Synthesis method of unsaturated silane modified tetrafluoroethylene-propylene rubber, tetrafluoroethylene-propylene rubber and composition thereof

Abstract

The invention relates to a synthetic method of tetrafluoroethylene-propylene rubber, the tetrafluoroethylene-propylene rubber and a composition thereof, the synthetic method of the tetrafluoroethylene-propylene rubber comprises the following steps: taking mixed monomers of tetrafluoroethylene and propylene monomers as raw materials, and preparing the tetrafluoroethylene-propylene rubber through an emulsion polymerization method. Water is adopted as a medium for reaction, the tetrafluoroethylene-propylene rubber with excellent low-temperature performance can be obtained under the condition that the low-cost unsaturated silane comonomer is added, the raw material cost is saved, and the operation is simple.

Description

Technical Field

[0001] The invention relates to the technical field of polymer synthesis, and in particular to a method for synthesizing unsaturated silane-modified tetrafluoroethylene rubber, the tetrafluoroethylene rubber and a composition thereof. Background Art

[0002] Modern automobile industry and petroleum industry have high requirements for the alkali resistance of fluororubber. Fluororubber is a polymethylene type fluororubber that uses vinylidene fluoride as a comonomer, contains fluorine, alkyl, perfluoroalkyl or perfluoroalkoxy substituents on the polymer chain, and has or does not have a vulcanization point monomer (with a reactive side group). Commonly used fluororubbers, such as type 26 and type 246 fluororubbers, are not alkali-resistant. The reason is that the VF2 unit in the composition of fluororubber is susceptible to attack by strong alkaline amines, HF is released, and unsaturated double bonds are formed on the polymer chain, which further reacts with the double bonds to make the crosslinking degree of the polymer quite high, resulting in a significant increase in the tensile stress of the fluororubber, and a significant decrease in the elongation at break and elasticity. Excessive elasticity loss causes cracks in the seals, resulting in liquid leakage.

[0003] Tetrafluoropropylene rubber (FEPM) is a polymethylene type fluororubber containing only one or more monomeric alkyl, perfluoroalkyl and / or perfluoroalkoxy groups, with or without cure site monomers (with reactive side groups).

[0004] Tetrafluoroethylene (TFE) and propylene (P) are alternately copolymerized in a high-pressure reactor in the presence of water, emulsifiers, initiators, etc. to form a polymer emulsion, gel emulsion, wet rubber, and then washed, dried, heat-treated, and rolled to obtain an elastomer. Its structural characteristics determine that it has excellent chemical stability. The difference from fluororubber is that tetrafluoroethylene (TFE) and propylene (P) do not contain VF2 in the composition of the polymer, so tetrafluoroethylene (PTFE) rubber has excellent alkali resistance. Tetrafluoroethylene (PTFE) rubber is highly resistant to corrosion by inorganic acids, alkalis, various bleaches, superheated water and steam, especially steam mixed with chemicals such as acids and alkalis, and phosphate ester hydraulic oils. Tetrafluoroethylene (PTFE) rubber, like other fluororubbers, can work for a long time below 230°C, but its low-temperature performance is poor (-40°C to 230°C when static, -3°C to 230°C when dynamic), but its excellent performance-price ratio is unmatched by other fluororubbers. Due to its excellent properties, this material is widely used in chemical, food, textile and other industrial sectors. The main products include various acid-resistant, corrosion-resistant and water vapor-resistant hoses, sealing rings, gaskets, diaphragms and so on.

[0005] The low temperature resistance of rubber refers to the ability of rubber to maintain its elasticity and normal operation at a specified low temperature, which mainly depends on two basic processes of polymers: glass transition and crystallization. The glass transition temperature is the transition temperature of the molecular chain segments of rubber from motion to freezing, and the segment motion is achieved by the rotation within the single bond of the main chain. Therefore, the flexibility of the molecular chain helps to improve the low temperature performance of the material, and increasing the polarity of the molecular chain helps to improve the oil resistance of the material.

[0006] However, the biggest disadvantage of tetrafluoroethylene rubber is its poor cold resistance. There are two ways to improve the cold resistance of tetrafluoroethylene rubber: ① synthesizing tetrafluoroethylene rubber containing a third monomer (such as Arias 200, which introduces a third monomer VDF, reducing alkali resistance; and Viton EPT, which introduces a third monomer perfluorovinyl ether monomer); ② using it in combination with other cold-resistant rubbers. Although the combined use method is simple and easy, the oil resistance or acid and alkali resistance of tetrafluoroethylene rubber is impaired after being used in combination with other rubbers. Therefore, the combined use ratio cannot be too large, and the improvement of its cold resistance is limited.

[0007] However, the cost of introducing low-temperature resistant modified monomers, such as perfluoroalkyl vinyl ether (PAVE) and perfluoroalkoxy alkyl vinyl ether (PAAVE), into tetrafluoropropylene rubber is high. At the same time, in order to achieve the curing of tetrafluoropropylene rubber polymerized with low-temperature resistant modified monomers, it is also necessary to introduce high-cost cross-linking point monomers, such as fluorine-containing, chlorine-containing, fluorine-containing, bromine-containing, or fluorine-containing, iodine-containing organic compounds. The tetrafluoropropylene rubber prepared in this way is very expensive, which seriously limits the promotion and application of low-temperature resistant tetrafluoropropylene rubber.

[0008] Therefore, it is necessary to provide a low-temperature resistant tetrafluoroethylene rubber with high cost performance and a suitable cross-linking system to meet its application requirements in cold regions. Summary of the invention

[0009] The purpose of the present invention is to provide a method for synthesizing unsaturated silane-modified tetrafluoroethylene rubber and the tetrafluoroethylene rubber and composition thereof, thereby improving the low-temperature resistance of the fluoroethylene rubber by adding a low-cost copolymer monomer to the structure of the tetrafluoroethylene rubber; and finding a suitable cross-linking point monomer to replace the use of the cross-linking point monomer with a higher cost.

[0010] The first aspect of the present invention provides a method for synthesizing unsaturated silane-modified tetrafluoroethylene rubber, wherein tetrafluoroethylene and propylene are used as raw materials, unsaturated silane comonomer is added, and the tetrafluoroethylene rubber is prepared by emulsion polymerization.

[0011] Preferably, the added amount of the unsaturated silane comonomer is 1.0 to 50% of the mass of the tetrafluoroethylene and propylene mixed monomer.

[0012] Preferably, the unsaturated silane monomer is an ethylenically unsaturated silane and / or a hydrolysis product of an ethylenically unsaturated silane; the unsaturated silane monomer has the general formula R″-CH=CH-Z(I), wherein Z represents an electron-withdrawing part substituted by a -SiRaR′(3-a) group, wherein Ra represents a hydrolyzable group, R′ represents a hydrocarbon group having 1-6 carbon atoms; a has a value of 1-3, including end values, and R″ represents hydrogen or a -CH=CH- or -C≡C- bond. Specifically, an ethylenically unsaturated silane may be a vinylsiloxane or an allylsiloxane, such as 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and vinyltri(2-methoxyethoxy)silane. Preferably, the unsaturated silane is vinyltrimethoxysilane.

[0013] Preferably, the emulsifier is a fluorine-free nonionic surfactant; the nonionic surfactant is a polyol nonionic surfactant, selected from any one or more of ethylene glycol esters, glycerol esters, polyglycerol esters, pentose and tetrol esters, sorbitol esters, anhydrous sorbitol esters, sucrose esters or polyoxyethylene polyol esters; preferably, the nonionic surfactant is polyoxyethylene sorbitan monostearate. The amount of the initiator added is 0.01% to 10% of the mass of deionized water.

[0014] Preferably, the method comprises the following steps: adding deionized water, pH buffer and emulsifier into a reactor, vacuumizing the reactor, adding tetrafluoroethylene and propylene mixed monomers into the reactor until the pressure in the reactor is 1.0-4.0 MPa, heating the reactor to 50-100° C., adding a redox initiator into the reactor to initiate a polymerization reaction, and during the reaction, the tetrafluoroethylene and propylene mixed monomers and unsaturated silane copolymer monomers are added to maintain the pressure in the reactor at the initial pressure, and the reaction is completed to obtain the product.

[0015] Preferably, the amount of the redox initiator added is 0.1 to 5.0% of the mass of the polymerization monomer.

[0016] Preferably, in the redox initiation system, the oxidizing initiator is a mixture of potassium persulfate and ammonium persulfate, and the mass ratio of potassium persulfate to ammonium persulfate is 1 to 5:1; the reducing initiator is sodium metabisulfite, and the mass ratio of sodium metabisulfite to the sum of potassium persulfate and ammonium persulfate is 1:1 to 3.

[0017] Preferably, the usage ratio of tetrafluoroethylene to propylene is 1:2 to 9:1.

[0018] The unsaturated silane serves as a cross-linking point monomer.

[0019] The second aspect of the present invention provides an unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber prepared according to a method for preparing tetrafluoropropylene rubber.

[0020] The third aspect of the present invention provides a tetrafluoroethylene rubber composition, comprising the following components in parts by weight: 100 parts of the unsaturated silane-modified low-temperature resistant tetrafluoroethylene rubber according to claim 8, 0 to 30 parts of carbon black N990, 0 to 10 parts of magnesium oxide, 0 to 10 parts of calcium stearate, and 0.5 to 10 parts of a vulcanization accelerator.

[0021] Preferably, the vulcanization accelerator is a dehydration catalyst, including alkyl tin, fatty acid tin, fatty acid stannous, fatty acid alkyl tin, organic titanium compound, zirconate, alkyl acid bismuth, benzenesulfonic acid, benzenesulfonated acetyl. Preferably, the vulcanization accelerator is dibutyltin dilaurate (DBTDL).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The method of the present invention adopts water as a medium for reaction, and adopts vinyl trimethoxy silane as a copolymer monomer and a vulcanization point monomer by selecting an initiator and an emulsifier, and does not need to add other various additives, thereby saving raw material costs, and the reaction can be carried out under a relatively low pressure, and the operation is simple, so that tetrafluoroethylene rubber with excellent low-temperature performance can be obtained.

[0024] The unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber provided by the present invention has low cost. Compared with the use of perfluoroalkyl vinyl ether (PAVE for short) and perfluoroalkoxyalkyl vinyl ether (PAAVE for short), the present invention uses unsaturated silane as a cross-linking point monomer to replace the use of bromine-containing and iodine-containing cross-linking point monomers with higher costs, which can improve the flexibility of the molecular chain, help improve the low-temperature performance of the material, and reduce costs.

[0025] The unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber provided by the present invention has a low glass transition temperature and a low TR-10. Compared with fluororubber, the other properties of the obtained unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber remain basically unchanged, which can ensure its application in the low-temperature field. After testing, its Mooney viscosity is 19 to 28 (1+10min@121°C), the tensile strength is 17.5 to 25.2MPa, the glass transition temperature is -7 to -33°C, the permanent compression deformation is 15 to 24% (hot air, 200°C×70h), and the low-temperature shrinkage temperature TR-10 is -5 to -23°C.

[0026] Since unsaturated silane is used as a polymerization monomer in the polymerization process of low-temperature resistant tetrafluoropropylene rubber, the unsaturated silane can produce polar hydroxyl groups (silicon-based hydroxyl groups), and polar hydroxyl groups are introduced into the molecular chain of fluororubber. On this basis, polyols in polyol nonionic surfactants are used instead of PFOA perfluorooctanoate as emulsifiers for emulsion polymerization. Using polyol nonionic surfactants as emulsifiers can attract the hydroxyl groups on the grafted unsaturated silanes in the polymers at the early stage of polymerization, and then form micelles; the polymers in the micelles can capture fluorinated monomers; at the same time, the hydroxyl groups of the polyol nonionic surfactants can form hydrogen bonds with the hydroxyl groups of the unsaturated silanes, attracting free unsaturated silanes, providing sufficient conditions for the chain growth reaction of the emulsion polymerization reaction, and the chain growth reaction is carried out in the micelles until a high molecular weight fluoropolymer is generated, and the micelle particles filled with polymers are stably present in the aqueous phase.

[0027] The present invention is based on introducing an unsaturated silane structure into the fluororubber polymerization structure, using a non-ionic surfactant to replace PFOA perfluorooctanoate as an emulsifier to carry out an emulsion polymerization reaction, providing a method of replacing PFOA as an emulsifier for preparing fluoropolymers, and expanding the PFOA replacement route.

[0028] Tetrafluoropropylene rubber is usually vulcanized with a dehydration catalyst system in the later stage. The present invention can generate hydroxyl groups by adding unsaturated silane vulcanization point monomers, which can provide crosslinking points for the dehydration catalyst vulcanization system during vulcanization to achieve a self-crosslinking curing reaction.

[0029] Dehydration is used to form ether bonds for cross-linking. The ether bonds are relatively flexible, and the prepared ether-bond cross-linked fluororubber has excellent low-temperature resistance. At the same time, the ether bonds are relatively stable, and the prepared fluororubber has good heat resistance, oil resistance, and aging resistance. Although a water absorbent is required to remove the water produced by the dehydration reaction, the magnesium oxide present in the vulcanization system has a water absorption function, and the magnesium hydroxide generated after absorbing water can be used as a filler. No other additives are required in the vulcanization system to remove hydrofluoric acid HF from the molecular chain, and unstable double bonds will not be formed. At a certain temperature, the vulcanization accelerator (dehydration catalyst) promotes the reaction of two hydroxyl groups to remove one water molecule H2O to form an ether bond, thereby allowing the unsaturated silane-modified low-temperature resistant tetrapropylene fluororubber to form a three-dimensional cross-linked structure. DETAILED DESCRIPTION

[0030] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0031] Example 1

[0032] This embodiment relates to a method for preparing tetrafluoroethylene rubber, comprising the following steps:

[0033] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (polyoxyethylene sorbitan monostearate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 70:30 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, and then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0034] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0035] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01MPa, TFE / P mixed monomer (molar ratio of 70:30) and comonomer vinyl trimethoxysilane (molar ratio of 8:100 to the mixed monomer) are alternately added to the reactor to maintain the pressure in the reactor at 2.5MPa. That is, when the pressure of the reactor drops to 2.49MPa, TFE / P mixed monomer (molar ratio of 70:30) is first introduced into the reactor to make the pressure in the reactor reach 2.5MPa; then vinyl trimethoxysilane (the molar ratio of vinyl trimethoxysilane to the amount of TFE / P mixed monomer introduced is 8:100) comonomer is injected into the reactor.

[0036] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain a tetrafluoroethylene rubber emulsion; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0037] Example 2

[0038] This embodiment relates to a method for preparing tetrafluoroethylene rubber, comprising the following steps:

[0039] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (polyoxyethylene sorbitan monostearate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 90:10 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0040] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0041] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01 MPa, TFE / P mixed monomers (molar ratio of 90:10) and comonomer vinyl trimethoxysilane (molar ratio of 8:100 to the mixed monomers) are alternately added to the reactor to maintain the pressure in the reactor at 2.5 MPa. That is, when the pressure of the reactor drops to 2.49 MPa, TFE / P mixed monomers (molar ratio of 90:10) are first introduced into the reactor to make the pressure in the reactor reach 2.5 MPa; then vinyl trimethoxysilane (the molar ratio of vinyl trimethoxysilane to the amount of TFE / P mixed monomers introduced is 8:100) comonomer is injected into the reactor.

[0042] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain a tetrafluoroethylene rubber emulsion; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0043] Example 3

[0044] This embodiment relates to a method for preparing tetrafluoroethylene rubber, comprising the following steps:

[0045] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (polyoxyethylene sorbitan monostearate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 50:50 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0046] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0047] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01MPa, TFE / P mixed monomers (molar ratio of 50:50) and comonomer vinyl trimethoxysilane (molar ratio of 8:100 to the mixed monomers) are alternately added to the reactor to maintain the pressure in the reactor at 2.5MPa. That is, when the pressure of the reactor drops to 2.49MPa, TFE / P mixed monomers (molar ratio of 50:50) are first introduced into the reactor to make the pressure in the reactor reach 2.5MPa; then vinyl trimethoxysilane (the molar ratio of vinyl trimethoxysilane to the amount of TFE / P mixed monomers introduced is 8:100) comonomer is injected into the reactor.

[0048] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain a tetrafluoroethylene rubber emulsion; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0049] Example 4

[0050] This embodiment relates to a method for preparing tetrafluoroethylene rubber, comprising the following steps:

[0051] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (polyoxyethylene sorbitan monostearate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 70:30 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, and then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0052] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0053] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01MPa, TFE / P mixed monomer (molar ratio of 70:30) and comonomer vinyl trimethoxysilane (molar ratio of 4:100 to the mixed monomer) are alternately added to the reactor to maintain the pressure in the reactor at 2.5MPa. That is, when the pressure of the reactor drops to 2.49MPa, TFE / P mixed monomer (molar ratio of 70:30) is first introduced into the reactor to make the pressure in the reactor reach 2.5MPa; then vinyl trimethoxysilane (the molar ratio of vinyl trimethoxysilane to the amount of TFE / P mixed monomer introduced is 4:100) comonomer is injected into the reactor.

[0054] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion containing unsaturated silane-modified low-temperature resistant tetrafluoroethylene rubber; coagulation is performed with an aqueous solution of magnesium chloride, and the emulsion is washed with deionized water. The emulsion is dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0055] Example 5

[0056] This embodiment relates to a method for preparing tetrafluoroethylene rubber, comprising the following steps:

[0057] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (polyoxyethylene sorbitan monostearate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 70:30 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, and then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0058] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0059] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01MPa, TFE / P mixed monomer (molar ratio of 70:30) and comonomer vinyl trimethoxysilane (molar ratio of 16:100 to the mixed monomer) are alternately added to the reactor to maintain the pressure in the reactor at 2.5MPa. That is, when the pressure of the reactor drops to 2.49MPa, TFE / P mixed monomer (molar ratio of 70:30) is first introduced into the reactor to make the pressure in the reactor reach 2.5MPa; then vinyl trimethoxysilane (the molar ratio of vinyl trimethoxysilane to the amount of TFE / P mixed monomer introduced is 16:100) comonomer is injected into the reactor.

[0060] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain a tetrafluoroethylene rubber emulsion; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0061] Comparative Example 1

[0062] Compared with Example 1, the difference is that sodium perfluorooctanoate emulsifier is added during the polymerization process to replace the polyoxyethylene sorbitan monostearate emulsifier.

[0063] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (sodium perfluorooctanoate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 90:10 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0064] 2) Add a mixture of 2.5 g of ammonium persulfate and 2.5 g of potassium persulfate, and 2.5 g of sodium metabisulfite as a redox initiator via a metering pump.

[0065] 3) At the beginning of the polymerization reaction, when the pressure of the reactor drops by 0.01MPa, TFE / P mixed monomers (molar ratio of 70:30) and comonomer vinyl trimethoxysilane (molar ratio of 8:100 to the mixed monomers) are alternately added to the reactor to maintain the pressure in the reactor at 2.5MPa. That is, when the pressure of the reactor drops to 2.49MPa, TFE / P mixed monomers are first introduced into the reactor to make the pressure in the reactor reach 2.5MPa; then vinyl trimethoxysilane (the molar ratio of the amount of vinyl trimethoxysilane to the amount of TFE / P mixed monomers introduced is 8:100) comonomer is injected into the reactor.

[0066] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain a tetrafluoroethylene rubber emulsion; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber raw rubber product.

[0067] Comparative Example 2

[0068] Compared with Example 1, the difference is that the comonomer vinyltrimethoxysilane is not added during the polymerization process.

[0069] 1) In a 5L stainless steel reactor with a stirrer, add 3L of deionized water, 2g of dipotassium hydrogen phosphate, and 3g of emulsifier (sodium perfluorooctanoate), and repeat nitrogen pressurization and vacuum degassing. When the oxygen content is ≤30PPM, add a mixed monomer with a molar ratio of tetrafluoroethylene to propylene of 70:30 to the reactor, raise the pressure to 0.5MPa, start the reactor stirrer, then raise the temperature to 70°C, continue to add the mixed monomer and raise the pressure to 2.5MPa.

[0070] 2) Add 10 g of perfluoroethyl bromide vinyl ether as a vulcanization point monomer, 2.5 g of a mixture of ammonium persulfate and 2.5 g of potassium persulfate as a redox initiator, 2.5 g of sodium metabisulfite, and 5 g of I(CF2CF2)2I as a vulcanization point monomer through a metering pump.

[0071] 3) When the polymerization reaction starts, TFE / P mixed monomer (molar ratio of 70:30) is added to the reactor every time the reactor pressure drops by 0.01 MPa to maintain the pressure in the reactor at 2.5 MPa.

[0072] 4) When the solid content of the emulsion reaches about 30wt%, the polymerization reaction is terminated, and the unreacted monomers are recovered to obtain an emulsion of tetrafluoroethylene rubber; the emulsion is condensed with an aqueous solution of magnesium chloride, washed with deionized water, and dried in a vacuum drying oven at 90°C and -0.08MPa for 12 hours to obtain a tetrafluoroethylene rubber product.

[0073] Performance Testing

[0074] The Mooney viscosity, fluorine content and glass transition temperature of the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber provided in the test examples and comparative examples are tested in the following manner:

[0075] Mooney Viscosity: Measured in accordance with ASTM D1646 using a L (large) spindle at 121°C (unless otherwise stated) with a one minute preheat time and a 10 minute spindle run time.

[0076] Glass transition temperature: GB / T19466.2 Plastics Differential Scanning Calorimetry (DSC) Part 2: Determination of glass transition temperature.

[0077] The Mooney viscosity, fluorine content and glass transition temperature of the rubber products of Examples 1-5 and Comparative Examples 1-2 are shown in the following table.

[0078] Table 1 Rubber properties of Examples 1-5 and Comparative Examples 1-2

[0079]

[0080]

[0081] Example 8

[0082] A fluororubber composition is prepared from the unsaturated silane-modified low-temperature resistant tetrapropylene fluororubber of Examples 1-5 and Comparative Examples 1-2. The specific formula and preparation method are as follows:

[0083] The formulations of the fluororubber compositions of Examples 1-5 and Comparative Example 1 include the following components in parts by weight: 100 parts of fluororubber, 10 parts of N990 carbon black, 4 parts of magnesium oxide, 4 parts of calcium stearate, and 2 parts of dibutyltin dilaurate (DBTDL).

[0084] The formula of the fluororubber composition of Comparative Example 2 includes the following components in parts by weight: 100 parts of fluororubber, 10 parts of N990 carbon black, 4 parts of bis(250) (75%), 3 parts of TAIC, and 4 parts of calcium stearate.

[0085] The first stage vulcanization is 175℃×10min, and the second stage vulcanization is 175℃×24h; the compression test conditions are: 25% compression rate, 200 degrees, 72 hours.

[0086] The performance test method is as follows:

[0087] Tensile properties: GB / T528 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber.

[0088] Compression set: hot air, 200℃×70h, GB / T7759 vulcanized rubber and thermoplastic rubber compression set determination at room temperature, high temperature and low temperature.

[0089] TR-10 Temperature: ASTM D1053 test method.

[0090] Table 2 Performance results of fluororubber compositions prepared from Examples 1-5 and Comparative Examples 1-2

[0091]

[0092]

[0093] As shown in Table 2, compared with tetrafluoroethylene rubber (Comparative Example 2) without adding vinyl trimethoxysilane comonomer, the low temperature performance of tetrafluoroethylene rubber (Examples 1-5 and Comparative Example 1) with adding vinyl trimethoxysilane comonomer is significantly improved. Compared with Comparative Example 2, the glass transition temperature is reduced by more than 7 degrees, and the maximum is reduced by 21 degrees (Example 5); the TR-10 brittle temperature is also significantly reduced, ranging from 6 degrees (Example 4) to 22 degrees (Example 5). It shows that adding vinyl trimethoxysilane comonomer to tetrafluoroethylene rubber can significantly improve the low temperature resistance of tetrafluoroethylene rubber.

[0094] By comparing the emulsifiers using polyoxyethylene sorbitan monostearate as an emulsifier (Example 1) and perfluorooctanoate as an emulsifier (Comparative Example 1), the performance of the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber obtained is slightly different; the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber prepared using polyoxyethylene sorbitan monostearate as an emulsifier is equivalent to that prepared using sodium perfluorooctanoate as an emulsifier, but perfluorooctanoate is not used in the synthesis process, which is more environmentally friendly.

[0095] The unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber adopts a vulcanization system with a dehydration catalyst. Compared with the ordinary tetrafluoropropylene rubber (Example 1 and Comparative Example 2) using a peroxide vulcanizer combined with an accelerator, the tensile strength is slightly improved, the pressure change is greatly improved, and the TR-10 brittle temperature is significantly increased. It can be considered that the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber can meet the use requirements of tetrafluoropropylene rubber. It also shows that vinyl trimethoxysilane, as a cross-linking point monomer (which can produce hydroxyl groups), can achieve cross-linking of the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber under the action of the vulcanization system with a dehydration catalyst.

[0096] The composition change of the mixed monomer of TFE and P (Example 1, Example 2 and Example 3) has a slight influence on the performance of the unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber.

[0097] The feeding ratio of vinyl trimethoxysilane (Example 1, Example 4 and Example 5) has a great influence on the performance of unsaturated silane modified low temperature resistant tetrafluoropropylene rubber. Compared with Example 1, the feeding ratio of vinyl trimethoxysilane is 8:100 (with the mixed monomer as 100), the feeding ratio of vinyl trimethoxysilane in Example 5 is high (16:100, with the mixed monomer as 100), the tensile strength of the unsaturated silane modified low temperature resistant tetrafluoropropylene rubber is reduced, the TR-10 brittle temperature is higher, and the pressure change is also increased; the feeding ratio of vinyl trimethoxysilane in Example 4 is low (4:100, with the mixed monomer as 100), the tensile strength of the unsaturated silane modified low temperature resistant tetrafluoropropylene rubber is improved, the TR-10 brittle temperature is significantly improved, and the pressure change is slightly increased.

[0098] In summary, the molar ratio of TFE:P in the mixed monomer is 70:30, the molar ratio of the mixed monomer to vinyltrimethoxysilane is 100:1, and polyoxyethylene sorbitan monostearate is used as an emulsifier. The prepared unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber has an optimized cost-effectiveness.

[0099] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A method for synthesizing tetrafluoroethylene rubber, characterized in that: Tetrafluoroethylene and propylene are used as raw materials, unsaturated silane copolymer is added, and tetrafluoropropylene rubber is prepared by emulsion polymerization.

2. The method according to claim 1, characterized in that The dosage ratio of tetrafluoroethylene to propylene is 1:2 to 9:1; the added amount of the unsaturated silane copolymer monomer is 1.0 to 50% of the mass of the tetrafluoroethylene and propylene mixed monomer.

3. The method according to claim 1, characterized in that: The unsaturated silane monomer is an ethylenically unsaturated silane and / or a hydrolysis product of an ethylenically unsaturated silane; the unsaturated silane monomer has the general formula R″-CH=CH-Z(I), wherein Z represents an electron-withdrawing part substituted by a -SiRaR′(3-a) group, wherein Ra represents a hydrolyzable group, R′ represents a hydrocarbon group having 1-6 carbon atoms; a has a value of 1-3, including the end values, and R″ represents hydrogen or a -CH=CH- or -C≡C- bond.

4. The method according to claim 1, characterized in that: The emulsifier is a fluorine-free nonionic surfactant; the nonionic surfactant is a polyol nonionic surfactant, selected from any one or more of ethylene glycol esters, glycerol esters, polyglycerol esters, aldopentose and tetrol esters, sorbitol esters, sorbitol esters, sucrose esters or polyoxyethylene polyol esters; the added amount of the initiator is 0.01% to 10% of the mass of deionized water.

5. The method according to claim 1, characterized in that The method comprises the following steps: adding deionized water, pH buffer and emulsifier into a reaction kettle, vacuumizing the reaction kettle, adding tetrafluoroethylene and propylene mixed monomers into the reaction kettle until the pressure in the reaction kettle is 1.0-4.0MPa, heating the reaction kettle to 50-100°C, adding a redox initiator into the reaction kettle to initiate a polymerization reaction, and during the reaction, the tetrafluoroethylene and propylene mixed monomers and unsaturated silane copolymer monomers are added to maintain the pressure in the reaction kettle at the initial pressure, and the reaction is completed to obtain the product.

6. The method according to claim 5, characterized in that The addition amount of the redox initiator is 0.1-5.0% of the mass of the polymerization monomer; in the redox initiation system, the oxidative initiator is a mixture of potassium persulfate and ammonium persulfate, and the mass ratio of potassium persulfate to ammonium persulfate is 1-5:1; the reducing initiator is sodium metabisulfite, and the mass ratio of sodium metabisulfite to the sum of potassium persulfate and ammonium persulfate is 1:1-3.

7. The method according to claim 1, characterized in that The unsaturated silane serves as a cross-linking point monomer.

8. A method for preparing tetrafluoropropylene rubber according to any one of claims 1 to 7, and obtaining unsaturated silane-modified low-temperature resistant tetrafluoropropylene rubber.

9. A tetrafluoroethylene rubber composition, characterized in that: The invention comprises the following components in parts by weight: 100 parts of the unsaturated silane-modified low-temperature-resistant tetrafluoropropylene rubber as described in claim 8, 0 to 30 parts of carbon black N990, 0 to 10 parts of magnesium oxide, 0 to 10 parts of calcium stearate, and 0.5 to 10 parts of a vulcanization accelerator.

10. A tetrafluoroethylene rubber composition according to claim 9, characterized in that: The vulcanization accelerator is a dehydration catalyst, including alkyl tin, fatty acid tin, fatty acid stannous, fatty acid alkyl tin, organic titanium compound, zirconate, alkyl acid bismuth, benzenesulfonic acid, benzenesulfonated acetyl.

Images