阅读说明：本技术 一种耐高温含氟聚酰亚胺热缩管及其制备方法 (High-temperature-resistant fluorine-containing polyimide heat-shrinkable tube and preparation method thereof ) 是由 冉祥海 付超 聂伟 钱景 于 2019-12-09 设计创作，主要内容包括：本发明属于热缩管技术领域,尤其涉及一种耐高温含氟聚酰亚胺热缩管及其制备方法。本发明提供的热缩管由具有形状记忆功能的含氟聚酰亚胺制成,所述含氟聚酰亚胺由式(i)结构单体、式(ii)结构单体和式(iii)结构单体聚合而成的预聚体与封端剂反应制成。本发明提供的热缩管由特定结构的含氟聚酰亚胺材料制成,既能够满足高温环境内线缆的防护需求,又具有较低的热收缩温度,可有效降低热缩管使用时所需能量；而且该热缩管的颜色较浅,疏水性能优异,因此其在热缩材料领域具有广阔的应用前景。实验结果表明：本发明提供的热缩管的热冲击温度≥320℃,热收缩温度在245～255℃,吸水率＜0.5％。<Image he="394" wi="700" file="DDA0002308875980000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(The invention belongs to the technical field of heat-shrinkable tubes, and particularly relates to a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube and a preparation method thereof. The heat shrinkable tube provided by the invention is made of fluorine-containing polyimide with a shape memory function, wherein the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with an end-capping reagent. The heat shrinkable tube provided by the invention is made of the fluorine-containing polyimide material with a specific structure, can meet the protection requirement of cables in a high-temperature environment, has a lower heat shrinkage temperature, and can effectively reduce the energy required by the heat shrinkable tube in use; and the color of the heat shrinkable tube is lighter, and the hydrophobic property is excellent, so that the heat shrinkable tube has a wide application prospect in the field of heat shrinkable materials. The experimental results show that: the thermal shock temperature of the thermal shrinkage pipe provided by the invention is more than or equal to 320 ℃, the thermal shrinkage temperature is 245-255 ℃, and the water absorption rate is less than 0.5%.)

1. A high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube is prepared from fluorine-containing polyimide with a shape memory function, wherein the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with a capping reagent:

2. the high temperature resistant fluorine-containing polyimide heat shrinkable tube according to claim 1, wherein the molar ratio of the structural monomer of formula (i) to the structural monomer of formula (ii) is 1: (0.2-5).

3. The high-temperature resistant fluorine-containing polyimide heat shrinkable tube according to claim 1, wherein the molar ratio of the sum of the structural monomers of formula (i) and formula (ii) to the structural monomer of formula (iii) is (0.15-0.3): (0.1-0.25).

4. The high temperature resistant fluorine-containing polyimide heat shrink tube according to claim 1, wherein the end-capping agent has a structure of formula (iv):

5. the high-temperature resistant fluorine-containing polyimide heat shrinkable tube according to claim 1, wherein the amount of the end-capping reagent is 15.5-28.5% of the total molar amount of the structural monomer of formula (i) and the structural monomer of formula (ii).

6. A preparation method of a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube comprises the following steps:

a) mixing and reacting a structural monomer shown in a formula (i), a structural monomer shown in a formula (ii) and a structural monomer shown in a formula (iii) in a solvent to obtain a prepolymer solution;

b) mixing the prepolymer solution and an end-capping reagent for reaction to obtain a sol solution;

c) heating and drying the sol solution in a mold to imidize and form the sol solution to obtain a tubular object;

d) and heating and expanding the tubular object, and then cooling and shaping to obtain the high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube.

7. The preparation method according to claim 1, wherein in the step a), the temperature of the mixing reaction is 5-10 ℃; the mixing reaction time is 5-10 h.

8. The preparation method according to claim 1, wherein in the step b), the temperature of the mixing reaction is 5-10 ℃; the mixing reaction time is 15-20 h.

9. The method according to claim 1, wherein in step c), the heating and drying process specifically comprises:

adding the sol solution into a mold, then raising the temperature of an inner cavity of the mold to 100-120 ℃, and keeping the temperature and drying for 0.8-1 h; then, continuously heating to 180-200 ℃, and keeping the temperature and drying for 1-1.5 h; then, continuously heating to 240-260 ℃, and keeping the temperature and drying for 2-2.5 h; and finally, continuously heating to 360-380 ℃, and keeping the temperature and drying for 1-1.5 h.

10. The method for preparing the composite material according to claim 1, wherein the temperature for the heating expansion in the step d) is 250 to 270 ℃; the expansion rate of the heating expansion is 1.1-1.25 times.

Technical Field

The invention belongs to the technical field of heat-shrinkable tubes, and particularly relates to a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube and a preparation method thereof.

Background

The heat shrinkable tube is made by utilizing the characteristics of a shape memory polymer material, is mainly applied to the wiring position, the connector, the tail end and the like of a wire and a cable, plays the protective roles of insulation protection, sealing, moisture prevention, corrosion prevention, wear prevention and the like, and has been widely applied to the fields of electronics, nuclear power, communication, petroleum, automobiles, military industry and the like due to the characteristics of simple and convenient use, stable performance, wide application occasions and the like.

The heat shrinkable tube is mainly made of a plurality of high polymer materials through blending, the main material comprises PVC, polyolefin, silicon rubber, PVDF, FEP, PTFE and the like, the use temperature grade and the use environment of the heat shrinkable tube are determined by the main material, and along with the development and application of high-power equipment in the fields of aviation, aerospace, nuclear power and the like, higher requirements are provided for the temperature resistance grade of the heat shrinkable tube, so that the working temperature range of the heat shrinkable tube can be widened through developing novel heat shrinkable tube materials, and the heat shrinkable tube is suitable for wires and cables at high-temperature parts of aerospace crafts such as engines, airplanes, missiles, rockets and the like.

At present, the maximum use temperature of a heat shrinkable tube made of PVC, polyolefin, PVDF, FEP and the like is not more than 200 ℃, although the heat shrinkable tube made of PTFE can continuously work within the temperature range of-270-260 ℃, the heat shrinkage temperature is as high as about 340 ℃, and the heat shrinkable tube can generate the shape memory effect by consuming a large amount of heat.

At present, the reported heat-shrinkable tube material which can be continuously used at more than 200 ℃ and has a low heat-shrinking temperature is a shape memory polyimide material, but the material has high water absorption (more than 3 percent) and is limited to be applied in the field of heat-shrinkable materials.

Disclosure of Invention

In view of this, the invention aims to provide a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube and a preparation method thereof.

The invention provides a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube which is prepared from fluorine-containing polyimide with a shape memory function, wherein the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with an end-capping reagent:

preferably, the molar ratio of the structural monomer of formula (i) to the structural monomer of formula (ii) is 1: (0.2-5).

Preferably, the molar ratio of the total of the structural monomers of the formula (i) and the structural monomers of the formula (ii) to the structural monomers of the formula (iii) is (0.15-0.3): (0.1-0.25).

Preferably, the capping agent has the formula (iv):

preferably, the amount of the end-capping reagent is 15.5-28.5% of the total molar amount of the structural monomer of formula (i) and the structural monomer of formula (ii).

The invention provides a preparation method of a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube, which comprises the following steps:

a) mixing and reacting a structural monomer shown in a formula (i), a structural monomer shown in a formula (ii) and a structural monomer shown in a formula (iii) in a solvent to obtain a prepolymer solution;

b) mixing the prepolymer solution and an end-capping reagent for reaction to obtain a sol solution;

c) heating and drying the sol solution in a mold to imidize and form the sol solution to obtain a tubular object;

d) and heating and expanding the tubular object, and then cooling and shaping to obtain the high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube.

Preferably, in the step a), the temperature of the mixing reaction is 5-10 ℃; the mixing reaction time is 5-10 h.

Preferably, in the step b), the temperature of the mixing reaction is 5-10 ℃; the mixing reaction time is 15-20 h.

Preferably, in step c), the heating and drying process specifically includes:

adding the sol solution into a mold, then raising the temperature of an inner cavity of the mold to 100-120 ℃, and keeping the temperature and drying for 0.8-1 h; then, continuously heating to 180-200 ℃, and keeping the temperature and drying for 1-1.5 h; then, continuously heating to 240-260 ℃, and keeping the temperature and drying for 2-2.5 h; and finally, continuously heating to 360-380 ℃, and keeping the temperature and drying for 1-1.5 h.

Preferably, in the step d), the temperature for heating and expanding is 250-270 ℃; the expansion rate of the heating expansion is 1.1-1.25 times.

Compared with the prior art, the invention provides a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube and a preparation method thereof. The high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube provided by the invention is prepared from fluorine-containing polyimide with a shape memory function, wherein the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with an end-capping reagent. The heat shrinkable tube provided by the invention is made of the fluorine-containing polyimide material with a specific structure, can meet the protection requirement of cables in a high-temperature environment, has a lower heat shrinkage temperature, and can effectively reduce the energy required by the heat shrinkable tube in use; and the color of the heat shrinkable tube is lighter, and the hydrophobic property is excellent, so that the heat shrinkable tube has a wide application prospect in the field of heat shrinkable materials. The experimental results show that: the thermal shock temperature of the thermal shrinkage pipe provided by the invention is more than or equal to 320 ℃, the thermal shrinkage temperature is 245-255 ℃, and the water absorption rate is less than 0.5%.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube which is prepared from fluorine-containing polyimide with a shape memory function, wherein the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with an end-capping reagent:

in the invention, the fluorine-containing polyimide is prepared by reacting a prepolymer formed by polymerizing a structural monomer of a formula (i), a structural monomer of a formula (ii) and a structural monomer of a formula (iii) with an end-capping reagent. Wherein the molar ratio of the structural monomer of formula (i) to the structural monomer of formula (ii) is preferably 1: (0.2-5), specifically 1:0.2, 1:0.5, 1:1, 1:1.2, 1:1.5, 1:1.7, 1:2, 1:2.3, 1:2.5, 1:2.7, 1:3, 1:3.2, 1:3.5, 1:3.7, 1:4, 1:4.2, 1:4.5, 1:4.7 or 1: 5; the molar ratio of the total structural monomer of the formula (i) and the structural monomer of the formula (ii) to the structural monomer of the formula (iii) is preferably (0.15-0.3): (0.1-0.25), specifically 0.3:0.25, 0.2:0.15, or 0.15: 0.1.

In the present invention, the capping agent preferably has the formula (iv):

in the present invention, the amount of the end-capping agent is preferably 15.5 to 28.5% of the total molar amount of the structural monomer of formula (i) and the structural monomer of formula (ii), and specifically may be 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, or 28.5%.

In one embodiment provided herein, the fluorine-containing polyimide has the structure of formula (I):

in the formula (I), R₁Is composed of

R₂Is composed of

R₃Is composed of

In the above embodiment provided by the present invention, the fluorine-containing polyimide having the structure of formula (I) includes a segment composed of a structural repeating unit of formula (a) and a structural repeating unit of formula (b), the segment is terminated with a structure of formula (c), and the end groups of different segments are bonded together through an opened carbon-carbon triple bond to form a cross-linked network structure:

in the above embodiment provided by the present invention, the polymerization degree of the structural repeating unit of formula (a) in the fluorine-containing polyimide is preferably 8 to 30, and specifically may be 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30; the polymerization degree of the structural repeating unit of the formula (b) in the fluorine-containing polyimide is preferably 10 to 30, and specifically may be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30.

The invention also provides a preparation method of the high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube, which comprises the following steps:

a) mixing and reacting a structural monomer shown in a formula (i), a structural monomer shown in a formula (ii) and a structural monomer shown in a formula (iii) in a solvent to obtain a prepolymer solution;

b) mixing the prepolymer solution and an end-capping reagent for reaction to obtain a sol solution;

c) heating and drying the sol solution in a mold to imidize and form the sol solution to obtain a tubular object;

d) and heating and expanding the tubular object, and then cooling and shaping to obtain the high-temperature-resistant fluorine-containing polyimide heat-shrinkable tube.

In the preparation method provided by the invention, firstly, the structural monomer of the formula (i), the structural monomer of the formula (ii) and the structural monomer of the formula (iii) are mixed and reacted in a solvent. Wherein the molar ratio of the structural monomer of formula (i) to the structural monomer of formula (ii) is preferably 1: (0.2-5), specifically 1:0.2, 1:0.5, 1:1, 1:1.2, 1:1.5, 1:1.7, 1:2, 1:2.3, 1:2.5, 1:2.7, 1:3, 1:3.2, 1:3.5, 1:3.7, 1:4, 1:4.2, 1:4.5, 1:4.7 or 1: 5; the molar ratio of the total structural monomer of the formula (i) and the structural monomer of the formula (ii) to the structural monomer of the formula (iii) is preferably (0.15-0.3): (0.1-0.25), specifically 0.3:0.25, 0.2:0.15, or 0.15: 0.1; the solvent is preferably N, N-Dimethylacetamide (DMF). In the invention, the mixing reaction is preferably carried out in a nitrogen atmosphere under a stirring condition, and the stirring speed is preferably 250-500 rpm, and specifically may be 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500 rpm; the temperature of the mixing reaction is preferably 5-10 ℃, and specifically can be 5 ℃, 6 ℃, 7 ℃, 8 ℃, 9 ℃ or 10 ℃; the mixing reaction time is preferably 5-10 h, and specifically can be 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10 h. And after the mixing reaction is finished, obtaining a prepolymer solution.

In one embodiment provided by the present invention, the structural monomer of formula (i), the structural monomer of formula (ii), the structural monomer of formula (iii), and the solvent are preferably mixed and reacted according to the following steps:

a1) mixing a structural monomer shown in a formula (i), a structural monomer shown in a formula (ii) and a solvent to obtain a diamine mixed solution;

a2) mixing the structural monomer shown in the formula (iii) with a solvent to obtain a dianhydride solution;

step a1) and step a2) are not in sequence;

a3) and mixing and reacting the diamine mixed solution and the dianhydride solution to obtain a prepolymer solution.

In the operation steps provided in the above embodiment of the present invention, in step a1), the ratio of the total of the structural monomers of formula (i) and formula (ii) to the solvent is preferably (0.15 to 0.3) mmol:1mL, specifically 0.15mmol:1mL, 0.16 mmol:1mL, 0.17 mmol:1mL, 0.18 mmol:1mL, 0.19 mmol:1mL, 0.2mmol:1mL, 0.21 mmol:1mL, 0.22 mmol:1mL, 0.23 mmol:1mL, 0.24 mmol:1mL, 0.25mmol:1mL, 0.26 mmol:1mL, 0.27 mmol:1mL, 0.28 mmol:1mL, 0.29 mmol:1mL or 0.3mmol:1 mL; the mixing is preferably carried out under stirring in a nitrogen atmosphere; the stirring temperature is preferably 15-35 ℃, and specifically can be 15 ℃, 20 ℃, 25 ℃ (room temperature), 30 ℃ or 35 ℃.

In the operation steps provided in the above embodiments of the present invention, in step a2), the ratio of the structural monomer of formula (iii) to the solvent is preferably (0.1 to 0.25) mmol:1mL, specifically 0.1 mmol:1mL, 0.11 mmol:1mL, 0.12 mmol:1mL, 0.13 mmol:1mL, 0.14 mmol:1mL, 0.15mmol:1mL, 0.16 mmol:1mL, 0.17 mmol:1mL, 0.18 mmol:1mL, 0.19 mmol:1mL, 0.2mmol:1mL, 0.21 mmol:1mL, 0.22 mmol:1mL, 0.23 mmol:1mL, 0.24 mmol:1mL or 0.25mmol:1 mL; the mixing is preferably carried out under stirring in a nitrogen atmosphere; the stirring temperature is preferably 15-35 ℃, and specifically can be 15 ℃, 20 ℃, 25 ℃ (room temperature), 30 ℃ or 35 ℃.

In the preparation method provided by the invention, after the prepolymer solution is prepared, the prepolymer solution and the end-capping reagent are mixed for reaction. Wherein the capping agent preferably has the formula (iv):

in the preparation method provided by the invention, in the process of mixing and reacting the prepolymer solution and the end-capping reagent, the amount of the end-capping reagent is preferably 15.5-28.5% of the total molar amount of the structural monomer of formula (i) and the structural monomer of formula (ii) used for preparing the prepolymer solution, and specifically may be 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28% or 28.5%; the mixing reaction is preferably carried out in a nitrogen atmosphere under the condition of stirring, and the stirring speed is preferably 250-500 rpm, and specifically can be 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500 rpm; the temperature of the mixing reaction is preferably 5-10 ℃, and specifically can be 5 ℃, 6 ℃, 7 ℃, 8 ℃, 9 ℃ or 10 ℃; the mixing reaction time is preferably 15-20 h, and specifically can be 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h or 20 h. After the mixing reaction, a viscous sol solution was obtained.

In the preparation method provided by the invention, after the sol solution is prepared, the sol solution is heated and dried in a mold. Wherein, the sol solution is preferably defoamed before being heated and dried. The bubble removing mode is preferably low-temperature heating, and the low-temperature heating temperature is preferably 30-50 ℃, and specifically can be 30 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃; the time for low-temperature heating is preferably 2-4 h, and specifically can be 2h, 2.5h, 3h, 3.5h or 4 h. In the present invention, the specific process of the heat drying preferably includes: adding the sol solution into a mold, then raising the temperature of an inner cavity of the mold to 100-120 ℃, recording as a first temperature, and carrying out heat preservation and drying for 0.8-1 h under the first temperature condition; then, continuously heating to 180-200 ℃, recording as a second temperature, and keeping the temperature and drying for 1-1.5 h under the condition of the second temperature; continuing to heat to 240-260 ℃, recording as a third temperature, and keeping the temperature and drying for 2-2.5 h under the condition of the third temperature; and finally, heating to 360-380 ℃, recording as a fourth temperature, and carrying out heat preservation and drying for 1-1.5 h under the fourth temperature condition. In the heating and drying process provided by the invention, the initial temperature of the inner cavity of the mold before temperature rise is preferably 25 ℃ (room temperature); the heating rate of heating to the first temperature is preferably 2-2.5 ℃/min, and specifically can be 2 ℃/min, 2.1 ℃/min, 2.2 ℃/min, 2.3 ℃/min, 2.4 ℃/min or 2.5 ℃/min; the first temperature may specifically be 100 ℃, 105 ℃, 110 ℃, 115 ℃ or 120 ℃; the heat preservation drying time under the first temperature condition can be specifically 0.8h, 0.85h, 0.9h, 0.95h or 1 h; the heating rate for heating to the second temperature is preferably 2-2.5 ℃/min, and specifically can be 2 ℃/min, 2.1 ℃/min, 2.2 ℃/min, 2.3 ℃/min, 2.4 ℃/min or 2.5 ℃/min; the second temperature may specifically be 180 ℃, 185 ℃, 190 ℃, 195 ℃ or 200 ℃; the heat preservation and drying time under the second temperature condition can be 1h, 1.05h, 1.1h, 1.15h, 1.2h, 1.25h, 1.3h, 1.35h, 1.4h, 1.45h or 1.5 h; the heating rate of heating to the third temperature is preferably 2-2.5 ℃/min, and specifically can be 2 ℃/min, 2.1 ℃/min, 2.2 ℃/min, 2.3 ℃/min, 2.4 ℃/min or 2.5 ℃/min; the third temperature may be 240 ℃, 245 ℃, 250 ℃, 255 ℃ or 260 ℃; the heat preservation drying time under the third temperature condition can be specifically 2h, 2.05h, 2.1h, 2.15h, 2.2h, 2.25h, 2.3h, 2.35h, 2.4h, 2.45h or 2.5 h; the heating rate of heating to the fourth temperature is preferably 2-2.5 ℃/min, and specifically can be 2 ℃/min, 2.1 ℃/min, 2.2 ℃/min, 2.3 ℃/min, 2.4 ℃/min or 2.5 ℃/min; the fourth temperature may be 360 ℃, 365 ℃, 370 ℃, 375 ℃ or 380 ℃; the heat preservation drying time under the fourth temperature condition can be 1h, 1.05h, 1.1h, 1.15h, 1.2h, 1.25h, 1.3h, 1.35h, 1.4h, 1.45h or 1.5 h. In the present invention, in the process of heating and drying, the sol solution is imidized and formed in a mold to obtain a tubular object.

In the preparation method provided by the invention, after the tubular object is prepared, the tubular object is heated and expanded. Wherein the thermal expansion is preferably performed in vacuum; the temperature of the heating and expanding is preferably 250-270 ℃, and specifically 250 ℃, 251 ℃, 252 ℃, 253 ℃, 254 ℃, 255 ℃, 256 ℃, 257 ℃, 258 ℃, 259 ℃, 260 ℃, 261 ℃, 262 ℃, 263 ℃, 264 ℃, 265 ℃, 267 ℃, 268 ℃, 269 ℃ or 270 ℃; the expansion rate of the heating expansion is preferably 1.1 to 1.25 times, and specifically may be 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24 or 1.25 times. And after heating and expanding are finished, cooling and shaping are carried out to obtain the high-temperature resistant fluorine-containing polyimide heat shrinkable tube.

The heat shrinkable tube provided by the invention is made of the fluorine-containing polyimide material with a specific structure, can meet the protection requirement of cables in a high-temperature environment, has a lower heat shrinkage temperature, and can effectively reduce the energy required by the heat shrinkable tube in use; and the color of the heat shrinkable tube is lighter, and the hydrophobic property is excellent, so that the heat shrinkable tube has a wide application prospect in the field of heat shrinkable materials. More specifically, the heat shrinkable tube provided by the invention has the following advantages:

1) the heat shrinkable tube provided by the invention is made of fluorine-containing polyimide material with a specific structure, the polymer material takes a cross-linked structure of thermosetting polyimide as a fixed phase of a shape memory polymer, and the flexibility of a molecular chain between cross-linked points is improved by utilizing a flexible ether bond group bonded between molecular chains, so that the polymer material is used as a reversible phase of the shape memory polymer, and the polymer material has a shape memory function. The thermal shock temperature of the polymer material is more than or equal to 320 ℃, and the protection requirement of the cable in a high-temperature environment is met;

2) the fluorine atoms are introduced into the polyimide monomer, and the larger electronegativity of the fluorine atoms can cut off the conjugation of electron clouds in a P1 molecular structure, so that the heat shrinkable tube provided by the invention has lighter color and tends to be transparent; moreover, the strong hydrophobicity of the fluorine atoms can reduce the water absorption of the heat-shrinkable tube and improve the environment resistance; in addition, the introduction of fluorine atoms can also reduce the glass transition temperature of polyimide, so that the heat shrinkage temperature of the heat shrinkage pipe provided by the invention is maintained at 245-255 ℃, and the energy required by the heat shrinkage pipe in use is effectively reduced;

3) in the preferred scheme provided by the invention, the proper proportion of diamine, dianhydride and end-capping reagent is selected, so that the reaction is completely generated, the obtained heat-shrinkable tube is basically free of residual monomers, and the stability of the heat-shrinkable tube performance is ensured.

For the sake of clarity, the following examples are given in detail.