Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-01-29
2002-06-11
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
06403754
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polycarbonate preparation, and more particularly to a method for producing polycarbonates which are consistent in their property profiles using the melt polymerization method.
Polycarbonates have long been prepared by the interfacial method, wherein a dihydroxy compound such as 2,2-bis(4-hydroxyphenyl)propane (“bisphenol A”) undergoes reaction with phosgene in a mixed aqueous-organic system under alkaline conditions. This method is problematic for several reasons, including the use of environmentally polluting solvents such as methylene chloride and the use of phosgene, a very toxic gas.
An alternative method of polycarbonate preparation, the transesterification or melt method, is superior from an environmental standpoint. It involves the reaction of the dihydroxy compound with a diaryl carbonate such as diphenyl carbonate. This reaction is conducted under melt conditions at temperatures in the range of about 250-350° C., normally in two stages: a first stage of oligomer formation and a second stage of molecular weight building. Catalysts are normally employed, in particular an alkali metal hydroxide and a tetraalkylammonium or tetraalkylphosphonium base, usually a hydroxide. The proportion of alkali metal hydroxide is typically about 0.01-1,000 and often about 1 molar ppm, and the proportion of quaternary compound in the range of about 1-10,000 molar ppm, based on dihydroxy compound.
The products of melt polycarbonate formation can, however, vary widely in their property profiles. For example, molecular weights and physical properties such as color and impact strength can vary over a wide range. It is frequently found that the proportion of “Fries product”, i.e., the branched product obtained by rearrangement of an aryl carbonate group to an o-hydroxyketoaryl group followed by continued polymerization, is higher than desired, and this and other variations can cause degradation of ductility, melt stability and hydrolytic stability.
The two most common reagents for melt polycarbonate formation, bisphenol A and diphenyl carbonate, are both typically synthesized under acidic conditions. Bisphenol A may be economically prepared by the reaction of phenol with acetone in the presence of a sulfonated polystyrene; i.e., a sulfonated ion exchange resin in the acid form. Also usually present as a promoter is a mercapto carboxylic acid such as 3-mercaptopropionic acid.
Diphenyl carbonate may be prepared from phenol by various methods. These include oxidative carbonylation with oxygen and carbon monoxide, condensation with phosgene and transesterification with a dialkyl carbonate. A by-product of any such reaction which involves distillation in the presence of an acidic compound is phenyl salicylate or its hydrolysis product, salicylic acid. The diphenyl carbonate-forming reaction is also carried out under conditions which often include the presence of metallic compounds, e.g., iron compounds formed by corrosion of iron-containing reaction vessels by strongly acidic compounds also present.
According to U.S. Pat. No. 5,026,817, melt polycarbonate formation is advantageously conducted under conditions which include low proportions of hydrolyzable chloride ion, sodium ion and “iron ion”. European patent application 677,545 suggests the use of diaryl carbonates substantially free from phenyl salicylate, o-phenoxybenzoic acid and its esters, “tin ion” and methyl phenyl carbonate. Beyond these two documents, however, little is known about the effect on melt polymerization of by-products in the polycarbonate-forming reagents.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the presence of even very small proportions of acidic impurities in the reagents for polycarbonate formation by the melt method has a significant effect on many properties of the product, and on the reaction itself. In part, the invention contemplates various procedures for eliminating the acidic impurities or minimizing their effect.
Accordingly, the invention is a method for optimizing polycarbonate formation by a transesterification reaction between the reagents diaryl carbonate and dihydroxyaromatic compound in the presence of a catalyst system comprising at least one alkali metal hydroxide, which comprises:
(A) analyzing at least one of said reagents for acidic impurities including at least one of sulfonic acids, mercaptocarboxylic acids, salicylic acid and ferric chloride, to determine whether the following threshold values have been exceeded:
sulfonic acids—0.1 molar ppm based on dihydroxyaromatic compound,
mercaptocarboxylic acids—5 molar ppm based on dihydroxyaromatic compound,
salicylic acid—0.15 molar ppm based on dihydroxyaromatic compound,
ferric chloride—200 ppb by weight based on dihydroxyaromatic compound;
and if so, either:
(B) discarding or recycling any reagent exceeding at least one of said threshold values, or
(C) establishing the level of alkali metal hydroxide in the polycarbonate-forming reaction mixture at a value which is at most 1 molar ppm, based on dihydroxyaromatic compound, in excess of that of at least one of sulfonic acid, mercaptocarboxylic acid, salicylic acid and ferric chloride.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
The polycarbonates whose formation may be optimized by the method of this invention include those comprising structural groups having one or more structures of the formula
wherein A is a divalent aromatic radical which may be an aromatic hydrocarbon or a substituted aromatic hydrocarbon radical, with illustrative substituents being alkyl, cycloalkyl, alkenyl (e.g., crosslinkable-graftable moieties such as allyl), halo (especially fluoro, chloro and/or bromo), nitro and alkoxy.
The preferred A values have the formula
—
A
1
—Y—A
2
—, (II)
wherein each of A
1
and A
2
is a monocyclic divalent aromatic radical and Y is a single bond or a bridging radical in which one or two atoms separate A
1
from A
2
. The free valence bonds in formula I are usually in the meta or para positions of A
1
and A
2
in relation to Y.
In formula II, the A
1
and A
2
values may be unsubstituted phenylene or substituted derivatives thereof wherein the substituents are as defined for A. Unsubstituted phenylene radicals are preferred, but it is also contemplated to employ, for example, polymers in which each of A
1
and A
2
has two methyl substituents in ortho positions to the free valence bond. Both A
1
and A
2
are preferably p-phenylene, although both may be o- or m-phenylene or one o- or m-phenylene and the other p-phenylene.
The bridging radical, Y, is one in which one or two atoms, preferably one, separate A
1
from A
2
. It is most often a hydrocarbon radical and particularly a saturated C
1-12
aliphatic or alicyclic radical. Illustrative radicals are methylene, cyclohexylmethylene, [2.2.1 ]bicycloheptylmethylene, ethylene, ethylidene, 2,2-propylidene, 1,1 -(2,2-dimethylpropylidene), phenylethylidene, cyclohexylidene, 3,3,5-trimethylcyclohexylidene, cyclopentadecylidene, cyclododecylidene, 9,9-fluorenylidene and 2,2-adamantylidene, especially an alkylidene radical. Aryl-substituted radicals are included, as are unsaturated radicals and radicals containing atoms other than carbon and hydrogen; e.g., oxy groups. Substituents such as those previously enumerated may be present on the aliphatic, alicyclic and aromatic portions of the Y group.
For most purposes, the preferred units containing moieties of formula II are those in which each of A
1
and A
2
is p-phenylene and Y is isopropylidene; i.e., those derived from bisphenol A.
The polycarbonate is prepared, according to the invention, by the transesterification reaction of at least one dihydroxyaromatic compound, preferably a bisphenol and most preferably bisphenol A (hereinafter sometimes simply “BPA” for brevity), with a diaryl carbonate, preferably diphenyl carbonate (hereinafter sometimes “DPC”). For the sake of convenience, frequent reference to BPA and DPC will be made hereinafter, but it should be understood that other dihydrox
Burnell Timothy Brydon
Fernandez Ignacia Vic
Hidalgo-Llinas Gerardo
McCloskey Patrick Joseph
Ordonez Juan Rodriques
Boykin Terressa M.
Caruso Andrew J.
General Electric Company
Johnson Noreen C.
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