RU2195465C1 - Method of synthesis of copolymer of tetrafluoro-ethylene with perfluoropropylvinyl ester - Google Patents

Abstract

FIELD: polymers, chemical technology. SUBSTANCE: invention relates to synthesis of copolymer of tetrafluoroethylene with perfluoropropyl-vinyl ester. Copolymer of tetrafluoroethylene with perfluoropropyl-vinyl ester is synthesized by copolymerization of indicated monomers in medium of liquefied octafluorocyclobutane in the presence of perfluorodiacyl peroxide as an initiating agent that is added to polymerization medium as solution in polyfluorinated organic solvent using charging mixture of indicated monomers under pressure maintaining by addition of monomers feeding mixture followed by separation of copolymer from reaction medium by distillation off of volatile components and product drying by the known procedures. Ozone-safety solvent taken among group including perfluoromethyl- cyclohexane, 1-hydro-4-chlorooctafluorobutane and perfluoropropylvinyl ester are used as polyfluorinated organic solvent. Invention allows to enhance thermal stability of copolymer, simplify technology of utilization of recurring monomers and solvent and decrease amount of unutilized waste. EFFECT: improved method synthesis. 2 cl, 3 tbl

Description

 The invention relates to methods for producing fluoropolymers, namely a copolymer of tetrafluoroethylene (TFE) with perfluoropropyl vinyl ether (PFPVE), a valuable material that combines the ability to be processed from a melt with high chemical resistance, heat resistance, and high dielectric properties.

A known method for producing a copolymer of TBE with PFPVE by copolymerization of these monomers in a medium of 1,1,2-trifluorotrichloroethane (freon 113) in the presence of a polymerization initiator - perfluoropropionyl peroxide, which is introduced into the polymerization medium in the form of a 1.5% (by weight) solution in Freon 113 or in cyclic HFP dimer. The copolymerization is carried out at a temperature of 30 ÷ 85 ^o C and an excess pressure of 0.1-7.0 MPa. 800 ml of Freon 113 and 60 g of PFPVE are placed in a 1 L steel reactor. The temperature in the reactor was raised to 40 ^° C, TFE was added to a pressure of 0.34 MPa gage. and 20.2 ml of a 1.5% by weight solution of perfluoropropionyl peroxide in a cyclic HFP dimer are added. The reaction is carried out for 43 min at 43 ^o C and a constant pressure maintained by the addition of TFE. Obtain 49 g of a copolymer containing 8 wt.% PFPVE, suitable for pressing thin films [US Pat. USA 3528954, CL 260-87.5, 1970].

 This method has a disadvantage caused by the use of freon 113 as the polymerization medium, in which the copolymer swells and forms a thick jelly-like mass, which leads to difficulties in mixing and isolation of the copolymer. In practice, the impossibility of isolating mechanically more than 80-85 wt.% Solvent. The remaining solvent is released during drying of the copolymer and pollutes the atmosphere, which requires a special system for its capture and return to the cycle.

 The closest set of essential features to the proposed one is a method of producing a TFE copolymer with PFPVE by copolymerizing these monomers in a medium of liquefied octafluorocyclobutane in the presence of a polymerization initiator, perfluorodiacyl peroxide, which is introduced into the polymerization medium in the form of a 6-10% (by weight) solution in chladone 113, using a loading mixture of monomers at a pressure maintained by adding tetrafluoroethylene or a feeding mixture of monomers, followed by separation of the copolymer T reaction mass to distill off volatile components and drying the product by conventional methods [US Pat. RF 2156777, class C 08 F 214/26, publ. 09/27/2000]. When implementing the known method at the end of the copolymerization process, unreacted monomers together with the solvent are blown into a separate container. This mixture without purification can be used repeatedly to prepare the boot mixture. With the accumulation of impurities in order to avoid deterioration in the quality of the resulting copolymer, the return mixture of monomers is rectified.

 The known method has disadvantages associated with the use of freon 113 as a solvent for the initiator. Since the TFE-PFPVE copolymer swells in HFC 113, the presence of traces of HFC 113 on the powder surface with peroxide and its decomposition products dissolved in it worsens the product thermal stability. In addition, with repeated use of the return mixture of monomers and solvent, as shown by analysis, impurities accumulate in this mixture: freon 113, peroxide residues and its decomposition products. Isolation from such a mixture of TFE and SFC suitable for copolymerization is easily achieved by distillation. The authors of the present invention found that the separation of the mixture of HFC 113 with PFPVE is not achieved not only by distillation, but even by using distillation, which leads to the formation of non-utilizable waste containing organofluorine. This leads to environmental pollution. In addition, Freon 113 is considered to be ozone-depleting, its use is currently prohibited.

 The technical task of the present invention is to improve the quality of the copolymer, namely, its thermal stability, as well as to simplify the process of disposal of the return solvent and monomers and to reduce the emission of harmful substances.

 The problem is solved by the method of producing a copolymer of tetrafluoroethylene with perfluoropropyl vinyl ether by copolymerizing these monomers in a medium of liquefied octafluorocyclobutane in the presence of a polymerization initiator, perfluorodiacyl peroxide, which is introduced into the polymerization medium in the form of a solution in a polyfluorinated halogen-containing organic solvent using the indicated solvent with an aqueous solvent adding a feed mixture of monomers, followed by separation m of copolymer from the reaction mass by distillation of the volatile components and drying of the product by known methods, in which according to the invention, as an polyfluorinated halogen-containing organic solvent of perfluorodiacyl peroxide, an ozone-free solvent selected from the group consisting of perfluoromethylcyclohexane, 1-hydro-4-chloro-octafluorobutane butane is used.

 Perfluorodiacyl peroxide can be administered as a 5-10% by weight solution in a selected solvent.

 The implementation of the method is confirmed by laboratory examples.

Example 1. The polymerization initiator - perfluorodicyclohexanoyl peroxide (DAP-c) is obtained in a glass apparatus cooled by brine, equipped with a stirrer and dispensers for supplying reagents. The initiator is obtained by reacting perfluorocyclohexanecarboxylic acid fluoride with a 32% (by weight) aqueous solution of hydrogen peroxide in a mixture of a 17% (by weight) aqueous solution of sodium hydroxide and an organic solvent, perfluoromethylcyclohexane (HFC 350) at a temperature of (-10) ÷ (-15) ^о С. At the end of the reaction, the organic layer is separated from the aqueous layer and washed with chilled water. The resulting solution of DAP-c peroxide in HFC 350 is analyzed iodometrically and used as a polymerization initiator in the preparation of the copolymer.

The copolymer is obtained in a 1.6-liter stainless steel reactor equipped with a high-speed propeller stirrer (1500 rpm), a heating jacket, a dropper, and a syringe device for introducing the polymerization initiator. The reactor was sealed, cooled to ^-25 ° C and evacuated to a residual pressure of 0.001 MPa. In a dropper cooled to the same temperature, 1 g of DAP-c initiator is placed in the form of a 10% (by weight) solution in HFC 350, 12.6 g of PFEPVE are added thereto, the dropper is sealed and its contents are poured into the reactor. Then, 600 g of liquefied octafluorocyclobutane (SFC) is charged into the reactor. With stirring, the contents of the reactor are heated to a predetermined temperature corresponding to the selected initiator, in this example 45 ^° C. 25 g of TFE are fed into the reactor and copolymerization is carried out at a constant temperature and steady pressure, adding to the reactor a make-up mixture containing 97 mol.% TFE and 3 mol.% PFPVE, to the initial pressure each time when it is reduced by 0.02 MPa.

The copolymerization process is carried out until 170 g of the make-up mixture is consumed for 3.7 hours. Then the reaction is stopped, the gas mixture is analyzed. Unreacted monomers and solvent are blown into a pre-cooled and evacuated container, where they are condensed. The condensed multicomponent mixture is distilled to use the components in the following experiments. The target fraction containing SFC and TFE with a slight admixture of PFPVE and HFC 350 is used in subsequent copolymerization experiments, and the bottom fraction containing SFC, PFPVE and HFC 350 is accumulated from several experiments and subjected to rectification. Rectification is carried out on a laboratory column with an efficiency of 40 tons with the selection of the fraction containing OFZB and PFPVE. A bottoms residue is obtained containing HFC 350. The copolymer in the reactor is heated at 50 ^{° C.} to remove most of the volatile components, then the reactor is cooled and opened. The resulting copolymer is discharged from the reactor, dried at a temperature of 120 ^o C for 24 hours and determine its properties. 200 g of a white powder of TFE-PFPVE copolymer are obtained. The properties of the obtained copolymer are determined as follows:
- the composition of the copolymer by IR spectroscopy of films with a thickness of 50 μm;
- melt flow rate (MFR) - according to GOST 11645-73 on an extrusion plastometer at 370 ^o C and a load of 5 kg;
- physical and mechanical properties: tensile strength and elongation at break according to GOST 11262-80;
- thermal stability at 300 ^o C for 3 hours (T ₃₀₀ ) and at 370 ^o C for 1 h (T ₃₇₀ ) - gravimetrically by weight loss of the powder.

 The copolymerization conditions, composition and properties of the copolymer obtained in example 1 and the following examples are presented in table. 1; the distillation results of the return mixture are in table. 2; the distillation results of the bottoms fraction - in table. 3.

 Example 2. The copolymerization process is carried out analogously to example 1, but when receiving the initiator solution, 1-hydro-4-chloroctafluorobutane (HFC 328) is used as a solvent. The initiator DAP-c in the amount of 1 g is introduced into the reactor in the form of a 10% (by weight) solution in HFC 328. The copolymerization process is carried out for 5 hours until 245 g of the make-up mixture is used up. After heating and drying, 235 g of a white powder of TFE-PFPVE copolymer are obtained. The condensed gas mixture is distilled to obtain the target fraction containing SFC and TFE with a slight admixture of PFVVE and HFC 328, and a bottoms fraction containing the main amount of PFPVE and HFC 328 along with the SFC. The bottoms fraction is combined from several experiments and rectified, as described in Example 1, by selecting the fraction of SFCs and PFPVE and obtaining Freon 328 in the bottoms. The results of distillation and rectification are given in table. 2 and 3, respectively.

 Example 3. The copolymerization process is carried out analogously to example 1, but when receiving the initiator solution, perfluoropropyl vinyl ether (PFPVE) is used as a solvent. The initiator DAP-c in the amount of 0.7 g is introduced into the reactor in the form of a 5% (by weight) solution in PFPVE. In the copolymerization process, 260 g of the make-up mixture are consumed for 3.8 hours. After heating and drying, 250 g of a white powder of TFE-PFPVE copolymer are obtained. The condensed gas mixture is distilled to recycle the residues of monomers and solvent for reuse, while a fraction containing SFC and TFE with a slight admixture of PFVE is taken, and a bottom fraction containing the main amount of PFVE is obtained. The distillation results are presented in table. 2.

Example 4. As the polymerization initiator, perfluoro-2-methyl-3-oxahexanoyl peroxide (PFOG) is used, which is prepared as described in Example 1, but perfluoro-2-methyl-3-oxahexanoic acid fluorohydride is used as the starting fluoride, and as a solvent, 1-hydro-4-chloroctafluorobutane (HFC 328). The copolymerization process is carried out analogously to example 1, but at a temperature of 35 ^o C, while 1 g of the indicated peroxide is used to initiate the process in the form of an 8% (by weight) solution in HFC 328. 180 g of the make-up mixture are consumed within 4 hours. After heating and drying, 170 g of a white powder of TFE-PFPVE copolymer are obtained. The condensed gas mixture is distilled, followed by distillation of the bottom fraction, as described in example 2.

 Example 5. The initiator solution is prepared as described in the previous example, but using PFPVE as a solvent. The copolymerization process is carried out under the conditions of example 4, while to initiate the process take 0.7 g of PFOG in the form of a 5% (by weight) solution in PFPVE. 180 g of the make-up mixture are consumed within 4 hours. After heating and drying, 170 g of a white powder of TFE-PFPVE copolymer are obtained. The condensed gas mixture is distilled to obtain fractions, as in example 3.

 Example 6 (control, prototype). An initiator solution is prepared as described in example 1, but using freon 113 as an organic solvent. The copolymerization process is carried out analogously to example 1, using 1 g of DAP-c as an 8% (by weight) solution in freon 113 to initiate 190 g of make-up mixture are consumed within 4 hours. After heating and drying, 180 g of a white powder of TFE-PFPVE copolymer are obtained. The condensed gas mixture is distilled to obtain the target fraction containing PFCB and TFE mixed with PFPVE and HFC 113, and the bottom fraction containing PFCB and the main amount PFPVE and HFC 113. The bottoms fraction is collected from several experiments and subjected to rectification with a 40 t laboratory column. t. with the selection of the fraction containing OFPCB and PFPVE mixed with freon 113. The bottom residue from rectification is a mixture of PFPVE with freon 113.

 The results of distillation and rectification are presented in table. 2 and 3.

 The tables show that freon 113, used in the known method as a solvent for the initiator, in the processes of distillation of the blown gas mixture and distillation of the bottom fraction is not completely separated from the monomers and octafluorocyclobutane. Reuse of components contaminated with HFC 113 is not permitted. The resulting copolymer has poor thermal stability (see Table 1), which is probably due to the presence of HFC 113 in the polymerization medium.

 From the above examples it is seen that the copolymer obtained by the proposed method has a higher thermal stability (i.e., lower mass loss at the processing temperature) than in the control example by the known method. In this case, the polymerization rate and product quality: melt flow, breaking stress and elongation do not deteriorate (see table 1).

 From the table. 2 and 3 it can be seen that according to the proposed method (i.e., using the initiator in the form of a solution in HFC 350, HFC 328 or in PFPVE) all components of the blown mixture: OFCB, HFC 350, HFC 328 and PFPVE are in the process of distillation and rectification stand out in almost pure form or in the form of mixtures that can be reused.

 Thus, the proposed method can significantly increase the thermal stability of the copolymer, simplify the technology of utilization of returnable monomers and solvent and reduce the amount of unused waste.

Claims (2)

 1. A method of producing a copolymer of tetrafluororatylene with perfluoropropyl vinyl ether by copolymerizing these monomers in a medium of liquefied octafluorocyclobutane in the presence of a polymerization initiator, perfluorodiacyl peroxide, which is introduced into the polymerization medium as a solution in a polyfluorinated organic solvent using a feed mixture of the indicated monomers at a pressure monomer mixtures, followed by separation of the copolymer from the reaction mass by distillation of of fluid components and drying the product by known methods, characterized in that an ozone-safe solvent selected from the group consisting of perfluoromethylcyclohexane, 1-hydro-4-chloroctafluorobutane and perfluoropropyl vinyl ether is used as a polyfluorinated organic solvent of perfluorodiacyl peroxide.  2. The method according to p. 1, characterized in that the perfluorodiacyl peroxide is introduced in the form of 5-10% by weight of a solution in a selected solvent.

Images