JPH09202814A - Polymerization of copolymer of tetrafluoroethylene and hexafluoropropylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject compound capable of being melted and secondarily processed, by carrying out copolymerization in an aqueous medium in the presence of a water-soluble initiator, a dispersant and a chain transfer agent.

SOLUTION: In preparing a partially crystallizable copolymer containing at least 0.3% total unstable part by copolymerizing (D) tetrafluoroethylene with hexafluoropropylene in an aqueous medium in the presence of (A) a water- soluble initiator, (B) a dispersant and optionally (C) a chain transfer agent, the amount of the component A is reduced, a part not more than a half of the copolymer is made to start by the component A, the amount of the component C is increased, the component A is supplemented with the component C in starting of the copolymer, the amount of the component E is adjusted to an amount corresponding to 2.0-5.0 HFPI, (F) the amount of a fluorinated vinyl ether is made 0.2-0.4wt.% and the copolymerization is carried out to give the objective copolymer containing ≤0.2% total unstable part in a polymerized state.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

[Related Application] This application is a continuation application and 19 of provisional application 60 / 012,241 filed on February 23, 1996.
Provisional application 60/002, filed August 17, 1995,
405 is a partial continuation application.

[0002]

FIELD OF THE INVENTION This invention is in the field of melt-fabricable tetrafluoroethylene and hexafluoropropylene copolymers.

[0003]

BACKGROUND OF THE INVENTION Melt-fabricable copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), as well as polymerization methods for making them, are well known. Bro and Sandt in frequently referenced US Pat. No. 2,946,763 disclose an aqueous method using a water soluble free radical initiator. As disclosed therein, high levels of HFP recruitment are very difficult due to the low reactivity of HFP compared to the high reactivity of TFE. The general method for increasing the reactivity of HFP is as high as possible, eg 100
It is to carry out the polymerization at a temperature of around ℃ and above. For a discussion of polymerization temperatures for TFE / HFP copolymers, see, eg, Morgan, US Pat.
6,639.

Under the influence of the initiator used, for example Bro
And TFE / HFP copolymers produced by aqueous methods such as Sandt's method have unstable end groups, especially --CO
It has OH or its salts, which can decompose during subsequent processing and lead to unacceptable bubble formation in the finished product. Various methods have been devised to stabilize the end groups of such polymers.
For example, Schreyer in U.S. Pat. No. 3,085,083 describes a labile carboxylate end group as a relatively stable --CF.
A wet heat treatment process is disclosed for improving the stability of such polymers by conversion to ₂ H (hydride) end groups.

It is believed that the second cause of instability in TFE / HFP copolymers is skeletal instability due to the presence of HFP diads. Morgan and
Sloan has TFE / HF in US Pat. No. 4,626,587.
Disclosed are high-shear adiabatic mechanical methods for reducing backbone instability in P-copolymers. It is disclosed that if the polymer contains labile end groups or has poor color after removal from the high-shear extruder, such problems can be eliminated by fluorination (contact with elemental fluorine). ing. TFE / HF produced by Bro and Sandt polymerization process and stabilized by high-shear extrusion
P-copolymers generally require post-treatment. The finishing step of such polymers is time consuming and expensive.

The use of certain chain transfer agents in the aqueous polymerization of TFE and PAVE binary polymers to control die swelling, which is attributed to the control of molecular weight distribution, is described by Gr.
US Pat. No. 3,635, by Esham and Vogelpohl,
No. 926. However, the use of chain transfer agents has a suppressive effect on the polymerization rate. This is especially undesirable in the copolymerization of TFE and HFP, in which the low reactivity of HFP itself has an unfavorable effect on the reaction rate.

It is common in the art that the HFP content of TFE / HFP copolymers is based on HFPI measurements. This amount was introduced by Bro and Sandt in US Pat. No. 2,946,763, which is
Multiple factor for obtaining HFP content (wt%) from 4.
5 was also introduced. Recent test methods have introduced another multiple factor, but H deduced from infrared measurements at various times.
FPI values are generally considered reliable.

There remains the problem of producing TFE / HFP copolymers by an aqueous process that are sufficiently stable for commercial use without the costly stabilizing finishing step. Such a copolymer must have not more than 0.2% total instability moieties as defined below.

[0009]

SUMMARY OF THE INVENTION The present invention is the copolymerization of tetrafluoroethylene with hexafluoropropylene in the presence of a water soluble initiator and dispersant in an aqueous medium to provide at least 0.3.
% Of total labile moieties to a partially-crystalline copolymer. According to an improvement in this method for reducing the total instability to no more than 0.2%, the copolymerization is carried out in the presence of a chain transfer agent, and the initiator is the copolymer produced. It is present in an amount effective to initiate no more than half of the molecule.

Another improvement in this method of copolymerizing tetrafluoroethylene with hexafluoropropylene is that the amount of hexafluoropropylene present is reduced to reduce the copolymerization rate caused by the amount of chain transfer agent used. And adding the fluorinated vinyl ether to the aqueous medium for copolymerization with tetrafluoroethylene and hexafluoropropylene,
When the reduction in hexafluoropropylene is the only change made to the copolymerization, it compensates for the toughness loss of the copolymer caused by the reduction in hexafluoropropylene. The resulting partially-crystalline copolymer was tetrafluoroethylene, an amount of hexafluoropropylene corresponding to HFPI of 2.0-5.0, and 0.2-4% by weight of at least one fluorinated. Comprising vinyl ether.

[0011]

Detailed Description of the Invention Produced using a water soluble free radical initiator and a high concentration of chain transfer agent (CTA) to initiate the formation of only a relatively small portion of the polymer molecule produced. It has been discovered that by initiating the formation of the relative majority of polymer molecules by chain transfer, TFE / HFP copolymers suitable for use in melt processing can be prepared without special stabilizing process steps. The proportion of polymer molecules initiated by the initiator and the chain transfer agent is lower in the former and higher in the latter, respectively, as compared to past polymerization methods. To obtain an acceptable reaction rate despite the use of high concentrations of CTA, the concentration of HFP in the polymerization and the resulting amount of HFP in the copolymer is reduced. To obtain satisfactory toughness, the HFP reduction is offset by a relatively small increase in the amount of fluorinated vinyl ether (FVE) in the copolymer. To obtain a satisfactory molecular weight in the presence of CTA, the initiator concentration is reduced compared to that required in the absence of CTA. Increased CTA
And the combined use of reduced initiators results in improved total stability, ie reduced skeletal instability and reduced --COOH end group combinations.

TFE / H produced by the method of the present invention
The FP / FVE copolymer has an HFP content corresponding to HFPI = 2.0-5.0, preferably HFPI = 2.0-4.1. For productivity reasons in polymerization, HFP
A HFP content corresponding to I = 2.0-3.5 is particularly preferred. HFPI is measured by the infrared method outlined below.

The FVE content of the copolymer produced by the process of the present invention is in the range of 0.2-4% by weight, preferably 0.4-2% by weight. Vinyl ethers that can be used in the method of the present invention include those of the formula CF ₂ = CFOR or CF ₂ = CF
-OR'-OR [wherein -R and -R'- are independently fully fluorinated or partially fluorinated linear or branched alkyl having 1 to 8 carbon atoms and An alkylene group] are included. The preferred -R group has 1-4 carbon atoms, and the preferred -R'- group has 2-carbon atoms.
4. FVEs of the formula CF ₂ = CFOR, especially perfluoro (alkyl vinyl ether) (PAVE), are preferred. Suitable PAVEs include perfluoro (methyl vinyl ether) (PMVE), perfluoro (ethyl vinyl ether) (PEVE), and perfluoro (propyl vinyl ether) (PPVE). PEVE is particularly preferred.

Those skilled in the art will recognize that one or more other copolymerizable monomers may be added into the TFE / HFP / FVE copolymer prepared by the process of the present invention. Will. The amount of such other monomers is determined by the detection of the melting endotherm by a differential scanning calorimeter with respect to the resin in which the resulting copolymer is polymerized, i.e., the resin which has not been previously melted. , Such that it remains partially crystalline.

The copolymers produced by the process of the present invention generally have a melt viscosity (MV) in the range of 0.5-50 × 10 ³ Pa.s. M in the range of 1-10 × 10 ³ Pa.s
V is preferred.

The polymerization method of the present invention is an aqueous dispersion polymerization method. As is well known, such methods can be carried out in the presence of organic liquids, generally halogenated compounds. However, in view of recent environmental concerns, polymerization in the absence of such compounds, ie solvent-free aqueous dispersion polymerization, is preferred.

The process of the present invention comprises known aqueous processes for polymerizing TFE / HFP copolymers, with very large amounts of chain transfer agent (CTA) and very small amounts of initiation with respect to the amount of polymer produced. The difference is that the agent is used. The amounts of CTA and initiator are not unrelated and are paired, ie chain transfer agent and initiator complement each other in initiating the total amount of polymer molecules produced.
With respect to the CTA and initiator selected, the selection of one amount used in the process of the invention to produce a copolymer having the selected composition and selected molecular weight will determine the other. Therefore, paired amounts can be expressed in terms of the amount of initiator used to make 1 mole of copolymer.

Initiators commonly used in emulsion (dispersion) polymerization of TFE copolymers are water-soluble free radical initiators such as ammonium persulfate (APS), potassium persulfate (KPS), or di-amber peroxide. Acids or redox systems, such as those based on potassium permanganate. Such initiators can be used in the method of the present invention. APS and / or KPS are preferred.
The amount of initiator used depends on the effective amount of CTA used. Due to the interaction between the chain transfer effect and the initiator effect, the combinatorial effect can be described in terms of the initiator. Reduced -COO due to varying initiator effects
It will be appreciated that the amount of initiator needed to obtain the number of H end groups will vary from initiator to initiator. However, for APS and KPS where the initiating effect reaches 100% at elevated temperatures (eg 100 ° C.), the amount of initiator with respect to the amount of polymer produced is generally less than 0.5 mol / mol and is desirable. Is not more than 0.35 mol / mol and preferably not more than 0.2 mol / mol.
When the initiator has a relatively low initiation effect, such as APS or KPS at low temperatures, the amount of these initiators is related to the proportion of polymer molecules initiated (produced) by the initiator. Both situations can be described as an effective amount of initiator per mole of polymer produced. Generally, by starting in proportion to the reduction in initiator-
A reduction in the number of COOH end groups would be obtained compared to a copolymer of the same MV made in the absence of CTA.

There is also a contribution to the number of -COOH end groups from the rearrangement of FVE (hydrolyzing in an aqueous medium to form the -COF end which becomes -COOH), which terminates the growing molecule. -FVE to COOH number
The dislocation contribution will depend at least on FVE type, FVE concentration, and reaction temperature. It is the combined contribution of FVE and CTA that contributes to the chain transfer that occurs in the polymerization reaction, in order to compensate for the initiation by the water soluble initiator, ie by initiating the production of molecules not initiated by the initiator. The contribution of the FVE rearrangement to the -COOH number can be offset by buffering the polymerization with a buffer such as ammonium carbonate or ammonia (ammonium hydroxide). US Patent No. 3,6
Such buffers generate amide end groups, as disclosed in 35,926.

A wide variety of compounds can be used as CTA in the method of the present invention. Such compounds include, for example, hydrogen-containing compounds, such as hydrogen itself,
Included are lower alkanes, and lower alkanes partially substituted with halogen atoms. Chain transfer activity of such compounds, when used in TFE / HFP polymerization can result in copolymer having a relatively stable -CF ₂ H end groups. Depending on the identity of CTA, CTA can also contribute to other relatively stable end groups. Suitable CTA
Include methane, ethane, and substituted hydrocarbons,
For example, methyl chloride, methylene chloride, chloroform, and carbon tetrachloride are included. The molar amount of CTA used to obtain the desired molecular weight will depend on the amount of initiator used and the effect of the chain transfer agent selected. Chain transfer effects can vary substantially from compound to compound. The amount of CTA used will also depend on the type and concentration of FVE used in the TFE / HFP polymerization process of the present invention, as possible FVE rearrangements also cause chain transfer.

Other effects of chain transfer, either by CTA or by FVE, are associated with termination of the growing molecule that is intrinsic to chain transfer. When a molecule is terminated by chain transfer, it cannot be terminated by coupling and, therefore, cannot precipitate during the formation of the HFP diad, which is the cause of the historically suspected skeletal instability.
Therefore, the high concentration of CTA used in the method of the present invention results in reduced skeletal instability as well as initiation-induced reduction of -COOH end groups.

TFE produced by the polymerization method of the present invention
The total stability, or instability, of the / HFP copolymer is characterized by weight loss as a result of controlled high temperature exposure. One method is total weight loss after a wet heat treatment (HHT) cycle. The following HHT is disclosed by Schreyer (US Pat. No. 3,085,083).
No.). A second method, set up to measure the Total Instability Fraction (TUF), was to measure the weight loss measured after high temperature exposure in dry nitrogen for various times, as also described below. Including the difference. The high temperature exposure of the TUF method is easy to control, and TUF is used here to characterize the effect of the invention. The TUF for the TFE / HFP copolymer produced by the process of the present invention is not more than 0.2%, preferably not more than 0.1%. As mentioned above, CTA contributes to a reduction in TUF in two respects by providing a relatively stable end group and reducing backbone instability.

A wide range of temperatures can be used. T
Due to the low reactivity of HFP compared to that of FE, relatively high temperatures, for example temperatures in the range of about 95 ° -115 ° C,
Is advantageous. 98 ° to prepare the copolymers of this invention by the aqueous semi-batch method used in the examples below.
Temperatures in the range of -108 ° C are preferred. Surfactants used in emulsion polymerization appear to be relatively ineffective at temperatures above 103 ° -108 ° C and tend to lose dispersion stability.

Surfactants suitable for use in dispersion polymerization of TFE / HFP copolymers can be used. Such surfactants include, for example, US Pat.
Ammonium perfluorooctanoate (C-8), ammonium perfluorononanoate (C-9), and perfluoroalkylethanesulfonic acids and salts thereof disclosed in US Pat. No. 6,618 are included.

The reactor was charged with water, surfactant and monomers, heated to the selected temperature and stirring was begun,
A solution of initiator is added at the indicated rate to initiate the polymerization. A pressure drop is a general indication that polymerization has started. The TFE addition is then initiated and adjusted according to the selected scheme to adjust the polymerization. An initiator solution, which may be the same as or different from the initial initiator solution, is generally added throughout the reaction.

There are several variations for adjusting the rate of TFE / HFP copolymerization, and these are applicable to the method of the present invention. It is common to most variants to first precharge all HFP monomer and then add TFE to the desired total pressure. After injecting the initiator and starting the reaction, additional TFE is then added to maintain the selected pressure. The TFE can be added at a constant rate, varying the speed of the stirrer as needed to increase or decrease the actual polymerization rate and consequently maintain a constant total pressure. Alternatively, both total pressure and agitator speed can be kept constant while TFE is added to maintain a constant pressure if desired. A third variant is to carry out the polymerization in multiple stages at a variable stirrer speed while regularly increasing the TFE feed rate.

Since the HFP monomer is much less reactive than the TFE monomer, the HFP / TFE ratio is high to ensure the desired HFP incorporation, but comparable toughness in the absence of FVE. Should not be as high as necessary to obtain, ie, as high as possible in comparable reaction rates in the absence of CTA.

Heretofore, FVE has been added to TFE / HFP copolymers to improve their properties for certain uses. In the present invention, FVE is increased primarily to restore lost properties by reducing HFP content, which restores the reaction rate lost by the addition of CTA. FVE can be added to the process either by precharging, precharging and subsequent addition (pump addition) or pump addition of FVE into the reactor. When the FVE is PAVE, the reactivity of PAVE when compared to TFE if PAVE is pre-charged into the reactor is satisfactorily uniform TFE compared to PAVE addition.
/ HFP copolymer is obtained.

TFE produced by the polymerization method of the present invention
The / HFP copolymer can be used for many purposes without special stabilizing finishing steps. Finishing can be carried out in a given extrusion stage that is used to make solids isolated from the dispersion products of the polymerization into commercially commercially satisfactory cubes (pellets). Such pellet production can be performed using extrusion equipment known in the art, including twin screw and single screw extruders.

[0030]

EXAMPLE Fluoropolymer compositions were measured using Fourier Transform Infrared (FTIR) spectroscopy on 0.095-0.105 mm thick films compression molded at 300 ° C. HF
For P measurement, the method described in US Pat. No. 4,380,618 was used. In applying this method, the band absorption seen at about 10.18 mm and about 4.25 mm was used. HFP content is the HFP index (H
FPI), ie absorption of 10.18mm vs. 4.25mm
Absorption ratio of, displayed as. HFP content (wt%) was calculated as 3.2 x HFPI.

PEVE was measured using FTIR spectroscopy from the infrared band at 9.17 mm. PEVE content (wt%) was calculated as the ratio of 1.3 x 9.17 mm absorption to 4.25 mm absorption. The absorption at 9.17 mm is measured with a TFE / HFP binary polymer reference film and the strong absorption overlying the 9.17 mm band is subtracted.
Absorption of 4.25 mm internal thickness was measured without the use of a reference film.

End group analysis was also performed by FTIR spectroscopy using a 100 mm thick film prepared by compression molding at room temperature, modifying the method disclosed in US Pat. No. 3,085,083. . Measuring the number of -COOH end groups using absorption at 3557cm ^-1, whereas -COOH dimers also called hydrogen using absorption at 1774 cm ^-1 compared to absorption at 1813cm ^-1 - coupled The number of -COOH groups was measured. When reported here, the total measured number of -COOH, the sum of monomer and dimer, is given.

The melt viscosity of fluoropolymers is reported in US Pat.
AS modified as described in 80,618
Measured by TM method D1238-52T.

The thermal characteristics of the fluoropolymer resin were measured by DSC.
It was measured by the method of STM D-4591-87.
The reported melting temperature is the endothermic peak temperature during the second melting.

Average size of the polymer particles in the polymerized state,
That is, untreated dispersion particles (RDPS) were measured by photon correlation spectroscopy.

A standard MIT folding endurance tester described in ASTM D-2176 was used to measure flex life (MIT flex life). The measurement was performed using a compression molded film that was quenched in cold water. The film thickness is about 0.008 ± 0.0005 inch (0.20 ± 0.01
3 mm).

In the following, unless otherwise stated, the solution concentrations indicated are based on the total weight of the solvent water and one or more solutes. The indicated concentration of polymer solids in the dispersion is based on the total weight of solids and aqueous medium,
And determined gravimetrically, i.e., by weighing the dispersion, drying, and weighing the dried solids, or by the established correlation method of dispersion specific gravity used with gravimetric methods. .

The total unstable part (TUF) was used as a measure of polymer instability. A weighed sample of the copolymer resin was heated to 360 ° C. under a nitrogen atmosphere and the weight losses DW ₁ and DW ₂ were measured after 1 hour and 2 hours, respectively. Next, TUF is TUF = 2DW
Calculated as _1- DW _{2 and} expressed in terms of initial weight (ie, in%). This difference was used to isolate the effects of unstable objects that were determined to have occurred within a relatively short time (within 1 hour) from the background decomposition that occurred at the high temperatures used. TUF is taken to be the sum of the weight loss due to the labile end groups and the weight loss due to the skeletal instability moiety generally due to the HFP diad.

As shown in the Examples below, a sample of untreated polymer was wetted by heating at 360 ° C. for 1.5 hours in moist air containing 13 mol% water. Subjected to heat treatment (HHT) stabilization method. HHT
The subsequent weight loss is a measure of the stability of the untreated polymer.

For use in determining the molar amount of a copolymer produced in a particular polymerization, the melt viscosity (MV) in Pa.s is calculated using the relation Mn = 10570 × (MV) ^0.29. The average molecular weight (Mn) was calculated. The total amount of copolymer produced was added to the TF added to the reactor during polymerization.
Calculated from the amount of E and the amount of comonomer units in the copolymer measured by infrared analysis.

Example 1 A cylindrical, horizontal, water covered, paddle stirred stainless steel reactor having a length to diameter of about 1.5 and a water capacity of 80 parts by weight was added to 50 Department of deionized water and 0.66 parts of ammonium perfluorooctanoate surfactant 20% by weight aqueous solution of ^{(C-8, Fluorad R FC} -143, 3M) was charged. While stirring the reactor with a paddle at 35 rpm, heat the reactor to 65 ° C., apply vacuum, flush with TFE, apply vacuum again, and 0.0046 parts (102 mm).
Ethane (calculated from Hg pressure increase) was added. The reactor temperature was then raised to 103 ° C. and 0.43 parts of liquid PEVE was injected into the reactor. After the temperature became constant at 103 ° C, the pressure was 350 psig (2.5 MPa)
HFP was slowly added to the reactor until. Then TF
E was added to the reactor to obtain a final pressure of 600 psig (4.2 MPa). Then 0.86 parts freshly prepared initiator aqueous solution containing 0.20% by weight ammonium persulfate (APS) and 0.20% by weight potassium persulfate (KPS) was added to the reactor at 0.11 parts / Charged in minutes, thereby adding 0.0034 parts of combined APS and KPS. This same initiator solution was then pumped into the reactor at 0.0074 parts / min for the remainder of the polymerization.
After the polymerization started, as indicated by a 10 psig (0.07 MPa) drop in reactor pressure, additional TFE was added to the reactor from the start until a total of 17.5 parts of TFE was added to the reactor. To 600 psig
It was maintained at (4.2 MPa). The total reaction time was 175 minutes at a TFE addition rate of 0.1 part / minute. The reaction rate was kept constant by adjusting the stirrer speed. At the end of the reaction period, stop the TFE feed and the initiator feed,
Then the reactor was cooled while continuing to stir. When the temperature of the reactor contents reached 90 ° C, the reactor was slowly evacuated. After venting to near atmospheric pressure, the reactor was flushed with nitrogen to remove residual monomer. Upon further cooling, the dispersion was discharged from the reactor below 70 ° C. The solids content of the dispersion was 30.4% by weight and the particle size (RDPS) of the untreated dispersion was 0.174 μm. After mechanical coagulation, the polymer was isolated by compressing excess water from the wet polymer and then drying the polymer in a convection air oven at 150 ° C. The TFE / HFP / PEVE copolymer has an MV of 3.30 × 10 ³ Pa.s and an HE of 2.53.
PI (8.1% by weight HFP), 1.45% by weight PEV
It had an E content and a melting point of 273 ° C. Total Unstable Fraction (TUF) for untreated polymer is 0.08
%, Indicating good thermal stability. The total amount of initiator used for 1 mole of copolymer produced was only 0.20 moles / mole based on the polymer molecular weight calculated from the MVs outlined above. . A sample of this polymer was stabilized by heating (wet heat treatment, HHT) to 360 ° C. in moist air containing 13% water for 1.5 hours. After that, the TUF was 0.03%. The total weight loss after wet heat treatment was only 0.16%, consistent with the low TUF value for the unstabilized polymer. The film molded from the stabilized copolymer resin then has a MIT flex life of 5300 cycles before breaking, and the TFE / HFP copolymer produced by the method of the present invention is relatively low. It was shown to have a good flex life despite the HFP content.

Example 2 CTA was replaced with 0.043 parts of chloroform instead of ethane.
The procedure of Example 1 was essentially followed, except that The product properties are summarized in Table 1, along with that of Example 1 for reference. Note: “nc” indicates that there is no change from Example 1. The data show that the use of chloroform in this method also produces TFE / HFP copolymers with good flex life. TUF before HHT
(0.13%) is as low as the weight loss after HHT, which indicates the overall stability of the copolymer produced by the process of the present invention. A finely divided TFE / HFP copolymer resin obtained by coagulation and drying was applied to a 1-inch (2.54-cm) single-screw Haake.
e) Using an extruder, extruded into a cube at a barrel temperature of 300 ° C and a die temperature of 340 ° -350 ° C at a rate of 5 lbs / hr (2.3 kg / hr). The TUF of this sample extruded product is 0.02%
And was very low.

Example 3 The procedure of Example 2 was essentially followed except that the amount of chloroform was 0.0163 parts and the differences shown in Table 1. Note: “nc” indicates that there is no change from Example 1 or 2. The product properties summarized in Table 1 are TFE / H with relatively high MV and relatively long flex life.
It shows that the FP copolymer was produced in this case.

Table 1. Conditions and Results for Example 2 and Controls A-C Example: 1 2 3 A B C Experimental Conditions : Chain Transfer Agent C ₂ H ₆ CHCl ₃ CHCl ₃ None None None PEVE Precharge (parts) 0.43 nc 0.56 nc 0.44 0.26 HFP pressure (MPa) 2.5 nc nc nc nc 3.0 Initiator prefill (part) 0.0034 nc 0.0033 0.0088 0.0095 0.0113 Initiator solution pump addition 0.0074 nc 0.013 0.042 0.044 0.048 (part / min) Dispersion property : solid Min (wt%) 30.4 30.3 30.2 31.7 28.3 31.2 RDPS (μm) 0.174 0.184 0.169 0.167 0.162 0.172 Resin properties ; MV (10 ³ Pa ・ s) 3.30 4.00 7.4 2.40 2.40 2.23 HFPI 2.53 2.16 2.2 3.38 3.13 4.03 HFP content (weight %) 8.1 6.9 7.0 10.8 10.0 12.9 PEVE content (wt%) 1.45 1.44 1.72 1.08 1.23 0.79 Melting point (℃) 273 280 269 258 MIT Flex life (cycle) 5300 6240 27000 4400 2950 5770 Initiator / polymer (mol / mol) ) 0.20 0.21 0.28 0.78 0.83 0.87 TUF before HHT (%) 0.08 0.13 0.14 0.38 0.52 0.60 TUF after HHT (%) 0.03 0.02 0.07 0.02 0.01 0.05 after HHT The amount loss (%) 0.16 0.27 0.31 0.47 0.55 0.56 HHT previous -COOH 330 215 174 630 --- 750 ( 10 6 C atoms per) HHT after -COOH 2 4 --- 1 0 0 ( 10 6 cells Controls A-C ( per C atom of) The procedure of Example 1 was essentially followed except for the differences shown in Table 1. In particular, no CTA was used and the initiator preload and pump loading were relatively high. Note "nc"
Indicates that there is no change from Example 1. The product properties are also summarized in the table. Relatively high TUF before HHT
The values, and the relatively high weight loss after HHT, indicate lower overall stability than that for the TFE / HFP copolymer produced by the method of the present invention. The data also show a relatively large number of labile end groups.

Example 4 Except for the amount of CTA (chloroform) set to obtain a copolymer resin having a relatively low MV, the initiator precharge, and the adjustment in the pumped initiator. Eleven batches of TFE / HFP copolymer were prepared by two general steps. Compared to Example 2, C
TA increased by 92% by weight and initiator preload was 28
% Increased. The amount of initiator that was pumped in was varied somewhat from the laboratory practice of adjusting the MV for formulation purposes, resulting in an average increase of 19% in pumped initiator. 8 of untreated dispersion for blending in pairs
Individual batches, then coagulate, dry, and Wer
ner & Pfleidere Kombiplast ^R extruder (28mm twin - screw and subsequent single - screw) was typical cubes (pellets) extruded using. For example, no post-treatment with elemental fluorine was used. Selected properties of the compounded copolymer resin both before and after extrusion are shown in Table 2.

Table 2. Resin properties for multiple batch tests Properties before extrusion: MV (10 ³ Pa · s) 2.04 HFPI 2.13 HFP content (wt%) 6.8 PEVE content (wt%) 1 .35 melting point (° C) 281 MIT flex life (cycle) 1500 initiator / polymer (mol / mol) 0.20 TUF before HHT (%) 0.07 TUF after HHT (%) 0.00 after HHT Weight loss (%) 0.21 Properties after extrusion: MV (10 ³ Pa · s) 1.85 HFPI 2.19 HFP content (wt%) 7.0 PEVE content (wt%) 1.34 MIT flex Life (cycle) 1000 TUF (%) 0.04 Example 5 Using the TFE / HFP copolymer prepared in Example 4, Nokia-Maillefer 60-mm was prepared by melt drawing extrusion technology.
AWG24 solid copper conductor (20.
Insulation extrusion molding on 1 mil = 0.51 mm diameter). The extruder has a length / diameter ratio of 30/1 and is equipped with a conventional mixing screw (see Saxton US Pat. No. 3,006,029) to provide a uniform melt. Was there. The die diameter is 0.32 inches (8.
13 mm) and the guide tip diameter is 0.19 inch (4.
83 mm) and the land length
Was 0.75 inch (19.1 mm). The cone length was 2 inches (51 mm) and the air gap to water quench was 33 feet (10 m). Temperature characteristics, other operating conditions, and results for extrusion starting from 1500 ft / min (456 m / min) and increasing in increments of 300 ft / min (91 m / min) to 2700 ft / min (823 m / min) Are shown in Table 3. Resin thin wall manufactured under laboratory processing conditions (0.1
2400 ft / min (732 mm) for 8 mm insulation
The absence of spark failure for extrusion speeds up to m / min) indicates that the TFE / HFP copolymer produced by the method of the present invention performed well.

[0047]

[Table 1]

The main features and aspects of the present invention are as follows.

1. Copolymerization with a water-soluble initiator in an aqueous medium,
Tetrafluoroethylene is copolymerized with hexafluoropropylene in the presence of a dispersant, and optionally a chain transfer agent, to form a partially-crystalline copolymer having at least 0.3% total labile moieties. In the method for producing, (a) reducing the amount of the water-soluble initiator, initiating not more than half of the copolymer molecules produced by the initiator, and (b) the chain optionally used. Increasing the amount of transfer agent, chain transfer compensating for the initiation of the copolymer molecules produced, (c) reducing the amount of hexafluoropropylene present, (a) and (b)
Offsets the decrease in copolymerization rate caused by, and when this is the only change made to the copolymer, it also causes a decrease in toughness of the copolymer, i.e., hexafluoro added to the copolymer. The amount of propylene corresponds to an HFPI of 2.0-5.0, and (d) fluorinated vinyl ether is added to the aqueous medium for copolymerization with the tetrafluoroethylene and hexafluoropropylene, hexafluoro. Add an amount to compensate for the loss of toughness caused by the reduction in propylene,
That is, by adjusting the amount of fluorinated vinyl ether added to the copolymer to 0.2 to 0.4% by weight, the copolymerization is carried out to obtain a polymerization having a total unstable portion of not more than 0.2%. An improvement comprising producing the copolymer in the as-prepared state.

2. Tetrafluoroethylene was copolymerized with hexafluoropropylene in an aqueous medium in the presence of a water-soluble initiator and a dispersant to provide a partial tetrafluoroethylene and hexafluoropropylene having a total labile moiety of at least 0.3%. -In a method of obtaining a crystalline copolymer, the copolymerization is carried out in the presence of a chain transfer agent and is effective for initiating not more than half of the copolymer molecules from which the initiator is produced. An improvement comprising obtaining the copolymer in polymerized state having a total labile moiety present in an amount of not more than 0.2%.

3. The improved process of claim 2 wherein said copolymer comprises hexafluoropropylene in an amount corresponding to HFPI of 2.0-5.0.

4. The copolymer further contains 0.2-4% by weight.
The process of claim 3 which also comprises at least one fluorinated vinyl ether of

5. Copolymerizing tetrafluoroethylene and hexafluoropropylene in an aqueous medium containing a water soluble initiator and a chain transfer agent,
No more than half of the copolymer molecules produced are initiated by the initiator, and chain transfer supplements the initiator with respect to the initiation of the copolymer molecules produced, tetrafluoroethylene and hexafluoropropylene. A method for aqueous dispersion polymerization of a partially-crystalline copolymer comprising.

6. The process of claim 5 wherein said copolymer comprises hexafluoropropylene in an amount corresponding to HFPI of 2.0-5.0.

7. The copolymer further contains 0.2-4% by weight.
The method of claim 6 also comprising at least one fluorinated vinyl ether of

8. The copolymer in a polymerized state is 0.2
The method of claim 5 having a total instability portion not greater than%.

9. The amount of the water-soluble initiator used is not more than 0.5 mol per 1 mol of the polymer produced,
the method of.

10. The process of 9 above, wherein the amount of said water-soluble initiator used is not more than 0.35 mol per 1 mol of polymer produced.

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[Procedure amendment]

[Submission date] March 10, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

[0030]

EXAMPLES Fluoropolymer compositions were measured using Fourier Transform Infrared (FTIR) spectroscopy on 0.095-0.105 mm thick films compression molded at 300 ° C. H
For FP measurements, the method described in US Pat. No. 4,380,618 was used. In applying this method, band absorptions found at about 10.18 μm and about 4.25 μm were used. The HFP content is the HFP index (HFPI), ie the absorption at 10.18 μm vs. 4.
It is expressed as the ratio of absorption at 25 μm . HFP content (wt%) was calculated as 3.2 x HFPI.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction contents]

PEVE was measured using FTIR spectroscopy from the infrared band at 9.17 μm . PEVE content (wt%) is 1.3 × 9.17 μm absorption vs. 4.25 μm
Calculated as ratio of absorption. The absorption at 9.17 μm is measured with a TFE / HFP binary polymer reference film and the strong absorption overlying the 9.17 μm band is subtracted. Absorption of 4.25 μm internal thickness was measured without the use of a reference film.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

The total unstable part (TUF) was used as a measure of polymer instability. A weighed sample of the copolymer resin was heated to 360 ° C. under a nitrogen atmosphere and weight loss Delta W ₁ and Delta W ₂ of 1 each
The measurement was performed after hours and after 2 hours. Then TUF to TU
Calculated as F = 2 DeltaW ₁ -DeltaW ₂ and expressed in terms of initial weight (ie, in%). This difference was used to isolate the effects of unstable objects that were determined to have occurred within a relatively short time (within 1 hour) from the background decomposition that occurred at the high temperatures used. TUF is taken to be the sum of the weight loss due to the labile end groups and the weight loss due to the skeletal instability moiety generally due to the HFP diad.

Claims (3)

[Claims] 1. Copolymerization is carried out in an aqueous medium in the presence of a water-soluble initiator, a dispersant, and optionally a chain transfer agent,
In a method for copolymerizing tetrafluoroethylene with hexafluoropropylene to produce a partially-crystalline copolymer having at least 0.3% total labile moieties, the amount of (a) the water-soluble initiator is Reducing, initiating not more than half of the copolymer molecules produced by the initiator, and (b) increasing the amount of the chain transfer agent optionally used, of the copolymer molecules produced. Chain transfer on initiation compensates for the initiator and (c) reduces the amount of hexafluoropropylene present, offsetting the reduction in copolymerization rate caused by (a) and (b),
If this is the only change made to the copolymer, it also causes a decrease in the toughness of the copolymer, i.e. the amount of hexafluoropropylene added to the copolymer is between 2.0 and 5.0. HFPI equivalent and (d) an amount of fluorinated vinyl ether in the aqueous medium for copolymerization with the tetrafluoroethylene and hexafluoropropylene in an amount to compensate for the loss of toughness caused by the reduction in hexafluoropropylene. In other words, by adding the amount of fluorinated vinyl ether added to the copolymer to 0.2-0.4% by weight, the copolymerization is carried out to obtain a total unstable portion of not more than 0.2%. An improvement comprising producing the copolymer in a polymerized state. 2. Tetrafluoroethylene is copolymerized with hexafluoropropylene in an aqueous medium in the presence of a water-soluble initiator and a dispersant to give tetrafluoroethylene and hexafluoroethylene having a total labile moiety of at least 0.3%. In a method of obtaining a partially-crystalline copolymer of fluoropropylene, the copolymerization is carried out in the presence of a chain transfer agent and the initiator is initiated in no more than half of the copolymer molecules produced. Is present in an effective amount to
An improvement comprising obtaining the copolymer in polymerized state having no more than 0.2% total labile moieties. 3. Copolymerizing tetrafluoroethylene and hexafluoropropylene in an aqueous medium containing a water-soluble initiator and a chain transfer agent, and not more than half of the copolymer molecules produced. A portion of the partially-crystalline copolymer comprising tetrafluoroethylene and hexafluoropropylene in which a moiety is initiated by the initiator and chain transfer complements the initiator with respect to the initiation of the copolymer molecule produced. Aqueous dispersion polymerization method.