High-temperature-resistant room-temperature curing silicone rubber and preparation method thereof

Abstract

The invention discloses a high-temperature resistant room-temperature curing silicone rubber and a preparation method thereof, relating to the technical field of silicone rubber, wherein the present invention is first prepared by reacting ferrocene with butyl lithium and tetramethylethylenediamine under nitrogen protection to form a multi-lithiated ferrocene lithium salt; hexamethylcyclotrisiloxane and 12-4 crown ether are subsequently added to react; a polymer containing silicon chlorine end groups is then extracted with toluene; finally, a final ferrocenesilazane cross-linking agent is obtained by reacting with ammonia gas, and after mixing with hydroxyl-terminated polydimethylsiloxane and white carbon black, the cross-linking agent is cured at room temperature to form silicone rubber. The room-temperature vulcanized silicone rubber cross-linking agent of the present invention significantly improves the thermal stability and antioxidant properties of silicone rubber by introducing ferrocene and silicon-nitrogen bonds. This novel cross-linking agent optimizes the high-temperature resistance of silicone rubber and allows it to be used in air without the need for an added antioxidant, thereby broadening its scope of application and extending its service life.

Description

Technical Field

[0001] The present invention relates to the technical field of silicone rubber, and in particular to a high-temperature resistant room-temperature curing silicone rubber and a preparation method thereof. Background Art

[0002] Due to its excellent high-temperature resistance, silicone rubber has become the material of choice for many high-temperature applications, especially in the fields of electronics, construction, and mold manufacturing. In particular, two-component room-temperature vulcanized silicone rubber (RTV-2) is widely used due to its easy operation and moderate curing speed. This type of silicone rubber usually relies on the participation of catalysts and trace amounts of water to undergo cross-linking and vulcanization to form the final elastomeric structure. In recent years, with the development of materials science, the introduction of new chemical bond structures, such as silicon-nitrogen bonds, through molecular design to improve the stability and service life of materials under extreme conditions has become a research hotspot.

[0003] Despite the numerous advantages of two-component room-temperature vulcanized silicone rubber (RTV) rubber, it still faces significant limitations in high-temperature applications. First, after conventional silicone rubber is vulcanized in the presence of a catalyst and moisture, residual crosslinking agent and its byproducts accelerate thermal degradation of the silicone rubber backbone at high temperatures. Furthermore, uncrosslinked hydroxyl groups in the silicone rubber and the adsorbed moisture they retain can cause structural instability at high temperatures, compromising the material's overall thermal stability. While the introduction of Si-N bonds can partially eliminate hydroxyl groups in the silicone rubber system and reduce thermal degradation, this strategy faces significant challenges in air-based applications. Due to the presence of oxygen, silicone rubber is susceptible to thermal oxidative crosslinking, which degrades its performance. Existing solutions include the addition of antioxidants, but these additives are often unstable and lack the ability to withstand long-term oxidative stress at high temperatures. Furthermore, while the introduction of ferrocene can enhance antioxidant properties, its role in the Si-N structure and its optimal ratio remain understudied, and existing technologies have failed to effectively address these high-temperature thermal stability issues.

[0004] Against this backdrop, the main objective of the present invention is to develop a novel heat-resistant, room-temperature vulcanized silicone rubber crosslinker that exhibits excellent high-temperature resistance in air without relying on the addition of antioxidants. Specifically, the present invention aims to address the thermal stability issues of silicone rubber in high-temperature applications by employing an innovative crosslinking strategy to significantly enhance the performance and stability of the material in sustained high-temperature, oxidative environments. Furthermore, this novel crosslinker will allow silicone rubber to replace current materials in a wider range of industrial applications, particularly in applications requiring extremely high heat resistance. By addressing this technical challenge, the present invention will propel silicone rubber technology forward and meet the demands of a wider range of high-performance applications. Summary of the Invention

[0005] In order to achieve the above-mentioned purpose of the invention and to solve the above-mentioned technical problems, the present invention provides a ferrocenylsilazane (FSCA) crosslinking agent, the specific scheme of which is as follows:

[0006] The cross-linking agent is prepared by the following steps:

[0007] A1: Under nitrogen protection, ferrocene and n-hexane are mixed and stirred until completely dissolved. A n-hexane solution of butyl lithium and tetramethylethylenediamine are added to the above solution. The reaction mixture is heated to n-hexane reflux and continuously stirred for reaction. The upper layer of the solution is then filtered and removed. The precipitate is washed three times with n-hexane and recrystallized from tetrahydrofuran to obtain a polylithiated lithium ferrocene salt.

[0008] A2: The lithium ferrocenium salt obtained in step A1 is completely dissolved in tetrahydrofuran under nitrogen protection, hexamethylcyclotrisiloxane and 1,2-4 crown ether are added to the solution, and the reaction is carried out at room temperature. The reaction solution is then added dropwise to tetrahydrofuran containing dimethyldichlorosilane and stirred at room temperature;

[0009] A3 removes unreacted dimethyldichlorosilane and solvent under vacuum conditions, and extracts the reaction product with toluene to obtain a polymer containing silicon-chloride end groups;

[0010] A4: Ammonia gas is introduced into the toluene solution obtained in step A3 at room temperature until no obvious ammonia absorption is observed, and then the temperature is increased and the ammonia gas is continued to be introduced to obtain a ferrocenylsilazane crosslinking agent.

[0011] Preferably, the molar ratio of ferrocene to butyllithium is 1:5-1:15.

[0012] Preferably, the cross-linking agent corresponding to each 1.86 g of ferrocene is prepared by:

[0013] B1: Under nitrogen, 1.86 g, 0.01 mol of ferrocene and 20 ml of n-hexane were mixed and stirred until completely dissolved. To the above solution were added 62.5 ml of a n-hexane solution containing 0.1 mol of butyl lithium and 11.2 ml of tetramethylethylenediamine. The reaction mixture was heated to n-hexane reflux and stirred for 10 hours. The upper layer of the solution was then filtered and removed. The precipitate was washed with 40 ml of n-hexane and recrystallized from tetrahydrofuran to obtain 1.4 g of polylithiated ferrocene lithium salt.

[0014] B2: The lithium ferrocenium salt obtained in step B1 was added to 120 ml of tetrahydrofuran under nitrogen protection to completely dissolve it, 23 g of hexamethylcyclotrisiloxane and 0.2 ml of 1,2-4 crown ether were added to the solution, and the reaction was carried out at room temperature for 1 hour. The reaction solution was then added dropwise to 50 ml of tetrahydrofuran containing 18 g of dimethyldichlorosilane for 1 hour, and stirred at room temperature for 12 hours;

[0015] B3: removing unreacted dimethyldichlorosilane and solvent under vacuum conditions, extracting the reaction product with toluene to obtain a polymer containing silicon-chloride end groups;

[0016] B4: The polymer containing silicon-chloride end groups obtained in step 3 is added to toluene at a concentration of 30%, and then ammonia gas is introduced at room temperature until no obvious ammonia absorption is observed. The temperature is then raised to 80°C and ammonia gas is continued to be introduced for 2 hours to obtain a ferrocenylsilazane crosslinker.

[0017] The present invention also provides a method for preparing high-temperature resistant room-temperature curing silicone rubber, comprising the following steps:

[0018] S1: 100 phr of hydroxyl-terminated polydimethylsiloxane (PDMS) and 20 phr of white carbon black were mixed evenly on a mixer;

[0019] S2: add 5-20 phr of ferrocenylsilazane crosslinker to the mixture in step S1 and mix well, then add 0.2 phr of dibutyltin dilaurate and stir at room temperature until the mixture is well mixed;

[0020] S3: pouring the mixture of step S2 into a mold, removing bubbles under vacuum, and then curing at room temperature to obtain high temperature resistant room temperature curing silicone rubber.

[0021] Preferably, the ferrocenylsilazane crosslinking agent is prepared by the above preparation method.

[0022] Preferably, the mixer is a three-roll mixer.

[0023] Preferably, the curing time in step S3 is 7-10 days.

[0024] The present invention also provides a high-temperature resistant room-temperature curing silicone rubber, which is prepared from the following raw materials in parts by mass: 100 phr hydroxyl-terminated polydimethylsiloxane (PDMS), 20 phr white carbon black, 0.2 phr dibutyltin dilaurate, and 1-20 phr ferrocenesilazane crosslinking agent (FSCA).

[0025] Preferably, the silicone rubber is prepared by the above preparation method.

[0026] Preferably, the ferrocenylsilazane crosslinking agent is prepared by the above preparation method.

[0027] The technical solution provided by the present invention brings beneficial effects:

[0028] The room temperature vulcanized silicone rubber crosslinker of the present invention primarily addresses the stability issues of silicone rubber under high temperature conditions. In particular, by introducing ferrocene and a silanol-nitrogen bond structure, it significantly improves the performance of silicone rubber at extreme temperatures. In traditional silicone rubber systems, the main chain rapidly breaks due to thermal degradation at high temperatures, especially in the presence of uncrosslinked hydroxyl groups and adsorbed water. These factors together lead to a decline in material performance. The silanol-nitrogen bond employed in the present invention effectively eliminates silanol groups in the system, reducing main chain breakage caused by thermal degradation and thereby improving the thermal stability of the silicone rubber.

[0029] The introduction of silicon-nitrogen bonds improves the stability of silicone rubber at high temperatures. In existing silicone rubber systems, silanol groups are prone to breaking or engaging in undesirable side reactions at high temperatures, but the presence of silicon-nitrogen bonds effectively prevents this process. This structural improvement allows silicone rubber to maintain its mechanical properties and chemical stability even in continuously high-temperature environments, extending the material's service life.

[0030] The introduction of ferrocene further enhances the antioxidant capacity of silicone rubber. Conventional silicone rubber is susceptible to oxidation in high-temperature environments and the presence of oxygen, leading to a rapid degradation of its physical properties. Ferrocene, due to its unique chemical structure, effectively captures free radicals and slows the oxidation process, thereby improving the high-temperature oxidation stability of silicone rubber without the addition of additional antioxidants.

[0031] This invention, through the synthesis of a room-temperature vulcanized silicone rubber crosslinker with ferrocene as the core and silicon-nitrogen bonds as crosslinking groups, enables the use of silicone rubber in an air atmosphere. While conventional silicone rubber requires additional antioxidants to maintain performance when used in air, the crosslinker of this invention achieves the same effect through its inherent chemical structure. This not only reduces the complexity of material preparation but also improves the material's economic benefits and environmental adaptability in practical applications.

[0032] In summary, the room-temperature vulcanized silicone rubber crosslinker of the present invention significantly improves the performance and stability of silicone rubber in high-temperature and oxidative environments. These technical benefits directly address the prior art issue of silicone rubber's performance degradation in high-temperature environments. Through these technical improvements, the present invention has significant practical and theoretical significance in expanding the application range and service life of silicone rubber. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The effect of FSCA content on the isothermal weight loss of vulcanized rubber in the present invention;

[0034] Figure 2 The effect of FSCA content on the tensile strength of the vulcanized rubber after aging.

[0035] Figure 3This is a photo of ferrocenylsilazane crosslinker. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example 1

[0038] The present invention provides a ferrocenylsilazane (FSCA) crosslinking agent, the specific scheme is as follows:

[0039] The cross-linking agent is prepared by the following steps:

[0040] B1: Under nitrogen, 1.86 g, 0.01 mol of ferrocene and 20 ml of n-hexane were mixed and stirred until completely dissolved. To the above solution were added 62.5 ml of a n-hexane solution containing 0.1 mol of butyl lithium and 11.2 ml of tetramethylethylenediamine. The reaction mixture was heated to n-hexane reflux and stirred for 10 hours. The upper layer of the solution was then filtered and removed. The precipitate was washed with 40 ml of n-hexane and recrystallized from tetrahydrofuran to obtain 1.4 g of polylithiated ferrocene lithium salt.

[0041] B2: The lithium ferrocenium salt obtained in step B1 was added to 120 ml of tetrahydrofuran under nitrogen protection to completely dissolve it, 23 g of hexamethylcyclotrisiloxane and 0.2 ml of 1,2-4 crown ether were added to the solution, and the reaction was carried out at room temperature for 1 hour. The reaction solution was then added dropwise to 50 ml of tetrahydrofuran containing 18 g of dimethyldichlorosilane for 1 hour, and stirred at room temperature for 12 hours;

[0042] B3: removing unreacted dimethyldichlorosilane and solvent under vacuum conditions, extracting the reaction product with toluene to obtain a polymer containing silicon-chloride end groups;

[0043] B4: The polymer containing silicon-chloride end groups obtained in step 3 is added to toluene at a concentration of 30%, and then ammonia gas is introduced at room temperature until no obvious ammonia absorption is observed. The temperature is then raised to 80°C and ammonia gas is continued to be introduced for 2 hours to obtain a ferrocenylsilazane crosslinker.

[0044] A method for preparing high-temperature resistant room-temperature curing silicone rubber comprises the following steps:

[0045] S1: 100 phr of hydroxyl-terminated polydimethylsiloxane (PDMS) and 20 phr of fumed silica were mixed uniformly on a three-roll mixer;

[0046] S2: add 10 phr of ferrocenylsilazane crosslinker to the mixture in step S1 and mix well, then add 0.2 phr of dibutyltin dilaurate and stir at room temperature until the mixture is well mixed;

[0047] S3: pouring the mixture of step S2 into a mold, removing bubbles under vacuum, and then curing at room temperature for 7 days to obtain high temperature resistant room temperature curing silicone rubber.

[0048] Example 2

[0049] The preparation was carried out in the same manner as in Example 1, except that the molar ratio of ferrocene to butyl lithium was 1:5.

[0050] Example 3

[0051] The preparation was carried out in the same manner as in Example 1, except that the molar ratio of ferrocene to butyl lithium was 1:15.

[0052] Example 4

[0053] The preparation was carried out according to the same preparation method as in Example 1, except that, in step S2, 5 phr of ferrocenylsilazane crosslinking agent was added.

[0054] Example 5

[0055] The preparation was carried out according to the same preparation method as in Example 1, except that, in step S2, 15 phr of ferrocenylsilazane crosslinking agent was added.

[0056] Example 6

[0057] The preparation method is the same as that in Example 1, except that in step S3, the curing time is 10 days.

[0058] Comparative Example 1

[0059] The preparation method is the same as that of Example 1, except that the ferrocenylsilazane crosslinking agent is replaced by tetraethyl orthosilicate crosslinking agent.

[0060] Experimental test:

[0061] 1. Mechanical properties: The prepared vulcanized rubber samples were cut into dumbbell-shaped strips according to the national standard GB528-98. The room temperature tensile test was performed on an Instron 5565 universal electronic material testing machine with a length between the clamps of 10 mm and a tensile rate of 200 mm / min.

[0062] 2. Isothermal thermal weight loss: Place the silicone rubber in a hot air circulation aging chamber for thermal oxygen aging at 300°C for 24 hours. The ratio of the sample's weight loss to its initial weight is the isothermal thermal weight loss.

[0063] 3. Hot air aging:

[0064] The aging temperature was 300°C and the atmosphere was air.

[0065] Table 1 Mechanical properties test data

[0066]

[0067] As shown in the table, the tensile strength and elongation at break of silicone rubber prepared using ferrocenylsilazane as a crosslinker are higher than those of silicone rubber prepared using ethyl orthosilicate as a crosslinker. After aging at 300°C for 24 hours, the silicone rubber crosslinked with ethyl orthosilicate has lost its physical and mechanical properties and cannot be tested. However, the silicone rubber crosslinked with ferrocenylsilazane maintains good tensile strength after vulcanization. After aging at 300°C for 24 hours, the silicone rubber crosslinked with ferrocenylsilazane exhibits less weight loss than the silicone rubber crosslinked with ethyl orthosilicate.

[0068] When the amount of FSCA is less than 5phr, the vulcanized rubber cannot be fully vulcanized, and the amount of FSCA should be greater than 5phr.

[0069] Isothermal weight loss performance is a key indicator of silicone rubber's thermal and oxidative stability. Residual silanol groups in silicone rubber can cause degradation at high temperatures, resulting in weight loss. Furthermore, oxidation of silicone rubber and the resulting silanol groups can also contribute to thermal weight loss. Si-nitrogen bonds can eliminate silanol groups in the system, while ferrocene groups inhibit the thermal oxidation of methyl groups. Figure 1 The weight loss of vulcanized rubber with FSCA dosage of 10 and 15 phr and that with crosslinker ethyl orthosilicate dosage of 10 phr at different times was compared. Figure 1 The isothermal thermal weight loss curves of the vulcanized rubber are compared in an air atmosphere at 300°C. As can be seen from the figure, with the increase of aging time, the thermal weight loss of the vulcanized rubber gradually increases, but the slope of the thermal aging curve gradually decreases, indicating that the rate of thermal weight loss gradually decreases. The thermal weight loss of the vulcanized rubber cross-linked with FSCA is lower than that of the vulcanized rubber cross-linked with tetraethyl orthosilicate. The weight loss changes of the vulcanized rubber with FSCA dosages of 10 and 15 phr are basically the same. After aging for 24 hours, the weight loss of the vulcanized rubber cross-linked with 10 phr silazane is 12%, while the weight loss of the vulcanized rubber cross-linked with the same amount of TEOS is 15%.

[0070] Figure 2The figure shows the effect of aging time on the tensile strength of vulcanized rubber. As can be seen from the figure, at the same aging time, the tensile strength of the vulcanized rubber with a FSCA of 10 phr is greater than that of the vulcanized rubber with a FSCA of 15 phr. After aging for 24 hours, the tensile strength of the former is 2.4 MPa, while that of the latter is 1.4 MPa. With increasing aging time, the tensile strength of the vulcanized rubber first decreases, then remains essentially unchanged. The initial decrease in tensile strength during aging is due to the depolymerization of the molecular chains, which is consistent with the high initial rate of thermal weight loss. As time increases, the tensile strength remains stable. However, the silicone rubber incorporating only TEOS suffers from severe oxidation after 24 hours at 300°C, making it impossible to test its mechanical properties.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A ferrocenylsilazane crosslinking agent, characterized in that The cross-linking agent is prepared by the following steps: A1: Under nitrogen, ferrocene and n-hexane are mixed and stirred until completely dissolved. A n-hexane solution of butyllithium and tetramethylethylenediamine are added to the above solution. The reaction mixture is heated to n-hexane reflux and continuously stirred for reaction. The upper layer of the solution is then filtered and removed. The precipitate is washed with n-hexane and recrystallized from tetrahydrofuran to obtain a polylithiated lithium ferrocene salt. A2: The lithium ferrocenium salt obtained in step A1 is completely dissolved in tetrahydrofuran under nitrogen protection, hexamethylcyclotrisiloxane and 1,2-4 crown ether are added to the solution, and the reaction is carried out at room temperature. The reaction solution is then added dropwise to tetrahydrofuran containing dimethyldichlorosilane and stirred at room temperature; A3 removes unreacted dimethyldichlorosilane and solvent under vacuum conditions, and extracts the reaction product with toluene to obtain a polymer containing silicon-chloride end groups; A4: Ammonia gas is introduced into the toluene solution obtained in step A3 at room temperature until no obvious ammonia absorption is observed, and then the temperature is increased and the ammonia gas is continued to be introduced to obtain a ferrocenylsilazane crosslinking agent.

2. The ferrocenylsilazane crosslinking agent according to claim 1, characterized in that The molar ratio of ferrocene to butyl lithium is 1:5-1:

15.

3. The ferrocenylsilazane crosslinking agent according to claim 2, characterized in that The preparation method of the cross-linking agent corresponding to each 1.86g of ferrocene is: B1 Under nitrogen, 1.86 g, 0.01 mol of ferrocene and 20 ml of n-hexane were mixed and stirred until completely dissolved. To the above solution were added 62.5 ml of a n-hexane solution containing 0.1 mol of butyl lithium and 11.2 ml of tetramethylethylenediamine. The reaction mixture was heated to n-hexane reflux and stirred for 10 hours. The upper layer of the solution was then filtered and removed. The precipitate was washed with 40 ml of n-hexane and recrystallized from tetrahydrofuran to obtain 1.4 g of polylithiated lithium ferrocene. B2: The lithium ferrocenium salt obtained in step B1 was added to 120 ml of tetrahydrofuran under nitrogen protection to completely dissolve it, 23 g of hexamethylcyclotrisiloxane and 0.2 ml of 1,2-4 crown ether were added to the solution, and the reaction was carried out at room temperature for 1 hour. The reaction solution was then added dropwise to 50 ml of tetrahydrofuran containing 18 g of dimethyldichlorosilane for 1 hour, and stirred at room temperature for 12 hours; B3: removing unreacted dimethyldichlorosilane and solvent under vacuum conditions, extracting the reaction product with toluene to obtain a polymer containing silicon-chloride end groups; B4: The polymer containing silicon-chloride end groups obtained in step 3 is added to toluene at a concentration of 30%, and then ammonia is introduced at room temperature until no obvious ammonia absorption is observed. The temperature is then raised to 80°C and ammonia is continued to be introduced for 2 hours to obtain a ferrocenylsilazane crosslinker.

4. A method for preparing high temperature resistant room temperature curing silicone rubber, characterized in that: The following steps are involved: S1: 100 phr of hydroxyl-terminated polydimethylsiloxane and 20 phr of white carbon black were mixed evenly on a mixer; S2: adding 5-20 phr of ferrocenylsilazane crosslinking agent to the mixture of step S1 and mixing evenly, then adding 0.2 phr of dibutyltin dilaurate and stirring at room temperature until the mixture is evenly mixed, wherein the ferrocenylsilazane crosslinking agent is prepared by the preparation method of claim 1; S3: pouring the mixture of step S2 into a mold, removing bubbles under vacuum, and then curing at room temperature to obtain high temperature resistant room temperature curing silicone rubber.

5. The preparation method according to claim 4, characterized in that: The mixing mill is a three-roll mixing mill.

6. The preparation method according to claim 4, characterized in that: The curing time in step S3 is 7-10 days.

7. A high temperature resistant room temperature curing silicone rubber, characterized in that: The silicone rubber is prepared from the following raw materials in parts by mass: 100 phr hydroxyl-terminated polydimethylsiloxane, 20 phr white carbon black, 0.2 phr dibutyltin dilaurate, and 1-20 phr ferrocenylsilazane crosslinker, wherein the ferrocenylsilazane crosslinker is prepared by the preparation method according to claim 1.

8. The high temperature resistant room temperature curing silicone rubber according to claim 7, characterized in that: The silicone rubber is prepared by the preparation method according to claim 4.

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