Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-03-02
2002-07-02
Richter, Johann (Department: 1621)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S198000, C568S716000, C568S717000, C568S722000, C568S723000, C568S724000, C568S749000, C568S750000
Reexamination Certificate
active
06414106
ABSTRACT:
BACKGROUND OF THE INVENTION
Dihydric phenols are useful in the commercial manufacture of various polymers including polyarylates, polyamides, epoxies, polyetherimides, polysulfones and polycarbonates. The acid catalyzed reaction of phenol with aldehydes or ketones is a well known method to prepare the 4,4′-dihydric phenol. In particular, when phenol is reacted with acetone, the dihydric phenol 2,2-bis(4-hydroxy-phenyl)propane, also known as bisphenol-A or BPA is formed. BPA may be used to prepare polycarbonates, polyarylates, and copolyestercarbonates, as well as epoxies.
The manufacture of dihydric phenols, such as BPA, requires the use of an acid catalyst. Residual acid from the crude, isolated dihydric phenol will cause subsequent cracking of the dihydric phenol during isolation and purification. In the case of BPA, for instance, the cracking process may lead to the formation of isopropenyl phenol, an unwanted side product. Further, residual acid remaining in the final dihydric phenol product can cause catalyst quenching if the dihydric phenol is used in the manufacture of polycarbonate by the melt process.
Typically, a low level of base, such as sodium hydroxide, is added to the crude dihydric phenol prior to purification to reduce the level of cracking during purification. The residual base will remain in the final dihydric phenol product, and in the final polymer product, if the dihydric phenol is used in a melt process. In particular, alkali metals in polycarbonate prepared by the melt process result in the undesirable formation of side branching reactions.
It would be desirable to reduce the level of cracking during the purification of a dihydric phenol. Further, it would be desirable to reduce cracking without the introduction of materials that result in the formation of side branching products in a polymer prepared from the dihydric phenols.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a method of neutralizing residual acid species in crude dihydric phenol comprising the step of introducing a thermally stable organic base selected from the group consisting of tetraalkyl phosphonium hydroxides, tetraorganophosphonium carboxylic acid salts, or a mixture thereof into the crude dihydric phenol.
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.
Before the present compositions of matter and methods are disclosed and described, it is to be understood that this invention is not limited to specific synthetic methods or to particular formulations, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
In the following specification, reference will be made to a number of terms that 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 “melt polycarbonate” refers to a polycarbonate made by the transesterification of a carbonate diester with a dihydroxy compound.
“BPA” is herein defined as bisphenol A or 2,2-bis(4-hydroxyphenyl)propane.
The terms “diphenol” and “dihydric phenol” as used herein are synonymous.
A known method for the preparation of bisphenols requires the condensation of ketones and phenol in the presence of a sulfonic acid based polystyrene ion exchange resin (IER), as described, for example in U.S. Pat. No. 5,783,733. The crude bisphenol product from these processes typically contain low levels of sulfonic acid polystyrene oligomers. The presence of these oligomers during subsequent heat treatment, for example desorption of phenol and/or melt crystallization, can result in cracking of bisphenol. In the case of BPA, cracking of the bisphenol produces isopropenyl phenol, an unwanted side product.
Typical IER used as catalysts in the production of dihydric phenols include cationic exchange resins, in particular strong-acid types of resins. Examples include, but are not limited to sulfonated copolymers of styrene and a cross-linking agent. e.g. a difunctional monomer such as divinylbenzene.
In order to reduce cracking, it is known to neutralize the sulfonic acid oligomers in the crude dihydric phenol prior to purification. Typically, a base, such as sodium hydroxide, is added to neutralize the sulfonic acids prior to purification. During isolation and purification of the dihydric phenol, however, such as in the case of sodium hydroxide, the sodium sulfonate salts and more basic forms of sodium, such as sodium hydroxide or salt of the dihydric phenol, can remain in the final dihydric phenol product.
If the dihydric phenol is used in a melt polymerization process, it is desirable to minimize the added level of excess base in the preparation and processing of the dihydric phenol, such as sodium hydroxide, to ensure maximum hydrolytic and thermal stability, as well as to minimize color generation in the final polymer. While alkali earth metal bases are the catalysts of choice for the melt polymerization process, the use of alkali earth metal bases, such as sodium hydroxide, also results in the generation of side products that cause branching in the melt resin. These side products include “Fries” products.
As used herein the term “Fries” or “fries” refers to a repeating unit in polycarbonate having the following formula (I):
where the X variable represents or
Variable R
c
and R
d
each independently represent a hydrogen atom or a monovalent hydrocarbon group and may form a ring structure. Variable R
e
is a divalent hydrocarbon group.
It is very desirable to have a low Fries content in the polycarbonate product, as Fries products reduce the performance characteristics of the polycarbonate, such as the ductility. Higher Fries contents results in lower ductility. Preparing polycarbonate by the melt process results in the formation of Fries products.
Minimizing or eliminating the alkali earth metal, such as sodium, in the process of preparing the dihydric phenols will minimize the branching side product formation in the melt process to prepare polymer from the dihydric phenols. In particular, reduction of residual alkali earth metal base in the bisphenol used to prepare polycarbonate is desirable. Excess residual acid in the dihydric phenol, however, that has not been neutralized, will negatively impact the polymerization rate as it will neutralize the alkali earth metal used as the catalyst in the melt polymerization.
In the present invention, it was unexpectedly found that the addition of a thermally stable organic base, preferably stable at temperatures above 200° C., selected from the group consisting of tetraalkyl phosphonium hydroxides, tetraorganophosphonium carboxylic acid salts, or a mixture thereof, to the crude dihydric phenol, effectively neutralizes the residual acid species, such as aryl sulfonic acid species, while producing a negligible amount of the branching side products, such as Fries product, in the final polymer prepared from the dihydric phenol. Preferably, the branching side products are present in the final polymer at less than 100 ppm, based on the polymer. The thermally stable organic bases, are strong enough bases to effectively neutralize the residual aryl sulfonic acid species introduced by the IER throughout the course of the melt polymerization.
The thermally stable organic base is preferably introduced into crude dihydric phenol in an amount of from about 1 to about 25 molar equivalents of thermally stable organic base per mole of sulfonic acid compound to provide effective neutralization; more preferably from about 1 to about 15 molar equivalents of thermally stable organic base per m
Burnell Timothy Brydon
McCloskey Patrick Joseph
Smigelski, Jr. Paul Michael
Price Elvis O.
Richter Johann
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