High-performance weather-resistant sealant for construction and method for preparing the same

Abstract

The application provides a high-performance weather-resistant sealant for buildings and a preparation method thereof. The high-performance weather-resistant sealant for buildings comprises the following raw materials in parts by mass: 100 parts by mass of 107 base glue, 5-10 parts by mass of modified cage polysilsesquioxane, 0.5-2 parts by mass of a crosslinking agent, 5-60 parts by mass of nano filler, 1-3 parts by mass of amino silane coupling agent, 0.1-0.5 parts by mass of a catalyst and 1-5 parts by mass of a plasticizer. The modified cage polysilsesquioxane comprises cage polysilsesquioxane grafted with long-chain alkyl functional groups and hindered amine light stabilizers grafted through disulfide bonds, and the carbon chain length of the long-chain alkyl functional groups is C8-C16. Through the above formula design, the long-term weather resistance of the silicone sealant can be improved while the mechanical properties of the silicone sealant are maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicone sealant, in particular to a high-performance weather-resistant sealant for buildings and a preparation method thereof. BACKGROUND

[0002] Silicone sealant is widely used in the sealing and bonding of building curtain walls, fabricated buildings, door and window joints, etc. due to its excellent high and low temperature resistance, elasticity and durability. Among them, the dealcoholized silicone sealant with hydroxyl-terminated polydimethylsiloxane (107 base glue) as the base polymer has become one of the mainstream products in the market because of the low toxicity and environmental protection of the alcohol released during the curing process.

[0003] However, the traditional silicone sealant based on 107 base glue still faces severe challenges in terms of performance when exposed to complex outdoor environments for a long time. First, ultraviolet light can directly cause degradation of the polysiloxane main chain, leading to molecular chain breakage and destruction of the crosslinking network, resulting in hardening, powdering and loss of elasticity of the sealant. Second, environmental factors such as humidity and temperature can accelerate the aging process of the material, affecting its long-term use.

[0004] To improve the weather resistance of silicone sealant, the existing technology usually adds conventional hindered amine light stabilizers or ultraviolet absorbers. However, these small molecule additives are prone to migration and volatilization in the silicone system, especially in a hot and humid environment, they will gradually seep out from the inside of the glue, leading to rapid decay of the anti-aging function, making it difficult to meet the requirements of building sealing for decades of service life. The current technical solution is difficult to balance the high elastic recovery rate and long-term weather resistance of the sealant.

[0005] Therefore, how to improve the long-term weather resistance of the sealant while ensuring its good mechanical properties is a technical problem that needs to be solved in the field. SUMMARY

[0006] The present application provides a high-performance weather-resistant sealant for buildings and a preparation method thereof. By introducing a modified cage polysilsesquioxane with long-chain alkyl and disulfide-hindered amine light stabilizer grafted on the surface into 107 base glue, and synergistically acting with amino silane coupling agent, the weathering life of silicone sealant under long-term outdoor ultraviolet light conditions is improved.

[0007] In a first aspect, the application provides a high-performance weather-resistant sealant for buildings, comprising the following raw materials by mass: 100 parts by mass of 107 base glue, 5-10 parts by mass of modified cage polysilsesquioxane, 0.5-2 parts by mass of crosslinking agent, 5-60 parts by mass of nano filler, 1-3 parts by mass of amino silane coupling agent, 0.1-0.5 parts by mass of catalyst, and 1-5 parts by mass of plasticizer; wherein the modified cage polysilsesquioxane comprises cage polysilsesquioxane grafted with long-chain alkyl functional groups and hindered amine light stabilizer grafted using a disulfide bond, the long-chain alkyl functional groups have a carbon chain length of C8-C16, and the preparation method of the modified cage polysilsesquioxane comprises the following steps:

[0008] M1: performing a first thiol-ene click reaction on octavinyl cage polysilsesquioxane and dodecanethiol initiated by a UV light initiator to obtain a partially alkylated POSS intermediate;

[0009] M2: performing a second thiol-ene click reaction on the partially alkylated POSS intermediate and 3-mercaptopropionic acid initiated by a UV light initiator to obtain carboxyl-functionalized POSS;

[0010] M3: performing an amidation reaction on the carboxyl-functionalized POSS and S-acetylcysteine hydrochloride in the presence of a coupling agent, followed by deprotection, to obtain thiol-functionalized POSS;

[0011] M4: performing a thiol-disulfide exchange reaction on the thiol-functionalized POSS and py-S-S-hindered amine light stabilizer to obtain modified cage polysilsesquioxane.

[0012] According to the application, by adding modified cage polysilsesquioxane to 107 base glue, the weather resistance of the silicone sealant under long-term ultraviolet light irradiation can be improved while the mechanical properties of the silicone sealant are maintained.

[0013] Specifically, 107-based glue provides better high and low temperature resistance, aging resistance and flexibility as a polymer matrix in the system, however, the molecular chain of 107-based glue will slowly degrade when exposed to ultraviolet light for a long time, resulting in the gradual loss of material elasticity; the preparation process of the modified cage polysilsesquioxane introduced in the application is based on multi-step controllable click reaction and thioester exchange reaction mechanism. First, octavinyl cage polysilsesquioxane and dodecanethiol undergo thiol-ene click reaction under the condition of ultraviolet light initiation to generate a partially alkylated POSS intermediate. The reaction introduces flexible long-chain alkyl groups into the surface of the cage by forming a C-S bond, thereby improving the compatibility of POSS with the polysiloxane matrix and reducing stress concentration in the system. Subsequently, the partially alkylated POSS and 3-mercaptopropionic acid undergo the same type of click reaction to introduce carboxyl functional groups, forming carboxyl functionalized POSS, and then the carboxyl functionalized POSS is converted into a higher active thiol group by amidation reaction with S-acetylated cystamine and hydroxylamine deprotection to obtain thiol functionalized POSS. Finally, the thiol functionalized POSS and the disulfide bond-containing py-S-S-hindered amine light stabilizer undergo thiol-disulfide exchange reaction to form a hindered amine group connected by a disulfide bond on the surface of the POSS. This structure has both light stabilization and dynamic reversibility, so that the modified POSS can not only capture free radicals and inhibit chain degradation under ultraviolet irradiation, but also release stress through the reversible breaking and recombination of disulfide bonds. Through the above functionalization design, the prepared modified cage polysilsesquioxane can provide good compatibility, long-term weather resistance and elastic recovery performance for silicone sealant. Part of the structure is modified by the above alkyl functional groups with different carbon chain lengths, which improves the compatibility and dispersibility of the cage polysilsesquioxane in the system through the principle of similar solubility. Further, each uniformly dispersed POSS core acts as a rigid three-dimensional crosslinking point, and the multiple long alkyl groups grafted on its surface act as flexible connecting arms to physically entangle with 107-based glue, improving the compactness of the crosslinked network of silicone sealant and enhancing the long-term durability of the material in use. On the one hand, the rigid POSS skeleton acts as a physical barrier to effectively scatter ultraviolet light and reduce material degradation and damage, and on the other hand, the flexible long-chain alkyl groups delay the performance degradation of the material in harsh environments by buffering stress and avoiding the formation of interface microcracks.Another part of the cage-shaped polysilsesquioxane is grafted with a hindered amine light stabilizer through a disulfide bond, which can fix the light stabilizer on the POSS, reduce the migration of the light stabilizer during use, and prolong the anti-ultraviolet aging performance of the silicone sealant. When the sealant is exposed to ultraviolet light, the disulfide bond with lower bond energy in the system may preferentially break to absorb energy, and at the same time, the broken sulfur radicals may recombine to form a disulfide bond again due to their close distance. In addition, when part of the sulfur radicals fail to recombine in time, the hindered amine light stabilizer may combine or interact with the sulfur radicals distributed on the surface of the POSS cage structure through its spatially large nitrogen-oxygen radical or amino site, thereby playing a role in "temporarily capturing" free radicals and stabilizing the system. In this process, the hindered amine light stabilizer is anchored on the POSS interface, thereby improving its stability in the system.

[0014] The disulfide bond can release and absorb stress through a reversible breaking and recombination process during external deformation, reducing irreversible damage to the material caused by stress or large deformation. The amino group in the amino silane coupling agent can reduce the activation energy of the dynamic reaction of the disulfide bond, helping the reversible breaking and recombination of the disulfide bond, and improving the buffering effect of the disulfide bond on stress or large deformation, thereby improving the elastic recovery rate of the silicone sealant. The amino structure also has electron-donating properties, which can optimize the environment for the hindered amine light stabilizer to function, helping to maintain the tertiary amine site in the hindered amine light stabilizer in a deprotonated state, thereby improving the durability and efficiency of the hindered amine light stabilizer in the system.

[0015] Therefore, through the synergistic effect of the modified cage-shaped polysilsesquioxane, the amino silane coupling agent, and the 107-based glue, the sealant can still maintain a high elastic recovery rate under long-term outdoor ultraviolet, ozone, and humid heat environments, improving the weathering life of the material.

[0016] In some embodiments, the amino silane coupling agent includes bis(3-trimethoxysilylpropyl)amine.

[0017] In some of the above embodiments, the inventors found that the mechanical properties and long-term weather resistance of the silicone sealant are better when bis(3-trimethoxysilylpropyl)amine is selected as the aminosilane coupling agent, which can be due to the fact that the bis-trimethoxysilane groups in the bis(3-trimethoxysilylpropyl)amine molecule can act as efficient crosslinking points, and by forming stable Si-O-Si covalent bonds, 107-based glue, nanofillers and modified cage-type polysilsesquioxane can be tightly bonded into a more dense three-dimensional network. This network can store more elastic potential energy when deformed, and after the external force is removed, it can produce a strong retraction force, thereby providing the silicone sealant with a higher elastic recovery rate. The basic environment provided by the secondary amine group can promote the dynamic exchange of disulfide bonds, and under stress, it can accelerate the recombination of disulfide bonds, thereby releasing local stress and avoiding irreversible damage. In addition, the moderate reactivity and higher chemical stability of the secondary amine group effectively avoid the side reactions and yellowing problem under UV light caused by primary amines, providing the system with more persistent catalytic efficiency and appearance stability, while also long-term neutralizing acidic substances, protecting the activity of disulfide bonds and hindered amine light stabilizers, thereby improving the elastic recovery rate and long-term weather resistance.

[0018] In some embodiments, the preparation method of the py-S-S-hindered amine light stabilizer comprises the following steps:

[0019] N1: reacting 4-amino-2,2,6,6-tetramethylpiperidine with N-succinimidyl-S-acetylthioacetate to form a thioacetate-protected intermediate, and deprotecting to obtain HALS-SH;

[0020] N2: HALS-SH and 2,2'-dipyridyl disulfide undergo a disulfide exchange reaction to form a py-S-S-hindered amine light stabilizer.

[0021] In some of the above embodiments, the ultraviolet-resistant hindered amine light stabilizer and the dynamic reversible disulfide bond are combined by a two-step method, providing a chemical connection basis for subsequent combination with POSS.

[0022] In some embodiments, the molar ratio of the octavinyl cage-type polysilsesquioxane to dodecanethiol is 1:4-5.

[0023] In some of the above embodiments, the octavinyl cage-type polysilsesquioxane has 8 reactive vinyl groups. By adding dodecanethiol in the above molar ratio, the number of grafts can be controlled, with 4-5 long-chain alkyl groups grafted on most POSS molecules, leaving 3-4 vinyl groups. These reserved vinyl groups provide active sites for the subsequent thiol-ene click reaction with 3-mercaptopropionic acid, thereby introducing carboxyl groups and creating conditions for subsequent grafting of -S-S-HALS.

[0024] In some embodiments, the molar ratio of the partially alkylated POSS intermediate to 3-mercaptopropionic acid is 1:4-5.

[0025] In some of the above embodiments, after the first click reaction, there are about 3-4 vinyl groups left on average for each POSS intermediate, and by adding 3-mercaptopropionic acid in the above molar ratio, the second click reaction can be driven to the right as much as possible, and as many carboxyl groups as possible can be introduced on each POSS molecule, so that more -S-S-HALS molecules can be grafted as much as possible in the subsequent step.

[0026] In some embodiments, the ultraviolet photoinitiator includes 2,2-dimethoxy-2-phenylacetophenone.

[0027] In some of the above embodiments, the above photoinitiator can be used to initiate a radical addition reaction between a mercapto group and an olefin under ultraviolet light irradiation, thereby driving the formation of a mercapto-olefin click reaction.

[0028] In some embodiments, the method for preparing the modified cage polysilsesquioxane includes the following steps:

[0029] M1: 1 mmol of octavinylcage polysilsesquioxane, 4-5 mmol of dodecanethiol, and 0.05-0.15 mmol of 2,2-dimethoxy-2-phenylacetophenone are mixed in 20-50 mL of tetrahydrofuran, and under a nitrogen atmosphere and ultraviolet light irradiation, the reaction is carried out at 20-30°C for 2-6 hours to obtain a partially alkylated POSS intermediate;

[0030] M2: 1 mmol of the partially alkylated POSS intermediate is mixed with 4-5 mmol of 3-mercaptopropionic acid and 0.05-0.15 mmol of 2,2-dimethoxy-2-phenylacetophenone in 20-50 mL of N,N-dimethylformamide, and under a nitrogen atmosphere and ultraviolet light irradiation, the reaction is carried out at 20-30°C for 3-8 hours to obtain a carboxyl-functionalized POSS;

[0031] M3: 1 mmol of the carboxyl-functionalized POSS is mixed with 4-5 mmol of S-acetylcysteine hydrochloride, 4-5 mmol of EDC-HCl, and 0.10-0.20 mmol of DMAP in 20-30 mL of DMF, and under a nitrogen atmosphere, the reaction is carried out at 20-25°C for 12-18 hours to obtain a thioacetyl-protected intermediate, then 8-12 mmol of hydroxylamine hydrochloride and 8-12 mmol of triethylamine are added to the system, and under a nitrogen atmosphere, the reaction is continued at 20-25°C for 0.5-2 hours to deprotect to obtain a mercapto-functionalized POSS.

[0032] M4: 1 mmol of the thiol-functionalized POSS is mixed with 4-5 mmol of py-S-S-HALS in 20-30 mL of acetonitrile, and the mixture is reacted at 25-35 °C for 1-4 hours under a nitrogen atmosphere to obtain the modified cage polysilsesquioxane.

[0033] In some of the above-mentioned manners, the reaction conditions and the amount ratio of each step in the preparation process of the modified cage polysilsesquioxane are specified. Under the conditions, the cage polysilsesquioxane grafted with long-chain alkyl functional groups and HALS grafted with disulfide bonds can be obtained, and the silicone sealant has better long-term weather resistance.

[0034] In some embodiments, the preparation method of the py-S-S-HALS includes the following steps:

[0035] N1: 1 mmol of 4-amino-2,2,6,6-tetramethylpiperidine is mixed with 1-2 mmol of N-succinimidyl-S-acetylthioacetate in 20-30 mL of N,N-dimethylformamide, and the mixture is reacted at 20-30 °C for 6-12 hours under a nitrogen atmosphere to obtain a thioacetate-protected intermediate. The intermediate is deprotected in 15-25 mL of methanol at 20-30 °C to obtain HALS-SH.

[0036] N2: 1 mmol of HALS-SH is mixed with 1.0-1.5 mmol of 2,2'-dipyridyl disulfide in 20-30 mL of acetonitrile, and the mixture is stirred and reacted at 25-35 °C for 4-8 hours under a nitrogen atmosphere to obtain py-S-S-HALS.

[0037] In some of the above-mentioned manners, the reaction conditions and the amount ratio of each step in the preparation process of the py-S-S-HALS are specified. Under the conditions, the pyridyl disulfide-functionalized HALS can be obtained, which contains both a light stabilizer unit and a highly reactive pyridyl disulfide bond in the molecular structure, providing a reaction basis for subsequent reaction with thiol-functionalized POSS.

[0038] In some embodiments, the 107-based adhesive includes a terminal hydroxyl group-terminated polydimethylsiloxane, and the terminal hydroxyl group-terminated polydimethylsiloxane has a viscosity of 25,000-60,000 mPa·s at 25 °C. Based on the above embodiments, the terminal hydroxyl group-terminated polydimethylsiloxane with a suitable viscosity range can ensure the basic mechanical properties of the silicone sealant while having good processing performance.

[0039] In some embodiments, the nanofiller includes fumed white carbon black, and the fumed white carbon black has a particle size of 10-30 nm. As an example, the fumed white carbon black used in an embodiment of the present application has a particle size of 20 nm.

[0040] In some embodiments, the cross-linking agent comprises a long-chain alkyl trimethoxysilane, and the carbon chain length of the long-chain alkyl trimethoxysilane is C8-C18. As an example, the long-chain alkyl trimethoxysilane used in an embodiment of the present application is dodecyl trimethoxysilane.

[0041] In some embodiments, the catalyst comprises dibutyl tin dilaurate. Based on the above embodiments, the commonly used dibutyl tin dilaurate can promote the condensation reaction of the 107-based adhesive and the cross-linking agent at a lower dosage, and is compatible with the long-chain alkyl component in the system.

[0042] In some embodiments, the plasticizer comprises dimethyl silicone oil, and the viscosity of the dimethyl silicone oil at 25°C is 100-1000 mPa·s. Based on the above embodiments, the dimethyl silicone oil in this viscosity range can effectively adjust the rheological property of the system during the mixing process, and improve the wetting and dispersibility of the filler; during the curing stage, the molecular chain segments thereof can be intercalated between the cross-linking network, thereby reducing the cross-linking density by weakening the interaction force between the polymer chains, forming a flexible intermolecular spacing layer, thereby dispersing stress and reducing local stress concentration, while maintaining the stable cohesive strength of the system, and finally improving the flexibility, elastic recovery ability and long-term durability of the silicone sealant.

[0043] In a second aspect, the present application provides a method for preparing a high-performance weather-resistant sealant for buildings, comprising:

[0044] Providing raw materials for the high-performance weather-resistant sealant for buildings according to any one of the embodiments of the first aspect;

[0045] Mixing the raw materials to obtain the high-performance weather-resistant sealant for buildings.

[0046] According to the present application, the above method can make the modified cage-type polyhedral silsesquioxane as a functional unit be uniformly dispersed in the cross-linking network, thereby improving the anti-ultraviolet aging ability and long-term weather resistance while ensuring the high elastic recovery rate of the sealant.

[0047] 100 parts by mass of 107-based adhesive, 1-3 parts by mass of amino silane coupling agent, 5-60 parts by mass of nano filler, and 5-10 parts by mass of modified cage-type polyhedral silsesquioxane are added to a kneader, and mixed and dehydrated at 100-130°C, a vacuum degree of 0.06-0.1 MPa for 30-360 minutes, and cooled to obtain a base material;

[0048] The silicone sealant is prepared by adding 0.5-2 parts by mass of a crosslinking agent, 0.1-0.5 parts by mass of a catalyst and 1-5 parts by mass of a plasticizer into a strong disperser in sequence, mixing with the above-mentioned base material, and mixing for 30-120 minutes at a vacuum degree of 0.06-0.1 MPa and a rotation speed of 600 rpm.

[0049] In the above embodiment, the mixing and dehydration stage is carried out under heating and vacuum conditions, the amino silane coupling agent preferentially reacts with the silicon hydroxyl on the surface of the nano filler to form a stable interfacial bonding layer, and the modified cage polysilsesquioxane realizes good compatible dispersion with the 107 base glue through the long-chain alkyl on its surface; the vacuum environment effectively removes moisture and volatile small molecules in the system, providing a stable basis for subsequent crosslinking reaction.

[0050] In the mixing and crosslinking stage, the crosslinking agent and the catalyst are uniformly dispersed in the base material under the action of shearing, the addition of the catalyst initiates the initial condensation reaction of the crosslinking agent and the hydroxyl group at the end of the 107 base glue, and a three-dimensional crosslinking network is constructed, and the plasticizer molecules are inserted between the crosslinking network to adjust the modulus and flexibility of the system.

[0051] Through the above two-stage process, a silicone sealant product with good mechanical properties and long-term weather resistance can be obtained.

[0052] Compared with the prior art, the beneficial effects of the present application are at least:

[0053] By synergistically introducing modified cage polysilsesquioxane (POSS) and amino silane coupling agent into the silicone sealant system, the long-chain alkyl functional group in the modified POSS forms good compatibility with the main chain of the base glue, the disulfide bond-hindered amine light stabilizing group on its surface can capture free radicals in ultraviolet and oxidation environment, and the reversible exchange ability of the disulfide bond can effectively dissipate internal stress of the material. Therefore, the silicone sealant prepared by the present application not only has good mechanical properties, but also shows long-term weather resistance, which can meet the use requirements of building and outdoor high-end sealing applications. DETAILED DESCRIPTION

[0054] Each embodiment or implementation in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments.

[0055] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the implementation or example are included in at least one implementation or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same implementation or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more implementations or examples as appropriate.

[0056] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0057] In the present application, the amount of each raw material in the preparation method of various substances is only exemplary, and those skilled in the art can increase or decrease the amount by the same multiple within a reasonable range according to actual needs.

[0058] In the present specification, "parts" refers to "mass parts" unless otherwise specified.

[0059] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only for the purpose of explaining the present application and cannot be understood as limiting the present application. If the specific technology or conditions are not specified in the embodiments, the technology or conditions described in the literature in the art or according to the product manual are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by purchase.

[0060] 107 Base gel, hydroxyl-terminated polydimethylsiloxane with a viscosity of 40000 mPa·s at 25°C;

[0061] Octavinylcage polysilsesquioxane, CAS: 69655-76-1;

[0062] Fumed white carbon, average particle size 20 nm;

[0063] Dimethyl silicone oil, viscosity 200 mPa·s at 25°C;

[0064] 4-amino-2,2,6,6-tetramethylpiperidine, CAS No. 36768-62-4;

[0065] 2,2,6,6-tetramethylpiperidin-4-ol, CAS No. 2403-88-5;

[0066] N-succinimidyl acetylthioacetate, CAS No.: 76931-93-6;

[0067] 2,2'-dipyridyl disulfide, CAS No.: 2127-03-9;

[0068] 2,2-dimethoxy-2-phenylacetophenone, CAS No.: 24650-42-8;

[0069] Dodecyltrimethoxysilane, CAS No.: 3069-21-4;

[0070] S-acetylcysteine hydrochloride, CAS No.: 28798-28-9;

[0071] Preparation of py-S-S-hindered amine light stabilizer:

[0072] N1: 1 mmol of 4-amino-2,2,6,6-tetramethylpiperidine and 1.2 mmol of N-succinimidyl-S-acetylthioacetate were mixed in 20-30 mL of N,N-dimethylformamide under a nitrogen atmosphere at 25°C for 8 hours to obtain a thioacetate-protected intermediate. After the intermediate was concentrated under reduced pressure, 20 mL of methanol and 2.0 mmol of hydroxylamine hydrochloride were added, and sodium bicarbonate was used to adjust the pH to 7.4. The deprotection was carried out under nitrogen protection at 25°C for 1 hour, and column chromatography was used for purification to obtain HALS-SH.

[0073] N2: 1 mmol of HALS-SH and 1.2 mmol of 2,2'-dipyridyl disulfide were mixed in 20-30 mL of anhydrous acetonitrile under a nitrogen atmosphere at 30°C for 6 hours of stirring reaction, and column chromatography was used for purification to obtain py-S-S-hindered amine light stabilizer.

[0074] Preparation Example 1

[0075] Preparation of modified cage polysilsesquioxane:

[0076] M1: 1 mmol of octavinyl cage polysilsesquioxane, 4.5 mmol of dodecanethiol, and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone were mixed in 40 mL of mass parts of tetrahydrofuran under a nitrogen atmosphere and 15 mW / cm 2 After irradiation under light intensity of 365 nm ultraviolet light at 25°C for 4 hours, the reaction solution was concentrated under reduced pressure in a 40°C water bath for 1 hour, washed with methanol three times, and dried to obtain a partially alkylated POSS intermediate;

[0077] M2: 1 mmol of the partially alkylated POSS intermediate was mixed with 4.5 mmol of 3-mercaptopropionic acid and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone in 40 mL of N,N-dimethylformamide under a nitrogen atmosphere and 15 mW / cm2of 365 nm UV light. The reaction was allowed to proceed at 25 °C for 6 hours, washed with diethyl ether three times, and dried to yield the carboxyl-functionalized POSS. 2 The reaction was allowed to proceed at 25 °C for 6 hours under 365 nm UV light irradiation, washed with diethyl ether three times, and dried to yield the carboxyl-functionalized POSS.

[0078] M3: 1 mmol of the carboxyl-functionalized POSS, 4.5 mmol of S-acetylcysteine hydrochloride, 4.5 mmol of EDC-HC1, and 0.15 mmol of DMAP were mixed in 25 mL of DMF, cooled to 25 °C using an ice water bath, and allowed to react at 25 °C for 15 hours under a nitrogen atmosphere to yield a thioacetyl-protected intermediate. Then, 10 mmol of hydroxylamine hydrochloride and 10 mmol of triethylamine were added to the reaction system, and the reaction was allowed to proceed at 25 °C for 1 hour under nitrogen protection to effect deprotection. After the reaction was completed, 200 mL of ice ethyl ether was added to the reaction system, and the mixture was filtered. The solid was washed with ice ethyl ether and dried to yield the mercapto-functionalized POSS.

[0079] M4: 1 mmol of the mercapto-functionalized POSS was mixed with 4.5 mmol of py-S-S-hindered amine light stabilizer in 25 mL of acetonitrile, and the reaction was allowed to proceed at 30 °C for 2 hours under a nitrogen atmosphere. The solid was washed with cold methanol three times to yield the modified cage polysilsesquioxane.

[0080] Comparative Preparation Example 1

[0081] Preparation of the modified cage polysilsesquioxane:

[0082] M1: 1 mmol of octavinyl cage polysilsesquioxane, 9 mmol of dodecanethiol, and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone were mixed in 40 mL of mass fraction tetrahydrofuran under a nitrogen atmosphere and 15 mW / cm2of 365 nm UV light. The reaction was allowed to proceed at 25 °C for 4 hours, and then concentrated under reduced pressure in a 40 °C water bath for 1 hour. The solid was washed with methanol three times and dried to yield the partially alkylated POSS, which was used as the modified cage polysilsesquioxane. 2 The reaction was allowed to proceed at 25 °C for 6 hours under 365 nm UV light irradiation, washed with diethyl ether three times, and dried to yield the carboxyl-functionalized POSS.

[0083] Comparative Preparation Example 2

[0084] Preparation of the modified cage polysilsesquioxane:

[0085] M1: 1 mmol of octavinyl cage polysilsesquioxane, 9 mmol of dodecanethiol, and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone were mixed in 40 mL of mass fraction tetrahydrofuran under a nitrogen atmosphere and 15 mW / cm2of 365 nm UV light. The reaction was allowed to proceed at 25 °C for 4 hours, and then concentrated under reduced pressure in a 40 °C water bath for 1 hour. The solid was washed with methanol three times and dried to yield the partially alkylated POSS, which was used as the modified cage polysilsesquioxane. 2The carboxyl-functionalized POSS was obtained by irradiating the light intensity of 365 nm ultraviolet light at 25°C for 6 hours, washing with ether three times, and drying.

[0086] M2: 1 mmol of the carboxyl-functionalized POSS, 4.5 mmol of S-acetyl cysteine hydrochloride, 4.5 mmol of EDC-HCl, and 0.15 mmol of DMAP were mixed in 25 mL of DMF, cooled to 25°C using an ice water bath, and reacted at 25°C for 15 hours under a nitrogen atmosphere to obtain a thioacetyl-protected intermediate. Then, 10 mmol of hydroxylamine hydrochloride and 10 mmol of triethylamine were added to the reaction system, and the reaction was continued at 25°C for 1 hour under nitrogen protection to deprotect. After the reaction was completed, 200 mL of ice ether was added to filter, the filter solid was washed with ice ether, and dried to obtain the thiol-functionalized POSS.

[0087] M3: 1 mmol of the thiol-functionalized POSS was mixed with 4.5 mmol of py-S-S-hindered amine light stabilizer in 25 mL of acetonitrile, and reacted at 30°C for 2 hours under a nitrogen atmosphere. The solid was washed with cold methanol three times to obtain a cage polysilsesquioxane grafted with a hindered amine light stabilizer through a disulfide bond, as a modified cage polysilsesquioxane.

[0088] Comparative Preparation Example 3

[0089] Preparation of a modified cage polysilsesquioxane:

[0090] M1: 1 mmol of octavinyl cage polysilsesquioxane, 4.5 mmol of dodecanethiol, and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone were mixed in 40 mL of mass fraction of tetrahydrofuran under a nitrogen atmosphere and 15 mW / cm 2 After the reaction was carried out at 25°C for 4 hours under irradiation of light intensity of 365 nm ultraviolet light, the reaction was concentrated under reduced pressure for 1 hour in a 40°C water bath, washed with methanol three times, and dried to obtain a partially alkylated POSS intermediate.

[0091] M2: 1 mmol of the partially alkylated POSS intermediate was mixed with 4.5 mmol of HALS-SH and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone in 40 mL of N,N-dimethylformamide under a nitrogen atmosphere and 15 mW / cm 2 After the reaction was carried out at 30°C for 5 hours under irradiation of light intensity of 365 nm ultraviolet light, the solid was washed with cold methanol three times to obtain a cage polysilsesquioxane grafted with a long-chain alkyl functional group and a hindered amine light stabilizer through a thioether bond, as a modified cage polysilsesquioxane.

[0092] Comparative Preparation Example 4

[0093] M1: 1 mmol of octavinyl-polyhedral oligomeric silsesquioxane, 4.5 mmol of dodecanethiol and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone were mixed in 40 mL of mass fraction of tetrahydrofuran under nitrogen atmosphere and 15 mW / cm 2 After 4 hours of reaction under 365 nm ultraviolet light irradiation at 25°C, the reaction mixture was concentrated under reduced pressure in a 40°C water bath for 1 hour, washed with methanol three times, and dried to obtain a partially alkylated POSS intermediate;

[0094] M2: 1 mmol of the partially alkylated POSS intermediate was mixed with 4.5 mmol of 3-mercaptopropionic acid and 0.1 mmol of 2,2-dimethoxy-2-phenylacetophenone in 40 mL of N,N-dimethylformamide under nitrogen atmosphere and 15 mW / cm 2 After 6 hours of reaction under 365 nm ultraviolet light irradiation at 25°C, the reaction mixture was washed with diethyl ether three times, and dried to obtain a carboxyl-functionalized POSS;

[0095] M3: 1 mmol of the carboxyl-functionalized POSS, 4.5 mmol of 2,2,6,6-tetramethylpiperidin-4-ol, 4.5 mmol of EDC·HCl and 0.15 mmol of DMAP were mixed in 25 mL of dichloromethane under nitrogen atmosphere at 25°C for 18 hours, the solid was precipitated and washed with cold methanol three times, and dried to obtain a cage polysilsesquioxane grafted with long-chain alkyl functional groups and a hindered amine light stabilizer grafted through an ester bond, as a modified cage polysilsesquioxane.

[0096] Example 1

[0097] Preparation of a high-performance weather-resistant sealant for buildings:

[0098] 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of bis(3-trimethoxysilylpropyl)amine, 30 parts by mass of fumed white carbon black and 7 parts by mass of the modified cage polysilsesquioxane obtained in Preparation Example 1 were added to a kneader, and mixed and dehydrated at 120°C under a vacuum degree of 0.08 MPa for 200 minutes to obtain a base material;

[0099] 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate and 3 parts by mass of dimethyl silicone oil were sequentially added to a high-speed disperser, mixed with the above-mentioned dehydrated base material at a vacuum degree of 0.08 MPa and a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0100] Example 2

[0101] Preparation of a high-performance weather-resistant sealant for buildings:

[0102] The same as Example 1, except that the amino silane coupling agent used is γ-aminopropyl triethoxysilane.

[0103] Example 3

[0104] Preparation of weather-resistant sealant for high-performance building:

[0105] The same as Example 1, except that the amino silane coupling agent used is N-β-(aminoethyl)-γ-aminopropyl trimethoxysilane.

[0106] Comparative Example 1

[0107] Preparation of weather-resistant sealant for high-performance building:

[0108] 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of bis(3-trimethoxysilylpropyl)amine, 30 parts by mass of fumed white carbon black, 1.5 parts by mass of 4-amino-2,2,6,6-tetramethylpiperidine, and 5.5 parts by mass of the modified cage polysilsesquioxane obtained in Comparative Preparation Example 1 are added to a kneader, and mixed and dehydrated at 120°C under a vacuum of 0.08 MPa for 200 minutes, and cooled to obtain a base material;

[0109] 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate, and 3 parts by mass of dimethyl silicone oil are sequentially added to a powerful disperser, and mixed with the above-mentioned dehydrated base material under a vacuum of 0.08 MPa at a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0110] Comparative Example 2

[0111] Preparation of weather-resistant sealant for high-performance building:

[0112] 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of bis(3-trimethoxysilylpropyl)amine, 30 parts by mass of fumed white carbon black, and 7 parts by mass of the modified cage polysilsesquioxane obtained in Comparative Preparation Example 2 are added to a kneader, and mixed and dehydrated at 120°C under a vacuum of 0.08 MPa for 200 minutes, and cooled to obtain a base material;

[0113] 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate, and 3 parts by mass of dimethyl silicone oil are sequentially added to a powerful disperser, and mixed with the above-mentioned dehydrated base material under a vacuum of 0.08 MPa at a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0114] Comparative Example 3

[0115] Preparation of weather-resistant sealant for high-performance building:

[0116] Into a kneader, 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of γ-(methacryloyloxy)propyltrimethoxysilane, 30 parts by mass of fumed white carbon black, and 7 parts by mass of the modified cage polysilsesquioxane obtained in Preparation Example 1 were added, and mixed and dehydrated at 120°C under a vacuum of 0.08 MPa for 200 minutes, and then cooled to obtain a base material;

[0117] Into a powerful disperser, 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate, and 3 parts by mass of dimethyl silicone oil were sequentially added, and mixed with the above-mentioned dehydrated base material at a vacuum of 0.08 MPa and a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0118] Comparative Example 4

[0119] Preparation of a high-performance weather-resistant sealant for construction:

[0120] Into a kneader, 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of di(3-trimethoxysilylpropyl)amine, 30 parts by mass of fumed white carbon black, and 7 parts by mass of the modified cage polysilsesquioxane obtained in Comparative Preparation Example 3 were added, and mixed and dehydrated at 120°C under a vacuum of 0.08 MPa for 200 minutes, and then cooled to obtain a base material;

[0121] Into a powerful disperser, 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate, and 3 parts by mass of dimethyl silicone oil were sequentially added, and mixed with the above-mentioned dehydrated base material at a vacuum of 0.08 MPa and a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0122] Comparative Example 5

[0123] Preparation of a high-performance weather-resistant sealant for construction:

[0124] Into a kneader, 100 parts by mass of a hydroxyl-terminated polydimethylsiloxane, 2 parts by mass of di(3-trimethoxysilylpropyl)amine, 30 parts by mass of fumed white carbon black, and 7 parts by mass of the modified cage polysilsesquioxane obtained in Comparative Preparation Example 4 were added, and mixed and dehydrated at 120°C under a vacuum of 0.08 MPa for 200 minutes, and then cooled to obtain a base material;

[0125] Into a powerful disperser, 1 part by mass of dodecyltrimethoxysilane, 0.2 parts by mass of dibutyltin dilaurate, and 3 parts by mass of dimethyl silicone oil were sequentially added, and mixed with the above-mentioned dehydrated base material at a vacuum of 0.08 MPa and a rotation speed of 600 rpm for 90 minutes to obtain a silicone sealant.

[0126] Test Section

[0127] Elastic recovery rate: the high-performance weather-resistant sealant obtained from each example and the comparative example was prepared into samples according to GB / T 13477.17-2017, and the elastic recovery rate Rc was tested;

[0128] Ultraviolet light irradiation elastic recovery rate retention rate: the high-performance weather-resistant sealant obtained from each example and the comparative example was prepared into samples according to GB / T 13477.17-2017, and the samples were placed in an ultraviolet light test box, and irradiated with ultraviolet light at a lamp power of 300 w and an ultraviolet irradiation intensity of 2500 µW / cm 2 for 500 h, the distance between the lamp and the test chamber was 250 mm, the temperature of the sample during irradiation was kept at 45 ℃, then the elastic recovery rate Rz of each sample was tested according to GB / T 13477.17-2017, and the elastic recovery rate retention rate δ (%) = Rz / Rc x 100% was calculated, and the results are shown in Table 1.

[0129] Table 1

[0130]

[0131] According to Table 1, compared with Comparative Examples 1-4, each of the embodiments shows a higher UV light irradiation elastic recovery rate retention rate, indicating that the technical solution provided in the present application can improve the long-term weather resistance of the silicone sealant; the reason may be that in Comparative Example 1, an additional physical mixing hindered amine light stabilizer is used, and under the action of long-term UV light and heat, small molecules will volatilize and migrate out of the polymer matrix in large quantities, the anti-UV function rapidly decays, and the material ages. At the same time, the system completely lacks a dynamic repair mechanism of disulfide bonds, and once the polysiloxane main chain or crosslinking point is broken due to UV radiation, the micro-damage generated in the material cannot be repaired, thereby causing a serious decrease in the elastic recovery rate; in Comparative Example 2, there is a lack of long-alkyl modified POSS, the compatibility of the POSS core and the polysiloxane matrix is poor, and agglomeration easily occurs, becoming a stress concentration point, in the aging process, micro-cracks are easily induced around these rigid agglomerates, accelerating the destruction of the material, thereby causing a decrease in the elastic recovery rate and the elastic recovery rate retention rate; in Comparative Example 3, an amino silane coupling agent is not used, which cannot assist in the dynamic repair of disulfide bonds and the removal of free radicals by hindered amine light stabilization, thereby causing a low elastic recovery rate and elastic recovery rate retention rate; in Comparative Example 4, a hindered amine light stabilizer is grafted through a thioether bond, and under UV light irradiation, the micro-cracks and segment damage generated in the material cannot be repaired by the dynamic bond exchange mechanism, which may cause stress concentration and irreversible damage, and the stress buffering effect of the disulfide bond is lacking, causing the elastic recovery rate of the material to decrease significantly after UV aging; in Comparative Example 5, a hindered amine light stabilizer is grafted through an ester bond, and under UV light irradiation, the ester bond can be degraded and broken, and the HALS molecules cannot be re-fixed after falling off from the POSS, thereby migrating and losing long-term protection effect, and the carboxylic acid produced by the hydrolysis of the ester bond easily forms a local acidic environment, inhibiting the ability of the HALS to capture free radicals, further reducing the weather resistance of the material, and causing a greater decrease in the elastic recovery rate retention rate after UV irradiation.

[0132] According to Examples 1-3, the use of different types of amino silane coupling agents has a certain effect on the elastic recovery rate and the elastic recovery rate retention rate of the silicone sealant. Among them, when di(3-trimethoxysilylpropyl)amine is used as the coupling agent (Example 1), the UV light irradiation elastic recovery rate retention rate is higher than that of γ-aminopropyl triethoxysilane (Example 2) and N-β-(aminoethyl)-γ-aminopropyl trimethoxysilane (Example 3), indicating that the amino silane coupling agent with a secondary amine group and a double trimethoxysilane end group has more advantages in promoting the dynamic exchange of disulfide bonds and constructing a crosslinked network, and is more suitable for long-term UV aging environment.

[0133] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high performance weather resistant sealant for construction, characterized by, The raw materials include the following quality parts: 100 quality parts of 107 base glue, 5-10 quality parts of modified cage polysilsesquioxane, 0.5-2 quality parts of crosslinking agent, 5-60 quality parts of nano filler, 1-3 quality parts of amino silane coupling agent, 0.1-0.5 quality parts of catalyst, 1-5 quality parts of plasticizer; The modified cage polysilsesquioxane is a cage polysilsesquioxane grafted with long-chain alkyl functional groups and hindered amine light stabilizer through disulfide bond; The carbon chain length of the long-chain alkyl functional group is C8-C16; The preparation method of the modified cage polysilsesquioxane includes the following steps: M1: Perform a first mercapto-alkene click reaction on octavinyl cage polysilsesquioxane and dodecanethiol through a UV light initiator to obtain a partially alkylated POSS intermediate; M2: Perform a second mercapto-alkene click reaction on the partially alkylated POSS intermediate and 3-mercaptopropionic acid through a UV light initiator to obtain carboxyl-functionalized POSS; M3: Perform an amidation reaction on the carboxyl-functionalized POSS and S-acetylcysteine hydrochloride under the action of a coupling agent, and then perform a deprotection to obtain mercapto-functionalized POSS; M4: Perform a mercapto-disulfide exchange reaction on the mercapto-functionalized POSS and py-S-S-hindered amine light stabilizer to obtain modified cage polysilsesquioxane.

2. The weather resistant sealant for high performance construction according to claim 1, wherein The amino silane coupling agent includes bis(3-trimethoxysilylpropyl)amine.

3. The weather resistant sealant for high performance construction according to claim 1, wherein The preparation method of the py-S-S-hindered amine light stabilizer includes the following steps: N1: React 4-amino-2,2,6,6-tetramethylpiperidine with N-succinimidyl-S-acetylthioacetate to generate a thioacetate-protected intermediate, and then perform a deprotection to obtain HALS-SH; N2: Perform a disulfide exchange reaction on HALS-SH and 2,2'-dipyridyl disulfide to generate py-S-S-hindered amine light stabilizer.

4. The weather resistant sealant for high performance construction according to claim 1, wherein The modified cage polysilsesquioxane meets at least one of the following conditions: 1) The molar ratio of the octavinyl cage polysilsesquioxane to dodecanethiol is 1:4-5; 2) The molar ratio of the partially alkylated POSS intermediate to 3-mercaptopropionic acid is 1:4-5; 3) The UV light initiator includes 2,2-dimethoxy-2-phenylphenacyl.

5. The weather resistant sealant for high performance construction according to claim 4, wherein The preparation method of the modified cage polysilsesquioxane includes the following steps: M1: Mix 1 mmol of octavinyl cage polysilsesquioxane, 4-5 mmol of dodecanethiol, and 0.05-0.15 mmol of 2,2-dimethoxy-2-phenylphenacyl in 20-50 mL of tetrahydrofuran, and then perform a reaction under the action of nitrogen atmosphere and UV light irradiation at 20-30°C for 2-6 hours to obtain a partially alkylated POSS intermediate; M2: Mix 1 mmol of the partially alkylated POSS intermediate with 4-5 mmol of 3-mercaptopropionic acid and 0.05-0.15 mmol of 2,2-dimethoxy-2-phenylacetophenone in 20-50 mL of N,N-dimethylformamide, and react at 20-30 °C for 3-8 hours under a nitrogen atmosphere and ultraviolet light irradiation to obtain carboxyl-functionalized POSS; M3: 1 mmol of the carboxyl-functionalized POSS was mixed with 4-5 mmol of S-acetylcysteine ​​hydrochloride, 4-5 mmol of EDC·HCl and 0.10-0.20 mmol of DMAP in 20-30 mL of LDM. The mixture was reacted at 20-25 °C for 12-18 hours under a nitrogen atmosphere to obtain a thioacetyl-protected intermediate. Subsequently, 8-12 mmol of hydroxylamine hydrochloride and 8-12 mmol of triethylamine were added to the system. The mixture was then reacted at 20-25 °C for 0.5-2 hours under a nitrogen atmosphere to deprotect the intermediate and obtain the thiol-functionalized POSS. M4: Mix 1 mmol of the thiol-functionalized POSS with 4-5 mmol of py-SS-hindered amine light stabilizer in 20-30 mL of acetonitrile, and react at 25-35 °C for 1-4 hours under a nitrogen atmosphere to obtain modified cage-type polysilsesquioxane.

6. The weather resistant sealant for high performance construction according to claim 3, wherein The preparation method of the py-SS-hindered amine light stabilizer includes the following steps: N1: 1 mmol of 4-amino-2,2,6,6-tetramethylpiperidine and 1-2 mmol of N-succinimide-S-acetylthioacetate were mixed in 20-30 mL of N,N-dimethylformamide and reacted at 20-30 °C for 6-12 hours under a nitrogen atmosphere to obtain a thioacetate-protected intermediate. The intermediate was then deprotected in 15-25 mL of methanol at 20-30 °C to obtain HALS-SH. N2: Mix 1 mmol HALS-SH with 1.0~1.5 mmol 2,2'-dipyridine disulfide in 20~30 mL acetonitrile, and stir the mixture at 25~35 °C for 4~8 hours under a nitrogen atmosphere to obtain py-SS-hindered amine light stabilizer.

7. The weather resistant sealant for high performance construction of claim 1, wherein The raw materials meet at least one of the following conditions: 1) The 107-based adhesive includes hydroxyl-terminated polydimethylsiloxane, wherein the viscosity of the hydroxyl-terminated polydimethylsiloxane at 25°C is 25,000~60,000 mPa·s; 2) The nanofiller includes fumed silica, wherein the particle size of the fumed silica is 10~30nm; 3) The crosslinking agent includes a long-chain alkyltrimethoxysilane, wherein the carbon chain length of the long-chain alkyltrimethoxysilane is C8~C18; 4) The catalyst comprises dibutyltin dilaurate; 5) The plasticizer includes dimethyl silicone oil, which has a viscosity of 100 to 1000 mPa·s at 25°C.

8. A method of preparing a high performance weather resistant sealant for construction, characterized by, include: Provide the raw materials for the high-performance weather-resistant sealant for building use according to any one of claims 1 to 7; The raw materials are mixed to obtain a high-performance weather-resistant sealant for building applications.

9. The method of claim 8, wherein, include: 100 parts by mass of 107 base glue, 1-3 parts by mass of amino silane coupling agent, 5-60 parts by mass of nano filler and 5-10 parts by mass of modified cage polysilsesquioxane are added into a kneader, and mixed and dehydrated at 100-130 DEG C, vacuum degree 0.06-0.1 MPa for 30-360 minutes, and cooled to obtain a base; 0.5-2 parts by mass of crosslinking agent, 0.1-0.5 parts by mass of catalyst and 1-5 parts by mass of plasticizer are added into a strong disperser in sequence, mixed with the above base at vacuum degree 0.06-0.1 MPa and rotation speed 600 rpm for 30-120 minutes to obtain a silicone sealant.

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