HK1135713B - Process for producing polylactic acid block copolymer - Google Patents

Description

Preparation method of polylactic acid block copolymer

Technical Field

The present invention relates to a method for preparing a polylactic acid block copolymer, and more particularly, to a polylactic acid block copolymer having a high molecular weight and capable of growing only a stereocomplex crystal by repeating a heat-melting treatment at a low cost.

Background

Plastics derived from petroleum are lightweight, tough, durable, can be easily and arbitrarily shaped, and are therefore mass produced, gradually supporting our lives in many ways. However, these plastics are not easily decomposed and accumulated when discarded in the environment. In addition, a large amount of carbon dioxide gas is released when the material is burned, and the global warming is accelerated.

In view of the current situation, resins composed of materials from which oil is removed or biodegradable plastics which can be decomposed by microorganisms have been widely studied. Most biodegradable plastics currently under study have aliphatic carboxylic acid ester units and are easily decomposed by microorganisms. On the other hand, they are poor in thermal stability, and are seriously deteriorated in molecular weight and hue in a molding process in which they are exposed to high temperature such as melt spinning, injection molding, melt film forming, etc.

Among them, polylactic acid (hereinafter, also referred to as PLA) is a plastic having good heat resistance and a balance between color and mechanical strength. The homopolymer of poly-L-lactic acid (hereinafter also referred to as PLLA) or poly-D-lactic acid (hereinafter also referred to as PDLA) (hereinafter also referred to as homo PLA or homo PLA) is produced by a ring-opening polymerization method using lactide as a raw material or a direct polymerization method using dehydration condensation of lactic acid. The melting points of the poly L-lactic acid and the poly D-lactic acid are generally about 170 ℃. Therefore, the heat resistance is low as compared with a petrochemical polyester represented by polyethylene terephthalate or polybutylene terephthalate, and there is a problem that when the prepared poly L-lactic acid is used as a fiber or the like, the product cannot be ironed. Therefore, it is currently required to have high heat resistance.

In order to solve the above problems, it has been studied to improve the heat resistance of polylactic acid. One of them is a stereocomplex polylactic acid (hereinafter, also referred to as scPLA) formed by mixing poly-L-lactic acid and poly-D-lactic acid.

However, when poly-L-lactic acid and poly-D-lactic acid are mixed at a mass ratio of 1: 1, not only stereocomplex crystals generally occur, but also homo-PLA crystals often occur particularly in the high molecular weight field. Further, since it is difficult to form scPLA having a stable stereocomplex crystal content of 100% by the heat melting process, there is a problem that the characteristics of scPLA having a high melting point cannot be sufficiently exhibited due to the presence of homo-PLA. Therefore, there is an urgent need for a method of preparing an article without doped homo-PLA with a stable scPLA content of 100%.

In addition to the method of preparing scPLA by mixing the poly L-lactic acid and the poly D-lactic acid, there is also a method of preparing a polylactic acid block copolymer by mixing poly L-lactic acid and poly D-lactic acid in equal amounts and reacting the poly L-lactic acid and poly D-lactic acid to covalently bond them (see, for example, JP-A2002-356543). Thus, scPLA was preferentially formed between the chain lock of L-lactic acid unit and the chain lock of D-lactic acid unit between the molecules of the polylactic acid block copolymer, and no characteristic peak of homo-PLA was observed on a graph showing Differential Scanning Calorimetry (DSC). That is, a product in which the content of scPLA was stabilized at 100% without being doped with homo-PLA could be prepared.

In addition, Japanese patent application laid-open No. 2003-342836 discloses a heat-bondable fiber which is a core-sheath composite fiber, and the core component is a polylactic acid polymer in which a polylactic acid polymer having a stereocomplex obtained by blending a polylactic acid having an optical purity of 70 to 100% and a polylactic acid having an optical purity of 70 to 100% ee is used.

Disclosure of Invention

However, at present, the source of D-lactide or D-lactic acid as a raw material of the component D is limited, and the amount of D-lactide or D-lactic acid to be circulated is small, so that the market price is higher than that of L-lactide or L-lactic acid as a raw material of the component L. Therefore, according to the conventional technique, when the component D and the component L are mixed in equal amounts, the production cost of the stereocomplex polylactic acid having a mass ratio of the component D to the component L of 1: 1 inevitably increases.

In addition, the above-mentioned Japanese patent application laid-open No. 2002-356543 discloses a method for producing a multiblock copolymer comprising poly-L-lactic acid and poly-D-lactic acid, the multiblock copolymer being a stereocomplex polylactic acid containing only stereocomplex crystals. However, there is a problem that reprecipitation is required every time the number of blocks of the multiblock copolymer is increased, and thus it is not suitable for industrial production. Therefore, a method for producing a polylactic acid block copolymer, which is capable of growing only a stereocomplex crystal by repeating melting and crystallization at low cost and a weight average molecular weight of 10 ten thousand or more, has not been proposed.

Furthermore, in the technique described in the above-mentioned Japanese patent application laid-open No. 2003-356543, when the mixing ratio of the poly L-lactic acid and the poly D-lactic acid is out of the range of 30/70-70/30 (mass ratio), the formation of a stereocomplex which inhibits stereospecific binding is inhibited, and it is difficult to control the crystal dissolution starting temperature of the resulting polylactic acid polymer to 180 ℃ or higher, and there is a problem that the technique cannot be applied to a wide molding temperature range.

Accordingly, an object of the present invention is to provide a method for producing a polylactic acid block copolymer having a high molecular weight and capable of growing only a stereocomplex crystal by repeating a heat-melting treatment at a low cost.

The present inventors have made extensive studies in view of the above-mentioned conventional techniques, and as a result, have found a method capable of achieving the above-mentioned object, thereby completing the present invention.

The present inventors have surprisingly found that, by the production method found by the present inventors, heat resistance equivalent to that of sbPLA obtained when L-lactic acid and D-lactic acid are mixed in equal amounts can be achieved even when the L-lactic acid unit (L component) and the D-lactic acid unit (D component) are in an unequal compositional ratio (mass ratio). Further, according to the present invention, it is possible to reduce the amount of D-lactide used, to significantly reduce the production cost of stereocomplex polylactic acid, and to find a solution to the problem that cannot be solved. Furthermore, even when the cost structure of L-form (poly L-lactic acid or L-lactide) and D-form (poly D-lactic acid or D-lactide) is reversed in the future, it is possible to realize heat resistance equivalent to sbPLA obtained when equal amounts of L-form and D-form are mixed by using a large amount of inexpensive raw materials, to significantly reduce the production cost, and to stably provide an inexpensive product without being limited by the price fluctuation of the raw materials.

That is, the method for producing a polylactic acid block copolymer of the present invention is characterized by (i) performing ring-opening polymerization of D-lactide (component D) in the presence of poly L-lactic acid (component L), or (ii) performing ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D);

wherein the mass ratio of the D component to the L component is 60/40-91/9 or 60/40-91/9.

The method for producing a polylactic acid block copolymer of the present invention is characterized by comprising a step of melt-mixing or solution-mixing the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer;

the 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), wherein the mass ratio of the component D to the component L is 60/40-91/9, and the weight average molecular weight is 8-50 ten thousand;

the 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), and the mass ratio of the component L to the component D is 60/40-91/9.

Further, the method for producing a polylactic acid block copolymer of the present invention is characterized by comprising a step of melt-mixing or solution-mixing the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer;

the 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), wherein the mass ratio of the component D to the component L is 60/40-91/9, and the weight average molecular weight is 8-50 ten thousand;

the 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), and the mass ratio of the component L to the component D is 60/40 to 91/9.

The polylactic acid block copolymer of the present invention is characterized in that the mass ratio of L-lactic acid units to D-lactic acid units is 60/40 to 91/9, or the mass ratio of D-lactic acid units to L-lactic acid units is 60/40 to 91/9; wherein the content of the stereocomplex crystal is 80-100%.

The present invention is also a molded article comprising the polylactic acid block copolymer.

According to the production method of the present invention, even when the composition (mass ratio) of the L component (poly L-lactic acid or L-lactide) and the D component (poly D-lactic acid or D-lactide) to be used is greatly inclined, the content of the stereocomplex crystal is extremely high, and a polylactic acid block copolymer can be produced. Therefore, when the production cost and/or price of the L component and the D component are/is low in the production stage, by using a large amount of inexpensive raw materials in the production method of the present invention, a product having the same characteristics as those of the conventional stereocomplex polylactic acid, which can be produced at an extremely low cost and is inexpensive, highly functional and highly added to value can be produced and provided.

Further, according to the production method of the present invention, it is possible to produce a polylactic acid block copolymer which has a high weight average molecular weight and in which only a stereocomplex crystal can be grown by repeating melting and crystallization, which is difficult to produce according to the conventional production method.

In addition, the preparation method can control the crystal melting point of the obtained polylactic acid block copolymer in a high-temperature field, and the obtained polylactic acid block copolymer has good heat resistance. Therefore, the polylactic acid block copolymer obtained by the production method of the present invention can be melt-molded to produce a yarn, a film, or various molded articles. Particularly, the use of the polylactic acid block copolymer obtained by the production method of the present invention as a fiber is not suitable as a conventional use of polylactic acid, and the fiber can be widely used in all fiber products because the texture of the fiber is not damaged even when the polylactic acid block copolymer is ironed at 160 ℃ or higher (180 ℃). In addition, the polylactic acid block copolymer prepared by the preparation method has biodegradability, so that a product which has little influence on the environment after being discarded and is beneficial to environmental protection can be provided.

Further objects, features and characteristics of the present invention will become apparent by referring to preferred embodiments illustrated in the following description and drawings.

Drawings

FIG. 1 is a DSC chart of a polylactic acid block copolymer (sample name: PLA20) obtained in comparative example 1 described later.

FIG. 2 is a DSC chart of a polylactic acid block copolymer (sample name: PLA21) obtained in comparative example 2 described later.

FIG. 3 is a DSC chart of a polylactic acid block copolymer (sample name: PLA22) obtained in example 1 described later.

FIG. 4 is a DSC chart of a polylactic acid block copolymer (sample name: PLA23) obtained in example 2 described later.

FIG. 5 is a DSC chart of a polylactic acid block copolymer (sample name: PLA24) obtained in example 3 described later.

FIG. 6 is a DSC chart of a polylactic acid block copolymer (sample name: PLA25) obtained in example 4 described later.

FIG. 7 is a DSC chart of a polylactic acid block copolymer (sample name: PLA26) obtained in comparative example 3 described later.

FIG. 8 is a DSC chart of a polylactic acid block copolymer (sample name: PLA27) obtained in example 5 described later.

FIG. 9 is a DSC chart of a polylactic acid block copolymer (sample name: PLA28) obtained in example 6 described later.

FIG. 10 is a DSC chart of a polylactic acid block copolymer (sample name: PLA29) obtained in example 7 described later.

FIG. 11 is a DSC chart of a polylactic acid block copolymer (sample name: PLA30) obtained in example 8 described later.

Detailed description of the invention

Hereinafter, embodiments of the present invention will be described in detail.

(method for producing polylactic acid Block copolymer >

The method for producing a polylactic acid block copolymer of the present invention is characterized by (i) performing ring-opening polymerization of D-lactide (component D) in the presence of poly L-lactic acid (component L), or (ii) performing ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D); wherein the mass ratio of the D component to the L component is 60/40-91/9 or 60/40-91/9. Hereinafter, the present invention will be described with respect to each constituent element.

(Poly L-lactic acid, Poly D-lactic acid)

The poly L-lactic acid (PLLA) of the above (i) or the poly D-lactic acid (PDLA) of the above (ii) is substantially composed of an L-lactic acid unit or a D-lactic acid unit represented by the following chemical formula (1).

[ CHEM 1]

Chemical formula (1)

In the chemical formula (1), C^*Represents chiral carbon atom, and the stereo configuration of the L-lactic acid unit is S configuration and the stereo configuration of the D-lactic acid unit is R configuration based on the chiral carbon atom.

The PLLA is preferably constituted by 90 to 100 mol%, more preferably 92 to 100 mol%, still more preferably 95 to 100 mol% of L-lactic acid units, based on 100 mol% of all the constituent units in the PLLA. When the L-lactic acid unit in the PLLA is less than 90 mol%, the melting point of the finally obtained polylactic acid block copolymer may not be easily increased.

The PLLA may contain a constituent unit other than an L-lactic acid unit. The content of the constituent unit other than the L-lactic acid unit is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, and still more preferably 5 to 0 mol% based on 100 mol% of all the constituent units in PLLA. Examples of the structural unit other than the L-lactic acid unit that may be contained in PLLA include a D-lactic acid unit, a structural unit derived from a compound other than lactic acid, and the like.

The PDLA is preferably composed of 90 to 100 mol%, more preferably 92 to 100 mol%, and still more preferably 95 to 100 mol% of D-lactic acid units, based on 100 mol% of all the constituent units in the PDLA. When the D-lactic acid unit in the PDLA is less than 90 mol%, the melting point of the finally produced polylactic acid block copolymer may not be easily increased.

The PDLA may contain a constituent unit other than a D-lactic acid unit. The content of the constituent units other than the D-lactic acid unit is preferably 10 to 0 mol%, more preferably 8 to 0 mol%, still more preferably 5 to 0 mol%, based on 100 mol% of all the constituent units in the PLDLA. Examples of the constituent unit other than the D-lactic acid unit that may be contained in PDLA include an L-lactic acid unit, a constituent unit derived from a compound other than lactic acid, and the like.

Examples of the constituent units derived from compounds other than lactic acid that may be contained in the PLLA or the PDLA include units derived from dicarboxylic acid, units derived from polyol, units derived from hydroxycarboxylic acid, or units derived from lactone, or units derived from polyester produced from the above-mentioned constituent units, units derived from polyether, or units derived from polycarbonate. However, the present invention is not limited to these.

Examples of the dicarboxylic acid include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the polyol include aliphatic polyols such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, octylene glycol, glycerol, sorbitan, neopentyl glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol, and aromatic polyols in which ethylene oxide is added to bisphenol. Examples of the hydroxycarboxylic acid include glycolic acid and hydroxybutyric acid, and examples of the lactone include glycolide, epsilon-caprolactone-glycolide, epsilon-caprolactone, beta-lactide, delta-butyrolactone, beta-or gamma-butyrolactone, pivalolactone and delta-valerolactone.

From the viewpoint of obtaining a polymer having a higher melting point, the mass ratio of the L-lactic acid units and the D-lactic acid units in the PLLA is preferably in the range of L-lactic acid units/D-lactic acid units being 95/5-100/0, and the mass ratio of the D-lactic acid units and the L-lactic acid units in the PDLA is preferably in the range of D-lactic acid units/L-lactic acid units being 95/5-100/0.

The weight average molecular weight of the PLLA or the PDLA is preferably 0.7 to 45 ten thousand, more preferably 0.7 to 20 ten thousand. When the weight average molecular weight of the PLLA or the PDLA falls outside the above range, the content of the stereocomplex crystal in the polylactic acid block copolymer produced by the production method of the present invention may sometimes be difficult to reach 80% or more. In the present invention, the weight average molecular weight is a polystyrene equivalent value measured by GPC (Gel Permationchromatography).

The method for obtaining the PLLA or the PDLA is not particularly limited, and for example, a method of dehydration condensation of L-lactic acid or D-lactic acid, and a method of ring-opening polymerization of L-lactide or D-lactide are cited, but a method of ring-opening polymerization of L-lactide or D-lactide is preferable from the viewpoint of easy availability of a high molecular weight compound and easy control of the molecular weight.

The purity of the L-lactide or D-lactide used for obtaining the PDLA or the PLLA is not particularly limited, but from the viewpoint of obtaining a polymer having a high molecular weight, the free acid contained in the L-lactide or D-lactide accounts for preferably 10% by mass or less, more preferably 1% by mass or less, still more preferably 0.15% by mass or less, and particularly preferably 0.05% by mass or less of 100% by mass of the L-lactide or D-lactide. When the free acid content in the L-lactide or the D-lactide exceeds 10% by mass, the ring-opening polymerization reaction may not be performed. The purification method of the L-lactide or the D-lactide is not particularly limited, and a conventionally known method such as crystallization or distillation, a method described in Japanese patent laid-open No. 2004-149418, a method described in Japanese patent laid-open No. 2004-149419, or the like can be appropriately selected and used.

The ring-opening polymerization is carried out in the presence of an organic solvent and a polymerization catalyst. The polymerization catalyst is not particularly limited as long as it promotes the polymerization reaction, and examples thereof include compounds containing at least 1 metal element selected from group II elements, rare earth metals, transition metals of the fourth period, aluminum, germanium, tin and antimony. Examples of the group II element include magnesium, calcium, strontium, and the like. Examples of the rare earth elements include scandium, yttrium, lanthanum, and cerium. Examples of the transition metal of the fourth period include iron, cobalt, nickel, zinc, titanium, and the like.

Examples of the polymerization catalyst containing the metal element include carboxylates of the metal elements exemplified above, alkoxides of the metal elements exemplified above, phenoxides of the metal elements exemplified above, and enols of β -diketone compounds of the metal elements exemplified above, which can be used alone or in combination of two or more kinds thereof. The polymerization catalyst containing the metal element is preferably at least one selected from the group consisting of tin 2-ethylhexanoate, titanium isopropoxide and aluminum isopropoxide in consideration of polymerization activity or hue.

The amount of the polymerization catalyst containing the metal element is preferably 0.001 to 0.5 part by weight, more preferably 0.001 to 0.1 part by weight, and still more preferably 0.003 to 0.01 part by weight, based on 100 parts by weight of the L-lactide or the D-lactide. If the amount of the polymerization catalyst containing the metal element is less than 0.001 parts by weight based on 100 parts by weight of the L-lactide or D-lactide, the reaction proceeds slowly, and there is a possibility that the effect of reducing the production cost of the lactic acid block copolymer produced by the production method of the present invention in which the composition ratio (mass ratio) of the L-component (poly L-lactic acid or L-lactide) and the D-component (poly D-lactic acid or D-lactide) is greatly inclined cannot be obtained. On the other hand, if the amount of the polymerization catalyst containing the metal element is more than 0.5 parts by weight based on 100 parts by weight of the L-lactide or the D-lactide, the reaction becomes difficult to control, racemization or dispersion degree may increase, coloring of the obtained polymer may become remarkable, and the use of the obtained polymer may be limited.

When the ring-opening polymerization is carried out in the presence of a polymerization catalyst containing the metal element, a polymerization initiator may be used. Examples of the polymerization initiator include alcohol compounds. The alcohol is preferably an alcohol which does not inhibit the polymerization of the polylactic acid and does not have volatility. Specific examples thereof include decyl alcohol, dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and lauryl alcohol. They may be used alone or in combination of two or more.

The amount of the polymerization initiator used is preferably 0 to 20 parts by weight, more preferably 0.1 to 15 parts by weight, based on 100 parts by weight of the L-lactide or the D-lactide. When the amount of the polymerization initiator used exceeds 20 parts by weight with respect to 100 parts by weight of the L-lactide or the D-lactide, it may be difficult to obtain a polymer of a target molecular weight.

The atmosphere in which the ring-opening polymerization of the L-lactide or the D-lactide is carried out in the presence of the polymerization catalyst containing the metal element is not particularly limited, but an atmosphere of an inert gas such as nitrogen or argon is preferable for the reason of suppressing coloring of a product and the like.

The reaction time of the ring-opening polymerization of the L-lactide or the D-lactide performed in the presence of the polymerization catalyst containing the metal element is preferably 15 minutes to 5 hours, more preferably 30 minutes to 2 hours. When the reaction time is less than 15 minutes, the reaction does not proceed sufficiently, and thus the target polymer may not be obtained; when it exceeds 5 hours, there is a possibility that the resulting polymer will be colored or its dispersibility will increase.

The reaction temperature of the ring-opening polymerization of the L-lactide or the D-lactide performed in the presence of the polymerization catalyst containing the metal element is preferably 100 to 250 ℃, more preferably 150 to 230 ℃, still more preferably 170 to 230 ℃. When the reaction temperature is less than 100 ℃, the reaction proceeds slowly, and there is a possibility that the effect of reducing the production cost of the polylactic acid block copolymer obtained by the production method of the present invention in which the composition ratio (mass ratio) of the L-component (poly L-lactic acid or L-lactide) and the D-component (poly D-lactic acid or D-lactide) is greatly inclined cannot be obtained. When the reaction temperature exceeds 250 ℃, the reaction becomes difficult to control, racemization or increase in dispersibility may be caused, and moreover, coloring of the resulting polymer may become significant, and the use of the resulting polymer may be limited.

The reaction pressure for the ring-opening polymerization of the L-lactide or D-lactide in the presence of the polymerization catalyst containing the metal element is not particularly limited as long as the ring-opening polymerization can be performed in a solution, and the reaction can be performed under atmospheric pressure, reduced pressure, or increased pressure. From the viewpoint that the production cost can be reduced without requiring an electrically resistant production apparatus, it is preferably carried out under atmospheric pressure.

The ring-opening polymerization of the L-lactide or D-lactide in the presence of the polymerization catalyst containing the metal element can be carried out by using a conventionally known production apparatus, for example, a vertical reaction vessel equipped with a high-viscosity stirring blade such as a helical ribbon blade.

The PLLA is preferably obtained by removing the remaining lactide after the ring-opening polymerization of L-lactide. Also, the PDLA is preferably subjected to ring-opening polymerization of D-lactide, and then the remaining lactide is removed. Preferably, the melting point of the finally prepared polylactic acid block copolymer may be increased by removing the remaining lactide from the PLLA or the PDLA.

The method for removing the remaining lactide is not particularly limited, and for example, the removal can be performed by reducing the pressure in the reaction system or by washing (purification) with an organic solvent, but from the viewpoint of ease of operation, it is preferably performed by reducing the pressure in the reaction system.

The reduced pressure condition is not particularly limited, but the temperature in the system after the completion of the polymerization reaction is preferably in the range of 130 ℃ to 250 ℃, more preferably 130 ℃ to 250 ℃. The pressure in the system is preferably 70kpa or less. When the temperature is less than 130 ℃, the viscosity in the system increases or the system is solidified, which makes the apparatus difficult to operate. On the other hand, when the temperature exceeds 250 ℃, depolymerization reaction of lactide occurs, resulting in an increase in the degree of dispersion of the resulting PLLA or PDLA. Further, when the pressure in the system exceeds 70kPa, the lactide removal becomes insufficient.

The atmosphere at the time of pressure reduction is not particularly limited, but from the viewpoint of suppressing decomposition of residual lactide or coloration of the polymer, an inert gas atmosphere such as nitrogen gas or argon gas is preferable.

In addition, when the amount of lactide remaining in the PLLA or the PDLA is large, the melting point of the finally produced polylactic acid block copolymer is lowered, and in consideration of this, the PLLA or the PDLA is preferably low in the content of L-lactide or D-lactide regardless of whether the removal treatment of the remaining lactide is performed. That is, the content of L-lactide in the poly L-lactic acid before the ring-opening polymerization of D-lactide is carried out in the presence of the poly L-lactic acid is preferably 0 to 5% by mass, more preferably 0 to 1% by mass, still more preferably 0 to 0.5% by mass, particularly preferably 0 to 0.1% by mass, based on the total mass of the poly L-lactic acid. Further, the content of D-lactide in the poly D-lactic acid before the ring-opening polymerization of L-lactide is carried out in the presence of the poly D-lactic acid is preferably 0 to 5 mass%, more preferably 0 to 1 mass%, still more preferably 0 to 0.5 mass%, particularly preferably 0 to 0.1 mass% based on the total mass of the poly D-lactic acid. When the content of L-lactide in the poly L-lactic acid or the content of D-lactide in the poly D-lactic acid exceeds 5 mass%, the melting point of the finally produced polylactic acid block copolymer is lowered.

(Ring opening polymerization of D-lactide or L-lactide)

After the poly L-lactic acid or the poly D-lactic acid is produced, (i) ring-opening polymerization of D-lactide is performed in the presence of the poly L-lactic acid, or (ii) ring-opening polymerization of L-lactide is performed in the presence of the poly D-lactic acid. The ring-opening polymerization of D-lactide or L-lactide after the production of the poly L-lactic acid or the poly D-lactic acid will be described.

The purity of the D-lactide is preferably 90 mol% to 100 mol%, more preferably 92 mol% to 100 mol%, and still more preferably 95 mol% to 100 mol%, based on the total mole of the D-lactide being 100 mol%. The content of components other than D-lactide is preferably 10 mol% to 0 mol%, more preferably 8 mol% to 0 mol%, and still more preferably 5 mol% to 0 mol%. When the purity of the D-lactide is less than 90 mol%, the content of the stereocomplex crystal in the polylactic acid block copolymer produced by the production method of the present invention is hardly 80% or more. Examples of the other components contained in the D-lactide include L-lactide, L-lactic acid, dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, and the like. Specific examples of the dicarboxylic acid, the polyol, the hydroxycarboxylic acid, or the lactone have been described above, and therefore, description thereof is omitted here.

The purity of the L-lactide is preferably 90 mol% to 100 mol%, more preferably 92 mol% to 100 mol%, and still more preferably 95 mol% to 100 mol%, based on the total mole of the L-lactide being 100 mol%. The content of components other than L-lactide is preferably 10 mol% to 0 mol%, more preferably 8 mol% to 0 mol%, and still more preferably 5 mol% to 0 mol%. When the purity of the L-lactide is less than 90 mol%, the content of the stereocomplex crystal in the polylactic acid block copolymer produced by the production method of the present invention is hardly 80% or more. Examples of the other components contained in the L-lactide include D-lactide, D-lactic acid, dicarboxylic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone, and the like. Specific examples of the dicarboxylic acid, the polyol, the hydroxycarboxylic acid, or the lactone have been described above, and therefore, description thereof is omitted here.

The content of the free acid in the D-lactide or the L-lactide is preferably 10% by mass or less, more preferably 1% by mass or less, still more preferably 0.15% by mass or less, and particularly preferably 0.05% by mass or less. When the content of the free acid exceeds 10%, the polymer finally obtained hardly has a high molecular weight, and the use of the polymer obtained is limited.

From the viewpoint of obtaining a copolymer having a higher melting point, the optical purity of the D-lactide or the L-lactide is, preferably, 90 to 100% ee, more preferably 95 to 100% ee, and still more preferably 98 to 100% ee. When the optical purity is less than 90% ee, the melting point and the crystalline melting enthalpy of the polymer to be produced are lowered. In the present invention, the optical purity is a value measured by the method described in the following examples.

The ring-opening polymerization of the D-lactide or the ring-opening polymerization of the L-lactide can be performed by the same method as described in the matter of the poly L-lactic acid or the poly D-lactic acid. That is, the kind and purity of lactide as a raw material for ring-opening polymerization, the kind and amount of various additives such as a polymerization catalyst and a polymerization initiator used, reaction conditions (temperature, time, pressure, atmosphere, etc.), a reaction apparatus, removal of residual lactide after polymerization, and the like have been already described in the above-mentioned items of poly-L-lactic acid and poly-D-lactic acid, and therefore, the description thereof is omitted here.

The reaction temperature in the reaction conditions may be the same as that in the production of the poly-L-lactic acid or the poly-D-lactic acid, but it is preferable to carry out the melt polymerization, the solid-phase polymerization, or the polymerization method using both of them, as selected as appropriate, depending on the melting point of the finally produced block copolymer or the residual amount of lactide in the poly-L-lactic acid or the poly-D-lactic acid. In the ring-opening polymerization after the preparation of PLLA or PDLA, the polymerization catalyst may be added in a larger amount or may not be added.

The amount of D-lactide or L-lactide to be added in the ring-opening polymerization of D-lactide or L-lactide performed after the production of the above-mentioned poly L-lactic acid or poly D-lactic acid is determined so that the mass ratio of L-lactic acid units to D-lactic acid units (L-lactic acid units/D-lactic acid units) or the mass ratio of D-lactic acid units to L-lactic acid units (D-lactic acid units/L-lactic acid units) in the finally produced polylactic acid block copolymer described below falls within the following range. Therefore, when ring-opening polymerization of D-lactide (component D) is carried out in the presence of poly L-lactic acid (component L), the mass ratio of component D to component L is 60/40-91/9 or 60/40-91/9, preferably 60/40-91/9. From the viewpoint of increasing the crystal melting enthalpy of the finally obtained polylactic acid block copolymer and improving the heat resistance, the mass ratio of the L component to the D component is preferably 71/29 to 91/9 or 71/29 to 91/9. From the viewpoint of obtaining a polymer having a higher molecular weight, the D component/L component is more preferably 71/29 to 91/9. When the mass ratio of the component D to the component L is 91/9 < component D/component L, it is difficult to produce a polylactic acid block copolymer having a stereocomplex crystal content of 80% or more and to produce a polylactic acid block copolymer having a high melting point. Further, when the mass ratio of the D component to the L component is 40/60 < D component/L component < 60/40, the composition of the D component (poly D-lactic acid or D-lactide) and the L component (poly L-lactic acid or L-lactide) is inclined, and therefore, when the price difference between the D component and the L component becomes large, it is difficult to stably produce a product with a low cost and a high value added.

When ring-opening polymerization of L-lactide (L component) is performed in the presence of poly D-lactic acid (D component), the mass ratio of the D component to the L component is: d component/L component is 60/40-91/9, or L component/D component is 60/40-91/9, preferably L component/D component is 60/40-91/9. From the viewpoint of increasing the crystal melting enthalpy of the finally obtained polylactic acid block copolymer and improving the heat resistance, the mass ratio of the L component to the D component is preferably 71/29 to 91/9 or 71/29 to 91/9. From the viewpoint of obtaining a polymer having a higher molecular weight, more preferably, the L component/D component is 71/29 to 91/9. When the mass ratio of the L component to the D component is 91/9 < L component/D component, it is difficult to produce a polylactic acid block copolymer having a stereocomplex crystal content of 80% or more and to produce a polylactic acid block copolymer having a high melting point. Further, when the mass ratio of the component D to the component L is 40/60 < component L/component D < 60/40, the composition of the component L (poly L-lactic acid or L-lactide) and the component D (poly D-lactic acid or D-lactide) is inclined, and therefore, when the price difference between the component L and the component D becomes large, it is difficult to stably produce a product with a low cost and a high value added.

The atmosphere of the polymerization reaction is preferably an inert gas atmosphere such as nitrogen or argon, from the viewpoint of suppressing coloration of the polymer to be produced.

By using the method described above, a polylactic acid block copolymer having a high molecular weight and capable of growing only a stereocomplex crystal by repeating melting and crystallization can be obtained.

The weight average molecular weight of the polylactic acid block copolymer produced by the above production method of the present invention is preferably 8 to 50 ten thousand, more preferably 10 to 40 ten thousand, and still more preferably 10 to 30 ten thousand. When the weight average molecular weight is within the above range, a polylactic acid block copolymer having good mechanical strength and molding processability can be obtained.

In Differential Scanning Calorimetry (DSC), the procedure consisting of a temperature rise process of 30 ℃ to 250 ℃ and a rapid cooling process of 250 ℃ to 30 ℃ is repeated 3 times, and the crystalline melting point observed in the temperature rise process is preferably 190 ℃ to 250 ℃, more preferably 195 ℃ to 250 ℃, and even more preferably 200 ℃ to 250 ℃.

Further, the content of the stereocomplex crystal of the polylactic acid block copolymer produced by the production method of the present invention is preferably 80% to 100%, more preferably 90 to 100%, still more preferably 95 to 100%. Further, the melting enthalpy (. DELTA. Hms) of the stereocomplex crystal occurring in the polylactic acid block copolymer of the present invention at 190-250 ℃ is preferably 10J/g or more, more preferably 20J/g or more, and still more preferably 30J/g or more. When the above-mentioned procedure is repeated 3 times and the melting point of the stereocomplex crystal is within the above-mentioned range, the stereocomplex crystal can grow only by repeating the melting and crystallization operations. When the melting point of the crystal observed during the temperature increase is less than 190 ℃ in the process of repeating the above procedure of melting and crystallizing 3 times, the performance of the polylactic acid block copolymer as a stereocomplex is deteriorated. On the other hand, when the temperature exceeds 250 ℃, the molecular weight is lowered by thermal decomposition of the polylactic acid block copolymer during molding. Destroying mechanical properties, etc. In the present invention, the content of the stereocomplex crystal is calculated by the method described in the following examples.

In order for the polylactic acid block copolymer produced by the production method of the present invention to exhibit good heat resistance, the content of the stereocomplex crystal, the melting point of the stereocomplex, and the melting enthalpy are preferably within the above numerical ranges.

The polylactic acid block copolymer according to the second aspect of the present invention is characterized in that the mass ratio of L-lactic acid units to D-lactic acid units is 60/40 to 91/9, or the mass ratio of D-lactic acid units to L-lactic acid units is 60/40 to 91/9, and the content of stereocomplex crystals is 80 to 100%.

The mass ratio of L-lactic acid units to D-lactic acid units in the polylactic acid block copolymer is 60/40-91/9 for L-lactic acid units/D-lactic acid units or 60/40-91/9 for D-lactic acid units/L-lactic acid units, preferably 71/29-91/9 for L-lactic acid units/L-lactic acid units or 71/29-91/9 for D-lactic acid units/L-lactic acid units, more preferably 71/29-85/15 for L-lactic acid units or 71/29-85/15 for D-lactic acid units/L-lactic acid units. When the mass ratio of the L-lactic acid unit to the D-lactic acid unit is 91/9 < L-lactic acid unit/D-lactic acid unit or 91/9 < D-lactic acid unit/L-lactic acid unit, the content of stereocomplex crystals in the obtained polylactic acid block copolymer is significantly reduced. On the other hand, when 40/60 < L-lactic acid unit/D-lactic acid unit < 60/40L, the composition of the L component (poly L-lactic acid or L-lactide) and the D component (poly D-lactic acid or D-lactide) is inclined, and therefore, when the price difference between the L component and the D component becomes large, it becomes difficult to stably produce a product having a low cost and a high value of added value.

Further, by melt-mixing or solution-mixing the 2 kinds of polylactic acid block copolymers prepared by the above-mentioned preparation method, a polylactic acid block copolymer having a high stereocomplex crystal content can also be obtained. That is, the present invention provides a method for preparing a polylactic acid block copolymer, which comprises a step of melt-mixing or solution-mixing a1 st polylactic acid block copolymer and a2 nd polylactic acid block copolymer. The 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), and the mass ratio of the component D to the component L is 60/40-91/9. The 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), wherein the mass ratio of the component L to the component D is 60/40-91/9, and the weight average molecular weight is 8-50 ten thousand.

Further, the present invention provides a method for producing a polylactic acid block copolymer, comprising a step of melt-mixing or solution-mixing a1 st polylactic acid block copolymer and a2 nd polylactic acid block copolymer. The 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), wherein the mass ratio of the component D to the component L is 60/40-91/9, and the weight average molecular weight is 8-50 ten thousand. The 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), and the mass ratio of the component L to the component D is 60/40 to 91/9.

The melt mixing and the mixing will be described below.

(melt mixing)

The melt mixing method is a method of mixing the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer in a molten state.

The melting temperature is not particularly limited as long as it is a melting temperature of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer, and it is preferable to lower the temperature as much as possible in a state where the molten mixture is not solidified in order to suppress the decomposition reaction during the melt mixing. Therefore, when the lower limit temperature is a temperature at which the melting point of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer is high, the upper limit temperature of the melting is preferably higher than the lower limit temperature by 50 ℃, more preferably higher by 30 ℃, and particularly preferably higher by 10 to 20 ℃. Further specifically, it is preferable to carry out melt mixing at 150 ℃ to 220 ℃.

The atmosphere during the melt mixing is not particularly limited, and may be performed under any conditions of normal pressure and reduced pressure. At normal pressure, it is preferable to circulate an inert gas such as nitrogen or argon. In addition, it is preferable to remove the monomer decomposed during melting under reduced pressure.

The order of charging the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer into an apparatus or the like at the time of melt mixing is not particularly limited. For example, the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer may be simultaneously charged into a mixing apparatus, or the 2 nd polylactic acid block copolymer may be charged and mixed after the 1 st polylactic acid block copolymer is melted. Examples of the apparatus that can be used for melt mixing include a roll mill (mill roll), a stirrer, a single-screw or double-screw extruder, and a batch type container (batch type container) that can be heated.

The mixing time in the melt-mixing is preferably 1 to 60 minutes, more preferably 1 to 10 minutes.

(solution mixing)

The solution mixing is a method of dissolving the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer in a solvent, mixing them, and then removing the solvent.

The solvent used in this case is not particularly limited as long as it dissolves the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer. Specific examples thereof include chloroform, dichloromethane, dichloroethane, tetrachloroethane, phenol, tetrahydrofuran, N-methylpyrrolidone, N-dimethylformamide, butyrolactone, trioxymethylene and hexafluoroisopropanol, and these can be used alone or in combination of two or more.

The content of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer in the solution is in the range of preferably 1 to 30 parts by weight, more preferably 1 to 10 parts by weight, of either one or both of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer, based on 100 parts by weight of the solvent.

The 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer may be mixed by dissolving them in respective solvents. One of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer may be dissolved in a solvent, and then the other may be added and mixed. The removal of the solvent used in the solution may be performed by heating, distillation under reduced pressure, extraction, or a combination thereof.

The mixing temperature at the time of mixing the solution is preferably 10 ℃ to 110 ℃, more preferably 10 ℃ to 30 ℃. Further, the mixing time is preferably 1 to 60 minutes, more preferably 1 to 10 minutes.

The mixing ratio of the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer is preferably 90/10 to 10/90, more preferably 75/25 to 25/75, and still more preferably 60/40 to 40/60, which are the 1 st polylactic acid block copolymer/the 2 nd polylactic acid block copolymer.

In addition, various terminal-sealed materials can be used for the 1 st polylactic acid block copolymer and the 2 nd polylactic acid block copolymer. Preferably, the polylactic acid block copolymer is subjected to end sealing by reacting a reactive end such as a carboxyl group or a hydroxyl group with an end sealing agent, whereby hydrolysis resistance and solution stability of the polylactic acid block copolymer can be improved. Examples of the terminal sealing group include an acetyl group, an ester group, an ether group, an amide group, and a urethane group.

The content of the stereocomplex crystal of the polylactic acid block copolymer obtained by melt-mixing or solution-mixing the above 2 kinds of polylactic acid block copolymers is preferably 80 to 100%, more preferably 90 to 100%, still more preferably 95 to 100%.

If necessary, general additives such as plasticizers, antioxidants, light stabilizers, ultraviolet absorbers, heat stabilizers, lubricants, mold release agents, various fillers, antistatic agents, flame retardants, foaming agents, fillers, antibacterial and antifungal agents, nucleating agents, colorants containing dyes and pigments, and the like may be added to the polylactic acid block copolymer of the present invention within a range not to impair the object of the present invention.

The polylactic acid block copolymer of the present invention can be formed by a conventionally known method such as injection molding, extrusion molding, blow molding, foam molding, pressure molding, or vacuum molding. That is, the third aspect of the present invention is a molded article comprising the polylactic acid block copolymer. Examples of the molded article obtained by the above molding method include films, sheets, fibers, fabrics, nonwoven fabrics, agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical products, electric and electronic parts, and the like.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Further, the measurement of the characteristic values in the preparation examples, examples and comparative examples was performed in the following manner.

(1) Optical purity of lactide

To 0.1g of the sample, 100ml of distilled water and 1.2ml of a 1N sodium hydroxide solution were added, and the mixture was stirred with heating at 95 ℃. The obtained solution was injected into a high performance liquid chromatograph, and the optical purity was calculated from the peak areas of L-lactic acid (L-lactic acid unit) and D-lactic acid (D-lactic acid unit) detected under ultraviolet light (wavelength 254 nm). The measurement conditions are shown in table 1 below, and the method for calculating the optical purity of lactide is shown in the following calculation formula 1.

[ Table 1]

A pump: manufactured by Shimadzu LC-6A K.K

A detector: manufactured by SHIMADE OF SPD-6AV corporation

Column box: manufactured by Shimadzu corporation CTO-6A

An integrator: manufactured by Shimadzu CR-5A K.K.

A chromatographic column: SUMICHIRAL OA-5000 manufactured by SuMICHIRAL CORPORATION ANALYSIS

Eluent: 1mmol copper sulfate solution

The determination method comprises the following steps: the temperature of the column box is 40 ℃, the wavelength of the detector is 254nm, the flow rate of the eluent is 1.0ml/min, the sample is dissolved in water to prepare a sample solution with the concentration of 20mg/ml, and the sample injection amount is 20 mul.

[ calculation 1]

Calculation of equation 1

(2) Weight average molecular weight (Mw)

The polystyrene equivalent was measured by a Gel Permeation Chromatography (GPC) method. The measurement conditions are shown in table 2 below.

[ Table 2]

A detector: RID-10A (differential refractometer) manufactured by Shimadzu corporation

A pump: manufactured by Shimadzu LC-6A K.K

Column box: manufactured by Shimadzu corporation CTO-6A

An integrator: manufactured by Shimadzu CR-7A K.K.

Calculating the molecular weight: CR-7A manufactured by Shimadzu corporation, GPC Programming

A chromatographic column: all made by Tosoh corporation

Mixing TSKgelG3000HXL, TSKgel3000HXL, and,

TSKG4000HXL, TSKgelG5000HXL and

TSKguardcolumnHXL-L series connection

Eluent: chloroform (for high performance liquid chromatograph, manufactured by pure chemical Co., Ltd.)

The determination method comprises the following steps: the temperature of the column box is 40 ℃, the flow rate of the eluent is 1.0ml/min, the sample is dissolved in the mixed solution of 1, 1, 1, 3, 3, 3-hexafluoro-propanol and chloroform to prepare a sample solution with the concentration of 20mg/ml, and the sample amount is 20 mu l for measurement.

(3) The charging ratio of the L component and the D component

In the column of "charging mass ratio (L component and D component)" in table 6, the charging mass ratio of the polylactic acid produced first and the lactide added later is described.

(4) Mass ratio of L component to D component in polymer

To 0.1g of the sample, 5ml of a 5N sodium hydroxide solution and 2.5ml of isopropyl alcohol were added, and after hydrolysis while heating and stirring at 30 ℃, neutralization with 1M sulfuric acid was performed. 1ml of the obtained neutralized solution was diluted to 25 times, and the solution concentration was adjusted. The obtained solution was injected into a high performance liquid chromatograph, and the mass ratio was calculated from the peak areas of L-lactic acid (L-lactic acid unit) and D-lactic acid (D-lactic acid unit) detected under ultraviolet light (wavelength 254 nm). The measurement conditions are shown in Table 1 above.

(5) Lactide content in polymer

The content of lactide in the polymer (unit: mass%) was determined by gas chromatography. The measurement conditions are shown in table 3 below.

[ Table 3]

The device comprises the following steps: manufactured by Shimadzu, GC-14B K.K

A detector: FID

Hydrogen pressure: 60kPa

Air pressure: 50kPa

Temperature of the column box: 175 deg.C

Detector temperature: 200 deg.C

Sample inlet temperature: 200 deg.C

Carrier gas: helium gas

Carrier gas flow: 50ml/min

A chromatographic column: FAL-M10% Shimalite (registered trademark) TPA60-80mesh and Tenax (registered trademark) TA 60-80mesh were mixed at a volume ratio of 1, and then packed into a glass column having an inner diameter of 2.6mm and a length of 1.5M.

An integrator: manufactured by Shimadzu CR-7A K.K.

The quantitative method comprises the following steps: to 1g of the polymer sample, 0.58g of triethylene glycol as an internal standard was added, dissolved in 25ml of chloroform, and measured in a sample amount of 1. mu.l.

(5) Thermal characteristics

A differential scanning calorimeter (DSC-60, manufactured by Shimadzu corporation) was used. A10 mg sample was put on an aluminum plate, and the heat of crystal fusion (. DELTA. Hms) and the crystal melting point (Tm) were measured in a nitrogen gas flow of 50ml/min according to the method described in Table 4 below. The melting enthalpy of each crystal was calculated from the area of the region surrounded by the crystal melting peak and the baseline shown in the DSC chart.

[ Table 4]

(a) The temperature is increased from 30 ℃ to 250 ℃ at the speed of 10 ℃/min.

(b) After reaching 250 ℃, it was cooled to 30 ℃ with dry ice.

(c) The above (a) and (b) were repeated 3 times.

(7) Content of stereocomplex crystals

When the homogeneous crystal melting heat (. DELTA. Hmh ℃) of the 100% crystallized polylactic acid block copolymer was-203.4J/g and the stereocomplex crystal melting heat (. DELTA. Hmh ℃) of the 100% crystallized polylactic acid block copolymer was-142J/g, the content of the stereocomplex crystal was calculated from the homogeneous crystal melting heat (. DELTA. Hmh ℃) exhibited at 150-190 ℃ and the thermal melting heat (. DELTA. Hmh ℃) exhibited at 150-190 ℃ as determined by DSC analysis, by the following calculation formula 2.

[ calculation 2]

Calculation formula 2

< preparation of homogeneous PLA (homoPLA) >

Preparation example 1

In a reaction vessel equipped with a stirring device, 100 parts by weight of L-lactide (polymerization grade, optical purity 100% ee, produced by Kyowa chemical Co., Ltd.) and 5 parts by weight of dodecanol as a polymerization initiator were added, and nitrogen substitution was performed 3 times. Melting at 190 ℃, adding 0.01 weight part of tin 2-ethylhexanoate as a polymerization catalyst, stirring for 3 hours, and ring-opening polymerization of L-lactide was carried out.

After the ring-opening polymerization reaction is completed, the reaction mixture is taken out from the reaction vessel in a molten state, and is cooled to form a sheet. Then, the sheet-like reaction product was pulverized and charged into a reaction vessel equipped with a stirrer, and the resultant was subjected to a pressure reduction treatment at 120 ℃ and 1.33kPa to remove the remaining L-lactide, thereby obtaining poly L-lactic acid (sample name: PLA 10). The Mw of the obtained PLA10, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. The obtained PLA10 was composed of 100 mol% of L-lactic acid units, and the content of L-lactide in the obtained PLA11 was 0.8 mass%.

(preparation example 2)

PLA11 was obtained in the same manner as in preparation example 1, except that D-lactide (prepared by Kyowa chemical Co., Ltd., optical purity 99.8% ee) was used in place of L-lactide. The Mw of the obtained PLA11, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. The obtained PLA11 was composed of 99.9 mol% of D-lactic acid units, and the content of D-lactide in the obtained PLA11 was 0.5 mass%.

Preparation example 3

PLA12 was obtained in the same manner as in preparation example 1, except that the amount of dodecanol was changed to 1 part by weight. The Mw of the obtained PLA12, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. The obtained PLA12 was composed of 100 mol% of L-lactic acid units, and the content of L-lactide in the obtained PLA12 was 0.8 mass%.

Preparation example 4

PLA13 was obtained in the same manner as in preparation example 3, except that D-lactide (prepared by Kyowa chemical Co., Ltd., polymerization grade, optical purity 99.8% ee) was used in place of L-lactide. The Mw of the obtained PLA13, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. Further, the obtained PLA13 was composed of 99.9 mol% of D-lactic acid units, and the content of D-lactide in the obtained PLA13 was 0.7 mass%.

Preparation example 5

PLA14 was obtained in the same manner as in preparation example 1, except that the amount of dodecanol was changed to 0.7 part by weight. The Mw of the obtained PLA14, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. Further, the obtained PLA14 was composed of 100 mol% of L-lactic acid units, and the L-lactide content in the obtained PLA14 was 1.1 mass%.

Preparation example 6

PLA15 was obtained in the same manner as in preparation example 5, except that D-lactide (prepared by Kyowa chemical Co., Ltd., optical purity 99.8% ee) was used in place of L-lactide. The Mw of the obtained PLA15, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. Further, the obtained PLA15 was composed of 99.9 mol% of L-lactic acid units, and the obtained PLA1The content of L-lactide in the composition was 0.5% by mass.

Preparation example 7

PLA16 was obtained in the same manner as in preparation example 1, except that the amount of dodecanol was changed to 0.4 part by weight. The Mw of the obtained PLA16, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. Further, the obtained PLA16 was composed of 99.9 mol% of L-lactic acid units, and the content of L-lactide in the obtained PLA16 was 0.6 mass%.

Preparation example 8

100 parts by weight of D-lactide (optical purity 90.5% ee, produced by Kyowa chemical Co., Ltd.) and 1 part by weight of dodecanol as a polymerization initiator were charged into a reaction vessel equipped with a stirrer, and nitrogen substitution was performed 3 times. Melting at 190 ℃, adding 0.01 weight part of tin 2-ethylhexanoate as a polymerization catalyst, stirring for 3 hours, and ring-opening polymerization of D-lactide was carried out.

After the ring-opening polymerization reaction is completed, the reaction mixture is taken out from the reaction vessel in a molten state, and is cooled to form a sheet. Then, the sheet-like reactant was pulverized and charged into a reaction vessel equipped with a stirrer, and subjected to a pressure reduction treatment at 120 ℃ and 1.33kPa to remove the remaining D-lactide, thereby obtaining PLA 17). The Mw of the obtained PLA17, the mass ratio of L-lactic acid units to D-lactic acid units, was measured. The measurement results are shown in Table 5. In addition, the obtained PLA1The content of D-lactide in the obtained PLA17 was 0.5% by mass, and the content of D-lactide was 90.3 mol% of D-lactic acid units.

(preparation example))

100 parts by weight of D-lactide (polymer grade, optical purity 99.8% ee, produced by Kyowa chemical Co., Ltd.) and 1 part by weight of dodecanol as a polymerization initiator were introduced into a reaction vessel equipped with a stirrer, and nitrogen substitution was performed 3 times. Melting at 190 ℃, adding 0.01 weight part of tin 2-ethylhexanoate as a polymerization catalyst, stirring for 3 hours, and ring-opening polymerization of D-lactide was carried out.

After the ring-opening polymerization reaction is completed, the reaction mixture is taken out from the reaction vessel in a molten state, and is cooled to form a sheet. The results of the PLA18 analysis are shown in table 1. The obtained PLA18 was composed of 99.7 mol% of D-lactic acid units, and the content of D-lactide in the obtained PLA18 was 48 mass%.

[ Table 5]

Sample name

Mw

Mass ratio of the feed

			(L component/D component)
				Preparation example 1	PLA10	8600	100/0
Preparation example 2	PLA11	9400	0/100
				Preparation example 3	PLA12	39900	100/0
Preparation example 4	PLA13	35300	0/100
				Preparation example 5	PLA14	56400	100/0
Preparation example 6	PLA15	53900	0/100
				Preparation example 7	PLA16	77200	0/100
Preparation example 8	PLA17	42100	0/100
				Preparation example 9	PLA18	39300	0/100

< preparation of polylactic acid Block copolymer >

Comparative example 1

100 parts by weight of PLA10 (poly L-lactic acid; component L) produced in production example 1 and 1570 parts by weight of the same D-lactide (component D) as used in production example 2 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component L to component D was 6: 94), and nitrogen substitution was performed 3 times. Then, 0.16 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain a polylactic acid block copolymer (sample name: PLA 20). PLA20, prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA20 feeding, the Mw of PLA20, the mass ratio of the L component and the D component in PLA20, Δ Hms, the crystal melting point (Tm), and the content of the stereocomplex crystal are shown in tables 6 and 7. In addition, the DSC diagram of PLA20 is shown in fig. 1.

Comparative example 2

100 parts by weight of PLA11 (poly D-lactic acid; component D) produced in production example 2 and 1570 parts by weight of the same L-lactide (component L) as used in production example 1 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component L to component D was 94: 6), and nitrogen substitution was performed 3 times. Then, 0.16 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of L-lactide was carried out at 190 ℃ for 3 hours to obtain PLA 21. PLA21, dissolved in 1000 parts by weight of chloroform per 100 parts by weight of polymer, was precipitated in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA21 feeding, the Mw of PLA21, the mass ratio of the L component and the D component in PLA21, Δ Hms, the crystal melting point (Tm), and the content of the stereocomplex crystal are shown in tables 6 and 7. In addition, the DSC chart of PLA21 is shown in fig. 2.

(example 1)

On tool100 parts by weight of preparation example was charged into a reaction vessel equipped with a stirrerPLA12 (Poly L-lactic acid; component L) prepared in (1) and 400 parts by weight and preparation exampleThe same D-lactide (component D) as used in (1) (i.e., the mass ratio of the component L to the component D was 20: 80), was subjected to nitrogen substitution 3 times. Then, 0.04 parts by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain a polylactic acid block copolymer (sample name: PLA 22). PLA22, dissolved in 1000 parts by weight of chloroform per 100 parts by weight of polymer, was precipitated in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA22 feeding, the Mw of PLA22, the mass ratio of the L component and the D component in PLA22, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. In addition, the DSC chart of PLA22 is shown in fig. 3.

(example 2)

In a reaction vessel equipped with a stirrer, 100 parts by weight of PLA1 prepared in preparation example 4 was charged3 (Poly D lactic acid; component D) and 400 parts by weight of the same L-lactide (component L) as used in preparation example 1 (i.e., the mass ratio of component L to component D was 80: 20) were subjected to nitrogen substitution 3 times. Then, ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to prepare a polylactic acid block copolymer (sample name: PLA 23). PLA23 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in methanol with the addition of 0.04 parts by weight of tin 2-ethylhexanoate as a polymerization catalyst per 6000 parts by weight of polymer. Subjecting the precipitated polymer to solid-liquid separationAnd dried and used for measurement. The mass ratio of the L component and the D component at the time of PLA23 feeding, the Mw of PLA23, the mass ratio of the L component and the D component in PLA23, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. In addition, the DSC chart of PLA23 is shown in fig. 4.

(example 3)

100 parts by weight of PLA14 (poly L-lactic acid; component L) produced in production example 5 and 186 parts by weight of D-lactide (component D) similar to that used in production example 2 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component D to component L was 35: 65), and nitrogen substitution was performed 3 times. Then, 0.02 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain PLA 24. PLA24 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA24 feeding, the Mw of PLA24, the mass ratio of the L component and the D component in PLA24, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. Further, the DSC chart of PLA23 is shown in fig. 5.

(example 4)

100 parts by weight of PLA15 (poly D-lactic acid; component D) produced in production example 6 and 186 parts by weight of the same L-lactide (component L) as used in production example 1 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component D to component L was 65: 35), and 3 nitrogen substitution was performed. Then, 0.02 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of L-lactide was carried out at 190 ℃ for 3 hours to obtain PLA 25. PLA25 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA25 feeding, the Mw of PLA25, the mass ratio of the L component and the D component in PLA25, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. Further, the DSC chart of PLA25 is shown in fig. 6.

Comparative example 3

100 parts by weight of PLA16 (poly D-lactic acid; component D) produced in production example 7 and 100 parts by weight of the same L-lactide (component L) as used in production example 1 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component D to component L was 50: 50), and nitrogen substitution was performed 3 times. Then, 0.01 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain a polylactic acid block copolymer (sample name: PLA 26). PLA26 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA26 feeding, the Mw of PLA26, the mass ratio of the L component and the D component in PLA26, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. In addition, the DSC chart of PLA26 is shown in fig. 7.

(example 5)

100 parts by weight of PLA16 (poly D-lactic acid; component D) prepared in production example 7 and 400 parts by weight of L-lactide (optical purity 99.8% ee, produced by Kyowa chemical research, K.K.) were charged into a reaction vessel equipped with a stirrer, and nitrogen substitution was performed 3 times (i.e., the mass ratio of component D to component L was 20: 80). Then, 0.04 parts by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain a polylactic acid block copolymer (sample name: PLA 27). PLA27 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA27 feeding, the Mw of PLA27, the mass ratio of the L component and the D component in PLA27, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. Further, the DSC chart of PLA27 is shown in fig. 8.

(example 6)

100 parts by weight of PLA17 (poly D-lactic acid; component D) produced in production example 8 and 400 parts by weight of the same L-lactide (component L) as used in production example 1 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component D to component L was 20: 80), and nitrogen substitution was performed 3 times. Then, 0.04 parts by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of D-lactide was carried out at 190 ℃ for 3 hours to obtain a polylactic acid block copolymer (sample name: PLA 28). PLA28 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component at the time of PLA28 feeding, the Mw of PLA28, the mass ratio of the L component and the D component in PLA28, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. Further, the DSC chart of PLA28 is shown in fig. 9.

(example 7)

100 parts by weight of PLA18 (poly D-lactic acid; component D) produced in production example 9 and 400 parts by weight of the same L-lactide (component L) as used in production example 1 were added to a reaction vessel equipped with a stirrer (i.e., the mass ratio of component D to component L was 20: 80), and nitrogen substitution was performed 3 times. Then, 0.04 part by weight of tin 2-ethylhexanoate as a polymerization catalyst was added thereto, and ring-opening polymerization of L-lactide was carried out at 190 ℃ for 3 hours to obtain PLA 29. PLA29 was prepared by dissolving in 1000 parts by weight of chloroform per 100 parts by weight of polymer and precipitating in 6000 parts by weight of methanol per 100 parts by weight of polymer. The precipitated polymer was subjected to solid-liquid separation and dried, and then used for measurement. The mass ratio of the L component and the D component of PLA29 at the time of charging, the Mw of PLA29, the mass ratio of the L component and the D component in PLA29, Δ Hms, Tm, and the content of stereocomplex crystals are shown in tables 6 and 7. Further, the DSC chart of PLA29 is shown in fig. 10.

(example 8)

100 parts by weight of PLA22 obtained in example 1 and 100 parts by weight of PLA23 obtained in example 2 were charged into a reaction vessel equipped with a stirrer, and nitrogen substitution was performed 3 times. Then, the mixture was heated and stirred at 200 ℃ for 10 minutes to obtain PLA30. the Mw of PLA30, the mass ratio of the L component to the D component in PLA30,. DELTA.Hms, Tm, and the content of the stereocomplex crystal are shown in tables 6 and 7. Further, the DsC chart for PLA30 is shown in fig. 11.

[ Table 6]

[ Table 7]

The 1 st, 2 nd and 3 rd DSC in table 7 show the number of repetitions of operations (a) to (b) described in table 4, and Δ Hms, the stereocomplex crystal content and the crystal melting point show the numerical values obtained in the respective operations at 1 st, 2 nd and 3 rd times.

As is apparent from tables 6 and 7, according to the production method of the present invention, even when the charge ratio (mass ratio) of the L component (poly L-lactic acid or L-lactide) to the D component (poly D-lactic acid or D-lactide) used is greatly inclined, a polylactic acid block copolymer having a content of stereocomplex crystals of 100% can be obtained. On the other hand, in comparative examples 1 and 2 in which the mass ratio of the L component and the D component in the polymer is out of the range of the present invention, the content of the stereocomplex crystal is significantly reduced. The polylactic acid block copolymer of comparative example 3, in which the mass ratio of the L component to the D component in the polymer was about 53: 47, had a high crystal melting point with a stereocomplex crystal content of 100%. However, the effect of reducing the production cost of the polylactic acid block copolymer is deteriorated due to the high content of the component D in the polymer.

The present application is proposed on the basis of Japanese patent application No. 2006-356241 filed on 28.12.2006, the disclosure of which is incorporated herein by reference in its entirety.

Claims (17)

1. A method for producing a polylactic acid block copolymer, characterized by (i) ring-opening polymerization of D-lactide (component D) in the presence of poly L-lactic acid (component L), wherein the mass ratio of the component D to the component L is component D/component L of 71/29-91/9;

or (ii) ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D); wherein the mass ratio of the L component to the D component is 71/29-91/9.

2. A preparation method of polylactic acid block copolymer is characterized by comprising the process of carrying out melt mixing or solution mixing on a1 st polylactic acid block copolymer and a2 nd polylactic acid block copolymer;

the 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), wherein the mass ratio of the component D to the component L is 60/40-91/9;

the 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), and the mass ratio of the component L to the component D is 60/40-91/9.

3. The method according to claim 2, wherein the weight ratio of the component D to the component L in the 1 st polylactic acid block copolymer is from 71/29 to 91/9; the weight ratio of the L component to the D component in the 2 nd polylactic acid block copolymer is 71/29-91/9.

4. A preparation method of polylactic acid block copolymer is characterized by comprising the process of carrying out melt mixing or solution mixing on a1 st polylactic acid block copolymer and a2 nd polylactic acid block copolymer;

the 1 st polylactic acid block copolymer is (i) a polylactic acid block copolymer obtained by ring-opening polymerization of D-lactide (component D) in the presence of poly-L-lactic acid (component L), wherein the mass ratio of the component D to the component L is 60/40-91/9;

the 2 nd polylactic acid block copolymer is (ii) a polylactic acid block copolymer obtained by ring-opening polymerization of L-lactide (component L) in the presence of poly D-lactic acid (component D), and the mass ratio of the component L to the component D is 60/40 to 91/9.

5. The method according to claim 4, wherein the weight ratio of the L component to the D component in the 1 st polylactic acid block copolymer is 71/29-91/9; the weight ratio of the component D to the component L in the 2 nd polylactic acid block copolymer is 71/29-91/9.

6. The process according to any one of claims 1 to 5, wherein the poly (L-lactic acid) has a mass ratio of L-lactic acid units to D-lactic acid units of 95/5 to 100/0; the mass ratio of the D-lactic acid unit to the L-lactic acid unit in the poly D-lactic acid is 95/5-100/0.

7. The production method according to any one of claims 1 to 5, wherein the optical purity of the D-lactide or the L-lactide is in the range of 90 to 100% ee.

8. The process according to claim 6, wherein the optical purity of the D-lactide or L-lactide is in the range of 90 to 100% ee.

9. The method according to claim 7, wherein the poly-L-lactic acid is obtained by ring-opening polymerization of L-lactide, and the poly-D-lactic acid is obtained by ring-opening polymerization of D-lactide.

10. The method according to claim 7, wherein the poly-L-lactic acid is obtained by ring-opening polymerization of L-lactide and then removing the remaining lactide; the poly-D-lactic acid is obtained by removing residual lactide after ring-opening polymerization of D-lactide.

11. The production method according to claim 10, wherein the residual lactide is removed by reducing the pressure in the reaction system.

12. The production method according to any one of claims 1 to 5, wherein the amount of D-lactide remaining in the reaction system before the ring-opening polymerization of D-lactide is carried out in the presence of the poly L-lactic acid is 0 to 5% by mass based on the mass of the poly L-lactic acid; before the ring-opening polymerization of L-lactide is carried out in the presence of the poly D-lactic acid, the residual amount of D-lactide in the reaction system is 0-5 mass% of the mass of the poly D-lactic acid;

13. a polylactic acid block copolymer produced by the production method according to claim 1 or 3, wherein the mass ratio of L-lactic acid units to D-lactic acid units is 71/29 to 91/9, or the mass ratio of D-lactic acid units to L-lactic acid units is 71/29 to 91/9; wherein the content of the stereocomplex crystal is 80-100%.

14. The polylactic acid block copolymer according to claim 13, having a weight average molecular weight (Mw) of 8 to 50 ten thousand.

15. The polylactic acid block copolymer according to claim 13 or 14, wherein a procedure consisting of a temperature rise process of 30 ℃ to 250 ℃ and a rapid cooling process of 250 ℃ to 30 ℃ is repeated 3 times in the differential scanning calorimetry, and a crystalline melting point observed in the temperature rise process is in the range of 190 ℃ to 250 ℃.

16. A molded article comprising the polylactic acid block copolymer according to claim 13 or 14.

17. A molded article comprising the polylactic acid block copolymer according to claim 15.