JPH0372654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polyphenylene ether.

The method of obtaining polyphenylene ether (polyphenylene oxide; hereinafter abbreviated as PPO) by oxidative coupling polymerization of 2,6-di-substituted phenol in the presence of a metal complex catalyst at room temperature in the atmosphere is well known and has been implemented in industry. has been done. PPO has strength, dielectric properties,
It is used as an engineering plastic with excellent heat resistance.

By the way, as shown in formula (), this reaction is a dehydrogenation oxidation reaction from phenol, and does not necessarily require oxygen oxidation using a complex catalyst.
PPO should be obtained by electrochemical oxidation.

In fact, it is known that when a water or alcohol solution containing a phenol derivative is electrolyzed, a strong thin film without pinholes is deposited on the anode. (J, E,
Dubois, Electrochimica Acta. 22 451−457
(1977)) However, at the same time as the thin film is formed, the electrode becomes nonconductive and the reaction stops.

On the other hand, PPO is converted from phenol derivatives by electrolysis.
As an attempt to obtain PPO, there is an old patent by GE that uses a mediator (redox medium), but the PPO yield is low, and because it uses a diaphragm electrolytic cell (WFH).
Borman, US Patent 3335075 (1967)) It has drawbacks such as high overvoltage, and there have been no subsequent reports.

The present invention provides 2,6-
This invention relates to a production method using electrolytic polymerization through electrolytic oxidation of dimethylphenol.

The present inventors investigated various solvents, supporting salts, electrode materials, applied voltages, and current densities for the electrolytic oxidation of 2,6-dimethylphenol. As a result, we found that using a solvent that dissolves PPO and minimizing the mixing of the reaction solution. By suppressing this, we succeeded in obtaining PPO in high yield.

The features of this production method are: (1) The yield of PPO is high and bisphenoquine is not produced as a by-product.

(2) Electrolysis can be carried out by placing the electrodes facing a simple reaction tank without using a diaphragm. The progress of the reaction can be tracked by the amount of current applied and the amount of by-product hydrogen, and the degree of polymerization can be adjusted.

The details of the present invention will be described below.

The essential monomer for the polyphenylene ether according to the present invention is 2,6-dimethylphenol represented by the general formula ().

Solvents that can be used as electrolytic solvents are those that dissolve the polymer and have a high dielectric constant. However, considering the solvent decomposition potential range, halogenated hydrocarbons such as dichloromethane and chloroform are suitable, and a mixed solvent of dichloromethane and methanol is particularly suitable for electropolymerization.

The supporting electrolyte is an electrolyte that is soluble in the above solvent, specifically lithium salts such as LiClO ₄ and LiBF ₄ ,
There are tetraalkylammonium salts such as (C ₂ H ₅ ) ₄ NBr and (C ₂ H ₅ ) ₄ NBF ₄ , and a typical supporting electrolyte is (C ₂ H ₅ ) ₄ NBr.

As the electrolyzer, a simple reaction tank with electrodes facing each other is used. A reference electrode is set when reading the voltage change accompanying the reaction, but this is not always necessary.

Metals such as gold, gold, copper, and graphite are used as electrode materials. Platinum is particularly suitable.

Electrolytic potential is phenol oxidation potential 0.8V or more solvent,
It is sufficient if the decomposition potential of the supporting salt is 2V or less.

The amount of electrolytic electricity is 1 to 10 of the theoretical amount of electrolytic electricity 2F/mol.
It requires twice as much current, usually 5 to 8 times as much.

The substrate phenol concentration is preferably 10 ^-3 mol/l or less, typically 10 ^-1 mol/l, and the supporting salt concentration is preferably equal to or several times the substrate concentration.

Further, it is desirable to replace the electrolytic reaction solution with an electrolytically inert gas such as nitrogen or a rare gas.

When electrolysis was carried out under the above typical electrolytic conditions, hydrogen generation was observed at the cathode due to reduction of protons released from phenol, and the amount of hydrogen generated was equal to the amount of phenol. Furthermore, when the reaction system is stirred, the amount of by-product biphenoquinone produced increases.
It is estimated that C-O coupling, which corresponds to PPO production, occurs within a few hundred angstroms near the electrode interface, and that active species leached out of the vicinity of the electrode due to stirring, resulting in an increase in C-O coupling-forming biphenoquinone. Conceivable. One key to increasing the PPO yield is to allow the reaction mixture to stand still for electrolysis.

Next, examples of the present invention will be shown.

Example 1 2.44 g of 2,6-dimethylphenol and 4.8 g of tetraethylammonium bromide were added to methanol.
Dissolve in 200 ml of a mixed solvent of 20% dichloromethane and 80%, and replace with nitrogen for about 10 minutes. Place this in an electrolytic bath and fix the distance between the 4cm x 10cm anode and cathode platinum plates to about 1cm.
Current density 20mA/cm ² between both electrodes, amount of electrolytic electricity
Constant current electrolysis at 12F/mol. After electrolysis for 25 minutes, the reaction mixture was washed several times with water and then dropped into methanol acidified with hydrochloric acid, and precipitation of PPO was observed. This was filtered and dried to obtain 2.06 g of white powder PPO. The yield was 80%. Results of molecular weight measurement using a vapor pressure osmometer in benzene solvent: molecular weight (number average molecular weight,
The same applies below) was 18,000.

In the infrared absorption spectrum of the produced polymer, the absorption due to 3400 ^-1 νOH, which is characteristic of the raw material phenol, completely disappeared. Further, the absorption of νc-oc (1180 cm ^-1 ), which can be confirmed to be the formation of polyether, became remarkable.

Example 2 2.44 g of 2,6-dimethylphenol and 8.4 g of tetraethylammonium bromide were dissolved in 200 ml of dichloromethane and subjected to constant current electrolysis at a current density of 10 mA/cm ² and an amount of electrolytic electricity of 12 F/mol.

PPO was obtained in the same manner as in Example 1. yield
75% molecular weight was 19,000.

Example 3 After dissolving 2,6-dimethylphenol and tetraethylammonium bromide in 160 ml of dichloromethane, electrolysis was carried out in the same manner as in Examples 1 and 2. The PPO yield was 82% and the molecular weight was 10,600.

Example 4 Dimethylphenol was electrolyzed in the same manner as in Example 1 using a graphite plate (40 x 100 mm) as an electrode. PPO with a molecular weight of 8000 was obtained with a PPO yield of 46%.

Example 5 160 ml of dichloromethane, 40 ml of methanol, 9.2 g of tetraethylammonium perchlorate, 2,6-
Dissolve 2.44 g of dimethylphenol.

After electrolysis as in Example 1, yield 81% molecular weight
Got 12000 PPO.

Claims (1)

[Claims] 1. Poly(2,6-dimethylphenylene ether) represented by general formula (1) When producing , direct current electrolysis is performed in a solution containing a supporting electrolyte and 2,6-dimethylphenol and dissolving the poly(2,6-dimethylphenylene ether) produced while the solution is left standing. A method for producing polyphenylene ether, characterized by: