Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-08-09
2001-02-13
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
06187895
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the preparation of polymers, and more particularly to their preparation by solid state polymerization.
Solid state polymerization (SSP) as a method for preparing polycarbonates is disclosed, for example, in U.S. Pat. Nos. 4,948,871, 5,204,377 and 5,717,056, the disclosures of which are incorporated herein. It is typically described as involving a first step of forming, typically by melt polymerization (i.e., transesterification) of a dihydroxyaromatic compound such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) with a diaryl carbonate such as diphenyl carbonate, a precursor polycarbonate which is often (though not necessarily) an oligomer; a second step of enhancing the crystallinity of the precursor polycarbonate; and a third step of building molecular weight by heating the enhanced crystallinity precursor polycarbonate to a temperature between its glass transition temperature and its melting temperature. Use of this method is of increasing interest by reason of its effectiveness and environmental benefits. A similar method is used for polyesters, especially bottle grade poly(ethylene terephthalate), for which an oligomer is prepared by the reaction of a dicarboxylic acid ester with a diol and is then crystallized and subjected to SSP to build molecular weight.
The crystallinity enhancement step is considered essential in accordance with the aforementioned prior art. As taught, for example, in U.S. Pat. No. 4,948,871, the crystallinity of the precursor polycarbonate should be in the range of about 5-55% as determined, for example, from powder X-ray diffraction patterns. If it is below 5%, the melting point of the precursor polycarbonate is so low that melting rather than SSP may occur. On the other hand, at crystallinity levels greater than 55% the polymerization rate is too low to be practical.
Crystallinity enhancement may be performed by several methods. These include heat treatment, solvent treatment, action of crystallization promoters and treatment with swelling agents. Each of these methods requires time input and/or treatment with extraneous chemicals which must be kept in inventory and stored. It would be desirable, therefore, to develop an SSP method which does not require the crystallinity enhancement step.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that the principal effect of enhancement of crystallinity is to provide a crystalline coating for the amorphous polymer particles, ensuring that they do not adhere to each other. Thus, condensation of polymer molecules with evolution of hydroxyaromatic compound, typically phenol, or diol in the case of polyesters occurs readily with an increase in molecular weight. In fact, SSP occurs readily and rapidly in the amorphous polymer phase if the desired coating is present, whether or not the overall crystallinity of the material is within the prior art-mandated range.
Accordingly, the invention in one of its aspects is a method for preparing a polymer by solid state polymerization which comprises:
(A) contacting particles of an amorphous precursor polymer selected from the group consisting of polycarbonates and polyesters with at least one other particulate material having a melting point higher than the glass transition temperature of said precursor polymer, under conditions whereby said particulate material coats said particles to produce a coated polymer composition comprising a major proportion of said amorphous precursor polymer; and
(B) subjecting said coated polymer composition to solid state polymerization conditions.
Another aspect of the invention is a coated precursor polymer composition comprising particles of which the major proportion is amorphous, said particles having a surface layer of at least one other particulate material as described above.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
The method of this invention may be performed on polycarbonates or polyesters. Suitable polyesters include principally the linear polyesters such as poly(ethylene terephthalate) and poly(1,4-butylene terephthalate). For the sake of brevity, the method will be principally described with respect to polycarbonates, but it should be understood that it is equally applicable to polyesters.
As used herein, “polycarbonate” includes copolycarbonates and polyestercarbonates. Suitable amorphous precursor polycarbonates for use in step A of the method of the invention may be oligomers, prepared, for example, 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 an intrinsic viscosity in the range of 0.06-0.30 dl/g, all intrinsic viscosity values herein being as determined in chloroform at 25° C.
The amorphous precursor polycarbonate may also be a high molecular weight homo- or copolycarbonate; i.e., one having an intrinsic viscosity above 0.30 dl/g. Numerous kinds of high molecular weight homo- and copolycarbonates are suitable, including conventional linear polycarbonates in virgin form. They may be prepared from any of the known dihydroxy compounds useful as monomers, including dihydroxyaromatic compounds such as bisphenol A, SBI and others designated by name or structural formula (generic or specific) in U.S. Pat. No. 4,217,438, the disclosure of which is incorporated by reference herein.
Also included are branched polycarbonates, 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. Copolycarbonates, particularly copolycarbonate oligomers and high molecular weight copolycarbonates containing units adapted to maximize solvent resistance, are also suitable. Such solvent resistance-maximizing units will typically comprise about 25-50% of total carbonate units in the polymer.
Recycled polycarbonates, for example from compact disks, may also be employed. Such recycled material typically has a molecular weight which has been degraded from that of the originally polymerized material as shown by an intrinsic viscosity in the range of about 0.25-1.0 dl/g. It may he obtained from scrap polycarbonate by dissolution in a chlorinated organic solvent such as chloroform, methylene chloride or 1,2-dichloroethane followed by filtration of the insoluble material or by other art-recognized procedures for separation of non-polycarbonate constituents. Other types of polycarbonate, such as interfacially prepared polycarbonate and polycarbonate extruder wastes, may also be employed as precursors.
For the most part, bisphenol A homo- and copolycarbonates are preferred in the method of the invention by reason of their commercial availability, relatively low cost and particular suitability.
In step A, particles of the amorphous precursor polycarbonate are contacted with at least one other particulate material, hereinafter sometimes “coating material”. By “particulate material” is meant any substance existing in the form of crystals or amorphous particles and suitable for coating of the precursor polycarbonate particles. The latter may be of any size, typically from about 100 microns to about 5 mm. A particle size larger than about 5 mm is generally disadvantageous since it may be difficult for hydroxyaromatic compound evolved in the SSP step to escape from the central regions of such large particles.
Thus, suitable coating materials include those useful as pigments and fillers. Among them are relatively inert inorganic substances such as sand, talc, titanium dioxide and carbon black and numerous organic substances, including particulate polymers. Of the polymers, the preferred ones are polycarbonates and especially those containing the same structural units as the precursor polycarbonate. Most preferred are crystalline polycarbonates, which may be prepared by art-recognized methods including those disclosed in the previously identified patents. The term “crystalline” with reference to polycarbonates, when used herein, includes partially crystalline polycarbonates, typ
Day James
Idage Bhaskar Bhairavnath
Varadarajan Godavarthi Satyana
Boykin Terressa M.
General Electric Company
Johnson Noreen C.
Stoner Douglas E.
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