Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2001-07-11
2002-07-23
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
06423812
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process of preparing polycarbonates and more particularly, to the process of preparing polycarbonates through a melt polymerization reaction of a dihydroxy compound with a diarylcarbonate, wherein said melt polymerization is performed in the presence of a mixed catalyst composed of an oxygen (O) or sulfur (S) containing compound having lone-pair electrons and an alkali metal or alkaline earth metal salt in an appropriate ratio at a reduced temperature by accelerating a reaction rate to obtain high quality polycarbonates with higher than 15,000 g/mole of a viscosity average molecular weight and improved color.
Polycarbonates are known to have excellent properties in terms of transparency, impact resistance, mechanical strength and heat resistance, and thus have been widely used in industry in manufacturing transparent sheets, packaging materials, vehicle bumpers, compact discs and the like.
A representative preparing method of polycarbonates is an interfacial polymerization employing aqueous bisphenol A(BPA) solution substituted with sodium and a phosgene-containing organic solution. However, there are some disadvantages regarding to safety and ecological problems in that the phosgene used as a starting material and a chlorine-containing organic solvent used in the polymerization are extremely toxic. Furthermore, it requires excessive use of water to wash off the remaining chlorine-containing salts and un-reacted reactants after the polymerization.
A melt polymerization method, which produces polycarbonates by direct polymerization of starting materials in melt state under vacuum without using any solvents, has been introduced to solve the above problems. This method has several advantages over the above-mentioned interfacial polymerization in that it is possible to lower manufacturing cost, pelletize produced polycarbonate directly without any other treatment, and perform relatively simple apparatus.
Generally, the melt polymerization is carried at a temperature of 180-350° C. If the reaction temperature is lower than 180° C., it is difficult to remove phenol produced as a by-product during the polymerization thus resulting in polycarbonates with low molecular weight. On the other hand, if it is higher than 350° C., a by-product, which changes the product to a yellow color, can be generated or decomposition of the product may occur. Although it is known that the melt polymerization can be carried in the absence of a catalyst, it has to be exposed for a prolonged time at an elevated temperature of over 280° C. to complete the reaction. So the use of an effective polymerization catalyst is critical to attain high quality polycarbonate.
Theoretically, it is required to use the same molar amounts of hydroxyl group in bisphenol A and ester group in diphenylcarbonate to obtain high molecular weight of polycarbonates. However, because diphenylcarbonate is more volatile than bisphenol A, a little more diphenylcarbonate than bisphenol-A is desirable to obtain polycarbonates with superior physical properties. Generally, the molar ratio of diphenylcarbonate/bisphenol A is within the range from 1.0 to 1.3.
There have been many prior arts disclosing the melt polymerization to prepare polycarbonates by using a catalyst (U.S. Pat. No. 5,221,761 (1993), EP Patent No. 584801 (1993), and JP Patent Publication Nos. 7-003003 (1995) and 3-174443). Previously, the melt polymerization was performed employing a catalyst used in esterification or ester exchange reaction: (i) an alkali metal or alkali earth metal oxide or hydroxide; (ii) an alkali metal or alkali earth metal organic acid of inorganic acid; (iii) a sodium or potassium salt of phenol or bisphenol A; and (iv) an organic phosphorus and the like. Besides these catalysts, a nitrogen- or phosphorus-containing basic compound has been recently used as a catalyst as shown in U.S. Pat. No. 5,142,018. However, the process of preparing polycarbonates employing the catalyst mentioned above has posed serious problems in that the reaction requires a high reaction temperature and prolonged reaction time and the product assumes a yellow color.
Consequently, development of novel catalysts is highly required in order to produce high quality polycarbonates having improved color at a reduced temperature within a short period of time.
SUMMARY OF THE INVENTION
To solve aforementioned problems of the conventional melt polymerization methods of preparing polycarbonates in the presence of the catalyst, the present invention was completed by performing the melt polymerization in the presence of a mixed catalyst composed of a oxygen (O) or sulfur (S) containing compound having lone-pair electrons and an alkali metal or alkaline earth metal salt in an appropriate ratio.
Consequently, an object of this invention is to provide a method of preparing polycarbonates by using the mixed catalyst, which expedites the rate of the polymerization at a low temperature to the production of polycarbonates with high quality and improved color.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process of preparing polycarbonates by melt polymerization of aromatic dihydroxy compound and diarylcarbonate in the presence of the catalyst, the present invention is characterized by using the mixed catalyst mixed in molar ratio of from 20:1 to 1:20 of an oxygen (O) or sulfur (S) containing compound having lone-pair electrons and an alkali metal or alkaline earth metal salt to produce high quality polycarbonates.
The present invention is described in detail as set forth hereunder.
The present invention relates to a process of preparing high quality polycarbonates with improved color tone by employing the mixed catalyst, which can expedite the rate of the polymerization at a low temperature.
The catalyst used in the present invention comprises a compound having lone-pair electrons of oxygen (O) or Sulfur (S) and an alkali metal or alkaline earth metal salt. The compound having lone-pair electrons in the catalyst provides excellent activity in the melt polymerization by incorporating with an alkali metal or alkaline earth metal salt. But when the compound having lone-pair electrons is used alone or when the alkali metal or alkaline earth metal salt is used alone, there is no significant catalytic activity increase in the polymerization and the polymerization rate is similar to that of the reaction performed without any catalyst. However, when the compound having lone-pair electrons is incorporated with an alkali metal or alkaline earth metal salt, it shows a synergy effect in the polymerization. In the preparation of the catalyst, it is prefer to mix to be a molar ratio of the compound having lone-pair electrons to alkali metal or alkaline earth metal salt in the range of from 20:1 to 1:20. If the ratio is below 20:1, the polymerization rate becomes slow. If it exceeds 1:20, it results in color deterioration of the resulting product.
Examples of the compound having lone-pair electrons include oxygen-containing compound, sulfur-containing compound and a mixture thereof. Particular examples of said oxygen-containing compound are tetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,3-dioxepane, 1,3-dioxolan-2-one, tetronic acid, trimethylene oxide, and 1,3,5-trioxane. Particular examples of said sulfur-containing compound are tetrahydrothiophene, tetrahydrothiopyran-4-one, 1,4-thioxane, 1,3-dithiane, 1,3-dithiolane, ethylene trithiocarbonate, tetrahydrothiophen-3-one, thianaphthene, trimethylene sulfide, and 1,3,5-trithiane. Besides these compounds, other oxygen-containing and sulfur-containing compounds having lone-pair electrons can also be used. Particular examples of the alkali metal or alkaline earth metal salt of the present invention include potassium acetate, sodium acetate, rubidium acetate, cesium acetate, calcium acetate, magnesium acetate, zinc acetate and the like. The more-detailed description of the present method of preparing polycarbonates by the melt polymerization of aromati
Choi Il Seok
Choi Kil-Yeong
Kim Cheol-Hyun
Kim Seung-Joo
Ko Young Chan
Boykin Terressa M.
Finnegan Henderson Farabow Garrett & Dunner LLP
Korea Research Institute of Chemical Technology
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