Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1998-11-16
2001-06-19
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
06248858
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polycarbonate preparation, and more particularly to the preparation of aromatic polycarbonates by solid state polymerization.
The methods widely known for preparation of polycarbonates are the interfacial method and the melt method. In interfacial polymerization; a dihydroxyaromatic compound is contacted with phosgene in a mixed aqueous-organic solution, in the presence of an acid acceptor and an amine as catalyst. This method is falling out of favor because of the toxicity of phosgene and the environmental hazards of methylene chloride, the most commonly employed organic solvent. A similar method, in which oligomeric chloroformates are prepared interfacially and are then converted to high molecular weight polycarbonate, has similar disadvantages.
In the melt preparation method, a bisphenol is contacted with a diaryl carbonate in the melt in the presence of a suitable catalyst. An oligomeric polycarbonate is first produced and it is converted to a high molecular weight polycarbonate by increasing the polymerization temperature. There are also disadvantages in this process, one of them being the high viscosity of the melt polymerization mixture, especially during the molecular weight building step, which causes difficulty of handling.
A third option for polycarbonate formation, solid state polymerization (hereinafter sometimes “SSP”), has become known in recent years. The first polymerization step in the solid state process is oligomer formation by melt polymerization. The oligomer is then subjected to treatment to induce crystallinity therein. The crystallinity-enhanced oligomer is finally heated to a temperature between its glass transition temperature (Tg) and its melting temperature (Tm) in the presence of a catalyst, whereupon polymerization occurs to produce a high molecular weight polycarbonate.
U.S. Pat. No. 4,948,871 and 5,214,073, the disclosures of which are incorporated by reference herein, disclose a method for solid state polymerization in which crystallinity is enhanced by solvent (typically acetone or some other ketone) treatment or heat treatment. The polymerization step is then conducted in one or more stages at temperatures of 180° C. and higher, often with ramping of the temperature during a stage.
One disadvantage of such a process is the fact that it cannot be conveniently conducted continuously. To do so would require multiple reaction vessels, one at each temperature level attained. Thus, ramping of the temperature would be impracticable and the number of necessary vessels would be prohibitively expensive. Further, polymerization rates at temperatures on the order of 180° C., the onset temperature for many SSP processes known in the art, are very slow. Still further, the process is, for the most part, incapable of yielding a polycarbonate having a number average molecular weight (Mn) higher than about 15,000. The only specifically disclosed products with higher Mn values are the product of Example 12 of 4,948,871, having a Mn value of about 25,000 (as calculated from the disclosed values of Mw and Mw/Mn) but requiring ramping of the temperature from 190° to 220° C., and that of Example 9 of 5,214,073, having progressively attained Mn values of 26,000 and 40,000 which require uneconomical polymerization temperatures as high as 230° or 240° C.
It remains of interest, therefore, to develop SSP processes which require a minimum of heating stages, all capable of being performed at a set temperature without ramping, and thus adaptable to continuous polycarbonate production. It is also of interest to develop processes of this type which permit rapid polymerization and which are adapted to produce a polymer having a Mn of 15,000 or greater.
SUMMARY OF THE INVENTION
The present invention is a polycarbonate production method adaptable to achieve the above-summarized goals. It is a method for preparing an aromatic polycarbonate which comprises:
(A) contacting precursor polycarbonate pellets having a diameter in the range of about 1-5 mm with at least one non-solvent therefor, said non-solvent comprising a C
1-20
alkanol in the liquid or vapor state, to produce an enhanced crystallinity precursor polycarbonate; and
(B) subjecting said enhanced crystallinity precursor polycarbonate to solid state polymerization conditions in a stream of inert gas, said conditions including a stage of heating at a constant temperature in the range of about 215-225° C., to produce a polycarbonate product having a number average molecular weight, as determined by gel permeation chromatography relative to polystyrene, of at least 15,000.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
Polycarbonates which may be prepared by the method of this invention typically comprise structural units of the formula
wherein at least about 60% of the total number of R groups are aromatic organic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. Preferably, each R is an aromatic organic radical and more preferably a radical of the formula
—A
1
—Y—A
2
— (II)
wherein each A
1
and A
2
is a monocyclic divalent aryl radical and Y is a bridging radical in which one or two carbonate atoms separate A
1
and A
2
. Such radicals are derived from dihydroxyaromatic compounds of the formulas HO—R—OH and HO—A
1
—Y—A
2
—OH respectively. For example, A
1
and A
2
generally represent unsubstituted phenylene, especially p-phenylene which is preferred, or substituted derivatives thereof.
The bridging radical Y is most often a hydrocarbon group, preferably an aliphatic or alicyclic hydrocarbon group and more preferably a saturated group such as methylene, cyclohexylidene, or isopropylidene which is preferred. Thus, the preferred polycarbonates are those consisting of structural units of formula I (which may be of only one structure or of several structures), in which R has formula II and Y is an aliphatic or alicyclic hydrocarbon group. Especially preferred are polycarbonates derived entirely or in part from 2,2-bis(4-hydroxyphenyl)propane, also known as “bisphenol A”.
The essential starting material in step A of the method of this invention is a precursor polycarbonate. It may be a polycarbonate oligomer of the type produced by the first step of a melt polycarbonate process or by bischloroformate oligomer preparation followed by hydrolysis and/or endcapping and isolation. Such oligomers most often have a weight average molecular weight (Mw) in the range of about 2,000-10,000, all molecular weights herein being determined by gel permeation chromatography relative to polystyrene, and an intrinsic viscosity in the range of about 0.06-0.30 dl/g, all intrinsic viscosity values herein being as determined in chloroform at 25° C.
Both homopolymer and copolymer precursor polycarbonates may be employed. Copolycarbonates include those containing, for example, bisphenol A carbonate structural units in combination with carbonate units derived from other bisphenols or from polyethylene glycols. Also included are copolyestercarbonates, such as those containing bisphenol dodecanedioate units in combination with carbonate units.
It may also be a relatively high molecular weight polycarbonate, generally having an Mw value in the range of about 10,000-35,000, for which it is desired to increase the molecular weight still further; e.g., up to a value in the range of about 50,000-80,000. For example, optical quality polycarbonate which is off-specification may be crystallized by the method of this invention prior to increasing its molecular weight so that it may be used in other applications.
The precursor polycarbonate may be a branched homo- or copolycarbonate, formed by the reaction of a linear polycarbonate or its precursor(s) with a branching agent such as 1,1,1-tris(4-hydroxyphenyl)ethane. Branched copolycarbonates include oligomers and high molecular weight copolycarbonates containing units adapted to maximize solvent resistance. Hydroquinone and methylhydroquinone carbonate units are particularly suitable for this purpose, as disclosed i
Day James
Varadarajan Godavarthi Satyana
Barker Robert T.
Boykin Terressa M.
General Electric Company
Johnson Noreen C.
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