JP5232986B2 - Polylactic acid modifier and polylactic acid resin composition. - Google Patents

Description

  The present invention relates to a polylactic acid modifier and a polylactic acid resin composition.

In recent years, research on biodegradable resins as environmentally friendly polymers has been actively conducted. In particular, not only from the viewpoint of biodegradation, but also polylactic acid made from plants that enable carbon neutrality has attracted a great deal of attention because of its high cost and physical properties. However, the molded product has a problem that the hydrolyzability is inferior, and has not yet been developed in earnest.
Examples of solutions to such disadvantages include (A) polylactic acid, (B) polyalkyl acrylate ester and / or polyvinyl ester, (C) polyolefin and (D) polyalkyl acrylate ester and polyolefin. A polylactic acid resin composition comprising a block copolymer and / or a block copolymer of a polyvinyl ester and a polyolefin is disclosed (Patent Document 1).

However, (A) polylactic acid, (B) polyacrylic acid ester or polyvinyl ester, (C) polyolefin, and (D) the block copolymer of (B) and (C) in the polylactic acid resin composition The ratio is 100% of (A) + (B) + (C) + (D) by weight, (A) being 5-30%, (B) being 20-50%, (C) being 5 There is a disclosure that -20% and (D) is 20-50%, and the blending amount of polylactic acid is 30% or less, and it is difficult to say that it is a modification of polylactic acid. In addition, by mixing and mixing polylactic acid with appropriate general-purpose plastics, the objective is to provide a novel polylactic acid resin composition that has a low environmental impact and significantly suppresses hydrolysis. Absent.
For the purpose of solving such problems, the use of an end-capping agent that reacts with a carboxyl group has been studied for polylactic acid as well as improving the hydrolysis resistance of general-purpose polyester resins. For example, a method of blocking terminal carboxyl groups of polylactic acid by condensation reaction of aliphatic alcohol and carboxyl group has been proposed (Patent Document 2, Patent Document 3). At the same time, moisture is generated as a by-product, and a vacuum dehydration step is required to remove the moisture. When such an alcohol compound is used in the molding process of polylactic acid, the generated moisture is vaporized or mixed into the molded product, so that the appearance of the molded product is not only inferior, but physical properties such as strength and heat resistance are also obtained. descend. Further, when used in the polylactic acid polymerization step, the polymerization rate is slowed, the molecular weight of polylactic acid is lowered, and the remaining unreacted product is increased.

JP-A-2005-239957 JP 7-316273 A JP-A-9-21017

  The subject of this invention is providing the polylactic acid resin composition excellent in the modifier for polylactic acid and hydrolysis resistance.

The present invention relates to the following inventions.
1. A modifier for polylactic acid, which is a block polymer having the following characteristics (a) to (c), which has a segment (A) consisting only of polymethyl methacrylate and a segment (B) consisting only of polystyrene.
(A) The weight ratio (A) / (B) of the segment (A) to the segment (B) is 0.4 to 9.0.
(B) The number average molecular weight of the block polymer is 10,000 to 100,000.
(C) Molecular weight distribution 1.0-2.0
2. The modifier for polylactic acid as described above, wherein the block polymer is a polymer obtained by polymerization using an organic tellurium compound-based polymerization initiator.
3. Organic tellurium compound polymerization initiator,
(A) an organic tellurium compound represented by formula (1),
(B) a mixture of an organic tellurium compound represented by formula (1) and an azo polymerization initiator,
(C) A mixture of an organic tellurium compound represented by formula (1) and an organic ditellurium compound represented by formula (2), or (d) an organic tellurium compound represented by formula (1), an azo polymerization initiator. And the modifier for polylactic acid as described above, which is any one of a mixture of organic ditellurium compounds represented by formula (2).

（式中、Ｒ^１は、Ｃ_１〜Ｃ_８のアルキル基、アリール基、置換アリール基又は芳香族ヘテロ環基を示す。Ｒ^２及びＲ^３は、水素原子又はＣ_１〜Ｃ_８のアルキル基を示す。Ｒ^４は、アリール基、置換アリール基、芳香族ヘテロ環基、アシル基、アミド基、オキシカルボニル基又はシアノ基を示す。）

(In the formula, R ¹ represents a C _{1 to} C ₈ alkyl group, an aryl group, a substituted aryl group or an aromatic heterocyclic group. R ² and R ³ represent a hydrogen atom or a C _{1 to} C ₈ alkyl group. R ⁴ represents an aryl group, a substituted aryl group, an aromatic heterocyclic group, an acyl group, an amide group, an oxycarbonyl group, or a cyano group.

(R ¹ Te) ₂ (2)
(In the formula, R ¹ is the same as above.)
4). A modified polylactic acid resin composition obtained by kneading polylactic acid and any of the above-described modifiers for polylactic acid.

  The polylactic acid modifier of the present invention can particularly modify hydrolysis resistance, and a polylactic acid resin composition containing the polylactic acid modifier is excellent in hydrolysis resistance. Surprisingly, the polylactic acid resin composition of the present invention has excellent hydrolysis resistance without impairing the transparency inherent in polylactic acid.

  The polylactic acid as referred to in the present invention is obtained by polymerizing oligomers such as lactic acid and lactide, and the optical purity of L-form or D-form is preferably 90% or higher because of its high melting point. In the present invention, L-form or D-form having an optical purity of 97% or more is called homopolylactic acid. Moreover, in the range which does not impair the property of polylactic acid, you may copolymerize components other than lactic acid, or may contain additives, such as a polymer other than polylactic acid, particle | grains, a flame retardant, and an antistatic agent. However, from the viewpoint of biomass utilization and biodegradability, it is important that the lactic acid monomer is 50% by weight or more as a polymer. The lactic acid monomer is preferably 75% by weight or more, more preferably 96% by weight or more. Further, the molecular weight of the polylactic acid polymer is preferably 50,000 to 500,000 in terms of weight average molecular weight, which is preferable because of a good balance between mechanical properties and moldability.

The modifier for polylactic acid of the present invention is a block polymer having a segment (A) consisting only of polymethyl methacrylate and a segment (B) consisting only of polystyrene, and having the following characteristics (a) to (c). is there.
(A) The weight ratio (A) / (B) of the segment (A) to the segment (B) is 0.4 to 9.0.
(B) The number average molecular weight of the block polymer is 10,000 to 100,000.
(C) Molecular weight distribution 1.0-2.0

The block polymer can be obtained, for example, by polymerization using an organic tellurium compound polymerization initiator. In particular,
(A) an organic tellurium compound represented by formula (1),
(B) a mixture of an organic tellurium compound represented by formula (1) and an azo polymerization initiator,
(C) A mixture of an organic tellurium compound represented by formula (1) and an organic ditellurium compound represented by formula (2), or (d) an organic tellurium compound represented by formula (1), an azo polymerization initiator. And an organic tellurium compound-based polymerization initiator selected from a mixture of organic ditellurium compounds represented by formula (2).

  The organic tellurium compound used in the present invention is represented by the formula (1).

（式中、Ｒ^１は、Ｃ_１〜Ｃ_８のアルキル基、アリール基、置換アリール基又は芳香族ヘテロ環基を示す。Ｒ^２及びＲ^３は、水素原子又はＣ_１〜Ｃ_８のアルキル基を示す。Ｒ^４は、アリール基、置換アリール基、芳香族ヘテロ環基、アシル基、アミド基、オキシカルボニル基又はシアノ基を示す。）

(In the formula, R ¹ represents a C _{1 to} C ₈ alkyl group, an aryl group, a substituted aryl group or an aromatic heterocyclic group. R ² and R ³ represent a hydrogen atom or a C _{1 to} C ₈ alkyl group. R ⁴ represents an aryl group, a substituted aryl group, an aromatic heterocyclic group, an acyl group, an amide group, an oxycarbonyl group, or a cyano group.

Specific examples of the group represented by R ¹ are as follows.
Examples of the C _{1 to} C ₈ alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, cyclopropyl group, n-butyl group, sec-butyl group, tert-butyl group, cyclobutyl group, and n-pentyl. Examples thereof include linear, branched or cyclic alkyl groups having 1 to 8 carbon atoms such as a group, n-hexyl group, n-heptyl group and n-octyl group. A preferable alkyl group is a linear or branched alkyl group having 1 to 4 carbon atoms. More preferably, a methyl group, an ethyl group, or an n-butyl group is good.
Examples of the aryl group include a phenyl group and a naphthyl group. A preferred aryl group is a phenyl group. Examples of the substituent of the substituted aryl, an alkyl group of _C 1 -C _8, alkoxy group of C 1 -C _8, a halogen atom, a hydroxyl group, an amino group, a nitro group, a cyano group, a carbonyl-containing group represented by -COR ^a (R ^a = C ₁ -C ₈ alkyl group, aryl group, C ₁ -C ₈ alkoxy group, aryloxy group), sulfonyl group, trifluoromethyl group and the like can be mentioned.
A preferred substituted aryl group is a trifluoromethyl-substituted phenyl group.
These substituents may be substituted one or two, and the para position or ortho position is preferable.
Examples of the aromatic heterocyclic group include a pyridyl group, a pyrrole group, a furyl group, and a thienyl group.

Each group represented by R ² and R ³ is specifically as follows.
Examples of the C _{1 to} C ₈ alkyl group include the same alkyl groups as those described above for R ¹ .

Specific examples of each group represented by R ⁴ are as follows.
Examples of the aryl group, substituted aryl group, and aromatic heterocyclic group include the same groups as those described above for R ¹ .
Examples of the acyl group include a formyl group, an acetyl group, and a benzoyl group.
Examples of the amide group include carboxylic acid amides such as acetamide, malonamide, succinamide, maleamide, benzamide, and 2-fluamide, thioamides such as thioacetamide, hexanedithioamide, thiobenzamide, and methanethiosulfonamide, selenoacetamide, hexanediselenoamide, Examples include selenoamides such as selenobenzamide and methaneselenosulfonamide, N-substituted amides such as N-methylacetamide, benzanilide, cyclohexanecarboxanilide, and 2,4′-dichloroacetanilide.
Examples of the oxycarbonyl group include a group represented by —COOR ^b (R ^b = H, C _{1 to} C ₈ alkyl group, aryl group).
Specifically, carboxyl group, methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, n-butoxycarbonyl group, sec-butoxycarbonyl group, tert-butoxycarbonyl group, n-pentoxycarbonyl group, phenoxycarbonyl group, etc. Can be mentioned.

Preferred oxycarbonyl groups are a methoxycarbonyl group and an ethoxycarbonyl group.
Each group represented by R ⁴ is preferably an aryl group, a substituted aryl group, an oxycarbonyl group or a cyano group.
A preferred aryl group is a phenyl group.
Preferred examples of the substituted aryl group include a halogen atom substituted phenyl group and a trifluoromethyl substituted phenyl group.
In addition, in the case of a halogen atom, these substituents are preferably substituted by 1 to 5 pieces.
In the case of an alkoxy group or a trifluoromethyl group, one or two substituents may be substituted. In the case of one substitution, the para position or the ortho position is preferable, and in the case of two substitutions, the meta position is preferable. .
Preferred oxycarbonyl groups are a methoxycarbonyl group and an ethoxycarbonyl group.

As the preferred organic tellurium compound represented by (1), R ¹ represents a C _{1 to} C ₄ alkyl group or phenyl group, and R ² and R ³ represent a hydrogen atom or a C _{1 to} C ₄ alkyl group. , R ⁴ is preferably an aryl group, a substituted aryl group, or an oxycarbonyl group.
Particularly preferably, R ¹ represents a C _{1 to} C ₄ alkyl group or a phenyl group, R ² and R ³ represent a hydrogen atom or a C _{1 to} C ₄ alkyl group, and R ⁴ represents a phenyl group, A substituted phenyl group, a methoxycarbonyl group, and an ethoxycarbonyl group are preferable.

The organic tellurium compound represented by the formula (1) is specifically as follows.
(Methylterranylmethyl) benzene, (methylterranylmethyl) naphthalene, ethyl-2-methyl-2-methylterranyl-propionate, ethyl-2-methyl-2-n-butylterranyl-propionate, Patent Documents 2 and 3, etc. All of the described organic tellurium compounds can be exemplified.

The method for producing the organic tellurium compound represented by the formula (1) is not particularly limited, and can be produced by a known method described in Patent Documents 4 and 5 and the like.
WO 2004/14848 WO 2004/14962 For example, a compound of formula (1) can be produced by reacting a compound of formula (3), a compound of formula (4) and metal tellurium. Specific examples of the compound of the formula (3) are as follows.

〔式中、Ｒ^２、Ｒ^３及びＲ^４は、上記と同じ。Ｘは、ハロゲン原子を示す。〕

[Wherein R ² , R ³ and R ⁴ are the same as above. X represents a halogen atom. ]

Examples of the group represented by X include halogen atoms such as fluorine, chlorine, bromine and iodine. Preferably, chlorine and bromine are good.
M (R ¹ ) m (4)
[R ¹ is the same as above. M represents an alkali metal, alkaline earth metal or copper atom. When M is an alkali metal, m is 1, when M is an alkaline earth metal, m is 2, and when M is a copper atom, m is 1 or 2. ]

Examples of M include alkali metals such as lithium, sodium and potassium, alkaline earth metals such as magnesium and calcium, and copper. Lithium is preferable.
When M is magnesium, the compound (4) may be Mg (R ¹ ) 2 or a compound represented by R ¹ MgX (X is a halogen atom) (Grignard reagent). X is preferably chlorine or bromine.

The organic ditellurium compound used in the present invention is represented by the formula (2).
(R ¹ Te) 2 (2)
(R ¹ represents a C _{1 to} C ₈ alkyl group, aryl group, substituted aryl group or aromatic heterocyclic group.)

The group represented by R ¹ is as shown in Formula (1).
A preferable compound represented by the formula (2) is a compound in which R ¹ is a C _{1 to} C ₄ alkyl group or a phenyl group.

  Specifically, the compound represented by the formula (2) includes dimethylditelluride, diethylditelluride, di-n-propylditelluride, diisopropylditelluride, dicyclopropylditelluride, di-n- Butyl ditelluride, di-sec-butyl ditelluride, di-tert-butyl ditelluride, dicyclobutyl ditelluride, diphenyl ditelluride, bis- (p-methoxyphenyl) ditelluride, bis- (p-aminophenyl) ditelluride, bis- (p -Nitrophenyl) ditelluride, bis- (p-cyanophenyl) ditelluride, bis- (p-sulfonylphenyl) ditelluride, dinaphthylditelluride, dipyridylditelluride and the like. Preferred are dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, di-n-butyl ditelluride, and diphenyl ditelluride.

  In the present invention, an azo polymerization initiator may be used for the purpose of accelerating the polymerization rate. The azo polymerization initiator can be used without particular limitation as long as it is an azo polymerization initiator used in normal radical polymerization.

  For example, 2,2′-azobis (isobutyronitrile) (AIBN), 2,2′-azobis (2-methylbutyronitrile) (AMBN), 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN), 1,1′-azobis (1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2′-azobisisobutyrate (MAIB), 4,4′-azobis (4-cyanovaleric acid) (ACVA) 1,1′-azobis (1-acetoxy-1-phenylethane), 2,2′-azobis (2-methylbutyramide), 2,2′-azobis (4-methoxy-2,4- Dimethylvaleronitrile), 2,2′-azobis (2-methylamidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], 2,2′-azobis [ 2-Methyl-N- 2-hydroxyethyl) propionamide], 2,2′-azobis (2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2′-azobis (N-butyl-2-methyl) Propionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide) and the like.

  These azo initiators are preferably selected as appropriate according to the reaction conditions. For example, in the case of low temperature polymerization (40 ° C. or lower), 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), In the case of medium temperature polymerization (40-80 ° C.), 2,2′-azobis (isobutyronitrile) (AIBN), 2,2′-azobis (2-methylbutyronitrile) (AMBN), dimethyl-2,2 '-Azobisisobutyrate (MAIB), 1,1'-azobis (1-acetoxy-1-phenylethane), 4,4'-azobis (4-cyanovaleric acid) (ACVA), 2,2'- Azobis (2-methylbutyramide), 2,2′-azobis (2-methylamidinopropane) dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane], high temperature polymerization ( 1,1'- in the case of 80 ° C or higher) Zobis (1-cyclohexanecarbonitrile) (ACHN), 2-cyano-2-propylazoformamide, 2,2′-azobis (N-butyl-2-methylpropionamide), 2,2′-azobis (N-cyclohexyl) 2-methylpropionamide), 2,2′-azobis (2,4,4-trimethylpentane), 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] Is good.

  The segment (A) of the block polymer of the present invention is obtained by polymerizing a methyl methacrylate monomer. The segment (B) of the block polymer of the present invention can be obtained by polymerizing a styrene monomer.

The modifier for polylactic acid of the present invention polymerizes segment (A) and then polymerizes segment (B). Depending on the order of reaction, the segment (B) -segment (A) can also be obtained.
In the above, after the segment is manufactured, the reaction of the next block may be started as it is, or after the reaction is finished once, the reaction of the next segment may be started after purification.
The proportion of the monomer and the compound of formula (1) used may be appropriately adjusted depending on the molecular weight or molecular weight distribution of the copolymer obtained. Usually, the monomer is used in an amount of 20 to 4 with respect to 1 mol of the compound of formula (1). 1,000 mol, preferably 40 to 1,300 mol.

  The use ratio of the compound of formula (1) and the azo polymerization initiator is usually 0.01-100 mol, preferably 0.1-10 mol, particularly azo polymerization initiator, with respect to 1 mol of the compound of formula (1). Preferably it is 0.1-5 mol.

  When the compound of the formula (1) and the compound of the formula (2) are used in combination, the use amount thereof is usually 0.01 to 100 mol of the compound of the formula (2) with respect to 1 mol of the compound of the formula (1), preferably Is 0.05 to 10 mol, particularly preferably 0.1 to 5 mol.

  When the compound of the formula (1), the compound of the formula (2) and the azo polymerization initiator are used in combination, the amount used is usually 1 mol of the total of the compound of the formula (1) and the compound of the formula (2). The azo polymerization initiator may be 0.01 to 100 mol, preferably 0.1 to 10 mol, and particularly preferably 0.1 to 5 mol.

  The reaction is usually carried out without a solvent, but an organic solvent or an aqueous solvent generally used in radical polymerization may be used. Examples of the organic solvent that can be used include benzene, toluene, N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, 2-butanone (methyl ethyl ketone), dioxane, hexafluoroisopropol, chloroform, tetrachloride. Examples thereof include carbon, tetrahydrofuran (THF), ethyl acetate, trifluoromethylbenzene and the like. Examples of the aqueous solvent include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, diacetone alcohol and the like. The amount of the solvent used may be adjusted as appropriate. For example, 0.01 to 50 ml, preferably 0.05 to 10 ml, particularly preferably 0.1 to 1 ml of the solvent is used per 1 g of the vinyl monomer. good.

  Next, the mixture is stirred. The reaction temperature and reaction time may be appropriately adjusted depending on the molecular weight or molecular weight distribution of the polymer to be obtained, but are usually stirred at 0 to 150 ° C. for 1 minute to 100 hours. Preferably, stirring is performed at 20 to 100 ° C. for 0.1 to 30 hours. More preferably, stirring is performed at 20 to 80 ° C. for 0.1 to 15 hours. It is a feature of the present invention that a high yield and a precise molecular weight distribution can be obtained even at such a low polymerization temperature and a short polymerization time. At this time, the pressure is usually a normal pressure, but may be increased or decreased.

  After completion of the reaction, the solvent or residual monomer is removed under reduced pressure by a conventional method to take out the target polymer, or the target product is isolated by reprecipitation using a target polymer insoluble solvent. The reaction treatment can be performed by any treatment method as long as there is no problem with the object.

Moreover, since the organic tellurium compound used as an initiator in the present invention is stable to water, the polymer of the present invention can be synthesized by an aqueous polymerization method described in Patent Document 6 and the like shown below.
That is, the emulsion polymerization method uses a surfactant and polymerizes mainly in micelles. You may use dispersing agents, such as water-soluble polymers, such as polyvinyl alcohol, as needed. These surfactants can be used alone or in combination of two or more. The amount of the surfactant used is preferably 0.3 to 50 parts by weight, more preferably 0.5 to 50 parts by weight with respect to 100 parts by weight of the total monomers. Moreover, it is preferable that the usage-amount of water is 50-2000 weight part with respect to 100 weight part of all the monomers, More preferably, it is 70-1500 weight part. Although superposition | polymerization temperature is not specifically limited, It is preferable to carry out in the range of 0-100 degreeC, More preferably, it is 40-90 degreeC. What is necessary is just to set reaction time suitably so that a polymerization reaction may be completed according to reaction temperature or the composition of the monomer composition to be used, the kind of surfactant or a polymerization initiator, etc. Preferably within 24 hours.

  In the suspension polymerization method, a dispersant is used, and polymerization is mainly performed without using micelles. If necessary, a dispersing aid such as sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, or manganese sulfate may be used in combination with these dispersing agents. The amount of the water dispersion stabilizer used is preferably from 0.01 to 30 parts by weight, more preferably from 0.05 to 10 parts by weight, particularly preferably from 0.1 to 100 parts by weight based on 100 parts by weight of the total monomers. 5 parts by weight. Moreover, it is preferable that the usage-amount of water is 50-2000 weight part with respect to 100 weight part of all the monomers, More preferably, it is 70-1500 weight part. Although superposition | polymerization temperature is not specifically limited, It is preferable to carry out in the range of 0-100 degreeC, More preferably, it is 40-90 degreeC. What is necessary is just to set reaction time suitably so that a polymerization reaction may be completed according to reaction temperature or the composition of the monomer composition to be used, the kind of water dispersion stabilizer, a polymerization initiator, etc. Preferably within 24 hours.

In the miniemulsion polymerization method, a surfactant and a co-surfactant are used, and after the monomers are forcibly dispersed using a homogenizer or an ultrasonic device, the polymerization is performed mainly without passing through micelles. The amount of the surfactant or cosurfactant used is 0.3 to 50 parts by weight, particularly preferably 0.5 to 50 parts by weight, based on the total monomers. The ultrasonic irradiation time is 0.1 to 10 minutes, particularly preferably 0.2 to 5 minutes.
JP 2006-225524 A

  The molecular weight of the polymer can be adjusted by the reaction time, the amount of the compound of formula (1) and the amount of the compound of formula (2), but it is preferable to use a polymer having a number average molecular weight of 10,000 to 100,000. More preferably, a polymer having a number average molecular weight of 40,000 to 80,000 is used. If the number average molecular weight is less than 10,000, mold contamination during molding and bleeding out after long-term use may occur. When the number average molecular weight exceeds 100,000, the resulting resin composition becomes opaque.

The molecular weight distribution (PD = Mw / Mn) of the polymer is controlled between 1.0 and 2.0. Furthermore, it is possible to obtain a modifier for polylactic acid having a molecular weight distribution of 1.05 to 1.90, and further narrow molecular weight distribution of 1.05 to 1.80.
The ratio of the segment (A) to the segment (B) can be adjusted by the reaction time, the amount of the compound of the formula (1) and the amount of the compound of the formula (2) as well as the molecular weight, but the weight ratio (A) / ( B) is 0.4 to 9.0, preferably 0.4 to 7.0, more preferably 0.6 to 5.0.

The total light transmittance of the modifier for polylactic acid is 95% or more, preferably 98% to 99.9%. If it is less than 95%, it will cause discoloration of the polylactic acid resin composition and give the molded product a color change.
Further, the transmittance at 500 nm is 95% or more, preferably 98% to 99.9%. If it is less than 95%, it will cause discoloration of the polylactic acid resin composition and give the molded product a color change.
Therefore, the copolymer has a total light transmittance of 95% or more and a transmittance at 500 nm of 95% or more. Preferably, the total light transmittance is 98% or more and the transmittance at 500 nm is 98% or more.

When the organic tellurium compounds represented by formula (1) and formula (2) are used as an initiator, a tellurium atom may remain at the polymer terminal in the form of -TeR ¹ (R ¹ is the same as above).
Since the polymer in which the tellurium atom remains at the terminal is colored and is a metallic element, the transparency of the polylactic acid resin composition containing the resulting polylactic acid modifier and the prevention of contamination Therefore, the metal content including the remaining tellurium atoms is 1000 ppm or less, and particularly preferably 200 ppm or less, based on the entire resin.

  The tellurium atom remaining at the molecular end is adsorbed after completion of the polymerization reaction using a radical reduction method such as tributylstannane or a thiol compound, and further activated carbon, silica gel, activated alumina, activated clay, molecular sieves and polymer adsorbent. , A method of adsorbing metal with ion exchange resin, etc., or adding a peroxide such as hydrogen peroxide or benzoyl peroxide, or blowing air or oxygen into the system to oxidize the tellurium atom at the end of the polymer In liquid state such as liquid-liquid extraction method or solid-liquid extraction method that removes residual tellurium compounds by combining with water washing and appropriate solvent, and ultrafiltration that extracts and removes only those with specific molecular weight or less A purification method and these methods can also be combined.

The resin composition of the present invention can be obtained by kneading a polylactic acid resin and the polylactic acid modifier. The proportion of the polylactic acid modifier in the resin composition is preferably 0.1 to 50% by weight. More preferably, it is 1-50 weight%, More preferably, it is 5-30 weight%.
There is no restriction | limiting in particular as a kneading method, What is necessary is just to be able to perform mechanical shearing in a polylactic acid melted state. As a specific apparatus, an extruder, particularly a twin screw extruder is preferable.
When using a twin screw extruder, polylactic acid is supplied from the feed port on the upstream side of the extruder and a modifier is supplied from the feed port on the downstream side, or polylactic acid and the modifier are mixed in advance by a blender or the like. A method of supplying from the feed port is conceivable, but there is no particular limitation. Although there is no restriction | limiting in particular also in the screw arrangement of an extruder, It is preferable to provide a kneading zone.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, it is not limited to these at all. In Examples and Comparative Examples, various physical properties were measured using the following equipment.
¹ H-NMR: Bruker BioSpin AVANCE 500 (500 MHz)
Molecular weight and molecular weight distribution: Gel permeation chromatograph Nippon Waters GPCV-2000 (Column: Tosoh TSK-GEL GMH _XL + TSK-GEL Multipore H _XL- M, polystyrene standard: Tosoh TSK
Standard)
Te content in polymer: ICP / MS

Example 1
(Synthesis of polystyrene-polymethyl methacrylate diblock polymer)
414 ml of deionized water was added to a 1 L four-necked flask, and argon gas was bubbled for 30 minutes, and 414 mg of polyvinyl alcohol KH-17 [Nippon Gosei Chemical Co., Ltd.] was added and dissolved. 125 g (1.20 mol) of styrene [Wako Pure Chemical Industries, Ltd.] was added to a 200 ml four-necked flask, and argon gas was bubbled for 30 minutes to give 1.54 g of ethyl-2-methyl-2-n-butylterranyl-propionate. (5.13 mmol), 947 mg (2.56 mmol) of dibutyl ditelluride, and 626 mg (2.56 mmol) of 1,1′-azobis (1-cyclohexanecarbonitrile) were added. The obtained styrene solution was added to the aqueous polyvinyl alcohol solution and reacted at 90 ° C. for 27 hours. According to NMR analysis, the polymerization rate was 98%. Moreover, it was number average molecular weight 20,200 and PD = 1.14 by GPC analysis.

  Next, water is removed from the polystyrene suspension obtained above, 280 g (2.80 mol) of methyl methacrylate [Mitsubishi Gas Chemical Co., Ltd.] is added, the polystyrene is dissolved, and the water removed earlier is added again. And reacted at 80 ° C. for 22 hours. After completion of the reaction, the reaction solution was filtered and washed with 828 mL of deionized water, and the resulting polymer beads were dissolved in 1 L of ethyl acetate. The solution was washed twice with 1 L of saturated brine containing 1 mol / l NaOH, then washed once with 1 L of saturated brine, dried over magnesium sulfate, and filtered. The obtained ethyl acetate solution was poured into 5 L of stirring methanol. The precipitated polymer was filtered and dried to obtain 329 g of polystyrene-polymethyl methacrylate diblock polymer (yield 81%). According to GPC analysis, the number average molecular weight was 48,800 and PD was 1.51. From the NMR analysis, the weight ratio (A) / (B) of the segment (A) and the segment (B) of the obtained block polymer was 2.13.

(Production and evaluation of biodegradable resin composition)
30% of the above block polymer was added to polylactic acid [TE-4000 manufactured by Unitika Ltd.] and kneaded with Laboplast Mill [manufactured by Toyo Seiki Co., Ltd.]. The kneading conditions were 200 ° C., 60 rpm, and 5 minutes. The taken out resin composition was pulverized and pelletized, and then a dumbbell piece having a thickness of 3 mm was produced by injection molding. Durability evaluation was performed using the pulverized pellets. In the durability evaluation method, the test piece was hydrolyzed under the conditions of 60 ° C. and 90% humidity, the number average molecular weight (Mn) was measured using GPC (manufactured by Waters), and the half lives were compared. In addition, transparency was evaluated using dumbbell pieces. For the evaluation of transparency, the transmittance of 700 nm obtained by a spectrophotometer was compared. The results are shown in Table 1.

Example 2
(Synthesis of polystyrene-polymethyl methacrylate diblock polymer)
400 ml of deionized water was added to a 1 L four-necked flask, and argon gas was bubbled for 30 minutes, and 400 mg of polyvinyl alcohol KH-17 [Nippon Gosei Chemical Co., Ltd.] was added and dissolved. To a 200 ml four-necked flask, 135 g (1.30 mol) of styrene [Wako Pure Chemical Industries, Ltd. reagent] was added, and argon gas was bubbled for 30 minutes to obtain 886 mg of ethyl-2-methyl-2-n-butylterranyl-propionate (2 .96 mmol), 545 mg (1.48 mmol) of dibutyl ditelluride, and 361 mg (1.48 mmol) of 1,1′-azobis (1-cyclohexanecarbonitrile) were added. The obtained styrene solution was added to the aqueous polyvinyl alcohol solution and reacted at 90 ° C. for 24 hours. According to NMR analysis, the polymerization rate was 96%. Moreover, it was number average molecular weight 28,600 and PD = 1.15 by GPC analysis.
Next, 107 g (1.06 mol) of methyl methacrylate [Mitsubishi Gas Chemical Co., Ltd.] was dropped into the polystyrene suspension obtained above at 80 ° C. over 12 hours. Reacted for hours. After completion of the reaction, the reaction solution was filtered and washed with 800 mL of deionized water, and the resulting polymer beads were dissolved in 800 mL of ethyl acetate. The solution was washed twice with 800 ml of saturated brine containing 1 mol / L NaOH, then washed once with 800 ml of saturated brine, dried over magnesium sulfate, and filtered. The obtained ethyl acetate solution was poured into 4 L of stirring methanol. The precipitated polymer was filtered and dried to obtain 210 g of polystyrene-polymethyl methacrylate diblock polymer (yield 87%). According to GPC analysis, the number average molecular weight was 39,100 and PD was 1.33. From the NMR analysis, the weight ratio (A) / (B) of the segment (A) and the segment (B) of the obtained block polymer was 0.69.

(Production and evaluation of biodegradable resin composition)
A resin test piece was prepared and tested in the same manner as in Example 1 except that 10% of the block polymer was added. The results are shown in Table 1.

Comparative Example 1
Resin test pieces made only of polylactic acid [TE-4000 manufactured by Unitika Ltd.] were prepared and tested. The results are shown in Table 1.

Comparative Example 2
A comparative resin composition was prepared using a commercially available Modiper MS10B (manufactured by NOF Corporation). A resin test piece was prepared in the same manner as in Example 1 by adding 10% to polylactic acid, and the test was performed.
Modiper MS10B is a polystyrene-polymethyl methacrylate diblock polymer. According to GPC analysis, the number average molecular weight was 89,200 and PD was 2.63.

Comparative Example 3 (Synthesis of polymethyl methacrylate-polystyrene diblock polymer)
144 ml of deionized water was added to a 1 L four-necked flask, and argon gas was bubbled for 30 minutes, and 432 mg of polyvinyl alcohol KH-17 [Nippon Gosei Chemical Co., Ltd.] was added and dissolved. To a 100 ml four-necked flask was added 44.9 g (450 mmol) of methyl methacrylate [Mitsubishi Gas Chemical Co., Ltd.], bubbled with argon gas for 30 minutes, and 1.93 g of ethyl-2-methyl-2-n-butylteranyl-propionate. (6.43 mmol), 475 mg (1.29 mmol) of dibutyl ditelluride were added. The obtained methyl methacrylate solution was added to the aqueous polyvinyl alcohol solution and reacted at 80 ° C. for 16 hours. According to NMR analysis, the polymerization rate was 100%. Moreover, it was number average molecular weight 7,250 and PD = 1.44 by GPC analysis.
Next, water was removed from the polymethyl methacrylate suspension obtained above, 844 g (8.10 mol) of styrene [Wako Pure Chemical Industries, Ltd.] was added, and polymethyl methacrylate was dissolved. The reaction was carried out at 30 ° C. for 30 hours. According to NMR analysis, the polymerization rate was 52.3%. Dilute with 1.5 L of ethyl acetate. The solution was washed twice with 1 L of saturated brine containing 1 mol / l NaOH, then washed once with 1 L of saturated brine, dried over magnesium sulfate, and filtered. The obtained ethyl acetate solution was poured into 6 L of stirring methanol. The precipitated polymer was filtered and dried to obtain 386 g of polymethyl methacrylate-polystyrene diblock polymer (43% yield). According to GPC analysis, the number average molecular weight was 58,800, and PD = 1.21. From the NMR analysis, the weight ratio (A) / (B) of the segment (A) and the segment (B) of the obtained block polymer was 0.09.

(Production and evaluation of biodegradable resin composition)
Resin test pieces were prepared and tested in the same manner as in Example 2. The results are shown in Table 1.

  As shown in Table 1, the resin compositions of Examples 1 and 2 according to the present invention have a significantly longer half-life for decreasing the number average molecular weight than the polylactic acid of Comparative Example 1 alone. Excellent in properties. Further, as can be seen from the transmittance, the decrease in transparency is suppressed. When synthesizing the block polymer, a resin composition having both high hydrolysis resistance and transparency was obtained by controlling the weight ratio, number average molecular weight, and molecular weight distribution of the segments. In Comparative Examples 2 to 3, the hydrolysis resistance was insufficient and opaque.

Claims (2)

A polylactic acid modifier having a segment (A) consisting only of polymethyl methacrylate and a segment (B) consisting only of polystyrene, which is a block polymer having the following characteristics (a) to (c) :
(A) The weight ratio (A) / (B) of the segment (A) to the segment (B) is 0.4 to 9.0.
(Ii) the number average molecular weight of the block polymer, 4 0,000～100,000
(C) Molecular weight distribution 1.0-2.0
The block polymer is a polymer obtained by polymerization using an organic tellurium compound-based polymerization initiator,
Organic tellurium compound polymerization initiator,
(A) an organic tellurium compound represented by formula (1),
(B) a mixture of an organic tellurium compound represented by formula (1) and an azo polymerization initiator,
(C) a mixture of an organic tellurium compound represented by formula (1) and an organic ditellurium compound represented by formula (2), or
(D) Mixture of organic tellurium compound represented by formula (1), azo polymerization initiator and organic ditellurium compound represented by formula (2)
The modifier for polylactic acid which is either.

(In the formula, R ¹ represents a C _{1 to} C ₈ alkyl group, an aryl group, a substituted aryl group or an aromatic heterocyclic group. R ² and R ³ represent a hydrogen atom or a C _{1 to} C ₈ alkyl group. R ⁴ represents an aryl group, a substituted aryl group, an aromatic heterocyclic group, an acyl group, an amide group, an oxycarbonyl group, or a cyano group.
(R ¹ Te) ₂ (2)
(In the formula, R ¹ is the same as above.) A modified polylactic acid resin composition obtained by kneading polylactic acid and the polylactic acid modifying agent according to claim 1 .