A perfluoroalkyl ether copolymer with low carbonyl end group content and its preparation method

Abstract

This invention belongs to the field of polymer materials, specifically relating to a perfluoroalkyl ether copolymer with low carbonyl end-group content and its preparation method. The preparation method employs a two-stage polymerization process. In the presence of a chain transfer agent containing halogen end groups, the polymerization of tetrafluoroethylene, perfluoroalkyl vinyl ether, and a monomer with a low sulfidation point is initiated in the first stage using a water-soluble inorganic initiator. In the second stage, polymerization is continuously initiated using a water-soluble organic initiator. This process introduces more organic groups into the polymer chain ends, reducing the proportion of ionic end groups in the polymer and consequently lowering the content of unstable carbonyl end groups formed by the hydrolysis of ionic end groups. The perfluoroalkyl ether copolymer prepared by this method not only exhibits good tensile strength and elongation at break but also excellent aging resistance and high-temperature compression set resistance.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer materials, specifically relating to a perfluoroalkyl ether copolymer with low carbonyl end group content and its preparation method. Background Technology

[0002] The carbonyl end groups of perfluoroalkyl ether copolymers are unstable under high temperature conditions (>250℃). If the proportion of such unstable end groups is not reduced, it will not only affect the sealing performance of perfluoroalkyl ether copolymer products and reduce the service life of perfluoroalkyl ether copolymers, but also make the vulcanization process of perfluoroalkyl ether copolymers difficult, thereby limiting the application of perfluoroalkyl ether copolymer products in high-tech fields.

[0003] CN1235572A discloses a stabilization method for fluoropolymers, which effectively removes unstable end groups from fluoropolymers during melt mixing using a twin-screw extruder. However, under high-temperature processing conditions, active crosslinking sites in the copolymer may be activated, making it prone to crosslinking, ultimately leading to excessively high viscosity and a noticeable yellowing of the processed polymer.

[0004] CN103172767A discloses a method for perfluorination of end groups of fluoropolymers, which uses end-group stabilizing reagents to perfluorinate the end groups of fluoropolymers. However, the fluoropolymers need to be in powder or flake form. For gel-like copolymers, it is difficult to achieve complete fluorination of carboxyl end groups using this method, and fluorination will reduce the sulfidation point.

[0005] CN102007150B discloses a perfluorinated elastomer with a low carbonyl end group ratio, which uses persulfate and perfluoroalkyl sulfinates as redox initiators to prepare perfluorinated copolymers. However, this method requires the synthesis of perfluoroalkyl sulfinates first, which leads to complex processes and increased costs.

[0006] CN101429264A discloses a method for preparing fluororubber with a wide molecular weight distribution. It uses an oil-soluble initiator to initiate the polymerization of fluorinated monomers to manufacture fluororubber. Although this method can effectively reduce the content of nonionic end groups, it makes the latex extremely unstable, prone to wall clumping and agglomeration, and difficult to wash.

[0007] Therefore, there is an urgent need to develop a perfluorinated copolymer that is simple to process, low in cost, and has high latex stability, so that the prepared perfluorinated copolymer has a lower carbonyl end group ratio, improved tensile strength and elongation at break, and excellent resistance to high temperature compression set. Summary of the Invention

[0008] The present invention aims to provide a perfluoroalkyl ether copolymer with low carbonyl end group content and its preparation method. The preparation method employs a two-stage polymerization process. In the presence of a chain transfer agent containing halogen end groups, the polymerization of tetrafluoroethylene, perfluoroalkyl vinyl ether, and sulfur-point monomers is initiated in the first stage using a water-soluble inorganic initiator. In the second stage, polymerization is continuously initiated using a water-soluble organic initiator. This process introduces more organic groups into the polymer chain ends, reducing the proportion of ionic end groups in the polymer and consequently lowering the content of unstable carbonyl end groups formed by the hydrolysis of ionic end groups.

[0009] The perfluoroalkyl ether copolymers prepared by this method not only have good tensile strength and elongation at break, but also excellent aging resistance and high-temperature compression set resistance.

[0010] The technical solution of this invention is as follows: A method for preparing a perfluoroalkyl ether copolymer, comprising the following steps: (1) Weigh out water, pH buffer, emulsifier and chain transfer agent and add them to the reactor; wherein, by weight, water is 100 parts, pH buffer is 0.1-0.5 parts, emulsifier is 0.1-5 parts and chain transfer agent is 0.01-0.5 parts.

[0011] (2) Add the initial monomers tetrafluoroethylene, perfluoroalkyl vinyl ether and sulfidation point monomer, stir at 200-500 rpm, polymerize at 55-90℃, and polymerize at 1.4-2.2 MPa; The molar ratio of tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfidation point monomer: chain transfer agent is (30-55):(40-70):(0.1-6):(0.05-2).

[0012] (3) In the first stage, an inorganic free radical initiator is added to initiate polymerization, and monomers are continuously added to maintain the polymerization pressure at 1.4-2.2 MPa; wherein, the molar ratio of the added monomers tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer is (50-65):(30-45):(0.1-6).

[0013] (4) After the reaction has been going on for 0.5-1h, the temperature of the reactor is raised to 65-100℃. The monomer is rapidly added to the reactor at a pressure of 2.3-3.5MPa according to the molar ratio of tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer of (30-55):(40-70):(0.1-6).

[0014] (5) In the second stage, an organic free radical initiator is added, the reaction temperature is maintained at 65-100℃, monomers are continuously added, and the polymerization pressure is maintained at 2.3-3.5MPa; When the total amount of the three monomers—tetrafluoroethylene, perfluoroalkyl vinyl ether, and sulfur point monomer—is 55%-56% of the amount of water added, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion.

[0015] The molar ratio of the added monomer tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer is (50-65):(30-45):(0.1-6).

[0016] (6) The polymer emulsion is coagulated, washed, dried, and then plasticized and shaped using an open mill.

[0017] Magnesium chloride can be used to coagulate the polymer emulsion. After washing several times with pure water, the emulsion is dried at 110°C for 10 hours and then plasticized and shaped using a two-roll mill.

[0018] In this invention, the chain transfer agent in step (1) of the preparation method of the perfluoroalkyl ether copolymer is a C1-C8 perfluoroalkane containing bromine and / or iodine atoms; its general formula is: R f2 I x Br y In the formula, x and y are integers from 0 to 2, and satisfy 1 ≤ x + y ≤ 2, R f2 C 1-8 Perfluoroalkyl chains.

[0019] Chain transfer agents can be, for example, diiodoperfluoromethane, 1,2-diiodoperfluoroethane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,5-diiodoperfluoropentane, 1,6-diiodoperfluorohexane, 1,7-diiodoperfluoroheptane, 1,8-diiodoperfluorooctane, 1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, etc.

[0020] Preferably, the chain transfer agent is at least one selected from 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, or 2-iodoperfluoropropane.

[0021] More preferably, the chain transfer agent is 1,4-diiodoperfluorobutane or 1,6-diiodoperfluorohexane.

[0022] In the present invention, the perfluoroalkyl ether copolymer preparation method, wherein the perfluoroalkyl vinyl ether in step (2) is at least one of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether or perfluoropropyl vinyl ether.

[0023] In this invention, the perfluoroalkyl ether copolymer preparation method, in step (2), uses a monomer with the general formula CF2=CFOR. f1 X, where R is... f1 It is C 1-10The perfluoroalkyl or perfluoroalkoxy chain, where X represents either iodine or bromine.

[0024] The sulfurization point monomer used is a sulfurization point monomer containing sulfur-curable end groups. The sulfurization point monomer can be: CF2 = CFO(CF2). n X, CF2 = CFO(CF2) n OCF2X, CF2=CFO(CF2) n OCF(CF3)X, CF2=CFO[CF2CF(CF3)O] m (CF2) n X; where X is a halogen group, n is, for example, 1-5, and m is, for example, 1-5.

[0025] Preferably, the sulfurization point monomer can be: CF2=CFO(CF2)2I, CF2=CFO(CF2)2Br, CF2=CFO(CF2)3Br, CF2=CFO(CF2)3I, CF2=CFO(CF2)4Br, CF2=CFO(CF2)4I, CF2=CFO(CF2)3OCF2I, CF2=CFO(CF2)3OCF2Br, CF2=CFO(CF2)4OCF2I, CF2 =CFO(CF2)2OCF(CF3)I, CF2=CFO(CF2)2OCF(CF3)Br, CF2=CFO(CF2)3OCF(CF3)I, CF2=CFOCF2CF(CF3)O (CF2)2I, CF2=CFOCF2CF(CF3)O(CF2)3I, CF2=CFO[CF2CF(CF3)O]2CFI, CF2=CFO[CF2CF(CF3)O]4CFI, etc.

[0026] More preferably, the sulfurization point monomer is at least one of CF2=CFO(CF2)2I, CF2=CFO(CF2)2Br, CF2=CFO(CF2)3Br, CF2=CFO(CF2)3I, CF2=CFO(CF2)3OCF2I, CF2=CFO(CF2)3OCF2Br, and CF2=CFO(CF2)4OCF2I.

[0027] In this invention, in the preparation method of the perfluoroalkyl ether copolymer, the amount of the inorganic free radical initiator in step (3) is 0.03-0.08% of the total mass of the monomer. The inorganic free radical initiator within the above dosage range helps to minimize the unstable carboxyl end groups at the molecular chain ends of the fluoropolymer.

[0028] In this invention, the inorganic free radical initiator in step (3) of the preparation method of the perfluoroalkyl ether copolymer is at least one of potassium persulfate, ammonium persulfate or sodium persulfate.

[0029] In the first stage of polymerization, a water-soluble inorganic free radical initiator is used, which can be sodium, potassium, or ammonium salts of persulfate, perboric acid, percarbonate, or perchloric acid.

[0030] In the present invention, in the preparation method of the perfluoroalkyl ether copolymer, the amount of the organic free radical initiator in step (5) is 0.1-0.2% of the total mass of the monomer.

[0031] In this invention, the organic free radical initiator in step (5) of the preparation method of the perfluoroalkyl ether copolymer is at least one of azoisobutylcyanoformamide, azobisisobutylamidine hydrochloride or azobisisobutylimidazolium hydrochloride.

[0032] Preferably, the organic free radical initiator is azobisisobutyramidine hydrochloride and / or azobisisobutyramidine hydrochloride.

[0033] In the second stage of polymerization, a water-soluble organic free radical initiator is used instead, which is a water-soluble azo compound.

[0034] In the present invention, the polymerization pressure in the first stage of step (3) of the preparation method of the perfluoroalkyl ether copolymer is 1.7-2.0 MPa.

[0035] When an organic initiator is used in the second stage of polymerization, there is a problem of low initiation efficiency caused by hydrolysis. In this stage, following the polymerization pressure range described above can not only increase the polymerization rate, but also ensure that the molecular weight of the raw rubber does not change significantly.

[0036] In the preparation method of the perfluoroalkyl ether copolymer of the present invention, the polymerization pressure in the second stage of step (5) is 2.4-3.0 MPa.

[0037] A perfluoroalkyl ether copolymer, prepared by the above method, wherein the monomer composition of the perfluoroalkyl ether copolymer is 40-75 mol of tetrafluoroethylene, 24-50 mol of perfluoroalkyl vinyl ether, and 0.01-10 mol of sulfurizing point monomer.

[0038] Preferably, the monomer composition of the perfluoroalkyl ether copolymer is 50-70 mol of tetrafluoroethylene, 29-44 mol of perfluoroalkyl vinyl ether, and 0.1-6 mol of sulfurization point monomer.

[0039] In this invention, the perfluoroalkyl ether copolymer has a carbonyl end group content of less than 0.01%; the Mooney viscosity of the perfluoroalkyl ether copolymer at ML1+10 and 121°C is 35-100 MU. The Mooney viscosity is measured according to ASTM D1646 standard.

[0040] Preferably, the perfluoroalkyl ether copolymer has a Mooney viscosity of 35-80 MU at ML1+10 and 121°C.

[0041] More preferably, the perfluoroalkyl ether copolymer has a Mooney viscosity of 60-80 MU at ML1+10 and 121°C.

[0042] Mooney viscosity is an indicator of different weight-average molecular weights: a higher Mooney viscosity value indicates a higher molecular weight. If the Mooney viscosity value is too high, the mixing process becomes difficult. Rubber with a Mooney viscosity between 35 MU and 80 MU is easy to mix, and the resulting vulcanized and crosslinked rubber exhibits excellent properties.

[0043] The absorbance of the perfluoroalkyl ether copolymer was measured using Fourier transform infrared spectroscopy, and the carbonyl end group content was found to be 1840 cm⁻¹. -1 ~1620cm -1 "Total absorbance" and "2740cm" -1 ~2220cm -1 The integral peak area ratio of the total absorbance is less than 0.01, meaning that the carbonyl end group content of the perfluoroalkyl ether copolymer provided by this invention is less than 0.01.

[0044] The products made from the perfluoroalkyl ether copolymer include gaskets, seals, and sealing rings.

[0045] The beneficial effects of this invention are as follows: The preparation method described herein employs a two-stage polymerization process, using at least two free radical initiators in an aqueous medium. A water-soluble inorganic free radical initiator is used in the first reaction stage, while a water-soluble organic free radical initiator is used in the second reaction stage. By adopting a two-stage polymerization approach to introduce organic groups at the ends of the polymer molecular chains, the content of unstable end groups formed by the hydrolysis of ionic end groups during polymerization is reduced, thus resolving the conflict between the increased reaction rate due to increased initiator dosage and the decreased carbonyl end group content.

[0046] The preparation method of the low carbonyl-terminated perfluoroalkyl ether copolymer described in this invention yields a perfluoroalkyl ether copolymer with fewer carbonyl end groups compared to existing products. This results in better tensile strength and elongation at break, as well as excellent aging resistance, high-temperature compression set resistance, and good sealing performance.

[0047] Compared with existing technologies, this invention proposes for the first time a process for initiating the polymerization of perfluoroalkyl ether copolymers in two stages using water-soluble inorganic initiators and water-soluble organic initiators. This reduces the proportion of unstable end groups while avoiding the problem of low initiation efficiency caused by using oil-soluble organic initiators in the later stages, thus solving the conflict between increasing the reaction rate and reducing the carbonyl end group content.

[0048] Furthermore, the use of a water-soluble organic initiator in the later stages makes the polymerization process easier to control, resulting in a latex that is less prone to wall clumping and easier to wash, and exhibits high latex stability. The resulting product is uniform and stable, ensuring the mechanical and sealing properties of the perfluoroalkyl ether copolymer. Attached Figure Description

[0049] Figure 1 Fourier transform infrared spectra of characteristic groups of perfluoroalkyl ether copolymers. Detailed Implementation

[0050] The technical solution of the present invention will be described in detail below.

[0051] 1. Testing Method NMR analysis: The polymer adhesive is subjected to NMR analysis to determine its composition.

[0052] FTIR: The carbonyl content was determined by the integrated absorbance ratio of the FTIR spectrum of the perfluoroalkyl ether copolymer. The Fourier transform infrared spectrum of the perfluoroalkyl ether copolymer was plotted, and the absorbance peak area (1840–1620 cm⁻¹) was used as the basis for the determination. -1 ) and peak area (2740~2220cm) -1 The carbonyl content is determined by the ratio of ( ) to ( ).

[0053] 2. Mooney viscosity determination: The Mooney viscosity was determined according to ASTM D1646 standard, using a 1-minute preheating period and a 10-minute test period, with a test temperature of 121°C.

[0054] 3. Physical and mechanical properties testing: The physical and mechanical properties of the perfluoroalkyl ether copolymer vulcanized rubber were determined according to ASTM D412 standard.

[0055] 4. Compression set test: The compression set of perfluoroalkyl ether copolymer vulcanized rubber was determined according to ASTM D395 standard. The test specimen was an O-ring, and the test conditions were 230℃ × 70h.

[0056] 5. Aging: The perfluoroalkyl ether copolymer vulcanized rubber was subjected to a hot air aging test according to GB / T3512-2014 standard. The hot air aging conditions were 230℃×70h.

[0057] Example 1 The specific steps for preparing the perfluoroalkyl ether copolymer are as follows: (1) Add 2700g of deionized water, 5g of dipotassium hydrogen phosphate, 60g of CF3(CF2OCF(CF3))2COONH4 (emulsifier) ​​and 10g of 1,4-diiodoperfluorobutane (chain transfer agent) to a 5L reactor with an oxygen content of less than 20ppm.

[0058] (2) Add the initial monomers tetrafluoroethylene, perfluoromethyl vinyl ether and sulfidation point monomer CF2=CFO(CF2)2I, stir at 400 rpm, polymerize at 60℃ and polymerize at 1.7 MPa.

[0059] The molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I is 40:59:1.

[0060] (3) In the first stage, 20 mL of 3 wt% inorganic free radical initiator ammonium persulfate was added to initiate polymerization, and monomers were continuously added to maintain the polymerization pressure at 1.7 MPa; wherein the molar ratio of the added monomers tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I was 55:43:2.

[0061] (4) After the reaction has been going on for 0.5 hours, the temperature of the reactor is raised to 65°C. The monomer is rapidly added to the reactor at a pressure of 2.4 MPa according to the molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I of 40:59:1.

[0062] (5) In the second stage, 60 mL of azobisisobutyramidine hydrochloride with a concentration of 3 wt% was added, the reaction temperature was maintained at 65 °C, and monomers were continuously added to maintain the polymerization pressure at 2.4 MPa. When the total amount of the three monomers, tetrafluoroethylene, perfluoromethyl vinyl ether and CF2=CFO(CF2)2I, is 1500g, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion.

[0063] The molar ratio of the added monomer tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized point monomer is 55:43:2.

[0064] (6) The emulsion was coagulated using magnesium chloride, washed, and then dried under vacuum at 100°C to obtain a perfluoroalkyl ether copolymer.

[0065] 100 parts of polymer raw rubber were mixed on a two-roll mill with 15 parts of carbon black (N990), 3 parts of triallyl isocyanurate as a crosslinking aid, and 1 part of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane as an organic peroxide.

[0066] The compound was vulcanized at 170℃ for 10 minutes and then at 230℃ for 4 hours.

[0067] The obtained perfluoroalkyl ether copolymer has a monomer composition of 55.4 mol tetrafluoroethylene, 42.9 mol perfluoroalkyl vinyl ether, and 1.7 mol sulfur point monomer.

[0068] Example 2 The specific steps for preparing the perfluoroalkyl ether copolymer are as follows: (1) Add 2700g of deionized water, 5g of dipotassium hydrogen phosphate, 60g of CF3(CF2OCF(CF3))2COONH4 (emulsifier) ​​and 13g of 1,4-diiodoperfluorobutane (chain transfer agent) to a 5L reactor with an oxygen content of less than 20ppm.

[0069] (2) Add the initial monomers tetrafluoroethylene, perfluoromethyl vinyl ether and sulfidation point monomer CF2=CFO(CF2)2I, stir at 400 rpm, polymerize at 60℃ and polymerize at 2.0 MPa.

[0070] The molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I is 43:55:2.

[0071] (3) In the first stage, 20 mL of 3 wt% inorganic free radical initiator ammonium persulfate was added to initiate polymerization, and monomers were continuously added to maintain the polymerization pressure at 2.0 MPa; wherein the molar ratio of the added monomers tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I was 58:39:3.

[0072] (4) After the reaction has been going on for 0.5 hours, the temperature of the reactor is raised to 65°C. The monomer is rapidly added to the reactor at a pressure of 2.9 MPa according to the molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)2I of 43:55:2.

[0073] (5) In the second stage, 80 mL of azobisisobutyramidine hydrochloride with a concentration of 3 wt% was added, the reaction temperature was maintained at 65 °C, and monomers were continuously added to maintain the polymerization pressure at 2.9 MPa; When the total amount of the three monomers, tetrafluoroethylene, perfluoromethyl vinyl ether and CF2=CFO(CF2)2I, is 1500g, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion.

[0074] The molar ratio of the added monomer tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized point monomer is 58:39:3.

[0075] (6) The emulsion was coagulated using magnesium chloride, washed, and then dried under vacuum at 100°C to obtain a perfluoroalkyl ether copolymer.

[0076] 100 parts of polymer raw rubber were mixed on a two-roll mill with 15 parts of carbon black (N990), 3 parts of triallyl isocyanurate as a crosslinking aid, and 1 part of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane as an organic peroxide.

[0077] The compound was vulcanized at 170℃ for 10 minutes and then at 230℃ for 4 hours.

[0078] The obtained perfluoroalkyl ether copolymer has a monomer composition of 58.3 mol% tetrafluoroethylene, 38.9 mol% perfluoroalkyl vinyl ether, and 2.8 mol% sulfurization point monomer.

[0079] Example 3 The specific steps for preparing the perfluoroalkyl ether copolymer are as follows: (1) Add 2700g of deionized water, 5g of dipotassium hydrogen phosphate, 60g of CF3(CF2OCF(CF3))2COONH4 (emulsifier) ​​and 10g of 1,4-diiodoperfluorobutane (chain transfer agent) to a 5L reactor with an oxygen content of less than 20ppm.

[0080] (2) Add the initial monomers tetrafluoroethylene, perfluoromethyl vinyl ether and sulfidation point monomers CF2=CFO(CF2)3OCF2Br, stir at 400 rpm, polymerize at 65℃ and polymerize at 1.8 MPa.

[0081] The molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)3OCF2Br is 40:59:1.

[0082] (3) In the first stage, 20 mL of 3 wt% inorganic free radical initiator ammonium persulfate was added to initiate polymerization, and monomers were continuously added to maintain the polymerization pressure at 1.8 MPa; wherein the molar ratio of the added monomers tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)3OCF2Br was 55:43:2.

[0083] (4) After the reaction has been going on for 0.5 hours, the temperature of the reactor is raised to 70°C. The monomer is rapidly added to the reactor at a pressure of 2.5 MPa according to the molar ratio of tetrafluoroethylene: perfluoromethyl vinyl ether: CF2=CFO(CF2)3OCF2Br of 40:59:1.

[0084] (5) In the second stage, 60 mL of azobisisobutyramidine hydrochloride with a concentration of 3 wt% was added, the reaction temperature was maintained at 70 °C, and monomers were continuously added to maintain the polymerization pressure at 2.5 MPa; When the total amount of the three monomers, tetrafluoroethylene, perfluoromethyl vinyl ether and CF2=CFO(CF2)3OCF2Br, is 1500g, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion.

[0085] The molar ratio of the added monomers tetrafluoroethylene, perfluoroalkyl vinyl ether, and CF2=CFO(CF2)3OCF2Br is 55:43:2.

[0086] (6) The emulsion was coagulated using magnesium chloride, washed, and then dried under vacuum at 100°C to obtain a perfluoroalkyl ether copolymer.

[0087] 100 parts of polymer raw rubber were mixed on a two-roll mill with 15 parts of carbon black (N990), 3 parts of triallyl isocyanurate as a crosslinking aid, and 1 part of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane as an organic peroxide.

[0088] The compound was vulcanized at 170℃ for 10 minutes and then at 230℃ for 4 hours.

[0089] The obtained perfluoroalkyl ether copolymer has a monomer composition of 55.3 mol% tetrafluoroethylene, 42.8 mol% perfluoroalkyl vinyl ether, and 1.9 mol% sulfurization point monomer.

[0090] Comparative Example 1 The preparation steps of Example 1 were repeated, except that the amount of water-soluble ammonium persulfate used in step (3) was 100 mL. That is, the amount of inorganic free radical initiator used was 0.2% of the total mass of the monomer.

[0091] The obtained perfluoroalkyl ether copolymer has a monomer composition of 55.4 mol tetrafluoroethylene, 42.8 mol perfluoroalkyl vinyl ether, and 1.8 mol sulfur point monomer.

[0092] Comparative Example 2 The preparation steps of Example 1 were repeated, except that the amount of azobisisobutyramidine hydrochloride used in step (5) was 200 mL. The amount of organic initiator was 0.4% of the total mass of the monomer.

[0093] The obtained perfluoroalkyl ether copolymer has a monomer composition of 55.2 mol% tetrafluoroethylene, 43.0 mol% perfluoroalkyl vinyl ether, and 1.8 mol% sulfurization point monomer.

[0094] Comparative Example 3 The preparation steps of Example 1 were repeated, except that in the preparation method of this comparative example, step (5) did not involve adding 60 mL of azobisisobutyramidine hydrochloride with a concentration of 3 wt% into the reactor.

[0095] Specifically, in step (5), the reaction temperature is maintained at 65°C, monomers are continuously added, and the polymerization pressure is maintained at 2.4 MPa. When the total amount of the three monomers, tetrafluoroethylene, perfluoromethyl vinyl ether and CF2=CFO(CF2)2I, is 1500g, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion.

[0096] The molar ratio of the added monomer tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized point monomer is 55:43:2.

[0097] The others are the same as in Example 1.

[0098] The obtained perfluoroalkyl ether copolymer has a monomer composition of 55.0 mol% tetrafluoroethylene, 43.1 mol% perfluoroalkyl vinyl ether, and 1.9 mol% sulfurization point monomer.

[0099] Comparative Example 4 The preparation steps of Example 1 were repeated, except that the pot temperature was maintained at 60°C in step (4).

[0100] The obtained perfluoroalkyl ether copolymer has a monomer composition of 53.3 mol% tetrafluoroethylene, 45.0 mol% perfluoroalkyl vinyl ether, and 1.7 mol% sulfurization point monomer.

[0101] Comparative Example 5 The preparation steps of Example 1 were repeated, except that in step (4), the monomer was added to the reactor pressure to 1.9 MPa.

[0102] The obtained perfluoroalkyl ether copolymer has a monomer composition of 54.8 mol% tetrafluoroethylene, 43.2 mol% perfluoroalkyl vinyl ether, and 2.0 mol% sulfurization point monomer.

[0103] Comparative Example 6 Repeat the preparation steps of Example 1, except that in step (5), 60 mL of tert-butyl hydroperoxide, an organic free radical initiator with a concentration of 3 wt%, is added in the second stage.

[0104] The obtained perfluoroalkyl ether copolymer has a monomer composition of 53.8 mol% tetrafluoroethylene, 44.7 mol% perfluoroalkyl vinyl ether, and 1.5 mol% sulfurization point monomer.

[0105] The performance of the perfluoroalkyl ether copolymers obtained in the above examples was tested, and the data are shown in Table 1 below.

[0106] Table 1 Properties of perfluoroalkyl ether copolymers

[0107] As can be seen from the examples and performance test results, by using the two-stage polymerization method within the scope of the present invention, the perfluoroalkyl ether copolymer not only has good tensile strength and elongation at break, but also good aging resistance and high-temperature compression set resistance.

[0108] As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, the amount of inorganic and organic initiators used in the polymerization reaction needs to be within the limits of this invention. If the amount of inorganic or organic initiators is too high, it will lead to a high content of unstable carbonyl end groups and poor resistance to compression set of the perfluoroalkyl ether copolymer.

[0109] As can be seen from the comparison between Example 1 and Comparative Example 3, the perfluoroalkyl ether copolymer produced by the two-stage polymerization process of the present invention not only has good tensile strength and elongation at break, but also good aging resistance and high-temperature compression set resistance.

[0110] As can be seen from the comparison between Example 1 and Comparative Examples 4 and 5, the polymerization reaction temperature and pressure must be within the limits of the present invention. If the polymerization pressure and temperature in the second stage are too low, the tensile strength of the copolymer will be too low.

[0111] As can be seen from the comparison between Example 1 and Comparative Example 6, the organic initiator should be a water-soluble organic initiator within the scope of the present invention. The copolymer obtained by using an oil-soluble initiator has poor resistance to compression set.

Claims

1. A method for preparing a perfluoroalkyl ether copolymer, characterized in that, Includes the following steps: (1) Weigh out water, pH buffer, emulsifier and chain transfer agent and add them to the reactor; wherein, by weight, water is 100 parts, pH buffer is 0.1-0.5 parts, emulsifier is 0.1-5 parts and chain transfer agent is 0.01-0.5 parts; (2) Add the initial monomers tetrafluoroethylene, perfluoroalkyl vinyl ether and sulfidation point monomer, stir at 200-500 rpm, polymerize at 55-90℃, and polymerize at 1.4-2.2 MPa; The molar ratio of tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfidation point monomer: chain transfer agent is (30-55):(40-70):(0.1-6):(0.05-2); (3) In the first stage, an inorganic free radical initiator is added to initiate polymerization, and monomers are continuously added to maintain the polymerization pressure at 1.4-2.2 MPa; wherein, the molar ratio of the added monomers tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer is (50-65):(30-45):(0.1-6); The amount of the inorganic free radical initiator is 0.03-0.08% of the total mass of the monomers; (4) After the reaction has been going on for 0.5-1h, the temperature of the reactor is raised to 65-100℃, and the monomer is rapidly added to the reactor at a pressure of 2.3-3.5MPa according to the molar ratio of tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer of (30-55):(40-70):(0.1-6). (5) In the second stage, an organic free radical initiator is added, the reaction temperature is maintained at 65-100℃, monomers are continuously added, and the polymerization pressure is maintained at 2.3-3.5MPa; When the total amount of the three monomers, namely tetrafluoroethylene, perfluoroalkyl vinyl ether and sulfur point monomer, is 55%-56% of the amount of water added, the reaction is stopped, the mixture is cooled, vented, and collected to obtain a polymer emulsion. The molar ratio of the added monomer tetrafluoroethylene: perfluoroalkyl vinyl ether: sulfurized monomer is (50-65):(30-45):(0.1-6); The amount of the organic free radical initiator is 0.1-0.2% of the total mass of the monomers; The organic free radical initiator is at least one of azoisobutylcyanoformamide, azobisisobutylamidine hydrochloride, or azobisisobutylimidazolium hydrochloride; (6) The polymer emulsion is coagulated, washed, dried, and then plasticized and shaped using an open mill.

2. The method for preparing the perfluoroalkyl ether copolymer according to claim 1, characterized in that, In step (1), the chain transfer agent is a C1-C8 perfluoroalkane containing bromine and / or iodine atoms; its general formula is: R f2 I x Br y In the formula, x and y are integers from 0 to 2, and satisfy 1 ≤ x + y ≤ 2, R f2 C 1-8 Perfluoroalkyl chains.

3. The method for preparing the perfluoroalkyl ether copolymer according to claim 2, characterized in that, In step (1), the chain transfer agent is at least one of 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, or 2-iodoperfluoropropane.

4. The method for preparing the perfluoroalkyl ether copolymer according to claim 1, characterized in that, The perfluoroalkyl vinyl ether mentioned in step (2) is at least one of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, or perfluoropropyl vinyl ether; The sulfurization point monomer has the general formula CF2=CFOR f1 X, where R is... f1 It is C 1-10 The perfluoroalkyl or perfluoroalkoxy chain, where X represents either iodine or bromine.

5. The method for preparing the perfluoroalkyl ether copolymer according to claim 4, characterized in that, The sulfurization point monomer mentioned in step (2) is at least one of CF2=CFO(CF2)2I, CF2=CFO(CF2)2Br, CF2=CFO(CF2)3Br, CF2=CFO(CF2)3I, CF2=CFO(CF2)3OCF2I, CF2=CFO(CF2)3OCF2Br, and CF2=CFO(CF2)4OCF2I.

6. The method for preparing the perfluoroalkyl ether copolymer according to claim 1, characterized in that, The inorganic free radical initiator mentioned in step (3) is at least one of potassium persulfate, ammonium persulfate, or sodium persulfate.

7. The method for preparing the perfluoroalkyl ether copolymer according to claim 1, characterized in that, The polymerization pressure in the first stage of step (3) is 1.7-2.0 MPa; the polymerization pressure in the second stage of step (5) is 2.4-3.0 MPa.

8. A perfluoroalkyl ether copolymer, characterized in that, The perfluoroalkyl ether copolymer is prepared by the method described in any one of claims 1-7; the monomer composition of the perfluoroalkyl ether copolymer is 40-75 mol% tetrafluoroethylene, 24-50 mol% perfluoroalkyl vinyl ether, and 0.01-10 mol% sulfurizing point monomer.

9. The perfluoroalkyl ether copolymer according to claim 8, characterized in that, The perfluoroalkyl ether copolymer has a carbonyl end group content of less than 0.01; the Mooney viscosity of the perfluoroalkyl ether copolymer at ML1+10, 121°C is 35-100 MU.

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