JPS62177032A - Production of optical disc substrate made of polycarbonate resin - Google Patents

Abstract

PURPOSE:To obtain the titled substrate having improved heat resistance and optical characteristics, by injection molding a polycarbonate resin containing a carbonate bond constituent unit having a suspended aromatic group and a carbonate bond constituent unit having a specific formula in a specific ratio, under a fixed condition. CONSTITUTION:A polycarbonate resin which contains (A) 95-5wt% carbonate bond constituent unit (based on total carbonate bond constituent unit) containing at least one suspended aromatic group in the unit constituting the carbonate bond and (B) 5-95wt% carbonate bond constituent unit containing a group shown by the formula (X, Y, Z and W are H or 1-6C aliphatic hydrocarbon) and has 9,500-22,000 average-molecular weight is molded at 300-400 deg.C resin temperature and at 50-150 deg.C mold temperature to give the aimed substrate. EFFECT:Especially has improved transparency and low optical strain.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical disk substrate made of polycarbonate resin, and more specifically, the present invention relates to a method for producing an optical disk substrate made of polycarbonate resin, and more specifically, it has excellent heat resistance, optical properties, particularly good transparency, and small optical distortion. The present invention relates to a method of manufacturing a polycarbonate optical disk substrate.

[Conventional technology]

Resin moldings used for optical recording and reproducing purposes are required to be transparent and have small optical distortion. Particularly for optical discs that use digital signals and are intended for reading and writing information, transparency requirements are extremely strict, and optical distortion is expressed as birefringence in actual molded products. The following is required.

Normally, injection molding is used as a simple method to mold objects of this shape, but methods to reduce optical distortion include raising the temperature of the molten resin or decreasing the molecular weight of the resin. A method is used to lower the melt fluidity and improve melt fluidity.

Furthermore, in the case of disks that are used continuously over a long period of time, heat resistance requirements are also strict because they must withstand harsh operating environments.

By the way, a polycarbonate resin consisting of carbonate bond constituent units having at least one pendant aromatic group as a unit constituting a carbonate bond is co, :l-
Bis(l-hydroxyphenyl)propane [Bisphenol All] has superior flame resistance compared to polycarbonate resin (commercially available so-called polycarbonate resin), and its application to optical disk substrates is being considered. However, this type of polycarbonate resin suffers from various problems because of its poor fluidity compared to the usual bisphenol A-based t)X'' recarbonate resin.

[Problem that the invention seeks to solve]

For example, if an attempt is made to increase the fluidity by raising the temperature of the molten resin in order to reduce the optical distortion of the obtained disk, various problems such as deterioration of the resin due to the high temperature will occur. Also, if you lower the molecular weight of the resin to increase fluidity,
The strength of the molded product decreases, making it impossible to obtain a satisfactory optical disk substrate.

[Means for solving problems]

In view of the above points, the present inventors have developed a polycarbonate resin that has excellent transparency and small optical distortion without impairing the excellent heat resistance of a polycarbonate resin consisting of a carbonate bonding unit having at least one pendant aromatic group. As a result of intensive research into methods for obtaining optical disk substrates, we have succeeded in producing optical disk substrates with excellent heat resistance and optical properties by injection molding polycarbonate resin with specified carbonate bonding constituent units and molecular weight under specific molding conditions. The present invention was achieved by discovering that it can be manufactured.

[Structure of the invention]

In the present invention, among the units constituting the carbonate bond, the carbonate bond constituent unit (component A) having at least one pendant aromatic group is 95 to 95% of the total carbonate bond constituent units! r weight% and a carbonate bond structure having a group represented by the following general formula (I) (where x, y, z, w are hydrogen atoms or hydrogen groups of aliphatic carbon atoms having 7 to 7 carbon atoms) The unit (component B) has a weight ratio of S~95 to all carbonate bond constituent units, and has an average molecular weight of 9! r Oθ~ here, θOQ polycarbonate resin at resin temperature 300-'100c, mold temperature jo~/
This is a method for manufacturing a polycarbonate resin optical disk substrate by injection molding at Sθ°C.

The present invention will be explained in detail below.

The carbonate bond in the present invention refers to a 10-C-O- bond obtained by reversing an alcoholic hydroxyl group or a phenolic hydroxyl group with, for example, phosgene, and the carbonate bond constituent unit is It refers to a covalent group interposed between such carbonate bonds. Further, other bond types such as ester bonds, amide bonds, carbamate bonds, ether bonds, etc. may be included in this carbonate bond structural unit.

Examples of the carbonate-bonded structural unit having at least one pendant aromatic group include those represented by the following general formula (]).

General formula (It) At least one is an aryl group or an aralkyl group, and 2' and V
is a hydrogen atom or an aliphatic hydrocarbon group having 1 to 2 carbon atoms.

Such polycarbonates containing carbonate bonding units having at least one pendant aromatic group may provide pendant aromatic groups, such as those of the following general formula (II
It can be obtained by reacting and polymerizing one or more of the bisphenol compounds shown below with phosgene.

General formula (11X') However, in the formula (1), X', Y', 2', and W' have the same meanings as in the above general formula (II).

Examples of such bisphenol compounds represented by the general formula (II) include bis(terhydroxyphenyl)
Phenylmethane, l', I-bis(terhydroxyphenyl)-7-phenylethane, /, I-bis(terhydroxyphenyl)-/-phenylpropane, bis(terhydroxyphenyl)diphenylmethane, bis(terhydroxyphenyl) 75f such as dibenzylmethane are listed.

A polycarbonate containing a carbonate bonding structural unit having a group represented by the general formula (1) can provide a group represented by the general formula (I), for example, one or more bisphenol compounds represented by the following general formula (1). It is obtained by reacting with phosgene and polymerizing it.

General formula (I) However, (I) In the formula, x, y, z, w are the general formula (1
) is synonymous with

Examples of such bisphenol compounds represented by the general formula (I) include
-methylphenyl)propane, u, corpis(lihydroxy-3-ethylphenyl)propane, co, corbis(lI-hydroxy-3-'r'')7'ropylphenyl)furopuff, :1.:1-bis(lI-hydroxy -J
Ie16 butylphenyl)propane, λl cocose (+-hydroxy-J-tartbutylphenyl)propane, bis(l-hydroxyphenyl)methane, /,
l-bis(couhydroxyphenyl)ethane, /, l-
Bis(lI-hydroxyphenyl)propane, co-bis(II-hydroxyphenyl)propane or lbisphenol A7. x,x-bis(lI-hydroxyphenyl)butane,co,corpis(4-monohydroxyphenyl)pentane,co,2-bis(l-hydroxyphenyl)-3-methylbutane,co,-bis(terhydroxyphenyl) ) hexane, co-2-bis(couhydroxyphenyl)-gumethylpentane, and the like.

In the present invention, first, a carbonate-bonded structural unit having at least one pendant aromatic group (hereinafter referred to as component A) and a carbonate-bonded constitutional unit having a group represented by the above general formula (1) (hereinafter referred to as component B) A polycarbonate resin having the following properties is prepared. As a method, when producing polycarbonate using a bisphenol compound having at least one pendant aromatic group, for example, a bisphenol compound represented by the general formula (It), A method of copolymerizing a bisphenol compound within a range that satisfies the requirements of the present invention is mentioned.Also, a method in which a bisphenol compound represented by the general formula (I) and a bisphenol compound represented by the general formula (I) are reacted with phosgene, respectively. The polycarbonates may then be mixed to meet the requirements of the invention.

To produce a polycarbonate resin containing components A and B, a bisphenol compound of general formula (I') and an aqueous alkali solution or Simply add an acid acceptor such as pyridine and introduce phosgene into it to cause a reaction.When using an alkaline aqueous solution as the acid acceptor, use a tertiary amine such as trimethylamine, triethylamine, or tetrabutylammonium chloride as a catalyst. The reaction rate is increased by using a q-class ammonium compound such as benzyltributylammonium bromide.Furthermore, monohydric phenol such as phenol or p-tert-butylphenol is allowed to coexist as a molecular weight regulator during packaging.

The reaction temperature is 0-/θO°C. The catalyst may be added from the beginning, or may be used in any desired manner, such as during the reaction, ie, after the oligomer has been produced, to allow polymerization reaction to occur in the presence of the catalyst.

The process of copolymerization of bisphenol compounds of general formula (I and (D) is as follows.

(b) Both are present in the reaction system from the beginning and reacted with phosgene at the same time for polymerization. (b) One is first reacted with phosgene and after a certain amount of reaction, the other is added and polymerized. (c) Any method can be used, such as making oligomers by reacting them separately with phosgene, and then mixing them and further reacting to polymerize them.

Furthermore, as a method of mixing separately polymerized materials,
After mixing each powder or granule, extrusion method,
A method of melting and mixing using a kneader 1 mixed wire roll or the like, or an arbitrary method of solution blending can be used.

Component A and B of the polycarbonate resin used in the present invention
The content of the components is A from the viewpoint of moldability and heat resistance.
The weight of the component is 95 to 5. The weight of the component is S to 95. When the A component exceeds 95% by weight, moldability is poor,
If the amount of component A is less than 5% by weight, the heat resistance will decrease. Among these, a more preferable range is 90-15% by weight of component A.

Further, the average molecular weight of the polycarbonate resin used in the present invention is 9. ! ;00~:12,000.

The average molecular weight obtained here is a value determined from the following formula (1) and formula (2) from ηIIp measured by COOC using a methylene chloride solution of polymer A and Of/l.

ηmp/a=[η'] (/ten'η@P ”)...
−・・(1) [η] = vcya・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...(2) In the formula, C polymer concentration P/l [η] Intrinsic viscosity, K'-0,2g K/, ko3xl0-1', α-0,g 3M
The average molecular weight is 9. ! If it is less than 00, the mechanical properties will not be sufficient, and if it exceeds θ00, it will be difficult to obtain an optical disk substrate with small optical distortion. Among these, the preferred average molecular weight is /0.000-20.00'
It is 0.

Refreshingly, when manufacturing optical disk substrates by injection molding the polycarbonate resin mentioned above, the resin temperature is kept between 30θ and 00
℃.

If the resin temperature is too high, decomposition of the resin will be unavoidable, resulting in discoloration, silver streaks, etc., which is undesirable. On the other hand, if the resin temperature is too low, a molded product with low optical distortion cannot be obtained even if the above-mentioned polycarbonate resin, which is less likely to cause optical distortion, is used.

Also, the mold temperature is 30-1! ;0℃, preferably 40-
74', t'C. If the mold temperature is too high, deformation during mold release will increase, making it impossible to obtain a molded product with small warpage. On the other hand, if it is too low, a molded product with small optical distortion cannot be obtained.

In injection molding, it is preferable to add 0.01 to -% by weight of phosphites to the polycarbonate resin in order to suppress discoloration and decrease in transparency due to decomposition of the resin.

Such phosphites include tributyl phosphite, tris(2-ethylhexyl) phosphite, tridecyl phosphite, tristearyl phosphite,
Examples include triphenyl phosphite, tricresyl phosphite, coethylhexyl diphenyl phosphite, decyl diphenyl phosphite, tricyclohexyl phosphite, distearyl pentaerythrityl diphosphite, and the like. Methods for incorporating such phosphite include a tri-blend method, a method of melt-mixing when pelletizing with an extruder, or a method in which master pellets with a high phosphite concentration are created and tri-blend with non-added pellets. Here are some ways to do it.

〔Example〕

Hereinafter, a specific method for producing the polycarbonate resin used in the present invention will be illustrated as a production example, and a method for producing an optical disk substrate using the obtained polycarbonate resin will be illustrated as an example.

Note that all parts indicating the amounts of each component below are parts by weight.

Further, the glass transition temperature was determined using a differential scanning calorimeter manufactured by PerkinElmer, and the flow value was determined according to JIS KARIQ.

The compositions and average molecular weights of the polycarbonate resins produced in Production Example/-44 and Comparative Production Example/-5 are described below.
Shown in l. Further, the measurement results of various physical property values of these poly=16-carbonate resins are shown in the section below.

Production Example 1 (a) Production of polycarbonate oligomer 1, /-bis(terhydroxyphenyl)-7-phenylethane t0
0 parts sodium hydroxide lIO parts water
600 parts Methylene chloride 375 parts The above mixture was charged into a reactor equipped with a stirrer and stirred at 1100 rpm. In this, phosgene St
1 hour to carry out interfacial polymerization.

After the reaction was completed, only the methylene chloride solution containing the polycarbonate oligomer was collected. The analysis results of the obtained oligomer solution in methylene chloride were as follows.

, t IJ sesame concentration -1, S 1)
Terminal chloroformate group concentration o, tI regulation □□
□2) Terminal phenolic hydroxyl group concentration 0.0 normal
Sail 3) Note 1) Measured after evaporation to dryness.

2) A obtained by reacting with aniline Niline hydrochloride as O, co-normal sodium hydroxide Neutralization titration with lium aqueous solution.

3) Titanium tetrachloride, color development when dissolved in acetic acid solution! Colorimetric determination at r'I b nm.

The oligomer solution obtained by the above method is hereinafter abbreviated as oligomer solution-A.

(b) Production of polycarbonate oligomer /A, 4% aqueous solution of bisphenol A sodium salt prepared by dissolving bisphenol A in thorium hydroxide aqueous solution
ioθ part P-tert-butylphenol 0.23 part methylene chloride tio part phosgene
A mixture having a composition of 7 parts to 100% was quantitatively supplied to a pipe reactor to perform interfacial polymerization.

The reaction mixture was separated and only the methylene chloride solution containing the polycarbonate oligomer was collected.

The analysis results of the obtained oligomer solution in methylene chloride were as follows.

Oligomer concentration: CotX, S weight % Terminal roloformate group concentration: i, 3N Terminal phenolic hydroxyl group concentration: 0.3N The oligomer solution obtained by the above method is hereinafter abbreviated as oligomer solution-B.

(c) Production of polycarbonate resin Oligomer solution - A 156 parts Oligomer solution - B / θθ part Salt part Nalen g 6 parts P-Tertiary-butylphenol t, bs parts were charged into a reactor equipped with a stirrer! r! ; Stirred with Orptn.

Furthermore, an aqueous solution having the following composition was charged and interfacial polymerization was carried out for one hour.

water lIo
Part hydroxide) IJum2jT heavy tht% aqueous solution go
Part i: Part (wt%) aqueous solution of triethylamine Part i: The reaction mixture is successively separated, and the methylene chloride solution containing the polycarbonate resin is washed with water, an aqueous hydrochloric acid solution, and water, and finally, the methylene chloride is evaporated to obtain the resin. I took it out. The average molecular weight of this resin is /3. ! ; It was 00.

Further, from the results of NMR analysis, the amount of copolymerized carbonate bond structural units derived from bisphenol A was 39.5% by weight based on the total carbonate bond structural units.

Production Example Production of copolycarbonate Oligomer solution - person - 〇g parts Oligomer solution - B, t4 (partial methylene sludge part P - tertiary butylphenol 2.0 g
1 part into a reactor with a stirrer! ;! ; Stirred at Orpm. An aqueous solution with the following composition was placed in the nest and interfacial forces were allowed to interact for one hour.

Water lI g part hydroxide) IJ Umco S 31% aqueous solution by weight 39 parts triethylamine aqueous solution by weight t, i parts Production Example 1
After washing with the same formulation as above, the average molecular weight of the resin taken out was /J, /00.

Further, from the results of NMR analysis, the amount of copolymerized carbonate bonding structural units derived from bisphenol A was 10.S by weight based on the total carbonate bonding structural units.

Production Example 3 (a) Production of polycarbonate oligomer Corbis(4-hydroxy-3-methylphenyl)propane 1
00 parts Sodium hydroxide 50 parts Water g'io parts Chloride parts Methylene chloride 530 parts P-tert-butylphenol
θ part: Charge the above mixture into a reactor equipped with a stirrer and go.

Stirred at rpm. 70 parts of phosgene was blown into this for a period of time to effect interfacial polymerization. After the reaction was completed, only the methylene chloride solution containing the polycarbonate oligomer was collected. The analysis results of the obtained oligomer solution in methylene chloride were as follows.

Oligomer concentration: 2'1.0% by weight Terminal chloroformate degree of leatheriness: O, SC normality: Terminal phenolic hydroxyl group concentration: θ, 13 normality The oligomer solution obtained by the method is hereinafter abbreviated as oligomer solution-〇.

(b) Production of polycarbonate Oligomer solution-A 2/41 parts Oligomer solution-CSO part Methylene chloride 9 parts p-tertiary-butylphenol t, tg parts were charged into a reactor equipped with a stirrer 5! The mixture was stirred at r Orpm. Furthermore, an aqueous solution having the following composition was charged and interfacial polymerization was carried out for 3 hours.

Water 56 parts Sodium hydroxide 1% aqueous solution 30 parts Triethylamine 1% aqueous solution /, / / parts The average molecular weight of the resin that was washed and extracted using the same recipe as in Production Example 1 was i3. It was qoo.

Also, tips on copolymerization based on NMR analysis results: 1-
The amount of carbonate-bonded structural units derived from bis(lI-hydroxy-3-methylphenyl)pronokone was /q,/% by weight based on the total carbonate-bonded structural units.

Production example ψ (→ Production of polycarbonate oligomer) 2-bis(terhydroxy-3-see 7'tylphenyl)furobuff Ioo parts Sodium hydroxide 35 parts Water Too parts Methylene chloride
Part JgS The above mixture was charged into a reactor equipped with a stirrer and stirred at 1100 rpm. 3 parts of Hostang was blown into this for 1 hour to effect interfacial polymerization. After the reaction was completed, only the methylene chloride solution containing the polycarbonate oligomer was collected.

The analysis results of the obtained methylene chloride solution of the oligomer were as follows.

= 23- Oligomer concentration 23.5 Weight ratio Terminated roloformate leather quality o, tIo Normal terminal phenolic hydroxyl group concentration o, o s o The oligomer solution obtained by the above method is hereinafter abbreviated as oligomer solution.

(b) Manufacturing bis-(4) of polycarbonate oligomer
=-Hydroxyphenyl)diphenylmethane ioθ parts Sodium hydroxide 50 parts Water
700 parts methylene chloride
JSO section Charge the above mixture into a reactor equipped with a stirrer and go.

Stirred at rpm. 0 parts of Phosdunk was blown into this for 7 hours to perform interfacial polymerization. After the reaction was completed, only the methylene chloride solution containing the polycarbonate oligomer was collected. The analysis results of the obtained methylene chloride solution of the oligomer were as follows.

Oligomer concentration: -% by weight Terminated polyroloformate Leather quality: 0.3g Concentration of phenolic terminal hydroxyl group: 0.072 The oligomer solution obtained by the method above normal is hereinafter abbreviated as oligomer solution-E.

(c) Production of polycarbonate Oligomer solution-D/O Part O Oligomer solution-E 700 parts Methylene chloride
/10 parts P-tert-butylphenol
Charge t and ab parts into a reactor with a stirrer! ;!
; Stirred at Orpm. Furthermore, an aqueous solution having the following composition was charged and interfacial polymerization was carried out for 5 hours.

water b
Part lI Sodium hydroxide heavy weight aqueous solution 27
Part: Triethylamine cowt% aqueous solution i, Part i: After washing with the same formulation as in Production Example 1, the average molecular weight of the resin taken out is /, ? ,? It was 00.

Based on the NMR analysis results, the amount of copolymerized carbonate bond constituent units derived from U,2-bis(lI-hydroxy-3-seebutylphenyl)propane is 4/, #weight based on the total carbonate bond constituent units. %Met.

Comparative Production Example 1 Production of Polycarbonate Oligomer Solution-A/Part P-Tertiary-Butylphenol. , 7 parts methylene chloride θ parts The above mixture was charged into a reactor equipped with a stirrer.

Stir at rpm. Furthermore, an aqueous solution having the following composition, i.e., an aqueous solution with a weight ratio of 7.3% (hydroxide)
Add 1 part of triethylamine cowt% aqueous solution and perform interfacial polymerization for 3 hours, separate the reaction mixture, wash the methylene chloride solution containing the polycarbonate resin with water, an aqueous hydrochloric acid solution, then water, and finally remove the methylene chloride. The resin was removed by evaporation. The average molecular weight of this resin was /'I, /θ0.

Comparative Production Example Production of copolycarbonate Oligomer solution-E Colo 0 parts P-tert-butylphenol 89 Methylene chloride 120 parts were charged into a reactor equipped with a stirrer 3! The mixture was stirred at r Orpm. Furthermore, an aqueous solution having the following composition was charged and interfacial polymerization was performed for 2 hours.

water ?
Part O: 25 parts by weight of sodium hydroxide; Part S: 0.9 parts by weight of triethylamine. It was g00.

Comparative Production Example 3 Production of Polycarbonate A polycarbonate was produced in the same manner as in Production Example 1 (c) except that 65 parts of P-tert-butylphenol was changed to 0 parts. The average molecular weight of this resin was 5°.

Furthermore, from the NMR analysis results, the number of copolymerized bisphenol A-derived carbonate bond structural units was 39.6% by weight based on the total carbonate bond structural units fc.

Comparative Production Example 1 Production of Polycarbonate A polycarbonate was produced in the same manner as in Production Example 1 (c) except that the amount of P-tert-butylphenol/A was changed to 2.31 parts.

The average molecular weight of this resin was g, tθθ.

Further, from the results of NMR analysis, the amount of copolymerized bisphenol-derived carbonate units was 39.5% by weight based on the total carbonate bonding constituent units.

Comparative Production Example S Polycarbonate Production Oligomer Solution-B / 1.0 parts P-tert-butylphenol 1.3 parts Methylene chloride 130 parts The above mixture was added to a reactor equipped with a stirrer (Charging SS).

Stirred at rpm. Furthermore, an aqueous solution having the composition shown below was prepared, and interfacial polymerization was carried out for a period of time.

A 16.6-weight aqueous solution of bisphenol A-sodium salt (go part hydroxide); a 15-weight solution of IJum;
After washing with the same formulation as in Production Example 1, the average molecular weight of the resin taken out was /S,000.

Table 1 Examples of various physical properties of resins in production examples and comparative production examples/
-5 and Comparative Example/-ff After adding coethylhexyl diphenyl phosphite/30 ppm to the polycarbonate resin produced in Production Example/-1 and Comparative Production Example/-1, 1IOI+Inlφ
Using an extruder, the mixture was melt-kneaded at 1 gO'c and extruded into pellets.

This pellet is molded into an injection molding machine (M-1'l0A manufactured by Takisha)
Using the molding conditions shown in Table 3, the thickness was 8-2111211.
A disk-shaped optical disk substrate with a diameter of 130 Lran was produced.

3. From the center of the obtained substrate. The phase difference due to birefringence at θ and 5.5CM (abbreviated as Δn3.G, Δns, and s, respectively) was measured using a polarizing microscope manufactured by Nippon Kogaku Kogyo ■.

Further, the amount of warpage was measured using a flatness tester #Tq manufactured by NI DBK.

These results are shown in Table 3.

Table 3 Substrate Molding Conditions and Physical Properties [Effects of the Invention] According to the method of the present invention, it is possible to obtain an optical disk substrate with good heat resistance and fluidity, low birefringence and warpage, and sufficient strength.

Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent Attorney Hase - 1 other person

Claims (4)

[Claims] (1) Among the units constituting the carbonate bond, the carbonate bond constituent unit (component A) having at least one pendant aromatic group is 95 to 5% by weight based on the total carbonate bond constituent units and the following general formula ( I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (In the formula, X, Y, Z, and W are hydrogen atoms or carbon atoms of 1 to 6
is an aliphatic hydrocarbon group. ) containing 5 to 95% by weight of a carbonate bonding structural unit (component B) having a group represented by
A method for manufacturing an optical disk substrate made of polycarbonate resin, characterized by injection molding at 0°C and a mold temperature of 50 to 150°C. (2) The polycarbonate resin contains a carbonate bond structural unit (component A) having at least one aromatic group suspended as a carbonate bond structural unit, and a carbonate bond structural unit (B) having a group represented by the general formula (I) above. The method according to claim 1, which is a copolymerized polycarbonate having a component). (3) The polycarbonate resin consists of a polycarbonate consisting of a carbonate bonding structural unit (component A) having at least one pendant aromatic group and a carbonate bonding structural unit (component B) having a group represented by the general formula (I) above. The method according to claim 1, which is a mixture with polycarbonate. (4) The above A component is the following general formula (II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(II) (In the formula, X' and Y' are hydrogen atoms, C1-C6 fat and at least one of X' and Y' is an aryl group or an aralkyl group, and Z' and W' are a hydrogen atom or an aliphatic group having 1 to 6 carbon atoms. The method according to any one of claims 1 to 3, which is a carbonate-bonded structural unit having a group represented by the formula (a hydrocarbon group).