Preparation method and application of high-flexibility high-temperature-resistant photosensitive resin

Abstract

This invention discloses a method for preparing and applying a highly flexible, high-temperature resistant photosensitive resin. The preparation method includes synthesizing an epoxy-containing acrylate resin and a photosensitive resin containing oxazolidinone bonds. A two-step reaction is used to synergistically improve the flexibility and heat resistance of the photosensitive resin: The first step employs RAFT living radical polymerization to precisely control the molecular weight of the acrylate copolymer segments, introducing glycidyl methacrylate to provide side-chain epoxy groups, and adjusting the balance between chain flexibility and rigidity using butyl acrylate and isobornyl ester to obtain a narrowly distributed epoxy-containing acrylate intermediate. The second step utilizes the epoxy group and diphenylmethane diisocyanate to undergo a cyclization addition reaction under a catalyst, generating a highly thermally stable oxazolidinone five-membered heterocyclic structure to impart excellent high-temperature resistance to the resin. The residual isocyanate groups are capped with hydroxy acrylate to introduce photosensitive double bonds, achieving a photosensitive resin with both good adhesion and temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a method for preparing and applying a highly flexible, high-temperature resistant photosensitive resin. Background Technology

[0002] UV adhesives are polymeric materials that achieve rapid curing under ultraviolet or visible light irradiation through free radical or cationic polymerization initiated by photoinitiators. As the core component of UV adhesives, the molecular structure, functionality, crosslinking density, and curing behavior of photosensitive resins directly determine the adhesive's mechanical properties, heat resistance, adhesion, and process adaptability.

[0003] Currently, high-end photosensitive resins are mainly divided into epoxy-modified photosensitive resins and polyurethane-modified photosensitive resins. Epoxy-modified photosensitive resins use epoxy resin as a backbone, introducing acrylate or epoxy groups to impart photocurability. After curing, these resins exhibit advantages such as high rigidity, strong structural stability, and high temperature resistance, making them particularly suitable for applications requiring high thermal stability. However, due to the high crosslinking density and rigid molecular chains of the epoxy backbone, the cured products are often brittle and lack flexibility, making them prone to cracking under impact or thermal cycling, thus limiting their application in conditions requiring stress buffering or dynamic loading.

[0004] Polyurethane-modified photosensitive resins use polyurethane as the main chain and achieve photocuring through acrylate end-capping. These resins possess advantages such as high flexibility, good adhesion, and a wide range of tunable mechanical properties. Their performance can be customized from high elasticity to high hardness by adjusting the ratio of soft to hard segments, making them widely used in fields requiring high flexibility and adhesive strength. However, the urethane bonds in the polyurethane structure are prone to thermal degradation at high temperatures, resulting in insufficient high-temperature resistance and making it difficult to meet the long-term use requirements of high-temperature environments such as automotive electronics, high-power device packaging, and aerospace. Summary of the Invention

[0005] This invention provides a method for preparing and applying a highly flexible, high-temperature resistant photosensitive resin, in order to solve the technical problem that current photosensitive resins are difficult to balance high-temperature resistance and flexibility.

[0006] In a first aspect, the present invention provides a method for preparing a highly flexible, high-temperature resistant photosensitive resin, comprising the following steps: (1) Synthesis of epoxy-containing acrylate resin: All acrylic monomers are mixed, and dithioester-based RAFT reagent and azobisisobutyronitrile initiator are added. The mixture is reacted at 80℃~90℃ for 3h~4h under inert gas protection. When the number average molecular weight of the reaction system reaches 3000, the reaction is terminated and a polymerization inhibitor is added. The residual monomers are removed to obtain epoxy-containing acrylate resin. The acrylic monomers include ethyl acrylate, butyl acrylate, isobornyl acrylate and glycidyl methacrylate. Ethyl acrylate, butyl acrylate and isobornyl acrylate are structural monomers, and glycidyl methacrylate is a functional monomer. (2) Synthesis of photosensitive resin with oxazolidinone bond: Under inert gas protection, diphenylmethane diisocyanate is heated to 80℃~90℃ to melt; the epoxy acrylate resin and catalyst are added, and the temperature is raised to 100℃~120℃ for reaction; then hydroxy acrylate is added for end-capping reaction, and after the reaction is completed, it is cooled to obtain a high-flexibility, high-temperature resistant photosensitive resin.

[0007] In some of these embodiments, in step (1), the mass ratio of ethyl acrylate, butyl acrylate, isobornyl acrylate and glycidyl methacrylate is 4:(2~2.5):(0.5~1):0.5.

[0008] In some of these embodiments, in step (1), the amount of the dithioester RAFT reagent added is 5% of the total molar amount of acrylic acid monomer; and the amount of the azobisisobutyronitrile initiator added is 10% of the molar amount of the dithioester RAFT reagent.

[0009] In some of these embodiments, the dithioester-type RAFT reagent includes at least one of tert-butylbenzocarbodisulfate, 1-cyano-1-methyl-4-oxo-4-(2-thiothiazolidin-3-yl)butyl dithiobenzoate, 4-cyano-4-(thiobenzoyl)valerate, 2-cyano-2-propylbenzodisulfide, 2-(thiobenzoylthio)propionic acid, 2-cyano-2-butylbenzene dithioester, 2-cyano-2-hexylbenzodithiol ester, 2-cyano-2-pentylbenzodithiol ester, 2-cyano-3-methyl-2-butylbenzodisulfide, 2-phenyl-2-propylbenzodisulfide, 2-phenylethylbenzene dithiol ester, and S-(thiobenzoyl)thioacetic acid.

[0010] In some of these embodiments, in step (1), the polymerization inhibitor is p-hydroxyanisole, and the amount added is 0.1% of the total mass of the reaction system of the epoxy acrylate resin.

[0011] In some of these embodiments, in step (2), the molar ratio of the diphenylmethane diisocyanate to the glycidyl methacrylate is (0.55~0.6):1.

[0012] In some of these embodiments, the catalyst is DMP-30.

[0013] In some of these embodiments, the hydroxyacrylate includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate. The molar ratio of the hydroxyacrylate to the glycidyl methacrylate is (0.1~0.2):1.

[0014] In some of these embodiments, in step (1), the removal of residual monomers is carried out by rotary evaporation at 100°C and a vacuum of <10 mbar; In step (2), the end-capping reaction is carried out at a temperature of 100°C for 1 hour.

[0015] Secondly, the present invention also provides the application of the high-flexibility, high-temperature resistant photosensitive resin prepared by the above preparation method in the preparation of UV adhesives.

[0016] Compared with the prior art, the present invention has the following beneficial effects: A specific molecular structure is constructed through a two-step reaction to synergistically enhance the flexibility and heat resistance of photosensitive resins: The first step employs RAFT living radical polymerization, precisely controlling the molecular weight of the acrylate copolymer segments with dithioester reagents. Glycidyl methacrylate is introduced to provide side-chain epoxy groups, and butyl acrylate and isobornyl ester are used to adjust the balance between chain flexibility and rigidity, obtaining narrowly distributed epoxy-bearing acrylate intermediates. The second step utilizes the cyclization addition reaction between epoxy groups and diphenylmethane diisocyanate under a catalyst to generate a highly thermally stable oxazolidinone five-membered heterocyclic structure, endowing the resin with excellent high-temperature resistance. Simultaneously, the residual isocyanate groups are capped with hydroxyacrylate, introducing photosensitive double bonds. This results in the resin molecule's main chain possessing both the flexibility of the acrylate segments and the rigid, heat-resistant framework of the oxazolidinone ring, achieving a photosensitive resin with both good adhesion and temperature resistance.

[0017] Furthermore, the production process of this invention is simple and meets the needs of industrial production. By preparing a highly flexible, high-temperature resistant photosensitive resin, UV adhesives can be used in high-temperature flexible bonding applications, such as high-temperature cable reinforcement and high-temperature sealing gaskets. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0019] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0020] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, it should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Unless otherwise specified, the raw materials used in the following examples and comparative examples are commercially available industrial products, and all conditions not otherwise specified are conventional. Example 1

[0022] (1) Synthesis of epoxy-containing acrylate resin: Ethyl acrylate, butyl acrylate, isobornyl acrylate and glycidyl methacrylate were mixed, and 5% of the total molar amount of dithioester RAFT reagent and 10% of the total molar amount of RAFT reagent azobisisobutyronitrile initiator were added. The mixture was stirred evenly. Nitrogen gas was introduced and maintained for 30 min. The reactor was heated to 80°C and kept at this temperature while maintaining nitrogen gas for 4 h. The molecular weight growth was monitored by gel permeation chromatography (GPC). When the number average molecular weight of the reaction system reached 3000, the reaction was terminated by cooling and 0.1% of the total mass of p-hydroxyanisole was added. The residual monomers were removed by rotary evaporation at 100°C and a vacuum degree of <10 mbar to obtain a solvent-free epoxy-containing acrylate resin with 100% solid content. (2) Synthesis of photosensitive resin with oxazolidinone bond: Under nitrogen protection, diphenylmethane diisocyanate was heated to 80°C to melt; the epoxy acrylate resin and DMP-30 catalyst were added, and the temperature was raised to 100°C for 2 hours; then hydroxy acrylate was added for end-capping reaction for 1 hour, and the reaction was cooled after completion to obtain a high-flexibility, high-temperature resistant photosensitive resin. The mass ratio of ethyl acrylate, butyl acrylate, isobornyl acrylate, glycidyl methacrylate, MDI, and hydroxyethyl acrylate is 40:20:5:5:5.28:0.816. Example 2

[0023] The difference from Example 1 is that the mass ratio of ethyl acrylate: butyl acrylate: isobornyl acrylate: glycidyl methacrylate: MDI: hydroxyethyl acrylate in Example 2 is 40:25:5:5:4.84:0.408. Example 3

[0024] The difference from Example 1 is that the mass ratio of ethyl acrylate: butyl acrylate: isobornyl acrylate: glycidyl methacrylate: MDI: hydroxyethyl acrylate in Example 3 is 40:20:10:5:5.28:0.816. Example 4

[0025] The difference from Example 1 is that the mass ratio of ethyl acrylate: butyl acrylate: isobornyl acrylate: glycidyl methacrylate: MDI: hydroxyethyl acrylate in Example 4 is 40:25:10:5:4.84:0.408. Example 5

[0026] The difference from Example 1 is that the reaction temperature in step (1) of Example 5 is 90°C and the reaction time is 3h. Example 6

[0027] The difference from Example 1 is that the reaction temperature of step (1) in Example 6 is 90°C and the reaction time is 3h, while the reaction temperature of step (2) is 120°C. Example 7

[0028] The difference from Example 1 is that the reaction temperature of step (2) in Example 7 is 120°C.

[0029] Comparative Example 1 Comparative Example 1 is a commercially available epoxy-modified photosensitive resin (DR-915 from Changxing Materials).

[0030] Comparative Example 2 Comparative Example 2 is a commercially available polyurethane modified photosensitive resin (Changxing Materials' DR-U299).

[0031] Comparative Example 3 The difference from Example 1 is that the amount of dithioester RAFT reagent used in Comparative Example 3 is 1% of the total moles of monomers.

[0032] Comparative Example 4 The difference from Example 1 is that the amount of dithioester RAFT reagent used in Comparative Example 4 is 10% of the total moles of monomers.

[0033] Comparative Example 5 The difference from Example 1 is that the monomers in Comparative Example 5 are ethyl acrylate: glycidyl methacrylate: MDI: hydroxyethyl acrylate in a mass ratio of 65:5:5.28:0.816.

[0034] Performance testing: A UV adhesive was prepared by mixing photosensitive resin, IBOA, TMPTA, and TPO in a mass ratio of 80:15:3:2. The tensile strength and elongation at break of the UV adhesive before and after baking at 260℃ for 1 hour were tested according to GB / T1040.1-2018. The Shore hardness was tested according to GB / T39693.4. The test results are shown in Table 1.

[0035] Table 1 Performance test results of the examples and comparative examples

[0036] As shown in Table 1, the photosensitive resins synthesized in Examples 1 to 7 of the present invention have low hardness, high tensile strength, and high elongation at break. After high temperature resistance testing, they still maintain about 80% of tensile strength and elongation at break, indicating that the photosensitive resins prepared by the present invention have good flexibility and high temperature resistance.

[0037] Although the commercially available epoxy-modified photosensitive resin of Comparative Example 1 exhibits good temperature resistance, it has high hardness and low elongation at break. While the commercially available polyurethane-modified photosensitive resin of Comparative Example 2 possesses good tensile strength and elongation at break, its high-temperature resistance is poor. The performance of Comparative Example 3 (too little RAFT reagent) and Comparative Example 4 (too much RAFT reagent) is significantly worse than that of Example 1, indicating that the specific amount of RAFT reagent is crucial for achieving high flexibility and high-temperature resistance in photosensitive resins. Comparative Example 5, using only one structural monomer combined with a functional monomer, yielded a product with low hardness and tensile strength, exhibiting poor mechanical properties, far inferior to Example 1. This demonstrates that the preferred monomer combination of the present invention can give the photosensitive resin moderate hardness, good tensile strength, and elongation at break.

[0038] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A method for preparing a highly flexible, high-temperature resistant photosensitive resin, characterized in that, Includes the following steps: (1) Synthesis of epoxy-containing acrylate resin: Mix all acrylic monomers, add dithioester-based RAFT reagent and azobisisobutyronitrile initiator, and react at 80℃~90℃ for 3h~4h under inert gas protection; when the number average molecular weight of the reaction system reaches 3000, terminate the reaction and add polymerization inhibitor; remove residual monomers to obtain epoxy-containing acrylate resin; the acrylic monomers include ethyl acrylate, butyl acrylate, isobornyl acrylate and glycidyl methacrylate; (2) Synthesis of photosensitive resin with oxazolidinone bond: Under inert gas protection, diphenylmethane diisocyanate is heated to 80℃~90℃ to melt; the epoxy acrylate resin and catalyst are added, and the temperature is raised to 100℃~120℃ for reaction; then hydroxy acrylate is added for end-capping reaction, and after the reaction is completed, it is cooled to obtain a high-flexibility, high-temperature resistant photosensitive resin.

2. The preparation method of the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, In step (1), the mass ratio of ethyl acrylate, butyl acrylate, isobornyl acrylate and glycidyl methacrylate is 4:(2~2.5):(0.5~1):0.

5.

3. The preparation method of the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, In step (1), the amount of the dithioester RAFT reagent added is 5% of the total molar amount of acrylic acid monomer; the amount of the azobisisobutyronitrile initiator added is 10% of the molar amount of the dithioester RAFT reagent.

4. The preparation method of the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, The dithioester-type RAFT reagents include at least one of tert-butylbenzocarbodisulfate, 1-cyano-1-methyl-4-oxo-4-(2-thiothiazolidin-3-yl)butyl dithiobenzoic acid, 4-cyano-4-(thiobenzoyl)valerate, 2-cyano-2-propylbenzodisulfide, 2-(thiobenzoylthio)propionic acid, 2-cyano-2-butylbenzene dithioester, 2-cyano-2-hexylbenzodithiolate, 2-cyano-2-pentylbenzodithiolate, 2-cyano-3-methyl-2-butylbenzodithiolate, 2-phenyl-2-propylbenzodisulfide, 2-phenylethylbenzene dithiolate, and S-(thiobenzoyl)thioacetic acid.

5. The method for preparing the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, In step (1), the polymerization inhibitor is p-hydroxyanisole, and the amount added is 0.1% of the total mass of the reaction system of the epoxy acrylate resin.

6. The method for preparing the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, In step (2), the molar ratio of the diphenylmethane diisocyanate to the glycidyl methacrylate is (0.55~0.6):

1.

7. The method for preparing the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, The catalyst is DMP-30.

8. The method for preparing the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, The hydroxyacrylate includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate. The molar ratio of the hydroxyacrylate to the glycidyl methacrylate is (0.1~0.2):

1.

9. The method for preparing the high-flexibility, high-temperature resistant photosensitive resin as described in claim 1, characterized in that, In step (1), the method for removing residual monomers is rotary evaporation at 100°C and a vacuum of <10 mbar; In step (2), the end-capping reaction is carried out at a temperature of 100°C for 1 hour.

10. The application of a highly flexible, high-temperature resistant photosensitive resin prepared by any one of claims 1 to 9 in the preparation of UV adhesives.

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