NL8104397A - COPOLYMERS OF TETRAFLUOROETHENE AND FLUORORATED ALKYLETHENS AND METHOD FOR PREPARING THE SAME - Google Patents

Description

s * - ♦ N.0. 30,414 -1- "

Copolymers of tetrafluoroethylene and fluorinated alkyl ethenes, and processes for their preparation.

The present invention relates to tetrafluoroethylene polymers and more particularly to copolymers of tetrafluoroethylene and fluorinated alkyl ethenes.

A number of copolymers of tetrafluoroethylene are known, but new copolymers of tetrafluoroethylene are always important because of the desire to obtain polymers with improved properties over the hitherto known polymers.

U.S. Pat. No. 4,123,602 discloses tetrafluoroethylene / ethylene copolymers modified with 0.1-10-10 moles of # K ^ CH5 Cl, wherein R ^. ^ M? 2n + 1, where n is an integer between 2 and 10. These polymers contain between 40 and 60 moles of ethylene. The thermal instability to oxidation limits their use above 150 ° C for extended periods of time.

U.S. Pat. No. 3,804,817 discloses copolymers of (perfluoropropyl) ethylene (PPPE) and tetrafluoroethylene (IPE) and copolymers of (perfluoroethyl) ethylene and tetrafluoroethylene.

These copolymers are elastomeric, soluble in fluorinated solvents and have only modest thermal stability as evidenced by the thermal gravimetric analysis (TGA) as indicated in the patent. In J. Poly. Sci. 8, (1970), 2441, Table 1 of U.S. Pat. No. 3,804,817 is reproduced and the article discloses that the copolymers of TEE and PEPE containing up to 89 moles of TEE are amorphous by X-ray diffraction measurement. The polymers appear amorphous when tested by differential scanning calorimetry (DSC) techniques.

Also in U.S. Pat. No. 3,804,817, a TFE copolymer containing about 6 moles # PEPE is described, in Example * IY. This copolymer has the following properties: 1. The melting behavior according to DSC is almost identical with PTEE.

It is known (Polymer Handbook, vol. 2, pV-32, (1975)) that polytetrafluoroethylene (PTEE) has a reproducible melting point at 327 ° C and sometimes contains phases, which show higher melting points at the initial heating cycle. The higher melting point can be 342 ° C. The 94/6 copolymer of Example IT of U.S. Pat. No. 3 3,804,817 exhibits both of these melting points and no lower melting points, which would correspond to crystalline copolymer phases.

2. The thermal stability of the melt at 350 ° C, that is to say about 8104397 * * v -2- about 20 ° C "above the melting point, as measured by isothermal TGA in air, is low. 7% was observed after 140 minutes.

3 · X-ray scattering at a small angle does not exhibit the wide diffraction peak at small angles (2Θ below 1 °) commonly observed for crystalline TEE copolymers. The 94/6 copolymer of Example 1Y of U.S. Pat. No. 3,804,817 instead shows the steady increase in intensity with decreasing angle shown by the homopolymer PTEE.

Based on these results, it is believed that the copolymer of Example IY of U.S. Pat. No. 3-804,817 consists largely of a fraction of crystalline TEE homopolymer with a minor fraction of amorphous TEE / PEPE copolymer .15 with a high PEPE content. . It is known that crystalline TEE homopolymer cannot be processed by melting techniques, and that blends of PTEE with melt-processable copolymers result in the formation of highly localized concentrations of PTEE or "fish eyes" in undesirable end products. In extreme cases, the presence of PTEE in a melt-processable copolymer can significantly decrease the strength of a final article. The object of copolymerizing small amounts, for example 1 - 10 mol% comonomer, with TEE is to prepare copolymers with homogeneous, easy to process melts, in which the melting point is lower than that of PTEE. U.S. Pat. No. 3,804,817 does not teach how this object can be achieved.

Copolymers of tetrafluoroethylene and fluorinated alkyl ethenes are obtained according to the present invention, wherein units of the copolymer from the ethylene comonomer are placed substantially evenly along the copolymer chain. This positioning results in insoluble copolymers which, after molding, are not elastomeric and show good thermal stability.

In contrast to the copolymers of U.S. Pat. No. 3,804,817, particularly the "94/6 copolymer" of Example IY, the copolymers of the present invention exhibit the following properties: 1. DSC melting points are important below that of PTEE and are in the range expected for true random copolymers The melting points are usually between 200 and 318 ° C.

4 8104397 # · -3- 2. The thermal stability according to isothermal TGA in air is good. These measurements were made at 350 ° C, that is, between 30 and 90 ° C above the melting points of these polymers. Weight loss is less than 5% at 140 minutes and is usually 1% or 5 less.

3. Small Angle Scattering X-ray Scans (SAXS) show a diffraction peak at very small angles (less than 1 ° 2 °) commonly seen with TEE semi-crystalline copolymers.

Thus, the term "substantially evenly placed" means that the copolymers meet the following conditions: DSC melting point is below about 318 ° C, the thermal stability is such that the weight loss after 140 minutes at 350 ° C in air is less than 5% and the X-ray scanning with small-angle scattering shows a diffraction peak at angles below 1 ° 2Θ.

By "insoluble" is meant that the copolymer does not dissolve in organic solvents, which are kept at 25 ° C.

By "non-elastomer" it is meant that the copolymer formed is not a material that can be repeatedly stretched at room temperature to at least twice its original length and will immediately return to about original strength after immediate release of tension. length of it.

The copolymers of the present invention may be more particularly described as copolymers of 93 to 99 mole percent tetrafluoroethylene and complementary 7-1 mole of fluorinated alkyl ether and comonomers of the formula R 1 CH 3 CH 2 wherein R 1 is perfluorinated alkyl of 2-10 carbon atoms or substituted perfluoroalkyl of 2-10 carbon atoms, wherein the perfluoroalkyl group may be substituted with up to 3 substituents selected from hydrogen, bromine, chlorine or iodine, the copolymer being characterized by the presence of units of the comonomer, which are placed almost uniformly, that is, evenly distributed along the copolymer chain.

The process aspect of the invention can be described as a process for the preparation of the described copolymer, which process is characterized by (a) bringing together and stirring tetrafluoroethylene and the fluorinated alkylene in the presence of a non-water containing-4q a solvent or in an aqueous medium in a reaction vessel 8104397 '-4- ♦ *' ..... _ reservoir "at a temperature between 30 ° G and 110 ° C and a pressure between 98 and 68 ° KPa and" at preferably between 294 and 3430 kPa, "in the presence of a free-radical polymerizing initiator, which brings together the tetrafluoroethylene and fluorinated alkyl.

.5 ethylene is carried out by continuously and uniformly adding fluorinated alkylene to the reaction vessel in such a way that a concentration of fluorinated alkylene in the vessel is maintained below 2.5 nol.% And preferably stirring below 1 mol%, based on tetrafluoroethylene, the stirring treatment is continued until copolymer formation has taken place, and (b) separating the copolymer from the other ingredients present in step (a).

The copolymer of the present invention is obtained by copolymerizing tetrafluoroethylene and fluorinated alkylene in either a non-aqueous solvent or an aqueous medium in such a way that the concentration of the fluorinated alkyl ethylene in the reaction mixture is maintained at a relatively constant and low concentration compared to the concentration of tetrafluoroethylene. When a large concentration, i.e. more than 2.5 mole percent perfluoroalkyl ethylene is used, the polymerization reaction is inhibited and a homogeneous copolymer is not obtained.

In the polymerization, non-aqueous solvents in the polymerization are fluoro or chlorofluorohydrocarbons (preferably 1 - 4 and especially 1 or 2 carbon atoms) known as a "Freon" solvent or solvents similar thereto. Freon "solvents or similar solvents include dichlorodifluoromethane, trichloronofluoromethane, dichloromonofluoromethane, monochlorodifluoromethane, chlorotrifluoromethane, tetrafluoroethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, fluoro-chloroblpropane. it is preferable to use a saturated fluorine or chlorofluorocarbon, which does not have a hydrogen atom in the molecule, such as dichlorodifluoromethane, trichloronofluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, perfluorocyclobutane, etc., since such solvents tend to have molecular weight increase the copolymer obtained. When using a "Freon" solvent or any such 40 solvent, good results are achievable. 8104397 η -5-V * Λ when used in amounts of 0.5 - 20 moles and in particular about 1-10 moles of solvent per mole monomer mixture of tetrafluoroethylene and pherluoroalkyl ethylene monomer.

The copolymerization reaction can be carried out using less than 0.5 mole of the solvent per mole of the monomer mixture. However, it is expedient to use more than 1 mole of solvent in order to increase the copolymerization rate. It is possible to use more than 20 moles of solvent, but it is expedient to use less than 10 moles per mole of monomer mixture for economic reasons, such as solvent recovery.

A mixture of a "Freon" solvent or the like solvent and other organic solvents or an aqueous medium can be used. For example, it is possible to use a mixed reaction medium of "Freon" solvent or the like solvent and water.

The advantage of using such a mixed solvent consists in easy stirring of the reaction system and easy removal of the heat of reaction. According to the method of the invention, the copolymerization conditions can be varied depending on the type of polymerization initiator or the reaction medium.

A wide variety of polymerization initiators can be used depending on the polymerization system. However, when a "Freon" solvent or a similar solvent is used, it is preferable to use a soluble free raikalen-forming polymerization initiator such as an organic peroxy compound. It is possible to use high energy ionizing irradiation of 10 - 10 ^ rad / hour dosing rate. Suitable peroxygen compounds can be the organic peroxides, for example benzoyl peroxide or lauroyl peroxide; peresters, for example tertibutylperoxyisobutyrate or peroxydicarbonates, for example diisopropylperoxydicarbonate, etc. It is particularly preferred to use a peroxide of the formula 55 0 0 H tl as initiator in non-aqueous systems

Hf0-0-0-C-Rf wherein each represents perfluoroalkyl groups having 3-13 carbon atoms in a "Freon" solvent or the like. Suitable peroxides include bis (perfluoropropionyl) peroxide, bis (per-8104397-6-fluorohexanoyl) peroxide, etc.

iS

When the solvent system is an aqueous system, initiators such as peroxides or persulfates, which are compatible with water, should be used, such as disuccinoyl peroxide or ammonium persulfate. A non-telogen and dispersant is usually used in an aqueous system.

The polymerization can be carried out at a temperature between 30 and 110 ° C and preferably at a temperature between 40 and 80 ° C. Pressures used in the polymerization are usually pressures between 98 and 6860 kPa and preferably between 294 and 3430 kPa.

It is often preferred to include a small amount of telogen material in the reaction medium to control the molecular weight of the resulting polymer. Alcohols such as methanol or ethanol and alkanes such as ethane, butane, cyclohexane, etc. are suitable telogens.

The comonomers mixture is stirred during the polymerization.

The reaction can be run until the solids content of the reaction mixture reaches about 20% by weight for aqueous reactions and about 12% for non-aqueous solvent reactions.

It is important to control the concentration of the fluorinated alkyl ethylene in the reaction mixture as described above and to maintain the concentration at a relatively constant level. Both of these features result in copolymers in which the units of fluorinated alkylethene are present substantially evenly distributed along the polymer chain.

Representative comonomers include perfluoroethyl ethylene, perfluoromethyl ethylene, d-chloroperfluoroethyl ethylene, u) -hydroperfluoro-2Q ethyl ethylene, Oj-bromo-perfluorocylethene, W-iodofluoroethyl ethylene (JCPgCIgCH ^ Hg), 1, 2, 8, 8-luoro-1, 2-hydroxy-8,8-luoro (CH ^ CTg ^ CH ^ CHg) or 1,1,2,4 "tetrahydrohexafluoropenten-1 (C] pJC3rHCF2CH = CH2). Preferably the comonomer will be a perfluoroalkyl ethylene and most preferably perfluorobutyl ether. jej The copolymers are suitable as insulating coatings for electrical wires and as coatings for equipment exposed to a harsh chemical environment.

Yoorimages.

In the following examples, the apparent melt viscosity 4Q was determined by calculations based on the flow velocity of the melt 8104397 Λ * -τ- * The flow velocity of the melt was determined according to ASTM method 3) 2116 under a load of 5000 g, except that the flow rate of the melt was determined in g / min. instead of g / 10 min. 3> e equation used to calculate the apparent melt-5 viscosity was: 10.65 x [total piston mass and weight (g)} m = -.

flow rate of the melt

The melting point was determined by differential scanning calorimetry at a rate of 15 ° C / min.

The elongation at break, the breaking strength and the tensile strength were determined according to ASTM method D1708.

Thermal stability was determined by isothermal thermogravimetric analysis (TSA) at 550 ° C in air using a Du Pont 900 instrument.

The solubility of the polymers prepared in Examples 15 was determined at 25 ° C in a number of conventional solvents, such as herafluorolefin, acetone and 1,1,2-trichloro-1,2,2-trifluoro-ethane. The polymers were insoluble.

X-ray scattering data were obtained with a Kratky diffractometer (Anton Kaar, K.G., Graz, Austria) by operating in a non-direct manner.

The X-ray intensities were determined with a scintillation counter followed by a single channel pulse height analyzer set to pass 9096 CuK radiation symmetrically. The X-ray beam was filtered with a 0.02 mm nickel foil and the thickness of the sample was in the range of 0.5-0.4 mm. The raw data (X-ray counts, time, position) were recorded on an 8-channel punched paper tape and read in an IBM 1150 computer. X-ray intensities were calculated as the ratio counts to time and these results were equalized 50 and corrected for sample thickness and instrumental background. The corrected intensities obtained were plotted as log intensity against diffraction angle (2-ö). The results were not corrected for slit lubrication, since such correction would not materially contribute to the distinction between samples, which are a separate small angle peak, and the samples, which do not contain this peak.

The comonomer content of the tetrafluoroethylene-perfluorobutyl-ethylene copolymers was determined by an infrared method or by a melting point method.

The infrared method involves the measurement of the intensity of -1-1 absorption bands in the 2360 cm and 1355 cm in the film formed under pressure. The hand 2360 cm is used to determine the thickness of the film 5 using the equation. 1 mil thickness (mils) = (ahscm-1) (0.081 ahs). (1 mil = * 25> 4 jam)

The comonomer concentration can then be calculated using the following equation? ______, ^ S1355 _ concentration (g / cmr) = (340 ahs cm ^) (thickness Ccm))

S

This equation gives the comonomer concentration in g / cm 2. Knowing the density of the polymer, it allows conversion to weight percent by the following equation: concentration (ff / cnr) / - / * scy x 100 = weight percent comonomer.

2.15 (density hex, g / cm>) ö

The factor absorbance used in this calculation was determined by standard methods using standard methods using

S

Singing of a homopolymer of perfluorobutyl ether in "Freon" F-113 solvent.

The results obtained by the infrared method voted. agrees well with those obtained using the melting point-20 data and the following equation: i. i „-hSè. (1 ° ¾) / ½ TTFE in which

= melting point of the copolymer in ° E

= melting point of the homopolymer ΡΤΙΈ (600 ° K) = mole fraction TFE in the copolymer.

This comparison was found to be in good agreement with the results obtained by the infrared method for polymers containing up to 5 moles of perfluorobutyl ether.

Example I.

800 ml of 1,1,2-trichloro-1,2,2-trifluoroethane solvent and 2 ml of perfluorobutyl ether were introduced into an airless stirred stainless steel autoclave. The temperature of the mixture was brought to 60 ° C and the stirring speed was set at about 10,000 revolutions per minute. Tetrafluoroethylene was added to this mixture to a total pressure of 892 kPa. Autoclave was then added 15 ml of a solution of 0.002 g / ml 8104397.

-9- * Λ bisperfluoropropionyl peroxide in the above solvent added. The pressure was kept constant by the continuous addition of tetrafluoroethylene. After 10 minutes, the aforementioned peroxide solution was fed to the reactor at a rate of 5 ml / min, as well as a solution of 0.04 g / ml perfluorobutyl ether in 1,1,2-trichloro-1,2,2 -trifluoroethane also at 1 ml / min. This rate maintained a perfluorobutyl ether concentration of less than about 1.1 mole percent based on total monomers. The polymerization was continued for a total time of 70 minutes, at which time the contents of the autoclave were discharged into a large stainless steel beaker. The polymer was recovered by drying in an air oven at 150 ° C for several hours. The dry polymer weighed 74 g. The polymer showed a sharp melting point at 315 ° C with a small shoulder at 287 ° C. The apparent melt viscosity was too high to measure. The polymer could be formed into tough films by compression. The comonomer content was 1.1 mol%. The isothermal TGA in air at 350 ° C showed a 4.8% weight loss after 140 minutes. X-ray scattering data showed a diffraction peak at angles below 1 ° 2Θ.

Example II.

800 ml of 1,1,2-trichloro-1,2,2-trifluoroethane solvent, 2 ml of perfluorobutyl ether and 0.25 ml of methanol were placed in an airless, stirred stainless steel autoclave of 1 liter. The temperature of the mixture was brought to 60 ° C and the stirring speed was set at about 1000 revolutions per minute. Tetrafluoroethylene was added to this mixture to increase the total pressure to 892 kPa. 15 ml of a solution of 0.002 g / ml bisperfluoropropionyl peroxide in the aforementioned solvent were then added to the autoclave. After 4 minutes, the peroxide solution was continuously added to the autoclave at a rate of 1 ml / min. After an additional 4 minutes, the addition of a solution of 0.04 g / ml perfluorobutyl ether in the same solvent was started, also at a rate of 1 ml / min. This rate maintained the perfluorobutyl ether at a concentration of less than 55 about 1.1 moles. Polymerization was continued for an additional 60 minutes at which time the contents of the autoclave were discharged into a large stainless steel beaker. The polymer was recovered by drying in an air oven at 150 ° C for several hours. The dry polymer weighed 55.5 g and had an apparent melt viscosity at 40 572 ° C of 27 x 10 ^ P. The polymer was compression molded 8104397

V W

* -10- to tough films »The comonomer content was 2.3 ml. The melting point was 303 ° C. The isothermal TGA in air at 350 ° C showed a 1% weight loss after 140 minutes. X-ray data indicated a diffraction peak at he angles less than 1 ° 2 ©.

Compression-formed films made from the polymer described above were placed in a forced air oven and aged at 250 ° C for 200 hours. The physical properties of the treated films were measured and are listed in Table A.

Table A.

10 Physical properties of films.

Taste! Yoorbeeld I Yoorbeeld II

(as such) (heat aged) Tensile strength 15 25 ° 0 28 960 kPa 22 340 kPa 250 ° C 10 205 kPa 9445 kPa breaking strength 25 ° C 1440 fcPa 15090 kPa elongation at break 20 25 ° 0 290% 250% 250 ° C '6i0 600 MIT folding time, no failure no failure cycles, film from 175-205 µm after after ASTM D2176 1.3MM cycles 1.7MM cycles.

25 Figure III ..

800 ml of 1,1,2-trichloro-1,2,2-trifluoroethane solvent and 1.6 ml of perfluoropropylate were placed in an airless, stirred stainless steel autoclave of 1 liter. The temperature of the mixture was raised to 60 ° C and the speed of the stirrer 30 was set at 1000 revolutions per minute. Tetrafluoroethylene was added to this mixture to bring the total pressure to 892 kPa. To the autoclave were then added 15 ml of 0.023 g / ml bisperfluoropropionyl peroxide in the above; listed solvent.

The peroxide delivery pump was then set to continuously add the peroxide solution to the autoclave at a rate of 1 ml / min. After 7 minutes, the addition of a solution of 0.04 g / ml perfluoropropylopene in the same solvent was started, also at a rate of 1 ml / min. This rate maintained the perfluoroproplethene at a concentration of. less than about 8104397 * m v -11- 4.1 mol%. Tetrafluoroethylene was added at such a rate that the autoclave pressure was kept constant. The polymerization was continued for an additional 60 minutes, at which time the contents of the autoclave were discharged into a large stainless steel 5 "beaker. The polymer was recovered by drying in an air oven at 150 ° C for several hours. The dry polymer weighed 48 »4 S and exhibited sharp melting points according to DSC he 284 and 310 ° C. The apparent melt viscosity he 372 ° C was too high to measure. The polymer could be compressed into tough films. The comonomer-10 content was 4» 3 mole% Isothermal TGA in air at 350 ° C showed a weight loss of 0.9% after 140 minutes X-ray scattering data showed a diffraction peak at angles less than 1 ° 29.

Toorheeld IT.

In a 1 liter airless stirred stainless steel autoclave, 800 ml of 1,1,2-trichloro-1,2,2-trifluoroethane solvent, 1.0 ml of 3,3,4 »4-tetrafluorobutene-1 and 0, 25 ml of methanol. The temperature of the mixture was raised to 60 ° C and the speed of the stirrer was set at about 1000 revolutions per minute. Tetrafluoroethylene was added to this mixture to bring the total pressure to 892 kPa. To the autoclave was then added 15 ml of 0.0023 g / ml per perfluoro rpro pi onylpe ro xi in the aforementioned solvent. The peroxide delivery pump was then set to continuously add the peroxide solution to the autoclave at a rate of 1 ml / min. After 15 minutes, the addition of a solution of 0.021 g / ml of 3,3,4,4-tetrafluorobutene-1 in the same solvent was started, also at a rate of 1 ml / min. This rate maintained the tetrafluorohutene at a concentration of less than about 1.1 mole percent. Tetrafluoroethylene 50 was added at a 2-hour rate to maintain the autoclave pressure constant. Polymerization was continued for an additional 60 minutes at which time the contents of the autoclave were discharged into a large stainless steel beaker. The polymer was recovered by drying in an air oven at 150 ° C for several hours.

The dry polymer weighed 32.1 g and showed a sharp melting point according to DSC he 291 ° C with a narrow shoulder he 312 ° C. The melt viscosity at 372 ° C was 0.62 x 10 ^ Pa.s (0.62 x 10 ^ poise). The comonomer content was 3.6 mol%. The isothermal TGA in air at 350 ° C showed a 1.1% weight loss after 140 minutes. E8nt- 40 gene beam scattering data showed a diffraction peak at * * 8104397 • ύ Vv '' -12 angles less than 1 ° 20.

Comparison.

To demonstrate the effect of adding perfluorobutyl ethylene in one initial addition prior to initiating the polymerization, the following experiment was performed.

A 110 ml stainless steel shaker tube was charged with 50 ml of 1,1,2-trichloro-1,2,2-trifluoroethane solvent, 0.74 S perfluorobutyl ethylene and 0.02 g bisperfluoropropionyl peroxide. The tube was cooled and evacuated and 10 g of tetrafluoroethylene was added. The tube was heated to 60 ° C and shaken for 4 hours. The product was isolated by air-drying at 150 ° C for several hours. The resulting dry polymer weighed 0.25 g (2.3%) and was strongly swollen with 1,2,1-trichloro-1,2,2-trifluoroethane. The polymer could not be formed into films by compression. The poly-15 · mer showed no sharp crystalline melting peaks according to DSC between 220 and 350 ° C.

8104397

Claims (6)

1. Copolymer consisting of: 93 - 99 mol. Your tetrafluoroethadiene units and complementary 7-1 mol. Your fluorinated alkyl ethylene phenomonomer units of the formula -CH-CH 2 -, wherein R 1 is perfluorinated alkyl of 2-10 carbon K atoms or substituted perfluoroalkyl of 2-10 carbon atoms in which the perfluoroalkyl group may be substituted by up to 3 substituents selected from hydrogen, bromine, chlorine or iodine, which polymer is characterized by the presence of units of the comonomer, which are placed substantially uniformly along the copolymer chain. Copolymer according to claim 1, characterized in that Rf in the formula -CH-CHg- of the fluorinated alkyl ethylene K is perfluorinated alkyl. 15 Copolymer according to claim 1 or 2, characterized in that the fluorinated alkylosdene comonomer is perfluoropropyl ethylene. Copolymer according to claim 1 or 2, characterized in that the fluorinated alkyl ethylene monomer is perfluorobutyl-20 ethylene. A process for the preparation of a copolymer of tetrafluoroethylene and a fluorinated alkylene of the formula R 1 CH 3 CHg, wherein R 1 is perfluorinated alkyl of 2-10 carbon atoms or substituted perfluoroalkyl of 2-10 carbon atoms, wherein the perfluoro-alkyl group is can be substituted with up to 3 substituents selected from hydrogen, bromine, chlorine or iodine, characterized in that (a) tetrafluoroethylene and the fluorinated alkyl ethylene are brought together and stirred in the presence of a non-aqueous solvent or in aqueous media in a reaction vessel at a temperature between 30 ° C and 110 ° C and a pressure between 98 kPa and 6860 fcPa and preferably between 294 kPa and 3430 kPa, in the presence of a free-radical polymerizing initiator, which together introduction of the tetrafluoroethylene and the fluorinated alkylethene is performed by adding continuous and uniformly fluorinated alkylene to the reaction vessel on a wheel It maintains a concentration of fluorinated alkylethene in the reservoir while stirring below 2.5 moles, and preferably below 8104397 V-14% -1 mo-1%, with respect to tetrafluoroethylene, which stirring treatment is continued until copolymer formation has occurred, and (b) separates the copolymer from the other ingredients present in step (a). 6. Copolymer consisting of 93 - 99 nol.% Tetrafluoroethylene units and complementary 7-1 mole.% Fluorinated alkyl ethylene comonomer units of the formula -CH-CHg-, wherein R 2 is perfluorinated alkyl with 2-10 carbon atoms or co-substituted perfluoroalkyl with Is 2-10 carbon atoms in which the Cu substituent may be hydrogen, bromine or chlorine, which copolymer is characterized by the presence of units of the comonomer which are placed substantially uniformly along the copolymer chain. 8104397