Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-02-27
2003-07-15
Troung, Duc (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C520S001000, C520S001000, C525S328500, C525S534000, C525S535000
Reexamination Certificate
active
06593445
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to new poly(biphenyl ether sulfones). More particularly, this invention relates to new poly(biphenyl ether sulfones) having improved color. This invention is also directed to an improved process for manufacturing poly(biphenyl ether sulfones).
Aryl ether polymers and copolymers are well known; they can be synthesized from a variety of starting materials and they can be made with different melting temperatures and molecular weights. Poly(aryl ethers) may be crystalline and, at sufficiently high molecular weights, they are tough, i.e., they exhibit high values (>50 foot-pounds per cubic inch) in the tensile impact test (ASTM D-1822). They have potential for a wide variety of uses, and their favorable properties class them with the best of the engineering polymers. Poly(aryl ether sulfone) polymers have become widely accepted for use under stress at high temperatures, often in excess of 150° C.
One commercially important group of poly(aryl ether sulfones) comprises polymers containing a biphenyl group or moiety, typically derived from the monomer 4,4′-biphenol. Poly(aryl ether sulfones) that contain at least in part the 4,4′-biphenyl or 4,4′-biphenylene moiety are hereinafter referred to as poly(biphenyl ether sulfones).
Poly(aryl ether sulfones) having the following structure:
are available from BP Amoco Polymers, Inc. under the tradename of Radel R®. These resins possess excellent mechanical and other properties and are readily fabricated to provide a variety of useful articles such as molded goods, films, sheets and fibers. Poly(biphenyl ether sulfones) are also highly resistant to environmental stress cracking, and are thus particularly useful for manufacturing articles that are exposed to solvents or chemical agents at elevated temperatures and for extended times. For example, Radel R resins have found wide acceptance in the manufacture of articles for use where exposure to repeated and rigorous sterilization procedures is contemplated, such as medical trays and the like.
A very broad range of poly(aryl ether) polymers can be formed by the nucleophilic aromatic substitution (solution condensation polymerization) reaction of an activated aromatic dihalide and an aromatic diol in a substantially anhydrous dipolar aprotic solvent at elevated temperature. Ether bonds are formed via displacement of halogen by phenoxide anions with removal of halogen as alkali metal halide. Such polycondensations are usually performed in certain sulfoxide or sulfone solvents and the use of these dipolar aprotic solvents is an important feature of the process. The anhydrous dipolar aprotic solvents dissolve both the reactants and the polymers, and their use to enhance the rates of substitution reactions of this general type is well known.
One-step and two-step nucleophilic aromatic substitution processes for preparing poly(aryl ethers) are disclosed and well described in the art. In a one-step process, a double alkali metal salt of a dihydric phenol is reacted with a dihalobenzenoid compound in the presence of a dipolar aprotic solvent having a high boiling point such as, for example, dimethylformamide, N-methyl pyrolidinone, dimethyl sulfoxide, diphenyl sulfone or the like under substantially anhydrous conditions. In a two-step process, a dihydric phenol is first converted, in situ and in the presence of a solvent, to the alkali metal salt by reaction with an alkali metal or alkali metal compound. After removing water, a dihalobenzenoid compound is reacted with the double salt. The alkali metal salt of the dihydric phenol may be added in the solvent to the dihalobenzenoid compound either continuously, incrementally or all at once to achieve the polymerization reaction.
Several other variations of the process have been disclosed. An alkali metal carbonate may be employed with equimolar amounts of a dihydric phenol and a dihalobenzenoid compound at a ratio of at least one mole of an alkali metal carbonate per mole of dihydric phenol. The dihydric phenol reacts in situ with the alkali metal carbonate to form the alkali metal salt thereof, and the formed salt reacts with the dihalobenzeoid compound to form the polyaryl ether in the usual fashion.
Mixtures of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate have been disclosed for use in the preparation of poly(aryl ether sulfones) and poly(aryl ether ketones), i.e. poly(aryl ethers) containing SO
2
and/or CO linkages. The alkali metal of the second alkali metal carbonate or bicarbonate has a higher atomic number than that of sodium. The process provides polymer having a high molecular weight, as reflected by the reduced viscosity, that forms a tough, off-white film. Where fluorophenols or difluorobenzenoid compounds are used as the halogen-containing reactants, the amount of alkali metal carbonate required may be reduced.
Sodium and potassium salts, singly or in combination, are usually used in commercial practice. Although sodium salts are advantageous from an economic point of view, potassium salts are often chosen because the nucleophilic properties of the phenoxide anion are excellent. In a particular case where the dihalobenzenoid compound selected has low reactivity, a high molecular weight aromatic polyether cannot be obtained unless a potassium salt is used.
After completion of the polymerization reaction, additional process steps are needed to remove by-produced salts and to isolate and purify the resulting polymers. Recovery of dipolar aprotic solvents having high boiling points adds still further process steps.
Even though the monomers and solvents that are employed are highly purified, it is difficult to produce poly(arylether sulfones) that have low color, i.e. that are water white when formed and remain so when molded or otherwise melt processed. Side reactions, including solvent decomposition, hydrolysis of the dihalobenzenoid component and oxidation of a diphenol component or of phenolic endgroups, may occur during the heat-up portion of the process or later in the polymerization and lead to formation of highly colored contaminants. These, together with other contaminants produced by further thermal decomposition during subsequent melt fabrication operations, can result in products having an undesirable off-white, straw or even yellow color.
The poly(biphenyl ether sulfones) currently available to the trade, such as Radel R, have a yellow coloration. Although the effect on mechanical properties may be minimal, the cosmetic appearance of articles made from resins that are off-white or yellow may be unacceptable. Moreover, off-white resins are more difficult to pigment or color reproducibly to provide clear, bright colors such as are required by the packaging trade. Color, particularly of resins intended to be used in fabricating articles visible to the consumer, thus may be the determining factor in deciding the commercial acceptability of such goods.
Poly(biphenyl ether sulfones) having an improved, lighter color, preferably water-white, could find wider acceptance for many applications where color is a concern. Such lower color resins are clearly needed by the art and would thus represent a significant improvement over the resins currently available to the trade.
SUMMARY OF THE INVENTION
This invention is directed to an improved method for making low color poly(aryl ether sulfone) resins, and more particularly for making poly(biphenyl ether sulfone) resins, characterized by having a color factor of up to about 200, preferably up to about 170, determined on molded articles by spectrophotometric means. The improved process of this invention employs low particle size alkali metal carbonate, preferably anhydrous potassium carbonate, having an average particle size of less than about 100 microns, and may be conducted at a lower reaction temperature using reduced reaction times, compared with prior art processes.
The invention may be further described as directed to low color poly(biphenyl ether sulfones) characterized by having a co
McDermott & Will & Emery
Solvay Advanced Polymers, LLC
Troung Duc
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