Melt polycarbonate catalyst systems

Details Melt polycarbonate catalyst systems Melt polycarbonate catalyst systems

2001-01-12

2001-10-16

Boykin, Terressa M. (Department: 1711)

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

Synthetic resins

From phenol, phenol ether, or inorganic phenolate

C528S198000

Reexamination Certificate

active

06303737

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method for preparing polycarbonates by a transesterification reaction between, for example, diaryl carbonate and aromatic bis hydroxy compounds. In particular, this invention relates to the melt polymerization reaction for the preparation of polycarbonates and novel polycarbonate catalysts comprised of certain phenanthroline compounds.
A large number of catalyst systems have been examined for application to the melt polymerization of polycarbonates. Most of these methods require either a variety of co-catalysts or the subsequent addition of a catalyst quencher to ensure polymer stability. The need for high purity, high quality thermoplastic resins requires the reduction of residual contaminants in the final resin. This need for very low residual impurities is particularly acute in optical quality (OQ) grade polycarbonate resins. One approach towards elimination of residual solvent contamination, particularly methylene chloride, is through the implementation of a solventless (i.e., melt) process.
The melt process generally involves a base catalyzed condensation polymerization of, for example, diphenyl carbonate, and a dihydroxy compound such as Bisphenol A. The reaction is conducted at high enough temperatures for the starting monomers and product to remain molten, while the reactor pressure is staged in order to effectively remove phenol, the by-product of the polycondensation reaction.
Most current melt technology programs employ a two component catalyst system. The first component is a tetralkylammonium hydroxide (TMAH ) co-catalyst which is used to initiate oligomer formation in the melt. The second catalyst is an alkali metal hydroxide (i.e., the “&agr;-catalyst”) which is the second part of the overall catalyst system. Due to its intrinsic thermal stability, the alkali metal salt must be quenched at the end of the polymerization. This quenching process requires the addition of yet another component to the polymer formation. All materials from the quenching process remain in the final resin, further compromising the final properties.
Although the alkali metal hydroxides in general are excellent melt polymerization catalysts they tend to generate substantial amounts of an additional undesired by-product which is a branched polycarbonate species typically referred to as Fries product which has the repeat unit as set forth below. The formation of Fries product during melt polycarbonate polymerization leads to changes in ductility and in general rheological properties of the polymer. Polycarbonates produced by the melt process typically have higher Fries content than polycarbonates produced by the interfacial method. As used herein the term “Fries” or “fries” refers to a repeating unit in polycarbonate having the following formula:
wherein the X variable represents
wherein variables R
c
and R
d
each independently represent a hydrogen atom or
a monovalent hydrocarbon group and may form a ring structure. Thus, a need exists for the development of alternative melt polycarbonate polymerization catalysts which produce less Fries product than conventional catalyst systems.
SUMMARY OF THE INVENTION
This invention provides a method for preparing polycarbonates, which utilizes polycondensation catalysts which are salts of certain phenanthroline compounds. We have found that this new class of catalysts provides excellent polymerization rates for the preparation of Bisphenol A polycarbonate from the melt polymerization of diphenyl carbonate and Bisphenol A. Moreover, the catalysts of the invention were found to be very selective in substantially reducing the level of branching side reaction, i.e., formation of Fries product, normally associated with the melt polycarbonate procedure. Examples of preferred catalysts include bathophenanthroline sulfonated sodium salt and bathocupproine disulfonate sodium salt.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method for preparing polycarbonates, which comprises the step of contacting a diaryloxy compound with a dihydric phenol compound in the presence of a compound of Formula (I):
wherein each X is independently selected from a sulfate, carboxylate or a phosphonate group;
Y is an alkali metal cation;
each R
10
is independently selected from the group consisting of C
1
-C
6
alkyl; C
1
-C
6
alkoxy; halo; aryl; and aryl substituted by one or two of C
1
-C
6
alkyl, C
1
-C
6
alkoxy, halo, aryl, or C
1
-C
6
alkylaryl;
v is 0, 1,or 2;
n is 1, 2, 3 or 4; and
optionally in the presence of a co-catalyst selected from tetraalkyl ammonium and tetraalkyl phosphonium salts; under polycarbonate melt polymerization conditions.
It should be understood that in the above Formula (I), the sulfate, carboxylate, and/or phosphonate groups are covalently bound to available sites on the aromatic carbon atoms of the phenanthroline ring structure.
As used herein, the term “aryl” preferably refers to a phenyl or naphthyl group.
Especially preferred compounds of Formula (I) include the following:
Bathophenanthroline sulfonated sodium salt;
Bathophenanthroline sulfonated potassium salt;
Bathophenanthroline sulfonated lithium salt;
Bathocupproine disulfonate sodium salt;
Bathocupproine disulfonate potassium salt;
Bathocupproine disulfonate lithium salt;
Bathophenanthroline sulfonated cesium salt; and;
Bathocupproine disulfonate cesium salt; and mixed potassium, sodium, lithium, and cesium salts thereof, i.e., wherein each metal salt is independently selected from potassium, sodium, lithium, and cesium salts.
In the method of the present invention, certain diaryloxy compounds which are useful in preparing the polycarbonates of the invention may be represented by the general formula
wherein:
R is independently selected from halogen, monovalent hydrocarbon, and monovalent hydrocarbonoxy radicals;
R
1
is independently selected from halogen, monovalent hydrocarbon, and monovalent hydrocarbonoxy radicals; and
wherein n and n
1
are independently selected from integers having a value of from 0 to 4 inclusive.
The monovalent hydrocarbon radicals represented by R and R
1
include the alkyl, cycloalkyl, aryl, aralkyl and alkaryl radicals. The preferred alkyl radicals are those containing from 1 to about 12 carbon atoms. The preferred cycloalkyl radicals are those containing from 4 to about 8 ring carbon atoms. The preferred aryl radicals are those containing from 6 to 12 ring carbon atoms, i.e., phenyl, naphthyl, and biphenyl. The preferred alkaryl and aralkyl radicals are those containing from 7 to about 14 carbon atoms.
The preferred halogen radicals represented by R and R
1
are chlorine and bromine.
The divalent hydrocarbon radicals represented by include the alkylene, alkylidene, cycloalkylene and cycloalkylidene radicals. The preferred alkylene radicals are those containing from 2 to about 30 carbon atoms. The preferred alkylidene radicals are those containing from 1 to about 30 carbon atoms. The preferred cycloalkylene and cycloalkylidene radicals are those containing from 6 to about 16 ring carbon atoms.
The monovalent hydrocarbonoxy radicals represented by R and R
1
may be represented by the formula—OR
1
′ wherein R
1
′ is a monovalent hydrocarbon radical of the type described herein. Preferred monovalent hydrocarbonoxy radicals are the alkoxy and aryloxy radicals.
Especially preferred diesters are the diesters of carbonic acid. As the diester of carbonic acid, various compounds may be used, including, but not limited to diaryl carbonate compounds, dialkyl carbonate compounds and alkylaryl carbonate compounds. Preferred diesters of carbonic acid include, but are not limited to, diphenyl carbonate; bis(4-t-butylphenyl)carbonate; bis(2,4-dichlorophenyl)carbonate; bis(2,4,6-trichlorphenyl)carbonate; bis(2-cyanophenyl)carbonate; bis(o-nitrophenyl)carbonate; bis(o-methoxycarbonylphenyl) carbonate;ditolyl carbonate; m-cresol carbonate; dinaphthyl carbonate; bis(diphenyl)carbonate; diethylcarbonate; dimethyl carbonate; dibutyl carbonate; dicyclohexyl carbonate; and mixt

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