JP2002322267A - Method for producing polycarbonate resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a polycarbonate resin derived from pentacyclopentadecane dimethanol and having an excellent hue by an ester interchange method. SOLUTION: This method for producing a polycarbonate resin comprises subjecting a carbonate diester and pentacyclopentadecane dimethanol compounds represented by general formula (1) and/or general formula (2) (R1 and R2 are each H, a 1 to 10C alkyl, a cycloalkyl, phenyl or a halogen atom) or the pentacyclopentadecane dimethanol compounds represented by general formula (1) and/or general formula (2) and an aromatic dihydroxy compound represented by general formula (3) [(m) and (n) are each an integer of 0 to 4; X is a single bond, CR3 R4 , O, CO, S, SO or SO2 ; R3 and R4 are each H, 1 to 12C alkyl or phenyl; or R3 and R4 may be bound to form a ring] to an ester interchange reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polycarbonate resin having excellent impact resistance, low photoelastic constant, high refractive index and inverse dispersion value, and excellent transparency and heat resistance. This polycarbonate resin can be suitably used for plastic optical materials such as various lenses, prisms and optical disk substrates.

[0002]

2. Description of the Related Art Pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2)
PCPDM) alone or a polycarbonate resin derived from PCPDM and bisphenols is disclosed in
No. 00-302860.

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[0003] The diols represented by the general formulas (1) and / or (2) are generally produced by reducing the corresponding dialdehyde. However, when the reaction does not proceed completely, compounds that remain partially as aldehyde groups are slightly mixed. When polymerization was carried out using PCPDM with the aldehyde group remaining, the polycarbonate resin was liable to be colored during melt polycondensation, and it was difficult to obtain a product having excellent color tone. .

[0004] Further, according to the investigations of the present inventors, it was found that the removal of the hydrogenation catalyst and the eluted metal was incomplete, and that the PCPD
It has also been clarified that the hydroxymethyl group is oxidized when M is distilled, and the aldehyde group-containing compound increases, making it difficult to obtain a sufficiently high-purity product.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a polycarbonate resin having an excellent color tone by a transesterification method. It is an object.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to develop a method for producing a polycarbonate resin which can be used as an optical material by a transesterification method. It has been found that the above object can be achieved by using PCPDM having a carbonyl group content of 500 ppm or less with respect to PCPDM. Further, a diol obtained by performing a reduction reaction in the presence of a hydrogenation catalyst and hydrogen using dialdehyde as a starting material is washed with acidic water having a pH of 0.01 to 5.0 and then purified by distillation to obtain a diol. It has also been found that the generation of aldehyde group-containing impurities due to the oxidation reaction at the time is suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, the present invention provides a pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2), or a pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2) In producing a polycarbonate resin by subjecting pentacyclopentadecane dimethanol and an aromatic dihydroxy compound represented by the general formula (3) to a transesterification reaction with a carbonic acid diester, a carbonyl group contained in pentacyclopentadecane dimethanol is contained. An object of the present invention is to provide a method for producing a polycarbonate resin using pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2) having an amount of 500 ppm or less.

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Embedded image (In the formula, R _{1 to} R ₂ are a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group, a phenyl group, or a halogen atom, and R ₁ and R ₂ may be the same or different. And n represent the number of substituents and are an integer of 0 to 4. X is a single bond,

Embedded image R _{3 to} R ₄ are each a hydrogen atom and a carbon number of 1 to
12 alkyl groups or phenyl groups, and R ₃ and R
₄ may combine to form a ring. )

The PCPDM represented by the general formulas (1) and / or (2) has a carbonyl group content of 500 ppm in the PCPDM derived from a compound contained as an impurity.
Or less, preferably 300 ppm, more preferably 100 ppm
What is less than ppm is used. Such PCP
By using DM, a polycarbonate having an excellent color tone can be obtained.

Here, the content of the carbonyl group contained as an impurity in PCPDM is 430 n of the reaction product of the carbonyl group and 2,4-dinitrophenylhydrazine.
It can be quantified by measuring the absorption spectrum of m.
The compound mainly considered as a detection target is PCPDM.
Is a compound in which a part of the hydroxy group has become an aldehyde group, but it is difficult to selectively quantify the compound. In this determination method, since both ketone and aldehyde are detected as carbonyl groups, in the present invention, the purity of PCPDM is defined not by the amount of aldehyde but by the amount of carbonyl.

The present inventors have found that the content of carbonyl groups is 5
As a method for obtaining PCPDM of not more than 00 ppm, the hydrogenation catalyst contained in the reaction solution is removed by a general method such as filtration, low-boiling substances such as a solvent are separated and distilled, and the obtained crude P is obtained.
After washing by contacting an acidic aqueous solution and then water in a state where CPDM is heated and melted, the crude PC separated from the aqueous layer is washed.
A method has been found for purifying PDM by distillation.

[0011] Further, the main washing is carried out in a solvent insoluble in water with PC.
After dissolving the PDM, the solution was washed by contacting it with an aqueous acidic solution and then with water, a solvent was removed from the crude PCPDM solution separated from the water bath, and a method of purifying the PCPDM by distillation was found. According to these methods, the amount of metal contained in the distillation can be significantly reduced, so that the oxidation reaction during the distillation, that is, the generation of carbonyl can be suppressed.

The solvent used in the above method is preferably one that dissolves PCPDM and easily separates into two layers with water. Specifically, dichloromethane, chloroform, hexanol,
Octanol, methyl propyl ketone, cyclohexanone, methyl isobutyl ketone and the like are preferably used.
Among the above, hexanol and chloroform are particularly preferably used.

When no solvent is used, the temperature at which the PCPDM is heated to a molten state is preferably from 70 to 100 ° C, more preferably from 75 to 85 ° C. PCPDM melts easily at this temperature. When a solvent is used, purification can be carried out at any temperature from the melting point of the solvent to the boiling point of the solvent, but preferably in the range of 5 to 50 ° C.

The acidic aqueous solution used in the present invention has a pH
Those having a pH of 0.01 to 5.0 are preferred, and those having a pH of 0.05 to 5.0.
3.0 is more preferred.

Examples of the acidic aqueous solution for washing the crude PCPDM used in the present invention include aqueous solutions of inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid and aqueous solutions of organic acids such as acetic acid and benzoic acid. Can be used, and there is no particular limitation.

When performing distillation after washing with an acid and water, a primary amine and a phosphite described in Japanese Patent Application No. 11-357530 can be added.
Distillation may be performed without addition.

As the aromatic dihydroxy compound represented by the general formula (3), bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) ) Propane, 2,2-bis (4-hydroxyphenyl) butane,
2,2-bis (4-hydroxyphenyl) octane, bis (4-hydroxyphenyl) phenylmethane, 2,2
-Bis (4-hydroxy-3-methylphenyl) propane, 1,1-bis (4-hydroxy-3-t-butylphenyl) propane, 2,2-bis (4-hydroxy-3
-Bromophenyl) propane, 1,1-bis (4-hydroxyphenyl) cyclopentane, 1,1-bis (4-
(Hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxy-3,3′-dimethylphenyl ether, 4,4'-dihydroxyphenyl sulfide, 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide, 4,4'-dihydroxydiphenyl sulfoxide, 4,4'-dihydroxy-3,3
-Dimethyldiphenylsulfoxide, 4,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxy-
3,3′-dimethyldiphenyl sulfone, 4,4′-
(9-Fluorenylidene) diphenol and the like are preferably used.

Of these, in particular, 2,2-bis (4-
Hydroxyphenyl) propane (hereinafter, referred to as BPA) or 1,1-bis (4-hydroxyphenyl) cyclohexane (hereinafter, referred to as BPZ) is preferable.

The present invention is directed to a homopolymer of PCPDM or a copolymer of PCPDM and an aromatic dihydroxy compound represented by the general formula (3), but further includes another aliphatic dihydroxy compound such as tricyclo [5.2]. 1.0 ^2,6 ] decandimethanol, spiroglycol, ^2,6- decalindimethanol or 1,4
-Cyclohexanedimethanol or the like can be used in combination.

The carbonic diester used in the present invention includes:
Diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate,
Dicyclohexyl carbonate and the like can be mentioned. Among these, diphenyl carbonate is particularly preferred. Further, the chlorine content in diphenyl carbonate, which causes coloring, is preferably 20 ppm or less. More preferably, it is 10 ppm or less. Diphenyl carbonate is used in an amount of 0.97 to 0.9 mol based on a total of 1 mol of the aromatic dihydroxy compound and the aliphatic dihydroxy compound.
It is preferably used in an amount of 1.10 mol, particularly preferably 0.99 to 1.04 mol.

In the production method of the present invention, a known transesterification catalyst is used as a catalyst. Generally, a basic compound is preferable, and specific examples thereof include an alkali metal compound, an alkaline earth compound, and a nitrogen-containing compound.

Specific examples of the alkali metal compound include sodium hydroxide, potassium hydroxide, cesium hydroxide, lithium hydroxide, sodium hydrogen carbonate, sodium carbonate, potassium carbonate, cesium carbonate, lithium carbonate, sodium acetate, and acetic acid. Potassium, cesium acetate, lithium acetate, sodium stearate, potassium stearate, cesium stearate, lithium stearate, sodium borohydride, sodium phenyl borohydride,
Sodium benzoate, potassium benzoate, cesium benzoate, lithium benzoate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, dilithium hydrogen phosphate, disodium phenylphosphate, disodium bisphenol A, disodium salt of bisphenol A, potassium salt Cesium salt, dilithium salt, phenol sodium salt, potassium salt, cesium salt, lithium salt and the like are used.

Specific examples of the alkaline earth metal compound include magnesium hydroxide, calcium hydroxide, strontium hydroxide, barium hydroxide, magnesium hydrogen carbonate, calcium hydrogen carbonate, strontium hydrogen carbonate, barium hydrogen carbonate, and magnesium acetate. , Calcium acetate,
Strontium acetate, barium acetate, magnesium stearate, calcium stearate, calcium benzoate, magnesium phenyl phosphate and the like are used.

Specific examples of the nitrogen-containing compound include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide,
Ammonium hydroxides having alkyl, aryl, alkylaryl groups such as trimethylbenzyl ammonium hydroxide, tertiary amines such as triethylamine, dimethylbenzylamine and triphenylamine, secondary amines such as diethylamine and dibutylamine, propyl Primary amines such as amine and butylamine;
Imidazoles such as 2-methylimidazole and 2-phenylimidazole, or basic salts such as ammonia, tetramethylammonium borohydride, tetrabutylammonium tetraphenylborate, and tetraphenylammonium tetraphenylborate are used.

Further, as the catalyst for producing polycarbonate by using PCPDM alone or in combination with PCDDM and another aliphatic dihydroxy compound, specific examples include a zinc compound, a tin compound, a lead compound, a zirconium compound and a hafnium compound. At least one compound selected from the group consisting of an oxide, a halide, a carboxylate, acetylacetonate, phenoxide, an alkoxide, and a hydride is used as the compound, and the compound may be used alone or as a combination of a plurality of compounds. . Particularly preferred catalysts include zinc acetate, zinc benzoate, zinc acetylacetonate, stannous acetate, stannic chloride,
Dibutyltin oxide, dibutyltin laurate, dibutyltin dimethoxide, lead (II) acetate, zirconium oxyacetate, zirconium acetylacetonate, zirconium chloride, zirconium phenoxide, zirconium butoxide and hafnium acetylacetonate are used.

The above catalyst is used in an amount of 1 mole of the aromatic dihydroxy compound and the aliphatic dihydroxy compound in total.
In an amount of 10 ^-9 to 10 ^-3 mol, preferably 10 ^-8 to 10 ^-5
It is used in molar amounts.

The transesterification according to the present invention can be carried out by a known melt polycondensation method. That is, melt polycondensation is carried out using the above-mentioned raw materials and a catalyst while removing by-products by transesterification under heating or normal pressure or reduced pressure. The reaction is generally carried out in two or more stages.

Specifically, the first-stage reaction is carried out at 120 to 2
0.1 ° C at a temperature of 60 ° C, preferably 180-240 ° C.
The reaction is performed for 5 hours, preferably 0.3 to 3 hours. Next, the reaction temperature is increased while increasing the degree of vacuum of the reaction system, and the reaction of the aromatic dihydroxy compound, the aliphatic dihydroxy compound, and the carbonic acid diester is carried out. Perform a condensation reaction.
The total reaction time is between 3 and 10 hours. Such a reaction may be carried out continuously or batchwise. The reaction apparatus used for performing the above reaction is:
Paddle wing, grid wing,
It may be a horizontal device provided with a stirring blade having excellent surface renewability, such as an eyeglass blade.

[0029]

Hereinafter, the present invention will be described specifically with reference to purification examples, examples, and comparative examples.
The examples are not subject to any restrictions.

The physical properties of the polycarbonates obtained in the following examples were measured as described below. (1) Weight average molecular weight (Mw) in terms of polystyrene: GPC (Shodex GP) using chloroform as a developing solvent
C system 21H). (2) Yellow index (YI): The obtained resin was press-molded into a disk having a thickness of 3 mm, and a color difference meter (Tokyo Denshoku T
C-1800MKZ) to measure the YI value (yellowness). (3) Nickel content: measured by inductively coupled plasma emission spectrometry (SPS-1200VR manufactured by Seiko Instruments Inc.).

(Analytical Method of Carbonyl Group) PCPDM60
mg was dissolved in 5 ml of methanol, and 1 ml was collected in a test tube. In this test tube, 2,4-
Dinitrophenylhydrazine saturated methanol solution 1ml
And 2 drops of concentrated hydrochloric acid.
Heated for 5 minutes, then allowed to cool to room temperature. further,
5ml of methanol and 4ml of 10wt% KOH aqueous solution
Was added to obtain a measurement solution. Here, methanol is
In all cases, those having a carbonyl compound content lower than the detection limit were used. As a blank, methanol subjected to the same operation as the above-mentioned measurement solution was used, and a difference spectrum was measured by a spectrophotometer (JASCO: Ubest 35-10).
The concentration was calculated from a calibration curve using benzaldehyde as a reference substance. The detection limit was 5 ppm. Note that the calibration curve was obtained by determining the relationship between the absorbance and the concentration using a benzaldehyde solution with a known concentration, and then calculating the same mole number of carbonyl groups when the absorbance was the same. That is, concentration [ppm] = (molar number of carbonyl group calculated from absorbance) / (molar number of 60 mg of PCPDM) × 10
Calculated as 6.

Example 1 (PCPDM-A) A reduction reaction was carried out in the presence of hydrogen using a Raney nickel catalyst, the catalyst was filtered through a 5C filter paper, and the solvent was distilled off to obtain crude PCPDM. And the carbonyl group is 2
41 ppm and 7.4 mg / g of nickel were detected. The crude PCPDM and a 1-fold aqueous solution of 1N hydrochloric acid were placed in a reactor capable of heating and stirring and heated. Liquid temperature is about 80
At 0 ° C., the PCPDM was completely melted and then stirred for 10 minutes to disperse well in hot water. After completion of the stirring, the mixture was allowed to stand and separated into two layers, and then the aqueous layer was removed. Furthermore this PCP
To the DM layer was added water four times the weight of the crude PCPDM, and the mixture was heated in the same manner to melt the PCPDM. Then, the mixture was thoroughly stirred at a liquid temperature of 80 ° C. for 10 minutes, and washed while being dispersed. After completion of the stirring, the mixture was allowed to stand and separated into two layers, and then the aqueous layer was removed.
The operation of washing the PCPDM layer with 4 times the weight is 3 times in total.
I went there. From the separated PCPDM layer, 2.1% of the total amount was distilled off by simple distillation under reduced pressure as an initial distillation, and further distillation was performed at a reduced pressure of 0.5 mmHg to obtain 185
PCPDM (PC of this main stream)
PDM amount was 93% of the whole). From this fraction, 29 ppm of carbonyl groups were detected.

Example 2 (PCPDM-B) 241 ppm of carbonyl group used in Example 1, 7.4
Crude PCPDM in which mg / g of nickel was detected was dissolved in 3 times the weight of hexanol. A 1N aqueous hydrochloric acid solution four times the weight of the PCPDM-hexanol solution and the crude PCPDM was placed in a reactor capable of heating and stirring. About 2
Washing was performed by stirring well at a liquid temperature of 0 ° C. for 10 minutes. After completion of the stirring, the mixture was allowed to stand and separated into two layers, and then the aqueous layer was removed. The layer of this PCPDM-hexanol solution is further
A total of 3 operations to wash the PDM with 4 times the weight of water
Hexanol was separated using an evaporator. The remaining PCPDM layer was distilled by simple distillation under reduced pressure to evaporate an amount corresponding to 7.7% of the whole as an initial distillation.
PCPDM (PCP of this main fraction)
DM amount was 90% of the total). The carbonyl group in this fraction was below the detection limit.

Example 3 (PCPDM-C) The same operation as in Example 2 was performed, except that chloroform was used instead of hexanol as the solvent for crude PCPDM. The carbonyl group in the obtained PCPDM was below the detection limit.

Comparative Example 4 (PCPDM-D) Crude PCPDM used in Example 1, in which 241 ppm of carbonyl groups and 7.4 mg / g of nickel were detected, was subjected to simple distillation under reduced pressure. First, an amount corresponding to 12.6% of the whole was distilled off as a first distillation, and then the degree of vacuum was further reduced to 0.5 mmHg.
PCPD as main fraction at 185-187 ° C
M (the amount of PCPDM contained in this main fraction was 82% of the whole). The carbonyl group in this fraction is 1490
ppm was detected.

Example 4 52.5 g (0.2 mol) of PCPDM-A, 43.7 g (0.204 mol) of diphenyl carbonate, and 2.2 × 10 ^-4 g (1.2 × 10 ⁻ ) of zinc acetate ⁶ mol) was placed in a 300 ml four-necked flask equipped with a stirrer and a distilling apparatus, heated to 180 ° C. under 760 mmHg in a nitrogen atmosphere, and stirred for 20 minutes. Thereafter, the degree of decompression is set to 150 mmH.
g, and at the same time, the temperature was raised to 200 ° C. at a rate of 60 ° C./hr, and held at that temperature for 20 minutes to perform melt polycondensation. Further, the temperature was raised to 225 ° C. at a rate of 75 ° C./hr.
The pressure was reduced to 1 mmHg over time. Then 60 ° C
/ Hr at a rate of 235 ° C., 1 mmHg, 23
Heating and stirring were performed at 5 ° C. for 40 minutes, and the reaction was performed under stirring for a total of 3.5 hours. After completion of the reaction, nitrogen was blown into the reactor to return to normal pressure, and the produced polycarbonate resin was taken out. The produced polycarbonate resin had Mw = 617.
00, YI = 1.85.

Example 5 In Example 4, PCPDM-A was not used and PCPDM-A was used.
Except for using 52.5 g (0.2 mol) of DM-B,
The same operation as in Example 4 was performed. The obtained polycarbonate resin had Mw = 63300 and YI = 1.79.

Example 6 In Example 4, PCPDM-A was not used, and PCPDM-A was used.
Except for using 52.5 g (0.2 mol) of DM-C,
The same operation as in Example 4 was performed. The obtained polycarbonate resin had Mw = 60900 and YI = 1.83.

Example 7 In Example 4, 26.2 g of PCPDM-A was used as a raw material.
(0.1 mol) and 22.8 g (0.1 mol) of BPA, 6.3 × 10 ⁻⁵ g of calcium acetate (4.0 × 10 ^5
-7 mol) in the same manner as in Example 4. The produced polycarbonate resin had Mw = 6180
0, YI = 1.83.

Example 8 In Example 7, PCPDM-A was not used, and PCPDM-A was used.
Except for using 26.2 g (0.1 mol) of DM-B,
The same operation as in Example 7 was performed. The obtained polycarbonate resin had Mw = 64900 and YI = 1.70.

Example 9 In Example 7, PCPDM-A was not used and PCPDM-A was used.
Except for using 26.2 g (0.1 mol) of DM-C,
The same operation as in Example 7 was performed. The obtained polycarbonate resin had Mw = 60400 and YI = 1.75.

Comparative Example 2 In Example 4, PCPDM-A was used without using PCP
Except for using 52.5 g (0.2 mol) of DM-D,
The same operation as in Example 4 was performed. The obtained polycarbonate resin had Mw = 58600 and YI = 3.80.

Comparative Example 3 In Example 7, PCPDM-A was not used, and PCPDM-A was used.
Except for using 26.2 g (0.1 mol) of DM-D,
The same operation as in Example 7 was performed. The obtained polycarbonate resin had Mw = 59400 and YI = 3.71.

[0044]

According to the present invention, the color tone can be improved while maintaining the excellent impact resistance, heat resistance, optical characteristics, etc. of polycarbonate, and plastic optical materials such as various lenses, prisms and optical disk substrates. Thus, it is possible to obtain a polycarbonate resin which can be suitably used for the purpose.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masamichi Minakami 22nd Wadai, Tsukuba-shi, Ibaraki F-term in Mitsubishi Gas Chemical Co., Ltd. Research Laboratory (reference)

Claims (6)

[Claims] 1. A pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2), or a pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2) and a general formula In producing a polycarbonate resin by subjecting the aromatic dihydroxy compound represented by (3) to a transesterification reaction with a carbonic acid diester, the content of carbonyl groups contained in pentacyclopentadecane dimethanol is 500 ppm.
A method for producing a polycarbonate resin, comprising using pentacyclopentadecane dimethanol represented by the following general formulas (1) and / or (2). Embedded image Embedded image Embedded image (In the formula, R _{1 to} R ₂ are a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group, a phenyl group, or a halogen atom, and R ₁ and R ₂ may be the same or different. And n represents the number of substituents and is an integer of 0 to 4. X is a single bond, R _{3 to} R ₄ are each a hydrogen atom and a carbon number of 1 to
12 alkyl groups or phenyl groups, and R ₃ and R
₄ may combine to form a ring. ) 2. The method for producing a polycarbonate resin according to claim 1, wherein the aromatic dihydroxy compound represented by the general formula (3) is 2,2-bis (4-hydrohistiphenyl) propane. 3. The method for producing a polycarbonate resin according to claim 1, wherein the carbonic acid diester is diphenyl carbonate. 4. A pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2) having a carbonyl group content of 500 ppm or less is obtained by using a dialdehyde as a starting material in the presence of a hydrogenation catalyst and hydrogen. The diol obtained by performing the reduction reaction under pH 0.01 ~
The method for producing a polycarbonate resin according to claim 1, which is obtained by distillation after washing with water of 5.0. 5. The process for producing a polycarbonate resin according to claim 4, wherein the pentacyclopentadecane dimethanol represented by the general formula (1) and / or (2) is dissolved in a water-insoluble solvent, followed by washing. . 6. The method for producing a polycarbonate resin according to claim 5, wherein the solvent contains any of dichloromethane, chloroform, hexanol, octanol, methyl propyl ketone, cyclohexanone, and methyl isobutyl ketone.