CN111875732B - Low-temperature-resistant fluororubber and preparation method thereof - Google Patents
Low-temperature-resistant fluororubber and preparation method thereof Download PDFInfo
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- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
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- C08F214/222—Vinylidene fluoride with fluorinated vinyl ethers
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- C08F2/00—Processes of polymerisation
- C08F2/001—Multistage polymerisation processes characterised by a change in reactor conditions without deactivating the intermediate polymer
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- C08F2/00—Processes of polymerisation
- C08F2/12—Polymerisation in non-solvents
- C08F2/16—Aqueous medium
- C08F2/22—Emulsion polymerisation
- C08F2/24—Emulsion polymerisation with the aid of emulsifying agents
- C08F2/30—Emulsion polymerisation with the aid of emulsifying agents non-ionic
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- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
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- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
- C08F214/28—Hexyfluoropropene
- C08F214/282—Hexyfluoropropene with fluorinated vinyl ethers
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- C08F216/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical
- C08F216/12—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical by an ether radical
- C08F216/14—Monomers containing only one unsaturated aliphatic radical
- C08F216/1408—Monomers containing halogen
Abstract
The invention belongs to the technical field of high polymer materials, and particularly relates to low-temperature-resistant fluororubber and a preparation method thereof, wherein the low-temperature-resistant fluororubber is prepared by suspension polymerization by using vinylidene fluoride, hexafluoropropylene and perfluoroalkyl vinyl ether as comonomers, using a mixture of olefin containing bromine in a main chain and bromine in a side chain as a vulcanization point monomer and using perfluoroalkyl iodide as a chain transfer agent, wherein two ends of a rubber molecular chain, the main chain and the side chain all contain vulcanizable groups, the glass transition temperature of the vulcanizable groups is as low as-30 to-35 ℃, and the low-temperature brittleness temperature of the vulcanizable groups is less than-40 ℃, so that the low-temperature property of the fluororubber is improved, and the fluororubber also has excellent mechanical strength and compression permanent deformation performance.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to low-temperature-resistant fluororubber and a preparation method thereof.
Background
Fluororubbers are widely researched and applied due to excellent comprehensive properties such as high temperature resistance, medium resistance and aging resistance, and become irreplaceable sealing materials. However, the conventional fluororubbers have poor low-temperature properties, and the lower use temperature for maintaining elasticity is only-15 ℃. With the continuous development of aerospace industry and national defense technology, the research on the low-temperature performance of fluororubber is increased day by day, and high-end perfluoroether rubber has excellent low-temperature resistance, but has high synthesis difficulty and extremely high production cost.
At present, fluororubber products in China are mainly the traditional 26 and 246 fluororubbers, the yield is high, the scale is large, copolymerization resistance modification is carried out on the basis of the traditional 26 and 246 fluororubbers, the low temperature resistance of the traditional fluororubbers is improved, and the method is an effective way for developing the low temperature resistant fluororubbers. The introduction of comonomer often damages the mechanical properties of fluororubbers and the post-vulcanization properties of fluororubbers. Therefore, it has been a technical problem in the art to balance various properties and to obtain a fluororubber having excellent low-temperature properties and also having excellent mechanical strength and compression set properties.
Disclosure of Invention
The low-temperature-resistant fluororubber is prepared by suspension polymerization by using vinylidene fluoride, hexafluoropropylene and perfluoroalkyl vinyl ether as comonomers, using a mixture of olefin containing bromine in a main chain and bromine in a side chain as a vulcanization point monomer and using perfluoroalkyl iodide as a chain transfer agent, wherein two ends of a rubber molecular chain, the main chain and the side chain all contain vulcanizable groups, the glass transition temperature of the vulcanizable groups is as low as-30 to-35 ℃, and the low-temperature brittleness temperature of the vulcanizable groups is less than-40 ℃, so that the low-temperature property of the fluororubber is improved, and the low-temperature-resistant fluororubber also has excellent mechanical strength and compression permanent deformation performance.
The innovation of the invention is that: in order to achieve the purpose, the inventor prepares the low-temperature-resistant fluororubber by suspension polymerization by using vinylidene fluoride, hexafluoropropylene and perfluoroalkyl vinyl ether as comonomers, using a mixture of olefin containing bromine in the main chain and bromine in the side chain as a vulcanization point monomer and using perfluoroalkyl iodide as a chain transfer agent.
The specific technical scheme of the invention is as follows:
the low temperature resistant fluororubber comprises the following raw materials in percentage by mass:
35-80 parts of vinylidene fluoride monomer, 20-55 parts of hexafluoropropylene and 1-15 parts of perfluoroalkyl vinyl ether; the molar ratio of the monomers containing the vulcanization points to the comonomer mixture is 0.01-0.2: 1;
wherein the perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether or perfluoroethyl vinyl ether or perfluoro-n-propyl vinyl ether;
the monomer containing the vulcanization point is a mixture of a main chain bromine-containing monomer and a side chain bromine-containing monomer, and the molar ratio of the mixture is 1: 0.5-2;
the main chain bromine-containing monomer comprises one or more of vinyl bromide, trifluorovinyl bromide, 2-bromine-1, 1-difluoroethylene and 2-bromine-3, 3, 3-trifluoropropene;
the side chain bromine-containing monomer comprises one or more of 3-bromo-3, 3-difluoropropene, 4-bromo-3, 3,4, 4-tetrafluorobutene, 4-bromo-1, 1, 2-trifluoro-1-butene, 1-bromo-2-chloro-1, 1, 2-trifluoro-3-butene, bromomethyl vinyl ether, 2-bromoperfluoro (ethyl vinyl ether) ether and 3-bromoperfluoro (propyl vinyl) ether;
on the basis of providing the raw materials, the inventor further provides a preparation method of the low temperature resistant fluororubber, which comprises the following specific synthetic steps:
(1) adding a mixed solvent of water and an organic solvent into a reaction container, wherein the volume of the mixed solvent accounts for 50-80% of the volume of the reaction container, adding a pH value regulator and an emulsifier, controlling the pH value to be 6-9, introducing a monomer mixture containing a comonomer and a vulcanization point monomer into the reaction container, enabling the pressure of the reactor to be 1.5-2.5 MPa and the temperature to be 70-90 ℃, then adding an initiator to initiate polymerization, and keeping the temperature stable in the polymerization process, wherein the fluctuation is not more than +/-2.5 ℃;
wherein the dosage of the initiator is as follows: the molar ratio of the initiator to the initial monomer mixture is 0.005-0.02: 50-300: 1; the molar ratio of the initial monomer mixture to the whole reaction monomer mixture is 1/4-3/4;
(2) because the comonomer is mostly a gas monomer, the system pressure is continuously reduced along with the polymerization, and when the pressure of a reaction vessel is reduced by 0.1-0.4 MPa, the comonomer is supplemented, so that the pressure of the reactor is kept at 1.5-2.5 MPa; until the addition of the comonomer is completed;
the molar ratio of the comonomer supplemented each time to the total amount of the whole comonomer is 0.01-0.2: 1;
(3) in the polymerization process, adding an initiator, a chain transfer agent and a vulcanization point monomer every 2-5 hours until the polymerization reaction is finished, wherein the polymerization reaction time is 10-15 hours, and obtaining a suspension product;
the molar ratio of the addition amount of the initiator to the initial addition amount of the initiator is 0.1-0.5: 1; the molar ratio of the initiator supplemented each time to the total amount of the initiator is 0.01-0.35: 1;
the molar ratio of the monomer addition amount of each vulcanization point to the monomer of the first vulcanization point is 0.01-0.4: 1, and the molar ratio of the monomer of each additional vulcanization point to the total monomer amount of the whole vulcanization point is 0.01-0.3: 1;
the molar ratio of the chain transfer agent replenished every time to the monomer mixture added for the first time is 0.001-0.02: 1, the molar ratio of the chain transfer agent replenished every time to the whole chain transfer agent addition is 0.1-0.5: 1.
the organic solvent in the step (1) is selected from one or a mixture of more than two of perfluorohexane, perfluorooctane, hydrofluoroether and fluoroether oil, and the adding amount of the organic solvent is 40-75% of the volume percentage of water;
the emulsifier is nonionic surfactant, ionic surfactant or a compound of the nonionic surfactant and the ionic surfactant, preferably, the emulsifier is a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate, and the mass ratio of the perfluoropolyether carboxylic acid to the polyoxyethylene oleate is 1: 0.2-0.5, and the mass volume ratio of the emulsifier to the water is 0.1-1.5 g/L;
the pH value regulator in the step (1) is one or a mixture of two of sodium dihydrogen phosphate, potassium dihydrogen phosphate and disodium hydrogen phosphate;
the pH value is controlled within 6-9 by the pH value regulator, and the main reason is that the strong acid environment is easy to cause polymerization acceleration and is uncontrollable, while the strong alkaline environment can cause polymerization stop, and the pH environment is the optimal reaction environment;
the initiator is bromo-fluoroalkoxy ether peroxide oligomer, and the molecular general formula of the initiator is as follows: (R)1(CF2OCF(CF3))nCOO)2Wherein R is1＝CBrF2Or CBrF2CF2；n＝1～3，
For example, (CBrF)2(CF2OCF(CF3))1COO)2Or (CBrF)2CF2(CF2OCF(CF3))2COO)2。
The chain transfer agent is perfluoroalkyl iodide, and the molecular general formula of the chain transfer agent is as follows: CF (compact flash)3CF2(CF2CF2)nI, n ═ 0 to 3, preferred perfluoroiodoalkanes are pentafluoroiodoethane, perfluoroiodobutane or perfluoroiodooctane;
the initiator adopts bromo-fluoroalkoxy ether peroxide oligomer containing crosslinking points capable of performing vulcanization crosslinking reaction, the initiator is decomposed to form perfluoroalkyl free radicals, and a stable perfluoro-terminal group structure can be formed after the polymerization of the initiating monomer, so that the influence of unstable terminal groups formed by common water-soluble initiators on the chemical stability of rubber can be avoided;
the chain transfer agent is a fluorine-containing alkyl compound, the end group formed after chain transfer is perfluoroalkyl, and the end group generated after the chain transfer of the common hydrocarbon chain transfer agent is non-fluorocarbon, so that the thermal stability and the chemical stability are poorer than those of the perfluoro end group.
After the polymerization reaction is finished, cooling the reaction container to room temperature, and recovering unreacted gas monomers; heating the suspension product to 70-90 deg.C to gasify the liquid reaction monomer and organic solvent, condensing and recovering; then, cooling the suspension, coagulating and filtering to obtain a solid product, and washing and drying to obtain the fluororubber solid.
The final fluororubber solid obtained by detection has the glass transition temperature of-35 to-30 ℃ and the molecular weight of 2 multiplied by 104-2×105g/mol, molecular weight distribution of 1.5-2.5. The glass transition temperature is far lower than 26 fluororubber, so that better fluororubber is endowedLow temperature resistance, and good mechanical property of the rubber with molecular weight and distribution close to 26 fluororubber.
Through the raw material selection and the corresponding preparation method, both ends of a molecular chain, a main chain and a side chain of the fluoroether rubber contain vulcanizable groups, and after the fluoroether-containing comonomer is added, the flexibility of the molecular chain of the fluoroether rubber can be effectively improved, the glass transition temperature of the material is reduced, the vulcanization speed and the mechanical property are not reduced due to a plurality of uniformly distributed vulcanization points in the molecular structure, and the problem that the introduction of the comonomer in the prior art often damages the mechanical property of the fluoroether and the later vulcanization property of the fluoroether rubber is solved. The initiator is bromo-fluoroalkoxy ether peroxide oligomer, a stable perfluoro-terminal group structure can be formed after the monomer is initiated to polymerize, the chain transfer agent is a fluoroalkyl compound, the terminal group formed after chain transfer is also perfluoroalkyl, the thermal stability and the chemical stability of the fluororubber can be obviously improved, and the problem that non-fluoroalkane unstable terminal groups are generated by common hydrocarbon chain transfer agents and water-soluble persulfate initiators is solved.
Overall the fluororubbers prepared according to the invention have improved flow properties, strength, compression set properties. The glass transition temperature can be as low as-35 to-30 ℃, and the excellent mechanical property and medium resistance of the traditional fluororubber are kept.
Detailed Description
The present invention is further illustrated below with reference to examples, which will enable those skilled in the art to more fully understand the present invention, but which are not intended to limit the invention in any way;
example 1:
a low temperature resistant fluororubber and a preparation method thereof, comprising the following steps:
2.5L of deionized water, 3.5g of sodium dihydrogen phosphate and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate in a mass ratio of 1: 0.5) were charged into a 6L stainless steel reaction vessel equipped with a stirrer, and after repeating pressurization with nitrogen and evacuation and degassing three times, 1.5L of fluoroether oil as an organic solvent and trifluorobromoethylene/3-bromoperfluoro (propylvinyl) as a main-chain type and side-chain type vulcanization site mixed monomer were charged through a metering pump40/60 (molar ratio) 35g of ether, 263g of mixed monomer of vinylidene fluoride/hexafluoropropylene/perfluoromethyl vinyl ether 55/40/5 (molar ratio) was charged into a reactor by a compressor, and the pressure was 1.75MPa at 80 ℃. 15g of bromofluoroalkoxy ether peroxyoligomer (CBrF) having a concentration of 10% by weight were added under pressure from a metering pump2(CF2OCF(CF3))1COO)2The fluoroether oil solution to initiate polymerization.
As the pressure of the reaction vessel decreases, every time the pressure of the reaction vessel decreases to 1.55MPa, 75/23/2 (molar ratio) of the mixed monomer of vinylidene fluoride/hexafluoropropylene/perfluoromethyl vinyl ether is added, and the pressure in the reaction vessel is kept at 1.75 MPa. During the reaction, 6g of the initiator solution is added every 3 hours, the vulcanization point mixed monomer trifluorobromoethylene/3-bromoperfluoro (propyl vinyl) ether is 40/60 (molar ratio) 10g, the chain transfer agent pentafluoroiodoethane is 9g, and when the amount of the added comonomer reaches 450g, the reaction is finished (the reaction time is 12 hours); recovering unreacted gas monomer, gasifying liquid reaction monomer and organic solvent, condensing and recovering to obtain 5kg of fluororubber resin suspension; cooling the suspension, coagulating with magnesium chloride water solution, filtering, washing, drying, and drying in 80 deg.c vacuum drying oven for 12 hr to obtain fluororubber product.
The glass transition temperature is detected to be-33 ℃, and the molecular weight is 4.9 multiplied by 104g/mol, molecular weight distribution 1.85.
Example 2:
a low temperature resistant fluororubber and a preparation method thereof, comprising the following steps:
2.5L of deionized water, 3.5g of sodium dihydrogen phosphate, and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate at a mass ratio of 1: 0.5) were charged into a 6L stainless steel reaction vessel equipped with a stirrer, nitrogen pressurization and evacuation degassing were repeated three times, and then 1.5L of fluoroether oil as an organic solvent, 35g of trifluorobromoethylene/3-bromoperfluoro (propyl vinyl) ether as a main-chain type and side-chain type vulcanization site mixed monomer (molar ratio), and 285g of mixed monomer of vinylidene fluoride/hexafluoropropylene/perfluoroethyl vinyl ether (molar ratio) 55/40/5 (molar ratio) was charged into the reaction vessel by a compressor, and the pressure at 80 ℃ was 1.78 MPa. Pass meter15g of bromofluoroalkoxy ether peroxyoligomer (CBrF) with a concentration of 10 wt.% were added under pressure from a pump2(CF2OCF(CF3))1COO)2The fluoroether oil solution to initiate polymerization.
As the pressure of the reaction vessel decreases, 75/23/2 mole ratio of vinylidene fluoride/hexafluoropropylene/perfluoroethyl vinyl ether was added each time the pressure of the reaction vessel decreased to 1.58MPa, and the pressure in the reaction vessel was maintained at 1.78 MPa. As the reaction proceeded, 6g of the above initiator solution was added every 3 hours, 6.5g of the vulcanization point mixed monomer trifluorobromoethylene/3-bromoperfluoro (propyl vinyl) ether (molar ratio) 60/40, and 7g of chain transfer agent pentafluoroiodoethane; when the amount of the additional comonomer reaches 465g, the reaction is ended (the reaction lasts for 12.5 hours); unreacted gas monomer is recovered, liquid reaction monomer and organic solvent are gasified and condensed for recovery, and about 5kg of fluororubber resin suspension is obtained. And (3) condensing the suspension by using a magnesium chloride aqueous solution after cooling, filtering, washing, drying, and continuously drying in a vacuum drying oven at the temperature of 80 ℃ for 12 hours to obtain the fluororubber product.
The glass transition temperature is detected to be-31 ℃, and the molecular weight is 8.7 multiplied by 104g/mol, molecular weight distribution 1.95.
Example 3:
a low temperature resistant fluororubber and a preparation method thereof, comprising the following steps:
2.5L of deionized water, 3.5g of sodium dihydrogen phosphate, and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate at a mass ratio of 1: 0.4) were charged into a 6L stainless steel reaction vessel equipped with a stirrer, nitrogen pressurization and evacuation degassing were repeated three times, and then 1.5L of fluoroether oil as an organic solvent, 50/50 (molar ratio) 35g of mixed monomers of main chain type and side chain type vulcanization site 2-bromo-1, 1-difluoroethylene/3-bromoperfluoro (propyl vinyl) ether, 295g of mixed monomers of vinylidene fluoride/hexafluoropropylene/perfluoropropyl vinyl ether (molar ratio) were charged into the reaction vessel by a compressor, and the pressure at 80 ℃ was 1.86MPa, were charged into the reaction vessel by a metering pump. 15g of bromofluoroalkoxy ether peroxyoligomer (CBrF) having a concentration of 10% by weight were added under pressure from a metering pump2(CF2OCF(CF3))1COO)2In a fluoroether oil solution, leadAnd (4) performing polymerization.
As the pressure of the reaction vessel decreased, every time the pressure of the reaction vessel decreased to 1.66MPa, 75/23/2 (molar ratio) of the mixed monomer of vinylidene fluoride/hexafluoropropylene/perfluoropropyl vinyl ether was additionally added, and the pressure in the reaction vessel was maintained at 1.86 MPa. As the reaction proceeded, 6g of the above initiator solution was added every 3 hours, 50/50 g (molar ratio) of 2-bromo-1, 1-difluoroethylene/3-bromoperfluoro (propyl vinyl) ether as a vulcanization point mixed monomer, and 6g of pentafluoroiodoethane as a chain transfer agent. When the amount of the additional comonomer reached 505g, the reaction was terminated (the reaction was continued for 13.5 hours); unreacted gas monomer is recovered, liquid reaction monomer and organic solvent are gasified and condensed for recovery, and about 5kg of fluororubber resin suspension is obtained. And (3) condensing the suspension by using a magnesium chloride aqueous solution after cooling, filtering, washing, drying, and continuously drying in a vacuum drying oven at the temperature of 80 ℃ for 12 hours to obtain the fluororubber product.
The glass transition temperature is detected to be-30 ℃, and the molecular weight is 1.02 multiplied by 105g/mol, molecular weight distribution 1.87.
Example 4:
a low temperature resistant fluororubber and a preparation method thereof, comprising the following steps:
2.5L of deionized water, 3.5g of sodium dihydrogen phosphate, and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate at a mass ratio of 1: 0.5) were charged into a 6L stainless steel reaction vessel equipped with a stirrer, nitrogen pressurization and evacuation degassing were repeated three times, and then 1.5L of fluoroether oil as an organic solvent, 50/50 g (molar ratio) of 2-bromo-1, 1-difluoroethylene/3-bromoperfluoro (propyl vinyl) ether as a main-chain type and side-chain type vulcanization site mixed monomer, 245g of vinylidene fluoride/hexafluoropropylene/perfluoropropyl vinyl ether 55/40/5 (molar ratio) mixed monomer was charged into the reaction vessel by a compressor, and the pressure was 1.50MPa at 80 ℃. 15g of bromofluoroalkoxy ether peroxyoligomer (CBrF) having a concentration of 10% by weight were added under pressure from a metering pump2(CF2OCF(CF3))1COO)2The fluoroether oil solution to initiate polymerization.
As the pressure of the reaction vessel decreased, every time the pressure of the reaction vessel decreased to 1.25MPa, 75/23/2 (molar ratio) of the mixed monomer of vinylidene fluoride/hexafluoropropylene/perfluoropropyl vinyl ether was additionally added, and the pressure in the reaction vessel was maintained at 1.50 MPa. As the reaction proceeded, 5g of the above initiator solution was added every 3 hours, 8g of 2-bromo-1, 1-difluoroethylene/3-bromoperfluoro (propyl vinyl) ether as a vulcanization point mixed monomer (molar ratio) 50/50, and 12g of perfluoroiodobutane as a chain transfer agent were added. When the additional comonomer amount reached 540g, the reaction was complete (reaction was continued for 14.5 hours); the unreacted monomer was recovered to give about 5kg of the fluororubber resin suspension. Heating to recover organic solvent, cooling, coagulating with magnesium chloride water solution, filtering, washing, drying, and drying in 80 deg.C vacuum drying oven for 12 hr to obtain fluororubber product.
The glass transition temperature is detected to be-31 ℃, and the molecular weight is 9.2 multiplied by 104g/mol, molecular weight distribution 2.03.
Comparative example 1
A common 26 fluororubber and a preparation method thereof comprise the following steps:
2.5L of deionized water, 3.5g of sodium dihydrogen phosphate and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate in a mass ratio of 1: 0.5) were charged into a 6L stainless steel reaction vessel equipped with a stirrer, nitrogen pressurization and evacuation and degassing were repeated three times, 1.5L of fluoroether oil as an organic solvent was then charged into the reaction vessel through a metering pump, 270g of a mixed monomer containing vinylidene fluoride/hexafluoropropylene (molar ratio) 60/40 was charged into the reaction vessel through a compressor, and the pressure was 1.65MPa at 80 ℃. 15g of bromofluoroalkoxy ether peroxyoligomer (CBrF) having a concentration of 10% by weight were added under pressure from a metering pump2(CF2OCF(CF3))1COO)2The fluoroether oil solution to initiate polymerization.
When the pressure in the reaction vessel was reduced to 1.45MPa, 75/25 (molar ratio) of the monomer mixture of vinylidene fluoride/hexafluoropropylene was added thereto, and the pressure in the reaction vessel was kept at 1.65 MPa. As the reaction proceeded, 6g of the above initiator solution was added every 3 hours, and 6g of pentafluoroiodoethane as a chain transfer agent was added. When the additional comonomer amount reached 490g, the reaction was complete (reaction lasted for 12 hours) and the unreacted monomers were recovered to give about 5kg of fluoroelastomer resin suspension. Heating to recover organic solvent, cooling, coagulating with magnesium chloride water solution, filtering, washing, drying, and drying in 80 deg.C vacuum drying oven for 12 hr to obtain common 26-fluororubber product.
The glass transition temperature is detected to be-14 ℃, and the molecular weight is 1.5 multiplied by 105g/mol, molecular weight distribution 2.56.
Comparative example 2
A common 26 fluororubber and a preparation method thereof comprise the following steps:
in a 6L stainless steel reaction vessel equipped with a stirrer, 2.5L of deionized water, 3.5g of sodium dihydrogenphosphate, and 3g of an emulsifier (a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate in a mass ratio of 1: 0.5) were charged, nitrogen pressurization and evacuation and degassing were repeated three times, and then 255g of a mixed monomer (molar ratio) of vinylidene fluoride/hexafluoropropylene/perfluoropropyl vinyl ether (75/23/2) was charged into the reaction vessel by a compressor, and the pressure was 1.98MPa at 80 ℃. Polymerization was initiated by adding 15g of a 10% strength by weight aqueous ammonium persulfate solution under pressure from a metering pump.
When the pressure in the reaction vessel was reduced to 1.78Mpa, 75/25 mole ratio of the vinylidene fluoride/hexafluoropropylene mixture was added, and the pressure in the reaction vessel was maintained at 1.98 Mpa. As the reaction proceeded, 6g of the initiator, i.e., 10 wt% aqueous ammonium persulfate solution, was supplemented every 3 hours, and 8g of pentafluoroethyl iodide, a chain transfer agent, was added. When the amount of the additional comonomer reached 480g, the reaction was terminated (the reaction was continued for 12 hours), and about 5kg of the fluororubber resin emulsion was obtained. And after cooling the emulsion, condensing by using a magnesium chloride aqueous solution, filtering, washing, drying, and continuously drying in a vacuum drying oven at the temperature of 80 ℃ for 12 hours to obtain a common 26 fluororubber product.
The glass transition temperature is detected to be-19 ℃, and the molecular weight is 1.3 multiplied by 105g/mol, molecular weight distribution 2.48.
The obtained fluororubber product was plasticized and molded on an open mill according to the formulation (as shown in table 1), and the properties of the fluororubber obtained by vulcanization are shown in table 2. As can be seen from the properties of the fluororubber products in examples 1 to 4, the fluororubber of the invention has better low temperature resistance and thermal aging resistance, and the tensile strength and the elongation at break are similar to those of the common 26 fluororubbers. The two ends, the main chain and the side chain of the molecular chain of the fluororubber prepared by the invention all contain the sulfurable groups, so that the problems of mechanical property of the fluororubber and later vulcanization property of the fluororubber are not damaged while the glass transition temperature of the material is reduced. The glass transition temperature of comparative example 1 is only-12 deg.c, while that of comparative example 2 can be lowered to-18 deg.c by adding fluoroether monomer, but the mechanical strength of the vulcanized rubber is remarkably lowered due to the decrease of vulcanization point and the decrease of crosslinking density.
TABLE 1 vulcanization formulation
TABLE 2 fluororubber article Properties
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not limited to the embodiments described above. Any equivalent modifications and substitutions to those skilled in the art are also within the scope of the present invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.
Claims (7)
1. A low temperature resistant fluororubber is characterized in that: the raw materials comprise the following components in percentage by mass:
the comonomers are: 35-80 parts of vinylidene fluoride monomer, 20-55 parts of hexafluoropropylene and 1-15 parts of perfluoroalkyl vinyl ether; the molar ratio of the monomer containing the vulcanization point to the comonomer is 0.01-0.2: 1;
wherein the perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether or perfluoroethyl vinyl ether or perfluoro-n-propyl vinyl ether;
the monomer containing the vulcanization point is a mixture of a main chain bromine-containing monomer and a side chain bromine-containing monomer, and the molar ratio of the main chain bromine-containing monomer to the side chain bromine-containing monomer in the mixture is 1: 0.5-2;
the specific synthesis steps comprise:
(1) adding a mixed solvent of water and an organic solvent into a reaction container, wherein the volume of the mixed solvent accounts for 50-80% of the volume of the reaction container, adding a pH value regulator and an emulsifier, controlling the pH value to be 6-9, introducing an initial monomer mixture containing a comonomer and a vulcanization point monomer into the reaction container, enabling the pressure of the reactor to be 1.5-2.5 MPa and the temperature to be 70-90 ℃, then adding an initiator to initiate polymerization reaction, and keeping the temperature stable in the polymerization process, wherein the fluctuation is not more than +/-2.5 ℃;
wherein the molar ratio of the initiator to the initial monomer mixture is 0.005-0.02: 50-300: 1; the molar ratio of the initial monomer mixture to the whole reaction monomer mixture is 1/4-3/4;
(2) when the pressure of the reaction container is reduced by 0.1-0.4 MPa, supplementing the comonomer, and keeping the pressure of the reactor at 1.5-2.5 MPa; until the addition of the comonomer is completed;
the molar ratio of the comonomer supplemented each time to the total amount of the whole comonomer is 0.01-0.2: 1;
(3) in the polymerization process, adding an initiator, a chain transfer agent and a vulcanization point monomer every 2-5 hours until the polymerization reaction is finished, wherein the polymerization reaction time is 10-15 hours, and obtaining a suspension product;
the molar ratio of the addition amount of the initiator to the initial addition amount of the initiator is 0.1-0.5: 1; the molar ratio of the initiator supplemented each time to the total amount of the initiator is 0.01-0.35: 1;
the molar ratio of the monomer addition amount of each vulcanization point to the monomer of the first vulcanization point is 0.01-0.4: 1, and the molar ratio of the monomer of each additional vulcanization point to the total monomer amount of the whole vulcanization point is 0.01-0.3: 1;
the molar ratio of the chain transfer agent supplemented each time to the initial monomer mixture is 0.001-0.02: 1, the molar ratio of the chain transfer agent replenished every time to the whole chain transfer agent addition is 0.1-0.5: 1.
2. the low temperature-resistant fluororubber according to claim 1, wherein:
the main chain bromine-containing monomer comprises one or more of vinyl bromide, trifluorovinyl bromide, 2-bromine-1, 1-difluoroethylene and 2-bromine-3, 3, 3-trifluoropropene;
the side chain bromine-containing monomer comprises one or more of 3-bromine-3, 3-difluoropropylene, 4-bromine-3, 3,4, 4-tetrafluorobutene, 4-bromine-1, 1, 2-trifluoro-1-butene, 1-bromine-2-chlorine-1, 1, 2-trifluoro-3-butene, bromomethyl vinyl ether, 2-bromine perfluoroethyl vinyl ether and 3-bromine perfluoropropyl vinyl ether.
3. The process for producing a low-temperature-resistant fluororubber according to claim 1, wherein: the specific synthesis steps comprise:
(1) adding a mixed solvent of water and an organic solvent into a reaction container, wherein the volume of the mixed solvent accounts for 50-80% of the volume of the reaction container, adding a pH value regulator and an emulsifier, controlling the pH value to be 6-9, introducing an initial monomer mixture containing a comonomer and a vulcanization point monomer into the reaction container, enabling the pressure of the reactor to be 1.5-2.5 MPa and the temperature to be 70-90 ℃, then adding an initiator to initiate polymerization reaction, and keeping the temperature stable in the polymerization process, wherein the fluctuation is not more than +/-2.5 ℃;
wherein the molar ratio of the initiator to the initial monomer mixture is 0.005-0.02: 50-300: 1; the molar ratio of the initial monomer mixture to the whole reaction monomer mixture is 1/4-3/4;
(2) when the pressure of the reaction container is reduced by 0.1-0.4 MPa, supplementing the comonomer, and keeping the pressure of the reactor at 1.5-2.5 MPa; until the addition of the comonomer is completed;
the molar ratio of the comonomer supplemented each time to the total amount of the whole comonomer is 0.01-0.2: 1;
(3) in the polymerization process, adding an initiator, a chain transfer agent and a vulcanization point monomer every 2-5 hours until the polymerization reaction is finished, wherein the polymerization reaction time is 10-15 hours, and obtaining a suspension product;
the molar ratio of the addition amount of the initiator to the initial addition amount of the initiator is 0.1-0.5: 1; the molar ratio of the initiator supplemented each time to the total amount of the initiator is 0.01-0.35: 1;
the molar ratio of the monomer addition amount of each vulcanization point to the monomer of the first vulcanization point is 0.01-0.4: 1, and the molar ratio of the monomer of each additional vulcanization point to the total monomer amount of the whole vulcanization point is 0.01-0.3: 1;
the molar ratio of the chain transfer agent supplemented each time to the initial monomer mixture is 0.001-0.02: 1, the molar ratio of the chain transfer agent replenished every time to the whole chain transfer agent addition is 0.1-0.5: 1.
4. the method for producing a low temperature-resistant fluororubber according to claim 3, characterized by comprising:
the organic solvent in the step (1) is selected from one or a mixture of more than two of perfluorohexane, perfluorooctane, hydrofluoroether and fluoroether oil, and the addition amount of the organic solvent is 40-75% of the volume percentage content of water;
the emulsifier is a nonionic surfactant, an ionic surfactant or a compound of the nonionic surfactant and the ionic surfactant, and the mass volume ratio of the emulsifier to water is 0.1-1.5 g/L;
the pH value regulator in the step (1) is one or a mixture of two of sodium dihydrogen phosphate, potassium dihydrogen phosphate and disodium hydrogen phosphate;
the initiator is bromo-fluoroalkoxy ether peroxide oligomer, and the molecular general formula of the initiator is as follows: (R)1(CF2OCF(CF3))nCOO)2Wherein R is1= CBrF2Or CBrF2CF2；n=1～3；
The chain transfer agent is perfluoroalkyl iodide, and the molecular general formula of the chain transfer agent is as follows: CF (compact flash)3CF2(CF2CF2)nI ；n = 0-3。
5. The method for producing a low temperature-resistant fluororubber according to claim 3, characterized by comprising: the emulsifier is a mixture of perfluoropolyether carboxylic acid and polyoxyethylene oleate, and the mass ratio of the perfluoropolyether carboxylic acid to the polyoxyethylene oleate is 1: 0.2 to 0.5.
6. The method for producing a low temperature-resistant fluororubber according to claim 3, characterized by comprising: the initiator is (CBrF)2(CF2OCF(CF3))1COO)2Or (CBrF)2CF2 (CF2OCF(CF3))2COO)2。
7. The method for producing a low temperature-resistant fluororubber according to claim 4, characterized by comprising: the perfluoro iodoalkane is pentafluoroiodoethane, pentafluoroiodobutane or perfluoro iodooctane.
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