A microcapsule sustained-release agent for UV-resistant pesticides and its preparation method

Abstract

This invention belongs to the field of pesticide formulation, specifically polyurethane pesticide microcapsule technology. A method for preparing a UV-resistant pesticide microcapsule sustained-release agent is disclosed. A polyurethane prepolymer grafted with a catechol structure is added to an aqueous phase containing a polymeric polyol and mixed. Then, an oil phase containing pesticide is added to form an emulsion. A curing agent is added to the emulsion to carry out a curing reaction. In preparing the polyurethane prepolymer, an acidic neutralizing agent containing a catechol structure and a hydrophilic chain extender containing a cationic group are selected. The anion of the neutralizing agent combines with the cationic group contained in the hydrophilic chain extender, introducing catechol groups into the polyurethane. Furthermore, the generated salt acts as a surfactant, so no additional surfactant is needed during the interfacial polymerization reaction. The resulting polyurethane microcapsules not only have excellent UV resistance but also high encapsulation efficiency, good hydrophilicity, and excellent suspension, dispersibility, and stability.

Description

Technical Field

[0001] This invention relates to the field of pesticide formulation technology, and in particular to the field of polyurethane pesticide microcapsule technology. Background Technology

[0002] Traditional pesticide formulations often fail to target plant leaves during spraying, and their effective duration on crop leaves is insufficient to provide adequate pest control. Problems encountered during spraying include droplet dispersion, jumping, rolling, rain washout, and decomposition, resulting in low pesticide utilization rates, typically <10%. Furthermore, ultraviolet radiation from sunlight can induce photodegradation of pesticides. Therefore, there is an urgent need to develop new methods to control pesticide loss and improve utilization efficiency.

[0003] Microencapsulation technology is a technique that uses natural or synthetic polymer film-forming materials to encapsulate dispersed solids, liquids, or gases, forming tiny particles. This technology isolates the target substance from its surrounding environment through a sealed or semi-permeable membrane. Pesticide microcapsules have become a hot topic in pesticide formulation research due to their advantages, including reducing pesticide toxicity, phytotoxicity, and environmental pollution, extending effective duration, and improving pesticide utilization.

[0004] Compared to traditional pesticides, microencapsulation formulations improve pesticide safety for users and reduce off-target effects. Polyurethane microcapsules enhance pesticide adhesion to leaves, provide sustained release, prolong pesticide exposure time, and improve pesticide utilization efficiency by enhancing pesticide deposition on crop leaves.

[0005] Waterborne polyurethanes (WPUs) exhibit good dispersibility in aqueous formulations. Based on the neutralizing charge of the emulsifier, waterborne polyurethanes can be classified into cationic, anionic, and nonionic types. Cationic and anionic waterborne polyurethanes demonstrate superior emulsifying and dispersing properties and environmental stability compared to nonionic waterborne polyurethanes. Compared to other waterborne polyurethanes, cationic waterborne polyurethanes (CWPUs) possess many unique properties, such as strong adhesion to anionic surfaces, responsiveness to bioactive stimuli, antibacterial activity, and drug loading capacity. However, compared to anionic waterborne polyurethanes, cationic waterborne polyurethanes inherently have weaker mechanical properties and water resistance, which limits their practical applications.

[0006] Furthermore, ultraviolet radiation in the environment can damage the structure of polyurethane microcapsules. Current methods typically involve adding UV-resistant substances to the microcapsule shell material during preparation. However, the compatibility of these UV-resistant substances with the polyurethane material is not always good, and they may even impair the mechanical strength or other properties of the polyurethane microcapsules.

[0007] Catechol groups have been identified as a common component of many natural adhesives used by certain marine organisms such as mussels and barnacles. A series of catechol-functionalized polymer systems based on polyamides, polyethylene glycols, polyurethanes, and polyacrylates have been reported to exhibit enhanced mechanical or adhesive properties, for example, through intermolecular crosslinking of polymer chains initiated by the coupling of two catechols.

[0008] The catechol group can not only serve as an intermolecular crosslinking unit to promote the optimization of the crosslinking structure, but the benzene conjugated system in the catechol group can also effectively absorb ultraviolet light, exhibiting excellent ultraviolet shielding effect, and can be potentially applied in ultraviolet protection materials.

[0009] Therefore, it is necessary to improve existing technologies by introducing catechol into waterborne polyurethane. This will not only improve the mechanical strength and adhesion of the polyurethane, but also give the waterborne polyurethane UV resistance. This will result in a new pesticide formulation with high plant adhesion, low environmental impact, and long-lasting efficacy, thereby reducing the risk of environmental pollution, reducing the amount applied, saving manpower, and lowering costs. Summary of the Invention

[0010] The present invention aims to provide a pesticide microcapsule sustained-release agent with anti-ultraviolet effect and high adhesion, and a preparation method thereof.

[0011] The technical solution of this invention is as follows:

[0012] A method for preparing a UV-resistant pesticide microcapsule sustained-release agent, comprising the following steps:

[0013] (1) The polyurethane prepolymer grafted with catechol structure was added to the aqueous phase containing polymeric polyol II and mixed well. Then, an oil phase was added to prepare an emulsion. The pesticide was dissolved in organic solvent II as the oil phase.

[0014] (2) Add a curing agent to the emulsion to carry out a curing reaction to obtain an anti-ultraviolet pesticide microcapsule sustained-release agent.

[0015] The method for preparing the polyurethane prepolymer grafted with a catechol structure is as follows:

[0016] (a) Polymerizing polyol I, polyisocyanate, catalyst and organic solvent I, and performing prepolymerization;

[0017] (b) Add a cationic hydrophilic chain extender and a small molecule chain extender to the prepolymerized system to carry out a chain extension reaction, and add a neutralizing agent containing a catechol structure to carry out a neutralization reaction to obtain a polyurethane prepolymer containing a catechol structure.

[0018] The cationic hydrophilic chain extender is a diol hydrophilic chain extender containing a tertiary amine group, with a structural formula as shown in formula A or B:

[0019]

[0020] Wherein R1-R3 are H or C1-C8 alkylene groups, preferably H or C1-C5 alkylene groups; R1-R3 can be the same or different groups; R4 is C1-C8 alkylene groups, preferably C1-C5 alkylene groups; R5 and R6 can be the same or different groups, and are C1-C8 alkyl groups, preferably C1-C5 alkylene groups.

[0021] Preferably, the hydrophilic chain extender containing a tertiary amine group is selected from 3-dimethylamino-1,2-propanediol (DMAD) or 4-dimethylamino-1,2-butanediol.

[0022] The neutralizing agent containing the catechol structure is an acidic neutralizing agent, and also contains at least one of carboxyl groups and sulfonic acid groups, preferably one or more of 3,4-dihydroxybenzoic acid (DBA), 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylpropionic acid, 4-(3,4-dihydroxyphenyl)butyric acid, and 3,4-dihydroxybenzenesulfonic acid.

[0023] The small molecule chain extender is a small molecule polyol selected from one or more of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,2,6-hexanetriol, pentaerythritol, glycerol, and trimethylolpropane.

[0024] Furthermore, the neutralizing agent containing the catechol structure is dispersed in water and then added to the reaction system under stirring to carry out the neutralization reaction. The stirring rate is 500-2500 rpm.

[0025] The polymeric polyols I and II are selected from at least one or more of polyester polyols, polybutadiene polyols, polytetrahydrofuran polyols, polycarbonate polyols, polycaprolactone polyols, polylactic acid polyols, and polyether polyols. The number-average molecular weight of polymeric polyols I and II is 200–4000. Preferably, the number-average molecular weight of polymeric polyol I is 200–4000, more preferably 400–2000. Preferably, the number-average molecular weight of polymeric polyol II is 200–1000, more preferably 200–800. Preferably, polymeric polyols I and II are polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetrahydrofuran glycol (PTMG). Polymeric polyols I and II may be the same or different.

[0026] The polyisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, tetramethylphenyldimethyl diisocyanate, lysine diisocyanate, and polymethylene polyphenyl isocyanate.

[0027] The mass ratio of the polyurethane prepolymer, based on the total amount of polyisocyanate and polymeric polyol I, to the pesticide technical is 1:0.3-6, preferably 1:0.5-3.

[0028] The prepolymerization conditions for step (a) are: reaction at 30-95℃ for 1-6 hours, preferably reaction at 60-90℃ for 1.5-4 hours.

[0029] In step (a), the amount of catalyst used is 0-3 wt%, preferably 0.1 wt%-1 wt%, based on the total amount of polyisocyanate and polymeric polyol I.

[0030] In step (a), the mass ratio of the polyisocyanate to the polymeric polyol I is 1:0.3-4; preferably 1:0.5-2.5. The mass ratio of the polyisocyanate to the organic solvent I is 1:0.3-3, preferably 1:0.3-1.5.

[0031] The chain extension reaction conditions for step (b) are: reaction at 20-90℃ for 1-6 hours, preferably at 50-80℃ for 1.5-4 hours.

[0032] The molar ratio of the neutralizing agent containing the catechol structure to the cationic hydrophilic chain extender is 1:0.8-1.1, preferably 1:1.

[0033] The mass ratio of polyisocyanate to small molecule chain extender is 1:0.05-1.5, preferably 1:0.1-0.6; the mass ratio of polyisocyanate to hydrophilic chain extender containing tertiary amine group is 1:0.01-1.5, preferably 1:0.1-0.6.

[0034] In step (1), the mass ratio of the oil phase to the water phase is 1:0.5-3, preferably 1:0.8-2.

[0035] The mass ratio of the polyisocyanate to the polymeric polyol II is 1:0.05-0.5, preferably 1:0.05-0.2.

[0036] The emulsification conditions described in step (1) are shearing at 5000-12000 rpm for 5-10 min.

[0037] In step (2), the amount of curing agent used is 0.5wt%-4wt% of the emulsion.

[0038] The curing reaction conditions are: reaction at 30-90℃ for 1-6 hours, preferably reaction at 40-80℃ for 1.5-4 hours. More preferably, the reaction is carried out under stirring at 100-800 rpm.

[0039] The curing agent mentioned in step (2) is an organic compound containing amines, selected from ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 3,3'-diaminodipropylamine, tris(2-aminoethyl)amine, bis(hexamethyltriamine), pentaethylenehexylamine, triethylenetetramine, polyethylene glycol diamine, isophorone diamine, meglumine, 2,2-dimethylolbutanol polyethylene glycol diamine, piperazine, 1,4-bis(3-aminoethyl)amine, etc. (N,N'-bis(3-aminopropyl)ethylenediamine), piperazine, polyetheramine D230, polyetheramine D400, lysine, diethyl lysine ester, guanidine, 1,3-diaminoguanidine hydrochloride, 1,1-dimethylbiguanidine hydrochloride, guanidine carbonate, bis(3-aminopropyl-1,3-propanediamine), branched polyethyleneimine, melamine, 3,5-diamino-1,2,4-triazole, tris(2-aminoethyl)amine, N,N'-bis(3-aminopropyl)ethylenediamine.

[0040] Preferably, the catalyst is one of the following: dibutyltin oxide, dibutyltin dibutyrate, dimethyltin dibutyrate, dioctyltin dibutyrate, dibutyltin diacetate, dimethyltin diacetate, dibutyltin dilaurate, dimethyltin dilaurate, dioctyltin dilaurate, dibutyltin dioleate, dimethyltin dioleate, dioctyltin dioleate, dioctyltin dithioacetate, dioctyltin dithioacetate, dioctyltin dioctanoate, dioctyltin dioctanoate, dioctyltin dioctanoate, dioctyltin diacetate, dibutyltin diacetate, and dimethyltin diacetate.

[0041] Organic solvent I and organic solvent II include, but are not limited to, esters, ketones, and aromatics.

[0042] The ester solvent is any one or more of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, amyl acetate, sec-butyl acetate, benzyl acetate, octyl acetate, isoamyl acetate, hexyl acetate, 3-octyl acetate, 1-octene-3-acetate, γ-valerolactone, propylene carbonate, ethyl acetoacetate, 3,5,5-trimethylhexyl acetate, 2-butenyl 3-methylacetate, isoamyl butyrate, hexyl butyrate, hexyl crotonate, ethyl isovalerate, ethyl 2-methylvalerate, ethyl hexanoate, allyl hexanoate, ethyl heptaate, ethyl octanoate, methyl 2-octanoate, methyl 2-nonanoate, isoamyl citrate, and divalent esters.

[0043] The ketone solvents are any one or more of acetone, butanone, methyl butanone, methyl isobutanone, toluenecyclohexanone, cyclohexanone, acetophenone, 2-heptanone, 2-octanone, 3-octanone, 2-nonanone, and 5-methyl-3-heptanone.

[0044] The aromatic solvent oil is selected from any one or more of xylene, trimethylbenzene, No. 100 solvent oil, No. 150 solvent oil, or No. 200 solvent oil.

[0045] Other solvents that can be used include N,N-dimethyldecylamide and N-octylpyrrolidone.

[0046] The above method can be used to obtain a UV-resistant pesticide microcapsule sustained-release agent, which uses cationic aqueous polyurethane modified with catechol as the capsule wall and the capsule core carries pesticide.

[0047] Preferably, the pesticide technical material is one or more of the following: cyhalothrin, prochloraz, chlorpyrifos, pendimethalin, azoxystrobin, trifluralin, flufenoxuron, cyhalofop-butyl, bifenthrin, isoprothiolane, pyraclostrobin, ethoxyflufenoxuron, diflubenzuron, pyrimethanil, hexaconazole, abamectin, carbendazim, emamectin benzoate, chlorothalonil, tebuconazole, metalaxyl, clodinafop-propargyl, butachlor, difenoconazole, propiconazole, oxadiazon, tebuconazole, cyproconazole, propargyl oxadiazon, triadimefon, pyrimethanil, flufenoxuron, flutriafol, clethodim, imazalil, triadimefon, bifenthrin, cycloheximefon, and gibberellin.

[0048] This UV-resistant pesticide microcapsule slow-release agent has an encapsulation rate of over 90% and exhibits good adhesion, dispersibility, stability, and suspension properties. Its adhesion rate exceeds 70%, and it has excellent UV protection, thus meeting the actual needs of agricultural production.

[0049] In preparing the polyurethane prepolymer, this invention selects an acidic neutralizing agent containing a catechol structure and a hydrophilic chain extender containing a cationic structure. The anion of the neutralizing agent combines with the cationic group on the hydrophilic chain extender, thereby introducing catechol-structured groups into the polyurethane. At the same time, the salt generated after the neutralization reaction of the polyurethane prepolymer has the effect of a surfactant. Therefore, when performing interfacial polymerization reaction with emulsion, there is no need to add additional surfactants, dispersants, etc. Moreover, the resulting polyurethane microcapsules have good hydrophilicity, excellent suspension, dispersibility and stability, and high encapsulation efficiency.

[0050] The catechol structure in the neutralizing agent is grafted onto the capsule wall via a hydrophilic chain extender, which not only gives it UV protection, preventing sunlight from damaging the polyurethane microcapsules, but also provides abundant hydrogen bonding reaction sites, greatly improving the mechanical properties of the microcapsule shell. Furthermore, the catechol structure can be used to increase the adsorption and adhesion properties of polyurethane pesticide microcapsules to the leaf surface, thereby enhancing the deposition time of pesticide microcapsules on crop leaves and improving pesticide utilization efficiency.

[0051] The beneficial effects of this invention are as follows:

[0052] 1) This invention uses a neutralization method by grafting catechol functional groups, which is different from traditional functionalization modification or the addition of UV protectants. It also does not require the addition of surfactants. The process is simple, green and environmentally friendly, and is conducive to large-scale industrial applications.

[0053] 2) By introducing catechol functional groups into the polyurethane molecular structure, the crosslinking, mechanical properties, adhesion and UV resistance of the polymer molecules are improved simultaneously.

[0054] 3) The catechol group further optimizes the performance of cationic waterborne polyurethane (CWPU) pesticide microcapsules. The resulting pesticide microcapsules have good dispersibility, suspension rate, high encapsulation rate, and good UV resistance, effectively reducing the damage of ultraviolet rays to the microcapsules. They also have strong adhesion properties, which improves the utilization rate of pesticides and can reduce the number of applications and dosage. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the prepolymer synthesis route for Example 1;

[0056] Figure 2 Here is an electron micrograph of the pesticide microcapsule sustained-release agent from Example 1;

[0057] Figure 3 This is an example of the UV protection effect of the pesticide microcapsule sustained-release agent in Example 1. Detailed Implementation

[0058] Example 1

[0059] (1) Prepolymer preparation

[0060] 20g of polytetrahydrofuran diol (PTMG-1000), 17.76g of isophorone diisocyanate (IPDI), 0.3g of dibutyltin laurate, and 10g of cyclohexanone were mixed and prepolymerized at 85°C for 2 hours. Then, 1.8g of 1,4-butanediol and 2.38g of 3-dimethylamino-1,2-propanediol (20 mmol) were added dropwise to the reaction system, and polymerization was carried out at 70°C for 3 hours for polyurethane chain extension.

[0061] The reactants were cooled to room temperature, and 3,4-dihydroxybenzoic acid dissolved in 5 g of distilled water was added under high-speed stirring at 1600 rpm to obtain a polyurethane prepolymer with a catechol structure. The molar ratio of 3-dimethylamino-1,2-propanediol to 3,4-dihydroxybenzoic acid was 1:1.

[0062] Prepolymer reaction route as follows Figure 1 As shown.

[0063] (2) Preparation of the oil phase

[0064] Weigh 31g of difenoconazole and 15.3g of pyraclostrobin, dissolve them in 15g of butyl acetate, and obtain the oil phase.

[0065] (3) Preparation of the aqueous phase

[0066] Polyethylene glycol PEG-400 was dissolved in deionized water to prepare a 2wt% solution, which was used as the aqueous phase.

[0067] (4) Preparation of microcapsules

[0068] The prepolymer mixture prepared in step (1) is mixed with the aqueous phase and stirred evenly. The amount of aqueous phase is 1.2 times the mass of the oil phase. Then the oil phase prepared in step (2) is added and emulsified by shearing at 10,000 rpm for 8 minutes.

[0069] 2g of diethylenetriamine was added to the emulsion for curing reaction. The mixture was stirred at 500rpm and reacted at 60℃ for 3h to obtain 24% difenoconazole·pyraclostrobin UV-resistant polyurethane microcapsule sustained-release agent, which was milky white.

[0070] The pesticide microcapsule sustained-release agent prepared in this embodiment was observed using a scanning electron microscope, and the resulting scanning electron microscope image is shown below. Figure 2 As shown.

[0071] from Figure 2 As can be seen, the pesticide microcapsules have a regular morphology, are spherical, and have a particle size distribution of 0.5-3 μm, which is relatively uniform. By observing the size and uniformity of the microcapsules under light and electron microscopes, and characterizing the specific particle size and PDI values ​​of the microcapsules using a laser particle size analyzer and a ZATA potential meter, the average particle size was measured to be 1.9 μm.

[0072] The suspension rate was determined using the method specified in GB / T 14825-2006. The microcapsule encapsulation efficiency was also determined using the following method:

[0073] Accurately weigh 0.01 g of the dried microcapsule sample, dilute to 100 mL with methanol, let stand for 5 min, centrifuge, and then measure the absorbance using ultraviolet spectrophotometry. After ultrasonic treatment for 30 min, centrifuge to release all pesticides, and measure the absorbance again. Calculate the mass of the active pesticide component in the microcapsules using the standard curve method, and calculate the encapsulation efficiency according to formula (I):

[0074] Encapsulation efficiency (%) = Mass of active ingredient in microcapsules / Mass of added raw drug × 100

[0075] The measured microcapsule suspension rate was greater than 90%, encapsulation efficiency was 92%, and adhesion rate exceeded 70%. Furthermore, it exhibited good stability, showing little tendency to separate or precipitate. It also demonstrated good self-dispersibility; after being diluted 100 times with water, mixed thoroughly, and allowed to stand for 4 hours, no separation or precipitation was observed.

[0076] Using a methanol-water solution with a volume ratio of 1:1 as the sustained-release medium, the release rate was measured. The cumulative release rate after 80 hours was 59%, indicating good sustained-release performance.

[0077] Compare with Example 1

[0078] (1) 20g of polytetrahydrofuran diol (PTMG-1000), 17.76g of isophorone diisocyanate (IPDI), 0.3g of dibutyltin laurylate, and 10g of cyclohexanone were mixed and prepolymerized at 85℃ for 2h. 3.6g of 1,4-butanediol was added, and the polymerization reaction was carried out at 70℃ for 3h for polyurethane chain extension to obtain polyurethane prepolymer.

[0079] (2) Weigh 31g of difenoconazole and 15.3g of pyraclostrobin, dissolve them in 15g of butyl acetate, and mix them with the polyurethane prepolymer obtained in step (1) to obtain the oil phase.

[0080] (3) Sodium dodecyl sulfonate was prepared into a 10 wt% solution with deionized water as the aqueous phase.

[0081] (4) The oil phase and water phase are mixed at a mass ratio of 1:1.2 and emulsified by shearing at 10,000 rpm for 8 min;

[0082] 2g of diethylenetriamine was added to the emulsion for a curing reaction. The mixture was stirred at 500rpm and reacted at 60℃ for 3h to obtain a polyurethane sustained-release capsule suspension.

[0083] The microcapsule suspension prepared in Example 1, the pesticide technical, and the microcapsule suspension prepared in Control Example 1 were all prepared into suspension dispersions with the same pesticide content using methanol. These were then irradiated under a UV lamp (36W, 254nm), and samples were taken at regular intervals. The concentrations were calculated using high-performance liquid chromatography (HPLC). The relationship between UV irradiation time (h) and pesticide retention rate is shown in the figure below. Figure 3 As shown. From Figure 3 As can be seen, both the microcapsules prepared by existing methods and the UV-resistant pesticide microcapsules prepared by the present invention have a protective effect against the degradation of the active ingredient under ultraviolet light. However, the degradation rate of the pesticide in the UV-resistant microcapsules of Example 1 is significantly lower than that of the unencapsulated active ingredient and the pesticide polyurethane microcapsules of Control Example 1, indicating that the microcapsules of the present invention have a good UV-resistant effect.

[0084] Example 2

[0085] (1) Prepolymer preparation

[0086] 18g of polyacrylamide (PPG-1000), 15.1g of hexamethylene diisocyanate, 0.2g of stannous octoate, and 10g of cyclohexanone were mixed and prepolymerized in a water bath at 85°C for 2 hours. 2g of 1,4-butanediol and 3g of 3-dimethylamino-1,2-propanediol (25.2 mmol) were added dropwise to the reaction system for polyurethane chain extension.

[0087] After reacting at 70°C for 3 hours, the reactants were cooled to room temperature, and 3,4-dihydroxybenzenesulfonic acid dissolved in 5g of distilled water was added under high-speed stirring (1600rpm) to obtain a polyurethane prepolymer with a catechol structure. The molar ratio of 3-dimethylamino-1,2-propanediol to 3,4-dihydroxybenzenesulfonic acid was 1:1.

[0088] (2) Preparation of the oil phase

[0089] 30g of isoprothiolane and 25g of prochloraz were dissolved in 20g of trimethylbenzene to obtain the oil phase.

[0090] (3) Preparation of the aqueous phase

[0091] A 3wt% solution of polyethylene glycol PEG-400 and deionized water was prepared as the aqueous phase.

[0092] (4) Preparation of microcapsules

[0093] The prepolymer mixture prepared in step (1) is mixed with the aqueous phase and stirred evenly. The amount of aqueous phase is 1 times the mass of the oil phase. Then the oil phase prepared in step (2) is added and emulsified by shearing at 10000 rpm for 10 min.

[0094] 2g of diethylenetriamine was added to the emulsion for a curing reaction. The mixture was stirred at 500rpm and reacted at 60℃ for 3h to obtain 28% isoprothiolane·prochloraz microcapsule sustained-release agent.

[0095] The microcapsules were tested and found to have an average particle size of 1.7 μm, a suspension rate of over 90%, and an encapsulation rate of 93%.

[0096] Example 3

[0097] (1) Prepolymer preparation

[0098] 16g of polyethylene glycol PEG-1000, 31.3g of dicyclohexylmethane diisocyanate, 0.3g of dibutyltin oxide, and 10g of cyclohexanone were mixed and prepolymerized at 80℃ for 2h. 4g of 1,6-hexanediol and 4g of 3-dimethylamino-1,2-propanediol (33.6mmol) were added dropwise to the reaction system for polyurethane chain extension. After reacting at 70℃ for 3h, the reactants were cooled to room temperature, and 3,4-dihydroxybenzenesulfonic acid dissolved in 5g of distilled water was added under high-speed stirring (1600rpm) to obtain a polyurethane prepolymer with a catechol structure. The molar ratio of 3-dimethylamino-1,2-propanediol to 3,4-dihydroxybenzenesulfonic acid was 1:1.

[0099] (2) Preparation of the oil phase

[0100] 20g of pyraclostrobin and 32g of difenoconazole were dissolved in 20g of thiamethoxam to obtain the oil phase.

[0101] (3) Preparation of the aqueous phase

[0102] A 2wt% solution of polyethylene glycol PEG-400 and deionized water was prepared as the aqueous phase.

[0103] (4) Preparation of microcapsules

[0104] The prepolymer mixture prepared in step (1) is mixed with the aqueous phase and stirred evenly. The amount of aqueous phase is 1.2 times the mass of the oil phase. Then the oil phase prepared in step (2) is added and emulsified by shearing at 12000 rpm for 6 minutes.

[0105] 4g of meglumine was added to the emulsion for a curing reaction. The mixture was stirred at 500rpm and reacted at 65℃ for 3h to obtain a 20% difenoconazole·pyraclostrobin microcapsule sustained-release agent.

[0106] The microcapsules were tested and found to have an average particle size of 2.2 μm, a suspension rate of over 90%, and an encapsulation rate of 95%.

[0107] The microcapsule sustained-release agents of Examples 2 and 3 have an adhesion rate of over 70%, and after the microcapsules are irradiated under ultraviolet light for 48 hours, the retention rate of the pesticide active ingredient is not less than 35%, which can meet the actual needs of agricultural production.

Claims

1. A method for preparing a microcapsule sustained-release agent for UV-resistant pesticides, characterized in that the steps include... include: (1) The polyurethane prepolymer grafted with catechol structure was added to the aqueous phase containing polymeric polyol II and mixed well, and then the oil phase was added to prepare an emulsion; the pesticide was dissolved in an organic solvent as the oil phase; (2) Add a curing agent to the emulsion to carry out a curing reaction to obtain an anti-ultraviolet pesticide microcapsule sustained-release agent; The method for preparing the polyurethane prepolymer grafted with a catechol structure is as follows: (a) Prepolymerization of polyol I, polyisocyanate, and catalyst; (b) Add a cationic hydrophilic chain extender and a small molecule chain extender to the prepolymerized system to carry out a chain extension reaction, and add a neutralizing agent containing a catechol structure to carry out a neutralization reaction to obtain a polyurethane prepolymer containing a catechol structure; the neutralizing agent containing a catechol structure is an acidic neutralizing agent and contains at least one of a carboxyl group and a sulfonic acid group.

2. The preparation method according to claim 1, characterized in that, The cationic hydrophilic chain extender is a diol hydrophilic chain extender containing a tertiary amine group, with a structural formula as shown in formula A or B: R1-R3 are H or C1-C8 alkylene compounds, R4 is a C1-C8 alkylene compound, and R5 and R6 are C1-C8 alkyl compounds.

3. The preparation method according to claim 2, characterized in that, The hydrophilic chain extender containing a tertiary amine group is 3-dimethylamino-1,2-propanediol or 4-dimethylamino-1,2-butanediol.

4. The preparation method according to claim 1, characterized in that, The neutralizing agent containing the catechol structure is 3,4-dihydroxybenzoic acid, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylpropionic acid, 4-(3,4-dihydroxyphenyl)butyric acid, or 3,4-dihydroxybenzenesulfonic acid.

5. The preparation method according to claim 1, characterized in that, The small molecule chain extender is a small molecule polyol.

6. The preparation method according to claim 1, characterized in that, The curing agent mentioned in step (2) is a polyamine.

7. The preparation method according to claim 1, characterized in that, The polymeric polyols I and II are selected from at least one of polyester polyols, polybutadiene polyols, polytetrahydrofuran polyols, polycarbonate polyols, polycaprolactone polyols, polylactic acid polyols, and polyether polyols.

8. A microcapsule sustained-release agent for UV-resistant pesticides, characterized in that, Prepared by the preparation method according to any one of claims 1-7.

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