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
2002-04-02
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
06365702
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention describes improved polyestercarbonates and methods for their synthesis that involves the incorporation of structural units derived from carboxylic acids and their derivatives into polycarbonate chains under solid state polymerization (SSP) conditions. These acids include branched diacids, diacid soft blocks, and p-hydroxybenzoic acid (PHB), preferably, phenyl p-hydroxybenzoate. The present invention also preferably employs a catalyst, Sb
2
O
3
, and diphenyl carbonate in the production of the improved polyestercarbonates. Using the method of the present invention aromatic triacids such as the trisphenyl ester of 1,3,5-benzenetricarboxylic acid, a branching agent, may also be incorporated into these precursors before subjecting the precursor to SSP to produce branched polycarbonates. Following SSP, the resulting polyestercarbonates exhibit superior physical characteristics such as improved flow or enhanced melt strength, and modified Tg in comparison to analogous polycarbonate compositions lacking ester linkages.
Traditionally, two techniques were utilized in the production of polyestercarbonates: interfacial polycondensation processes and melt phase carbonate interchange reactions. Interfacial polycondensation routes to polyestercarbonates involve contacting a bisphenol and a diacid or diacid chloride with phosgene in a mixed aqueous-organic solution. An acid acceptor and optionally a catalytic amine are also present.
Interfacial polycondensation processes suffer several disadvantages. First, toxic and hazardous phosgene is utilized in these reactions. Also, the interfacial polycondensation process employs a chlorinated hydrocarbon, such as methylene chloride, as the organic solvent which requires substantial and costly environmental management to prevent unintended solvent emissions. Furthermore, the product polyestercarbonate contains residual sodium and chloride ions which adversely affect the hydrolytic stability of the product.
Methods for the preparation of polyestercarbonates through melt phase carbonate interchange reactions are also known. In a typical melt phase process, a bisphenol and a diacid or diester is contacted with a diaryl carbonate in the melt in the presence of a suitable catalyst. An oligomeric polyestercarbonate is produced, usually with a weight average molecular weight in the range of 2,000-10,000 daltons as determined by gel permeation chromatography, which may be relative to polycarbonate or polystyrene standards. The oligomer generally has an intrinsic viscosity between 0.06 and 0.30 dl/g as determined in chloroform at 25° C. The oligomer is then converted to a high molecular weight polyestercarbonate by increasing the polymerization temperature.
Melt phase processes also suffer from a number of disadvantages. For example, at very high conversions (>98%), the melt viscosity increases considerably. Handling of high viscosity melt polymerization mixtures at high temperature is difficult. There is an increased chance of poor mixing and generating hot spots, which lead to the loss of product quality. In addition, this route requires specially designed equipment such as a Helicone mixer operating at temperatures in the range of 270-300° C. Polyestercarbonates are susceptible to degradation at high temperature to a greater extent than are homopolycarbonates.
More recently, SSP has been used as an alternative process for the preparation of high molecular weight polycarbonates. SSP utilizes substantially lower temperatures than the melt process. Typically SSP is carried out in a range between about 180 and about 230° C. The SSP process does not require handling molten polymer (melt) at high temperatures and the equipment needed to perform the reaction is very simple. In a typical solid state polycondensation process, a suitable polycarbonate oligomer is subjected to programmed heating above the glass transition temperature of the polymer but below its sticking temperature with removal of the volatile by-product. The polycondensation reaction proceeds strictly in the solid state under these conditions.
The SSP process is typically conducted in two stages. In the first stage, a low melt viscosity linear polycarbonate oligomer is synthesized by the melt phase reaction of a bisphenol with diaryl carbonate. Usually, a mixture of a dihydroxydiaryl compound and a diaryl carbonate is heated at 150° C. to 325° C. for 4 to 10 hours in presence of a transesterification catalyst to prepare an oligomer having weight average molecular weight of 2,000-10,000 daltons and having both hydroxyl and carbonate end groups. This oligomeric polycarbonate is referred to as the precursor or precursor polycarbonate. Thereafter, crystallization of the linear polycarbonate oligomer may be effected either by (a) dissolving the oligomer in a solvent and evaporating the solvent in presence of a suitable catalyst or (b) suspending the oligomer in diluent and refluxing it for 0 to 10 hrs in presence of a suitable catalyst followed by evaporating the diluent or (c) heating the oligomer at a temperature which is higher than the glass transition temperature of the oligomeric polycarbonate undergoing crystallization but below its melting point, in the presence of a suitable catalyst. It has been observed that diphenyl carbonate serves as a crystallization aid during thermal crystallization. Illustrative solvents and diluants 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 a differential scanning calorimeter.
In a typical process, SSP, sometimes referred to as solid state polycondensation, is carried out by heating the crystallized oligomer along with a suitable catalyst. The reaction temperature and time may vary according to the type (chemical structure, molecular weight, etc.) of crystallized oligomer. However, it should be at least above the glass transition temperature and below the melting or sticking point of the oligomer. At this temperature the oligomer should not fuse 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. Generally the temperature should be 10-50° C. below the melting point of the oligomer and it should be in the range of 150-250° C. and more preferably between 180 and 220° C.
During the process of solid state polycondensation, the by-products (e.g. phenol, diphenyl carbonate, bisphenol) should be removed from the reaction system so as to allow the reaction to progress. For this purpose an inert gas is passed through the system which carries out the by-product. The inert gases which are generally used are N
2
, He, Ar etc. and the flow rate of the carrier gas varies from 0.1 to 4 L/min depending upon the type of reactor and the particle size of the oligomer. The rate of polycondensation may depend on the type and the flow rate of the carrier gas.
Certain types of monomers are usually preferred for providing aliphatic ester units in polyestercarbonates prepared using the interfacial and melt preparation methods. One known method uses aliphatic alpha omega dicarboxylic acids that contain between 8 and 20 carbon atoms, and preferably about 9 or 10 carbon atoms, with saturated acids being preferred. Another method involves the utilization of aliphatic diacids that have between 4 and 8 carbon atoms. Diacids with 6 carbon atoms, such as adipic acid, are preferred. In addition, one method details the use of saturated aliphatic dibasic acids that are derived from straight chain paraffin hydrocarbons such as oxalic acid, malonic acid, dimethyl malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. It is stated that aliphatic carboxylic acids that contain heteroatoms in their aliphatic chain, such as diglycollic acid and thio-diglycollic acid, may a
Amaratunga Mohan Mark
Hait Sukhendu Bikash
Mobley David Paul
Boykin Terressa M.
Caruso Andrew J.
General Electric Company
Johnson Noreen C.
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