RU2528226C1 - Triple tetrafluoroethylene-based copolymers for chemical and heat-resistant materials - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: triple copolymers have the general formula

where n=50/0-70/0 mol.%; m=29/0-49/0 mol.%; p=0.3-3.0 mol.%; k=2÷6.

EFFECT: obtained are copolymers, based on which vulcanisates possess improved compression set values together with the preservation of other good physical-mechanical parameters.

3 tbl, 13 ex

Description

Tetrafluoroethylene-based triple copolymers for thermally aggressive materials.

The present invention relates to the field of producing new triple copolymers of the general formula

где

Where

R _f = -CF ₃ , -CF ₂ CF ₂ CF ₃

n = 50.0-70.0 mol.%

m = 29.0-49.0 mol.%

p = 0.3-3.0 mol.%

k = 2 ÷ 6

Such compounds are vulcanized by peroxides and are intended to produce sealing materials that are capable of operating in aggressive environments at high temperatures.

Known copolymers based on tetrafluoroethylene (TFE) obtained by the water-emulsion copolymerization of TFE, perfluoroalkyl vinyl ethers (PFAVE) and bromine-containing comonomers (BSM). The process is carried out by the method of continuous copolymerization at 70 ° C and a pressure of 4.2 MPa and initiation by a redox system based on ammonium persulfate (PSA) and sodium sulfate. As BSM, for example, bromotrifluoroethylene (BTFE), bromodifluoroethylene, perfluoroallyl bromide or 3.3 difluoroallyl bromide are used, but BTFE is most preferred. As PFAVE, an ester is used in which the alkyl group contains 1-5 carbon atoms, but perfluoromethylvinyl ether (PFMVE) is most preferred. The molar ratio of TFE: PFAVE = 50-80: 20-50, and the content of BSM reaches 3 mol.%, However, in the examples, preference is given to copolymers with the ratio of TFE: PFAVE: BSM = 66-69.6: 30-33: 0.37-1.5.

These copolymers are easily vulcanized by peroxides, however, vulcanizates based on them have an unsatisfactory complex of physical and mechanical properties. So, with good strength characteristics (tensile strength is 10.3-19.4 MPa), vulcanizates have a low relative elongation (60-140%) and extremely unsatisfactory residual deformation under compression (ODS) after holding at 204 ° C for 70 h (50- 99%), which significantly limits the scope of their use. The disadvantages of the proposed method for producing these copolymers are the need to use high pressure (4.2 MPa) and, as a consequence, the use of complex hardware design (US Pat. USA 4035565, publ. 12.07.77, C08F 214/16).

A TFE-based ternary copolymer is known containing 50-70 mol% of TFE units, 29-49 mol% of PFAVE units and 0.3-2.5 mol% of ω-bromoperfluoroalkylallyl ether units.

This copolymer is easily vulcanized by peroxides and gives vulcanizates with good tensile strength (14-19 MPa).

The disadvantage of this copolymer is the rather high ODS after exposure already at 200 ° C for 24 hours (up to 38%) (US Pat. Ru 2408608., C08F 14/16, prior. 03.23.09). The closest analogue in structure is a TFE-based copolymer containing TFE, PFAVE and 0.6-1.8 mol% comonomer of the general formula

where Z- (per) fluoropolyoxyalkylene radical

R _1-6- H, C _1-5 alkyl

The copolymers are vulcanized by peroxides and have high physical and mechanical properties after temperature control at 290 ° C,

tensile strength (MPa) 15.4-18.6,

elongation (%) 180-190.

However, these physical and mechanical parameters undergo a significant change after thermal aging at 316 ° C for 70 hours.

Δ% change in strength at break from -40 to -75%.

Δ% change in elongation from +70 to + 173%.

The index of ODS after exposure for 70 hours at 316 ° C is 63-75%.

(U.S. Pat. No. 7408006, C08F 259/00, prior. 06.22.04).

The objective of this technical solution is to create triple copolymers based on tetrafluoroethylene, peroxide vulcanizates of which have a good set of physico-mechanical properties and improved values of ODS after holding at 316 ° C for 70 hours.

The problem is solved by synthesis of a copolymer of the General formula

, где

where

R _f = -CF ₃ , -CF ₂ CF ₂ CF ₃ ,

n = 50.0-70.0 mol.%

m = 29.0-49.0 mol.%

p-0.3-3.0 mol.%

k = 2 ÷ 6

The proposed copolymers are preferably prepared by the aqueous emulsion copolymerization of TFE, PFAVE and perfluoroalkyl vinyl ether with an internal double bond (PFIVE) of the general formula CF ₂ = CF-O (CF ₂ ) _k CF = CFCF ₃ , where k = 2 ÷ 6. Ammonium persulfate (PSA) or a redox system based on PSA and sodium metabisulfite (MBS) are used as initiators. As an emulsifier, ammonium salts of perfluorocarboxylic or perfluoroxacarboxylic acids are used. It is preferable to carry out the copolymerization process at 50-80 ° C and a pressure of 0.8-1.1 MPa. The copolymerization is possible both in the presence of a molecular weight regulator and without it. As the latter, iodine or bromine-containing compounds, for example 1,4-diiodoperfluorobutane (DIPB), can be used. It is possible to carry out the process using a loading and make-up charge, with fractional supply of a functional monomer. Perfluoromethylvinyl (PFMVE) or perfluoropropylvinyl ether (PFVVE) is used as PFAVE. From latex, the copolymers are isolated by high-speed mechanical stirring with the addition of nitric acid, washed with water, ethanol and dried at 55-70 ° C under vacuum or in a stream of dry air.

The composition and structure of the obtained copolymers are determined using ¹⁹ F NMR spectroscopy. The molar ratio of TFE and PFAVE is calculated from the NMR spectra of the samples in a solution of hexafluorobenzene obtained at 50 ° C (Bruker AM-500 spectrometer). The Mooney viscosity of the obtained copolymers is determined according to GOST 10722-26. The proposed copolymers are subjected to peroxide vulcanization at 170-180 ° C for 15-20 minutes with a rise in temperature to 290 ° C for 8 hours. As the vulcanization agent, it is preferable to use 2.5-bis (tert-butyl peroxy) -2.5-dimethylhexane, sold, for example, under the trademarks Luperox® 101xL, Varox® DBPH-50.

The vulcanization process is carried out without the use of vulcanization coagents. As a filler, various soot can be used, for example T900, No. 990. The composition may additionally also contain metal oxides and hydroxides, for example Ca (OH) ₂ , ZnO, PbO.

Physical and mechanical parameters of vulcanizates, namely: Shore hardness, stress at 100% elongation, conditional tensile strength, elongation at break and relative residual deformation after compression are determined according to relevant standards (GOST 263-76, GOST 12535-78, GOST 9.029-74).

The following examples illustrate the invention.

Example 1

Into a 0.5 L stainless steel reactor pre-purged with nitrogen and evacuated, equipped with a shielded drive motor, a mechanical propeller stirrer (1400 rpm), temperature and pressure sensors, a thermostatic jacket and two reagent nozzles, 290 is loaded without access to air g of a freshly prepared aqueous phase consisting of a solution of 4.35 g of ammonium perfluorooctanoate and 1.74 g of ammonium persulfate (PSA) in distilled water. the pH of the aqueous phase is 4.3. The stirrer is turned on and the contents of the reactor are heated to 60 ° C in 10 minutes, after which 30 g of a pre-prepared mixture of monomers containing 56.6 mol.% TFE, 42.5 mol.% PFMVE are fed into the gas phase of the reactor from a metal ampoule (cylinder) equipped with a siphon and 0.9 mol.% PFIVE (k = 2) until a pressure of 1.0 MPa is reached. In the copolymerization process, when the pressure in the reactor is lowered to 0.9 MPa, the next portion of the mixture of monomers is fed to a pressure of 1.0 MPa, maintaining the process temperature within 60 ± 0: 5 ° С. The copolymerization is carried out for 4.8 hours and 166 g of a mixture of monomers are fed, after which the reactor is cooled to room temperature. Unreacted monomers are trapped for recycling and 425 g of latex with a solids content of 25.7% of the mass are recovered. latex pH 3.0.

The latex copolymer is isolated by high-speed mechanical stirring with the addition of an aqueous solution of nitric acid, washed with hot water, then with a mixture of water and ethanol, squeezed and dried in a vacuum oven at a temperature of 60 ° C and a residual pressure of 3 mm RT. Art. to constant weight. The resulting copolymer (135 g) does not contain a gel and has a Mooney viscosity of 71. The yield of the copolymer (on the used mixture of monomers) is 78.9% of the mass. Conversion (to reacted monomers) - 96.3%.

According to NMR ¹⁹ F spectroscopy, the resulting copolymer corresponds to formula 1, where

R _f = -CF ₃

n = 62.1 mol%

m = 37.3 mol%

p = 0.6 mol%

k = 2

The copolymerization conditions, composition and properties of the copolymers obtained according to this and the following examples are summarized in tables 1 and 2 for convenience of consideration. Of the copolymers synthesized according to examples 1-13, compositions containing:

copolymers 1-13 100.0 parts by weight soot T900 25.0 parts by weight calcium hydroxide 3.0 parts by weight Luperox®101XL (45 (active substance) 2.5 parts by weight

The compositions were vulcanized in a press at 177 ° C for 15 minutes, followed by heating from room temperature to 290 ° C for 8 hours and thermostated at 290 ° C for 16 hours. The vulcanized compositions were released in the form of plates (120 × 120 × 1 ) mm for testing physical and mechanical properties and cylinders (10 × 10) mm for testing ODS.

The properties of the vulcanizates are shown in table 3.

Thus, as can be seen from the data given in the tables, the proposed copolymers allow one to obtain vulcanizates with significantly improved ODS at 316 ° × 70 h while maintaining good other physical and mechanical properties.

table 2 Copolymer properties No. Latex The amount and composition of the copolymer Mooney Viscosity (1-10 @ 100 ° C) Amount, g Dry rest.,% Of the mass. pH The output% of the mass. Conversion,% of the mass. Estimated data, mol.% TFE (n) PFAVE (m) PFIVE (p) one 425 25.7 3.0 78.9 96.3 62.1 37.3 0.6 71 2 430 29.8 1.9 78.0 97.9 59.9 39.3 0.8 66 3 430 30.1 2.0 76.8 94.0 60.6 37.7 1.7 67 four 430 31.3 2.1 75.3 90.4 64.1 32.9 3.0 90 5 430 32.5 2.1 79.8 96.6 63.8 35.9 0.3 82 6 430 29.7 2.1 78.4 97.0 60.5 38.8 0.7 69 7 430 31.9 2.1 79.3 96.9 60.6 38.6 0.8 69 8 430 29.2 2.1 75.0 94.0 57.6 42.0 0.4 60 9 430 31.0 2.2 75.1 94.0 60.1 39.1 0.8 thirty 10 430 30.9 5.3 86.3 96.7 49.8 49.1 1.2 32 eleven 430 31.5 3.6 84.7 97.2 54.8 43.9 1.3 65 12 460 32.1 2.2 76.8 99.2 69.4 29.0 1.6 85 13 460 31.1 1.9 75.3 98.0 70.0 29.2 0.8 54

Table 3 Properties of vulcanizates Number No. Hardness Stress at 100% elongation, MPa Tensile strength, MPa Elongation at break,% Relative deformation after compression by 20% at 290 ° С 24 h Butylamine Swelling 50 ° C one 72 6.0 16.0 155 42 4.0 2 73 6.3 17.0 160 41 4.0 3 73 6.0 17.5 150 40 4.0 four 80 8.0 19.5 170 44 4.0 5 76 3.5 15.5 210 43 4.0 6 75 3.5 15.5 160 41 3.1 7 74 6.3 16.0 160 40 3.0 8 76 5.9 15.1 190 44 4.0 9 70 5.0 150 180 45 4.0 10 70 5.5 14.8 160 40 4.0 eleven 71 7.0 19.5 16.5 41 4.0 12 80. 8.5 19.5 150 43 4.0 13 80 8.4 15.4 145 42 4.0 Change in the physicomechanical properties of vulcanizates after holding for 70 hours at 316 ° C (± Δ%) one -2 - -39 +55 51 2 -one - -36 +45 52 3 -2 - -32 +40 51 four -2 - -29 +35 53 5 -2 - -36 +45 52 6 -3 - -35 +46 54 7 -2 - -34 +44 52 8 -2 - -36 +43 54 9 -one - -33 +41 53 10 -2 - -35 +46 54 eleven -3 - -34 +45 52 12 -2 - -33 +44 53 13 -2 - -34 +43 53

Claims (1)

Tetrafluoroethylene-based copolymers of the general formula

Where
R _f = -CF ₃ , -CF ₂ CF ₂ CF ₃
n = 50.0-70.0 mol.%
m = 29.0-49.0 mol.%
p = 0.3-3.0 mol.%
k = 2 ÷ 6
for thermally aggressive materials.