JPS6050813B2 - Method for producing tetrafluoroethylene-hexafluoropropylene copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to tetrafluoroethylene (hereinafter referred to as TFE).

) and hexafluoropropylene (hereinafter referred to as dried), particularly TFE-H, which has excellent thermal stability.
The present invention relates to a method for economically producing FP copolymers. Conventionally, ammonium persulfate (Japanese Patent Publication No. 34-8544) has been well known as a polymerization initiator for producing TFE-HFP copolymer by copolymerizing TFE and HFP.
There is.

However, when this polymerization initiator is used, a functional group is introduced at the end of the resulting TFE-HFP copolymer, so the thermal stability is significantly poor and it cannot be used as a molding material as it is. Therefore, post-treatment such as terminal stabilization treatment (Japanese Patent Publication No. 37-3127) is required, which is disadvantageous for industrial production. Therefore, di(chlorofluoroacyl) peroxide (Japanese Patent Publication No. 47-44031) is used as a polymerization initiator that makes it possible to obtain terminally stable TFE-HFP copolymers that do not require the above-mentioned post-treatment step.
Yaji (Fluoroacyl) Peroxide (Special Publication 1977
-2867) has been proposed for use.

When such polymerization initiators are used, in fact, fairly thermally stable TFE-HFP copolymers can be obtained, but the molecular weight of the resulting copolymers tends to be too high; Its melt viscosity often exceeds the practical range. If a molecular weight regulator such as methanol is used in combination, this disadvantage can be overcome, but on the other hand, the disadvantage is that the polymerization rate is reduced. In addition, considering the decomposition rate of these polymerization initiators, it is considered appropriate to set the polymerization temperature to about 0 to 350°C or less, and in particular, it is preferable to use a relatively low temperature such as 10°C. is preferred. However, at such low temperatures, the amount of polymerization initiator used is several times that when polymerizing at 20 to 30°C, and considering that this polymerization initiator is extremely expensive, this is a significant disadvantage industrially. Become. Therefore, in reality, polymerization is carried out at a temperature of about 20 to 30°C, where high initiator efficiency is achieved, and during this period, polymerization is carried out several times in order to replenish the polymerization initiator lost through decomposition. A polymerization initiator will be added to the system. For this reason, the concentration of the polymerization initiator in the polymerization system is not constant and constantly fluctuates, and the resulting polymer inevitably has a large molecular weight distribution, resulting in poor stress cracking resistance. Become. Few general organic peroxides other than those listed above exhibit polymerization activity at low temperatures in the above-mentioned copolymerization reaction, and raising the reaction temperature inevitably requires raising the reaction pressure, and the equipment cannot withstand high pressure. I don't like being asked for it.

Even in the case of organic peroxides that are active at relatively low temperatures, the reaction rate is slow, and the resulting copolymer is often colored when dissolved. The present inventors have conducted various studies in search of a method for economically producing TFE-HFP copolymers that overcomes the above-mentioned drawbacks, and as a result, the inventors have succeeded in polymerizing diisopropyl peroxydicarbonate as a polymerization initiator. We have learned that this purpose can be achieved by using monomers in a certain proportion.

That is, in the copolymerization reaction of TFE and HFP, if a certain amount of diisopropyl peroxydicarbonate is used as a polymerization initiator for the monomer, an appropriate melt viscosity can be obtained without using a molecular weight regulator. ``A TFE-FIF'P copolymer having a poise of 101 to 1σ can be obtained, and this effect can be applied to this polymerization initiator.
There are advantages that can be achieved over the entire range from 0 to 60°C.
Furthermore, since this polymerization initiator is relatively inexpensive, it can be used at relatively high concentrations, thereby avoiding complicated operations such as multiple charging and the associated broadening of the molecular weight distribution of the resulting copolymer. I can do it. Therefore, the obtained copolymer has excellent physical properties such as high stress crack resistance and no die swell during extrusion. In general, for the polymerization of fluorinated olefins, hydrocarbon-based polymerization initiators, with very few exceptions such as vinylidene fluoride, have low polymer yields and unsatisfactory physical properties such as heat resistance. , it has been considered that it cannot be used industrially.

The same applies to the polymerization reaction of TFE (511F'P), which is the subject of the present invention; until now, hydrocarbon-based polymerization initiators have not been used in the industrial production of TFE-]+'P copolymers. Therefore, as mentioned above, diisopropyl peroxydicarbonate was
The fact that P has an excellent effect as a polymerization initiator in the copolymerization reaction is a completely exceptional and unexpected discovery. The gist of the present invention is to polymerize TFE, (5HFP) in the presence of a polymerization initiator in an aqueous medium to obtain a TFE-HFP copolymer with an HFP content of 8 to 2% by volume. T characterized in that diisopropyl peroxy sidicarbonate is used in a proportion of 0.05 to 5% by weight based on the monomer in the polymerization system.
FE-1 Consists in a method for producing a 1,000-thousand copolymer. In the method of the present invention, the polymerization initiator used is diisopropyl peroxydicarbonate.If other hydrocarbon peroxides are used, the yield of the copolymer produced may be unsatisfactory, or the copolymer may not melt. Favorable results such as inappropriate viscosity cannot be obtained.The amount of diisopropyl peroxydicarbonate used is 0.05% of the monomer in the polymerization system.
~5% by weight is required. When the amount is less than this, the yield of the copolymer is low and the physical properties are also poor. When the amount is more than this, the molecular weight decreases too much, which is not preferable. The polymerization reaction may be carried out according to a conventional procedure.

For example, the polymerization reaction is initiated by charging deaerated and demineralized water into a pressure vessel, adding TFE (51+'P), and further adding a polymerization initiator.
The water:monomer ratio may be about 1:1 to 10:1, particularly about 2:1 to 5:1, in terms of volume ratio. Water is used as the reaction medium, but if necessary, an appropriate amount of a solvent capable of dissolving TFE or HFP may be added. Further, suspension stabilizers and other additives may be added as appropriate. For example, the presence of a small amount of acetone in the reaction system accelerates the reaction rate and improves reaction efficiency. Also,
The presence of acetone is also preferred in that a TF'E-HFP copolymer with excellent physical properties can be obtained. The reaction temperature is usually 10
to 60°C, and the reaction pressure is generally 0.5
~15 kg/CItG.

Since the TFE-HFP copolymer obtained by the method of the present invention has a specific melt viscosity in the range of 101 to 1σ poise, it can be processed by melt processing methods such as compression molding, extrusion molding, injection molding, and fluidized dip coating. On the other hand, it has sufficient mechanical strength required for practical use.

In addition, the copolymer has excellent physical properties such as a narrow molecular weight distribution, high stress crack resistance, and no die swell during extrusion. It is stable over a wide temperature range from extremely low temperatures to high temperatures, regardless of whether it comes into contact with various chemicals such as reducing agents.
Note that the polymerization initiator diisopropyl peroxydicarbonate used in the method of the present invention is relatively inexpensive, so it can be used in one charge at a high concentration that does not change during polymerization, and is called additional charge. It also has the advantage of not requiring complicated operations. The present invention will be explained in more detail below with reference to Examples, Comparative Examples, and Test Examples.

Note that 1 part refers to parts by weight. In addition, the HF'P content (wt%) of the produced copolymer is determined by the absorbance at a wave number of 980 cm-1 measured by infrared absorption spectrum analysis of a film with a thickness of about 40p at 2350 cm-1.
It is obtained by multiplying the value divided by the absorbance at a wave number of 1 by 3.2. Furthermore, the specific melt viscosity was determined using a Koka-type flow tester, and the copolymer was measured with an inner diameter of 9.5 m.
The sample was loaded into a cylinder of 380°C, kept at a temperature of 380°C for 5 minutes, and extruded at the same temperature under a piston load of 7kg through an orifice with an inner diameter of 2.1mm and a length of 8TfUn. It was obtained by dividing 53150.Example 1 SUS-32 with a jacket capable of containing 300V of water
Deoxygenated and demineralized water 1 in a stirring autoclave
000 parts of HFP6OO and TFE9 (2
).

While maintaining the temperature inside the system at 25°C, 2 parts of diisopropyl peroxydicarbonate and 8 parts of acetone were introduced under pressure. At this time, the internal pressure of the autoclave was 8 kg/DG, and the reaction started immediately. Thereafter, as the reaction progressed, the pressure inside the autoclave decreased, so TFE was successively injected to keep it constant. After 24 hours of reaction, unreacted monomers were purged and a white powdery product was collected.

This was thoroughly washed with water and then dried at a temperature of 120°C for 48 hours to obtain 276 parts of TFE-HFP copolymer. The dry content of this copolymer is 12.0%, and the specific melt viscosity is 1.2.
X101) It was poise. Example 2 In addition to 8 parts of acetone, 8 parts of methanol was added as a molecular weight regulator.
The operation was carried out in the same manner as in Example 1 except that HF was used.
TFE-HFP copolymer 25 with a P content of 12.2% and a specific melt viscosity of 5.0×101 poise. I got it.

Example 3 'IFE-11FP copolymer 18?' was prepared in the same manner as in Example 1 except that acetone was not used. I got it.

Example 4 The procedure of Example 1 was repeated except that acetone was not used and 2 parts of methanol was used as a molecular weight regulator to obtain 87 parts of an 'IFE-1 dried copolymer.

Example 5 TFE-1 (F
84 parts of P copolymer were obtained.

Comparative Example 1 24 parts of TFE-HFP copolymer was obtained in the same manner as in Example 3, except that 2 parts of isobutyl peroxide was used instead of diisopropyl peroxydicarbonate.

Comparative Example 2 The procedure was repeated in the same manner as in Example 3 except that 2 parts of perhexaacetylcyclohexylsulfonynorperoxide was used instead of diisopropyl peroxydicarbonate, but traces of TFE-HFP copolymer were observed to form. It wasn't too much.

Comparative Example 3 The procedure was the same as in Example 1 except that 2 parts of ditertiary butyl peroxide and 2 parts of trimethylamine were used instead of diisopropyl peroxydicarbonate and acetone, but traces of TFE were used. Only the formation of -HFP copolymer was observed.

Comparative Example 4 The procedure was repeated as in Example 1 except that 2 parts of tertiary butyl hydroperoxide and 2 parts of sodium hydroxide were used instead of diisopropyl peroxydicarbonate and acetone, but traces of TFE-HFP copolymer were removed. The formation was only recognized.

Comparative Example 5 In the same manner as in Example 1, 10 (4) parts of deoxygenated and demineralized pure water and 8 parts of ammonium perfluorooctanoate were charged into the reaction apparatus, and after the internal space was sufficiently replaced with nitrogen gas, the inside of the autoclave was Exhaust.

While stirring, the temperature is raised to 80°C, and HFP is introduced until the internal pressure of the autoclave reaches 5.3 kg/DG. 80℃
8.0k9/c by introducing TFE while keeping it at 8.0k9/c! Make it TG.

When 0.4 part of ammonium persulfate is dissolved in 1 part of water and the solution is pressurized into an autoclave, the reaction begins. As the reaction progresses, the pressure in the autoclave decreases, but the reaction continues while introducing a mixed gas of TFE and HFP (weight ratio 88:12). In order to prevent the reaction rate from decreasing, 3. While adding 0.1 part of ammonium persulfate aqueous solution every hour, 1yIT! After continuing the reaction for a while, the reactor was cooled to room temperature and evacuated, and then the autoclave was opened. A white powdery product was separated from the reaction mixture, washed with water, and dried to obtain a 2TFE-FIF'P copolymer 2-part. The HFP content of this copolymer is 12.0% by weight, and the specific melt viscosity is 8.
*104 poise (380°C). Test Example 1 22 parts of the 'IFE-HFP copolymers of Examples and Comparative Examples were loaded into a cylinder with an inner diameter of 9 mm, and heated to a temperature of 38 cm in a sealed state.
After holding at 0'C for 2 minutes, the inner diameter is 2.1? , and the colored state was observed by extruding through orifices of 8 lengths.

The results are shown in Table 1. Test Example 2 The copolymers obtained in Example 1 and Comparative Example 5 were exposed to
It was heat treated at ℃ and the change in melt viscosity was measured.

Claims (1)

[Claims] 1. A tetrafluoroethylene-hexafluoropropylene copolymer having a hexafluoropropylene content of 8 to 20% by weight, obtained by polymerizing tetrafluoroethylene and hexafluoropropylene in an aqueous medium in the presence of a polymerization initiator. A tetrafluoroethylene-hexafluoropropylene copolymer characterized in that diisopropyl peroxydicarbonate is used as a polymerization initiator in a proportion of 0.05 to 5% by weight based on the monomers in the polymerization system. Method of manufacturing coalescence. 2. The method according to 1 above, wherein the polymerization temperature is 10 to 60°C. 3. The method described in 1 or 2 above, in which acetone is coexisting in the polymerization system.