A process for the preparation of a styrene-isoprene block copolymer for medical hot-melt pressure sensitive adhesives

Abstract

This invention relates to the field of polymer material synthesis technology, and discloses a method for preparing a styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive, comprising the following steps: under anhydrous and oxygen-free conditions and under high-purity nitrogen protection, a refined mixed solvent is added to a polymerization reactor, and after impurity removal titration with alkyl lithium, an alkyl lithium initiator is added; refined styrene is added to carry out a polymerization reaction to obtain active polystyrene segments; a composite polarity modifier is added, and then refined isoprene is added to carry out a polymerization reaction to obtain an active styrene-isoprene diblock copolymer; medical-grade epoxidized soybean oil is added to the system as a halogen-free coupling agent to carry out a coupling reaction to obtain a star-shaped styrene-isoprene block copolymer; an antioxidant terminator is added to terminate the reaction, and after coagulation, dehydration, and hot air drying, a medical-grade finished product is obtained. Using the method of this invention, a medical-grade copolymer with regular structure, excellent performance, and safety and non-toxicity can be obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, specifically to a method for preparing a styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesives. Background Technology

[0002] Styrene-isoprene block copolymers combine the toughness of rubber with the strength of plastics, exhibiting excellent adhesion, flexibility, and biocompatibility. They are the core matrix material for medical hot-melt pressure-sensitive adhesives and are widely used in medical tapes, wound dressings, and other products. Currently, these polymers are mostly prepared using anionic polymerization. However, in traditional industrial production, to improve the cohesiveness and creep resistance of styrene-isoprene block copolymers, multifunctional coupling agents are typically used for star-shaped chain extension. Although these coupling agents have high reactivity, their reaction byproducts or residual inorganic salts are difficult to completely remove. In clinical applications, human sweat can cause ion migration with residual halide ions, inducing contact dermatitis, redness, swelling, and even allergic reactions, posing a potential biosafety risk in medical applications. Furthermore, in conventional styrene-isoprene block copolymers, the microstructure of isoprene segments is mainly 1,4-structure, and the glass transition temperature of its rubber phase is extremely low. This leads to insufficient cohesion or abnormal viscosity of the colloid at room temperature, resulting in poor clinical performance. When patients remove medical tape, the high peeling force forcibly detaches the stratum corneum, causing severe pain and even epidermal tearing and secondary infection. Therefore, developing a halogen-free, safe, moderately performing, and biocompatible method for preparing medical-grade styrene-isoprene block copolymers has significant practical importance and application value. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing a styrene-isoprene block copolymer for medical hot melt pressure-sensitive adhesive. Using the method of the present invention, a medical-grade copolymer with regular structure, excellent performance and safety and non-toxicity can be obtained.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive, comprising the following steps:

[0005] S1: Under anhydrous and oxygen-free conditions and with high-purity nitrogen protection, a refined mixed solvent is added to the polymerization reactor, the temperature is raised to 25-40℃, and after titration with alkyl lithium to remove impurities, an alkyl lithium initiator is added; the refined mixed solvent is a compound of cyclohexane and dearomaticated raffinate from a fraction distilled at 65-90℃, with a mass ratio of cyclohexane to raffinate of 75-98:2-25;

[0006] S2: Add 12%-28% of refined styrene by mass of total monomers, and carry out polymerization reaction at 40-65℃ to obtain active polystyrene segments;

[0007] S3: Add a composite polarity modifier composed of N,N,N',N'-tetramethylethylenediamine and 2,2-bis(2-tetrahydrofuranyl)propane, and then add 72%-88% of refined isoprene by mass of the total monomers. The polymerization reaction is carried out at 55-85℃ to obtain an active styrene-isoprene diblock copolymer.

[0008] S4: Medical-grade epoxidized soybean oil was added to the system as a halogen-free coupling agent, and a coupling reaction was carried out at 65-90℃ to obtain a star-shaped styrene-isoprene block copolymer.

[0009] S5: Add a terminator with antioxidant function to terminate the reaction, and after coagulation, dehydration and hot air drying, obtain medical-grade finished product.

[0010] Furthermore, in S1, the initiation temperature is 30-35°C.

[0011] Furthermore, the polymerization reaction time in S2 is 15-35 min.

[0012] Furthermore, the total molar amount of the composite polarity regulator in S3 is 0.5-1.5 times the molar amount of active lithium ions in the system, the mass ratio of N,N,N',N'-tetramethylethylenediamine to 2,2-bis(2-tetrahydrofuranyl)propane is 1:1.5-3, and the polymerization reaction time is 25-50 min.

[0013] Furthermore, the coupling reaction time in S4 is 25-55 min; the molar ratio of the epoxy groups of epoxidized soybean oil to the active lithium ions in the system is 1.0:1-1.1:1.

[0014] Furthermore, the terminator in S5 is di-tert-butylhydroxytoluene or medical-grade vitamin E, and the hot air drying temperature is 60-85℃.

[0015] Furthermore, the refined mixed solvent, refined styrene, and refined isoprene are all purified by distillation and dehydration by adsorption using 3Å / 4Å molecular sieves, with the moisture content controlled to ≤10ppm.

[0016] Furthermore, the total monomer concentration in the mixed solvent is 15%-20% by mass.

[0017] Furthermore, the copolymer has a molecular weight distribution index (PDI) ≤ 1.05, a residual halogen content ≤ 5 ppm, a 3,4-structure mass content of 25%-35% in the polyisoprene segments, a glass transition temperature of -45℃ to -35℃ in the rubber phase, and a total proportion of three-armed and four-armed star structures in the main body of the product ≥ 85%, meeting the ISO 10993 medical biocompatibility non-irritating grade.

[0018] Furthermore, the styrene-isoprene block copolymer is used in the preparation of medical hot melt pressure-sensitive adhesives, medical wound dressings, or medical tapes.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] This invention utilizes a mixture of cyclohexane and 65-90℃ dearomaticated raffinate as a solvent, resulting in improved solubility and heat transfer uniformity, effectively enhancing the stability of the polymerization reaction. The resulting copolymer exhibits a narrow molecular weight distribution and a regular structure. The use of N,N,N',N'-tetramethylethylenediamine and 2,2-bis(2-tetrahydrofuranyl)propane as a composite polar modifier allows for control of the 3,4-structure content of the polyisoprene segments, ensuring the glass transition temperature of the rubber phase falls within the suitable range for medical hot-melt pressure-sensitive adhesives, balancing adhesion and flexibility. The use of medical-grade epoxidized soybean oil as a halogen-free coupling agent avoids the halogen residue problem associated with traditional halogen-containing coupling agents, with residual halogen content ≤5ppm, significantly improving medical safety and meeting ISO 10993 biocompatibility requirements. Strict 3Å / 4Å molecular sieve adsorption and dehydration of the solvent and monomers, controlling moisture content below 10ppm, ensures the activity and coupling efficiency of anionic polymerization. The method of this invention is mild and highly controllable, and the resulting copolymer has a narrow molecular weight distribution (PDI≤1.05), moderate bonding strength, no cytotoxicity, and no skin irritation or sensitization. It can reduce the risk of medical adhesive-associated skin injury (MARSI) and is applicable to the field of medical hot melt pressure-sensitive adhesives. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The reagents used in the following specific embodiments are of analytical grade. Additionally:

[0023] Medical-grade epoxidized soybean oil: epoxidation value is 6.23%.

[0024] Example 1

[0025] A method for preparing a styrene-isoprene block copolymer for use in medical hot-melt pressure-sensitive adhesives includes the following steps:

[0026] S1: Under anhydrous and oxygen-free conditions and with high-purity nitrogen protection, 42.5 kg of refined mixed solvent was added to the polymerization reactor, the temperature was raised to 25°C, and after titration with alkyl lithium to remove impurities, 9.6 g of n-butyllithium initiator was added; the refined mixed solvent was prepared by compounding cyclohexane with dearomaticated raffinate from the 65-90°C fraction, with a cyclohexane to raffinate mass ratio of 75:25;

[0027] S2: Add 0.90 kg of refined styrene (accounting for 12% of the total monomer mass), and polymerize at 40°C for 15 min to obtain active polystyrene segments;

[0028] S3: Add 0.45g of N,N,N',N'-tetramethylethylenediamine and 1.35g of 2,2-bis(2-tetrahydrofuranyl)propane to form a composite polarity modifier with a mass ratio of 1:3, then add 6.60kg of refined isoprene (accounting for 88% of the total monomer mass), and polymerize at 55℃ for 25min to obtain an active styrene-isoprene diblock copolymer;

[0029] S4: Add 38.6g of medical-grade epoxidized soybean oil to the system and couple it at 65℃ for 25min. The molar ratio of the epoxy groups of the epoxidized soybean oil to the active lithium ions in the system is 1:1, thus obtaining a star-shaped styrene-isoprene block copolymer.

[0030] S5: Add 4.5g of di-tert-butylhydroxytoluene to terminate the reaction, followed by coagulation, dehydration, and hot air drying at 60℃ to obtain the medical-grade finished product.

[0031] The refined mixed solvent, refined styrene, and refined isoprene are all purified by distillation and dehydration by adsorption with 3Å / 4Å molecular sieves, with the moisture content controlled to be ≤10ppm; the total monomer concentration in the mixed solvent is 15%.

[0032] Example 2

[0033] A method for preparing a styrene-isoprene block copolymer for use in medical hot-melt pressure-sensitive adhesives includes the following steps:

[0034] S1: Under anhydrous and oxygen-free conditions and with high-purity nitrogen protection, 30.0 kg of refined mixed solvent is added to the polymerization reactor, the temperature is raised to 40°C, and after titration with alkyl lithium to remove impurities, 14.4 g of n-butyllithium initiator is added; the refined mixed solvent is prepared by compounding cyclohexane with dearomaticated raffinate from the 65-90°C fraction, with a cyclohexane to raffinate mass ratio of 98:2;

[0035] S2: Add 2.10 kg of refined styrene (accounting for 28% of the total monomer mass), and polymerize at 65°C for 35 min to obtain active polystyrene segments;

[0036] S3: Add 0.90g of N,N,N',N'-tetramethylethylenediamine and 1.35g of 2,2-bis(2-tetrahydrofuranyl)propane to form a composite polarity modifier with a mass ratio of 1:1.5, then add 5.40kg of refined isoprene (accounting for 72% of the total monomer mass), and polymerize at 85℃ for 50min to obtain an active styrene-isoprene diblock copolymer;

[0037] S4: Add 63.6g of medical-grade epoxidized soybean oil to the system and couple it at 90℃ for 55min. The molar ratio of the epoxy groups of the epoxidized soybean oil to the active lithium ions in the system is 1.1:1, thus obtaining a star-shaped styrene-isoprene block copolymer.

[0038] S5: Add 4.5g of medical-grade vitamin E to terminate the reaction, and then proceed with coagulation, dehydration, and hot air drying at 85℃ to obtain the medical-grade finished product.

[0039] The refined mixed solvent, refined styrene, and refined isoprene are all purified by distillation and dehydration by adsorption with 3Å / 4Å molecular sieves, with the moisture content controlled to be ≤10ppm; the total monomer concentration in the mixed solvent is 20%.

[0040] Example 3

[0041] A method for preparing a styrene-isoprene block copolymer for use in medical hot-melt pressure-sensitive adhesives includes the following steps:

[0042] S1: Under anhydrous and oxygen-free conditions and with high-purity nitrogen protection, 35.4 kg of refined mixed solvent was added to the polymerization reactor, the temperature was raised to 32.5°C, and after titration with alkyl lithium to remove impurities, 12.0 g of n-butyllithium initiator was added; the refined mixed solvent was prepared by compounding cyclohexane with dearomaticated raffinate from the 65-90°C fraction, with a cyclohexane to raffinate mass ratio of 86.5:13.5;

[0043] S2: Add 1.50 kg of refined styrene (accounting for 20% of the total monomer mass), and polymerize at 52°C for 25 min to obtain active polystyrene segments;

[0044] S3: Add 0.60g of N,N,N',N'-tetramethylethylenediamine and 1.35g of 2,2-bis(2-tetrahydrofuranyl)propane to form a composite polarity modifier with a mass ratio of 1:2.25, then add 6.00kg of refined isoprene (accounting for 80% of the total monomer mass), and polymerize at 70℃ for 38min to obtain an active styrene-isoprene diblock copolymer;

[0045] S4: Add 50.6g of medical-grade epoxidized soybean oil to the system and couple it at 78℃ for 40min. The molar ratio of the epoxy groups of the epoxidized soybean oil to the active lithium ions in the system is 1.05:1, thus obtaining a star-shaped styrene-isoprene block copolymer.

[0046] S5: Add 4.5g of di-tert-butylhydroxytoluene to terminate the reaction, and after coagulation, dehydration, and hot air drying at 72℃, obtain the medical-grade finished product.

[0047] The refined mixed solvent, refined styrene, and refined isoprene are all purified by distillation and dehydration by adsorption with 3Å / 4Å molecular sieves, with the moisture content controlled to be ≤10ppm; the total monomer concentration in the mixed solvent is 17.5%.

[0048] Comparative Example 1

[0049] The main difference between this comparative example and Example 3 is that: in S1, the mixed solvent of cyclohexane and 65-90℃ dearomatic raffinate is not used, but only an equal amount of cyclohexane is used alone. The rest of the process, parameters, and feed amount are exactly the same as in Example 3.

[0050] Comparative Example 2

[0051] The main difference between this comparative example and Example 3 is that: in S3, N,N,N',N'-tetramethylethylenediamine and 2,2-bis(2-tetrahydrofuranyl)propane composite modifier are not used, and only an equal amount of N,N,N',N'-tetramethylethylenediamine is used alone. The rest of the process, parameters, and feed amount are exactly the same as in Example 3.

[0052] Comparative Example 3

[0053] The main difference between this comparative example and Example 3 is that medical-grade epoxidized soybean oil is not used as a coupling agent in S4; instead, conventional silicon tetrachloride is used for coupling. The remaining processes, parameters, and feed amounts are exactly the same as in Example 3.

[0054] Comparative Example 4

[0055] The main difference between this comparative example and Example 3 is that the mixed solvent, styrene, and isoprene are only distilled and not dehydrated by adsorption through 3Å / 4Å molecular sieves, and the moisture content is controlled to be >10ppm. The other processes, parameters, and feed amounts are exactly the same as in Example 3.

[0056] Performance testing

[0057] The styrene-isoprene block copolymers for medical hot melt pressure-sensitive adhesives prepared according to the preparation methods of Examples 1-3 and Comparative Examples 1-4 were subjected to performance testing.

[0058] Test Example 1

[0059] (1) Determination of molecular weight and distribution

[0060] The determination was performed using a gel permeation chromatography (GPC, Waters 1515, equipped with a differential refractive index detector). Test conditions: HR 3, HR 4, and HR 5 columns in series (Waters Styragel series); column temperature 35℃; mobile phase tetrahydrofuran (THF); flow rate 1.0 mL / min; injection volume 50 μL; sample concentration 2.0 mg / mL. A standard curve was established using narrow-distribution polystyrene standards (Mp = 1,000–2,000,000 g / mol). Number-average molecular weight (Mn), weight-average molecular weight (Mw), and molecular weight distribution index (PDI = Mw / Mn) were calculated from the chromatograms.

[0061] (2) Determination of the microstructure of polyisoprene segments

[0062] Analysis was performed using ¹H NMR (Bruker Avance III 400 MHz). Sample preparation: 30 mg of polymer sample was dissolved in 0.6 mL of deuterated chloroform (CDCl3), and after complete dissolution, transferred to a 5 mm NMR sample tube. Test parameters: pulse delay time 2 s, 64 scans. The mass content of 3,4-structure in the polyisoprene segments was calculated based on the integral of the characteristic peak areas δ4.5–4.8 ppm (olefin protons of 1,2- and 3,4-structures) and δ5.0–5.2 ppm (olefin protons of 1,4-structure) in the spectrum.

[0063] (3) Determination of glass transition temperature

[0064] The measurements were performed using a differential scanning calorimeter (DSC, TA Instruments Q2000). Test conditions: Under a nitrogen atmosphere (flow rate 50 mL / min), 5-10 mg of sample was weighed and sealed in an aluminum crucible. Test procedure: The temperature was increased from -80℃ to 150℃ at a rate of 10℃ / min, held for 3 min to eliminate thermal history, then decreased to -80℃ at a rate of 10℃ / min, held for 3 min, and finally increased to 150℃ at a rate of 10℃ / min. The midpoint of the heat flux inflection point of the second heating curve was taken as the glass transition temperature (Tg).

[0065] (4) Determination of residual halogen content

[0066] The analysis was performed using an ion chromatograph (IC, Thermo Fisher Dionex ICS-5000). Pretreatment: 0.5 g of the polymer sample was accurately weighed and placed in an oxygen bomb combustion flask. Oxygen was introduced at 2.0 MPa for combustion decomposition, and the combustion products were absorbed with 20 mL of ultrapure water. The absorption solution was filtered through a 0.22 μm filter membrane before injection analysis. Chromatographic conditions: IonPac AS19 anion exchange column (4 mm × 250 mm), eluent of 20 mmol / L KOH solution, flow rate 1.0 mL / min, injection volume 25 μL. Chloride ions (Cl...) were used for analysis. - ), bromide ions (Br) - Quantification was performed using the external standard method with standard solutions. Residual halogen content was expressed as the total mass of halide ions.

[0067] (5) Analysis of the number of coupling arms and star structure

[0068] The determination was performed using gel permeation chromatography-multi-angle laser light scattering (GPC-MALS, Wyatt Dawn HELEOSII). Test conditions: two columns (HR 4E and HR 5E) in series (Agilent PLgel); mobile phase: THF; flow rate: 0.8 mL / min; sample concentration: 3.0 mg / mL; injection volume: 100 μL. The multi-angle laser light scattering instrument detected 18 angles (20°–160°), and a differential refractometer (dRI) was used as the concentration detector. The absolute molecular weight was calculated based on the light scattering signal, and the proportions of the three-armed and four-armed star-shaped structures were determined by combining the peak shape and shoulder characteristics of the GPC chromatogram.

[0069] The test results are shown in Table 1.

[0070] Table 1: Test Example 1

[0071]

[0072] As shown in Table 1, the copolymers prepared in Examples 1-3 have a narrow molecular weight distribution (PDI ≤ 1.05), a high proportion of star-shaped structures (≥ 89%), and no halogen residue. The content of 3,4-structures in the polyisoprene segments is controlled between 25% and 35%, and the glass transition temperature (Tg) of the rubber phase is -45℃ to -35℃, all within the suitable range for medical hot-melt pressure-sensitive adhesives. Comparative Example 1, due to the use of a single cyclohexane solvent, has a wider PDI to 1.19; Comparative Example 2, due to the use of a single polarity modifier, has a 3,4-structure content reduced to 16.2% and a Tg reduced to -50℃; Comparative Example 3, using silicon tetrachloride coupling, has a halogen residue as high as 68.5 ppm; Comparative Example 4, without strict dehydration, has a star-shaped structure proportion of only 45%.

[0073] Test Example 2

[0074] Tape preparation: The block copolymer obtained above is melt-blended with hydrogenated petroleum resin (tackifying resin) and naphthenic oil (softener) at a mass ratio of 100:100:20 at 160°C for 30 min to obtain medical hot melt pressure-sensitive adhesive. Then, it is uniformly coated on a 25μm thick PET substrate with a coating thickness of 30μm to make test tape.

[0075] (6) 180° peel strength test

[0076] The test was conducted using a universal testing machine (Instron 3343) in accordance with GB / T 2792 standard. Test conditions: 23℃±2℃, relative humidity 50%±5%, peel speed 300mm / min. A 25mm wide test strip was applied using the same method and conditions as the holding power test. After standing for 20 minutes, the tape was peeled off at a 180° angle, and the average force during peeling was recorded (unit: N / 25mm). Each sample was tested in parallel five times, and the average value was taken.

[0077] (7) Cytotoxicity test

[0078] Referring to ISO 10993-5 standard, mouse fibroblast L-929 cells were tested using the agar diffusion method. Sample preparation: 1 g of styrene-isoprene block copolymer was extracted at a ratio of 0.2 g / mL in serum-containing MEM medium at 37°C for 24 h. L-929 cells were then cultured at a rate of 1×10⁻⁶. 5 Cells were seeded at a density of 1 / mL into culture dishes and cultured for 24 hours to form a monolayer, then covered with an agar layer. Filter paper discs (10 mm in diameter) containing the extract were placed on the agar surface, and cultured for another 24 hours. Cell morphology and cell lysis areas were observed under a microscope and evaluated using a 0-4 grade system (Grade 0: no cytotoxicity; Grade 4: severe cytotoxicity). Passing grade: ≤2.

[0079] (8) Skin irritation and sensitization test

[0080] Referring to ISO 10993-10 standard, albino rabbits (skin irritation) and guinea pigs (skin sensitization) were used.

[0081] Intradermal reaction test: Three New Zealand white rabbits were used, with hair removed from both sides of their backs. 0.2 mL of SIS copolymer extract (0.9% sodium chloride injection and cottonseed oil solvent, extracted at 50℃ for 72 h) was injected intradermally at one point. A blank control was injected with the same volume of solvent. Erythema and edema at the injection site were observed at 24 h, 48 h, and 72 h, and the irritation index (PII) was calculated. Passing criteria: no irritation (PII < 0.5) or slight irritation (0.5 ≤ PII < 2.0).

[0082] Maximum dose sensitization test: 20 Hartley guinea pigs (10 in the experimental group and 10 in the control group). Induction phase: Intradermal injection of Freund's complete adjuvant and extract emulsion, followed by patch application for 48 hours 7 days later. Challenge phase: Patient application of patch for 24 hours 14 days after the last induction. Skin reactions were observed 24 hours and 48 hours after patch removal and graded according to sensitization rate. Passing criteria: Sensitization rate <8% was considered no sensitization; 8%-28% was considered mild sensitization (acceptable).

[0083] The test results are shown in Table 2.

[0084] Table 2: Test Example 2

[0085]

[0086] As shown in Table 2, the peel strength of Examples 1-3 was 7.5-8.2 N / 25mm, which is mild and moderate, and can effectively reduce the risk of medical adhesive-associated skin injury (MARSI) in clinical use; the cytotoxicity was grade 0, the skin irritation index was less than 0.5, and there was no sensitization, meeting the ISO 10993 requirements for medical biocompatibility. Comparative Example 1 had a slightly higher peel strength of 9.5 N / 25mm due to a wider PDI, but it was still basically usable; Comparative Example 2 had an abnormally high peel strength of 16.8 N / 25mm due to an excessively low Tg (-50℃) and excessively high viscosity of the adhesive at room temperature, which could easily cause stratum corneum tearing in clinical use; Comparative Example 3 showed cytotoxicity (grade 2), skin irritation (PII 1.9), and sensitization (18%) due to halogen residue; Comparative Example 4 had poor cohesion, with a peel strength of only 3.8 N / 25mm and residual adhesive, rendering it impractical.

[0087] The above data show that the present invention obtains a medical-grade copolymer with regular structure, excellent performance and safety and non-toxicity through the synergistic effect of mixed solvents, composite regulators, halogen-free coupling and deep dehydration.

[0088] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0090] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A method for preparing a styrene-isoprene block copolymer for use in medical hot-melt pressure-sensitive adhesives, characterized in that, Includes the following steps: S1: Under anhydrous and oxygen-free conditions and with high-purity nitrogen protection, a refined mixed solvent is added to the polymerization reactor, the temperature is raised to 25-40℃, and after titration with alkyl lithium to remove impurities, an alkyl lithium initiator is added; the refined mixed solvent is a compound of cyclohexane and dearomaticated raffinate from a fraction distilled at 65-90℃, with a mass ratio of cyclohexane to raffinate of 75-98:2-25; S2: Add 12%-28% of refined styrene by mass of total monomers, and carry out polymerization reaction at 40-65℃ to obtain active polystyrene segments; S3: Add a composite polarity modifier composed of N,N,N',N'-tetramethylethylenediamine and 2,2-bis(2-tetrahydrofuranyl)propane, and then add 72%-88% of refined isoprene by mass of the total monomers. The polymerization reaction is carried out at 55-85℃ to obtain an active styrene-isoprene diblock copolymer. S4: Medical-grade epoxidized soybean oil was added to the system as a halogen-free coupling agent, and a coupling reaction was carried out at 65-90℃ to obtain a star-shaped styrene-isoprene block copolymer. S5: Add a terminator with antioxidant function to terminate the reaction, and after coagulation, dehydration and hot air drying, obtain medical-grade finished product.

2. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, In S1, the initiation temperature is 30-35℃.

3. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The polymerization reaction time in S2 is 15-35 min.

4. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The total molar amount of the composite polarity modifier in S3 is 0.5-1.5 times the molar amount of active lithium ions in the system; the mass ratio of N,N,N',N'-tetramethylethylenediamine to 2,2-bis(2-tetrahydrofuranyl)propane is 1:1.5-3; and the polymerization reaction time is 25-50 min.

5. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The coupling reaction time in S4 is 25-55 min; the molar ratio of the epoxy groups of epoxidized soybean oil to the active lithium ions in the system is 1.0:1-1.1:

1.

6. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The terminator in S5 is di-tert-butylhydroxytoluene or medical-grade vitamin E, and the hot air drying temperature is 60-85℃.

7. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The refined mixed solvent, refined styrene, and refined isoprene are all purified by distillation and dehydration by adsorption using 3Å / 4Å molecular sieves, with the moisture content controlled to ≤10ppm.

8. The method for preparing the styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive according to claim 1, characterized in that, The total monomer concentration in the mixed solvent is 15%-20%.

9. A styrene-isoprene block copolymer for medical hot-melt pressure-sensitive adhesive prepared by the preparation method according to any one of claims 1-8, characterized in that, The copolymer has a molecular weight distribution index (PDI) ≤ 1.05, a residual halogen content ≤ 5 ppm, a 3,4-structure content of 25%-35% in the polyisoprene segments, a glass transition temperature of -45℃ to -35℃ in the rubber phase, and a total proportion of three-armed and four-armed star structures in the main body of the product ≥ 85%, meeting the ISO 10993 medical biocompatibility non-irritating grade.

10. The use of the styrene-isoprene block copolymer of claim 9 in the preparation of medical hot melt pressure-sensitive adhesives, medical wound dressings, or medical tapes.

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