Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-07-24
2002-07-16
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, C528S176000, C528S211000, C528S219000
Reexamination Certificate
active
06420512
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of preparing polycarbonates using an extruder to convert component monomers, ester substituted diaryl carbonates and dihydroxyaromatic compounds, into product polycarbonates. The invention further relates to the preparation of polycarbonates in which a precursor polycarbonate comprising ester-substituted phenoxy endgroups is subjected to extrusion to produce a polycarbonate having a higher molecular weight. More particularly, the instant invention relates to the formation under mild conditions of polycarbonates having extremely low levels of Fries rearrangement products and possessing a high level of endcapping.
Polycarbonates, such as bisphenol A polycarbonate, are typically prepared either by interfacial or melt polymerization methods. The reaction of a bisphenol such as bisphenol A (BPA) with phosgene in the presence of water, a solvent such as methylene chloride, an acid acceptor such as sodium hydroxide and a phase transfer catalyst such as triethylamine is typical of the interfacial methodology. The reaction of bisphenol A with a source of carbonate units such as diphenyl carbonate at high temperature in the presence of a catalyst such as sodium hydroxide is typical of currently employed melt polymerization methods. Each method is practiced on a large scale commercially and each presents significant drawbacks.
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 expensive precautions must be taken to guard against any adverse environmental impact. 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 chloride content, which can cause corrosion.
The melt method, although obviating the need for phosgene or a solvent such as methylene chloride requires high temperatures and relatively long reaction times. As a result, by-products may be formed at high temperature, such as the products arising by Fries rearrangement of carbonate units along the growing polymer chains. Fries rearrangement gives rise to undesired and uncontrolled polymer branching which may negatively impact the polymer's flow properties and performance. The melt method further requires the use of complex processing equipment capable of operation at high temperature and low pressure, and capable of efficient agitation of the highly viscous polymer melt during the relatively long reaction times required to achieve high molecular weight.
Some years ago, it was reported in U.S. Pat. No. 4,323,668 that polycarbonate could be formed under relatively mild conditions by reacting a bisphenol such as BPA with the diaryl carbonate formed by reaction phosgene with methyl salicylate. The method used relatively high levels of transesterification catalysts such as lithium stearate in order to achieve high molecular weight polycarbonate. High catalyst loadings are particularly undesirable in melt polycarbonate reactions since the catalyst remains in the product polycarbonate following the reaction. The presence of a transesterification catalyst in the polycarbonate may shorten the useful life span of articles made therefrom by promoting increased water absorption, polymer degradation at high temperatures and discoloration.
It would be desirable, therefore, to minimize the amount of catalyst required in the melt preparation of polycarbonate from bisphenols and ester substituted diaryl carbonates such as bis-methyl salicyl carbonate (BMSC). In addition, it would be desirable to provide a method for the melt preparation of polycarbonate using simple melt mixing equipment such as an extruder.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method for the preparation of polycarbonate comprising extruding at one or more temperatures in a temperature range and at one or more screw speeds in a screw speed range, at least one starting material selected from the group consisting of
(A) a mixture comprising an ester-substituted diaryl carbonate, a transesterification catalyst and at least one dihydroxy aromatic compound; and
(B) at least one precursor polycarbonate comprising ester-substituted phenoxy terminal groups.
The present invention further relates to a single step method for preparing highly endcapped, polycarbonates having very low levels of Fries rearrangement products, said polycarbonates comprising ester substituted phenoxy endgroups.
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 therein. In the following specification and 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 a diaryl carbonate with a dihydroxy aromatic compound.
As used herein the term “precursor polycarbonate” refers to a polycarbonate which when subjected to extrusion in the presence of a transesterification catalyst affords a polycarbonate having a higher molecular weight after the extrusion than before it.
“BPA” is herein defined as bisphenol A or 2,2-bis(4-hydroxyphenyl)propane.
“Catalyst system” as used herein refers to the catalyst or catalysts that catalyze the transesterification of the bisphenol with the diaryl carbonate in the melt process.
The terms “bisphenol”, “diphenol” and “dihydric phenol” as used herein are synonymous.
“Catalytically effective amount” refers to the amount of the catalyst at which catalytic performance is exhibited.
As used herein the term “Fries product” is defined as a structural unit of the product polycarbonate which upon hydrolysis of the product polycarbonate affords a carboxy-substituted dihydroxy aromatic compound bearing a carboxy group adjacent to one or both of the hydroxy groups of said carboxy-substituted dihydroxy aromatic compound. For example, in bisphenol A polycarbonate prepared by a melt reaction method in which Fries reaction occurs, the Fries product comprises structure VIII below, which affords 2-carboxy bisphenol A upon complete hydrolysis of the product polycarbonate.
The terms “Fries product” and “Fries group” are used interchangeably herein.
The terms “Fries reaction” and “Fries rearrangement” are used interchangeably herein.
The terms “double screw extruder” and “twin screw extruder” are used interchangeably herein.
As used herein the term “monofunctional phenol” means a phenol comprising a single reactive hydroxy group.
As used herein the term “aliphatic radical” refers to a radical having a valence of at least one comprising 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 “aromatic radical” refers to a radical having a valence of at least one comprising at least one aromatic group. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl,
Day James
Maxam John Lester
McCloskey Patrick Joseph
Osaheni John Aibangbee
Smigelski Paul Michael
Boykin Terressa M.
Caruso Andrew J.
Johnson Noreen C.
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