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
2002-02-26
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
Reexamination Certificate
active
06350846
ABSTRACT:
BACKGROUND OF INVENTION
The present invention describes improved aromatic-aliphatic copolycarbonates and a method for their synthesis that involves the reaction of polycarbonate resin and an aliphatic diol carbonate such as polyhexamethylene carbonate (PHMC) under solid state polymerization (SSP) conditions. More particularly, the present invention employs diphenyl carbonate to assist in the production of crystalline mixtures of polycarbonate oligomers and aliphatic diol carbonates which when subjected to solid state polymerization afford high molecular weight copolycarbonates that demonstrate better flow and ductility behavior and lower glass transition temperature (T
g
) values than corresponding homopolycarbonates.
In recent years, significant attention has focused on aromatic-aliphatic copolycarbonates. These valuable materials have several desirable properties, including enhanced tensile elongation, transparency, and excellent low-temperature characteristics. Traditionally, two techniques have been utilized in the production of polycarbonates: melt phase carbonate interchange reactions and interfacial polycondensation processes.
In a typical melt phase process, a bisphenol is contacted with a diary carbonate in the melt in the presence of a suitable catalyst. An oligomeric polycarbonate is produced, usually with a weight average molecular weight in the range of 2,000-10,000 as determined by gel permeation chromatography, which may be relative to polycarbonate or polystyrene. The oligomer is then converted to a high molecular weight polycarbonate by increasing the polymerization temperature.
Significant disadvantages accompany melt phase processes. 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 generation of hot spots leading to loss of product quality. In addition, this route requires specially designed equipment such as a Helicone mixer operating at temperatures in the range of 270 350° C.
Methods in the second category, i.e., interfacial polycondensation reactions, utilize a dihydroxyaromatic compound such as bisphenol A (BPA). The dihydroxyaromatic compound is contacted with phosgene in a mixed aqueous-organic solution in the presence of an acid acceptor such as sodium hydroxide and an amine as catalyst. An alternative technique involves the interfacial preparation of oligomeric chloroformates, which are subsequently converted to high molecular weight polycarbonates via condensation polymerization.
Like melt phase carbonate interchange reactions, however, 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 poly(arylcarbonate) contains residual sodium and chloride ions which adversely affect the hydrolytic stability of the product.
Recently, SSP has been used to prepare high molecular weight polycarbonates. SSP utilizes substantially lower temperatures, in the range of 180-230° C., than those required in the melt process. This process does not require handling melt at high temperatures and the equipment needed to perform the reaction is very simple. In a typical solid state polycondensation process, a suitable oligomer in the form of a pellet or a powder is subjected to programmed heating above the glass transition temperature of the polymer but below its sticking temperature with removal of volatile by-product such as phenol and diphenyl carbonate. The polycondensation reaction proceeds strictly in the solid state under these conditions.
In a typical SSP process, a low melt viscosity linear oligomer is synthesized by the melt phase reaction of a bisphenol with a 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 an average molecular weight of 2,000-10,000 and having both hydroxyl and carbonate end groups. Thereafter, crystallization of the linear poly (arylcarbonate) oligomer may be effected either by dissolving the oligomer in a solvent and evaporating the solvent in presence of a suitable catalyst, or suspending the oligomer in a diluent and refluxing the mixture for 0 to 10 hrs in the presence of a suitable catalyst followed by evaporating the diluent. Alternatively, heating the oligomer at a temperature which is greater than its glass transition temperature but less than its melting point (T
m
) in the presence of a suitable catalyst may be used to effect a thermal crystallization of the polycarbonate. Illustrative solvents 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 calorimetry.
SSP, sometimes referred to as solid state polycondensation may be effectuated by heating the crystallized oligomer and 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 over the course of the solid state polymerization reaction. Generally the temperature should be 10-50° C. below the melting point of the oligomer and in the range of 150-250° C., preferably between 180 and 220 ° C.
To allow the reaction to progress, the by-product can be removed from the reaction system during the SSP process. To achieve this objective, an inert gas is passed through the system which aids the removal of by-products. The inert gases which are generally used are N
2
, He, Ar and the like, 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 be dependent on the type and the flow rate of the carrier gas.
It is sometimes desirable to incorporate monomer units other than bisphenols, such as BPA, into the polycarbonate backbone in order to modify the physical properties of the polycarbonate. Where a polycarbonate having different physical properties, such as a lower Tg, than the bisphenol homopolycarbonate is desired, certain types of aliphatic comonomers may be incorporated affording a copolycarbonate possessing a new set of physical properties. Usually it is preferred that these comonomers provide aliphatic ester units in the resultant copolycarbonates. One method of copolycarbonate formation involves the interfacial copolymerization in the presence of phosgene, an acid acceptor and an amine catalyst of a bisphenol and an aliphatic alpha, omega- dicarboxylic acid that contains between 6 and 20 carbon atoms. Saturated acids are frequently preferred. Polycarbonates incorporating aliphatic chains derived from such aliphatic dibasic acids are prized for their enhanced melt flow characteristics which are in turn attributed the lower Tg's these copolycarbonates exhibit relative to the corresponding homopolycarbonate.
The present invention improves upon existing copolycarbonate products and methods for their synthesis providing a polycarbonate comprising both aromatic and aliphatic carbonate linkages via a solid state polymerization process. It has been unexpectedly found that the incorporation of aliphatic diol carbonates into polycarbonate cha
Boykin Terressa M.
Caruso Andrew J.
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