JPH04142329A - Production of polycarbonate - Google Patents

Abstract

PURPOSE:To obtain a colorless and transparent high-molecular weight polycarbonate at good efficiency by melting a starting monomer mixture in a preparation tank, polycondensing the monomer mixture in a tank reactor and increasing the viscosity-average molecular weight on a specified twin-screw extruder. CONSTITUTION:A process for producing a polycarbonate by melt-polycondensing a dihydroxyl compound [e.g. 2,2-bis-(4-hydroxyphenyl) propane] with a bisaryl carbonate (e.g. diphenyl carbonate) by transesrterification, wherein the above monomer are molten in a preparation tank (step 1), the molten monomer mixture is polycondensed in a tank reactor to obtain a polycarbonate of a viscosity- average molecular weight of 5000-30000 (step 2), and a polycarbonate of a viscosity-average molecular weight of 12000-60000 is obtained on a paddle-type self-cleaning twin-screw extruder (step 3). According to the above process, a colorless and transparent high-molecular weight polycarbonate can be produced at good efficiency.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing polycarbonate, and more specifically, a method for producing polycarbonate by melt polycondensing a divalent hydroxy compound and a bisaryl carbonate by a transesterification method. It's about how to do it.

BACKGROUND OF THE INVENTION Polycarbonate is a general purpose engineering thermoplastic that has a wide range of uses, particularly for injection molding or as glass sheets in place of window panes.

Conventionally, interfacial polycondensation methods, transesterification methods, and the like have been applied to the production of these polycarbonates.

Although the interfacial polycondensation method is generally effective in producing polycarbonate, it has drawbacks such as the use of toxic phosgene and the fact that chlorine ions remain in the polycarbonate produced. In order to eliminate these drawbacks, a method for manufacturing polycarbonate by using liquid trichloromethyl chloroformate, which is a dimer of phosgene, instead of toxic phosgene, and carrying out an interfacial polycondensation reaction with a special dihydric phenol has been disclosed. It is disclosed in Publication No. 182336/1983. However, as a special dihydric phenol, 9
, 9-bis(4-hydroxyphenyl)fluorenes. In addition, a method for obtaining polycarbonate from 2,2-bis(4-hydroxyphenyl)propane using triphosgene instead of toxic phosgene was described by Angew, Chew+ (Angepante.
Hemi) similar, 922 (1987), German patent 063
440141, a reaction mechanism in which phosgene is generated has also been proposed.

In the transesterification reaction, a transesterification catalyst is added to diphenyl carbonate and an aromatic dihydroxy compound, and a prepolymer is synthesized while distilling phenol under heating and reduced pressure.Finally, the prepolymer is heated to 290"C or higher under high vacuum. phenol is distilled off to obtain high molecular weight polycarbonate (U.S. Pat. No. 4,345,062).
However, unlike other engineering plastics, high-molecular-weight polycarbonate has an extremely high melt viscosity, so it requires a high temperature of 290°C or higher as a reaction condition, and a high vacuum is required to distill off phenol, which has a high boiling point. (10-2 Torr), it is difficult to industrialize from the equipment standpoint, and it is also known that residual phenol in the polycarbonate produced has an unfavorable effect on hue and physical properties.

However, since the transesterification method can carry out the reaction by melt polycondensation and is an industrially economical method, various studies have been made. In particular, as the polycondensation reaction approaches completion, the viscosity of the reaction system increases, so attempts have been made to use various types of equipment to handle highly viscous reaction products. For example, Tokuko Sho 52-361
No. 59, JP-A-2-86618, JP-A-2-
Nos. 153923 to 153927 and the like are disclosed. In Japanese Patent Publication No. 52-36159, an intermeshing twin-screw extruder with a screw evaporator is used.
It has the disadvantage that black foreign matter is easily generated in the retention area of the screw groove, and it is difficult to control the retention time to efficiently remove the degree of coloration of the product due to thermal history and distillates such as by-product phenol. There are some difficulties in doing so.

In addition, in JP-A-2-153923 to 153927, a horizontal stirring polymerization tank is used, but although the hold amplifier can be increased, the liquid thickness becomes large and phenol, etc. produced as a by-product from the high viscosity reaction liquid is distilled out. This becomes rate-limiting, and as a result, it is necessary to lengthen the residence time. Therefore, exposure to thermal history at high temperatures causes coloring of the reaction product.

These methods cannot be said to be sufficient as methods for producing colorless and transparent polycarbonate industrially and efficiently.

Therefore, an object of the present invention is to overcome the drawbacks of the conventional method for producing polycarbonate by transesterification reaction and to provide a method for efficiently producing polycarbonate that is colorless and transparent and has a high molecular weight.

[Means to solve the problem]

The present inventors have discovered that in a method for producing polycarbonate, the reaction is carried out in a tank-type reaction tank, a horizontal polymerization machine, and a paddle-type self-cleaning twin-screw extruder, and the viscosity average molecular weight is increased stepwise, resulting in colorless and transparent polycarbonate. They have discovered that high molecular weight polycarbonate can be efficiently produced using the method, and have completed the present invention.

That is, the present invention provides a method for producing polycarbonate by melt polycondensing a divalent hydroxy compound and a bisaryl carbonate by a transesterification method, in which the above monomer is melted in a regulating tank as a first step, and the monomer is melted as a second step. Polycondensation reaction is performed in a tank-type reaction tank while the mixture is melted to obtain polycarbonate having a viscosity average molecular weight of 5,000 to 30,000, and then at least one paddle-type self-cleaning twin-screw extruder is used as the third step. A method for producing polycarbonate, characterized in that a polycarbonate having a viscosity average molecular weight of 12,000 to 60,000 is obtained, and after the first step, a polycondensation reaction is carried out in a tank-type reaction tank while melting the monomer mixture as a second step. to produce a polycarbonate prepolymer with a viscosity average molecular weight of 5,000 to 20,000, and as a third step, the polycondensation reaction of the prepolymer obtained in the second step is further carried out in a tank-type reaction tank or horizontal polymerization machine to increase the viscosity. After obtaining a polycarbonate having an average molecular weight of 10,000 to 30,000, the fourth step is to use at least one paddle type self-cleaning twin screw extruder to obtain a polycarbonate having a viscosity average molecular weight of 12,000 to 60,000. The present invention provides a method for producing polycarbonate.

Examples of divalent hydroxy compounds used in the present invention include the following general formulas (I), (II), (I[[)
Or a compound represented by (IV) can be mentioned.

R.

(In the formula, R+, Rz, Ri, R4, and Rs each represent a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, or a phenyl group, X represents a halogen atom, and n = o ~ 4, +a = 1 to 4.) Specifically, 2,2-bis-(4-hydroxyphenyl)
Propane, 2,2-bis-(4-hydroxyphenyl)
Butane, 2,2-bis-(4-hydroxyphenyl)-
4-methylpentane, 2,2-bis-(4-hydroxyphenyl)octane, 4,4'-dihydroxy-2,2
, 2-triphenylethane, 2.2-bis-(3,5-
dibromo-4-hydroxyphenyl)propane, 2,2
-bis-(4-hydroxy-3-methylphenyl)propane, 2,2-bis-(4-hydroxy-3-isopropylphenyl)propane, 2,2-bis-(4-hydroxy-5-sec, butylphenyl) Propane, 2.2-
Bis-(3,5-dimethyl-4-hydroxyphenyl)
Propane, 2,2-bis-(4-hydroxy-3-tert-butylphenyl)propane, 1,1'-bis-
(4-hydroxyphenyl)-P-diisopropylbenzene, 1,1゛-bis=(4-hydroxyphenyl)-
Examples include m-diisopropylbenzene, l11-bis-(4-hydroxyphenyl)cyclohexane, and the like.

Furthermore, it is also possible to produce a copolymerized polycarbonate by combining two or more of these divalent hydroxy compounds.

Bisaryl carbonates used in the present invention include diphenyl carbonate, bis(2,4-dichlorophenyl) carbonate, bis(2,4,6-dolychlorophenyl) carbonate, and bis(2-cyanophenyl) carbonate.
carbonate, bis(0-nitrophenyl) carbonate, ditolyl carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate, and the like. Preferably it is diphenyl carbonate.

Further, in the present invention, a polymerization catalyst can be used if desired, and a normal transesterification catalyst can be used as the polymerization catalyst.

Typical examples of transesterification catalysts that can be used in the present invention include (a) catalysts similar to metal-containing catalysts such as lithium borohydride, sodium borohydride, potassium borohydride, rubidium borohydride, Cesium boron, beryllium borohydride, magnesium borohydride, calcium borohydride, strontium borohydride, barium borohydride, aluminum borohydride, titanium borohydride, tin borohydride,
Germanium borohydride, lithium tetraphenoxy, potassium tetraphenoxy, potassium tetraphenoxy, tetraphenoxyrubidium, tetraphenoxycesium, sodium 1,000 sulfate, beryllium oxide, magnesium oxide, tin(IV) oxide, dibutyltin oxide, beryllium hydroxide, water Magnesium oxide, germanium hydroxide, beryllium acetate, magnesium acetate, tin acetate (■), germanium acetate, lithium carbonate, sodium carbonate, potassium carbonate, beryllium carbonate, magnesium carbonate, tin carbonate (■), germanium carbonate, tin nitrate (
(2), germanium nitrate, antimony dioxide, bismuth trimethyl carboxylate, etc.

et al.) As a catalyst similar to an electron-donating amine compound, N
, N-dimethyl-4-aminopyridine, 4-diethylaminopyridine, 4-aminopyridine, 2-aminopyridine, 2-hydroxypyridine, 2-methoxypyridine,
4-methoxypyridine, 4-hydroxypyridine, 2-
Examples include dimethylaminoimidazole, 2-methoxyimidazole, 2-mercaptoimidazole, aminoquinoline, imidazole, 2-methylimidazole, 4-methylimidazole, diazabicyclooctane (DABCO), and the like.

Further, (C) carbonate, acetic acid, formic acid, nitric acid, nitrous acid, oxalic acid, fluoroboric acid, hydrofluoride, etc. of the above-mentioned electron-donating amine compounds can be mentioned.

(d) Catalysts similar to electron-donating phosphorus compounds include triethylphosphine, tri-n-propylphosphine,
triisopropylphosphine, tri-n-butylphosphine, triphenylphosphine, tri-〇-dimethoxyphenylphosphine, tri-p-1 lylphosphine, tri-o-tolylphosphine, tributylphosphine,
Examples include triphenylphosphite, tri-P-)lylphosphite, tri-p-1lylphosphine, and the like.

Furthermore, (e) catalysts similar to borane complexes include complexes of borane and the following compounds, namely ammonia, dimethylamine, trimethylamine, triethylamine, t-
Butylamine, dimethylaniline, pyridine, dimethylaminopyridine, morpholine, piperazine, virol,
Tetrahydrofuran, dimethyl sulfide, tri-n-
Examples include complexes with butylphosphine, triphenylphosphine, triphenylphosphite, and the like.

These catalysts may be used alone or in combination of two or more, and the amount used is usually in the range of lXl0-' to 1 mol based on the divalent hydroxy compound. , preferably 5X10-S to 5X10-
If the amount of catalyst used is less than 1xio-mol, the polymerization rate will be slow and cause coloring. Moreover, if it exceeds 1 mol, the catalyst remaining in the obtained polycarbonate becomes a factor that adversely affects the physical properties, for example, decreases in mechanical properties.

In the present invention, a two-stage reaction system is generally used as a method for producing polycarbonate by a transesterification method using a divalent hydroxy compound and a bisaryl carbonate. That is, the first stage reaction involves transesterification of the raw materials in the presence of a transesterification catalyst to produce a relatively low molecular weight polycarbonate in a molten state, and the polymerization is further advanced under high viscosity to produce the desired high molecular weight polycarbonate. This is the second stage reaction to obtain.

The reaction temperature in the first stage reaction is 100°C or higher
℃ or less, preferably 130°C or more and 280°C or less. If the reaction temperature is less than 100°C, the reaction rate will be slow, and if it exceeds 300°C, side reactions will likely occur. After removing predetermined phenol and other distillates under reduced pressure, a second stage reaction is carried out to further increase the molecular weight.

The reaction temperature in the second stage reaction is 180'C or more 35
The temperature is 0°C or less, preferably 200°C or more and 320'C or less. If the reaction temperature is less than 180°C, it will be difficult to remove phenol, etc. to increase the molecular weight, and 35
If the temperature exceeds 0°C, coloring of the resin and side reactions will be promoted, which is not desirable. Furthermore, this reaction is preferably carried out under high vacuum, with a degree of vacuum of 10 Torr or less, preferably I Torr or less.

Further, as for the timing of adding the catalyst, it is also possible to use appropriate catalysts for the initial charge or for the first-stage reaction and the second-stage reaction.

Further, details of the manufacturing method of the present invention will be explained, but the manufacturing method of the present invention is not limited thereto.

l] Shinjiguchi - First, the first step can be carried out in a general stirring tank, and the stirring tank is an adjustment tank for melting and dissolving the divalent hydroxy compound and bisaryl carbonate, etc., which are raw material monomers. It is.

The second step may be carried out either batchwise or continuously. When the reaction is carried out in a batchwise manner, the reaction may be carried out using one tank-type reaction vessel equipped with a conventional stirrer, or a plurality of such reaction vessels may be used to carry out the reaction. The agitator is equipped with turbine blades, paddle blades, anchor blades, helical ribbon blades, and improved types of these blades. Particularly preferred from the viewpoint of molecular weight distribution and thermal history are helical ribbon blades or blades used in high-viscosity seed types of improved types thereof. However, since the viscosity of the reaction product increases in the later stages of the reaction, a tank-type reaction tank equipped with a paddle, lattice blade, hemi-cone blade, etc. as a stirrer for higher viscosity is also suitable. In the second step, a transesterification catalyst is added while the divalent hydroxy compound and bisaryl carbonate are melted as raw material monomers in the tank-type reaction tank under nitrogen purging, and the temperature is gradually raised as the reaction progresses. In addition, by-product phenols are removed by gradually reducing the pressure. When removing by-products such as phenol, the reaction tank is preferably equipped with a distillation column in order to avoid as much as possible the raw materials in the system from being distilled off to the distillate side. Further, the production method of the present invention also includes a heat supply method in which a draft tube or the like is installed in the reactor in order to compensate for the lack of heat due to the latent heat of vaporization during the removal of by-products such as phenol.

Reaction temperature is 130°C ~ 300"C1 vacuum degree is 400
A range of Torr to 0.5 Torr is preferred. The viscosity average molecular weight of the polycarbonate obtained in the second step is 50
00-30000.

The third step is a step of increasing the molecular weight of the polycarbonate obtained in the second step.

In the third step, the viscosity of the reaction mixture is very high and special polycondensation equipment is required in the post-polycondensation step to synthesize high molecular weight polymers. Traditionally, as an applicable device (mandatory)
High-viscosity processing equipment such as thin-film evaporators and horizontal two-wheel polymerization machines are used, but they generate black scorched foreign matter and require a relatively long residence time to achieve high molecular weight, so they are not always sufficient. It is difficult to obtain a polycarbonate polymer with a high molecular weight, and it is difficult to say that it is industrially effective.In the present invention, the above-mentioned drawbacks are solved by using at least one paddle-type self-cleaning twin-screw extruder in the third step. can be overcome. In contrast to a screw, the paddle shape refers to a blade that is discontinuous (that is, the valley part of the blade is not continuous and connected), and includes a convex lens type or a pseudo-triangular shape, but is not limited to these. do not have. In addition, the cell cleaning function is a pair of left and right paddles built into two shafts that are out of phase, maintaining a constant minute gap so that the tip of one paddle cleans the side of the other paddle. It is brought about by rotating while moving. Normally L/D=1~
35 (L is the length of the jacket, D is the rotating diameter of the paddle)
In the range, preferably L/D=1 to 20. However, the present invention is not necessarily limited to this.

The reaction temperature in the third step is usually 200'C to 320'C.
℃, and the degree of vacuum is I Torr~0. It is in the range of I Torr.

Residence time is 0.2-2 hours, preferably 0.4-1.0
It is time, and it is something that is manipulated continuously.

As the surface of the reaction mixture is renewed within the system, by-products such as phenol are removed from a distillation port connected to the vacuum system. The viscosity average molecular weight of the polycarbonate obtained in the third step is 12
000 to 60000.

1 Exclusion fil In another method of the present invention, the first step is the manufacturing method (1)
The second step is to perform a polycondensation reaction in a tank-type reaction tank while melting the monomer mixture to produce a polycarbonate prepolymer having a viscosity average molecular weight of 5,000 to 20,000. As a step, the polycondensation reaction of the prepolymer obtained in the second step is further carried out in a tank-type reaction tank or horizontal polymerization machine until the viscosity average molecular weight is 10.
A polycarbonate having a molecular weight of ooo to 30,000 is obtained.

The second step of this method may be carried out either batchwise or continuously, similarly to the second step of production method (1). When the reaction is carried out in a batchwise manner, the reaction may be carried out using one or more tank-type reaction vessels equipped with a conventional stirrer as described above. The agitator is equipped with turbine blades, paddle blades, anchor blades, helical ribbon blades, and improved types of these blades. The viscosity average molecular weight of the polycarbonate prepolymer obtained in the second step is 5000~
It is 20,000.

Next, as a third step, the polycondensation of the polycarbonate polymer obtained in the second step is further carried out in a tank-type reaction tank or a horizontal polymerization machine. A tank-type reaction tank similar to that used in can be used. However, as a stirrer for higher viscosity, there is a paddle-shaped stirrer.
Tank-type reactors with lattice airfoils, hemi-cone airfoils, etc. are also suitable. Moreover, in this method, a horizontal polymerization machine can also be used. Here, a horizontal polymerization machine has one or two horizontal rotating shafts, and these have a disk type, bottle type,
It has glasses-shaped, wheel-shaped, etc. wings, and usually has a residence time of 1 hour or more, and is a high-hold type among horizontal types. The reaction temperature in the third step is 200”C~
320'C, vacuum degree 10 Torr - 0.5 Torr
A range of r is preferred. The viscosity average molecular weight of the polycarbonate obtained in the third step is in the range of 10,000 to 30,000.

The fourth step is a step in which the polycarbonate obtained in the third step is made to have a higher molecular weight, using at least one paddle-type self-cleaning twin-screw extruder as in the third step of production method (1), A polycarbonate having a viscosity average molecular weight of 12,000 to 60,000 is obtained by carrying out the reaction under similar conditions.

〔Example〕

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Bisphenol A 4566 g (20 mol), diphenyl carbonate 4392 g (20.5 mol), 4
-dimethylaminopyridine 4.88 g (0.04 mol) and sodium acetate 0.033 g (0.00
04 mol) was placed in a seed-shaped stirring tank 201, and after purging with nitrogen, the temperature was raised to 180°C and dissolved.

Next, 20! equipped with a distillation column! The above monomer mixture is supplied to a tank-type reaction tank, and the temperature is gradually raised from 180°C to 260°C, and the pressure is reduced to 2 Torr, and by-produced phenol is distilled off. After about 4 hours, the viscosity average molecular weight 13
000 polycarbonate prepolymer was obtained.

Furthermore, with a gear pump, the temperature is 280°C and the pressure is 0.2 To.
Paddle type self-cleaning twin-screw extruder controlled by rr (L/D=8.9, paddle rotation diameter 50cm)
, shaft length 445, 5 m), and discharged using a gear pump at 850 g/Hr. The residence time is approximately 45 minutes. Viscosity average molecular weight (Mv) of the obtained polycarbonate
When measured, Mv = 28,000.

Further, the hue was A38O-A580=0.110.

Here, the method for measuring the viscosity average molecular weight is to measure the intrinsic viscosity [η1 of a methylene chloride solution at 20°C using an Ubbelohde viscometer, and calculate the viscosity average molecular weight (Hν
) was calculated.

[77] = 1.11X10-'(Mv)""Also, to evaluate the hue, use a 10% methylene chloride solution of polycarbonate, and measure the difference in absorbance in the 380- and 580-In wavelength regions using a Uv@ constant device. The larger the value, the more colored it is.

Example 2 In Example 1, after obtaining a polycarbonate prepolymer with a viscosity average molecular weight of 13,000, this polycarbonate prepolymer was transferred to a 20 f tank type reaction tank using a gear pump, and further polycondensed at a temperature of 280 ° C. and a pressure of I Torr. proceeded with the reaction. At this stage, the viscosity average molecular weight of the polycarbonate was 20,000.

Furthermore, with a gear pump, the temperature is 280°C and the pressure is 0.2 To.
The above polycarbonate was fed into a paddle type self-cleaning twin-screw extruder (L/D = 8.9, paddle rotation diameter 50 heel, shaft length 445.5 mm) controlled at 800 g/Hr using a gear pump. Exhausted. The residence time is approximately 45 minutes. When the viscosity average molecular weight Uv) of the obtained polycarbonate was measured, it was Mv-
It was 27,000. Also, the hue is A38O-A580
=0.101.

Example 3 In Example 2, 3.28 g of 2-methylimidazole was used instead of 4-dimethylaminopyridine as a catalyst.
In fact, under the same preparation conditions as in Example 2 except that (0.04 mol) was used, a polycarbonate prepolymer with a viscosity average molecular weight of 14,000 was obtained in the tank-type reaction tank used in Example 2, and then further processed with a gear pump. Polycondensation was further carried out in a similar seed-type reaction layer to obtain a polycarbonate having a viscosity average molecular weight of 18,000.

Next, this reaction mixture was pumped using a gear pump at a temperature of 280°C.
Feed into a paddle-type self-cleaning twin-screw extruder controlled at a pressure of 0.2 Torr and produce 900 g/H.
Discharge was carried out using a gear pump.

The viscosity average molecular weight of the obtained polymer was 29,000. Also, the hue is A380- A380 = 0.10
It was 5.

Example 4 After obtaining a polycarbonate prepolymer with a viscosity average molecular weight of 14,000 in a tank-type reaction tank under the same charging conditions as in Example 2, this was further charged into a horizontal polymerization machine using a gear pump under the conditions of a temperature of 280° C. and a pressure of I Torr. Perform the reaction below,
After obtaining polycarbonate with a viscosity average molecular weight of 20,000, the temperature was 280°C and the pressure was 0.2 Torr using a gear pump.
The polymer was fed into a paddle type self-cleaning twin-screw extruder controlled at 900 g/l (r) and discharged at 900 g/l (r).
Met.

Moreover, the hue was A380-A380=0.102.

Comparative Example 1 After obtaining polycarbonate under the same conditions as in Example 2, this polycarbonate was further fed into a horizontal twin-screw polymerization machine instead of the paddle-type self-cleaning twin-screw extruder, and was heated at a temperature of 280° C. and a pressure of 0.2 Torr. 800g under conditions
/Hr using a gear pump. The residence time was about 3 hours, and the viscosity average molecular weight of the obtained polymer was 2200.
It was 0.

Moreover, the hue was A380-A380=0.27.

Comparative Example 2 After obtaining polycarbonate under the same conditions as in Example 2, the polycarbonate was further fed into a screw evaporator instead of the paddle-type self-cleaning twin-screw extruder.
900g/H under the conditions of 300℃ and pressure 0.2Torr
It was discharged using a gear pump. The residence time was about 10 minutes, and the viscosity average molecular weight of the obtained polymer was 24,000. Also, the hue is A380-A380 = 0.
50, black burnt-like material was observed locally.

〔Effect of the invention〕

According to the present invention, a colorless, transparent, high molecular weight polycarbonate can be efficiently produced.

Claims (1)

[Claims] 1. A method for producing polycarbonate by melt polycondensing a divalent hydroxy compound and a bisaryl carbonate by a transesterification method, in which the monomer is melted in a regulating tank as a first step, and as a second step. A polycondensation reaction is performed in a tank-type reaction tank while the monomer mixture is melted to obtain a polycarbonate having a viscosity average molecular weight of 5,000 to 30,000, and then the third step is to use at least one paddle-type self-cleaning twin-screw extruder. A method for producing polycarbonate, characterized in that a polycarbonate having a viscosity average molecular weight of 12,000 to 60,000 is obtained using the method. 2 In a method for producing polycarbonate by melt polycondensing a divalent hydroxy compound and a bisaryl carbonate by transesterification, the first step is to melt the above monomer in a regulating tank, and the second step is to melt the above monomer mixture. A polycondensation reaction is carried out in a tank-type reaction tank to produce a polycarbonate prepolymer having a viscosity average molecular weight of 5,000 to 20,000, and as a third step, the polycondensation reaction of the prepolymer obtained in the second step is further subjected to a tank-type reaction. Proceed in a tank or horizontal polymerization machine, and the viscosity average molecular weight is 10,000.
After obtaining polycarbonate with a viscosity average molecular weight of 12,000, the fourth step is to use at least one paddle type self-cleaning twin screw extruder to obtain a polycarbonate with a viscosity average molecular weight of 12,000.
60,000 polycarbonate.