Polylipoic acid-based silane coupling agent and application thereof in preparation of rubber composite material

Abstract

The invention provides a polylipoic acid-based silane coupling agent and application thereof in preparation of a rubber composite material, the structural formula of the polylipoic acid-based silane coupling agent is # imgabs0, and the high-density silane coupling agent of a side chain can be covalently coupled with multiple sites of an inorganic filler in rubber blending and vulcanization processes, so that a rubber main chain is bridged, and the organic-inorganic interface interaction is remarkably enhanced. Meanwhile, the rubber composite material interpenetrates and entangles with a rubber molecular chain to form a physical cross-linked network, so that the mechanical strength of the rubber composite material is improved. A disulfide bond on a main chain has a dynamic covalent characteristic, can be fractured to dissipate energy and improve toughness under the action of external force, and can be recombined under a mild condition to endow the material with self-repairing capability. Besides, migration and diffusion of the inorganic filler in a rubber matrix are effectively avoided through multi-site covalent coupling and an enveloping effect, so that the material has excellent stability and long-term durability, and the service life is remarkably prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of silane coupling agents, and in particular relates to a polylipoic acid-based silane coupling agent and application thereof in preparing a rubber composite material. Background Art

[0002] With the advancement of modernization and the popularization of green environmental protection concepts, it is particularly important to develop rubber composite materials with excellent comprehensive performance and long-lasting durability. In industrial production, nano inorganic fillers (such as carbon black, white carbon black, clay, etc.) are compounded with rubber to enhance material properties. However, due to the thermodynamic incompatibility between inorganic fillers and organic rubber matrix, simple physical mixing is difficult to make inorganic fillers uniformly dispersed in the rubber matrix. This causes the inorganic fillers to easily agglomerate, and then form defects and stress concentration points inside the rubber composite material, so that the reinforcement effect is not obvious.

[0003] Silane coupling agent is a kind of organosilicon compound with a special structure, and its general structural formula is RSiX3. Among them, R is an active group such as amino, thiol, vinyl, epoxy, etc., which can produce strong reactivity with the polymer matrix; X is usually an alkoxy or acyloxy group that can undergo hydrolysis. When the silane coupling agent is added to the polymer composite system, it can not only undergo condensation reaction with the hydroxyl group in the inorganic substance, but also produce physical or chemical interaction with the polymer chain, thereby playing the role of bridging the organic and inorganic components, and significantly improving the comprehensive performance of the polymer composite material. Based on this, a large number of studies have reported the application of small molecule silane coupling agents in rubber composites, and have achieved significant practical applications and economic value.

[0004] However, the rapid development of modern industry has put forward higher requirements on the performance of rubber composite materials. The core issue is to further enhance the organic-inorganic interface interaction between rubber and inorganic fillers, so as to give full play to the functional properties of inorganic reinforcing fillers. Therefore, it is necessary to enhance the bridging force of existing small molecule silane coupling agents and enrich the types of interactions between them and polymer matrices. This will help to further enhance the mechanical properties and stability of rubber composite materials to meet higher demands in production and life. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a polylipoic acid-based silane coupling agent.

[0006] Another object of the present invention is to provide the use of the polylipoic acid-based silane coupling agent in the preparation of rubber composite materials.

[0007] The technical solution of the present invention is as follows:

[0008] A polylipoic acid-based silane coupling agent, the structural formula of which is Among them, R is selected from n1=5-2000,n2=2-5.

[0009] In a preferred embodiment of the present invention, its structural formula is n=5-2000.

[0010] The polylipoic acid-based silane coupling agent is prepared by ring-opening polymerization of a silane coupling agent having terminal groups of -NH2, -SH, -OH or epoxy groups and lipoic acid to obtain a silane coupling agent polymerization monomer containing a dithiolane ring.

[0011] Application of the polylipoic acid-based silane coupling agent in the preparation of rubber composite materials.

[0012] In a preferred embodiment of the present invention, the rubber composite material is prepared by uniformly mixing a base rubber, the polylipoic acid-based silane coupling agent, an inorganic filler, zinc oxide, stearic acid, a vulcanizing agent, an accelerator, an antioxidant and paraffin, followed by vulcanization and hot pressing; the surface of the inorganic filler contains active hydrogen sites (preferably hydroxyl groups) that can undergo a condensation reaction with the polylipoic acid-based silane coupling agent.

[0013] Further preferably, the base rubber is selected from natural rubber, styrene-butadiene rubber, butadiene rubber and chloroprene rubber, and the inorganic filler is selected from white carbon black, metal organic framework (MOF), two-dimensional transition metal carbide (MXene), silicate, inorganic metal oxide and hydroxide.

[0014] More preferably, the mass ratio of the base rubber, polylipoic acid-based silane coupling agent, inorganic filler, zinc oxide, stearic acid, vulcanizing agent, accelerator, antioxidant and paraffin is 60-100:1-30:10-80:2-4:1-3:1-4:1-4:1-3:1-3.

[0015] A rubber composite material, characterized in that its raw materials include the above-mentioned polylipoic acid-based silane coupling agent.

[0016] In a preferred embodiment of the present invention, it is prepared by uniformly mixing a base rubber, the polylipoic acid-based silane coupling agent, an inorganic filler, zinc oxide, stearic acid, a vulcanizing agent, an accelerator, an antioxidant and paraffin wax, followed by vulcanization and hot pressing; the surface of the inorganic filler contains active hydrogen sites (preferably hydroxyl groups) that can undergo a condensation reaction with the polylipoic acid-based silane coupling agent.

[0017] Further preferably, the base rubber is selected from natural rubber, styrene-butadiene rubber, butadiene rubber and chloroprene rubber, and the inorganic filler is selected from white carbon black, metal organic framework (MOF), two-dimensional transition metal carbide (MXene), silicate, inorganic metal oxide and hydroxide.

[0018] More preferably, the mass ratio of the base rubber, polylipoic acid-based silane coupling agent, inorganic filler, zinc oxide, stearic acid, vulcanizing agent, accelerator, antioxidant and paraffin is 60-100:1-30:10-80:2-4:1-3:1-4:1-4:1-3:1-3

[0019] The beneficial effects of the present invention are:

[0020] 1. The polythioic acid-based silane coupling agent of the present invention is prepared by ring-opening polymerization of silane coupling agent containing thioctic acid. Due to the high activity of dithiolane, the polymerization reaction conditions are warm and simple to operate. In the rubber blending and vulcanization process, the high-density silane coupling agent grafted on the side chain of the polythioic acid-based silane coupling agent can covalently couple inorganic fillers through multiple sites and bridge the rubber main chain. Compared with small molecule silane coupling agents, this multi-site synergistic coupling effect significantly enhances the organic-inorganic interface interaction. In addition, during processing, interpenetration and entanglement occur between the polythioic acid-based silane coupling agent and the rubber molecular chain, forming a rich physical cross-linking network, thereby significantly increasing the mechanical strength of the rubber composite material.

[0021] 2. The disulfide bonds on the main chain of the polythioic acid-based silane coupling agent of the present invention have dynamic covalent chemical properties. Under the action of external force, the disulfide bonds can break, release energy and play a dissipative role, thereby improving the toughness of the rubber composite material. At the same time, these disulfide bonds can be reorganized under mild conditions, giving the material good self-repairing ability. By adjusting the molecular weight, molecular weight distribution and blending ratio of the polythioic acid-based silane coupling agent with rubber, the wide spectrum of comprehensive performance of the rubber composite material can be achieved to meet the needs of different application scenarios.

[0022] 3. Customized and functionalized rubber composite materials can be prepared according to the inherent properties of inorganic fillers. The multi-site covalent coupling of the polylipoic acid-based silane coupling agent of the present invention and the enveloping effect on the inorganic filler effectively prevent the migration and diffusion of the inorganic filler in the rubber matrix during long-term storage or use. Therefore, this rubber composite material not only has excellent stability, but also has long-term durability, which can significantly extend the service life of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1These are optical photographs of the lipoic acid-containing silane coupling agent polymerization monomer LMTES and the polylipoic acid-based silane coupling agent p (LMTES) prepared in Example 1 of the present invention.

[0024] Figure 2 This is the infrared spectrum of the polylipoic acid-based silane coupling agent p (LMTES) prepared in Example 1 of the present invention.

[0025] Figure 3 This is the infrared spectrum of the polylipoic acid-based silane coupling agent p(LATES) prepared in Example 2 of the present invention.

[0026] Figure 4 The UV-visible absorption spectra of the lipoic acid-containing silane coupling agent polymerized monomer LMTES and the polylipoic acid-based silane coupling agent p (LMTES) prepared in Example 1 of the present invention are shown.

[0027] Figure 5 The vulcanization curves of the rubber composite materials prepared in Examples 1 and 2 of the present invention are shown.

[0028] Figure 6 This is an optical photograph of the rubber composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further illustrated and described below through specific implementation modes in combination with the accompanying drawings.

[0030] Example 1

[0031] (1) The synthetic route of thioctic acid-containing silane coupling agent S-(3-(triethoxysilyl)propyl)5-(1,2-dithiocyclopent-3-yl)thiopentanoate (LMTES) is as follows:

[0032]

[0033] Specifically, it includes: placing lipoic acid (LA) (5.12g, 24.8mmol) and N,N′-carbonyldiimidazole (CDI) (4.83g, 29.8mmol) in a round-bottom flask, adding 30mL of tetrahydrofuran (THF) at room temperature and mixing. The reaction mixture is heated to reflux for 1h, and the by-product CO2 gas is discharged within 10-15min. After the reflux is completed, it is cooled to room temperature, 1 equivalent of mercaptopropyltriethoxysilane (MPTES) is added, and heating is continued for 8h. After the reaction is completed, an appropriate amount of 25wt% brine is added to the reaction mixture for washing. After extraction with dichloromethane (DCM), the organic phase is dried with anhydrous sodium sulfate (Na2SO4), and the solvent is removed to obtain the following Figure 1 The target product LMTES is shown.

[0034] (2) The synthetic route of polysilane coupling agent p(LMTES) is as follows:

[0035]

[0036] Specifically, the above LMTES (5 g, 11.7 mmol) was dissolved in 20 mL of dry THF, and then 5 μL of trifluoromethanesulfonic acid (TfOH) was added. The mixture was stirred for 2 h and then 1-propanethiol was used to terminate the polymerization. The solvent was evaporated, and the obtained crude product was washed with ethanol (EtOH) and dried in a vacuum at 40°C to constant weight to obtain the target product polylipoic acid-based silane coupling agent p (LMTES), with a number average molecular weight of Polydispersity coefficient Its infrared spectrum is Figure 2 shown.

[0037] (3) Preparation of inorganic filler MOF: 5-(Pyrimidinyl)isophthalic acid (4 mmol, 0.98 g) and Zn(NO3)2·6H2O (6 mmol, 1.78 g) were dissolved in 50 mL of a mixed solution of DMF / H2O (v / v = 1:1), stirred for 30 min, and then transferred to a hydrothermal reactor and reacted at 120°C for 72 h. After the reaction was completed, it was cooled to room temperature at a rate of 5°C / h to obtain MOF crystals.

[0038] (4) By weight, 100 parts of natural rubber, 4 parts of polysilane coupling agent p (LMTES), 40 parts of inorganic filler MOF, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin were mixed in an internal mixer for 8 minutes and then sheeted through an open mixer to obtain a rubber prepolymer. Figure 5 As shown in the vulcanization curve, the positive vulcanization time is determined to be 10.8 minutes by the rotorless vulcanizer. The following is obtained after hot pressing at 15MPa pressure and 150℃ for 10.8 minutes using a flat hot press. Figure 6 The rubber composite material shown.

[0039] Example 2

[0040] The difference between this embodiment and embodiment 1 is that the polysilane coupling agent in the components of the rubber composite material is p(LATES).

[0041] (1) The synthetic route of LATES is as follows:

[0042]

[0043] Specifically include: Preparation of silane coupling agent 5-(1,2-dithiocyclopentane-3-yl)-N-(3-(triethoxysilyl)propyl)pentanamide (LATES) containing lipoic acid: Under nitrogen (N2) protection, aminopropyltriethoxysilane (APTES) (4.80g, 21.7mmol) was dissolved in 30mL dry dichloromethane (DCM), and then lipoic acid (LA) (5.12g, 24.8mmol) and N,N-dicyclohexylcarbodiimide (DCC) (4.92g, 23.8mmol) were successively added to the mixed solution, and the mixture was stirred for 2.5h. After the reaction was completed, the crude product was obtained by filtering and removing the solvent, and dry toluene was added to remove the solvent, and the target product LATES was obtained after repeating 3 times.

[0044] (2) The synthetic route of polylipoic acid-based silane coupling agent p(LATES) is as follows:

[0045]

[0046] Specifically, the above LATES (5 g, 12.2 mmol) was dissolved in 20 mL of dry DCM, and then 5 μL of trifluoromethanesulfonic acid (TfOH) was added. The mixture was stirred for 2 h and then 1-propylsulfide was used to terminate the polymerization. The solvent was evaporated, and the obtained crude product was washed with ethanol (EtOH) and dried in a vacuum at 40°C to constant weight to obtain a polysilane coupling agent p(LATES) with a number average molecular weight of Polydispersity coefficient Its infrared spectrum is Figure 3 shown.

[0047] (3) Preparation of vulcanized rubber: By weight, 100 parts of natural rubber, 4 parts of polylipoic acid-based silane coupling agent p (LATES), 40 parts of the inorganic filler MOF prepared in Example 1, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfonamide and 1 part of paraffin were mixed in an internal mixer for 8 minutes and then sheeted through an open mixer to obtain a rubber prepolymer.

[0048] The remaining steps are the same as those in Example 1 to obtain a rubber composite material, the vulcanization curve of which is as follows: Figure 5 shown.

[0049] Example 3

[0050] The difference between this embodiment and embodiment 1 is that the inorganic filler is white carbon black. Specifically, by weight, 100 parts of styrene-butadiene rubber, 4 parts of polylipoic acid-based silane coupling agent p (LMTES), 40 parts of inorganic filler white carbon black, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in an internal mixer for 8 minutes, and then sheeted through an open mixer to obtain a rubber prepolymer.

[0051] The remaining steps are the same as those in Example 1 to obtain a rubber composite material.

[0052] Example 4

[0053] The difference between this embodiment and embodiment 1 is that the inorganic filler is aluminum hydroxide. Specifically, by weight, 100 parts of styrene-butadiene rubber, 4 parts of polythioic acid-based silane coupling agent p (LMTES), 40 parts of inorganic filler aluminum hydroxide, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfonamide and 1 part of paraffin are mixed in an internal mixer for 8 minutes, and then sheeted through an open mixer to obtain a rubber prepolymer.

[0054] The remaining steps are the same as those in Example 1 to obtain a rubber composite material.

[0055] Example 5

[0056] The difference between this embodiment and embodiment 1 is that the rubber matrix is ​​styrene-butadiene rubber. Specifically, by weight, 100 parts of styrene-butadiene rubber, 4 parts of polythioic acid-based silane coupling agent p (LMTES), 40 parts of inorganic filler MOF, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in an internal mixer for 8 minutes, and then sheeted through an open mixer to obtain a rubber prepolymer.

[0057] The remaining steps are the same as those in Example 1 to obtain a rubber composite material.

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that no polysilane coupling agent p(LMTES) is added. Specifically, by weight, 100 parts of natural rubber, 40 parts of inorganic filler MOF, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in an internal mixer for 8 minutes, and then sheeted out through an open mixer to obtain a rubber prepolymer.

[0060] The remaining steps were the same as those in Example 1 to prepare a comparative rubber composite material.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that the silane coupling agent LMTES containing lipoic acid is used instead of the polylipoic acid-based silane coupling agent p(LMTES). Specifically, by weight, 100 parts of natural rubber, 40 parts of inorganic filler MOF, 4 parts of LMTES, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in a mixer for 8 minutes, and then the rubber prepolymer is obtained by discharging the sheet through an open mixer.

[0063] The remaining steps were the same as those in Example 1 to prepare a comparative rubber composite material.

[0064] Comparative Example 3

[0065] The difference between this comparative example and Example 2 is that the polylipoic acid-based silane coupling agent p(LATES) is replaced by the silane coupling agent LATES containing lipoic acid. Specifically, by weight, 100 parts of natural rubber, 40 parts of inorganic filler MOF, 4 parts of LATES, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in an internal mixer for 8 minutes, and then sheeted out through an open mixer to obtain a rubber prepolymer.

[0066] The remaining steps were the same as those in Example 2 to prepare a comparative rubber composite material.

[0067] Comparative Example 4

[0068] The difference between this comparative example and Example 3 is that the silane coupling agent LMTES containing lipoic acid is used to replace the polylipoic acid-based silane coupling agent p (LMTES). Specifically, by weight, 100 parts of styrene-butadiene rubber, 4 parts of LMTES, 40 parts of inorganic filler white carbon black, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in a mixer for 8 minutes, and then the rubber prepolymer is obtained by discharging the sheet through an open mixer.

[0069] The remaining steps were the same as those in Example 3 to prepare a comparative rubber composite material.

[0070] Comparative Example 5

[0071] The difference between this comparative example and Example 4 is that the silane coupling agent LMTES containing lipoic acid is used to replace the polylipoic acid-based silane coupling agent p (LMTES). Specifically, by weight, 100 parts of styrene-butadiene rubber, 4 parts of LMTES, 40 parts of inorganic filler aluminum hydroxide, 2 parts of stearic acid, 3 parts of zinc oxide, 2 parts of antioxidant N-isopropyl-N-phenyl-p-phenylenediamine, 2.5 parts of sulfur, 1.4 parts of accelerator N-cyclohexyl-2-benzothiazole sulfenamide and 1 part of paraffin are mixed in a mixer for 8 minutes, and then the rubber prepolymer is obtained by discharging the sheet through an open mixer.

[0072] The remaining steps were the same as those in Example 4 to obtain a comparative rubber composite material.

[0073] Test method:

[0074] The following performance tests were performed on Examples 1 to 5 of the present invention and Comparative Examples 1 to 6, and the test items and methods are as follows:

[0075] Structural characterization of polylipoic acid-based silane coupling agent: The chemical structure of polylipoic acid-based silane coupling agent was characterized by Fourier transform infrared (FTIR) spectrometer (Nicoleti S10, USA) using the attenuated total reflection (ATR) method in the wave number range of 500-4000cm -1 The scanning number is 32. The absorption spectra of silane coupling agent containing lipoic acid and polylipoic acid-based silane coupling agent were characterized by UV-visible spectrometer (Shimadzu UV-2550, Japan), and the test wavelength range was 200-800nm.

[0076] Determination of vulcanization curve: The vulcanization curve of the rubber composite prepared above was tested using a BL-6190 rotorless vulcanizer (Baisheng Machinery Equipment Factory). According to GB / T 9869-2014 standard, the temperature was set at 150°C and the duration was set at 30 min. The vulcanization curve of the mixed rubber was measured and the vulcanization time T was determined. 90 .

[0077] Stress-strain property test: According to the method specified in GB / T 528-2009, the 100% modulus stress, 300% modulus stress, tensile strength and elongation at break of the rubber composite material prepared as above were measured.

[0078] Toughness characterization: The toughness of rubber is characterized by comparing the integrated area of ​​the stress-strain curve.

[0079] Crosslink density test: The crosslink density of vulcanized rubber was determined by the equilibrium expansion method. 1g of vulcanized rubber was immersed in 30mL of toluene for 3 days, and the toluene was replaced every 24 hours. After the immersion was completed, the solvent was quickly absorbed with filter paper, and the sample mass was weighed and recorded as m1; then the sample was dried to a constant weight and recorded as m2. The crosslink density V of the sample c According to the Flory-Rehner equation:

[0080]

[0081] Where M c is the molecular weight between cross-linking points, calculated by the following formula:

[0082]

[0083] In the formula, ρ p is the density of NR (0.912 g / cm 3 ), V s is the molar volume of toluene (106.3 cm 3 / mol), χ is the interaction parameter between NR and toluene, V r is the volume fraction of the sample after swelling, V r Calculated by the following formula:

[0084]

[0085] In the formula, m f is the mass of filler in the sample, ρ s is the density of toluene (0.866 g / cm 3 )

[0086] All test results are shown in Table 1 and Table 2.

[0087] Table 1 Test results of Examples 1 to 5

[0088]

[0089] Table 2 Test results of comparative examples 1 to 5

[0090]

[0091] Experimental data analysis:

[0092] Figure 1 The optical photographs are of the thioctic acid-containing silane coupling agent LMTES and the polythioctic acid-based silane coupling agent p(LMTES) obtained in Example 1. Before polymerization, LMTES is a flowable yellow liquid, and the p(LMTES) obtained after ring-opening polymerization is a yellow block solid. Figure 4The UV-visible absorption spectra of LMTES and p(LMTES) are shown in the figure. Due to the 1,2-dithiolane structure in the LMTES monomer, there is an absorption peak at 330nm. After the ring-opening polymerization of the dithiolane, p(LMTES) only has linear disulfide bonds, so the absorption peak at 330nm disappears. The above results prove that the silane coupling agent LMTES containing lipoic acid is successfully ring-opened and polymerized to obtain the polylipoic acid-based silane coupling agent p(LMTES).

[0093] The test data of the above-mentioned Examples 1 to 5 and Comparative Examples 1 to 6 are shown in Tables 1 and 2 above. From the test results, it can be seen that the 100% tensile stress of Example 1 is 3.4MPa, the 300% tensile stress is 11.2MPa, the tensile strength is 31.8MPa, and the elongation at break is 608%. Compared with Comparative Example 1 without adding polylipoic acid-based silane coupling agent, its tensile strength, tensile stress, elongation at break and toughness are greatly improved. The curing time (T 90 ) is 10.8min, while the vulcanization time of Comparative Example 1 is 20.3min. This shows that the polylipoic acid-based silane coupling agent can improve the dispersion compatibility of the inorganic filler MOF in the rubber matrix, avoid the adsorption of the inorganic filler on the rubber additive, shorten the vulcanization time, and significantly enhance the interaction between the organic-inorganic component interface, thereby improving the mechanical properties of the rubber composite material.

[0094] The experimental results of Example 1 and Example 2 show that changing the chemical structure of the silane coupling agent in the polylipoic acid-based silane coupling agent does not affect the reinforcing effect of the inorganic filler MOF on the rubber composite material, because the terminal active group of the silane coupling agent only condenses with lipoic acid to play a role of covalent coupling, and does not affect the interface modification between the polylipoic acid-based silane coupling agent and the inorganic filler. It can be seen from Example 1 and Examples 3 to 4 that, in addition to the inorganic filler MOF, the polylipoic acid-based silane coupling agent is also effective for reinforcing inorganic fillers such as white carbon black and aluminum hydroxide in rubber, because the surfaces of these inorganic fillers all contain active hydroxyl groups that can react with the polylipoic acid-based silane coupling agent to condense, thereby exerting the reinforcing effect of the inorganic filler in the rubber matrix. The experimental results of Example 1 and Example 5 confirm that replacing the rubber matrix will hardly affect the interface regulation performance of the polylipoic acid-based silane coupling agent for the inorganic filler in the rubber. The above results show that polylipoic acid-based silane coupling agent is highly effective and universal in improving the comprehensive mechanical properties of rubber composites with inorganic fillers containing active hydroxyl groups on the surface.

[0095] The effects of polythioic acid-based silane coupling agents and small molecule silane coupling agents on the comprehensive mechanical properties of rubber composites are compared. The tensile strength, tensile stress, and toughness of Examples 1, 3, and 4 are significantly improved compared to Comparative Examples 2, 4, and 5. The crosslinking density of the rubber composite is determined by the equilibrium swelling method, and the crosslinking density of Examples 1, 3, and 4 is higher than that of Comparative Examples 2, 4, and 5. This is because compared to small molecule silane coupling agents, polythioic acid-based silane coupling agents can covalently couple inorganic fillers at multiple sites. In addition, a physical crosslinking network can be constructed by interpenetrating and entangled with rubber molecular chains, and has a higher crosslinking density. Under the action of external force, the rupture of the dynamic disulfide bonds on the main chain of the polythioic acid-based silane coupling agent has an energy dissipation effect, and therefore has enhanced comprehensive mechanical properties.

[0096] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A polylipoic acid-based silane coupling agent, characterized in that: Its structural formula is Among them, R is selected from n1=5-2000, n2=2-5.

2. A polylipoic acid-based silane coupling agent as claimed in claim 1, characterized in that: Its structural formula is n＝5-2000。 3. Use of the polythioctic acid-based silane coupling agent according to claim 1 or 2 in the preparation of rubber composite materials.

4. The use according to claim 3, characterized in that: The rubber composite material is prepared by uniformly mixing a base rubber, the polylipoic acid-based silane coupling agent, an inorganic filler, zinc oxide, stearic acid, a vulcanizing agent, an accelerator, an antioxidant and paraffin wax, followed by vulcanization and hot pressing; the surface of the inorganic filler contains active hydrogen sites that can undergo a condensation reaction with the polylipoic acid-based silane coupling agent.

5. The use according to claim 4, characterized in that: The base rubber is selected from natural rubber, styrene-butadiene rubber, butadiene rubber and chloroprene rubber, and the inorganic filler is selected from white carbon black, metal organic framework, two-dimensional transition metal carbide, silicate, inorganic metal oxide and hydroxide.

6. The use according to claim 5, characterized in that: The mass ratio of the base rubber, polylipoic acid-based silane coupling agent, inorganic filler, zinc oxide, stearic acid, vulcanizing agent, accelerator, antioxidant and paraffin is 60-100:1-30:10-80:2-4:1-3:1-4:1-4:1-3:1-3.

7. A rubber composite material, characterized in that: The raw materials include the polythioctic acid-based silane coupling agent according to claim 1 or 2.

8. A rubber composite material according to claim 7, characterized in that: The invention is prepared by uniformly mixing base rubber, the polylipoic acid-based silane coupling agent, inorganic filler, zinc oxide, stearic acid, a vulcanizing agent, an accelerator, an antioxidant and paraffin, followed by vulcanization and hot pressing; the surface of the inorganic filler contains active hydrogen sites, which can undergo condensation reaction with the polylipoic acid-based silane coupling agent.

9. A rubber composite material according to claim 8, characterized in that: The base rubber is selected from natural rubber, styrene-butadiene rubber, butadiene rubber and chloroprene rubber, and the inorganic filler is selected from white carbon black, metal organic framework, two-dimensional transition metal carbide, silicate, inorganic metal oxide and hydroxide.

10. A rubber composite material according to claim 9, characterized in that: The mass ratio of the base rubber, polylipoic acid-based silane coupling agent, inorganic filler, zinc oxide, stearic acid, vulcanizing agent, accelerator, antioxidant and paraffin is 60-100:1-30:10-80:2-4:1-3:1-4:1-4:1-3:1-3.

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