Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2002-05-17
2004-08-10
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S179000, C528S190000, C528S193000, C528S194000, C528S206000, C528S212000, C528S274000, C528S298000, C528S302000, C528S308000, C528S308600
Reexamination Certificate
active
06774203
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing a liquid crystalline polyester, especially an all-aromatic type liquid crystalline polyester, endowed with excellent mechanical characteristics and heat resistance, and more particularly, to a method for producing a liquid crystalline polyester comprising performing two-stage polymerization, i.e., melt polymerization for producing a prepolymer and solid-state polymerization, wherein solid-state polymerization is performed after completion of control of the number of aromatic ring terminal groups contained in the prepolymer to be present at a ratio not less than a predetermined value.
BACKGROUND ART
Recent years have seen increasing demand for a material having excellent rigidity, strength, and heat resistance regardless of whether the material is in the form of fiber, film, or in the form of a molded product. Polyester has already found a wide range of uses in ordinary molded products. However, most polyesters are not suited for uses requiring high modulus and strength, in view of its poor modulus and strength.
All-aromatic type liquid crystalline polyesters are endowed with excellent properties; particularly, remarkable heat resistance, by virtue of the structural characteristics thereof. Among them, aromatic polyesters prepared from at least terephthalic acid or isophthalic acid; p-hydroxybenzoic acid or its derivatives; and 4,4′-dihydroxydiphenyl or its derivatives are known to be injection-moldable resins endowed with a variety of important properties (required performance) for use as plastic products; e.g., excellent mechanical and electrical properties, high heat resistance, high resistance to chemicals, oil, and radiation, and dimensional stability.
The all-aromatic type polyesters are produced through condensation-polymerization (also called polycondensation) of, for example, an aromatic hydroxycarboxylic acid, or an aromatic diol and an aromatic dicarboxylic acid. Some of the above polyesters have an amino-group-containing aromatic unit in the skeleton thereof. The bond between aromatic units in the polyesters is an ester bond formed from, for example, a carboxylic group contained in an aromatic compound and a phenolic hydroxyl group. However, formation of the ester bond through direct dehydration-condensation of the carboxylic group and the phenolic hydroxyl group is usually difficult.
One possible method to overcome the difficulty has been disclosed (Japanese Patent Application Laid-Open (kokai) Nos. 64-33123 and 63-284221). Specifically, the phenolic hydroxyl group is acylated in advance by use of an aliphatic carboxylic acid anhydride such as acetic anhydride, to thereby form an aromatic compound; e.g., p-acetoxybenzoic acid, and the thus-formed aromatic compound serving as a raw material undergoes transesterification with an aromatic carboxylic acid while the by-produced aliphatic carboxylic acid is removed through distillation, to thereby produce a polyester.
Japanese Patent Application Laid-Open (kokai) Nos. 62-267323, 1-230629, and 7-10975 disclose another method for synthesizing a liquid crystalline polyester containing an aliphatic polyester, which method includes adding an aliphatic carboxylic acid anhydride (e.g., acetic anhydride) in an amount of 0.01-0.5 times to total phenolic hydroxyl group equivalent and reacting with an aromatic carboxylic acid.
These liquid crystalline polyesters are produced through any of known polymerization methods, such as melt polymerization, solid-state polymerization, and suspension polymerization. Generally, polymers for which high heat resistance is required are produced through solid-state polymerization. However, solid-state polymerization must be carried out at a temperature lower than the heat distortion temperature or the melting point of a target polymer, inevitably causing problematic retardation in rate of polymerization as compared with polymerization at a molten state; i.e., melt polymerization.
Thus, solid-state polymerization requires a longer period of time for completion of polymerization as compared with melt polymerization, and there still remains an unsolved question “how to shorten the reaction time” in relation to solid-state polymerization.
DISCLOSURE OF THE INVENTION
The present inventors have carried out extensive studies so as to solve the aforementioned problem, and have found that regulating the terminal group composition of the prepolymer can enhance the rate of solid-state polymerization for producing a prepolymer, or shorten the polymerization time, without deteriorating heat resistance or hue of the produced polymer. The present invention has been accomplished on the basis of this finding.
Accordingly, in a first mode of the present invention, there is provided a method for producing a liquid crystalline polyester comprising at least an aromatic carboxylic acid (A) and a compound having a hydroxyl group (B) and exhibits anisotropy when stationary in a molten state, wherein the method comprises a polymerization step (1) for producing a prepolymer of the liquid crystalline polyester so as to satisfying the following equation (i);
[(the number of aromatic ring terminal groups)/[(the number of carboxylic terminal groups)+(the number of aromatic ring terminal groups)]]×100≧7(%) (i),
and a solid-state polymerization step (2) for elevating the polymerization degree of the resultant prepolymer,
In a second mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in the first mode, wherein the aromatic carboxylic acid (A) is an aromatic dicarboxylic acid (a) and/or an aromatic hydroxycarboxylic acid (c), and the compound having a hydroxyl group (B) is an aromatic diol (b), an aromatic hydroxycarboxylic acid (c), and/or an aromatic hydroxylamine (d).
In a third mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in the first or second mode, wherein the aromatic hydroxycarboxylic acid (c) is p-hydroxybenzoic acid and/or 2-hydroxy-6-carboxynaphthalene.
In a fourth mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in any one of the first to third modes, wherein the liquid crystalline polyester is a liquid crystalline all-aromatic type polyester including at least p-hydroxybenzoic acid.
In a fifth mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in any one of the first to fourth modes, wherein polymerization for producing the prepolymer is performed by employing an aliphatic carboxylic acid anhydride (E) in an amount of 1.02-1.08 times to hydroxyl group equivalent of a phenolic-hydroxyl-group-containing aromatic compound.
In a sixth mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in the fifth mode, wherein the aliphatic carboxylic acid anhydride (E) is acetic anhydride.
In a seventh mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in any one of the first to sixth modes, wherein polymerization for producing the prepolymer is performed in the presence of a metallic catalyst in an amount of 200 ppm or lower by weight as reduced to a metallic element based on the prepolymer.
In an eighth mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in any one of the first to seventh modes, wherein the prepolymer has an intrinsic viscosity [&eegr;], as measured in pentafluorophenol at 60° C., of 0.2-3.0 dl/g.
In a ninth mode of the present invention, there is provided a method for producing a liquid crystalline polyester as described in any one of the first to eighth modes, wherein the solid-state polymerization step (2) is performed at 200-400° C.
In a tenth mode of the present invention, there is provided a method for producing a liquid crysta
Acquah Samuel A.
Nixon & Vanderhye P.C.
Polyplastics Co. Ltd.
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