Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2001-07-13
2003-02-25
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S178000, C522S162000, C522S163000, C522S001000, C528S196000, C528S198000
Reexamination Certificate
active
06525109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process of preparing polycarbonates, more specifically to a process of preparing polycarbonates by solid state polymerization using microwave radiation, which comprises steps of preparing polycarbonate prepolymer having a certain range of viscosity average molecular weight; converting said polycarbonate prepolymer into crystalline particles having a certain degree of crystallinity; and producing polycarbonates by solid state polymerization of said crystalline particles by applying microwave radiation. In particular, the use of microwave radiation during solid state polymerization enables to maintain the internal temperature of a reactor uniformly by using the heat produced from the reactants themselves. Consequently, it also drastically reduces melt adhesion among polycarbonate prepolymer particles during solid state polymerization, thus resulting in the production of high quality polycarbonates.
2. Description of the Prior Art
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.
There are generally three different methods in preparing polycarbonates: interfacial polymerization method, melt polymerization method, and solid state polymerization method. In an interfacial polymerization method, polycarbonates are produced by vigorous mixing aqueous bisphenol A(BPA) solution substituted with sodium with a phosgene-containing organic solution. However, this method has not been shown very advantageous in that the phosgene used as a starting material is an extremely toxic gas. In addition, the solvent being used in the polymerization reaction is volatile chlorine containing organic solvent, so that it can pollute the air as well as the working environment. Furthermore, the polycarbonate obtained according to this method shall contain the salts produced during polymerization and remaining un-reacted reactants, which should be washed off with excessive amount of water. After washing, it should be dried again. However, it has been commercially widely used because it has an advantage to produce products having various characters and clear color.
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. In this method, it is quite necessary to remove phenol, a reaction by-product of the polymerization reaction, in order to increase the molecular weight of polycarbonates being produced. However, the viscosity of reaction mixtures also drastically increases and the removal of phenol becomes more difficult as the melt polymerization goes on. Therefore, this method requires a powerful vacuum system sufficient to get rid of phenol from highly viscous reaction mixtures and a facility to stir the viscous reaction mixtures. And further, color of the product becomes deteriorated due to high reaction temperature. Solid state polymerization is a method designed to produce polycarbonates of high molecular weight having high purity and excellent color by polymerizing at reaction temperature below the melting point in solid states, comprising the formation of polycarbonate prepolymers having relatively low molecular weight, converting them into solid particles, and finally producing polycarbonates via solid polymerization (U.S. Pat. Nos. 5,266,659 and 5,717,056).
The solid state polymerization method performs a polymerization by supplying the heat required for the reaction from external sources by electric heater, a heat carrier, or a heating gas. However, these conventional solid state polymerization methods do not seem to deliver the desired heat uniformly enough into the reactor to maintain uniform reaction temperature distribution throughout reaction medium and thus result in either melt adhesion of polycarbonate prepolymer particles due to local overheating or insufficient polymerization rate due to locally reduced reaction temperature. These local melt adhesion and low temperature eventually make unable to obtain high quality polycarbonates.
Consequently, a new method of preparing polycarbonates is highly required in order to produce high quality polycarbonates with high molecular weight that can control the internal temperature of a reactor well and also increase the polymerization rate as compared to that of a conventional solid state polymerization methods of external heating.
SUMMARY OF THE INVENTION
To solve aforementioned problems of the conventional methods of preparing polycarbonates, the present invention was completed by taking preparation steps comprising a) preparing polycarbonate prepolymers having a viscosity average molecular weight of 4,000-18,000 g/mole through conventional interfacial polymerization of dihydroxyaryl compounds and phosgene or melt polymerization of dihydroxyaryl compounds and diarylcarbonates; b) converting said polycarbonate prepolymers into crystalline particles having 5-50% of crystallinity; and c) producing polycarbonates by solid state polymerization of said crystalline particles by applying microwave radiation for heat generation during said solid state polymerization reaction, thus resulting in production of high quality polycarbonates with high molecular weight and high purity within a short period of time.
Consequently, the object of this invention is to provide a method of preparing polycarbonates by solid state polymerization of polycarbonate prepolymers having desired viscosity average molecular weight and crystallinity using microwave radiation instead of external heat sources, which not only expedites the rate of solid state polymerization but also simplifies the process directed to the production of polycarbonates with high quality.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to preparing polycarbonates by solid state polymerization comprising the following steps:
a) preparing polycarbonate prepolymers having a viscosity average molecular weight of 4,000-18,000 g/mole of through conventional interfacial polymerization of dihydroxyaryl compounds and phosgene or melt polymerization of dihydroxyaryl compounds and diarylcarbonates;
b) converting said polycarbonate prepolymers into crystalline particles having 5-50% of crystallinity; and
c) producing polycarbonates by solid state polymerization of said crystalline particles by using microwave radiation.
The detailed description of the present invention is given hereunder.
The present invention relates to a process of preparing polycarbonates having high molecular weights by using microwave radiation wherein the solid state polymerization is conducted not by supplying heat from the external sources but by the heat generated from the inside of polycarbonate prepolymer particles, thus enabling to simplify the polymerization process, controlling the reaction temperature easy, reducing the melt adhesion of polycarbonate prepolymer particles, and increasing the polymerization rate.
The more-detailed description of the present method of preparing polycarbonates is given hereunder.
The first step is to prepare polycarbonate prepolymers having a viscosity average molecular weight of 4,000-18,000 g/mole by performing the interfacial polymerization method, wherein polycarbonate prepolymers are produced by vigorous mixing aqueous bisphenol A(BPA) solution substituted with sodium with a phosgene-containing organic solution or by the melt polymerization, wherein polycarbonate prepolymers are produced by melting dihydroxyaryl compounds and diarylcarbonates at 160-180° C., reacting at an increased temperature of 200-280° C. under atmospheric pressure, and further reacting at vacuum pressure below 1 torr.
The typical reaction conditions for preparing said polycarbonate prepolymers are same as those of conventional int
Choi Il Seok
Choi Kil-Yeong
Kim Cheol-Hyun
Ko Young Chan
Lee Jae Heung
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Korea Research Institute of Chemical Technology
McClendon Sanzal
Seidleck James J.
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