic molecular arrangement, the liquid crystal polymer material with low mechanical anisotropy of the present application can form a preferred orientation of the molecules and maintain a certain degree of molecular spiral arrangement after extrusion molding, thereby achieving low mechanical anisotropy of the material under the premise of ensuring high strength of the material and regular molecular orientation.

In a second aspect, the present application provides a method for preparing the above-mentioned liquid crystal polymer with low mechanical anisotropy. The preparation method described in the present application includes two methods: a solution method and a melt method, wherein the solution method includes:

The monomer 2, the monomer 3 and acetic anhydride are dissolved in a solvent to carry out an acetylation reaction; the monomer 1 is then added and reacted at 110-130° C.; after the reaction, the small molecules are removed by vacuum to obtain a liquid crystal polymer with low mechanical anisotropy.

Among them, the general structural formula of monomer one is HOOC-X-COOH; the general structural formula of monomer two is HO-Y-OH; and the general structural formula of monomer three is HO-Z-OH.

The melting method comprises:

Mixing monomer 2 and monomer 3 with acetic anhydride, and performing acetylation reaction at 140-150°C; then adding monomer 1, heating the reaction solution to 310-330°C, and vacuuming to remove small molecules after the reaction, thereby obtaining a liquid crystal polymer with low mechanical anisotropy;

Among them, the general structural formula of monomer one is HOOC-X-COOH; the general structural formula of monomer two is HO-Y-OH; and the general structural formula of monomer three is HO-Z-OH.

The preparation method of the present application has a synthetic reaction formula of:

The preparation method of the present application has a simple process, the prepared liquid crystal polymer is easy to shape and process, and has low mechanical anisotropy.

The liquid crystal polymer with low mechanical anisotropy prepared in the present application can be used to prepare mechanically isotropic liquid crystal polymer fibers or mechanically isotropic liquid crystal polymer films by extrusion molding. In the liquid crystal polymer fibers or crystal polymer films, the molecules are orderly oriented and can maintain high strength and regular molecular arrangement, which can be used in 5G antennas, high-frequency communication devices, electronic devices, optical fiber wrapping layers and other fields.

The present application is further described below by way of examples.

Example 1

This embodiment provides a liquid crystal polymer with low mechanical anisotropy, in which X is a structure represented by formula (1), Y is a structure represented by formula (12), Z is a structure represented by formula (17), a=51.67%, b=46.97%, and c=1.37%.

The preparation method thereof comprises:

1. Dissolve 0.1 mol of resorcinol, 0.0029 mol of isosorbide and 0.15 mol of acetic anhydride in 200 ml of pyridine, inject the solution into a 500 ml flask, and react for 100 min to fully acetylate the monomers;

2. A nitrogen atmosphere was introduced into the flask, 0.11 mol of 4,4'-dicarboxybiphenyl was added into the flask, and the temperature was gradually raised to 120 °C. The reaction was carried out for 10 h to polymerize. The acetic acid produced during the polymerization was collected, and the nitrogen atmosphere was gradually stopped;

3. Evacuate the flask after the reaction and stir for 30 minutes to remove unreacted small molecule monomers and small molecule by-products;

4. The reaction product was placed under nitrogen protection for 12 h and then cooled to room temperature to obtain a liquid crystal polymer with low mechanical anisotropy.

Example 2

This embodiment provides a liquid crystal polymer with low mechanical anisotropy, in which X is a structure represented by formula (1), Y is a structure represented by formula (12), Z is a structure represented by formula (17), a=50.97%, b=46.33%, and c=2.7%.

The preparation method thereof comprises:

1. Dissolve 0.1 mol of resorcinol, 0.0058 mol of isosorbide and 0.15 mol of acetic anhydride in 200 ml of pyridine, inject the solution into a 500 ml flask, and react for 100 min to fully acetylate the monomers;

2. A nitrogen atmosphere was introduced into the flask for protection, 0.11 mol of 4,4'-dicarboxybiphenyl was added into the flask, and the temperature was gradually raised to 120 °C. The flask was polymerized for 10 h, acetic acid produced during the polymerization was collected, and the nitrogen atmosphere was gradually stopped;

3. Evacuate the flask after the reaction and stir for 30 minutes to remove unreacted small molecule monomers and small molecule by-products;

4. The reaction product was placed under nitrogen protection for 12 h and then cooled to room temperature to obtain a liquid crystal polymer with low mechanical anisotropy.

Example 3

This embodiment provides a liquid crystal polymer with low mechanical anisotropy, in which X is the structure shown in formula (1), Y is the structure shown in formula (12), Z is the structure shown in formula (17), a=50.3%, b=45.7%, and c=4%.

The preparation method thereof comprises:

1. Dissolve 0.1 mol of resorcinol, 0.0087 mol of isosorbide and 0.15 mol of acetic anhydride in 200 ml of pyridine, inject the solution into a 500 ml flask, and react for 100 min to fully acetylate the monomers;

2. A nitrogen atmosphere was introduced into the flask for protection, 0.11 mol of 4,4'-dicarboxybiphenyl was added into the flask, and the temperature was gradually raised to 120 °C. The flask was polymerized for 10 h, acetic acid produced during the polymerization was collected, and the nitrogen atmosphere was gradually stopped;

3. Evacuate the flask after the reaction and stir for 30 minutes to remove unreacted small molecule monomers and small molecule by-products;

4. The reaction product was placed under nitrogen protection for 12 h and then cooled to room temperature to obtain a liquid crystal polymer with low mechanical anisotropy.

Example 4

This embodiment provides a liquid crystal polymer with low mechanical anisotropy, in which X is a structure represented by formula (1), Y is a structure represented by formula (12), Z is a structure represented by formula (17), a=49.63%, b=45.11%, and c=5.26%.

The preparation method thereof comprises:

1. Dissolve 0.1 mol of resorcinol, 0.01165 mol of isosorbide and 0.15 mol of acetic anhydride in 200 ml of pyridine, inject the solution into a 500 ml flask, and react for 100 min to fully acetylate the monomers;

2. A nitrogen atmosphere was introduced into the flask for protection, 0.11 mol of 4,4'-dicarboxybiphenyl was added into the flask, and the temperature was gradually raised to 120 °C. The flask was polymerized for 10 h, acetic acid produced during the polymerization was collected, and the nitrogen atmosphere was gradually stopped;

3. Evacuate the flask after the reaction and stir for 30 minutes to remove unreacted small molecule monomers and small molecule by-products;

4. The reaction product was placed under nitrogen protection for 12 h and then cooled to room temperature to obtain a liquid crystal polymer with low mechanical anisotropy.

Comparative Example

This comparative example provides a nematic non-chiral liquid crystal polymer, wherein X is the structure shown in formula (1), Y is the structure shown in formula (12), and Z is the structure shown in formula (17).

In the comparative example, the chiral molecules providing the Z structure are replaced by half chiral molecules and half racemic chiral molecules to obtain a nematic phase achiral liquid crystal polymer, in which a=51.67%, b=46.97%, and c=0. The preparation method comprises:

1. Dissolve 0.1 mol of resorcinol, 0.005 mol of isosorbide, 0.005 mol of dehydrated mannitol and 0.15 mol of acetic anhydride in 200 ml of pyridine, inject the solution into a 500 ml flask, and react for 100 min to fully acetylate the monomers;

2. A nitrogen atmosphere was introduced into the flask for protection, 0.11 mol of 4,4'-dicarboxybiphenyl was added into the flask, and the temperature was gradually raised to 120 °C. The flask was polymerized for 10 h, acetic acid produced during the polymerization was collected, and the nitrogen atmosphere was gradually stopped;

3. Evacuate the flask after the reaction and stir for 30 minutes to remove unreacted small molecule monomers and small molecule by-products;

4. The reaction product was placed under nitrogen protection for 12 h and then cooled to room temperature to obtain a liquid crystal polymer with low mechanical anisotropy.

The texture of the liquid crystal polymer prepared in Example 1 was observed with a polarizing microscope, as shown in Figure 1. As can be seen from Figure 1, the liquid crystal polymer prepared in Example 1 has a typical cholesteric liquid crystal temperature range.

The texture of the liquid crystal polymer prepared in Comparative Example 1 was observed using a polarizing microscope, as shown in Figure 2. As can be seen from Figure 2, the liquid crystal polymer prepared in Comparative Example has a typical nematic phase liquid crystal temperature range.

Figure 3 is a schematic diagram of the mechanical anisotropy mechanism of the cholesteric liquid crystal polymer prepared in Example 1 and the nematic liquid crystal polymer prepared in the comparative example. As can be seen from Figure 1, the cholesteric liquid crystal polymer prepared in Example 1 has a helical structure; as can be seen from Figure 2, the nematic liquid crystal polymer prepared in the comparative example has a straight chain structure; as can be seen from Figure 3, the nematic liquid crystal polymer in the comparative example forms a preferred orientation of the molecules after stretching, but the molecular chains are approximately parallel and have no helical structure, the tensile stress in the direction of the molecular orientation is high, and the tensile stress in the direction perpendicular to the molecular orientation is low, and it has high mechanical anisotropy; while the cholesteric liquid crystal polymer prepared in Example 1 can form a preferred orientation of the molecules after stretching, and can also maintain a certain degree of molecular helical arrangement, thereby achieving low mechanical anisotropy of the material under the premise of ensuring high strength and regular molecular orientation of the material.

The tensile stress of the liquid crystal polymer materials prepared in Examples 1-4 and the comparative example was tested, and the results are shown in FIG4 .

As can be seen from Figure 4, the tensile stress in the molecular orientation direction of the liquid crystal polymer without chirality in the comparative example is as high as 130MPa, while the tensile stress in the direction perpendicular to the molecular orientation is only 14MPa, and its mechanical anisotropy is very high. With the increase of the molar proportion of chiral groups in the raw materials of the liquid crystal polymer, such as Examples 1-4, the tensile stress of the liquid crystal polymer in the molecular orientation direction gradually decreases, while the tensile stress in the direction perpendicular to the molecular orientation increases rapidly. When the molar proportion of the chiral group is 5.26%, the tensile stress in the molecular orientation direction is 100MPa, and the tensile stress in the direction perpendicular to the molecular orientation is 80MPa, which has low mechanical anisotropy.

In the present application, by introducing chiral groups, the tensile stress of the liquid crystal polymer in the direction perpendicular to the molecular orientation can be increased, and the tensile stress in the molecular orientation direction can be reduced, thereby reducing the mechanical anisotropy of the liquid crystal polymer.

Although the present application has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application are within the scope of protection claimed in the present application.

Claims (8)

1. A liquid crystal polymer with low mechanical anisotropy is characterized in that the repeating unit has a chemical structure shown in the following formula:

Wherein X is a rod-shaped structure formed by rigid groups;

y is a non-liquid crystal structure consisting of a flexible chain, a heterogeneous rigid group or a kinking group;

Z is a chiral group;

b. c is the molar ratio of X, Y and Z respectively, a, b, c are each independently selected from any ratio between 0.1% and 90%, and the sum of a, b and c is 100%;

The preparation method comprises the following steps:

dissolving a monomer 2, a monomer 3 and acetic anhydride in a solvent for acetylation reaction; then adding the monomer 1, and reacting at 110-130 ℃; vacuum pumping is carried out after the reaction to remove small molecules, thus obtaining the liquid crystal polymer with low mechanical anisotropy;

Or:

Mixing the monomer 2 and the monomer 3 with acetic anhydride, and performing acetylation reaction at 140-150 ℃; then adding the monomer 1, heating the reaction solution to 310-330 ℃, and vacuumizing to remove small molecules after the reaction to obtain the liquid crystal polymer with low mechanical anisotropy;

wherein the structural general formula of the monomer 1 is HOOC-X-COOH;

The general formula of the monomer 2 is HO-Y-OH;

the structural general formula of the monomer 3 is HO-Z-OH;

the solvent is N, N-dimethylamide or pyridine.

2. The liquid crystal polymer having low mechanical anisotropy according to claim 1, wherein X is selected from structures represented by formulae (1) to (10):

。

3. the liquid crystal polymer having low mechanical anisotropy according to claim 1, wherein Y is selected from structures represented by formulae (11) to (16):

wherein m and n are integers, m is more than or equal to 0, and n is more than or equal to 0.

4. The liquid crystal polymer having low mechanical anisotropy according to claim 1, wherein Z is selected from structures represented by formulae (17) to (19):

。

5. the liquid crystal polymer having low mechanical anisotropy according to claim 1, wherein,

The structural formula of X is as follows: The structural formula of Y is as follows: the structural formula of Z is: c is selected from 1.37% -5.26%.

6. The liquid crystal polymer having low mechanical anisotropy according to claim 1, wherein,

The molecular weight of the liquid crystal polymer with low mechanical anisotropy is more than 5000, and the glass transition temperature is higher than room temperature.

7. An isotropic liquid crystalline polymer material in the form of a fiber or film prepared from the liquid crystalline polymer having low mechanical anisotropy according to any one of claims 1 to 6 by extrusion molding.

8. Use of the isotropic liquid crystalline polymer material according to claim 7 in 5G antennas, high frequency communication devices, electronic devices or optical fiber packages.