Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-06-12
2004-04-20
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C502S200000, C502S208000, C528S198000
Reexamination Certificate
active
06723823
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for the preparation of polycarbonate. More particularly the method relates to a method of preparing polycarbonate by the melt reaction of at least one dihydroxy aromatic compound with at least one diaryl carbonate, said melt reaction being mediated by a transesterification catalyst, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and a co-catalyst.
Conventionally, polycarbonate is prepared by the reaction of a dihydroxy aromatic compound such as bisphenol A with phosgene in the presence of an aqueous phase comprising an acid acceptor such as sodium hydroxide and an organic solvent such as dichloromethane. Typically, a phase transfer catalyst, such as a quaternary ammonium compound or a low molecular weight tertiary amine, such as triethylamine is added to the aqueous phase to enhance the polymerization rate. This synthetic method is commonly known as the “interfacial” method for preparing polycarbonate.
The interfacial method for making polycarbonate has several inherent disadvantages. First it is a disadvantage to operate a process which requires phosgene as a reactant due to obvious safety concerns. Second it is a disadvantage to operate a process which requires using large amounts of an organic solvent because elaborate precautions must be taken to prevent adventitious release of the volatile solvent into the environment. Third, the interfacial method requires a relatively large amount of equipment and capital investment. Fourth, the polycarbonate produced by the interfacial process is prone to having inconsistent color, higher levels of particulates, and higher chlorine content, which can cause corrosion.
More recently polycarbonate has been prepared on a commercial scale in a solventless process involving the transesterification reaction between a dihydroxy aromatic compound (e.g. bisphenol A) and a diaryl carbonate (e.g., diphenyl carbonate) in the presence of a transesterification catalyst. This reaction is performed in a molten state in the absence of solvent, and is driven to completion by mixing the reactants under reduced pressure and high temperature with simultaneous distillation of the phenol by-product produced by the reaction. This method of preparing polycarbonate is referred to as the “melt” process. In some respects the melt process is superior to the interfacial method because it does not employ phosgene, it does not require a solvent, and it uses less equipment. Moreover, the polycarbonate produced by the melt process does not contain chlorine contamination from the reactants, has lower particulate levels, and has a more consistent color. Therefore it is highly desirable to use the melt process when making polycarbonate in commercial manufacturing processes.
A wide variety of transesterification catalysts have been evaluated for use in the preparation of polycarbonate using the melt process. Alkali metal hydroxides, in particular sodium hydroxide, have proven to be particularly effective as transesterification catalysts. However, while alkali metal hydroxides are useful polymerization catalysts, they are also known to promote Fries reaction along the growing polycarbonate chains which results in the production of branched polycarbonate products. The presence of branching sites within a polycarbonate chain can causes changes in the melt flow behavior of the polycarbonate, which can lead to difficulties in processing.
It would be desirable, therefore, to develop a catalyst system which effects melt polymerization while minimizing undesirable reaction products, such as branched side reaction products.
BRIEF SUMMARY OF THE INVENTION
In one aspect, the present invention provides a method of preparing polycarbonate, said method comprising reacting under melt polymerization conditions in the presence of a transesterification catalyst at least one dihydroxy aromatic compound and at least one diaryl carbonate, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and at least one co-catalyst, said co-catalyst comprising a quaternary ammonium salt, a quaternary phosphonium salt or a mixture thereof.
In another aspect, the present invention relates to polycarbonates prepared by the method of the present invention, said polycarbonates having lower levels of Fries product than polycarbonates prepared by conventional melt polymerization methods.
DETAILED DESCRIPTION OF THE INVENTION
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included herein. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
As used herein the term “polycarbonate” refers to polycarbonates incorporating structural units derived from one or more dihydroxy aromatic compounds and includes copolycarbonates and polyester carbonates.
As used herein, the term “melt polycarbonate” refers to a polycarbonate made by the transesterification of at least one diaryl carbonate with at least one dihydroxy aromatic compound.
“BPA” is herein defined as bisphenol A and is also known as 2,2-bis(4-hydroxyphenyl)propane, 4,4′-isopropylidenediphenol and p,p-BPA.
As used herein, the term “bisphenol A polycarbonate” refers to a polycarbonate in which essentially all of the repeat units comprise a bisphenol A residue.
As used herein, the term “polycarbonate” includes both high molecular weight polycarbonate and oligomeric polycarbonate. High molecular weight polycarbonate is defined herein as having number average molecular weight, M
n
, greater than 8000 daltons, and an oligomeric polycarbonate are defined as having number average molecular weight, M
n
, less than 8000 daltons.
As used herein the term “percent endcap” refers to the percentage of polycarbonate chain ends which are not hydroxyl groups. In the case of bisphenol A polycarbonate prepared from diphenyl carbonate and bisphenol A, a “percent endcap” value of about 75% means that about seventy-five percent of all of the polycarbonate chain ends comprise phenoxy groups while about 25% of said chain ends comprise hydroxyl groups. The terms “percent endcap” and “percent endcapping” are used interchangeably.
As used herein the term “aromatic radical” refers to a radical having a valence of at least one and comprising at least one aromatic ring. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group, a phenethyl group or a naphthylmethyl group. The term also includes groups comprising both aromatic and cycloaliphatic groups for example 4-cyclopropylphenyl and 1,2,3,4-tetrahydronaphthalen-1-yl.
As used herein the term “aliphatic radical” refers to a radical having a valence of at least one and consisting of a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of aliphatic radicals include methyl, methylene, ethyl, ethylene, hexyl, hexamethylene and the like.
As used herein the term “cycloaliphatic radical” refers to a radical having a valance of at least one and comprising an array of atoms which is cyclic but which is not aromatic, and which does not further comprise an aromatic ring. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloaliphatic radicals include cyclopropyl, cyclopentyl cyclohexyl, 2-
Grimmond Brian James
McCloskey Patrick Joseph
Reilly Warren William
Boykin Terressa
Caruso Andrew J.
General Electric Company
Patnode Patrick K.
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