Solvent-free photocuring high-temperature-resistant optical fiber coating and preparation method thereof

Abstract

The invention discloses a solvent-free photocuring high-temperature-resistant optical fiber coating and a preparation method thereof, and relates to the technical field of high-temperature-resistant optical fiber coating. Comprising the following raw materials in parts by weight: 45-95 parts of polymerizable polyimide resin containing unsaturated bonds, 40-100 parts of a reactive diluent, 5-10 parts of a cross-linking agent and 2-5 parts of a photoinitiator, the polymerizable polyimide resin containing unsaturated bonds has a structural formula as shown in the following formula (I): # imgabs0 #, wherein m, n, x and y are all integers between 1 and 200. The polymerizable polyimide resin containing the unsaturated bonds can be dissolved in the reactive diluent, the photoinitiator generates free radicals under ultraviolet light, the polyimide resin containing the unsaturated bonds, the reactive diluent and the cross-linking agent are initiated to generate polymerization reaction, the high-temperature-resistant optical fiber coating paint is obtained, other high-boiling-point solvents do not need to be additionally added, and the cost is low. And the photocured coating does not need to be subjected to a high-temperature baking solvent removal process, and has the advantages of high solid content, no solvent, high temperature resistance and the like.

Description

Technical Field

[0001] The invention relates to the technical field of high temperature resistant optical fiber coatings, and in particular to a solvent-free photocurable high temperature resistant optical fiber coating and a preparation method thereof. Background Art

[0002] Optical fiber coatings play an important role in protecting optical fibers and stabilizing optical fiber transmission performance, and are an indispensable component of communication optical fibers. With the expansion of optical fiber application areas and the increase in environmental complexity, various new types of special optical fiber coatings have developed rapidly.

[0003] High temperature resistant optical fiber coating is a special coating, which is mainly used to coat the surface of optical fiber to improve the high temperature resistance of optical fiber. High temperature resistant optical fiber coating can be used to coat the surface of optical fiber of temperature, pressure, flow and other sensors to improve the high temperature resistance of sensors. It has important applications and prospects in industrial fields such as petrochemical, steel, and electricity, aerospace fields such as aircraft engines and spacecraft, energy fields such as solar energy and nuclear energy, and in medical and scientific research fields. Polyimide is a high temperature resistant polymer material with excellent thermal stability, mechanical properties and chemical stability. Therefore, it is widely used in high temperature resistant optical fiber coatings, which can provide excellent protection for optical fiber, extend the service life of optical fiber, and improve the transmission efficiency and stability of optical fiber.

[0004] At present, high-temperature resistant optical fiber coatings are mainly thermosetting coatings. Thermosetting coatings need to be treated at high temperatures during use, which can easily damage the optical fiber. At the same time, the curing rate is relatively slow, which is not conducive to the rapid production of optical fiber. In addition, polyimide materials have poor solubility and require a large amount of high-boiling point solvents to dissolve. After the optical fiber is coated, it needs to be heated and baked to remove a large amount of solvent, which consumes a lot of energy and causes serious pollution.

[0005] Photocurable polyimide optical fiber coating can be quickly cured by ultraviolet or visible light irradiation, which improves production efficiency; the shrinkage rate during the curing process is low, reducing the stress effect on the optical fiber; it can effectively protect the optical fiber from physical damage, chemical corrosion and environmental influences; the loss of light is small and does not affect the transmission performance of the optical fiber; it has excellent high temperature resistance.

[0006] However, a large amount of high-boiling-point solvents are needed to prepare polyimide optical fiber coatings, which increases the cost of the coating. After the optical fiber is coated, heat baking is required to remove the solvent in the coating. Long-term high-temperature baking will cause damage to the optical fiber and affect signal transmission. The rapid volatilization of the solvent requires a large amount of energy, which increases the process steps and costs. In addition, it will cause serious environmental pollution problems.

[0007] Therefore, it is necessary to provide a solvent-free photocurable polyimide optical fiber coating to avoid the above disadvantages and improve the production efficiency of optical fiber. Summary of the invention

[0008] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art, to propose a solvent-free photocurable high-temperature resistant optical fiber coating and a preparation method thereof, to solve the technical problems of the prior art such as high content of high boiling point solvents, high energy consumption, and environmental pollution.

[0009] In order to achieve the above technical objectives, the present invention mainly adopts the following technical solutions:

[0010] The invention discloses a solvent-free photocurable high temperature resistant optical fiber coating, comprising the following raw materials in parts by weight: 45-95 parts of a polymerizable polyimide resin containing an unsaturated bond, 40-100 parts of a reactive diluent, 5-10 parts of a crosslinking agent and 2-5 parts of a photoinitiator;

[0011] The polymerizable polyimide resin containing unsaturated bonds has a structural formula as shown in the following formula (I):

[0012]

[0013] In formula (I), m, n, x and y are all integers between 1 and 200.

[0014] In a preferred embodiment of the present invention, the molecular weight of the polymerizable polyimide resin containing unsaturated bonds is between 5000 and 100000.

[0015] In a preferred embodiment of the present invention, the active diluent is selected from any one of N-vinyl pyrrolidone, isobornyl acrylate, isooctyl acrylate, and 4-acryloylmorpholine.

[0016] In a preferred embodiment of the present invention, the crosslinking agent is selected from 1,6-hexanediol diacrylate.

[0017] In a preferred embodiment of the present invention, the photoinitiator is selected from any one of 1-hydroxycyclohexyl phenyl ketone (184), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959), 2,4,6-trimethylbenzoylphosphonic acid ethyl ester (TPO-L), and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO).

[0018] In a preferred embodiment of the present invention, the polymerizable polyimide resin containing unsaturated bonds is prepared by the following method:

[0019] (1) Dissolving different proportions of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 2,2-bis(4-aminophenyl)hexafluoropropane in N-methylpyrrolidone, and stirring in an ice bath to dissolve;

[0020] (2) adding hexafluorodianhydride and maleic anhydride in batches, stirring in an ice bath, warming to room temperature, stirring overnight; then raising the temperature to react;

[0021] (3) After cooling to room temperature, glycidyl methacrylate (GMA), triethylamine and p-hydroxyanisole were added, and the temperature was raised under nitrogen protection to react;

[0022] (4) After the reaction is completed, the reaction solution is gradually poured into a mixed solution of ethanol / water, stirred, filtered, and washed with ethanol for multiple times. After drying in a vacuum drying oven, a polymerizable polyimide resin containing unsaturated bonds is obtained.

[0023] Furthermore, in step (2), after stirring in an ice bath for 2 hours, the mixture is heated to room temperature and then heated to 150° C. for reaction for 8 hours; in step (3), the mixture is reacted at 100° C. for 5 hours under nitrogen protection.

[0024] Preferably, the coating does not contain any solvent that needs to be removed later.

[0025] The present invention also discloses a method for preparing the solvent-free photocurable high-temperature resistant optical fiber coating as described above, comprising the following steps: uniformly mixing a polymerizable polyimide resin containing an unsaturated bond, an active diluent, a crosslinking agent, and a photoinitiator, heating the mixture under the protection of nitrogen in a dark place until the photoinitiator is completely dissolved, and filtering out insoluble matter to obtain a photocurable high-temperature resistant optical fiber coating.

[0026] In a preferred embodiment of the present invention, the heating temperature is 40-50°C.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The low molecular weight polymerizable polyimide resin containing unsaturated bonds of the present invention can be dissolved in a reactive diluent, and a photoinitiator generates free radicals under ultraviolet light to initiate a polymerization reaction among the polyimide resin containing unsaturated bonds, the reactive diluent, and the crosslinking agent, thereby preparing a high-temperature resistant optical fiber coating without the need to add other high-boiling point solvents. After light curing, the coating does not need to be subjected to a high-temperature baking process to remove the solvent, and has the advantages of high solid content, no solvent, high temperature resistance, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a thermogravimetric image of the solvent-free photocurable optical fiber coating prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] In the present invention, the low molecular weight polymerizable polyimide resin containing unsaturated bonds has a structural formula as shown in the following formula (I):

[0032]

[0033] In formula (I), m, n, x and y are all integers between 1 and 200.

[0034] It is used as the main raw material with active diluent, crosslinking agent and photoinitiator to prepare solvent-free photocurable optical fiber coating.

[0035] Among them, the active diluent in the present invention is mainly N-vinyl pyrrolidone, and other specific types are not limited, and those skilled in the art can select according to actual conditions. For example, the active diluents are isobornyl acrylate, isooctyl acrylate, 4-acryloylmorpholine, etc.

[0036] The present invention does not limit the specific type of the crosslinking agent, and those skilled in the art can select it according to actual conditions. For example, 1,6-hexanediol diacrylate.

[0037] The present invention does not limit the specific type of photoinitiator, and those skilled in the art can select it according to actual conditions. For example, the photoinitiator can be 1-hydroxycyclohexyl phenyl ketone (184), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959), 2,4,6-trimethylbenzoylphosphonic acid ethyl ester (TPO-L), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), etc.

[0038] The following is a specific description through examples.

[0039] Example 1

[0040] Synthesis of low molecular weight polymerizable polyimide resin containing unsaturated bonds: 15.697g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 14.325g of 2,2-bis(4-aminophenyl)hexafluoropropane were dissolved in 150mL of N-methylpyrrolidone (NMP), and stirred in an ice bath to dissolve. Then 44.424g of hexafluorodianhydride and 1.401g of maleic anhydride were added in batches, stirred in an ice bath for 2h, warmed to room temperature, and stirred overnight. Then the temperature was raised to 150℃ for reaction for 8h. After cooling to room temperature, 12.184g of glycidyl methacrylate (GMA), 200mg of triethylamine and 0.2g of p-hydroxyanisole were added, and the reaction was carried out at 100℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered, and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin is obtained for use.

[0041] Preparation of solvent-free photocurable optical fiber coating: 50 g of polymerizable polyimide resin containing unsaturated bonds, 40 g of N-vinyl pyrrolidone, 10 g of 1,6-hexanediol diacrylate and 2 g of photoinitiator 1-hydroxycyclohexyl phenyl ketone (184) were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0042] The coating was cured by UV using a 500W UV lamp. The coating was cured in 10 seconds and the coating thickness was about 40 to 50 microns. The optical fiber curing experiment was conducted at a drawing speed of 10 m / min and 20 m / min. At a drawing speed of 10 m / min, the surface was not sticky; at a drawing speed of 20 m / min, the surface was not sticky.

[0043] like Figure 1 As shown, after the coating is cured, it can maintain no mass loss in a 200°C environment, only 2% mass loss at 250°C, and the mass loss rate of the coating at 294°C does not exceed 5%, demonstrating the high temperature resistance of the coating.

[0044] Example 2

[0045] Synthesis of low molecular weight polymerizable polyimide resin containing unsaturated bonds: 21.9755g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 13.3704g of 2,2-bis(4-aminophenyl)hexafluoropropane were dissolved in 150mL of NMP and placed in an ice bath to stir and dissolve. Then 44.4240g of hexafluorodianhydride and 0.7004g of maleic anhydride were added in batches, stirred in an ice bath for 2h, warmed to room temperature, and stirred overnight. Then the temperature was raised to 150℃ for reaction for 8h. After cooling to room temperature, 11.372g of GMA, 200mg of triethylamine and 0.2g of p-hydroxyanisole were added, and the reaction was carried out at 100℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin was obtained for use.

[0046] Preparation of solvent-free photocurable optical fiber coating: 45 g of polymerizable polyimide resin containing unsaturated bonds, 50 g of N-vinyl pyrrolidone, 5 g of 1,6-hexanediol diacrylate and 2 g of photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0047] The coating was cured by UV using a 500W UV lamp. The coating was cured in 10 seconds and the coating thickness was about 40 to 50 microns. The optical fiber curing experiment was conducted at a drawing speed of 10 m / min and 20 m / min. At a drawing speed of 10 m / min, the surface was not sticky; at a drawing speed of 20 m / min, the surface was not sticky.

[0048] Example 3

[0049] Synthesis of low molecular weight polymerizable polyimide resin containing unsaturated bonds: 31.394g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 28.65g of 2,2-bis(4-aminophenyl)hexafluoropropane were dissolved in 250mL of NMP and placed in an ice bath to stir and dissolve. Then 88.848g of hexafluorodianhydride and 0.5604g of maleic anhydride were added in batches, stirred in an ice bath for 2h, warmed to room temperature, and stirred overnight. Then the temperature was raised to 150℃ for reaction for 8h. After cooling to room temperature, 24.368g of GMA, 300mg of triethylamine and 0.4g of p-hydroxyanisole were added, and the reaction was carried out at 100℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin was obtained for use.

[0050] Preparation of solvent-free photocurable optical fiber coating: 95 g of polymerizable polyimide resin containing unsaturated bonds, 100 g of N-vinyl pyrrolidone, 5 g of 1,6-hexanediol diacrylate and 5 g of photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0051] The coating was cured by UV using a 500W UV lamp. The coating was cured in 10 seconds and the coating thickness was about 40 to 50 microns. The optical fiber curing experiment was conducted at a drawing speed of 10 m / min and 20 m / min. At a drawing speed of 10 m / min, the surface was not sticky; at a drawing speed of 20 m / min, the surface was not sticky.

[0052] Example 4

[0053] Synthesis of low molecular weight polymerizable polyimide resin containing unsaturated bonds: 313.94g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 286.5g of 2,2-bis(4-aminophenyl)hexafluoropropane were dissolved in 2500mL of NMP and placed in an ice bath to stir and dissolve. Then 888.48g of hexafluorodianhydride and 1.226g of maleic anhydride were added in batches, stirred in an ice bath for 2h, warmed to room temperature, and stirred overnight. Then the temperature was raised to 150℃ for reaction for 8h. After cooling to room temperature, 243.68g of GMA, 3g of triethylamine and 4g of p-hydroxyanisole were added, and the reaction was carried out at 100℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin was obtained for standby use.

[0054] Preparation of solvent-free photocurable optical fiber coating: 900 g of polymerizable polyimide resin containing unsaturated bonds, 1000 g of N-vinyl pyrrolidone, 100 g of 1,6-hexanediol diacrylate and 50 g of photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0055] The coating was cured by UV using a 500W UV lamp. The coating was cured in 10 seconds and the coating thickness was about 40 to 50 microns. The optical fiber curing experiment was conducted at a drawing speed of 10 m / min and 20 m / min. At a drawing speed of 10 m / min, the surface was not sticky; at a drawing speed of 20 m / min, the surface was not sticky.

[0056] Example 5

[0057] Synthesis of low molecular weight polymerizable polyimide resin containing unsaturated bonds: 156.97g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 143.25g of 2,2-bis(4-aminophenyl)hexafluoropropane were dissolved in 1500mL of NMP and placed in an ice bath to stir and dissolve. Then 444.24g of hexafluorodianhydride and 0.7g of maleic anhydride were added in batches, stirred in an ice bath for 2h, warmed to room temperature, and stirred overnight. Then the temperature was raised to 150℃ for reaction for 8h. After cooling to room temperature, 121.84g of GMA, 2g of triethylamine and 2g of p-hydroxyanisole were added, and the reaction was carried out at 100℃ for 5h under nitrogen protection. After the reaction was completed, the reaction solution was gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin was obtained for standby use.

[0058] Preparation of solvent-free photocurable optical fiber coating: 500 g of polymerizable polyimide resin containing unsaturated bonds, 450 g of N-vinyl pyrrolidone, 50 g of 1,6-hexanediol diacrylate and 20 g of photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0059] The coating was cured by UV using a 500W UV lamp. The coating was cured in 10 seconds and the coating thickness was about 40 to 50 microns. The optical fiber curing experiment was conducted at a drawing speed of 10 m / min and 20 m / min. At a drawing speed of 10 m / min, the surface was not sticky; at a drawing speed of 20 m / min, the surface was not sticky.

[0060] Comparative Example 1

[0061] Synthesis of unsaturated polyimide resin: Dissolve 18.313g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 10.012g of 4,4'-diaminodiphenyl ether in 200mL of NMP, place in an ice bath and stir to dissolve. Then add 44.424g of hexafluorodianhydride in batches, stir in an ice bath for 2h, warm to room temperature, and stir overnight. Then heat to 150℃ and react for 8h. After reaching room temperature, add 14.215g of GMA, 200mg of triethylamine and 0.2g of p-hydroxyanisole, and react at 100℃ under nitrogen protection for 5h. After the reaction is completed, the reaction solution is gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin is obtained for standby use.

[0062] Preparation of optical fiber coating: 30 g of polyimide resin containing unsaturated bonds, 20 g of N-vinyl pyrrolidone, 5 g of 1,6-hexanediol diacrylate, 45 g of NMP solvent and 2 g of photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under the protection of nitrogen in a dark place until it was completely dissolved, and the insoluble matter was filtered out. The coating was a yellow transparent viscous solution, which was stored in a dark place for later use.

[0063] The coating was cured by UV light using a 500W UV lamp. The coating was cured in 10 seconds and then placed in an oven at 80°C for 6 hours to remove the solvent. The coating thickness was about 40 to 50 microns.

[0064] Comparative Example 2

[0065] Synthesis of unsaturated polyimide resin: Dissolve 18.313g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 10.012g of 4,4'-diaminodiphenyl ether in 200mL of NMP, place in an ice bath and stir to dissolve. Then add 44.424g of hexafluorodianhydride in batches, stir in an ice bath for 2h, warm to room temperature, and stir overnight. Then heat to 150℃ and react for 8h. After reaching room temperature, add 14.215g of GMA, 200mg of triethylamine and 0.2g of p-hydroxyanisole, and react at 100℃ under nitrogen protection for 5h. After the reaction is completed, the reaction solution is gradually poured into a mixed solution of ethanol / water, stirred for 5h, filtered and washed with ethanol several times. After drying in a vacuum drying oven, the solid resin is obtained for standby use.

[0066] Preparation of optical fiber coating: 40 g of a polymerizable polyimide resin containing an unsaturated bond, 10 g of 1,6-hexanediol diacrylate, 50 g of an NMP solvent, and 2 g of a photoinitiator 184 were mixed evenly, and the resulting mixture was heated to 50°C under a light-proof nitrogen atmosphere. The polymerizable polyimide resin containing an unsaturated bond could not be completely dissolved, the system had a high viscosity, and the resin directly gelled when heated for a long time to dissolve, and could no longer be used.

[0067] Comparative Example 3

[0068] Synthesis of thermosetting polyimide resin: Dissolve 20.024g of 4,4'-diaminodiphenyl ether in 300mL of NMP and stir in an ice bath to dissolve. Then add 44.424g of hexafluorodianhydride in batches, stir in an ice bath for 2h, warm to room temperature, and stir overnight. Then heat to 150℃ and react for 8h. After the reaction is completed, gradually pour the reaction solution into a mixed solution of ethanol / water, stir for 5h, filter and wash with ethanol several times. Dry in a vacuum drying oven to obtain a solid resin for use.

[0069] Preparation of optical fiber coating: Heat and dissolve 30 g of solid resin in 70 g of NMP solvent, filter to remove insoluble matter, and the coating is a yellow transparent viscous solution for later use.

[0070] After the above thermosetting polyimide is coated on the surface of the optical fiber, it is placed in an oven and heated at 80°C for 6 hours to remove the solvent. The coating thickness is about 40 to 50 microns.

[0071] Comparative Example 4

[0072] Synthesis of thermosetting polyimide resin: Dissolve 20.024g of 4,4'-diaminodiphenyl ether in 200mL of NMP and stir in an ice bath to dissolve. Then add 44.424g of hexafluorodianhydride in batches, stir in an ice bath for 2h, warm to room temperature, and stir overnight. Then heat to 180℃ and react for 12h. After the reaction is completed, gradually pour the reaction solution into a mixed solution of ethanol / water, stir for 5h, filter and wash with ethanol several times. Dry in a vacuum oven to obtain a solid resin for use.

[0073] Preparation of optical fiber coating: 40 g of solid resin was heated and dissolved in 60 g of NMP solvent. The polyimide resin could not be completely dissolved and the system had high viscosity and could not flow.

[0074] In summary, the light-curable high-temperature resistant optical fiber coating prepared by the present invention does not contain high-boiling point solvents, does not require thermal baking to remove solvents, has a high curing rate (10s fast curing, and a curing rate of 20m / s is achieved on an optical fiber curing machine) and high temperature resistance.

[0075] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A solvent-free photocurable high temperature resistant optical fiber coating, characterized in that: The invention comprises the following raw materials in parts by weight: 45-95 parts of a polymerizable polyimide resin containing an unsaturated bond, 40-100 parts of a reactive diluent, 5-10 parts of a crosslinking agent and 2-5 parts of a photoinitiator; The polymerizable polyimide resin containing unsaturated bonds has a structural formula as shown in the following formula (I): In formula (I), m, n, x and y are all integers between 1 and 200.

2. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 1, characterized in that: The molecular weight of the polymerizable polyimide resin containing unsaturated bonds is between 5000 and 100000.

3. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 1, characterized in that: The active diluent is selected from any one of N-vinyl pyrrolidone, isobornyl acrylate, isooctyl acrylate and 4-acryloylmorpholine.

4. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 1, characterized in that: The crosslinking agent is selected from 1,6-hexanediol diacrylate.

5. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 1, characterized in that: The photoinitiator is selected from any one of 1-hydroxycyclohexyl phenyl ketone (184), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (2959), 2,4,6-trimethylbenzoylphosphonic acid ethyl ester (TPO-L), and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO).

6. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 1, characterized in that: The polymerizable polyimide resin containing unsaturated bonds is prepared by the following method: (1) Dissolving different proportions of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and 2,2-bis(4-aminophenyl)hexafluoropropane in N-methylpyrrolidone, and stirring in an ice bath to dissolve; (2) adding hexafluorodianhydride and maleic anhydride in batches, stirring in an ice bath, warming to room temperature, stirring overnight, and then raising the temperature to react; (3) After cooling to room temperature, glycidyl methacrylate (GMA), triethylamine and p-hydroxyanisole were added, and the temperature was raised under nitrogen protection to react; (4) After the reaction is completed, the reaction solution is gradually poured into a mixed solution of ethanol / water, stirred, filtered, and washed with ethanol for multiple times. After drying in a vacuum drying oven, a polymerizable polyimide resin containing unsaturated bonds is obtained.

7. The solvent-free photocurable high temperature resistant optical fiber coating according to claim 6, characterized in that: In step (2), the mixture was stirred in an ice bath for 2 h, then warmed to room temperature and then heated to 150° C. for reaction for 8 h. In step (3), the mixture was reacted at 100° C. for 5 h under nitrogen protection.

8. The solvent-free photocurable high temperature resistant optical fiber coating according to any one of claims 1 to 7, characterized in that: The coating does not contain any solvent that needs to be removed later.

9. A method for preparing a solvent-free photocurable high temperature resistant optical fiber coating according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: uniformly mixing a polymerizable polyimide resin containing unsaturated bonds, an active diluent, a crosslinking agent and a photoinitiator, heating the mixture under the protection of nitrogen gas to completely dissolve the photoinitiator, filtering and removing insoluble matter, and obtaining a light-cured high-temperature resistant optical fiber coating.

10. The preparation method according to claim 9, characterized in that: The heating temperature is 40-50℃.

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