RU2791384C1 - Heat-resistant protective coatings from polyimides based on 3,5-diaminobenzoic acid - Google Patents

Abstract

FIELD: polymer production for optics.

SUBSTANCE: manufacture of a protective coating for optical fibers. A heat-resistant solvent-borne coating of an optic fiber is made by pulling the light fiber through an orifice containing a polyimide solution, followed by removal of the solvent. The polyimide is a homo- or copolyimide of formula I with a molecular weight of 45-350 kDa

,

where x:y=(0.25-1):(0.75-0);

.

EFFECT: enhancement of the coating adhesion to the light fiber.

2 cl, 2 dwg, 1 tbl, 26 ex

Description

The invention relates to highly thermally stable protective coatings, namely to primary polyimide coatings of optical fibers (light guides). The coating is formed by pulling the light guide formed from the workpiece through a solution of polyimide (PI) in an organic solvent and subsequent removal of the solvent by heat treatment.

The invention can be most effectively used in fiber optic systems in high-tech areas: aerospace, oil and gas and automotive industries, energy, medicine, (micro)electronics, etc., however, the scope of the claimed coatings is not limited to optical fibers. The developed polyimide coatings are also applicable for the protection of electrical wires, circuit boards, metal or composite turbine blades, and other materials and products.

At present, polyimides are widely used as coatings that provide protection against mechanical impacts and moisture and are operable under critical temperature conditions. For example, optical fibers with polyimide coatings are successfully used both at high (briefly up to 430°C) and at low temperatures (up to -196°C) [Bin W., et al. Study on temperature sensing properties of different fiber Bragg grating at low temperature // 2015 IEEE International Conference on Estimation, Detection and Information Fusion (ICEDIF), 393-396; Gorshkov B.G., et al. Distributed fiber-optic temperature sensor for cryogenic applications based on detection of boson components of Raman light scattering // Quantum Electronics, 50 (5), 506-509 (2020)].

Widespread commercial PI coatings are based on the use of solutions of polyimide precursors - polyamic acids (PAA) [CA 1325316 (1993); WO 9736837 (1997); RU 2169713 (1997); US 9063268 (2015); US 6711335 (1999)]. The main supplier of PAK varnishes for optical fibers is HD Microsystems. After the application of the PAA solution to the optical fiber during drawing, it is imidized to PI. Due to the short residence time in the oven (several seconds), incomplete imidization of PAA occurs, as a result of which the resulting coatings contain non-cyclized amido acid fragments that worsen their quality. In [US 6711335 (1999)], this problem and ways to solve it are discussed in detail. Due to the hydrolytic instability of PAA, the service life of products made from them is low.

This disadvantage of PAA can be easily eliminated by using solvent-soluble PIs. Until recently, there was no information on the use of such polymers in the manufacture of optical fiber coatings, however, over the past 7 years, a number of works have been published [Haldeman A.T., et al. Tetrimide™: Soluble polyimide optical fiber coatings for avionics // 2014 IEEE Avionics, Fiber-Optics and Photonics Technology Conference, pp.83-84 (2014); Semenov SL. et al. High-temperature polyimide coating for optical fibers // Quantum Electronics, 45 (4), 330-332 (2015); Kosolapov A.F. et al. High-tech polyimide lacquer for the manufacture of a coating for a fiber light guide // Brief reports on physics FIAN, No. 6, 9-14 (2017); Sapozhnikov D.A. et al., High-temperature-resistant polymeric coatings of light guides, Vysokomolek. conn., Ser. C, 62 (2), 166-173 (2020); RU 2610503 (2017); US 10487177 (2019)], which describe the various structures of solvent-soluble PIs and demonstrate the promise of their use as fiber coatings. Such coatings have a number of advantages over traditional ones: they are formed from a completely imidized polymer and do not contain defective amido acid units, the required coating thickness (5-10 μm) is achieved in one application cycle, the PI solution does not require special storage conditions, after applying the varnish, only removal is necessary. solvent.

For example, coatings of expensive fluorinated polyimides are described [WO 9736837 (1997); RU 2169713 (1997); Semenov S.L. et al. High-temperature polyimide coating for optical fibers // Quantum Electronics, 45 (4), 330-332 (2015)], the structure of which is presented below:

The American patent [US 10487177 (2019)] covers a wide range of possible PI structures applicable as fiber coatings. It describes methods for the formation of coatings from both the corresponding PAA and solvent-soluble PIs. The patent presents PIs obtained from the following monomers: o-, m- and p-phenylenediamines, 1,4-, 1,5- and 2,6-diaminoanthalene, 2,6-diaminoanthraquinone, benzidine, 2,2'- and 3,3'-dimethylbenzidines, 2,2'-bys(trifluoromethyl)benzidine, 3,3'-dihydroxybenzidine, 3,3',5,5'-tetramethylbenzidine, 3,3-dimethoxybenzidine, 4,4'-, 3 ,4'- and 3,3'-oxydianilines, 1,4- and 1,3-di(4-aminophenoxy)benzenes, 1,4- and 1,3-di(3-aminophenoxy)benzenes, 4,4' -di(4-amino-2-trifluoromethylphenoxy)biphenyl, 4,4'-di(4-aminophenoxy)biphenyl, 1,4-di(4-amino-2-trifluoromethylphenoxy)benzene, 5-(trifluoromethyl)-1, 3-phenylenediamine, 2-(trifluoromethyl)-1,4-phenylenediamine, 3,3'-, 4,4'- and 3,4'-diaminobenzophenones, 2,5-di(4-aminophenoxy)biphenyl, di(3 -aminophenyl)sulfone, di(3-amino-4-hydroxyphenyl)sulfone, 2,2-di(3-amino-4-hydroxyphenyl)hexafluoropropane, 5,5'-(hexafluoroisopropylidene)di-o-toluidine, 3.3 ',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 2,2-di[4-(4-aminophenoxy)phenyl]propane, 2,2-di[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-di(3- and 4 -aminophenyl)hexafluoropropanes, 1,3-di[2-(4-aminophenyl)-2-propyl]benzene, 2,7-diaminofluorene, 1,1-di(4-aminophenyl)cyclohexane, 2,3,5,6 -tetrafluoro-1,4-phenylenediamine, 2,3,5,6-tetramethyl-1,4-phenylenediamine, 2,4,5,6-tetrafluoro-1,3-phenylenediamine, 9,9-di(4-aminophenyl )fluorene, 9,9-di(3-amino-4-hydroxyphenyl)fluorene, 1,3-, 1,6-, 1,8-, and 2,7-diaminosine, 2,3-, 2,4-, 2,5- and 2,6-diaminotoluenes, 2,3-, 2,5-, 2,6- and 3,4-diaminopyridines, 6-methyl-1,3,5-triazine-2,4-diamine, 2,4-diamino-6-phenyl-1,3,5-triazine, 2,4-diamino-6-hydroxypyrimidine, 1,1-binaphthyl-2,2'-diamine, 4,4'-diaminooctafluorobiphenyl, 3, 7-diamino-2,8-dimethyldibenzothiophenesulfone, 3,4'- and 4,4'-oxydiphthalic anhydrides, 3,3',4,4'-tetracarboxydiphenylsulfone dianhydride, 4,4'-(ethane-1,2-diyl ) diphthalic anhydride, 1,4-bms(3,4-dicarboxyphenoxy)benzene dianhydride, benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride (BZF dianhydride), 2,2',3,3'- dianhydrides and 2,3,3',4'-tetracarboxybiphenyls, 4,4'-(hexafluoroisopropylidene) diphtale vogo anhydride, 4,4'-(4,4'-isopropylidene diphenoxy) diphthalic anhydride (dianhydride A), 9,9-bms(trifluoromethyl)-2,3,6,7-tetracarboxyxanthene dianhydride. However, this patent does not present polyimides containing free carboxyl groups.

It was previously found that the introduction of side carboxyl groups into PI leads to an improvement in the adhesion of coatings made from them to the surface of a quartz fiber [Sapozhnikov D.A., et al. The influence of organosoluble (co)polyimides side functionalization and drawing parameters on the optical fiber coatings formation and properties // High Performance Polymers, 29 (6), 663-669 (2017); Sapozhnikov D.A. Synthesis of organosoluble polyimides and protective coatings of optical fibers based on them // Vysokomolek. conn., Ser. B, 62 (1), 44-52 (2020)]. This eliminates the need to use coupling agents, the use of which is associated with a number of disadvantages, the main of which is the gelation of the mixture for a short time.

The closest analogue, i.e. The prototype of the claimed coatings are previously developed and patented coatings of optical fibers based on solvent-soluble PIs [RU 2610503 (2017)] of the following structure:

The disadvantages of the prototype are the use of relatively expensive tetracarboxylic acid dianhydrides, and also, in the synthesis of PI in m-cresol, the need to isolate and purify the polyimide before subsequent preparation of a varnish based on it.

The objective of the invention is to create new highly thermally stable coatings with improved adhesion, formed from solvent-soluble polyimides based on 3,5-diaminobenzoic acid and commercially available inexpensive tetracarboxylic acid dianhydrides, primarily in relation to the protection of quartz fibers.

The problem is solved by the inventive heat-resistant organic-soluble coatings, in particular, fiber light guides, from homo- and copolyimides of the general formula I with a molecular weight of 45 to 350 kDa, made by pulling a light guide drawn from a workpiece through a spinneret containing a solution of polyimide I with a viscosity of 2400-18,000 mPax , and subsequent removal of the solvent by heating in an oven at 200-350°C.

where x:y=(0.25-1):(0.75-0);

To form the coating, an in situ solution of polyimide I is used, which is formed during its preparation in an aprotic amide-type solvent, such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

As dianhydride monomers in the synthesis of polyimides I, inexpensive products of large-scale production are used - benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride and 4,4'-(4,4'-isoprogashidendiphenoxy)diphthalic anhydride, as one of diaminomonomers - necessarily 3,5-diaminobenzoic acid.

The original homo - and copolyimide I with a wide range of molecular weights M _w -from 45 to 350 kDa get one-step method according to [Vinogradova SV. etc. Carded polyheteroarylenes. Synthesis, properties and originality // Uspekhi khimii, 65 (3), 266-285 (1996)]. For coating, a reaction solution of the synthesized polyimide is used without its isolation (in situ), which greatly simplifies the process.

In all cases, the solution is diluted with the solvent in which the PI synthesis was carried out to a viscosity of 2400–18000 mPaxs, since it was found that a smooth uniform coating is formed on the fiber in this viscosity range. At lower or higher viscosity values, the probability of formation of defective areas increases [RU 2610503 (2017)].

To obtain polyimides I and form coatings from them, aprotic amide-type solvents are used, such as N-methyl-2-pyrrolidone (N-MP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAA). An attempt was made to obtain polyimides in cyclohexanone followed by the formation of coatings from reaction solutions, however, it turned out that only two of the six compounds according to the invention are soluble in this solvent (see table).

The solution of polyimide I used may additionally contain a coupling agent, in particular 3-aminopropyltriethoxysilane, however, as was shown (examples 21-26), in the manufacture of at least coatings of optical fibers, its addition does not affect the properties of the coatings. All polyimides according to the invention contain free carboxyl groups, which contributes to increased adhesion of the coatings formed from them to the surface of optical fibers without the addition of a coupling agent.

Varying the structure of (co)monomers used in the synthesis of (co)polyimides I makes it possible to change the thermal, mechanical, and other properties of coatings.

The heat resistance (T _c ) of all considered polyimides exceeds 225°C, and the heat resistance (T _10% ) is more than 470°C (see table), which makes it possible to use coatings based on them under extreme conditions (from -196 to 350°C ). The thermal stability of the coatings from the claimed PI is comparable or even exceeds the stability of the PI coatings of the prototype [RU 2610503 (2017)].

The main requirement for coating materials is the ability to form strong, flexible films, and this ability is confirmed by the values of the tensile strength of the films of the claimed PI, their tensile modulus and elongation at break (see table).

In addition to high performance, coatings according to the invention have the ability to dissolve in organic solvents of the amide type, which is important when carrying out installation and repair work.

The result of the invention is the development of new relatively inexpensive heat-resistant organosoluble coatings of optical fibers with improved adhesion to them from carboxyl-containing homo- and copolyimides of structure I.

Note that it is possible to use homo- and copolyimides I in the manufacture of coatings of other materials and products.

The invention is illustrated by the following examples and FIGS. 1 and 2.

In FIG. 1 shows a diagram of an installation for manufacturing a fiber with a polymer coating, where 1 is a workpiece; 2 - oven; 3 - die; 4 - furnace; 5 - coil.

In FIG. Figure 2 shows the dependences of the strength of fiber samples with PI coatings on thermal test conditions in the form of Weibull plots (the abscissa is the strength; the ordinate is the Weibull function, where F is the accumulated probability of failure of the fiber.

General procedure for the manufacture of polyimide coating

Homo - or copolyimide I of the formula is obtained in a single-stage method according to [Vinogradova SV. etc. Carded polyheteroarylenes. Synthesis, properties and originality // Advances in Chemistry, 65 (3), 266-285 (1996)] in M-methyl-2-pyrrolidone or other suitable solvent. The resulting PI solution is cooled and brought to a viscosity of 2400–18,000 mPa×with the addition of a solvent in which PI synthesis was carried out, after which the solution is filtered and used for application to an optical fiber.

At the installation for the manufacture of a polymer-coated light guide (Fig. 1), a fiber with a diameter of 110–150 μm is drawn from a preform 1 heated in an oven 2 and pulled through a spinneret 3 with a hole diameter of 250 μm containing a solution of the corresponding PI. Then the light guide with the applied solution enters furnace 4, where the solvent is removed within 3–8 s at a temperature in the furnace of 200–350°C. fibers, coating thickness and drying time. The difference between the diameter of the spinneret opening and the diameter of the pulled fiber determines the thickness of the applied layer of the polyimide solution. The thickness of the produced layer of the polyimide coating of the light guide for one cycle of application of the solution reaches 5-15 microns.

Example 1

Copolyimide coating based on benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride, 3,5-diaminobenzoic acid and 9,9-di(4'-aminophenyl)fluorene with a molar ratio of monomers of 1.0:0, 5:0.5

are made from a solution of PI in N-methyl-2-pyrrolidone in the absence of a coupling agent. Temperature in the furnace 300-350°С

The coating has a glass transition temperature of about 325°C and a temperature of 10% weight loss in air of about 510°C. The tensile strength of the film samples is 95 MPa, the elastic modulus is 750 MPa at a relative elongation of 20% (table). The strength of a fiber coated with such a copolyimide does not decrease upon exposure for 24 and 72 h at 350 and 300°C, respectively. A critical decrease in strength occurs only after a 72-hour exposure at 350°C (Fig. 2).

Example 2

Copolyimide coating based on benzophenone-3,3',4,4'-tetracarboxylic acid dianhydride, 3,5-diaminobenzoic acid and 9,9-di(4'-aminophenyl)fluorene with a molar ratio of monomers of 1.00:0, 75:0.25

are made from a solution of PI in N-methyl-2-pyrrolidone in the absence of a coupling agent. The temperature in the oven is 300-350°C.

The coating is characterized by a glass transition temperature of about 300°C and a temperature of 10% weight loss in air of about 540°C. Films made from said copolyimide have high mechanical properties: tensile strength of 110 MPa, elastic modulus of 1360 MPa, and relative elongation of about 13% (table). The strength of a fiber coated with said copolyimide remains unchanged after 72 hours at 300°C and only decreases by 10% after 24 hours at 350°C (FIG. 2).

Example 3

Copolyimide coating based on 4,4'-(4,4'-isopropylidene diphenoxy) diphthalic anhydride, 3,5-diaminobenzoic acid and 1,3-di(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane with a molar monomer ratio 1.0:0.5:0.5

are made from a solution of PI in M-methyl-2-pyrrolidone in the absence of a coupling agent. The temperature in the oven is 300-350°C.

The polymer coating of the presented structure has a glass transition temperature of about 210°C and a temperature of 10% weight loss in air of about 510°C. Polymer film samples demonstrate a tensile strength of about 100 MPa, an elastic modulus of 1750 MPa, and an elongation at break of about 12% (table).

The strength of a fiber coated with said polyimide remains unchanged after 72 hours at 250° C. (FIG. 2).

Example 4

Polyimide coating based on 4,4'-(4,4'-isopropylidene diphenoxy) diphthalic anhydride and 3,5-diaminobenzoic acid

are made from a solution of PI in M-methyl-2-pyrrolidone in the absence of a coupling agent. The temperature in the oven is 300-350°C.

The coating is characterized by a glass transition temperature of about 270°C and a temperature of 10% weight loss in air of about 470°C. Films made of this polyimide have high mechanical properties: tensile strength of 95 MPa, elastic modulus of 860 MPa, and elongation at break of about 14% (table). The strength of a fiber coated with such a polyimide is retained after exposure for 72 h at 300°C and 1 h at 350°C (Fig. 2).

Example 5

Copolyimide coating based on 4,4'-(4,4'-isopropylidenedifenoxy)-diphthalic anhydride, 3,5-diaminobenzoic acid and 4,4,-diaminodiphenyl oxide, with a molar ratio of monomers 1.0:0.5:0, 5

are made from a solution of PI in N-methyl-2-pyrrolidone in the absence of a coupling agent. The temperature in the oven is 300-350°C.

The polymer coating of the presented structure has a glass transition temperature of about 250°C and a 10% weight loss temperature in air of about 510°C. The strength of the fiber coated with said copolyimide before and after heat treatment is comparable to that of the fiber described in Example 4.

Example 6

Copolyimide coating based on 4,4'-(4,4'-isopropylidenedifenoxy)-diphthalic anhydride, 3,5-diaminobenzoic acid and 2,2-di-[4-(4-aminophenoxy)phenyl]propane with a mole ratio of monomers 1.0:0.5:0.5

are made from a solution of PI in N-methyl-2-pyrrolidone in the absence of a coupling agent. The temperature in the oven is 300-350°C.

The polymer coating of the presented structure has a glass transition temperature of about 225°C and a temperature of 10% weight loss in air of about 525°C. . The strength of the fiber coated with said copolyimide before and after heat treatment is comparable to that of the fiber described in Example 4.

Examples 7-20

The production of coatings is carried out as described in examples 1-6, but N,N-dimethylacetamide, N,N-dimethylformamide or cyclohexanone is used as a solvent, and the oven temperature is 200-350°C.

The properties of the coatings are similar to those of the coatings described in examples 1-6 using N-methyl-2-pyrrolidone as a solvent.

Examples 20-26

The production of coatings is carried out as described in examples 1-6, but 1-2 wt. % 3-aminopropyltriethoxysilane per polymer.

The properties of the resulting coatings are similar to the properties of the coatings described in examples 1-6, without the use of sizing.

Properties of polyimides, PI coatings and PI films

The most important distinguishing feature of the proposed coatings compared to most of those used in industry is the use of ready-made polyimides, and not their precursors - polyamic acids, which causes the absence of non-cyclized amido acid fragments in the final coatings and, as a result, ensures a significant stability of the properties of such coatings and an increase in their service life.

The claimed invention has the following advantages over the prototype: the use in the synthesis of the original polyimides cheaper, which are products of large-scale production of monomers; simplification of the process due to the use of solutions formed during the production of polyimides, without their isolation, purification and re-dissolution; better adhesion of coatings to fiber due to the introduction of carboxyl groups into polyimides; increased heat resistance (up to 24 h at 350°C without changing the properties of the light guide).

The claimed invention makes it possible to produce polyimide coatings with properties varying over a wide range: heat and heat resistance, solubility, etc. At the same time, they are applicable to protect not only optical fibers, but also electrical wires, circuit boards, metal or composite turbine blades, etc.

EFFECT: new heat-resistant solvent-borne coatings of fiber light guides with improved adhesion to fiber based on inexpensive carboxylated homo- and copolyimides.

Claims (7)

1. Heat-resistant solvent-borne coating of a fiber light guide obtained from homo- or copolyimide of formula I with a molecular weight of 45-350 kDa

, where x:y=(0.25-1):(0.75-0);

pulling the light guide drawn from the preform through a spinneret containing a solution of polymer I with a viscosity of 2400-18000 mPa·s, and then removing the solvent by heating in an oven at 200-350°C. 2. The coating according to claim 1, in the manufacture of which a solution of polyimide I is used, which is formed during its preparation in situ in an aprotic amide-type solvent, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide.

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