Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-05-31
2002-08-13
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
06433126
ABSTRACT:
BACKGROUND OF INVENTION
This invention relates generally to the production of improved copolycarbonates incorporating varying structural units and a method for their preparation via solid state polymerization.
There is intense interest in new processable materials for use in a wide variety of challenging mechanical and optical applications. One such application is the production of modern optical devices such as optical data storage disks. Several polycarbonate based materials have been investigated for this purpose.
Polycarbonate resin that is suitable for optical applications requires special properties such as appropriate glass transition temperature, high purity and low water absorption. Traditionally, these polycarbonates are prepared by either interfacial polycondensation, or by a melt phase carbonate interchange reaction.
In a typical melt phase reaction process, a bisphenol, a diaryl carbonate and a suitable catalyst are combined to yield an oligomeric polycarbonate, usually with an average molecular weight ranging from 2,000 to 10,000 as determined by gel permeation chromatography, relative to polycarbonate or polystyrene. The oligomer produced typically has an intrinsic viscosity between 0.06 and 0.30 dl/g as determined in chloroform at 25° C. The oligomer may be converted to a high molecular weight polycarbonate through an increase in the polymerization temperature.
The melt phase process has a variety of disadvantages. For example, the melt viscosity of the oligomer greatly increases at very high conversions (>98%), thereby rendering the handling of such high viscosity melt polymerization mixtures difficult. This difficulty in handling increases the likelihood of hot spots along the reactor walls and poor mixing. Another disadvantage to the melt-phase process is that it requires special equipment such as a Helicone mixer, operating at temperatures in the range of 270 350° C. at subambient pressure.
In a typical interfacial polycondensation process, a dihydroxyaromatic compound, such as bisphenol A, is reacted with phosgene in a mixed aqueous-organic solution in the presence of an acid acceptor, and an appropriate catalyst, for example an amine.
The interfacial polycondensation process suffers from a variety of disadvantages as well. Toxic and hazardous phosgene is utilized in these reactions. Further, the interfacial polycondensation process typically employs a chlorinated hydrocarbon, such as methylene chloride, as an organic solvent and therefore carries the burden of substantial and costly environmental management of the solvent to prevent unintended emissions. Furthermore, the product will contain residual sodium and chloride ions that negatively affect the product's hydrolytic stability and water absorption characteristics.
More recently, solid state polymerization (“SSP”) has been utilized as an improved process for preparing high molecular weight polycarbonates. SSP offers several advantages over both the melt phase process and the interfacial polycondensation process. SSP utilizes considerably lower temperatures than the melt phase process, (i.e., in the range of 180-230° C.). Also, the SSP process does not require handling melt at high temperatures like the melt phase process, and no special equipment is required to perform the process. Further, toxic chemicals such as phosgene are not utilized in the SSP process, and because an organic solvent is unnecessary, the process does not raise environmental concerns attendant upon the use of volatile organic solvents. Polycarbonate produced by SSP may be prepared largely free of the high levels of sodium and chloride ions found in interfacially prepared polycarbonate. As such, polycarbonates prepared by SSP are anticipated to show improved hydrolytic stability.
Typically in an SSP process, a partially crystalline polycarbonate oligomer is heated at a temperature below the sticking temperature of the polymer, but above the glass transition temperature of the polymer, and the volatile by-products, phenol, diphenyl carbonate and the like, are removed. The polycondensation reaction which converts the low molecular weight oligomer to high polymer proceeds strictly in the solid state under these conditions.
Melt transesterification routes to copolymers which involve the reaction of a dihydroxyaromatic compound and a comonomer with a diaryl carbonate at high temperature, may be of limited use when the comonomer has limited thermal stability and decomposes under the conditions of the melt reaction. Therefore the use of solid state polymerization conditions, which are usually milder and require lower polymerization temperatures than melt polymerization, could be of use for the preparation of copolycarbonates containing soft blocks and/or birefringence-decreasing units which may suffer thermal degradation under the more forcing conditions used for melt polymerization. Many monomers, however, especially soft block monomers such as polyethylene glycol and polytetrahydrofuran, may degrade even under standard SSP conditions and new methods of preparing copolycarbonates by solid state polymerization continue to be sought. An alternative method of incorporating the copolymeric units in a polymer ultimately produced by SSP is therefore necessary.
Solid state polymerization utilizes a substantially lower temperature, in the range of 180-230 C., than a simple melt process. SSP does not require handling molten polymer at high temperatures. The use of the soft block requires the process to be run at relatively low temperatures. This process is also capable of being performed with very simple equipment that limits the problems which larger, more complex equipment may cause.
Solid state polymerization, specifically polycondensation, may be executed by heating a crystallized polycarbonate oligomer in powder or pelletized form, and optionally a suitable catalyst, in a fixed bed configuration while passing a stream of inert gas through the crystallized oligomer. The reaction temperature and time may vary according to the type (chemical structure, molecular weight, etc.) of the crystallized oligomer. However, the reaction temperature should be at least above the glass transition temperature and below the melting or sticking point of the oligomer. Observation of these temperature limits prevents the oligomer from fusing during the solid state polycondensation. Since the melting point of the crystallized oligomer increases during the course of polycondensation, it is therefore desirable to increase the polycondensation temperature gradually over the course of the reaction. Generally the temperature should be 10-50° C. below the melting point of the oligomer and in the range of 180-230° C. If the reaction is allowed to take place within this range of temperatures, a high molecular weight polycarbonate can be formed.
A typical SSP process has two stages. First, a low melt viscosity linear oligomer is created by reacting in the molten phase a bisphenol with a diaryl carbonate. Typically, a mixture of a bisphenol compound and a diaryl carbonate is heated at 150° C. to 325° C. for approximately 4 to 10 hours along with a transesterification catalyst to prepare an oligomer having an average molecular weight of 2,000-20,000, and having both hydroxyl and carbonate end groups. Subsequent crystallization of the linear polycarbonate oligomer may be effected by: (a) dissolving the oligomer in a solvent and evaporating the solvent in presence of a suitable catalyst; (b) suspending the oligomer in a diluent and refluxing it for 0 to 10 hours in presence of a suitable catalyst followed by evaporating the diluent; or (c) heating the oligomer with a catalyst at a programmed temperature (greater than the glass transition temperature of the oligomer, but less than the melting point of the oligomer). Preferable solvents and diluents include aliphatic aromatic hydrocarbons, ethers, esters, ketones, and halogenated aliphatic and aromatic hydrocarbons. The resulting oligomer has a crystallinity of between 5% and 55% as measured by differential scanning c
Boykin Terressa M.
Caruso Andrew J.
Johnson Noreen C.
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