Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-06-29
2001-05-15
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
06232432
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of polycarbonates, more specifically to a process for the preparation of polycarbonates through solid-state polymerization of a prepolymer from aromatic dihydroxides and diarylcarbonates, which comprises
a) preparing a prepolymer having a viscosity average molecular weight from 4,000 to 18,000 g/mole;
b) preparing microporous prepolymer foams by introducing a high-pressure inert gas; and
c) preparing polycarbonates by a solid-state polymerization,
which facilitates the removal of phenol, a by-product, and enhances molecular weight of polycarbonates without using any catalyst due to the relatively high polymerization.
Polycarbonates are widely used in the manufacture of transparent sheets, packaging materials, bumpers for automobiles and compact discs due to its superior transparency, impact resistance, mechanical strength and heat resistance.
Polycarbonates are generally prepared by an interfacial polymerization, where polycarbonates are generated by vigorously mixing aqueous bisphenol-A solution substituted with sodium with a phosgene-containing organic solution. However, this method has the drawbacks that the phosgene used as a starting material is a toxic gas and the solvent used in the polymerization is a chlorine-containing organic solvent that can pollute the air. Moreover, the excessive amount of water used in the production of polycarbonates even after the polymerization requires a further purification of said polycarbonates. A melt polymerization method, which prepares polycarbonates by direct polymerization of monomers without using solvent, has been introduced to solve the above problems. However, the melt polymerization method is also disadvantageous in that it requires not only such a reaction condition of high temperature and high vacuum to remove phenol, by-product but special apparatus also to stir high viscose reaction mixture to obtain the high molecular weight polycarbonates.
A solid-state polymerization method was disclosed in U.S. Pat. Nos. 5,266,659 and 5,717,056 as a way to remedy the melt polymerization method, where a melt polymerization is terminated at a state with a low viscosity to generate solid particles and said particles are allowed to undergo a polymerization while maintaining the solid state. However, the solid-state polymerization method, which requires a reaction between solid-state prepolymers with high molecular weight as well as the easy removal of a reaction by-product, does not appear plausible because its low polymerization rate results in a poor productivity. A catalyst can be added to increase the above polymerization rate in the solid-state polymerization; however, the method using a catalyst is not only costly but can also deteriorate the properties of polycarbonates due to the residues of said catalyst in the final polymers. U.S. Pat. Nos. 4,948,871 and 5,204,377 disclosed the processes of preparing polycarbonates without using a catalyst by a solid-state polymerization at a temperature over 200 by preparing prepolymer from bisphenol-A and diphenylcarbonate, crystallizing in solvents such as acetone and toluene and maintaining the prepolymer in a solid-state to facilitate the easier remove of phenol, a reaction by-product. However, this method also has a low rate of the reaction.
As shown above, the conventional preparation methods of polycarbonates have been shown to have a rather slow reaction rate and be not suitable for the easier removal of the by-product, thus necessitating an urgent emergence of a new version of polycarbonate preparation method.
SUMMARY OF THE INVENTION
To solve said problems, the present invention was performed as follows: a) preparing a prepolymer with a specific viscosity average molecular weight by reacting aromatic dihydroxides with diarylcarbonates; b) preparing prepolymer foam by introducing high-pressure inert gas and discharging the prepolymer by means of a solidification; and c) performing a solid-state polymerization.
Accordingly, an object of this invention is to provide a process of preparing polycarbonates through a solid-state polymerization, wherein the removal of phenol, a by-product, is facile and said polymerization progresses rapidly in the absence of a catalyst.
DETAILED DESCRIPTION OF THE INVENTION
The present invention for preparing polycarbonates by crystallizing a prepolymer synthesized from aromatic dihydroxides and diarylcarbonates and performing a solid-state polymerization comprises the following steps:
a) preparing a prepolymer having a viscosity average molecular weight of 4,000-18,000 g/mole by the melt polymerization of aromatic dihydroxides and diarylcarbonates;
b) preparing a prepolymer foam having a specific gravity of 0.5-1.15 by introducing high-pressure inert gas, stirring and then draining the prepolymer;
c) preparing a solid particle with a crystallinity of 10-50% by crushing the prepolymer foam to the average size of 0.1-2 mm and stirring in the solvent; and
d) preparing polycarbonates by performing a solid-state polymerization of the solid particles at a temperature of 190-240.
The detailed description of the present invention is given hereunder.
The present invention relates to a process for the preparation of polycarbonates by preparing microporous foams and transforming the same to solid particles for a solid-state polymerization, and removing the phenol, a by-product, to enhance the reaction rate in the absence of a catalyst.
The concrete description of the present method of preparing polycarbonates is given hereunder.
The first step is to prepare a prepolymer by polymerizing aromatic dihydroxides expressed in the following formula (1) and diarylcarbonates through a melt polymerization method,
HO—Ar
1
—Z—Ar
2
—OH (1)
wherein
a) Ar
1
and Ar
2
represent the same or different phenyl group or its derivatives; and
b) Z represents a single bond or —O—, —CO—, —S—, —SO
2
—, —SO—, —CON(R
1
)— or —C(R
2
R
3
)— linkage; R
1
, R
2
and R
3
repsectively represents H or —(CH
2
)
n
CH
3
; and n is an integer in the range of 0-4.
Polycarbonate prepolymer having a viscosity average molecular weight of 4,000-18,000 g/mole is prepared by reacting 1-1.2 molar equivalents of diarylcarbonates with 1 molar equivalent of the aromatic dihydroxide in the vacuous melt-state. If the molar equivalence of the diarylcarbonates is smaller than 1, or if it exceeds 1.2, it becomes difficult to obtain a high-molecular-weight product.
Especially, if the viscosity average molecular weight of the prepared prepolymer is smaller than 4,000 g/mole, it is difficult to obtain a prepolymer foam; on the other hand, if it exceeds 18,000 g/mole, it becomes difficult to obtain fine particles. Also, the molar ratio of the phenyl and hydroxyl end groups in the prepolymer plays an important role in increasing molecular weight during a solid-state polymerization. The molar ratio of end phenyl/hydroxyl group of the intermediate is preferred to be in the range of 90/10-10/90, and if it is beyond this range, it is difficult to obtain polycarbonates with a high molecular weight.
The second step is to prepare microporous foams having 0.5-1.15 of specific gravity by a) introducing a high-pressure (1-20 atm) inert gas into the prepolymer melt and stirring the same for 1-200 min; and b) releasing the high pressure and ejecting the same with cooling. If the porosity in the foam is excessive, the specific gravity becomes lower than 0.5, and therefore the particle becomes brittle; on the other hand, if the specific gravity exceeds 1.15, the molecular weight does not become high enough during a solid-state polymerization.
The third step is to obtain solid particles having 10-50% of crystallinity by crushing the foam; sieving the same to 0.1-2 mm; and stirring the same in a solvent for 5-120 min; drying the same in an oven. If the particle size is smaller than 0.1 mm, partial fusion tends to occur during a solid-state polymerization; otherwise if the particle size exceeds 2 mm, the polymerization
Choi Il Seok
Choi Kil-Yeong
Ko Young Chan
Lee Jae Heung
Lee Sung-Goo
Boykin Terressa M.
Korea Research Institute of Chemical Technology and S-Oil Corpor
McGuireWoods LLP
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