A fluorine-free transparent polyimide conduit, its preparation method and application

Abstract

This invention discloses a fluorine-free transparent polyimide catheter, its preparation method, and its application. The preparation method of the fluorine-free transparent polyimide catheter includes: using a block polyimide polymer as a molding solution; the block polyimide polymer has a soluble polyimide structure and is composed of block molecular segments; wherein, the block molecular segments are composed of highly transparent segments; this invention employs a multi-stage dip-coating and pre-baking adhesive process and a multi-stage gradient high-temperature curing process to improve the transparency of the polyimide catheter, reduce yellowing, and maintain the mechanical properties of the block polyimide polymer. This allows it to not only meet the mechanical properties required for interventional treatment devices but also improve catheter transparency, enhance visualization during interventional procedures, and thus improve surgical precision.

Description

Technical Field

[0001] This invention relates to the field of polyimide materials technology, and more particularly, to the field of minimally invasive interventional medical device technology. Specifically, it relates to a fluorine-free transparent polyimide catheter, its preparation method, and its application. Background Technology

[0002] Minimally invasive interventional therapy requires instruments to possess excellent delivery capability, flexibility, kink resistance, and precise maneuverability when navigating narrow and tortuous internal pathways (such as blood vessels, urethra, and digestive tract). Polyimide catheters are an ideal choice to meet these requirements. Firstly, polyimide possesses excellent mechanical properties, such as tensile strength ≥200MPa and modulus ≥3GPa, meaning it is not easily compressed, elongated, or damaged during delivery, ensuring precise and reliable force transmission during surgery. Simultaneously, it is highly flexible, easily passing through complex anatomical structures (such as intracranial vessels and coronary arteries), and resists kinking, preventing collapse or kinking at sharp bends, ensuring unobstructed passage for contrast agents, drugs, or other instruments (such as microwires and coils). Secondly, the high strength of the polyimide catheter itself allows for the fabrication of very thin yet robust walls. A small outer diameter reduces trauma to the puncture site or tissue, achieving true "minimally invasive" results. A large inner lumen, with the same outer diameter, provides a larger inner diameter, facilitating the delivery of more complex instruments or providing better flow rates. In addition, polyimide catheters have excellent thermal stability and biocompatibility. They can withstand high-temperature sterilization (such as ethylene oxide and gamma ray sterilization) without deformation or performance degradation. They can pass rigorous biocompatibility tests (such as ISO 10993), are non-irritating and non-toxic to human tissues, and are suitable for long-term or short-term implantation.

[0003] In recent years, the introduction of "fluoride restrictions" (i.e., regulatory restrictions on perfluorinated and polyfluoroalkyl substances, PFAS) by the EU and other countries has had a profound and complex impact on the entire medical catheter industry, especially on transparent medical catheters, such as commonly used fluorinated FEP, PFA, and ETFE catheters, which have been subject to strict restrictions. These transparent catheters offer excellent visibility and real-time monitoring capabilities, allowing for real-time observation of fluid status, such as bubble detection to identify and remove air bubbles within the catheter; blood flow confirmation, where doctors can visually and quickly confirm whether the catheter tip is located within the target blood vessel by observing blood return; and the transparent wall allows doctors to observe the surrounding anatomical structures or the position of auxiliary instruments through the catheter wall, enabling more precise positioning.

[0004] Chinese invention patent CN 1282713C discloses a transparent and heat-resistant polyimide optical waveguide, but the high transparency achieved by using fluorine-containing structures such as 2,2-bis(4-aminophenyl)hexafluoropropane and 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride cannot meet the fluorine-free requirements for medical applications. Chinese invention patent CN118852621A discloses a medical polyimide catheter, using a block-type polyimide polymer obtained by combining rigid and flexible segments as the catheter material. It possesses good mechanical properties and solvent resistance, but its light transmittance is poor (≤60%), limiting its application in high-precision interventional surgeries for visualization.

[0005] Therefore, how to develop a fluorine-free transparent polyimide catheter that can fully utilize the excellent properties of polyimide materials, avoid the limitations of fluorine-containing transparent materials, and significantly enhance surgical visibility, improve operational precision and safety, and promote the development of minimally invasive treatment technology towards a more complex and refined direction has become an urgent technical problem to be solved for polyimide catheters.

[0006] Based on the problems existing in the prior art, the present invention provides a highly transparent polyimide catheter, which creates a clear, controllable, and precise minimally invasive treatment channel that directly reaches the lesion for interventional surgery. Summary of the Invention

[0007] The main objective of this invention is to provide a fluorine-free transparent polyimide conduit, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing a fluorine-free transparent polyimide conduit, using a block polyimide polymer as the molding solution. The block polyimide polymer has a combination of block molecular chain segments that achieve its high transparency, low yellowing and high mechanical properties, and the use of a soluble polyimide structure avoids yellowing caused by high-temperature imidization; wherein, the block molecular chain segments are composed of highly transparent segments and highly transparent segments.

[0010] The specific steps include:

[0011] S1. Provide a polyamic acid precursor solution;

[0012] Highly transparent dianhydride monomers and highly transparent diamine monomers are added to a first polar aprotic solvent, dissolved, and subjected to a first-stage reaction to obtain polyamic acid oligomers with dianhydride end groups; then, a highly mechanical diamine monomer is added for a second-stage reaction, followed by the addition of a highly mechanical dianhydride monomer for a third-stage reaction; finally, an end-capping agent is added until the reaction is complete, thus obtaining the polyamic acid precursor solution.

[0013] S2. Block polyimide polymer;

[0014] The polyamic acid precursor solution prepared in S1 is heated once to react and obtain a polyimide resin solution. After precipitation in a poor solvent, post-treatment is performed, followed by imidization treatment by heating a second time to obtain the block polyimide polymer.

[0015] S3. Dip coating and setting: The block polyimide polymer prepared in S2 is dissolved in a second polar aprotic solvent. A multi-stage dip coating and pre-drying coating process is used to dip the block polyimide polymer solution onto the outer wall of the core. After pre-drying and setting treatment, a uniform adhesive film is formed on the surface of the core.

[0016] Then, a polyimide conduit is obtained on the surface of the core through a multi-stage gradient high-temperature curing process;

[0017] S4. The polyimide conduit is removed from the surface of the core to obtain the final product.

[0018] Preferably, in S1, the viscosity of the polyamic acid precursor solution is 100-100000 cP, more preferably 1000-10000 cP, and even more preferably 3000-8000 cP.

[0019] Preferably, the first polar aprotic solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, tetrahydrofuran, dioxane, dichloromethane, chloroform, hexamethylphosphoric triamide, γ-butyrolactone, cyclopentanone, m-cresol, diethyl ether, p-cresol methyl ether, etc., but is not limited thereto.

[0020] Preferably, the capping agent is any one or a combination of several of phthalic anhydride (PA), 4-phenylethynyl phthalic anhydride (PEPA), maleic anhydride (MA), and 5-norbornene-dicarboxylic anhydride (NA), but is not limited thereto.

[0021] Preferably, the solid content of the block polyimide polymer solution in S3 is 5-50 wt%, more preferably 10-40 wt%, and even more preferably 12-30 wt%.

[0022] Preferably, the first polar aprotic solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, tetrahydrofuran, dioxane, dichloromethane, chloroform, hexamethylphosphoric triamide, γ-butyrolactone, cyclopentanone, m-cresol, diethyl ether, p-cresol methyl ether, etc., but is not limited thereto.

[0023] Preferably, the first polar aprotic solvent used in S1 and the second polar aprotic solvent used in S3 are the same or different.

[0024] Preferably, the multi-stage dip coating and characterization includes at least three dip-coating-pre-drying cycles.

[0025] In some specific embodiments, the dip-coating-pre-baking process includes: injecting the block polyimide polymer into a glue tank, passing the core through the bottom of the glue tank at a speed of 0.1 to 50 m / min for dip coating, and then setting it at 60 to 150°C; after multiple dip-coating-pre-baking processes, drying is performed using a multi-stage gradient high-temperature curing process, first drying at high temperature to remove the solvent, and then annealing at low temperature to reduce the interlayer stress between the core and the glue layer, thereby obtaining the polyimide conduit.

[0026] In some specific embodiments, the multi-stage gradient high-temperature curing process includes gradually increasing the temperature and then gradually annealing by setting multiple temperature gradients.

[0027] Preferably, the temperature gradients are 180℃, 200℃, 220℃, 240℃, 200℃, 150℃, and 100℃.

[0028] As another objective of the invention, the present invention also provides a fluorine-free transparent polyimide conduit, wherein the material of the fluorine-free transparent polyimide conduit is a block polyimide polymer composed of highly transparent segments and highly mechanical segments on the same molecular backbone.

[0029] The block polyimide polymer has the structural formula shown in formula (1):

[0030] (1);

[0031] Among them, X1 and Y1 are highly transparent segments, and X2 and Y2 are highly mechanical segments.

[0032] X1 and X2 are tetracarboxylic acid dianhydride residues in tetravalent organic groups. X1 is a highly transparent dianhydride segment, and X2 is a highly mechanical dianhydride segment.

[0033] Y1 and Y2 are diamine residues in divalent organic groups. Y1 is a highly transparent segmental diamine, and Y2 is a highly mechanical segmental diamine.

[0034] m represents the molar percentage of the high-transparency segment in both the high-transparency and high-mechanical-strength segments as 65-75 moles.

[0035] n represents the molar percentage of the high-mechanical-strength segment in both the high-transparency and high-mechanical-strength segments as 35–25 moles.

[0036] In a preferred embodiment, X1 is a residue of at least one of the following: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, but is not limited thereto.

[0037] Preferably, X1 is a residue of at least one of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride and cyclobutanetetracarboxylic dianhydride.

[0038] In a preferred embodiment, Y1 is a residue of at least one of 9,9-bis(4-aminophenyl)fluorene, 9,9-dimethylfluorene-2,7-diamine, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 2,2-bis[4-(4-aminophenoxyphenyl]propane, 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diaminophenyl sulfone, bis(3-amino-4-hydroxyphenyl) sulfone, etc., but is not limited thereto.

[0039] Preferably, Y1 is a residue of at least one of 9,9-bis(4-aminophenyl)fluorene and 4,4'-diaminophenyl sulfone.

[0040] In a preferred embodiment, X2 is a residue of at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, p-phenylene-bis(phenyltriterpenoid) dianhydride, (4-phthalic anhydride)formyloxy-4-phthalate, 2,6-naphthobis(triterpenoid monoester anhydride), bis[(3,4-dianhydride)phenyl]terephthalate, but is not limited thereto.

[0041] Preferably, X2 is a residue of at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and p-phenylene-bisphenyltriester dianhydride.

[0042] In a preferred embodiment, Y2 is a residue of at least one of the following: 4-aminobenzoic acid (4-aminophenyl) ester, 4,4'-diaminobenzoyl aniline, bis(4-aminophenyl) terephthalate, [4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate, 4-aminobenzoic acid 4-aminophenyl ester, N,N'-bis(4-aminophenyl) terephthalamide, bisphenol A diester diamine, 2,4,6-trimethyl-1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, etc., but is not limited thereto.

[0043] Preferably, Y2 is a residue of at least one of 4-aminobenzoic acid (4-aminophenyl) ester and 4,4'-diaminobenzoyl aniline.

[0044] In a preferred embodiment, the polyimide conduit has a light transmittance ≥89%, a yellowness index ≤2.3, a haze of 0.3~0.6, a tensile strength of 200~220MPa, a Young's modulus of 3~4GPa, and an elongation at break of 79~90%.

[0045] In a preferred embodiment, the wall thickness of the fluorine-free transparent polyimide conduit is 10~80μm.

[0046] Preferably, the pipe wall thickness is 12~25μm.

[0047] As a third objective of the invention, the present invention also provides the application of the fluorine-free transparent polyimide catheter as described above as a medical device, particularly its application in cardiovascular interventional therapy devices.

[0048] In the preparation of polyimide catheters, this invention uses block polyimide polymers as the molding solution and employs a multi-stage dip-coating and pre-baking adhesive process and a multi-stage gradient high-temperature curing process to obtain polyimide catheters. This improves the transparency of the polyimide catheters, reduces yellowing, and maintains the mechanical properties of the block polyimide polymers. This not only meets the mechanical properties required for interventional treatment devices but also improves the transparency of the catheters, enhancing the visualization during interventional procedures and thus improving the precision of the surgery.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] This invention uses block polyimide polymers as molding solutions. The combination of block molecular chain segments enables high transparency and high mechanical properties. Furthermore, the use of soluble polyimide structures avoids yellowing caused by high-temperature imidization, enabling its widespread application in high-end medical devices. Attached Figure Description

[0051] Figure 1This is a photograph of the polyimide conduit provided in Embodiment 1 of the present invention. Detailed Implementation

[0052] Detailed embodiments of the invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0053] First, the terminology used in this invention will be explained.

[0054] "Block polyimide" is a polymer in which the structural unit shown in the following general formula (1) is the repeating unit.

[0055]

[0056] In the general formula, X represents a tetracarboxylic acid dianhydride residue in a tetravalent organic group, X1 is a highly transparent dianhydride segment, X2 is a highly mechanical dianhydride segment, Y represents a diamine residue in a divalent organic group, Y1 is a highly transparent diamine segment, Y2 is a highly mechanical diamine segment, that is, the two segments are on the same molecular backbone, where m accounts for 65-75 mol%, and n accounts for 35-25 mol%.

[0057] The dianhydride X1 in the high-transparency segment mainly includes 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic acid 1,4:2,3-dianhydride, etc., with 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride and cyclobutanetetracarboxylic dianhydride being particularly preferred.

[0058] The diamine Y1 in the highly transparent segments mainly includes 9,9-bis(4-aminophenyl)fluorene, 9,9-dimethylfluorene-2,7-diamine, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 2,2-bis[4-(4-aminophenoxyphenyl]propane, 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diaminophenyl sulfone, bis(3-amino-4-hydroxyphenyl) sulfone, etc., with 9,9-bis(4-aminophenyl)fluorene and 4,4'-diaminophenyl sulfone being particularly preferred.

[0059] X2 is a high-mechanical-strand dianhydride, mainly including 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, p-phenylene-bisphenyltrilate dianhydride, (4-phthalic anhydride)formyloxy-4-phthalate, 2,6-naphthobis(trilate anhydride), bis[(3,4-dianhydride)phenyl]terephthalate, etc., with 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and p-phenylene-bisphenyltrilate dianhydride being particularly preferred.

[0060] Y2 is a high-mechanical-strand dianhydride, mainly composed of 4-aminobenzoic acid (4-aminophenyl) ester, 4,4'-diaminobenzoyl aniline, bis(4-aminophenyl) terephthalate, [4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate, 4-aminobenzoic acid 4-aminophenyl ester, N,N'-bis(4-aminophenyl) terephthalamide, bisphenol A diester diamine, 2,4,6-trimethyl-1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, etc., with 4-aminobenzoic acid (4-aminophenyl) ester and 4,4'-diaminobenzoyl aniline being particularly preferred.

[0061] In this invention, the solvents used to prepare the soluble polyimide resin and solution are mainly polar aprotic solvents, including N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), diphenyl sulfone, tetramethyl sulfone, tetrahydrofuran (THF), dioxane, dichloromethane, trichloromethane, hexamethylphosphoric triamide, γ-butyrolactone, cyclopentanone, m-cresol, diethyl ether, p-cresol methyl ether, etc. These solvents are usually used alone, or two or more are mixed as needed.

[0062] The method for preparing soluble polyimide resin in this invention involves first preparing a polyamic acid solution. When the molar amount X1 > Y1, a polar aprotic solvent is first added to the reaction apparatus, followed by the dissolution of diamine Y1. Then, dianhydride X1 is added, and after it is completely dissolved, the reaction continues for 1-5 hours. Next, diamine Y2 is added, and after it is dissolved, the reaction continues for 1-5 hours. Finally, all of the dianhydride X2 is added, and the reaction continues for 10-14 hours to complete the reaction. When the molar amount X1 < Y1, the order of addition is Y1, X1, X2, Y1, ensuring that there is no competitive polymerization reaction between the two free diamines in the solution system, which would lead to structural sequence disorder. Phthalic anhydride and other end-capping agents are then added. Then, the polyamic acid is imidized using a xylene reflux method. 20% xylene by mass of the solution is added, the solution is heated to 170-180℃, and refluxed for 24 hours to remove water. The solution is then washed clean with solvents such as ethanol or methyl ethyl ketone, dried, and then redissolved in solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), γ-butyrolactone, and cyclopentanone to prepare a soluble polyimide resin solution for catheter coating.

[0063] The polyimide resin solution prepared using the present invention is preferably 5-50 wt%, more preferably 10-40 wt%, and even more preferably 12-30 wt%. If the solid content is less than 5 wt%, the amount of resin applied to the core in a single dip will be too small, the tube wall will be too thin, and the efficiency will be too low. If the solid content is higher than 50 wt%, problems such as excessive viscosity, decreased leveling, and uneven coating will occur.

[0064] The viscosity of the polyamic acid precursor solution prepared by the present invention is preferably 100-100000 cP, more preferably 1000-10000 cP, and even more preferably 3000-8000 cP. If the viscosity is less than 100 cP, the solution is too dilute and there is too little adhesion to the core surface. If the viscosity is greater than 10000 cP, the solution is too thick, resulting in uneven surface adhesive and an uneven film surface.

[0065] To improve the leveling and adhesion properties of the polyamic acid precursor solution prepared by this invention, leveling agents, surfactants, thickeners, plasticizers, fillers, etc., can be added to the solution. The amount of addition is preferably 0.001 to 5 wt%, more preferably 0.01 to 3 wt%.

[0066] To avoid the wall thickness deviation (thicker at the bottom and thinner at the top) caused by gravity during the horizontal transport of the resin solution after the core is coated into the pre-drying oven, this invention uses a slender, vertical resin tank. The core is transported from bottom to top and then enters the pre-drying oven through a die that controls the wall thickness. The die is installed at the connection between the top of the resin tank and the bottom of the pre-drying oven, thus employing vertical resin coating. The preferred transport speed of the core in the resin solution is 0.1–50 m / min, more preferably 0.5–30 m / min, and even more preferably 1–10 m / min. The wall thickness is controlled by the die orifice size, and for thick-walled tubes, the number of coating passes is determined based on the thickness of a single layer. A transport speed less than 0.1 m / min results in low production efficiency and no economic benefit, while a speed greater than 50 m / min leads to excessively fast coating, insufficient wetting and coating time on the core surface, and uneven surface resin coating. In order to improve the wetting ability of the core and the adhesive, the core needs to be cleaned and activated. First, the surface dust is washed with deionized water, then the surface organic oil stains are removed by ultraviolet light irradiation, and finally the surface is activated by atmospheric plasma bombardment, thereby improving the wetting ability.

[0067] In this invention, the pre-baking process aims to dry most of the solvent in the core adhesive layer, thus setting its shape. Hot air drying is more efficient, and the hot air carries away volatile solvents, making operation safer. The preferred hot air temperature is 60–150°C, more preferably 70–140°C, and even more preferably 80–130°C. The preferred hot air velocity is 0.1–10 m / s, more preferably 0.5–8 m / s, and even more preferably 2–6 m / s. Temperatures below 60°C or air velocities above 10 m / s will result in excessively low baking temperatures or short dwell times, failing to dry the tubes in time. Temperatures above 200°C or hot air velocities below 0.1 m / s will result in excessively high baking temperatures or long dwell times, easily leading to air bubbles on the tube wall and causing defects in the conduit. After pre-baking, the conduit is further dried using methods such as hot air, electric heating elements, or infrared radiation. The preferred processing temperature is 160–250°C, and even more preferably 200–240°C. The number of pre-drying and drying cycles depends mainly on the thickness after a single die coating and the target thickness. It can be done through multiple cycles of dip coating, pre-drying, drying, re-drying, re-pre-drying, and re-drying.

[0068] In this invention, the polyimide conduit after final drying is initially inspected for appearance defects, color difference, and thickness uniformity. Then, the conduit that meets the quality requirements is cut according to the product specifications, the core is extracted, and finally, various key performance indicators are tested.

[0069] To better understand the technical solution of the present invention, the mechanism of polyimide will be further explained below.

[0070] The main reason for the deep yellow or opaque nature of the polyimide obtained by this invention is analyzed. The polyimide product formed by the technical solution of this invention is an intramolecular charge-transfer complex. The intramolecular CTC effect formed by a strong electron donor (diamine) and a strong electron acceptor (dianhydride) causes the electron cloud of the polyimide to shift, absorbing energy in the visible light region and thus producing color. This invention adopts a block molecular chain structure. The transparent segment is introduced by introducing a large-volume, twisted non-coplanar structure or alicyclic monomer to disrupt the regular stacking of the molecular chain, such as the large-volume 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride. Weak electron donor / acceptor monomers are used to reduce the CTC intensity by balancing the intramolecular electron cloud distribution, such as 4,4'-bis(3-aminophenoxy)diphenyl sulfone.

[0071] Furthermore, during the high-temperature thermal imidization process of polyimide, the residual polyamic acid structure is unstable, and the terminal amino groups oxidize and turn yellow, causing a decrease in the light transmittance of the polyimide catheter. By employing a soluble structure, polymerization and imidization are completed in solution, and a capping agent is added to cap the terminal amino groups. The high transparency characteristic introduces twisted structures or aliphatic molecules that cause loose molecular chain stacking, reducing strength and toughness. Introducing structures containing amide bonds or ester bonds to copolymerize and form high-mechanical-strength segments provides polyimide with excellent mechanical properties, enabling it to be used as a polyimide catheter in minimally invasive interventional therapy.

[0072] Based on the special requirements of polyimide catheter applications, the polyimide molecular structure provided by this invention consists of highly transparent segments and highly mechanical segments, wherein the proportion of highly transparent segments is 65-75 mol% and the proportion of highly mechanical segments is 35-25 mol%.

[0073] This invention addresses the synthesis of soluble polyimide by adjusting and optimizing various process parameters, such as the water content of the reaction solvent, the purity of the raw materials, the reaction atmosphere, the reaction temperature, the stirring speed, the reaction time, and the order of feeding. This enables controllable polymerization of the resin viscosity, solid content, molecular weight and distribution, as well as excellent optical and mechanical properties.

[0074] The present invention relates to a core wire for polyimide conduit molding. The core wire is made of smooth glass rod, quartz rod, stainless steel wire, copper wire, silver-plated copper wire, etc., or coated with PTFE, nylon-12 or other lubricating materials to facilitate subsequent peeling of the conduit from the core. The core wire has a diameter of 30-500μm.

[0075] In this invention, the glue tank used for core dip coating is a long and slender vertical cylinder with a round die at the end for controlling the tube wall thickness and scraping off excess glue. The pre-drying oven is a hot air tube oven to remove volatile solvents in time. Its airflow direction is opposite to the direction of core movement, and its temperature can be between 80 and 150°C. The glue tank and the pre-drying oven are unit combinations. The high-temperature drying oven is a hot air tube oven or an infrared oven. Since it has already been imidized, the temperature can be between 150 and 250°C. Different die diameters and dip coating times are selected according to different thickness requirements.

[0076] The fluorine-free transparent polyimide catheter prepared in this invention has an inner diameter of 30-500 μm and a wall thickness of 10-100 μm. Its length can be cut before or after the separation of the tubing and the core, depending on the user's needs.

[0077] The technical solution of the present invention will be described in detail below through specific embodiments.

[0078] Example 1

[0079] This embodiment provides a method for preparing a polyimide conduit, the specific steps of which include:

[0080] 1. Preparation of polyamic acid resin solution

[0081] In a Class 1000 cleanroom, maintained at a constant temperature of 25°C and a constant humidity of 50% RH, DMAc (18.3 kg) and 4,4'-diaminophenyl sulfone monomer (4,4'-DDS, 3.5 mol, 0.8692 kg) were added to a 50 L reactor equipped with mechanical stirring, a cooling / heating medium jacket, a condenser reflux device, and a water separator. The reaction temperature was set to 25°C, and the mixture was stirred for 2 hours. Then, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF, 4 mol, 1.834 kg) was added, and the mixture was stirred uniformly for 4 hours to form a polyamic acid oligomer with dianhydride end groups. The solution was then... Add 4-aminobenzoic acid (4-aminophenyl) ester (APAB, 1.5 mol, 0.342 kg) to the solution and stir for 2 h to dissolve and react fully. Then, slowly add 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (4,4'-BPDA, 0.95 mol, 0.280 kg) in multiple batches until the resin viscosity reaches about 50,000 cP. Stir for 2 h to dissolve and react fully. Then, add phthalic anhydride (PA, 0.1 mol, 0.148 kg) for end-capping. Finally, stir for 12 h to obtain a polyamic acid resin solution with a solid content concentration of 16 wt%.

[0082] 2. Preparation of polyamic acid resin films

[0083] Add 4.34 kg of xylene to the above resin solution, then heat the resin solution to 170-180℃ and reflux with water for 24 h. Then, place it in ethanol (a poor solvent) to precipitate white resin. Next, wash the resin five times with clean anhydrous ethanol, filter, and dry under vacuum at 120℃ for 2 h. Finally, treat it in a nitrogen oven at 240℃ for 2 h to ensure complete imidization. Weigh 2 kg of resin powder and dissolve it in 8 kg of a mixed solvent of N,N-dimethylacetamide (DMAc) and γ-butyrolactone (volume ratio 7:3). After complete dissolution and clarity, remove residual bubbles in the solution under vacuum (<1 Pa) for 24 h. Pass the solution through a 1 μm filter to remove impurities. Take a small amount of the solution and coat it into a 25 μm flat film. After drying the solvent at 240℃, perform optical testing. The test results are shown in Table 1 below. Other resins were used for catheter preparation.

[0084] 3. Preparation of polyimide conduits

[0085] Silver-plated copper wire with a diameter of 0.60 mm was selected as the molding core. Before coating, it underwent three processes in sequence: deionized water cleaning and drying, ultraviolet irradiation, and oxygen plasma treatment to clean and activate its surface. Then, the prepared polyimide was poured into a first-stage slender vertical cylindrical glue tank with a diameter of 0.05 m and a height of 2 m. The core was passed through the bottom of the glue tank at a speed of 1 m / min. After being immersed in the glue solution, it was passed through a die with a diameter of 0.70 mm to scrape off excess glue solution. Then, it was pre-baked in a 150℃ oven to dry and set the glue solution. After the first setting, it was passed through a second-stage glue tank, die, and pre-baking tunnel by guide wheels to complete the second immersion coating and setting. This process was repeated in a third stage. The glue tanks, glue solutions, drying tunnels, and temperatures of the second and third stages were the same as those of the first stage. The diameters of the dies for the second and third stages were 0.72 mm and 0.74 mm, respectively. Then, guided by guide wheels, the core coated with adhesive film was sequentially passed through a seven-stage high-temperature furnace. The furnace temperatures for each stage were set at 180, 200, 220, 240, 200, 150, and 100°C. First, high-temperature drying was used to remove the solvent, followed by low-temperature annealing to reduce the interlaminar stress between the core and the adhesive layer. After heat treatment, the core was cut into 1m segments according to the product length specifications, and a core extraction device was used to separate the core from the polyimide conduit. The resulting conduit had a diameter of 0.60mm and a wall thickness of approximately 0.025mm. Finally, the conduit's performance was evaluated, and the test results are shown in Table 1.

[0086] See Figure 1 The image shown is a photograph of the polyimide conduit prepared in this embodiment.

[0087] Example 2

[0088] The only difference between this embodiment and Example 1 is that the transparent polyimide catheter formulation is replaced with a new structure: 9,9-bis(4-aminophenyl)fluorene (FDA, 3.5 mol, 1.219 kg), cyclobutanetetracarboxylic dianhydride (CBDA, 4 mol, 0.784 kg), 4,4'-diaminobenzoylaniline (DABA, 1.5 mol, 0.342 kg), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (4,4'-BPDA, 0.95 mol, 0.280 kg). The other catheter structures and manufacturing processes are the same as in Example 1.

[0089] Example 3

[0090] The only difference between this embodiment and Example 1 is that the transparent polyimide catheter formulation is replaced with a new structure: 9,9-bis(4-aminophenyl)fluorene (FDA, 3.5 mol, 1.219 kg), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF, 4 mol, 1.834 kg), 4-aminobenzoic acid (4-aminophenyl) ester (APAB, 1.5 mol, 0.342 kg), and p-phenylene-bisphenyltriester dianhydride (TAHQ, 0.95 mol, 0.435 kg). The other catheter structures and manufacturing processes are the same as in Example 1.

[0091] Example 4

[0092] The only difference between this embodiment and Embodiment 1 is that: a silver-plated copper wire with a diameter of 0.10 mm is used as the forming core, and the diameters of the first, second, and third stage dies are 0.15, 0.158, and 0.166 mm, respectively. The final prepared conduit has a diameter of 0.10 mm and a wall thickness of 0.012 mm. In addition, an optical test is conducted using a 12 μm thick planar film. The other conduits, formulations, structures, and manufacturing processes are the same as in Embodiment 1.

[0093] Example 5

[0094] The only difference between this embodiment and Embodiment 1 is that a silver-plated copper wire with a diameter of 1 mm is used as the forming core, and the diameters of the first, second, and third stage dies are 1.413 mm, 1.446 mm, and 1.479 mm, respectively. The final prepared conduit has a diameter of 1 mm and a wall thickness of 80 μm. In addition, an optical test is conducted using a 100 μm thick planar film. The other conduits, formulations, structures, and manufacturing processes are the same as in Embodiment 1.

[0095] Comparative Example 1

[0096] The only difference between this comparative example and Example 1 is that the transparent polyimide catheter formulation is replaced with a new structure: 4,4'-diaminophenyl sulfone (4,4'-DDS, 5 mol, 1.242 kg) and 9,9-bis(3,4-dicarboxyphenyl)fluorenic anhydride (BPAF, 4.95 mol, 2.269 kg). The other catheter structures and manufacturing processes are the same as in Example 1.

[0097] Comparative Example 2

[0098] The only difference between this comparative example and Example 1 is that the transparent polyimide catheter formulation is replaced with a new structure: 4-aminobenzoic acid (4-aminophenyl) ester (APAB, 5 mol, 1.141 kg) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (4,4'-BPDA, 4.95 mol, 1.456 kg). The other catheter structures and manufacturing processes are the same as in Example 1.

[0099] Comparative Example 3

[0100] The only difference between this comparative example and Example 1 is that the transparent polyimide catheter formulation is replaced with a new structure: 4,4'-diaminophenyl sulfone monomer (4,4'-DDS, 3.5 mol, 0.8692 kg), 9,9-bis(3,4-dicarboxyphenyl)fluorenyl dianhydride (BPAF, 4 mol, 1.834 kg), 4-aminobenzoic acid (4-aminophenyl) ester (APAB, 1.5 mol, 0.342 kg), and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (4,4'-BPDA, 1 mol, 0.294 kg). Phthalic anhydride (PA) is not added for end-capping. The other catheter structures and manufacturing processes are the same as in Example 1.

[0101] Comparative Example 4

[0102] The only difference between this comparative example and Example 1 is that the furnace temperature of each section in the seven-section high-temperature furnace in step 3 is set to 180, 200, 300, 350, 200, 150, and 100°C. The other conduits, formulas, structures, and manufacturing processes are the same as in Example 1.

[0103] Comparative Example 5

[0104] This comparative example provides a polyimide conduit. The specific steps include: in a Class 1000 cleanroom with a constant temperature of 25°C and a constant humidity of 50%RH, DMAc (11.7 kg) and 4,4'-diaminodiphenyl ether (4,4'-ODA, 5 mol, 1.001 kg) are added to a 50 L reactor equipped with a mechanical stirrer, a hot and cold medium jacket, a condenser reflux device, and a water separator. The reaction temperature is set to 25°C. After stirring for 2 hours, pyromellitic anhydride (PMDA, 4.95 mol, 1.079 kg) is added in batches. After uniform stirring until the resin viscosity reaches about 50,000 cP, phthalic anhydride (PA, 0.1 mol, 0.148 kg) is added for end capping. Finally, the mixture is stirred for 12 hours to obtain a polyamic acid resin solution with a solid content concentration of 16 wt%. Then, residual bubbles in the solution were removed by vacuum (<1 Pa) and standing for 24 hours, and impurities were removed by passing it through a 1 μm filter. A small amount of solution was coated into a 25 μm planar film, the solvent was dried, and it was imidized at high temperature (350 °C) before optical testing. The test results are shown in Table 1. Other resins were used for catheter preparation. The other catheter structures and fabrication processes were the same as in Example 1.

[0105] Comparative Example 6

[0106] The only difference between this comparative example and Example 1 is that a silver-plated copper wire with a diameter of 1 mm was used as the forming core, and the diameters of the first, second, and third stage dies were 1.413, 1.446, and 1.479 mm, respectively. The final prepared conduit had a diameter of 1 mm and a wall thickness of 100 mm. In addition, an optical test was conducted using a 100 μm thick planar film. All other conduits, formulations, structures, and manufacturing processes were the same as in Example 1.

[0107] Performance testing methods

[0108] (1) Tensile strength, modulus and elongation at break test

[0109] Referring to standard GB / T15812.1-2005, the Instron universal testing machine was used, with a test span of 100 mm, a test rate of 50 mm / min, and the modulus value ranged from 0.1% to 0.5% of the strain.

[0110] (2) Transmittance and haze test

[0111] According to GB / T 2410-2008 Determination of transmittance and haze of transparent plastics, a spectrophotometer / haze meter was used for measurement. Since the sample needs to be flat, the soluble resin was first coated into a 25μm flat film, and the solvent was dried at 240℃ before testing.

[0112] (3) Yellowness index test

[0113] According to GB / T 39822-2021 Test Method for Yellow Index of Plastics, a colorimeter was used for measurement. The soluble resin was first coated into a 25μm flat film, and the solvent was dried at 240℃ before testing.

[0114] (4) Biocompatibility test

[0115] In accordance with the ISO 10993 series of standards, the samples were tested for three key biocompatibility parameters: cytotoxicity, skin sensitization, and skin irritation, to ensure that they would not cause unacceptable biological reactions in their intended use.

[0116] The test results are shown in Table 1.

[0117] Table 1. Performance results of polyimide catheters prepared in each example and comparative example. ; As shown in Table 1, the performance results of Examples 1-3, which use block molecular structures with high transparency and high mechanical strength segments, can achieve relatively balanced optical and mechanical properties and can achieve high transparency in a fluorine-free structure. Comparative Example 1, which uses only high transparency segments, can achieve optimal optical performance, but its mechanical properties are insufficient. Comparative Example 2, which uses only high mechanical strength segments, can achieve extremely high strength and modulus to support the push and torsional forces of the conduit, but its transparency is relatively low. Further analysis of Comparative Example 3 shows that it lacks the end-capping agent phthalic anhydride (PA), which undergoes high-temperature oxidation during the drying process of the exposed terminal amino groups, resulting in yellowing and a decrease in optical performance. Compared with Comparative Example 4, the higher the temperature of the high-temperature curing oven, the more obvious the yellowing and the greater the decrease in light transmittance. Analysis of Comparative Example 5 shows that the commonly used PMDA-ODA type structure cannot meet the requirements for high transparency. Analysis of Examples 4 and 5 shows that soluble transparent polyimide resin can be used to prepare transparent conduits with different diameters and thicknesses according to the core and die. However, the thickness is inversely proportional to the optical performance; the thinner the conduit, the higher the light transmittance.

[0118] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this document is not intended to limit the invention to the specific embodiments disclosed for carrying out the invention, but rather to include all embodiments falling within the scope of the appended claims.

Claims

1. A method for preparing a fluorine-free transparent polyimide conduit, characterized in that, Block polyimide polymers are used as molding solutions. These block polyimide polymers have a soluble polyimide structure and are composed of block molecular segments. The block molecular segments are composed of highly transparent segments.

2. The preparation method according to claim 1, characterized in that, The specific steps include: S1. Provide a polyamic acid precursor solution; Highly transparent dianhydride monomers and highly transparent diamine monomers are added to a first polar aprotic solvent, dissolved, and subjected to a first-stage reaction to obtain polyamic acid oligomers; then, highly mechanical diamine monomers are added for a second-stage reaction, followed by the addition of highly mechanical dianhydride monomers for a third-stage reaction, and finally, an end-capping agent is added until the reaction is complete, thus obtaining the polyamic acid precursor solution. S2. Block polyimide polymer; The polyamic acid precursor solution prepared in S1 is heated once to react and obtain a polyimide resin solution. After precipitation in a poor solvent, post-treatment is performed, followed by imidization treatment by heating a second time to obtain the block polyimide polymer. S3. Dip coating and setting: The block polyimide polymer prepared in S2 is dissolved in a second polar aprotic solvent. A multi-stage dip coating and pre-drying coating process is used to dip the block polyimide polymer solution onto the outer wall of the core. After pre-drying and setting treatment, a uniform adhesive film is formed on the surface of the core. Then, a polyimide conduit is obtained on the surface of the core through a multi-stage gradient high-temperature curing process; S4. The polyimide conduit is removed from the surface of the core to obtain the final product.

3. The preparation method according to claim 1, characterized in that, In S1, the viscosity of the polyamic acid precursor solution is 100-100000 cP, preferably 1000-10000 cP, and more preferably 3000-8000 cP; And / or, the first polar aprotic solvent is any one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, tetrahydrofuran, dioxane, dichloromethane, chloroform, hexamethylphosphoric triamide, γ-butyrolactone, cyclopentanone, m-cresol, diethyl ether, and p-cresol methyl ether; And / or, the end-capping agent is any one or a combination of several of phthalic anhydride, 4-phenylethynyl phthalic anhydride maleate, and 5-norbornene-dicarboxylic anhydride; The solid content of the block polyimide polymer solution in S3 is 5-50 wt%, preferably 10-40 wt%, and more preferably 12-30 wt%. And / or, the first polar aprotic solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, diphenyl sulfone, tetramethyl sulfone, tetrahydrofuran, dioxane, dichloromethane, chloroform, hexamethylphosphoric triamide, γ-butyrolactone, cyclopentanone, m-cresol, diethyl ether, and p-cresol methyl ether; And / or, the first polar aprotic solvent used in S1 and the second polar aprotic solvent used in S3 may be the same or different.

4. The preparation method according to claim 1, characterized in that, The multi-stage dip coating and characterization includes at least three dip coating-pre-drying-drying cycles; The dip coating-pre-baking process involves injecting the block polyimide polymer into a glue tank, passing the core through the bottom of the glue tank at a speed of 0.1 to 50 m / min for dip coating, and then setting it at 60 to 150°C. After multiple dip coating and pre-baking processes, the polyimide conduit is dried using a multi-stage gradient high-temperature curing process. First, high-temperature drying removes the solvent, and then low-temperature annealing reduces the interlayer stress between the core and the adhesive layer, thus obtaining the polyimide conduit.

5. The preparation method according to any one of claims 1-4, characterized in that, The multi-stage gradient high-temperature curing process includes gradually increasing the temperature and then gradually annealing by setting multiple temperature gradients. The temperature gradients are 180℃, 200℃, 220℃, 240℃, 200℃, 150℃, and 100℃, respectively.

6. A fluorine-free transparent polyimide conduit, prepared by the preparation method according to any one of claims 1-5, wherein the material of the polyimide conduit is a block polyimide polymer composed of highly transparent segments and highly mechanical segments on the same molecular backbone; The block polyimide polymer has the structural formula shown in formula (1): （1）； in, X1 and Y1 are highly transparent segments, while X2 and Y2 are highly mechanical segments; X1 and X2 are tetracarboxylic acid dianhydride residues in tetravalent organic groups. X1 is a highly transparent segment dianhydride, and X2 is a highly mechanical segment dianhydride. Y1 and Y2 are diamine residues in divalent organic groups. Y1 is a highly transparent segmental diamine, and Y2 is a highly mechanical segmental diamine. m represents the molar percentage of the high-transparency segment in the total of the high-transparency and high-mechanical segments being 65-75 mol%, and n represents the molar percentage of the high-mechanical segment in the total of the high-transparency and high-mechanical segments being 25-35 mol%.

7. The fluorine-free transparent polyimide conduit according to claim 1, characterized in that, X1 is a residue of at least one of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,3-dimethyl-cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 3-carboxymethyl-1,2,4-cyclopentanetricarboxylic dianhydride, 1,4:2,3-dianhydride; preferably, a residue of at least one of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride and cyclobutanetetracarboxylic dianhydride. Y1 is a residue of at least one of 9,9-bis(4-aminophenyl)fluorene, 9,9-dimethylfluorene-2,7-diamine, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 2,2-bis[4-(4-aminophenoxyphenyl]propane, 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindene, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-diaminophenyl sulfone, and bis(3-amino-4-hydroxyphenyl) sulfone; preferably, a residue of at least one of 9,9-bis(4-aminophenyl)fluorene and 4,4'-diaminophenyl sulfone. X2 is a residue of at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, p-phenylene-bisphenyltrilate dianhydride, (4-phthalic anhydride)formyloxy-4-phthalate, 2,6-naphthobis(trilate monoester anhydride), and bis[(3,4-dianhydride)phenyl]terephthalate; preferably, a residue of at least one of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and p-phenylene-bisphenyltrilate dianhydride. Y2 is a residue of at least one of the following: 4-aminobenzoic acid (4-aminophenyl) ester, 4,4'-diaminobenzoyl aniline, bis(4-aminophenyl) terephthalate, [4-(4-aminobenzoyl)oxyphenyl]4-aminobenzoate, 4-aminobenzoic acid 4-aminophenyl ester, N,N'-bis(4-aminophenyl) terephthalamide, bisphenol A diester diamine, 2,4,6-trimethyl-1,3-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, etc.; preferably, a residue of at least one of 4-aminobenzoic acid (4-aminophenyl) ester and 4,4'-diaminobenzoyl aniline.

8. The fluorine-free transparent polyimide conduit according to claim 1, characterized in that, The polyimide conduit has a light transmittance of ≥89%, a yellowness index of ≤2.3, a haze of 0.3~0.6, a tensile strength of 200~220MPa, a Young's modulus of 3~4GPa, and an elongation at break of 79~90%.

9. The fluorine-free transparent polyimide conduit according to claim 1, characterized in that, The wall thickness of the polyimide conduit is 10~80μm; preferably, the wall thickness is 12~25μm.

10. The application of a fluorine-free transparent polyimide catheter as described in any one of claims 6-9 as a medical device, particularly in cardiovascular interventional therapy devices.

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