Poly(arylene ether) and process for making the same

Details Poly(arylene ether) and process for making the same Poly(arylene ether) and process for making the same

2000-07-14

2002-06-18

Truong, Duc (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Treating polymer containing material or treating a solid...

C528S50200C, C528S50200C, C528S503000

Reexamination Certificate

active

06407202

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method for making poly(arylene ether), and especially relates to a method for making substantially pure polyphenylene ether.
BACKGROUND OF THE INVENTION
Poly(arylene ether) constitutes a large class of polymers which are employed pure or as blends in a wide variety of applications in the automotive, liquid handling and electronics industries. Poly(arylene ethers) are formed by reacting the monomer, either phenol or a substituted phenol, dissolved in an organic solvent, with oxygen in the presence of a catalyst. Copper-amine complexes are the most widely used catalysts for these reactions, although there are several other catalysts known in the art. Catalysts generally contain at least one heavy transition metal compound such as copper, manganese or cobalt compound, usually in combination with various other materials. Catalyst compounds can either be soluble in the reaction solvent or in solid form, i.e. supported on a solid substrate like silica, alumina or other insoluble support materials. Such catalysts are disclosed, for example, in U.S. Pat. Nos. 3,306,874, 3,306,875, 3,914,266 and 4,028,341 which are incorporated by reference herein.
The end point of the polymerization reaction is controlled by a number of methods known in the art such as in-line viscometry, molecular weight measurement, reaction run time, endgroup content, or oxygen concentration or oxygen consumption. When the end point is reached the polymerization reaction is stopped by halting addition of the oxygen reactant or removing the catalyst.
Several methods of catalyst removal are known in the art, most involving the use of an aqueous solution of a complexing agent. When the aqueous solution is added to the organic solution of the polymerization reaction two phases result. The complexing agent reacts with the catalyst and makes the resulting complex soluble in the aqueous phase (catalyst phase). The catalyst and poly(arylene ether) phases must then be separated and the poly(arylene ether) phase is carried on for isolation.
Good phase separation is essential to producing good quality poly(arylene ether). Without good phase separation the organic layer retains a significant amount of copper. Residual copper has an adverse affect on the properties of the polymer, with the sensitivity to oxidation and the inherent color particularly affected. Poly(arylene ether) oxidation causes black specs in most types of poly(arylene ether) processing such as extrusion and injection molding. German Patent Application No. 2,640,147 discloses improved phase separation through the use of an alcohol containing diluent. This method however has several disadvantages: the complexing reaction and the diluent addition require separate mixing units, a large amount of alcohol is required and the resulting copper containing solution is very dilute which complicates waste treatment. Other approaches to improved phase separation rely on anionic, cationic or non-ionic surfactants and de-emulgators. A de-emulgator is a substance that de-stabilizes an emulsion, allowing the resulting phases to be separated.
An alternate approach to catalyst removal, as disclosed in U.S. Pat. No. 4,654,418, involves a series of mixer-settler stages. The reaction mixture is combined with an aqueous complexing agent solution in a mixing stage, sent to a settler where the phases are separated and the process is repeated with additional aqueous complexing agent solution. The aqueous complexing agent solution is recycled from the second step to the first step, which improves the overall organic to aqueous phase ratio of 1.0:0.2-1.0:0.8, but increases the complexity of the apparatus. The resulting polyphenylene ether solution has a copper content less than 1 mg/kg and can be isolated using methods known in the art such as spray drying, steam precipitation, crumb formation with hot water, and multi stage devolatization.
Multistage devolatization is the most economically advantageous method of isolation because the isolation and extrusion are handled all in one step. However, there are numerable difficulties. The typically high solvent load to the extruder causes vent plugging and decreases operational stability. A low viscosity polymer, like polystyrene, is required to form a melt seal at the throat of the extruder to prevent toluene from being vented into the atmosphere. Thus the resulting poly(arylene ether) resins contain the low viscosity polymer which reduces the glass transition temperature and the viscosity of the final product. The poly(arylene ether) resin isolated by multistage devolatization frequently has high color and a high incidence of black specs. Good quality poly(arylene ether) resin has low color (a low yellowness index (YI)) and a low incidence of black specs. The color, as well as processing stability, can be improved by the addition of a thermal/oxidative stabilizer, such as hindered phenol or phosphites. Use of stabilizers increases the number of steps in the manufacturing process and the cost. Although multistage devolatization is economically advantageous it has not reached its full potential due to processing and color issues.
Accordingly, there remains a continuing need in the art for a method to produce substantially pure poly(arylene ether) with good processing stability, low color and a low incidence of black specs.
SUMMARY OF THE INVENTION
The above discussed drawbacks and deficiencies of the prior art are overcome or alleviated by the method of the present invention. The present invention relates to an improved process for producing substantially pure poly(arylene ether) comprising: a.) a process for removing the catalyst from a poly(arylene ether) polymerization reaction comprising adding a polar liquid and centrifuging, and b.) isolating the poly(arylene ether) polymer from the reaction mixture without the addition of a low viscosity polymer other than poly(arylene ether). Isolation of the poly(arylene ether) polymer comprises an optional concentration step and a method of using a devolatizing extruder.
BRIEF DESCRIPTION OF THE DRAWINGS
Not Applicable
DETAILED DESCRIPTION OF THE INVENTION
The above discussed drawbacks and deficiencies of the prior art are overcome or alleviated by the method of the present invention. The present invention relates to an improved process for producing substantially pure poly(arylene ether) comprising: a.) a process for removing the catalyst from a poly(arylene ether) polymerization reaction comprising adding a polar liquid and centrifuging, and b.) isolating the poly(arylene ether) polymer from the reaction mixture without the addition of a low viscosity polymer other than the poly(arylene ether) that is being isolated. Isolation of the poly(arylene ether) polymer comprises an optional concentration step and a method of using a devolatizing extruder.
The process of removing catalyst from a poly(arylene ether) polymerization reaction comprises: a) adding at least one polar solution to the reaction mixture to form a first at least two phase mixture, wherein one phase of said first at least two phase mixture is a polymer phase; b) liquid/liquid centrifuging said first at least two phase mixture to separate the phases; c) removing said polymer phase from said first at least two phase mixture; d) adding water to said polymer phase to form a second at least two phase mixture, where one phase of said second at least two phase mixture is a second polymer phase; e) separating said second polymer phase from said second at least two phase mixture.
The invention further relates to a process for isolating the poly(arylene ether) from the polymer phase. The isolation process can include a process for concentrating a mixture, comprising: heating the mixture at a first pressure; introducing the mixture to a vessel, wherein said vessel is at ambient temperature or cooled; and flashing the mixture to a second pressure lower than said first pressure and greater than atmospheric pressure. Either following the concentration step or immediately following catalyst removal

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