Polyurethane joint mixture and preparation method thereof

Abstract

The invention belongs to the technical field of caulking agents, and particularly relates to a polyurethane caulking agent and a preparation method thereof.The polyurethane caulking agent is prepared from, by mass, 35%-40% of siloxane modified dendritic polyether tetrahydric alcohol, 35%-40% of diphenylmethane diisocyanate, 5%-10% of plasticizer chlorinated paraffin, 3%-4% of 2-phenyl-5-trifluoromethyl-1, 3-oxazolidine latent curing agent, 1%-2% of foam stabilizer and 1%-2% of catalyst 2. 0.5-0.8% of 2, 2 '-dimorpholinyl diethyl ether, 5-8% of dimethyl ether and 5-8% of propane and butane. According to the polyurethane joint mixture, the 2-phenyl-5-trifluoromethyl-1, 3-oxazolidine latent curing agent is added, in the curing process, the latent curing agent reacts with water in advance of the diphenylmethane diisocyanate to form an amine substance, amido in the amine substance reacts with the diphenylmethane diisocyanate to generate a macromolecular polymer, curing of the polyurethane joint mixture is achieved, and the polyurethane joint mixture has the advantages that the curing effect is good; the curing time can be shortened, and the construction speed is increased.

Description

Technical Field

[0001] This invention belongs to the field of sealant technology, specifically relating to a polyurethane sealant and its preparation method. Background Technology

[0002] Polyurethane sealant can be used for sealing leaks, filling gaps, and providing thermal and sound insulation. It is especially suitable for sealing and waterproofing PVC and aluminum alloy doors, windows, or walls.

[0003] Polyurethane sealant is divided into two categories: single-component polyurethane sealant and two-component polyurethane sealant.

[0004] One-component polyurethane sealant (OCF) is a moisture-curing one-component polyurethane foam material. It is made by filling isocyanate, polyether polyol, plasticizer, catalyst, foaming agent, etc. into a pressure-resistant aerosol can using a special aerosol filling machine, and then shaking and mixing it evenly to form a stable polyurethane prepolymer. Because all components are coexisting in the aerosol can, it is called one-component.

[0005] When using it, the prepolymer is sprayed into the gaps or holes using a special tool. The prepolymer quickly foams and expands, reacting with moisture in the air or on the substrate and then curing. The cured foam has multiple effects such as adhesion, sealing, sound insulation, heat insulation, and waterproofing. Therefore, OCF has become an ideal caulking material with a wide range of applications.

[0006] However, existing single-component polyurethane foam sealants generally have a surface drying time of about 10 minutes, and the full drying time varies with the ambient temperature and humidity. The full drying time is shorter in summer and longer in winter when the temperature is around zero degrees Celsius, which seriously affects the construction speed of the construction team and wastes time. Summary of the Invention

[0007] The purpose of this invention is to provide a polyurethane sealant and its preparation method to solve the above-mentioned technical problems.

[0008] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows: A polyurethane sealant, by mass percentage, comprises the following components: 60-65% siloxane-modified dendritic polyether tetraol, 10-15% diphenylmethane diisocyanate, 5-10% chlorinated paraffin plasticizer, 3-4% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 1-2% foam leveling agent, 0.5-0.8% catalyst 2,2′-bismorpholinodiethyl ether, 5-8% dimethyl ether, and 5-8% propane-butane.

[0009] This invention also provides a method for preparing a polyurethane sealant, comprising the following steps: S1, Preparation of siloxane-modified dendritic polyether tetraol; Pentamethyldisiloxane and isopropanol were mixed and heated to 80-85°C under a nitrogen atmosphere. Then, chloroplatinic acid catalyst was added to activate the mixture for 0.5-0.8 h. The temperature was then raised to 100-110°C, and dendritic polyether tetraol was added dropwise over a period of 30-40 min. After the addition was complete, the mixture was reacted for 4-6 h. The mixture was then distilled under reduced pressure and cooled to room temperature to obtain siloxane-modified dendritic polyether tetraol. S2. Preparation of polyurethane sealant; The siloxane-modified polyether tetraol and the plasticizer chlorinated paraffin were mixed, vacuum dehydrated at 105°C for 1 hour, and then cooled to 25~30°C. A latent curing agent, a foaming agent and a catalyst were added to the mixture, and after stirring evenly, the polyether composite material was obtained. Polyether compound and diphenylmethane diisocyanate are added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane are pressed in. The can is shaken at a constant speed for 10-20 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

[0010] As a further improvement, in step S1, the preparation method of the dendritic polyether tetraol is as follows: pentaerythritol, sodium hydroxide and deionized water are ultrasonically mixed and dissolved, heated to 90~95℃ under a nitrogen atmosphere, and then allyl glycidyl ether is added dropwise over a time of 30~40 min. After the addition is complete, the reaction is carried out for 3 h. After the reaction is completed, cation exchange resin is added to neutralize to neutrality, the filtrate is obtained by vacuum distillation and then cooled to room temperature to obtain the dendritic polyether tetraol.

[0011] As a further improvement, the molar ratio of pentaerythritol to allyl glycidyl ether is 1:4, and the mass of sodium hydroxide is 2.8 to 3% of the mass of pentaerythritol.

[0012] As a further improvement, in step S1, the molar ratio of pentamethyldisiloxane to dendritic polyether tetraol is 4:1, and the mass ratio of pentamethyldisiloxane to isopropanol is 1:1.5~2.

[0013] As a further improvement, in step S2, the preparation method of the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent is as follows: 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and cyclohexane are mixed, benzaldehyde is added to it under stirring, the temperature is controlled at 35~40℃, the reaction is kept at this temperature for 1 hour, then the temperature is raised and refluxed to remove moisture, then cooled to room temperature, and impurities are removed by vacuum distillation to obtain the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent.

[0014] As a further improvement, the molar ratio of the 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride to the benzaldehyde is 1:1.

[0015] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: This invention provides a polyurethane sealant and its preparation method. A 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent is added to the polyurethane sealant. During the curing process, the latent curing agent reacts with water before diphenylmethane diisocyanate to form an amine substance. The amine groups react with diphenylmethane diisocyanate to generate a macromolecular polymer, thereby achieving the curing of the polyurethane sealant. This method can shorten the curing time and improve the construction speed.

[0016] This invention uses 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, which, compared with imine latent curing agents, can prevent the polyurethane sealant from curing too quickly, resulting in excessively fast gelation and weakened material strength.

[0017] The trifluoromethyl group in 2-phenyl-5-trifluoromethyl-1,3-oxazolane, as a strong electron-withdrawing group, reduces the electron cloud density of the carbon atoms on the oxazolane ring, enhances its positive charge, and makes it more susceptible to attack by water molecules, thereby accelerating the hydrolysis of 2-phenyl-5-trifluoromethyl-1,3-oxazolane and reducing curing time. Furthermore, the trifluoromethyl group can also reduce the electron cloud density on the nitrogen atom through inductive and conjugation effects, weakening its alkalinity and improving the storage stability of polyurethane sealant.

[0018] The benzene ring in 2-trifluoromethyl-3-phenyl-1,3-oxazolidine can also further reduce the electron cloud density of nitrogen atoms through the conjugation effect, thereby further improving the storage stability of polyurethane sealant.

[0019] This invention uses siloxane-modified dendritic polyether tetraol, which can improve the crosslinking degree of the system, increase the strength of the microporous membrane wall of the foam, and reduce the shrinkage tendency of polyurethane sealant during curing. Furthermore, the near-spherical structure of the siloxane-modified dendritic polyether tetraol can reduce the viscosity of the isocyanate prepolymer, improve storage stability, and prevent the increase in system viscosity and decrease in storage stability caused by the increase in crosslinking degree. In addition, siloxane modification can also improve the strength of polyurethane sealant. Attached Figure Description

[0020] Figure 1 The infrared spectrum of the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent in Example 1; Figure 2 The infrared spectrum of the siloxane-modified dendritic polyether tetraol in Example 1 is shown. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0022] In this invention, the foam leveling agent is an organosilicon-polyether copolymer, specifically QG-6855, QG-8526, etc. Other types of foam leveling agents can also be used. The type of foam leveling agent does not have a significant impact on the beneficial effects of this invention. Foam leveling agents used in polyurethane sealants in the prior art can all be used as foam leveling agents in this invention.

[0023] Example 1 A polyurethane sealant, comprising the following components by mass percentage: 36% siloxane-modified dendritic polyether tetraol, 39% diphenylmethane diisocyanate, 8% chlorinated paraffin plasticizer, 3% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 1.4% silicone-polyether copolymer foam leveler, 0.6% 2,2′-bismorpholino diethyl ether catalyst, 6% dimethyl ether, and 6% propane-butane.

[0024] This embodiment also provides a method for preparing the above-mentioned polyurethane sealant, specifically including the following steps: S1. 3.4 g (0.025 mol) pentaerythritol, 0.95 g sodium hydroxide and 10 mL deionized water were ultrasonically mixed and dissolved. The mixture was heated to 90 °C under a nitrogen atmosphere. Then, 11.42 g (0.1 mol) allyl glycidyl ether was added dropwise over a period of 30 min. After the addition was complete, the mixture was reacted for 3 h. After the reaction was completed, cation exchange resin was added to neutralize the mixture to neutral. The mixture was filtered to obtain the filtrate. Unreacted reactants were removed by vacuum distillation. The mixture was cooled to room temperature to obtain dendritic polyether tetraol. The reaction equation is: ; S2. Mix 5.89 g (0.04 mol) pentamethyldisiloxane and 8.84 g isopropanol, stir and heat to 80 °C under a nitrogen atmosphere, then add chloroplatinic acid catalyst to activate for 0.5 h, then heat to 100 °C, and add 5.92 g (0.01 mol) dendritic polyether tetraol dropwise over a period of 30 min. After the addition is complete, react for 4 h, remove solvent and unreacted substances by vacuum distillation, and cool to room temperature to obtain siloxane-modified dendritic polyether tetraol. The reaction equation is: ; S3. Mix 0.25 mol of 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and 20 mL of cyclohexane. Add 0.25 mol of benzaldehyde under stirring. Control the temperature at 35°C and keep the reaction at this temperature for 1 h. Then, heat the mixture to reflux to remove moisture. Cool the mixture to room temperature and remove impurities by vacuum distillation to obtain 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent. The reaction equation is: ; S4. Mix siloxane-modified polyether tetraol and plasticizer chlorinated paraffin, dehydrate under vacuum at 105°C for 1 hour, then cool to 25°C, add latent curing agent, foam stabilizer and catalyst, stir evenly to obtain polyether composite material. Polyether compound and diphenylmethane diisocyanate were added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane were pressed in. The can was shaken at a constant speed for 10 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

[0025] like Figure 1 The image shown is the infrared spectrum of the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent in this embodiment. It can be seen that in the range of 3000~3100 cm⁻¹... -1 A stretching vibration peak of CH in the benzene ring appears at 1542 cm⁻¹. -1 and 1632cm -1 A stretching vibration peak of C=C in the benzene ring appears at 1100~1220 cm⁻¹. -1 The peak at this point represents the overlapping vibrational stretching peaks of CF3 and oxazolidine.

[0026] like Figure 2 The image shown is the infrared spectrum of the siloxane-modified dendritic polyether tetraol in this embodiment. It can be seen that at 3400 cm⁻¹... -1 There is a stretching vibration peak of hydroxyl groups at 1260 cm⁻¹. -1 1070cm -1 and 840cm -1The vibrational absorption peaks are for Si-CH3, Si-O-Si, and Si-(CH3)3, respectively.

[0027] Example 2 A polyurethane sealant, by mass percentage, comprises the following components: 35% siloxane-modified dendritic polyether tetraol, 40% diphenylmethane diisocyanate, 5% chlorinated paraffin plasticizer, 4% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 2% silicone-polyether copolymer foam leveler, 0.5% 2,2′-bismorpholino diethyl ether catalyst, 8% dimethyl ether, and 5.5% propane-butane.

[0028] This embodiment also provides a method for preparing the above-mentioned polyurethane sealant, specifically including the following steps: S1. 3.4 g (0.025 mol) pentaerythritol, 0.1 g sodium hydroxide and 10 mL deionized water were ultrasonically mixed and dissolved. The mixture was heated to 95 °C under a nitrogen atmosphere. Then, 11.42 g (0.1 mol) allyl glycidyl ether was added dropwise over a period of 40 min. After the addition was complete, the mixture was reacted for 3 h. After the reaction was completed, cation exchange resin was added to neutralize the mixture. The mixture was filtered to obtain the filtrate. Unreacted reactants were removed by vacuum distillation. The mixture was cooled to room temperature to obtain dendritic polyether tetraol. S2. Mix 5.89 g (0.04 mol) pentamethyldisiloxane and 11.78 g isopropanol, stir and heat to 85 °C under nitrogen atmosphere, then add chloroplatinic acid catalyst to activate for 0.8 h, then raise the temperature to 110 °C, and add 5.92 g (0.01 mol) dendritic polyether tetraol dropwise over a period of 40 min. After the addition is complete, react for 6 h, remove solvent and unreacted substances by vacuum distillation, and cool to room temperature to obtain siloxane-modified dendritic polyether tetraol. S3. Mix 0.25 mol of 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and 20 mL of cyclohexane. Add 0.25 mol of benzaldehyde under stirring. Control the temperature at 40℃ and keep the reaction at this temperature for 1 h. Then, heat the mixture to reflux to remove moisture. Cool the mixture to room temperature and remove impurities by vacuum distillation to obtain 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent. S4. Mix siloxane-modified polyether tetraol and plasticizer chlorinated paraffin, dehydrate under vacuum at 105°C for 1 hour, then cool to 30°C, add latent curing agent, foam stabilizer and catalyst, and stir evenly to obtain polyether composite material. Polyether compound and diphenylmethane diisocyanate were added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane were pressed in. The can was shaken at a constant speed for 20 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

[0029] Example 3 A polyurethane sealant, comprising the following components by mass percentage: 40% siloxane-modified dendritic polyether tetraol, 35% diphenylmethane diisocyanate, 10% chlorinated paraffin plasticizer, 3.2% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 1% silicone-polyether copolymer foam stabilizer, 0.8% 2,2′-bismorpholino diethyl ether catalyst, 5% dimethyl ether, and 5% propane-butane.

[0030] This embodiment also provides a method for preparing the above-mentioned polyurethane sealant, specifically including the following steps: S1. 3.4 g (0.025 mol) pentaerythritol, 0.1 g sodium hydroxide and 10 mL deionized water were ultrasonically mixed and dissolved. The mixture was heated to 93 °C under a nitrogen atmosphere. Then, 11.42 g (0.1 mol) allyl glycidyl ether was added dropwise over a period of 35 min. After the addition was complete, the mixture was reacted for 3 h. After the reaction was completed, cation exchange resin was added to neutralize the mixture to neutral. The mixture was filtered to obtain the filtrate. Unreacted reactants were removed by vacuum distillation. The mixture was cooled to room temperature to obtain dendritic polyether tetraol. S2. Mix 5.89 g (0.04 mol) pentamethyldisiloxane and 10.3 g isopropanol, stir and heat to 83 °C under nitrogen atmosphere, then add chloroplatinic acid catalyst to activate for 0.6 h, then heat to 105 °C, and add 5.92 g (0.01 mol) dendritic polyether tetraol dropwise over a period of 35 min. After the addition is complete, react for 5 h, remove solvent and unreacted substances by vacuum distillation, and cool to room temperature to obtain siloxane-modified dendritic polyether tetraol. S3. Mix 0.25 mol of 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and 20 mL of cyclohexane. Add 0.25 mol of benzaldehyde under stirring. Control the temperature at 38°C and keep the reaction at this temperature for 1 h. Then, heat the mixture to reflux to remove moisture. Cool the mixture to room temperature and remove impurities by vacuum distillation to obtain 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent. S4. Mix siloxane-modified polyether tetraol and plasticizer chlorinated paraffin, dehydrate under vacuum at 105°C for 1 hour, then cool to 28°C, add latent curing agent, foam stabilizer and catalyst, stir evenly to obtain polyether composite material. Polyether compound and diphenylmethane diisocyanate were added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane were pressed in. The can was shaken at a constant speed for 15 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

[0031] Example 4 A polyurethane sealant, comprising the following components by mass percentage: 37% siloxane-modified dendritic polyether tetraol, 35% diphenylmethane diisocyanate, 10% chlorinated paraffin plasticizer, 3.2% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 1% silicone-polyether copolymer foam stabilizer, 0.8% 2,2′-bismorpholino diethyl ether catalyst, 5% dimethyl ether, and 8% propane-butane.

[0032] This embodiment also provides a method for preparing the above-mentioned polyurethane sealant, specifically including the following steps: S1. 3.4 g (0.025 mol) pentaerythritol, 0.1 g sodium hydroxide and 10 mL deionized water were ultrasonically mixed and dissolved. The mixture was heated to 93 °C under a nitrogen atmosphere. Then, 11.42 g (0.1 mol) allyl glycidyl ether was added dropwise over a period of 35 min. After the addition was complete, the mixture was reacted for 3 h. After the reaction was completed, cation exchange resin was added to neutralize the mixture to neutral. The mixture was filtered to obtain the filtrate. Unreacted reactants were removed by vacuum distillation. The mixture was cooled to room temperature to obtain dendritic polyether tetraol. S2. Mix 5.89 g (0.04 mol) pentamethyldisiloxane and 10.3 g isopropanol, stir and heat to 83 °C under nitrogen atmosphere, then add chloroplatinic acid catalyst to activate for 0.6 h, then heat to 105 °C, and add 5.92 g (0.01 mol) dendritic polyether tetraol dropwise over a period of 35 min. After the addition is complete, react for 5 h, remove solvent and unreacted substances by vacuum distillation, and cool to room temperature to obtain siloxane-modified dendritic polyether tetraol. S3. Mix 0.25 mol of 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and 20 mL of cyclohexane. Add 0.25 mol of benzaldehyde under stirring. Control the temperature at 38°C and keep the reaction at this temperature for 1 h. Then, heat the mixture to reflux to remove moisture. Cool the mixture to room temperature and remove impurities by vacuum distillation to obtain 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent. S4. Mix siloxane-modified polyether tetraol and plasticizer chlorinated paraffin, dehydrate under vacuum at 105°C for 1 hour, then cool to 28°C, add latent curing agent, foam stabilizer and catalyst, stir evenly to obtain polyether composite material. Polyether compound and diphenylmethane diisocyanate were added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane were pressed in. The can was shaken at a constant speed for 15 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

[0033] Comparative Example 1 A polyurethane sealant, by weight percentage, comprises the following components: 37% siloxane-modified dendritic polyether tetraol, 41% diphenylmethane diisocyanate, 8% chlorinated paraffin plasticizer, 1.4% organosilicon-polyether copolymer foam stabilizer, 0.6% 2,2′-bismorpholino diethyl ether catalyst, 6% dimethyl ether, and 6% propane-butane.

[0034] Comparative Example 2: A polyurethane sealant, comprising the following components by weight percentage: 36% siloxane-modified dendritic polyether tetraol, 39% diphenylmethane diisocyanate, 8% chlorinated paraffin plasticizer, 23% diimide latent curing agent Alt-10, 1.4% foam leveling agent silicone-polyether copolymer, 0.6% catalyst 2,2′-bismorpholino diethyl ether, 6% dimethyl ether, and 6% propane-butane.

[0035] Comparative Example 3: A polyurethane sealant, comprising the following components by weight percentage: 36% siloxane-modified dendritic polyether tetraol, 39% diphenylmethane diisocyanate, 8% chlorinated paraffin plasticizer, 3% (2,5) dimethyl-1,3-oxazolidine, 1.4% silicone-polyether copolymer foam stabilizer, 0.6% 2,2′-bismorpholino diethyl ether catalyst, 6% dimethyl ether, and 6% propane-butane.

[0036] Comparative Example 4: A polyurethane sealant, comprising the following components by weight percentage: 31.2% polyether polyol JX-220 (hydroxyl value 56 mg KOH / g), 31.2% polyether polyol JX-330N (hydroxyl value 35 mg KOH / g), 12.6% diphenylmethane diisocyanate, 8% plasticizer chlorinated paraffin, 3% 2-trifluoromethyl-3-phenyl-1,3-oxazolidine latent curing agent, 1.4% foam leveling agent silicone-polyether copolymer, 0.6% catalyst 2,2′-bismorpholino diethyl ether, 6% dimethyl ether, and 6% propane-butane.

[0037] The curing time, compressive strength, and storage stability of the polyurethane sealants obtained in Example 1 and Comparative Examples 1-4 were determined.

[0038] The specific method for determining curing time is as follows: under the conditions of temperature (23±2)℃ and relative humidity (50±5)%, the well-shaken polyurethane sealant is sprayed into foam strips (diameter 25mm and length 100mm), and the time it takes for the interior to fully cure is used as the measurement index.

[0039] The compressive strength was tested according to GB / T 8813—2008 "Determination of compressive properties of rigid foamed plastics".

[0040] The specific method for determining storage stability is as follows: First, the initial extrusion rate of the polyurethane sealant is measured. Then, the polyurethane sealant is stored at (50±2)℃ for 4 weeks for accelerated aging. After aging, the polyurethane sealant is cooled to room temperature for at least 24 hours, and the extrusion rate after aging is tested. Storage stability is evaluated by the retention rate of the extrusion rate. The method for determining the extrusion rate is to measure the extruded mass (g / min) per unit time under standard conditions.

[0041] The curing time, compressive strength, and storage stability test results of the polyurethane sealants of Examples 1 and Comparative Examples 1-4 are shown in Table 1.

[0042] Table 1. Performance test results of polyurethane sealants in Examples 1 and 1-4

[0043] As can be seen from Table 1, compared with Example 1, Comparative Example 1 has a significantly increased curing time, while the compressive strength and storage stability are slightly reduced. This indicates that the latent curing agent in this invention can effectively improve the curing rate of polyurethane sealant.

[0044] Compared with Comparative Example 2 and Examples 1 and 3, Comparative Example 2 had the fastest curing rate, followed by Example 1, while Comparative Example 3 had the slowest curing rate. This indicates that diimine-based latent curing agents are more effective in improving the curing rate than oxazolidine-based latent curing agents. Compared with Comparative Example 3, the oxazolidine-based latent curing agent prepared in this invention, with trifluoromethyl as a strong electron-withdrawing group, reduces the electron cloud density of carbon atoms on the oxazolidine ring, enhances its positive charge, and makes it more susceptible to attack by water molecules, thereby accelerating the hydrolysis of 2-trifluoromethyl-3-phenyl-1,3-oxazolidine and reducing the curing time.

[0045] Compared with Comparative Example 1 and Comparative Example 3, Comparative Example 2 showed a significant decrease in compressive strength. This indicates that although diimide-based latent curing agents can increase the curing rate of polyurethane sealant, the excessively rapid curing rate can lead to a decrease in the strength of the polyurethane sealant. In this invention, 2-trifluoromethyl-3-phenyl-1,3-oxazolidine latent curing agent is used. Compared with imide-based latent curing agents, this can prevent the excessively rapid curing speed during the curing process of polyurethane sealant from causing the system to gel too quickly and weakening the material strength.

[0046] Compared with Comparative Example 1, Comparative Example 3, and Comparative Example 1, Comparative Example 2 showed the worst storage stability. Comparative Example 3 showed slightly better storage stability than Comparative Example 2, while Comparative Example 1 showed a significant improvement in storage stability. This indicates that the addition of a latent curing agent reduces the storage stability of the polyurethane sealant, and the effect of diimide latent curing agents is even greater. In this invention, trifluoromethyl can reduce the electron cloud density on nitrogen atoms and weaken its alkalinity through induction and conjugation effects, thereby improving the storage stability of the polyurethane sealant. The benzene ring can also further reduce the electron cloud density of nitrogen atoms through conjugation effects, further improving the storage stability of the polyurethane sealant.

[0047] Compared with Example 1, Comparative Example 4 shows that the present invention uses siloxane-modified dendritic polyether tetraol, which can improve the crosslinking degree of the system, increase the strength of the foam microporous membrane wall, and reduce the shrinkage tendency of polyurethane sealant during curing. Furthermore, the near-spherical structure of siloxane-modified dendritic polyether tetraol can reduce the viscosity of isocyanate prepolymer, improve storage stability, and prevent the increase in system viscosity and decrease in storage stability caused by the increase in crosslinking degree. In addition, siloxane modification can also improve the strength of polyurethane sealant.

[0048] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A polyurethane sealant, characterized in that, By mass percentage, it includes the following components: 35-40% siloxane-modified dendritic polyether tetraol, 35-40% diphenylmethane diisocyanate, 5-10% chlorinated paraffin plasticizer, 3-4% 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent, 1-2% foam stabilizer, 0.5-0.8% catalyst 2,2′-bismorpholino diethyl ether, 5-8% dimethyl ether, and 5-8% propane and butane.

2. The method for preparing the polyurethane sealant according to claim 1, characterized in that, Includes the following steps: S1, Preparation of siloxane-modified dendritic polyether tetraol; Pentamethyldisiloxane and isopropanol were mixed and heated to 80-85°C under a nitrogen atmosphere. Then, chloroplatinic acid catalyst was added to activate the mixture for 0.5-0.8 h. The temperature was then raised to 100-110°C, and dendritic polyether tetraol was added dropwise over a period of 30-40 min. After the addition was complete, the mixture was reacted for 4-6 h. The mixture was then distilled under reduced pressure and cooled to room temperature to obtain siloxane-modified dendritic polyether tetraol. S2. Preparation of polyurethane sealant; The siloxane-modified polyether tetraol and the plasticizer chlorinated paraffin were mixed, vacuum dehydrated at 105°C for 1 hour, and then cooled to 25~30°C. A latent curing agent, a foaming agent and a catalyst were added to the mixture, and after stirring evenly, the polyether composite material was obtained. Polyether compound and diphenylmethane diisocyanate are added sequentially to a tin can. After sealing the can with an aerosol filling machine, dimethyl ether and propane are pressed in. The can is shaken at a constant speed for 10-20 minutes and left at room temperature for 24 hours to obtain polyurethane sealant.

3. The method for preparing the polyurethane sealant according to claim 2, characterized in that, In step S1, the dendritic polyether tetraol is prepared by ultrasonically mixing and dissolving pentaerythritol, sodium hydroxide and deionized water, heating to 90-95°C under a nitrogen atmosphere, then adding allyl glycidyl ether dropwise over a period of 30-40 minutes. After the addition is complete, the reaction is carried out for 3 hours. After the reaction is complete, cation exchange resin is added to neutralize the solution. The solution is then filtered to obtain a filtrate, which is then distilled under reduced pressure and cooled to room temperature to obtain the dendritic polyether tetraol.

4. The method for preparing the polyurethane sealant according to claim 3, characterized in that, The molar ratio of the pentaerythritol to the allyl glycidyl ether is 1:4, and the mass of the sodium hydroxide is 2.8 to 3% of the mass of the pentaerythritol.

5. The method for preparing the polyurethane sealant according to claim 2, characterized in that, In step S1, the molar ratio of pentamethyldisiloxane to dendritic polyether tetraol is 4:1, and the mass ratio of pentamethyldisiloxane to isopropanol is 1:1.5~2.

6. The method for preparing the polyurethane sealant according to claim 2, characterized in that, In step S2, the preparation method of the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent is as follows: 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride and cyclohexane are mixed, benzaldehyde is added to it under stirring, the temperature is controlled at 35~40℃, the reaction is kept at this temperature for 1 hour, then the temperature is raised and refluxed to remove moisture, then cooled to room temperature, and impurities are removed by vacuum distillation to obtain the 2-phenyl-5-trifluoromethyl-1,3-oxazolidine latent curing agent.

7. The method for preparing the polyurethane sealant according to claim 6, characterized in that, The molar ratio of 2-amino-3,3,3,-trifluoro-1-propanol hydrochloride to benzaldehyde is 1:1.

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